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.
Provide an example of a chemical messenger released by endothelial cells that influences smooth muscle cells.
Nitric oxide is an example of a chemical messenger released by endothelial cells that influences smooth muscle cells.
What is the role of nitric oxide in vascular regulation?
Nitric oxide released from endothelial cells relaxes the contractile state of smooth muscle cells. It achieves this by activating a pathway that reduces the entry of calcium into the muscle cells.
While discussing endothelial cells, what is an example of a potent vasoconstrictor released by them?
Endothelin is a potent vasoconstrictor released by endothelial cells.
What is the dual role of endothelial cells in vascular regulation?
Endothelial cells play a dual role in vascular regulation. While they release relaxing chemicals like nitric oxide, they also release vasoconstrictors such as endothelin.
How does nitric oxide achieve smooth muscle relaxation?
Nitric oxide achieves smooth muscle relaxation by activating a pathway that reduces the entry of calcium into the muscle cells.
what is endothelin?
peptides released by endothelial cells of vasculature
What is histamine, and how does it relate to vasodilation?
Histamine is a chemical that can cause vasodilation independent of tissue metabolic activity. It is released during tissue damage or allergic reactions and acts as a paracrine molecule, leading to the relaxation of smooth muscle cells and vasodilation.
When is histamine released in the body?
Histamine is released when there is tissue damage or during allergic reactions.
How does histamine cause vasodilation?
Histamine acts as a paracrine molecule, causing the relaxation of smooth muscle cells, which results in vasodilation.
What is the visual indication of increased blood flow due to histamine release?
Increased blood flow due to histamine release can be visually observed as redness in the affected area.
Besides vasodilation, what is another effect of increased blood flow caused by histamine release?
Increased blood flow caused by histamine release contributes to swelling in the affected area.
Which of the following situation leads to vasodilation?
- Adenosine release
- Decreased carbonic acid in the blood
- Decreased potassium
- Increased oxygen
adenosine release
Which of the following accurately describes intrinsic control?
- Can be either chemical or electrical in natural
- Occurs within the body itself to regulate its own bloody supply
- Includes only neural inputs
- May involve histamine, which acts directly on vascular smooth muscle
May involve histamine, which acts directly on vascular smooth muscle
What is the effect of applying heat to an area on arteriolar tone?
Applying heat to an area causes vasodilation and increases blood flow.
How does applying cold to an area influence arteriolar tone?
Applying cold to an area causes vasoconstriction and reduces blood flow.
What is shear stress, and how does it influence arteriolar tone?
Shear stress is the frictional force at the endothelial surface produced by flowing blood. When shear stress increases, endothelial cells release nitric oxide, leading to vasodilation and a reduction in shear stress.
What is the myogenic response to stretch in the context of arteriolar tone regulation?
The myogenic response to stretch is an intrinsic property of smooth muscle cells. When these cells are passively stretched, such as during an increase in blood pressure, they exhibit a myogenic response causing vasoconstriction to oppose the stretch and maintain lumen diameter.
Describe the myogenic response when there is less stretch in smooth muscle cells.
When there is less stretch in smooth muscle cells, they respond by relaxing, resulting in vasodilation.
What is the definition of shear stress?
Shear stress is the external force acting on a surface parallel to the slope in which it lies. In the context of arteriolar tone regulation, it is the frictional force at the endothelial surface produced by flowing blood.
What is reactive hyperemia, and when does it occur?
Reactive hyperemia occurs when blood supply to a region increases. It is often observed in response to changes in blood flow, such as those caused by a sphygmomanometer.
How do both chemical and physical influences work together to increase blood flow in reactive hyperemia?
In reactive hyperemia, when a sphygmomanometer cuff is initially inflated, the brachial artery is compressed, leading to a cessation of blood flow to the lower arm. The response includes profound vasodilation caused by both myogenic factors (due to decreased pressure) and chemical influences (decreased oxygen, increased carbon dioxide, and acids).
What happens if the cuff pressure in a sphygmometer is suddenly decreased during reactive hyperemia?
If the cuff pressure is suddenly decreased, blood flow to the lower arm is briefly much higher than normal as arterioles are widely dilated. This can visually appear as increased redness in the lower arm.
What is the primary purpose of the increased blood flow during reactive hyperemia?
The primary purpose of the increased blood flow during reactive hyperemia is to rapidly restore local chemical balances in the affected area.
What follows the initial increase in blood flow during reactive hyperemia?
Following the initial increase in blood flow during reactive hyperemia, there is a subsequent increase in vascular tone.
What does extrinsic control of arteriolar tone refer to?
