Chapter 9 - Cardiovascular System
The cardiovascular system transports blood to and from tissues. It is composed of the following structures:
- Heart - pumps blood through the system
- Arteries - vessels that deliver blood to tissues
- Capillaries - network of vessels to perfuse tissues
- Veins - vessels that return blood to the heart
The heart is the pump of the cardiovascular system.
The contractile wall of the heart (myocardium) is composed of cardiac muscle cells.
Myocardium is the muscular middle layer of the wall of the heart. It is composed of cardiac muscle cells.
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 are the smallest blood vessels in the body. They are responsible for the exchange of gases, nutrients, and other substances between blood and tissues.
Three types of capillaries can be distinguished:
- Continuous capillaries - continuous endothelium and basement membrane
- Fenestrated capillaries - endothelial cells contain small, 80 to 100 nm pores called fenestrations (typically with thin diaphragms)
- Sinusoidal capillaries - discontinuous endothelium and incomplete basement membrane
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 the control of blood flow, blood-brain barrier, angiogenesis, and muscle regeneration.
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 are larger than other capillaries and have a discontinuous endothelium. This allows easier movement of cells and serum proteins between blood and tissues. Sinusoidal capillaries are found in a number of organs including the liver, spleen, and bone marrow.