Special Circulations: Heart and Skin

Question	Answer
What are 2 special requirements of the coronary circulation?	1. Needs a high constant supply of oxygen 2. Needs the ability to alter oxygen supply according to demand
What is a special structural feature of cardiac muscle?	The muscle fibres are smaller so the capillary density is higher. This allows a larger surface area for diffusion of oxygen and CO2 (=quicker diffusion due to Fick's Law).
Name 3 special functional features of the coronary circulation at rest?	1. High blood flow 2. Basal NO released which causes vasodilation 3. High oxygen extraction
What happens during metabolic hyperaemia? (3)	1. Blood flow increases 2. Coronary vessels dilate 3. There is a large uptake of fatty acids for energy
What causes the coronary vessels to dilate during metabolic hyperaemia? (2)	1. Vasodilators produced (e.g. adenosine) 2. Release of adrenaline onto beta 2 receptors
Name 3 potential problems that can occur within the coronary circulation.	1. Ischaemic Heart Disease (IHD) 2. Angina 3. Thrombosis
Why is the myocardium especially susceptible to ischaemia?	The coronary arteries are functional end arteries so each supply one area of the heart with little cross branching.
What are the 2 outcomes of ischaemia?	1. Sudden blockage of a vessel = MI 2. Slow narrowing of a vessel due to atheroma = angina
What is the result of a thrombosis?	Blockage of the coronary vessels leading to an MI
Give 5 effects of an MI.	1. Ischaemic tissue 2. Acidosis 3. Pain (due to stimulated nociceptors) 4. Increased sympathetic stimulation (leading to arryhthmias?) 5. Necrosis
What is the effect of angina?	Stenosis (narrowing) causes resistance in coronary vessels to increase. This means that during exercise when smaller branches dilate, the overall resistance still remains high so the oxygen needs of the cardiac muscle are not met, causing chest pain.
When does coronary blood flow occur?	During diastole
When can this be a problem? (3)	1. If diastole time is reduced due to high HR 2. If the L ventricular EDP is increased 3. If diastolic arterial pressure is reduced
So what do many angina drugs target and why?	Target HR so that a longer time for diastole (and therefore coronary blood flow) can be achieved.
Name 3 special requirements of the cutaneous circulation.	1. Needs to defend against the environment 2. Lewis triple response to trauma 3. Temperature regulation
What does skin temperature depend on? (2)	1. Blood flow in the skin 2. Ambient temperature
What is the special structural feature of the cutaneous circulation?	AVAs - Arterio-Venous Anastomoses. These are vessels that directly link arteries and veins, bypassing capillaries.
What do the AVAs do?	Upon lack of sympathetic innervation or vasodilation, blood gets 'shunted' from arteries to veins, which are more effective at causing heat loss through the skin by radiation, conduction-convection and evaporation due to their more compliant walls.
Where would you find AVAs?	In the extremities
What happens on sympathetic innervation to the AVAs?	They constrict so limit blood flow and prevent heat loss through the skin
How does the cutaneous circulation respond to ambient temperature?	Increased ambient temperature causes vaso- and venodilation to help heat loss through the skin. Decreased temp causes constriction of vessels and therefore prevents heat loss through the skin.
How does the cutaneous circulation respond to changes in core temperature?	Receptors in the hypothalamus detect core temperature and control the sympathetic output to the vessels.
What can occur at very low temperatures?	Paradoxical cold vasodilatation
What is this?	After prolonged exposure to cold and the vasoconstriction that accompanies it, the sympathetic transmission becomes paralysed and causes vasodilation instead. It is thought to be a protective measure against death of skin tissue.
What is the body's response to an increased core temperature (e.g. after exercise)? (2)	1. Sweating - release of ACh on sweat glands 2. Vasodilation
How else can the cutaneous circulation be controlled? (3)	1. Baroreflex-stimulated vasoconstriction 2. Emotions 3. Response to skin injury
How is the baroreflex-stimulated vasoconstriction response helpful?	Blood can be directed elsewhere (away from the skin) to more important tissues in times of low BP.
What mediates this response? (4)	1. Sympathetic vasoconstrictor fibres 2. Adrenaline 3. Vasopressin 4. Ang II
Give an example of how emotions can control cutaneous circulation.	Blushing
What is the skin's response to injury?	The Lewis Triple Response to Trauma
What is this?	--> Local redness at the exact site of injury --> Swelling (wheal) at site of injury due to inflammatory oedema --> Spreading redness (flare) due to vasodilation around site of injury.
How is this helpful?	Allows increased blood flow to the site of injury, to give faster delivery of WBCs and antibodies to deal with invading pathogens.
What mediates the 'flare' stage of this response?	The C-fibre axon reflex
How does this work?	When the main axon sends its signal to the dorsal root ganglion, a message is also sent to the axon collateral, which causes Substance P release and degranulation of mast cells to release histamine, both of which cause vasodilation.
When areas of skin are compressed for a long time, _________ _________ can begin to take place, known as '___ ______'. These can be prevented by regularly ________ _________.	tissue necrosis, bed sores, changing position
Standing up for a long time in warm weather can cause __________ ____________ or __________ due to the gravitational effect of blood. __ __ __ decreases and ____________ _____________ increases, causing the hypotension and oedema.	postural hypotension, oedema, CVP, capillary permeability

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Special Circulations: Heart and Skin

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	Created by Hannah Tribe almost 11 years ago