Chemical Signaling which can be located on the

cell surface or inside the cell.

1. Overview of Chemical Signaling
o Binding triggers a cascade of
• Definition: Chemical signaling is the
intracellular events leading to
process by which cells communicate
a cellular response.
with each other through the release
and reception of signaling molecules. • Second Messengers:

• Importance: Essential for regulating o Many hormones utilize second

physiological processes, including messengers (e.g., cAMP,
growth, metabolism, and calcium ions) to amplify the
homeostasis. signal.

2. Types of Chemical Signaling o Example: cAMP is produced

when a hormone binds to its
A. Local Signaling
receptor, activating protein
1. Paracrine Signaling: kinases that initiate a
phosphorylation cascade.
o Definition: A cell releases a
chemical signal that affects 4. Characteristics of Signaling Molecules
nearby cells.
• Types of Signaling Molecules:
o Example: Growth factors
o Hormones: Chemical
stimulating nearby cells to
messengers produced by
divide.
endocrine glands.
2. Autocrine Signaling:
o Neurotransmitters:
o Definition: A cell releases a Chemicals released by
signal that binds to receptors neurons to communicate with
on itself, inducing a response. other cells.

o Example: Immune cells o Cytokines: Signaling proteins

releasing cytokines that act on involved in immune
themselves. responses.

3. Synaptic Signaling: • Diversity of Effects:

o Definition: Neurons release o A single signaling molecule

neurotransmitters into a can have different effects
synapse, affecting adjacent depending on the type of
neurons or muscle cells. target cell and the receptors
present.
o Example: Acetylcholine
released at the o Example: Epinephrine can
neuromuscular junction. increase heart rate in cardiac
cells and stimulate glycogen
B. Long-Distance Signaling breakdown in liver cells.
1. Endocrine Signaling: 5. Signaling Pathways
o Definition: Hormones are • G-Protein Coupled Receptors
secreted into the bloodstream (GPCRs):
and travel to distant target
cells. o A large family of receptors that
activate G-proteins upon
o Example: Insulin released ligand binding, leading to
from the pancreas affecting various intracellular
glucose uptake in various responses.
tissues.
• Receptor Tyrosine Kinases (RTKs):
3. Mechanism of Action
o Receptors that, upon binding
• Hormone Reception: to a ligand, undergo
o Hormones bind to specific dimerization and
receptors on target cells, autophosphorylation,
 activating downstream 2. Hormonal Secretion: Produce
signaling pathways. hormones that regulate various
physiological processes.
6. Integration of Signaling
3. Widespread Effects: Hormones can
• Cross-Talk Between Pathways:
affect multiple target organs and
o Different signaling pathways tissues throughout the body.
can interact and influence
4. Long-lasting Effects: Hormonal
each other, allowing for
effects can be prolonged, influencing
complex regulation of cellular
processes over minutes to hours or
functions.
even longer.
• Feedback Mechanisms:
C. Examples
o Negative feedback loops help
• Pituitary Gland: Produces growth
maintain homeostasis by
hormone, thyroid-stimulating
inhibiting further signaling
hormone, etc.
once a desired effect is
achieved. • Thyroid Gland: Secretes thyroid
hormones (T3 and T4) that regulate
7. Clinical Relevance
metabolism.
• Targeting Signaling Pathways:
• Adrenal Glands: Produce cortisol,
o Many drugs are designed to adrenaline, and other hormones
target specific signaling involved in stress response.
pathways to treat diseases
3. Exocrine Glands
(e.g., cancer therapies
targeting RTKs). A. Definition

• Disruption of Signaling: • Exocrine glands are glands that

secrete their products into ducts that
o Abnormal signaling can lead
lead to the surface of an organ or to
to diseases such as diabetes,
the outside of the body.
cancer, and autoimmune
disorders. B. Characteristics

1. Ducts Present: Secrete substances

through ducts to specific sites.

2. Variety of Secretions: Produce a

Comparison of Endocrine and Exocrine
wide range of substances, including
Glands
enzymes, sweat, saliva, and mucus.
1. Introduction
3. Localized Effects: The effects of
• Glands: Specialized organs that exocrine secretions are typically
produce and secrete substances localized to the area where they are
necessary for various bodily released.
functions.
4. Rapid Response: Exocrine secretions
• Types of Glands: Primarily classified can produce immediate effects.
into two categories: endocrine and
C. Examples
exocrine glands.
• Salivary Glands: Secrete saliva into
2. Endocrine Glands
the mouth for digestion.
A. Definition
• Sweat Glands: Release sweat to
• Endocrine glands are ductless glands regulate body temperature.
that secrete hormones directly into
• Pancreas: Functions as both an
the bloodstream or surrounding
endocrine (insulin) and exocrine gland
extracellular fluid.
(digestive enzymes).
B. Characteristics
4. Comparison of Endocrine and Exocrine
1. Ductless: No ducts; hormones are Glands
released directly into the blood.
Functional Integration o Oxytocin and Antidiuretic
Hormone (ADH): Stored and
• Cooperation: Endocrine and exocrine
released from the posterior
glands often work together to
pituitary.
maintain homeostasis. For example,
the pancreas releases insulin B. Pituitary Gland
(endocrine) to regulate blood sugar
• Location: Base of the brain,
levels while also secreting digestive
connected to the hypothalamus.
enzymes (exocrine) to aid in digestion.
• Function: Often referred to as the
• Feedback Mechanisms: Hormonal
"master gland" due to its regulatory
signals from endocrine glands can
role over other endocrine glands.
influence the activity of exocrine
glands, demonstrating the • Hormones Secreted:
interconnectedness of these systems.
o Anterior Pituitary: Growth
Clinical Relevance hormone (GH), thyroid-
stimulating hormone (TSH),
• Disorders: Dysfunction in endocrine
adrenocorticotropic hormone
glands can lead to hormonal
(ACTH), prolactin (PRL),
imbalances (e.g., diabetes, thyroid
luteinizing hormone (LH), and
disorders), while issues in exocrine
follicle-stimulating hormone
glands can result in digestive
(FSH).
problems (e.g., pancreatitis).
o Posterior Pituitary: Oxytocin
• Therapeutic Targets: Understanding
and ADH.
the differences between these glands
is crucial for developing targeted C. Thyroid Gland
therapies for various diseases.
• Location: Anterior neck, around the
trachea.

• Function: Regulates metabolism,

growth, and development.
Organs with Endocrine Roles
• Hormones Secreted:
1. Introduction
o Thyroid Hormones (T3 and
• Endocrine System: A complex
T4): Increase metabolic rate
network of glands and organs that
and influence growth.
secrete hormones to regulate various
physiological processes. o Calcitonin: Lowers blood
calcium levels by inhibiting
• Endocrine Roles: Several organs in
osteoclast activity.
the body have dual functions, serving
both endocrine and non-endocrine D. Parathyroid Glands
roles.
• Location: Four small glands located
2. Major Organs with Endocrine Functions on the posterior surface of the thyroid
gland.
A. Hypothalamus
• Function: Regulates calcium levels in
• Location: Below the thalamus, part of
the blood.
the brain.
• Hormones Secreted:
• Function: Regulates the pituitary
gland and maintains homeostasis. o Parathyroid Hormone (PTH):
Increases blood calcium
• Hormones Secreted:
levels by stimulating
o Releasing Hormones: osteoclasts, increasing
Stimulate the anterior intestinal absorption, and
pituitary (e.g., TRH, CRH). promoting renal reabsorption
of calcium.
o Inhibiting Hormones: Inhibit
the anterior pituitary (e.g., E. Adrenal Glands
PIH).
• Location: On top of each kidney.
 • Function: Involved in stress response o Thymosins: Promote the
and regulation of metabolism. development and maturation
of T-lymphocytes (T-cells).
• Hormones Secreted:
I. Other Organs with Endocrine Functions
o Adrenal Cortex: Cortisol
(stress response), aldosterone • Heart: Produces atrial natriuretic
(regulates sodium and peptide (ANP) to regulate blood
potassium), and androgens pressure.
(sex hormones).
• Kidneys: Secrete erythropoietin (EPO)
o Adrenal Medulla: to stimulate red blood cell production
Epinephrine and and renin to regulate blood pressure.
norepinephrine (fight-or-flight
• Liver: Produces insulin-like growth
response).
factors (IGFs) that mediate growth
F. Pancreas hormone effects.

