S1: Introduction to the Cardiovascular System (CVS) Flashcards
Why do we need a CVS?
- Transport of respiratory gases, nutrients and waste products (e.g. O2/CO2)
- As a signalling system for distributing hormones, inflammation molecules etc. to target tissues (to help ward off infections)
- Temperature regulation through cutaneous heat conservation/dissipation
- Importance in reproduction as needed for male erection
What is diffusion?
Random, undirected, thermal movement of molecules
What is diffusion an inappropriate transport mechanism for the body?
It is very slow over distances bigger than 1mm
It therefore takes too long to move molecules over a far distance
What mechanism does the cardiovascular system use?
Apart from diffusion
Convection which is movement by a pressure gradient
It provides fast and directional transport
What organ generates the convection current used in CVS and how?
The heart
It uses a lot of energy to generate the convection current through producing pressure differences between arteries and veins (pressure decreases as gets further from the heart)
Why does the CVS use a combination of convection and diffusion?
Diffusion is still crucial over short distances
Explain how pressure differences move blood in the pulmonary and systemic circulation
The heart cycle starts with the great veins (superior and inferior vena cava) depositing deoxygenated blood into the right atrium, which then gets pushed into the right ventricle. Blood is pushed out of the right ventricle to the lungs via the pulmonary artery, this is under low pressure, to allow good gaseous exchange. The blood gets oxygenated by diffusion. It then comes back to the heart and enters via the four pulmonary veins into the left atrium. From the left atrium it is pumped into the left ventricle, it is then finally pumped out of the left ventricle under high pressure into the aorta which supplies the whole body with blood.
There blood moves from the chambers due to the pressure gradients across them. The valves open/close depending on these pressures. E.g. when the pressure in the left ventricle is higher than in the aorta, the aortic valve is open. But once the pressure in the aorta is greater than in the left ventricle the valve (semilunar) closes.
What is cardiac output?
It is the volume of blood ejected from the ventricles per minute
CO= SV x HR
SV (stroke volume)= Volume of blood pumped from the left ventricle per beat
HR (Heart rate)= Speed of heartbeat measured by number of contractions of the heart per minute - bpm
What does cardiac output distribution mean?
From the aorta, the blood supply from the heart supplies various organs.
Name an organ that is well perfused for the amount of oxygen they recieve
Kidneys
They use much less oxygen in relation to the amount of blood they receive (oxygen consumption is lower that cardiac distribution)
Name 2 organs that are underperfused
Myocardium and brain
They extract and use a greater percentage of oxygen compared to the volume of blood received.
Which organs suffer the most when there is insufficient blood supply?
e.g. Angina
Organs which are underperfused
Why is it important that cardiac output is carefully controlled?
Clinical problems e.g. angina, myocardinal infarction, stroke are triggered as a result of a moderate fall in perfusion.
The heart and brain are critical to life, so CO should be controlled.
What are the three main factors controlling cardiac output?
1) Filing pressure (starlings law) = The more blood coming to the heart, the more blood will leave the heart. If it stretches more, it contracts more. If filling pressure drops, CO drops.
2) Sympathetic/parasympathetic autonomic nerves: Symp nerves release NA acting at B1 receptors cause increase in heart rate and contractility (SV) so CO increases.
Parasym nerves release Ach at M2 receptors causing decrease of activity at SAN reducing HR,
3) Chemical Factors: Substances such as hormones that influence HR and so can effect CO
What is the relationship between blood pressure and blood flow?
Blood flow is proportional to pressure across blood vessels (so greater pressure=greater flow) and is inversely proportional to resistance across blood vessels (greater resistance, less flow)
