HORMONES
are organic substances, produced in small
amounts by specific tissue (endocrine
glands), secreted into the blood stream to
control the metabolic and biological activities
in the target cells.
They mediate between the functions of
nervous system and the action of enzymes
immediately involved in the metabolism rate
control.
CLASSIFICATION OF
HORMONES
Based on the chemical nature
Protein or peptide hormones e.g.
insulin, glucagon, ADH, oxytocin.
Amino acid derivatives e.g.
epinephrine, norepinephrine,
thyroxine (T4), triiodothyronine (T3).
Steroid hormones e.g. glucocorticoids,
mineralocorticoids, sex hormones.
Based on the mechanism of action
Group I. Steroid hormones
bind to intracellular
receptors to form receptor-
hormone complexes that
binds with DNA. This leads
to stimulation of the
mRNA synthesis.
Translation of the mRNA
produces proteins which
are responsible for certain
biological effects.
Group II.
• Protein hormones bind
to cell surface (plasma
membrane receptors
and stimulate the
release of certain
molecules, namely the
second messengers
which, in turn,
perform the
biochemical functions.
Hypothalamic hormones
• Thyrotropin - releasing hormone
(TRH) stimulates anterior pituitary
to release thyroid stimulating
hormone (TSH).
• Corticotropin releasing hormone
(CRH) stimulates anterior pituitary
to release adrenocorticotropic
hormone (ACTH).
• Gonadotropin-releasing hormone
(GnRH) stimulates anterior
pituitary to release gonadotropins:
luteinizing hormone (LH) and
follicle stimulating hormone (FSH).
• Prolactin release-inhibiting
hormone (PRIH) inhibits the
release of prolactin from
anterior pituitary.
• Growth hormone-releasing hormone
(GRH) stimulates the release of
growth hormone which promotes
growth.
• Growth hormone release-inhibiting
hormone (GRIH) inhibits the release
of growth hormone from anterior
pituitary.
Anterior pituitary hormones
Biochemical function of GH
Оn protein metabolism.
promotes the uptake of amino acids
into the tissue and increases the
protein synthesis
• On carbohydrate metabolism GH is
antagonistic to insulin and causes
hyperglycemia.
• GH promotes lipolysis in the adipose
tissue and increases the circulatiry
levels of free fatty acids and their
oxidation.
• GH promotes bone mineralization
and its growth.
Abnormalities of GH production
Deficiency of GH in growing age
causes dwarfism.
Overproduction of GH
Gigantism Acromegaly
(befor puberty) (after puberty)
increased growth of long • increase in the size of hands,
bones • enlarge nose,
• protruding jaw),
• excessive hair,
• thickening of skin etc.
• Prolactin initiates and
maintenace lactation in
mammals.
TSH functions
• Promotes the uptake of iodine
from the circulation by thyroid
gland for synthesis of T3 and T4.
• Increases the synthesis of
proteins, nucleic acids and
phospholipids in thyroid gland.
• LH and FSH are responsible
for the development and
maintenance of secondary
sexual characteristic.
Gonadotropins
FSH in females stimulates follicular
growth, increases the weight of the
ovaries and enhances the production
of estrogens.
FSH in males stimulates follicular
growth, required for spermatogenesis,
and promotes growth of seminiferous
tubules.
• LH stimulates the production
of progesterone from corpus
luteum cells and testosterone
from Leyding cells in males.
• Human chorionic gonadotropin
(HCG). The level of HCG in plasma
and urine increase almost
immediately after the implantation
of fertilized ovum. The detection of
HCG in urine is used for the early
detection of pregnancy.
• ACTH promotes secretion of
adrenocortical hormones.
POSTERIOR PITUITARY HORMONES
• The release of oxytocin from posterior
pituitary gland is caused by the neural
impulses of nipple stimulation.
Oxytocin causes the contraction of
• pregnant uterus (smooth muscles) and
induces labor.
• myoepithelial cells of breast causing
milk ejection from the breast.
• The release of ADH controlled by
osmoreceptors of hypothalamus and
baroreceptors of heart. Any increase in
the osmolarity of plasma stimulates ADH
secretion.
• Biochemical function ADH acts on the
distal convoluted tubules of kidneys and
causes water reabsorption.
• Diabetes insipidus is the excretion of large
volumes of dilute urine (polyuria). It may
be due to insufficient levels of ADH or a
defect in the receptors of target cells.
THYROID HORMONES
Thyroid hormones promotes protein
synthesis by acting at the transcriptional
level and cause positive nitrogen balance
and promote growth and development.
On carbohydrate metabolism promote
intestinal absorption of glucose and its
utilization. Increase gluconeogenesis and
glycogenolysis, with overall effects of
enhancing blood glucose level.
Stimulate lipid turnover and utilization.
Abnormalities of thyroid function
Simple endemic goiter is due to iodine
deficiency in the diet. It is mostly
found in the geographical regions
away from sea coast where the water
and soil are low in iodine content.
Hypothyroidism is decreased
production of T3 and T4.
reduced BMR,
slow heart rate,
weight gain,
sluggish behavior,
constipation,
sensitivity to cold, dry skin.
Hypothyroidism in
children known as
cretinism, is associated
with physical and mental
retardation.
Hypothyrodism in adult
causes myxoedema,
characterized by bagginess
under the eyes, puffiness of
face, slowness in physical and
mental activities.