• Location: Posterior to the stomach. • Adipose Tissue: Secretes leptin,

which regulates energy balance and
• Function: Regulates blood glucose
appetite.
levels and aids in digestion.

• Hormones Secreted:
Types of Hormones
o Insulin: Lowers blood glucose
levels by promoting glucose 1. Introduction
uptake.
• Hormones: Chemical messengers
o Glucagon: Raises blood produced by glands in the endocrine
glucose levels by stimulating system that regulate various
glycogen breakdown. physiological processes in the body.

o Somatostatin: Inhibits insulin • Classification: Hormones can be

and glucagon secretion. classified based on their chemical
structure, source, and mechanism of
G. Gonads (Ovaries and Testes)
action.
• Location: Ovaries in the female
2. Major Types of Hormones
pelvis; testes in the male scrotum.
A. Based on Chemical Structure
• Function: Produce sex hormones and
gametes. 1. Steroid Hormones

• Hormones Secreted: o Definition: Lipid-soluble

hormones derived from
o Ovaries: Estrogens (regulate
cholesterol.
menstrual cycle, secondary
sexual characteristics) and o Characteristics:
progesterone (maintains
▪ Can easily cross cell
pregnancy).
membranes due to
o Testes: Testosterone their lipophilic nature.
(regulates sperm production
▪ Bind to intracellular
and male secondary sexual
receptors in the
characteristics).
cytoplasm or nucleus.
H. Thymus
▪ Act as transcription
• Location: In the upper chest, behind factors, influencing
the sternum. gene expression.

• Function: Plays a role in immune o Examples:

function, particularly during
▪ Cortisol: Produced by
childhood.
the adrenal cortex;
• Hormones Secreted: regulates metabolism
and stress response.
 ▪ Testosterone: ▪ Thyroid Hormones
Produced by the (T3 and T4): Derived
testes; regulates male from tyrosine; regulate
secondary sexual metabolism and
characteristics. energy production.

▪ Estrogens: Produced ▪ Epinephrine

by the ovaries; (Adrenaline):
regulate female Produced by the
reproductive adrenal medulla;
functions. involved in the fight-or-
flight response.
2. Peptide and Protein Hormones
▪ Melatonin: Derived
o Definition: Hormones
from tryptophan;
composed of chains of amino
regulates sleep-wake
acids.
cycles.
o Characteristics:
B. Based on Source
▪ Water-soluble and
1. Endocrine Hormones
cannot cross the cell
membrane. o Definition: Hormones
secreted directly into the
▪ Bind to receptors on
bloodstream by endocrine
the cell surface,
glands.
activating second
messenger systems. o Examples: Insulin, cortisol,
thyroid hormones.
o Examples:
2. Paracrine Hormones
▪ Insulin: Produced by
the pancreas; o Definition: Hormones that act
regulates blood on nearby cells within the
glucose levels. same tissue.

▪ Growth Hormone o Examples: Growth factors,

(GH): Produced by the histamine.
anterior pituitary;
3. Autocrine Hormones
stimulates growth and
cell reproduction. o Definition: Hormones that act
on the same cell that secretes
▪ Oxytocin: Produced
them.
by the hypothalamus;
stimulates uterine o Examples: Certain cytokines
contractions and milk in immune responses.
ejection.
C. Based on Mechanism of Action
3. Amine Hormones
1. Water-Soluble Hormones
o Definition: Hormones derived
from single amino acids o Characteristics: Include
(tyrosine or tryptophan). peptide and amine hormones;
cannot cross the cell
o Characteristics: membrane.
▪ Can be either water- o Mechanism: Bind to cell
soluble or lipid- surface receptors, activating
soluble, depending on second messenger systems
the specific hormone. (e.g., cAMP, calcium ions).
▪ Bind to specific o Examples: Insulin, glucagon,
receptors on target epinephrine.
cells.
2. Lipid-Soluble Hormones
o Examples:
 o Characteristics: Include • Characteristics: Include peptide
steroid and thyroid hormones; hormones and most amine hormones
can cross the cell membrane. (e.g., epinephrine).

o Mechanism: Bind to • Mechanism of Action:

intracellular receptors,
1. Binding to Cell Surface
influencing gene expression
Receptors:
and protein synthesis.
▪ Water-soluble
o Examples: Cortisol,
hormones cannot
testosterone, thyroid
cross the lipid bilayer
hormones.
of the cell membrane.
3. Hormonal Regulation
▪ They bind to specific
• Feedback Mechanisms: Hormonal receptors located on
secretion is often regulated by the surface of target
feedback loops (negative and positive cells.
feedback).
2. Activation of Second
o Negative Feedback: Reduces Messengers:
the output of a system to
▪ The binding of the
maintain homeostasis (e.g.,
hormone to its
insulin secretion in response
receptor activates
to high blood glucose).
intracellular signaling
o Positive Feedback: Enhances pathways, often
the output of a system (e.g., involving second
oxytocin during childbirth). messengers.

4. Clinical Relevance ▪ Common second

messengers include:
• Hormonal Imbalances: Can lead to
various disorders (e.g., diabetes, ▪ Cyclic AMP
thyroid dysfunction, adrenal (cAMP):
insufficiency). Activates
protein
• Hormone Replacement Therapy:
kinases,
Used to treat deficiencies (e.g.,
leading to
insulin for diabetes, thyroid hormones
phosphorylatio
for hypothyroidism).
n of target
proteins.

▪ Calcium Ions
(Ca²⁺):
Pathways of Hormone Action Involved in
1. Introduction various
cellular
• Hormone Action: Hormones exert processes,
their effects on target cells through including
specific signaling pathways, which muscle
can vary based on the type of contraction
hormone and its mechanism of and
action. neurotransmitt
• Importance: Understanding these er release.
pathways is crucial for ▪ Inositol
comprehending how hormones Triphosphate
regulate physiological processes and (IP3) and Diac
maintain homeostasis. ylglycerol
2. Types of Hormones and Their (DAG):
Mechanisms of Action Involved in the
phospholipase
A. Water-Soluble Hormones C pathway,
 leading to 4. Gene Expression Regulation:
increased
▪ The binding of the
intracellular
complex to DNA
calcium and
initiates transcription
activation of
of target genes,
protein kinase
leading to the
C (PKC).
synthesis of specific
3. Cellular Response: proteins.

