Physiology 1 Flashcards
Which part of the nervous system increases HR?
Sympathetic
Which part of the nervous system decreases HR?
Parasympathetic
Which nerve provides parasympathetic supply to the heart?
Vagus
Which neurotransmitter is responsible for slowing the heart rate (parasympathetic) and through which receptors?
Acetyl choline through
muscarinic M2 receptors
Which drug can be used to treat extreme bradycardia by speeding up the heart and how does it work?
Atropine
Competitive inhibitor of acetylcholine
Which neurotransmitter is responsible for increasing HR (sympathetic) and through which receptors?
Noradrenaline through
Beta-1 adrenoceptors
How does normal cardiac excitation spread through the heart?
SA node –> AV node –> Bundle of His –> Bundle of His left and right branches –> Purkinje fibres
What is stroke volume?
The volume of blood ejected by each ventricle per heart beat
SV = end diastolic volume (EDV) - end systolic volume (ESV)
What determines the cardiac preload?
End diastolic volume (venous return)
What is afterload?
Resistance into which the heart is pumping
What happens if there is a persistently increased afterload e.g. hypertension?
Ventricular muscle mass increases to overcome the resistance
–> ventricular hypertrophy
What is an inotropic effect?
Effect on force of contraction
What is a chronotropic effect?
Effect on heart rate
e.g. positive chronotropic effect = increases HR
What is cardiac output and how is it calculated?
The volume of blood pumped by each ventricle per minute
CO = SV x HR
When do normal heart valves produce a sound?
When they shut
not normally when they open
What are the 5 stages of the cardiac cycle?
- Passive filling
- Atrial contraction
- Ventricular contraction
- Ventricular ejection
- Ventricular relaxation
What produces the first heart sound?
When the ventricular pressure exceeds atrial pressure, the AV valves shut (mitral and tricuspid)
What produces the second heart sound?
After ventricular ejection, when the ventricular pressure falls below the aortic/pulmonary pressure –> aortic and pulmonary valves shut
Where does S1 fall in systole and diastole?
Beginning of systole
Where does S2 fall in systole and diastole?
End of systole/beginning of diastole
What does the P wave represent on an ECG?
Atrial depolarisation
What does the QRS complex represent on an ECG?
Ventricular depolarisation
What does the T wave represent on an ECG?
Ventricular repolarisation
Which part of the ECG represents ventricular contraction (systole)?
ST segment
Which part of the ECG represents ventricular relaxation (diastole)?
TP segment
What does the PR interval represent?
AV nodal delay
How do you calculate rate on an ECG?
300/number of large squares between beats
Which lead is usually used as the rhythm strip?
Lead 2
What are the 6 steps to describing an ECG?
- Verify patient details
- Check date and time ECG was taken
- Check calibration of paper
- Determine axis
- Work out rate and rhythm
- Look at individual leads for voltage criteria or ST/T-wave changes
Which 7 questions should you address when looking at rate/rhythm on an ECG?
- Is electrical activity present?
- Is the rhythm regular or irregular?
- What is the heart rate?
- Are P-waves present?
- What is the PR interval?
- Is each P-wave followed by a QRS complex?
- Is the QRS duration normal?
What is a normal PR interval?
0.12 - 0.20 seconds
How is mean arterial pressure (MAP) calculated?
MAP = ( (2 x diastolic pressure) + systolic pressure ) / 3
What is normal MAP?
70 - 105 mmHg
What is the minimum MAP required to perfuse coronary arteries, brain and kidneys?
60 mmHg
How does MAP relate to CO?
MAP = CO x SVR (systemic vascular resistance)
Which vessels are responsible for creating systemic vascular resistance?
Arterioles
Which mechanism is responsible for moment-to-moment regulation of PB e.g. prevention of postural changes?
Baroreceptors Reflex
What results from a failed baroreceptor response and how is it defined?
Postural (orthostatic) hypotension
Drop in BP within 3 mins of standing from lying:
- systolic at least 20 mmHg (with or without symptoms)
- diastolic at least 10 mmHg (with symptoms)
What is the principle of long term control of blood pressure?
Control of blood volume via
Extra-cellular fluid volume
Which 2 main factors affect extracellular fluid volume?
Water excess or deficit
Sodium excess or deficit
Which hormones regular extracellular fluid volume?
- Renin-Angiotensin-Aldosterone System (RAAS)
- Natriuretic peptides
- Antidiuretic hormone (vasopressin)
Which two key factors does RAAS affect in the regulation of MAP?
Plasma volume
Systemic vascular resistance
Describe the RAAS
- renin released from kidneys, stimulates formation of angiotensin I in the blood from angiotensinogen (produced by liver)
- angiotensin I is covered to angiotensin II by ACE
- angiotensin II has 3 effects:
1. stimulates release of aldosterone from adrenal cortex
2. causes systemic vasoconstriction –> increases SVR
3. Stimulates thirst and ADH release –> increases plasma volume - Aldosterone acts on kidneys to increase sodium and water retention –> increases plasma volume
Where is ACE produced?
Pulmonary vascular endothelium
Where is renin released from?
Granular cells in juxtoglomerular apparatus of kidney
Which 3 mechanisms stimulate renin release?
- renal artery hypotension
- stimulation of renal sympathetic nerves
- decreased sodium in renal tubular fluid
Which hormones provide a counter-regulatory system for the RAAS?
Natriuretic peptides (NPs)
How do NPs work?
- cause excretion of salt and water
- decrease renin release
- act as vasodilators
- -> decrease BP
What are the type types of NPs?
ANP
BNP
Which hormone can be measured in patients with suspected HF?
Serum BNP
Where is ADH synthesised and stored?
Synthesised in hypothalamus
Stored in posterior pituitary
What is the main stimulus for ADH secretion?
Increased plasma osmolality
How does ADH work?
Acts in kidney tubules to increase reabsorption of water
–> increase plasma volume/BP
