Chapter 24 Urinary System

Urinary Tract System includes positions in body, sections of the kidney, and nephrons ins the kidney.

Kidney

• The kidney functions to eliminate metabolic waste, regulate ion levels, regulate pH levels, regulate blood pressure, climate biological molecule elimination, forms calcitriol, produces and releases erythropoietin, and Gluconeogenesis.

• The renal medulla and renal cortex function the kidney tissue

• Order of blood supple to the kidneys

  1. renal artery
  2. segmental artery
  3. interlobar artery
  4. arcuate artery
  5. interlobular artery
  6. afferent arteriole
  7. glomerulus
  8. afferent arteriole
  9. peritubular capillaries or vasa recta
  10. interolubular vein
  11. arcuate vein
  12. interlobar vein
  13. renal vein

• the intercalated disks regulate urine and pH of blood

• each kidney has about million of nephrons.

  • cortical nephrons are in the renal cortex and the loops dips into the renal medulla
  • 85% of the nephrons are cortical
  • juxtamedullary nephrons contains the loop of Henle and goes into renal medulla and controls urine concentration by ADH (antidiuretic hormone)
  • 15% of the nephrons are juxtamedullary

• Each kidney is innervated by both divisions of autonomic nervous system

  • sympathetic nerves from T10-T12 inervate the kidney with the blood vessels of kidney and juxtaglomerular apparatus and decrease uring production
  • parasympathic nerves from CN X cause specific effects not known.

Types of Cells

• Type A cells eliminate Acid (H+)
• Type B cells eliminate Base (HCO3-)
• Principal cells respond to hormones aldosterone and ADH
• Granular cells function to synthesize, store, release renin, and contract when stretched.

Juxtaglomerular Apparatus

• juxtaglomerular apparatus regulates blood filtrate and systemic B.P.
  • filtrate is formed as it flow through the glomerulus
  • macula densa → detect NaCl fluid change → granular cells → release renin in response to low BP/ SNS stimulation)
• endothelium of juxtaglomerular apparatus is fenestrated which allows plasma and dissolved substances to be filtered however it restricts passage of large structure (for example erythrocytes).
• basement membrane is a porous middle layer that contains glycoprotein and proteoglycan molecules which restricts passage of large plasma proteins
• visceral layer is the outermost layer that has podocyte, pedicels, and filtration slits that restricts passage of most small proteins.
  • podocytes are specialized cells
  • pedicles are long processes
  • filtration slits are separated by thin spaces
• tubular secretion is the movement of solutes out of blood within peritubular and vases recta capillaries into tubular fluid by active transport where after those materials are moved selectively into tubules and are excreted.

Filtrate

• filtrate includes ==H2O==, ==C6H12O6==, ==A.A==., ==ions==, ==urea==, some ==hormones==, ==Vit. B==, ==Vit. C==, ==ketones==, very small ==protein== amounts

• net filtration pressure is the Glomerulus hydrostatic blood pressure. The opposing pressures include Osmotic blood pressure, fluid pressure in capsular space of renal corpuscle.

• Glomerular hydrostatic blood pressure (HPg) involves glomerular blood pressure pushing water and some solutes out of glomerulus into capsular space of renal corpuscle which is higher than BP of other systemic capillaries.

• Pressures opposing HPg involves OPg and HPc

  • Blood colloid osmotic pressure (OPg) is where osmotic pressure exerted by dissolved solutes opposes filtration and draws fluid back into glomerulus
  • Capsular hydrostatic pressure (HPc) is pressure in glomerular capsule due to filtrate which impedes movement of additional fluid.

• Net filtration pressure (NFP) is when filtration is greater than opposing pressure

  • ==HPg - (OPg + HPc) =NFP==

• Glomerular filtration rate (GFR) is the rate at which filtrate volume (per unit of time) is formed.

• Increase in NFP increases GFR, solutes, h2o, substance in urine, and decreases

• Regulation of GFR is tightly regulated and helps kidney control urine production based on physiologic conditions also known as hydration status.

Renal Autoregulation

• intrinsic controls: intrinsic ability of kidney to maintain constant blood pressure and GFR. Maintains in spite of changes in systemic arterial pressure.
  • renal auto regulation functions by the myogenic response and tubuloglomerular feedback mechanism.
• myogenic response is the contraction of smooth muscle of afferent arteriole wall with decrease blood pressure and less stretch of smooth muscle in arteriole that causes smooth muscle cells to relax and vessels to dilate which allows more blood into glomerulus.

Clinical Views

• Glucosuria is the excretion of glucose in urine where plasma glucose levels are above 300mg/dL.
  • glucose acts as an osmotic diuretic that pulls water into tubular fluid and causes loss of fluid in urine which is a classic symptom of diabetes along with frequent urination and thirst.
• Renal Calculi is also known as kidney stones which are formed from crystalline minerals building up in the kidneys.
  • kidney stones are a result of inadequate fluid intake, reduced urinary flow, frequent urinary tract infections, abnormal chemical or minerals levels in urine.
  • small kidney stones are asymptomatic
  • large kidney stones are obstructed in kidney, renal pelvis, ureter, with sever pain in loin-to-groing region.
  • most kidney stones pass on their own if less than 4mm in diameter others may require lithotripsy or ureteroscopy.