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