The endocrine system consists of glands that secrete hormones directly into the bloodstream. The major glands include the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, pancreas, and thymus gland. The pituitary gland regulates most other endocrine glands and consists of the anterior and posterior lobes. The anterior lobe secretes growth hormone, prolactin, thyroid stimulating hormone, adrenocorticotropic hormone, follicle stimulating hormone, and luteinizing hormone. The posterior lobe secretes vasopressin and oxytocin.

1. THE ENDOCRINE
SYSTEM

2. INTRODUCTION
The endocrine system consist of glands widely
distributed from each other with no physical connection.
These are groups of secretory cells surrounded by an
extensive network of capillaries that facilitated diffusion
of hormones into blood stream, known as ductless
glands.
From blood stream to target tissue and organ where they
influence cellular growth and metabolism

3. GLANDS:
An organ which secretes particular chemical
substances for use in the body or for discharge into
the surroundings.
🞭 There are three types of glands in our body:
 Endocrine glands
 Exocrine glands
 Heterocrine glands

4. EXOCRINE GLANDS
Exocrine glands are glands that secrete their
products into ducts
EXAMPLE:
 Sweat glands
 Salivary glands
 Mammary glands
 Stomach
 Liver

5. ENDOCRINE GLANDS
Glands that secrete their product (hormones)
directly into the blood rather than through a duct
EXAMPLE:
 Pituitary gland
 Pancreas
 Thyroid gland
 Adrenal glands

6. HETEROCRINE GLANDS
These are glands that perform both exocrine and
endocrine functions. For example pancreas

7. Hormone action
 When a hormone arrives at its target cell, it binds to a
specific receptor, where it acts as a switch influencing
chemical or metabolic reaction inside the cell.
 The receptors for peptide hormones are situated on cell
membrane and those for lipid based hormones are
inside the cell.
 The level of a hormone in the blood is variable and self
regulating within its normal range.

8.  A hormone is released in response to a specific stimulus and
usually its action reverses or negates the stimulus through a
negative feedback mechanism.
 This may be controlled either indirectly through the release
of hormones by the hypothalamus & the anterior pituitary
glands e.g.- steroid and thyroid hormones or directly by
blood levels of the stimulus e.g.- inulin and glucagon.
 Effect of positive feedback mechanism is amplification of
the stimulus and increasing release of hormones until a
particular process is complete and the stimulus ceases e.g. –
oxytocin.

9. Endocrine system continue…
🞭 It consists of a number of glands:
Pituitary gland
Thyroid gland
Parathyroid gland
Adrenal gland
Pancreases
Thymus gland

10. PITUTORY GLAND
 The pituitary gland and the hypothalamus acts as a
unit regulating the activity of most of the other
endocrine glands.
 The pituitary gland lies in the hypophyseal fossa of a
sphenoid bone below the hypothalamus.
 It is a size of a pea weigh about 500 mg and consist of
three distinct parts that originates from different types
of cell.

11. Pituitary gland continue…
🞭 The pituitary gland consists of:
1. Adenohyphophysis: - Anterior lobe, an up growth of
glandular epithelium from the pharynx. It is influenced by
hormones which come from the hypothalamus.
2. Neurohypophysis: - Posterior lobe, down growth of
nervous tissue from the brain. It is influenced by neurons
which convey hormones directly from hypothalamic nuclei
for storage of posterior lobe

13. Influence of the hypothalamus on
anterior pituitary gland
 The arterial blood supplied to the hypothalamus through a
capillary network.
 This network of blood vessels forms part of pituitary
portal system, which transport blood from the
hypothalamus to the anterior pituitary where it enters thin
walled sinusoids that are In close contact with the
secretory cells.
 Provide oxygen and nutrients, this blood transport
releasing and inhibiting hormones secreted by the
hypothalamus.

14. On posterior pituitary
 This is formed from nervous issue and consist of nerve cells
surrounded by supporting cells called pituicytes.
 These neurones have their cell bodies in the supraoptic and
Para ventricular nuclei of the hypothalamus and their axon
forms a bundle , the hypothalamohypopyseal tract
 Posterior pituitary hormones are synthesized in the nerve cell
bodies, transported along the axons and stored in vesicles
within the axon terminal in the posterior pituitary
 Their release by exocytosis is triggered by nerve impulses
from the hypothalamus.

