The Urinary System DeShawn Lowery Nate Falk Period 3
Functions • The Urinary system removes certain salts and nitrogenous wastes. • Helps maintain the normal concentrations of water and electrolytes within body fluids. • Regulates the pH and volume of body fluids. • Helps control red blood cell production and blood pressure.
Major Organs • Kidneys: on the posterior wall of the abdominal cavity. • Ureters: extends downward behind the parietal peritoneum and runs parallel to the vertebral column. • Urinary Bladder: within the pelvic cavity, behind the symphysis pubis and beneath the parietal peritoneum. • Urethra: its wall is lined with mucous membrane and contains a thick layer of smooth muscle tissue.
Functions • Kidneys: Removes substance from blood, form urine, and help regulate certain metabolic processes • Ureters: transport urine from the kidneys • Urinary Bladder: Stores urine • Urethra: conveys urine to the outside of the body.
Kidneys • The kidneys are high on the posterior wall of the abdominal cavity. • An adult kidney is about 12 cm long, 6 cm wide, and 3 cm thick. • The left kidney is usually 1.5 – 2.0 cm higher than the right one.
Kidney Structure • A kidney contains a hollow renal pelvis. • The ureter expands into the renal pelvis. • Renal papillae project into the renal sinus • Each kidney divides into a medulla and a cortex
Kidney Functions • Maintain homeostasis by removing metabolic wastes from blood and excreting them. • Regulates….. • Red blood production • Blood volume • Blood pressure • The volume, composition, and pH of body fluids.
Pathway of blood in the kidney Renal Artery hilum interlobar arteries arcuate arteries interlobar arteries afferent arterioles renal vein
Nephrons • A nephron is the functional unit of the kidney • A kidney contains about 1 million nephrons. • It is make up of a renal corpuscle and a renal tubule.
Nephrons • A renal corpuscle is composed of a tangled cluster of blood capillaries called a glomerulus. • Glomerular capillaries filter fluid (first step of urine formation). • Segments of the renal tubule include the proximal convoluted tubule, nephron loop, and distal convoluted tubule, which empties into a collecting duct. • The collecting duct empties into the minor calyx of the renal pelvis.
Urine Formation • Glomerular Filtration: filtration of plasma by the glomerular capillaries. • Tubular reabsorption: moves substances from the tubular fluid back into the blood within the peritubular capillary into the renal tubular. • Tubular Secretion: moves substances from the blood within the peritubular capillary into the renal tubule.
Glomerular Filtration • The first step in urine formation is filtration of substances out of glomerular capillaries and into the glomerular capsule. • Glomerular filtrate passes through the fenestrate of the capillary endothelium.
Filtration Rate • As colloid osmotic pressure in the glomerulus increases, filtration rate decreases. • As hydrostatic pressure in the glomerular capsule increases, filtration rate decreases. • The kidneys produce about 125 milliliters of glomerular fluid per minute, most of which is reabsorbed.
Filtration Pressure • Filtration is due mainly to hydrostatic pressure inside glomerular capillaries. • The osmotic pressure of plasma and the hydrostatic pressure in the glomerular capsule also affect filtration.
Regulation of filtration rate • When the macula densa senses decreased amounts of chloride, potassium, and sodium ions in the distal tubule, it causes juxtaglomerulaar cells to release renin. • This triggers a series of changes leading to vasoconstriction of afferent and efferent arterioles, which may affect glomerular filtration rate, and aldosterone secretion, which stimulates tubular sodium reabsorption.
Tubular Reabsorption • Substances are selectively reabsorbed from glomerular filtrate. • The peritubular capillaries permeability adapts it for reabsorption. • Most reabsorption occurs in the proximal tubule, where epithelial cells have microvilli.
Tubular Secretion • Secretion transports substances from plasma to the tubular fluid. • Potassium and hydrogen ions are secreted both actively and passively.
Urine Composition • Urine is about 95% water, and it also usually contains urea and uric acid. • Urine volume varies with fluid intake and with certain environmental factors
Urine Composition • Urea is a by-product of amino acid catabolism. • Urea enters the renal tubule by filtration, about 50% of it is reabsorbed, and the rest is excreted by urine. • Uric acid is a product of the metabolism of certain organic bases in the nucleic acids. • Active transport reabsorbs uric acid. Some uric acid is secreted into the renal tubule.
Urine Elimination • Peristaltic waves in the ureter force urine to the urinary bladder. • The urinary bladder stores urine and forces it through the urethra during micturition. • Micturition expels urine from the urinary bladder. • In micturition, the detrusor muscle contracts, along with the abdominal wall and pelvic floor.
Diseases • Kidney Stones: kidney stones are formed in uric acid, calcium oxalate, calcium phosphate, or magnesium phosphate, and can form in the collecting ducts and renal pelvis. • Causes include excess vitamin D, blockage of the urinary tract, or a complication of a urinary tract infection. • Can be avoided by drinking a lot of water.