▪ The activation of ▪ This process can take

second messengers hours to days to
leads to a cascade of produce a cellular
events that result in a response, as it
specific cellular involves changes in
response (e.g., gene expression.
secretion,
3. Comparison of Pathways
metabolism, gene
expression). 4. Feedback Mechanisms in Hormonal
Action
B. Lipid-Soluble Hormones
• Negative Feedback: Most hormonal
• Characteristics: Include steroid
pathways are regulated by negative
hormones (e.g., cortisol,
feedback loops, where the output of a
testosterone) and thyroid hormones
process inhibits its own production.
(T3 and T4).
o Example: Increased blood
• Mechanism of Action:
glucose levels stimulate
1. Crossing the Cell Membrane: insulin secretion, which
lowers blood glucose,
▪ Lipid-soluble
reducing the stimulus for
hormones can easily
further insulin release.
diffuse through the
lipid bilayer of the cell • Positive Feedback: Less common,
membrane. where the output enhances the
process.
2. Binding to Intracellular
Receptors: o Example: Oxytocin release
during childbirth enhances
▪ Once inside the cell,
uterine contractions, leading
these hormones bind
to more oxytocin release.
to specific receptors
located in the 5. Clinical Relevance
cytoplasm or nucleus.
• Hormonal Dysregulation:
▪ The hormone-receptor Understanding hormone action
complex may undergo pathways is essential for diagnosing
a conformational and treating endocrine disorders (e.g.,
change, activating the diabetes, thyroid diseases).
receptor.
• Pharmacological Interventions:
3. Translocation to the Many drugs target specific hormone
Nucleus: pathways to modulate their effects
(e.g., insulin for diabetes,
▪ The hormone-receptor
corticosteroids for inflammation).
complex translocates
to the nucleus, where
it binds to specific
Factors Affecting Target Cell Response
DNA sequences
(hormone response 1. Introduction
elements).
• Target Cell Response: The
effectiveness of a hormone in eliciting
a response in target cells is
 influenced by various factors. o Antagonistic Effects: When
Understanding these factors is crucial one hormone opposes the
for comprehending hormonal action of another (e.g., insulin
regulation and its physiological lowers blood glucose, while
effects. glucagon raises it).

2. Key Factors Affecting Target Cell C. Affinity of Receptors

Response
1. Receptor-Hormone Binding:
A. Receptor Availability
o The strength of the binding
1. Receptor Expression: between a hormone and its
receptor (affinity) affects the
o Only cells with specific
response.
receptors for a hormone can
respond to it. o Higher affinity results in a
more effective response at
o The number of receptors on a
lower hormone
target cell can vary based on
concentrations.
several conditions.
2. Receptor Types:
2. Upregulation and Downregulation:
o Different types of receptors
o Upregulation: When hormone
(e.g., G-protein coupled
levels are low, target cells may
receptors, nuclear receptors)
increase the number of
can have varying affinities and
receptors to become more
mechanisms of action,
sensitive to the hormone.
influencing the overall
o Downregulation: When response.
hormone levels are
D. Signal Transduction Pathways
persistently high, target cells
may decrease the number of 1. Second Messengers:
receptors to reduce
o Water-soluble hormones often
sensitivity, preventing
utilize second messenger
overstimulation.
systems (e.g., cAMP, calcium
B. Hormone Concentration ions) to amplify the signal
within the cell.
1. Circulating Levels:
o The efficiency and availability
o The concentration of a
of these second messengers
hormone in the bloodstream
can affect the strength and
directly affects the magnitude
duration of the response.
of the target cell response.
2. Post-Receptor Events:
o Higher concentrations
generally lead to a stronger o The activation of downstream
response, while lower signaling pathways (e.g.,
concentrations may result in protein kinases) and the
minimal or no response. subsequent cellular
responses (e.g., gene
2. Hormonal Interactions:
expression, enzyme activity)
o Hormones can interact with are crucial for the overall
each other, influencing their effect of the hormone.
effects on target cells.
E. Cellular Context
o Synergistic Effects: When
1. Cell Type:
two or more hormones work
together to produce a greater o Different cell types may
effect (e.g., glucagon and respond differently to the
epinephrine both increase same hormone due to
blood glucose). variations in receptor types,
signaling pathways, and
cellular machinery.
 o For example, insulin promotes levels are maintained in response to
glucose uptake in muscle and the body's needs.
fat cells but has different
2. Mechanisms of Hormone Regulation
effects in liver cells.
A. Feedback Mechanisms
2. Physiological State:
1. Negative Feedback:
o The target cell's physiological
state (e.g., developmental o Definition: A process where
stage, health status) can the output of a system inhibits
influence its responsiveness its own production,
to hormones. maintaining homeostasis.
o Conditions such as stress, o Example:
illness, or metabolic changes
can alter receptor expression ▪ Thyroid Hormones:
and signaling pathways. Increased levels of T3
and T4 inhibit the
F. Environmental Factors release of Thyroid-
Stimulating Hormone
1. Nutritional Status:
(TSH) from the anterior
o Nutrient availability can affect pituitary and
hormone levels and receptor Thyrotropin-Releasing
sensitivity (e.g., insulin Hormone (TRH) from
sensitivity is influenced by diet the hypothalamus.
and body composition).
▪ Blood Glucose
2. Circadian Rhythms: Regulation: Elevated
blood glucose levels
o Hormone levels can fluctuate
stimulate insulin
based on time of day, affecting
secretion, which
target cell responsiveness
lowers blood glucose,
(e.g., cortisol levels peak in
reducing the stimulus
the morning).
for further insulin
3. Clinical Relevance release.

• Hormonal Disorders: Understanding 2. Positive Feedback:

these factors is essential for
o Definition: A process where
diagnosing and treating conditions
the output enhances or
related to hormonal imbalances (e.g.,
increases its own production.
insulin resistance in diabetes).
o Example:
• Therapeutic Interventions:
Knowledge of how to manipulate ▪ Oxytocin during
receptor expression or hormone Childbirth: Stretching
levels can lead to effective treatments of the cervix
(e.g., hormone replacement therapy). stimulates oxytocin
release, which
increases uterine
Regulation of Hormone Secretion contractions, leading
to more oxytocin
1. Introduction release until delivery
• Hormone Secretion: The release of occurs.
hormones from endocrine glands into B. Hormonal Regulation
the bloodstream, which is crucial for
maintaining homeostasis and 1. Tropic Hormones:
regulating physiological processes.
o Definition: Hormones that
• Regulation: Hormone secretion is stimulate other endocrine
tightly controlled through various glands to release their
mechanisms to ensure appropriate hormones.

o Example:
 ▪ Adrenocorticotropic ▪ Epinephrine:
Hormone (ACTH): Released from the
Stimulates the adrenal adrenal medulla in
cortex to release response to
cortisol. sympathetic nervous
system activation
▪ Luteinizing Hormone
during stress (fight-or-
(LH): Stimulates the
flight response).
ovaries and testes to
produce sex ▪ Oxytocin: Released
hormones. from the posterior
pituitary in response to
2. Hypothalamic-Pituitary Axis:
nerve impulses from
o Role of the Hypothalamus: the hypothalamus
Produces releasing and during childbirth and
inhibiting hormones that breastfeeding.
regulate the anterior pituitary.
E. Circadian Rhythms
o Example:
1. Biological Clocks:
▪ Corticotropin-
o Hormone secretion can be
Releasing Hormone
influenced by the body's
(CRH) stimulates the
internal biological clock,
release of ACTH from
leading to fluctuations in
the anterior pituitary.
hormone levels throughout
C. Humoral Regulation the day.

