Renal Lectures 3 & 4 Flashcards

Flashcards on Renal Processes, Glomerular Filtration Rate (GFR), Reabsorption, and Urine Concentration to aid in exam preparation.

What are the three key renal processes?

Filtration, Reabsorption, and Secretion

What is the average GFR for males?

125ml/min

What is the average GFR for females?

105ml/min

What happens if GFR is too high?

Too little reabsorption may occur

What happens if GFR is too low?

Too much reabsorption may occur

What is the volume of blood filtered per day?

150-180 Litres/day

What three things are required to produce a normal GFR?

A large total surface area for filtration, a thin porous membrane, and a positive glomerular filtration pressure

What three pressures determine filtration pressure?

Glomerular Hydrostatic Pressure (GHP), Capsular Hydrostatic Pressure (CsHP), and Blood Colloid Osmotic pressure (BCOP)

How do changes in the afferent and efferent arterioles affect GFR?

Dilation of afferent arteriole OR Constriction of efferent arteriole increases GFR. Constriction of afferent arteriole OR Dilation of efferent arteriole decreases GFR.

What are three pathological mechanisms that can cause Glomerular Filtration Rate to fall?

Reduction in blood flow to the kidney/fall in BP, rise in capsular hydrostatic pressure, increase in protein concentration in the plasma

What are the three mechanisms for the regulation of GFR?

Autoregulation, Hormonal regulation, and Neural regulation

What is myogenic autoregulation?

Effect produced by smooth muscle in arterioles where ↑BP causes constriction and ↓BP causes dilation of afferent arterioles.

How does tubuloglomerular feedback regulate GFR?

Macula densa cells detect ↑Na+, CL- and water in filtrate, release vasoconstrictor, reducing blood flow and GFR.

Which two hormones regulate GFR?

Angiotensin II and Atrial natriuretic peptide (ANP)

What is the effect of sympathetic nerve stimulation on GFR?

Sympathetic vasoconstriction decreases blood flow, GFR and urine output

What substance is used clinically to estimate GFR?

Creatinine

What factors are included in the formula to calculate estimated GFR (eGFR)?

Patient's age, sex, and weight

What does GFR give an idea of?

The number of functioning nephrons

Why does a gradual drop in GFR occur in chronic kidney disease?

Due to clogged up filter or destruction of nephrons, leading to reduced surface area of filter

In the tubules, from where to where are substances re-absorbed?

From filtrate into blood capillaries

What substances are reabsorbed in the tubules?

Water, Glucose, Amino acids, Ions (eg Na+, Ca+, HCO3-)

In the tubules, from where to where are substances secreted?

From blood capillaries into filtrate

What substances are secreted in the tubules?

Ions (H+ K+), Ammonia, Urea, Toxins and drugs

How much filtered NaCl is reabsorbed by the Proximal convoluted tubule (PCT)?

65%

What two structural features of the epithelial cells of the PCT promote bulk reabsorption?

Microvilli to increase surface area and Lots of mitochondria to provide ATP

How much filtered salt and water is reabsorbed by the Loop of Henle?

reabsorbs filtered salt (20-35%) and water (15%)

What three hormones control reabsorption in the Distal convoluted tubule & collecting duct?

Aldosterone, Parathyroid hormone, Anti-diuretic hormone

What is Transport maximum (Tmax)?

The rate of reabsorption when all carriers for a substance are saturated

What is Renal threshold?

Concentrations in filtrate above the renal threshold will exceed the reabsorptive capacity of the nephron

What happens when transporters in the PCT reabsorb filtered glucose by secondary active transport when the plasma [glucose] exceeds ~10mmol/L

Glucose will spill into the urine (glucosuria)

Why is Na+ reabsorption so important?

Sodium (& chloride) ions are the main solutes in extracellular fluid (ECF) which are the main determinants of ECF osmolarity and reabsorption of other solutes depends on sodium reabsorption

How does Na+ move from lumen across the tubule epithelium?

Diffusion, Co-transport, and Counter transport

Which parts of the nephron reabsorb Na+ and water?

PCT, LoH, DCT and collecting duct

How is water re-absorption regulated by anti-diuretic hormone (ADH)?

Body can regulate water loss through the kidney

What does Anti-diuretic hormone (ADH) do?

Stimulates thirst; Acts on the collecting ducts to increase water reabsorption

What happens in the descending limb of the Loop of Henle?

It is highly permeable to WATER but less so to salt, increasing fluid concentration towards the tip of the loop.

What happens in the ascending limb of the Loop of Henle?

Actively transports salt out of the tubule into the interstitial fluid but water cannot follow, This lowers the concentration of the tubular fluid