Venous return and distribution of cardiac output Flashcards
Name the five venous return mechanisms
Gravity Muscle pump Respiratory pump Smooth muscle Pocket valves
Describe gravity
Aids vins in the upper body
Describe the muscle pump
Many veins are situated between skeletal muscles so squeeze veins when thy contract
Describe the respiratory pump
- Helps to return blood in the thoracic cavity and abdomen to the heart
- When exercising, blood pressure changes in the thorax between high and low to squeeze blood to the heart
Describe smooth muscle
On the wall of each vein, contracts to push blood towards the heart
Describe pocket valves
Located in the veins to prevent back flow of blood and pushes it to the heart
How much blood must be part of venous return?
3 fifths of circulating blood
What is the average cardiac output?
Rest: 5l/min
Exercise: 14-20l/min
Describe the cardiac control centre
(Medulla oblongata)
Autonomic nervus system
Sympathetic nervous system (increases HR)
Parasympathetic nervous system (decreases HR)
SA Node
What neural controls input the autonomic nervous system?
Chemoreceptors
Proprioreceptors
Baroreceptors
Describe chemoreceptors
Located in muscles, aorta and carotid arteries
Inform CCC of chemical changes in the blood e.g. increased CO2
Describe proprioreceptors
Located in the muscles, tendons and joints
Inform the CCC of motor activity
Describe baroreceptors
Located in the walls of blood vessels
Inform the CCC of blood pressure
What intrinsic controls input the autonomic nervous system?
Temperature and venous return
Describe temperature as an intrinsic control
Temperature changes will affect the viscosity of blood and speed up nerve impulse transmission
Describe venous return as an intrinsic control
Venous return changes affect the stretch in the ventricle walls and force of ventricular contraction and therefore stroke volume
Describe the hormonal controls inputting the autonomous nervous system
Adrenaline and noradrenaline released from the adrenal glands increase the force of ventricular contraction and speed of cardiac electrical activity
How does the sympathetic nervous system increase HR?
Releases adrenaline and sends stimulation to the SA node via the accelerator (cardiac) nerve
How does the parasympathetic nervous system decrease HR?
Actioned to inhibit the effects of adrenaline via the vagus nerve
Describe the vasomotor control centre
Medulla oblongata
Redistributes cardia output
Vascular shunt mechanism
What inputs info to the Vasomotor control centre?
Chemo and baro receptors
What does the VCC do during exercise?
- Decreases sympathetic stimulation in the muscle cells
- Arterioles and pre-capillary sphincters vasodilate
- Increase blood flow to muscles
- Sympathetic stimulation increased to organs
- Arterioles and pre-capillary sphincters vasoconstrict
- Decrease blood flow to organs
What does the VCC do during recovery?
- Increase sympathetic stimulation in muscle cells
- Arterioles and pre-capillary sphincters constrict
- Decrease blood flow to muscles
- Sympathetic stimulation decreased to organs
- Arterioles and pre-capillary sphincters dilate
- Increased blood flow to organs
Describe the vasomotor control when blood pressure decreases
- Stimulates baroreceptors
- Vasoconstriction of arterioles
- Blood pressure increases
Describe the vasomotor control when blood pressure increases
- Stimulates baroreceptors
- Vasodilates arterioles
- Decreases blood pressure
Describe venomotor control
- Stimuli from sympathetic and parasympathetic nervous system
- Veins alter their shape to increase the venomotor tone of their walls
- Increase or decrease blood pressure
- Not as effective as vasomotor control
How does blood flow increase during physical activity?
- Metabolism speed increases
- Muscle oxygen demand increases
- Heart rate increases
- Speed of blood flow increases
