pt3: capillaries & veins- structure, funtion and flow

What are capillaries and what is their main role in circulation?

the smallest blood vessels, consisting of a single layer of endothelial cells.

Their primary function is to facilitate exchange of gases, nutrients, and waste between blood and tissues.

Name and describe the three structural types of capillaries.

• Continuous capillaries: tight junctions; found in skin, muscle, CNS

• Fenestrated capillaries: pores for filtration; found in kidneys, intestines

• Sinusoidal capillaries: large gaps; found in liver, bone marrow, spleen

Describe the path and regulation of blood flow in capillary beds.

Blood enters via arterioles, passes through capillary beds, and exits via venules. Flow is regulated by precapillary sphincters, which open or close to control perfusion.

What are venules and how do they function in circulation?

small vessels that collect blood from capillaries and begin the return journey to the heart. They gradually transition into larger veins.

What defines a vein and how is its structure adapted to its function?

Veins carry blood toward the heart, usually deoxygenated. They have:

• Thinner walls than arteries

• Larger lumens

• Valves to prevent backflow

• Low pressure, requiring external assistance for blood return

How does blood return to the heart through veins despite low pressure?

• Skeletal muscle pump: muscle contractions squeeze veins

• Respiratory pump: thoracic pressure changes during breathing

• Venous valves: ensure one-way flow

Compare the roles of arteries, capillaries, and veins.

• Arteries: pressure vessels; distribute oxygenated blood

• Capillaries: exchange vessels; site of nutrient/gas transfer

• Veins: volume reservoirs; return deoxygenated blood to heart

Name two common venous disorders.

• Varicose veins: valve failure leads to blood pooling

• Deep vein thrombosis (DVT): clot formation in deep veins, risk of embolism

What structural features make capillaries efficient for exchange?

• Thin walls (single endothelial layer)

• Small diameter slows blood flow

• Close proximity to tissues for diffusion

Trace the flow of blood from arteries to veins.

Arteries → Arterioles → Capillaries → Venules → Veins → Heart