Past Entrance Papers

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(d) The juxtaglomerular cells of kidney produce peptide hormone called erythropoietin which stimulates (erythropoiesis). It stimulates the stem cells of the bone marrow to increase red blood cell production.

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(b) Option (b) is correct match which is as follows
Pituitary hormones are chemically peptides and proteins. Epinephrine is a biogenic amine. Endorphins are neuropeptides. Cortisol is a steroid hormone.

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(c)

– Pituitary gland-Diabetes insipidus
– Thyroid gland-Grave’s disease
– Adrenal gland-Addison’s disease
– Pancreas-Diabetes mellitus

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(d) Statement in option (d) is correct. Rest statements can be corrected as
Glucagon is associated with hyperglycemia. Insulin acts on hepatocytes and adipocytes and is associated with hypoglycemia.

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(b) The fall in blood \(\mathrm{Ca}^{{ }^{+2}}\) levels is the condition which will stimulate parathyroid gland to release parathyroid hormone. This hormone exerts its effects on bones and kidneys. When calcium levels are low, parathyroid hormone is released by the parathyroid glands into the blood and causes the bones to release calcium and increase levels in the bloodstream.

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(c) GLUT IV is an insulin dependent glucose transporter. It helps in the transport of glucose into muscles and adipose cells under anabolic conditions. It permits the facilitated diffusion of circulating glucose down its concentration gradient into muscle and fat cells. On the other hand, GLUT I, II and III are insulin independent glucose transporters.

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(b) Artificial light, extended work time and reduced sleep time disrupt the activity of pineal gland. It is a small pea-shaped gland in the brain. It produces melatonin, which helps maintain circadian rhythm and regulate reproductive hormones.

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(c)

– Insulin deficiency leads to diabetes mellitus
– Hypersecretion or hyposecretion of thyroxine can be associated with enlargement of thyroid gland called goitre
– Deficiency of corticoids (Glucocorticoid + mineralocorticoid) leads to Addison’s disease
– Growth hormone hypersecretion in adults leads to Acromegaly

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(a) Steroid hormones are able to bind to DNA and form a gene-hormone complex. These hormones can easily cross the lipid bilayer of the cell and do not require secondary messengers for the same. Steroid hormones bind to intracellular receptors in the nucleus to form hormone receptor complex which in turn interact with the genome.
cAMP pathway, secondary messengers and change in cell membrane permeability is required in case of proteinaceous hormones which cannot pass through lipid bilayer on their own.

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(b)
In the given mechanism of hormone action, the labels are
A-Protein hormone
B-Receptor
C-Cyclic AMP
Hormones which interact with membrane bound receptors do not enter the target cell. These bind with membrane proteins (receptors) and generate second messengers which in turn regulate cellular metabolism, e.g. \(\mathrm{FSH}\) on ovarian cell membrane.

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(a) Estrogen and parathyroid hormone can play significant role in osteoporosis. It is caused due to the deficiency of estrogen and excessive activity of parathormones. Estrogen helps to promote the activity of osteoblast (helps in the formation of bone cells) and inhibits osteoclast (destruct the bones). On the other hand, parathormone promotes the mobilisation of calcium from bones into blood hence causes demineralisation. The other listed hormones also contribute to osteoporosis but their effects are insignificant or very less. e.g., low level of progesterone and aldosterone causes bone loss whereas raised level of prolactin have been linked with osteoporosis.

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(b) Limbic system consists of four major components namely hippocampus, amygdala, septal nuclei and mammilary bodies. It controls the emotional behaviour, food habits and sex behaviour of an organism. It is not involved in controlling movements. The rest three options are correctly paired with their functions.

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(a) Epinephrine is derived from tyrosine by the removal of carboxyl group. It is a catecholamine.

Epinephrine and norepinephrine are very similar neurotransmitters and hormones. While epinephrine has slightly more of an effect on your heart, norepinephrine has more of an effect on your blood vessels. Both play a role in your body’s natural fight-or-flight response to stress and have important medical uses as well.

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(a) Gonadotropin releasing hormone ( \(\mathrm{GnRH})\) is secreted by the hypothalamus which stimulates the anterior lobe of pituitary gland to secrete luteinising hormone (LH) and Follicle Stimulating Hormone \((\mathrm{FSH})\).

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(a) Epiphyseal plate is a hyaline cartilage plate in the metaphysis at each end of long bone. It is part of long bone where new bone growth takes place. In adults, elevated levels of \(\mathrm{GH}\) results in acromegaly where no increase in height occurs because of ossified epiphyseal plate.

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(b) Corpus luteum is a temporary endocrine gland in human females. It secretes progesterone which stimulates the uterine glands to produce increased amount of watery mucus and is also essential for maintenance of endothelium. In absence of fertilisation, corpus luteum disintegrate leading to menstruation.

