Chemical Coordination and Integration ISC Class 11: Endocrine Glands and Hormones

What Chemical Coordination and Integration is about

Weightage: Chemical Coordination and Integration belongs to the unit Human Physiology, which CISCE weights at 18 of the 70 marks in the ISC Class XI Biology Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Biology syllabus, examination year 2028, Class XI unit weightage

Key concepts

Hormones, endocrine glands and the hypothalamus

Hormones are non-nutrient chemical signals, produced in trace amounts, that carry information between cells; they act on specific target cells that have receptors for them. Most are secreted by ductless (endocrine) glands directly into the blood, though some come from scattered tissues (heart, kidney, GI tract). Chemically, hormones are peptides/proteins (insulin, glucagon, pituitary and hypothalamic hormones), steroids (cortisol, testosterone, oestradiol, progesterone), iodothyronines (thyroid hormones) or amino-acid derivatives (adrenaline). Hypothalamus (location: base of the forebrain, the basal part of the diencephalon): it contains groups of neurosecretory cells that make hormones regulating the pituitary. Releasing hormones stimulate the pituitary (e.g. GnRH stimulates release of gonadotrophins; TRH stimulates TSH; CRH stimulates ACTH; GHRH stimulates GH). Inhibiting hormones stop secretion (e.g. somatostatin inhibits GH release). These hormones travel through a portal circulation (hypophyseal portal system) to the anterior pituitary. The posterior pituitary is under direct neural regulation: axons from the hypothalamus carry oxytocin and vasopressin down to it for storage and release.

Worked example

Why is the hypothalamus said to link the nervous and endocrine systems?

Try it first, then show the solutionSolution

1. It is part of the brain and receives nerve signals about the body's state
2. Its neurosecretory cells release hormones that control the pituitary, which controls many other endocrine glands

Answer: It converts nervous information into hormonal signals

Pituitary gland: lobes and their hormones

Location: in a bony cavity, the sella turcica, attached to the hypothalamus by a stalk. Divisions: the adenohypophysis (pars distalis, commonly called the anterior pituitary, and pars intermedia) and the neurohypophysis (pars nervosa, the posterior pituitary). Pars distalis: (1) Growth hormone (GH): growth of body tissues, especially bones and muscles. (2) Prolactin (PRL): growth of mammary glands and milk formation. (3) Thyroid-stimulating hormone (TSH): synthesis and release of thyroid hormones. (4) Adrenocorticotrophic hormone (ACTH): synthesis and release of glucocorticoids from the adrenal cortex. (5) Luteinising hormone (LH) and (6) follicle-stimulating hormone (FSH) (gonadotrophins): in males, LH stimulates the synthesis of androgens by the testis, and FSH with androgens regulates spermatogenesis; in females, LH induces ovulation and maintains the corpus luteum, and FSH stimulates growth of ovarian follicles. Pars intermedia: melanocyte-stimulating hormone (MSH), which acts on melanocytes and regulates skin pigmentation (in humans this part is almost merged with the pars distalis). Neurohypophysis stores and releases two hypothalamic hormones: oxytocin, which contracts smooth muscle, causing vigorous uterine contraction during childbirth and milk ejection; and vasopressin (ADH), which increases reabsorption of water and electrolytes in the distal tubules of the kidney, reducing water loss.

Worked example

Which pituitary hormones would be at work in a mother breastfeeding her baby, and what does each do?

Try it first, then show the solutionSolution

1. Prolactin from the anterior pituitary stimulates milk formation in the mammary glands
2. Oxytocin from the posterior pituitary causes milk ejection (let-down) when the baby suckles

Answer: Prolactin (milk production) and oxytocin (milk ejection)

Feedback control of tropic hormones

A tropic hormone is one that stimulates another endocrine gland: TSH (thyroid), ACTH (adrenal cortex), LH and FSH (gonads). Their secretion is regulated by negative feedback through a three-tier hypothalamus–pituitary–target gland axis. Example: the hypothalamus releases TRH → the anterior pituitary releases TSH → the thyroid releases T₃ and T₄. When T₃ and T₄ in blood rise above normal, they inhibit TRH release by the hypothalamus and TSH release by the pituitary, so the thyroid is stimulated less and hormone levels fall back. When thyroid hormone levels drop, the inhibition is lifted and TRH and TSH rise again. The same pattern controls CRH → ACTH → cortisol and GnRH → LH/FSH → sex steroids. Negative feedback keeps hormone levels within a narrow range (homeostasis). This explains goitre: in iodine deficiency the thyroid cannot make enough T₄, so feedback inhibition is lost, TSH stays high and continuously stimulates the thyroid, which enlarges.

