Urinary System

• The kidneys regulate blood volume and composition, help regulate blood pressure, synthesize glucose, release erythropoietin, participate in vitamin D synthesis, and excrete wastes by forming urine.
• The ureters transport urine from the kidneys to the urinary bladder.
• The urinary bladder stores urine.
• The urethra discharges urine from the body.
• There are two types of acidosis: respiratory acidosis and metabolic acidosis.
• Acidosis occurs when pH of blood falls below 7.35.
• More H+ is secreted into urine when pH is decreasing and less H+ is secreted into urine when pH is increasing.
• Alkalosis occurs when pH of blood increases above 7.45.
• Kidneys secrete H+ into urine and directly regulate pH of body fluids.
• The kidneys are a major organ of the urinary system, bean-shaped and weigh 5 oz (bar of soap or size of fist), located between the 12th thoracic and 3rd lumbar vertebra, retroperitoneal and partially protected by the eleventh and twelfth pairs of ribs.
• The kidneys regulate blood ionic composition, including sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), chloride ions (Cl-), and phosphate ions (HPO42-).
• The kidneys regulate blood pH by secreting H+ and reabsorbing HCO3-.
• The kidneys regulate blood volume through the RAAS system.
• The kidneys regulate blood pressure through the RAAS system.
• The kidneys maintain blood osmolarity through water and electrolyte reabsorption.
• The kidneys produce hormones such as Vitamin D and Erythropoietin.
• The kidneys regulate blood glucose level through gluconeogenesis and if glucose exceeds the renal threshold (160 – 180 mg/dL), it will begin to appear in the urine.
• The kidneys excrete wastes and foreign substances that have no useful function in the body, such as ammonia, urea, bilirubin in the form of urobilin, creatinine, uric acid.
• The kidneys have an external anatomy, bean-shaped and weigh 5 oz (bar of soap or size of fist), located between the 12th thoracic and 3rd lumbar vertebra, retroperitoneal and partially protected by the eleventh and twelfth pairs of ribs.
• The kidneys have an internal anatomy consisting of the renal cortex, which is superficial and light red, and the renal medulla, which is deep and darker reddish-brown.
• The filtration membrane is leaky due to fenestrations (holes), containing mesangial cells, which are contractile cells that help regulate filtration.
• The collecting duct empties into calyces and carries fluid from the cortex through the medulla.
• Glomerular Filtrate is the fluid that passes across the filtration membrane.
• Any change in the three pressures (Glomerular Hydrostatic Pressure, Capsular Hydrostatic Pressure, and Blood Colloid Osmotic Pressure) will affect GFR.
• The distal tubule is a structure between the Loop of Henle and the collecting duct.
• A decrease in oncotic pressure results in fluids escaping the capillaries, increased interstitial fluid, and EDEMA.
• The three basic processes of the nephron are: Glomerular filtration, Tubular Reabsorption, and Tubular Secretion.
• The Loop of Henle contains both descending and ascending loops, where water and solutes pass through thin walls by diffusion.
• Albumin is the primary contributor of oncotic pressure, holding the fluids in the capillaries.
• The final part of the ascending loop of Henle comes in contact with the afferent arteriole, forming a macula densa, a cluster of columnar tubular cells of the loop of Henle.
• Glomerular Filtration Rate (GFR) is the rate of filtration of the glomerulus, too high means substances to be reabsorbed are not reabsorbed, too low means nearly all filtrate may be reabsorbed and some waste products are not excreted.
• The proximal tubule is where filtrate passes first.
• The basal lamina (basement membrane) is acellular and contains collagen, preventing negatively charged particles from being filtered.
• Juxtaglomerular cells are modified smooth muscle cells that regulate blood pressure within the kidneys.
• The filtration membrane includes glomerular capillaries, podocytes, and the basement membrane, filtering water and small solutes but not plasma proteins.
• Renal Tubule and Collecting Ducts contain simple cuboidal epithelial cells with a prominent brush border resembling intestine, increasing surface area for absorption and secretion.
• The kidneys consist of 2 kidneys, 2 ureters, 1 urinary bladder, and 1 urethra.
• Filtration stops when hydrostatic pressure drops to 45.
• Tubular Reabsorption and Tubular Secretion involve the reabsorption of essential substances such as water and solutes, which are normally 99% reabsorbed by the proximal convoluted tubule.
• Renal Autoregulation involves two mechanisms: Myogenic mechanism and Tubuloglomerular Feedback.