Physiology Flashcards
What are the functions of the CVS?
Bulk flow
Thermoregulation
Protection
Fluid balance
What are is the arrangement of most vascular bed?
Parallel
How is flow calculated?
Change in pressure/resistance
What controls pressure?
MAP- CVP
What controls resistance?
Radius
What are resistance vessels?
Restrict and dilate to alter blood flow
Arterioles
What are capacitance vessels?
Hold and store blood
Venules and veins
What are exchange vessels?
Capillaries
What are the features of excitation- contraction coupling in cardiac muscle?
Functional syncytium- intercalated discs
- Gap junctions (electrical connection)
- Desmosomes (physical connection)
Long action potential (250ms)
Pacemaker cells have unstable resting membrane potentials
What are the features of non-pacemaker cell action potential?
RMP- high resting PK+
Depolarisation- increased PNa+
Plateau- decreased PK+, Increased PCA2+ (L)
Repolarisation- Increased PK+, Decreased PCa2+ (L)
What are the features of pacemaker cell action potential?
Pacemaker potential:
- Decrease in PK+
- Early increase in PNa+
- Late increase in PCa2+ (T)
Action potential:
- Increase in PCa2+ (L)
What are the components of the special conducting system?
SA node- pacemaker
Annulus fibrosis- non conducting ring of tissue
AV node- delay box
Bundle of His
Purkinje fibres
What does each part of the ECG mean?
P= atrial depolarisation
QRS= ventricular depolarisation
T= ventricular repolarisation
What do standard limb leads show?
Events in the frontal pain
What does SLL I show?
Left arm wrt right arm
What does SLL II show?
Left leg wrt right arm
What does SLL III show?
Left leg wrt left arm
What does PR interval show?
Time for atrial to ventricular depolarisation
Due to transmission through AV node
What does QRS interval show?
Time for whole of ventricle to depolarise
What does QT interval show?
Time spent while ventricles are depolarised
Why is R wave biggest in SLL II?
Main vector of depolarisation is in line with axis of recording
What are the augmented limb leads?
aVR- right arm
aVL- left arm
aVF- foot
What are the precordial chest leads?
V1-V6
What are the steps of the cardiac cycle?
- Late diastole
- Atrial systole
- Isovolumic ventricular contraction
- Ventricular systole
- Isovolumic ventricular relaxation
What does mitral valve closure indicate?
Start of systole
What does aortic valve closure indicate?
Start of diastole
What is end diastolic and end systolic volume?
EDV= 140ml
ESV= 60ml
What is stroke volume?
Volume of blood pumped out with each beat of the heart
EDV-ESV= 80ml
What is ejection fraction?
Stroke volume as a fraction of the end diastolic volume
80/140= 2/3
What is 1st heart sound?
Closure of AV valves (mitral and tricuspid)
What is 2nd heart sound?
Closure of semilunar valves (aortic and pulmonary)
What are the 2 causes of abnormal heart sounds?
Stenosis
Regurgitation
What regulates heart rate?
Sympathetic and parasympathetic
What regulates stroke volume?
Preload
Afterload
Contractility
What is preload?
Length of muscle fibre before contraction
Preload is affected by EDV
What is afterload?
Load against which muscle tries to contract
Afterload affected by TPR
What is contractility?
Strength of contraction
Affected by sympathetic nervous system acting on B1 receptors on myocytes
What controls cardiac output?
Hr x SV
Why does CO increase in exercise?
HR increases (SNS)
Contractility increases (SNS)
Venous return increases (venoconstriction)
TPR falls (arteriolar dilatation)
What is the function of elastic arteries?
Dampen down pressure variations
Pressure reservoir
Why does pressure fall through the vascular tree?
Arteries- 95 to 90mmHg
Arterioles 90- 40mmHg
Capillaries- low pressure
Veins- 20- 5mmHg
Where is velocity of blood fastest?
Aort anad vena cava
Slowest in capillaries
What influences flow in veins?
Gravity
Skeletal muscle pump
Respiratory pump
Venomotor tone
Systemic filling pressure
What are the parts of the anticlotting mechanism?
Inhibit platelet aggregation
- Stop blood contacting collagen
- Produce prostacyclin and NO
Inhibit thrombin production
- Tissue factor inhibitory pathway
- Thrombomodulin
- Heparin
Activate plasmin from plasminogen to digest the clot
- Tissue factor plasminogen activator (t-PA)
What are the different structures of capillaries?
Continuous- no clefts/pores (brian)
Fenestrated- clefts and pores (intestine)
Discontinuous- clefts and massive pores (liver)
What does MAP =?
MAP= CO X TPR
How is MAP controlled?
Local mechanisms
Central mechanisms- maintain TPR
What are the local mechanisms for controlling MAP?
Active hyperaemia (metabolic activity increases flow)
Pressure autoregulation (reduced MAP, decreases flow causing dilatation)
Reactive hyperaemia (occlusion of blood supply increases flow)
Injury response (delivers WBCs to area)
What are the central mechanisms for controlling MAP?
Neural- sympathetic NS
Hormonal- adrenaline binds to a1 receptors causing constriction
What is the arterial baroreflex?
Stretch receptors in aortic arch and carotid sinus
Firing rate of baroreceptors indicates MAP
What nerves are involved in arterial baroreflex?
Aortic arch- vagus nerve
Carotid sinus- glossopharyngeal nerve
What is valsalva manouvre?
Forced expiration against a closed glottis
What are the steps to Valsalva manoeuvre?
- Increased thoracic pressure transmitted through aorta
- Reduces venous return which reduces MAP
- Baroreceptors detect MAP
- Reflex increase in CO and TPR
- Venous return restored so SV increases
What organ mediates long term control of BP?
Kidneys
How do the kidneys regulate plasma volume?
Renal counter current system creates high osmolarity outside collecting duct
Increase collecting duct permeability = water reabsorption and retained plasma volume
Decrease collecting duct permeability= water retained and reduced plasma volume
What hormones regulate control of PV?
Renin- angiotensin-aldosterone system
Antidiuretic factors
Atrial natriuretic peptide and brain natriuretic peptide
What is Renin- angiotensin-aldosterone system?
Renin converts angiotensin I into angiotensin II
- Stimulates aldosterone release which increases Na+ reabsorption (increased PV)
- Stimulates ADH release from pituitary which increases collecting duct permeability
- Vasoconstrictor so increases MAP
What is antidiuretic hormone?
Synthesised in hypothalamus and released from pituitary
Release triggered by decreased blood volume, increased osmolarity and circulating angiotensin II
- Increases permeability of collecting duct
- Vasoconstrictor so increases MAP
What is atrial natriuretic peptide and brain natriuretic peptide?
Produced from myocardial cells in atria and ventricles
Released by distention of atria and ventricles
- Increase excretion of Na+
- Inhibit renin release
- Reduce MAP
Therefore, decrease PV and BP
