FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.

BELANDRES
PUBERTY - Eicosanoid Hormones:
- marks a period where significant physical and o derived from arachidonic acid.
behavioral differences between girls and boys o two main types of eicosanoids:
become evident, largely influenced by the prostaglandins (PGs) and leukotrienes
endocrine system. (LTs).
- Girls
o estrogens play a crucial role by I. HYPOTHALAMUS
promo>ng the accumula>on of adipose - a region of the brain located below the
>ssue in the breasts and hips, giving rise thalamus
to a more feminine physique. - serves as the major connec>on between the
- Boys nervous and endocrine systems
o increasing testosterone levels - hormones secreted are essen>al for regula>ng
contribute to muscle mass development various aspects of:
and the enlargement of vocal cords, o Growth
resul>ng in a deeper voice. o Development
o Metabolism
ENDOCRINE GLAND o Homeostasis
- endocrine system controls body func>ons
through the release of hormones
- ductless glands

Hormones
- released by endocrine glands and travel through
the bloodstream to reach target cells
throughout the body.
- Responses in the endocrine system are
generally slower compared to the nervous
system.
- may take minutes to hours to ini>ate a response
- influence of the endocrine system is broad,
affec>ng virtually all types of body cell.
- In some cases, chemicals can func>on as both
neurotransmiDers and hormones, such as
norepinephrine, which can be released as a
neurotransmi?er by sympathe>c postganglionic
neurons and as a hormone by chromaffin cells
- plays a crucial role in regulaOng the secreOon of
of the adrenal medulla.
anterior pituitary hormones through the
release of specific hormones
Chemical Classes of Hormones
- These hypothalamic hormones can either
1. Lipid-Soluble Hormones
s>mulate or inhibit the anterior pituitary,
- Steroid Hormones:
depending on the desired hormonal response
o derived from cholesterol
o Examples include cor>sol, aldosterone,
STIMULATING HORMONES:
and sex hormones (estrogen,
- Growth hormone-releasing hormone (GHRH):
progesterone, testosterone).
o aka somatocrinin
- Thyroid Hormones:
o s>mulates the secre>on of growth
o Thyroid hormones (T3 and T4) are
hormone (GH) from the anterior
synthesized by aDaching iodine to the
pituitary à plays a role in body growth.
amino acid tyrosine.
- Thyrotropin-releasing hormone (TRH):
- Nitric Oxide (NO):
o s>mulates the secre>on of thyroid-
o unique hormone that is both a
sOmulaOng hormone (TSH) from the
hormone and a neurotransmiDer.
anterior pituitary.
o has various roles, including vasodila>on
● TSH, in turn, regulates the
and neurotransmission
thyroid gland's ac>vity and the
2. Water-Soluble Hormones
produc>on of thyroid
- Amine Hormones:
hormones.
o synthesized by modifying specific amino
- CorOcotropin-releasing hormone (CRH):
acids
o prompts the secre>on of
o Examples include catecholamines
adrenocorOcotropic hormone (ACTH)
(epinephrine, norepinephrine,
from the anterior pituitary
dopamine), histamine, serotonin, and
melatonin. ● ACTH regulates the adrenal
- PepOde and Protein Hormones cortex and the produc>on of
o Examples include an>diure>c hormone glucocor>coids like corOsol
(ADH) and oxytocin, and protein - ProlacOn-releasing hormone (PRH):
hormones include growth hormone and o s>mulates the secre>on of prolacOn
insulin. (PRL) from the anterior pituitary à

