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NEET Biology: Human Physiology · Chapter 6

Chemical Coordination and Integration

What to remember

  • Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts. The pituitary is the master gland, controlled by the hypothalamus through releasing and inhibiting hormones.
  • Calcium is balanced by two opposing hormones: parathyroid hormone (PTH) raises blood calcium, and thyrocalcitonin (TCT) lowers it. Blood glucose is balanced by insulin (lowers it) and glucagon (raises it).
  • Adrenal medulla hormones (adrenaline and noradrenaline) prepare the body for fight or flight. Adrenal cortex hormones are glucocorticoids (cortisol), mineralocorticoids (aldosterone) and small amounts of androgens.
  • Hormones with membrane receptors act through second messengers such as cAMP, IP3 and Ca²⁺. Steroid hormones and iodothyronines (thyroid hormones) have intracellular receptors and act on genes.

Hormones and the human endocrine system

Endocrine glands are ductless. They release their secretions, the hormones, directly into the blood. Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in very small (trace) amounts.

The endocrine organs and tissues of the human body are the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas (islets of Langerhans), testis in males and ovary in females. Some organs, such as the heart, kidney and gastrointestinal tract, also secrete hormones.

The hypothalamus

The hypothalamus is the basal part of the forebrain. It contains neurosecretory cells, which are groups of neurons that secrete hormones. These hormones regulate the synthesis and secretion of pituitary hormones.

  • Releasing hormones stimulate the secretion of pituitary hormones. Example: gonadotropin releasing hormone (GnRH) stimulates the pituitary to release gonadotropins (LH and FSH).
  • Inhibiting hormones inhibit the secretion of pituitary hormones. Example: somatostatin inhibits the release of growth hormone.

Hypothalamic hormones reach the anterior pituitary (adenohypophysis) through a portal circulation called the hypophyseal portal system. The posterior pituitary (neurohypophysis) is under the direct neural regulation of the hypothalamus. Its hormones, oxytocin and vasopressin, are made in the hypothalamus and pass along axons to the pars nervosa for storage and release.

The pituitary gland

The pituitary gland lies in a bony cavity called sella tursica and is attached to the hypothalamus by a stalk. It has two main divisions.

  • Adenohypophysis consists of the pars distalis and the pars intermedia. The pars distalis is commonly called the anterior pituitary.
  • Neurohypophysis (pars nervosa) is commonly called the posterior pituitary.
HormonePartMain actionDisorder
Growth hormone (GH)Pars distalisGrowth of tissues and bones; affects protein, carbohydrate and fat metabolismExcess in childhood: gigantism. Excess in adults: acromegaly (disfigured face, enlarged hands and jaw). Low in childhood: pituitary dwarfism
Prolactin (PRL)Pars distalisGrowth of mammary glands and formation of milk-
Thyroid stimulating hormone (TSH)Pars distalisStimulates the thyroid to make and release T3 and T4-
Adrenocorticotropic hormone (ACTH)Pars distalisStimulates the adrenal cortex to make and release steroid hormones-
Luteinising hormone (LH)Pars distalisMales: stimulates Leydig cells to make androgens. Females: induces ovulation and maintains the corpus luteum-
Follicle stimulating hormone (FSH)Pars distalisMales: with androgens, regulates spermatogenesis. Females: stimulates follicle growth-
Melanocyte stimulating hormone (MSH)Pars intermediaActs on melanocytes and regulates skin pigmentation-
OxytocinPars nervosaContraction of the uterus at childbirth; milk ejection from the mammary gland-
Vasopressin (ADH)Pars nervosaActs on the distal tubules of the kidney and promotes water reabsorption, which reduces loss of water in urineDeficiency: diabetes insipidus (large volume of dilute urine, dehydration)

LH and FSH are together called gonadotropins.

Pineal, thyroid, parathyroid and thymus

Pineal gland lies on the dorsal side of the forebrain. It secretes melatonin, which helps to maintain the 24-hour (diurnal) rhythm of the body, including the sleep-wake cycle and body temperature. It also influences metabolism, pigmentation, the menstrual cycle and defence capability.