• Hyperthyroidism is overproduction
of thyroid hormones. It is
characterized by increased
metabolic rate, nervousness,
irritability, anxiety, rapid heart
rate, loss of weight despite increased
appetite, weakness, diarrhea,
sweating, sensitivity to heat and
often protrusion of eyeballs
(exopthalmos).
PTH is secreted by two pairs
of parathyroid glands.
The rate of formation and the
secretion of PTH are
promoted by low Ca 2+
concentration.
PTH causes
decalcification or demineralization
of bone
Ca reabsorption by kidney
tubules
the intestinal absorption of Ca by
promoting the synthesis of
calcitriol in the kidney
Calcitonin promotes
• mineralization of bone by
increasing the activity of
octeoblasts
• increase the excretion of Ca
into urine
Hypercalcemia is associated
with increased activity of
parathyroid glands.
The symptoms include lethargy,
muscle weakness, loss of
appetite, constipation, nausea,
increased myocardial
contractility and suspectibility
to fractures.
• Hypocalcemia is mostly
due to hypoparathyrodism,
and causes tetany.
• The symptoms include
neuromuscular irritability,
spasms and convulsions.
HORMONES OF PANCREASE
Insulin is produced by the β-
cells of islets of Langerhance of
pancreas.
Insulin exerts anabolic and
anticatabolic influences on
body metabolism.
Effect of insulin
On carbohydrate metabolism
increases
uptake of glucose by skeletal
muscle, cardiac and smooth,
adipose tissue
glycolysis in muscle and liver
glycogen production
decreases
gluconeogenesis
glycogenolysis
Overall effect decrease blood
glucose level
On lipid metabolism
• reduce the release of fatty
acids from the stored fat
• decrease the production of
ketone bodies.
On protein metabolism
• stimulates the entry of amino
acids into the cells
• enhances protein synthesis
and reduces protein
degradation.
• promotes cell growth and
replication.
Glucagon, secreted by α-cells of the
pancreas, oppose the action of insulin.
The secretion of glucagon is stimulated by
• low blood glucose concentration,
• amino acids derived from dietary
protein
• low levels of epinephrine.
• Increased blood glucose level inhibits
glucagon secretion.
Glucagon promotes
• synthesis of glucose
• degradation of glycogen on liver
• fatty acid oxidation
• ketone body synthesis
• the amino acid uptake by liver
for promoting gluconeogenesis.
Deficiency of insulin leads to
diabetes mellitus (DM).
IDDM (type I diabetes,
juvenile onset diabetes).
NIDDM (type II diabetes,
adult – onset diabetes).
IDDM, mainly occurs in
childhood and
characterized by almost
total deficiency of insulin
due to destruction of β-cells
of pancreas.
NIDDM occurs in adults. It
more commonly occurs in
obese individuals.
Obesity leads increasing the
resistance to the action of
insulin due to a decrease in
insulin receptors on target
cells.
STEROID HORMONES
Adrenocortical hormones
Glucocorticoids (cortisol)
Biochemical functions
in carbohydrate m/b
increase blood glucose by increasing
gluconeogenesis
in lipid m/b
increase breakdown of TG in
adipose tissue
reduce synthesis of triacylglycerols
in protein m/b
promote protein biosynthesis
in liver
cause degradation of proteins
in extrahepatic tissue
Mineralocorticoids
Aldosterone
promotes Na+ reabsorption at the
distal convoluted tubules of
kidney
increases excretion of K+, H+ and
NH4+ ions
Abnormalities of adrenal cortex
Hypofunction Hyperfunction
Addison’s disease Cushing syndrome
low blood glucose level hyperglycemia
muscle weakness, muscle wasting
loss of weight, edema
loss of appetite, osteoporosis
low blood pressure, negative nitrogen
low Na+, high K+ level balance
increased susceptibility hypertension
to stress. moon-face
Hormones of adrenal medulla
Catecholamines are produced in
response to fight, fright and flight.
Catecholamines
• Mobilizes fuels during acute stress
(shock, cold, low blood glucose)
Stimulates
• glucose production from glycogen
(muscle and liver)
• fatty acid release from adipose issue
Elevate blood glucose level
HORMONES OF GONADS
Androgens
Biochemical functions
• promote RNA synthesis and protein
synthesis.
• cause positive nitrogen balance and
increase the muscle mass.
• increase rate of glycolysis, citric acid
cycle and fatty acid synthesis.
• promote mineral deposition and bone
growth
Female sex hormones
Biochemical functions
Estrogens
increase lipogenesis in adipose tissue
lower the plasma total cholesterol
LDL is decreased, HDL is increased
promote transcription and
translation
calcification and bone growth
• Progesteron is synthesized and
secreted by corpus luteum and
placenta.
• It is required for implantation of
fertilized ovum and maintenance of
pregnancy.
• It promotes the growth of glandular
tissue in uterus and mammary
gland.
Eicosanoids
are paracrine hormones, secreted into the
interstitial fluid (not primarily into the
blood) and acting on nearby cells.
Prostaglandins
promote the contraction of
smooth muscle of the intestine
and uterus (used to induce
labor).
They are mediators of pain and
inflammation.
• Thromboxanes regulate platelet
function (blood clotting).
• Leukotrienes act through plasma
membrane receptors to stimulate
contraction of smooth muscle in
the intestine, pulmonary airways,
and trachea.
