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Questions and Answers
What is the primary function of the circulatory system?
Which of the following blood vessels is responsible for carrying blood away from the heart?
What is the location of exchange between blood and interstitial fluid?
What is the outermost layer of the blood vessel wall?
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What is the layer of elastic fibers in the outer margin of the tunica intima called?
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What separates the tunica media from the tunica externa in some vessels?
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What is the layer of the blood vessel wall that contains concentric sheets of smooth muscle?
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What is the circulatory system composed of?
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What is the main function of postcapillary venules and muscular venules?
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Which of the following is a characteristic of medium-sized veins?
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What is the primary function of vein valves?
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What is a characteristic of large veins?
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What is a key difference between arteries and veins?
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What is a characteristic of the lumen of a collapsed artery?
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What is a characteristic of muscular venules?
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Which of the following is a characteristic of both arteries and veins?
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What is the main component of the tunica externa in large arteries and veins?
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What is the function of the vasa vasorum?
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What is a characteristic of capillaries?
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What type of capillary is found in the CNS and thymus?
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What is the function of fenestrated capillaries?
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What is a characteristic of sinusoids?
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What is the function of arteriovenous anastomoses?
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What is a characteristic of elastic arteries?
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What is a characteristic of muscular arteries?
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What is the function of veins?
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Study Notes
The Circulatory System
- The circulatory system is a transport system that carries blood and lymph to and from the tissues of the body.
- The circulatory system consists of the cardiovascular system and the lymphatic system.
Cardiovascular System
- The cardiovascular system includes the heart and vessels.
- The cardiovascular system is composed of two main parts: macrovasculature (>0.1mm) and microvasculature (interchanges).
Blood Vessels
- There are five classes of blood vessels:
- Arteries: carry blood away from the heart.
- Arterioles: smallest branches of arteries.
- Capillaries: smallest blood vessels, location of exchange between blood and interstitial fluid.
- Venules: collect blood from capillaries.
- Veins: return blood to the heart.
Structure of Blood Vessels
- The wall of blood vessels is composed of three layers called tunics:
- Tunica intima: innermost layer, includes endothelial lining and connective tissue layer.
- Tunica media: middle layer, contains smooth muscle and elastic fibers.
- Tunica externa: outer layer, contains connective tissue and elastic fibers.
Capillaries
- Capillaries are the smallest blood vessels.
- They have small diameter and thin walls.
- Chemicals and gases diffuse across walls.
- No tunica media and externa.
- Endothelial cell inside thin basal lamina and pericytes.
- There are three types of capillaries:
- Continuous capillaries: have complete endothelial lining, found in all tissues except epithelia and cartilage.
- Fenestrated capillaries: have pores in endothelial lining, permit rapid exchange of water and larger solutes.
- Discontinuous capillaries (sinusoids): have enlarged diameter, endothelial cells with wide space, and basal lamina is discontinuous.
Arteriovenous Anastomoses
- Direct connections between arterioles and venules.
- Bypass the capillary bed.
- Endothelium lies directly upon a specialized tunica media comprising a sphincter.
- Are in skeletal muscle and skin of the hands and feet, and tissue that metabolic activity is intermittent (thyroid and digestive system).
- Serve a thermoregulatory function.
Arteries
- Arteries change from elastic arteries to muscular arteries to arterioles.
- Elastic arteries: large vessels, tunica media has many elastic fibers and few muscle cells.
- Muscular arteries: medium-sized, tunica media has many muscle cells.
- Arterioles: small, have little or no tunica externa, and thin or incomplete tunica media.
Veins
- Collect blood from capillaries in tissues and organs.
- Return blood to the heart.
- There are three categories of veins based on size:
- Small veins or venules: very small veins, collect blood from capillaries.
- Medium-sized veins: have tunica intima, thin tunica media, and tunica externa with longitudinal bundles of elastic fibers.
- Large veins: have all three tunica layers, thin tunica media, and thick tunica externa.
Vein Valves
- Valves are an important feature of large and medium veins.
- Folds of tunica intima, rich in elastic fibers, and covered on both sides by endothelium.
- Prevent blood from flowing backward.
- Compression pushes blood toward the heart.
Comparison of Arteries and Veins
- Arteries and veins run side-by-side.
- Arteries have thicker walls and higher blood pressure.
- Arteries are more elastic.
- Veins have a higher content of collagen than arteries.
- Collapsed artery has a small, round lumen, while a vein has a large, flat lumen.
- Veins have valves.
- Veins are larger in diameter and have thinner walls.
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Description
Learn about the circulatory system, its functions, and components, including the cardiovascular system and lymphatic system.
