Microcirculation, Venous Blood Flow and Return

Question 1

What is the intersitium? What is the interstitial fluid?

Answer 1

• collagen and proteoglycan filaments

- fluid trapped amongst filaments

Question 2

what is filtration?

Answer 2

• what happens with water

- water being pushed out or pulled in by various forces

Question 3

What are crystalloids?

Answer 3

• sodium ions
• chloride ions
• potassium ions

Question 4

What do crystalloids do?

Answer 4

transfer of fluids by diffusion or follow bulk flow of fluid around and filtered out as solution

Question 5

where do colloids exist? where are they most greatly concentrated?

Answer 5

• interstitial fluid and and capillaries

- but highest concentration is in the plasma

Question 6

Discuss the permeability of the capillary wall.

Answer 6

• permeable to water and most solutes
• barrier to protein
• permeability ofr albumin

Question 7

Discuss the composition of the extracellular matrix.

Answer 7

interstitial spaces formed of proteins which trap water

Question 8

What is oncotic pressure? which protein is mostly responsible for this?

Answer 8

• proteins attract and have a pull on water which creates pressure
• albumin pulls fluid across the capillary membrane back into it

Question 9

What is capillary hydrostatic pressure?

Answer 9

• force of fluid out of capillaries and into the interstitium
• this force drops from the arterial to the venous end of the capillary

Question 10

What does a positive and negative interstitial hydrostatic pressure mean?

Answer 10

• positive means fluid is forced into the capillary

- negative means fluid drains into the intersitium

Question 11

what is the starling hypothesis?

Answer 11

• oncotic pressure pulling fluid into the capillary as a result of the high capillary albumin content
• hydrostatic pressure pushing fluid out of the capillaries

Question 12

Are the starling forces balanced?

Answer 12

• oncotic pressure is even across the capillary, albumin and other like proteins pulling fluid in
• hydrostatic pressure however varies from the arterial to venous end with more fluid pushed out at the arterial end therefore at the arterial end more fluid is pushed out than is brought back in

Question 13

What is the overall fluid movement through capillaries? what anatomical structure is therefore required?

Answer 13

• capillaries lose more water than they gain

- lymphatic system is required to remove the excess fluid to prevent oedema

Question 14

What are the 3 main structural features of the lymph system?

Answer 14

• large fenestrated walls of capillaries
• drain via lymphatic vessels
• pass through lymph nodes

Question 15

what 4 things does the lymphatic system control?

Answer 15

• proteins from interstitial fluid
• volume of interstitial fluid
• interstitial fluid pressure
• immune response

Question 16

What does increased venous return mean?

Answer 16

increase venous return, increase arterial pressure and end diastolic ventricular volume and therefore increase the stroke volume and therefore the cardiac output

Question 17

what factors affect venous return?

Answer 17

• blood volume
• skeletal muscle pumps- muscle contractions pushing muscle back to the heart
• sympathetic tone of veins increased
• inspiration

Question 18

how does inspiration increase venous return?

Answer 18

change in pressure in the thorax, increase in abdominal pressure due to the diaphragm descending, decrease in thoracic pressure and in the inter thoracic veins and R atrium hence increasing the pressure difference between peripheral veins and the heart

Question 19

What effect does gravity have on blood pressure when standing still? what is the effect on hydrostatic pressure?

Answer 19

• pressure you are experiencing in your feet is greater than the blood pressure in your head
• in lower body there is therefore much greater hydrostatic pressure in capillaries pushing more water out

Question 20

What effect does being in the recumbent position have on pressure in capillaries?

Answer 20

means pressures are more equal with gravity and therefore the effect of gravity is diminished

Question 21

What is orthostatic hypertension? what is the reflective compensatory mechanism?

Answer 21

• immediate effect of moving from supine to upright
• rapid decrease in venous return hence decrease in cardiac output and therefore in blood pressure
• vasoconstriction in legs and lower abdomen to compensate