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AN69.1-3 | Blood Vessels — Gate Quiz
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The innermost layer of a blood vessel wall, consisting of a single layer of endothelial cells lining the lumen, is called the:
Correct! The tunica intima (interna) is the innermost layer, comprising the endothelium, subendothelial connective tissue, and the internal elastic lamina.
The three tunics from lumen outward: intima → media → adventitia. The endothelium is always the first cell layer the blood contacts.
Incorrect. The innermost layer is the tunica intima. Tunica media is the middle layer (smooth muscle); tunica adventitia is the outermost layer.
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A histology slide shows a large artery with 50 concentric fenestrated elastic lamellae in its wall. The vessel wall stores elastic energy during systole and releases it during diastole. Which artery is most likely depicted?
Correct! The thoracic aorta is the classic elastic (conducting) artery with 40–70 elastic lamellae in the tunica media. This structure enables the Windkessel effect — storing energy during systole and maintaining flow during diastole.
Elastic arteries (aorta, pulmonary trunk, brachiocephalic, common carotid) have multiple elastic lamellae in media. Muscular arteries have a prominent internal + external elastic lamina with 10–40 layers of smooth muscle in the media.
Incorrect. Femoral, radial, and renal arteries are muscular arteries with a prominent internal elastic lamina but few medial elastic sheets. The aorta has numerous lamellae.
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Under the light microscope, a vessel shows a prominent wavy internal elastic lamina, a thick tunica media with circularly arranged smooth muscle cells (15 layers), and a well-developed adventitia with a faint external elastic lamina. What type of vessel is this?
Correct! The prominent internal elastic lamina plus thick smooth muscle media (10–40 layers) plus external elastic lamina identifies this as a muscular (distributing) artery.
Identification hierarchy: See two distinct elastic lines (IEL + EEL) sandwiching smooth muscle → muscular artery. See many elastic lamellae (>10) in media → elastic artery. Thin wall, large lumen, no elastic lines → vein. Tiny, 1–3 smooth muscle layers → arteriole.
Incorrect. The key features of a muscular artery are: (1) prominent internal elastic lamina as a wavy line, (2) 10–40 layers of smooth muscle in the media, (3) a fainter external elastic lamina.
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Weibel-Palade bodies are specific ultrastructural organelles of endothelial cells that store von Willebrand factor. Their release is stimulated by thrombin during vascular injury. In which tissue layer are these organelles found?
Correct! Weibel-Palade bodies are found in endothelial cells, which form the tunica intima. They are released when endothelium is activated (injury, inflammation), increasing local coagulation and leukocyte adhesion.
Weibel-Palade bodies are pathognomonic ultrastructural markers of endothelial cells. They contain von Willebrand factor (promotes platelet adhesion at injury sites) and P-selectin (mediates early leukocyte rolling). Von Willebrand disease results from deficiency of this stored factor.
Incorrect. Weibel-Palade bodies are endothelial organelles, and endothelial cells line the tunica intima (innermost layer).
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A medical student examining a liver biopsy under electron microscopy notes that the sinusoidal endothelial cells have large gaps between them and the basement membrane is discontinuous. This structural feature primarily facilitates:
Correct! Sinusoidal capillaries (liver, spleen, bone marrow) have large inter-endothelial gaps and incomplete basement membrane, allowing plasma proteins, lipoproteins (chylomicrons), and even cells (blood cell precursors in bone marrow) to pass freely between the vascular and tissue compartments.
Three capillary types: (1) Continuous — tight junctions; BBB, muscle, lung. (2) Fenestrated — pores with diaphragms; kidney, gut, endocrine glands. (3) Sinusoidal — large gaps, incomplete BM; liver, spleen, bone marrow.
Incorrect. The blood-brain barrier relies on continuous capillaries with tight junctions. Glomerular filtration uses fenestrated capillaries. Platelet aggregation prevention is a function of intact endothelium. Sinusoids allow large-molecule exchange.
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Compared to an artery of similar external diameter, a vein on a histology slide would characteristically show:
Correct! Veins have a larger lumen, thinner wall, and less organised layers compared to arteries of the same external diameter. The tunica media of veins is poorly developed with sparse smooth muscle, and no distinct internal elastic lamina is visible.
