Section 3 Flashcards
How do arterioles differ from arteries in terms of their connective tissue content and size?
Arterioles have walls similar in structure to arteries but lack the high content of collagen and elastin in their connective tissues, and they are much smaller in size than arteries.
Considering the relationship between resistance and vessel radius, what is likely to happen to mean arterial pressure in arterioles compared to arteries?
Due to their smaller diameter compared to arteries, arterioles have much greater resistance, leading to a substantial decrease in mean arterial pressure.
Why are arterioles considered the resistance vessels of the circulatory system?
Arterioles, being much smaller in diameter, exhibit much higher resistance compared to arteries, and therefore, they are considered the resistance vessels of the circulatory system.
What is the average mean arterial pressure at the beginning of arterioles, and how does it change by the end of the arterioles?
The mean arterial pressure at the beginning of the arterioles is on average 93 mmHg, but by the end of the arterioles, it has substantially dropped to around 37 mmHg.
What is the significance of the large drop in pressure at the end of arterioles?
The large drop in pressure at the end of arterioles helps maintain the pressure gradient necessary for the forward flow of blood, and at this point, there are no more pulsatile fluctuations in pressure.
What is another term for arteriolar resistance, and why is it important in calculating mean arterial pressure?
Arteriolar resistance is also called total peripheral resistance (TPR), and it is important in the calculation of mean arterial pressure.
Why is arteriolar resistance not a constant value?
Arteriolar resistance is not a constant value because arterioles are dynamic and can regulate their radius, adjusting to different physiological needs.
hat are the two major reasons for adjusting the arteriolar radius?
The two major reasons for adjusting the arteriolar radius are:
- To distribute cardiac output to various organs based on the body’s needs.
- To help regulate arterial blood pressure.
Explain the process of shunting in the context of arteriolar regulation.
At rest, more blood is needed in the digestive system, so arterioles supplying the digestive system increase their radius to lower resistance and increase blood flow. During exercise, the opposite occurs, and these arterioles decrease their radius to decrease blood supply, allowing blood to go to other organs. This process is called shunting.
How do arterioles help regulate arterial blood pressure?
When there is a need to increase blood pressure, arterioles can decrease their radius, increasing resistance and, consequently, increasing arterial blood pressure.
What is the equation for blood flow through blood vessels?
The equation introduced for blood flow through blood vessels is: Pressure Gradient (∆P) / Resistance (R) = Flow (F)
What does the Pressure Gradient (∆P) represent in the context of blood flow?
The Pressure Gradient (∆P) represents the pressure gradient for the entire body, where MAP (Mean Arterial Pressure) is typically 93 mmHg, and blood returning to the heart is near 0 mmHg.
What does Resistance (R) represent in the context of blood flow?
Resistance (R) represents the summation of all the resistance of the systemic peripheral vessels. In this context, it is referred to as Total Peripheral Resistance (TPR), focusing on the resistance at the level of the arterioles as they contribute the most to resistance.
What does Flow (F) represent in the context of blood flow?
Flow (F) represents total cardiac output.
Given that MAP is 93 mmHg and blood returning to the heart is near 0 mmHg, what is the value of the Pressure Gradient (∆P)?
The value of the Pressure Gradient (∆P) is 93 mmHg, which is the MAP (Mean Arterial Pressure).
How is the smooth muscle in the walls of arterioles innervated, and what influences their contraction and relaxation?
The smooth muscle in the walls of arterioles is highly innervated by the sympathetic nervous system, and they also respond to circulating hormones and other chemicals.
What happens to the radius of an arteriole when the smooth muscle is stimulated to contract?
When the smooth muscle in the walls of arterioles is stimulated to contract, the radius of the arteriole becomes smaller. This phenomenon is known as vasoconstriction.
What is vasoconstriction?
Vasoconstriction is the contraction of smooth muscle in the walls of arterioles, leading to a reduction in the radius of the arteriole.
Define vasodilation.
Vasodilation is the relaxation of smooth muscle in the walls of arterioles, resulting in an increase in the radius of the arteriole.
What is vascular tone?
Vascular tone refers to the state of partial constriction of the smooth muscle in the walls of arterioles.
Why is vascular tone important?
Vascular tone is crucial as it allows arterioles to either constrict or dilate as needed, influencing blood flow.
Into what two categories does the regulation of vascular tone fall?
The regulation of vascular tone falls into two categories: Intrinsic Control and Extrinsic Control.
What is Intrinsic Control in the context of vascular tone?
Intrinsic controls, also known as local controls, occur within organs to regulate their own blood supply.
They can be chemical (local metabolic changes and histamine) or physical (responses to shear stress and the myogenic response to stretch).
What are some examples of local chemical influences in intrinsic control?
Local chemical influences in intrinsic control include local metabolic changes and histamine.
What are some examples of physical influences in intrinsic control?
Physical influences in intrinsic control include chemical responses to shear stress and the myogenic response to stretch.
What does extrinsic control of arteriolar tone refer to?
Extrinsic control of arteriolar tone refers to metabolic or non-local factors that affect vasodilation or vasoconstriction. It includes both neural and hormonal inputs.
Why are extrinsic controls important in regulating blood pressure?
Extrinsic controls are important in regulating blood pressure by influencing vasodilation or vasoconstriction through neural and hormonal inputs.
What are the two sub-divisions of intrinsic control in the regulation of arteriole radius?
Intrinsic control sub-divides into chemical changes and physical influences as types of input leading to the control of arteriole radius.
What are the two sub-divisions of extrinsic control in the regulation of arteriole radius?
Extrinsic control sub-divides into neural and hormonal inputs as types of input leading to the control of arteriole radius.
Why does blood supply need to increase with increased metabolic activity in an organ?
Blood supply needs to increase with increased metabolic activity to deliver more oxygen and nutrients and prevent the buildup of wastes.
What metabolic changes result in vasodilation?
Metabolic changes that result in vasodilation include:
- Decreased Oxygen (resulting from increased oxidative metabolism).
- Increased Carbon Dioxide (due to increased oxidative metabolism).
- Increased Acid (from carbonic acid produced during carbon dioxide production and lactic acid from anaerobic metabolism).
- Adenosine Release (from increased metabolic activity or oxygen deprivation).
- Increased Potassium (occurs in very active muscles if action potentials exceed the capacity of the Na+/K+ pump).
- Increased Osmolarity (resulting from the release of osmotically active particles in high metabolically active tissues).
- Prostaglandin Release (local chemical messengers derived from fatty acid chains in the plasma membrane of cells).
Why is increased oxygen a factor in vasodilation?
Increased oxygen is a factor in vasodilation because it is a result of increased oxidative metabolism, signaling the need for enhanced blood flow to the active tissue.
What is the role of prostaglandin release in vasodilation?
Prostaglandin release, as local chemical messengers derived from fatty acid chains, contributes to vasodilation by influencing arteriolar smooth muscle.
How do local metabolic factors influence vascular regulation?
Local metabolic factors do not act directly on smooth muscle cells. Instead, they trigger endothelial cells lining the vessels to release chemical messengers that target the smooth muscle cells.
