11. Physiology - Blood Flow Regulation

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Questions and Answers

What is the primary neurotransmitter released by sympathetic post-ganglionic neurons?

Dopamine

Serotonin

Acetylcholine

Norepinephrine (correct)

Which effect does the binding of norepinephrine to alpha adrenergic receptors primarily cause?

Decreased heart rate

Increased nitric oxide production

Vasodilation of all blood vessels

Vasoconstriction of arterioles and venules (correct)

How is angiotensin II formed from its precursor molecules?

Renin converts angiotensinogen into angiotensin I, which is then activated into angiotensin II. (correct)

Angiotensinogen is converted directly into angiotensin II by the kidneys.

Angiotensin I is converted into angiotensin II through direct vascular stimulation.

Renin acts directly on angiotensin II to enhance its effects.

Which of the following tissues primarily experience vasodilation via sympathetic active vasodilator nerves?

Skeletal muscle and skin Signup and view all the answers

What initiates the release of renin from juxtaglomerular cells in the kidneys?

Decreased arterial pressure and renal sympathetic nerve activity Signup and view all the answers

What is the primary function of endothelin (ET-1) once released into the bloodstream?

It causes smooth muscle contraction. Signup and view all the answers

Which of the following factors stimulates the formation and release of ET-1?

Reactive oxygen species Signup and view all the answers

The process of reactive hyperemia is primarily characterized by what physiological change?

Increased blood flow following a period of occlusion. Signup and view all the answers

Which of the following molecules inhibits the release of ET-1?

Atrial natriuretic peptide Signup and view all the answers

How does endothelial-derived ET-1 primarily influence vascular smooth muscle?

By causing the sarcoplasmic reticulum to release calcium. Signup and view all the answers

What determines the extent and duration of reactive hyperemia?

The duration of the blood flow occlusion. Signup and view all the answers

Which of the following vasoactive metabolites is continuously produced during normal metabolism?

Lactate Signup and view all the answers

Endothelin is derived from a precursor of how many amino acids?

39 Signup and view all the answers

Which of the following is considered one of the most potent vasoconstrictors known?

Endothelin Signup and view all the answers

What role does nitric oxide play in relation to ET-1?

It inhibits the synthesis of ET-1. Signup and view all the answers

What triggers the vasodilation of arterioles during reactive hyperemia?

Accumulate of metabolites due to low blood flow Signup and view all the answers

Which of the following plays a significant role in mediating active hyperemia?

Increased production of vasoactive metabolites Signup and view all the answers

What is the effect of nitric oxide (NO) blockade during reactive hyperemia?

Reduces basal blood flow levels Signup and view all the answers

The increase in blood flow during reactive hyperemia primarily serves what purpose?

To wash away accumulation of metabolites Signup and view all the answers

Active hyperemia is best described by which statement?

Blood flow increases proportionally with metabolic activity Signup and view all the answers

Which of the following metabolites is NOT typically associated with vasodilation during active hyperemia?

Norepinephrine Signup and view all the answers

How does flow-mediated vasodilation occur in relation to shear stress?

Greater shear stress promotes the release of nitric oxide Signup and view all the answers

What is the primary physiological significance of autoregulation?

Maintains constant blood flow despite pressure variations Signup and view all the answers

During vasodilation in skeletal muscle, what role does your body’s metabolism play?

It increases the production of vasodilators. Signup and view all the answers

What is the primary function of autoregulation in blood flow?

To maintain constant blood flow despite changes in perfusion pressure. Signup and view all the answers

Which hypothesis explains the initial increase in blood flow due to increased perfusion pressure as well as the subsequent decrease?

Metabolic Hypothesis. Signup and view all the answers

Which vascular beds are noted to display effective autoregulation?

Kidney and brain. Signup and view all the answers

What occurs in the myogenic hypothesis in response to an increase in perfusion pressure?

Vascular smooth muscle contracts due to increased tension. Signup and view all the answers

How does decreased perfusion pressure affect blood flow according to the metabolic hypothesis?

Blood flow decreases leading to vasodilation to return to normal. Signup and view all the answers

Which of the following statements about autoregulation is NOT true?

