23 Urinary System PDF

URINARY SYSTEM MAJOR FUNCTIONS Kidneys, a major excretory organ, maintain the body’s internal environment by: – Regulating total water volume and total solute concentration in water – Regulating ion concentrations in extracellular fluid (ECF) – Ensuring long-term acid-base balance – Excreting metabo...

URINARY SYSTEM MAJOR FUNCTIONS Kidneys, a major excretory organ, maintain the body’s internal environment by: – Regulating total water volume and total solute concentration in water – Regulating ion concentrations in extracellular fluid (ECF) – Ensuring long-term acid-base balance – Excreting metabolic wastes, toxins, drugs – Producing erythropoietin (regulates blood pressure) and renin (regulates RBC production) – Activating vitamin D – Carrying out gluconeogenesis, if needed OTHER PARTS Kidneys are part of the urinary system, which also includes: – Ureters: transport urine from kidneys to urinary bladder – Urinary bladder: temporary storage reservoir for urine – Urethra: transports urine out of body URINARY SYSTEM EXTERNAL GROSS ANATOMY - 1 Location and External Anatomy Retroperitoneal, in the superior lumbar region One is more superior Adrenal (suprarenal) gland sits atop each kidney Convex lateral surface Concave medial surface with vertical renal hilum leads to internal space. – Ureters, renal blood vessels, lymphatic vessels, and nerves enter and exit at hilum EXTERNAL GROSS ANATOMY - 2 Three layers of supportive tissue surround kidney – Fibrous capsule Transparent capsule that prevents spread of infection to kidney – Perirenal fat capsule Fatty cushion – Renal fascia Anchoring outer layer of dense fibrous connective tissue INTERNAL GROSS ANATOMY - 1 Internal kidney has three distinct regions 1. Renal cortex: granular-appearing superficial region 2. Renal medulla: deep to cortex, composed of cone-shaped medullary (renal) pyramids Broad base of pyramid faces cortex Papilla, tip of pyramid, points internally Renal pyramids are separated by renal columns, inward extensions of cortical tissue INTERNAL GROSS ANATOMY - 2 INTERNAL GROSS ANATOMY - 3 3. Renal pelvis Funnel-shaped tube continuous with ureter Minor calyces – Cup-shaped areas that collect urine draining from pyramidal papillae Major calyces – Areas that collect urine from minor calyces – Empty urine into renal pelvis Urine flow – Renal pyramid → minor calyx → major calyx → renal pelvis → ureter BLOOD FLOW BLOOD FLOW THROUGH THE KIDNEY Aorta Renal Artery Segmental Artery Interlobar Artery Arcuate Artery Cortical Radiate Artery aka Interlobular Artery Afferent Arteriole Glomerulus Efferent Arteriole Peritubular capillaries or Vasa Recta Cortical Radiate Veins aka Interlobular Veins Arcuate Vein Interlobar Vein Renal Vein Inferior Vena Cava NEPHRONS Nephrons are the structural and functional units that form urine > 1 million per kidney Two main parts – Renal corpuscle – Renal tubule RENAL CORPUSCLE Two parts of renal corpuscle 1. Glomerulus – Tuft of capillaries composed of fenestrated endothelium 2. Glomerular capsule AKA Bowman’s capsule cup-shaped, hollow structure surrounding glomerulus – Consists of two layers Parietal layer : simple squamous epithelium Visceral layer : clings to glomerular capillaries; branching epithelial podocytes – Filtration slits allow filtrate to pass into capsular space FENESTRATED CAPILARIES PODOCYTES AND PEDICELS RENAL TUBULE AND COLLECTING DUCT Renal tubule: Consists of single layer of epithelial cells, but each region has its own unique histology and function Three major parts 1. Proximal convoluted tubule 2. Nephron loop 3. Distal convoluted tubule Distal convoluted tubule drains into collecting duct – fuse into papillae HOW IS THE BLOOD ACTUALLY CLEANED? CLASSES OF NEPHRONS Two major groups of nephrons – Cortical nephrons Make up 85% of nephrons – Juxtamedullary nephrons 15% Important in production of concentrated urine PHYSIOLOGY OF KIDNEYS 180 L of fluid processed daily, but only 1.5 L of urine is formed Kidneys filter body’s entire plasma volume 60 times each day Consume 20–25% of oxygen used by body at rest Filtrate (produced by glomerular filtration) is basically blood plasma minus proteins Urine is produced from filtrate – Urine 300 mOsm to conserve water Overhydration produces large volume of dilute urine – ADH production decreases; urine ~100 mOsm – If aldosterone present, additional ions can be removed, causing water to dilute to ~50 mOsm HOW HORMONES AFFECT OSMOLALITY - 2 Dehydration produces small volume of concentrated urine – Maximal ADH is released; urine ~1200 mOsm – Severe dehydration: 99% water reabsorbed CLINICAL EVALUATION OF URINE -1 Urinalysis: urine is examined for signs of disease – Can also be used to test for illegal substances Assessing renal function requires both blood and urine examination CLINICAL EVALUATION OF URINE - 2 Characteristic Normal values Color Pale yellow to deep amber Odor Odorless Volume 750–2000 mL/24 hour 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 (per high-power field of microscope) Leukocyte esterase None Protein None or trace Bilirubin