Renal System Part 1: Filtration and Reabsorption

Practice flashcards covering renal anatomy, physiological pressures, filtration barriers, and the mechanisms of reabsorption and secretion based on Chapter 1-8 lecture notes.

Renin

A key enzyme produced by the kidney that functions in the pathway generating angiotensin II, a hormone regulating sodium, potassium, and blood pressure.

Glomerular Filtration Rate (GFR)

The volume of plasma filtered across the glomerular capillaries, which is normally $180\,\text{liters per day}$ for a healthy adult with two healthy kidneys.

Ultrafiltration

The passage of fluid and small dissolved solutes, such as water, glucose, and sodium, across the glomerular capillary wall into Bowman's capsule.

Nephron

The functional unit of the kidney; there are approximately $1,000,000$ per kidney.

Afferent Arteriole

The specific arteriole that supplies blood arriving to the glomerular capillaries for filtration.

Efferent Arteriole

The specific arteriole where blood exits the glomerular capillaries.

Cortical Nephron

A type of nephron with a relatively short loop of Henle that dips only a small distance into the medulla.

Juxtamedullary Nephron

A type of nephron with a long loop of Henle that dips deep into the medulla, specialized for extensive countercurrent exchange.

Vasa Recta

Long straight blood vessels that follow the long loops of Henle in juxtamedullary nephrons to facilitate countercurrent exchange.

Podocyte

A specialized cell type in the glomerulus with foot processes that wrap around capillaries, forming part of the filtration barrier.

Fenestrations

The pores within endothelial cells of the glomerular capillaries that allow for high permeability during filtration.

Glomerular Basement Membrane

A filtration barrier composed of extracellular matrix molecules like collagen and glycoproteins that serves a size-selective function.

Hydrostatic Pressure ($P_h$)

The blood pressure in the glomerular capillaries that serves as the main driving force for filtration, normally measured at $55\,\text{mm Hg}$.

Colloid Osmotic Pressure

The osmotic pressure (approximately $30\,\text{mm Hg}$) exerted largely by serum albumin in the plasma that tends to keep fluid in the blood vessels.

Net Filtration Pressure

The final pressure driving fluid into Bowman's capsule, calculated as $10\,\text{mm Hg}$ after accounting for opposing pressures.

Myogenic Response

An autoregulatory mechanism where smooth muscle cells in the afferent arteriole contract in response to stretch from increased blood flow.

Macula Densa Cells

Specialized cells in the ascending limb of the loop of Henle that sense fluid flow and release paracrine factors to regulate GFR.

Tubuloglomerular Feedback

An intrinsic control mechanism where the macula densa senses increased flow and releases adenosine to constrict the afferent arteriole.

Atrial Natriuretic Peptides (ANP)

Hormones released by the atria of the heart in response to stretch that cause vasodilation of the afferent arteriole and increase GFR.

ENaC (Epithelial Sodium Channel)

A continuously open channel on the apical membrane of proximal tubule cells that allows sodium to diffuse down its concentration gradient.

SGLT (Sodium-Glucose Cotransporter)

A symporter that performs secondary active transport, using the sodium gradient to move glucose into the cell against its concentration gradient.

Secretion

The active movement of substances, such as penicillin or foreign organic molecules, from the peritubular capillaries into the tubular lumen.

Excretion

The process by which the final fluid (urine) is eliminated from the body, calculated as $\\text{Filtered} - \\text{Reabsorbed} + \\text{Secreted}$.

Transport Maximum ($T_m$)

The saturation level of the transport mechanism, which for glucose in the kidneys is approximately $375\,\text{mg/min}$.

Renal Threshold

The plasma concentration at which a substance, such as glucose at $300\,\text{mg/dL}$, begins to appear in the urine because transport mechanisms are saturated.

Osmotic Diuresis

An increase in urine volume (diuresis) caused by the presence of a non-reabsorbed solute like glucose, which creates an osmotic effect.

Polyuria

Frequent urination resulting from high levels of non-reabsorbed solutes in the filtrate, commonly seen in unmanaged diabetes.

Canagliflozin

A pharmacological drug that inhibits SGLT2 in the proximal tubule to prevent glucose reabsorption and lower blood glucose levels.