Heart and Blood Vessels Chapter 8: Lectures 21 and 23
Blood Vessels Transport Blood:
Arteries
– Carry blood away from the heart
– Transport blood under high pressure
– Are thick-walled
Capillaries
– Exchange solutes and water with cells of the body
– Are microscopic
Veins
– Return blood to the heart
– Are thin-walled
Arteries Transport Blood Away from the Heart:
Structure
– Thick-walled, three layers
– Innermost layer: endothelium of squamous epithelial cells
– Middle layer: smooth muscle
– Outer layer: connective tissue
Function
– Arteries carry blood away from heart
– Carry blood under pressure
Aneurism—defect in arterial wall
– Ballooning of the arterial wall
– Some bulge inward, obstructing flow
– Others bulge outward
– Often develop slowly over time
– Often symptomless, until they rupture
– Rupture of aortic aneurism can be rapidly fatal
– May be detected by careful screening and surgically repaired
Arterioles and Precapillary Sphincters Regulate Blood Flow:
Blood flow
– Heart → Arteries → Arterioles → Capillaries
Arterioles: smallest arteries
Precapillary sphincters: control blood flow from arterioles into capillaries
– Vasodilation
– Relaxation of vascular smooth muscle
– Increases blood flow to capillaries
, – Vasoconstriction
– Contraction of vascular smooth muscle
– Decreases blood flow to capillaries
Capillaries: Where Blood Exchanges Substances with Tissue:
Structure
– Smallest blood vessels, microscopic
– Thin-walled: one cell layer thick
– Porous
Capillary beds: extensive networks of capillaries
Function: selective exchange of substances with the interstitial fluid
Lymphatic System Helps Maintain Blood Volume:
Function
– Maintains blood volume
– Returns excess interstitial fluid to circulatory system
– Also functions in immune defenses
Structure
– Blind-ended capillaries
– Lymphatic vessels (similar to venous system)
– Lymph—derived from interstitial fluid
Veins Return Blood to the Heart:
Structure
– Three layers, thin-walled
– Larger lumen than arteries
– High distensibility
Functions
– Carry blood toward the heart
– Blood flow
– Capillaries → Venules → Veins → Heart
– Serve as blood volume reservoir
Three mechanisms assisting in blood return
1. Contraction of skeletal muscles
2. One-way valves permit only one-way blood flow
3. Pressure changes associated with breathing push blood toward the heart
The Heart is Mostly Muscle:
Surrounded by fibrous sac—pericardium
– Protects and anchors the heart
Layers of the heart
Blood Vessels Transport Blood:
Arteries
– Carry blood away from the heart
– Transport blood under high pressure
– Are thick-walled
Capillaries
– Exchange solutes and water with cells of the body
– Are microscopic
Veins
– Return blood to the heart
– Are thin-walled
Arteries Transport Blood Away from the Heart:
Structure
– Thick-walled, three layers
– Innermost layer: endothelium of squamous epithelial cells
– Middle layer: smooth muscle
– Outer layer: connective tissue
Function
– Arteries carry blood away from heart
– Carry blood under pressure
Aneurism—defect in arterial wall
– Ballooning of the arterial wall
– Some bulge inward, obstructing flow
– Others bulge outward
– Often develop slowly over time
– Often symptomless, until they rupture
– Rupture of aortic aneurism can be rapidly fatal
– May be detected by careful screening and surgically repaired
Arterioles and Precapillary Sphincters Regulate Blood Flow:
Blood flow
– Heart → Arteries → Arterioles → Capillaries
Arterioles: smallest arteries
Precapillary sphincters: control blood flow from arterioles into capillaries
– Vasodilation
– Relaxation of vascular smooth muscle
– Increases blood flow to capillaries
, – Vasoconstriction
– Contraction of vascular smooth muscle
– Decreases blood flow to capillaries
Capillaries: Where Blood Exchanges Substances with Tissue:
Structure
– Smallest blood vessels, microscopic
– Thin-walled: one cell layer thick
– Porous
Capillary beds: extensive networks of capillaries
Function: selective exchange of substances with the interstitial fluid
Lymphatic System Helps Maintain Blood Volume:
Function
– Maintains blood volume
– Returns excess interstitial fluid to circulatory system
– Also functions in immune defenses
Structure
– Blind-ended capillaries
– Lymphatic vessels (similar to venous system)
– Lymph—derived from interstitial fluid
Veins Return Blood to the Heart:
Structure
– Three layers, thin-walled
– Larger lumen than arteries
– High distensibility
Functions
– Carry blood toward the heart
– Blood flow
– Capillaries → Venules → Veins → Heart
– Serve as blood volume reservoir
Three mechanisms assisting in blood return
1. Contraction of skeletal muscles
2. One-way valves permit only one-way blood flow
3. Pressure changes associated with breathing push blood toward the heart
The Heart is Mostly Muscle:
Surrounded by fibrous sac—pericardium
– Protects and anchors the heart
Layers of the heart
