Unit 5 CHEMICAL CONTROL AND INTEGRATION

CHEMICAL CONTROL AND INTEGRATION

Endocrinology : 

The branch of biology which deals with the study of endocrine system and its physiology is known as Endocrinology’’. 

‘’Thomas Addision’’ is known as father of Endocrinology. Whereas the gland with duct is called exocrine gland which secretes enzyme etc. Endocrine glands pour their secretion directly into blood. These glands lack ducts, so these glands are called ductless glands. Where as, the work of co-ordination by endocrine system is slowly by secretion of some chemical substances. 

 Co-ordination in the body of almost all the higher vertebrates is controlled by two systems Nervous system and endocrine system. 

HORMONE :  The term hormone was coined by Starling.  First discovered hormone is secretin. It was discovered by Bayliss & Starling in 1902.  Hormones are also called ‘’Primary messengers’’ or chemical messengers.’’ 

Chemical Nature of Hormone : 

The animal hormones may be classfied into 6 categories. 

1. Protein : The gonadotropic, thyrotropic and somatotropic hormones from the anterior lobe of pituitary are protein with high molecular weights.

 2. Steroids (Fat soluble) : The hormones like cortisol and aldosterone from adrenal cortex, testosterone from interstitial cells of testes, estrogen and progesterone from Graaffian follicles of ovary and placenta are the examples of steroid hormones. The hormones contain cholesterol and bile salts.

 3. Fatty acid derivative : - Prostaglandin 

4. Amino acid derivatives : The hormones epinephrine and norepinephrine from the adrenal medulla and thyroxine from the thyroid gland are derived from amino acid.

 5. Short peptides : The hormones oxytocin and vasopression from the posterior lobe of the pitutary gland are short peptides of 9 amino acid. The melanocyte stimulating hormone (MSH) from the intermediate lobe of the pituitary gland is also short peptide of 13 amino acids. 

6. Long peptides : The hormones insulin from the pancrease, adrenocortico tropin (ACTH) from the anterior lobe of the pituitary gland, calcitonin from the parathyroid gland consists of 84 amino acids. 

Physical & Chemical Specialities of Hormones : - 

 Hormones are non-antigenic & non species specific substances. 

 Hormones are soluble in water and are easily diffusible in tissues.  

The secretion of hormone is always in very small quantity because these are most reactive substances  Hormones are destroyed after use.  

Hormones can not be stored in the body except Thyroxine.  Hormones are soluble in water and blood.  

The molecules of most of the hormones are small, and their molecular weight is low.

 Liver and kidneys separate them from blood and decompose them. The waste product formed after decomposition, hormones are excreted with urine. 

It can not be reutilized. 

Usually, hormones do not participate in the metabolic activities of target cells but they affect and control the activity level of these target cells. 

Due to the effect of hormones, not only the rate of metabolic activites is effected but also the permeability of cell membrane is changed so the nature of reaction is also changed. so the nature of reaction is also changed. 

CHEMICAL COORDINATION & INTEGRATION 

INTEGRATIVE SYSTEMS 

 Neural system and endocrine system jointly co-ordinate and regulate the physiological functions of the body. 

 Note: Nervous system provides rapid co-ordination where endocrine system provides slow co-ordination with different body parts. 

 Hormone :- Secretion of endocrine glands (Ductless glands) called as hormones. "Hormones are non-nutrient chemicals which act as intercellular messenger and are produced in trace amounts."

 Note: Intercellular messenger = Passes message from one cell to another cell by binding with membrane bound receptors or receptors located inside the cell. 

Receptors :- Protein molecules specific for particular hormone molecules.“Position of Receptors - Located on cell surface or intracellular. 

 Organised endocrine Glands (Whole gland) : Pituitary gland, Pineal gland, Thyroid.gland, Adrenal Gland, Pancreas, Parathyroid gland, Thymus and Gonads. 

Other unorganised endocrine tissue (Diffused tissue) : GIT, Kidney, Heart etc.

 HYPOTHALAMUS 

 Basal part (ventral part) of Diencephalon. 

 Group of neurosecretory cells known as nuclei (Nuclei = group of cyton in CNS) secrete 7 releasing hormones (which stimulate secretion) and 3 inhibiting (which inhibit secretion) hormones.

 These hormone regulate the synthesis and secretion of pituitary hormones. 

 Hypothalamo hypophyseal portal system regulate functions of anterior pituitary. 

 In this portal system releasing and inhibiting hormones are transfer to anterior pituitary by hypophyseal portal veinand stimulate hormone synthesis & secretion of anterior pituitary. 

 Posterior pituitary is under the direct regulation of the hypothalamus. 

 Hormones of posterior pituitary are synthesised into hypothalamic nuclei (Paraventricular nuclei and supra optic nuclei) and secreted into posterior pituitary through axons. So these are stores and again release into body via blood stream. 

PINEAL GLAND (Dorsal side of forebrain) 

 Hormone = Melatonin 

 Melatonin regulate 24 hours diurnal rhythms of body. 

 Melatonin maintain rhythms of body like - sleep wake cycle, body temperature. 

 Melatonin also influence metabolism, pigmentation, menstrual cycle and defense capability. 

After 7 year of birth pineal gland undergo involution and crystal of CaCO3 and Ca3 .PO4 are deposited in it called "Brain sand".