lec5-Kidney Function I: Filtration, Reabsorption, and Secretion

These flashcards cover the primary functions, anatomy, and physiological processes of the kidney, including glomerular filtration dynamics, tubular transport mechanisms for glucose and ions, and the role of key renal hormones.

Urea

A metabolite produced from protein catabolism that is excreted by the kidney.

Uric acid

A metabolite produced from nucleic acid breakdown that is excreted by the kidney.

Nephron

The functional unit of the kidney, consisting of a renal corpuscle and a tubule, with over 1 million present per kidney.

Renal corpuscle

The component of the nephron comprised of the glomerulus (glomerular capillaries) and Bowman's capsule.

Glomerular capillaries

Fenestrated endothelium with pores up to $15\,nm$ that act as the primary site for filtration.

Podocytes

Tubular epithelial cells with foot processes (pedicels) that form filtration slits of approximately $8\,nm$.

Cortical nephrons

Nephrons located in the outer 2/3 of the cortex (representing 85% of all nephrons) characterized by a short Loop of Henle.

Juxtamedullary nephrons

Nephrons located in the inner 1/3 of the cortex (representing 15% of all nephrons) with a long Loop of Henle used for producing concentrated urine.

Juxtaglomerular apparatus

A structure consisting of the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells.

Macula densa

A specialized group of cells found at the end of the thick ascending limb of the Loop of Henle.

Glomerular Filtration

The process where fluid and solutes move from the glomerular capillaries into Bowman's space; typically 20% of plasma entering the glomerulus is filtered.

Tubular Secretion

The movement of solutes from the peritubular capillaries into the renal tubules.

Tubular Reabsorption

The movement of materials from the filtrate within the tubules into the peritubular capillaries.

Glomerular Filtration Rate (GFR)

The volume of fluid filtered from the glomeruli per minute, typically measured as $125\,ml/min$ (or $180\,l/day$).

Net glomerular filtration pressure

The pressure driving filtration, calculated as $(60-15)-(29-0) = 16\,mmHg$.

SGLT (Na+-dependent glucose co-transporter)

A secondary active co-transporter that moves glucose into the proximal tubule cell against its gradient by using the energy from Na+ moving down its concentration gradient.

GLUT (Facilitated diffusion transporter)

A transporter on the basolateral membrane that moves glucose down its concentration gradient from the cell into the interstitial fluid.

Renal threshold for glucose

The plasma glucose concentration ($200\,mg/dl$ or $11\,mM$) at which glucose begins to be excreted in the urine because the reabsorption system is saturated.

Para-aminohippuric acid (PAH)

An exogenous organic acid used as a diagnostic agent that is secreted in the proximal tubule.

Creatinine

An endogenous organic base (cation) derived from muscle creatine that is secreted in the proximal tubule.

ADH (Anti-diuretic hormone)

A peptide hormone released by the posterior pituitary that promotes water reabsorption in the collecting duct.

Aldosterone

A steroid hormone produced by the adrenal cortex that promotes sodium reabsorption in the collecting ducts.

Renin

A protein released by the juxtaglomerular apparatus that results in the formation of angiotensin II to promote sodium retention and vasoconstriction.

Natriuretic peptides

Hormones produced by cardiac cells that promote sodium excretion in the collecting ducts.