Artery vs vein comparison: Artery = thick wall, small rounded lumen, visible IEL, prominent media. Vein = thin wall, large irregular collapsed lumen, no IEL, sparse media. On a slide, arteries are often found alongside veins (vascular bundle) — they contrast clearly.
Incorrect. Veins have thinner walls and poorly developed tunics compared to arteries. The distinguishing features are: large lumen, thin collapsed wall, absent or minimal internal elastic lamina.
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A 55-year-old diabetic patient from Chennai with longstanding poorly controlled diabetes presents with progressive kidney failure. Electron microscopy of the glomerular basement membrane shows uniform thickening. The primary ultrastructural component responsible for this barrier is:
Correct! Type IV collagen is the major structural component of the basement membrane (basal lamina). In diabetic nephropathy, non-enzymatic glycosylation of type IV collagen and related matrix proteins causes thickening and loss of charge selectivity of the glomerular basement membrane.
Basement membrane composition: Type IV collagen (structural network) + laminin (cell adhesion) + heparan sulphate proteoglycans (charge barrier, esp. important in glomerulus). Thickened basement membrane in diabetes is a hallmark of diabetic microangiopathy in retina, kidney, and peripheral nerves.
Incorrect. The basement membrane scaffold is built on type IV collagen (not type I, which is found in tendons and skin). Fibrillin is in elastic fibres; elastin is the elastic fibre core protein.
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During a practical class in Puducherry, a student examines a slide and identifies a very small vessel (approximately 30 µm diameter) with an endothelial lining and only 2 layers of smooth muscle cells in its wall. No elastic lamina is visible. This vessel is best identified as:
Correct! Arterioles (10–100 µm diameter) have 1–3 layers of smooth muscle in the tunica media with a very thin or absent internal elastic lamina. They are the primary resistance vessels regulating blood pressure.
Arteriole identification: small diameter + visible smooth muscle (1–3 layers) + endothelium + absent or minimal IEL. Arterioles are critical resistance vessels — their contraction raises blood pressure; their dilation lowers it.
Incorrect. Capillaries have NO smooth muscle (endothelium + basement membrane only). Venules have pericytes but no smooth muscle in the smallest ones. Small veins have thin walls but a larger lumen. Arterioles are defined by 1–3 smooth muscle layers.
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Vasa vasorum are small blood vessels found in the walls of large arteries. They are primarily located in which layer of the vessel wall?
Correct! Vasa vasorum ("vessels of the vessels") run in the tunica adventitia and penetrate the outer portion of the tunica media. The inner media and intima receive oxygen and nutrients by direct diffusion from the lumen — no vasa vasorum are needed there.
Vasa vasorum are seen in elastic arteries (aorta) and large veins. Atherosclerotic plaques can occlude vasa vasorum, contributing to medial ischaemia. This weakens the wall, predisposing to aneurysm formation.
Incorrect. Vasa vasorum supply the outer wall of large vessels (adventitia + outer media). The intima and inner media are thin enough to be nourished by diffusion from the lumen.
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The blood-brain barrier in the central nervous system is maintained by continuous capillaries with specialised tight junctions (zonula occludens) between endothelial cells. Which of the following would most directly disrupt this barrier?
Correct! The blood-brain barrier depends on tight junctions (zonula occludens) between brain capillary endothelial cells. Pro-inflammatory cytokines (TNF-α, IL-1β) downregulate tight junction proteins (claudins, occludins), causing BBB breakdown in conditions such as meningitis, multiple sclerosis, and septic encephalopathy.
BBB elements: (1) Tight junctions between endothelial cells (primary barrier), (2) Astrocyte end-feet (induction and maintenance), (3) Pericytes (regulation). Breakdown occurs in CNS infections, ischaemia, autoimmune diseases — allowing edema, leukocyte entry, and protein leak into brain parenchyma.
Incorrect. The BBB is structurally maintained by tight junctions. Basement membrane thickening affects kidney; vasa vasorum are in large vessel walls; pericyte contractility affects flow but not junction integrity.
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