Podcast
Questions and Answers
What determines cardiac output?
What determines cardiac output?
How is preload defined in relation to cardiomyocytes?
How is preload defined in relation to cardiomyocytes?
Which nerve is primarily responsible for regulating heart rate through the medulla?
Which nerve is primarily responsible for regulating heart rate through the medulla?
What does afterload measure in cardiac function?
What does afterload measure in cardiac function?
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What is the equation for calculating cardiac output?
What is the equation for calculating cardiac output?
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What two factors primarily determine blood pressure in the circulatory system?
What two factors primarily determine blood pressure in the circulatory system?
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Which term describes the resistance faced by blood flow in the circulatory system?
Which term describes the resistance faced by blood flow in the circulatory system?
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How does an increase in cardiac output affect blood pressure, assuming total peripheral resistance remains constant?
How does an increase in cardiac output affect blood pressure, assuming total peripheral resistance remains constant?
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Which aspect of heart physiology is primarily affected by changes in total peripheral resistance?
Which aspect of heart physiology is primarily affected by changes in total peripheral resistance?
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What happens to total peripheral resistance when blood vessels dilate?
What happens to total peripheral resistance when blood vessels dilate?
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What is the relationship between pressure, resistance, and flow in blood vessels?
What is the relationship between pressure, resistance, and flow in blood vessels?
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What factor primarily influences capillary exchange in tissues?
What factor primarily influences capillary exchange in tissues?
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Which of the following correctly describes the role of stroke volume in determining blood flow?
Which of the following correctly describes the role of stroke volume in determining blood flow?
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How does vascular resistance affect blood pressure regulation?
How does vascular resistance affect blood pressure regulation?
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Which statement best describes bulk flow in capillaries?
Which statement best describes bulk flow in capillaries?
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Study Notes
Physiology of Circulation
- The session will continue the introduction to the cardiovascular system, focusing on the vasculature and blood pressure regulation.
- Review the cardiovascular system and heart functions from Week 3.
- Students need a pen and paper or laptop for the session.
Session Outcomes
- Explain relationships between pressure, resistance, and blood flow.
- Describe how pressure changes across the circulatory system.
- Explain how venous return increases unidirectional blood flow.
- Explain mechanisms that regulate mean arterial pressure.
- Describe forces influencing fluid movement within capillaries (capillary exchange and bulk flow).
Learning Outcome 1
- Understand the relationship between pressure, resistance, and blood flow.
Cardiac Output
- Cardiac output (CO) is equal to heart rate (HR) multiplied by stroke volume (SV).
- CO = HR x SV
- Stroke volume (SV) is the volume of blood ejected per beat.
- Heart rate (HR) is the number of beats per minute.
- Cardiac output (CO) is the volume of blood flowing through the circulation per minute
Regulation of Heart Rate
- The medulla controls heart rate.
- The vagus nerve slows heart rate.
- The cardiac accelerator nerve speeds up heart rate.
Factors Affecting Stroke Volume
- Preload: The amount of sarcomere stretch in cardiomyocytes at the end of ventricular filling.
- Contractility: The relative ability of the heart to eject a stroke volume at a given preload and afterload.
- Afterload: The amount of work the heart has to do to pump blood to the rest of the body.
Determinants of Mean Arterial Pressure
- Cardiac output
- Total peripheral resistance
- Heart rate
- Stroke volume
- Vessel radius
- Blood viscosity
- Vessel length
Blood Pressure
- Systolic blood pressure (SBP) is the pressure exerted against the artery walls during systole (contraction).
- Diastolic blood pressure (DBP) is the pressure exerted against the artery walls during diastole (relaxation).
- Mean arterial pressure (MAP) is the average pressure exerted against the vessels. MAP = Diastolic pressure + 1/3 pulse pressure
Pressures Within the Systemic Circulation
- Blood pressure drops as it moves through the systemic circulation (from aorta to vena cava).
- Systolic pressure is highest in the aorta, and diastolic pressure is lowest in the vena cava.
Vasculature
- Elastic arteries experience high pressure and dampen pulsatility.
- Muscular arteries distribute blood flow and regulate blood flow.
- Arterioles are the primary site for vascular resistance and regulate blood flow to tissues.
Factors Affecting Venous Return
- Postural changes
- Muscular pump
- Respiratory pump
- Venoconstriction
Learning Outcome 3
- Describe the mechanisms that increase venous return.
Veins
- Veins serve as conduits and capacitance vessels.
- The venous system (64%) distributes blood throughout the body at rest, with remaining blood in pulmonary vessels (9%), heart (7%), systemic arteries and arterioles (13%), and systemic capillaries (7%)
Learning Outcome 4
- Describe the main mechanisms to regulate blood pressure.
Autonomic Innervation
- Baroreceptors in the aortic arch and carotid sinus detect changes in blood pressure.
- This information is relayed to the cardiovascular center in the medulla.
- The medulla adjusts sympathetic and parasympathetic activity.
- SA and AV nodes are innervated by both sympathetic and parasympathetic systems.
- Ventricles are innervated only by the sympathetic system.
- Blood vessels are innervated only by the sympathetic system.
Short-Term Control of Blood Pressure: The Baroreceptor Reflex
- The baroreceptor reflex is a feedback loop to regulate blood pressure.
- The increase/decrease activates baroreceptors, which regulates heart rate and vasodilation/vasoconstriction, returning blood pressure to normal.
The Sympathetic Nervous System
- The sympathetic nervous system (SNS) is responsible for immediate changes in blood flow, like during exercise.
- SNS fibers release noradrenaline (NA).
- Noradrenaline acts on β1-receptors in the heart to increase heart rate (HR) and stroke volume (SV).
- Noradrenaline acts on α1-receptors in blood vessels to cause vasoconstriction and on β2-receptors in blood vessels to cause vasodilation.
Long-Term Control of Blood Pressure
- The kidneys and renin-angiotensin-aldosterone system regulate blood pressure via adjusting the volume of blood.
- This system reacts by changing water and sodium reabsorption in the kidneys.
Learning Outcome 5
- Describe the forces influencing fluid movement in capillaries.
Capillary Exchange
- Oxygen, carbon dioxide, nutrients, and wastes diffuse across capillaries.
- This occurs through diffusion as substances move from high to low concentration.
- Lipid-soluble substances diffuse through the lipid bilayer.
- Small, water-soluble substances diffuse between cells.
Fluid Filtration Across Capillaries (Starling Forces)
- Hydrostatic pressure: The pressure exerted against the capillary walls.
- Osmotic pressure: The osmotic pressure created by proteins in the blood.
- Net filtration pressure: The difference between hydrostatic and osmotic pressures.
Net Filtration Pressure
- NFP = (BHP + IFOP) – (BCOP + IFHP).
- Net Pressure = Net pressure out – Net pressure in
- BHP: Blood hydrostatic pressure; IFOP: Interstitial fluid osmotic pressure; BCOP: Blood colloidal osmotic pressure; IFHP: Interstitial fluid hydrostatic pressure.
- NFP= (BHP + IFOP) - (BCOP + IFHP)
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Description
Test your knowledge on key concepts in cardiovascular physiology, including cardiac output, preload, afterload, and the role of blood pressure. This quiz covers fundamental relationships in the circulatory system, such as resistance and flow, as well as the impact of heart rate regulation. Prepare to explore important equations and physiological principles related to heart function.
