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Blood Vessels Summary
Health and the Human Body II - Systemic Human Physiology (BMS162)
Charles Sturt University
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Blood Vessels Summary
Define the terms artery, vein, capillary, systemic vessels, pulmonary vessels
Artery: blood vessel carrying blood away from the heart Vein: blood vessel carrying blood towards the heart Capillaries: smallest vessels that function in exchange of nutrients and wastes between blood and body cells Systemic vessels: Transport blood through most body parts from the left ventricle and back to the right atrium Pulmonary vessels: Transport blood from the right ventricle through lungs and back to left atrium
Describe the layers that typically form the wall of a blood vessel and state the
function of each
1. Tunica intima
2. Tunica media
3. Tunica externa (adventitia)
Tunica intima - Endothelium - Basement membrane - Lamina propria (C. layer) - Internal elastic membrane. Fenestrated layer of elastic fibers. Tunica media : smooth muscle cells arranged circularly around the blood vessel. - Vasoconstriction : smooth muscles contract, decrease in blood flow - Vasodilation : smooth muscles relax, increase in blood flow Tunica externa ( adventitia ) : connective tissue, varies from dense regular near the vessel to loose that merges with the surrounding C.
Distinguish between the different types of capillary based on function and
location
Describe blood flow through the capillary network
Blood flows from arterioles through metarterioles, then through capillary network. Flow through thoroughfare channel fairly consistent while flow through arterial capillaries is intermittent. Smooth muscle in arterioles, metarterioles, precapillary sphincters regulates blood flow.
Define vasoconstriction and vasodilation
Vasoconstriction: smooth muscles (tunica media) contract, decreasing blood flow Vasodilation: smooth muscles relax (tunica media), increasing blood flow
Describe the structure and function of arteries, arterioles, capillary beds,
venules and veins
Elastic or conducting arteries - Largest diameters, pressure high and fluctuates between systolic and diastolic. More elastic tissue than muscle. - Relatively thick tunica intima, thin tunica adventitia Muscular arteries - Smooth muscle allows vessels to regulate blood supply by constricting or dilating - Most of the smaller unnamed arteries
- Thick walls due to 25-40 layers of smooth muscle.
- Also called distributing arteries because smooth muscle allows vessels to partially regulate blood
supply to different regions of the body.
- Smaller muscular arteries
- Adapted for vasodilation and vasoconstriction. Arterioles
- Transport blood from small arteries to capillaries
- Smallest arteries where the three tunics can be differentiated
- Like small arteries, capable of vasoconstriction and dilation Venules and Small Veins
- Venules: drain capillary network. Endothelial cells and basement membrane with a few smooth
muscle cells. As the diameter of venules increases, the amount of smooth muscle increases.
- Small veins : Smooth muscle cells form a continuous layer. Addition of tunica adventitia made of
collagenous connective tissue
Medium and Large Veins
- Medium veins. Go-between small veins and large veins.
- Large veins. Tunica intima is thin: endothelial cells, relatively thin layer of C and a few scattered
elastic fibers. Tunica media has circularly arranged smooth muscle cells. Adventitia is predominant
layer.
Define the terms vasa vasorum and portal veins
Vasa vasorum: blood vessels that supply the walls of arteries and veins. Penetrate the vessel walls from the exterior. Branches of arteries. Portal veins: veins that begin in a primary capillary network, extend some distance and end in a secondary capillary network without a pumping mechanism, such as the heart, between (eg hepatic portal vein).
Describe the neural innervation of blood vessels
- Unmyelinated sympathetic nerve fibers form plexi in tunica adventitia: vasoconstriction
- Small arteries and arterioles innervated to greatest extent
- Vessels of penis and clitoris innervated by parasympathetic
- Some blood vessels innervated by myelinated fibers and act as baroreceptors that monitor stretch
and detect changes in blood pressure
Discuss some arterial changes that occur with age
- Arteriosclerosis
o General term for degeneration changes in arteries making them less elastic
- Atherosclerosis
o Deposition of plaque on walls
How does oedema occur?
If capillaries become more permeable, proteins can leak into the IF increasing ICOP. More fluid moves from the capillaries into the IF: oedema (US spelling is edema ).
List the factors that are involved in the
dynamics of blood flow
Interrelationships between Pressure Flow Resistance Control mechanisms that regulate blood pressure and blood flow
Define blood flow, blood pressure, and
resistance, and explain the relationship
between these factors
Blood pressure: Measure of the force exerted by blood against the vessel wall. Blood flow: Rate of flow through a tube is expressed as the volume that passes a specific point per unit of time Directly proportional to pressure differences Inversely proportional to resistance
o Tendency for blood vessel volume to increase as blood pressure increases
What is pulse pressure?
Pulse Pressure: difference between systolic and diastolic pressures. - Increases when stroke volume increases or vascular compliance decreases. Compliance tends to
decrease with age (arteriosclerosis) and pressure rises.
- Pulse pressure can be used to take a pulse to determine heart rate and rhythmicity
- Most frequent site used to measure pulse rate is in the carpus with the radial artery- the radial
pulse.
- Compliance tends to decrease with age (arteriosclerosis) and pressure rises
Discuss the pressures involved in fluid exchange across capillary walls
Net filtration pressure (NFP) force responsible for moving fluid across capillary walls. Two forces affect pressure. Hydrostatic pressure physical pressure of blood flowing through the vessels or of fluid in interstitial spaces. Osmotic pressure movement of solutes (plasma or tissue fluid) through a membrane (plasma membrane) in the presence of a non- diffusible solute (large proteins). Large proteins do not freely pass through the capillary walls and the difference in protein concentrations between the blood and interstitial fluid is responsible for osmosis.
Describe the nervous control of blood flow in tissues
- Important in minute-to-minute regulation of local circulation
- Provides a means by which blood can be shunted from one large area of the peripheral circulatory system to another area by increasing resistance
- Sympathetic division most important. Innervates all vessels except capillaries, precapillary sphincters, and most metarterioles.
- Vasomotor center in lower pons and upper medulla oblongata.
- Excitatory part is tonically active. Causes vasomotor tone. Norepinephrine
- Inhibitory part can cause vasodilation by decreasing sympathetic output
- Sympathetic stimulation of adrenal medulla increases output of norepinephrine and epinephrine into the circulation. Resulting in vasoconstriction in vessels (α-adrenergic receptors) except in skeletal muscle where vasodilation takes place (ß-adrenergic receptors)
Describe the mechanisms involved in the short-term regulation of blood
pressure
Baroreceptor reflexes
- change peripheral resistance, heart rate, and stroke volume in response to changes in blood
pressure
Chemoreceptor reflexes: - sensory receptors sensitive to oxygen, carbon dioxide, and pH levels of blood Central nervous system ischemic response:
- results from high carbon dioxide or low pH levels in medulla and increases peripheral resistance
Describe the mechanisms involved in the long-term
regulation of blood pressure
Atrial natriuretic hormone released from cardiac muscle cells when atrial blood pressure increases, simulating an increase in urine production, causing a decrease in blood volume and blood pressure Fluid shift
movement of fluid from interstitial spaces into capillaries in response to decrease in blood pressure to maintain blood volume and vice versa. Stress-relaxation response adjustment of blood vessel smooth muscle to respond to change in blood volume. When blood volume suddenly declines and pressure drops, smooth muscles contract and vice versa.
Blood Vessels Summary
Course: Health and the Human Body II - Systemic Human Physiology (BMS162)
University: Charles Sturt University
