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
HEART
The heart is the pump of the cardiovascular system.
The endocardium lines the chambers and valves of the heart.
The contractile wall of the heart (myocardium) is composed of branching cardiac muscle cells with a single, centrally located nucleus, and show the same striations as skeletal muscle.
Cardiac muscle cells are joined by specialized structures known as intercalated discs . These discs are unique to cardiac tissue and help maintain strong mechanical connections and pass electrical impulses between 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.
Three types of capillaries can be distinguished:
- Continuous capillaries - continuous endothelium and basement membrane
-
Fenestrated capillaries
- endothelial cells contain fenestrations, or pores, 80 to 100 nm in diameter (typically with thin diaphragms)
- Rapid bidirectional movement of hormones, nutrients, and small molecules while preventing cellular passage
-
Sinusoidal capillaries
- discontinuous endothelium and incomplete basement membrane
- Facilitate the movement of cells, such as blood cells entering or leaving the circulation
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 the control of blood flow, blood-brain barrier, angiogenesis, and muscle regeneration.
Fenestrated Capillaries
Fenestrated capillaries are typically found in organs involved in filtration, secretion, or absorption of molecules - including endocrine glands, the kidneys, and the intestinal villi. The pores increase permeability compared to continuous capillaries.
Sinusoidal Capillaries
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.
