Short notes on Biochemistry of Hormones, Hypophysis,Pancreatic hormones and Adrenal glands


Biochemistry of Hormones or Chemical nature of hormones:
Most hormones are proteins (Polypeptides) derivates of amino acids (amines) or steroids. A few are fatty acid derivates e.g. most invertebrate neurosecretary cells produce polypeptides called neuropeptides. Hormones that the vertebrate pancreas secretes are proteins; those that the thyroid gland secretes are amines. The ovaries, testes and cortex of adrenal glands secrete steroids. Hormones are effective in small amount. Only few molecules of hormone may be enough to produce a dramatic response in a target cell. In target cell hormones help to control biochemical reactions in three ways: (i) A hormone can increase the rate at which other substances enter or leave the cell. (ii) It can stimulate a target cell to synthesize enzymes, proteins or other substances. (iii) It can prompt a target cell to activate or suppress existing cellular enzymes. Hormones are not changed by reaction they regulate.

Lobes of pituitary glands (Hypophysis):
Pituitary gland has two lobes, the anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). Two lobes differ in several ways (i) Adenohypophysis is larger than neurohypohysis (ii) Secretary cells called pituicytes are in adenohypophysis but not in neurohypophysis (iii) Neurohypophysis has greater supply of nerve endings. Pituicytes produce and secrete hormones directly from adenohypophysis whereas neurohypophysis obtains it hormones from neurosecretory cells in hypothalamus, storing and releasing then when they are needed. These modified hypothalamic nerve cells project their axons down a stalk of nerve cells and blood vessels called infundibulum into pituitary gland directly linking the nervous and endocrine system.

Pancreatic hormones:
Pancreas is an elongated fleshy organ posterior to stomach, endocrine portion of which makes up only about 1% of the gland. This portion synthesizes, stores and secretes hormones from clusters of cells called pancreatic islets of langerhans which are many in number scattered throughout the gland. Each islet has four groups of cells called alpha (α), beta (β), delta (δ), and F cells. Alpha cells produce hormone glucagons and beta cells produce insulin. Delta cells secrete somatostatin. The hypothalamic growth hormone inhibiting factor that also inhibits glucagons and insulin secretion. F cells secrete pancreatic polypeptide into blood stream after a meal and inhibits somatostain secretion, gall bladder contraction and secretion of pancreatic digestive enzymes, when glucose concentration in blood is high such as after a meal, beta cells secrete insulin which promotes uptake of glucose by body cells including liver cells, where excess glucose can be converted to glycogen.

Adrenal glands:
In mammals two adrenal glands rest on top of the kidney. Each gland consists of inner portion medulla and outer cortex.
Adrenal cortex: It secretes three steroid hormones: cortisol, aldosterone and sex hormones (anderogens, estrogens). The cotrisal helps to regulate over all metabolism and the responses to infection or tissue injury. Aldosterone helps to maintain concentration of solutes (such as sodium) in the extra cellular fluid when either food intake or metabolic activity.
Adrenal Medulla: It is under neural control. It contains neurosecretory cells that secrete epinephrine (adrenaline) control heart rate and carbohydrate metabolism. Brain centres and hypothalamus govern the secretions via sympathetic nerves.

Comments

Post a Comment

Popular posts from this blog

What is the Dynamic Theory of Profit

Image
Clark's Dynamic Theory of Profit And Its Criticism The Dynamic Theory of Profit is associated with the name of an American Economist, J. B. Clark. In the world of reality, according to J. B. Clark, profit arises only in a dynamic economy. An economy is said to be dynamic when there is a change in population growth or change in the method of production or a change in the consumer’s wants, etc. A society which is without these changes is called a static society. In a static society, only monopoly profits continue to exist. All other economic profits are gradually eliminated by competition. In a dynamic society, an entrepreneur is always confronted with continuous unpredictable changes in demand for his product. The variation in demand may take place due to changes in fashions, tastes, the standard of living, distribution of income, population, new inventions, international repercussions, technological advances, etc. A prudent entrepreneur will always keep an eye on future demand
Read more

Compare the anatomy of Bifacial and Isobilateral leaves

BIFACIAL LEAF: It is also called dorsiventral leaf. This leaf is more strongly illuminated on upper surface than on lower surface. This unequal illumination induces a difference in the internal structure between upper and lower sides. Its internal structure shows: (1)        Upper Epidermis This is single layer of cells with thick cuticle which checks excessive evaporation of water from the surface. It does not contains chloroplasts, stomata are also absent. (2)        Lower Epidermis This is also single layer but with a thin cuticle. It bears many stomata, two guard cells of which contain some chloroplast, none are present in the epidermal cells. Internal to each stomata is large cavity called respiratory cavity. Lower epidermis of leaf is meant for exchange of gases (oxygen and carbon dioxide) between the atmosphere and the plant body. Excess water also evaporates from lower epidermis. (3)        Mesophyll The ground tissue lying between upper epidermis and th
Read more

osmoregulation in terrestrial and aquatic animals

Mechanism of osmoregulation is very important for all groups of animals whether inhibting land or water. Unlike plant cells, animal cells when placed in hypotonic solution burst due to the continuous absorption of water. On the contrary they would shrink and die if constantly placed in hypertonic solution. Normally uptake and loss of water are in balance for proper survival of cell. (1)        Osmoregulation in terrestrial animals: Terrestrial animals are more likely to loose water by evaporation through their permeable surfaces exposed to amsophere. Among various animal groups only Arthropods and vertebrates became the most successful land dwellers. They have developed number of strategies to maintain osmoregulation of their body fluid. (a) Water proof external coverings: To prevent water loss through external surfaces, vertebrates like reptiles, birds and mammals have water proof keratinized epidermis. Similarly the insects have developed external water proof layer called
Read more