Assist prof. of Medical Physiology. Body functions are regulated by 2 systems; Nervous system Rapid...

Assist prof. of Medical Physiology

• Body functions are regulated by 2 systems;

nervous system

Blood vessels

Endocrine gland

Biological effect

Receptor

Target cell

• Endocrine glands are groups of cells that produce specific chemicals, called hormones, having well defined effects on body functions.

• Also, called ductless glands since their secretion is not conveyed along ducts but pass directly into blood and lymphatic vessels.

General features of hormones (def.)1) A specific chemical substance2) Secreted by ductless gland3) In a catalytic amount (very small amounts), 4) Transported by the blood (directly or through

lymphatics), To a specific target cells (which have a specific hormone receptors),

5) Where it produces: »physiologic, »morphologic and »biochemical responses

• Both nervous and endocrine systems form together a biological communication network for integration of the body response to a changing environment.

• Examples of this link:• 1) Hypothalamic neurosecretory cells, • A) Some neurons delivered substances

through hypothalamo-hypophyseal portal vessels to the ant. pituitary to regulate its secretions.

• • B) Other hypothalamic neurons send their

axons to the post pituitary, where they release neurosecretory products directly into the blood stream.

Hypothalamic neurosecretory cells

2- Innervation of the endocrine glands: Most,

endocrine glands, receive nerves that appear to

control their blood supply and secretory activity.

3- Also, thyroid, gonadal and adrenocortical

hormones act on the CNS to inhibit or stimulate the

secretory activity of the hypothalamic neurons.

Secretion of adrenaline and noradrenaline from adrenal medulla by symp. N.F.

Feedback of Thyroid Hormones on Pituitary Gland

• Virtually all organs of the body exhibit endocrine function

I-Endocrine glands II- Organs with endocrine functions1- Hypothalamus2- Pituitary gland3- Thyroid gland. 4- Parathyroid glands 5- Suprarenal glands6- Endocrine portion of the pancreas7- Primary sex organs: testes and ovaries 8- Thymus gland9- Pineal gland

1- Heart 2- Kidney 3- Liver 4- Skin5-GIT6- Placenta

Some hormones act only locally, e.g.:

1- Paracrine hormones, which diffuse for a short

distance through the interstitial space to affect

neighbouring cells.

2- Autocrine hormones, which act on the same cells.

3- Juxtacrine, whereby one cell interact with specific

receptor on juxta-posed cells.

Example: PGs, histamine, serotonin, bradykinin,

epinephrine, acetylcholine, endorphins,

encephalins, GIT hormones.

Biological effect

Biological effect

Chemical nature of hormones Chemical nature of hormones

Protein H. Steroid H.

From cholesterol:

A) Adrenal cortical H.

B) Sex H.

C) D3.

From cholesterol:

A) Adrenal cortical H.

B) Sex H.

C) D3.

P.PP.P A.AA.A

-Thyroid h.-Catechol.-Melatonin

-Thyroid h.-Catechol.-Melatonin

-Pituitary gland

-Hypothalamus

-Calcitonin.

-Parathyroid H. -

Pancreatic H.

-GIT H.

-Pituitary gland

-Hypothalamus

-Calcitonin.

-Parathyroid H. -

Pancreatic H.

-GIT H.

Synthesis:Synthesis:• Amino acid and steroid hormones are

synthesized through series of enzymatic reactions • Peptide hormones are synthesized as proteins in

the ribosomes.

Storage :Storage :• Catecholamines and polypeptide hormones are

stored in secretory granules • thyroxin and steroid hormones not stored in

granules & present in the free form within the cytoplasm .

• 2 groups of hormones derived from the amino acid tyrosine

• Thyroid hormones and Catecholamines

Most endocrine glands produce their hormones continually at levels determined by:

a) Body requirements.b) Rate of hormone inactivation.c) Rate of hormone clearance from the body.

1. Catecholamine and polypeptide hormones

are stored in secretory granules, are released by the

process of exocytosis.

2. Thyroxin and steroid hormones are present in

the free form within the cytoplasm and leave the cell

by simple transfer through the plasma membrane.

The released hormones enter the blood, where they may circulate in 2 forms:– 1. Free (unbound) part: the active part which

binds to receptor. – 2. Bound part: carried by specific albumins

and globulins which are synthesized in the liver.

In general, steroid and thyroid hormones are bound to transport proteins,

whereas polypeptide and other amine hormones circulate in a free form.

The plasma half-life of a hormone (time needed for the

concentration of the hormone to decrease to its half) is correlated with the % of protein binding.

For example, – Thyroxin is 99.98% protein bound and has a

plasma half-life of 6 days, – Whereas aldosterone, a steroid hormone, is

only 15% bound and its plasma half-life of 25 minutes.