B Raghunath Arts Commerce and Science College Parbhani

B. Raghunath Arts, Commerce and Science College, Parbhani Dr. Anil M. Khole (MSc, Bed, M. Phil, Ph. D) Head, Department of Zoology B. Raghunath Colllege, Parbhani

ENDOCRINOLOGY, ANATOMY & BIOCHEMISTRY PAPER No. IX Endocrine Glands § Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands.

ENDOCINOLOGY § The hypothalamus and pituitary gland are neuroendocrine organs. Local chemical messengers, not generally considered part of the endocrine system, include autocrines, which act on the cells that secrete them, and paracrines, which act on a different cell type nearby. § The ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormone can bind. § Hormone receptors are dynamic structures. Changes in number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones. § Blood levels of hormones reflect a balance between secretion and degradation/excretion. The liver and kidneys are the major organs that degrade hormones; breakdown products are excreted in urine and feces.

ENDOCRINOLOGY Control of hormone release § The endocrine glands belong to the body's control system. The hormones which they produce help to regulate the functions of cells and tissues throughout the body. Endocrine organs are activated to release their hormones by humoral, neural or hormonal stimuli. § Negative feedback is important in regulating hormone levels in the blood. § The nervous system, acting through hypothalamic controls, can in certain cases override or modulate hormonal effects.

ENDOCRINOLOGY HORMONES § The first hormone was discovered by the English physiologist William M. Baylies and Ernest H. Starling in 1903. The term hormone was introduced by Starling in 1905. § A hormone may be defined as a specific product (organic substance) of an endocrine gland secreted into the blood which carries it to specific part of the body where it produces a definite physiological effect. This effect may be either excitatory or inhibitory in its action. § Endocrine glands have no ducts and liberate hormones directly into the bloodstream. For this reason, the endocrine glands are referred to as the ductless glands.

ENDOCRINOLOGY Properties of Hormones § Hormones are produced by specialized glands and are secreted directly into the blood stream. § Hormones are transported by the blood stream from the endocrine cells to serve as chemical messengers who act on target cells or organs by regulating the rates of specific metabolic reactions. § Hormones exert their effects not where they are locally produced, but on other tissues of the body § Hormones are required in very small amounts and their effect may be excitatory or inhibitory depending upon their concentration and the physiological state of the responding tissue. § A hormone belongs to different types of chemical structure. They may be steroids, proteins, peptides of amino acid derivatives.

ENDOCRINOLOGY Chemical Nature of Hormones All the hormones are organic substances of varying structural complexity. Chemically, they may belong to any of the following categories. a) Steroid Hormones b) Proteineous Hormones c) Catecholamine d) Amino acid derivatives e) Peptide Hormones

PITUITARY GLAND Pituitary gland (Hypophysis) – § The pituitary gland or hypophysis cerebri is one of the well protected glands of the body. It is unpaired organ located in the sella turcica, a concavity in the sphenoid bone. § The gland is closely applied to the floor of the fare brain (hypothalamus) and remains attached to it by means of a stalk containing nerve fibers and blood vessels. § In adult the pituitary gland consists of two distinct adjacent lobes called the adenohypophysis anterior pituitary and the neurohypophysis posterior pituitary. § The pituitary gland is a source of at least of anterior and posterior pituitary hormones. It is the smallest endocrine gland.

PITUITARY GLAND § Your pituitary gland is about the size of a pea and is situated in a bony hollow, just behind the bridge of your nose. It is attached to the base of your brain by a thin stalk. § The hypothalamus, which controls the pituitary by sending messages, is situated immediately above the pituitary gland. § The pituitary gland is often called the master gland because it controls several other hormone glands in your body, including the thyroid and adrenals, the ovaries and testicles. § It secretes hormones from both the front part (anterior) and the back part (posterior) of the gland. Hormones are chemicals that carry messages from one cell to another through your bloodstream. § If your pituitary gland is not producing sufficient amounts of one or more hormones this is called hypopituitarism.

PITUITARY GLAND Structure § The pituitary gland is pea-sized gland sits in a protective bony enclosure called the sella turcica. It is composed of three lobes. In animals these three lobes are distinct. In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary which is an extension of the ventral diencephalon or Hypothalamus. § The anterior lobe of the pituitary can be divided into the pars tuberalis and pars distalis that constitutes 80% of the gland. The posterior lobe develops as an extension of the hypothalamus.