16. HORMONES:
Anterior lobe:
• Growth hormone (GH)
• Prolactin
• Thyroid stimulating hormone (TSH)
• Adrenocorticotrophic hormone (ACTH)
• Follicle stimulating hormone (FSH)
• Luteinizing hormone (LH)
Intermediate lobe:
• A and B melanocyte stimulating hormone
Posterior lobe:
• Vasopressin (ADH)
• oxytocin

18. ANTERIOR PITUITARY

19. GROWTH HORMONE (GH):
1. Most abundant hormone synthesized by the anterior pituitary.
2. Stimulate growth and division of most body cells, specially
skeletal muscles.
3. Body growth mainly evidenced in childhood and
adolescence.
4. Regulates aspects of metabolism in many organs e.g.- liver,
intestine, and pancreas stimulates protein synthesis
especially growth and repair.
5. Promotes breakdown of fat and increase blood glucose level.

20.  Its release is stimulated by growth hormone releasing
hormone (GHRH) and suppressed by GHRIH also
known as somatostatin, BOTH are released by
hypothalamus,.
 Secretion of GH is greater at night during sleep and also
stimulated by hypoglycemia, exercise and anxiety..
 The daily amount is peaks in adolescence and decline
with age
 GHRIH also suppress TSH and gastro-intestinal
secretions e.g.- gastric juice, gastrin and
cholecystokinin.

21. • This hormone is secreted during pregnancy to
prepare the breast for lactation after child birth.
• Immediately after birth sucking stimulate
prolactin secretion and lactation.
• It maintain lactation with estrogens,
corticosteroids, insulin and thyroxin.
2. Prolactin:

22. Control of prolactin secretion:
A. Stimulating factors:
They act via stimulating Prolactin releasing factor.
e.g. Exercise, emotional stress, pregnancy and
breast feeding.
B. Inhibitory factors:
which is released by the hypothalamus inhibits
prolactin secretion from the anterior pituitary
Dopamine may be the main prolactin inhibiting
factor.

23. 3.Thyroid-stimulating hormone(TSH) :
It stimulates the thyroid gland to produce:
 Thyroxin (T4), and
 Triiodothyronine (T3)
 Its release is stimulated by thyrotrophin releasing hormone
(TRH) from the hypothalamus.
 Release is lowest in the early morning and highest during the
night ,
 When blood level of thyroid hormone is high secretion of TSH
is reduced and vice versa

24. ACTH
 Corticotrophin releasing hormone (CRH) from the
hypothalamus promotes the synthesis and release of ACTH by
the anterior pituitary.
 This increase the concentration of cholesterol and steroids
within the adrenal cortex and the output of steroid hormones
especially cortisol.
 ACTH level are highest at about 8:00 am and fall to their
lowest about midnight and sometimes high level is at midday
and 6pm .

25. 5. FOLLICLE STIMULATING HORMONE(FSH):
 It is synthesized and secreted
by anterior pituitary gland
 FSH regulates the development,
growth, pubertal maturation
and reproductive processes
of the body and stimulates production of both
gametes by the gonads.

26. 6. LUTEINIZING HORMONE(LH):
 It is a hormone produced by the anterior pituitary
gland.
 In females, an acute rise of LH
triggers ovulation and
development of
the corpus luteum
 In males, it stimulates the
production of testosterone

27. HORMONES OF INTERMEDIATE LOBE:
It secretes:
 α melanocyte stimulating hormone
 β melanocyte stimulating hormone
Function:
They stimulate the production of melanin by
melanocytes
in skin and hair
 MSH signals to the brain have
effects on appetite and sexual arousal.

28. POSTERIOR
PITUITARY:

29. A. Anti-diuretic hormone (ADH) /vasopressin:
 The main effect of antidiuretic hormone is to reduce urine output.
 ADH acts on nephron of the kidneys increasing their permeability
of water.
 The amount of ADH secreted is determined by the osmotic
pressure of the blood circulating to the osmoreceptors in the
hypothalamus.
 As the osmotic pressure rises e.g.- in dehydration, excessive blood
loss more .
 More water is reabsorbed, urine output is increased.

30.  When the osmotic pressure of the blood is low e.g.
after a large fluid intake secretion of ADH is reduced,
less water is reabsorbed and more urine is produced.
 At high concentration in case of severe blood loss,
ADH causes smooth muscle contraction especially
vasoconstriction in small arteries.
 This has a pressure effect raising systemic blood
pressure the alternative name vasopressin reflect this
effect.

