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