PITUITARY GLAND § The simple arrangement differs sharply from that of the adjacent anterior pituitary, which does not develop from the hypothalamus. The release of pituitary hormones by both the anterior and posterior lobes is under the control of the hypothalamus. The pituitary gland has three distinct parts – i) The anterior lobe or pars anterior or adenohypophysis ii) The middle lobe or intermediate lobe or pars intermedia iii) The posterior lobe or pars nervosa or neurohypohysis

PITUITARY GLAND Hormones of the anterior lobe or pars anterior or adenohypophysis 1) Somatotrophic Hormone or Growth Hormone (STH) – The growth hormone stimulates growth of all the body cells including the skeletal and muscular tissue. It promotes protein metabolism, the absorption of calcium from the bowel and the conversion of glycogen to glucose. 2) Thyrotrophic Hormone or Thyroid Stimulating Hormone (TSH) – This hormone controls the growth and activity of the thyroid gland. It influences the uptake of iodine, the synthesis of the hormones, thyroxine and tri-iodothyronineby the thyroid gland the release of stored hormones into the blood stream.

PITUITARY GLAND 3) Adrenocorticotrophic Hormone (ACTH) – This hormone stimulates the cortex of the adrenal glands to produce its hormones. 4) Prolactin Hormone (PRL) – The prolactin hormone has a direct effect upon the breasts or mammary glands immediately after delivery of a baby and the expulsion of the placenta. In conjunction with other hormone it stimulates the breasts to secrete milk. It also stimulates the corpus luteum of the ovary to secrete progesterone hormone. 5) Gonadotrophic Hormones These are as follows – (i) Follicle-stimulating hormone (FSH) – It stimulates growth of ovarian follicles and their secretion of oestrogens in the female, and spermatogenesis (formation of sperms) in the male. (ii) Interstitial-cell stimulating hormones (ICSH) – It activates the Leydig’s cells of the testis to secrete androgens. In female, it stimulates the corpus luteum of the ovary to secrete progesterone.

PITUITARY GLAND Hormones of the Intermediate lobe or Pars intermedium The secretion of the posterior lobe is known as pituitrin and it contains two hormones. Oxytocin (OT) – Oxytocin promotes contraction of the uterine muscle and contraction of the myoepithelial cells of the lactating breast, squeezing milk into the large ducts behind the nipple. In late pregnancy the uterus becomes very sensitive to oxytocin. Antidiuretic hormone (ADH) or Vasopressin – This hormone has two functions. (a) Antidiuretic effect. It increases the reabsorption of water in the distal convoluted tubule, collecting tubules and collecting ducts of the nephrons of the kidney. (b) Pressor effect. Involuntary muscles in the walls of the intestine, gall bladder, urinary bladder and blood vessels are stimulated to contract by ADH. Contrraction of the walls of the blood vessels raises the blood pressure and this may be its most important pressor effect.

PITUTARY GLAND Pituitary Disorders Pituitary Dwarfism – It is caused by the deficiency of growth hormones (GH) from childhood. It is characterized by small but well proportioned body and sexual immaturity. The dwarfs produced by the deficiency of growth hormone are different from those which are formed from the deficiency of thyroid hormone in having normal intelligence. Gigantism – It is caused by excess of growth hormone from early age. It is characterized by large and well proportioned body. If size of pituitary gland increases, it affects optic chiasma and ultimately affects vision. Acromegaly – It is caused by excess of growth hormone after adult size is reached. It is characterized by disproportionate increase in size of bones of face, hands and feet. Diabetes insipidus – It is caused by the deficiency of ADH. It is characterized by excessive excretion of dilute urine. High blood level of ADH – It is caused by excessive secretion of ADH. It is characterized by excessively dilute blood and low plasma sodium.

ENDOCRINOLOGY PITUITARY DWARFISM

ENDOCRINOLOGY GIGANTISM

ENDOCRINOLOGY ACROMAGLY

THYROID GLAND § The thyroid gland is located in the lower part of the neck at about the level of the larynx and upper part of the trachea in the neck region. It is the largest endocrine gland in the body of mammals. § The thyroid gland consists of two lobes connected by a narrow bridge (isthmus) across the ventral surface of the trachea. § The functional units of the gland are called follicles. These are separated by inter follicular connectives tissue containing numerous capillaries. Each follicle consists of a single peripheral layer of cuboidal cells surrounding a cavity filled with a colloid protein secretion called thyroglobulin.

