The Urinary System
Introduction to the Urinary System
- Functions:
- Waste removal:
- Nitrogenous wastes: urea, uric acid, creatinine
- Homeostasis:
- Regulation of fluid, electrolyte, pH, plasma osmolarity, plasma volume, and composition
- Erythropoietin secretion: hormone produced to stimulate red blood cell production
- Urine formation: approximately 1.5 L/day of urine produced
Organs of the Urinary System
- Major Organs:
- 2 kidneys
- 1 urinary bladder
- 2 ureters
- 1 urethra
Structure of the Kidneys
- Kidney Characteristics:
- Paired retroperitoneal organs
- Typical dimensions: 10 cm long, 5.5 cm wide, 3 cm thick
- Weight: approximately 150 g
- Hilum:
- Medial indentation; entry/exit points for renal artery, renal nerves, renal vein, and ureter
Kidney Location
- Positioning:
- Located on either side of the vertebral column
- Protected by visceral organs anteriorly and body wall musculature and ribs posteriorly
- The left kidney is slightly superior to the right
Supporting Structures of the Kidneys
- Connective Tissues:
- Fibrous capsule: collagen layer covering the kidney
- Perinephric fat: thick layer of adipose tissue providing cushioning
- Renal fascia: dense connective tissue anchoring kidneys to surrounding structures
Kidney Gross Anatomy
- Outer structures:
- Renal Cortex: the outer region
- Renal Medulla: the inner region
- Renal Pyramids: cone-shaped structures in the medulla
- Renal Columns: extensions separating the pyramids
- Minor and Major Calyx: collect urine from lobes of the kidneys
- Renal Pelvis: funnel-shaped area that collects urine from the major calyces
Nephrons: Functional Units of the Kidney
- Composition of Nephrons:
- About 1 million nephrons per kidney
- Cortical Nephrons (85%): primarily in the cortex, performing most regulatory functions
- Juxtamedullary Nephrons (15%): longer loops extending into the medulla, important for producing concentrated urine
Nephron Structure
- Main Components:
- Renal Corpuscle:
- Glomerulus: capillary network for filtration
- Glomerular Capsule: surrounds the glomerulus to collect filtrate
- Renal Tubule:
- Proximal Convoluted Tubule (PCT): major site for reabsorption
- Nephron Loop: responsible for establishing concentration gradients
- Distal Convoluted Tubule (DCT): adjusts tubular fluid composition
- Collecting Duct: collects urine from many nephrons and carries it through the renal medulla
Blood Flow in the Kidneys
- Arterial Supply:
- Blood enters via the renal artery, which branches into segmental, interlobar, and arcuate arteries, culminating in afferent arterioles supplying the glomeruli
- Venous Drainage:
- Blood is collected from peritubular capillaries into cortical radiate veins, and drains through progressively larger veins to the renal vein and subsequently to the inferior vena cava
Urine Formation Processes
- Three Main Processes:
- Filtration:
- Occurs in the glomerulus; blood pressure forces water and solutes into the glomerular capsule
- Reabsorption:
- Tubular fluid is modified as substances are returned to the blood
- Secretion:
- Additional materials from blood are transferred into the renal tubule
Hormonal Regulation of Kidney Function
- ADH (Antidiuretic Hormone): increases water reabsorption in the collecting duct
- Aldosterone: regulates sodium and potassium levels
- Renin-angiotensin system: responds to low blood pressure by promoting retention of water and sodium to increase volume and pressure
Renal Failure
- Chronic Renal Failure: gradual loss of kidney function; non-reversible and managed by dietary restrictions
- Acute Renal Failure: rapid loss of kidney function; potential for recovery if treated promptly
- Dialysis: artificial process to filter blood, substituting kidney function
Urinary Disorders
- Common signs: changes in urine volume or appearance, increased urgency or frequency, pain during urination, or signs of infection
- Conditions affecting kidney function: e.g., kidney stones, infections (pyelonephritis), and functional disorders leading to incontinence or urinary retention
Urinary Tract Overview
- Comprises ureters, urinary bladder, and urethra, responsible for transporting, storing, and eliminating urine
- Ureters are muscular tubes; the urinary bladder is a distensible organ; the urethra varies in length and function between genders