1. Blood Levels of Ions and Nutrients: o Example:

o Hormone secretion can be ▪ Cortisol: Levels peak

directly influenced by the in the early morning
levels of certain ions or and decline
nutrients in the blood. throughout the day.

o Example: ▪ Melatonin: Secreted

by the pineal gland,
▪ Insulin: Secretion is increases in the
stimulated by high evening and
blood glucose levels. decreases in the
▪ Parathyroid Hormone morning.
(PTH): Released in 3. Factors Influencing Hormone Secretion
response to low blood
calcium levels. • Physiological State: Stress, illness,
and physical activity can alter
2. Other Humoral Factors: hormone secretion patterns.
o Hormones can also be • Age and Gender: Hormone levels can
regulated by other substances vary with age and between genders
in the blood, such as (e.g., sex hormones).
hormones from other glands
or metabolites. • Environmental Factors: Light
exposure, temperature, and nutrition
D. Neural Regulation can influence hormone levels.
1. Nervous System Influence: 4. Clinical Relevance
o The nervous system can • Hormonal Disorders: Dysregulation
directly stimulate hormone of hormone secretion can lead to
secretion through nerve various disorders (e.g., diabetes,
impulses. thyroid diseases).
o Example:
 • Therapeutic Interventions: A. Releasing and Inhibiting Hormones
Understanding hormone regulation is
• Function: The hypothalamus secretes
essential for developing treatments
hormones that regulate the secretion
(e.g., hormone replacement therapy,
of anterior pituitary hormones.
medications that modulate hormone
levels). • Examples:

o Thyrotropin-Releasing
Hormone (TRH): Stimulates
Endocrine Control by the Hypothalamus
the release of Thyroid-
and Pituitary Gland
Stimulating Hormone (TSH).
1. Introduction
o Corticotropin-Releasing
• The hypothalamus and pituitary gland Hormone (CRH): Stimulates
form a critical part of the endocrine the release of
system, often referred to as the Adrenocorticotropic Hormone
"master control" of hormonal (ACTH).
regulation in the body.
o Gonadotropin-Releasing
• They work together to maintain Hormone (GnRH): Stimulates
homeostasis by regulating various the release of Luteinizing
physiological processes through Hormone (LH) and Follicle-
hormone secretion. Stimulating Hormone (FSH).

2. Anatomy of the Hypothalamus and o Growth Hormone-Releasing

Pituitary Gland Hormone (GHRH): Stimulates
the release of Growth
A. Hypothalamus
Hormone (GH).
• Location: A small region of the brain
o Somatostatin: Inhibits the
located below the thalamus and
release of Growth Hormone
above the pituitary gland.
(GH) and Thyroid-Stimulating
• Structure: Composed of several Hormone (TSH).
nuclei that produce various hormones
o Prolactin-Inhibiting
and regulatory factors.
Hormone (PIH): Inhibits the
• Functions: Integrates the nervous release of Prolactin (PRL).
system with the endocrine system,
4. Hormones of the Anterior Pituitary
regulating body temperature, hunger,
thirst, sleep, and circadian rhythms. A. Major Hormones

B. Pituitary Gland • Growth Hormone (GH): Stimulates

growth and metabolism in tissues.
• Location: A pea-sized gland located
at the base of the brain, suspended • Thyroid-Stimulating Hormone (TSH):
from the hypothalamus by the Stimulates the thyroid gland to
infundibulum (pituitary stalk). produce thyroid hormones (T3 and
T4).
• Divisions:
• Adrenocorticotropic Hormone
1. Anterior Pituitary
(ACTH): Stimulates the adrenal cortex
(Adenohypophysis):
to produce cortisol.
Composed of glandular
tissue; produces and secretes • Luteinizing Hormone (LH):
several hormones. Stimulates ovulation in females and
testosterone production in males.
2. Posterior Pituitary
(Neurohypophysis): • Follicle-Stimulating Hormone (FSH):
Composed of neural tissue; Stimulates follicle development in
stores and releases hormones females and spermatogenesis in
produced by the males.
hypothalamus.
• Prolactin (PRL): Stimulates milk
3. Hormones of the Hypothalamus production in lactating females.
B. Regulation of Anterior Pituitary o Hyperpituitarism: Excess
Hormones hormone production, leading
to conditions like acromegaly
• The release of anterior pituitary
(excess GH).
hormones is regulated by
hypothalamic releasing and inhibiting o Diabetes Insipidus: Caused
hormones through the hypothalamic- by insufficient ADH
hypophyseal portal system, a production, leading to
specialized blood vessel system that excessive urination and thirst.
allows for rapid communication.

5. Hormones of the Posterior Pituitary

Thyroid Gland
A. Major Hormones
1. Introduction
• Oxytocin: Stimulates uterine
• The thyroid gland is a vital endocrine
contractions during childbirth and
organ responsible for regulating
milk ejection during breastfeeding.
metabolism, growth, and
• Antidiuretic Hormone (ADH, also development through the secretion of
known as Vasopressin): Regulates thyroid hormones.
water balance by promoting water
• It plays a crucial role in maintaining
reabsorption in the kidneys.
homeostasis and overall health.
B. Regulation of Posterior Pituitary
2. Anatomy of the Thyroid Gland
Hormones
A. Location
• The posterior pituitary does not
produce hormones; it stores and • The thyroid gland is located in the
releases hormones synthesized in the anterior neck, just inferior to the
hypothalamus. larynx and anterior to the trachea.
• Hormone release is triggered by nerve • It has a butterfly shape, consisting of
impulses from the hypothalamus in two lateral lobes connected by a
response to physiological stimuli narrow isthmus.
(e.g., increased blood osmolality
stimulates ADH release). B. Structure

6. Feedback Mechanisms • Thyroid Follicles: The gland is

composed of numerous spherical
• Negative Feedback: Most hormonal units called thyroid follicles, which
pathways involving the hypothalamus are lined by follicular cells.
and pituitary operate on a negative
feedback system to maintain • Colloid: The central cavity of each
homeostasis. follicle contains colloid, a sticky fluid
rich in thyroglobulin, the precursor to
o Example: Increased levels of thyroid hormones.
thyroid hormones (T3 and T4)
inhibit TRH and TSH release. • Parafollicular Cells (C Cells):
Located between the follicles, these
• Positive Feedback: Occurs in cells produce calcitonin, a hormone
specific situations, such as during involved in calcium regulation.
childbirth with oxytocin, where the
hormone release enhances the 3. Hormones Produced by the Thyroid
process. Gland

7. Clinical Relevance A. Thyroid Hormones

• Disorders of the Hypothalamus and 1. Thyroxine (T4):

Pituitary: Dysregulation can lead to o Composed of four iodine
various endocrine disorders, such as: atoms.
o Hypopituitarism: Insufficient o The primary hormone
hormone production from the produced by the thyroid gland,
pituitary gland. accounting for about 90% of
thyroid hormone output.
 o Functions to regulate • Thyroid-Stimulating Hormone (TSH)
metabolism, increase basal from the anterior pituitary stimulates
metabolic rate, and influence the uptake of colloid by follicular cells
growth and development. through endocytosis.

2. Triiodothyronine (T3): • Lysosomal enzymes break down

thyroglobulin, releasing free T3 and T4
o Composed of three iodine
into the bloodstream.
atoms.
5. Regulation of Thyroid Hormone
o More potent than T4, but
Secretion
produced in smaller
quantities (about 10% of A. Hypothalamic-Pituitary Axis
output).
• The secretion of thyroid hormones is
o T3 is primarily formed from the regulated by a feedback loop involving
conversion of T4 in peripheral the hypothalamus and pituitary gland.
tissues.
• Thyrotropin-Releasing Hormone
o Plays a critical role in (TRH): Released by the
regulating metabolism and hypothalamus, stimulates the
energy expenditure. anterior pituitary to secrete TSH.

B. Calcitonin • Thyroid-Stimulating Hormone (TSH):

Stimulates the thyroid gland to
• Produced by parafollicular cells (C
produce and release T3 and T4.
cells).
B. Feedback Mechanism
• Functions to lower blood calcium
levels by inhibiting osteoclast activity • Increased levels of T3 and T4 inhibit
in bones and promoting calcium the release of TRH and TSH,
excretion in the kidneys. maintaining homeostasis.

4. Synthesis and Release of Thyroid 6. Physiological Effects of Thyroid

Hormones Hormones

A. Hormone Synthesis A. Metabolism

1. Iodine Uptake: • Increase basal metabolic rate (BMR)

and oxygen consumption.
o Follicular cells actively
transport iodide ions from the • Stimulate carbohydrate and lipid
bloodstream into the cells. metabolism, promoting energy
production.
o Iodine is essential for the
synthesis of thyroid B. Growth and Development
hormones.
• Essential for normal growth and
2. Thyroglobulin Production: development in children, particularly
for brain development.
o Follicular cells synthesize
thyroglobulin, which is • Influence protein synthesis and
secreted into the colloid. overall growth.

