Ultrafiltration and Glomerular filtration Rate Flashcards
- what percentage of blood is plasma?
55%
- How much blood do kidneys receive every minute and therefore how much plasma is filtered every minute?
- receive ~1.25L blood/min
- therefore 625ml/min of plasma is filtered
- What are the three basic renal processes?
- Glomerular filtration
- Tubular reabsorption
- Tubular Secretion
- Define glomerular filtration.
the transfer of fluid and solutes from the glomerular capillaries along a pressure gradient into Bowman’s capsule
define tubular reabsorption
selective movement of filtered substances from the tubular lumen into the peritubular capillaries
define tubular secretion
selective movement of non filtered substances from the peritubular capillaries into the tubular lumen
- What percentage and therefore amount in ml of plasma is filtered in each filtration cycle?
20% AKA 125ml/min
- What is the glomerular filtration rate?
the rate at which plasma is filtered by both kidneys
- How can the glomerular filtration rate be expressed numerically?
120 + or - 25ml/min/1.73m^2
- What are the 3 filtration layers of the glomerular filtration barrier?
- the fenestrated endothelium
- Glomerular basement membrane
- Podocytes
- What does kD mean in unit of measure?
a kilodalton
- What is filtered into the tubules where it is is then excreted?
plasma and anything < 70kD
- What stays in the blood and is not filtered? Give examples as well.
Anything > 70kD stays in the blood
- Examples: Immunoglobulins, Ferritin, Cells, Plasma Proteins
- Why can’t albumin be filtered?
- Because it is negatively charged
- What 4 forces, in order, are responsible for driving ultrafiltration?
- Glomerular blood hydrostatic pressure
- Capsular hydrostatic pressure
- Blood colloid osmotic pressure
- Net filtration Pressure
- What is the value and units for Glomerular blood hydrostatic pressure?
55 mmHg
- What is the value and units for capsular hydrostatic pressure?
15 mmHg
- What is the value and units for blood osmotic pressure
30 mmHg
- What is the normal value and units for Net filtration pressure?
10 mmHg
- How is net filtration pressure calculated?
NFP = GBHP - CHP - BCOP
- Does GFR change when blood pressure changes?
No
- What is the definition of autoregulation?
the ability of a tissue to automatically adjust its blood flow to match its metabolic demands without nerves or hormones
- What 2 ways is negative feedback achieved in autoregulation of renal blood flow?
- Tubuloglomerular feedback
2.Myogenic control
- What is Tubuloglomerular feedback
When tubular flow rate is detected by the macula densa & vasoactive mediators are released from the JGA to act on the arterioles.
what do the chemicals do in tubular feedback
The chemicals dilate or constrict the afferent arteriole as needed to keep the GFR within normal range
- Give examples of vasoactive mediators that 1. Vasocontrict 2. Vasodilate that are released from the JGA in Tubuloglomerular feedback
Vasoconstrict:
- Angiotension II & endothelin
Vasodilate:
- Atrial natriuretic peptide, prostaglandins nitric oxide
- What is myogenic control?
The afferent or efferent arteriolar
diameter automatically increases
or reduces to oppose pressure changes
- What mean arterial pressure range is the GFR autoregulated at
80-180mmHg
- How do the efferent and afferent arterioles constrict?
sympathetic nerves which constrict the vessels via α1adrenoceptors
- What does constriction of the efferent and afferent arterioles do?
reduces plasma flow to the glomerular filter and slows filtration. This means less is excreted. This conserves plasma in the circulation to help maintain blood pressure.
what 2 ways can tubuloglomerular feedback and myogenic control be reduced
Pathological conditions
- Glomerulopathies
- E.g. immune complexes, toxins,
- Inherited disease
Non-pathological conditions
Pregnancy, kidney removal, ageing
GFR may be reduced