It is effective outside of the autoregulatory range. Signup and view all the answers

What is the consequence of increased blood flow through metabolic vasodilators, according to the metabolic hypothesis?

Washing out of metabolic vasodilators and vasoconstriction. Signup and view all the answers

Which statement best describes the relationship between perfusion pressure (P), flow (F), and resistance (R)?

F is independent of changes in P if R does not change. Signup and view all the answers

What is primarily responsible for the decrease in blood flow back toward normal levels in the myogenic hypothesis?

Contraction of smooth muscle due to increased tension. Signup and view all the answers

What primary factors regulate local blood flow?

Intrinsic tissue factors Signup and view all the answers

Which hypothesis explains autoregulation related to blood pressure changes in tissues?

Myogenic hypothesis Signup and view all the answers

Which substance, produced by the endothelium, plays a crucial role in vasodilation?

Nitric Oxide Signup and view all the answers

What role does soluble guanylate cyclase play in the vasodilation process initiated by nitric oxide?

Synthesizes cyclic-GMP from GTP Signup and view all the answers

Which receptors are involved in remote control of circulation through hormonal signals?

Alpha, beta, AII, and V1 receptors Signup and view all the answers

How does tissue pressure influence local blood flow regulation?

By causing mechanical compression of vessels Signup and view all the answers

What is the primary function of the endothelium in blood vessel regulation?

Regulates smooth muscle activity through factor release Signup and view all the answers

Which term describes the increase in blood flow that occurs after a period of occlusion?

Reactive hyperemia Signup and view all the answers

What stimulates the additional release of endothelin (ET-1) from the vascular endothelium?

Reactive oxygen species Signup and view all the answers

Which physiological process is primarily characterized by elevated blood flow after the release of an obstruction?

Reactive hyperemia Signup and view all the answers

What is the primary effect of endothelin (ET-1) binding to its receptors in vascular smooth muscle?

Increased calcium release from the sarcoplasmic reticulum Signup and view all the answers

How is the extent of reactive hyperemia influenced?

By the duration of blood flow occlusion Signup and view all the answers

Which of the following substances inhibits the release of endothelin (ET-1)?

Atrial natriuretic peptide Signup and view all the answers

Which of the following best describes the difference between active hyperemia and reactive hyperemia?

Active hyperemia occurs due to increased metabolic demand, while reactive hyperemia occurs after a period of reduced blood flow. Signup and view all the answers

What role does Nitric Oxide play in the regulation of vascular smooth muscle activity?

It diffuses into vascular smooth muscle to stimulate the production of cyclic-GMP, promoting vasodilation. Signup and view all the answers

Which hypothesis explains the initial increase in blood flow due to an increase in perfusion pressure?

The myogenic hypothesis, which suggests that smooth muscle cells respond to stretch. Signup and view all the answers

Which type of receptor is NOT typically associated with the remote control of circulation?

Dopamine receptors Signup and view all the answers

What is the primary physiological mechanism of autoregulation in response to increased perfusion pressure?

Constriction of arterial smooth muscle in response to stretch to stabilize blood flow. Signup and view all the answers

What mechanism is primarily involved in the decrease of blood flow following an increase in perfusion pressure according to the metabolic hypothesis?

Decreased concentration of metabolic vasodilators Signup and view all the answers

Which statement accurately reflects the relationship between perfusion pressure, blood flow, and vascular resistance?

Blood flow increases when perfusion pressure increases at constant resistance Signup and view all the answers

In the myogenic hypothesis, what is the primary response of vascular smooth muscle when subjected to increased tension?

Contraction occurs to decrease blood flow Signup and view all the answers

Which of the following best describes the autoregulatory range?

A range of perfusion pressures where blood flow regulation is effective Signup and view all the answers

What occurs in vascular beds that do not exhibit marked autoregulation when perfusion pressure changes?

Significant changes in blood flow occur with changes in perfusion pressure Signup and view all the answers

According to the myogenic hypothesis, what happens to blood flow when perfusion pressure decreases?

Vascular smooth muscle relaxes, which increases blood flow Signup and view all the answers

What defines the metabolic hypothesis in the context of blood flow regulation?

