Histology of the Circulatory System Flashcards
What are the 3 types of blood vessels?
- Arteries
- Veins
- Capillaries
What are the 4 types of arteries?
- Large artery
- Medium artery
- Small artery
- Arteriole
What are the 4 types of veins?
- Large vein
- Medium vein
- Small vein
- Venule
What are the 3 types of capillaries?
- Continuous
- Fenestrated
- Discontinuous
What are the three layers of blood vessels?
- Tunica intima (innermost)
- Tunica media
- Tunica adventitia (outermost)
What are the layers of the tunica intima?
- Endothelium
- Subendothelium
- Internal elastic lamina (IEL) - in arteries only
What are the layers of the tunica media?
- Smooth muscle layer
2. External elastic lamina (EEL) - in large/medium arteries only
What are the layers of the tunica adventitia?
- Connective tissue and fibroblasts
- Longitudinal smooth muscles - in veins only
- Vasovasorum - in large vessels only (small vessels supplying oxygen and nutrients to the external layers of a vessel)
The endothelium is composed of a single layer of ___ cells.
Squamous
How are small arteries different from medium arteries?
Smaller diameter, no external elastic lamina, fewer layers of smooth muscle cells
How many layers of smooth muscle cells are seen in arterioles?
1-2
What is not seen in arterioles?
Both layers of elastic lamina and subendothelial layers
Describe the tunica media in each of the 4 types of arteries.
- Large arteries: smooth muscle cells, lots of elastic fibers
- Medium arteries: multiple layers of smooth muscle cells (6-40)
- 2-6 layers of smooth muscle
- Arterioles: 1-2 layers of smooth muscle
What is the function of large arteries?
Conduct blood to the heart, accommodate pressure changes, maintain continuous blood flow during diastole
What is the function of medium arteries?
Distributing blood
What is the function of small arteries?
Control and modulation of blood pressure
What is the function of arterioles?
Control blood flow to capillaries, regulate blood pressure
What are examples of large arteries?
Aorta and its branches (subclavian, carotid, iliac)
What are examples of medium arteries?
Coronary, renal
What are the smallest vessels and what is there function?
Capillaries; connect arterioles and venules
Capillaries have ___ layer(s) of endothelial cells with a basal lamina.
1
What is the difference between fenestrated and discontinuous capillaries?
Fenestrated: have holes/pores in the endothelial layer
Discontinuous: have holes in the endothelial layer and basal lamina
What is the difference between venules and small veins?
Small veins: slightly larger lumen, more visible smooth muscle layer
Venules: small lumens, thin walls, only one layer of endothelium; also have surrounding connective tissue
What is unique about the tunica adventitia in a vein?
It is very wide (as opposed to the tunica media being the widest part of an artery)
How are smooth muscles organized in medium veins?
Into bundles
What are valves?
Folds in the intima seen in media and large veins, also in lymphatics
The number of valves ___ with the size of the vessel.
Increase
What is the function of valves?
Prevent backflow of blood
Compare the lumen of arteries and veins.
Arteries: smaller, rounder, prominent internal elastic lamina
Veins: larger, flatter
Compare the tunica media and adventitia in arteries and veins.
Arteries: media thicker than adventitia
Veins: adventitia thicker than media + longitudinal smooth muscle bundles
Which vessels have valves?
Veins (not arteries)
What is the purpose of the lymphatic system?
Collect and drain interstitial fluid from the tissues