3. Iodination: C. Cardiovascular Effects

o Iodide ions are oxidized and • Increase heart rate and cardiac
attached to the tyrosine output.
residues in thyroglobulin,
• Enhance the sensitivity of tissues to
forming monoiodotyrosine
catecholamines (e.g., epinephrine).
(MIT) and diiodotyrosine (DIT).
D. Thermoregulation
4. Hormone Formation:
• Play a role in maintaining body
o MIT and DIT combine to form
temperature by regulating metabolic
T3 and T4 within the colloid.
heat production.
B. Hormone Release
7. Clinical Relevance
A. Thyroid Disorders • Most individuals have four parathyroid
glands, but the number can vary from
1. Hypothyroidism:
two to six.
o Insufficient production of
B. Structure
thyroid hormones.
• Shape and Size: The glands are
o Symptoms: Fatigue, weight
small, round, and usually measure
gain, cold intolerance,
about 3-4 mm in diameter.
depression, and goiter.
• Types of Cells:
o Common causes:
Hashimoto's thyroiditis, iodine o Chief Cells: The primary cell
deficiency. type responsible for producing
and secreting parathyroid
2. Hyperthyroidism:
hormone (PTH).
o Excessive production of
o Oxyphil Cells: Their function
thyroid hormones.
is not well understood; they
o Symptoms: Weight loss, heat appear later in life and may
intolerance, anxiety, increased have a role in the regulation of
heart rate, and goiter. PTH.

o Common causes: Graves' 3. Hormone Produced by the Parathyroid

disease, toxic nodular goiter. Glands

3. Goiter: A. Parathyroid Hormone (PTH)

o Enlargement of the thyroid • Structure: A peptide hormone

gland, which can occur in composed of 84 amino acids.
both hypothyroidism and
• Function: PTH is the primary regulator
hyperthyroidism.
of calcium levels in the blood and has
o Often due to iodine deficiency several key actions:
or autoimmune conditions.
1. Bone Resorption: Stimulates
B. Diagnostic Tests osteoclasts to break down
bone tissue, releasing calcium
• Thyroid Function Tests: Measure into the bloodstream.
levels of TSH, T3, and T4 to assess
thyroid function. 2. Renal Reabsorption:
Increases calcium
• Thyroid Antibodies: Detect reabsorption in the kidneys,
autoimmune thyroid diseases. reducing calcium excretion in
urine.

Parathyroid Glands 3. Intestinal Absorption:

Enhances the absorption of
1. Introduction calcium from the intestines by
• The parathyroid glands are small promoting the activation of
endocrine glands that play a critical vitamin D (calcitriol).
role in regulating calcium and 4. Regulation of PTH Secretion
phosphate levels in the body.
A. Calcium Levels
• They secrete parathyroid hormone
(PTH), which is essential for • Primary Regulator: The secretion of
maintaining calcium homeostasis. PTH is primarily regulated by the
levels of ionized calcium in the blood.
2. Anatomy of the Parathyroid Glands
• Low Calcium Levels: When blood
A. Location calcium levels drop, the parathyroid
• The parathyroid glands are typically glands increase PTH secretion.
located on the posterior surface of the • High Calcium Levels: Elevated
thyroid gland. calcium levels inhibit PTH release,
 reducing its effects on bone, kidneys, and compensatory PTH
and intestines. overproduction.

B. Feedback Mechanism 2. Hypoparathyroidism:

• The regulation of PTH operates on a o Caused by damage to the

negative feedback loop: parathyroid glands (e.g.,
during thyroid surgery) or
o Increased blood calcium
autoimmune conditions.
levels lead to decreased PTH
secretion. o Symptoms: Hypocalcemia,
muscle cramps, tetany
o Decreased blood calcium
(muscle spasms), and
levels stimulate PTH
seizures.
secretion.
B. Diagnostic Tests
5. Physiological Effects of PTH
• Serum Calcium Levels:
A. Bone Metabolism
Measurement of calcium levels to
• PTH promotes the mobilization of assess parathyroid function.
calcium from bones, increasing
• PTH Levels: Measurement of PTH
serum calcium levels.
levels to differentiate between
• It stimulates osteoclast activity, primary and secondary
leading to bone resorption. hyperparathyroidism.

B. Renal Function • Bone Density Tests: To assess the

impact of altered calcium
• PTH enhances the reabsorption of metabolism on bone health.
calcium in the renal tubules,
decreasing urinary calcium excretion.

• It also promotes the excretion of Adrenal Glands

phosphate, helping to maintain
1. Introduction
phosphate balance.
• The adrenal glands are small,
C. Intestinal Absorption
triangular-shaped endocrine glands
• PTH indirectly increases intestinal located on top of each kidney.
calcium absorption by stimulating the
• They play a crucial role in the body's
conversion of vitamin D to its active
response to stress and regulate
form (calcitriol) in the kidneys.
various physiological processes
6. Clinical Relevance through the secretion of hormones.

A. Disorders of the Parathyroid Glands 2. Anatomy of the Adrenal Glands

1. Hyperparathyroidism: A. Structure

o Primary • Location: Each adrenal gland is

Hyperparathyroidism: situated atop a kidney, embedded in a
Caused by an adenoma or fibrous capsule.
hyperplasia of the parathyroid
• Divisions:
glands, leading to excessive
PTH secretion. 1. Adrenal Cortex: The outer
region, which is further
▪ Symptoms:
divided into three zones.
Hypercalcemia,
kidney stones, 2. Adrenal Medulla: The inner
osteoporosis, fatigue, region, which functions as
and abdominal pain. part of the sympathetic
nervous system.
o Secondary
Hyperparathyroidism: Often B. Zones of the Adrenal Cortex
due to chronic kidney disease,
1. Zona Glomerulosa:
leading to low calcium levels
o The outermost layer.
 o Produces mineralocorticoids, 3. Androgens:
primarily aldosterone, which
o Dehydroepiandrosterone
regulates sodium and
(DHEA): The primary androgen
potassium balance.
produced by the adrenal
2. Zona Fasciculata: cortex.

o The middle layer. o Functions: Contributes to the

development of male and
o Produces glucocorticoids,
female secondary sexual
primarily cortisol, which is
characteristics and is a
involved in stress response,
precursor for sex hormones
metabolism, and immune
like testosterone and
regulation.
estrogen.
3. Zona Reticularis:
B. Hormones of the Adrenal Medulla
o The innermost layer.
1. Catecholamines:
o Produces androgens (sex
o Epinephrine (Adrenaline):
hormones), such as
The primary hormone
dehydroepiandrosterone
released in response to stress.
(DHEA), which contribute to
the development of secondary o Norepinephrine
sexual characteristics. (Noradrenaline): Functions
alongside epinephrine in the
3. Hormones Produced by the Adrenal
"fight or flight" response.
Glands
o Functions:
A. Hormones of the Adrenal Cortex
▪ Increase heart rate
1. Mineralocorticoids:
and blood pressure.
o Aldosterone: The primary
▪ Dilate airways and
mineralocorticoid, which
increase blood flow to
regulates sodium and
muscles.
potassium levels, and
maintains blood pressure and ▪ Mobilize energy stores
fluid balance. by increasing glucose
availability.
o Mechanism of Action:
Increases sodium 4. Regulation of Hormone Secretion
reabsorption and potassium
A. Adrenal Cortex Regulation
excretion in the kidneys.
1. Renin-Angiotensin-Aldosterone
2. Glucocorticoids:
System (RAAS):
o Cortisol: The primary
o Low blood pressure or low
glucocorticoid, often referred
sodium levels stimulate the
to as the "stress hormone."
kidneys to release renin.
o Functions:
o Renin converts
▪ Increases blood angiotensinogen (from the
glucose levels by liver) to angiotensin I, which is
promoting converted to angiotensin II in
gluconeogenesis in the lungs.
the liver.
o Angiotensin II stimulates
▪ Suppresses the aldosterone secretion from
immune response and the zona glomerulosa.
inflammation.
2. Hypothalamic-Pituitary Axis:
▪ Aids in the
o Corticotropin-Releasing
metabolism of fats,
Hormone (CRH): Released by
proteins, and
the hypothalamus, stimulates
carbohydrates.
 the anterior pituitary to 2. Addison's Disease:
secrete Adrenocorticotropic
o Caused by insufficient
Hormone (ACTH).
production of adrenal
o Adrenocorticotropic hormones (cortisol and
Hormone (ACTH): Stimulates aldosterone).
cortisol secretion from the
o Symptoms: Fatigue, weight
zona fasciculata.
loss, low blood pressure, and
B. Adrenal Medulla Regulation hyperpigmentation of the skin.

