L46: Tubular Reabsorption and Secretion

What is a disorder of glucose metabolism associated with elevated plasma levels?

Diabetes mellitus

The ‘diabetes’ of diabetes mellitus refers to the fact that this metabolic disease first presents with … symptoms

urinary

What is the term for glucose in urine?

Glycosuria

What is the term for increase urine production?

Polyuria

What are the 2 symptoms of diabetes mellitus?

Glycosuria and polyuria

What are the 3 general functions of the renal tubule (and collecting ducts)

Removes nutrients and proteins from tubular fluid, reabsorbs filtered fluid, and concentrate waste products in tubular fluid

What does PCT stand for?

Proximal convoluted tubule

Which part of the nephron is responsible for most of the reabsorption and a significant amount of secretion?

Proximal convoluted tubule

The proximal convoluted tubule is the only part of the nephron capable of absorbing … such as nutrients and filtered proteins

organic substances

What is the proximal convoluted tubule lined by?

Leaky simple cuboidal epithelium with microvilli

How many potential routes for fluid and solute movement do all epithelia have?

2

Where does reabsorption occur along?

Proximal convoluted tubule

Where are co-transporters for filtered nutrients (e.g. glucose) found on?

Apical surface of the PCT epithelium

What does the apical surface of the PCT epithelium express?

Co-transporters (for sodium and glucose or sodium and amino acids)

What does the basolateral surface of the PCT epithelium express?

Transporters (for glucose or amino acids) and sodium/potassium ATPases (to maintain sodium gradient)

What percentage of filtered nutrients does co-transport with sodium allow to be actively removed from tubular fluid?

99%

Co-transport with sodium allows for 99% of filtered nutrients to be actively removed from tubular fluid through … transport

transcellular

Glucose diffuses into ISF using … transport

passive (facilitated)

Co-transporters will rapidly remove glucose … its concentration gradient due to favourable gradient for sodium

against

Glucose in the ISF is returned to … capillaries through diffusion

peritubular

Reabsorption of water occurs in the PCT through … via the … route

osmosis, paracellular

If glucose (and other small molecules) are pumped out of the lumen into PCT cells (and then into ISF), the osmolarity of tubular fluid will … and the osmolarity of ICF and ISF will …

decrease, increase

If glucose (and other small molecules) are pumped out of the lumen into PCT cells (and then into ISF), this … gradient draws water into ISF (through leaky tight junctions of epithelium)

osmotic

About how much of fluid is reabsorbed by osmotic reabsorption within the PCT every day?

108-116L

If plasma (and filtrate) concentrations of glucose are high, glucose transport by the PCT will …

saturate

What does saturable mean?

Having a limited number of binding sites available

Transporter (and co-transporter) proteins are …

saturable

What would happen if filtered glucose is NOT pumped out of the lumen into PCT cells?

1. Osmolarity of tubular fluid will remain high

2. Osmotic gradient from the lumen to ISF will be reduced

3. Less water will be reabsorbed by the PCT epithelium, and more water will remain within the lumen (turning into urine)

PCT cells reabsorb … and other filtered proteins via …?

albumin, receptor-mediated endocytosis

Reabsorption of organic molecules is restricted to the …?

PCT

What is secreted by both the PCT/DCT?

Nitrogenous wastes, metabolic acids, and toxins/drugs

PCT and DCT cells regulate … through the secretion of H⁺

pH

Epithelial cells in the PCT and DCT express …, which allow them to convert CO2 to H₂CO₃ (i.e. H⁺ and HCO₃^-)

carbonic anhydrase

H⁺ can be excreted into the lumen via …?

counter-transporters

Once in the lumen, H⁺ can reform H₂CO₃ and allow for … (as CO₂)

HCO₃^- reabsorption

Amino acid catabolism within PCT and DCT cells makes … and …

ammonium ions (NH₄⁺), ammonia (NH₃)

What nitrogenous compound is excreted by counter-transport?

Ammonium ions

What nitrogenous compound diffuses through the plasma membrane?

Ammonia

The PCT secrete toxins and drugs via … and .. transporters

organic cation (OC⁺), organic anion (OA^-)

What drugs are capable of causing damage to kidney tissue, especially tubular cells within nephrons?

Nephrotoxic drugs

What are the common drugs to STOP in acute kidney injury?

Diuretics, ACEi/ARBS, aminoglycosides, metformin, NSAIDS

DAAMN drugs are often safe for generally healthy people under normal use, but can become toxic if:

1. Taken in high doses

2. Present when kidney function is reduced due to other causes (e.g. physical injury or blood loss)

What occurs because kidney cells must concentrate and/or process drugs and toxins intracellulary in order to excrete them?

Nephrotoxicity