Regulation of the CVS 2 Flashcards
What is perfusion?
The flow of blood through a tissue
Adequate tissue perfusion is essential to maintain its nutritive demands.
What happens with too little perfusion?
Hypoxia, impaired metabolism, necrosis
Insufficient blood flow can lead to tissue damage.
What happens with too much perfusion?
Capillary/endothelial damage, fluid exudation
Excessive blood flow can harm the tissue structure.
What drives flow through a tube?
Pressure, opposed by resistance
This relationship is fundamental in understanding perfusion.
What is the major determinant of perfusion pressure?
Systemic arterial pressure
It is critical for driving tissue perfusion.
What are the two conditions that can affect arterial pressure?
Hypertension (high bp), Hypotension (low bp)
Both conditions impact tissue perfusion.
What factors can cause normal arterial pressure to vary?
Age, physiological status, species and breed, systole and diastole
Variability in arterial pressure is influenced by multiple factors.
How can adequate perfusion be maintained?
Change cardiac output AND/OR change vascular resistance
Adjusting these factors helps regulate blood flow.
What is the formula for mean arterial pressure?
Cardiac output / systemic vascular resistance
This formula helps assess the effectiveness of blood circulation.
How is arterial pressure controlled?
Negative feedback mechanisms
Both short-term and long-term feedback systems are involved.
What are the short-term mechanisms for controlling arterial pressure?
Baroreceptor regulation (ANS)
This allows for rapid adjustments to blood pressure.
What are the long-term mechanisms for controlling arterial pressure?
Circulating fluid volume, ADH, RAAS
These mechanisms include hormonal regulation.
What cardiovascular reflexes regulate arterial pressure?
Heart rate, contractility, tone of resistance vessels, volume of capacitance vessels
These factors work together to maintain blood pressure.
What are the three requirements for cardiovascular reflexes?
Sensors, integrating centre, effectors
These components are essential for pressure regulation.
What are baroreceptors?
Sensors for blood pressure, mechanoreceptors in arteries
They increase firing rate in response to pressure changes.
Where are baroreceptors located?
In adventitial layer of arteries (aortic arch and carotid sinus)
Their location is crucial for effective monitoring of blood pressure.
What is the role of the central axons of baroreceptors?
Terminate in the medulla oblongata (CV centre)
They relay information to the central nervous system.
What type of autonomic output do baroreceptors provide?
Sympathetic to heart and vessels, Parasympathetic to heart
This output helps modulate cardiovascular responses.
What is the baroreceptor reflex?
An extremely fast-acting mechanism that provides pressure buffering for short or acute changes in blood pressure
Changes occur in seconds, allowing for rapid adjustments.
How do baroreceptors respond to prolonged pressure alterations?
They exhibit evidence of ‘resetting’
This indicates that baroreceptors can adapt to sustained changes in blood pressure.
What does the RAAS stand for?
Renin-Angiotensin-Aldosterone System
It is a hormone system regulating fluid balance and blood pressure.
What triggers the release of renin in the RAAS?
Reduced perfusion of the kidney and sympathetic stimulation
These triggers activate the RAAS to help regulate blood pressure.
What is the function of renin in the RAAS?
It cleaves angiotensinogen into angiotensin I
Renin is an enzyme that initiates the RAAS response.
What enzyme converts angiotensin I to angiotensin II?
ACE (Angiotensin Converting Enzyme)
This conversion mainly occurs in the lungs.
List the effects of angiotensin II.
- Vasoconstriction (↑ SVR)
- Na+ reabsorption in kidney (↑ CO/preload)
- Increase sympathetic activity (↑HR & SV)
- Release anti-diuretic hormone (↑ CO/preload)
- Release aldosterone (more Na+ resorption)
Angiotensin II has multiple roles in regulating blood pressure and fluid balance.
What immediate control does the renin-angiotensin-aldosterone axis provide?
Immediate, potent control of MAP via angiotensin II
MAP stands for Mean Arterial Pressure.
What slower regulation does the RAAS provide?
Slower, prolonged regulation of MAP via volume control (aldosterone + ADH)
Aldosterone and ADH help maintain blood volume and pressure over time.
What are volume receptors and where are they located?
Atrial receptors in the heart act as low-pressure baroreceptors and volume receptors
They detect changes in blood volume based on stretch.
What happens when high volume is detected by atrial receptors?
- Inhibition of sympathetic pathways -> renal vasodilation (diuresis)
- Inhibition of ADH/vasopressin
- Other effects via Atrial Natriuretic Peptide (ANP)
These responses help regulate blood volume and pressure.
What is an example of a coordinated response in the cardiovascular system?
Acute hemorrhage
This triggers acute cardiovascular reflexes and longer-term volume restoration.
What cardiovascular reflexes are involved in response to acute hemorrhage?
Baroreceptor reflex and atrial volume receptors
These reflexes quickly respond to changes in blood pressure and volume.
What is the longer-term mechanism for volume restoration after acute hemorrhage?
RAAS
RAAS helps restore blood volume and pressure over time.