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(a) A decrease in blood pressure / volume stimulates the release of renin, aldosterone, and \(\mathrm{ADH}\) while increase in blood pressure / volume stimulates the release of Atrial Natriuretic Factor (ANF) secreted by atria of heart, which causes vasodilation and also inhibits RAAS (Renin Angiotensin Aldosterone System) mechanism that decreases the blood volume/ pressure.

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(b) Exophthalmic goitre or Graves’ disease is a thyroid enlargement (goitre) in which the thyroid secretes excessive amount of thyroid hormone. It is characterised 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.

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(a) Insulin is a peptide hormone, secreted by the \(\beta\) cells of the islets of Langerhans in the pancreas, that promotes the uptake of glucose by body cells, particularly in the liver (hepatocytes) and muscles (adipocytes), and thereby controls its concentration in the blood.

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(b) Posterior lobe of pituitary gland does not secrete any hormone. Its hormones are synthesised by the hypothalamus. It only stores and releases these hormones. Hence, it cannot be considered as true gland.

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(b) Relaxin hormone is secreted by ovary and placenta during pregnancy, which relaxes ligaments in pelvis and softens and widens cervix during childbirth. Inhibin secreted by granulosa cells in the ovaries inhibits secretion of FSH by anterior pituitary. Thus, relaxin and inhibin have different functions and are not antagonistic.

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(c) Tryptophan is an essential amino acid which is precursor for the synthesis of melatonin and serotonin.

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(a) At the pituitary, GnRH stimulates the synthesis and secretion of the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone \((\mathrm{LH})\). These processes are controlled by the size and frequency of GnRH pulses, as well as by feedback from progesterone and estrogens. Low-frequency \(\mathrm{GnRH}\) pulses are required for \(\mathrm{FSH}\) release, whereas high-frequency \(\mathrm{GnRH}\) pulses stimulate \(\mathrm{LH}\) pulses in a one to one manner.

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(a) A decrease in blood pressure / volume stimulates the release of renin, aldosterone, and \(\mathrm{ADH}\) while increase in blood pressure / volume stimulates the release of Atrial Natriuretic Factor (ANF) secreted by atria of heart, which causes vasodilation and also inhibits RAAS (Renin Angiotensin Aldosterone System) mechanism that decreases the blood volume/ pressure.

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(d) Aldosterone (salt-retaining hormone) is the principal mineralocorticoid in humans, secreted by adrenal cortex. Its main function is to regulate sodium content of the body.

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(c) Two hormones viz oxytocin (OT) and antidiuretic hormone \((\mathrm{ADH})\) are synthesised in the hypothalamus, but stored and released by the posterior lobe of pituitary gland.

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(a) Hormones epinephrine and norepinephrine are secreted from adrenal medulla. They are emergency hormones released in condition of stress, emergency, etc. Epinephrine and norepinephrine are also released by adrenergic nerve fibres of sympathetic nervous system where they act as neurotransmitters.

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(b) Oxytocin is produced by hypothalamus and generally secreted by posterior pituitary. It stimulates the secretion of milk from mammary glands; causes contraction of the uterus at the time of childbirth.

Progesterone is secreted by the corpus luteum. It stimulates the uterus for pregnancy, implantation, formation of placenta, and development of mammary glands.

Atrial natriuretic factor is secreted by atrial wall in response to an increased return of the venous blood. This hormone regulates the blood volume through increased excretion of ions and water.

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(c) The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine. These are commonly called as catecholamines. Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones or hormones of Fight or Flight. These hormones increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, etc. Both the hormones increase the rate of heartbeat, the strength of heart contraction, and the rate of respiration. In addition, they also stimulate the breakdown of lipids and proteins.

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(c) In the given figure, \(A\) is adrenal gland which secretes two catecholamines; adrenaline (epinephrine) and noradrenaline (norepinephrine). Adrenaline increases the conversion of glycogen to glucose providing quick energy for “fight or flight” response. \(B\) is renal pelvis which is a sac like cavity of the kidney leading to ureters, is not directly connected to loop of Henle. \(\mathrm{C}\) is medulla, the inner region of kidney containing loop of Henle, collecting ducts and ducts of Bellini. \(\mathrm{D}\) is cortex which has proximal and distal convoluted tubules and contains Malpighian corpuscles.

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c) Iodine is needed for the synthesis of \(T_{3}\) and \(\mathrm{T}_{4}\). Iodine binds to the tyrosine residues in thyroglobulin, which is then hydrolysed into iodotyrosines that combine to form triiodothyronine \(\left(T_{3}\right)\) or thyroxine (tetra-iodothyronine or \(T_{4}\) ). Therefore, deficiency of iodine in the diet of a pregnant female will lead to improper synthesis of thyroid hormones in newly borne infant. The deficiency of thyroid hormones in infants causes ‘cretinism’ whose symptoms are slow heartbeat, lower blood pressure, decrease in temperature, stunted growth, low intelligence quotient, and abnormal skin.

