Vascular Physiology 3

Question 1

capillary structure

Answer 1

*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

Question 2

4 things which affect the diffusion rate across the capillary

Answer 2

1. concentration difference (ΔX)
2. surface area for exchange (A)
3. diffusion distance (ΔL)
4. capillary wall permeability

note: surface area and concentration difference are proportional, while diffusion distance is inverse

Question 3

capillary variation in water permeability

Answer 3

*brain capillaries are an example of capillary beds with lower water permeability
*capillary beds with higher water permeability include: kidney, bone marrow, liver

Question 4

capillary variation in protein permeability

Answer 4

*continuous capillaries: do NOT let protein into the tissues
*discontinuous & fenestrated capillaries: very “leaky” to proteins

Question 5

continuous capillaries

Answer 5

*prevent translocation of proteins from the capillary into the surrounding tissues
*ex: brain

Question 6

fenestrated capillaries

Answer 6

*small holes in the capillary allow for the passage of electrolytes, fluids, and small proteins
*ex: kidneys, intestines

Question 7

sinusoidal capillaries

Answer 7

*larger holes/gaps in the capillary allow for the passage of electrolytes, fluids, proteins, and RBCs
*ex: bone marrow, liver, spleen

Question 8

pressure gradient across the capillary

Answer 8

*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

Question 9

capillary hydrostatic pressure (Pc)

Answer 9

*Pc is MUCH MORE influenced by changes in Pv (pressure in the venule) than by changes in Pa (pressure in the arterioles)

Question 10

fluid exchange at the capillary

Answer 10

*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)

Question 11

capillary oncotic pressure (Πc)

Answer 11

*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)

Question 12

tissue oncotic pressure (Πi)

Answer 12

*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)

Question 13

capillary filtration and absoprton

Answer 13

*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)

Question 14

post-capillary sphincter

Answer 14

*if pressure in capillary falls (too much or inappropriately), post-capillary sphincter tightens to increase capillary pressure

Question 15

pitting edema

Answer 15

*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

Question 16

non-pitting edema

Answer 16

*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

Question 17

compartment syndrome

Answer 17

*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

Question 18

veins and hydrostatic pressure when lying down

Answer 18

*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

Question 19

venous return: skeletal muscle pump

Answer 19

*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

Question 20

venous return: respiratory cycle

Answer 20

*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

Question 21

venous return curve

Answer 21

*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

Question 22

factors that can increase venous return

Answer 22

*IV fluids, venoconstriction (increases venous pressure) → mean circulatory filling pressure increases

*exercise, decreased systemic vascular resistance → mean circulatory filling pressure does not change

Question 23

factors that decrease venous return

Answer 23

*volume loss (ex. hemorrhage), venodilation (decreases venous pressure) → mean circulatory filling pressure decreases

*increased systemic vascular resistance → mean circulatory filling pressure does not change

Question 24

aerobic exercise - overview

Answer 24

*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

Question 25

1 MET

Answer 25

*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

Question 26

effects of aerobic exercise on CV system (overall)

Answer 26

*decreased systemic vascular resistance
*increased contractility
*increased relaxation
*increased preload
*increased HR

Question 27

effects of aerobic exercise on systemic vascular resistance

Answer 27

decreases due to muscle arteriolar vasodilation

Question 28

effects of aerobic exercise on contractility

Answer 28

increases due to sympathetic through beta 1 activation

Question 29

effects of aerobic exercise on relaxation

Answer 29

increases due to sympathetic through beta 1 activation

Question 30

effects of aerobic exercise on preload

Answer 30

increases due to skeletal muscle pump

Question 31

effects of aerobic exercise on heart rate

Answer 31

increase due to sympathetic through beta 1 activation

Question 32

long-term adaptations to exercise

Answer 32

*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

Question 33

anaerobic exercise - overview

Answer 33

*a physical exercise intense enough to cause lactate to form
*examples: weight lifting, push-ups, squats, sprints

Question 34

arteriovenous malformations (AVMs) - overview

Answer 34

*a connection directly between an artery and vein
*no capillary/arteriole between them
*consequently, a significant amount of blood can pass through quickly

Question 35

cardiovascular changes in spaceflight

Answer 35

*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

Question 35

physiology of arteriovenous malformations (AVMs)

Answer 35

*by blood shunting quickly from the arteries to the veins without being resisted by arterioles, AVMs primarily INCREASE PRELOAD by increasing venous return

Question 36

cardiovascular changes when returning back to earth from space

Answer 36

*due to lack of resistance, muscles atrophy → substantial reduction in exercise tolerance
*frequently encounter orthostatic hypotension and postural tachycardia