Physiology 1 Flashcards
How many nephrons does each kidney have?
1 million
When do nephron number start reducing?
30
Consequences of high potassium?
V Fib (and death)
Consequences of low potassium?
Weakness and malaise
What does the kidney seek to regulate ahead of all else?
Water and Sodium
Two hormones secreted from the kidney?
Renin
Erythropoitin
What vitamin is secreted from the kidney?
What is its role?
Vit D3
Calcium re-absorption from the gut
What prostaglandin is secreted by the kidnye?
PGI2 (prostacyclin)
- This lowers blood pressure it is a vasodilator
What is the filtration unit of the kidney called?
The glomerulus
Where is the initial filtrate from the kidney formed?
Bowman’s capsule
What are the size of the holes in the capillaries in Bowman’s capsule?
2nm slits
What prevents some molecules from moving through the capillaries in a healthy kidney?
Negative charge on the filtration slits which repels negatively charged ions.
This also allows some bigger positively charged proteins to get into the filtrate
What is the most important negatively charged protein which is not filtered by the kidney?
Albumin
What is the GFR per day and minute?
180L/day
125mls/min
= 60nL/min (per nephron)
What is a feature of the proximal tubule?
It is convoluted (to give it extra length)
What is the order of the segments of the kidney?
- Bowman’s capsule
- Proximal Tubule – pars recta and PCT (convoluted tubule)
- Thin descending limb of Henle’s Loop – tDLH
- Thin ascending limb of Henle’s Loop – tALH this is very short in superficial cortical nephrons It is long in JM nephrons
- Thick Ascending limb – TAL
- Distal Tubule –DT
- Collecting Duct – CD
What percentage of kidneys have a loop of Henle which delves into the medulla?
85% only delve to a shallow degree (short loops of henle)
15% have long nephrons which go down to the very tip of the medulla (the papilla)
What happens are the junction between the ascending limb of the loop of Henle and the distal tubule?
Makes contact with its home glomerulus
It occurs in the crevice between the afferent and efferent arterioles
What is the contact point between the between the ascending limb of the loop of Henle and the distal tubule as well as the glomerulus called?
Macula densa
What is a feature of the distal tubule?
It is convoluted (gives it extra length)
Where do the distal tubules end up?
The collecting ducts.
Several distal tubules generally form one collecting duct
How much of the water and NaCl is absorbed by the proximal tubule?
65%
And majority of solutes
Which section of the kidney is responsible for absorption of glucose, amino acids and metabolic intermediates (eg lactic acid)?
The proximal tubule (will absorb 100% of them)
What is the role of the thin loops of Henle?
It concentrates the filtrate (4x the concentration of plasma)
What does the thick ascending loop of Henle do?
It is the dilutor (gets down to pretty low osmolarity)
What is the macular densa a part of?
The juxtaglomerular apparatus
What is the role of the distal tubule?
It is the fine tuner - it reacts to specific needs and carries out alterations in the concentration of urine according to need.
This also occurs through the collecting ducts
What is the role of the collecting duct?
It is an aldosterone -dependant equilibrator
What happens to the concentration of urine in the collecting duct?
If the permeability to water is high it will become concentrated.
If the permeability to water is low it will stay dilute
What dictates if the permeability to water in the collecting duct is high or low?
Aldosterone - They determine how many aquaporin channels are present
How does water move from the collecting duct into the interstitium?
It is not by bulk flow as one might expect but rather by aquaporin channels which allow the movement of single molecules
What are the two types of nephrons called?
Superficial Cortical Glomeruli
Juxtamedullary Glomeruli
What are Superficial Cortical Glomeruli?
They are nephrons located close to the surface of the kidney and have short loops
What are Juxtamedullary Glomeruli?
These are nephrons with long loops and are located close to the cortico-medullary junction though still in the cortex
Which of the nephrons are responsible for forming the high concentrations?
Those that delve deepest into the papilla (JM)
What are the vasa recta?
These are the capillaries which surround the nephron and absorb anything which leaves the nephron and goes into the interstitium
What is the order of blood supply to the nephron?
Afferent arteriole
Capillaries
Reform into a Efferent arteriole
Peritubular capillaries which surround the nephron at every point
What is the only part of the nephron where there is no reabsorption?
Thin ascending limb of Henle
How much urine is produced per day?
1-2 Litres (178-179 litres reabsorbed each day by the kidney)
Aside from filtration how else can substances gain access to the lumen?
Secretion
How does secretion occur?
It is an active process
Where does secretion occur?
In the proximal tubule
In the distal tubule
In the collecting duct
Secretion is an active process, which part of the kidneys are expending the energy?
Movement into the interstitium is passive (capillaries are very permeable).
The active process is carried out by the epithelial cell lining the kidney tubule. It pumps the substance into the lumen
How is excretion calculated?
Filtrate - reabsorbed + secreted = excreted
as long as something isn’t made or broken down in the kidney, this is true for proteins
When is secretion important?
Some xenobiotics where filtration does not remove them quick enough - in order to prevent them from rising from toxic levels they need to be both filtered and secreted
How thick is the nephron?
All of it is one epithelial layer thick
What are the two membranes of the nephron?
Luminal membrane
Basolateral membrane
What is one function of the Macula densa?
It provides tubular globerular feedback