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(a) Releasing and inhibiting factors are released by hypothalamus. The hypothalamus is connected to adenohypophysis by hypophysial portal vein and is connected to the neurohypophysis by axons of neurosecretory cells. Hence, neurohypophysis is directly under the neural control. The cardiocytes of atria of the heart secrete peptide hormone, called atrial natriuretic factor (ANF) in response to an increased return of the deoxygenated (venous) blood. The liver produces angiotensinogen which is changed to angiotensin II by an enzyme renin secreted by the juxtaglomerular apparatus (JGA).

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(a) Iodine is required for the production of thyroxine, thus lack of iodine results in hyposecretion of thyroxine. To compensate, the thyroid gland enlarges and the condition is known as goitre. Corpus luteum secretes progesterone which maintains uterine endothelium and mucus secretion in uterus, Fallopian tubes, and vagina. Oxytocin stimulates uterine contractions but is secreted by posterior pituitary. Anterior pituitary secretes \(\mathrm{GH}\), whose oversecretion causes abnormal growth.

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(c) Interstitial cells (or Leydig ‘s cells) are the cells interspersed between the seminiferous tubules of the testis. They secrete androgens including testosterone in response to stimulation by luteinizing hormone from the anterior pitutary gland. Androgens produce and maintain male characteristics and stimulate germinal epithelium to undergo spermatogenesis.

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(a) Norepinephrine is secreted by some neurons of the sympathetic nervous system and also by adrenal medulla. It accelerates the heart rate.

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(b) Insulin is secreted from the \(\beta\)-cells of islets of Langerhans of pancreas. Insulin acts on hepatocytes and adipocytes and increases the uptake of cellular glucose and its utilisation. This results in rapid movement of glucose from blood to hepatocytes and adipocytes and leads to decreased glucose levels in blood. This condition is known as hypoglycaemia. Insulin also stimulates the conversion of glucose to glycogen in target cells and this process of formation of glycogen is called glycogenesis.

So, the correct answer is ‘Decreases blood glucose levels by forming glycogen’.

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(a) Epinephrine and norepinephrine are released by the adrenal medulla and nervous system respectively. They are the flight/fight hormones that are released when the body is under extreme stress. They are also called as emergency hormone as it initiates quick reaction which makes the individual to think and respond quickly to the stress. The hormone increases metabolic rate. Dilation of blood vessels going to the heart and the brain occurs. So, the correct answer is option \(\mathrm{A}\).

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(d) Steroid hormones such as cortisol, testosterone, estradiol, and progesterone, mostly regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome. So, these easily pass through the cell membrane of the target cell and bind to a receptor inside it.

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(c) Hormone action involves their reception by target cells. Specific proteins called hormone receptors that are located in target tissues only bind with these hormones. Hormone receptor may be of two types: membrane-bound receptor and intracellular receptors. Steroid hormones etc., bind with intracellular receptors while some hormones e.g., pituitary hormones like FSH, etc., bind with membrane-bound receptors.

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(b) Posterior lobe of pituitary stores and releases two hormones, called oxytocin and vasopressin. These hormones are actually produced by the neurosecretary cells in the hypothalamus and stand in the terminals of their axons that pass into the posterior lobe through a stalk. They are released via posterior lobe when required. Vasopressin is also called antidiuretic hormone \((\mathrm{ADH})\). It decreases the loss of water in the urine by increasing reabsorption of water in the distal convoluted tubules, collecting tubules, and collecting ducts in the kidneys.

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(a) The correct option for the three blanks A, B, and C are ovary, glucagon, and growth hormone respectively.

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(d) Melatonin is a hormone secreted by the pineal gland and retinas of vertebrates. Melatonin secretion by the pineal gland is linked to the dark light cycle of the organism’s environment, being greatest at night and lowest by day. The hormone is involved in regulating certain diurnal and seasonal changes in the body, such as the reproductive cycle in seasonally breeding animals. It is used as a drug to treat sleep disorders and symptoms of jet lag.

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(c) Adrenal glands or (suprarenal glands) are two triangular endocrine glands, each of which covers the superior surface of a kidney. Each gland has two parts, the medulla, and cortex. The medulla forms the grey core of the gland; it consists mainly of chromaffin tissue and is stimulated by the sympathetic nervous system to produce adrenaline and noradrenaline. The cortex is a yellowish tissue surrounding the medulla. It is stimulated by pituitary hormones (principally \(\mathrm{ACTH})\) to produce three kinds of corticosteroid hormones, which affect carbohydrate metabolism (e.g., cortisol), electrolyte metabolism (e.g., aldosterone), and the sex glands (oestrogens and androgens). Thus injury to adrenal cortex is not likely to affect the secretion of adrenaline.