31. B. OXYTOCIN: -
 Oxytocin is synthesized in the hypothalamus
 Stored in the posterior lobe of pituitary gland

32.  Oxytocin stimulates two target tissues during and after childbirth
(parturition) uterine smooth muscle and the muscle cells of the
lactating breast.
 During childbirth increasing amount of oxytocin is released into
the blood stream in response to distension of sensory receptors in
the uterine cervix by the baby’s head
 Sensory impulses are generated and they stimulate hypothalamus
to stimulate posterior pituitary to release more oxytocin.

33. • This causes greater stretching of the uterine cervix
as the baby’s head forced further downwards.
• Also involves in lactation and prolong the secretion
of prolactin hormone by inhibiting PIH.

34. THYROID GLAND
 The thyroid gland is situated in the neck in front of the larynx and trachea at
the level of 5th, 6th, 7th cervical vertebrae and 1st thoracic vertebrae.
 It weighs about 25g and surrounded by fibrous capsule.
 It looks like butterfly in shape, Consisting of two lobes
 The two lobes are joined by a narrow isthmus, lying in front of trachea.
 The lobes are roughly cone shaped about 5cm long and 3cm wide.
 The blood supplied by superior and inferior thyroid arteries.
 Venous return is by thyroid vein, which drain into the internal jugular
veins.

36.  the gland is composed of cuboidal epithelium
that form spherical follicles.
 These secret and store colloid, a thick sticky
protein material.
 Between the follicles there are other cells found
singly or in small groups Para follicular cells also
called c cells which secrete the hormone
calcitonin.

38. Iodine is essential for the formation of the thyroid
hormones.
 Triiodothyronine (T3):
It affects almost every physiological process in the body:
 Growth and development, (skeletal and nervous system)
 Metabolism,
 Body temperature, and
 Heart rate
 Thyroxin (T4):
 Controls development and maturation
 Excess thyroxin results rapid development
 Deficiency of thyroxin results in delayed development

39.  The thyroid hormones are synthesized as large precursor
molecules called thyroglobulin the major constituent of colloid.
 The release of both hormones into the blood is stimulated by
TSH from the anterior pituitary.
 Secretion of TSH is stimulated by thyroprotein releasing
hormone (TRH) from the hypothalamus and is stimulated by
exercise, stress, malnutrition, low plasma glucose levels and
sleep.
 The secretion of TSH depend on plasma levels both hormones

41.  Both these hormones affect the most cells of
the body by-
 Increasing the basal metabolic rate and heat
production.
 Regulating metabolism of carbohydrates,
protein and fats.

42.  Calcitonin: It is a hormone secreted by the C cells of the
thyroid gland, it acts on the bone cells and the kidneys to
reduce blood calcium level, when they are raised.
 Inhibits reabsorption of calcium by renal tubules
Its main actions are :-
 to increase bone calcium
 to decrease blood calcium
levels
 Important during childhood
Calcitonin opposes the effects of parathyroid hormone, which
acts to increase the blood level of calcium.

43. REGULATION OF THYROID
SECRETION
Thyroid stimulating hormone (TSH) controls the regulation of
thyroid hormones.
The release of TSH by the
anterior lobe of the pituitary,
is regulated by the hypothalamus
via negative feedback mechanism.
It is a reaction that causes a decrease
in function. It occurs in response
to some kind of stimulus.

44. PARATHYROID GLANDS
 In humans there are 4 parathyroid glands 2 situated in
posterior surface of each lobe of thyroid gland
 Surrounded by fine connective tissue .
 The cells forming the glands are spherical in shape and
arranged I columns with sinusoids containg blood in
between them.

46. FUNCTION OF PTH
 Parathyroid glands secretes parathyroid hormone(PTH).
 Secretion is regulated by blood calcium level, when they fall
secretion of PTH is increased and vice versa.
 The main function of parathyroid hormone is to increase the
blood calcium level when its low.
 And this is achieved by increasing the absorption of calcium from
small intestine and reabsorption from tubules
 If this fails then PTH stimulates osteoclasts and calcium is released
from bones into the blood.

47.  Parathormone and calcitonin from the thyroid
glands act in a complementary manner to maintain
blood calcium level. This is needed for –
1. Muscle contractions
2. Nerve transmission
3. Blood clotting
4. Normal action of many enzymes.