• The adrenal medulla is stimulated by 3. Adrenal Insufficiency:

the sympathetic nervous system
o Can be primary (Addison's
during stress (fight or flight response).
disease) or secondary (due to
• Nerve impulses from the pituitary dysfunction).
hypothalamus trigger the release of
o Symptoms: Fatigue,
catecholamines (epinephrine and
weakness, low blood
norepinephrine).
pressure, and electrolyte
5. Physiological Effects of Adrenal imbalances.
Hormones
4. Pheochromocytoma:
A. Effects of Mineralocorticoids
o A tumor of the adrenal
• Aldosterone: Regulates sodium and medulla that secretes excess
potassium balance, affecting blood catecholamines.
volume and pressure.
o Symptoms: Hypertension,
B. Effects of Glucocorticoids palpitations, sweating, and
anxiety.
• Cortisol:
B. Diagnostic Tests
o Increases blood glucose
levels. • Hormone Level Tests: Measure levels
of cortisol, aldosterone, and
o Suppresses inflammation and
catecholamines.
immune responses.
• Imaging Studies: CT or MRI scans to
o Affects metabolism of
identify tumors or abnormalities in the
proteins, fats, and
adrenal glands.
carbohydrates.

C. Effects of Androgens
Adrenal Medulla
• Contribute to the development of
secondary sexual characteristics and 1. Introduction
influence libido.
• The adrenal medulla is the inner part
D. Effects of Catecholamines of the adrenal glands, which are
located on top of each kidney.
• Prepare the body for rapid response to
stress by increasing heart rate, blood • It plays a crucial role in the body's
pressure, and energy availability. response to stress by producing
catecholamines, which are hormones
6. Clinical Relevance
that prepare the body for "fight or
A. Disorders of the Adrenal Glands flight" situations.

1. Cushing's Syndrome: 2. Anatomy of the Adrenal Medulla

o Caused by excessive cortisol A. Location

production, often due to a
• The adrenal medulla is situated at the
pituitary tumor (Cushing's
center of the adrenal gland,
disease) or adrenal tumors.
surrounded by the adrenal cortex.
o Symptoms: Weight gain,
B. Structure
hypertension, diabetes, and
characteristic "moon face." • Cell Types:
 o Chromaffin Cells: The o Functions primarily as a
primary cell type in the neurotransmitter in the
adrenal medulla, responsible central nervous system but
for producing also has peripheral effects.
catecholamines.
4. Regulation of Catecholamine Secretion
o Supportive Cells: Include
A. Neural Regulation
various types of cells that
provide structural support and • The adrenal medulla is primarily
assist in hormone secretion. regulated by the sympathetic nervous
system.
3. Hormones Produced by the Adrenal
Medulla • Stress Response:
A. Catecholamines o In response to stressors
(physical or emotional), the
1. Epinephrine (Adrenaline):
hypothalamus activates the
o The primary hormone sympathetic nervous system.
produced by the adrenal
o Preganglionic sympathetic
medulla, accounting for about
fibers stimulate chromaffin
80% of catecholamine output.
cells in the adrenal medulla to
o Functions: release catecholamines into
the bloodstream.
▪ Increases heart rate
and cardiac output. B. Feedback Mechanisms

▪ Dilates airways to • Catecholamine release is not typically

improve oxygen intake. regulated by negative feedback
mechanisms like other hormones;
▪ Mobilizes energy
instead, it is a rapid response to acute
stores by increasing
stress.
glucose availability.
5. Physiological Effects of Catecholamines
▪ Enhances blood flow
to skeletal muscles A. Cardiovascular Effects
while redirecting blood
• Increased Heart Rate: Epinephrine
flow away from non-
increases heart rate and contractility,
essential organs.
enhancing cardiac output.
2. Norepinephrine (Noradrenaline):
• Vasodilation and Vasoconstriction:
o Accounts for about 20% of
o Epinephrine causes
catecholamine output.
vasodilation in skeletal
o Functions: muscles and vasoconstriction
in the gastrointestinal tract
▪ Increases peripheral
and skin, optimizing blood
vascular resistance,
flow to essential organs during
leading to elevated
stress.
blood pressure.
B. Respiratory Effects
▪ Enhances alertness
and arousal. • Bronchodilation: Epinephrine relaxes
bronchial smooth muscle, increasing
▪ Works alongside
airflow to the lungs and improving
epinephrine to prepare
oxygen delivery.
the body for stress
responses. C. Metabolic Effects

3. Dopamine: • Increased Blood Glucose Levels:

o A precursor to norepinephrine o Epinephrine stimulates

and epinephrine, though glycogenolysis (breakdown of
produced in smaller amounts glycogen to glucose) in the
in the adrenal medulla. liver and muscle, increasing
 blood glucose levels for Disorders Involving the Adrenal Glands
energy.
1. Introduction
o It also promotes lipolysis
• The adrenal glands are essential for
(breakdown of fats) to provide
producing hormones that regulate
additional energy sources.
metabolism, immune response,
D. Central Nervous System Effects blood pressure, and stress responses.

• Increased Alertness: • Disorders of the adrenal glands can

Catecholamines enhance mental lead to significant health issues,
alertness and cognitive function affecting various bodily functions.
during stressful situations.
2. Overview of Adrenal Gland Structure and
• Mood and Behavior: They can Function
influence mood and behavior,
• Adrenal Cortex: Produces
contributing to feelings of anxiety or
corticosteroids (mineralocorticoids,
excitement.
glucocorticoids, and androgens).
6. Clinical Relevance
• Adrenal Medulla: Produces
A. Disorders Related to the Adrenal catecholamines (epinephrine and
Medulla norepinephrine).

1. Pheochromocytoma: • Hormonal imbalances can result from

dysfunction in either the cortex or
o A tumor of the adrenal
medulla.
medulla that secretes excess
catecholamines, leading to 3. Common Disorders of the Adrenal
symptoms such as Glands
hypertension, palpitations,
A. Cushing's Syndrome
sweating, and anxiety.
1. Definition: A condition characterized
o Diagnosis involves measuring
by excessive cortisol production.
plasma and urinary
catecholamine levels and 2. Causes:
imaging studies.
o Primary: Adrenal tumors
2. Adrenal Crisis: (adenomas or carcinomas)
producing excess cortisol.
o A severe deficiency of adrenal
hormones, including o Secondary: Pituitary
catecholamines, can lead to adenoma secreting excess
an adrenal crisis, Adrenocorticotropic Hormone
characterized by low blood (ACTH) (Cushing's disease).
pressure, severe fatigue, and
shock. o Tertiary: Hypothalamic
dysfunction leading to
B. Stress-Related Disorders increased CRH and ACTH.
• Chronic stress can lead to prolonged 3. Symptoms:
catecholamine secretion,
contributing to various health issues, o Weight gain (especially in the
including hypertension, anxiety trunk and face, known as
disorders, and metabolic syndrome. "moon face").

o Hypertension.

o Hyperglycemia (diabetes).

o Osteoporosis and muscle

weakness.

o Skin changes (thinning, easy

bruising, striae).

