Blood Pressure Regulation

Are cardiac output (CO) and total peripheral resistance (TPR) independent variables?

No, they are interdependent—changes in one affect the other.

What happens to cardiac output if TPR doubles?

Cardiac output decreases, and mean arterial pressure (Pa) increases only slightly.

What happens to TPR if cardiac output is reduced by half?

There is a compensatory increase in TPR, and Pa will decrease.

What is the formula for arterial pressure (Pa)?

Pa = Cardiac Output × Total Peripheral Resistance (TPR)

What mechanisms monitor arterial pressure (Pa)?

Cardiovascular reflexes respond when Pa increases or decreases beyond a set point.

What happens when Pa changes above or below the set point?

Cardiovascular reflexes activate to restore it toward normal.

What are the two main types of arterial pressure control mechanisms?

Short-term (neural) and long-term (hormonal) control mechanisms.

What reflex monitors arterial pressure through stretch receptors in the carotid sinus and aortic arch?

Baroreceptor reflex.

What reflex responds to changes in blood oxygen, carbon dioxide, and pH levels?

Chemoreceptor reflex.

What reflex is triggered by severely reduced cerebral blood flow (ischemia)?

CNS ischemic response.

What low-pressure receptors help regulate blood volume and pressure?

Atrial and pulmonary artery reflexes.

What reflex connects the atria to the kidneys and influences urine output?

Atrial reflex to the kidney.

What reflex increases heart rate in response to increased venous return?

Bainbridge reflex.

What is the primary long-term hormonal system regulating arterial pressure?

Renin-Angiotensin-Aldosterone System (RAAS).

Which organ plays a key role in long-term arterial pressure regulation through hormonal control?

The kidneys.

Which branch of the autonomic nervous system regulates circulation?

Sympathetic nervous system (SNS).

Which branch of the autonomic nervous system primarily regulates heart function?

Parasympathetic nervous system (PNS).

Where is the vasomotor center located?

In the reticular substance of the medulla and the lower third of the pons.

How does the vasomotor center transmit parasympathetic impulses?

Through the vagus nerve to the heart.

How does the vasomotor center transmit sympathetic impulses?

Through the spinal cord and peripheral sympathetic nerves to all arteries, arterioles, and veins in the body.

What is the function of the vasomotor center?

To regulate vascular tone and heart activity via sympathetic and parasympathetic output

What type of reflexes are baroreceptors involved in?

Fast, neurally mediated reflexes that help maintain constant arterial pressure.

Where are the carotid baroreceptors located?

In the carotid sinus, which is located at the bifurcation (split) of the common carotid artery into the internal and external carotid arteries.

Where are the aortic baroreceptors located?

In the aortic arch.

What nerve carries signals from the carotid baroreceptors to the brain?

The glossopharyngeal nerve (cranial nerve IX).

What nerve carries signals from the aortic baroreceptors to the brain?

The vagus nerve (cranial nerve X).

What is the function of the baroreceptor reflex?

It detects blood pressure changes and activates afferent neurons to relay signals to the brainstem, which then sends efferent signals to adjust heart rate and blood vessel tone.

Where are baroreceptors located?

In the carotid sinus and aortic arch.

What is the central processing area for baroreceptor signals?

The medulla in the brainstem.

When is the chemoreceptor reflex most active?

During severe hypoxia, hemorrhage, or hypotension.

What stimulates the chemoreceptor reflex?

↓ PaO₂, ↑ PaCO₂, and ↓ pH.

What physiological response does hypoxia cause in real-life conditions?

Tachycardia.

When is the CNS ischemic response triggered?

When MAP drops below 60 mmHg

blood flow to brain is below adequate level -cerebral ischemia

CO2 and H+ increase

What does the chemosensitive area in the VMC do when activated by cerebral ischemia?

It sends strong signals to stimulate both vagal and sympathetic nerves.

Why does the body reduce blood flow to most tissues during the CNS ischemic response?

To maintain adequate blood flow to the brain and heart, which are vital organs.

What is the effect of stimulating both vagal and sympathetic nerves during cerebral ischemia?

It triggers bradycardia (via vagal stimulation) and intense vasoconstriction and increased contractility (via sympathetic stimulation) to preserve central perfusion.

What triggers the CNS ischemic response?

Cerebral ischemia due to mean arterial pressure (PA) < 60 mmHg and increased CO2 and H+ levels

Which brain center is activated during cerebral ischemia?

The Vasomotor Center (VMC) in the. brain

What is the autonomic resopnse of the VMC to cerebral ischemia?

Increased sympathetic activity and decreased parasympathetic activity

What cardiovascular changes occur due to sympathetic stimulation in CNS ischemia?

increased heart rate (tachycardia), increased contractility, and increased total peripheral resistance (TPR)

What is the overall goal of the CNS ischemic response?

To increase cerebral blood flow

What happens to blood flow to other tissues during the CNS ischemic response?

blood flow to all other tissues decreases due to increased TPR

What happens if cerebral ischemia becomes more severe?

parasympathetic activity increases, potentially leading to bradycardia

What are the two types of low-pressure atrial receptors?

A fibers and B fibers.

When do A fibers fire, and what do they monitor?

A fibers fire in synchrony with atrial systole and monitor heart rate.