Thyroid gland is composed of two lobes on either side of the trachea, joined by an isthmus. It is made of follicles and stromal tissue. The follicular cells make two hormones: tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3). Iodine is essential for their synthesis.

  • Thyroid hormones control the basal metabolic rate (BMR), support the formation of red blood cells, and influence carbohydrate, protein and fat metabolism and the balance of water and electrolytes.
  • Thyrocalcitonin (TCT) regulates the blood calcium level. It lowers it.
Thyroid disorderCauseFeatures
Simple (iodine-deficiency) goitreDeficiency of iodine in the diet leads to hypothyroidismEnlarged thyroid gland
CretinismHypothyroidism during pregnancyDefective development and growth of the baby, mental retardation, low intelligence quotient, abnormal skin, deaf-mutism
Hypothyroidism in adult womenLow thyroid hormonesIrregular menstrual cycle
Hyperthyroidism, Graves' disease (exophthalmic goitre)Excess thyroid hormone, for example from a nodule or cancer of the thyroidEnlarged thyroid, protruding eyeballs, high BMR, weight loss, rapid heartbeat

Parathyroid glands are four small glands on the back (dorsal) side of the thyroid, two in each lobe. They secrete parathyroid hormone (PTH), which increases the blood Ca²⁺ level. PTH acts on bone and stimulates the dissolution or demineralisation of bone. It also increases Ca²⁺ reabsorption by the renal tubules and Ca²⁺ absorption from digested food. It is called the hypercalcemic hormone. PTH and TCT together maintain calcium balance.

Thymus is a lobular gland located between the lungs behind the sternum, close to the heart and aorta. It secretes thymosins, which play a major role in the differentiation of T-lymphocytes, which provide cell-mediated immunity. Thymosins also promote antibody production and so help humoral immunity. The thymus degenerates with age, so thymosin output falls and the immune response of old people is weaker.

The adrenal gland

The adrenal glands are at the anterior (upper) part of each kidney. Each has an outer cortex and an inner medulla.

Adrenal medulla secretes adrenaline (epinephrine) and noradrenaline (norepinephrine). They are called catecholamines. They are released rapidly in response to stress and emergency, so they are called emergency hormones or hormones of fight or flight. They increase alertness, dilate the pupil, cause piloerection (raising of hairs), increase sweating, heart rate, strength of heart contraction and breathing rate. They stimulate the breakdown of glycogen, which raises blood glucose. They also stimulate the breakdown of lipids and proteins.

Adrenal cortex has three layers.

LayerPositionHormone group
Zona glomerulosaOuterMineralocorticoids (aldosterone)
Zona fasciculataMiddleGlucocorticoids (cortisol)
Zona reticularisInnerSmall amounts of androgens
  • Glucocorticoids: cortisol is the main hormone. It stimulates gluconeogenesis, lipolysis and proteolysis, and inhibits the cellular uptake and use of amino acids. It maintains the cardiovascular system and kidney functions, produces anti-inflammatory reactions, suppresses the immune response and stimulates the production of red blood cells.
  • Mineralocorticoids: aldosterone acts mainly on the kidney tubules. It increases reabsorption of Na⁺ and water and the excretion of K⁺ and phosphate ions. It helps to maintain electrolytes, body fluid volume, osmotic pressure and blood pressure.
  • Androgens: the adrenal cortex produces small amounts of androgenic steroids, which play a role in the growth of axillary hair, pubic hair and facial hair during puberty.
  • Addison's disease: it is caused by deficiency of adrenal cortical hormones. It affects carbohydrate metabolism and causes weakness and fatigue.

Pancreas and gonads

Pancreas is a composite gland. It acts as both an exocrine gland (digestive enzymes) and an endocrine gland. The endocrine part consists of the islets of Langerhans. A normal human pancreas has 1 to 2 million islets, forming only 1 to 2 per cent of the pancreatic tissue. Two cell types are the most abundant: alpha cells secrete glucagon and beta cells secrete insulin.

