Post on 24-May-2015
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Section 4, Chapter 15
Blood vessels
ivyanatomy.com
Arteries• Convey blood away from
the heart
Arterioles• Thinner vessels that
convey blood towards capillaries
Capillaries• Site of exchange between
blood and body tissues
Venules• Receives blood from
capillaries
Veins• Returns blood towards
the heart
Endothelium • A layer of smooth simple squamous
epithelium
• Secretes biochemicals with a wide variety of functions.
Basement membrane• Bed of connective tissue with elastic &
collagenous fibers
Tunica Interna (inner)
Walls of the blood vessels – 3 Layers
Walls of the blood vessels – 3 Layers
Tunica Media (middle)Smooth Muscles • Vasoconstriction – muscles contract,
decreasing diameter of vessel
• Vasodilation – muscles relax, allowing vessel diameter to increase
Elastic Connective tissue• Recoil of elastic fibers helps propel
blood through vessels
Tunica Externa (outer)Fibrous Connective Tissue• Elastic and collagenous fibers
• Attaches blood vessel to organs
Vasa Vasorum “vessels of the vessels”• Provide blood supply to walls of thicker
arteries
Walls of the blood vessels – 3 Layers
Figure 15.27An arteriovenous shunt provided by a metarteriole.
•Arterioles are smaller divisions of arteries.
• metarterioles – small arterioles that join capillaries
• Arteriovenous shunt – connects an arteriole directly to a venuleShunt allows blood to bypass a capillary bed.
Arterioles
Figure 15.28 Substances are exchanged through openings (slits) separating endothelial cells.
•Capillaries - smallest diameter blood vessels• Consists of a single layer of endothelial cells
• Site of gas, nutrient, and waste exchange
Capillaries
Slits • Spaces between endothelia that
facilitate diffusion across vessel wall
Figure 15.26 A precapillary sphincter at the base of a capillary.
Capillaries
Precapillary sphincters • Smooth muscles that regulate the
flow of blood through a capillary
• Closes a capillary bed when oxygen demand to an organ is low
Artificially colored electron micrograph depicts sinusoids throughout the liver.
Capillaries
Sinusoids• large cavities within discontinuous
capillaries
• Allows a rapid exchange of nutrients, debris, proteins, and even cells.
• located throughout the liver and spleen.
•Venules• Continue from capillaries and merge to form veins
•Veins• Convey blood from body back to the atria of heart
• Veins follow a pathway roughly parallel to arteries
• Vessel wall of veins has 3 layers (tunics) similar to arteries
Figure 15.31. Venous valves (a) open as blood moves towards the heart, but (b) close to prevent blood from moving backward away from the heart.
– Veins have poorly developed tunica media• Thinner walls, and a larger luman than arteries
– Tunica Interna of veins contain valves• Valves prevent blood from flowing backwards towards capillaries.
– Veins act as blood reservoirs• Most blood (60-70%) is in the veins and venules.
Differences between veins and arteries
Figure 15.25 Blood vessels (a) the wall of an artery. (b) The wall of a vein. (c) cross section of an arteriole (bottom) and a venule (top).
Differences between veins and
arteries
End of Section 4, Chapter 15