2-Mark Question Answers

1. Nuclei Present in the Hypothalamus

• Supraoptic nucleus (produces ADH/vasopressin)
• Paraventricular nucleus (produces ADH and oxytocin)
• Anterior nucleus (thermoregulation - heat dissipation)
• Preoptic nucleus (temperature, sexual behavior)

• Ventromedial nucleus (satiety center)
• Dorsomedial nucleus (feeding behavior, aggression)
• Arcuate nucleus (releasing hormones - GHRH, dopamine)
• Lateral hypothalamic nucleus (hunger center)

• Posterior nucleus (heat conservation, consciousness)
• Mammillary nuclei - lateral and medial (relay hippocampal input via fornix to anterior thalamic nuclei; involved in memory)
• Supramammillary nucleus

The supraoptic and paraventricular nuclei are particularly important - they synthesize ADH and oxytocin, which are released from the posterior pituitary. (Guyton and Hall Textbook of Medical Physiology; Neuroanatomy through Clinical Cases 3rd Edition)

2. Major Salivary Glands

• Largest salivary glands; located anterior to the ear, overlying the masseter muscle
• Purely serous secretion (watery, enzyme-rich saliva)
• Duct: Stensen's duct opens into the oral cavity opposite the upper 2nd molar
• Contains the facial nerve (CN VII) running through it
• Contributes ~25% of total saliva

• Located in the floor of the mouth, in the submandibular triangle
• Mixed secretion (predominantly serous, some mucous)
• Duct: Wharton's duct opens at the sublingual caruncle beneath the tongue
• Contributes ~70% of total resting saliva
• CT attenuation is similar to muscle (more predictable than parotid)

• Smallest of the three; lie in the floor of the mouth beneath the tongue
• Predominantly mucous secretion
• Multiple small ducts (Rivinus' ducts), some opening via a common duct (Bartholin's duct) into Wharton's duct
• Contributes ~5% of total saliva

3. When Growth Hormone Levels Are Low or High

• In childhood: Growth failure - children are of normal size at birth but progressively fall behind peers. Results in pituitary dwarfism (adult height ~1.0 m in extreme cases).
• In adulthood: Decreased lean body mass, increased body fat, possibly reduced sense of well-being and vigor.
• GH-deficient adults respond to recombinant GH replacement with improved body composition.

• In childhood (before epiphyseal plate closure): Excessive linear bone growth → Gigantism (adult heights exceeding 2.7 m in extreme cases).
• In adulthood (after epiphyseal plate closure): Long bone elongation is not possible; instead, Acromegaly develops:
  • Progressive thickening of bones and soft tissues of the head, hands, and feet
  • Growth of skin, muscle, heart, liver, and GI tract
  • Causes joint deformity, hypertension, pulmonary insufficiency, and heart failure if untreated
  • Shorter life expectancy

GH is produced by somatotrophs in the anterior pituitary and acts mainly via IGF-1 (insulin-like growth factor 1) produced by the liver. (Medical Physiology, Boron & Boulpaep)

4. Labelled Diagram of Sperm

5. Brief Note on Estrogen

• Primarily produced by granulosa cells of ovarian follicles (via aromatization of androgens)
• Also produced by the corpus luteum, adrenal cortex, placenta (during pregnancy), and adipose tissue
• In males: small amounts from testicular Sertoli cells and peripheral aromatization

• Reproductive tract: Development and maintenance of female secondary sex characteristics; growth of uterus, vagina, fallopian tubes, and breast tissue
• Uterus: Proliferation of endometrium (proliferative phase); increases uterine contractility
• Cervix: Increases cervical mucus production and makes it thin/watery (favors sperm entry)
• Bone: Promotes epiphyseal closure; protects against bone resorption - estrogen deficiency at menopause leads to osteoporosis
• Cardiovascular: Favorable lipid profile (raises HDL, lowers LDL)
• CNS: Affects mood, cognition, and thermoregulation (loss causes hot flushes at menopause)
• Feedback: At low levels - negative feedback on FSH/LH; at high levels (pre-ovulatory surge) - positive feedback triggering the LH surge

6. Short Note on Spermatogenesis

1. Mitotic phase: Spermatogonia undergo repeated mitotic divisions to maintain the germ cell pool. Some differentiate into primary spermatocytes (diploid, 2n), the largest cells in the seminiferous tubules.
2. First meiotic division: Each primary spermatocyte undergoes meiosis I → two secondary spermatocytes (haploid, 1n, but each chromosome still consists of 2 chromatids).
3. Second meiotic division: Each secondary spermatocyte undergoes meiosis II → four spermatids (haploid, 1n). Each primary spermatocyte ultimately yields 4 spermatids.
4. Spermiogenesis: Spermatids undergo morphological transformation into mature spermatozoa (no further division):
   • Acrosome forms from the Golgi apparatus
   • Flagellum develops
   • Most cytoplasm is shed as residual bodies
   • Nucleus condenses

• Sertoli cells: Nurture developing germ cells; blood-testis barrier; secrete inhibin and androgen-binding protein
• Leydig (interstitial) cells: Produce testosterone (essential for spermatogenesis)

7. BMR - Definition and Factors Affecting It

8. Functions of the Pineal Gland and Thymus

Pineal Gland

• Circadian rhythm regulation: Melatonin production increases in darkness and is suppressed by light (via the retinohypothalamic tract → suprachiasmatic nucleus → superior cervical ganglion → pineal gland). This creates a daily rhythmic signal that helps entrain the sleep-wake cycle.
• Seasonal rhythm and reproduction: In many animals, melatonin signals day length and regulates seasonal reproductive cycles. In humans, the role is less prominent but similar mechanisms exist.
• Onset of puberty: The pineal is thought to inhibit the hypothalamic-pituitary-gonadal axis prior to puberty; declining melatonin influence may contribute to puberty initiation.
• Antioxidant: Melatonin has free-radical scavenging properties.

Thymus

• T-lymphocyte maturation: The primary function. Immature T-cell precursors (thymocytes) migrate from the bone marrow to the thymus, where they mature and acquire antigen specificity in the thymic cortex, then undergo positive selection (recognize self-MHC) and negative selection (eliminate self-reactive clones) in the medulla.
• Central tolerance: Medullary thymic epithelial cells express self-antigens (via AIRE gene), ensuring autoreactive T-cells are deleted - preventing autoimmunity.
• Endocrine function: Produces thymic hormones - thymosin, thymopoietin, thymulin - which promote T-cell differentiation and maturation both within and outside the thymus.
• Immunological development: Produces a pool of naive T-cells (CD4+ helper and CD8+ cytotoxic) that seed peripheral lymphoid organs for lifelong immune surveillance.

DiGeorge syndrome (22q11 deletion) results in thymic aplasia with deficient T-cell immunity, illustrating the organ's importance.