Anatomy & Physiology of Endocrine System

1. Endocrine
system
Mr. Mayur Gaikar
Assistant Professor
Department of Pharmacology
College of Pharmacy (For Women), Chincholi, Nashik.

2. The endocrine system consists of glands widely
separated from each other with no physical connections.
Endocrine glands are groups of secretory cells surrounded by
an extensive network of capillaries that facilitates diffusion of
hormones (chemical messengers) from the secretory cells into
the bloodstream.
They are commonly referred to as ductless glands
because hormones diffuse directly into the bloodstream.
Hormones are then carried in the bloodstream to target tissues
& organs that may be quite distant, where they influence
cellular growth & metabolism.

4. What is the endocrine system?
The primary
endocrine glands
are the pituitary
(the master gland),
pineal, thyroid,
parathyroid, islets
of Langerhans,
adrenals, ovaries in
the female and
testes in the male.
The function of the endocrine system is
the production & regulation of chemical
substances called hormones.

5. Hormones…
A hormone is a chemical transmitter. It is released
in small amounts from glands, & is transported in the
bloodstream to target organs or other cells. Hormones
are chemical messengers, transferring information &
instructions from one set of cells to another.

6. Hormones… Hormones regulate growth,
development, mood, tissue
function, metabolism, & sexual
function.
Hyposecretion or
hypersecretion of
any hormone can
be harmful to the
body. Controlling
the production
of hormones can
treat many
hormonal disorders
in the body.

7. Hormones…
The endocrine system & nervous system work together to
help maintain homeostasis…balance. The hypothalamus is
a collection of specialized cells located in the brain, & is the
primary link between the two systems. It produces
chemicals that either stimulate or suppress hormone
secretions of the pituitary gland.
The pituitary gland has 2
lobes…

8. A.Pituitary
Gland

10. Hypothalamus Anterior
pituitary
Targe t gland or
tissue
GHRH GH Most tissues
Many organs
GHRIH GH inhibition Thyroid gland
TSH inhibition Pancreatic islets
Most tissues
TRH TSH Thyroid gland
CRH ACTH Adrenal cortex
PRH PRL Breast
PIH PRL inhibition Breast
LHRH or FSH Ovaries and testes
GnRH LH Ovaries and testes
a. Anterior pituitary

11. The release of an anterior pituitary hormone follows
stimulation of the gland by a specific releasing hormone
produced by the hypothalamus & carried to the gland
through the pituitary portal system of blood vessels.
The whole system is controlled by a negative
feedback mechanism.

12. When there is a low level of a hormone in the blood
supplying the hypothalamus it produces the appropriate
releasing hormone that stimulates release of a trophic
hormone by the anterior pituitary.
This in turn stimulates the target gland to produce &
release its hormone. As a result the blood level of that hormone
rises & inhibits the secretion of releasing factor by the
hypothalamus

13. Negative feedback
regulation of secretion
of hormones by the
anterior lobe of the
pituitary gland.

14. Secretions from the anterior pituitary gland…
Growth Hormone (GH):
Essential for the growth &
development of bones,
muscles, other organs.
It also enhances protein
synthesis, decreases the use
of glucose, & promotes fat
destruction.

15. Its release is stimulated by growth hormone releasing
hormone (GHRH) & suppressed by growth hormone release
inhibiting hormone (GHRIH), also known as somatostatin, both of
which are secreted by the hypothalamus.
Secretion of GH is greater at night during sleep & is also
stimulated by hypoglycaemia, exercise & anxiety. The daily amount
secreted peaks in adolescence & then declines with age.
Inhibition of GH secretion occurs by a negative feedback
mechanism when the blood level rises & also when GHRIH is
released by the hypothalamus. GHRIH also suppresses secretion of
TSH & gastrointestinal secretions, e.g. gastric juice, gastrin &
cholecystokinin.

