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Gazi Medical College — 2nd Term Final Anatomy (SAQ) — Full Answers

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Q1 (SEQ) — Option A

a) Stages of Neural Tube Formation (with diagram)

1. Induction of neural plate (Day 18): Notochord induces overlying ectoderm → neural plate forms.
2. Neural plate shaping: Cells elongate and narrow → plate narrows and elongates.
3. Neural folding (Day 20–22): Lateral edges elevate as neural folds; a midline groove (neural groove) forms.
4. Neural fold fusion (Day 22–23): Folds converge and fuse at the dorsal midline, beginning in the cervical region and zipping cranially and caudally.
5. Neural tube closure: Cranial neuropore closes ~Day 25; caudal neuropore closes ~Day 27. The tube separates from surface ectoderm.

Neural Plate       Neural Groove         Neural Tube
  ___________        __   __              [_______]
 |___________|  →   |  | |  |    →        (closed)
  (flat ecto)       Neural folds        Neural crest cells
                                          migrate laterally

b) Two Derivatives of the Neural Tube

c) Two Neural Tube Defects with Cause

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Q1 — Option B (OR questions)

a) General Plan of Histological Structure of GIT (with diagram)

1. Mucosa — innermost; has 3 sub-layers:
   • Epithelium (lines lumen)
   • Lamina propria (loose CT, glands, lymphatics)
   • Muscularis mucosae (thin smooth muscle)
2. Submucosa — dense irregular CT; contains Meissner's (submucosal) nerve plexus, blood vessels
3. Muscularis externa — 2 smooth muscle layers:
   • Inner circular
   • Outer longitudinal
   • Auerbach's (myenteric) plexus between them
4. Serosa/Adventitia — outermost; serosa = mesothelium + CT (intraperitoneal), adventitia = CT only (retroperitoneal)

  Lumen
  |——— Epithelium          ←┐
  |——— Lamina propria       ├ MUCOSA
  |——— Muscularis mucosae  ←┘
  |——— SUBMUCOSA (Meissner's plexus)
  |——— Circular muscle     ←┐ MUSCULARIS
  |——— Auerbach's plexus    ├ EXTERNA
  |——— Longitudinal muscle ←┘
  |——— SEROSA/ADVENTITIA

b) Cells of Gastric Glands with Function

c) Histological Structure of Villi (with diagram)

• Epithelium: Simple columnar cells (enterocytes) with microvilli (brush border); goblet cells interspersed
• Lamina propria core: Loose CT, smooth muscle fibers, lymphocytes, plasma cells
• Central lacteal: Blind-ending lymphatic capillary (absorbs fat)
• Blood capillaries: Absorb amino acids, sugars
• Nerve fibers

       |  |  | ← Microvilli (brush border)
  Enterocytes (columnar)
  Goblet cells
  |—— Lamina propria ——|
  |  Central lacteal   |
  |  Blood capillaries |
  |——————————————————|

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Q2 — Problem Based Question

a) Birth Defect Most Likely Present

b) Embryological Basis

• The esophagus and trachea both develop from the foregut.
• Normally, the tracheoesophageal septum (lateral ridges) divides the foregut into the ventral trachea and dorsal esophagus between weeks 4–5.
• Failure of this septum to form properly → esophageal atresia ± TEF.
• Polyhydramnios occurs because the fetus cannot swallow amniotic fluid (blocked by the atretic esophagus), so fluid accumulates.

c) Other Birth Defects to Examine For — and Why

• Vertebral anomalies
• Anal atresia
• Cardiac defects
• TE — Tracheo-Esophageal fistula
• Renal anomalies
• Limb defects

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Q3 — Draw & Label

a) Histological Structure of Spleen

• Capsule: Dense fibrous + smooth muscle; trabeculae extend inward
• White pulp: Lymphoid tissue; periarteriolar lymphoid sheath (PALS) around central artery (T cells); lymphoid follicles (B cells) with germinal centers
• Marginal zone: Between white and red pulp
• Red pulp: Splenic sinusoids + splenic cords (of Billroth) — filters blood, removes old RBCs

Capsule
 └── Trabecula
      └── White pulp:
           - Central artery
           - PALS (T cells)
           - Lymphoid follicle (B cells)
      └── Marginal zone
      └── Red pulp:
           - Splenic sinusoids
           - Splenic cords

b) Histological Structure of Testis

• Tunica albuginea: Thick fibrous capsule → septa divide testis into ~250 lobules
• Seminiferous tubules: Site of spermatogenesis
  • Sertoli cells: Supporting cells; blood-testis barrier; secrete inhibin
  • Spermatogenic cells: Spermatogonia → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa
• Interstitium (between tubules): Loose CT + Leydig (interstitial) cells → secrete testosterone

Tunica albuginea
└── Lobule
     └── Seminiferous tubule:
          - Spermatogonia (base)
          - Primary spermatocytes
          - Secondary spermatocytes
          - Spermatids
          - Sertoli cells
     └── Interstitium:
          - Leydig cells (testosterone)
          - Blood/lymph vessels

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Q4 — Two Differentiating Points (Any Two)

a) Upper Limb vs Lower Limb Development

b) Serous vs Mucous Acini (Histologically)

c) Gastroschisis vs Omphalocele

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Q5 — Classify

a) Blood Capillaries with Example

b) Organizers (Embryological) with Example

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Q6

a) Developmental Source of Excretory Part of Kidney (3 marks)

1. Ureteric bud (from mesonephric/Wolffian duct):
   • Forms: ureter, renal pelvis, major & minor calyces, collecting ducts
2. Metanephric mesoderm (metanephric blastema):
   • Induced by ureteric bud → forms nephrons (excretory units):
     • Glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule
   • This is the excretory part — derived from intermediate mesoderm (metanephric mesenchyme)

b) Congenital Anomalies of Uterus (2 marks)

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Q7

a) Neural Crest Cell Migration Failure → Congenital Heart Anomalies (3 marks)

• Pharyngeal arches (3rd, 4th, 6th)
• Outflow tract of the heart (truncus arteriosus, conus cordis)

• Septation of the truncus arteriosus into aorta and pulmonary trunk
• Formation of aorticopulmonary septum
• Development of semilunar valves and smooth muscle of great vessels

b) Structure-Function Relationship of Macrophage in Liver (Kupffer Cells) (2 marks)

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