48. THYMUS GLAND
Thymus is located in the anterior part of the upper
mediastinum
 At birth it weighs 10-12 gms
 During childhood and adolescence 20-30 gms
 During old age it weighs 3-6 gms

49. Functions:-
🞭 It initiates and maintain T- lymphocytes
HORMONE : -
Thymosin:-
🞭 It is required for
the development of
T-lymphocytes for cell
mediated immunity

50. ADRENAL
GLANDS
 There are two adrenal glands,
situated on upper pole of
kidney.
 About 4 cm long and 3 cm thick
 It has two parts:
 outer part is cortex and
 the inner part is medulla.

51. 1. ADRENAL CORTEX: -
🞭 It produces three steroid hormones from cholesterol, which are
called adrenocorticoids (corticosteroids):
 Glucocorticoids
 Mineralocorticoids
 Sex hormones (androgens)

53. A. Glucocorticoids: -
 Cortisol, corticosterone and cortisone are the main
Glucocorticoids
 They are essential for life, regulating metabolism and
stress
 Controlled through negative feedback mechanism
 Stimulated by ACTH from anterior pituitary and stress.
 They are high in between 4 to 8 am
 Lowest between midnight and 3 am
 Concerned with catabolism of protein and fat that makes
glucose.

55. Effects:
 Gluconeogenesis (formation of new sugar) from protein and
raising blood glucose level.
Lipolysis (breakdown of triglycerides into fatty acids and
glycerol for energy production).
Breakdown of protein releasing amino acids used for
energy production.
Promoting absorption of sodium and water from tubules
(mineralocorticoid effect)

56. In pathology and pharmacology
glucocorticoid effects:
 Have an anti-inflammatory action.
 Suppress the immune response.
 Suppress the response of tissue to injury.
 Delay wound healing.

57. B. Mineralocorticoids (aldosterone): -
 Is the main mineralocorticoids
 It maintains Water and electrolyte balance.
 It stimulates the reabsorption of sodium by tubules
and excretion of potassium in the urine.
 Involved in regulation of blood volume and blood
pressure too.
 The blood potassium level regulates the amount of
aldosterone, when level is low secretion is more.

58. Renin-angiotensin –aldosterone
system
 Renal blood flow is reduced or blood sodium level
falls, renin is secreted by the kidney cells.
 Renin converts the plasma protein angiotensinogen,
produced by the liver to angiotensin 1.
 ACE formed in small quantities in the lungs, tubules
and other tissues, converts angiotensin 1 to angiotensin
2.
 Which stimulates secretion of aldosterone.
 Cause vasoconstriction.

60. C. Sex hormones: -
 Androgens are the main sex hormones
 They contribute to the onset of puberty

61. 2. ADRENAL MEDULLA: -
🞭 It is surrounded by the cortex, it develops from
nervous tissue in the embryo and is part of
ANS.(sympathetic division)
🞭 It produces two hormones
 adrenaline and
 noradrenaline.

62. Adrenaline and noradrenaline:
 Noradrenaline and adrenaline are released into the blood
 They are structurally very similar and have similar effects
 Together they potentiate by:
 Increasing heart rate
 Increasing blood pressure
 Increasing metabolic rate
 Dilating the pupils

63. DISORDERS OF ADRENAL
MEDULLA: -
The effects of excess adrenaline and
noradrenaline are: -
 Hypertension
 Hyperglycemia
 Raised metabolic rate
 Nervousness
 Headache

64. PANCRE
ASE

65. - Del acell(secretes
somatostain)
Bloodcapillary
?'---- -
,., .,._,v.
Fcell(secretes pancreatic
polypeptide)

66. PANCREATIC
HORMONES
1. INSULIN:
Actions:
 On carbohydrate metabolism:
 Insulin increases the glucose
entry into most of body cells
 Insulin produce hypoglycemia
 On protein metabolism:
 Insulin promotes amino-acid uptake
 It decrease protein breakdown
 It promotes protein synthesis especially in muscles

67. DISEASES RELATED TO
INSULIN: -
DIABETES MELLITUS
🞭 It is a group of metabolic diseases
in which there are high blood sugar
over a prolonged period.
🞭 This high blood sugar produces
the symptoms of
 frequent urination,
 increased thirst, and
 increased hunger.

68. hormones
continue…
2. GLUCAGON: -
Glucagon act mostly on the liver and adipose tissues where it
antagonizes the actions of insulin
 Stimulate glycogenolysis
 Promotes gluconeogenesis

69. hormones
continue…
3. SOMATOSTATIN:
A hormone that is widely distributed throughout the body, especially
in the hypothalamus and pancreas
Action:
 It regulates the endocrine and
Nervous system functions