Chapter Fifteen The Urinary System

Urinary System Contribution to Homeostasis Regulates body water levels Excess water taken in is excreted Output varies from 2-1/2 liter/day to 1 liter/hour Regulates nitrogenous and other solute waste Nitrogen from amino acids are made into urea in liver and transported to kidney as waste Other solutes Sodium, chloride, potassium, calcium, hydrogen ions, creatinine

Urinary System Kidney Cortex Renal artery Renal vein Nephrons Aorta Inferior vena cava Medulla Renal pelvis Medulla Collecting duct Ureter Bladder Ureter Urethra a) The components of the urinary system. b) Internal structure of the kidney. c) The cortex and medulla of the kidney are composed of numerous nephrons.

Organs of the Urinary System Kidneys Principle organ Cortex - outer Medulla - inner

Urinary System Kidney Cortex Renal artery Renal vein Nephrons Aorta Inferior vena cava Medulla Renal pelvis Medulla Collecting duct Ureter Bladder Ureter Urethra a) The components of the urinary system. b) Internal structure of the kidney. c) The cortex and medulla of the kidney are composed of numerous nephrons.

Organs of the Urinary System Ureters Transport urine to bladder Urinary bladder Stores urine (600–1000 ml) Urethra Carries urine from body Two sphincters Males about 20 cm, females about 4 cm

Organs of the Urinary System Urinary bladder Rectum Internal urethral sphincter Prostate gland Uterus Vagina External urethral sphincter Penis Rectum Urethra Testis a) The male b) The female

Tubular and Vascular Nephron Components

Nephrons: Produce Urine Tubules Function Filter fluid and reabsorb needed substances Structures Proximal tubule Loop of Henle Distal tubule Collecting duct

Nephrons: Produce Urine Blood vessels associated with tubules Arterioles Afferent Efferent Capillaries Glomerular Peritubular Vasa recta

Formation of Urine

Formation of Urine: Glomerular Filtration Filters fluid from capillaries into glomerular capsule Rate of filtration Resting rate under local chemical control Stress causes sympathetic nervous system to reduce blood flow to kidneys

Formation of Urine: Tubular Reabsorption Tubular reabsorption returns water and needed solutes to blood capillaries Sodium moved by active transport from tubule cells to interstitial fluid and diffuses to capillaries Chloride passively accompanies sodium (balanced charge) Water reabsorbed with salts Movement of sodium creates energy to transport glucose and amino acids into renal tubule then diffuses to the interstitial fluid

Tubular Secretion Tubular secretion removes other substances from blood Purpose Regulation of chemical levels in body Excretion of harmful chemicals Substances secreted Penicillin, cocaine, marijuana, pesticides, preservatives, hydrogen ions, ammonium, potassium

Concentration or Dilution of Urine: ADH (anti-diuretic hormone) Formation of Dilute urine (see next slide for diagram) Excreting excess water Mechanism Cycling of NaCl and urea create a concentration gradient in the medulla that allows water to diffuse from the renal tubules into the interstitial fluid and then into the blood capillaries

Formation of Dilute Urine

Concentration or Dilution of Urine: ADH Formation of concentrated urine (see next slide) Conserving water Mechanism Countercurrent exchange Increased ADH causes increased permeability to the collecting tubules and increased conservation of water

Formation of Concentrated Urine

Urination Micturition reflex Internal urethral sphincter Smooth muscle External urethral sphincter Skeletal muscle

Kidney’s Role in Homeostasis Maintains water balance Adjusts blood volume and blood pressure Aldosterone, renin, ANH help maintain salt balance in order to control blood volume Maintains acid–base balance and blood pH Regulates red blood cell production via erythropoietin Activates an inactive form of vitamin D

Kidney’s Role in Homeostasis

Kidney’s Role in Homeostasis