HormoneCellTargetActionEffect on blood glucose
GlucagonAlpha cellsHepatocytes (liver cells)Stimulates glycogenolysis; stimulates gluconeogenesisRaises (hyperglycemia)
InsulinBeta cellsHepatocytes and adipocytesIncreases glucose uptake into cells and use of glucose; glycogenesis (glucose to glycogen)Lowers (hypoglycemia)

Diabetes mellitus is a disease with prolonged high blood glucose (hyperglycemia). Glucose is lost in the urine, and harmful compounds called ketone bodies are formed. Patients are treated with insulin therapy.

Testis is a pair of organs in the scrotal sac. It has seminiferous tubules and interstitial (stromal) tissue. The Leydig cells (interstitial cells) make androgens, mainly testosterone. Androgens regulate the development, maturation and function of the male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate gland, urethra). They stimulate muscular growth, growth of facial and axillary hair, aggressiveness and low pitch of the voice. They have a stimulatory role in spermatogenesis, influence male sexual behaviour (libido) and have anabolic effects on protein and carbohydrate metabolism.

Ovary is a pair of organs in the abdomen. It has follicles and stromal tissue. The ovarian follicles make estrogen. After ovulation, the ruptured follicle is converted into the corpus luteum, which secretes progesterone.

  • Estrogen stimulates growth and activities of the female accessory organs and secondary sex characters (for example, high pitch of the voice), mammary gland development and female sexual behaviour.
  • Progesterone supports pregnancy. It acts on the mammary glands and stimulates the formation of alveoli (sac-like structures) and milk secretion.

Hormones of the heart, kidney and gastrointestinal tract

OrganHormoneAction
Heart (atrial wall)Atrial natriuretic factor (ANF)Causes dilation of blood vessels and so lowers blood pressure
Kidney (juxtaglomerular cells)ErythropoietinStimulates erythropoiesis (formation of red blood cells)
StomachGastrinActs on gastric glands to stimulate secretion of HCl and pepsinogen
DuodenumSecretinActs on the exocrine pancreas to stimulate secretion of water and bicarbonate ions
DuodenumCholecystokinin (CCK)Acts on the pancreas and gall bladder to stimulate secretion of pancreatic enzymes and bile juice
DuodenumGastric inhibitory peptide (GIP)Inhibits gastric secretion and motility

Mechanism of hormone action

A hormone acts on its target tissue through a specific receptor. The receptor is a protein on or in the target cell.

  • Membrane-bound receptors: the hormone (usually a protein, peptide or amino acid derivative) cannot enter the cell. It binds to the receptor on the cell membrane. This forms a hormone-receptor complex that generates second messengers inside the cell, such as cyclic AMP (cAMP), inositol triphosphate (IP3) and calcium ions (Ca²⁺). The second messengers regulate cellular metabolism.
  • Intracellular receptors: steroid hormones and iodothyronines (thyroid hormones) pass through the membrane and bind to receptors inside the cell, mostly in the nucleus. The hormone-receptor complex acts on the genome and regulates gene expression. The resulting biochemical changes bring about the physiological and developmental effects.
FeatureMembrane receptorIntracellular receptor
Hormone typePeptide, protein, amino acid derivativesSteroids, iodothyronines
Enters the cellNoYes
MessengercAMP, IP3, Ca²⁺Hormone-receptor complex itself
Site of effectCell metabolismGene expression

NEET traps

  • 1. Gigantism is excess GH in childhood; acromegaly is excess GH in adults; pituitary dwarfism is low GH in childhood.
  • 2. Diabetes insipidus is a lack of ADH (vasopressin) and gives dilute urine; diabetes mellitus is a lack of insulin action and gives high blood glucose.
  • 3. Oxytocin and vasopressin are made in the hypothalamus but released from the pars nervosa, not made in the pituitary.
  • 4. The hypophyseal portal system joins the hypothalamus to the adenohypophysis, not to the neurohypophysis.
  • 5. PTH raises blood calcium; thyrocalcitonin lowers it.
  • 6. Insulin lowers glucose (beta cells); glucagon raises glucose (alpha cells).
  • 7. Cretinism is hypothyroidism in the baby; Graves' disease (exophthalmic goitre) is hyperthyroidism.
  • 8. Zona glomerulosa is the outer layer and makes aldosterone; zona reticularis is the inner layer.
  • 9. Adrenaline and noradrenaline come from the medulla; cortisol and aldosterone come from the cortex.
  • 10. LH acts on Leydig cells in males; FSH, with androgens, acts on spermatogenesis. Do not swap them.

