Class 8-2: Exchange with the Environment

what are the main ideas of exchange with the environment?

• exchange = physical transfer across a surface

• homeostasis & feedback

how does the small intestine maximize rate of transfer of nutrients (across a surface) into the body?

• enabling a continual gradient = amt on one side - amt on other side

• between two things close together = distance across

• over a large area = surface area

rate of transfer equation (ficks law)

define homeostasis

• stability in the chemical & physical conditions within an organisms cells, tissues, and organs

• regulated through negative feedback loops returning to a set point

what are examples of things that organisms regulate?

• temp and blood pH

• salt and water

• blood glucose and calcium levels

• blood pressure and hormones

why in general do organisms regulate anything?

• to work within specific set of physical conditions where life works

what is thermoregulation?

• an ectotherm coiled around an endotherm

endotherms vs ectotherms

• endotherms: animals create their own heat from metabolism (mammals & birds)

• ectotherms: animals receive heat from external sources (reptiles & fish)

what happens when mammals get hot?

• start losing H2O & salt - kidneys respond to loss and sensory makes thirst

• increase in metabolism therefore heat - pants, more blood flow, and heart rate inc

what happens when mammals are cold?

• shiver & restricts blood flow to keep heat

• circulatory system arranged in coutercurrent flow to minimize heat loss

concurrent vs countercurrent flow

• concurrent: fluid flow in the same direction, less efficient large gradient disappears as fluids move

• countercurrent: fluid flow in opposite directions, highly efficient maintain small exchange gradient along entire length

why don’t we look at osmotic stress?

• they have to be adapted to be isotonic to their environment

• diffusion & osmosis don’t affect their water and salt balance

what is the physiological challenge & response to osmotic stress in water in a hypertonic environment? (salt water)

• fish lose water by osmosis & gain salts by passive transport

• drink water & pump ions out

what is the physiological challenge & response to osmotic stress in water in a hypotonic environment? (fresh water)

• gain water & lose salts

• excrete water & bring in extra electrolytes

what are physiological solutions?

• system of parts & processes that interact to produce a specific effect & solve the challenge in its environment

summarize filtration in the renal corpuscle

• blood enters & filtration occurs as it passes through

• pre-urine ie. filtrate

what is filtrate?

• water & small solutes

• all nutrients are reabsorbed (NaCl & water filtered by renal corpuscle)

descending vs ascending limbs

• descending: water reabsorbed (aquaporins) using salt gradient

• ascending: Na & Cl reabsorbed using and making salt gradient

what’s the role of the antidiuretic hormone (ADH)?

• production of concentrated or dilute urine

• part of negative feedback loop returning system to a set point