CVS Adaptations Flashcards
What is the skeletal muscle pump
During muscle contraction blood is squeezed towards the heart, valves prevent back flow.
What happens to your cardiovascular system when you stand up
- Orthostatic/Postural Hypotension
- Gravity induced blood pooling
What is a baroreceptor, what does it detect and where is it found
A stretch sensitive mechanoreceptor that responds to changes in pressure, located in the carotid and aortic arteries.
When baroreceptors sense a decrease in blood pressure what response do they trigger
They trigger a response via a homeostatic mechanism that increases heart rate and force of contraction, causes vasconstriction, which increases peripheral resistance and cardiac output, returning BP to normal
What neurotransmitter do sympathetic vasoconstrictor nerve fibres secrete
Noradrenaline
What effect does the noradrenaline from sympathetic vasoconstrictor nerve fibres have the blood flow
Decreases it through resting muscles to as little as half or a third.
When is the action of sympathetic vasoconstrictor nerve fibres physiologically important
Circulatory shock
Hypotensive crisis
During exercise how do muscles react to Noradrenaline
They become unresponsive to the vasoconstriction effect from NA
During exercise what do the two adrenal medullae do
They secrete large amounts of NA and adrenaline
During exercise what effect does adrenaline have
It mainly acts on Beta2 adrenergic receptors and result in vasodilation
During exercise what effect does the capillaries opening have
All the capillaries open
Increases blood flow
Increased surface area for exchange
Increase nutrient and oxygen supply to muscle
How does decreased oxygen in the muscle affect the control of blood flow
Greatly enhances flow and also causes the release of local vasodilator substances
Name a few vasodilator substances and which is the most important
Adenosine - most important K+ ATP Lactic Acid Carbon Dioxide
What 3 main receptors provide feedback to the higher brain centres to drive the CVS
Chemoreceptors
Mechanoreceptors
Baroreceptors
What effect does shock have on he blood flow/supply
Generalised severe reduction in blood supply to the body tissues. Inadequate tissue perfusion leads to cellular hypoxia and tissue damage
What is Hypovolemic shock
Refers to a medical or surgical condition in which rapid fluid loss results in multiple organ failure due to inadequate perfusion
What can cause hypovolemic shock
- Trauma
- Haemorrhage
- Vomiting/diarrhoea
- Burns
What 4 major physiological systems does the human body activate to respond to acute haemorrhage
The Haematological system
The Cardiovascular system
The Renal system
The Neuroendocrine system
What effect does hypovolemic shock have on the CVS
Increases heart rate
Increases myocardial contractility
Contrstricts peripheral vessels
How does the CVS re-distribute blood due to hypovolemic shock
Redistributes blood to the brain, heart and kidneys and away from the skin, muscles and GI tract.
How does the renal system respond to hypovolemic shock
The kidneys respond by stimulating an increase in renin secretion from the juxtaglomerular apparatus
What does renin do
Cleaves angiotensinogen into Angiotensin 1 and ACE converts AT1 into AT2
What effects does AT2 have in response to hypovolemic shock
AT2 has 2 main effects to reverse hypovolemic shock.
Vasoconstriction of arteriolar smooth muscle and stimulation of aldosterone secretion by the adrenal cortex
How does the neuroendocrine system react to hypovolemic shock
Cause an increase in circulating ADH
What do baroreceptors detect to cause ADH release
Decreased BP
Decreased [Na+]
How does the haematological system respond to hypovolemic shock
Activating the coagulation cascade and contracting the bleeding vessels, via local Thromboxane A2 release
- Platelets are activated to form an immature clot on the bleeding source, the damaged vessel exposes collagen that causes fibrin deposition and stabilisation of the clot
What is the response to <15% blood loss haemorrhage (class 1)
minimal fast heart rate, normal blood pressure
What is the response to 15-30% blood loss haemorrhage (class 2)
Fast heart rate, minimal low blood pressure
What is the treatment for class 2 haemorrhage
Intravenous fluids
What is the response to 30-40% blood loss haemorrhage (class 3)
Very fast heart rate, low blood pressure, confusion, almost no blood flow to the kidney and liver, reduced blood flow to brain and heart
What is the treatment for class 3 haemorrhage
Fluids and packed RBCs
What is the response to >40% blood loss haemorrhage (class 4)
Severe hypotension and tachycardia