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
involved in milk producOon in the 2. Thyrotrophs
mammary glands - secrete thyroid-sOmulaOng hormone (TSH),
- Gonadotropin-releasing hormone (GnRH): also known as thyrotropin
o encourages the secre>on of follicle- o controls the secre>ons and ac>vi>es of
s>mula>ng hormone (FSH) and the thyroid gland, which plays a crucial
luteinizing hormone (LH) from the role in metabolism
anterior pituitary 3. Gonadotrophs
● FSH and LH are important for - secrete two gonadotropins:
reproduc>ve func>ons in both o follicle-sOmulaOng hormone (FSH)
men and women o luteinizing hormone (LH).
INHIBITING HORMONES: - FSH and LH have dis>nct roles in both men and
- Growth hormone-inhibiOng hormone (GHIH): women
o Aka somatostaOn o Men: s>mulate the testes to produce
o inhibits the secre>on of growth sperm and secrete testosterone
hormone (GH) o Women: s>mulate the ovaries to
o acts as a nega>ve feedback mechanism mature oocytes (eggs) and secrete
to control GH levels estrogens and progesterone
- ProlacOn-inhibiOng hormone (PIH): 4. Lactotrophs
o This is dopamine - secrete prolacOn (PRL)
● inhibits the secre>on of o ini>ates and regulates milk produc>on
prolac>n (PRL). in the mammary glands
● regulates the release of PRL, 5. CorOcotrophs
primarily involved in milk - secrete adrenocorOcotropic hormone (ACTH),
produc>on. also known as cor>cotropin
o s>mulates the adrenal cortex to
produce glucocor>coids, including
II. PITUITARY GLAND
cor>sol, which are involved in various
- small, pea-shaped
physiological processes.
- situated in the hypophyseal fossa within the
- secrete melanocyte-sOmulaOng hormone
sella turcica of the sphenoid bone
(MSH)
- connected to the hypothalamus by a stalk
known as the infundibulum
POSTERIOR PITUITARY
- aka neurohypophysis
- made up of neural >ssue
- consists of 2 parts:
o pars nervosa
o infundibulum
2 posterior pituitary hormones:
- secre>on controlled by the hypothalamus
- Neurosecretory cells in the paraventricular and
supraop>c nuclei of the hypothalamus secrete
these 2 hormones
1. Oxytocin
- Produced in the paraventricular nucleus of the
hypothalamus
- During Childbirth: Oxytocin is released in
response to the stretching of the cervix of the
uterus during labor.
- has two dis>nct por>ons: o enhances uterine contrac>ons, which
ANTERIOR PITUITARY are essen>al for the progress of labor
- aka adenohypophysis and the delivery of the baby
- cons>tutes approximately 75% of the gland's - Breast Milk EjecOon: promote milk ejec>on
total weight (commonly referred to as "letdown") from the
- composed of epithelial >ssue mammary glands.
- further divided into 2: o triggered by the mechanical s>mulus
o pars distalis provided by a suckling infant, allowing
o pars tuberalis milk to flow from the mammary glands.
- Parental Behavior: Experiments with animals
5 anterior pituitary cells: have suggested that oxytocin may have ac>ons
1. Somatotrophs within the brain that foster parental caretaking
- secrete growth hormone (GH), also known as behavior toward young offspring.
human growth hormone (hGH) or - Sexual Pleasure: may also be par>ally
somatotropin. responsible for the feelings of sexual pleasure
o responsible for s>mula>ng general body experienced during and ader intercourse.
growth and regula>ng metabolic
processes

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
2. AnOdiureOc hormone (ADH) III. THYROID GLAND
- Decreasing Urine ProducOon: It acts on the - bu?erfly-shaped organ
kidneys, specifically on the renal tubules, to - located below the larynx
promote the reabsorp>on of water, thus - consis>ng of right and led lateral lobes
reducing urine volume. connected by an isthmus
o In the absence of ADH, urine output - The normal mass of the thyroid is around 30g.
increases significantly.
- Influence on Blood Pressure: It causes the
constric>on of arterioles (small arteries), which
increases peripheral vascular resistance and,
consequently, blood pressure.
- The release of ADH is influenced by two main
s>muli: a rise in blood osmolarity (the
concentra>on of solutes in the blood) and a
decrease in blood volume.
o hypothalamus's osmoreceptors detect
changes in blood osmolarity,
o volume receptors in the atria of the
heart and baroreceptors in certain
blood vessels sense changes in blood
volume
o When these receptors are ac>vated,
they s>mulate the synthesis and release
of ADH from neurosecretory cells in the
hypothalamus
- Other factors s>mula>ng ADH secre>on
o pain, stress, trauma, anxiety,
acetylcholine, nico>ne, and certain - Microscopically composed of spherical sacs
drugs (e.g., morphine, tranquilizers, known as thyroid follicles.
some anesthe>cs - Thyroid follicles is composed of:
o Follicular cells:
§ produce 2 hormones: thyroxine
(T4) and triiodothyronine (T3),
collec>vely referred to as
thyroid hormones.
§ When the follicular cells are
inacOve, their shape is low
cuboidal to squamous, but
under the influence of TSH they
become acOve in secre>on and
range from cuboidal to low
columnar in shape
o Parafollicular cells (C cells)
§ located between follicles
§ produce calcitonin
• regulates calcium
homeostasis.

