Urinary System

Kidney Functions Kidneys filter the blood and create urine They filter ~200 liters of fluid from the bloodstream every day Excess water, toxins, metabolic wastes and excess ions normally make up urine

Renal arteries deliver Renal arteries deliver .25 of the total cardiac output to the kidneys each minute

Kidney Functions Regulate the volume and chemical makeup of the blood Maintain balance of water and salts acids and bases

Kidney Functions Gluconeogenesis Glycerol and amino acids are converted to glucose when glucose reserves have been depleted Produce the enzyme renin which helps regulate blood pressure

Kidney Functions Produce the hormone erythropoietin which stimulates red blood cell production Metabolizes dietary Vitamin D to its active form that can be used by the body

Other Urinary Organs Ureters – tubes that lead from the kidneys to the bladder Bladder – muscular sac that holds urine prior to leaving the body Urethra – tube that carries urine out of the body

Kidney Anatomy ~size of a large bar of soap A kidney has 3 distinct regions Cortex – most external region (glomeruli of nephrons found here) Medulla – middle region (loop of Henle & collecting duct found here) Pelvis – most internal region (urine collected here)

Nephrons Filtering units of the kidneys Each kidney contains > 1 million

Multiple nephrons attach to one collecting duct

Parts of the Nephron Glomerulus – a ball of capillaries held in Bowman’s capsule The site of filtration The filtrate is collected in Bowman’s capsule and travels through the proximal convoluted tubule (PCT) the Loop of Henle and the distal convoluted tubule (DCT)

Kidney Physiology: Urine Formation Step 1 – Glomerular Filtration The kidneys process about 180 L of blood derived fluid (filtrate) daily Filtrate contains everything found in plasma except the proteins Blood cells remain in blood

Between Podocytes are spaces called filtration slits where filtrate moves through

Kidney Physiology: Urine Formation Step 2 – Tubular Reabsorption Reabsorption may be passive (no energy required) or active (energy required) depending on the substance.

Kidney Physiology: Urine Formation Substances that are reabsorbed are Na+, K+, Mg2+, Ca2+, Cl-, HCO3-, Glucose, Amino acids, Vitamins, Water, Urea, and fat-soluble substances

Kidney Physiology: Urine Formation Nonreabsorbed substances creatinine and uric acid Incompletely reabsorbed - urea

Kidney Physiology: Urine Formation Step 3 – Tubular Secretion - substances are secreted from peritubular capillaries into the filtrate Secreted substances include certain drugs, urea, uric acid, K+, Na+, and H+

Kidney Physiology: Urine Formation Only about 1.8 L of filtrate leaves the body as urine Urine normally contains mostly water, urea, uric acid, creatinine, Na+, K+, PO43-, SO42-, Ca2+, Mg2+, and HCO3-