Case 1 Physiology Flashcards
What is the function of the tunica intima in capillaries?
Provides a semi permeable barrier
What is the function of the tunica media?
Provides elastic tension and can change vessel diameter to withstand and maintain the pressure
What is the function of the tunica adventitia?
Prevents over expansion of the vessel
What is the compensatory mechanism of hypertension?
the baroreceptors ‘reset’ at a higher pressure so no longer try to lower the blood pressure leading to chronic hypertension
How does standing up affect blood pressure?
standing up causes blood to pool in the lower limbs due to gravity, so less blood returns to the heart, so there is a decrease in blood pressure of the aorta
How does the body correct the blood pressure changes from standing up?
the decrease in blood pressure causes baroreceptors to increase the firing rate when stretched increasing sympathetic firing and decreases parasympathetic firing , increasing vasoconstriction and increasing heart contraction, returning blood pressure back to normal
How do local factors affect arterioles?
increased metabolism -> increased CO2 -> vasodilation
increased stretch of myocytes -> vasoconstriction
How do external factors affect arterioles?
increased sympathetic activity -> vasoconstriction
adrenaline -> vasoconstriction of vessels to gut etc, vasodilation of vessels to skeletal muscles
angiotensin II -> vasoconstriction
ADH -> vasoconstriction
Why is the heart important as a pump?
To deliver a continuous supply of oxygen and other nutrients to the brain an vital organs via the circulation and removal of waste products
Which factors determine resistance?
viscosity of blood, length of vessel and vessel radius
What is the equation for resistance?
R∝(ηL)/r⁴
η is blood viscosity; L is vessel length and r is vessel radius
What is the equation for blood flow?
Q=ΔP/R
Q is blood flow; ΔP is change in pressure and R is resistance
Describe the pressure in the aorta
High and fluctuating
Describe the pressure in the capillaries
Decreasing as you get further from the heart
Describe the pressure in the veins
Low and stable
Describe the velocity in the aorta
High and fluctuating
Describe the velocity in the capillaries
Low
Describe the velocity in the veins
Higher than the capillaries and stable
Why does the capillaries cause a change in pressure?
Because they have a large total cross-sectional area
Where are high pressure baroreceptors found?
In aortic arch and carotid sinus
What change in pressure does high pressure baroreceptors detect?
60 to 180mmHg
How do high pressure baroreceptors respond to a change in pressure?
When the vessel wall is stretched more, they fire more action potentials.
Where are low pressure baroreceptors found?
Atria and venoatrial junctions of the heart
What is another name for low pressure bars receptors?
Cardiopulmonary receptors