One-liners

  • 1. Hormones are non-nutrient chemicals produced in trace amounts that act as intercellular messengers.
  • 2. The neurohypophysis is also called pars nervosa.
  • 3. MSH is secreted by the pars intermedia.
  • 4. Prolactin stimulates milk formation; oxytocin causes milk ejection.
  • 5. LH and FSH are the gonadotropins.
  • 6. Iodine is needed to make T3 and T4.
  • 7. The thyroid is made of follicles and has two lobes joined by an isthmus.
  • 8. There are four parathyroid glands, on the dorsal side of the thyroid.
  • 9. Thymosins promote the differentiation of T-lymphocytes.
  • 10. The thymus shrinks with age.
  • 11. Adrenaline and noradrenaline are catecholamines.
  • 12. Cortisol is the main glucocorticoid and aldosterone is the main mineralocorticoid.
  • 13. Islets of Langerhans form only 1 to 2 per cent of the pancreas.
  • 14. Corpus luteum secretes progesterone.
  • 15. ANF lowers blood pressure and erythropoietin raises red blood cell production.

Practice questions

  1. Hormones are best described as

    1. enzymes secreted through ducts into the gut
    2. nutrients stored in the target cells
    3. non-nutrient chemicals that act as intercellular messengers
    4. structural proteins of the cell membrane
    Answer

    C. non-nutrient chemicals that act as intercellular messengers

    Hormones are non-nutrient chemicals produced in trace amounts that act as intercellular messengers.

  2. The hypophyseal portal system carries hypothalamic hormones to the

    1. adenohypophysis
    2. thyroid gland
    3. pars nervosa
    4. pineal gland
    Answer

    A. adenohypophysis

    Releasing and inhibiting hormones reach the adenohypophysis through the hypophyseal portal system.

  3. Excess secretion of growth hormone in childhood causes

    1. acromegaly
    2. gigantism
    3. pituitary dwarfism
    4. cretinism
    Answer

    B. gigantism

    Excess GH in childhood causes gigantism; in adults it causes acromegaly.

  4. Which hormone is released from the pars nervosa of the pituitary?

    1. Thyroid stimulating hormone
    2. Luteinising hormone
    3. Prolactin
    4. Oxytocin
    Answer

    D. Oxytocin

    Oxytocin and vasopressin are released from the neurohypophysis (pars nervosa).

  5. Deficiency of vasopressin (ADH) results in

    1. diabetes mellitus
    2. Addison's disease
    3. Graves' disease
    4. diabetes insipidus
    Answer

    D. diabetes insipidus

    Without ADH the kidney reabsorbs less water, giving a large volume of dilute urine (diabetes insipidus).

  6. Melanocyte stimulating hormone is secreted by the

    1. pars nervosa
    2. pars distalis
    3. pars intermedia
    4. pineal gland
    Answer

    C. pars intermedia

    MSH is secreted by the pars intermedia of the adenohypophysis.

  7. Which element is essential for the synthesis of thyroid hormones?

    1. Iodine
    2. Sodium
    3. Iron
    4. Phosphorus
    Answer

    A. Iodine

    T3 and T4 contain iodine; lack of iodine in the diet causes hypothyroidism and goitre.

  8. The hormone that increases the level of Ca²⁺ in the blood is

    1. insulin
    2. parathyroid hormone
    3. glucagon
    4. thyrocalcitonin
    Answer

    B. parathyroid hormone

    Parathyroid hormone is the hypercalcemic hormone. Thyrocalcitonin lowers blood calcium.

  9. Thymosins promote the differentiation of

    1. red blood cells
    2. melanocytes
    3. T-lymphocytes
    4. platelets
    Answer

    C. T-lymphocytes

    Thymosins from the thymus differentiate T-lymphocytes, which give cell-mediated immunity.

  10. The adrenal medulla secretes

    1. thyroxine and calcitonin
    2. adrenaline and noradrenaline
    3. glucagon and insulin
    4. cortisol and aldosterone
    Answer

    B. adrenaline and noradrenaline

    The medulla secretes the catecholamines adrenaline and noradrenaline.

