Urine Formation Flashcards
How many nephrons are there in a human kidney?
1 million
What is unique about a glomerulus as a capillary bed in terms of the vessels present?
The is an afferent renal arteriole and an efferent renal arteriole instead of an arteriole and a venule.
List the major sections of a nephron in order of fluid passing them.
Glomerulus, Bowman’s capsule, proximal tube, descending loop of Henle, ascending loop of Henle, distal tubule, ureter.
What are the three processes involved in urine formation?
Glomerular filtration, tubular reabsorption, tubular secretion.
What is glomerular filtration?
The passive, non-selective movement of fluid and solutes from the glomerular capillaries into the Bowman’s capsule
What substances move into the Bowman’s capsule during glomerular filtration?
Most substances, excluding proteins.
How does filtrate in the Bowman’s capsule differ from that in the plasma?
It lacks proteins (0.02% content)
How much of plasma passing through the glomerulus is filtered?
20%
What is tubular reabsorption?
Movement of materials (beneficial substances) from the renal tubules into the peritubular capillaries.
What is tubular secretion?
Movement of solutes (exogenous substances, H+, ammonium ions) from peritubular capillaries into the tubules.
Why can glomerular capillaries have relatively high pressures (55 mmHg vs 18)?
Due to the presence of two arterioles instead of a venule.
What are the 3 glomerular filtration layers?
Endothelium- single celled
Non-cellular basement membrane
Epithelial lining of Bowman’s capsule- single celled.
What special structures are present in capillary endothelium in the glomerulus?
Fenestrae/pores. These are not present in other capillaries
What are the special structures on
Podocytes (foot-like processes)
Filtration slits in between podocytes.
What force favours glomerular filtration?
High glomerular hydrostatic pressure (BP in capillaries)
What forces oppose glomerular filtration?
High blood colloid/oncotic osmotic pressure
High capsular hydrostatic pressure (pressure of liquid in Bowman’s capsule).
What gives rise to high blood colloid osmotic pressure (30mmHg)?
Presence of plasma proteins that can not cross membranes.
How is the GFP calculated?
GFP = Pgc - (Pbc + Pi gc)
What would a low GFR indicate?
Reabsorption is increased and wastes are not excreted.
What would a high GFR indicated?
Inadequate reabsorption and substances that shouldn’t be lost are lost in urine.
How much of the plasma passing through the Bowman’s capsule in excreted as urine?
1%
Is the process of reabsorption of sodium active of passive?
Active.
How much of reabsorption of filtrate is controlled hormonally?
10%
What is the transport maximum, why does it occur and what are the units for it?
The limit to the rate at which the solute can be transported into the peritubular capillaries due to saturation of carrier molecules.
Units: mg/min
What is the relationship between filtration of glucose and plasma concentration?
Filtration is proportional to the concentration.
When is the filtration of glucose no longer proportional to the plasma concentration of glucose?
Once the transport maximum (Tm) is reached.
What is the renal threshold for glucose (point at which glucose appears in urine)?
300mg/100mL
Why is the medullary interstitial hyperosmotic gradient important in human kidneys?
It allows to concentrate (hyperosmotic) urine.
What are the two types of nephrons in the human kidney?
Cortical and Juxtamedullary.
How do the Cortical and Juxtamedullary nephrons differ in terms of glomerulus position?
Cortical: in the cortex
Juxtamedullary: border of cortex and medulla
How do the Cortical and Juxtamedullary nephrons differ in terms of the length of the loop of Henle?
The loop of Henle is longer in juxtamedullary nephrons and protrudes into the medulla when compared to cortical nephrons.
What percentage of human nephrons are juxtamedullary?
25%
What is the function of the vasa recta in juxtamedullary nephrons?
Preserve the hyperosmotic gradient to act as countercurrent exchangers.
Is the descending loop of Henle permeable to sodium and water?
Permeable to water
Impermeable to sodium.
What occurs in the ascending loop of Henle?
Sodium is actively transported out.
What occurs in the cortical and medullary collecting ducts?
Water leaves the ducts, following a concentration gradient.
