Vascular Physiology 3 Flashcards
capillary structure
*the capillary is composed of a single cell-layer with an adjoining basement membrane
*fluid/electrolytes/small hydrophilic compounds are able to pass through small water-filled CHANNEL
*lipids and cholesterol are able to pass through the endothelial CELL itself
4 things which affect the diffusion rate across the capillary
- concentration difference (ΔX)
- surface area for exchange (A)
- diffusion distance (ΔL)
- capillary wall permeability
note: surface area and concentration difference are proportional, while diffusion distance is inverse
capillary variation in water permeability
*brain capillaries are an example of capillary beds with lower water permeability
*capillary beds with higher water permeability include: kidney, bone marrow, liver
capillary variation in protein permeability
*continuous capillaries: do NOT let protein into the tissues
*discontinuous & fenestrated capillaries: very “leaky” to proteins
continuous capillaries
*prevent translocation of proteins from the capillary into the surrounding tissues
*ex: brain
fenestrated capillaries
*small holes in the capillary allow for the passage of electrolytes, fluids, and small proteins
*ex: kidneys, intestines
sinusoidal capillaries
*larger holes/gaps in the capillary allow for the passage of electrolytes, fluids, proteins, and RBCs
*ex: bone marrow, liver, spleen
pressure gradient across the capillary
*pressure varies from one end of the capillary to the other
*pressure on the arteriole side of the capillary (30 mmHg) is higher than pressure on the venule side of the capillary (10 mmHg)
*this pressure difference drives blood flow from the arteriole to the venule
capillary hydrostatic pressure (Pc)
*Pc is MUCH MORE influenced by changes in Pv (pressure in the venule) than by changes in Pa (pressure in the arterioles)
fluid exchange at the capillary
*arteriolar side of the capillary = filtration (fluid exiting the capillary, going into the interstitium)
*venule side of the capillary = reabsorption (fluid re-entering the capillary)
capillary oncotic pressure (Πc)
*because the capillary barrier is readily permeable to ions, the osmotic pressure within the capillary is principally determined by PLASMA PROTEINS that are relatively impermeable (ex. albumin)
*several different types of disease manifest as a reduced capillary oncotic pressure: advance liver disease (reduced protein synthesis), nephrotic syndrome (kidney spills a lot of protein into the urine)
tissue oncotic pressure (Πi)
*the oncotic pressure of the interstitial fluid depends on the interstitial protein concentration and the reflection coefficient of the capillary wall
*in a “typical” tissue, tissue oncotic pressure is about 5 mmHg (much lower than capillary plasma oncotic pressure)
capillary filtration and absoprton
*the relationship among the factors which cause filtration and absorption is referred to as Starling’s law: (Pc - Pi) - 1(Πc - Πi)
*net filtration: (Pc-Pi) > (Πc-Πi)
*net absorption: (Pc-Pi) < (Πc-Πi)
*no net fluid movement: (Pc-Pi) = (Πc-Πi)
post-capillary sphincter
*if pressure in capillary falls (too much or inappropriately), post-capillary sphincter tightens to increase capillary pressure
pitting edema
*caused by increased capillary pressure leading to excess fluid filtration or decreased oncotic pressure leading to fluid going to the tissues
*when you press, it leaves a thumbprint
non-pitting edema
*caused by lymphatic obstruction or translocation of proteins in the tissue, which draws out fluid (myxedema)
*when you press, it does not leave a thumbprint
compartment syndrome
*when Pi (pressure in the interstitial space/tissues) > venous pressure, it may limit/stop flow leading to critical ischemia of affected distribution
*if blood can’t exit, new blood can’t enter
*often caused by a knife wound, gunshot wound, injury, bone fracture
veins and hydrostatic pressure when lying down
*when lying down: pressure in the veins is higher than pressure in the right atrium, and blood flows from higher pressure to lower pressure
*if someone is light-headed from low blood pressure, have them lie down
venous return: skeletal muscle pump
*veins in the legs have VALVES to prevent venous blood from going backwards
*when skeletal muscle contracts, it helps to propel blood back up to the heart
venous return: respiratory cycle
*inspiration: negative thoracic pressure when we breathe in PROMOTES VENOUS RETURN (right ventricle gets bigger); however, due to low pressure, blood stays in lungs rather than go to the left ventricle
*expiration: positive thoracic pressure when we exhale reduces venous return and goes in opposite direction of inspiration
venous return curve
*venous return is greater when the pressure in the right atrium is lower
*as the right atrial pressure increases, less venous blood is returning to the heart
*many factors can influence venous return
factors that can increase venous return
*IV fluids, venoconstriction (increases venous pressure) → mean circulatory filling pressure increases
*exercise, decreased systemic vascular resistance → mean circulatory filling pressure does not change
factors that decrease venous return
*volume loss (ex. hemorrhage), venodilation (decreases venous pressure) → mean circulatory filling pressure decreases
*increased systemic vascular resistance → mean circulatory filling pressure does not change
aerobic exercise - overview
*any sustained exercise which improves heart muscle and lung function, thereby optimizing out body’s use of oxygen
*includes jogging, rowing, swimming, cycling
*typically lasts longer than 20 minutes
1 MET
*met: metabolic equivalent
*helps to define intensity of aerobic exercise
*the value of 1 MET is approximately equal to a person’s resting energy expenditure
effects of aerobic exercise on CV system (overall)
*decreased systemic vascular resistance
*increased contractility
*increased relaxation
*increased preload
*increased HR
effects of aerobic exercise on systemic vascular resistance
decreases due to muscle arteriolar vasodilation
effects of aerobic exercise on contractility
increases due to sympathetic through beta 1 activation
effects of aerobic exercise on relaxation
increases due to sympathetic through beta 1 activation
effects of aerobic exercise on preload
increases due to skeletal muscle pump
effects of aerobic exercise on heart rate
increase due to sympathetic through beta 1 activation
long-term adaptations to exercise
*body adapts more to intensity than duration
*increased vascularity of used muscle
*increased resting reserve (body can do more with less at rest)
*increased vagal tone
*improves glucose and lipid metabolism
*improves functional status
*heart may dilate due to having increased cardiac output with exercise
anaerobic exercise - overview
*a physical exercise intense enough to cause lactate to form
*examples: weight lifting, push-ups, squats, sprints
arteriovenous malformations (AVMs) - overview
*a connection directly between an artery and vein
*no capillary/arteriole between them
*consequently, a significant amount of blood can pass through quickly
cardiovascular changes in spaceflight
*without significant gravity, the chest expands: leads to redistribution of blood to the chest, head, and neck; atria dilate without overt increase in pressure
*redistribution of blood and fluid to thorax and head activates the carotid/aortic/atrial baroreceptors → decreases sympathetic tone, increases parasympathetic tone, releases ANP and BNP
*consequently: HR decreases, MAP decreases, urine output transiently increases
physiology of arteriovenous malformations (AVMs)
*by blood shunting quickly from the arteries to the veins without being resisted by arterioles, AVMs primarily INCREASE PRELOAD by increasing venous return
cardiovascular changes when returning back to earth from space
*due to lack of resistance, muscles atrophy → substantial reduction in exercise tolerance
*frequently encounter orthostatic hypotension and postural tachycardia
