urinary system

• kidneys

  in retroperitoneal cavity surrounded by adipose tissue
• ureters

  in retroperitoneal cavity, allow urine to flow to bladder
• bladder

  in extraperitoneal space
• urethra

  in extraperitoneal space and allows urine to flow out of the body
• exocrine functions

  excretion of waste, water and electrolyte balance, blood pressure regulation, acid base balance
• endocrine functions

  release of renin, regulation of erythropoiesis, synthesis of vitamin D, gluconeogenesis
• metabolic wastes

  urea, uric acid, creatinine, and hormone metabolites
• urea

  from protein metabolism
• uric acid

  from nucleic acid metabolism
• hydrophilic drugs are easily excreted by the urinary system
• hydrophobic drugs are normally attached to proteins and require metabolism by the liver before excretion
• sodium is regulated at 150mmol
• potassium is regulated at 4.5mmol
• sodium regulates almost all excretory processes in the kidney
• blood pressure regulation steps

  sodium excretion, water output, vasoconstriction
• Kidneys regulate H+ excretion, HCO3- excretion, and synthesis of new HCO3-
• Kidneys produce erythropoietin
• erythropoietin is a peptide hormone produced by interstitial cells within the peritubular capillary bed of the renal cortex
• hypoxia leads to increased EPO production, stimulating erythropoiesis in bone marrow, increased RBC, oxygen level returned to normal
• kidneys are capable of producing a significant as much as 50% of the glucose our bodies need
• Capsule has 3 components: renal fascia, perirenal fat capsule, renal capsule
• Renal fascia: tough CT, outermost
• Perirenal fat capsule: anchors kidneys in place
• Renal capsule: has 3 regions (outer cortex, medulla, and renal pelvis)
• Hilum is concave part of bean shape where blood vessels and nerves enter and exit the kidney, also point of exit for the ureters that transport urine to the bladder
• Medulla consists of renal pyramids with spaces called renal columns sitting between them
• Outer cortex: granular due to nephrons
• Blood vessels pass through renal column to get to cortical region of the nephron where filtration occurs
• Renal pelvis: leads to the ureter on the outside of the kidney, and branches to the major calyces on the inside
• Kidneys receive about 20% of total cardiac output.
• Resting cardiac output of 5L/min translates to ~1L/min received by the kidneys
• Kidneys filter plasma, not whole blood (excluding cells and proteins).
• With a hematocrit of ~60%, 1L/min of blood flow equates to ~600mL of plasma entering the kidneys per minute
• Renal plasma flow is approximately ~600mL/min
• Glomerular filtration rate (GFR) is the rate at which filtrate is formed by nephrons from this 600mL of plasma.
• In a young, healthy kidney, GFR is ~125mL/min
• ~25% of plasma that enters the kidney each minute is filtered by nephrons
• GFR of 125mL/min equates to 180L of plasma filtered by nephrons each day
• With a plasma volume of ~3L in the average person, the entire plasma volume is filtered 60 times per day.
• Kidneys have an enormous capacity to regulate fluid and electrolyte levels in the body for homeostasis.