Urinary Class Notes

The KIDNEYS regulate:

• Blood composition

• Blood pressure and volume

• Blood pH

• Blood calcium concentration

• RBC concentration

To use protiens, you need to break of the AMINE group of a protien (amino acid)

• NH2 + H2O —> NH3 + OH-

You need to pee to get RID of ammonia, which is poisonous

• You pee out ammonia + water (from blood volume) —> this is how blood volume (AND blood pressure) is regulated

• You can also pee hydrogen ions out → helps with blood acidity

Urinary system parts:

• Kidney:

  • Makes pee

  • Lots of blood, at high pressure

  • Recieve blood from renal artery, from aorta

  • Behind the peritoneal cavity (retroperitoneal)

    • Peritoneal cavity = all abdominal organs

    • Kidney surgeries are done from back

  • Protected by floating ribs

  • Right kidney is lower than left

  • Makes 6 kidneys → break down as you are grown

    • Pronephros, mesonephros, metanephros!, next nephro (right side) cannot arise as high because of liver

  • Regions:

    • Cortex (outside)

    • Medulla (inside)

      • Pyramids → where urine is made; called basin

      • Drips into pelvis → travels to ureter

    • Calyces/Calyx - Funnel

• Ureter:

  • Kidney to bladder

  • Most common abnormality → extra ureter, which may empty in a way that is not easily controllable

• Urinary bladder:

  • Stores pee

• Urethra:

  • Bladder to exterior

The Nephron: Functional unit of the kidney

• About 1 million nephrons per kidney

• The renal corpuscle

  • Bowman’s capsule

    • Filled with filtrate, NOT urine

  • Glomerulus

    • Fenestrated capillaries

    • Filters ANYTHING small enough, including good stuff

    • Podocytes: Cells which can restrict the fenestrations, reducing loss of water

• The renal tubules

  • Proximal convoluted tubule (PLT)

    • To bowman’s capsule

    • Gets the goodstuff back

  • Loop of henli

    • Goes into medulla (everything else is in cortex)

    • Descending is thinner than ascending

  • Distal convoluted tubule

    • To bowman’s capsule

    • Gets the goodstuff back

• Arterioles

  • Afferent comes in, efferent leaves

  • Afferent is bigger —> PRESSURE

  • Fenestrated → Allows things to leave

• Collecting duct

  • Collects all urine

• Peritubular capillaries: Efferent arteriole wraps around tubules and collects back the good stuff

3 steps of making urine:

• Filtration

• Reabsorption

• Secretion

Filtration: Bowman’s capsule

• Substances forced through glomerular fenestrations

• Using PRESSURE!

  • NFP (Net Filtration Pressure) → NFP = bp-op-cp → ~ 10mmHg

    • bp = blood pressure (+ pressure ~ 55)

      • Very high from aorta, but split between millions of capilarries

    • op = osmotic pressure (- pressure ~ 55)

      • Working against filtration

    • cp = capsular pressure (- pressure ~ 15)

      • time it takes to get filtrate to leave

• How fast you can pee, how fast you use NFP = Glomerular filtration rate (GFR)

  • What happens if we CHANGE the variables?

    • Increased bp → stress→ Less urine, poison body

    • Decrease op → starvation → More urine, dehydration

    • Increase cp →kidney stone → block urine, poison body

      • Kidney stone blocks urine from leaving

Reabsorption: Renal tubules

• Reclaiming the good stuff back into the blood stream

• Uses ATP, diffusion and osmosis

  • Water always follows salt

  • You get back ~99% of what is released:

    • PCT - 65%

      • Good at absorbing because of microvilli

      • Increases surface area

      • Has mitochondria → K/Na pump

    • Loop of Hemle - 15%

    • DCT and Collecting Duct - 19%

• Howver, it reclaims both good and bad stuff.

Secretion: Renal tubules

• Mobing large, unfiltered and reabsorbed toxins back into the renal tubules.

• Reverse reapsorption

• Elimanates nitrogenous wastes: reabsorped urea and uric acid

• Rids the body of excess K+

• Controls pH

• Allows molecules too big to be filtered to leave the body (penecilin, example)

Composition of urine:

• 95% water

• 5% solids

  • Mostly urea, uric acid, and creatinine (waste product of creatine)

• pH ~ 6 (May be as high as 8)

• Slightly odorous

• Slightly colored

  • Pigment called urochrome

Ureters: Slender, muscular tubes conveying urine into the bladder via peristalsis (smooth muscle contractions)

• Becomes smaller toward the bladder

  • ~ 6-8 mm diameter proximal

  • ~ 2.2-1.8 mm diameter distal

• Empties in the back wall, underneath the bladder (like a J-hook)

Urinary bladder: Storage for urine

• Trigone: Where ureters enter, and urethra exits (triangular region)

  • Where most bacterial infectiosn occur; bacteria festers here

  • UTI - Urinary tract infection

    • Opened fenestrations with swelling

    • Glomerulonephritis - Inflammation of glomerulus

• Detrusor muscle

  • Aids in micturition - When stretched, it’s reflex is to contract

  • Urges you to pee

  • Only when you have 1/3 of bladder full

Urethra: Drains urine from the bladder

• ~ 8-9mm diameter

• External urethral sphincter

  • Voluntary

• Internal urethral sphincter

  • Involuntary

Urine does not have bacteria - it is ASEPTIC

Only time there will be bacteria is if bacteria comes from the outside

Regulating Blood Pressure

DCT splits the afferent and efferent arteriole

Around the arterioles are juxtaglomerular cells → sense pressure/stretch

In DCT, where afferent and efferent split → Sensitive to chemicals, specificaly chlorine → chemoreceptors → macula densa

more pressure → arterioles stretch → GFR (Glomelular filtration rate - how fast you make urine) increases, less reabsorption

• Myogenic mechanism is triggered causing the smooth muscle of the arterioles to contract

• Too little Na+ and Cl- is reclaimed stimulating the macula densa cells to inhibit nitric oxide from the juxtaglomular apparatus causing arterioles to constrict

  • nitric oxide = vasodialator

Chronic hypertension!

• Can cause damage to renal vessels → shred inside of vessels

• Nephrons dont recieve adequate oxygen

• Less blood is filtered

• Fluid is retained → lots of edema in tissues

• Blood pressure rises → POSITIVE FEEDBACK

Low blood pressure situations:

• Juxtaglomerular cells do not stretch (afferent arteriole does not fill as much)

• Blood flow slows in glomerulus

  • GFR too slow, too much reabsorption (including toxins

• Solution: Body releases renin (since they cannot stretch)

  • It is a catalyst to convert angiotensinogen into angiotensin I

    • Inactive, intermediary product

  • Angiotensin converting enzyme from lungs will turn into angiotensin II

    • Angiotensin II is most powerful vasocnstrictor

    • Increases blood pressure

  • Give ACE INHIBITORS

• Brain will release antidiuretic hormone, which increases the permeability of the renal tubules to water → reclaims water, less pee

• Adrenal galnds release aldosterone → reabsorb more sodium