Topic 40 - Basic physiological functions of the kidney: filtration, reabsorption, secretion, excretion Flashcards
1
Q
Words to include in filtration
A
- Permability of the barriers
- Capillary Filtration Coefficient (CFOC)
- Ultrafiltration
- Renal glomerulus
- Lamina densa of the basal membrane
- Negatively charged
- Mesangial cells containing myogen elements
- Size of filtrating surface
- Effective filtration pressure (EFP)
- Ultrafiltration
- Pressure gradient
- Ratio:
- Hydrostatic blood pressure
- Tissue pressure
- Colloid osmotic pressure
- Components of EFP:
- Hydrostatic pressure of the glomerulus (GP)
- Bowman-sheath’s pressure (CP)
- Colloid-osmotic pressure of the plasma (GCP)
- EPF = GP - (CP + GCP)
- Oncotic pressure
- Vas eferent
- Vas afferent
- Protein concentration
Anatomic basis of glomerular filtration
- Filtration barrier layers
- Fenestrated endothelium
- Glomerular basement membrane (GBM)
- Podocyte foot processes (outermost)
- Size-selective filter
- Plasma macromolecules
- Negatively charge molecules (filtered in smaller amounts)
- Negative < neutral < positive
- Type IV collagen
- Nidogen
- Laminin
- Proteoglycan (glycosaminoglycans)
- Negative charge
- Anion filtration barrier
2
Q
Words to include in reabsorption
A
- 90% of filtrated amount is reabsorbed
- Pathways of the reabsorption of the ultrafiltrate
- Paracellular
- Transcellular
- Reabsorption maximum (Tm)
- Tm (Transfer Maximum)
- Upper limit of reabsorption
- Tm (Transfer Maximum)
3
Q
Words to include in secretion
A
- Directly from the blood vessel
- Plasma
- Glomerulus
- Efferent arteriole
- Tubular lumen
- Peritubular capillaries
- Can occur:
- Transcellular
- Paracellular
- Nephrons
- Secreting maximum
- Active cellular work
4
Q
Words to include in excretion
A
- Result of:
- Filtration
- Reabsorption
- Secretion
- End of tubular system
- Secondary filtrate of urine
- Rate of excretion = urine of seleced material excreted
- Filtration + secretion = excretion
Autoregulation of renal circulation
- Independent of blood pressure (midpressure)
- Autoregulation of renal perfusion
5
Q
Filtration
A
- The rate of filtration is determined by:
- Effective Filtration Pressure (EFP)
- Permability of the barriers
- Proteins are not filtrated
-
Capillary filtration coefficient
- The degree of ultrafiltration taking place in the renal glomerulus is a hundred times higher than in any other capillary areas
- Most important factor: lamina densa of the basal membrane
- Negatively charged
- The size of the filtrating surface is regulated by the mesangial cells containing myogen elements
- Total filtration: 180-200 liter/100 kg bwt/day
-
Effective Filtration Pressure (EFP)
- The extent of ultrafiltration depends on the pressure gradient
- Depends on the ratio of:
- Hydrostatic blood pressure
- Tissue pressure
- Colloid osmotic pressure
- Components of EFP:
- Hydrostatic pressure of the glomerulus (GP)
- Bowman-Sheath’s pressure (CP)
- Colloid-osmotic pressure of the plasma (GCP)
- EFP = GP - (CP + GCP)
- The oncotic pressure increases in the direction of the vas efferent, as the protein content increases due to ultrafiltration
Anatomic basis of glomerular filtration
- The filtration barrier consists of three layers:
- Fenestrated epithelium
- Glomerular basement membrane (GBM)
- Outermost epithelial podocyte foot processes
- Behaves as a size-selective filter that restricts the passage of plasma macromolecules based on their size, shape, and charge
- Negatively charged molecules are filtered in smaller amounts than neutral molecules of comparable size, and the traversal of positively charged molecules is actually facilitated.
- Negative < neutral < positive
-
Molecular scaffold:
- Independent structural networks of type IV collagen and laminin
- Linked through nidogen
- The role of negatively charged proteoglycans (glycosaminoglycans) is to serve as an anionic filtration barrier
- The GBM therefore can restrict the traversal of large plasma proteins
6
Q
Give the valuse for the vas afferent and vas efferent occuring in effective filtration pressure
A
- Vas afferent:
- GP: 60 mmHg
- CP: 20 mmHg
- GCP: 28 mmHg
- EFP: 12 mmHg
- Vas efferent:
- GP: 60 mmHg
- CP: 20 mmHg
- GCP: 36 mmHg
- EFP: 4 mmHg
7
Q
Reabsorption
A
- The extremely large filtration rate could mean a fatal loss of fluid, if it appeared in full amount in the urine
- Only a small fraction of it (0,5-1%) becomes urine, made possible by reabsorption
- More than 90% of the filtrated amount is reabsorbed
- Two main pathways for the reabsorption of the ultrafiltrate:
- Paracellular
- Transcellular
-
Reabsorption maximum (Tm):
- Tm (Transfer maximum)is theupper limit of reabsorption
8
Q
Secretion
A
- Some substances are either secreted:
- after filtration and reabsorption
- Directly from the blood vessel
- Secretion: From the plasma leaving the glomerulus through the efferent arteriole further substances can get into the tubular lumen at the site of the peritubular capillaries
- Can occur:
- Transcellular
- Paracellular
- Above certain plasma concentration, the secretion becomes constant
- All of the nephrons participating in secretion reaches the secreting maximum
- Proves that the secretion is a active cellular work
9
Q
Excretion
A
- As a result of the filtration, reabsorption and secretion by the end of the tubular system the secondary filtrate of urine is formed
- Rate of excretion = the urine or selected material excreted
- Average excretion rate of urine is 2-3 ml/min/100 kg bodyweight
- Filtration + secretion = excretion
- Phases of excretion:
- Linear phase
- SDL phase (Self depression limit)
- Saturation phase
10
Q
Figure to draw in the essay
A