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(a) Tetany is a spasm and twitching of the muscles, particularly those of the face, hands, and feet. Tetany is usually caused by a reduction in the blood calcium level, which may be due to underactive parathyroid glands, rickets, or alkalosis.

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(a) Glucagon is a hormone, secreted by the cells of the islets of Langerhans in the pancreas, that increases the concentration of glucose in the blood by stimulating the metabolic breakdown of glycogen. It thus antagonizes the effects of insulin.

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(c) Toxic agents in food which interfere with thyroxin synthesis will lead to simple goitre. Thyrotoxicosis and toxic goitre are under the category of hyperthyroidism.

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(b) Vasopressin reduces water loss through urine by stimulating resorption of water by the distal tubules of the kidney. Glucagon is released from \(\alpha\)-cells. Prolactin is produced from anterior pituitary.

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(b) Myxoedema is caused by deficiency of thyroid hormone or thyroxine in adults. It is characterized bylow metabolic rate, body gain, puffy appearance, low body temperature, etc. This disease can be treated by the administration of thyroid hormones.

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(b) 0xytocin (child birth hormone) secreted by neurohypophysis of pituitary gland stimulates contraction of uterus muscles. It stimulates labour pain for child birth. When secretion of progesterone hormone declines it will result in making the end of pregnancy. As the sensory impulse of increasing labour pain reaches hypothalamus, more and more oxytocin is released from posterior pituitary under a positive feedback regulation, it dilates the cervix (vaginal stretching).

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(c) Parathyroid and adrenal glands are the endocrine glands because they manufacture hormones and secretes them directly into the blood stream to act at distant sites in the body. Thyroid and pituitary are other examples.

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(c) Parathormone is secreted by chief cells of the parathyroid that regulates the metabolism of calcium and phosphate. It increases calcium absorption from the intestine and also increases calcium resorption from the nephrons of the kidneys. So its deficiency leads to low blood calcium levels.

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(a) Adrenaline (epinephrine), also called emergency hormone, is a hormone, produced by the medulla of the adrenal glands, that increases heart activity, improves the power and prolongs the action of muscles, and increases the rate and depth of breathing to prepare the body for ‘fright, flight, or fight’. At the same time, it inhibits digestion and excretion. Similar effects are produced by stimulation of the sympathetic nervous system.

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(d) Parathyroid glands located behind the thyroid gland, produce a hormone called parathormone. This hormone maintains calcium and phosphorus balance in the body. Thus, if a person is having problems with calcium and phosphorus metabolism in the body, this means, his parathyroid glands are not functioning properly.

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(d) Graafian follicle – the ovarian medulla contains many rounded or oval bodies, called ovarian, or graafian follicles, at various stages of development. Each follicle contains a large ovum surrounded by many layers of follicle cells.

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(c) When the production of progesterone and estrogen hormone stops in blood this leads to the shedding of the lining of the uterine endometrium. Therefore, by the supply of oestrogen and progesterone the menstruation can be deferred.

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(c) Testes are degenerated due to which testosterone level in blood is reduced. This hormone promotes the growth of many body tissues such as muscles.

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(d) Adrenaline is the hormone secreted by adrenal medulla. It prepares the animal to face special conditions created by physical stress. All these conditions require more energy which is provided by increasing heartbeat, blood pressure, respiratory rate, the sugar level of blood, the blood supply of heart and skeletal muscles and brain through dilation of their small arteries, and oxidative metabolism. It also stimulates the breakdown of liver and muscle glycogen (glucogenesis) to provide glucose for respiration.

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(b) Neurohormones are actually secreted by the neurosecretory cells of the hypothalamus. They are circulated to the posterior part of the pituitary gland through the blood & stored there and released when required.

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(b) Cortisol or glucocorticoid hormone is a steroid hormone produced by the adrenal cortex. It is released in response to stress and a low level of blood glucose. Its functions are to increase blood sugar through gluconeogenesis and to aid the metabolism of fat, protein, and carbohydrate.

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(d) Secondary messengers are low-weight diffusible molecules that are used to relay signals within a cell. They are synthesized or released by specific enzymatic reactions, usually as a result of an

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(c) The endocrine system links the brain to the organs that control body metabolism, growth and development, and reproduction. The endocrine system is regulated by feedback. For example, the hormones that are regulated by the pituitary gland, a signal is sent from the hypothalamus to the pituitary gland in the form of a “releasing hormone,” which stimulates the pituitary to secrete a “stimulating hormone” into the circulation. The stimulating hormone then signals the target gland to secrete its hormone. As the level of this hormone rises in the circulation, the hypothalamus and the pituitary gland shut down secretion of the releasing hormone and the stimulating hormone, which in turn slows the secretion by the target gland. This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland.

