Introduction to the CVS Flashcards
Why do we need the CVS?
- to pump blood through the lungs and carry oxygen
- to transport nutrients to the muscles and organs
- to circulate hormones and immune mediators
- as a connection to the lymphatic system
- for human reproduction
- for temperature regulation
What is passive diffusion, and what is its relative equation?
Passive diffusion is the random, undirected thermal movement of molecules
The time needed to diffuse a given distance is proportional to the square of the distance: t ∝ d²
Diffusion is fast in μm but very time consuming over distances over 1 mm and inappropriate for transport throughout the body
Describe blood circulation on the right (deoxygenated) side of the heart
The CVS uses convection, which is the movement by a pressure gradient. It provides fast and directional transport; however, diffusion is still crucial for transport over short distances.
Describe blood circulation on the left (oxygenated) side of the heart
Blood returns to the heart from the lungs via the left atrium and is pumped through the body by the left ventricle
What is the significance of having pressure differences in the heart
- The output of blood at high pressure creates a pressure difference with distant blood vessels
- This pressure difference drives blood flow
- Systole = contraction
- Diastole = relaxation
- 120 (systolic)/80 (diastolic) mmHg is typical resting blood pressure
What controls cardiac output?
- Filling pressure (Starling’s Law)
- Sympathetic (faster and harder heart beat) and parasympathetic autonomic nerves
- Chemical factors and hormones (adrenaline)
What is the equation for calculating cardiac output?
Cardiac Output = Heart Rate x Stroke Volume
CO = HR x SV
Why are blood flow and blood pressure important?
- Blood flow and blood pressure are critical for correct bodily functioning
- Controlling the resistance of the vessels gives some control of blood flow
What is the equation for calculating blood flow?
Blood flow = (Pa - Pv)/resistance
Pa is the pressure at the artery, while Pv is the pressure at the vein (varies with location & posture)
An increase in resistance causes a decrease in blood flow
Blood flow is:
1) proportional to pressure across the blood vessel
2) inversely proportional to resistance of the blood vessel
What is systemic and pulmonary circulation
- Systemic = High pressure to pump around body
- Pulmonary = Low pressure allows gas exchange
What are the four main functional groups of blood vessels?
ARTERIES (ELASTIC VESSELS)
Large arteries accomodate stroke volume and convert intermittent ejection into continuous flow
ARTERIOLES (RESISTANCE VESSELS)
Control arterial blood pressure and regulate local blood flow
CAPILLARIES (EXCHANGE VESSELS)
Nutrient delivery to cells and tissues for water and lymph formation and removal of metabolic waste
VENULES AND VEINS (CAPACITANCE VESSELS)
Control the filling pressure and provide a reservoir of blood, so the veins can constrict and send blood to the heart if needed
This is the direction of blood flow from the heart, and blood moves from larger to smaller vessels
List differences between the structures of arteries and veins.
ARTERIES:
- thicker elastic wall to maintain blood pressure
- have high pressure that ensures blood flows in one direction
BOTH:
- have 3 basic layers
VEINS:
- thinner elastic walls
- have valves to ensure no blood backflow
Describe cardiac output distribution at rest
- Mainly liver & GI (25%)
- Least myocardium (tissue of the brain, 4%)
Myocardium and brain are relatively under perfused, creating potential clinical problems, e.g. stroke
Describe oxygen consumption at rest
- Mainly liver & GI (30%)
- Least myocardium and kidneys (10%)
What are arterioles
Resistance vessels and control arterial BP by determining total peripheral resistance (TPR). Downstream/after arterioles, the systolic pressure decreases and plateus until it gets back to the heart
