Transcript Physiology of Endocrine

Assist prof. of Medical Physiology
Def.
• Growth refers to an increase in some quantity over
time.
• The quantity can be:
1. Physical (e.g., growth in height, growth in an amount
of money)
2. Abstract (e.g., a system becoming more complex, an
organism becoming more mature).
Rate of Growth:
 Body growth is a continuing process throughout childhood and
adolescence.
 Rapid in the first 2 years of life and
 Slow during the middle years of childhood.
 A 2nd phase of rapid growth at puberty
 Cessation of growth when the adult height is reached.
Factors affecting growth
1. Hormones
2. Genetic Factors
3. Extrinsic Factors
4.Growth regulating peptides
1. Growth H plays an important role in growth in
infancy, where its plasma level is elevated.
2. Thyroid hormones :
1. Stimulate physical growth: as they activate the
action of somatomedins.
2. Essential for mental and sexual growth.
• 3. Insulin potentiates growth.
 Important for the formation of somatomedins.
 Child with juvenile diabetes have stunted growth.
• 4. Glucocorticoids:
– Physiological levels facilitate growth
– Large pharmacological doses inhibit GH release &
suppress growth .
• 5. Androgens, & estrogen,
– Responsible for the second growth spurt at puberty
– Have strong anabolic effect which independent on
somatomedins.
– Growth is initially stimulated and then stops as they
cause fusion of the epiphyseal cartilage of long
bones.
• 6. Parathyroid H and vitamin D are essential for
normal bone ossification.
 Genetic determines ;
1. The growth rate,
2. The age of puberty
3. Adult height
• A) Dietary factor:
– Balanced diet which rich in proteins and
vitamins is important for a normal growth
process in children.
• B) Infections:– Exposure to stress of infections in children
leads to suppression of growth.
– Followed by, in recovery period, by a stage
of enhanced growth rate called “catch-up
period”.
 Are growth modulators such as:
1. Fibroblast growth factors
2. Epidermal growth factors
3. Growth promoting
4. Growth inhibiting peptides.
• Chemistry:
 Polypeptide H. (199 a.a.)
 Structurally similar to GH and human chorionic
somatomammotropin (hCS).
Source
 Secreted by mammotrop acidophil cells of the ant pituitary.
• Plasma concentration :
• In men 5 ng/ml
• In women 8 ng/ml.
1. Stimulate the development of breast tissue:
a) During prepubertal and postpubertal life, prolactin,
stimulates the proliferation and branching of milk ducts of
the breast (with estrogen, progesterone, cortisol and GH).
b) During pregnancy, prolactin, with estrogen and
progesterone, causes development of milk alveoli.
c) After parturition, prolactin stimulates milk synthesis and
secretion.
• 2. In lactating women
 Responsible for maternal behavior
 High prolactin levels inhibit the secretion of GnRH, causing a
loss of normal LH peak and preventing ovulation.
 This accounts for the absence of menstruation
during lactation ( lactation amenorrhea) .
• 3. Stimulates lymphocyte proliferation & differentiation,
with GH.
1. Hypothalamic control
2. Feed-back mechanism
3. Drugs
4. Pregnancy
5. Suckling
6. Other factors
a. Sleep: prolactin secretion rises at night.
b. Stress: increase prolactin secretion.
c. Oxytocin, TRH, VIP, angiotensin II, significant
increase prolactin secretion.
• The hypothalamus secrete both :
1. Prolactin releasing hormone (PRH) and
2. Prolactin release inhibiting hormone (PRIH) which
is structurally similar to dopamine.
– Effect of hypothalamus is mainly inhibitory.
• Cutting the pituitary stalk leads to increase in the
plasma prolactin level
 Prolactin stimulate the release of dopamine at the
median eminence, which inhibits prolactin secretion.
 This is a short loop negative feedback mechanism
+
Hypothalamus
PRIH (dopamine)
PRH
_
Short loop
-ve feed back
+
Ant Pituitary
+
Prolactin
Hypothalamic & Feed-back control of PH
• a) L-dopa decrease prolactin secretion by:
– increasing the formation of dopamine.
• b) Bromocriptine & Apomorphine reduce prolactin
secretion
– through stimulate dopamine receptors.
• c) Chlorpromazine
– blocks dopamine receptors, So increase prolactin secretion.
• During pregnancy prolactin secretion increase
steadily, & its plasma levels reach up to 20 folds at
term.
Mechanism
During pregnancy, the increased oestrogen, stimulates:
1. Hyperplasia of mamotrops (prolactin-secreting cells),
and
2. Prolactin synthesis, but not release.
• Stimulation of the nipples by suckling:
– Cause rapid rise in prolactin level
– especially during the first 12 weeks of lactation.
• Mechanism
– Suckling of nipple of breast → stimulation of touch
receptors → afferent impulses → reflex inhibition of
PRIH secretion
Hypothalamus
Prolactin and Oxytocin
Milk production and Ejection
Afferents
Touch receptors
• a) Sleep:
– prolactin secretion rises at night.
• b) Stress: all increase prolactin release.
– As anaesthesia, surgery, insulin-induced
hypoglycemia, fear and mental tension
• c) Oxytocin, TRH, VIP, angiotensin II &
substance P
– produce significant increase prolactin secretion.