Question

Chemical coordination and regulation 1 neet notes

Answer 1

Revision Notes on Chemical Coordination and Regulation

Properties of hormones

(a) These are secreted by endocrine gland (biogenic in origin).
(b) Their secretions is released directly into blood (except local hormones e.g. gastrin).
(c) These are carried to distantly locate specific organs, called target organ.
(d) These have specific physiological action (excitatory or inhibatory). These co-ordinate different physical, mental and metabolic activities and maintain homeostasis.
(e) The hormones have low molecular weight e.g.ADH has a molecular weight of 600–2000 daltons.
(f) These act in very low concentration e.g.around10–10 molar.
(g) Hormones are non antigenic.
(h) These are mostly short-lived. So have a no camulative effect.
(i) Some hormones are quick acting e.g.adrenalin, while some acting slowly e.g. ostrogen of ovary.
(j) Some hormones secreted in inactive form called Prohormone e.g. Pro-insulin.
(k) Hormones are specific. They are carriers of specific information to their specific target organ. Only those target cell respond to a particular hormone for which they have receptors.

Origin of different endocrine glands

Endocrine glands
Weight
Origin
Pituitary
0.5 gm
Ectoderm
Pineal
5.0 mg
Ectoderm
Thymus (up to 12 yrs.)
20.0 gm
Mesoderm
Thyroid
25.0 gm
Endoderm
Parathyroid
20.0 mg
Endoderm
Adrenal cortex
4.0 gm
Mesoderm
Adrenal medulla
1.0 gm
Ectoderm
Testes
–
Mesoderm
Ovary
–
Mesoderm
Pancrease
60.0 gm
Endoderm

Pituitary Gland (Hypophysis)

(1) Pituitory is known as hypophysis cerebri, its name pituitary was given by vesalius.
(2) Muller’s gland of amphioxus and subneural gland of hardmania is homologous to pituitary of vertebrates.

Parts and component

(1) Adenohypophysis (Anterior lobe)
(i) Pars distalis
(ii) Pars tuberalis               
(iii) Pars intermedia
(2) Neurohypophysis (Posterior lobe)
(i) Pars nervosa         
(ii) Infundibulum               

Hypothalamus   

(i) Position and Structure: Hypothalamus is the floor of diencephalon. It is formed of masses of grey matter, called hypothalmic nuclei, containing neurosecretory cells. It is connected with anterior pituitary lobe by blood capillaries of hypophyseal portal system and with the posterior pituitary lobe by axons of its neurons, both passing through the pituitary stalk.
(ii) Hormones of hypothalamus: Neurosecretory cells of hypothalamus secrete neurohormones called releasing factors (RF) or inhibiting factors (IF). These neurohormones are carried by hypophyseal portal system to adenohypophysis (primary target organ) and stimulate or inhibit the release of trophic hormones from adenohypophysis. These neurohormones are proteinous in nature and formed of 3 – 20 amino acids.

Neurohormones of Adenohypophysis

Neurohormones
Physiological effects
(1) TSH-RF
 
(Thyroid Stimulating Hormone – Releasing Factor)
Increased ACTH secretion from adenohypophysis.
(2) ACTH-RF
 
(Adrenocorticotrophic Hormone-Releasing Factor)
Increased ACTH secretion from adenohypophysis.
(3) STH-RF
 
(Somatotrophic Hormone-Releasing Factor)
Increased STH secretion from adenohypophysis
(4) SOMATOSTATIN (GROWTH INHIBITING HORMONE)
Decreased STH secretion from adenohypophysis.
(5) GTH-RF
 
(Gonadotrophic Hormone-Releasing Factor)
 
(i) FSH-RF
 
(Follicular Stimulating Hormone-Releasing Factor)
Increased FSH secretion from adenohypophysis.
(ii) LH-RH (In female)
 
(Luteinising Hormone – Releasing Factor)
Increased LH secretion from adenohypophysis.
or ICSH-RF (In male)
 
(Interstitial Cells stimulating Hormone-Releasing Factor)
 
(6) Prolactin-Releasing hormone (P-RH)

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