  11. Which layer of the adrenal cortex secretes mineralocorticoids?

    1. Zona reticularis
    2. Adrenal medulla
    3. Zona fasciculata
    4. Zona glomerulosa
    Answer

    D. Zona glomerulosa

    The outer zona glomerulosa secretes mineralocorticoids such as aldosterone.

  12. Glucagon is secreted by

    1. alpha cells of the islets of Langerhans
    2. follicular cells of the thyroid
    3. Leydig cells
    4. beta cells of the islets of Langerhans
    Answer

    A. alpha cells of the islets of Langerhans

    Alpha cells make glucagon; beta cells make insulin.

  13. Leydig cells of the testis secrete

    1. estrogen
    2. androgens
    3. progesterone
    4. inhibin only
    Answer

    B. androgens

    Leydig (interstitial) cells secrete androgens, mainly testosterone.

  14. After ovulation, the ruptured follicle becomes the corpus luteum, which secretes

    1. estrogen only
    2. FSH
    3. oxytocin
    4. progesterone
    Answer

    D. progesterone

    The corpus luteum secretes progesterone, which supports pregnancy.

  15. Which hormone stimulates the exocrine pancreas to secrete water and bicarbonate ions?

    1. Secretin
    2. Erythropoietin
    3. Gastrin
    4. Gastric inhibitory peptide
    Answer

    A. Secretin

    Secretin acts on the exocrine pancreas to release water and bicarbonate. Gastrin acts on the gastric glands.

  16. Atrial natriuretic factor (ANF) produces which effect?

    1. Formation of red blood cells
    2. Constriction of blood vessels and rise in blood pressure
    3. Dilation of blood vessels and fall in blood pressure
    4. Release of gastric acid
    Answer

    C. Dilation of blood vessels and fall in blood pressure

    ANF from the atrial wall dilates blood vessels and lowers blood pressure.

  17. Given below are two statements. Statement I: The pars intermedia is a part of the adenohypophysis. Statement II: The pars nervosa is a part of the adenohypophysis. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    The pars nervosa forms the neurohypophysis.

  18. Given below are two statements. Statement I: Oxytocin and vasopressin are made by neurosecretory cells of the hypothalamus. Statement II: They are released from the neurohypophysis. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    The hormones are made in the hypothalamus, travel along axons and are released from the pars nervosa.

  19. Given below are two statements. Statement I: Glucagon acts on adipocytes to lower blood glucose. Statement II: Insulin promotes glycogenesis. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Glucagon acts on liver cells and raises blood glucose. Insulin promotes the conversion of glucose to glycogen.

  20. Which of the following statements are correct? 1. Graves' disease is a form of hyperthyroidism. 2. Cretinism results from hypothyroidism during pregnancy. 3. Simple goitre is caused by an excess of iodine in the diet.

    1. 1 only
    2. 1 and 2 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Answer

    B. 1 and 2 only

    Simple goitre is caused by iodine deficiency, so statement 3 is wrong.

  21. Given below are two statements. Statement I: Steroid hormones act through intracellular receptors. Statement II: Peptide hormones act through membrane receptors and second messengers such as cAMP. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Steroids and iodothyronines enter cells and act on genes; peptide hormones use membrane receptors and second messengers.

  22. Given below are two statements. Statement I: Cortisol suppresses the immune response. Statement II: Aldosterone increases the reabsorption of K⁺ and the excretion of Na⁺. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Aldosterone increases Na⁺ and water reabsorption and K⁺ excretion.

  23. Given below are two statements. Statement I: Melatonin is secreted by the thyroid gland. Statement II: Thyrocalcitonin raises the blood calcium level. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Melatonin comes from the pineal gland, and thyrocalcitonin lowers blood calcium.

  24. Which of the following statements are correct? 1. ACTH acts on the adrenal cortex. 2. TSH stimulates the thyroid gland. 3. FSH acts on the Leydig cells to make androgens.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    LH, not FSH, acts on the Leydig cells.

  25. Given below are two statements. Statement I: Estrogen is made by the ovarian follicles. Statement II: Progesterone is made by the Leydig cells. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Progesterone is made by the corpus luteum; Leydig cells make androgens.

