1.1 cardiovascular system Flashcards
Describe the cardiac conduction system
- heart is myogenic it generates its own impulse
- impulse begins in the SAN
- impulse spreads through the heart in a wave of excitation
- from the SAN the electrical impulse spreads through the walls of the atria, causing them to contract
- impulse passes through the AVN, the AVN delays the transmission for 0.1 seconds (so atria fully contract)
- impulse passed down through the bundle of His (located in the septum) and spreads down the purkinje fibres that spread through the walls of the ventricles, causing them to contract
Define systole
when the heart contracts
Define myogenic
the capacity of the heart to generate its own impulses
Define diastole
when the heart relaxes and fills with blood
What is the sympathetic system?
a part of the autonomic nervous system that speeds up heart rate
What is the parasympathetic system?
a part of the autonomic nervous system that decreases heart rate
What is the medulla oblongata?
the most important part of the brain as it regulates processes that keeps us alive e.g. breathing and heart rate
What are chemoreceptors?
tiny structures in the carotid arteries and aortic arch that detect changes in blood acidity caused by and increase or decrease in carbon dioxide concentration
Where are chemoreceptors found?
carotid arteries and aortic arch
What happens if there is an increase in carbon dioxide concentration in the blood?
the chemoreceptors will detect an increase in blood acidity and will stimulate the sympathetic nervous system which will increase heart rate
What are baroreceptors?
special sensors in tissues in the aortic arch, carotid sinus, heart and pulmonary vessels that respond to changes in blood pressure to either increase or decrease heart rate
How do baroreceptors work?
- nerve endings that respond to stretching of the arterial wall caused by changes in blood pressure
- establish a set point for blood pressure
What happens if there is an increase in blood pressure?
baroreceptors detect the decrease in blood pressure above a set point results in a decrease of heart rate through parasympathetic system
What happens if there is a decrease in blood pressure?
decrease in stretch in the stretch of the baroreceptors and results in an increase in heart rate
What are proprioceptors?
sensory nerve endings in the muscles, tendons and joints that detect changes in muscle movement
What happens to the baroreceptor blood pressure set point before exercise?
increases so enough oxygen is still delivered to the working muscles
What happens if there is an increase in muscle movement?
proprioceptors detect increase in muscle movement, they send an impulse to the medulla, which sends an impulse through the sympathetic nervous system to the SAN to increase heart rate
What’s adrenaline?
a stress hormone that is released by the sympathetic nerves and cardiac nerve during exercise which causes an increase in HR
What node does adrenaline stiumlate?
sinoatrial node
How does adrenaline increase cardiac output?
stimulates SAN which results in an increase in the speed and force of contraction if the heart
What is stroke volume?
the volume of the blood pumped out by the heart ventricles in each contraction
What 3 factors does stroke volume depend on?
- venous return: the volume of blood returning to the heart in the veins (increased venous return=increased stroke volume)
- contractility of the cardiac tissue: the greater contractility, the greater the force of contraction= increase in stroke volume
- elasticity of the cardiac fibres: greater stretch, the greater force of contraction and ejection fraction
Define the ejection fraction
the percentage of blood pumped out by the left ventricle per beat
What is starling’s law?
increased venous return —> greater diastolic filling of heart —> cardiac muscle stretched —> more force of contraction —> increased ejection fraction
How do you determine ejection fraction?
stroke volume/end diastolic volume (volume of blood in ventricles at rest
What is bradycardia?
a decrease in resting heart rate to below 60bpm
What is cardiac output?
the volume of blood pumped out by the heart ventricles per minute
Define cardiac hypertrophy
the thickening of the muscular wall of the heart so it becomes bigger and stronger; also can mean a larger ventricular cavity
How do you determine cardiac output?
stroke volume x heart rate
What is an average stroke volume?
70ml
What is an average heart rate?
72bpm
How do you determine max heart rate?
220- age
Define anticipatory rise
an increase in heart rate prior to exercise, due to the release of adrenaline
What are the effects of cardiac hypertrophy
- increased stroke volume
- resting heart rate will decrease (bradycardia)
What is the effect of exercise on stroke volume?
it will increase as exercise intensity increases up to 40-60% max effort
after this, stroke volume plateaus because the increased HR results in shorter diastolic phases
What is atherosclerosis?
Atherosclerosis occurs when arteries harden and narrow as they become clogged up by fatty deposits(atheroma)
What are the causes of atherosclerosis?
- high blood pressure
- high levels of cholesterol
- lack of exercise
- smoking
How does a heart attack occur?
Heart attacks can occur when a piece of fatty deposit (atheroma) breaks off to cause a blood clot which results in a blockage that can cut off the supply of oxygenated blood to the heart
What is angina?
Angina is the pain and discomfort that occurs as a result of the coronary arteries narrowing because they are unable to deliver enough oxygen to the heart
What are the benefits of exercise in terms of heart disease?
Benefits of regular exercise for reducing risk of heart attacks:
- helps to keep the heart in shape
- cardiac muscle bigger and stronger so increased stroke volume
- maintains the flexibility of blood vessels which ensures good blood flow
- low cholesterol levels
- normal blood pressure
What is blood pressure?
Blood pressure is the force exerted by the blood against the blood vessel walls
What are the effects of high blood pressure?
High blood pressure puts extra strain on the arteries and the heart. If left untreated high blood pressure increases risk of heart attack, kidney disease, heart failure, stroke or dementia
What is the effect of regular exercise on blood pressure?
Regular exercise can reduce blood pressure by:
Reducing the risk of heart attack by up to 20% because exercise lowers systolic and diastolic pressure by up to 5-10mmHg
What are the two types of cholesterol?