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(c) Epinephrine or adrenaline, norepinephrine or noradrenaline, and acetylchloline are the neurotransmitters. These are released by the nerve fibres to transmit the impulse to the next neuron. Cortisone is not the neurotransmitter.

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(d) Menstruation is caused by the reduction of oestrogen and progesterone. Hormone level, (especially progesterone) at the end of monthly ovarian cycle. The first effect is
decreased stimulation of the endometrial cells by these two hormones followed rapidly by involution of the endometrium itself to about \(65 \%\) of its previous thickness.

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(a) Sertoli cells are the cells that line the seminiferous tubules in the testis. These
cells protect the spermatids and convey nutrients to both the developing and mature spermatozoa. Sertoli cells are regulated by FSH(Follicle Stimulating Hormone)as the FSH receptors are confined to the Sertoli cells.

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(c) Parkinson’s disease (Paralysis agitans)
(i) It develops due to deficiency of neuro transmitter, dopamine. The dopamine is not produced due to gradual destruction of neurons in the substantia nigra.
(ii) It produces muscle tremors so-called shaking palsy.
(iii) There is lack of control and coordination of movements resulting in an expressionless face and stooping posture which gradually produces physical disability.

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(a) Epinephrine is synthesized from tyrosine which is a non-essential amino acid possessing cyclic structure with a straight side chain bearing carboxylic and amino group. The conversion of tyrosine to epinephrine involves 4 steps – (i) ring hydroxylation
(ii) decarboxylation, (iii) side-chain hydroxylation (iv) N-methylation.

Tyrosine \(\rightarrow\) Dopa \(\rightarrow\) Dopamine \(\rightarrow\) Norepinephrine \(\rightarrow\) Epinephrine.

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(a) Ovulation occurs under the influence of luteinizing hormone and \(\mathrm{FSH}\) (follicle stimulating hormone) of the anterior pituitary gland. Thus, deficiency of luteinizing hormone results in failure of ovulation.

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(b) Hormones are chemical messengers produced by the ductless glands (sometimes by neurons) and transported in the circulation to target cells. They regulate metabolic processes. Chemically hormones are of different nature like biogenic amines (like thyroxine, adrenaline, etc), proteinaceous or polypeptide (like hypothalamic hormones, etc.), and steroids (like sex hormones and adrenocorticoids).

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(b) Prolactin is secreted by anterior pituitary gland (not human placenta) which stimulates mammary gland development during pregnancy and lactation after childbirth.

Placenta is a connection between the uterine wall of the mother and the foetus. It helps in the exchange of material between these two. Placenta secretes human chorionic gonadotropin, oestrogen and progesterone.

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(a)
Ovulation occurs under the influence of LH and FSH of anterior pituitary gland.

\(
\begin{array}{ll}
\hline \text { Disease } & \text { Deficiency } \\
\hline \text { Diabetes mellitus } & \text { Insulin } \\
\hline \text { Tetany } & \text { Parathormone } \\
\hline \text { Diabetes insipidus } & \text { ADH } \\
\hline
\end{array}
\)

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(b) Mast cells are granulated leucocyte cells. Their granules contain histamine which is a vasodilator and heparin (an anticoagulant). These take part in body defence and allergic reaction. Vasopressin is released by the posterior lobe of pituitary. Relaxin is released by the placenta. Calcitonin is released by thyroid. Serotonin and melanin are released by intermediate lobe of the pituitary gland.

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(c) Hypoparathyroidism is the state of decreased secretion or activity of parathyroid hormone (PTH). This leads to decreased blood levels of calcium (hypocalcemia) and increased levels of blood phosphorus (hyperphosphatemia). Symptoms range from quite mild tingling in the hands, fingers, and around the mouth to more severe forms of muscle cramps. The most severe symptoms are tetany (severe muscle cramping of the entire body) and convulsions.

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(a) Acromegaly is caused by the excess STH (somatotrophic hormone), released by the anterior lobe of the pituitary after adolescence. The bones of the lower jaw and limbs become abnormally enlarged but the body does not attain a giant stature. Excess of thyroxine causes cretinism and myxoedema. Excess adrenaline causes increased BMR, heartbeat, excitement, etc.

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(a) Adrenaline directly affects the SA node to increase the rate of heartbeat. Adrenaline prepares the body for emergency reactions like fight and flight. Thus there is an increase in heart rate, breathing rate, blood pressure, the glucose level in the blood, peripheral circulation, etc.

