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Pathology Mini-Lesson: Structure and Function of Circulatory Vessels
November 14, 2025
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The circulatory system constitutes the central hub sustaining human life activities. Vessels, functioning as the “pipeline network” for blood transport, are anatomically and functionally classified into arteries, veins and capillaries. Their morphological traits are highly adapted to physiological demands, jointly guaranteeing systemic material exchange and metabolic homeostasis.
I. Basic Vascular Wall Architecture
Arterial and venous walls conform to a tunica intima–media–adventitia trilaminar pattern from inner to outer aspect. Capillaries, specialized for exchange, display a simplified architecture.
- Tunica intima: Innermost layer composed of endothelial cells (ECs), sub-endothelial connective tissue and the internal elastic lamina (IEL). ECs present a non-thrombogenic luminal surface enriched in plasmalemmal vesicles and Weibel-Palade bodies, minimizing frictional resistance; the IEL, constructed of elastin, demarcates the intima–media boundary.
- Tunica media: Functional core whose composition varies by vessel type. In elastic arteries the media contains concentric elastic lamellae; in muscular arteries it is dominated by circumferentially oriented vascular smooth-muscle cells (VSMCs). Venous media is comparatively thin with sparse VSMCs.
- Tunica adventitia: Outermost layer of loose connective tissue rich in collagen fibres, fibroblasts and vasa vasorum. An external elastic lamina may be present, providing tensile strength and structural support.
II. Arterial Classification and Structural–Functional Specialization
Arteries convey blood from the ventricles to peripheral tissues and are hierarchically categorized into four caliber-based classes that sequentially accomplish “pressure buffering – distribution – micro-regulation”.
- Large (elastic) arteries: Caliber > 10 mm; thickest media with 40–70 elastic lamellae that transform intermittent cardiac ejection into continuous flow and maintain diastolic pressure.
- Medium (muscular) arteries: Caliber 1–10 mm; prominent IEL and EEL; media contains 10–40 VSMC layers enabling active regulation of organ perfusion.
- Small arteries: Caliber 0.3–1 mm; distinct IEL; 3–9 VSMC layers; principal determinants of systemic vascular resistance.
- Arterioles: Caliber < 0.3 mm; 1–2 VSMC layers; devoid of IEL/EEL; finely control local blood flow and contribute to blood-pressure homeostasis.
III. Capillary Structure and Subtypes
Capillaries constitute the primary interface for blood–tissue exchange. Luminal diameter 6–8 µm; wall formed by 1–3 overlapping ECs supported by a basal lamina and pericytes.
- Continuous capillaries: ECs joined by tight junctions, intact basal lamina, abundant pinocytotic vesicles; low permeability; found in muscle, lung, connective tissue.
- Fenestrated capillaries: ECs perforated by transcellular fenestrae (60–80 nm) bridged by a diaphragm; continuous basal lamina; high permeability; located in renal glomeruli, endocrine glands, intestinal villi.
- Sinusoids (discontinuous capillaries): Irregularly enlarged lumen, discontinuous ECs with wide intercellular gaps, incomplete basal lamina; highest permeability; present in liver, spleen, bone marrow.
IV. Venous Classification and Structural–Functional Characteristics
Veins return blood to the heart and exhibit “wide lumen, thin wall, loose architecture, valves present” relative to corresponding arteries.
- Categories: Post-capillary venules → small veins → medium veins → large veins; caliber progressively increases while wall thickness remains modest.
- Structural hallmarks: Large irregular lumen; indistinct trilaminar boundaries; thin media with sparse VSMCs and poor elasticity; thick adventitia rich in collagen; venous valves (especially limbs) prevent retrograde flow.
- Functional adaptation: Low elasticity and high capacitance enable veins to accommodate 60–70 % of total blood volume (“venous reservoir”); skeletal-muscle pump and respiratory pump assist venous return.
Fig: Venule Fig. 9: Small vein Fig. 10: Medium vein Fig. 11: Large vein
V. Functional Synergy of the Vascular System
Arterial “pressure propulsion”, capillary “exchange interface” and venous “return & reservoir” form a closed loop: cardiac output is distributed via arteries, material exchange (O₂, nutrients, metabolites) occurs in capillaries, and veins collect blood back to the heart, ensuring organ homeostasis.