Worked example

A person is given large doses of thyroxine tablets for a long time. Predict what happens to TSH and to their own thyroid gland.

Try it first, then show the solutionSolution

1. High blood thyroxine inhibits TRH from the hypothalamus and TSH from the pituitary (negative feedback)
2. With little TSH, the person's own thyroid is not stimulated and becomes less active and may shrink

Answer: TSH falls and the thyroid becomes underactive

Pineal, thyroid, parathyroid and thymus

Pineal gland (dorsal side of the forebrain): secretes melatonin, which regulates the 24-hour (diurnal) rhythm of the body: the sleep–wake cycle and body temperature; it also influences metabolism, pigmentation, the menstrual cycle and defence. Thyroid (two lobes on either side of the trachea, joined by a thin isthmus): made of follicles and stromal tissue. Follicular cells make thyroxine (T₄, tetraiodothyronine) and triiodothyronine (T₃), which need iodine. Functions: regulate the basal metabolic rate (BMR); support RBC formation; control the metabolism of carbohydrates, proteins and fats; maintain water and electrolyte balance. The thyroid also secretes thyrocalcitonin (TCT), a protein hormone that lowers blood calcium. Parathyroid glands (four, on the back of the thyroid, one pair in each lobe): secrete parathyroid hormone (PTH), a peptide, whose release depends on circulating Ca²⁺. PTH raises blood Ca²⁺ (it is hypercalcaemic): it stimulates bone resorption (dissolving bone minerals), increases Ca²⁺ reabsorption by the kidney tubules and increases Ca²⁺ absorption from digested food. With TCT it keeps blood calcium balanced. Thymus (a lobular structure between the lungs, behind the sternum, on the ventral side of the aorta): secretes thymosins, which help the differentiation of T-lymphocytes (cell-mediated immunity) and promote antibody production (humoral immunity). The thymus is large in children and degenerates with age, so thymosin levels fall and immune responses weaken in old people.

Worked example

After accidental removal of the parathyroids during thyroid surgery, a patient develops muscle spasms. Explain.

Try it first, then show the solutionSolution

1. Without PTH, blood Ca²⁺ falls because bone resorption, kidney reabsorption and gut absorption of calcium decrease
2. Low Ca²⁺ makes nerves and muscles over-excitable, causing tetany

Answer: Loss of PTH lowers blood calcium, leading to tetany

Adrenal glands

Location: one adrenal gland sits on the anterior (upper) part of each kidney. Each has an outer cortex and an inner medulla. Adrenal medulla: secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), together called catecholamines. They are released rapidly in stress or emergency and are therefore called emergency hormones ('fight or flight'). Effects: alertness, dilation of pupils, piloerection (hair standing), sweating, faster heartbeat and stronger heart contraction, faster breathing, and breakdown of glycogen to raise blood glucose; they also stimulate breakdown of lipids and proteins. Adrenal cortex: three layers, outer zona glomerulosa, middle zona fasciculata and inner zona reticularis, secreting corticoids. (1) Glucocorticoids, mainly cortisol: stimulate gluconeogenesis, lipolysis and proteolysis, and inhibit the uptake and use of amino acids by cells; help maintain the cardiovascular system and kidney function; are anti-inflammatory and suppress the immune response; stimulate RBC production. (2) Mineralocorticoids, mainly aldosterone: act on the renal tubules to reabsorb Na⁺ and water and excrete K⁺ and phosphate, so they maintain electrolytes, body fluid volume, osmotic pressure and blood pressure. (3) Small amounts of androgenic steroids, which play a part in the growth of axial, pubic and facial hair at puberty. Addison's disease: underproduction of adrenal cortex hormones, which alters carbohydrate metabolism and causes acute weakness and fatigue.

Worked example

A student about to sit an important exam notices a pounding heart, sweaty palms and quick breathing. Which hormone is responsible, and from which gland?

