US Lecture 4 - Tubular function Flashcards Preview

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What is the function of the kidney?

Central regulator of homeostasis - consume more salt and water than needed so we need to lose this and other waste products


What is osmolarity?

Measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane - each ion is counted seperately


Fill in the blanks of the kidney nephron during filtration


What does the renal tubular wall look like diagramatically?


Through which pathways does reabsorption and secretion take place?

Paracellular and transcellular from/to peritubular capillary to/from tubular fluid


What are the types of transport that can occur in the tubules?

Osmosis, Active transport, Co-transport, movement down electrical gradient and passive transport


What are the 2 types of passive protein transport?

Protein INdependent (lipophilic molecules) and dependent (hydrophilic molecules) transport


How do the graphs of conc vs time appear with protein IN/dependent transport?


How does active movement occur?

Directly coupled to ATP hydrolysis or in directly coupled


What is the graph of conc vs rate with active movement?


How does water transport occur?

By osmosis - through tight junctions or aquaporins


How is a passive uptake system regulated?

By reducing the number of channel proteins in the membrane, so the molecule only has one output, leading to regulation


How are proteins reabsorbed?

Protein attaches to membrane receptor, which is then endocytosed, and the protein and membrane receptor break apart


How does transport maxima vary?

Depending on circumstances and applies to whole individual


What does secretion do in the nephron?

Moves substances from peritubular capillaries into tubular lumen - constitutes of a pathway into the tubule, either by diffusion/transcellular mediated transport Active secretion from blood side into tubular cell and then into lumen


What are the most important substances secreted?

H+ and K+ Choline, creatinine, penicillin and other drugs are also secreted NB: creatinine secretion levels are so low that they aren't very relevant, hence can be used as clearance


How uniform is reabsorption at the proximal convoluted tubule, distal convoluted tubule, collecting duct and loop of henle?


What is the structure of each of the cells lining the PCT, LoH, DCT and collecting duct?


What substances are reabsorbed in the proximal convoluted tubule?


What do the Na/K pumps in the basolateral membrane of PCT do?

Na/K pump keeps intracellular [Na] low and [K] high Large conc. and electrical gradients favour Na movement into the cell (occurs in most nephron segments)


What does Na help to occur in reabsorption in the early proximal tubule?

Na+ entry down a large electrochemical gradient can bring about the “uphill” entry of glucose and a-a’s and exit of H+


What is the function of carbonic anhydrase in the early proximal tubule?

Leads to Na reabsorption and increased urinary activity


What is passively and actively reabsorbed in the PCT?

Passive: urea and water Active: Glucose, a.a., Na, K, Ca, Vit C, Uric acid Reabsorption of all solutes/water is sensitive to metabolic poisons


Is there any secretion in the proximal tubule and why is this important?

Net secretion of some substances from plasma into proximal tubular fluid, important because some drugs and other substances are excreted in this way and some drugs enter the tubular fluid and act further down the nephron


What is reabsorbed in the descending limb of loop of henle?

Water passively reabsorbed through squamous epithelium Na and K drawn in


What is reabsorbed in the ascending limb of loop of henle?

Cl actively reabsorbed, Na passively reabsorbed with it Bicarbonate reabsorbed Impermeable to water - cuboidal epithelium, few microvilli - high energy requirement so prominent mitochondria


What osmolarity is the tubular fluid leaving the loop of Henle?

Hypo-osmolar with respect to plasma


How are the substances reabsorbed in the loop of henle?


What can loop diuretics do?

Block the Na/K/Cl co-transporter in the ascending loop of Henle


What is the proximal part of the DCT's structure?

Cuboidal epithelium, with few microvilli Complex lateral membrane interdigitations with Na pumps Numerous large mitochondria