renal system Flashcards
what are the 5 functions of the renal system
what is a nephron
Nephrons are the structural and functional units of the kidney. Each kidney has over 1 million of these units.
Each nephron consists of a renal corpuscle, which
contains the glomerulus (which is a tuft of capillaries) and a renal tubule.
The tubule forms a cup shape around the glomerulus called the glomerular capsule (Bowman’s capsule).
what is the Juxtaglomerular Apparatus
The juxtaglomerular cells are mechanoreceptors (they sense blood pressure) in the afferent arteriole.
The macula densa cells are chemoreceptors that respond to changes in the NaCl content of the filtrate
excretion
The excretion of a substance is equal to the amount filtered plus the amount secreted minus the amount reabsorbed
Thus: Amount excreted =
Amount filtered+Amount secreted - Amount reabsorbed
what is Glomerular Filtration (GFR)
The GFR is the amount of blood filtered by the glomeruli each minute.
what factors influence the GFR
Capillary permeability [+]
Surface area (the size of the capillary bed)
Hydrostatic pressure that drives fluid out of the
capillaries Osmotic forces within the capillaries,
which oppose the exit of fluid
what is the Net filtration pressure
Net filtration pressure = ∆P - ∆∏
Where ∆P is the transcapillary hydrostatic pressure gradient, and ∆π is the colloid osmotic pressure gradient.
what is starling force?
hydrostatic pressure difference across capillary wall favoring filtration
vs
protein conc. difference across the wall that creates an osmotic force
what is GFR controlled by
vascular changes by effecting the afferent or efferent artiole
why is the kidneys glomeruli more efficient filter then capillary beds?
Filtration membrane is a large surface area and very permeable to water and solutes.
Glomerular pressure is higher (~55 mm Hg), so they produce 180 L/day vs. 3-4 L/day formed by other capillary beds.
That’s 125 mL/min of total plasma volume (~3 L total PV)
Thus, kidney’s filter the entire PV ~ 60 times in a day
what happens to plasma proteins during filtrations
During filtration plasma proteins remain in
plasma to maintain osmotic pressure.
Blood cells or protein in the urine (proteinuria)
indicates a problem with the filtration membrane.
what is tubular reabsorption
Tubular reabsorption begins as soon as filtrate enters thetubule cells.
Paracellular transport occurs between cells (even though they have tight junctions) and is seen mainly with ions.
Transport can be active (requires ATP) or passive (no ATP)
what is tubular secretion
Substances such as hydrogen ion, potassium, and organic anions move from the peritubular capillaries into the tubular lumen.
Tubular secretion is an important mechanism for:
1. disposing of drugs and drug metabolites.
2. eliminating undesired substances or end products that have reabsorbed by
passive processes (urea and uric acid).
3. removing excess K+.
4. controlling blood pH.
what is division of labour in the tubules
The majority of the reabsorption is accomplished by the proximal tubule and the loop of Henle.
Extensive reabsorption by the proximal tubule and Henle’s loop ensures that the masses of solutes and the volume of water entering the tubular segments beyond Henle’s loop are relatively small.
These distal segments then do the fine-tuning for most substances,
determining the final amounts excreted in the urine by adjusting their rates of reabsorption and, in a few cases, secretion
what is renal clearance
Renal Clearance (mL/min) is the amount of a substance filtered per minute, divided by its plasma concentration. The clearance for any substance can be calculated.
RC=(U*V)/P
U=concentration of the substance in the urine (mg/mL)
V=flow rate of urine formation (mL/min)
P=concentration of substance in the plasma (mg/mL)