THYROID GLAND

THYROID GLAND Structure § The thyroid gland is a butterfly-shaped organ and is composed of two cone-like lobes or wings, lobus dexter (right lobe), and lobus sinister (left lobe), connected via the isthmus. Each lobe is about 5 cm long, 3 cm wide and 2 cm thick in man. § The organ is situated on the anterior side of the neck, lying against and around the larynx and trachea, reaching posteriorly the oesophagus and carotid sheath. It is conical shape and extends from the upper part of the isthmus, up across the thyroid cartilage to the hyoid bone. § The thyroid gland is covered by a thin fibrous sheath, the capsula glandulae thyroideae. § The gland is covered anteriorly with infrahyoid muscles and laterally with the sternocleidomastoid muscle also known as sternomastoid muscle. Histologically, thyroid gland shows three primary features discovered by (Geoffary Websterson, 1664):

THORID GLAND Structure I) Follicles, the thyroid is composed of spherical follicles that selectively absorb iodine from the blood for production of thyroid hormones. 25% of the body’s iodide ions are in the thyroid gland. II) Follicular cells, the follicles are surrounded by a single layer of follicular cells, which secrete T 3 and T 4 hormones. III) Parafollicular cells, Scattered among follicular cells and in spaces between the spherical follicles are another type of thyroid cell, secretes calcitonin hormone. Thyroid Hormones – § The thyroid hormone consist of at least four physiologically active iodinated organic compounds collectively called iodothyronines or thyroid hormones. § The most important and abundant (about 93%) of the four is thyroxin or tetraiodothyronine (T 4). Other thyroid hormones are triiodothyronine (T 3) and calcitonin.

THYROID GLAND § This gland is stimulated to secrete its hormones by TSH secreted by the anterior lobe of pituitary gland. Iodine is essential component of both T 4 and T 3. § The gastrointestinal tract converts most of the ingested iodine in food to iodide (iodized form) which is transported via blood to the thyroid follicular cells. § Inside the follicular cells, the iodide is oxidized and converted back to iodine, which is then used, along with tyrosine, for the synthesis of T 4 and T 3. A variety of factors influence the secretion of the thyroid gland. § These include the anterior pituitary, dietary components such as iodine, temperature, the adrenal glands, and stress. Physiological effects of thyroid hormones are widespread. § They can be categorized in two general groups. (1) Metabolic effects and, (2) Growth promoting developmental actions.

THYROID GLAND Functions of thyroid hormones Both thyroxine (T 4) and tri-iodothyronine (T 3) perform the following functions. § These hormones increase the metabolic rate of the body and thus increase heat production and maintain basal metabolic rate (BMR). § They also increase active transport of ions through the cell membrane. One of the enzymes that are increased in response to thyroid hormone is Na, K-ATP ase which in turn increase the rate of transport of both Na and K through the cell membranes. § They promote growth of body tissue and development of mental faculties. § These hormones stimulate tissue differentiation. Because of this function, they help in metamorphosis of tadpoles into adult frogs. § Thyroxine also affects the physiology of excretion. Its deficiency causes decreased urine output.

THYROID GLAND § Calcitonin, secreted by thyroid gland in human beings, tends to reduce the blood calcium ion concentration. It works with parathyroid hormone in regulation of blood calcium. THYROID DISORDERS A) Hyperthyroidism – § The phenomenon of over secretion by the thyroid gland is called hyperthyroidism or thyroxicosis. Graves disease or exophthalmic goiter. It is a thyroid enlargement (goitre) in which the thyroid secretes excessive amount of thyroid hormones. § It is characterized by exophthalmia (protrusion of eye balls because of fluid accumulation behind them), loss of weight, slightly rise in the body temperature, excitability, rapid heartbeat, nervousness and restlessness.

THYROID GLAND [B] Hypothyroidism (Hyposecretion of thyroid hormones) (a) Cretinism § This disorder is caused by deficiency of thyroid hormones in infants. A cretin has slow body growth and mental development of reduced metabolic rate. § Other symptoms of this disorder are slow heartbeat, lower blood pressure, and decrease in temperature, stunted growth, pot-belly, pigeon chest and retarded sexual development. This disease can be treated by an early administration of thyroid hormones. (b) Myxeodema § It is caused by deficiency of thyroid hormones in adults. This disease is characterized by puffy appearance due to accumulation of fat in the subcutaneous tissue because of low metabolic rate.