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
THYROID HORMONES
AcOons:
1. Increase basal metabolic rate
- s>mulate synthesis of addi>onal Na+/K+
ATPases
- increase the concentra>ons of enzymes
involved in cellular respira>on, which increases
the breakdown of organic fuels and increase ATP
produc>on
- increase the number and ac>vity of
mitochondria in cells, which also increases ATP
produc>on
2. Enhance acOon of catecholamines
- have permissive effects on the catecholamines
(epinephrine and norepinephrine) because they
up-regulate β-adrenergic receptors
- symptoms of excess levels of thyroid hormone
include increased heart rate, more forceful
heartbeats, and increased blood pressure
3. Regulate development and growth of nervous
Ossue and bones
- necessary for the development of the nervous
system: CALCITONIN
o promote synapse forma>on, myelin - Produced by the Parafollicular cells
produc>on, and growth of dendrites - decrease the level of calcium in the blood by
- required for growth of the skeletal system: inhibiOng the acOon of osteoclasts
o promote forma>on of ossifica>on - inhibiOng bone resorpOon (breakdown of bone
centers in developing bones extracellular matrix) by osteoclasts
o promote synthesis of many bone - accelera>ng uptake of calcium and phosphates
proteins into bone extracellular matrix thus decreasing
o promote secre>on of growth hormone levels in the blood
(GH) and insulin-like growth factors
(IGFs) IV. PARATHYROID GLAND
- Deficiency of thyroid hormones during fetal - par>ally embedded in the posterior surface of
development, infancy, or childhood causes the lateral lobes of the thyroid gland
severe mental retardaOon and stunted bone - several small, round masses of >ssue
growth - Each has a mass of about 40mg (0.04 g).
RegulaOon: - Usually, one superior and one inferior
- Trigger: Low blood levels of T3 and T4 or low parathyroid gland are aDached to each lateral
metabolic rate thyroid lobe, for a total of 4
- s>mulate the hypothalamus to secrete TRH.
- TRH enters the hypothalamic–hypophyseal
portal system and flows to the anterior pituitary,
where it s>mulates thyrotrophs to secrete TSH.
- TSH s>mulates virtually all aspects of thyroid
follicular cell ac>vity, including iodide trapping,
hormone synthesis and secre>on, and growth of
the follicular cells.
- The thyroid follicular cells release T3 and T4 into
the blood un>l the metabolic rate returns to
normal.
- Trigger: Elevated level of T3 inhibits release of
TRH and TSH (negaOve feedback inhibiOon)

