Intro to the CVS Flashcards
What are the 6 main reasons why we need the CVS?
- Pump blood through Lungs & carry Oxygen, take away CO2
- Transport nutrients to muscle and organs, take away waste and metabolises
- Circulates hormones & immune mediators
- Connection to lymphatic system
- Human reproductive system (in ejection/ejaculation)
- Temperature regulation (need to distribute heat)
What is passive diffusion?
Random movement of undirected thermal movement of molecules
What is the time needed to diffuse a given distance proportional to?
square of the distance
At what distance does diffusion become time consuming?
> 1mm, then diffusion becomes inappropriate as the mode of transport throughout the body
Time taken to diffuse across 0.1 um
0.005 ms, e.g. Synapse
Time taken to diffuse across 10 um
50 ms, e.g. from Capillary to Cell
Time taken to diffuse across 1 mm
8 min, e.g. through Cartilage
Time taken to diffuse 1 cm
13 hours, e.g. through Left Ventricle Wall
what does pressure difference drive?
blood flow
Systole
Contraction
Diastole
Relaxation
Cardiac output=
Volume of blood ejected from the heart per minute, normally around 5 litres/min
What is the main method of molecule movement within the CVS?
- CVS uses convection (movement by a pressure gradient)
- provides fast and directional transport
- diffusion still crucial for transport over short distances
Distribution of cardiac output
- Liver & GI: 25%
- Muscle: 20%
- Brain: 13%
- Kidneys: 20%
- Myocardium: 4%
- Other: 18%
Oxygen consumption at rest
- Liver & GI: 30%
- Muscle: 20%
- Brain: 18%
- Kidneys: 10%
- Myocardium: 10%
- Other: 12%
What two areas are of clinical significance to cardiac output distribution?
- The brain and myocardium (muscular heart tissue)
- Places are relatively under-perfused
- Whenever there is a problem with blood supply, these two places are at risk (Stroke, Heart attack, angina, MI)
- Therefore, need to carefully control cardiac output
What three factors control cardiac output?
- Filing pressure (Starling’s law)
- Sympathetic and parasympathetic autonomic nerves
- Chemical factors & 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 pressure important?
- Blood flow and pressure are critical for correct bodily functioning
- Because they are linked in the proper distribution of blood
- E.g. if there is poor perfusion in the kidneys: could cause renal failure and death
Blood flow is…
- Proportional to pressure across blood vessel
2. Inversely proportional to resistance of blood vessel
What is the equation for calculating blood flow?
- Blood flow = (Pa -Pv) / resistance
- Pa is the pressure at the artery
- Pv is the pressure at the vein
BP for Systemic circulation
120 (systolic) / 80 (diastolic)
- high pressure to pump around the body
BP for Pulmonary circulation
25 (systolic) / 15 (diastolic)
- low pressure allows gas exchange
What type of vessels are arterioles?
Resistance vessels
- They control arterial BP by determining total peripheral resistance (TPR)
Why does blood slow down at the capillaries?
The velocity of blood is much slower at the capillaries to allow for gaseous/nutrient exchange to occur
What is the equation for calculating blood velocity?
- Blood velocity (cm/s) = blood flow (cm3/s) / cross sectional area (cm2)
- To calculate cross sectional area, do a number of vessels x (pi r squared) per vessel
Describe how dual circulation can be in parallel or in series?
• IN SERIES (PORTAL): - Same blood supply between organs - Lower perfusion pressures - Medically significant if the first organ is being under perfused • IN PARALLEL: - Cardiac output is split up - Safeguards O2 supply in organs - Most organs are supplied this way
Difference between structure of arteries and veins
• ARTERIES:
- Thicker elastic wall to maintain blood pressure
- Have high pressure that ensures blood flow in one direction
• VEINS:
- Thinner elastic walls
- Have valves to ensure no blood backflow
ELASTIC VESSELS: ARTERIES function
Large arteries accommodate stroke volume and convert intermittent ejection into continuous flow
RESISTANCE VESSELS: ARTERIOLES function
Control arterial blood pressure and regulate local blood flow
EXCHANGE VESSELS: CAPILLARIES function
Nutrient delivery to cells and tissues for water and lymph formation, and removal of metabolic waste
CAPACITANCE VESSELS: VENULES AND VEINS function
Control the filling pressure and provide a reservoir of blood, so the veins can constrict and send blood to the heart if needed
Distribution of blood volume
- Small veins and venues: 24%
- Capillaries: 5%
- Arteries: 10%
- Heart: 10%
- Lungs: 10%
- Large veins: 24%
- Systemic veins and venues serve as a reservoir holding 65% of volume
Two types of circulation?
- Systemic circulation
2. Pulmonary circulation
Systemic circulation
Takes oxygenated blood and nutrients (e.g. glucose) around the body and removes waste like amino acids and lactate
Pulmonary circulation
Takes oxygen from lungs and releases carbon dioxide into the lungs
