Cardiovascular Physiology Quiz

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)