Lecture 26/Osmoregulation

1 2 3 4 5 6

Q. How do we gain water?
- by drinking fluids, eating water-containing foods, as a product of metabolism. Plants combined CO₂and H₂O to make carbohydrates, when we break them down, we get H₂O as well as CO₂.

The breakdown of

1 g glucose[!]0.6 ml H₂O 1 g protein[!]0.3 ml H₂O 1 g fat[!]1.1 ml H₂O

Q. How do we lose water?
- evaporation from skin and moist surface (breathing), eliminated in feces and urine. The amount of water lost in urine can vary somewhat, but at least some is required to remove wastes (500 ml/day for humans).

Look at Figure 44.13 and compare the water balance of humans and kangaroo rats.

B. Transport epithelium
The problem of movingwater usually comes down to a problem of moving solutes; move the salts and the water will follow. This requires a transport system to move the ions and a barrierto prevent them from diffusing back. These functions are performed by a transport epithelium. As you should remember, an epithelium is a layer of cells connected by tight junctions which forms a barrier. Things can only move past the barrier by moving through the cells themselves.

Q. What plant cells in the root does this remind you of?
-endodermis

Movement of solutes across the barrier is governed by the ion channels and transport proteins of the cells.

1. Chloride cells in fish gills44.11 Fish face very different challenges depending on whether they live in salt water or fresh water.

a. Marine
Marine fishneed to take in waterby drinking sea water. They dispose of the


		Q. How do we gain water? - by drinking fluids, eating water-containing foods, as a product of metabolism. Plants combined CO₂and H₂O to make carbohydrates, when we break them down, we get H₂O as well as CO₂.
		The breakdown of		1 g glucose[!]0.6 ml H₂O 1 g protein[!]0.3 ml H₂O 1 g fat[!]1.1 ml H₂O
		Q. How do we lose water? - evaporation from skin and moist surface (breathing), eliminated in feces and urine. The amount of water lost in urine can vary somewhat, but at least some is required to remove wastes (500 ml/day for humans). Look at Figure 44.13 and compare the water balance of humans and kangaroo rats. B. Transport epithelium The problem of movingwater usually comes down to a problem of moving solutes; move the salts and the water will follow. This requires a transport system to move the ions and a barrierto prevent them from diffusing back. These functions are performed by a transport epithelium. As you should remember, an epithelium is a layer of cells connected by tight junctions which forms a barrier. Things can only move past the barrier by moving through the cells themselves. Q. What plant cells in the root does this remind you of? -endodermis Movement of solutes across the barrier is governed by the ion channels and transport proteins of the cells. 1. Chloride cells in fish gills44.11 Fish face very different challenges depending on whether they live in salt water or fresh water. a. Marine Marine fishneed to take in waterby drinking sea water. They dispose of the