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 growthFactors affecting growth
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. Suckling6. 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 Hypothalamus
Ant Pituitary Ant Pituitary
Prolactin
Short loop-ve feed back
_
Hypothalamic & Feed-back control of PH
+
PRHPRIH (dopamine)
+
• 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
Touch receptors Afferents
Hypothalamus
Prolactin and Oxytocin
Milk production and Ejection
• 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.