Urinary System and Urine Characteristics

Urinary System

• The urinary system cleanses the blood and eliminates wastes.
• It regulates pH and blood pressure.
• It plays a role in red blood cell concentration and vitamin D production.
• Urine color is primarily determined by the breakdown products of red blood cell destruction (urochrome).
• Liver heme, from hemoglobin, is converted to water-soluble forms and excreted in bile and urine.
• Urine color can be affected by liver disease, kidney stones, dehydration, and certain foods.
• Kidneys need to produce a minimum of 500ml of urine daily to eliminate waste.
• Urine pH typically ranges from 4.5 to 8.0 and is influenced by diet and disease.
• Specific gravity measures the concentration of solutes in urine.

Urine Characteristics

• Normal values:
• Color: Pale yellow to deep amber
• Odor: Odorless
• Volume: 750-2000 ml/24 hours
• pH: 4.5-8.0
• Specific gravity: 1.003-1.032
• Osmolarity: 40-1350 mOsmol/kg
• Urobilinogen: 0.2-1.0 mg/100 mL
• White blood cells: 0-2 HPF
• Leukocyte esterase: None
• Protein: None or trace
• Bilirubin: <0.3 mg/100 mL
• Ketones: None
• Nitrites: None
• Blood: None
• Glucose: None

Nephron Structure

• The nephron is the functional unit of the kidney.
• It has two major components: glomerulus and tubules.
• The glomerulus is a tuft of capillaries that filters blood, and the tubules are responsible for reabsorption and secretion.
• Filtration occurs in the glomerulus.
• The glomerulus and Bowman's capsule form the renal corpuscle.
• Tubules include proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

Renal Blood Flow

• The kidneys have two capillary beds: Glomerular and peritubular.
• The arrangement of these vessels helps regulate the hydrostatic pressures.
• The renal blood flow is regulated by the kidneys to maintain a constant glomerular filtration rate (GFR) despite changes in blood pressure.

Glomerular Filtration Rate (GFR)

• GFR is the volume of filtrate formed by both kidneys per minute.
• It's a crucial indicator of kidney function.
• Factors influencing GFR include net filtration pressure (NFP), hydrostatic and osmotic pressure and membrane surface area.
• Disruptions to GFR can lead to conditions like edema and altered urine volume.

Urine Formation

• Urine formation involves three main processes: filtration, reabsorption, and secretion.
• The glomerulus filters blood to form initial urine.
• Reabsorption is the process of reclaiming useful substances (water, glucose, amino acids).
• Tubular secretion removes unwanted substances from the blood into the filtrate.

Kidney Anatomy

• Outer Cortex: Light-colored, granular appearance.
• Renal Pyramids: Cone-shaped structures in the medulla.
• Renal Pelvis: Funnel-shaped structure.
• Ureters: Tubes that carry urine from the kidneys to the bladder.
• Bladder: Stores urine until micturition.
• Urethra: Tube that transports urine from the bladder to the outside.

Types of Nephrons

• Cortical nephrons: Located mainly in the cortex, responsible for most of the glomerular filtration.
• Juxtamedullary nephrons: Located near the cortex-medullary junction, crucial for concentrating urine.

Tubular System Function

• Reabsorption and secretion of materials
• Reabsorption of water and solutes.
• Regulation of the filtrate, maintaining stable urine output
• The tubular system, including the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, plays a major role in this process.
• It plays a critical role in maintaining homeostasis by regulating the composition and volume of urine, and regulating blood pressure and electrolyte balance.

Urinary System Regulation (e.g.: hormonal influences)

• The Renin-Angiotensin-Aldosterone System (RAAS) is a collection of hormones/enzymes that regulate blood pressure via multiple mechanisms.
• The hormone ADH (antidiuretic hormone) plays a role in regulating water balance.
• Other hormones and factors also influence urine production, including nitric oxide, prostaglandins, endothelin.

Additional Clinical Considerations

• GFR measurements and estimations are used to assess kidney function.
• Blood pressure has a direct relationship with GFR.
• Specific diseases and conditions (e.g. diabetes, kidney stones) can impact urine characteristics, production, and the urinary system.