Microcirculation, Venous Blood Flow and Return Flashcards
What is the intersitium? What is the interstitial fluid?
- collagen and proteoglycan filaments
- fluid trapped amongst filaments
what is filtration?
- what happens with water
- water being pushed out or pulled in by various forces
What are crystalloids?
- sodium ions
- chloride ions
- potassium ions
What do crystalloids do?
transfer of fluids by diffusion or follow bulk flow of fluid around and filtered out as solution
where do colloids exist? where are they most greatly concentrated?
- interstitial fluid and and capillaries
- but highest concentration is in the plasma
Discuss the permeability of the capillary wall.
- permeable to water and most solutes
- barrier to protein
- permeability ofr albumin
Discuss the composition of the extracellular matrix.
interstitial spaces formed of proteins which trap water
What is oncotic pressure? which protein is mostly responsible for this?
- proteins attract and have a pull on water which creates pressure
- albumin pulls fluid across the capillary membrane back into it
What is capillary hydrostatic pressure?
- force of fluid out of capillaries and into the interstitium
- this force drops from the arterial to the venous end of the capillary
What does a positive and negative interstitial hydrostatic pressure mean?
- positive means fluid is forced into the capillary
- negative means fluid drains into the intersitium
what is the starling hypothesis?
- oncotic pressure pulling fluid into the capillary as a result of the high capillary albumin content
- hydrostatic pressure pushing fluid out of the capillaries
Are the starling forces balanced?
- 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
What is the overall fluid movement through capillaries? what anatomical structure is therefore required?
- capillaries lose more water than they gain
- lymphatic system is required to remove the excess fluid to prevent oedema
What are the 3 main structural features of the lymph system?
- large fenestrated walls of capillaries
- drain via lymphatic vessels
- pass through lymph nodes
what 4 things does the lymphatic system control?
- proteins from interstitial fluid
- volume of interstitial fluid
- interstitial fluid pressure
- immune response
What does increased venous return mean?
increase venous return, increase arterial pressure and end diastolic ventricular volume and therefore increase the stroke volume and therefore the cardiac output
what factors affect venous return?
- blood volume
- skeletal muscle pumps- muscle contractions pushing muscle back to the heart
- sympathetic tone of veins increased
- inspiration
how does inspiration increase venous return?
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
What effect does gravity have on blood pressure when standing still? what is the effect on hydrostatic pressure?
- 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
What effect does being in the recumbent position have on pressure in capillaries?
means pressures are more equal with gravity and therefore the effect of gravity is diminished
What is orthostatic hypertension? what is the reflective compensatory mechanism?
- 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
