Human Anatomy
Blood Vessels Histology
Blood vessel histology for MBBS: tunica layers, elastic and muscular arteries, capillary types and veins, mapped to NMC codes AN69.1 to AN69.3.
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Blood Vessels Histology
Blood vessel histology for MBBS: tunica layers, elastic and muscular arteries, capillary types and veins, mapped to NMC codes AN69.1 to AN69.3.
This chapter describes the three-layered wall of blood vessels and classifies arteries, capillaries and veins by their microscopic structure. It correlates each type with its role in conducting, distributing and exchanging blood.
High-yield: Blood Vessels Histology
- The walls of arteries and veins have three coats: the tunica intima, tunica media and tunica adventitia.
- The tunica intima is lined by endothelium resting on a thin subendothelial layer.
- The tunica media contains smooth muscle and elastic fibres and is the thickest coat of arteries.
- The tunica adventitia is connective tissue and carries the vasa vasorum that nourish the outer wall.
- Elastic or conducting arteries, such as the aorta, have abundant elastic laminae in the media to smooth pulsatile flow.
- Muscular or distributing arteries have a media rich in smooth muscle and a prominent internal elastic lamina.
- Arterioles regulate blood pressure and control flow into the capillary beds through their smooth muscle.
- Capillaries have only an endothelium and basement membrane and are the site of exchange.
- Continuous capillaries are found in muscle and the nervous system, with tight endothelial junctions.
- Fenestrated capillaries, with pores, occur in the kidney glomerulus, gut and endocrine glands.
- Sinusoidal capillaries are wide and leaky and are found in the liver, spleen and bone marrow.
- Veins have a thinner media and a wider lumen than the accompanying arteries.
- Many veins, especially in the limbs, have valves that prevent backflow of blood.
- The internal elastic lamina lies between the intima and media and is prominent in muscular arteries.
- The external elastic lamina lies between the media and adventitia in larger muscular arteries.
Vessel types under the microscope
- **Elastic artery:** Aorta and large arteries. Media rich in elastic laminae; smooths pulsatile flow.
- **Muscular artery:** Named distributing arteries. Media rich in smooth muscle; prominent internal elastic lamina.
- **Capillary:** Endothelium and basement membrane only. Continuous, fenestrated or sinusoidal types.
- **Vein:** Thin media, wide lumen; limb veins carry valves preventing backflow.
NMC competencies in this chapter
- **AN69.1:** Identification of elastic and muscular vessels and capillaries under the microscope
- **AN69.2:** Types and structure-function correlation of blood vessels
- **AN69.3:** Ultrastructure of blood vessels
Frequently Asked Questions
What are the three coats of a blood vessel?
The tunica intima with its endothelium, the tunica media with smooth muscle and elastic tissue, and the tunica adventitia of connective tissue carrying the vasa vasorum.
How do elastic and muscular arteries differ?
Elastic arteries such as the aorta have a media full of elastic laminae to buffer the pulse, while muscular arteries have a media dominated by smooth muscle with a prominent internal elastic lamina to distribute blood.
What are the three types of capillary?
Continuous capillaries with tight junctions in muscle and nerve, fenestrated capillaries with pores in the kidney and gut, and sinusoidal capillaries that are wide and leaky in the liver, spleen and bone marrow.
Why do many veins have valves?
Venous pressure is low, so valves prevent the backflow of blood and, with the pumping action of surrounding muscles, help return blood towards the heart against gravity.
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