Human physiology exam 4

urinary system

functions of kidneys

• regulation of extracellular fluid volume and blood pressure (volume effects pressure; partner CU)

• regulation of osmolarity (ex. thirst; reflex)

• maintenance of ion balance (ex. Na+)

• homeostasis regulation of pH (exchange of H+ and bicarb; bigger influence-lungs)

• excretion of wastes (color, clarity, smell, taste)

• production of hormones (EPO-make rbc, renin-blood pressure low;kidney, convert vit D-affects calcium uptake)

Most important function of the kidney

• salt and water balance

• not waste removal (myth)

kidneys located

retroperitoneally at the level of the lower ribs

Nephrons

• modify fluid composition functional inot of the kidney

• 80% in cortex (cortical nephron)

• 20% in extend into medulla (juxtamendullary nephron)

• some dip deep into the medulla

renal corpuscle

glomerulus (capillaries) + bowman’s capsule

• the epithelium around glomerular capillaries is modified into podocytes.

• alter blood flow by contraction

• secrete cytokines

• podocyte foot processes surround each capillary, leaving slits through which filtration takes place.

one nephron

has two arterioles ( afferent and efferent)

two sets of capillaries (high-pressure glomerulus for filtration and peritubular capillaries (vasa recta) for reabsorption)

juxtamedullary nephron with vasa recta

• increase flow GFR → renin secretion → aff constriction decrease GFR

kidney function

kidney filatration

• blood to lumen

• pass hydrophilic/ small

• 90% of fluid is filtered → filtrate (not including bigger particles) → eliminated

• Hypo

kidney reabsorption

move substances from lumen → blood

kidney secretion

• blood to lumen

• same direction as filtration

• more selective; use membrane proteins

kidney excretion

• lumen to external environment

• excretion leaves the body as urine

changes in filtrate volume and osmolarity along the nephron

• eventually ~ 90% reabsorbed

Urinary excretion of substance

amount filtered- positive

amount absorbed- negative

amount secreted- positive

= amount of solute excreted

The filtration fraction

• if more than 1/5 was filtered, the blood would be too viscous for normal flow

• filtrate is like plasma minus proteins what is left? water and dissolved solute

Three filtration barrier

1. glomerulus capillary endo

2. basal lamina

3. epithelium of capsule

• fenestrated capillaries with large pores

• filtered substances pass through endothelial pores and filtration slits.

• water soluble, hydrophobic, small

forces that influence filtration

• hydrostatic pressure(blood pressure); forces fluid through endothelium

• colloid osmotic pressure; higher in capillaries vs bowman

• fluid pressure created by fluid in bowman’s capsule; opposes fluid movement into capsule

glumerular filtration

• filration pressure in the renal corpuscle depends on hydrostatic pressure, and is opposed by colloid osmotic pressure and capsule fluid pressure.

• if blood pressure is high GFR will increase temporarily

GFR

a test that measures how well your kidneys filter waste and excess water from your blood

filtration autoregulation

• autoregulation of glomerular filtration rate takes place over a wide range of blood pressues.

• autoregulation maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mm Hg.

• if not reabsorbed no plasma in 24 mins

filtration influenced by

• net filtration

• filtration coefficient

• surface area

• permeability

• not influenced as much by pressure change

increased resistance in afferent arteriole

• restrict less to go out to filtration

• caused by losing too much fluid, dehydrated, or low BP

• decreased RBF

• increase blood flow to other organs

• Decreased GFR

• Decreased capillary blood pressure

increased resistance in efferent arteriole

• caused by high BP

• decreased RBF

• increased Ph

• increased GFR

GFR regulation

myogenic response (due top Bp) (ex. release fluid, vasoconstrict/ dialate)

• similar to auto-regulation in other systemic arterioles (stretch/ pressure sensitive)

Tubuloglomerular feedback

• paracrine control (macula densa)- changes in fluid flow through loop of Henle

Hormones and autonomic neurons (ex. angiontension)

• by changing resistance in arterioles (afferent/ efferent)

• by altering the filtration coefficient

chronic high bp can be damage filtration barrier

tubuloglomerular feedback

reabsorption

• principle governing the tubular reabsorption of solutes and water