16. This hormone is synthesised by the anterior pituitary & its release is
stimulated by thyrotrophin releasing hormone (TRH) from the hypothalamus.
It stimulates growth & activity of the thyroid gland, which secretes the
hormones thyroxine (T4) and tri-iodothyronine (T3). Release is lowest in the
early evening & highest during the night. Secretion is regulated by a negative
feedback mechanism.
When the blood level of thyroid hormones is high, secretion of TSH is
reduced, & vice versa.
Thyroid stimulating hormone (TSH)

17. Adrenocorticotrophic hormone (ACTH,
corticotrophin)
Essential for the growth
of the adrenal cortex.
Corticotrophin releasing hormone (CRH) from the hypothalamus
promotes the synthesis & release of ACTH by the anterior pituitary.
This increases the concentration of cholesterol & steroids
within the adrenal cortex & the output of steroid hormones, especially
cortisol.

18. ACTH levels are highest at about 8 a.m. & fall to their
lowest about midnight, although high levels sometimes occur at
midday & 6 p.m. This circadian rhythm is maintained throughout
life. It is associated with the sleep pattern & adjustment to changes
takes several days, following, e.g., changing work shifts, travelling
to a different time zone.
Secretion is also regulated by a negative feedback
mechanism, being suppressed when the blood level of ACTH rises.
Other factors that stimulate secretion include hypoglycaemia,
exercise & other stressors, e.g. emotional states & fever.

19. Stimulates the
development &
growth of the
mammary glands
and milk production
during pregnancy.
The sucking motion of the
baby stimulates prolactin
secretion.
Prolactin (PRL):

20. This hormone is secreted during pregnancy to prepare the
breasts for lactation (milk production) after childbirth. The blood
level of prolactin is stimulated by prolactin releasing hormone
(PRH) released from the hypothalamus & it is lowered by prolactin
inhibiting hormone (PIH, dopamine) & by an increased blood level
of prolactin.
Immediately after birth, suckling stimulates prolactin
secretion & lactation.

21. Prolactin, together with oestrogens, corticosteroids,
insulin & thyroxine, is involved in initiating & maintaining
lactation.
Prolactin secretion is related to sleep, i.e. it is raised
during any period of sleep, night or day.

22. Gonadotrophins
Just before puberty 2 gonadotrophins (sex hormones) are
secreted in gradually increasing amounts by the anterior pituitary in
response to luteinising hormone releasing hormone (LHRH), also
known as gonadotrophin releasing hormone (GnRH).
At puberty secretion increases, further enabling normal
adult functioning of the reproductive organs; in both males &
females the hormones responsible are:
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH).

23. FSH stimulates
production of
gametes (ova or
spermatozoa) by the
gonads.
Is a gonadotropic
hormone.
Follicle-Stimulating Hormone (FSH):

24. In females
LH and FSH are involved in secretion of the
hormones oestrogen & progesterone during the menstrual
cycle. As the levels of oestrogen & progesterone rise,
secretion of LH & FSH is suppressed.
In males
LH, also called interstitial cell stimulating hormone
(ICSH) stimulates the interstitial cells of the testes to secrete
the hormone testosterone

25. Is a gonadotropic
hormone
stimulating the
development of
corpus luteum in
the female ovarian
follicles & the
production of
testosterone in the
male.
The yellow corpus luteum
remains after ovulation; it
produces estrogen and
progesterone.
Luteinizing Hormone (LH):

26. Melanocyte-stimulating
hormone (MSH): regulates skin
pigmentation & promotes the
deposit of melanine in the skin
after exposure to sunlight

27. Posterior pituitary (simple neurons str. present )
This is formed from nervous tissue & consists of nerve
cells surrounded by supporting cells called pituicytes. These
neurones have their cell bodies in the supraoptic &
paraventricular nuclei of the hypothalamus & their axons form
a bundle known as the hypothalamohypophyseal tract.
Posterior pituitary hormones are synthesised in the nerve
cell bodies, transported along the axons & stored in vesicles
within the axon terminals in the posterior pituitary. Their release
by exocytosis is triggered by nerve impulses from the
hypothalamus.

