Mairead - Capillary Exchange Flashcards
Write about the structure of capillaries
One tunica of simple squamous epithelia (endothelium)
Classify capillaries
Continuous
Fenestrated
Sinusoids
What is endotehlium
Simple squamous epithelia
Write a note on capillary exchange
(4)
In peripheral tissue water and solutes and pushed out of the plasma
This movement mixes the EC fluid and delivers nutrients
Most fluid is returned to the venules, the rest is returned to the circulation via the lymphatic system
With this lymphatic shunt there is accelerated delivery of nutrients and flushing out of bacteria, toxins and debris
What are the three stages to capillary exchange?
Diffusion
Filtration
Reabsorption
What is diffusion
The net movement of ions or molecules, from a high concentration to a low concentration
When is diffusion rapid?
Distances are small
Pressure gradient is large
Molecules are small
What are the five principal diffusion routes?
Between endothelial cells
Through protein channels
Across the lipid
Through fenestrations
Through sinusoid gaps
What molecules diffuse between endothelial cells?
(3)
Water glucose
Amino acids
Glucose
What diffuses through protein channels?
Ions
What diffuses through fenestrations?
Water
Large solutes
What diffuses through sinusoid gaps?
Water
Large solutes
Where can diffusion of water and soluble compounds occur?
Pores allow the movement of water and soluble compounds ONLY in the fenestrated capillaries of the kidney, hypothalamus and glands
What does diffusion through the cell membrane allow?
Allow passage of lipids, steroids, gases
What type of diffusion do the sinusoids allow?
The movement of plasma proteins and hormones into the bloodstream at the liver
What is filtration?
The movement of water out of and into the capillary
What is the driving force of filtration?
Hydrostatic pressure
What is CHP
Capillary hydrostatic pressure
Blood pressure in a capillary
How does hydrostatic pressure drive filtration?
This pressure drives water across the capillary membrane and solutes travel within the water
Only small molecules will be able to pass the rest are filtered (stay in the blood -> formed elements and plasma proteins)
What is capillary hydrostatic pressure?
The difference in blood pressure between the 2 ends of the capillary bed
35 - 18 mmHg
In relation to pressure, where does most filtration occur?
Where hydrostatic pressure is highest -> the arterial end
How does reabsorption occur?
Due to osmosis
What is osmosis
The movement of water across a selectively permeable membrane
What is osmotic pressure?
The force on the water to move
How are plasma proteins present in blood?
As colloids
What does blood colloid osmotic pressure do?
(2)
It pulls water (i.e. reabsorbs it) from the interstitial space into the blood
This movement draws fluid from the capillary bed at the venous end
Write a note on the interplay between filtration and reabsorption
Hydrostatic pressure forces water out of the blood i.e. out of solution
Osmotic pressure pulls water back into the vessels i.e. into solution
Rates of filtration and absorption vary along the capillary
What is IHP
Interstitial hydrostatic pressure
Give a value for capillary hydrostatic pressue
35mmHg - 18mmHg
Give a value for Interstitial hydrostatic pressure
0
Give a value for osmotic forces
BCOP
Give a value for interstitial colloid osmotic pressure
0
What is the equation for net filtration pressure
Net hydrostatic pressure - net osmotic pressure
Comment on filtration vs reabsorption
Filtration occurs for most of the length as the net filtration pressure > net reabsorption pressure
How much fluid is filtered each day
24.6L
How much of the 24.6L fluid filtered by blood is reabsorbed by veins?
85%
How much fluid flows through lymphatic vessels each day?
