Skin and heart circulation Flashcards
Properties of special circulations
Where do the coronary arties originate from? [1 mark]
The root of the aorta
Where do coronary veins carry deoxygenated blood from? [2 marks]
- From the myocardium to the right atrium
- To the coronary sinus
Does coronary circulation need a high basal supply of O2? [1 mark]
YES
What are the special structural features of cardiac muscle? [4 marks]
- High capillary density (to reduce diffusion distance)
- Large surface area for O2 transfer
- High blood flow
- Sparse sympathetic innervation
- High levels of nitric oxide (leading to vasodilation)
- High O2 extraction
What happens to coronary circulation during increased demand? [3 marks]
- Blood flow increases
- Vasodilators outcompete low sympathetic vasoconstriction
- Circulating adrenaline dilates coronary arties (due to lots of beta 2 adrenoceptors)
What causes more oxygen to be extracted in the myocardium? [2 marks]
- Bohr shift
- Vasodilation
Why are coronary arteries functional end-arteries? [2 marks]
- There are lots of capillaries in the heart
- So there is less arterio-arterial anastomoses
What is the result of a thrombus in the left anterior descending coronary artery? [6 marks]
- Ischaemia and cell death
- Acidosis
- Pain due to C-fibres being stimulated
- Impaired contractility
- Sympathetic activation
- Arrhythmia
What happens to arteries and arterioles to meet increased demand of oxygen in healthy coronary vessels? [2 marks]
- Resistance in large coronary artery is low but resistance in arteriole is high
- Resistance in arteriole is reduced
Why can’t vessels with atheromas meet increased demands of oxygen? [3 marks]
- Resistance in large coronary artery is high due to the atheroma
- The arteriole dilates to try and reduce resistance but total resistance is still too high
- Angina develops
Does blood pass through coronary vessels in systole? [2 marks]
NO
Only in diastole are vessels able to pass blood, in systole they are compressed.
What does the left ventricle and aorta do in systole? [4 marks]
- Left ventricle contracts and empties its blood into the aorta
- Aorta expands a little due to compliance
- Aortic valve closes and blood enters systemic circulation
- Aorta still has high pressure and it contracts
How does a myocardial infarction affect ventricles? [2 marks]
- Stiffening of ventricles means that they can’t fully relax
- Ventricular pressure remains high, even in diastole
What happens to the aorta in hypotension? [2 marks]
- If the aortic valves are damaged, there is aortic regurgitation
- Less blood enters systemic circulation
What are the special properties of the skin? [3 marks]
- Defence against the environment
- Lewis triple response to trauma
- Temperature regulation
What does the Lewis triple response to trauma involve? [3 marks]
- Redness
- Swelling
- Flare
What is involved in temperature regulation of the heart? [4 marks]
- Blood flows from core to the skin surface
- Radiation is proportional to skin temperatures
- Conduction to skin and convection from skin
- Sweating (latent heat of evaporation)
What does poikilothermic mean? [1 mark]
Large variation in temperature (a property the skin, without damage)
What does skin temperature depend on? [2 marks]
- Skin blood flow
- Ambient temperatures
What is cold induced vasoconstriction? [4 marks]
- Helps to conserve heat
- Sympathetic nerves release noradrenaline that binds to alpha 2 receptors
- alpha 2 receptors bind to noradrenaline at lower temperatures that alpha 1 receptors.
- Anastomoses open and capillaries close to maintain heat
What is paradoxical cold vasodilation? [3 marks]
- Caused by paralysis of sympathetic transmission (that cause vasoconstriction)
- To protect the skin from damage
- Long term exposure causes oscillations of contraction and relaxation as temperatures fluctuate.
What do sympathetic vasoconstrictor fibres do? [2 marks]
- Help arterio-venous anastomoses constrict
- Release noradrenaline and acts on alpha 1 adrenoceptors
What do sudomotor vasodilator fibres do? [2 marks]
- Release acetylcholine and act to increase nitric oxide production
- Driven by temperature regulation nerves in the hypothalamus
What is sweating caused by? [1 mark]
Increased sympathetic activity to sweat glands
What do the baroreflex, RAAS system and ADH do? [2 marks]
- Constrict arteries to skin
- Divert blood to central organs after drop in BP (caused by sepsis, haemorrhage, acute cardiac failure)
What is baroreflex/RAAS/ADH-mediated vasoconstriction caused by? [4 marks]
- Vasoconstrictor fibres
- Adrenaline
- Vasopressin
- Angiotensin II
Why is it dangerous to warm up a body too quickly during a haemorrhage? [1 mark]
It can reduce cutaneous vasoconstriction and less blood is able to reach the central organs
What causes blushing? [1 mark]
Sympathetic sudomotor nerves