Immediate vasodilation followed by sustained vasoconstriction Signup and view all the answers

In what way does autoregulation differ between the kidneys and skeletal muscle?

Kidneys and the brain demonstrate effective autoregulation while others do not Signup and view all the answers

How does sustained increased perfusion pressure affect blood flow over time?

Blood flow initially rises and then decreases back toward normal Signup and view all the answers

Study Notes

Local Control Mechanisms

Endothelium
- Plays an active role in regulating vascular smooth muscle activity by releasing vasoconstrictors and vasodilators.
- Nitric Oxide (NO):
  - Endothelial cells constantly produce nitric oxide.
  - NO is a vasodilator.
  - NO is synthesized by nitric oxide synthase (NOS) from L-arginine.
  - NO diffuses into vascular smooth muscle and stimulates soluble guanylate cyclase, increasing cGMP levels.
- Endothelin (ET-1):
  - A potent vasoconstrictor.
  - A 21 amino acid peptide produced by the vascular endothelium.
  - Released by stimulation by angiotensin II (AII), antidiuretic hormone (ADH), thrombin, cytokines, reactive oxygen species, and shearing forces.
  - Inhibition by prostacyclin, atrial natriuretic peptide, and nitric oxide.
  - Binds to receptors on vascular smooth muscle, increasing calcium release from the sarcoplasmic reticulum and promoting contraction.
Reactive Hyperemia:
- Increase in blood flow to an organ after a period of occlusion.
- Caused by:
  - Tissue hypoxia
  - Build-up of vasoactive metabolites
- The extent and duration of reactive hyperemia depend on the duration of the occlusion.
- Role of Nitric Oxide:
  - Increased shear stress on the endothelium during the increased blood flow stimulates NO production and release.
  - NO blockade reduces the peak and duration of reactive hyperemia.
Active Hyperemia:
- Increase in blood flow to an organ due to increased metabolic activity.
- The extent of the increase in blood flow is proportional to the magnitude of the increase in metabolic rate.
- Similar mechanisms to reactive hyperemia:
  - Increased production of vasodilators (H+, lactate, K+, CO2, adenosine, prostaglandins)
  - Flow mediated vasodilation via NO release
Autoregulation:
- The ability of an organ or tissue to maintain a relatively constant blood flow despite changes in perfusion pressure.
- Two major hypotheses explain autoregulation:
  - Metabolic Hypothesis: Increased pressure leads to initial increased blood flow, which washes out vasodilators and causes vasoconstriction.
  - Myogenic Hypothesis: Increased pressure causes tension on vascular smooth muscle, leading to contraction and vasoconstriction.
- Autoregulation is most effective within a specific range of arterial pressures (autoregulatory range).

Remote Control Mechanisms

Neural Control:
- Control by the autonomic nervous system, primarily the sympathetic nervous system.
- Sympathetic post-ganglionic neurons use norepinephrine (NE) as the primary neurotransmitter.
- NE binds to alpha adrenergic receptors, causing vasoconstriction in arterioles and venules.
- Sympathetic active vasodilator nerves cause vasodilation in skeletal muscle and skin; the neurotransmitter is unknown.
- Parasympathetic nervous system innervates blood vessels in the genitals, heart, and brain.
- Parasympathetic activation releases acetylcholine (Ach), which binds to muscarinic receptors on the endothelium, leading to NO release.
Circulating Factors:
- Renin-Angiotensin II System:
  - Renin is released from the juxtaglomerular cells of the kidneys in response to decreased arterial pressure, increased renal sympathetic nerve activity, or decreased sodium load.
  - Renin converts angiotensinogen to angiotensin I.
  - Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE).
  - Angiotensin II activates vascular AII receptors, causing vasoconstriction.
  - The renin-angiotensin II system is a key player in blood pressure regulation.

Local – Remote Interaction

Local control and remote control mechanisms interact to regulate blood flow.

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Description

Explore the vital roles of the endothelium in vascular regulation. This quiz covers the mechanisms of nitric oxide as a vasodilator and endothelin as a vasoconstrictor, including their biochemical pathways and physiological effects. Test your understanding of how these substances impact vascular smooth muscle activity.