1. The Blood Vessels UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
The Blood Vessels
The circulatory system has three types of blood vessels.
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.
circulatory system: a type of organ system containing the heart and blood vessels; responsible for moving blood and substances throughout the body
arteries: types of blood vessel that carry blood away from the heart to the capillaries
capillaries: types of blood vessels that permit exchange of material with the tissues
veins: types of blood vessels that return blood from the capillaries to the heart
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2. The Arteries UNIT B The largest artery in the body is the aorta.
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
The Arteries
The largest artery in the body is the aorta.
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
aorta: the largest artery in the human body that carries oxygen-rich blood from the heart to other parts of the body
Figure 10.1 Blood vessels. The walls of arteries and veins have three layers. The inner layer is composed largely of endothelium, with a basement membrane that has elastic fibres; the middle layer is smooth muscle tissue; the outer layer is connective tissue (largely collagen fibres).
a. Arteries have a thicker wall than veins because they have a larger middle layer than veins.
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3. Arterioles are small arteries that branch off from an artery.
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
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 contracts: blood vessel constricts, resulting in higher blood pressure
Outer layer: fibrous connective tissue
arterioles: small arteries just visible to the naked eye
Smooth muscle contracts: blood vessel constricts, resulting in higher blood pressure
Smooth muscle relaxes: blood vessel relaxes, resulting in lower blood pressur
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4. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
The Veins
Veins and venules (small veins) take blood from the capillary beds to the heart.
Veins and venules have the same three layers as arteries, but there is less smooth muscle and connective tissue
Veins have valves that prevent backflow
venules: small veins that drain blood from the capillaries and then join to form a vein
Veins have valves, which allow blood to flow toward the heart when open and prevent backflow of blood from flowing backward when closed
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5. Veins act as a blood reservoir:
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
Veins act as a blood reservoir:
Since their walls are thinner, they can expand to a greater extent
About 70% of blood is in the veins
The largest veins in the body are the venae cavae (superior vena cava, inferior vena cava)
venae cavae: the largest veins; include the superior vena cava and the inferior vena cava, both of which deliver oxygen-poor blood into the heart
Veins are more superficial than arteries
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6. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
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
4 to 10 microns
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7. Only certain capillary beds are open at any given time:
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
Only certain capillary beds are open at any given time:
Sphincter muscles – relax to open/ contract to close bed
When bed is closed, blood flows through anastomoses (arteriovenous shunts)
After eating, capillary beds that serve the digestive system are open, and those that serve the muscles are mostly closed
Sphincter muscles relax to open the bed and allow blood flow
Sphincter muscles contract to close the bed and prevent blood flow
When the bed is closed, blood flows through anastomoses (arteriovenous shunts) directly from arterioles to venules, bypassing the bed
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8. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
Figure 10.2 Anatomy of a capillary bed. A capillary bed forms a maze of capillary vessels that lies between an arteriole and a venule. When precapillary sphincter muscles are relaxed, the capillary bed is open, and blood flows through the capillaries. When sphincter muscles are contracted, blood flows through a shunt (anastomosis) that carries blood directly from an arteriole to a venule. As blood passes through a capillary in the tissues, it gives up its oxygen. Therefore, blood goes from being O2-rich in the arteriole (red colour) to being O2-poor in the vein (blue colour).
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9. CAPILLARY FLOW
Two forces control movement of fluid through capillary walls:
Osmotic pressure: draw of fluid to the dissolved solutes that can’t cross semipermeable membrane
Tends to cause water to move from tissue fluid to blood
Created by salts and plasma proteins
Hydrostatic Pressure (Blood Pressure): tends to cause water to move in the opposite direction.
Osmotic pressure, causes water to move from tissue fluid to blood
BP – tends to cause water to move in the opposite (hydrostatic pressure- pressure of fluid inside vessel extert on inner walls pushing out.

