BIOB32H3 Lecture Notes - Lecture 4: Nephron, Brainstem, Collecting Duct System
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BIOB32 Lecture 3: Body Fluid Regulation in Vertebrates
Three Environments: Physiological Challenges
• Vertebrates live in diverse habitats
• Terrestrial: land, dry, ion poor environment
• Freshwater: rivers, lakes, wet, ion poor environment
• Marine: ocean, wet, salty
Homeostasis of the Extracellular Fluids: Regulatio of its iteral ediu frees a aial fro its exteral eiroet; thus, aials
ca adapt to freshater ad deserts alike
• Animals are able to thrive in different environments by homeostasis of the extracellular fluids.
• Bernard emphasizes that the vast majority of cells that make up an organism are not exposed to the external environment but
instead; they are exposed to the internal medium called the interstitial fluid that serves as the environment for the cells. If animals
regulate interstitial fluid, properties of external environment are not relevant.
• Animals regulate interstitial fluid by regulating blood because the nature of this fluid is dependent on the nature of the blood.
• Osmolarity is the total solute concentration of a fluid
• If you put cells in a hypotonic solution (low osmotic pressure = low solute, diluted solution), you will see the cells swell. There are
lots of solutes inside the cells so if you place the cells in a dilute solution with a few solutes, the favourable osmotic gradient will
cause water to move from the fluid into the cells and causing the cells to swell.
• If you put the cell in a concentrated hypertonic solution, the osmotic gradient will pull water out of the cell.
• It is important to regulate osmolarity of interstitial fluid because that has an effect on the volume of cells and things like cell-cell
• Changes in cell volume that are induced by osmolarity of the surrounding environment can have catastrophic effects for
• E.g. neurons have to be close to each other to interact with each other. If the neurons shrivel up and pull away from each
other, this has a consequence on neuronal communication.
• When regulating the osmolarity of the interstitial fluid you have to regulate the osmolarity of the blood.
• Extracellular fluid osmolarity (of blood and interstitial fluid). There is a narrow range of EFO of these animals (200-350). This is the
range that animals regulate their interstitial fluid. The outliers are sharks and other marine animals. Most animals keep their EFO
regulated in this range and it is surprising bc a lot of factors can affect this range to not be maintained like:
• There are constantly salts that try to change the EFO. The food you eat has ions and salts that enter your blood and it will
push your blood plasma osmolarity and interstitial fluid osmolarity higher and this will have catastrophic affects on cellular
• Skin and lungs lose a lot of water. Every time you breathe you lose water that came from blood and goes out through your
• Water affects osmolarity of blood. More water dilutes blood.
• How do we keep osmolarity level constant for cell function?
1. Water consumption is a way to regulate. Drinking a lot of water will come into blood and dilutes it reduces its
osmolality. So to regulate we consume or do not consume water.
2. Kidney function: it takes ions and water out of your blood and determines how much ion and water needs to be put
back into your blood so that osmolarity of blood and interstitial fluid is appropriately kept in the EFO range.
Drinking Water: Terrestrial Vertebrates
• Mouth drinking
• Not all vertebrates drink water from their mouth
• Aphiias do’t drik uh fro its outh.
Drinking Water: Terrestrial Vertebrates: Lack of Mouth Drinking in Amphibians
• The ventral skin has a region that is different from other regions and this is called the pelvic patch. It has a special physiological role
where this is the region where they drink water.
• 20% of water they drink comes from their mouth and 80% comes from skin in this pelvic region.
• Water is polar ad a’t peetrate freel through the ski of the frog ad it a’t pass ell erae so the ells that ake up their
skins have aquaporin's that allow water to pass through skin cell membrane.
• The direction of water movement is determined by osmotic gradient. If a frog wants to drink water it can only drink freshwater in
lakes and streams (water that have few ions) bc if it drinks saltwater, it will further dehydrate bc there are so many ions in the water
so the osmolarity is so high that it will draw water out through aquaporin's.
• Dorsal skin has no aquaporins bc its dorsal skin is going to be constantly exposed to dry air, and if it has aquaporin it will release
water through evaporation from dorsal skin. The lack of aquaporins in dorsal skin is like a water conservation mechanism.
• Nao is original Na level. Na is Na level at a particular water loss.
• Another major source of water for most amphibians is their urinary bladder that can contain 500 ml of water and that’s the max
capacity of the urinary bladder and we don’t let it fill up that much. 500 ml represents 1 % of your body.
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