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
- Microscopically, the parathyroid glands contain PARATHYROID HORMONE
2 kinds of epithelial cells: Effects:
o Chief cells - major regulator of the levels of calcium (Ca2+),
§ Aka Principal cells magnesium (Mg2+), and phosphate (HPO4 2−)
§ more numerous ions in the blood
§ produce parathyroid hormone - increase the number and ac>vity of osteoclasts
(PTH), also called o releases Ca2+ and phosphates (HPO4
parathormone. 2−) into the blood
o Oxyphil cell - Kidneys
§ func>on is not known in a o slows the rate at which Ca2+ and Mg2+
normal parathyroid gland are lost from blood into the urine
o increases loss of HPO4
o promote forma>on of the hormone
calcitriol
§ Calcitriol, also known as 1,25-
dihydroxyvitamin D3
• increases the rate of
Ca2+, HPO4 2−, and
Mg2+ absorp>on from
the gastrointes>nal
tract into the blood
- overall increase in Calcium, Magnesium
decrease Phosphates in the blood
Events:
- Trigger: higher-than-normal level of calcium
ions (Ca2+) in the blood s>mulates parafollicular
cells of the thyroid gland to release more
calcitonin.
- Calcitonin inhibits the acOvity of osteoclasts,
thereby decreasing the blood Ca2+ level.
- Trigger: lower-than-normal level of Ca2+ in the
blood s>mulates chief cells of the parathyroid
gland to release more PTH.
- PTH:
o promotes resorpOon of bone
extracellular matrix, which releases
Ca2+ into the blood and slows loss of
Ca2+ in the urine, raising the blood
level of Ca2+.
o s>mulates the kidneys to synthesize
calcitriol, the ac>ve form of vitamin D.
§ Calcitriol s>mulates increased
absorpOon of Ca2+ from foods
in the gastrointesOnal tract,
which helps increase the blood
level of Ca2+

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
V. ADRENAL GLAND MINERALOCORTICOID (ALDOSTERONE)
- aka Suprarenal glands - It regulates homeostasis of two mineral ions:
- paired adrenal glands - one of which lies o sodium ions (Na+)
superior to each kidney in the retroperitoneal o potassium ions (K+)
space - helps adjust blood pressure and blood volume
- 2 structurally and func>onally dis>nct regions: - promotes excre>on of H+ in the urine
o this removal of acids from the body can
help prevent acidosis (blood pH below
7.35)

RENIN-ANGOTENSIN-ALDOSTERONE SYSTEM (RAAS)

PATHWAY
Events in the RAAS Pathway:
- S>muli: decrease blood volumeà decrease BP
o Dehydra>on
o Na+ deficiency
o Hemorrhage
- Decrease BP s>mulates Juxtoglomerular cells
(kidneys) to secrete RENIN, an enzyme.
- RENIN converts ANGIOTENSINOGEN (liver), a
plasma protein, into ANGIOTENSIN I
- ANGIOTENSIN-COVERTING ENZYME (ACE) in
the lungs, coverts ANGIOTENSINOGEN I into
ANGIOTENSIN II
- ANGIOTENSINOGEN II s>mulates the adrenal
cortex to secrete ALDOSTERONE
- In the kidneys, aldosterone does the ff:
1. Adrenal Cortex o Increases reabsorp>on of Na+
- a large, peripherally located adrenal cortex, § Causes reabsorp>on of water
comprising 80–90% of the gland, and a small, • Less water loss in urine
centrally located adrenal medulla. o Increase secre>on of K+ and H+
- produces steroid hormones that are essen>al - The increase water absorp>on will increase the
for life. blood volume which then increases blood
o Complete loss of adrenocor>cal pressure to normal levels
hormones leads to death due to - ANGIOTENSIN II also s>mulate smooth muscle
dehydra>on and electrolyte imbalances contrac>on in the walls of arterioles
in a few days to a week, unless o Leads to vasoconstric>on which helps
hormone replacement therapy begins increase BP back to normal
promptly. - Increase K+ levels in the blood (inters>>al fluid)
- 3 zones: o S>mulates the secre>on of Aldosterone
o Zona Glomerulosa à secre>on of K+ to the urine and then
§ Outer zone out of the body à lower K+ in the
§ Underneath the capsule blood
§ Cells are closely packed and
arranged in spherical clusters
and arched columns
§ secrete mineralocorOcoids,
mainly Aldosterone, that affect
mineral homeostasis
o Zona Fasciculata
§ Middle zone
§ widest of the three zones
§ consists of cells arranged in
long, straight columns
§ secrete mainly glucocorOcoids,
primarily corOsol, that affect
glucose homeostasis.
o Zona ReOcularis
§ Inner zone
§ arranged in branching cords
§ synthesize small amounts of
weak androgens, steroid
hormones that have
masculinizing effects

Last hurrah! Do your best and God will do the rest.

FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
GLUCOCORTICOIDS (CORTISOL)
Func>on:
- Protein breakdown
o mainly in muscle fibers
o increase the libera>on of amino acids
into the bloodstream
§ will be used by body cells for
synthesis of new proteins or for
ATP produc>on
- Glucose formaOon
o liver cells may convert certain amino
acids or lac>c acid to glucose,
§ neurons and other cells can use
for ATP produc>on
§ conversion of a substance other
than glycogen or another
monosaccharide into glucose is
called gluconeogenesis
- Lipolysis
o breakdown of triglycerides (storage
form of lipids) and release of fa?y acids
from adipose >ssue into the blood
- Resistance to stress
o addi>onal glucose supplied by the liver
cells provides >ssues with a ready
source of ATP to combat a range of
stresses (exercise, fas+ng, fright,
temperature extremes, high al+tude,
bleeding, infec+on, surgery, trauma,
and disease)
o make blood vessels more sensiOve to
other hormones that cause
vasoconstricOon
§ they raise blood pressure
§ would be an advantage in cases
of severe blood loss, which
causes blood pressure to drop ANDROGEN (DEHYDROEPIANDROSTERONE/DHEA)
- AnO-inflammatory effect - primary androgen secreted by the adrenal gland
o inhibit white blood cells that par>cipate - s>mulated by ACTH
in inflammatory responses. - s>mulate the growth of axillary and pubic hair in
o retard Ossue repair both boys and girls
§ they slow wound healing - contribute to the prepubertal growth spurt
o very useful in the treatment of chronic - Males, ader puberty:
inflammatory disorders such as o testes release a significant quan>ty of
rheumatoid arthri>s. the androgen testosterone, rendering
§ Although high doses can cause the effects of adrenal androgens
severe mental disturbances negligible in males
- Decrease immune response - Females, important func>ons:
o High doses of glucocor>coids depress o promote libido (sex drive)
immune responses o can be converted into estrogens
§ glucocor>coids are prescribed (feminizing sex steroids) by other body
for organ transplant recipients >ssues
to retard >ssue rejec>on by the o Ader menopause, when ovarian
immune system. estrogen secre>on stops, all female
NegaOve Feedback control of CorOsol levels estrogens come from the conversion of
- Trigger: Low blood levels of glucocor0coids adrenal androgens
- trigger neurosecretory cells in the hypothalamus
to secrete cor0cotropin-releasing hormone (CRH).
- CRH, along with low cor;sol levels, promotes the
2. Adrenal Medulla
release of adrenocor0cotropic hormone (ACTH)
from the anterior pituitary.
- Inner region of the adrenal gland
- ACTH then circulates in the bloodstream and - Modified ganglion of the ANS
s;mulates the adrenal cortex: - Originates from the same embryonic >ssue as
o leading to the secre0on of other sympathe>c ganglia but is unique
glucocor0coids. o Lacks axons
o minor role in s;mula;ng the secre0on of o Cluster around blood vessels
aldosterone o Secretes hormones instead of
neurotransmiDers
Last hurrah! Do your best and God will do the rest.
FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
- Chromaffin cells - Glucagon – increases blood sugar levels
o Hormone-producing cells o Can directly s>mulate insulin release
o Innervated by the sympathe>c o S>mulated by increase Sympathe>c NS
preganglion neurons of the ANS via exercise and elevated amino acid
§ allowing for rapid hormone levels when blood glucose is low ader
release under the direct control protein-rich meal
of the ANS - Insulin – decreases blood sugar levels
- produces three catecholamine hormones: o Suppress glucagon secre>on
o norepinephrine – almost 20% o Can be s>mulated by Acetylcholine
o epinephrine – 80% released by the parasympathe>c vagus
o small amount of dopamine nerve fibers
o Can be indirectly s>mulated by GH
Events leading to the release of hormones: (Growth hormone) and ACTH
- In stressful situa>ons and during exercise, (Adrenocor>cotropic hormone) by
impulses from the hypothalamus s>mulate raising blood glucose levels
sympatheOc preganglionic neurons. - SomatostaOn
- These preganglionic neurons, in turn, s>mulate o acts in a paracrine manner to inhibit
the chromaffin cells in the adrenal medulla to both insulin and glucagon release from
secrete epinephrine and norepinephrine. neighboring beta and alpha cells.
- Epinephrine and norepinephrine play a o also serve as a circula>ng hormone to
significant role in enhancing the fight-or-flight slow the absorp>on of nutrients from
response the gastrointes>nal tract
o increase heart rate and the force of o inhibit the secre>on of growth
heart contrac>ons à resul>ng in higher hormone.
cardiac output and increased blood - PancreaOc polypepOde
pressure. o inhibits somatosta>n secre>on,
o boost blood flow to essen>al organs like gallbladder contrac>on, and the
the heart, liver, skeletal muscles, and secre>on of diges>ve enzymes by the
adipose >ssue, pancreas.
o dilate airways to the lungs
o elevate blood levels of glucose and faDy
acids, preparing the body for the
demands of stress or exercise

