These notes for CBSE Class 11 Biology, Chapter 22, focus on Chemical Coordination and Integration. They detail the endocrine system, explaining the roles of various glands like the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, testes, and ovaries. Key hormones such as GH, TSH, ACTH, oxytocin, vasopressin, melatonin, thyroxine, TCT, PTH, thymosins, adrenaline, cortisol, aldosterone, glucagon, insulin, testosterone, estrogen, and progesterone are discussed. The notes also cover hormones secreted by non-endocrine tissues like the heart, kidney, and gastrointestinal tract, and explain the mechanism of hormone action through membrane-bound and intracellular receptors. These comprehensive notes are ideal for students preparing for their board exams, offering a clear and concise overview of the chapter's essential concepts.
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Endocrine glands : These are ductless glands which secrete hormones directly into the blood stream.
Hormones : Non-nutrient chemicals, synthesised in trace amounts, acts as intracellular messengers and are specific in their action.
•It is basal part of diencephalon. •Has neurosecretory cells called nuclei which produce hormones to regu late the synthesis and secretion of pituitary gland hormones.
Releasing hormones : Stimulate secretion of pituitary hormones, e.g., Gona- dotropin releasing hormone stimulates pituitary gland to synthesise gonadotrophins.
Inhibiting hormones : Inhibit secretions of pituitary hormones, e.g., Soma- tostatin 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 and Neurohypophysis. •Hormones released from hypothalamic neurons reach anterior pituitary through portal system. •Direct neural regulation by hypothalamus occurs in posterior pituitary.
Adenohypophysis : Pars intermedia : Produces only one hormone melanocyte stimulating hormone.
•Growth hormone (GH) : Oversecretion leads to gigantism and low secretion causes dwarfism. •Prolaction (PRL) : Growth of mammary glands 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 steroid 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 hormone (FSH) : Regulate spermatogenesis in males, and growth and development of ovarian follicles in females.
Pars Nervosa : •Oxytocin helps in contraction of uterus during child birth and milk ejection from mammary gland in females. •Vasopressin : Acts on kidney and stimulates reabsorption of water and elec- trolytes by distal tubules to reduce water loss through urine. It is also called as Anti Diuretic Hormone (ADH).
•Located on dorsal side of forebrain. •Secretes melatonin to regulate 24-hour rhythm, sleep-wake cycle, menstrual cycle, pigmentation etc.
•Has two lobes on either side of trachea interconnected by isthmus (connective tissue). •Composed of follicles and stromal tissues. •Follicular cells synthesise thyroxine (T 4 ) and triiodothyronine (T) •Iodine is necessary for normal functioning in of thyroid. •Goitre (Hypothyrodism) : Enlargement of thyroid gland. Hypothyrodism may lead to mental retardation and stunted growth (cretinism) in the baby if it occurs during pregnancy. •Hyperthyroidism : Occurs due to cancer or due to development of nodules in thyroid glands. Effects body physiology as abnormal high levels of thyroid hormones is synthesised. 3 ). •Also secretes a protein hormone called Thyrocalcitonin (TCT) which regulates blood calcium level.
•Present on back side of thyroid gland. Each lobe of thyroid gland has its one pair. •Secrete peptide hormone called parathyroid hormone (PTH) which increases 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.
•Located on dorsal side of heart and aorta. •Secrete peptide hormones called thymosins 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 degenerated with age.
•Located at anterior part of each kidney.
•Has centrally located adrenal medulla and at periphery is adrenal cortex.
•Adrenal medulla secretes adrenaline (epinephrine) and nor adrenaline (nore-
pinephrine), commonly called as catecholamines or emergency hormones or
hormones of flight and fight.
•These hormones increase heart beat, rate of respiration, breakdown of glycogen
thus increase blood glucose level, breakdown of lipids and proteins, alertness,
raising of hairs, sweating etc.
•Adrenal Cortex (3 layers) : Zona reticularis (inner layer)
•Adrenal cortex secretes : Androgenic steroids :
Zona fasciculata (middle layer)
Zona glomerulosa (outer layer)
•Secreted in small amounts.
•Play role in growth of axial pubic and facial hair during puberty.
Glucocorticoids:
•Involved in carbohydrate metabolism.
•Stimulates gluconeogenesis, lipolysis and proteolysis.
•e.g., Cortisol which is also involved in cardio-vascu
lar and kidney functions.
•It also suppresses immune response and stimulates
RBC production.
Mineralocorticoids :
•Regulate balance of water and electrolytes in body.
•e.g., Aldosterone which also helps in reabsorption
of Na + and water excretion of K
ions from renal tubules. + and phosphate
PANCREAS
•Has both exocrine and endocrine function.
•Contains about 1-2 million islets of langerhans which has glucagon secreting
?-cells and insulin secreting ?-cells.
•Glucagon : Peptide hormone, stimulates glycogenolysis by acting on liver
cells. Also, stimulates gluconeogenesis. Hence called hyperglycemic hormone.
•Insulin : Peptide hormone, acts on hepatocytes and adipocytes to enhance
cellular glucose uptake, stimulates conversion of glucose to glycogen (glycogenesis),
so decreases blood glucose level called hypoglycemic hormone.
•Deficiency of insulin causes diabetes mellitus in which loss of glucose occurs
through urine.
TESTIS
•A pair of testis composed of seminiferous tubules and interstilial cells is present
in the scrotal sac of males.
•Leydig 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.
(i) Ovary :
•Aair of ovaries which produce one ovum in each menstrual
cycle are present in abdomen in females.
•Ovary composed of ovarians follicles and stromal tissue.
•Estrogen synthesised by growing ovarian follicles helps in stimulation of growth
of female secondary sex organs, female behaviour, mammary gland development
and female secondary sex characters.
•Ruptured follicle forms corpus luteum which secretes progesterone. Progesterone
supports pregnancy and stimulates alveoli formation and milk secretion in 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) Kidney : Juxtaglomerular cells secretes erythropoietin which stimulates erythropoiesis
(RBC formation).
(c) Gastrointestinal tract : It secrets 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 bicarbon-
ate ions.
•Cholecystokinin (CCK) : Acts on pancreas and gall bladder to stimulate
secretion of pancreatic juice and bile juice respectively.
Gastric inhibitory peptide (GIP) : Inhibits gastric secretion and motility.
Mechanism of hormone action : By hormone 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 messengers like
(cyclic AmP, IP
[148] 3 , Ca
etc.) which regulate
cellular metabolism.
(b) Located inside the target cell
These are intracellular receptors.
•Hormones (steroid hormones, iodothyronines etc.) interact with them and
cause physiological and developmental effects of regulating gene expression.
Endocrine glands are ductless glands that secrete hormones directly into the bloodstream.
The hypothalamus produces hormones that regulate the synthesis and secretion of pituitary gland hormones, acting as releasing or inhibiting hormones.
The pituitary gland is anatomically divided into Adenohypophysis (pars distalis and pars intermedia) and Neurohypophysis (pars nervosa).
Melatonin, secreted by the pineal gland, helps regulate the 24-hour rhythm and the sleep-wake cycle.
Goitre is an enlargement of the thyroid gland, often due to hypothyroidism, where iodine is necessary for normal thyroid function.
Adrenaline and noradrenaline, secreted by the adrenal medulla, are commonly called catecholamines or emergency hormones, preparing the body for 'flight and fight'.
Insulin, secreted by the pancreas, lowers blood glucose levels by enhancing cellular glucose uptake and promoting the conversion of glucose to glycogen.
Hormones act via receptors located either on the cell membrane or inside the target cell, leading to biochemical changes or regulation of gene expression.
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