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Questions and Answers
What is the primary role of baroreceptors in the body?
How does increased blood pressure affect the firing rate of the SA node?
What physiological changes occur when a person changes from a supine to a standing position?
Which of the following factors directly affects stroke volume?
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Which system is NOT involved in the regulation of arterial resistance?
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What effect does the brain have on heart rate in response to a drop in mean arterial pressure (MAP)?
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What role do baroreceptors play in the cardiovascular response to postural changes?
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How does sympathetic nervous system activation affect stroke volume?
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Which hormone primarily promotes sodium and water retention to increase blood volume?
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What is the effect of increased norepinephrine on the heart's sinoatrial (SA) node?
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What happens to total peripheral resistance when the sympathetic nervous system is activated?
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Which of the following increases stroke volume primarily by enhancing ventricular contractility?
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How does blood volume affect blood pressure?
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Study Notes
Baroreceptor Reflex
- The baroreceptor reflex, also known as the baroreflex, regulates blood pressure in response to changes in blood flow.
- It is distinct from the chemoreflex, which responds to alterations in arterial oxygen and/or carbon dioxide levels.
- Baroreceptors are located in the aortic arch and carotid sinus.
- They sense pressure through stretch:
- Increased pressure stretches the receptors, leading to more action potentials sent to the medulla.
- Decreased pressure reduces receptor stretch, resulting in fewer action potentials sent to the medulla.
Primary Variables
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Heart Rate:
- Controlled by sinoatrial (SA) node firing rate.
- Regulated by the parasympathetic nervous system (PNS) and sympathetic nervous system (SNS).
- Increased SNS activity increases heart rate by releasing norepinephrine, which activates β-adrenergic receptors, leading to more open Na+ channels and steeper drift.
- Increased PNS activity decreases heart rate by releasing acetylcholine which activates muscarinic cholinergic receptors, leading to fewer open K+ channels and a steeper drift.
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Stroke Volume:
- Controlled by ventricular contractility.
- Regulated by the SNS.
- Increased SNS activity increases stroke volume by releasing norepinephrine, which activates β-adrenergic receptors, leading to more open Ca2+ channels and increased ventricular contractility.
-
Resistance:
- Controlled by arteriole radius.
- Regulated by the SNS.
- Increased SNS activity increases resistance by releasing epinephrine and angiotensin II, which activate α-adrenergic receptors, causing vasoconstriction.
Example: Changing Body Positions
- Going from a supine (lying down) to standing position causes a drop in mean arterial pressure (MAP) as blood pools in the lower extremities.
- Baroreceptors sense this decrease in MAP, sending fewer action potentials to the brain.
- The brain interprets this as a low MAP and activates mechanisms to increase it.
Response to Low MAP
- The brain increases SNS activity.
- Heart Rate: Increased SNS activity increases heart rate by releasing norepinephrine, which activates β-adrenergic receptors, leading to more open Na+ channels and steeper drift.
- Stroke Volume: Increased SNS activity increases stroke volume by releasing norepinephrine, which activates β-adrenergic receptors, leading to more open Ca2+ channels and increased ventricular contractility.
- Total Peripheral Resistance (TPR): Increased SNS activity increases TPR by releasing epinephrine and angiotensin II, which activate α-adrenergic receptors, causing vasoconstriction.
- The brain decreases PNS activity, further increasing heart rate.
Summary
- A drop in MAP reduces firing rate of baroreceptors, which signals the brain.
- The brain responds by increasing SNS activity, increasing heart rate, stroke volume, and TPR, while decreasing PNS activity.
- These actions elevate MAP back to normal.
Systolic and Diastolic Blood Pressure
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Systolic Blood Pressure:
- Caused by the amount of blood leaving the ventricle.
- Directly impacted by heart rate and stroke volume (higher heart rate and stroke volume lead to higher systolic blood pressure).
-
Diastolic Blood Pressure:
- Caused by the recoil of the systemic arteries.
- Directly impacted by TPR (higher TPR leads to higher diastolic blood pressure).
Blood Volume
- Blood volume also influences blood pressure, with increased blood volume leading to increased blood pressure.
- The body can adjust blood volume through hormonal mechanisms to maintain or alter blood pressure.
Hormones Affecting Blood Volume
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Increased Blood Volume:
- Angiotensin II: Increases sodium and water retention, leading to increased blood volume.
- Aldosterone: Increases sodium and water retention, leading to increased blood volume.
- Anti-diuretic hormone (vasopressin): Increases water retention, leading to increased blood volume.
-
Decreased Blood Volume:
- Atrial natriuretic peptide (ANP): Increases sodium and water excretion, leading to decreased blood volume.
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Description
This quiz explores the baroreceptor reflex, a vital physiological mechanism for regulating blood pressure. It examines how baroreceptors in the aortic arch and carotid sinus respond to changes in blood flow and their interaction with heart rate regulation through the autonomic nervous system. Test your knowledge on this critical aspect of cardiovascular physiology.