When do B fibers fire, and what do they monitor?

B fibers fire during ventricular systole and gradually increase their firing rate as the atria fill. They monitor rising atrial volume.

At what point do B fibers reach their maximum firing frequency?

At the peak of the v wave of the atrial pressure curve.

What do low-pressure receptors primarily monitor?

Effective circulating volume and venous return.

Where are low-pressure receptors located?

In the atria, ventricles, and pulmonary artery.

How are low-pressure receptors innervated?

Their afferent signals join the vagus nerve and project to the Nucleus of the Solitary Tract (NTS) in the brainstem.

What is the renal response to activation of low-pressure receptors?

Dilation of kidney afferent arterioles, leading to increased GFR (glomerular filtration rate).

What hormones are inhibited by this reflex?

Angiotensin, Aldosterone, and ADH (which reduces fluid reabsorption).

What is the overall cardiovascular effect of low-pressure receptor activation?

A decrease in mean arterial pressure (MAP)

What is the main stimulus for the release of atrial natriuretic factor (ANF)?

Distention of the atria during volume expansion (increased atrial pressure)

What is the most important vascular effect of ANF?

Relaxation of vascular smooth muscle, causing vasodilation and a decrease in total peripheral resistance (TPR).

How does ANF affect the kidneys?

It causes vasodilation in the kidneys, leading to increased sodium and water excretion.

What is the overall effect of ANF on blood pressure?

Reduces blood pressure by decreasing blood volume and TPR.

Where does ANF inhibit sodium reabsorption in the nephron?

At the inner medullary collecting duct.

How does ANF affect ADH?

It inhibits both the release and action of ADH.

How does ANF affect renin?

It inhibits renin secretion.

How does ANF affect aldosterone?

It inhibits angiotensin-induced aldosterone secretion.

How does ANF increase GFR (glomerular filtration rate)?

By relaxing the afferent arteriole and causing mild constriction of the efferent arteriole, which increases pressure in the glomerular capillaries.

What defines the equilibrium point in the renal regulation of blood pressure?

When salt and water output equals intake.

Why is this equilibrium important for blood pressure?

It helps maintain a stable extracellular fluid volume, which in turn helps keep arterial pressure within normal limits.

How does the renal–body fluid system regulate arterial pressure?

It regulates slowly but powerfully by adjusting salt and water excretion

What happens if blood volume increases and vascular capacitance stays the same?

Arterial pressure increases.

How does the kidney respond to a rise in arterial pressure?

It increases excretion of excess volume, helping to bring pressure back to normal.

What is the overall effect of the renal–body fluid system on long-term BP?

It stabilizes arterial pressure by balancing fluid intake and output.

What are the two main determinants of long-term arterial pressure?

• Degree of shift of the renal function curve along the pressure axis

• Level of salt and water intake

What can cause a shift in the renal output curve?

Abnormalities in the kidney function.

How much can the renal output curve shift due to kidney abnormalities?

Up to 50 mmHg.

What happens to blood pressure if salt and water intake increases 4 times?

Blood pressure can increase to 160 mmHg.

What is the first event in this volume-mediated pathway for BP regulation?

Increased extracellular fluid volume.

What does increased extracellular fluid volume lead to?

Increased blood volume.

What effect does increased blood volume have on circulation?

Increased mean circulatory filling pressure.

What does increased mean circulatory filling pressure cause?

Increased venous return to the heart.

What does increased venous return result in?

Increased cardiac output (CO).

How does the body respond to increased cardiac output?

Through autoregulation, which increases total peripheral resistance (TPR)

What is the net effect of increased CO and TPR?

Increased arterial pressure.

How does the body correct increased arterial pressure?

Increased urine output, which reduces extracellular fluid volume, completing the feedback loop.

What does the RAAS primarily regulate?

Arterial pressure (PA) by regulating blood volume.

When is the RAAS activated?

In response to a drop in blood pressure (BP).

How long does it take for angiotensin to become fully active?

About 20 minutes.

What can angiotensin do during severe hemorrhage?

It is strong enough to return blood pressure halfway back to normal.

What is one of the most important functions of the renin-angiotensin system?

To allow a person to ingest very small or very large amounts of salt without causing major changes in extracellular fluid volume or arterial pressure

What happens with increased salt intake?

1. Increased extracellular fluid volume

2. Increased arterial pressure

How does the body respond to increased extracellular fluid volume and arterial pressure?

Decreased renin and angiotensin levels.

What effect does decreased renin and angiotensin have on the kidneys?

It leads to decreased renal retention of salt and water.

What is the outcome of decreased renal retention of salt and water?

Return of extracellular volume and arterial pressure almost back to normal.

What are the expected physiological changes in response to traumatic injury with bleeding (e.g., hand severed in a machine accident)?

• Baroreceptor firing frequency: Decreases due to blood loss.

• Sympathetic system: Activated to maintain blood pressure.

• Heart rate (HR): Increases due to sympathetic stimulation.

• Cardiac contractility: Increases to support circulation.

• Total peripheral resistance (TPR): Increases due to vasoconstriction.

• Renin secretion: Increases to activate the renin-angiotensin system.

• Venous system: Venoconstriction increases venous return.

• Angiotensin II: Increases to raise blood pressure and conserve fluids.