THYROID GLAND CRETINISM

THYROID GLAND MYXEODEMA

THYROID GLAND § The patient lacks alertness, intelligence and initiative. He suffers from slow heart beat, low body temperature and retarded sexual development. This disease can be treated by administration of thyroid hormones. (c) Simple goiter § It is caused by deficiency of iodine because iodine is needed for the synthesis of thyroid hormones. It causes thyroid enlargement. It may lead to cretinism or myxoedema. This is common in hilly areas. (d) Hashimoto’s disease § In this disease all the aspects of thyroid function are impaired. It is an autoimmune disease in which the thyroid gland is destroyed by autoimmunity.

THYROID GLAND S I M P L E G O I T R E

ADRENAL GLAND § In the mammals, the adrenal glands are oval masses embedded in fatty tissue resting near the anterior poles of the kidney. § The adrenal gland is composed of an outer cortex and inner medulla. The cortex is divided into three layers which secrete five own steroid hormones, namely, dehydroepiandrosterone, androstenedione, corticosterone, cortisol, and aldosterone. § The medulla is responsible for the synthesis of and norepinephrine which are catecholamines. These are paired structures located superior to the kidneys. Structure § The adrenal glands are located on both sides of the body in the retroperitoneum, above and slightly medial to the kidneys. § The adrenal glands are surrounded by a fatty capsule and lie within the renal fascia, which also surrounds the kidneys.

ADRENAL GLAND

ADRENAL GLAND § A weak of connective tissue separates the glands from the kidneys. The adrenal glands are directly below the diaphragm, and are attached to the crura of the diaphragm by the renal fascia. § Each adrenal gland has two distinct parts, each with a unique function, the outer adrenal cortex and the inner medulla, both of which produces hormones. Adrenal Cortex is the outer most layer and composed of large fat rich epithelial cells arranged in three zones (i) Zona glomerulosa, (ii) Zona fasciculate, and (iii) Zona reticularis. Each layer has distinct appearance, and each has a different function.

ADRENAL GLAND § More than 40 different cortical steriods have been extracted from various animal adrenal glands, probably half dozen are normally active. § Only three appear chiefly responsible for the multitudinous effects of these hormones – they mineralocorticoids, glucocorticoids and sex hormones. Adrenal Medulla, the adrenal medulla is at the centre of each adrenal gland, and is surrounded by the adrenal cortex. Approximately 20% noradrenaline and 80% adrenaline are secreted here (both form the catecholamines). § The adrenal medulla consists of masses of polyhedral cells separated by large blood sinuses and richly supplied by a plexus of sympathetic filaments.

ADRENAL GLAND Hormones of the Adrenal cortex and its functions: § The outermost cortical layer, the zona glomerulosa, consists of columnar cells responsible for the secretion of hormones. § The adrenal cortex has several hormones and it ranks next to the adenohypophysis of the pituitary gland in endocrine importance. § Secretion of the cortical hormones is under the control of Adrenocorticotropic Hormone (ACTH) from the pituitary. All the adrenocortical hormones are steroid hormones. (i) Mineralocorticoids – § As the name indicates, they are responsible for the regulation of mineral metabolism. Aldosterone (salt retaining hormone) is one of the important Mineralocorticoids in humans. § Its main function is to regulate the sodium content of the body. It acts on the kidneys to cause more sodium to be returned to the blood (when the level is low) and more potassium to be excreted.

ADRENAL GLAND § As the sodium concentration in the blood increase, water follows it by osmosis, so the volume also increases. § Aldosterone also promotes sodium retention in the salivary glands, sweat glands, and colon, and the excretion of magnesium in the urine. (ii) Glucocorticoids – § As their name suggest, they affect-carbohydrate metabolism; however they also affect proteins and fats metabolism. § Cortisol is one of the important example of glucocorticoids, other being cortisome and corticosterone. § Cortisol stimulates the liver to synthesize carbohydrates from noncarbohydrates such as amino-acids and glycerol; stimulates the degradation of proteins within cells thus causing concentration of amino-acids in the blood to increase; and it stimulates the breakdown of fats in adipose tissue.

