Physiology Flashcards
Which nerve descends across the lateral borders of both sides of the pericardium?
Phrenic nerve
Which sinus do surgeons use to correctly identify and isolate the great vessels for cardiopulmonary bypass?
The transverse pericardial sinus
The first heart sound (lub) indicates which 2 valves closing?
Mitral and Tricuspid
The second heart sound (dub) indicates which 2 valves closing?
Aortic and Pulmonary
What does the P wave in the ECG signify?
Atrial Depolarisation
At what stage in the ECG do the atria contract?
Between the P wave and the QRS complex
Ventricular contraction occurs where on the ECG?
Immediately after the QRS complex (signals ventricular depolarisation) (becoming more +ve)
What does the T wave on an ECG signify?
Ventricular repolarisaton
S1 signifies the beginning of what?
Systole
S2 signifies what?
The end of systole and beginning of diastole
What is shock?
An abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation
What is stroke volume?
The volume of blood pumped by each ventricle of the heart every heart beat
What is cardiac output?
The volume of blood pumped by each ventricle of the heart each minute
How can we calculate cardiac output?
Stroke Volume x Heart rate
How can we calculate the Mean Arterial Pressure?
Cardiac output x Total Vascular Resistance
What is cardiogenic shock?
Sustained hypotension caused by decreased cardiac contractility
Decreased cardiac contractility resulting in decreased stroke volume resulting in decreased CO and BP which results in inadequate tissue perfusion.
What is an inotrope?
A drug that is positively inotropic is one which increases the force of muscular contractions e.g. adrenaline
In haemorrhagic shock, compensatory mechanisms can maintain blood pressure until what percentage of blood volume is lost?
After >30% of blood volume is lost, compensatory mechanisms can no longer cope
What is meant by mean arterial pressure?
The average arterial blood pressure during a single cardiac cycle.
How is mean arterial pressure calculated?
(2 x diastolic pressure) + Systolic pressure
DIVIDED by 3
What is the normal range of mean arterial pressure?
70-105mmHg, a MAP of at least 60 is required to perfuse the kidneys, brain and coronary arteries.
What is the normal range of blood pressure
No greater than 140 over 90
Which vessels are the major resistance vessels?
The arterioles
What act as short term regulators of mean arterial pressure?
The baroreceptors.
The baroreceptors are innervated by the vagus nerve, therefore when they fire they have bradycardic effects. Therefore when someone stands up, the baroreceptors stop firing so as to allow sympathetic firing to be dominant to produce constriction and increased HR so as to not get postural hypotension.
Where are the 2 groups of baroreceptors?
1) Aortic Arch (Vagus nerve)
2) Carotid Sinus (Glossopharyngeal nerve CN IX)
The RAAS system
Plays an important role in the regulation of plasma volume and TPR and hence the regulation of MAP
Has three important components (1) Renin (2) Angiotensin (3) Aldosterone
Renin is released from the kidneys and stimulates the formation of angiotensin I in the blood from angiotensinogen (produced by the liver)
Angiotensin I is converted to angiotensin II by Angiotensin converting enzyme - ACE (produced by pulmonary vascular endothelium)
Angiotensin II (1) stimulates the release of Aldosterone from the adrenal cortex (2) Causes systemic vasoconstriction - increases TPR … Also stimulates thirst and ADH release - i.e. contributes to increasing plasma volume mainly brought about by aldosterone
Aldosterone (a steroid hormone) acts on the kidneys to increase sodium and water retention – increases plasma volume
What is the rate limiting step in the RAAS?
Renin Secretion (from the juxtaglomerular apparatus)
What is the role of ANP (atrial natureuretic peptide)?
- Released in response to arial distension (hypervolaemic states)
- Causes excretion of salt and water in the kidneys, in turn reducing blood volume and blood pressure
- Acts as a vasodilator
- Decreases renin release
