Blood Pressure Regulation in Upright Posture

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Questions and Answers

What type of receptors respond to changes in blood volume?

Baroreceptors in the aorta and carotid arteries

Chemoreceptors in the brain and peripheral vessels

Mechanoreceptors in the heart and small pulmonary vessels

Cardio-pulmonary stretch receptors in the heart and large pulmonary vessels (correct)

What is the effect of decreased blood volume on thirst and water reabsorption?

Increased thirst and increased water reabsorption (correct)

No effect on thirst and water reabsorption

Decreased thirst and increased water reabsorption

Decreased thirst and decreased water reabsorption

Which of the following is NOT a stimulus for peripheral chemoreceptors?

Increased pCO2

Increased pH (correct)

Decreased pO2

Decreased pCO2

What is the effect of cardio-pulmonary stretch receptors on BP and CO?

Support BP and CO Signup and view all the answers

What is the response to activation of peripheral chemoreceptors?

Sympathetic vasoconstriction Signup and view all the answers

What hormone is released in response to decreased blood volume?

ADH (vasopressin) Signup and view all the answers

What is the approximate change in foot artery pressure when transitioning from a supine to an upright position?

80 mmHg Signup and view all the answers

Which of the following is NOT a direct consequence of the increased foot capillary pressure during upright posture?

Increased blood flow through the foot vascular bed Signup and view all the answers

What is the primary mechanism by which venous valves in the limbs transiently shut when transitioning to an upright position?

Reduced blood flow through the veins Signup and view all the answers

What is the approximate volume of blood that accumulates in the veins below the heart after 45 seconds of standing?

300-600 ml Signup and view all the answers

What is the primary mechanism by which the increased blood volume in the veins below the heart contributes to the decrease in cardiac output?

Reduced venous return Signup and view all the answers

Which of the following best describes the effect of gravity on blood flow in the legs during upright posture?

Gravity indirectly affects blood flow in the legs by affecting venous return Signup and view all the answers

How does the distensibility of the vascular system contribute to the circulatory response to standing?

Distensibility allows the veins to accommodate the increased blood volume during standing Signup and view all the answers

What is the approximate decrease in central venous pressure when transitioning from a supine to an upright position?

3 mmHg Signup and view all the answers

What is the primary role of peripheral chemoreceptors in response to blood gas changes?

Sense decreased pO2, increased pCO2, and decreased pH Signup and view all the answers

What is the effect of sympathetic drive during a hemorrhage?

Increases heart rate and contractility Signup and view all the answers

Which of the following best describes the baroreceptor reflex when blood pressure decreases?

Sympathetic drive is increased, heart rate increases Signup and view all the answers

What physiological response accompanies pallor and cold/clammy skin during hemorrhage?

Sympathetic-mediated vasoconstriction Signup and view all the answers

How does the renin-angiotensin-aldosterone system get activated during hemorrhage?

Due to renal vasoconstriction Signup and view all the answers

What is the consequence of a significant reduction in sympathetic system activity during hemorrhage?

Increased susceptibility to severe blood loss Signup and view all the answers

What changes occur to total peripheral resistance (TPR) during a hemorrhage?

TPR increases due to vasoconstriction Signup and view all the answers

What is the Bezold-Jarisch reflex believed to trigger in response to changes in blood pressure?

Bradycardia and vasodilatation Signup and view all the answers

What is a notable outcome of mobilization of blood from the splanchnic circulation during hemorrhage?

Increased cardiac output Signup and view all the answers

What is the most common cause of circulatory shock?

Haemorrhage Signup and view all the answers

What happens to blood pressure when a person faints and remains upright?

Blood pressure remains low, risking brain damage Signup and view all the answers

What impact does chronic, slow blood loss have on the body?

It results in iron deficiency anemia Signup and view all the answers

Which of the following conditions exemplifies concealed hemorrhage?

Ruptured ectopic pregnancy Signup and view all the answers

What is a potential consequence of prolonged circulatory shock?

Tissue damage due to inadequate nutrient delivery Signup and view all the answers

What physiological response meets the body's needs when fainting occurs?