4. Diagnosis:
 o 24-hour urinary free cortisol 5. Treatment:
test.
o Hormone replacement
o Late-night salivary cortisol therapy (hydrocortisone for
test. cortisol, fludrocortisone for
aldosterone).
o Dexamethasone suppression
test. o Patient education on stress
management and emergency
5. Treatment:
steroid use.
o Surgical removal of tumors.
C. Hyperaldosteronism (Conn's Syndrome)
o Medications to inhibit cortisol
1. Definition: A condition characterized
production (e.g.,
by excessive production of
ketoconazole, metyrapone).
aldosterone.
o Radiation therapy for pituitary
2. Causes:
adenomas.
o Adrenal adenoma (primary
B. Addison's Disease
hyperaldosteronism).
1. Definition: A condition characterized
o Bilateral adrenal hyperplasia.
by insufficient production of adrenal
hormones (cortisol and aldosterone). o Rarely, adrenal carcinoma.

2. Causes: 3. Symptoms:

o Autoimmune destruction of o Hypertension (often resistant

the adrenal cortex (most to treatment).
common).
o Hypokalemia (low potassium
o Infections (e.g., tuberculosis, levels), leading to muscle
HIV). weakness and cramps.

o Adrenal hemorrhage or o Metabolic alkalosis.

metastasis.
4. Diagnosis:
3. Symptoms:
o Plasma aldosterone and renin
o Fatigue and weakness. levels (high aldosterone, low
renin).
o Weight loss and decreased
appetite. o Saline infusion test (failure to
suppress aldosterone).
o Hyperpigmentation of the skin
(especially in areas exposed o Imaging studies (CT scan) to
to friction). identify adenomas.

o Low blood pressure 5. Treatment:

(hypotension).
o Surgical removal of adenoma.
o Salt cravings due to low
o Medications (e.g.,
aldosterone levels.
spironolactone or eplerenone)
o Nausea, vomiting, and to block aldosterone effects.
abdominal pain.
D. Adrenal Insufficiency
4. Diagnosis:
1. Definition: A condition where the
o Serum cortisol and ACTH adrenal glands do not produce
levels (low cortisol, high adequate amounts of hormones.
ACTH).
2. Types:
o ACTH stimulation test (failure
o Primary Adrenal
to increase cortisol levels).
Insufficiency: Due to adrenal
o Imaging studies (CT scan) to gland damage (Addison's
assess adrenal glands. disease).
 o Secondary Adrenal o Surgical removal of the tumor.
Insufficiency: Due to
o Preoperative management
insufficient ACTH production
with alpha-blockers (e.g.,
from the pituitary gland.
phenoxybenzamine) to control
o Tertiary Adrenal hypertension.
Insufficiency: Due to lack of
CRH from the hypothalamus.
the Pancreas (Section 17.4f)
3. Symptoms:
1. Introduction
o Fatigue, weakness, and
lethargy. • The pancreas is a vital organ that
serves both exocrine and endocrine
o Hypotension and dizziness.
functions.
o Nausea, vomiting, and
• It plays a crucial role in digestion and
abdominal pain.
the regulation of blood glucose levels.
o Hyperpigmentation (in primary
2. Anatomy of the Pancreas
adrenal insufficiency).
A. Location
4. Diagnosis:
• The pancreas is a long, slender organ
o Serum cortisol and ACTH
located posterior to the stomach.
levels.
• It is situated in the upper abdomen,
o ACTH stimulation test.
extending horizontally across the
o Insulin tolerance test (for posterior abdominal wall.
secondary adrenal
B. Structure
insufficiency).
• The pancreas is divided into three
5. Treatment:
main parts:
o Hormone replacement
1. Head: The broadest part,
therapy (hydrocortisone).
nestled in the curve of the
o Education on stress duodenum.
management and emergency
2. Body: The central portion of
steroid use.
the pancreas.
E. Pheochromocytoma
3. Tail: The tapered end that
1. Definition: A tumor of the adrenal extends toward the spleen.
medulla that secretes excess
3. Functions of the Pancreas
catecholamines (epinephrine and
norepinephrine). A. Exocrine Function
2. Symptoms: • The majority of the pancreas is
composed of exocrine tissue, which
o Paroxysmal episodes of
produces digestive enzymes.
hypertension.
• Digestive Enzymes:
o Palpitations, sweating, and
anxiety. o Amylase: Breaks down
carbohydrates into simple
o Headaches and tremors.
sugars.
3. Diagnosis:
o Lipase: Digests fats into fatty
o Measurement of plasma free acids and glycerol.
metanephrines or urinary
o Inactive Proteases: Such as
catecholamines.
trypsinogen and
o Imaging studies (CT or MRI) to chymotrypsinogen, which are
locate the tumor. activated in the small
intestine to digest proteins.
4. Treatment:
 • These enzymes are secreted into the 4. Regulation of Hormone Secretion
pancreatic duct and then into the
A. Insulin Secretion
duodenum to aid in digestion.
• Stimulus: Elevated blood glucose
B. Endocrine Function
levels (e.g., after a meal).
• The pancreas contains clusters of
• Mechanism: Beta cells sense
endocrine cells known as pancreatic
increased glucose and secrete
islets (islets of Langerhans).
insulin, which facilitates glucose
• The islets are composed of four main uptake by cells and promotes
types of cells, each producing glycogen synthesis in the liver.
specific hormones:
B. Glucagon Secretion
1. Alpha Cells:
• Stimulus: Low blood glucose levels
▪ Produce glucagon. (e.g., during fasting or exercise).

▪ Function: Raises • Mechanism: Alpha cells detect

blood glucose levels decreased glucose and secrete
by stimulating glucagon, which stimulates the liver
glycogenolysis to release glucose into the
(breakdown of bloodstream.
glycogen) in the liver
C. Somatostatin Secretion
and promoting
gluconeogenesis • Stimulus: Elevated levels of glucose
(conversion of amino and amino acids.
acids to glucose).
• Mechanism: Delta cells release
2. Beta Cells: somatostatin to inhibit the secretion
of both insulin and glucagon, helping
▪ Produce insulin.
to maintain glucose homeostasis.
▪ Function: Lowers
D. Pancreatic Polypeptide Secretion
blood glucose levels
by facilitating the • Stimulus: Food intake and fasting.
uptake of glucose into
cells, particularly in • Mechanism: PP cells release
muscle and adipose pancreatic polypeptide, which may
tissue, and promoting help regulate appetite and digestive
glycogen storage in the processes.
liver. 5. Clinical Relevance
3. Delta Cells: A. Diabetes Mellitus
▪ Produce somatostati • A condition characterized by
n. insufficient insulin production (Type 1)
▪ Function: Inhibits the or insulin resistance (Type 2), leading
release of growth to elevated blood glucose levels.
hormone (GH), • Type 1 Diabetes: Autoimmune
glucagon, and insulin, destruction of beta cells, resulting in
playing a role in little to no insulin production.
regulating the
endocrine system. • Type 2 Diabetes: Insulin resistance in
target tissues, often associated with
4. PP Cells (Pancreatic obesity and lifestyle factors.
Polypeptide Cells):
B. Pancreatitis
▪ Produce pancreatic
polypeptide (PP). • Inflammation of the pancreas, which
can be acute or chronic.
▪ Function: Involved in
appetite regulation • Acute Pancreatitis: Often caused by
and the control of gallstones or excessive alcohol
pancreatic secretions.
 consumption, leading to abdominal • The thymus receives blood supply
pain and digestive issues. from the internal thoracic arteries and
the inferior thyroid arteries.
• Chronic Pancreatitis: Long-term
inflammation that can result in • Blood vessels enter the thymus at the
permanent damage to the pancreas corticomedullary junction, where they
and affect both exocrine and branch into smaller capillaries.
endocrine functions.
3. Functions of the Thymus
C. Pancreatic Cancer
A. T Cell Development
• A serious condition that often
• The primary function of the thymus is
presents with vague symptoms and is
the maturation of T lymphocytes from
typically diagnosed at an advanced
precursor cells originating in the bone
stage.
marrow.
• Risk factors include smoking, obesity,
• Thymocyte Development:
and chronic pancreatitis.
1. Progenitor Cells: Immature T
cells migrate from the bone
the Thymus marrow to the thymus.

