Chapter 20: Blood Vessels

What are the three main types of blood vessels and their functions

• Arteries: Carry blood away from the heart

• Capillaries: Allow exchange between blood and tissues

• Veins: Carry blood toward the heart

What are the three layers (tunics) of blood vessels

• Tunica intima – inner layer; contains endothelium

• Tunica media – middle layer; smooth muscle and elastic fibers

• Tunica externa – outer layer; collagen fibers

What are elastic arteries and their function?

Largest arteries (like the aorta); stretch and recoil to dampen blood pressure surges

What is the key feature of muscular arteries?

Thick tunica media and elastic laminae; distribute blood to organs

What controls the diameter of arterioles?

Local tissue factors and the autonomic nervous system

What are the main functions of capillaries in the body?

• Lungs: Exchange gases

• Intestines: Absorb nutrients

• Kidneys: Filter waste

• Glands: Pick up hormones

What do precapillary sphincters do?

Control blood flow into true capillaries

What are the 3 types of capillaries?

• Continuous: Least permeable; most common

• Fenestrated: Have pores; more permeable

• Sinusoid: Most permeable; found in liver, spleen, marrow

What are the 4 main routes molecules can pass through capillaries?

1. Direct diffusion (e.g., O₂, CO₂)

2. Intercellular clefts

3. Pinocytotic vesicles

4. Fenestrations (pores)

What makes the blood-brain barrier unique?

• Tight junctions only

• No intercellular clefts

• Selective transport

• Blocks most substances except O₂, CO₂, some anesthetics

How do veins differ from arteries?

• Lower blood pressure

• Thin walls

• Thick tunica externa

• Valves prevent backflow

• Rely on skeletal muscle pump

What is a vascular anastomosis?

Interconnection between vessels that provides alternate routes for blood flow

What is the function of the vasa vasorum?

Small vessels in large arteries that supply nutrients to their outer layers

What does the hepatic portal system do?

• Picks up nutrients from digestive organs

• Delivers them to the liver for processing

What are the two way fetal circulation happens

• placenta → umbilical vein: carries O2 rich blood → inferior vena cava

• Then both rich and poor O2 enter right atrium

  1. travels opening into foramen ovale (right atrium into left)

  2. right atrium to right ventricle to pulmonary artery into “ductless artosis”

What fetal structures close after birth?

• Foramen ovale → becomes fossa ovalis

• Ductus arteriosus → becomes ligamentum arteriosum

• Ductus venosus → becomes ligamentum venosum

What vein is commonly used in coronary bypass surgery?

The great saphenous vein from the leg

What is the goal of coronary bypass?

Reroute blood around a blocked coronary artery