ADRENAL GLAND (iii) Sexcorticoids – § Large quantities of male sex hormones called androgens than female sexcorticods are produced. § Androgens stimulate the development of male secondary sexual characters. Androgens include androstenedione and dehydroplandrosteron. § Although the female sex hormones have also been detected in cortical extracts, it is believed that they are simply intermediates in the formation of other adreno-corticosteroids.

ADRENAL GLAND Adrenal disorders: Hypoadrenalism Addison’s disease – § This disease is caused by the deficiency of Mineralocorticoids and glucocorticoids. § In this disease the adrenal cortex degenerates, resulting in a number of symptoms, including a characteristic bronzing of the skin, muscular weakness, low blood pressure and digestive disturbance. Cushing’s syndrome – § It is caused by excess of cortisol which may be due to tumor of the adrenal cortex or due to excessive section of ACTH. § It is characterized by high blood pressure, salt retention, swelling of the tissues with water, demineralization of the bones, loss of sexual function, obesity and wasting of muscles of thighs and pectoral and pelvic girdles.

ADRENAL GLAND DISORDERS Hypoadrenalism Addison’s disease –

ADRENAL GLAND DISORDER Hypoadrenalism Cushing’s syndrome –

ADRENAL GLAND Aldosteronism – § Excessive production of aldosterone from an adrenal cortical tumor cause this disease. Its symptoms include a high plasma Na+, low plasma K+, rise in blood volume and high blood pressure. Adrenal Virilism – § Appearance of male characters in female is called virilism. Excessive production of male Sexcorticoids (androgens) produces male secondary sexual characters like beard, moustache, and hoarse voice in woman.

ADRENAL GLAND Hormones of the Adrenal medulla: The medulla of the adrenal glands secretes two hormones: norepinephrine (noradrenaline) and epinephrine (adrenaline) (i) Norepinephrine (Noradrenaline) – § It regulates the blood pressure under normal condition. It causes constriction of essentially all the blood vessel or body. It causes increased activity of the heart, inhibition of gastrointestinal tract, dilation of the pupils of the eyes and so forth. (ii) Epinephrine (Adrenaline) – § It functions as the so-called ‘emergency’ hormone for the body because the general secretion of this hormone centers on emergency functions of the body, such as those of fear, fight and rage, etc. § Adrenaline also tends to increase the flow of blood in skeletal muscles, heart and viscera by dilating the blood vessels.

ADRENAL GLAND § In this way it serves to direct the circulation of blood where necessary during exertion of increased activity. Because of the role of their hormones, the adrenal glands are also called ‘glands of emergency. ’ § The hormones of the adrenal medulla are secreted in response to sympathetic stimulation. In turn, these hormones cause almost the same effects as direct stimulation of the sympathetic nerves in all parts of the body. § Since sympathetic adrenal system and the adrenal medulla functions as an integrated system, it is called sympathetic adrenal system.

PANCREAS GLAND ISLET’S OF LANGERHNS (PANCREAS) § The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. § The former quality results in the formation of many digestive enzymes and the latter in the regulation of carbohydrate metabolism. It lies transversely below the stomach between the curve duodenum and spleen. Structure § The pancreas is an endocrine organ that lies in the abdomen, specifically the upper left abdomen. It is found behind the stomach, with the head of the pancreas surrounded by the duodenum. § It is about 15 cm (6 inch) long. Anatomatically, the pancreas is divided into a head, which rests within the concavity of the duodenum, a body lying behind the base of the stomach, and a tail, which ends abutting the spleen.

PANCREAS GLAND ISLET’S OF LANGERHNS (PANCREAS)

PANCREAS GLAND § The neck of the pancreas lies between the body and head, and lies anterior to the superior mesenteric artery and vein. § The pancreas is secretary structure with an internal hormonal role (endocrine) and an external digestive role (exocrine). It has two main ducts, the main pancreatic duct, and the accessory pancreatic duct. Histology § Histologically, pancreas is a compact and lobulated organ. The exocrine function of the pancreas is accomplished by epithelial cells grouped into hollow spheres. § These are drained by ducts and open into the upper duodenum via the pancreatic duodenal ducts. § Scattered throughout the pancreas are small islets (group of specialized) which secrete the hormones insulin, glucagon, somatostatin, and pancreatic polypeptide which circulate in the blood.

