Circulation Flashcards
What is microcirculation
No arteries or veins
arterioles, capillaries, venules
What is calculation for flow rate?
Pressure gradient / resistance
Blood flow rate = Volume of blood passing through a vessel per unit time
What is the aim of cardiovascular system
Adequate blood flow
through the capillaries
What is resistance?
Hindrance to blood flow due to friction between moving fluid and stationary vascular walls’
What happens to the pressure gradient , resistance, flow when:
Blood pressure increase?
Arteriolar vasoconstriction?
BP : Increases pressure gradient, increase flow, no change do resistance
AV : no pressure change, resistance increases, flow decreases
Darcys law?
Fluid circuit ( another name for it )
Flow rate = Pressure gradient / resistance
Flow to organ calculation?
F (organ) = Pressure/R organ
- Without this pressure difference blood would not reach tissue capillary beds
During contraction what happens to radius, resistance, flow?
Radius decreases
resistance increases
Flow decreases
= vasoconstriction
During relaxation what happens to radius, resistance, flow?
Radius increases
Resistance decreases
Flow increases
= vasodilation
What are the two functions of arterioles?
Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs) :
Regulated by local (intrinsic) controls and independent of nervous or endocrine stimulation
and
Help regulate systemic arterial blood pressure:
Regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
What is hyperaemia?
Increase of metabolites and oxygen usage leads to vasodilation of arterials so blood flow can meet needs
= increase in blood
What is myogenic autoregulation?
Regulation due to temp in this case
Decreased blood temperature causes increased stretch due to higher blood pressure
= vasoconstriction of arterioles
= arteries vasoconstrict to increase temp
How do the following create an equation for flow across the whole circulation?
Cardiac output
Blood pressure
total peripheral resistance
Blood pressure = cardiac output x TPT
Where in the CVS is the greatest drop in pressure?
From one end of an arteriole to the other
What is the Neural pathway utilising arterioles for vasoconstriction ?
CVS control in medulla = vasoconstriction
What ia the hormonal pathway utilising arterioles for vasoconstriction ?
ADH from pituitary
Angiotensin II
Adrenaline/NA
all lead to vasoconstriction
What is the purpose of capillary exchange?
delivery of metabolic substrates to the cells of the organism [which is the ultimate function of the CVS]
- 7uM lumen
1uM cell wdith
Why is capillary density important?
Specially designed to:
Minimise the diffusion distance
- Maximise the surface area and time for diffusion
- Highly metabolically active tissues have denser capillary networks
What capillary capacity do the following have:
Skeletal muscle?
Myocardium brain?
Lung?
100cm2/g
500cm2/g
3500cm2/g
What type of continous vessel do capillaries have?
H20 filled gap junction, wit continuous cells
and
Fenestrated : 80nm
What law do capillaries link to?
Fick’s law:
Ideally suited to enhance diffusion
What is capillary bulk flow?
A volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed
( due to the hydrostatic and oncotic flow )
What is starling’s hypothesis regarding capillary pressures?
Capillary pressure determines transudation, and the osmotic pressure of the proteins of the serum determines absorption
What leads to capillary ultrafiltration?
Pressure inside greater than Interstitial fluid
What leads to capillary reabsorption?
Inward driving pressure greater than outward pressure
Characteristics of the lymphatic system?
- No pump to induce flow
- Drainage into right lymphatic duct - thoracic duct
- Right and left subclavian veins
- 3 L per veins
What happens in rate of lymphatic production exceeds rate of drainage?
Oedema can form
( another issue is Parasitic blockage of lymph nodes )
Both can cause Elphantiasis
