Kidney Function 1 Flashcards
Give the 3 main functions of the kidney and some information on each
- Excretion of metabolites or ingested substances
- urea from protein catabolism
- uric acid from nucleic acid breakdown
- creatinine from muscle creatine
- hormone metabolites
- foreign chemicals
- end products of haemoglobin breakdown - Control of body fluid composition
- volume regulation (linked to sodium concentration)
- osmoregulation
- pH regulation (can secrete/excrete H+) - Endocrine
- Hormones that act on the kidney e.g. ADH, aldosterone
- Hormones produced by the kidney e.g. Vitamin D3, renin
What is the role of the ureter?
Brings urine from the kidney to the bladder to be stored.
What does the glomerulus sit in?
A fluid filled space
What are the 3 layers that the fluid has to pass through in the bowmans capsule to get to the rest of the nephron?
- Fenestrated capillary endothelium
- Basement membrane
- Tubular epithelium (podocytes)
Why is the capillary endothelium fenestrated?
What is the basement membrane a site of?
What do podocytes have?
To increase permeability
Negative charges
Filtration slits
What are 3 important parts of a podocyte?
Podocyte cell body
Primary process of podocyte
Branching pedicels
What is the name of two important filtration slit proteins?
Nephrin and Podocin
What are the 2 sections of the renal corpuscle?
- Glomerulus
2. Bowmans space in Bowmans capsule
What are the 8 sections of the renal tubule?
- Proximal convoluted tubule
- Proximal straight tubule
- Descending thin limb of Henle’s loop
- Ascending thin limb of Henle’s loop
- Thick ascending limb of Henle’s loop
- Distal convoluted tubule
- Cortical collecting duct
- Medullary collecting duct
When do the nephrons merge together?
In the collecting duct
What percentage of the nephrons are cortical and which are juxtamedullary?
Give some info on each
Cortical - 85%
Juxtamedullary - 15%
Cortical - outer 2/3 of cortex
Short loop of Henle
Juxtamedullary - inner 1/3 of cortex
Long loop of Henle
Produces concentrated urine
What parts of the nephron are juxtaglomerular apparatus?
Extraglomerular mesangial cells (responsible for generating extracellular matrix) Juxtaglomerular cells (secretes renin which is an enzyme to regulate blood pressure) Mucula densa (cells lining the distal tubule at the point where the thick ascending limb meets the distal convoluted tubule)
What are the two sets of capillary beds we have in series in the kidney?
The glomerulus and the peritubular (arise from the efferent arteriole).
What are the peritubular capillaries in the loop of Henle called?
Vasa recta
What are the three basic renal processes?
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Explain glomerular filtration
The movement of fluid and solutes from the glomerular capillaries to the Bowmanss space.
20% of the plasma that enters the glomerulus is filtered
Explain tubular secretion
The secretion of solutes from the peritubular capillaries into the tubules
Explain tubular reabsorption
The movement of materials from the filtrate into the tubules into the peritubular capillaries
Finish this equation -
volume excreted in urine =
volume filtered + volume secreted - volume reabsorbed
Give 3 options that can happen to substances when filtered
- Filtered and secreted but not reabsorbed
- Filtered and some is reabsorbed e.g. water and most electrolytes
- Filtered and completely reabsorbed e.g. glucose
What gets through the glomerular filtration?
Proteins are not freely filtered as filtration depends on size, shape and charge.
Most plasma constituents are freely filtered except proteins.
What happens to the value between 0 and 1 (total block to free passage) as molecular radius increases?
What does 1 mean?
The value decreases from 1 to 0. Glucose and insulin have a value of 1 and albumin of 0.
At 1, the concentration of the substance is the same as the plasma.
Why is it easier for positively charged molecules to be filtered?
Does higher molecular mass make it easier or harder to filter?
Fixed sites of negative charge
Harder
Give information on the composition of the ultrafiltrate
A similar composition to plasma with important differences in the concentration of certain molecules e.g. proteins and molecules that can bind to proteins.
What percentage of calcium is bound to protein and cannot be filtered?
What drugs does albumin and A1 - acid glycoprotein bind?
40%
acidic drugs, basic drugs
What is used so that drugs aren’t filtered out the system?
They are bound to proteins
What can infection, damage to the glomerulus and high blood pressure result in?
- protein in urine
- haemoglobin in urine
- red cells in urine
What is glomerular filtration rate?
What does it depend on?
What is it regulated by?
Volume of fluid filtered from the glomeruli per minute.
Depends on Starling forces, hydraulic permeability, surface area.
Regulated by neural and hormonal input
What are 2 Starling forces involved in filtration?
- Hydrostatic pressures
2. Colloid osmotic/oncotic pressure
What do we need to know about the protein concentration in Bowmans space filtrate?
It is so low that the oncotic pressure is considered to be zero.
What two things will cause a decrease in glomerular filtration rate?
2 things that will increase?
Decrease = constrict afferent or dilate efferent
Increase = constrict efferent or dilate afferent
What system innovates the Bowmans capsule?
The sympathetic nervous system
What is the usual amount of filtrate formed a day?
How does this compare to all the other capillaries in the body?
What is the urine output at why?
180l/day
4 litres/day across all other capillaries
1.5l/day because reabsorption occurs
Where does reabsorption mainly occur?
In the proximal convoluted tubule and proximal straight tubule
What do the luminal membrane of tubule cells face?
How about the basolateral membrane?
Faces filtrate
Faces peritubular capillary
What are 3 ways that proximal reabsorption of organic nutrients occurs?
- Na+ coupled co-transporter
- A tubular maximum system
- Specific transporters
Give some features of proximal tubule cells
- walls are a single layer of columnar cells
- microvilli (brush-border to increase surface area)
- packed with mitochondria
Give some information on glucose reabsorption
Filtered glucose is normally reabsorbed. How? 1. SGLT-Na+ dependant glucose co-transporter 2. GLUT facilitated transporter 3. NA+ - K+ - ATPase pump
Glucose is moved from the lumen on the cell and then into the interstitial fluid
What is the renal threshold?
If the glucose concentration increases, no more glucose will be able to leave the filtrate and enter the blood.
Give some information on amino acids in the kidney
- reabsorbed at proximal tubule
- at least 8 amino acid transporters
- overlapping amino acid specificity
- 6 NA+ dependant
What are Na+ coupled transporters for?
What is reabsorbed passively?
Glucose, amino acids, phosphate, sulphate.
Urea, potassium, chloride, calcium
What occurs during secretion in the proximal tubule?
- Two stage process
- involves luminal and basolateral membrane transporters
- transporters broadly selective
- only means of excretion for some protein bound molecules
Organic acids (anions) such as endogenous molecules (bile salts, fatty acids), drugs and diagnostic agents
Explain anion secretion in the proximal tubule
Organic anion enters cell in exchange for dicarboxylate organic anion transporters.
DC- accumulate in cells by metabolusm and Na+ coupled cotransporters.
OA- enters tubule lumen via ATP-dependant transporters
Explain organic cation secretion in the proximal convolted tubule
- Enter cell via facilitated organic cation transporters
2. Enter tubule lumen via multidrug and toxin extrusion proteins antiporter in exchange for H+