PANCREAS GLAND § The specialized cells are called islets of Langerhans. The islets contain at least four distinct cell types: Alpha cells or A-cells (about 25%), Beta cells or B-cells (about 60%), Delta cells or D-cells (about 10%) and Pancreatic polypeptide or PP cells, each of which secretes a different hormone. § Insulin is formed in the beta cells and glucagon is formed in the alpha cells. There are two other pancreatic hormone somatostatin and pancreatic polypeptide by gama cells. § F cells hormones functions are not known. B- cells are more abundant; A cells are less abundant and tend to be arranged about the periphery of the islets. Hormones of Pancreas and their role (i) Insulin – the term insulin was given in 1916 and it was first extracted by Banting in 1922. Insulin is a proteinaceous hormone, consisting of 51 amino acid residues in the form of two linked peptide chains of 21 and 30 amino acids respectively.

PANCREAS GLAND § It is antagonistic to glucagon and decreases the level of glucose in the blood. It acts by increasing the rate at which glucose is transported out of the blood and into cells and by stimulating muscle cells to take up sugar from the blood and convert it into glycogen. § Insulin is primarily regulated by feedback from the glucose concentration. When the blood sugar level drops, the secretion of insulin is suppressed and when the blood sugar increases, the secretion of insulin is stimulated. § It promotes protein synthesis in tissues from amino acids. § Insulin reduces catabolism of proteins, thus functions as an anabolic hormone. § It increases the synthesis of fats in the adipose tissue from fatty acids. § Insulin reduces the breakdown and oxidation of fats.

PANCREAS GLAND (ii) Glucagon – it stimulates the liver to convert stored glycogen into glucose. Glucagon is controlled by feedback in accordance with the level of blood like insulin. When the blood sugar rises, the secretion of glucagon is suppressed and when it drops, the secretion of glucagon is stimulated. (iii) Somatostatin – the same substance as growth glycogen hormone from the hypothalamus, is produced not only by the pancreas and hypothalamus but also by some cells of the digestive tracts. The action of somatostatin seems to be to suppress the release of other hormones from the pancreas and the digestive tract. (iv) Pancreatic Polypeptide (PP) – It appears that pancreatic polypeptide inhibits the release of digestive secretion of the pancreas.

PANCREAS GLAND Disorder of the Pancreas (1) Diabetes mellitus (Hyperglycemia) – It is exist in two forms – The insulin-dependent diabetes mellitus (IDDM) is caused by the failure of the Beta-cells to produce adequate amounts of insulin while the non-insulin dependent diabetes mellitus (NIDDM) appears to involve failure of insulin to facilitate the movement of glucose into cells.

PANCREAS GLAND (2) Hypoglycemia – It occurs when the blood glucose level falls below normal. It is caused by an excess of insulin (hyperinsulinism), a deficiency of glucagon, or a failure of the secretion of the two hormones to regulate the blood sugar. Symptoms of hypoglycemia include weakness, profuse sweating, confusion and unconsciousness.

MENSTRUAL CYCLE § In most mammals, the endometrium (epithelium of the uterus) undergoes rhythmic cycle along with ovulatory and estrus cycles. § Female attains puberty at about the age of thirteen years. At this time, the pituitary gland begins producing follicle-stimulating hormone (FSH) which induces the development of ovaries, which in turn produce the hormone oestrogen. § This hormone is responsible for the development of the secondary female sexual characters. The onset of the menstrual cycle is signaled by a rapid regression and sloughing off the superficial layer of endometrium. § This results in the rupture of blood vessels which causes bleeding through the vagina. As the endometrium is highly vascular, the bleeding is rather substantial and lasts for 4 to 7 days. § The entire phenomenon is known as menstruation.

MENSTRUAL CYCLE

MENSTRUAL CYCLE § Menstrual phase is regarded as the beginning of the primate reproductive cycle. This is because it corresponds with the formation of new follicles in the ovaries, and is the easiest period of the cycle recognize. § Menstrual cycle regulates at intervals of one lunar month (28 days) on an average in female. § It is regulated by certain hormone, some of which are secreted by the pituitary glands. § Menopause is a phase in woman’s life when ovulation and menstruation stops. It occurs between 45 to 55 years.

THANK YOU