Try it first, then show the solutionSolution

1. These are emergency responses to stress
2. They are caused by adrenaline (and noradrenaline) from the adrenal medulla

Answer: Adrenaline from the adrenal medulla

Pancreas, gonads and hormones of the GI tract, heart and kidney

Pancreas: a composite gland, both exocrine (digestive juice) and endocrine. The endocrine part is the islets of Langerhans (about 1–2 million, roughly 1–2% of pancreatic tissue). α-cells secrete glucagon and β-cells secrete insulin, both peptides. Glucagon acts mainly on liver cells: it stimulates glycogenolysis (glycogen → glucose) and gluconeogenesis, and reduces cellular glucose uptake, so it raises blood glucose (hyperglycaemic). Insulin acts mainly on liver cells and adipocytes: it increases cellular glucose uptake and use, and promotes glycogenesis (glucose → glycogen), so it lowers blood glucose (hypoglycaemic). The balance of the two keeps blood glucose normal. Gonads: the testes (in the scrotum) have interstitial (Leydig) cells that secrete androgens, mainly testosterone, which controls the development and function of male accessory sex organs, male secondary sex characters (muscle growth, facial and body hair, deeper voice, aggressiveness), stimulates spermatogenesis, influences male sexual behaviour and has anabolic effects. The ovaries secrete oestrogen (from growing follicles), which controls the growth of female accessory sex organs, development of follicles, female secondary sex characters and mammary gland development, and progesterone (from the corpus luteum), which supports pregnancy and stimulates the formation of milk-secreting alveoli in the mammary glands. GI tract hormones (from cells of the stomach and intestine): gastrin acts on gastric glands to stimulate secretion of HCl and pepsinogen; secretin acts on the exocrine pancreas to secrete water and bicarbonate ions; cholecystokinin–pancreozymin (CCK-PZ) acts on the pancreas and gall bladder, stimulating secretion of pancreatic enzymes and release of bile; gastric inhibitory peptide (GIP) inhibits gastric secretion and motility. Heart: the atrial walls secrete atrial natriuretic factor (ANF), which lowers blood pressure by vasodilation. Kidney: juxtaglomerular cells secrete erythropoietin, which stimulates RBC formation.

Worked example

When acidic chyme enters the duodenum, the pancreas releases a bicarbonate-rich juice and the gall bladder contracts. Name the hormones responsible.

Try it first, then show the solutionSolution

1. Secretin acts on the exocrine pancreas to release water and bicarbonate, neutralising the acid
2. CCK-PZ stimulates release of pancreatic enzymes and contraction of the gall bladder to release bile

Answer: Secretin and cholecystokinin–pancreozymin (CCK-PZ)

Mechanism of hormone action: cAMP and steroid hormones (elementary idea)

Hormones act by binding specific receptors in their target cells; each receptor binds only its own hormone, forming a hormone–receptor complex that triggers biochemical changes. Receptors are of two types. (1) Membrane-bound receptors: used by hormones that cannot cross the plasma membrane, such as protein, peptide and amino-acid-derived hormones (e.g. insulin, glucagon, adrenaline). The hormone (the first messenger) binds the receptor on the cell surface; this activates (via a G protein) the enzyme adenylate cyclase on the inner side of the membrane, which converts ATP into cyclic AMP (cAMP). cAMP is the second messenger: it activates protein kinases, which change the activity of enzymes and produce the physiological response, for example glycogen breakdown in liver cells in response to glucagon or adrenaline. Because each step activates many molecules, a small amount of hormone produces a large response (amplification). Other second messengers include IP₃ and Ca²⁺. (2) Intracellular receptors: used by lipid-soluble hormones such as steroid hormones (cortisol, aldosterone, testosterone, oestrogen) and iodothyronines. The hormone diffuses through the plasma membrane and binds a receptor in the cytoplasm or nucleus. The hormone–receptor complex enters the nucleus and binds to specific sites on DNA, switching particular genes on or off. This changes mRNA and protein synthesis, producing physiological and developmental effects. Steroid action is therefore slower but often longer-lasting than cAMP-mediated action.

Worked example

Why can adrenaline produce an effect in seconds, whereas a steroid such as cortisol takes hours?