Core mIHC Panel for Vascular Assessment
1. Vascular Structure Markers
| Marker | Abbreviation | Biological significance | Application |
|---|---|---|---|
| CD31 | CD31 | Pan-endothelial marker; evaluates vessel density, distribution, integrity | Tumor angiogenesis, vascular remodelling in CVD |
| Vascular endothelial cadherin | VE-cadherin | Endothelial adherens junctions; reflects barrier function | Vascular permeability, normalization studies |
| Endoglin | CD105 | Proliferating EC marker; indicates active neovessels | Breast-cancer MVD, neo-angiogenesis detection |
| Neuron-glial antigen 2 | NG2 | Pericyte marker; reflects vessel maturity | Vascular normalization, collateral assessment |
| Collagen IV | Col-IV | Basement-membrane component; structural integrity | Aberrant tumor vessels, remodelling analysis |
| α-smooth-muscle actin | α-SMA | VSMC & pericyte contractility; vessel maturity | Maturation scoring, wall architecture |
2. Angiogenesis Regulators
| Marker | Abbreviation | Biological significance | Application |
|---|---|---|---|
| Vascular endothelial growth factor | VEGF | Angiogenic activity; therapy response | Anti-angiogenic therapy monitoring |
| Angiopoietin-1/2 | Ang-1/2 | Ang-1/Ang-2 ratio indicates vessel stability | Angiogenesis mechanism, repair assessment |
| Hypoxia-inducible factor-1α | HIF-1α | Hypoxic niches; links angiogenesis & immunity | Glioma hypoxic-zone vascular mapping |
| Glucose transporter 1 | GLUT1 | Hypoxic burden; correlates with grade & density | Glioma progression, hypoxia-driven aberrancy |
3. Vascular Function & Quantitative Indices
| Parameter | Abbreviation | Biological significance | Application |
|---|---|---|---|
| Micro-vessel density | MVD | Quantifies vascular abundance; key prognostic index | Breast-cancer prognosis, collateral evaluation |
| Endothelial/pericyte ratio | CD31⁺/NG2⁺ | Reflects vascular normalization | Peri-operative therapy monitoring |
| Functional/non-functional vessel ratio | - | Discriminates perfused vs non-perfused vessels | Tumor vascular efficacy, ischaemic zones |
| Micro-vascular morphometry | - | Mean diameter, perimeter, total length; structural anomaly | Tumor vascular malformation, remodelling |
4. Vascular–Immune Interface Markers
| Marker | Abbreviation | Biological significance | Application |
|---|---|---|---|
| Vessel / cytotoxic T-cell co-localization | CD31⁺/CD8⁺ | Immune-infiltration efficiency | Tumor immuno-vascular crosstalk |
| Vessel / TAM co-localization | CD31⁺/CD68⁺ | Immunosuppressive micro-environment | Glioma hypoxic niche interactions |
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Item NO. |
Product Name |
Size |
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Absin 4-Color IHC Kit (Anti-Rabbit and Mouse Secondary Antibody) |
20T/100T |
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Absin 4-Color IHC Kit(Anti-Rabbit Secondary Antibody) |
20T/100T |
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Absin 5-Color IHC Kit (Anti-Rabbit and Mouse Secondary Antibody) |
20T/100T |
|
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Absin 5-Color IHC Kit (Anti-Rabbit Secondary Antibody) |
20T/100T |
|
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Absin 6-Color IHC Kit (Anti-Rabbit and Mouse Secondary Antibody) |
20T/100T |
|
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Absin 6-Color IHC Kit (Anti-Rabbit Secondary Antibody) |
20T/100T |
|
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Absin 7-Color IHC Kit (Anti-Rabbit and Mouse Secondary Antibody) |
20T/100T |
|
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Absin 7-Color IHC Kit(Anti-Rabbit Secondary Antibody) |
20T/100T |
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Antibody eluent (for mIHC) |
30ml |
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Absin Bioscience Inc. |
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