28. Oxytocin &
Antidiuretic hormone (ADH or vasopressin)
are the hormones synthesised in nerve cell bodies in the
hypothalamus & then stored in the axon terminals within
the posterior pituitary gland.

29. Stimulates the uterus to contract
during labor, delivery, and parturition.
A synthetic version of this
hormone, used to induce labor, is called
pitocin. It also stimulates the mammary
glands to release milk.
Oxytocin:

30. Oxytocin stimulates two target tissues during & after childbirth
(parturition): uterine smooth muscle & the muscle cells of the lactating
breast.
During childbirth increasing amounts of oxytocin are released by
the posterior pituitary into the bloodstream in response to increasing
distension of sensory stretch receptors in the uterine cervix by the baby’s
head. Sensory impulses are generated & travel to the control centre in the
hypothalamus, stimulating the posterior pituitary to release more oxytocin.
In turn this stimulates more forceful uterine contractions & greater
stretching of the uterine cervix as the baby’s head is forced further
downwards. This is an example of a positive feedback mechanism which
stops soon after the baby is delivered and distension of the uterine cervix is
greatly reduced.

31. The process of milk ejection also involves a positive
feedback mechanism. Suckling generates sensory impulses that are
transmitted from the breast to the hypothalamus. Oxytocin
stimulates contraction of the myoepithelial cells around the
glandular cells & ducts of the lactating breast to contract, ejecting
milk.
Suckling also inhibits the release of prolactin inhibiting
hormone (PIH), prolonging prolactin secretion & lactation. The role
of this hormone in males and non-lactating females remains unclear.

32. Stimulates the reabsorption of
water by the renal tubules.
Hyposecretion of this hormone can
result in diabetes insipidus.
The main effect of
antidiuretic hormone is to reduce
urine output (diuresis is the
production of a large
volume of urine).
Antidiuretic hormone (ADH, vasopressin)

33. ADH acts on the distal convoluted & collecting ducts of
the nephrons of the kidneys, increasing their permeability to
water. As a result, the reabsorption of water from the glomerular
filtrate is increased. The amount of ADH secreted is determined
by the osmotic pressure of the blood circulating to the
osmoreceptors in the hypothalamus.

34. B.Pineal gland

36. The pineal gland is a small body attached to the roof
of the third ventricle & is connected to it by a short stalk
containing nerves, many of which terminate in the
hypothalamus.
The pineal gland is about 10 mm long, is reddish
brown in colour & is surrounded by a capsule. The gland
tends to atrophy after puberty and may become calcified in
later life.

37. This is the main hormone secreted by the pineal gland.
Secretion is controlled by daylight & levels fluctuate during
each 24-hour period, being highest at night & lowest around
midday. Secretion is also influenced by the number of daylight
hours, i.e. seasonal variations.
melatonin is believed to be associated with:
coordination of the circadian & diurnal rhythms of many
tissues, possibly by influencing the hypothalamus inhibition of
growth & development of the sex organs before puberty,
possibly by preventing synthesis or release of gonadotrophins.
Melatonin

38. A neurotransmitter that
regulates intestinal
movements and affects
appetite, mood, sleep, anger,
and metabolism.
Serotonin:

39. C.Thyroid gland

40. The thyroid gland is situated in the neck in front of
the larynx & trachea at the level of the 5th, 6th & 7th
cervical &1st thoracic vertebrae.
•Weighs about 25 g.
•Butterfly in shape, consisting of two lobes, lobes are
joined by a narrow isthmus, lying in front of the trachea.
•The gland is composed of cuboidal epithelium that forms
spherical follicles. These secrete & store colloid, a thick
sticky protein material

41. The thyroid hormones are synthesised as large precursor
molecules called thyroglobulin, the major constituent of
colloid. The release of T3 and T4 into the blood is stimulated
by thyroid stimulating hormone (TSH) from the anterior
pituitary.