Supine position which enhances venous return Signup and view all the answers

Which of the following best describes revealed hemorrhage?

Bleeding that is obvious but uncertain in volume Signup and view all the answers

What is the effect of a blood pressure decrease to less than 50 mmHg on the central nervous system?

Profound vasoconstriction Signup and view all the answers

Which factor primarily initiates the renal mechanisms for restoring blood volume?

Decreased blood volume Signup and view all the answers

How does 'internal transfusion' contribute to blood volume restoration?

By reabsorbing fluid from the interstitium into plasma Signup and view all the answers

What initiates the increase in renin release during blood loss?

Reduced carotid blood pressure Signup and view all the answers

What condition results from the hemoglobin level being normal immediately after a hemorrhage?

Equal decrease in RBCs and plasma volume Signup and view all the answers

What role do atrial natriuretic peptide (ANP) levels play in blood volume restoration?

Inhibits renin release Signup and view all the answers

What characterizes the change in reticulocyte count after a mid-moderate blood loss?

Increase peaking at 5-15% after 5-7 days Signup and view all the answers

What drives fluid movement from intracellular compartments during the restoration of blood volume?

Increased hepatic glucose production Signup and view all the answers

How does blood loss specifically affect cardiac output (CO) allocation?

CO is protected for key organs like the brain and heart Signup and view all the answers

Which physiological response occurs due to a prolonged loss of blood volume?

Increased sympathetic activity Signup and view all the answers

Study Notes

Blood Vessels and Postural Changes

Blood vessels are distensible; they adapt to varying pressures and volumes.
Upright posture increases vascular pressures by approximately 90 mmHg in the feet.
Foot capillary pressure rises, leading to increased filtration and swelling, though the flow remains unchanged due to a constant pressure gradient.
Upon standing, venous valves in limbs close temporarily, causing blood to pool below the heart, resulting in spillage of 300-600 ml after about 45 seconds.

Hemorrhage and its Types

Revealed hemorrhage is visibly obvious, while concealed hemorrhage may occur from conditions like a ruptured spleen or ectopic pregnancy.
The effects of blood loss depend on volume and speed: chronic blood loss can lead to iron deficiency anemia; acute large loss reduces circulating volume significantly.

Circulatory Shock

Defined as inadequate blood flow throughout the body, leading to potential tissue damage.
Common causes include hemorrhage, burns, severe vomiting, and diarrhea alongside other hypovolemic states.

Reflex Responses to Hemorrhage

Reflex mechanisms triggered in response to low blood pressure include increased heart rate, contractility, and peripheral vasoconstriction.
Sympathetic responses with reduced parasympathetic drive work to elevate cardiac output and total peripheral resistance (TPR).
Symptoms from response include pallor, cold sweating, fatigue, and activation of the renin-angiotensin-aldosterone system (RAAS).

Baroreceptor Reflex

Baroreceptors respond to diminished blood pressure, leading to increased heart rate and cardiac output via sympathetic stimulation.
The sympathetic system is crucial; blood loss greater than 15-20% induces rapid death if this system is blocked.

Chemoreceptor and Central Nervous System Responses

Peripheral chemoreceptors detect alterations in blood gas composition, stimulating sympathetic vasoconstriction and increasing ventilation.
The CNS ischaemic response activates profound vasoconstriction when blood pressure falls below 50 mmHg, prioritizing blood flow to essential organs like the brain and heart.

Restoration Mechanisms

Recovery from moderate hemorrhage occurs through “internal transfusion” involving hemodilution and increased water absorption.
Renal mechanisms play a significant role, driving renin-angiotensin pathways to restore blood volume through salt and water reabsorption.

Blood Quality Restoration After Hemorrhage

The quality of blood, specifically hemoglobin levels, initially appears normal post-hemorrhage due to the simultaneous decline in both red blood cells and plasma volume.
The reticulocyte count generally peaks 5-7 days post-hemorrhage, as the body responds to anemia and stimulates red blood cell production.

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Description

This quiz explores the effects of upright posture on blood pressure in the feet and the role of blood vessels in regulating pressure. It covers the changes in mean capillary pressure and arterial pressure in supine and orthostatic positions.