1. Introduction 2. Positive Selection:

Thymocytes that can
• The thymus is a specialized organ of
recognize self-MHC
the immune system that plays a
molecules are selected for
crucial role in the development and
survival in the cortex.
maturation of T lymphocytes (T cells),
which are essential for adaptive 3. Negative Selection:
immunity. Thymocytes that strongly bind
to self-antigens are eliminated
• It is most active during infancy and
in the medulla to prevent
childhood and undergoes involution
autoimmunity.
(shrinkage) with age.
4. Mature T Cells: Surviving
2. Anatomy of the Thymus
thymocytes differentiate into
A. Location various T cell subtypes (e.g.,
CD4+ helper T cells, CD8+
• The thymus is located in the anterior cytotoxic T cells) and enter the
mediastinum, just behind the bloodstream.
sternum and above the heart.
B. Hormonal Function
• It is situated between the lungs and
extends from the lower neck to the • The thymus produces several
upper thorax. hormones, collectively known as
thymosins, which play a role in T cell
B. Structure development and immune function.
• The thymus is a bilobed organ, with • Thymosins:
each lobe (thymic lobe) consisting of:
o Promote the proliferation and
1. Cortex: The outer region, differentiation of T cells.
densely packed with
immature T cells (thymocytes) o Influence the maturation of T
and epithelial cells. cells and their ability to
respond to antigens.
2. Medulla: The inner region,
containing fewer thymocytes • Other hormones produced include
and more mature T cells, thymulin and thymopoietin, which
along with Hassall's also contribute to T cell maturation.
corpuscles (clusters of
4. Regulation of Thymic Function
epithelial cells).
A. Age-Related Changes
C. Blood Supply
 • The thymus is most active during immune response, which is critical for
childhood, with peak size and activity the effectiveness of vaccines.
occurring during puberty.
• A well-functioning thymus ensures
• After puberty, the thymus gradually the production of diverse and
undergoes involution, leading to a functional T cells that can respond to
decrease in T cell production and pathogens.
thymic hormones.

B. Immune System Signals

Hormonal Functions of Various Organs
• The development and maturation of T
1. The Heart
cells in the thymus are influenced by
various cytokines and growth factors, A. Anatomy and Function
including interleukins (IL-7) and
thymic stromal lymphopoietin (TSLP). • The heart is a muscular organ
responsible for pumping blood
5. Clinical Relevance throughout the body.
A. Thymic Disorders • It consists of four chambers: two atria
and two ventricles.
1. Thymic Hyperplasia:
B. Hormonal Function
o An increase in thymic size,
often associated with • Atrial Natriuretic Peptide (ANP):
autoimmune diseases (e.g.,
myasthenia gravis). o Source: Secreted by
specialized cells in the atrial
o Can lead to increased walls in response to increased
production of T cells and blood volume or pressure.
potential autoimmunity.
o Function: ANP promotes
2. Thymoma: sodium excretion in the urine
by the kidneys, leading to
o A tumor of the thymus, which
decreased blood volume and
can be benign or malignant.
pressure through osmosis.
o Associated with autoimmune
2. The Gastrointestinal Tract
conditions and can cause
symptoms due to mass effect A. Anatomy and Function
or paraneoplastic syndromes.
• The gastrointestinal (GI) tract includes
3. Thymic Atrophy: organs such as the stomach and
small intestine, responsible for
o Can occur due to aging,
digestion and nutrient absorption.
stress, malnutrition, or certain
infections (e.g., HIV). B. Hormonal Function
o Results in decreased T cell • Gastrin:
production and impaired
immune function. o Source: Secreted by G cells in
the stomach in response to
B. Role in Autoimmunity food intake and stomach
distention.
• The thymus plays a critical role in
establishing self-tolerance through o Function: Stimulates the
negative selection. release of hydrochloric acid
(HCl) from parietal cells,
• Failure of this process can lead to
aiding in digestion.
autoimmune diseases, where the
immune system attacks the body's • Other Hormones:
own tissues.
o Hormones such as secretin
C. Thymus and Vaccination and cholecystokinin (CCK) are
produced by intestinal cells
• The thymus is essential for the
and help regulate digestive
development of a functional adaptive
 processes and nutrient protecting against
absorption. cardiovascular disease.

3. The Kidneys • Other Adipokines: Various hormones

produced by adipose tissue that
A. Anatomy and Function
influence metabolism, inflammation,
• The kidneys are bean-shaped organs and cardiovascular health.
that filter blood, remove waste, and
5. The Skin
regulate fluid and electrolyte balance.
A. Anatomy and Function
B. Hormonal Function
• The skin is the largest organ of the
• Erythropoietin (EPO):
body, providing a barrier and playing a
o Source: Secreted by role in thermoregulation and
interstitial cells in the kidneys sensation.
in response to low oxygen
B. Hormonal Function
levels.
• Vitamin D3 (Calcitriol):
o Function: Stimulates the
production of red blood cells o Source: Synthesized in the
(erythrocytes) in the bone skin from cholesterol upon
marrow, enhancing oxygen exposure to ultraviolet (UV)
delivery to tissues. radiation.

• Renin: o Function: Converted to its

active form in the liver and
o Source: Released by
kidneys, vitamin D3 regulates
juxtaglomerular cells in
calcium absorption in the
response to low blood
intestines and supports
pressure or low sodium levels.
immune function.
o Function: Initiates the renin-
6. The Liver
angiotensin-aldosterone
system (RAAS), which A. Anatomy and Function
regulates blood pressure and
• The liver is a large organ involved in
fluid balance.
metabolism, detoxification, and the
4. Adipose Tissue production of various proteins.

A. Anatomy and Function B. Hormonal Function

• Adipose tissue is specialized • Insulin-like Growth Factor (IGF):

connective tissue that stores fat and
o Source: Produced by the liver
regulates energy metabolism.
in response to growth
B. Hormonal Function hormone (GH) stimulation.

• Leptin: o Function: Promotes growth

and development in various
o Source: Secreted by
tissues.
adipocytes (fat cells) in
proportion to body fat levels. • Angiotensinogen:

o Function: Signals satiety to o Source: Secreted by the liver

the brain, reducing appetite as a precursor to angiotensin.
and regulating energy
o Function: Involved in the
expenditure.
regulation of blood pressure
• Adiponectin: and fluid balance.

o Source: Also produced by • Thrombopoietin:

adipocytes.
o Source: Produced by the liver.
o Function: Enhances insulin
o Function: Stimulates the
sensitivity and has anti-
production of platelets in the
inflammatory effects,
bone marrow.
• Hepcidin:

o Source: Secreted by the liver.

o Function: Regulates iron

homeostasis in the body.