Try it first, then show the solutionSolution

1. Adrenaline binds a membrane receptor and acts through cAMP and protein kinases, which modify existing enzymes immediately
2. Cortisol enters the cell and alters gene expression; new mRNA and proteins must be made before the effect appears

Answer: Second-messenger action modifies existing enzymes; steroid action needs new protein synthesis

Disorders of hypo- and hypersecretion

Pituitary dwarfism: too little GH in childhood; growth is stunted though the body is proportionate. Gigantism: excess GH in childhood; abnormal height. Acromegaly: excess GH in adults (especially middle age); bones of the face, hands and feet thicken, causing severe disfigurement; it may go unnoticed for years. Diabetes insipidus: lack of ADH (vasopressin) action; the kidneys cannot reabsorb enough water, so large volumes of dilute urine are passed (diuresis), causing dehydration and great thirst. Goitre (simple): enlargement of the thyroid due to iodine deficiency and the resulting high TSH. Cretinism: hypothyroidism during pregnancy or infancy; stunted growth, mental retardation, low intelligence, abnormal skin and deaf-mutism. Hypothyroidism in adult women may cause irregular menstrual cycles. Exophthalmic goitre (Graves' disease): a form of hyperthyroidism with an enlarged thyroid, protruding eyeballs, increased BMR and weight loss. Diabetes mellitus: lack of insulin (or its action); prolonged hyperglycaemia, glucose lost in urine (glycosuria) and formation of harmful ketone bodies; treated with insulin therapy. Addison's disease: underproduction of adrenal cortex hormones; acute weakness and fatigue.

Worked example

Two patients both pass large volumes of urine and feel very thirsty. In one, urine contains glucose; in the other, urine is very dilute with no glucose. Identify each disorder.

Try it first, then show the solutionSolution

1. Glucose in urine with excess urine: diabetes mellitus (insulin problem)
2. Very dilute urine without glucose: diabetes insipidus (ADH deficiency)

Answer: First: diabetes mellitus; second: diabetes insipidus

Chemical Coordination and Integration in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Hypothalamus, Pituitary and Hormone Action
• Thyroid, Parathyroid, Adrenal, Pancreas and Gonadal Hormones

Chemical Coordination and Integration: key facts

Thyroid axis (negative feedback)

$\text{hypothalamus (TRH)}\to \text{anterior pituitary (TSH)}\to \text{thyroid}(T_3,T_4)⊣\text{hypothalamus, pituitary}$

Same pattern for CRH–ACTH–cortisol and GnRH–LH/FSH–sex steroids.

cAMP pathway

$\text{hormone}+\text{receptor}\to \text{adenylate cyclase}\to ATP\to cAMP\to \text{protein kinase}\to \text{response}$

For protein, peptide and catecholamine hormones.

Steroid pathway

$\text{steroid}\to \text{intracellular receptor}\to \text{nucleus (DNA)}\to mRNA\to \text{protein}\to \text{response}$

Lipid-soluble hormones; slower, longer-lasting.

Blood glucose control

$\text{insulin }(\beta \text{-cells})\downarrow \text{glucose};\text{glucagon }(\alpha \text{-cells})\uparrow \text{glucose}$

Glycogenesis vs glycogenolysis and gluconeogenesis.

Calcium balance

$PTH\uparrow C{a}^{2+}(\text{bone, kidney, gut});TCT\downarrow C{a}^{2+}$

Low PTH leads to tetany.

Chemical Coordination and Integration: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Chemical Coordination and Integration

The question patterns to expect, and the method that works for each.

Tricks to remember Chemical Coordination and Integration

Short memory aids. Say each one aloud once, then use it on a question the same day.

• FLAT PiG

  Anterior pituitary: FSH, LH, ACTH, TSH, PRL, GH.

  Use it when: Pars distalis hormones.

• Post office stores O and V

  Posterior pituitary stores (does not make) Oxytocin and Vasopressin.

  Use it when: Neurohypophysis.

• GFR: salt, sugar, sex

  Zona Glomerulosa (mineralocorticoids, salt), Fasciculata (glucocorticoids, sugar), Reticularis (androgens, sex), from outside in.

  Use it when: Adrenal cortex layers.

• Glucagon = glucose gone up

  Glucagon (α) raises blood glucose; insulin (β) lowers it.

  Use it when: Pancreatic hormones.

• Gas-Sec-CCK-GIP

  Gastrin: acid; Secretin: bicarbonate; CCK-PZ: enzymes and bile; GIP: stop the stomach.

  Use it when: GI hormones.

Chemical Coordination and Integration: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Chemical Coordination and Integration

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying the posterior pituitary makes oxytocin

  Storage and synthesis are confused.

  Wrong working

  Oxytocin and ADH are synthesised in the posterior pituitary.

  Right working

  They are made in the hypothalamus and stored and released by the posterior pituitary.

  ✓Do this: Post office stores, does not make.

  Usually costs: 1 mark.

