Functions of the Urinary System

• Excretion: Removal of waste materials from blood plasma to urine.

• Elimination: Waste removal from various organ systems:

  • From digestive: undigested food, water, salts, drugs.

  • From respiratory: CO2, H+, water, toxins.

  • From skin: water, NaCl, nitrogenous wastes (urea, uric acid, ammonia, creatinine).

• Water Balance: Kidneys regulate water reabsorption and urine concentration.

• Regulation of pH: Affects volume and composition of body fluids.

• Hormone Production: Produces erythropoietin (for hematopoiesis) and renin (for blood pressure regulation).

Anatomy of the Urinary System

• Kidneys: Pair of bean-shaped organs located retroperitoneally, responsible for blood filtering and urine formation.

• Renal Capsule: Fibrous connective tissue covering the kidneys.

• Renal Cortex: Outer kidney region where most nephron structures are located.

• Renal Medulla: Inner kidney region, collects urine to be excreted.

• Renal Calyx: Collecting ducts for urine from nephrons leading into the renal pelvis.

• Renal Pyramid: Supports various kidney structures with connective tissue.

• Renal Pelvis: Central area collecting urine from the medulla.

• Ureter: Tubule transporting urine from kidneys to the urinary bladder via peristalsis.

• Urinary Bladder: Spherical storage organ capable of holding 400 ml of urine.

• Urethra: Tubule excreting urine outside via the urethral orifice.

Microscopic Anatomy of the Kidney

• Each kidney has ~1 million nephrons (functional units for blood filtering and urine formation).

• Nephron Structure:

  • Afferent arteriole → Glomerulus → Bowman's capsule → Efferent arteriole → Proximal convoluted tubule (PCT) → Descending limb → Loop of Henle (ascending limb) → Distal convoluted tubule (DCT) → Collecting duct.

Urine Formation Processes

1. Filtration: Small molecules filtered from glomerulus to Bowman's capsule.

2. Reabsorption: Nutrients transported from PCT and DCT to peritubular capillaries.

3. Concentration: Water reabsorbed from descending limb and collecting duct.

4. Secretion: Waste/harmful substances moved from peritubular capillaries to PCT and DCT.

Glomerular Filtration

• Small plasma molecules are forced from glomerulus to Bowman's capsule via capillary pores.

• Molecules smaller than plasma proteins (e.g., water, glucose, amino acids) can be filtered.

Functions of Nephron Components

• Glomerulus: Filtration of water and dissolved substances.

• Bowman's Capsule: Receives glomerular filtrate.

• Proximal Convoluted Tubule (PCT): Reabsorbs glucose, amino acids, creatine, and more using active transport, pinocytosis, and osmosis; also actively secretes substances (e.g., penicillin).

Glomerular Filtration Rate (GFR)

• GFR can change due to regulation by neural or hormonal mechanisms, affecting kidney function based on blood pressure and solute concentration levels.

Role of Hormones

• ADH (Antidiuretic Hormone): Released to increase kidney reabsorption of water, concentrating urine when body fluids are low.

• Aldosterone: Stimulates sodium reabsorption and indirectly influences water reabsorption.

Physical Properties of Urine

• Transparency: Clear; indicates no large solutes.

• Color: Light yellow to amber, influenced by various factors (e.g., food).

• Odor: Aromatic to slightly ammonia-like; changes indicate possible health issues.

• pH: Ranges from 4.6 to 8.0; average 6.0.

• Specific Gravity: 1.001 to 1.035, indicating solute concentration.

• Volume: Typically 1-2 liters per day, varies with hydration status.

Abnormal Constituents of Urine

• Presence of substances such as albumin, glucose, blood, hemoglobin, leukocytes, ketones, or bilirubin indicates possible pathology (e.g., infection, diabetes).

Clinical Terms

• Bacteriuria: Presence of bacteria in urine.

• Dysuria: Painful urination.

• Hematuria: Blood in urine.

• Polyuria: Excessive urine production.

• Uremia: Presence of urine in blood.

• Urinalysis: Analysis for health diagnosis.