Cardiovascular System
- Created by: felixshears
- Created on: 01-05-18 20:20
Cardiovascular System
Conduction System Diagram
Conduction system - electrical impulse movement per heartbeat
Heart is myogenic - generates + controls input
Conduction System Process
1. SA node in right atrial wall generates electical impulse + fires through atria wall, causing them to contract - known as pacemaker as firing rate determines heart rate
2. AV node collects impulse + delays it for around 0.1 seconds to allow atria to finish contracting, then releases impulse to bundle of his
3. Bundle of his in septum splits impulse in 2, ready to be seperately distributed through each ventricle
4. Bundle of his branches carry impulse to base of each ventricle
5. Purkinje fibres distribute the impulse through ventrical walls, causing them to contract
Once electrical impulse journey is complete, atria + ventricles relax + heart refills with blood
This process is one heartbeat
Cardiac Cycle
The mechanical events of one heartbeat - movement of blood through heart
Systole - contraction of heart chambers
Diastole - relaxation of heart chambers
EDV - ventricle volume when full
ESV - ventricle volume after systole
SV = EDV - ESV
Cardiac Cycle Process
1. Both atria fill with blood + AV valves close
2. Atrial blood pressure rises above ventricular pressure
3. Rising blood pressure forces AV valves to open + blood passes passively into both ventricles + semilunar valves close
4. Both atria contract, forcing remaining atrial blood to move actively into ventricles
5. AV valves close
6. Both ventricles contract, increasing ventricular pressure
7. Semilunar valves forced open + AV valves still closed
8. Blood forced out of body + into muscles
9. Diastole of next cardiac cycle begins
Conduction System Control of Cardiac Cycle
No electrical impulse - causes diastole + cardiac muscle relaxes so SL valves close, atria fill with blood opening the AV valves + blood starts to enter ventricles
SA node fires and electrical impulse through atria walls to AV node + AV node delays impulse - causes atrial systole as atrial muscle contracts so AV valves forced open + blood is pushed into ventricles until atria finish contracting
Bundle of his splits + passes impulse through 2 branches to purkinje fibres in bothe venricle walls - causes ventricular systole as ventricular muscle cntracts so AV valves close + blood is pushed into the arteries, forcing SL valves open until ventricles finish contracting
Heart Rate, Stroke Volume + Cardiac Output
Heart Rate (HR):
- number of cardiac cycles completed in one minute (BPM)
- lower HR - more efficient cardiac muscle
- maximal heart rate estimated by subtracting age from 220
- bracycardia - when HR less than 60 BPM
- tachycardia - when HR higher than 100 BPM
Stroke Volume (SV):
- volume of blood ejected from left ventricle per beat (ml)
- occurs during ventricular systole
- dependant on venous return + ventricular elasticity
Cardiac Output (Q):
- the volume of blood ejected from left ventricle per minute (L/min)
- caridac output = heart rate x stroke volume (Q = HR x SV)
- cardiac hypertrophy makes cardiac muscle more efficient as greater volume of blood ejected per beat
Heart Rate, Stroke Volume + Cardiac Output Table
Control of HR in Exercise - Neural
Chemoreceptors:
- located in muscles, aorta + carotid arteries
- detect chemical changes in blood stream
- detect decreased pH (increased lactic acid) + increase CO2
Proprioreceptors:
- located in muscles, tendons + joints
- inform of increased motor activity during exercise (movement)
Baroreceptors:
- located in blood vessel walls
- informs of increased blood pressure in blood vessels
Control of HR in Exercise - Hormonal + Intrinsic
Hormonal Control - Adrenaline:
- released from adrenal glands
- increased force of ventricular contraction (SV)
- increased spread of electrical activity through heart (HR)
- sympathetic nervous system stimulated
Intrinsic Control:
- increased temperature - decreased blood viscocity so increased speed of nerve impulse
- increased VR - increased stretch on right atrium causes SA node to increase firing rate and therefore increase stroke volume
Control of HR in Exercise - CCC
Cardiac control centre is medulla oblongata in brain
1. Control mechanisms send information to CCC
2. If increase in HR required, sympathetic nervous system activated, releasing adrenaline, noradrenaline + sending stimulation to SA node via accelerator nerve
3. If decrease in HR required, parasympathetic nervous system actioned to inhibit effects via vagus nerve
Blood Vessels - Arteries + Arterioles
Transports oxygenated blood from heart to muscles + organs
The main artery is aorta + subdivides into arterioles
Have large layer of small muscle + elastic tissue to:
- allow vasoconstricton + vasodilation
- regulates blood flow
- controls blood pressure
Pre-capillary sphincters:
- ring of smooth muscle muscle surrounding entry of capillary bed
- dilate + constrict to control blood flow through capillary bed
Blood Vessels - Veins + Venules
Transport oxygenated blood from muscles + organs back to heart
Venules leaving capillary bed reconnect to form veins
Main vein is vena cava + carried blood back to atria
Have small layer of smooth muscle allowing them to vasoconstrict + vasoldilate to maintain slow blood flow towards heart
Veins have one-way pocket valves to prevent backflow of blood
Blood Vessels - Capillaries
Capillaries:
- bring blood into close contact with muscle + oxygen cells for gaseous exchange
- capillary walls - composed of single layer of cells thin enough for gas, nutrient + waste exchange
Distribution of Q at Rest + During Exercise
During maximal exericse cardiac output distributed to skeletal muscle instead of body organs
This redistribution is known as vascular shunt mechanism
Occurs due to:
- 1. vasodilation of arterioles supplying muscles
- 2. vasodilation of pre-capillary sphincters supplying muscles
- 3. vasoconstriction of arterioles supplying organs
- 4. vasoconstriction of pre-capillary sphincters supplying organs
Control/Regulation of Distribution of Blood
Baroreceptors send information about increased blood pressure during exercise in blood vessels supplying muscles
Chemoreceptors send information about decreased pH during exercise to blood supplying muscles
Information sent to Vasomotor Control Centre (VCC)
After recieving information either:
- increased sympathetic nerve activity causes vasoconstriction
- decreased sympathetic nerve activity causes vasoldilation
Venous Return
Venous return - the return of blood to the heart through the venules + veins to the right atrium
During exercise - VR = SV so need to maintain high VR during exercise as done by the 5 mechanisms
During recovery:
- cardiac output remains high but blood pressure too low to return blood from muscles back to heart
- causes dizziness + heavy legs known as blood pooling
- active cool down prevents this, maintaing venous return via muscle pump + respiratory pump
Venous Return Mechanisms
Pocket Valves - prevent backflow of blood
Muscle Pump - contracting muscles squeeze blood back to heart
Smooth Muscles - middle layer of veins contracts + relaxes
Respiratory Pump - increases pressure in abdomen, squeezes large veins forcing blood back to the heart
Gravity - blood from upper body aided by gravity
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