Flashcards in Review of posters 08/05/2016 Deck (29):
What is blood pressure?
The outwards hydrostatic pressure the blood exerts on the walls of the blood vessels.
Systemic systolic arterial blood pressure
The hydrostatic pressure the blood exerts on the blood walls during the hearts contraction
Systemic diastolic arterial blood pressure.
The hydrostatic pressure the blood exerts on the blood vessels when the heart is relaxed.
How does a sphygmanometer work?
If an external pressure greater than systole is applied to an artery- it cuts the blood supply off to that area. This is not audible.
However if you apply a pressure between that of systole and diastole to the blood vessel, the flow through the vessel will be turbulent and this will be audible.
Therefore when the cuff is pumped above systole you can't hear anything, yet when it reaches systole you begin to hear a noise, then at diastole the noise stops.
What drives blood flow around the body?
The pressure gradient between the aorta and the right atrium.
How can the pressure gradient be calculated?
Mean arterial pressure- central venous pressure (pressure in the right atrium)
What is mean arterial pressure?
The average blood pressure throughout one cardiac cycle (includes diastole).
What are the equations that allow you to calculate MAP?
Diastole + 1/3 (systole-diastole)
In terms of commonly used cardiac physiology outputs, how would you describe MAP?
MAP= CO x TPR
CO= cardiac output which equals the HR x SV
Total peripheral resistance is the sum of the resistance in all the systemic vessels
What should your MAP be?
Below 60 would struggle to perfuse brain, kidney.
What are baroreceptors responsible for?
Short term regulation of MAP. Do so in a negative feedback system.
Where are baroreceptors in the body?
Aortic arch and carotid sinus.
Process of standing up too quickly in a normal individual.
When the person gets up too quickly, it causes a drop in the venous return to the heart (due to gravity). This means there is a decrease in MAP. The baroreceptors stop firing as much now. The sympathetic tone to the heart increases and the vagal tone decreases. Also the sympathetic constrictor tone to venules and arterioles increases increasing venous return to the heart. This all drives MAP up.
Are baroreceptors a good long term MAP control?
No this is because they re-set to the higher steady state. E.g. if the person has high blood pressure, the baroreceptors wouldn't recognise this as being abnormal because they are used to that 'steady state'. They will only fire again if there are acute changes from the new normal.
What is internal respiration?
The intracellular mechanisms consuming O2 and producing CO2
What is external respiration?
The process that lead to exchange of O2 and CO2 between the atmosphere and the cells.
What are the four stages to external respiration?
Ventilation- process of getting atmospheric air in to the alveoli
Gas exchange between the alveoli and the blood
Transport in the blood
Gas exchange between the alveoli and the tissues.
What is ventilation?
The mechanical process of moving air between the atmosphere and the alveoli.
Pressure exerted by a gas decreasing as the volume increases.
How do changes in pressure draw air into the lungs?
Chest expands causing the lungs to expand. Volume is increasing in the thorax and therefore pressure is decreasing to below that of atmospheric pressure. Air then moves down its pressure gradient into the lungs.
What causes the lungs to expand when they are not actually attached to the chest wall?
Negative intrapleural pressure
Intrapleural fluid cohesiveness- water molecules in the pleural fluid have a strong surface tension and therefore resist being pulled apart. This means the two pleural layers stick together- making the lungs expand.
Involves diaphragm contracting and flattening
External intercostal muscles contracting and lifting the rib cage up and out.
Inspiratory muscles contract and due to elastic recoil lungs and chest wall spring back into original shape.
What causes the lungs to adopt their original shape during expiration?
The elastic connective tissue
Alveolar surface tension
What is alveolar surface tension?
The water molecules on the liquid-air interface have a strong attraction to each other and therefore resist being pulled apart.
What is surfactant and why do we need it?
Surfactant is a mixture of lipids and proteins that sit in between the water molecules in the alveoli. This reduces the surface tension slightly so that the lungs can still expand.
Neonatal respiratory distress syndrome
Babies born with not enough surfactant- therefore they have extreme difficulty breathing.
The smaller the alveoli, the greater the tendency there is to collapse. Therefore smaller alveoli have more surfactant.