Biology 172 Exam 1; Lecture 4: Kidney

Serum osmolarity

The solute concentration of the extracellular fluid in your body. (how salty your body fluid is)

Epithelium

Layer of cells at the interface between the inside and outside of your body.

Apical surface

The membrane that contacts the outside of your body, has differing transport protiens from the inside surface.

Basal surface

The membrane that contacts the inside of the body, has differing transport protiens than the outside surface.

Kidney

Eliminates wastes, retains water, salts, glucose, and vitamins, and controls serum osmolarity.

Nephron

The functional unit of the kidney.

Bowmans capsule

The starting point of the nephron to filter the blood into urine, has the glomerulus inside.

Glomerulus

Blood vessels within the Bowmans capsule.

Proximal tube

Where pre urine goes once it exits the Bowmans capsule; glucose, salt, and water are reabsorbed through active and passive transporters to be picked up by blood vessels outside the epithelium.

Descending loop of henle

Comes before ascending loop in the nephron, further reabsorbs water and salt. Is also permeable to water as the cells have many aquaporins.

Ascending loop of henle

Comes after the descending loop in the nephron, further reabsorbs water and salt. Is NOT permeable to water as there are no aquaporins.

Na+/K+-ATPase

The source that powers the system that brings in water, salt, glucose, and vitamins from outside the body (lumen) to inside the body. This creates a Na+ gradient across the apical membrane.

Na+/glucose co-transporter

Uses the Na+ gradient for secondary active transport of glucose up the concentration gradient into the cell.

Na+/Vitamin co-transporter

Uses the Na+ gradient for secondary active transport of vitamins up their concentration gradient into the cell.

Na+/Cl- co-transporter

Na+ gradient for secondary active transport of Cl- up the concentration gradient into the cell.

Where does the energy come from to drive water or solute movement in the proximal tubule?

The energy comes from ATP hydrolysis which powers the Na+/K+-ATPase pump.

Why is cell polarity critical for kidney function?

It allows the one-way movement of water and solutes between the urine (tubule lumen) and the blood.

How is the glomerulus different in function from the proximal tubule?

The glomerulus has the key function of filtration powered by blood pressure while the proximal tubule has the key function of reabsorption of nutrients using energy from the Na+/K+ ATPase pump.

How does water get drawn out of pre-urine into the proximal tubule?

The osmolarity gradient.

How does the Loop of Henle carry out different functions in the descending and ascending regions?

The descending limb is only permeable to water allowing water to exit while the ascending limb is impermeable to water but pumps out sodium and chloride, which dilutes the fluid while creating the high-salt gradient in the surrounding tissue.

When does urea get “outside the body”?

After leaving the collecting duct and enters the renal pelvis which leads to the bladder.

A symporter in the apical membrane of cells in the kidney proximal convoluted tubule transports a sodium ion down its concentration gradient while transporting a glucose molecule up its concentration gradient. Which describes the mode of glucose transport?

Secondary active transport

Protein in urine is a test for damage to which part of the kidney?

Glomerulus