Capillaries Flashcards
What is the function of capillaries?
Exchange between blood and interstitial fluid
What cells are present in capillaries?
Epithelial cells
What makes up micro circulation ?
Capillary beds
What is the name of the direct pathway from the arteriole to the venule?
Metarteriole
What is the name of the smooth muscle present on the entry to the capillary bed from the arteriole ?
Precapillary sphincters
When the precapillary sphincters are closed where does the blood flow ?
Through the metarteriole
What is vasomotion?
Spontaneous contraction and relaxation of the smooth muscle within the precapillary sphincters and the metarterioles
What are the types of capillaries?
Continuous
Fenestrated
Discontinuous
Where are fenestrated capillaries found?
Exocrine glands, endocrine glands, renal glomeruli and intestinal mucosa
Where are discontinuous capillaries found?
Liver, spleen and bone marrow
Blank
Blank
What are the three ways substances can be exchanged across the capillary wall?
- Diffusion
- Vesicular transport
- Bulk flow (ultrafiltration and reabsorption)
How does bulk flow come about ?
Due to hydrostatic (pressure exerted from waste of fluid) and osmotic pressures (Starling’s forces)
What is the name given to the main driving force of inwards?
Plasma oncotic pressure (due to plasma proteins in the capillary )
What pressure is there in interstitial fluid hydrostatic pressure ?
1 mmHg
What pressure is there in capillary hydrostatic pressure ?
Arteriolar - 37mmHg
Venular - 17mmHg
Mean - 20mmHg
What pressure is there in plasma oncotic pressure?
25mmHg
What are the inward and outward driving pressures?
Inward - capillary hydrostatic pressure
interstitial fluid hydrostatic pressure
Outward - interstitial fluid oncotic pressure
plasma oncotic pressure
How can we tell from the net exchange value that ultrafiltration has taken place?
The value is positive and therefore the net is outward (arteriolar end)
How can we tell that reabsorption has taken place by looking at the net exchange value?
The value is negative and therefore the net is inward (venular end)
What happens the bulk flow when vasodilation occurs?
The capillary pressure will increase and ultrafiltration takes place longer than the hydrostatic pressure and this results in a net loss of fluid from plasma and expansion of interstitial fluid in tissue - oedema
What is an oedema ?
Excessive fluid accumulation in interstitium due to alteration in balance of Starling forces
What happens when venous pressure increases ?
More ultrafiltration than reabsorption and therefore oedema is formed
When does increased venous pressure occur?
Congestive heart failure
