Venous Return

Question 1

describe venous resistance compared to arteriole

Answer 1

Q= P/R or R= P/Q. Since P is much smaller in the venous system, resistance is much lower as well

Question 2

what is the average pressure (MAP) in the arteriole system? in (art and ven) capillaries? in the venous system? in the right atrium?

Answer 2

arteriole- 100
art side of capillaries- 30
ven side of capillaries 15
veins -15
right atrium 5

Question 3

do veins or arteries have a higher capacitance? what does this mean?

Answer 3

veins- it means they are easier to expand. Capacitance = V/P

Question 4

explain the affect gravity has on venous pressure. what are dependent regions

Answer 4

in the blood column, the inferior blood has the added pressure of the blood superior to it. this can cause pooling in dependent regions, and the body has evolved mechanisms to overcome this

Question 5

what are the mechanisms in the venous system to overcome gravity

Answer 5

1. valves
2. skeletal pump
3. suction of the heart
4. respiratory pump

Question 6

how does the body regulate blood pressure (3 methods). what is longest acting mechanism

Answer 6

1. changes in heart
2. changes in VSM
3. changes in blood volume- longest acting

Question 7

where are the receptors for blood volume?

Answer 7

1. brain- osmolarity receptor that sense when blood is too concentrated
2. kidney- high pressure
3. heart- in right atrium, low pressure

Question 8

if MAP is low in the kidneys _________ happens. if MAP is high in the kidneys, ______ happens

Answer 8

is pressure is low, the fluid will not leave the tubules and volume will be retained. if it is high, fluid will be forced out the tubules and volume will be lost

Question 9

describe how the RAAS system works

Answer 9

the kidney releases renin into the blood in response to decreased pressure (baroreceptor). renin converts angiotensinogen in the blood to angiotensin 1. angiotensin 1 gets converted by angiotensin 2 converter enzyme in lungs. angiotensin 2 increases BV and MAP

Question 10

angiotensin 2 actions

Answer 10

increases ADH secretion and thirst. causes release of aldosterone which increases fluid retention. increases vasoconstriction. all increase MAP.

Question 11

how does the heart regulate blood volume?

Answer 11

1. baroreceptor- high stretch = decrease sympathetic innervation for renal renin release
2. high stretch causes atrial naturetic peptide (ANP) release- release of volume water and salt

both decrease blood volume

Question 12

what are the 4 types of nutrient transport in capillaries?

Answer 12

1. diffusion- gas
2. pinocytosis
3. transport protein mediated- glucose into the brain
4. ultrafiltration- thru tiny pores

Question 13

what is the starling hypothesis?

Answer 13

ultrafiltration is dictated by the balance of transmural pressure (net out) and oncotic pressure (net in). proteins are more concentrated in the blood, which means fluid wants to move in. pressure is higher on the inside, which means fluid wants to move out.

Question 14

how can edema be caused in relation to capillary action

Answer 14

a blockage of the draining lymph system
an decrease in protein concentration- malnutrition/starvation
an increase in K (capillary permeability constant)

Question 15

what is autotransfusion?

Answer 15

when the pressure in the capillaries decreases, the Pout is decreased, causing fluid retention to increase BV and thus MAP.

Question 16

why does the hematocrit decrease in response to blood loss.

Answer 16

autotransfusion is interstitial fluid and not blood; thus it dilutes the blood decreasing the hematocrit

Question 17

true or false: VR = CO

Answer 17

true- averaged over time