10. Wastes (carbon dioxide) diffuse into the capillary
UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.2 .
Exchange of substances takes place across the thin walls of the capillaries.
Oxygen and nutrients diffuse out of the capillary and into the tissue fluid that surrounds cells
Wastes (carbon dioxide) diffuse into the capillary
Some water leaves the capillaries, and excess is picked up by lymphatic vessels
Figure 10.9 Capillary exchange in the systemic circuit. At the arterial end of a capillary (left) the blood pressure is higher than the osmotic pressure; therefore, water tends to leave the bloodstream. In the midsection, molecules, including oxygen and carbon dioxide, follow their concentration gradients. At the venous end of a capillary (right), the osmotic pressure is higher than the blood pressure; therefore, water tends to enter the bloodstream. Notice that the red blood cells and the plasma proteins are too large
to exit a capillary.
At arterial end of capillary, BP is higher than osmotic pressure so water exits capillary at this end.
Midway along cap, where BP is lower,two forces cancel each other  no net movement of water. Solutes diffuse according to conc grad: Nutrients (glucose and O2) diffuse out of cap, wastes (CO2) diffuse in. RBCs and almost all plasma proteins (too large) remain in caps.
Substances that leave cap contribute to tissue fluid. Mostly all components of plasm except large plasm proteins.
At venous end of cap where BP has fallen, osmotic pressure > BP and water tens to move into the cap. Almost same amnt of fluid that left returns. Some excess tissue fluid is alsways collected by lymphatic capillaries (lymph). Lymph is returned to systemic venous blood when major lymphatic vessels enter the subclavian vein in the shoulder region.
Arterial End of Capillary
Blood pressure (hydrostatic pressure) is higher than osmotic pressure of blood
Water exits capillary
Midway Along the Capillary
Blood pressure and osmotic pressure cancel each other out
No net movement of water
Solutes diffuse according to concentration gradient
Nutrients and oxygen diffuse out of the capillary; wastes and carbon dioxide diffuse into the capillaries
Small substances leaving capillaries contribute to tissue fluid
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11. Capillary Exchange
At arterial end of capillary, BP is higher than osmotic pressure so water exits capillary at this end.
Midway along cap, where BP is lower,two forces cancel each other  no net movement of water. Solutes diffuse according to conc grad: Nutrients (glucose and O2) diffuse out of cap, wastes (CO2) diffuse in. RBCs and almost all plasma proteins (too large) remain in caps.
Substances that leave cap contribute to tissue fluid. Mostly all components of plasm except large plasm proteins.
At venous end of cap where BP has fallen, osmotic pressure > BP and water tens to move into the cap. Almost same amnt of fluid that left returns. Some excess tissue fluid is alsways collected by lymphatic capillaries (lymph). Lymph is returned to systemic venous blood when major lymphatic vessels enter the subclavian vein in the shoulder region.
Arterial End of Capillary
Blood pressure (hydrostatic pressure) is higher than osmotic pressure of blood
Water exits capillary
Midway Along the Capillary
Blood pressure and osmotic pressure cancel each other out
No net movement of water
Solutes diffuse according to concentration gradient
Nutrients and oxygen diffuse out of the capillary; wastes and carbon dioxide diffuse into the capillaries
Small substances leaving capillaries contribute to tissue fluid
Exchange of substances takes place across the thin walls of the capillaries.
Oxygen and nutrients diffuse out of the capillary and into the tissue fluid that surrounds cells
Wastes (carbon dioxide) diffuse into the capillary
Some water leaves the capillaries, and excess is picked up by lymphatic vessels

12. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.2
Excess tissue fluid is collected by lymphatic capillaries, where it becomes lymph
lFigure Lymphatic capillaries. A lymphatic capillary bed (shown here in green) lies near a blood capillary bed. When lymphatic capillaries take up excess tissue fluid, it becomes lymph.
ymphatic capillaries: collect excess tissue fluid called lymph
lymph: tissue fluid contained within lymphatic vessels
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13. Lymphatic Capillaries

14. Check Your Progress UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
Check Your Progress
Describe how blood flow is controlled in each of the three major types of blood vessels.
List several specific substances that diffuse across capillary walls.
ANSWERS
1. Blood flow is controlled in arteries by contraction of smooth muscle in artery walls. Capillary blood flow is affected by the pressure of arterial supply plus the contraction of pre-capillary sphincters. Venous blood flow is affected by arterial and capillary blood flow and valves that prevent blood from flowing backward.
2. Substances that diffuse across capillary walls include oxygen, carbon dioxide, glucose, amino acids.
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15. UNIT B
Chapter 10: Circulatory System and Lymphatic System
Section 10.1
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