Extrinsic control of arteriolar tone refers to non-local or metabolic factors that influence vasodilation or vasoconstriction. It includes both neural and hormonal inputs.
Which part(s) of the nervous system innervates arteriolar smooth muscle for neural regulation?
Only the sympathetic nervous system innervates arteriolar smooth muscle for neural regulation.
How is neural regulation of arteriolar tone achieved?
Neural regulation of arteriolar tone is achieved solely by sympathetic activity.
What is the effect of increasing sympathetic activity on arteriolar tone?
Increasing sympathetic activity will increase arteriolar tone.
How does decreasing sympathetic activity affect arteriolar tone?
Decreasing sympathetic activity will decrease arteriolar tone.
Why is neural regulation of arteriolar tone considered a generalized response?
Neural regulation of arteriolar tone does not occur in single organs. Instead, it is a generalized response that affects all arterioles, influencing arteriolar resistance or total peripheral resistance, and can regulate blood pressure globally.
What neurotransmitter is released by sympathetic nerve endings on smooth muscle?
Sympathetic nerve endings on smooth muscle release norepinephrine.
What is the result of norepinephrine binding to α1-adrenergic receptors on smooth muscle cells?
Norepinephrine binding to α1-adrenergic receptors increases calcium entry into smooth muscle cells, leading to arteriolar contraction.
Why do arterioles in the brain not respond to changes in sympathetic activity?
Arterioles in the brain do not have α1-adrenergic receptors and, therefore, do not respond to changes in sympathetic activity. Blood flow to the brain is under local or metabolic control to maintain constant blood flow at all times.
Under what conditions can local control be a stronger influence than sympathetic inputs?
Under some conditions, such as during increased activity in the skeletal muscles (e.g., riding a bicycle), local control can be a stronger influence than sympathetic inputs in increasing blood supply. Even in the presence of sympathetic activity, the metabolic influences are stronger, leading to arteriolar dilation.
Why would the adrenal glands release the neurohormone epinephrine?
The adrenal glands release epinephrine, as part of the sympathetic nervous system’s fight-or-flight response, to prepare the body for activity in a stressful or emergency situation. This response includes increasing blood flow to the heart and working muscles, raising blood sugar, dilating pupils, and increasing cardiac output.
Why does epinephrine have a preference for β2-adrenergic receptors?
Epinephrine has a preference for β2-adrenergic receptors because, at low hormonal doses, it tends to bind more to these receptors. β2-adrenergic receptors are found in the heart, where they can affect rate and contractility, as well as in the smooth muscle of the vasculature, where they cause vasodilation.
Identify a reason that explains why the adrenal glands would release the neurohormone epinephrine, and why epinephrine has a preference for β2-adrenergic receptors.
Recall that the sympathetic nervous system’s primary role is to stimulate the fight-or-flight response.
During this response, the adrenal medulla produces epinephrine and norepinephrine. This response
increases blood flow to the heart and working muscles, increases cardiac output, dilates pupils, and
raises blood sugar. This response prepares the body for activity in a stressful or emergency situation
What are two hormones that play important roles in the regulation of arteriolar tone as potent vasoconstrictors?
Vasopressin (antidiuretic hormone, ADH) and angiotensin II are two hormones that play important roles in the regulation of arteriolar tone as potent vasoconstrictors.
In what situations are the roles of vasopressin and angiotensin II as vasoconstrictors crucial?
In times of massive blood volume loss, such as hemorrhage.
Why are vasopressin and angiotensin II released during rapid blood volume loss?
to help maintain blood pressure despite the decreased volume.
What is another name for vasopressin?
Vasopressin is also known as antidiuretic hormone (ADH)
How do vasopressin and angiotensin II contribute to the regulation of arteriolar tone?
by acting as potent vasoconstrictors, particularly during situations of significant blood volume loss.
Is heat application (therapeutic use) part of intrinsic (local) control or extrinsic control?
local (intrinsic) control
Is cold application (therapeutic use) part of intrinsic (local) control or extrinsic control?
local (intrinsic) control
Is the response to shear stress part of intrinsic (local) control or extrinsic control?
intrinsic (local) control
Is histamine release part of intrinsic (local) control or extrinsic control?
intrinsic (local) control
Are local metabolic changes in O2 and other metabolites part of intrinsic (local) control or extrinsic control?
intrinsic (local) control
Is vasopressin part of intrinsic (local) control or extrinsic control?
extrinsic control
Is Angiotensin II part of intrinsic (local) control or extrinsic control?
extrinsic control
Is Epinephrine part of intrinsic (local) control or extrinsic control?
extrinsic control
Is Sympathetic activity part of intrinsic (local) control or extrinsic control?
extrinsic control
