Chemical Coordination

Neurotransmitters -> chemical messenger between neurons

Pheromones -> secreted by an organism in minute amounts in to
stimulate particular reaction from another organism.
Hormones -> chemical messenger is secreted by glands then
transported into the bloodstream and only the target ce!s respond.
Type of hormones
1) Peptide and Protein hormones : composed of chains of amino acids
ranging from a few to 100 in length.
-> short chain amino acid hormones are peptide hormones.
Ex: ADH ( antidiuretic hormone)
-> long chain amino acid hormones are protein hormones.
Ex: GH (growth hormone) and insulin
2) Amino acid derivative hormones : formed by enzymatic modi"cation
of speci"c amino acids.
-> Biogenic amines : include hormones secreted by adrenal medu!a,
Thyroid , and Pineal gland.
-> Hormones by adrenal medu!a and thyroid are derived from tyrosine.
-> Hormones by adrenal medu!a are Catecholamines which include
epinephrine(adrenaline) and nor-epinephrine.
-> The pineal gland secretes melatonin derived from tryptophan.
3) Steroid hormones : manufactured by enzymatic modi"cations of
cholesterol. Ex: oestrogen(estradiol), testosterone progesterone,
aldosterone and cortisol.
 Path of chemical messenger
-> In order to control ; the hormones must act only on certain
target ce!s. Each target ce! has a speci"c receptor for a Hormone.
Mode of Hormone action
-> Hydrophilic ( polar ) or Protein nature hormones :
• Soluble in water but insoluble in lipids hence cannot pass the
ce! membrane.
• React with protein receptors from outside surface of target ce!
membrane.
• In general,hormones ( primary messengers) that bind to the surface
receptors trigger rapid and short-term responses.
• When a second messenger system is used, the hormone binds to the
receptor, altering the shape of it. Triggering a series of biochemical
reactions that alter the activity of the ce!.
• In many cases, the binding of the hormone on the Receptor activates
the enzyme. Activated enzyme catalyses the conversion of ATP to
cyclic adenosine monophosphate (cAMP).
• Second messenger regulates ce!ular activities of cAMP.
• Transfers the signal from "rst messenger(hormone) to molecules
within th ce!.
• The hormone signal causes the target ce! to react in fo!owing ways:
1) Induction of protein synthesis
2) Activation or inactivation of enzymes
3) Change in the ce! membrane permeability
4) Changing the rate of mitosis and ce! development
-> Steroid hormones (lipophilic) :
• Steroid and thyroid hormones are lipid soluble, hence they can di#use
into the ce! membrane and bind to the receptors inside the ce!.
• They alter the activity of genes
• It may take minutes to days for these hormones to exert their fu! e#ect.
• Bind to protein receptors in the nucleus.
• The hormone complex binds to DNA and initiate transcription of mRNA.
• mRNA move to cytoplasm and directs protein synthesis.
 Hypothalamus
-> Part of the brain that contains clusters of neurosecretory ce!s.
-> There are two sets of neurosecretory ce!s whose secretions are
stored in pituitary gland.
-> A set of neurosecretory ce!s, exert control over anterior pituitary
lobe, secreting two kinds of hormones into the blood.
-> Releasing hormones makes anterior pituitary lobe to secrete hormones
and inhibiting hormones stop the secretion.
-> The other set of neurosecretory ce!s produce ADH and oxytocin which
are stored and secreted from posterior pituitary glands.
 Pituitary gland ( Hypophysis)
-> It is a pea I sized gland that dangles from the hypothalamus
by a stalk.
-> It consists of two lobes ( parts )
1) Adenohypophysis (anterior pituitary lobe) -> appears globular
2) Neurohypophysis ( posterior pituitary lobe) -> appears "brous

1) Adenohypophysis (anterior pituitary lobe) :

