Introduction to CVS Flashcards
why do we need the CVS?
→pump blood through the lungs and carry oxygen
→transport nutrients to the muscles and organs
→circulate hormones and immune mediators
→connection to the lymphatic system
→ human reproduction
→ temperature regulation
what is passive diffusion?
→random, undirected thermal movement of molecules.
what is the equation for passive diffusion?
→ time needed to diffuse a given distance is proportional to the square of the distance: t ∝ d².
what is the main method of molecule movement within the CVS and what does it provide?
→CVS uses convection
→ movement by a pressure gradient
→ It provides fast and directional transport
→diffusion is still crucial for transport over short distances.
what is the significance of having pressure differences?
→output of blood at high pressure creates a pressure difference with distant blood vessels.
→This pressure difference drives blood flow.
where does cardiac output go?
→blood is distributed to various parts of the body, such as the kidneys, liver and GI
what are the brain and myocardium relative to other tissues?
→relatively under perfused.
what controls cardiac output?
→filling pressure (Starling’s Law)
→sympathetic and parasympathetic autonomic nerves
→chemical factors and hormones (eg. adrenaline)
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
→ linked in the proper distribution of blood
what happens if there is poor perfusion of the kidney?
→ renal failure and death
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.
what is blood flow proportional to and inversely proportional to?
1) proportional to pressure across the blood vessel
2) inversely proportional to the resistance of the blood vessel
why does blood slow down in the capillaries?
→to allow for gaseous/nutrient exchange to occur.
equation for calculating blood velocity?
→Blood velocity (cm/s) = blood flow (cm³/s) / total cross-sectional area (cm²)
→To calculate cross-sectional area, we do the number of vessels times the πr² per vessel.
describe in series blood circulation
→same blood supply between organs
→lower perfusion pressures
→medically significant if the first organ is being underperfused
describe parallel blood circulation
→cardiac output is split up
→safeguards O₂ supply in organs
→most organs are supplied this way
what are 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
VEINS:
→thinner elastic walls
→ have valves to ensure no blood backflow
what are elastic vessels?
ELASTIC VESSELS: ARTERIES
what are resistance vessels?
RESISTANCE VESSELS: ARTERIOLES
what are exchange vessels?
EXCHANGE VESSELS: CAPILLARIES
what are capacitance vessels?
CAPACITANCE VESSELS: VENULES AND VEINS
where is most of the blood volume distributed?
→mostly found in large and small veins and venules. →Systemic veins and venules serve as a reservoir, holding about 65% of the volume.
What do large arteries do?
→Large arteries accomodate stroke volume
→convert intermittent ejection into continuous flow
What do resistance vessels do?
→Control arterial blood pressure and regulate local blood flow
What do exchange vessels do?
→Nutrient delivery to cells and tissues for water and lymph formation, and removal of metabolic waste
What do capacitance vessels do?
→Control the filling pressure and provide a reservoir of blood, so the veins can constrict and send blood to the heart if needed
What is the typical resting blood pressure
120/80 mmHg is typical resting blood pressure- the systemic pressure
What are the pressures in the aorta and large veins?
Aorta >100 mmHg
Large veins 5-10 mmHg
Recall the resting and exercising cardiac output
Rest 70/min x 70 ml = 5 litres/min
Exercise 180/min x 120 ml = 20 litres/min
What happens if pressure at both ends are the same?
No flow if pressure at both ends is the same. The higher the pressure difference, the faster the flow
Summarise the systolic and diastolic pressures in systemic and pulmonary circulation
Systemic= 120/80 Pulmonary= 25/15
How does venous pressure vary?
Venous pressure (Pv) varies with location & posture, generally around 3-12mmHg
What are the roles of venules/veins?
Control filling pressure of the heart & provide a reservoir of blood.
They can stretch and contract but do not as much.
Have a lot of blood at anytime
Where does the main drop in pressure occur?
arterioles and even lower in capillaries
How do arterioles control BP?
by determining total peripheral resistance (TPR)
What do the endothelium release?
nitric oxide which relaxes the vessels leading to vasodilation
What is vascular tone?
innervations all the time and is balanced by the parasympathetic Noxide.
Allows control of the dilation- held in the middle to react immediately
What do the sympathetic nerves in the tunica adventitia do?
Sympathetic nerves in the tunica adventitia release noradrenaline which stimulates α1 receptors leading to vasoconstriction
Where is the majority of blood volume at any given time?
Systemic veins and venules- 65%
Lungs-10%
Heart-10%
Capillaries-5%
Where does the cardiac output go?
Cardiac output and oxygen consumption
1. Liver &GI Kidneys Brain Muscle Other
Oxygen consumption
- Liver and GI
- Muscle
- Brain
- Kidneys
