APK2105C Chapter 18: The Urinary System: Renal Function

Vocabulary-style practice flashcards covering the anatomy, basic functions, and physiological processes of the urinary system based on Chapter 18 lecture notes.

Primary functions of the kidneys

The kidneys regulate plasma ionic composition ($Na^+$, $K^+$, $Mg^{2+}$, $Ca^{2+}$, $Cl^-$, $HCO_3^-$), volume, osmolarity, $pH$, and metabolic wastes/foreign substances.

Kidney Cardiac Output

The kidneys represent less than $1\%$ of total body weight but receive approximately $20\%$ of cardiac output (CO) at rest.

Renal Hilus

The indentation on the kidney where the renal artery, renal vein, and ureter are located.

Nephron

The functional unit of the kidney consisting of the renal corpuscle and the renal tubule.

Renal Corpuscle

Composed of Bowman’s capsule and the glomerulus.

Cortical Nephron

A type of nephron with its loop of Henle primarily located within the renal cortex.

Juxtamedullary Nephron

A type of nephron with long loops of Henle extending deep into the renal medulla, specialized to create an osmotic gradient for water conservation.

Juxtaglomerular Apparatus

A specialized structure formed by the macula densa of the distal tubule and the granular cells (juxtaglomerular cells) of the afferent and efferent arterioles.

Filtration

The relatively non-specific bulk flow of protein-free plasma from the glomerulus into Bowman’s capsule.

Reabsorption

The transport of molecules from the renal tubule lumen into the peritubular capillaries (moving from the external to the internal environment).

Secretion

The transport of molecules from the peritubular capillary lumen into the renal tubules (moving from the internal to the external environment).

Renal Filtrate

The plasma-derived liquid that is filtered at the renal corpuscle and travels through the tubular portion of the nephron.

Glomerular Filtration Pressure (GFP)

The net filtration pressure of four combined forces, calculated as: $GFP = (P_{GC} + \pi_{BC}) - (P_{BC} + \pi_{GC})$.

Starling Forces in the Glomerulus

The four forces driving filtration: Glomerular capillary hydrostatic pressure ($P_{GC}$), Bowman’s capsule osmotic pressure ($\pi_{BC}$), Bowman’s capsule hydrostatic pressure ($P_{BC}$), and Glomerular osmotic pressure ($\pi_{GC}$).

Glomerular Filtration Rate (GFR)

The volume of plasma filtered per minute; the average rate is $125\,mL/min$.

Filtration Fraction

The ratio of GFR to plasma flow rate, calculated as $\frac{125\,mL/min}{625\,mL/min} = 0.20$ or $20\%$.

Filtered Load

The quantity of a solute filtered per minute, calculated as: $Filtered\,Load = GFR \times Plasma [X]$.

Myogenic Regulation

An intrinsic control mechanism where increased MAP causes the stretch of arteriolar smooth muscle, leading to constriction of the afferent arteriole to maintain GFR.

Tubuloglomerular Feedback

An intrinsic control mechanism where the macula densa senses increased flow and triggers paracrine secretion to cause afferent arteriole constriction and decrease GFR.

Transport Maximum ($T_m$)

The highest rate in $mg/min$ at which reabsorption can occur for a substance when carrier proteins become saturated.

Renal Threshold

The plasma concentration of a solute at which "spillover" into the urine begins to occur.

Glucose Reabsorption in Diabetes

High plasma [glucose] leads to excess solute in the filtrate, increasing osmolarity and decreasing water reabsorption, resulting in diuresis and dehydration.

Proximal Convoluted Tubule (PCT) Specialization

The site of nonregulated reabsorption where $100\%$ of glucose and $70\%$ of both $Na^+$ and $H_2O$ are reabsorbed; characterized by a brush border of microvilli.

Distal Convoluted Tubule (DCT) and Collecting Duct Specialization

The site of regulated reabsorption and secretion where hormone receptors are present on the basolateral membrane and the epithelium has "tight" tight junctions.

Excretion

The elimination of solute and water from the body in the form of urine.