Chapter-22
Chemical Coordination and Integration
- Points to Remember
- Enocrine glands : These are ductless glands which secrete hormones directly into the blood stream.
- Hormones : Mon-nutrient chemicals synthesised in trace amount by Endocrine glands that act as intracellular messangers and are specific in their action which are transpoted by blood form site of production to site of action.
Hypothalamus :
- It is basal part of diencephalon.
- Has neurosecretory cells nuclei which produce hormones to regulate the synthesis and secretion of pituitary gland bormones.
- Two types of hormones released are :
- Releasing Hormones : Stimulate secretion of pituitary hormones, e.g., Gonadotrophin releasing hormones stimulates pituitary gland to synthesis gonadotrophins.
- Inhibiting Hormones : Inhibit secretions of pituitary hormones, e.g., Somatostatin inhibits secretion of growth hormone.
Pituitary Gland :
- Located in bony cavity called as sella tursica.
- Attached to hypothalamus by a stalk.
- Divided anatomically into : Adenohypophysis (Anterior lobe) and Neurohypophysis (Posterior lobe).
- Hormones released from hypothalamic neurons reach anterior pituitary through portal system and through neurons in Posterior pituitary.
- Posterior pituitary is under neural control of hypothalamus.
1. Pituitary Gland
Adenohypophysis : (Anterior lobe of Pituitary)
- Growth Hormone (GH) : Oversecretion leads to gigantism and low secretion causes dwarfism and Proper secretion leads to proper growth of body.
- Prolactin (PRL) : Growth of mammar gland and formation of milk in them.
- Thyroid stimulating Hormone (TSH) : Stimulates synthesis and secretion of thyroid hormones from thyroid gland.
- Adrenocorticotrophic Hormone (ACTH) : Stimulates synthesis and secretion of steriod hormones called glucocorticoids from adrenal cortex.
- Luteinizing Hormone (LH) : Synthesis and secretion of hormones called androgens in males, and helps in ovulation and maintenance of corpus luteum in females.
- Follicle Stimulating Hormones (FSH) : Regulate spermatogenesis in males, and growth and development of overian follicles in females.
Neurohypo physis (Posterior lobe of Pituitary) :
- Oxytocin : Helps in contraction of uterus during child birth and milk ejection from mammary gland in females.
- Vasopression : Acts on kidney and stimulates reabsorption of water and electroytes by distal tubules to reduce water loss through urine. It is also called as Anti Diuretic Hormone (ADH).
- Impairment of synthesis of ADH : Impairment of synthesis of ADH
- (i) Diminished abililty of kidney to conserve water.
- (ii) Water loss and dehydration.
- (iii) Can be overcome by taking more water.
Excessive Secretion of Growth Hormones :
- Acromegaly : It is a condition when the pituitary gland makes too much growth hormone. It is due to a tumour in pituitary gland. Person. suffering from acromegaly (acro means tip and megaly means enlargement) may gradually develop a long face with protruding lower jaw, enlagred nose and wider spaceing between teeth and enlarged hands and feet.
2. Pineal Gland :
- Located on dorsal side of forebrain.
- Secretes Melation to regualion 24-hours rhythm, sleep-wake cycle, menstrual cycle, pigmentaition etc.
3. Thyroid Gland :
- Has two lobes on either side of trachea interconnected by isthmus (connective tissue).
- Composed of follicles and stromal tissues.
- Follicular cells synthesis thyroxine (T4) and tri-iodothyronine (T3).
- Iodine is necessary for normal functioning of thyroid.
- Goire (Hypothyroidism) : Enlargement of thyroid gland; Hypothyroidism may lead to mental retardation and stunted growth (cretinism) Deaf-mutism in the baby if it occurs during pregnancy.
- Hyperthyroidism : Occurs due to cancer or due to development of nodules in thyroid glands, affects body physiology as abnormal high levels of thyroid hormones is synthesis. Basic metabolic rate increase.
- Exopthalmic goitre : It is a form of hyperthyroidism, characteristics by enlargement of thyroid gland, portrusion of eye balls and increased BMR
- Thyroid hormone controls carbohydrates, proteins & fats metabolism.
- Also secretes a proteins hormone called Thyrocalcitonin (TCT) which regulates blood calcium level.
4. Parathyroid Gland :
- Present on back side of thyroid gland. Each lobe of thyroid gland has its one pair.
- Secrete peptide hormone called parathyroid hormone (PTH) which increase calcium levels in blood so called hypercalcemic hormone.
- PTH stimulates bone resorption, and reabsorption of calcium from blood and reabsorption of calcium by renal tubules, thus increasing blood Ca++ level.
5. Thymus Gland
- Located on dorsal side of heart and aorta.
- Secrete peptide hormones called Tymosins which play role in differentiation of T-lymphocytes (help in cell mediated immunity).
- Thymosins also produce antibodies and provide humoral immunity.
- Immunity of old people usually becomes weak as thymus gets deenerated with age.
6. Adrenal Gland
- Located at anterior part of each kidney.
- Has centrally located adrenal medualla and at periphery in adrenal cortex.
