Properties of special circulation Flashcards
What 3 characteristics need to be considered for special circulations?
Special requirements are met by circulation
Special structural or functional features of the circulation
Specific problems relating to that circulation
Where do the two coronary arteries originate from?
Two coronary arteries originate from the left side of the heart at the beginning (root) of the aorta, just after it exits the left ventricle
What do cardiac veins carry?
Cardiac veins carry blood with a poor level of oxygen, from the myocardium to the right atrium.
Where does most of the blood of the coronary veins return through?
Most of the blood of the coronary veins returns through the coronary sinus
What does the heart need a high supply of?
Needs a high basal supply of O2 – 20x resting skeletal muscle
What are the structural features of the heart?
- High capillary density
- Large surface are for O2 transfer
- Time proportional to d^2
- Cardiac muscles contain high number of fibres and capillaries giving rise to shorter diffusion paths
Blood flow during normal activity
High blood flow – x10 the flow per weight of rest of the body
Sympathetic innervation during normal activity
Relatively sparse sympathetic innervation
What is released during normal activity
High NO released during vasodilation
What is there a high extraction of?
High O2 extraction(75%)
What increases during increased demand?
Coronary blood flow increases in proportion to demands
What is produced during increased demand?
Production of vasodilators (adenosine, K+, acidosis) out-compete relatively low sympathetic vasoconstriction
What does circulating adrenaline do during increased demand?
Circulating adrenaline dilates coronary vessels due to abundance of β2-adrenoreceptors
What blood has a greater CO2 content and due to what reason?
Coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content
Due to high capillary density, surface area and small diffusion distance
What does high CO2 and low pH do to the bohr curve and what affect does this have?
- The high CO2 and low pH has shifted the curve to the right meaning that haemoglobin has less affinity for oxygen and more O¬2 is given up to the myocardial tissues
What percentage of oxgen does myocardium extract from haemoglobin compared to other tissue?
- The myocardium is able to extract 75% of the oxygen as opposed to typically 25% in other tissues
What does an increased O2 requirement produce?
Increased O2 Requirement Produces Increased Blood Flow
What does myocardium metabolism generate in order to increase blood flow?
- Myocardium metabolism generates metabolites to produce vasodilation which increases blood flow (metabolic hyperaemia)
What is there an increase of in order to increase blood flow?
- There is also an increase in pCO2, H+, K+ levels
What are human coronary arteries?
- Coronary arteries are functional end-arteries and therefore decreased perfusion produces major problems
Example of suden obstruction
o Acute thrombosis, produces myocardial infarction
Example of slow obstruction
o Atheroma (sub-endothelium lipid plaques) o Chronic narrowing of lumen, produces angina
What can thrombosis result in?
total occlusion of the left anterior descending coronary artery
What can occlusion lead to and result in?
- Occlusion leading to obstruction of blood flow to anterior (front) left ventricle
and can lead to MI
How do you calculate total resistance in series?
Add them together
What happens to total resistance during exercise and how is this brought about?
exercise, metabolic vasodilation of arterioles reduces total R
What leads to angina?
- Stenosis in large coronary artery
Effect of stenosis on resistance
o Increases resistance
What causes angina to develop?
total resistance is still too high due to dominance of stenosis
o O2 demand cannot be met, so angina develops
What is restricted during diastole?
Coronary Blood Flow Is Restricted During Diastole
What are the mechanical factors reducing coronary flow?
- Shortening diastole
- Increased ventricular end-diastolic pressure
- Reduced diastolic arterial pressure
What are special properties of the cutaneous circulation?
Defence against the environment
- Lewis triple response to trauma (increased blood flow)
Temperature regulation in cutaneous circulation
Temperature regulation
o Blood flow delivers heat from body core
o Radiation (proportional to skin temperature)
o Conduction to skin – convection from skin (skin temperature)
o Sweating (latent heat of evaporation)
o Skin is an organ
o Skin temperature can rage from 0 o C to 40 o C (briefly) without damage
Poikilothermic rather than homeothermic
What does skin temperature depend on in cutaneous circulation?
- Skin temperature depends on
o Skin blood flow
o Ambient temperature
What does direct connections of arterioles and venules (AVAs)expose?
- Direct connections of arterioles and venules expose blood to regions of high surface area
What does the sympathetic vasoconstrictor fibres release and act on?
- Release noradrenaline acting on α1 receptors
What does acetylcholine act on and produces what in sudomotor vasodilator fibres?
- Acetylcholine acting on endothelium to produce NO
What does a cold temperature induce?
Induces vasoconstriction
How do sympathetic nerves react to local cold?
- Sympathetic nerves react to local cold by releasing noradrenaline which binds to α2 receptors on vascular smooth muscle in the skin
o α2 receptors bind to noradrenaline at lower temperatures than α1 receptors
What does paradoxical cold vasodilation protect?
-Protects against skin damage
What is paradoxical cold vasodilation caused by?
Caused by paralysis of sympathetic transmission
What does long-term exposure to cold eventually lead to?
Long-term exposure leads to oscillations of contraction/relaxation
What happens to cutaneous perfusion as temperature increases?
Increased cutaneous perfusion with increased core temperature
What does an increased core temperature stimulate?
Stimulate warmth receptors in anterior hypothalamus
What does the stimulation of warmth receptors in anterior hypothalamus cause?
CAUSING…
Sweating
Increased sympathetic activity to sweat glands mediated by acetylcholine
Vasodilation
Increased sympathetic sudomotor activity such that acetylcholine acts on endothelium to produce NO
NO dilates arterioles in extremities
When is blood directed to more vital organ/tissue?
Blood directed to more important organs/tissues during loss of BP following haemorrhage, sepsis, acute cardiac failure
What is vasoconstriction of skin blood vessels mediated by?
Mediated by sympathetic vasoconstrictor fibres + adrenaline + vasopressin + angiotensin II
What may reduce when the body is warmed up to quickly during a haemorrhage?
During a haemorrhage, warming up the body too quickly may reduce cutaneous vasoconstriction and be potentially dangerous
Blood flows to the skin and not to the vital organs
What is blushing mediated by?
blushing (sympathetic sudomotor nerves)
What is the lewis triple response?
Response Of Skin To Trauma
What are the 3 responses?
Local redness
Site of trauma
Local swelling
Inflammatory oedema (wheal)
Spreading flare
Vasodilation spreading out from the site of traumaWhat mediates the flare to trauma?
The C-fibre axon reflex mediates the flare to trauma
What is there an increased delivery of to site of damage?
Increased delivery of immune cells & antibodies to the site of damage to deal with invading pathogens
What can prolonged obstruction of flow by compression cause?
Severe tissue necrosis
Where do bed sores usually occur?
Heels, buttocks, weight bearing areas
How are bedsores avoided?
Shifting position/turning which causes reactive hyperaemia (on removal of compression
High skin tolerance to ischemia
What can standing for long periods decrease?
Often standing for long periods in hot weather will decrease central venous pressure (hypotension)
As well as increased capillary permeability (oedema)