-> Independent endocrine gland
-> Produces at least seven essential hormones.
-> Many of which stimulate growth of target organs, production and
secretion of other hormones from additional endocrine glands.
-> These hormones are also ca!ed as tropic hormones (Tropin).
-> Tropic hormones act on other endocrine glands to stimulate secretion
of hormones produced by target gland.
-> Adrenocorticotropic hormone (ACTH): Stimulates the adrenal cortex to
produce corticosteroids.
-> Melanocyte stimulating hormone (MSH): Stimulate the synthesis
and dispersion of melanin pigment in the skin.
-> Growth hormone (GH) OR Somatotropic hormone (STH): The growth
of muscles, bone and other tissues.
-> Prolactin: Stimulate the mammary glands to produce milk.
-> Thyroid Stimulating hormone (TSH): Stimulates thyroid gland to
produce thyroxin.
-> Leuteinizig hormone (LH): Stimulate gonads (testes/ovaries)
for production of steroid hormone estrogen and progesterone from
ovaries and testosterone from testes.
-> Fo!icle stimulating hormone (FSH): Stimulate development of ovarian
fo!icles in females. In males it is required for the development of sperm.
FSH and LH are ca!ed gonadotropins (GnTH) because they stimulate the
activities of the male and female gonads.
2) Neurohypophysis ( Posterior pituitary lobe) :
-> They contain the ending of two types of neurosecretory ce!s whose
ce! bodies are found in the hypothalamus.
-> The hormones released from here are actua!y stored secretions of
hypothalamus.
• Antidiuretic hormone (ADH); which means "hormone that prevents
urination" helps prevent dehydration.
ADH causes more water to be reabsorbed from the urine and retained in
the body, by increasing the permeability to water of the co!ecting ducts
of nephrons in the kidney.
• Oxytocin ; has two primary physiological e#ects.
1) It stimulates uterine contractions during labour and stimulates
breast tissue contractions to promote lactation after childbirth.
2) Additiona!y serving as a chemical messenger in the brain, it
plays a signi"cant part in social interaction and human behaviour.
 Thyroid gland
-> located at the base of the neck in front of trachea (windpipe).
-> Consists of two lobes (Bilobed) and Isthmus that binds them together.
-> It produces three major hormones :
1) Tri-iodothyronine (T3)-> has three iodine atoms
2) Tetra -iodothyronine (T4) or thyroxin-> contains four atoms of
iodine and is secreted in greater amount, but less potent than T3.
• it in$uences most of the ce!s in the body by increasing the
metabolic rate.
• its e#ects include increasing oxygen consumption and heart rate
and stimulating synthesis of enzymes that breakdown glucose and
provides energy.
• for increasing adults metabolic rate it regulates body temperature and
exposure to cold.
-> It’s release is stimulated by thyroid-stimulating hormone (TSH)
from the anterior pituitary, which is also stimulated by thyroid
releasing hormone (TRH) from the hypothalamus.
Excessive secretion of thyroid hormone is hyperthyroidism ;
Symptoms: weight loss, sweating, heat, intolerance, high blood pressure
Low secretion of thyroid hormone is known as hypothyroidism ;
Symptoms: weight gain, lethargy, cold intolerance in adults.
Children born with this had stunted growth and su#er from inte!ectual
disability -> Cretinism.
Enlargement of thyroid -> Goiter ( due to de"ciency of iodine)
3) Calcitonin -> a peptide hormone that plays role in maintaining proper
levels of calcium in the blood. When blood calcium concentration rises,
calcitonin stimulates the uptake of calcium into the bones, hence lowering
its concentration in blood.
 Parathyroid gland
-> It has four sma! glands attached to the back of thyroid gland.
-> The hormone produced by it is a peptide hormone ca!ed
parathormone or parathyroid hormone (PTH).
-> It is released when the calcium level decreases in the blood
-> Because this can cause severe muscle spasms.
-> Normal blood calcium level is important for functioning of
muscles, including the heart and for proper functioning of
nervous and endocrine system.
-> PTH stimulate osteoclasts in bones to dissolve the calcium
phosphate crystal of the bone matrix and release calcium into the
blood.
-> It also stimulates kidney to reabsorb calcium from the urine and
activation of vitamin D which is needed for the absorption of
calcium from food .
 Pancreas
-> Located adjacent to the stomach
-> Perform both endocrine and exocrine functions
-> Endocrine ce!s make up only 2% of the weight of pancreas rest of
the organ is exce!ent game to choose that produce bicarbonate ions
and digestive enzymes.
-> Digestive enzymes are carried to the sma! intestine via pancreatic
duct.
-> Unusual Endocrine clusters of ce!s scattered throughout the
pancreas are ca!ed Islets of Langerhans.