42. Secretions of the thyroid gland…
Thyroxine (T4) and
triodothyronine (T3):
essential to BMR – basal
metabolic rate (the rate at
which a person’s body
burns calories while at rest);
influences physical/mental
development and growth
Hyposecretion of T3 and T4 = cretinism,
myxedema, Hashimoto’s disease
Hypersecretion of T3 and T4 = Grave’s disease,
goiter, Basedow’s disease

43. Calcitonin
This hormone is secreted by the parafollicular or C-cells
in the thyroid gland. It acts on bone cells & the kidneys to
reduce blood calcium (Ca2+) levels when they are raised.
It promotes storage of calcium in bones and inhibits
reabsorption of calcium by the renal tubules. Its effect is
opposite to that of parathyroid hormone, the hormone secreted
by the parathyroid glands. Release of calcitonin is stimulated by
an increase in the blood calcium levels.

44. D.Parathyroid
Gland

45. Secretions of the parathyroid gland…
The two pairs of
parathyroid glands are
located on the dorsal or
back side of the thyroid
gland. They secrete
parathyroid (PTH) which
plays a role in the
metabolism of phosphorus.
Too little results in
cramping; too much
results in osteoporosis or
kidney stones.

46. Function
The parathyroid glands secrete parathyroid
hormone (PTH, parathormone). Secretion is regulated by
blood calcium levels. When they fall, secretion of PTH is
increased and vice versa.
The main function of PTH is to increase the blood
calcium level when it is low.

47. E. Thymus
glands

48. The thymus gland has
two lobes, and is part
of the lymphatic
system. It is a
ductless gland, and
secretes thymosin.
This is necessary for
the Thymus’ normal
production of T cells
for the immune
system.

49. F.Adrenal glands

50. The triangular-
shaped adrenal glands are
located on the top of each
kidney.
The inside is called
the medulla & the outside
layer is called the cortex.

51. Adrenal cortex
The adrenal cortex produces three groups of steroid
hormones from cholesterol. They are collectively called
adrenocorticocoids (corticosteroids). They are:
a. Glucocorticoids
b. Mineralocorticoids
c. Sex hormones (androgens).

52. Cortisol: regulates carbohydrate, protein,
and fat metabolism; has an anti-
inflammatory effect; helps the body cope
during times of stress
Hyposecretion results in
Addison’s disease;
hypersecretion results in
Cushing’s disease
Corticosterone: like cortisol,
it is a steroid; influences
potassium and sodium
metabolism
Glucocorticoids:
Cortisol (hydrocortisone) is the main
glucocorticoid but small amounts of
corticosterone & cortisone are also
produced.

53. Aldosterone: essential in regulating electrolyte &
water balance by promoting sodium & chloride
retention & potassium excretion.
Androgens: several hormones
including testosterone; they
promote the development of
secondary sex characteristics in
the male.
Mineralocorticoids (aldosterone)

54. Renin–angiotensin–aldosterone system
When renal blood flow is reduced or blood sodium levels
fall, the enzyme renin is secreted by kidney cells. Renin
converts the plasma protein angiotensinogen, produced by
the liver, toangiotensin
1. Angiotensin converting enzyme (ACE), formed in small
quantities in the lungs,

55. Sex hormones
Sex hormones secreted by the adrenal cortex are mainly
androgens (male sex hormones) & the amounts produced
are insignificant compared with those secreted by the
testes and ovaries in late puberty and adulthood

56. Adrenal medulla
It is stimulated by its extensive
sympathetic nerve supply to produce the
hormones
Adrenaline(epinephrine)&
noradrenaline (norepinephrine).

57. Secretions from the adrenal
medulla…
Dopamine is used
to treat shock. It
dilates the
arteries, elevates
systolic blood
pressure,
increases cardiac
output, and
increases urinary
output.

58. Secretions
from the
adrenal
medulla…
Epinephrine is also called adrenalin. It elevates
systolic blood pressure, increases heart rate and
cardiac output, speeds up the release of glucose
from the liver… giving a spurt of energy, dilates
the bronchial tubes and relaxes airways, and
dilates the pupils to see more clearly. It is often
used to counteract an allergic reaction.