• ✗Mistake: Mixing up diabetes mellitus and insipidus

  Both cause excessive urination.

  Wrong working

  Diabetes insipidus is due to lack of insulin.

  Right working

  Mellitus: insulin deficiency, glucose in urine; insipidus: ADH deficiency, very dilute urine.

  ✓Do this: Mellitus = honey (sweet urine).

  Usually costs: 1-2 marks.

• ✗Mistake: Wrong hormone for goitre types

  Hypo- and hyperthyroidism both enlarge the gland.

  Wrong working

  Exophthalmic goitre is due to iodine deficiency.

  Right working

  Simple goitre: iodine deficiency; exophthalmic goitre (Graves'): hyperthyroidism.

  ✓Do this: Bulging eyes = too much hormone.

  Usually costs: 1 mark.

• ✗Mistake: Steroids acting through cAMP

  One mechanism is applied to all hormones.

  Wrong working

  Testosterone binds a membrane receptor and forms cAMP.

  Right working

  Steroids cross the membrane and bind intracellular receptors that change gene expression.

  ✓Do this: Water-soluble = surface receptor; fat-soluble = inside receptor.

  Usually costs: 1-2 marks.

• ✗Mistake: Wrong GI hormone function

  Four similar names.

  Wrong working

  Secretin stimulates bile release.

  Right working

  Secretin: bicarbonate and water from pancreas; CCK-PZ: pancreatic enzymes and bile.

  ✓Do this: Secretin = soda (bicarbonate).

  Usually costs: 1 mark.

Practice questions on Chemical Coordination and Integration

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Melatonin is secreted by the:
   (a) pituitary
   (b) pineal gland
   (c) thymus
   (d) thyroid

   Hint

   Sleep–wake cycle.

   Answer

   (b)

2. Q2 · 1 mark · MCQExam level

   Which hormone stimulates secretion of HCl and pepsinogen?
   (a) secretin
   (b) gastrin
   (c) GIP
   (d) CCK

   Hint

   Gastric.

   Answer

   (b)

3. Q3 · 1 mark · Very short answerExam level

   Name the hormone that helps differentiate T-lymphocytes.

   Hint

   Thymus.

   Answer

   Thymosins

4. Q4 · 1 mark · Very short answerExam level

   Name the second messenger formed from ATP by adenylate cyclase.

   Hint

   Cyclic.

   Answer

   Cyclic AMP (cAMP)

5. Q5 · 2 marks · Short answerExam level

   What is Addison's disease?

   Hint

   Adrenal cortex.

   Answer

   A disorder due to underproduction of adrenal cortex hormones (corticoids), which alters carbohydrate metabolism and causes acute weakness and fatigue.

6. Q6 · 2 marks · Short answerHarder exam level

   Distinguish between the actions of LH and FSH in males and females.

   Hint

   Gonadotrophins.

   Answer

   Males: LH stimulates androgen synthesis by the testis; FSH with androgens regulates spermatogenesis. Females: LH induces ovulation and maintains the corpus luteum; FSH stimulates growth of ovarian follicles.

7. Q7 · 2 marks · Short answerHarder exam level

   State four effects of adrenaline.

   Hint

   Fight or flight.

   Answer

   Increases heart rate and strength of contraction; increases breathing rate; dilates pupils and causes piloerection and sweating; breaks down glycogen to raise blood glucose; increases alertness.

8. Q8 · 3 marks · Short answerHarder exam level

   List the hormones of the anterior pituitary with one function each.

   Hint

   Six.

   Answer

   GH: body growth; PRL: mammary growth and milk formation; TSH: thyroid hormone release; ACTH: glucocorticoid release from adrenal cortex; LH: androgen synthesis in males, ovulation in females; FSH: spermatogenesis in males, follicle growth in females.

9. Q9 · 3 marks · Short answerHarder exam level

   Describe the functions of thyroid hormones.

   Hint

   BMR.

   Answer

   T₃ and T₄ regulate the basal metabolic rate; support RBC formation; control the metabolism of carbohydrates, proteins and fats; maintain water and electrolyte balance. Thyrocalcitonin lowers blood calcium.

10. Q10 · 3 marks · Short answerHarder exam level

    Explain feedback control of tropic hormones with the example of the thyroid.

    Hint

    TRH, TSH, T₄.

    Answer

    The hypothalamus secretes TRH, stimulating the anterior pituitary to release TSH, which stimulates the thyroid to release T₃ and T₄. High T₃ and T₄ inhibit TRH and TSH secretion (negative feedback); low levels remove the inhibition. This keeps thyroid hormones within a normal range.

