INTRODUCTION :
♦ The branch of biology which deals with the study of endorcine 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.
♦ Co-ordination in the body of almost all the higher vertebrates is controlled by two systems Nervous system and endocrine system.
♦ Nervous system and endorcine system are called Integrative system of the body.
♦ Nervous system carries informations in the form of impulses to the different parts of body. High speed services are offered by this system.
♦ Where as, the work of co-ordination by endocrine system is slowly by secretion of some chemical substances.
♦ Substances secreted by these glands are known as hormones. The meaning of work 'hormone' in Greek is ''to excite'' = hormaein.
Differences between Nervous and Endocrine Coordinations
HORMONE :
→ The term hormone was coined by Starling.
→ Hormones are also called ''Primary messengers'' or chemical messengers.''
→ First discovered hormone is secretin. It was discovered by Bayliss & Starling in 1902.
Source & Chemical Nature : - Hormones are chemical messengers which are secreted by one part of body and are poured directly into the blood stream, and they reach at their target place with the help of blood. A small amount of hormone affects some specific cells or physiology of cells of organ according to atmospheric conditions.
Chemical Nature of Hormone :
The animal hormones may be classfied into 6 categories.
1. Amino acid derivatives : The hormones epinephrine and norepinephrine from the adrenal medulla and thyroxine from the thyroid gland are derived from amino acid.
2. 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.
3. 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.
4. Protein : The gonadotropic, thyrotropic and somatotropic hormones from the anterior lobe of pituitary are protein with high molecular weights.
5. 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.
6. Fatty acid derivative : - Prostaglandin
Physical & Chemical Specialities of Hormones : -
→ The moleucles of most of the hormones are small, and their molecular weight is low.
→ 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.
→ 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.
→Hormones are non-antigenic & non species specific substances.
→ 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.
