Physiology 2 Flashcards
How and where is SVR regulated?
Vascular smooth muscles
Mainly in arterioles
e.g. contraction –> vasoconstriction –> increased SVR and MAP
How are nerves involved in the regulation of systemic vascular resistance? What are the neurotransmitters/receptors involved?
Vascular smooth muscle supplied by SYMPATHETIC nerves
- neurotransmitter is noradrenaline acting on alpha receptors
Increased sympathetic discharge –> vasoconstriction
Decreased sympathetic discharge –> vasodilatation
Which hormone is involved in control of vascular smooth muscle and where does it come from?
Adrenaline
From adrenal medulla
How does adrenaline effect vascular smooth muscle?
Depends on type of receptor:
- alpha –> vasoconstriction
- beta-2 –> vasodilatation
Alpha receptors in skin, gut and kidneys
Beta-2 receptors in cardiac and skeletal muscle
Allows strategic distribution of blood during exercise
Which 2 other hormones affect vascular smooth muscle and what is their effect?
Angiotensin II
ADH
–> both cause vasoconstriction
Give some examples of chemical factors which cause vasodilatation
- decreased local PO2
- increased local PCO2
- increased local H+
- increased extracellular K+
- adenosine release (from ATP)
- histamine
- bradykinin
- nitric oxide
Give some examples of chemical factors which cause vasoconstriction
- serotonin
- thromboxane A2
- leukotrienes
- endothelin
What is shock?
An abnormality of the circulatory system –> inadequate tissue perfusion and oxygenation
What is hypovolaemic shock? Give some examples
Loss of blood volume –> decreased CO and decreased BP
e.g. haemorrhage, D&V, excessive sweating
What is cardiogenic shock? Give an example
Sustained hypotension caused by decreased cardiac contractility
e.g. acute MI
What is obstructive shock? Give some examples
Obstruction leading to reduced CO
e.g. cardiac tamponade, tension pneumothorax, PE
What is neurogenic shock? Give an example
Loss of sympathetic tone to blood vessels and heart
- -> massive vasodilatation
- -> decreased HR (unlike other types of shock)
e.g. spinal cord injury
What is vasoactive shock? Give some examples
Release of vasoactive mediators –> vasodilatation and increased capillary permeability
e.g. septic shock, anaphylactic shock
How is syncope defined?
Transient loss of consciousness due to cerebral hypoperfusion, characterised by:
- rapid onset
- short duration
- spontaneous complete recovery
What are the three different types of syncope?
- reflex syncope
- orthostatic hypotension
- cardiac syncope
What is reflex syncope?
Neural reflexes –> decreased HR and/or decreased vascular tone (vasodilatation)
What are the three different types of reflex syncope?
- vasovagal syncope
- situational syncope
- carotid sinus syncope
What is the most common type of syncope?
Vasovagal syncope
What is vasovagal syncope?
FAINT triggered by emotional distress (e.g. pain, fear, blood phobia) or orthostatic stress
What happens before a vasovagal episode?
Typical prodrome of
- pallor
- sweating
- nausea
How can a vasovagal episode be averted?
Adopting a horizontal position or leg crossing
–> increases venous return
What is situational reflex syncope?
Faint during or immediately after a specific trigger e.g.
- cough
- micturition
- swallowing
What is carotid sinus reflex syncope?
Faint triggered by mechanical manipulation of the neck e.g.
- shaving
- tight collar
May occur after head and neck surgery or radiation
What causes postural hypotension?
Failure of baroreceptor responses to gravitational shifts in blood when going from lying to standing
What is the criteria for postural hypotension?
Drop, within 3 minutes of standing from lying:
- in systolic BP of at least 20 mmHg (with or without symptoms) or
- in diastolic BP of at least 10 mmHg (with symptoms)
What is cardiac syncope?
Cardiac event –> sudden drop in cardiac output
What are some causes of cardiac syncope?
- arrhythmias
- acute MI
- structural disease e.g. aortic stenosis, hypertrophic cardiomyopathy
- other CV disease e.g. PE, aortic dissection
What should the initial investigation of a patient with transient loss of consciousness involve?
- careful history
- full examination
- lying standing BP
- 12 lead ECG
How does blood arrive at/drain from the cardiac muscle?
Comes from left and right coronary arteries (arising from base of aorta)
Drain via coronary sinus into right atrium
During which part of the cardiac cycle does blood flow in the coronary arteries?
Diastole
What effect would increased HR have on coronary blood flow?
Reduced –> less time in diastole
At which MAP does autoregulation of cerebral blood flow fail?
MAP < 60 mmHg or
MAP > 160 mmHg
What is the effect of PCO2 on cerebral blood flow?
Increased PCO2 –> cerebral vasodilatation
Decreased PCO2 –> cerebral vasoconstriction (this is why hyperventilation can cause fainting)
How is cerebral perfusion pressure calculated?
CPP = MAP - ICP
How does pulmonary capillary pressure compare to systemic capillary pressure?
Pulmonary is lower
What is the effect of hypoxia on pulmonary arterioles?
Vasoconstriction
opposite effect on systemic arterioles
What happens if valves in lower limb veins become incompetent?
Blood pools in lower limb veins –> varicose veins
If blood is gathered in varicose veins, why does this not lead to a reduced CO?
Chronic compensatory increase in blood volume
What is oedema?
Accumulation of fluid in the interstitial space
What are the 4 physiological causes of oedema?
- Raised capillary pressure
- Reduced plasma osmotic pressure
- Lymphatic insufficiency
- Changes in capillary permeability
What are the causes of raised capillary pressure as a cause of oedema?
Arteriolar dilatation
Raised venous pressure
- left ventricular failure
- right ventricular failure
- prolonged standing (swollen ankles)
What type of oedema results from left ventricular failure?
Pulmonary oedema
What type of oedema results from right ventricular failure?
Peripheral oedema (ankle, sacral)
What are the causes of reduced plasma osmotic pressure as a cause of oedema?
Plasma protein < 30 g/l
- malnutrition
- protein malabsorption
- excessive renal excretion of protein
- hepatic failure
What are the causes of lymphatic insufficiency as a cause of oedema?
Lymph node damage
Filariasis - elephantiasis
What are the causes of changes in capillary permeability as a cause of oedema?
Inflammation
Histamine increases leakage of protein
