water balance and urine formation

how does urine form? general 3 step process

• glomerular filtration

• tubular reabsorption and secretion

• water reabsorption

glomerular filtration

• first step of urine formation

• water, salt, nutrients and waste molecules move from glomerulus to bowman’s capsule

• extreme pressure creates filtrate: liquid waste

• large macromolecules not pushed through

why is filtrate needed?

waste removal, without it we would become sick and die

renal medulla

middle, salty area since salt is being pumped out of loop of henle to ensure water is reabsorbed by body

tubular reabsorption and secretion: proximal tubule

• occurs in cortex

• reabsorb nutrients into circulatory system

• nutrients, water, salt, and bicarbonate reabsorbed

• hydrogen ions, some drugs and poisons secreted into proximal tubule

tubular reabsorption and secretion: loop of henle

• occurs mainly in medulla

• descending: passive transport of water

• ascending: active transport of salt

• both absorbed into circulatory system

tubular reabsorption and secretion: distal tubule

• occurs in cortex

• salt, water, bicarbonate absorbed by body

• potassium and hydrogen ions secreted into distal tubule

water reabsorption

• opportunity for body to reabsorb salt and water through osmosis

• increases concentration of filtrate → now urine

• environmental and what you consume: dehydration, hot temps

• collecting duct can change permeability regulated by ADH

• reabsorption of salt, water, urea

to maintain water balance, humans must consume how much fluids?

1.5 to 2 L daily

A  decrease  in  fluid  intake  by  as little as 1% of ____ will cause..

your body mass will cause thirst

a decrease in fluid of 5% of your body mass will cause

extreme pain and make you collapse

a decrease in fluid of 10% of your body mass will cause

death

ADH

• antidiuretic hormone

• release of ADH allows body to conserve water, producing more concentrated urine

how is ADH released?

• osmoreceptors in hypothalamus detect change in osmotic pressure

• osmotic pressure: high is dehydration, low is overhydration

• pituitary gland releases or prevents release of ADH into blood depending on current fluid amount

high blood osmotic pressure

• blood is too concentrated = dehydration

• osmoreceptors in hypothalamus detect change

• you feel thirsty and hypothalamus send signal to pituitary gland

• pituitary releases ADH

• ADH travels to kidney

• increases permeability of collecting duct, more water reabsorption

• drink water due to thirst

• lowers osmotic pressure

ADH not present

• 85% of water reabsorbed into body from proximal tubule and descending loop of Henle regardless of ADH presence

• Distal tubule and collecting duct cannot reabsorb since no ADH

• 15% of water is lost in urine

• Diluted, watery, pale urine

ADH present

• makes upper part of distal tubule and collecting duct permeable

• Water diffuses into peritubular capillaries

• High concentration of salt in interstitial fluid here

Interstitial fluid

watery fluid filling spaces between cells that delivers oxygen and nutrients from capillaries to cels and caries away waste

Low blood pressure and blood volume

• RAAS system

• dehydrated

• JGA detects low bp and releases renin

• Renin converts a protein in blood to angiotensin

• Angiotensin increases bp signals adrenal gland to secrete aldosterone

• Aldosterone carried in blood to kidneys

• Aldosterone increases sodium and water absorption

Urinalysis

• non invasive tests for kidney function

• Tests for kidney damage

• Diabetes mellitus

• Kidney stones

• Bacterial infections

• Pregnancy

• Dehydration

Acetone and ketones, albumin (protein), bilirubin, calcium, colour and clarity, glucose, pH, urea, Uris acid values in accepted healthy urine test

• Acetone and ketones, albumin (protein), bilirubin, glucose: 0

• Calcium: less than 150 mg/day

• Colour and clarity: pale yellow to light amber; transparent