Endocrine System

Question 1. (4 marks)

• Endocrine glands are ductless; they secrete hormones directly into the blood/bloodstream (1). Example: thyroid / pituitary / adrenal (1).
• Exocrine glands secrete their products through ducts onto a surface or into a cavity (1). Example: salivary / sweat / pancreatic (exocrine part) glands (1). Why: The key distinction is mode of secretion (blood vs duct), the defining feature of the two gland types.

Question 2. (5 marks) — 1 mark each

Why: Recall of gland anatomical positions and their signature hormones.

Question 3. (4 marks) (a) Steroid hormones are derived from cholesterol (lipid); peptide hormones are made of amino acids/proteins (1). Steroids are lipid-soluble; peptides are water-soluble (1). (b) Steroid → intracellular receptor because they can cross the lipid plasma membrane (1). Peptide → cell-surface (membrane) receptor because they cannot cross the membrane (1). Why: Solubility determines whether a hormone passes the membrane, which dictates receptor location.

Question 4. (4 marks)

• The peptide hormone acts as the first messenger and binds to a receptor on the cell surface membrane (1)(1).
• This activates an enzyme (e.g. adenylyl cyclase) that produces a second messenger such as cyclic AMP inside the cell (1).
• The second messenger activates enzymes / a signalling cascade, producing the cellular response (1). Why: Water-soluble hormones cannot enter the cell, so they relay their signal via surface receptors and internal second messengers.

Question 5. (5 marks) (a) Hypothalamus and pituitary gland (1). (b) Anterior pituitary: e.g. TSH / ACTH / FSH / LH / GH (1). Posterior pituitary: ADH (vasopressin) or oxytocin (1). (c) The hypothalamus secretes releasing (or inhibiting) hormones into the hypophyseal portal blood vessels (1), which travel to the anterior pituitary and stimulate/inhibit its hormone secretion (1). Why: Anterior pituitary control is chemical (via portal vessels), unlike the posterior which is neural.

Question 6. (5 marks) (a) Insulin — beta (β) cells of islets of Langerhans (1). Glucagon — alpha (α) cells (1). (b) Insulin lowers/decreases blood glucose (1); it stimulates glucose uptake by cells / glycogen synthesis (glycogenesis) in the liver (1). (c) Glucagon raises/increases blood glucose (1). Why: The antagonistic pair maintains glucose homeostasis via opposite actions.

Question 7. (4 marks) (a) Thyroxine (T4) and triiodothyronine (T3) (1); element = iodine (1). (b) Any two: increases basal metabolic rate; increases heat production; increases oxygen consumption; promotes growth/development (1+1). Why: Thyroid hormones set the body's overall metabolic pace and require iodine for synthesis.

Question 8. (4 marks) (a) Adrenaline (epinephrine) (1). (b) Adrenal cortex (1). (c) Any two: increased heart rate; raised blood glucose; dilated bronchioles/airways; blood diverted to muscles; dilated pupils (1+1). Why: Medulla gives fast fight-or-flight response; cortex secretes steroid cortisol.

Question 9. (3 marks)

• Negative feedback: a change in a variable triggers a response that opposes/reverses the change, returning it toward normal (1)(1).
• Example: high thyroxine inhibits TSH/TRH release; or high blood glucose triggers insulin to lower it (1). Why: Negative feedback maintains homeostasis by self-correction.

Question 10. (2 marks)

• FSH and LH (1). LH triggers ovulation (1). Why: The LH surge causes the mature follicle to release the ovum.

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  {"claim": "Q6 insulin secreting cells are beta cells and glucagon alpha cells - two distinct cell types",
   "code": "cells={'insulin':'beta','glucagon':'alpha'}; result = (cells['insulin']=='beta') and (cells['glucagon']=='alpha') and (cells['insulin']!=cells['glucagon'])"},
  {"claim": "Q2 mark allocation: 5 sub-cells at 1 mark each equals 5 marks",
   "code": "subcells=5; per=1; result = subcells*per==5"},
  {"claim": "Total paper marks sum to 40",
   "code": "marks=[4,5,4,4,5,5,4,4,3,2]; result = sum(marks)==40"},
  {"claim": "Q7 thyroid hormones both contain iodine; T4 has 4 and T3 has 3 iodine atoms",
   "code": "T4=4; T3=3; result = (T4==4) and (T3==3) and (T4>T3)"}
]