3.4L
Write a note on lymphatic drainage
(3)
Important to prevent fluid accumulation in the interstitial space
Returns fluid and proteins to the circulation
Moves fluid into the lymphatic vessels and hence through the lymph nodes
What is oedema
(2)
Disturbance in net filtration pressure
The abnormal accumulation of interstitial fluid, is not usually detected until the volume has increased by 30%
What factors will affect Oedema
Any factors that affects HP or COP will shift the balance between filtration and reabsorption
Give three examples of things that disturb NFP
Haemorrhage (decrease CHP)
No Protein synthesis (COP)
Dehydration
List some of the causes of oedema
(5)
Damage causes proteins to cross the capillary wall -> increases ICOP and results in swelling in bruised areas
Starvation and lock of protein synthesis -> decreases BCOP
Circulatory obstruction -> CHP increases -> clot, high pressure or coronary problems
Blockage of the lymphatics
Fluid retention -> CHP increases
Write a note on renal filtration
In kidney blood is filtered to form filtrate
Forces within renal corpuscle force fluid out from the glomerular blood capillaries across the filtration membrane and into Bowman’s capsule
What cannot happen without renal filtration?
Urine cannot be formed and water soluble waste will not be removed
What is GFT
Glomerular Filtration Rate
What is glomerular filtration rate
The amount of filtrate that flows out of all the renal corpuscles every minute (and into the nephron)
What percentage of plasma entering the nephrons becomes glomerular filtrate
!6-20%
How are renal corpuscles particularly suited to filtration
(4)
The surface area for filtration (6m2)
The histology of the endothelial-capsular membrane
The efferent arteriole is smaller in diameter than the afferent arteriole, giving a blood hydrostatic pressure of 50mmHg
The endothelial-capsular membrane is very thin
Describe the histology of the endothelial-capsular membrane
(3)
Endothelial pores
Basement membrane
Filtration slits
What does filtration of blood depend on?
(4)
Glomerular hydrostatic blood pressure (50 mmHg)
Capsular hydrostatic pressure (15mmHg)
Colloid Osmotic pressure (25mmHg)
Capsular colloid osmotic pressure (0mmHg -> no protein present)
What is effective filtration pressure also called?
Peff
What is the equation for peff?
Net hydrostatic pressure - net colloid osmotic pressure
usually 10 mmHg
Name two abnormalities in filtration
(2)
A decrease in arterial blood pressure -> reduces the glomerular hydrostatic pressure below 40 mmHg -> no filtration will occur
Glomular capillaries become too permeable, as in glomerulonephritis, proteins pass into the filtrate -> increases the Peff
What is the term for a renal output of less than 50ml/day
Anuria
What is anuria
A renal output of less than 50ml/day
What happens if there is no glomerular filtration?
Waste products are not eliminated
pH control is reduced and blood volume control is lost
How is GFR controlled
(3)
Controlled by local autoregulation
Controlled by hormonal regulation
Controlled by neural ANS regulation
Write a note on local autoregulation of GFR
Regulation of GFR despite changes in local
blood pressure and blood flow.
Achieved by altering the diameter of the
efferent and afferent arteriole
If blood pressure drops, GFR is sustained by what?
dilation of afferent arteriole
dilation of capillaries and
constriction of the efferent arteriole
If blood pressure rises, GFR is sustained by what?
Constriction of the afferent arteriole
What hormones are responsible for controlling filtration
Renin and atrial natiuretic peptide (ANP)
Where is renin released from?
The JGA
When is renin released from the JGA?
The renal blood flow declines
The osmotic pressure of the filtrate in the DCT declines
Why would renal blood flow decline
(3)
Reduced blood volume
Reduced blood pressure
Vascular blockage
What does angiotensin do?
Has widespread effects to restore blood pressure
What does angiotensin do in the capillary beds
Causes general vasoconstriction of all arterioles and precapillary sphincters
What does angiotensin do in the nephron
It causes constriction of efferent arteriole (including GFR)
What does angiotensin do in the adrenal gland
It causes release of aldosterone (including Na+ reabsorption in DCT)
What does angiotensin do in the CNS
It causes the sensation of thirst increased vasomotor tone and the release of ADH (including body water)
ANP and BNP
joweeb
ANS regulation of GFR
vnwob