  26. Given below are two statements. Statement I: Secretin is secreted by the stomach. Statement II: Vasopressin promotes water reabsorption in the distal tubules of the kidney. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Secretin comes from the duodenum, not the stomach. Statement II is correct.

  27. Assertion (A): A diet lacking iodine can cause goitre. Reason (R): Iodine is required for the synthesis of thyroid hormones.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Without iodine, thyroid hormones cannot be made, which leads to hypothyroidism and enlargement of the thyroid.

  28. Assertion (A): Diabetes insipidus causes a large volume of dilute urine. Reason (R): Vasopressin is synthesised by neurosecretory cells of the hypothalamus.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both are true, but dilute urine is explained by lack of vasopressin action on water reabsorption, not by where it is made.

  29. Assertion (A): Adrenaline increases the heart rate. Reason (R): Adrenaline is secreted by the adrenal cortex.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Adrenaline is secreted by the adrenal medulla, not the cortex.

  30. Assertion (A): Prolactin causes contraction of the uterus at childbirth. Reason (R): Oxytocin causes contraction of the uterine muscles.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Prolactin stimulates milk formation. Oxytocin causes uterine contraction.

  31. Assertion (A): Peptide hormones act through second messengers such as cAMP. Reason (R): Peptide hormones cannot enter the target cell and bind to receptors on the cell membrane.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Because they cannot enter the cell, the receptor complex on the membrane produces second messengers inside.

  32. Assertion (A): Parathyroid hormone is called the hypercalcemic hormone. Reason (R): Thyrocalcitonin is secreted by the thyroid gland.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both are true, but the source of thyrocalcitonin does not explain why PTH raises calcium.

  33. Match List I with List II. List I: a. Pineal gland b. Thymus c. Corpus luteum d. Zona fasciculata List II: i. Cortisol ii. Progesterone iii. Melatonin iv. Thymosins

    1. a-i, b-iv, c-ii, d-iii
    2. a-iv, b-iii, c-ii, d-i
    3. a-iii, b-iv, c-i, d-ii
    4. a-iii, b-iv, c-ii, d-i
    Answer

    D. a-iii, b-iv, c-ii, d-i

    Pineal makes melatonin, thymus makes thymosins, corpus luteum makes progesterone and zona fasciculata makes cortisol.

  34. Match List I with List II. List I: a. Excess GH in adults b. Deficiency of vasopressin c. Hypothyroidism in pregnancy d. Deficiency of adrenal cortical hormones List II: i. Cretinism ii. Acromegaly iii. Diabetes insipidus iv. Addison's disease

    1. a-ii, b-iii, c-iv, d-i
    2. a-iii, b-ii, c-i, d-iv
    3. a-ii, b-i, c-iii, d-iv
    4. a-ii, b-iii, c-i, d-iv
    Answer

    D. a-ii, b-iii, c-i, d-iv

    Acromegaly is excess GH in adults, diabetes insipidus is lack of ADH, cretinism follows hypothyroidism in pregnancy and Addison's disease follows adrenal cortical deficiency.

  35. Match List I with List II. List I: a. ANF b. Erythropoietin c. Gastrin d. Secretin List II: i. Formation of red blood cells ii. Lowers blood pressure iii. Secretion of HCl and pepsinogen iv. Water and bicarbonate from the pancreas

    1. a-i, b-ii, c-iii, d-iv
    2. a-ii, b-i, c-iii, d-iv
    3. a-ii, b-i, c-iv, d-iii
    4. a-iii, b-i, c-ii, d-iv
    Answer

    B. a-ii, b-i, c-iii, d-iv

    ANF lowers blood pressure, erythropoietin forms red blood cells, gastrin stimulates HCl and pepsinogen, secretin stimulates water and bicarbonate.

  36. Match List I with List II. List I: a. ACTH b. TSH c. LH d. MSH List II: i. Thyroid gland ii. Adrenal cortex iii. Leydig cells iv. Melanocytes

    1. a-iii, b-iv, c-ii, d-i
    2. a-i, b-ii, c-iii, d-iv
    3. a-ii, b-i, c-iii, d-iv
    4. a-ii, b-i, c-iv, d-iii
    Answer

    C. a-ii, b-i, c-iii, d-iv

    ACTH targets the adrenal cortex, TSH the thyroid, LH the Leydig cells and MSH the melanocytes.

