Urinary System

functions:

  • remove toxic metabolic waste (excretion)

  • regulate water (volume and blood pressure)

  • assists in rbc production

  • regulate salt and ph levels

waste excretion

  • excretes wastes present in bloodstream:   * metabolic wastes   * excess water   * drugs   * hormones   * excess salt

structures:

  • kidneys (2)
  • ureters (2)
  • urinary bladder
  • urethra

kidneys

  • one on each side of the spine against the posterior abdominal wall
  • filter the bloodstream to remove wastes as urine   * blood vessels enter and ureters leave, through the hilum

kidney: interior

  • renal cortex: site of urine production   * where most of the nephron is located   * outer cortex regions has extensions (renal columns) that divides inner regions into renal pyramids
  • renal medulla: collects urine, moves more interior (some of nephron located here)   * the pyramids form the medulla

    →tip of pyramid called renal papilla - collect urine and sends it into:     * minor calyx, which join and form     * major calyx

  • renal pelvis: moves urine from kidney to ureters   * the major calyx converge to form the pelvis   * the pelvis continues as the ureter to move urine to the urinary bladder

pathway of urine:

  • forming:   * renal cortex
  • collecting:   * minor calyx   * major calyx   * renal pelvis   * ureter

renal circulation

  • blood enters the kidney through the renal artery
  • artery eventually branches into capillaries   * this is where filtration happens (using the nephron)   * filtered blood then leaves via renal vein

nephrons: filtration unites of the kidneys

  • approx. 1 million of them located in kidney
  • mostly located in the cortex (dips into medulla)
  • filtration involves:   * glomerular filtration   * tubular reabsorption and secretion

glomerular structure

  • afferent arteriole

            - blood to glomerular capillaries

renal corpsucle

  • glomerulus   * blood capillaries that have entered kidney
  • efferent arteriole   * blood from glomerular capillaries
  • glomerular capsule (bowman’s capsule)   * part of kidney that surrounds glomerulus   * made of epithelial cells

glomerular filtration

  • filtration form gromerulus into bowman’s capsule   * water, waste (urea), ions, glucose, amino acids can pass through   * large blood proteins (e.g albumin) and RBCs cannot
  • everything filtered into bowman’s capsule travels further into nephron

tubular reabsorption/secretion

  • filtrate leaves glomerulus and enters renal tubules
  • 4 region in order of flow:   * proximal convoluted tubules   * loop of henle   * distal convoluted tubule   * collecting duct

proximal convoluted tubule: most of reabsorption/secretion

  • tubules reabsorb anything useful back into the bloodstream   * ex. water, glucose, amino acids, ions
  • anything to be excreted in urine is secreted from capillaries to tubule   * ex. urea, acids, ions

loop of henle: filtrate is concentrated here

  • more water reabsorbed back into the bloodstream
  • additional NaCl is also reabsorbed

distal convoluted tubules: fine tuning of reabsorption/secretion occurs here

  • some additional water and ions reabsorbed back into the bloodstream
  • some additional ions are secreted from capillaries to tubules   * especially h+ and k+

collecting duct: concentrated filtrate collected here

  • continues to reabsorb water back into the bloodstream to further concentrate urine
  • last section, collects urine (i.e waste from the bloodstream)
  • merges with other collecting ducts to drain urine

hormonal influence

  • hormones can influence water reabsorption   * aldosterone

    → causes more water to be reabsorbed from distal convoluted tubule

    → reabsorbs sodium and water

    →secretes potassium in water   * ADH

    → causes more water to be reabsorbed from collecting duct

    →reabsorbs water   * PTH

    →reabsorbs calcium

NEPHRON

  • bowman’s capsule: filters capillaries
  • proximal convoluted tubules: first reabsorbs and secretes into surrounding blood capillaries
  • loop of henle: concentrates filtrate ; dips into medulla
  • distal convoluted tubule: final part of nephron for reabsorption and secretion
  • collecting ducts: receives filtrate from tubules (waste and ions to be excreted)

                       → merges with other collecting ducts to drain into minor calyx - major calyx - renal pelvis

BLOOD

  • afferent arterioles: brings blood towards capillaries
  • glomerulus: capillaries where blood gets filtered (into bowman’s capsule)
  • efferent arteriole: after blood filtered in glomerulus it leaves and becomes part of capillary network
  • network of capillaries: surround renal tubules and is where water and solutes are reabsorbed into or secreted out of
  • renal veins: filtered blood leaves kidneys through the veins

\ kidney function

  • filters many substance out of blood - glomerular filtration
  • gets rid of things it didnt the first time - tubular secretion
  • puts back in what it still needs - tubular reabsorption
  • sends all the waste to the bladder - ureters

regulation of glomerular filtration rate

  • glomerular filtration rate should be constant
  • if flow is too high, the body will lose excessive water and nutrients
  • if flow is too low, tubules may absorb reabsorb toxins
  • the renin-angiostensin-aldosterone system is key to maintaining blood pressure and steady glomerular filtration

renin-angiotensin-aldosterone system

  • afferent arterioles detect a decrease in blood flow (low bp): release the hormone renin
  • renin converts plasma protein to angiotensin I in liver
  • coverted to angiostensin II in lungs
  • causes adrenal glands to release aldosterone
  • causes increased water reabsorption in tubules= increased bp

urine composition

  • 95% water; 5% dissolves substances
  • reveals information about health of kidneys and other organs
  • colour, odour and pH of urine can all indicate health issues
  • the contents of urine can also indicate problems:   * RBCs, hemoglobin, albumin and the bile pigments are not normally found in urine

ureters

  • move urine from kidneys to bladder

urinary bladder

  • muscular sac that stores urine
  • sphincters control release of urine

urethra

  • small tube that carries urine from bladder to outside of body

urinary bladder in depth

  • mucous layer: traps pathogens
  • internal urethral sphincter: involuntary control of urine leaving bladder
  • external urinary sphincter: voluntary control of urine leaving bladder
  • smooth muscle: contracts to expel urine

urination:

  • stretch receptors in bladder send impulses to spinal cord
  • spinal cord sends motor impulses to internal sphincters of bladder   * involuntary release urine, unless..
  • pons and cerebrum in brain may override impulses (also receive signal from bladder)
  • brain sends signals to contract or relax external sphincters   * voluntary release of urine

urethra

  • urethra varies between biological females and males
  • females: short 3cm
  • males: long 20cm; dual role in production

\