Part 1: Blood Osmotic Pressure

Water Balance

UrineDrinkDrink

FoodEvaporation

Water Input Water Output

Feces

Urine

Sweat

Blood Osmotic PressureTo maintain proper water balance, body must regulate urine outputWater intake high - more urine produced

“Balance” achieved through interaction of nervous and endocrine systems

Water intake low - less urine produced

Review of Osmosis

cytoplasm

Osmosis - movement of water through a semi-permeable membrane,

from area of low solute concentration to area of

high solute concentration

Homeostasis:Increase inblood osmotic pressure(e.g. sweating, dehydration)

Osmoreceptors locatedin hypothalamus detectchanges in osmotic pressure Nerve message sent to

pituitary glandAllows increased water absorption

Release of ADHPituitary gland stores and releases ADH into blood

Water reabsorption prevents osmotic pressure of body fluids from increasing any further

High

Cells of hypothalamus shrink:Behavioral response:

Drinking lowers osmotic pressure of blood

Blood Osmotic Pressure and Blood Volume

Sensation of thirst

As osmoreceptors return to normal size, ADH production stops, and thirst subsidesNegative feedback system

Shrinking of osmoreceptors also leads to sensation of thirstDrinking water reduces osmotic pressure of blood

Osmoreceptors in hypothalamus can detect changes in osmotic pressure (“saltiness”) of bloodHigh blood osmotic pressure makes osmoreceptors shrink, causing them to send a nerve impulse to pituitary glandPituitary gland responds by secreting antidiuretic hormone (ADH)ADH travels through bloodstream to kidneys where it causes proximal tubule to reabsorb more waterCauses body to retain water by making urine more concentrated

Blood Osmotic Pressure