- Adrenal medualla secretes adrenaline (epinephrine) and nor adrenaline (norepinephrine), commonly called as catecholamines or emergency hormones or hormones of fight or flight.
- These hormones increase heart beat, rate of respiration, breakdown of glycogen thus increase blood glucose level, breakdown of lipids and protein, alertness, raising of hairs, sweating etc.
- Adrenal Cortex-(3 layers) :
- -Zona reticularis (inner layer)
- -Zona fasciculata (middle layer)
- -Zona glomerulosa (outer layer)
• Adrenal Cortex Secretes :
- 1. Androgenic steriods : (Secreted by Zona reticularis)
- Secreted in small amounts.
- Play role in growth of axial pubic and facial hair during puberty.
- 2. Glucocorticoids : (Secreted by fasciculata)
- Involved in carbohydrates metabolism.
- Stimulate gluconeogenesis, lipolysis and proteolysis.
- e.g., Cortisol which is also invloved in cardio-vasuclar and kidney fucntions.
- It also suppresses immune respone and stimulates RBC production.
- 3. Mineralocorticoids : (Secreted Zona glomerulosa)
- Regulate balance of water and electroytes in body.
- e.g., Aldosterone which also helps in reabsorption of Na+ and water excretion of K+ and phosphates ions from renal tubules.
- When adrenal cortex is damaged, it does not produce enough cortisols (which regulate body's reaction to stressful situations) and aldosterone.
- It result in Addison's disease. Symptons fo addion's disease are weak muscles, extreme fatigue, increased skin pigmentaition, weight loss, sores in mouth and depression.
The Major Causes :
- 1. Primary adrenal insufficiency where our immune system mistake adrenal for an antigen and tries to damage it.
- 2. Secondary adrenal insufficiency-when pituitary gland can't produce ACTH
7. Pancreas :
It is called composite/dual gland. As it acts as Exocrine and endocine gland i.e., has both exocrine and endocrine function.- Contains about 1-2 million islets of Langerhans which has glucagon secreting a-cell and insulin secreting b-cell.
- Glucagon : Peptide hormone, stimulates glycogenolysis by acting on liver cells. Also, stimulates gluconeogenesis. Hence called hyperglycemic hormone.
- Insulin : Peptide hormone, acts on hepatocytes and hepatocytes and adipocytes to enhance cellular glucose uptake, stimulates coversion of glucose to glycogen (glycogenolysis), so decrease blood glucose level. Hence called hypoglycemic hormone.
- Deficiency of insulin causes diabetes mellitus in which loss of glucose occurs through urine. Excessive hunger and thirst (polydipsia) are other symptoms of Diabetes.
- Insulin and glucagon are antagonistic hormones i.e. play opposite role.
- Glycogenolysis : Breaking of glycogen into glucose.
- Gluconeogenesis : Formation of glucose from substances other than glycogen.
- Glycogenesis : Conversion of glucose into glycogen.
8. Testis :
- A pair of testis composed of seminiferous tubules and interstitial cells is present in the scortal sac of males.
- Leyding cells (interstitial cells) produce androgens (mainly testosterone) which regulate development and maturation of male accessory sex organs, formation of secondary sex characters and play stimulatory role in spermatogenesis.
Male sexual behaviour (libido) is influenced by androgens.
9. Ovary :
A pair of ovaries which produce one ovum in each menstrual cycle are present in abdomen in females.- Ovary composed of overian follicles and stormal tissuce.
- Estrogen synthesised by growing overian follicles helps in stimulation of growth of female secondary sex organs, female behaviour, mammary gland development and female secondary sex characters.
- Ruptured follicle form corpus luteum which secretes progesterone. Progesterone supports pregnancy and stimulates alveoli formation and milk secretion im mammory glands.
Hormones secreted by tissues which are not endocrine glands :
- (a) Heart : Atrial wall secrets Atrial Natriuretic factor (ANF) which decreases blood pressure by dilation of the blood vessels.
- (b) Kidndy : Juxtaglomerular cells secretes erythropoientin which stimulates erythropoientin (RBD formation).
- (c) Gastro-intestinal tract : It secretes four peptide hormones.
- Gastrin : Acts on gastric glands and stimulates secretion of hydrochloric acid and pepsinogen.
- Secretin : Acts on pancreas and stimulates secretion of water and bicarbonateion.
- Cholecystokinin (CCk) : Acts on pancreas and gall bladder to stimulate secretion of pancreatic juice and bile respectively.
- Gastric Inhibitory Peptide (GIP) : Inhibits gastric secretion and motility.
Mechanism of Hormone action : By hormone gastric receptors of two kinds i.e.,
- (a) Located on membrane of target cell
- These are membrane bound receptors.
- Form hormone receptor complex.
- Leads to biochemical changes in tissue.
- Release of second messangers like (cyclic AMP, IP3, Ca2+ etc.) which regulate cellular metabolism.
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- (b) Located inside the target cell
- These are intra cellular receptors.
- Hormones (steroid hormones iodothyronines etc.) interact with them and cause physiological and development effects of regulating gene expression.