VI. PANCREAS
- The pancreas is both an endocrine gland and an
exocrine gland
- located in the curve of the duodenum
- consists of a head, a body, and a tail
- Roughly 99% of the exocrine cells of the
pancreas are arranged in clusters called acini

PANCREATIC ISLETS (ISLETS OF LANGERHANS)

- ScaDered among the exocrine acini
- contain four types of hormone-secre>ng cells:
o Alpha or A cells: make up roughly 17%
of the pancrea>c islet cells and secrete
glucagon.
o Beta or B cells: cons>tute
approximately 70% of pancrea>c islet
cells and secrete insulin.
o Delta or D cells comprise around 7% of
pancrea>c islet cells and secrete
somatostaOn.
o F cells account for the remaining
pancrea>c islet cells and secrete
pancreaOc polypepOde.
Last hurrah! Do your best and God will do the rest.
FINALS LECTURE 1: ENDOCRINE SYSTEM DR. C.L.L.BELANDRES
VII. PINEAL GLAND IX. TESTES AND OVARIES
- small, cone-shaped gland that hangs from the TESTES
roof of the third ventricle of the brain - paired oval testes of the male are suspended in
- Secretes MELATONIN a sac, the scrotum, outside the pelvic cavity
o a “sleep trigger” that plays an - produce the following:
important role in establishing the body’s o sperm
day-night cycle o male sex hormones (androgens)
o levels of melatonin rise and fall during e.g. Testosterone
the course of the day and night. - Testosterone:
o Peak levels occur at night and make us o S>mulated by LH (Luteinizing hormone)
drowsy o Puberty:
o lowest levels occur during daylight § promotes growth and
around noon matura>on of the reproduc>ve
- In humans, it is believed to coordinate the system to prepare the young
hormones of fer>lity and to inhibit the man for reproduc>on
reproduc>ve system (especially the ovaries of § Cause the male’s secondary sex
females) un>l adult body size has been reached. characteris>cs
• Facial hair
• Heavy bones
• Increase muscle mass
• Lowering of voice
§ S>mulates sex drive
o Adulthood:
§ For con>nuous sperm
produc>on

VIII. THYMUS
- located in the upper thorax, posterior to the
sternum
- Large in infants and children
- decreases in size throughout adulthood OVARIES
- At old age, it is composed mostly of fibrous - paired, almond-sized organs located in the
connec>ve >ssue and fat pelvic cavity
- produces a hormone called THYMOSIN - produce the following:
o essen>al for normal development of a o ova (eggs)
special group of white blood cells (T o estrogen
lymphocytes, or T cells) and the o progesterone
immune response. - Estrogen:
o S>mulate the growth and matura>on of
the reproduc>ve organs
o Appearance of the secondary sex
characteris>cs in females
§ Hair in the pubic and axillary
regions
§ Widening of hips
§ Increase fat mass
- Progesterone and Estrogen
o Promote breast development
o Cyclic changes in the uterine lining
(menstrual cycle)

Last hurrah! Do your best and God will do the rest.