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