Renal Physiology: Filtration and Reabsorption

Vocabulary practice flashcards covering renal anatomy, pathways of renal circulation, filtration pressures, and segmental nephron transport mechanisms.

Nephron

The smallest functional and structural unit of the kidneys responsible for filtration, reabsorption, and secretion to produce urine.

Ureters

Long tubular structures that transport urine from the kidneys to the urinary bladder using peristaltic contractions and gravity.

Internal Urethral Sphincter

An involuntary smooth muscle sphincter that opens and closes automatically as the urinary bladder accumulates fluid.

External Urethral Sphincter

A voluntary skeletal muscle sphincter that provides conscious control over urination and is developed during potty training.

Trigon

A triangular area clinically relevant for infections formed by the low posterior entry of the ureters into the bladder and the urethral orifice.

Glomerulus

A cluster of fenestrated capillaries with large gaps between simple squamous endothelial cells that serves as the site of nonspecific filtration.

Afferent Arteriole

The arteriole that branches from the cortical radiate artery and delivers blood directly into the glomerular capillaries.

Efferent Arteriole

The vessel that carries unfiltered blood away from the glomerulus and leads into the peritubular capillaries and vasa recta.

Glomerular Capsule

Also known as Bowman's capsule; a structure that encases the glomerulus to capture ultrafiltrate and direct it into the proximal convoluted tubule.

Net Filtration Pressure

The net pressure driving filtration, calculated as the sum of filtration forces minus reabsorptive forces: $(\text{Hydrostatic Pressure}_{\text{glomerular capillaries}} + \text{Osmotic Pressure}_{\text{capsular space}}) - (\text{Hydrostatic Pressure}_{\text{capsular space}} + \text{Osmotic Pressure}_{\text{glomerular capillaries}})$.

Hydrostatic Pressure of Glomerular Capillaries

The blood pressure within the glomerulus that acts as a filtration force pushing fluid outward into the capsular space.

Ultrafiltrate

The fluid filtered at the glomerulus totaling approximately $180\,\text{L}$ per day, which has an initial osmolarity of about $300\,\text{mOsm}$.

Minimum Daily Urine Volume

The minimum volume of urine required each day to excrete metabolic wastes, which is approximately $400\,\text{mL}$.

Proximal Convoluted Tubule

The first segment of the nephron tubule responsible for approximately $80\%$ of all reabsorption and $100\%$ of glucose and amino acid reabsorption.

Basolateral $\text{Na}^+/\text{K}^+$ ATPase

A primary active transport pump on the basolateral membrane that moves $3\,\text{Na}^+$ out and $2\,\text{K}^+$ in, generating the sodium gradient used for tubular reabsorption.

Sodium-Glucose Symporter

A secondary active cotransporter on the apical membrane that utilizes the sodium concentration gradient to move sodium and glucose into the cell together.

Aquaporins

Specialized water channel proteins present on cell membranes that allow water to follow reabsorbed solutes by osmosis.

Renal Threshold for Glucose

The blood glucose concentration limit of $180\,\text{mg/dL}$, beyond which glucose transport proteins become saturated.

Glycosuria

The presence of glucose in the urine, occurring when blood glucose levels exceed $180\,\text{mg/dL}$ and surpass the reabsorptive capacity of the proximal convoluted tubule.

Polyuria

The excretion of excessive volumes of urine resulting from the osmotic effect of unabsorbed solutes like glucose pulling water into the filtrate.

Descending Limb of the Nephron Loop

The segment of the loop of Henle that is permeable to water but impermeable to salt, which concentrates the filtrate up to $1,200\text{ to }1,600\,\text{mOsm}$.

Ascending Limb of the Nephron Loop

The segment of the loop of Henle that is impermeable to water but permeable to salt, which reabsorbs sodium chloride and dilutes the filtrate.

Distal Convoluted Tubule

The tubule segment that performs selective secretion, fine-tuned reabsorption of $10\text{ to }15\%$ of remaining sodium, chloride, and water, and parathyroid hormone-regulated calcium reabsorption.

Collecting Duct

The terminal portion of the nephron system representing the final site for water and salt reabsorption under the influence of aldosterone, antidiuretic hormone, and atrial natriuretic peptide.