RUS L35 - 39

Chronic renal failure can cause anaemia.

Which of these is an unhealthy glomerular filtration rate (GFR)?

Choose the incorrect statement about renal blood flow.

There are forces which drive glomerular filtration and those that oppose it. The effective filtration pressure is always about [blank_start]+10[blank_end]mmHg. You can calculate it by adding together the forces that drive filtration (glomerular [blank_start]hydrostatic[blank_end] pressure and capsular [blank_start]osmotic[blank_end] pressure) and minusing the forces that oppose filtration (glomerular [blank_start]osmotic[blank_end] pressure and capsular [blank_start]hydrostatic[blank_end] pressure). Remember that [blank_start]capsular[blank_end] osmotic pressure is negligible i.e. zero.

Which equation describes renal clearance?

Choose the incorrect statement about glomerular filtration rate(GFR).

The filtration fraction is the amount of the plasma (non-cellular component of blood—red blood cells are too big) which is filtered through the glomerulus. It can be calculated by [blank_start]multiplying[blank_end] the glomerular filtration rate by the renal [blank_start]plasma[blank_end] flow rate. (The renal plasma flow rate can be taken as [blank_start]half[blank_end] of the renal blood flow, i.e. if renal blood flow is 1.25L/min, renal plasma flow is [blank_start]625ml[blank_end]/min.) The equation is then [blank_start]FF = GFR x RPF[blank_end].

The filtered load is the amount of substance filtered per minute. Choose the best equation for filtered load.

Choose all the molecules that are ONLY ever reabsorbed in the nephron's tubules. (In a healthy person.)

Which of these molecules can be both secreted and reabsorbed in the nephron's tubules?

PAH (p-aminohippurate) is only ever secreted in the nephron, and this secretion is always active.

Choose the incorrect statement about the proximal convoluted tubule.

There are 4 sites of Na+ reabsorption: 66% of Na+ is reabsorbed in the [blank_start]PCT(proximal convoluted tubule)[blank_end]. 25% of Na+ is reabsorbed in the [blank_start]TAL(Thick ascending limb)[blank_end]. 5% of Na+ is reabsorbed in the [blank_start]DCT(distal convoluted tubule)[blank_end]. 3% of Na+ is reabsorbed in the [blank_start]CD(collecting duct)[blank_end].

Choose the correct statement about transporters.

The normal filtered load of glucose should be 0.

In leaky epithelium such as the [blank_start]PCT[blank_end], the water permeability is high. Water can be reabsorbed via the paracellular or transcellular pathway. [blank_start]With[blank_end] ADH, aquaporins AQP1 and AQP2 move into the [blank_start]apical[blank_end] membrane to move water into the cell. AQP3 and AQP4 move water out of the cell. In tight epithelium such as the [blank_start]collecting duct[blank_end], water permeability is low. The only aquaporin used is [blank_start]AQP2[blank_end].

The loop of Henle in the [blank_start]juxtamedullary[blank_end] nephrons is crucial for production of concentrated urine, i.e. it is important for [blank_start]absorbing[blank_end] the water and NaCl. The thin descending limb removes [blank_start]water[blank_end] (i.e. it is leaky) while the thick ascending limb removes [blank_start]NaCl[blank_end](i.e. it is tight).

Which of these are appropriate average values for total body water?

Typical NaCl concentration in the body (ICF/ECF) is 145mM. This means typical fluid osmolarity is around:

The kidneys are crucial for maintaining body water balance. If a person's water intake was 2400mL in a day, what could be a reasonable value for water excretion contribution by the kidneys?

Reabsorption of water in the PCT is driven by Na+ reabsorption and is isotonic.

Primary urine in the PCT is [blank_start]isotonic[blank_end]. Due to water reabsorption in the tDLH, it becomes [blank_start]hypertonic[blank_end]. It turns [blank_start]hypotonic[blank_end] due to Na+ reabsorption in the TAL, and can become hypertonic again in the [blank_start]collecting duct[blank_end] during [blank_start]anti-diuresis[blank_end].

Choose the incorrect statement.

With ADH, the collecting duct is relatively permeable to water and 8% of filtered water can be excreted.

Choose the incorrect statement about isosmotic losses.

Choose the incorrect statement about isosmotic gains.

There are two systems for regulating fluid gains and losses. An osmotic change (just water loss/gain) will be [blank_start]spread between the ICF and ECF[blank_end]. This effects cells. It can be corrected with [blank_start]ADH release[blank_end] changes, which is a [blank_start]fast[blank_end] response system. An isosmotic change will be [blank_start]limited to the ECF[blank_end]. This causes changes to blood pressure and volume which the heart can cope with. It can be corrected via [blank_start]Na+ excretion/retention[blank_end], which is a [blank_start]slow[blank_end] response system.