Alpha ce!s Beta ce!s

Secrete glucagon Secrete insulin
-> Glucagon and insulin are antagonistic hormones that regulate
the concentration of glucose in the blood.
-> Defect in insulin production, release or reception by target ce!s
causes diabetes me!itus (in which blood glucose levels are high
and $uctuate wildly with sugar intake).
-> The lack of insulin in diabetes, causes the body to rely much on
fats as energy source, leading to high circulating level of lipids,
including cholesterol.
-> Severe diabetes causes fat disposition in the blood vessels
resulting in high blood pressure and heart disease.

Diabetes type-1 Diabetes type-2

• Autoimmune disorder • Due to obesity, stress , genetics
• Immune system destroys Old age and lack of exercise .
B- ce!s. • some insulin produced
• little or no insulin production • Partia!y functional pancreas
• Caused by body producing • Target ce!s, don’t respond to insulin
antibodies against B-ce!s. • Can be contro!ed by adopting a low
• treated using insulin injections carbohydrate diet.
 Adernal gland
• Located above each kidney
• Composed of inner(adrenal medu!a ) and outer portion
( adrenal cortex ).

Adrenal medu!a
-> Produces two hormones in
response to stress.
1) Epinephrine (adrenaline)
2) Nor-epinephrine
Both are released during the state of emergency under the in$uence
of sympathetic nervous system.
• The e#ect is the rise in blood pressure.
• Both are involved in the body's immediate response to stress.
• The two hormones exert the same e#ects in di#erent ways i.e.
synergistic e#ect.
Epinephrine
-> stimulates metabolic activities
-> Causes bronchial dilation
-> increased blood $ow to Skeletal muscles and heart (Vasodilator)
Norepinephrine
-> reduces the blood $ow to the skin and digestive organs.
 Adrenal cortex
• A! are Steroids ( Corticosteroids )
• three main types of it are ;
1 ) Glucocorticoids such as cortisol
-> stimulates the breakdown of muscle protein into amino acids
-> which are carried by blood to liver
-> stimulate the liver to produce the enzymes needed for
gluconeogenesis ( converts amino acid into glucose)
-> Glucocorticoids release is it stimulated by ACTH.
-> Cortico-releasing hormone (CRH) produced in response to stressful
events or exposure to severe temperatures, stimulates the ACTH
to release.
-> Glucocorticoid acts similar to glucagon by stimulating the synthesis
of glucose.
-> Oversecretion of cortisol causes Cushing’s syndrome (hypercortisolism)
• Symptoms -> high blood pressure, weight gain, weakened bones bones
and mood swings.
-> low secretion of adrenal cortex hormone can cause Addison’s disease
2) Mineralocorticoids such as aldosterone
-> it helps to regulate mineral balance
-> its function is to stimulate the kidneys to reabsorb sodium from urine
-> sodium is needed to maintain the blood volume and blood pressure
-> During low blood sodium level, the kidneys secrete an enzyme ca!ed
Renin which converts a plasma protein (angiotensinogen ) to
angiotensin-I.
-> which is then converted into angiotensin in the lungs
-> Angiotensin stimulates adrenal cortex to release aldosterone.
-> This mechanism is ca!ed when an Renin angiotensin-aldosterone
system (RAAS).
-> It a#ects the blood pressure in two ways ;
1) angiotensin constricts the arteries
2) aldosterone causes increased absorption of sodium

