Post on 24-Feb-2016
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CHAPTER 15
Urinary System
Functions
Filter bloodDispose of wastes and excess ionsRegulate blood volume and blood pressureMaintain chemical make up (solute balance)
of bloodRegulate acid/base balance of bloodStimulate formation of erythrocytesReservoir for urine
Anatomy Review
Blood filtered within nephronFlow of blood:
Filtrate travels from nephron to collecting ducts and from collecting ducts to minor calyx, major calyx, and into ureters
Nephron
Functional unit of the kidneyFilters blood, forming filtrate which
eventually becomes urineTwo types: cortical nephron (cortex),
juxtamedullary nephron (extends into medulla
Nephron
Glomerulus –capillary knotMaintains Bowman’s Capsule –
collects filtrate Renal tubules: proximal
convoluted tubule, loop of Henle, distal convoluted tubule
Distal convoluted tubule of the nephron empties into the collecting duct
Urine Formation
Three main processes Glomerular filtration Tubular reabsorption Tubular secretion
As filtrate moves through the nephron water and solutes are exchanged between the tubules of the nephron and capillary beds
Glomerular Filtration
Dependent upon blood pressure Too high and blood loses solutes and large proteins
(albumin) Too low and blood is not adequately filtered
Podocytes wrap around glomerular capillaries forming filtration slits
Tubular Reabsorption
Cells lining tubules take up (reabsorb) solutes and water from filtrate, returning them to blood Urea, uric acid, creatinine, are poorly reabsorbed PCT: NaCl, HCO3
-, H2O, Glucose, Amino Acids Loop of Henle: H2O, NaCl DCT: NaCl
See Red and Blue Arrows
Tubular Secretion
Cells lining tubules secrete (remove from blood) solutes, drugs, poisons, ion, and place them into filtrate PCT: drugs, poisons, H+
Loop of Henle: none DCT: K+ and drugs
Renin-Angiotension cause secretion of aldosterone from the adrenal medulla Aldosterone causes the reabsorption of Na+ which
causes reabsorption of H2O See green arrows
Collecting Ducts
Depending on presence or absence of hormones Reabsorb water and Urea Secrete water and potassium
Antidiuretic Hormone (ADH) secreted from posterior pituitary causes aquaporins to be inserted in the collecting duct to facillitate reabsorption of water
Fluid, Electrolyte, and Acid Base Balance
Water is on of the most important molecules: transport solutes in blood Universal solvent Proper protein folding
Water is found in the cytosol, extracellular fluid, blood Solute concentrations of each affect flow or
accumulation of water…..water follows its best friend sodium
Water Regulation
Thirst mechanism –driving force for water intake
Response to rising solute levels in blood Solute levels are detected by osmoreceptors found in
the hypothalamus High solute content of blood activates the thirst
center in the hypothalamus triggering the desire to drink water
ADH causes insertion of aquaporins in collecting duct to reabsorb water
Alcohol inhibits ADH
Electrolyte Balance
The movement of water is coupled to electrolytes
Aldosterone is released from the adrenal gland in response to low Na+ levels in blood Na+ is reabsorbed in the presence of aldosterone Reabsorption of Na+ causes the secretion of other ions Water follows its best friend sodium, aldosterone
indirectly regulates water balance of blood and thus blood volume and pressure
Electrolyte Balance
Aldosterone release is controlled by the Juxtaglomerular cells (JG cells) within the kidney
JG cells secrete renin in response to low blood pressure…they are baroreceptors!
Renin converts to angiotension II and triggers the adrenal cortex to secrete aldosterone
Electrolyte Balance
Acid-Base Balance
Respiratory, cardiovascular and urinary systems all work in conjunction of maintain the acid-base balance of blood Respiratory off loads CO2 from tissues preventing acid
buildup within extracellular fluid Cardiovascular system binds H+ ions to hemeglobin
and converts CO2 to bicarbonate (HCO3-) to prevent acid buildup within blood
Kidneys remove HCO3- from blood by secreting it in urine or reabsorbing and recycling HCO3- when needed
Homeostatic Imbalances
Hydronephrosis –kidney damage due to improper drainage of urine through ureters
Renal calculi –uric acid or salt crystrals from highly concentrated urine
Urethritis – inflamed urethraCystitis –inflamed bladderPyelitis –inflamed kidneyIncontenence –loss of voluntary control of bladder sphinctersDiabetes insipidus –inability of kidneys to conserve waterPolyuria –excretion of large amounts of waterGlomerulonephritis –build up of antibody-antigen complexes
within the glomerulus