2.Endocrine physiology (Part2).pptx

Growth Hormone (GH)

• _{secreted by the somatotrophs that make up 40-50% of the}

anterior pituitary cells. It’s derived from a larger precursor peptide, pre GH.

• _{GH release is stimulated by GHRH (}which binds to a plasma

membrane receptor and medicates its primary action through cAMP & Ca++_).

• _{Another hypothalamic peptide GHIH (Somatostatin) is a}

powerful inhibitor of GH release.

• _{GH is secreted in pulses, which are due to pulsatile release of}

• Daily GH secretion is slightly increased in

children;

• increase further during the period of puberty and then declines to adult levels,

• _{a further late reduction}

Action of GH

:

1. The most specific effect is the

stimulation of linear

growth

Effect of growth hormone on bone include:

(1) increased deposition of protein by the

chondrocytic

and osteogenic cells that cause bone growth, (2) increased rate of reproduction of these cells,and

Epiphysis of the femur (F) before and (G)

after it unites with the shaft femur

•

Visceral organs

(liver, kidneys, pancreas, intestine),

endocrine glands (Adrenals, parathyroid, pancreatic

islets), skeletal muscles, heart, skin and connective tissue

all undergo hypertrophy and hyperplasia in response to

GH.

• _{Renal plasma flow,} • _{Glomerular filtration,} • _{cardiac output and} • _{hepatic clearance are}

2. GH has several actions on Carbohydrates and

lipid metabolism

.

• _{GH is diabetogenic because it increases hepatic glucose output}

and exerts an anti-Insulin effect in muscle.

• _{It is ketogenic because it increases circulatory free fatty acid}

3

.

Effects on protein and electrolyte

metabolism

:

GH is a

protein anabolic hormone

, a rise in plasma

phosphorus and a fall in the blood urea nitrogen and

amino acid levels.

It also stimulates

erythropoiesis

.

Physiology of Growth

:

• _{Growth is a complex phenomenon that is affected not only by GH}

and somatomedin but also by thyroid hormones, androgens, estrogens, glucocorticoids and insulin. It is also affected by genetic factors and it depends on adequate nutrition.

• _{It involves increase in length and size not just an increase in}

weight In humans.

• _{There are two periods of rapid growth. The first is in infancy and}

• _{Although androgens and estrogens initially stimulate growth they}

will terminate growth by causing the epiphyses to fuse to the long bones (epiphyseal closure). Once the epiphyses have closed linear growth stops.

• _{Thyroid hormone has permissive action to that of GH by}

potentiating the actions of somatomedins.

• _{Thyroid hormone have wide spread effects on the ossification of}

GH Exerts Much of Its Effect Through

“Somatomedins”

GH causes the liver (and, to a much less extent, other

tissues) to form several small proteins called somatomedins

Short Duration of Action of Growth Hormone but

Prolonged Action of Somatomedin C.

1. Gigantism:

GH hyper secretion before closure of epiphyses.

Syndromes of ant.pituitary hyper-secretion

2. Acromegally:

3. Dwarfism:

short stature can be due to GHRH deficiency, GH deficiency, or other causes.

Clinical Syndromes of GH Dysfunction

In people who have lost the ability to secrete growth hormone, some features of the aging process accelerate.

The physical and

physiological effects are - increased wrinkling of the skin,

- diminished rates of function of some of the organs, &

- diminished muscle

Possible role of decreased GH secretion in causing

changes associated with aging

The aged appearance seems to result mainly from decreased protein deposition in most

tissues of the body and increased fat

Adrenocorticotrophic hormone

(ACTH)

• _{ACTH stimulates adrenocortical}

secretion and growth.

• _{The pigmentary changes in several}

endocrine diseases are probably due to changes in circulatory

Prolactin

•

principally concerned with stimulating

breast

development

&

milk production.

Posterior Pituitary Gland and Its Relation to the

Hypothalamus

The nerve endings contain many secretary granules. These endings lie on the surfaces of capillaries, where they secrete two posterior pituitary hormones:

(1) antidiuretic hormone (ADH), also called vasopressin, (2) oxytocin.

the hormones are initially synthesized in the cell bodies of the supraoptic and paraventricular nuclei and are then transported in

Vasopressin (ADH) action

• _{The retention of water by the; Anti Diuretic Hormone (ADH).}

• _{It increases the permeability of the collecting ducts of the}

kidney, so the urine becomes concentrated and its volume decreases.

•

(The overall effect is therefore retention of water in

excess of solute).

Physiological function of ADH

Immediately inside the cell membrane are a large number of special vesicles that have highly water permeable pores called

aquaporins.

When ADH acts on the cell it causes the vesicles to insert into the apical cell membranes, thus providing many areas of high water permeability. All this occurs within 5 to 10

minutes.

Diabetes Insipidus

:

•

disease processes in the

hypothalamic nuclei ,

the

posterior pituitary gland

or

the tract between them

.

Is the syndrome that results when

vasopressin deficiency

develops

•

The symptoms of diabetes insipidus

are passage of large amounts of dilute

urine

(polyuria).

•

and the drinking of large amount of

fluid

(polydipsia).

Oxytocin function

• Oxytocin acts primarily on the breasts and uterus.

• _{Suckling is the major stimulus for oxytocin release.}

• _{Oxytocin has another effect which is a powerful action on smooth}

muscle in the uterus (Rhythmic contractions of the myometrium are stimulated by very small dose).

•

• _{hormone oxytocin, in accordance with its name, powerfully stimulates}

contraction of the pregnant uterus, especially toward the end of

Oxytocin causes contraction of

myoepithelial cells

surrounding the alveoli of the mammary glands.