Download 10.1 vessels notes

Chapter 10: Circulatory System and Lymphatic System In this
chapter, you will learn about the structure and function of the
circulatory system and lymphatic system.
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10.1 The Blood Vessels The circulatory system has three types of
blood vessels.
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• Arteries: carry blood away from the heart to the capillaries
• Capillaries: permit exchange of material with the tissues
• Veins: return blood from the capillaries to the heart
All three blood vessel types have an inner endothelium, a simple
squamous epithelium attached to a connective tissue basement
membrane that has elastic fibres.
Fig 10.1 McGraw-Hill
The Arteries The largest artery in the body is the aorta, which
carries O2-rich blood from the heart to other parts of the body.
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The arterial wall has three layers.
• Inner layer: endothelium
• Middle layer: smooth muscle that contracts and relaxes to regulate
blood flow and pressure
• Outer layer: fibrous connective tissue
Arterioles are small arteries that branch off from an artery. Arterioles
have three layers:
• Inner layer: endothelium
• Middle layer: some elastic tissue but mostly smooth muscle
*smooth muscle that contracts: blood vessel constricts, resulting in
higher blood pressure
*smooth muscle relaxes: blood vessel relaxes, resulting in lower
blood pressure
• Outer layer: fibrous connective tissue
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The Capillaries
Capillaries are narrow blood vessels that join arterioles to venules.
• Composed of a single layer of epithelium with a basement
membrane
• Form vast networks (capillary beds) throughout the body
Only certain capillary beds are open at any given time. o After
eating, capillary beds that serve the digestive system are open, and
those that serve the muscles are mostly closed
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o Sphincter muscles relax to open the bed and allow blood flow
o Sphincter muscles contract to close the bed and prevent blood flow
o When the bed is closed, blood flows through anastomoses
(arteriovenous shunts) directly from arterioles to venules, bypassing
the bed
Fig 10.2
Exchange of substances takes place across the thin walls of the
capillaries.
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o Oxygen and nutrients diffuse out of the capillary and into the tissue
fluid that surrounds cells
o Wastes (carbon dioxide) diffuse into the capillary
o Some water leaves the capillaries, and excess is picked up by
lymphatic vessels
The Veins Veins and venules (small veins) take blood from the
capillary beds to the heart.
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• Veins and venules have the same three layers as arteries, but
there is less smooth muscle and connective tissue
• Veins have valves, which allow blood to flow toward the heart
when open and prevent blood from flowing backward when
closed
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• Veins act as a blood reservoir
o Since their walls are thinner, they can expand to a greater extent
o About 70% of blood is in the veins
• The largest veins in the body are the venae cavae (superior vena
cava, inferior vena cava), which deliver O2-poor blood to the
heart
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Check Your Progress
1.Describe how blood flow is controlled in each of the three major
types of blood vessels.
2. List several specific substances that diffuse across capillary walls.