The Endocrine System
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Posterior Pituitary Gland (Neurohypophysis)
Does not synthesize hormones
Consists of axon terminals of hypothalamic neurons
Neurons release two neurotransmitters that enter capillaries
– antidiuretic hormone
– oxytocin
1. Oxytocin
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Function of Oxytocin during Labor :
Stimulation of uterus by baby
Hormone release from posterior pituitary
Uterine smooth muscle contracts until birth of baby
Baby pushed into cervix, increase hormone release
More muscle contraction occurs
When baby is born, positive feedback ceases
1. Antidiuretic Hormone (ADH)
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Known as vasopressin
Functions
1. decrease urine production by increasing H2o absorption from collecting tubules of
kidney.
2. decrease sweating
3. increase BP as it has vasopressor effect and control blood pressure
4. its deficiency leads to polyuria and polydipsia(excessive drinking)
2. Thyroid Gland
It is the largest endocrine gland
It lies in front of the neck
It is formed of 2 lobes connected by the isthmus which crosses the trachea
It secretes 2 hormones:
1. Thyroxine&triiodothyronine: both are iodine containing aa
2. Calcitonin: it is a Ca++ lowering hormone, polypeptide, secreted by the parafollicular cells
Control of thyroid secretion:
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Hypothalamus secretes TRF….. Stimulates the ant. Pituitary to secrete TSH…….↑synthesis
and secretion of thyroid
↑ T3 & T4……↓TSH secretion (-vefeed back mechanism)
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Calcitonin – accelerates storage of calcium in bones and lowers blood calcium levels;
99% of calcium in the body is stored in bones, necessary for blood clotting, and holding
cells together
Decreases blood calcium levels by causing its deposition on bone
Antagonistic to parathyroid hormone
Produced by C (parafollicular) cells
Action of thyroid T3 ND T4 hormones :
1. Increase oxygen consumption and enhance the metabolism of all body tissues,
2. On protein metabolism: they increase protein synthesis in muscles , liver and
kidney .they stimulate growth. They increase activity of most enzymes in cells .In
large doses they are catabolic.
3. On carbohydrates: they increase the rate of glucose absorption, uptake and
utilization by tissues .glycogenolysis and gluconeogenesis are enhanced .
4. On fat: they increase the mobilization of fat from its stores and use its fat for
production of energy e.g. lipolytic effect .it decreases level of plasma cholesterol .
5. On cardiovascular system they accelerate heart rate and force of contraction,
increase systolic blood pressure and decrease diastolic blood pressure .
6. On G.I.T. :increase appetite ,mobility and secretion of G.I.T.
7. On C.N .S: they are important for normal development ,myelination and
maturation of C.N .S.
8. On blood :increase erythropoiesis
9. Help development of skin ,hair,nails ,….
Hypo function:
a) Before puberty:--cretinism .mental retardation , retarded growth ,intolerance of cold,
muscle weakness(ABDOMINAL MUSCLE WEAKNESSPROTRUDED
VISCERA),PROTURUDED ENLARED TONGUE, thick skin . infantile sexual organs, increase
cholesterol
b) After puberty-myxedema : slow mental activity, sensitive to cold ,firm non pitting
oedema, hair is coarse and space, dry skin. sexual hypo function (female irregular
menstrual cycle and male impotence), anaemia ,high cholesterol ,weakness and
increase cholesterol.
Hyper function: (Grave ,disease)
1. exophthalmos due to excessive degenerative tissues behind the eyes and weakness of
extra ocular muscles
2. Goitre
3. Warm sweating palm due to V.D.
4. Rapid heart rate
5. Loss of weight
6. Fine tremors in hands and tongue
7. Intolerance of heat
8. Demineralization of bones with loss of calcium
9. General weakness
10. Insomnia ,diarrhoea
3. Parathyroid Glands
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Raise blood calcium levels – lose bone )(it causes resorption of Ca and P from bone) By increase
activity of osteoclasts
On intestine : it increases Ca and P absorption by increasing formation of 1,25,(H2o) vit.D3
which help absorption of Ca and Phosphate.
On kidney : it increases reabsorption of Ca from renal tubules and increases P excretion
Opposite function of calcitonin
Control of parathyroid H.:
1. Negative feedback. If Ca ions increases in blood ,the secretion of H. decreases and
visa versa.
