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

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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.