59. Secretions from the
adrenal medulla…
Norepinephrine, like epinephrine, is released when
the body is under stress. It creates the underlying
influence in the fight or flight response. As a drug,
however, it actually triggers a drop in heart rate.

60. Secretions of the ovaries…
The ovaries produce
several estrogen hormones
and progesterone. These
hormones prepare the
uterus for pregnancy,
promote the development
of mammary glands, play a
role in sex drive, and
develop secondary sex
characteristics in the
female.
Estrogen is essential for the growth, development,
and maintenance of female sex organs.

61. The testes produce
the male sex
hormone called
testosterone. It is
essential for normal
growth and
development of the
male sex organs.
Testosterone is
responsible for the
erection of the
penis.
Secretions of the testes…

62. During pregnancy, the
placenta serves as an
endocrine gland.
Secretions of the placenta…
It produces
chorionic
gonadotropin
hormone,
estrogen, and
progesterone.

63. The mucosa
of the pyloric
area of the
stomach
secretes the
hormone
gastrin, which
stimulates the
production of
gastric acid
for digestion.
Secretions of the gastrointestinal
mucosa…

64. The mucosa of
the duodenum
and jejunum
secretes the
hormone
secretin, which
stimulates
pancreatic juice,
bile, and
intestinal
secretion.
Secretions of the gastrointestinal
mucosa…

65. Pancreatic islets

66. The cells that make up the pancreatic islets (islets of Langerhans)
are found in clusters irregularly distributed throughout the substance of
the pancreas. Unlike the exocrine pancreas, which produces pancreatic
juice, there are no ducts leading from the clusters of islet cells. Pancreatic
hormones are secreted directly into the bloodstream and circulate
throughout the body.
There are three main types of cells in the pancreatic islets:
α (alpha) cells, which secrete glucagon
β (beta) cells, which are the most numerous, secrete insulin
δ (delta) cells, which secrete somatostatin (GHRIH)

67. The islets of Langerhans…
The islets of Langerhans are small clusters of
cells located in the pancreas.

68. Secretions from the islets of
Langerhans… Beta cells secrete the
hormone insulin, which is
essential for the maintenance
of normal blood sugar levels.
Inadequate levels result in
diabetes mellitus.
Delta cells suppress
the release of
glucagon and
insulin.
Alpha cells
facilitate the
breakdown of
glycogen to
glucose. This
elevates the blood
sugar.

69. THE PANCREAS
• Since the pancreas is classified as both and endocrine organ
and an exocrine organ, it will also be discussed again with the
digestive system.
• There are three main types of cells in the pancreatic islets:
• (alpha) cells, which secrete glucagon
• (beta) cells, which are the most numerous, secrete
insulin
• (delta) cells, which secrete somatostatin (GHRIH,

71. • The normal blood glucose level is between 3.5 & 8
mmol/litre (63 to 144 mg/100 mL).
• Blood glucose levels are controlled mainly by the opposing
actions of insulin & glucagon:
• glucagon increases blood glucose levels
• insulin reduces blood glucose levels.

72. Insulin
• Its main function is to lower raised blood nutrient levels, not
only glucose but also amino acids and fatty acids.
• These effects are described as anabolic, i.e. they promote
storage of nutrients. When nutrients, especially glucose, are in
excess of immediate needs insulin promotes their storage by:

73. • Mechanism by which insulin lowers the blood glucose
level:
• acting on cell membranes and stimulating uptake and use of
glucose by muscle and connective tissue cells
• increasing conversion of glucose to glycogen (glycogenesis),
especially in the liver and skeletal muscles
• accelerating uptake of amino acids by cells, and the synthesis
of protein
• promoting synthesis of fatty acids & storage of fat in adipose
tissue (lipogenesis)
• Decreasing glycogenolysis (breakdown of glycogen into
glucose)

74. Glucagon
Glucagon increases blood glucose levels by stimulating:
• conversion of glycogen to glucose in the liver and skeletal
muscles (glycogenolysis)
• Secretion of glucagon is stimulated by low blood glucose
levels and exercise, and decreased by somatostatin and
insulin.