11. Q11 · 5 marks · Long answerHarder exam level

    (a) Describe the hormones of the pancreas and gonads. [3]
    (b) Why are the testes and ovaries described both as primary sex organs and as endocrine glands? Name the cells of the testis that secrete androgens. [2]

    Hint

    α, β; testosterone, oestrogen, progesterone.

    Answer

    (a) Pancreatic islets: α-cells secrete glucagon (raises blood glucose by glycogenolysis and gluconeogenesis); β-cells secrete insulin (lowers it by glucose uptake and glycogenesis). Testes: testosterone (male accessory organs, secondary sex characters, spermatogenesis, anabolic effects). Ovaries: oestrogen (female sex organs and characters, mammary development) and progesterone (supports pregnancy, mammary alveoli). (b) They produce the gametes (sperm and ova), so they are the primary sex organs, and they also secrete sex hormones directly into the blood (testosterone; oestrogen and progesterone), so they are endocrine glands. Androgens are secreted by the interstitial (Leydig) cells of the testis.

12. Q12 · 5 marks · Long answerHarder exam level

    (a) Give the location of the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus and adrenals. [3]
    (b) Name the disorders caused by hyposecretion of GH in childhood and hypersecretion of GH in adults. [2]

    Hint

    Head, neck, chest, abdomen.

    Answer

    (a) Hypothalamus: base of forebrain (diencephalon); pituitary: in the sella turcica, attached to the hypothalamus by a stalk; pineal: dorsal side of forebrain; thyroid: either side of the trachea, lobes joined by isthmus; parathyroids: four, on the back of the thyroid; thymus: between the lungs behind the sternum; adrenals: on the anterior part of each kidney. (b) Pituitary dwarfism; acromegaly.

13. Q13 · 2 marks · Short answerHarder exam level

    How many iodine atoms are needed to make 500 molecules each of T₄ and T₃?

    Hint

    4 and 3.

    Answer

    T₄ has 4 iodine atoms and T₃ has 3: 500 × 4 + 500 × 3 = 2000 + 1500 = 3500 iodine atoms.

14. Q14 · 3 marks · Short answerHOTS / competency

    A person has very high TSH but low T₄ in blood. Suggest two possible causes and explain your reasoning.

    Hint

    Feedback.

    Answer

    Low T₄ means the thyroid is underactive; high TSH shows the pituitary is responding normally by trying to stimulate it, because negative feedback from T₄ is missing. Causes: iodine deficiency (the thyroid lacks raw material, as in simple goitre) or damage to the thyroid itself. A pituitary fault is unlikely, since it would cause low TSH.

15. Q15 · 3 marks · Short answerHOTS / competency

    Insulin is a protein hormone and is given by injection, not by mouth. Use your knowledge of digestion and hormone action to explain why, and state where its receptors are.

    Hint

    Proteases; membrane receptors.

    Answer

    Taken by mouth, insulin would be digested by proteases (pepsin, trypsin) into amino acids and lose its activity. Injected insulin reaches the blood intact. Being a protein, it cannot cross the plasma membrane, so it acts through receptors on the cell surface of its targets, mainly liver cells and adipocytes.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Cavity holding the pituitary?Show answer

   Sella turcica.

2. 2.Hormone inhibiting GH release?Show answer

   Somatostatin.

3. 3.Hormone causing milk ejection?Show answer

   Oxytocin.

4. 4.Number of parathyroid glands?Show answer

   Four.

5. 5.Mineralocorticoid?Show answer

   Aldosterone.

6. 6.Cells secreting glucagon?Show answer

   α-cells of islets of Langerhans.

7. 7.Hormone from corpus luteum?Show answer

   Progesterone.

8. 8.Hyperthyroidism with bulging eyes?Show answer

   Exophthalmic goitre (Graves' disease).

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name the location of each endocrine gland?
• ☐Can you list all pituitary hormones by lobe?
• ☐Can you explain negative feedback using the thyroid axis?
• ☐Can you give the functions of PTH and thyrocalcitonin?
• ☐Can you compare adrenal cortex and medulla hormones?
• ☐Can you state the effects of insulin and glucagon?
• ☐Can you name four GI hormones and their actions?
• ☐Can you contrast cAMP and steroid mechanisms?

Chemical Coordination and Integration: frequently asked questions