Low density lipoproteins (LDLs)
High density lipoproteins (HDLs)
What do LDLs do?
LDLs transport cholesterol in the blood to the tissues and are considered ‘bad’ cholesterol because they increase the risk of heart disease
What do HDLs do?
HDLs transport cholesterol in the blood to the liver where it is broken down. Classed as ‘good’ cholesterol
What is the effect of exercise on cholesterol levels?
Regular exercise increases HDLs and lowers LDL levels
What is a stroke?
A stroke occurs when the blood supply to the brain is cut off
Define disability
physical, sensory or mental impairment which adversely affects performacne
What are the 2 main types of stroke?
2 main types of stroke:
- Ischaemic (most common) when a blood clot stops blood supply
- Haemorrhagic occurs when a weakened blood vessel supplying the brain bursts
What is the effect of exercise on strokes?
Regular exercise can help lower your blood pressure and help you maintain a healthy weight which can reduce the risk of a stroke by 27%
What is cardiovascular drift?
a progressive decrease in stroke volume and arterial blood pressure, together with a progressive rise in heart rate. this occurs during prolonged exercise (after 10 mins) in a warm environment and intensity of exercise remaining the same
Why does cardiovascular drift occur?
- some of plasma volume is lost as sweat which reduces venous return and stroke volume
- HR increases to compensate and maintain higher cardiac output in order to create more energy to cool the body down
How can cardiovascular drift be minimised?
maintain high fluid consumption before and during exercise
What are the 2 types of circulation?
1) Pulmonary- deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart
2) Systemic- oxygenated blood from the heart round the body and deoxygenated blood back to heart
Define systolic pressure
the pressure in the arteries when the ventricles are contracting
Define diastolic pressure
the pressure in the arteries when the ventricles are relaxing
Define venous return
the return of the blood to the right side of the heart via the vena cava
What are the 3 mechanisms to aid venous return?
- pocket valves: to prevent backflow of blood
- respiratory pump: when muscles contract and relax during breathing in and out, pressure changes occur in the thoracic and abdominal cavities which compress the nearby veins and assist blood return to the heart
- skeletal muscle pump: when muscles contract and relax they change shape which presses on the nearby veins and causes a pumping effect to squeeze blood back to the heart
What 3 other factors aid venous return?
1) gravity- helps return blood from the upper body
2) smooth muscle in the walls of veins- helps squeeze blood back to heart
3) suction pump action of the heart
What is the effect of blood pressure on venous return?
when systolic pressure is increased there is an increase in venous return
when systolic pressure decreases there is a decrease in venous return
How many oxygen molecules can haemoglobin take up when fully saturated?
4
Define plasma
the fluid part of the blood (mainly water) that surrounds blood cells and transports them
What is formed when oxygen combines with haemoglobin?
oxyhaemoglobin
Define haemoglobin
an iron-containing pigment found in red blood cells, which combines with oxygen to form oxyhaemoglobin
Define myoglobin
often called ‘muscle haemoglobin’ it’s an iron-containing muscle pigment in slow-twitch muscle fibres which has a higher affinity for oxygen than haemoglobin. it stores the oxygen in the muscle fibres which can be used quickly when exercise begins
When does haemoglobin become fully saturated with oxygen?
when the partial pressure of oxygen is high in the blood e.g. in the alveoli
What is oxyhaemoglobin dissociation?
the release of oxygen from oxyhaemoglobin to the tissues
What is Bohr shift?
when an increase in blood carbon dioxide and a decrease in blood pH results in a reduction in the affinity of haemoglobin for oxygen. results in a shift to the right of the oxyhaemoglobin dissociation curve
What are the 3 factors responsible for the increase in dissociation of oxygen from oxyhaemoglobin?
- increase in blood temperature: means oxygen dissociates more easily
- partial pressure of carbon dioxide increases: oxygen will dissociate faster
- pH: lower pH results in faster dissociation
Define vascular shunt mechanism
the redistribution of cardiac output
Why should sports performers not eat less than an hour before competition?
blood would be directed to the stomach instead of the working muscles so less oxygen available for performance
Why does blood flow to the brain remain constant?
ensure brain function is maintained as the brain needs oxygen for energy
Where is the vasomotor centre located?
medulla oblongata
Why does blood need to go to the skin during exercise?
energy is needed to cool the body down
What does the vasomotor centre control?
blood pressure and blood flow
Define vasodilation
the widening of the blood vessels to increase the flow of blood into the capillaries
Define vasoconstriction
the narrowing of the blood vessels to reduce blood flow into the capillaries
During exercise where does vasoconstriction and vasodilation occur?
vasodilation will occur at the arterioles supplying the working muscles with blood
vasoconstriction will occur at the arterioles supplying the non-essential organs e.g. intestines or liver
What is the role of the chemoreceptors in vascular shunting?
detect chemical changes during exercise (increase in CO2 and lactic acid) and they stimulate the vasomotor centre in the medulla oblongata which redistributes blood through vasoconstriction or vasodilation
What happens when sympathetic nerve stimulation increases in vascular shunting?
vasoconstriction occurs and blood flow is reduced
opposite for decrease in sympathetic nerve stimulation decreasing
What are pre-capillary sphincters?
tiny rings of muscle located at the opening of capillaries. when they contract, blood flow is restricted, when they relax blood flow is increased
Why is redistribution important?
- increase supply of oxygen to working muscles
- remove waste products from the muscles e.g. CO2 and lactic acid
- ensure more blood goes to the skin during exercise to regulate body temperature and get rid of heat through radiation, evaporation and sweating
- direct more blood to the heart as it requires extra oxygen during exercise
Define arterio-venous difference
the difference between the oxygen content of the arterial blood arriving at the muscles and the venous blood leaving the muscles
