Histology Guide

virtual microscopy laboratory

Chapter 9 - Cardiovascular System

The cardiovascular system transports blood to and from tissues. It is composed of the following structures:

HEART

The heart is the pump of the cardiovascular system. The contractile wall of the heart (myocardium) is composed of cardiac muscle cells.

BLOOD VESSELS

Blood vessels transport blood throughout the body. Arteries, arterioles, and capillaries carry blood away from the heart. Veins carry blood from the capillaries back towards the heart.

CAPILLARIES

Capillaries are the smallest blood vessels in the body. They are responsible for the exchange of gases, nutrients, and other substances between blood and tissues.

Continuous Capillaries

Continuous capillaries completely enclose the lumen of the blood vessel. Typically found in muscle, nerve, and connective tissue.

Pericytes are mesenchymal cells with long cytoplasmic processes that partly wrap around continuous capillaries. They are involved in blood flow, blood-brain barrier, angiogenesis, and muscle regeneration.

Fenestrated Capillaries

Fenestrated capillaries contain numerous small pores (or fenestrations) that make them far more permeable than continuous capillaries. Typically found in tissues involved in absorption (e.g., small intestine and kidneys) and some endocrine glands.

Sinusoidal Capillaries

Sinusoidal capillaries are larger than other capillaries and have a discontinuous endothelium. This allows easier movement of cells between the blood and tissues. Sinusoidal capillaries are found in a number of organs including the liver, spleen, and bone marrow.