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Lecture 4

BIOB32H3 Lecture Notes - Lecture 4: Extracellular Fluid, Ocean, Body Fluid

Biological Sciences
Course Code
Jason Brown

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Lecture 4: Comparative Physiology of Body Fluid Regulation in Vertebrates
Three Environments
Terrestrial, Freshwater, Marine
Three Different Physiological Challenges
o Terrestrial
Dry land
Inavailability of water
Difficulty of obtaining water humans have built infrastructure for water
Dryness of air
o Freshwater
Lakes, rivers, streams
Low ion content in the water
Almost pure water
o Marine
Ocean, seas
Large concentration of ions in the water (salty)
Homeostasis of the Extracellular Fluids (Claude Bernard)
“Regulation of its internal medium frees an animals from its external environment; thus,
animals can adapt to freshwater and deserts alike.”
Most cells in an animal’s body are not exposed to the environment
Cells are bathing in an extracellular fluid (interstitial fluid in vertebrates) which Bernard
referred to as the internal medium
o Regulate interstitial fluid composition to be ideal for cells
o Important because of the way animals regulate their structure
The structure of an animal cell is driven by the amount of fluid in them
Animal cell walls are dependent on the volume of water in the cell
Plant cell walls are a rigid structure
and maintain structural integrity
o Hypotonic water flows into cells and cell
o Hypertonic water flows out of cells and
they shrink
In neurons that need to interact, if the
cells pull away from each other they
lose their functionality since they can
no longer communicate
Want no net movement

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o Vast majority of vertebrates maintain osmolarity
between 200-350 milliosmol
o No net movement into or out of the cells at this
o Compare this to the environments where these
animals live:
Freshwater environment has very low
osmolarity, between 4-5 milliosmol
Far below vertebrate extracellular
Water wants to enter animals to dilute
their extracellular fluid
Marine environment has about 1000
Far above vertebrate extracellular fluid
Water is drawn out of animals to try to dilute the environment
Osmolarity of the ECF will also increase
Terrestrial environment also sucks water out due to its dryness and pushes
osmolarity up in the same way as a marine environment
Need to maintain a water balance
o Lose water via integumentary system (evaporation, sweating) and respiratory
Breathing in and out, lose water to environment
Fish gills, water goes into and out of body via the gills
o Gain water via digestive tract
Consuming water and absorbing it through intestine
Kidneys (focus of the lab)
Maintain body fluid osmolarity
Kidneys try to increase or decrease urine production to maintain water balance
o Losing a lot of water to environment and not consuming much, decrease urine
o Gaining a lot of water and not losing much by other avenues, increase urine
Increase osmolarity of urine when consuming too much salt
o When water loss is high and osmolarity of ECF increases, increase urine
Decrease osmolarity of urine when consuming too little salt
o Produce diluted urine when consuming a lot of water and losing very little by
respiration or skin
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