Chapter 24: Urinary System Overview and Functions

Urinary System

Organ system responsible for waste elimination.

Nephron

Functional unit of the kidney for urine formation.

Micturition

The process of urination.

Urine Formation

Concentration of filtrate in the nephron.

Glomerular Filtration

First step in urine formation at glomerulus.

Glomerulus

Tuft of capillaries for blood filtration.

Afferent Arteriole

Supplies blood to the glomerulus.

Filtration Membrane

Thin structure filtering blood in glomerulus.

Endothelium

Inner layer of glomerular capillaries.

Basement Membrane

Prevents large proteins from exiting capillaries.

Visceral Layer

Podocytes wrapping around glomerular capillaries.

Capsular Space

Area where filtrate accumulates before PCT.

Filtrate Composition

Includes water, glucose, ions, urea, vitamins.

Glomerular Filtration Rate (GFR)

Volume of filtrate formed per minute.

Normal GFR

Typically 120-125 mL/min in healthy kidneys.

Creatinine

By-product used to estimate GFR.

Net Filtration Pressure (NFP)

Main factor regulating GFR.

Hydrostatic Pressure

Pushing force due to fluid presence.

Osmotic Pressure

Pulling force due to solutes in solution.

NFP Equation

NFP = outward pressures - inward pressures.

Vasoconstriction

Narrowing of arterioles to regulate pressure.

Vasodilation

Widening of arterioles to increase blood flow.

Myogenic Response

Intrinsic control mechanism regulating blood flow in kidneys.

Afferent Arteriole Vasodilation

Increases blood flow into glomerulus, enhancing GFR.

Afferent Arteriole Vasoconstriction

Decreases blood flow into glomerulus, reducing GFR.

Tubuloglomerular Feedback

Response to NaCl concentration changes in glomerulus.

Macula Densa Cells

Detect sodium chloride levels, influencing JG cells.

Juxtaglomerular Cells

Release renin affecting blood pressure and GFR.

Mesangial Cells

Regulate glomerular surface area for filtration.

Mean Arterial Pressure (MAP)

Normal range for intrinsic controls: 80-180 mmHg.

Extrinsic Controls

Neural and hormonal regulation of GFR for homeostasis.

Sympathetic Nervous System

Stimulates renin release, decreasing GFR during low BP.

Atrial Natriuretic Peptide (ANP)

Increases GFR by inducing vasodilation in high BP.

Net Filtration Pressure

Hydrostatic pressure in glomerulus affecting GFR.

Surface Area Regulation

Number of functional glomeruli impacts filtration rate.

Membrane Permeability

Fenestrated capillaries allow selective filtration in glomeruli.

Paracellular Route

Solutes move between cells during reabsorption.

Transcellular Route

Solutes move through cells during reabsorption.

Apical Surface

First membrane solutes cross in tubular cells.

Basal Surface

Second membrane solutes cross into interstitial space.

Filtration Membrane

Composed of fenestrated capillaries and podocytes.

Renin-Angiotensin-Aldosterone System (RAAS)

Hormonal system regulating blood pressure and fluid balance.

Filtration Slits

Openings formed by podocytes enhancing filtration.

Glomerular Capsule

Structure housing glomeruli, facilitating filtration process.

Transport Maximum

Limit on nutrient reabsorption by channel number.

Proximal Convoluted Tubule (PCT)

Primary site for nutrient and water reabsorption.

Reabsorption Percentage of Water in PCT

Approximately 85% of water reabsorbed here.

Reabsorption Percentage of Ions in PCT

About 65% of ions reabsorbed in PCT.

Nephron Loop

Site for additional water and ion reabsorption.

Countercurrent Mechanism

Process enhancing water and solute reabsorption.

Antidiuretic Hormone (ADH)

Regulates water reabsorption in nephron loop.

Distal Convoluted Tubule (DCT)

Final regulation of urine composition occurs here.

Aldosterone

Hormone regulating sodium and water reabsorption.

Atrial Natriuretic Peptide (ANP)

Inhibits sodium reabsorption, increasing urine output.

Intercalated Cells

Regulate pH and H+/HCO3- reabsorption.

Cotransporter Protein

Facilitates simultaneous transport of multiple substances.

Symporter Protein

Transports two substances in the same direction.

Antiporter Protein

Transports two substances in opposite directions.

Glucose Reabsorption

Involves symporter and uniporter proteins in PCT.

Endocytosis of Proteins

Process to reclaim proteins in nephron.

Filtered Proteins

Includes insulin, angiotensin, and small albumin.

Sodium Reabsorption in PCT

Approximately 65% reabsorbed via active transport.

Sodium Reabsorption in Nephron Loop

About 25% reabsorbed as part of countercurrent.

Obligatory Water Reabsorption

Water reabsorption via always-present aquaporins.

Facultative Water Reabsorption

ADH increases aquaporins in collecting duct.

Potassium Handling

Potassium is both reabsorbed and secreted.

Type A cells

Always reabsorb potassium in kidneys.

Principal cells

Secrete potassium based on aldosterone levels.

Aldosterone

Hormone that regulates sodium and potassium balance.

Na+/K+ channels

Facilitate sodium reabsorption and potassium secretion.

Potassium secretion

Increased by aldosterone, more in urine.

Calcium phosphate

Main storage form of calcium and phosphate.

PTH

Hormone that regulates calcium and phosphate levels.

DCT cells

Distal convoluted tubule cells involved in calcium transport.

Bicarbonate reabsorption

90% occurs in proximal convoluted tubule.

Intercalated cells

Regulate urine pH in collecting duct.

Acidosis

Condition with low blood pH, Type A cells secrete H+.

Alkalosis

Condition with high blood pH, Type B cells reabsorb H+.

Nitrogenous wastes

Includes urea, uric acid, and creatinine.

Urea

Reabsorbed and secreted, from protein breakdown.

Uric acid

Reabsorbed and secreted, from nucleic acid breakdown.

Creatinine

Only secreted, from muscle metabolism.

Glucose in urine

Indicates diabetes mellitus when transport maximum exceeded.

Ketone bodies

Produced during fat metabolism in diabetes.

Erythrocytes in urine

Indicates bleeding or severe injury.

Leukocytes in urine

Indicates infection, often from bacteria.

Protein in urine

Normal levels are less than 150 mg/day.

Bile pigments

Indicate liver disease or bile duct obstruction.