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(c) Ovary secretes two hormones. Oestrogen before ovulation and progesterone after ovulation. Oxytocin, prolaction are pituitary hormones and gonadotropin releasing factor is secreted by hypothlalamus of the brain to stimulate pituitary for the secretion of gonadotropic hormones.

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(c) Menstrual cycle is controlled by several endocrinal parameters.

In beginning of the cycle FSH (follicle stimulating hormone) of pituitary initiates development of an ovarian follicle. A growing ovarian follicle gradually secretes increasing amount of estrogen. This in turn leads to sudden surge of \(\mathrm{LH}\) secretion by the pituitary. As the LH (leutinising hormone) level in blood suddenly increases there is ovulation.

Thus only FSH or \(\mathrm{LH}\) cannot control all the events of menstrual cycle. Progesteron is released by a corpus luteum after ovulation which actually prepares the uterus for a possible pregnancy.
If there is no fertilisation progesteron level falls and there is the beginning of a new cycle.

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(a) Radioactive iodine, i.e. lodine-131 is administered to patients suffering from thyroid cancer for its detection.

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(a) Melanin is a protective pigment synthesised from tyrosine. Melanocytes
under the influence of melanocyte secreting hormone secrete melanin
which protects the body from the harmful effects of UV rays.

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(b) Cholesterol forms a major component of animal cell membranes. Liposomes
(artificially created spheres surrounded by a phospholipid bilayer like a
membrane) are used for transformation (transgenics).

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(a) After ovulation many of the follicular cells remain in the collapsed Graafian follicle on the surface of the ovary. The antrum (cavity) of the collapsed follicle fills with a partially clotted fluid. The follicular cells enlarge and fill with a yellow pigment, lutein. Such a follicle is called a corpus luteum.

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(a) Melatonin is secreted by pineal gland present between the cerebral hemispheres. Melatonin concentration in blood follows a diurnal cycle, it rises in the evening and drops at noon. Melatonin lightens skin colour in certain animals and regulates working of gonads.

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(c) The anal glands are small paired sacs located on either side of the anus between the external and internal sphincter muscles. These sebaceous glands within the lining secrete a foul-smelling liquid that is used for the identification of members within a species. These glands are found in all carnivora except bears.

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(b) Middle lobe of the pituitary secretes a hormone named melanocyte-stimulating hormone. It stimulates the synthesis of the black pigment melanin in the skin, and also causes the dispersal of melanin granules in the pigment cells, thereby darkening the colour in certain animals (fishes amphibians). In man, it has no such role. Anterior lobe of pituitary secretes \(\mathrm{FSH}, \mathrm{LH}, \mathrm{TSH}\), \(\mathrm{ACTH}\) and STH. Posterior lobe of pituitary secretes oxytocin and vasopressin.

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(c) Contraceptive pills have estrogen and progesterone. Progesterone suppresses ovulation and production of \(\mathrm{LH}\) while estrogen suppresses the production of FSH.

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(b) Oxytocin causes contraction of the smooth muscles of myometrium forcing the foetus out of the uterus. Oxytocin is also involved in the ejection of milk, but not lactation (actual production of milk). For milk to be produced, prolactin must be present.

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(c) Progesterone is a steroid hormone secreted by corpus luteum and causes routine temporary changes in the endometrial lining of uterus. Follicle stimulating hormone secreted by anterior pituitary lobe stimulates spermatogenesis in testes of males. Luteinizing hormone activates Leydig’s cells of testes to secrete testosterones.

The TYR gene provides instructions for making an enzyme called tyrosinase. This enzyme is located in melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. Tyrosinase is responsible for the first step in melanin production.

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(d) Insulin is released from the pancreas it helps in conversion of glucose to fatty acids. It increases fat synthesis in adipose tissues.

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(c) Thymus gland is present in children with maximum development at puberty and thereafter it begins to shrink and atrophies with the development of sex glands.

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(d) Electroencephalogram is the recording of electric potentials originating from different parts of the brain in the form of waves. Fractionation is the technique of rupturing cells and separating their components especially cell organelles for studying their chemistry and functions. Electrophoresis is the technique of separation of charged solutes on the basis of their differential migration in an applied electric field.

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(c) Cholecystokinin and duocrinin are secreted by intestine. It stimulates pancreas to release enzymes in pancreatic juice and stimulates the gall bladder to release bile. Duocrinin causes the release of viscous mucus from Brunner’s glands into intestinal juice.

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(d) Luteinsing Hormone (LH) in the male, induces the interstitial cells of the testes to produce male sex hormones named androgens such as testosterone. In the female, the luteinising hormone causes ovulation, secretion of female sex hormone, estrogen from the maturing ovarian follicle, and progesterone by the corpus luteum.