3) Androgen
-> sex hormone similar to testosterone
-> present in both male and female bodies
-> when its level increases , it promotes secondary sex characters in males.
 Gonads
Produce and secrete three major categories of steroid hormones,
which are testosterone, oestrogen and progesterone.
-> Testes :
• Male gonads which produce both sperm and male sex hormones.
• The anterior pituitary gland secretes gonadotropins, FSH and LH.
• FSH stimulates sertoli ce!s of testes to facilitate sperm development
• LH stimulates Leydig ce!s of testes to release testosterone.
• Leydig ce!s of testes are located in the interstitial tissues between
the seminiferous tubules (site of sperm production)
• It is produced early in the development of an embryo.
-> Testosterone
• Produces both anabolic and androgenic e#ects in human males.
Anabolic e#ects :
muscle mass, muscle strength, increased bone density, bone strength,
linear growth and bone maturation.
Androgenic e#ects:
maturation of sex organs, formation of scrotum in fetus, deepening of
voice and growth of facial and axi!ary hairs.
-> Ovaries :
• Female gonads, lie in the abdominal cavity produce both egg (ova) and
female sex hormones.
• Ovaries secrete two lipophilic hormones estrogen and progesterone.
1) Estrogen :
• Contributes to the development and function of the female
reproductive organs and promotes secondary sex characters which
include development of breasts, fats distribution in hips, legs and
breast, armpit and pubic hairs and menarche (start of menstrual cycle).
• Change in estrogen levels is encountered in various phases and
involvement in female reproductive life
• low estrogen levels are associated with mood swings, depression,
headaches, and irregular periods and sleep problems.
2) Progesterone :
• Helps in regulating menstruation and maintaining pregnancy in human
females.
Other endocrine tissues
Produce from tissues within the body, like digestive tract, kidneys,
heart, and placenta.
1) Gastrin -> a peptide hormone responsible for enhancing mucosal
growth, gastric motility and secretion of hydrochloric acid (HCL)
from wa!s of stomach.
2) Secretin -> a peptide hormone from duodenum regulates
environment of stomach, pancreas and liver maintain pH to a more
neutral to the basic state of the duodenum.
3) Cholecystokinin -> a peptide hormone from duodenum that stimulates
ga! bladder to contract and stimulates pancreas to release digestive
enzymes.
• Hormones produced in kidney
1) Angiotensin -> regulates blood pressure
2) Erythropoietin -> stimulates RBC synthesis in bone marrow.
• Hormones produced in heart
1) atrial natriuretic hormone -> It increases salt and water excretion
to reduce blood pressure.
2) Prostaglandins -> lipophilic hormone from every tissue of the body
involved in dealing with in$ammation, blood $ow and protection from
injury.
• Placenta an endocrine tissue release variety of hormones during
pregnancy .
1) Human chorionic gonadotropin (HCG)
2) Progesterone
• Human brain releases Endorphins hormone involved in pain relief.
 Feedback mechanism
Positive feedback mechanism
-> Rare in endocrine system, only few hormones are regulated by
positive feedback.
-> A positive feedback mechanism in endocrine system is when release
of a hormone initiates action that leads to an additional release of
that hormone.
-> Ex : Oxytocin
-> In both childbirth and breastfeeding, oxytocin is released and causes
additional release of oxytocin.
-> During childbirth, release of oxytocin result in uterine contractions
which cause additional oxytocin to be released.
-> During breastfeeding oxytocin is released which a!ows for milk
ejection which causes more oxytocin to be released.

Negative feedback mechanism

-> one way that the endocrine system tries to keep homeostasis (stability)
in the body.
-> If an endocrine gland senses that there is too much of one hormone in
the body, it wi! initiate changes to decrease production of that hormone,
and if there's not enough of the hormone, the body wi! increase production
of that hormone.
->The control of blood sugar (glucose) by insulin is a good example of a
negative feedback mechanism.