Abnormalities:
2. Deficiency :causestetany which is an increase neuromuscular excitability due to
decrease ionized calcium in plasma. The normal level of plasma calcium is 9-11 mg
%
3. Increase:  increase Ca ion which -hypercalcemia .Ca and P may be deposited in
kidney forming stones bone is affected and becomes decalcified and easily
fractured.
4. Adrenal Glands
5. One on top of each kidney
6. 3 x 3 x 1 cm in size and weighs 5 grams
7. Cortex produces mineralocorticoids, glucocorticoids, and androgens
8. Medulla produces epinephrine & norepinephrine
Mineralocorticoids
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Functions :
Hormones that regulate mineral balance:
increase reabsorption of Na+ with Cl- by renal tubules and water due to osmotic obligation
decrease reabsorption of K ,Magnesium and hydrogen. Also, cause reabsorption of Na and Cl
form G.I.T ,saliva and sweat and K secretion in them .
• 95% of hormonal activity due to aldosterone
------Cortex – Glucocorticoids
• Hormones that regulate glucose balance
• 95% of hormonal activity is due to cortisol
• Functions : help regulate metabolism
– increase rate of protein (catabolic )and fat breakdown (lipolytic ); mobilize fat from fat
depots and ketogenic.
– provide resistance to stress by making nutrients available for ATP production
– raise BP by vasoconstriction
– anti-inflammatory effects reduced (as in skin cream).it decrease vascular permeability.
– antiallergic action opposing the effect of histamine
– decrease eosinophil count and lymphocytes but increase erythrocytes and neutrophils.
– On C N S :give sense of well
– Permissive role in all body function
Control of cortical secretion
1. Hypothalamus :ACTRH increase secretion of ACTH
2. Anterior pituitary :ACTH increase its secretion
3. Physical and mental stress increase ACTRHincrease ACTHincrease its
secretion
------Cortex – Androgens
• Small amount of male hormone produced
– insignificant in males
– may contribute to sex drive in females
– is converted to estrogen in postmenopausal females
Abnormalities of adrenal cortex functions
Hyper function:
1. Cushing syndrome: It is characterized by:
a) Wasting and weakness of muscles (catabolic effect)
b) Increase Na and water retention in blood oedema ,hypertension and decreas of blood K
c) Hyperglycemia
d) Redistribution of fat; thin extremities ,accumulation in abdominal wall,face (moon face )
andupper back (buffalo trunk )
e) Skin is thin and with striae
f) Gonadal disturbances
2. Adreno-genital syndrome:.
Due to excess sex hormons secondary to adrenal hyperfunction due to yumour of cortex
precocious puberty in males and adrenal virilism, in females due to exess androgens.
Hypo function:
Addisons disease: due to adrenal cortex insufficiency
It is characterized by:
1. Loss of appetite ,vomiting ,diarrhoea ile.GIT disturbances
2. Muscle weakness due to anabolic effect of androges
3. Decrease Na ,increase K in blood . water moves intracellularly—>decreas blood
volume and hypotension and may be shock
4. Hypoglycaemia
5. Bronze hyperpigmentation of skin due to high level of ACTH secondary to low level
of glucocorticoids.ACTH has melanocytic stimulating activity
6. Decrease sexual function
D. Pancreatic Hormones
• Endocrine cells in pancreatic islets produce hormones
Cell Types in the Pancreatic Islets
• Alpha cells (20%) produce glucagon
• Beta cells (70%) produce insulin
• 2 others
Function of insulin:
a) Increases glycogen deposition in liver and skeletal muscle
b) Increases glucose uptake by tissues and its oxidation
c) Inhibits gluconeogenesis and glycogenolysis
d) Help protein deposition in cells
e) Help fat formation help growth of tissues
f) Introduces K intracellularly .thus decreases it in serum
Diabetes Mellitus
Due to failure of pancreas to secreate insulinincrease glucose in blood ,polyuria
,polydypesia and polyphagia .
Function of glucogon
Elevates blood glucose by increasing glycogeolysis and gluconeogenesis .also , increases heart
rate and force of cardiac contraction
Regulation of Glucagon & Insulin Secretion
• Low blood glucose stimulates release of glucagon
• High blood glucose stimulates secretion of insulin
E. Ovaries and Testes
1. Ovaries
a. estrogen, progesterone, relaxin&inhibin
b. regulate reproductive cycle, maintain pregnancy & prepare mammary glands for
lactation
2. Testes
a. produce testosterone
b. regulate sperm production & 2nd sexual characteristics