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(a) Gonadotrophic hormones are secreted by anterior lobe of pituitary gland. They are as follows:
(i) Follicle-stimulating hormone (FSH): It stimulates growth of ovarian follicles and their secretion of estrogens in the female, and spermatogenesis (formation of sperms) in the male.
(ii) Interstitial cell-stimulating hormone (ICSH): It activates the Leydig’s (interstitial) cells of the testis to secrete androgens. In female, it stimulates the corpus luteum of the ovary to secrete progesterone. In female it is termed luteinizing hormone (LH).

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(d) Diabetes mellitus is caused by the deficiency of hormone insulin which is secreted by pancreas. Insulin lowers the blood-glucose level. Deficiency of antidiuretic hormone ( \(\mathrm{ADH})\) leads to diabetes insipidus.

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(a) The chief cells of the parathyroid secrete parathormone. Its deficiency causes the lowering of blood calcium level. This increases the excitability of nerves and muscles causing cramps and convulsions. This causes parathyroid tetany characterised by sustained contractions of the muscles of larynx, face, hands and feet.

Calcitonin is secreted when calcium level is high in blood. It has an opposite action to that of parathyroid hormone and lowers the calcium level by suppressing release of calcium ions from the bones.

Thyroxine is secreted from the thyroid gland. It regulates the metabolic rate of the body and thus, maintain basal metabolic rate, stimulate protein synthesis and therefore, promotes growth of the body tissues.

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(d) Calcitonin is secreted by the C cells. It regulates the concentration of calcium and phosphorus in the blood. It is under the feedback control of plasma calcium concentration, and is secreted when concentration of calcium rises in the blood. It then lowers the concentration of calcium and phosphorus in the plasma by decreasing their release from the bones.

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(c) Gastrin hormone is secreted by mucosa of stomach and it stimulates secretion of gastric juice. Enterogastrone is secreted by duodenal epithelium. Enterokinase is an enzyme that converts trypsinogen into trypsin. Renin is secreted by kidneys. It acts on angiotensinogen to form angiotensin-II.

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(a) Cholecystokinin is secreted by duodenal epithelium and it stimulates the gall bladder to release bile that causes emulsification of fats to increase lipase action on them. Enterogastrone and secretin are also secreted by duodenal epithelium. Enterogastrone slows gastric contractions to delay its emptying and also stops secretion of gastric juice. Secretin causes release of sodium bicarbonate in pancreatic juice, steps up secretion of bile, and inhibits secretion of gastrin. Gastrin stimulates secretion of gastric juice and is secreted by mucosa of pyloric stomach.

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(d) The basal metabolism is the minimum amount of energy the body uses in order to maintain vital processes of the body. Generally, this expenditure of energy is expressed in terms of heat production per unit of body surface per day on the basal metabolic rate (BMR). Thyroid is the largest endocrine gland secreting three hormones thyroxine, triiodothyronine and calcitonin. Thyroxine and triiodothyronine control BMR of the body by regulating the rate of oxidation and production of energy.

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(d) Use of contraceptive pills is a widespread form of birth control. Contraceptive pills contain estrogen and progesterone. The production of the pituitary hormones \(\mathrm{FSH}\) \& \(\mathrm{LH}\) in the normal sexual cycle of a female is shut down by these hormones. In the absence of FSH, the ovarian follicles do not ripe and ovulation does not occur in the absence of LH.

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(d) The endocrine part of the testis is formed of groups of cells, called interstitial cells or Leydig’s cells, scattered in the connective tissue between the sperm producing seminiferous tubules of the testis.
These cells are stimulated to produce male sex hormones, called androgens by ICSH of the anterior pituitary. Testosterone is the main androgen and it is a steroid hormone.

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(a) Hormones thyroxine, adrenaline, and the pigment melanin are formed from tyrosine. Tyrosine is transformed into dopa through the enzyme tyrosinase. Then through different metabolic pathways, it produces thyroxine, adrenaline, melanin, etc.

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(d) Prolactin hormone stimulates the growth of milk glands during pregnancy and the secretion of milk after delivery. Oxytocin causes release of milk during sucking by the infant. \(\mathrm{LH}\) causes ovulation and secretion of estrogen and progesterone from the ovarian follicle and corpus luteum respectively. Oxytocin, LH, and prolactin are released by the anterior lobe of the pituitary gland. Progesterone is secreted by the corpus luteum.

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(c) According to the immunity theory aging occurs due to the loss of power of defence against the invasion of germs and pathogens. The process starts with the gradual atrophy and disappearance of the thymus gland during middle age.

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(d) Oxytocin also known as pitocin. It is an important hormone which is released in neurohypophysis of pituitary. It stimulate the contraction of smooth muscles. It stimulate labour pain and also increase labour pain. It is a hormone for quick birth. Its more secretion results in parturition.