  37. Match List I with List II. List I: a. Zona glomerulosa b. Zona fasciculata c. Zona reticularis d. Adrenal medulla List II: i. Glucocorticoids ii. Androgens iii. Mineralocorticoids iv. Adrenaline

    1. a-iii, b-i, c-ii, d-iv
    2. a-i, b-iii, c-ii, d-iv
    3. a-iii, b-ii, c-i, d-iv
    4. a-ii, b-i, c-iii, d-iv
    Answer

    A. a-iii, b-i, c-ii, d-iv

    Glomerulosa makes mineralocorticoids, fasciculata makes glucocorticoids, reticularis makes androgens and the medulla makes adrenaline.

  38. Match List I with List II. List I: a. Alpha cells b. Beta cells c. Leydig cells d. Follicular cells of thyroid List II: i. Insulin ii. Glucagon iii. T3 and T4 iv. Androgens

    1. a-ii, b-i, c-iii, d-iv
    2. a-ii, b-iii, c-iv, d-i
    3. a-ii, b-i, c-iv, d-iii
    4. a-i, b-ii, c-iv, d-iii
    Answer

    C. a-ii, b-i, c-iv, d-iii

    Alpha cells make glucagon, beta cells insulin, Leydig cells androgens and thyroid follicular cells T3 and T4.

  39. A tumour in the pituitary of a ten-year-old child produces too much growth hormone. Which condition is most likely to result?

    1. Diabetes insipidus
    2. Cretinism
    3. Acromegaly
    4. Gigantism
    Answer

    D. Gigantism

    Excess GH before growth stops causes gigantism. In adults it causes acromegaly.

  40. A person's blood calcium level falls below normal. Which change in hormone secretion is expected?

    1. Increase in thyrocalcitonin
    2. Increase in parathyroid hormone
    3. Increase in aldosterone
    4. Increase in insulin
    Answer

    B. Increase in parathyroid hormone

    PTH raises blood calcium by acting on bone, kidney and the gut; thyrocalcitonin lowers it.

  41. A person eats a meal rich in carbohydrates and blood glucose rises. Which response follows?

    1. Parathyroid releases more PTH
    2. Beta cells release more insulin
    3. Alpha cells release more glucagon
    4. Adrenal medulla releases cortisol
    Answer

    B. Beta cells release more insulin

    Insulin from beta cells lowers blood glucose by increasing uptake and glycogenesis.

  42. People living in an area where the diet has very little iodine often show enlarged thyroid glands. The most likely reason is

    1. failure of the parathyroid to secrete PTH
    2. excess secretion of GH
    3. damage to the thymus
    4. low T3 and T4 production, causing hypothyroidism and goitre
    Answer

    D. low T3 and T4 production, causing hypothyroidism and goitre

    Lack of iodine reduces thyroid hormone synthesis, causing hypothyroidism and an enlarged thyroid (goitre).

  43. Which of the following hormones is most likely to bind to a receptor inside the target cell and regulate gene expression?

    1. Glucagon
    2. Adrenaline
    3. Cortisol
    4. Insulin
    Answer

    C. Cortisol

    Cortisol is a steroid hormone, and steroids act through intracellular receptors on genes. The others use membrane receptors.

  44. A patient has an enlarged thyroid, protruding eyeballs, weight loss and a high basal metabolic rate. The most likely diagnosis is

    1. Graves' disease
    2. Diabetes insipidus
    3. Addison's disease
    4. Cretinism
    Answer

    A. Graves' disease

    These are features of hyperthyroidism, called Graves' disease or exophthalmic goitre.

  45. A person is suddenly frightened. The heart rate rises, pupils dilate and hairs stand erect. Which gland is responsible for the hormones involved?

    1. Pineal gland
    2. Thymus
    3. Adrenal cortex
    4. Adrenal medulla
    Answer

    D. Adrenal medulla

    The adrenal medulla releases adrenaline and noradrenaline, the fight or flight hormones.

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