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(b) Prolactin is a proteinaceous hormone released by the anterior lobe of the pituitary. Prolactin supplements the action of gonadal hormones in stimulating the growth and activity of the female mammary gland during pregnancy and lactation. Oxytocin released by the posterior lobe of the pituitary gland is important for the mechanism of ejection of milk from the mammary glands due to sucking of breasts by infant. Progesterone, released by corpus luteum brings about pregnancy changes such as uterine growth, implantation of the embryo, etc. Relaxin is a proteinaceous hormone secreted by the corpus luteum towards the end of the gestation period for loosening and softening pelvic ligaments, and relaxing of the uterus for easing parturition.

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(b) The thyroid gland secretes three hormones: thyroxine or tetraiodothyronine \(\left(\mathrm{T}_{4}\right)\), triiodothyronine \(\left(\mathrm{T}_{3}\right)\) and calcitonin. Thyroxine and Triiodothyronine are iodinated forms of the amino acid tyrosine. They are stored in the colloid that fills the follicles, and are released into the blood when needed. The storage occurs in an unusual place, the extracellular colloid.

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(b) The molecules of hormones that are amino acid derivatives, peptides, or proteins are large and insoluble in lipids, and cannot enter the target cell. Therefore, they act at the cell surface. They bind to specific receptor molecules located on the surface of the cell membrane. Therefore, if receptor molecules are removed from target organs, then the target organ will not respond to the hormone.

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(b) Mammalian corpus luteum produces progesterone. It is essential for the continuation of pregnancy and it also stimulates acini glands.

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(b) Nicotine and acetylcholine have the same receptors-Nicotinic cholinergic receptors and hence have the same action.

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(a) LH (luteinising hormone) is released by anterior lobe of pituitary gland. It causes ovulation, secretion of estrogen from mature ovarian follicle and progesterone from corpus luteum. FSH stimulates sperm formation in the male and growth of ovarian follicles in the female. Progesterone suspends ovulation during pregnancy, fixes the foetus to the uterine wall, forms placenta and controls the development of the foetus in the uterus. Estradiol is the major estrogen in humans.

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(c) Enterogastrone is a hormone released by the upper intestinal mucosa that inhibits gastric motility and secretion.

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(a) Luteinizing Hormone (LH) induces the Leideyg’s cells in males to produce testosterone and in female it causes ovulation and secretion of female sex hormone estrogen from mature ovarian follicle & progesterone by corpus luteum.

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(b) Interstitial cells (or Leydig ‘s cells) are the cells interspersed between the seminiferous tubules of the testis. They secrete androgens including testosterone in response to stimulation by luteinizing hormone from the anterior pitutary gland. Androgens produce and maintain male characteristics and stimulate germinal epithelium to undergo spermatogenesis.

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(a) Enterogastrone is secreted by duodenal epithelium and it slows gastric contractions to delay its emptying and also stops the secretion of gastric juice. Gastrin stimulates the secretion of gastric juice. Cholecystokinin stimulates the release of enzymes in pancreatic juice and the release of bile from the gall bladder. Cholecystokinin is also known as pancreozymin.

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(d) Male hormones are secreted by the Interstitial or Leydig’s cells present in the stroma of connective tissue in between the seminiferous tubules in testis. They produce androgens (mainly testosterone) Sertoli cells are elongated epithelial cells present inside the seminal vesicle to nourish the growing spermatozoa.

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(b) ADH: Antidiuretic hormone vasopressin is secreted by neurohypophysis (posterior lobe) of the pituitary gland. This hormone increases the reabsorption of water from the urine and hence urine gets concentrated and ECF gets diluted. Diabetes insipidus is caused by the hyposecretion of ADH.

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(d) Leydig’s cells are present in testes and they secrete the male hormone testosterone.

Small groups of polygonal, large cells present in the connective tissue in between the seminiferous tubules are known as Leydig’s cells are interstitial cells. They secrete the male sex hormone, testosterone.

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(c) Insulin is a hormone secreted by the b-cells of the pancreas and it controls the sugar level in the blood.

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(b) In 1912, Gudernatsch discovered that metamorphosis in frog’s tadpole is increased by the thyroxine hormone which has iodine as the main constituent. If thyroxine or iodine is added to water having tadpoles in it, then it increases the rate of metamorphosis in tadpole.

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(a) Insulin decreases the level of glucose in the blood while cortisol (secreted by middle region of adrenal cortex) increases the blood-glucose level by converting proteins and fats into carbohydrates which are, in turn, converted to glucose.

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(a) Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells – basophils, chromophobes, and colloid-filled cysts. This area produces melanocyte stimulating hormone or MSH. It stimulates the synthesis of the black pigment melanin in the skin and also causes dispersion of melanin granules in the pigment cells, thereby darkening the colour in certain animals (fishes; amphibians). In man, it has no such role.