Bio 104 5/15/96

Toxins

ammonia is a byproduct of nitrogen and protein metabolism: it is very toxic and needs to be flushed out with a lot of water.
urea is less toxic: enzymes in the liver detoxify it and this saves water.

Three ways of eliminating toxins from the body:

flushing
detoxification
insolubilization

Osmoconformers: Sharks retain urea in their blood, which is isotonic with their environment.

Differences between fresh water and marine water fish:

Fresh water teleost are hypertonic; they drink water and excrete copious amounts of water.
Marine teleost drink water and excrete salt through channels to get rid of salt and have sparse urine.

Sharks

isotonic
retain urea and have dilute urine
water balance and excretion coupled together

Humans

We have an excretory system for:
1. water balance
2. elimination of waste
Kidneys process blood and get rid of molecules of toxins. It's basically a filter.

Mechanics of filtration

cardiac blood output approx. 5000 ml per min.
renal blood flow approx. 1000 ml per min.
- renal fraction: 20% of total blood through kidneys per minute
entire blood goes through kidneys in 5 min.
- The renal artery divides into arterioles which end up as the nephrons of the kidneys, which are the functional unit of the kidneys. See figure 42.12
Structure of the human kidney. Figure 42.12
divided into cortex and medulla: in the medulla is where the loop of Henle is located.
- all the collecting ducts converge on the pelvis of the kidneys then down the ureter which goes to the bladder.
The arteriole coming into the kidney is the afferent arteriole which forms a tuft of capillaries called a glomerulus. Out of the glomerulus is a efferent arteriole which forms a capillary bed, which surrounds the nephron and ends up at the renal venule.
At the glomerulus is where you have the exchange of toxins, which are enclosed in Bowman's capsule.

Structure:: blood goes in, under pressure, to the glomerulus.

Glomerulus	PTC	Collecting Duct
Cells----------x
protein--------x
water---------->	some reabsorption---------------->	water
glucose-------->	reabsorbed
amino acids---->	reabsorbed
sodium-------->	some reabsorption----------------->	sodium
urea-------------------------------------------------->		urea
toxins------------------------------------------------>		toxins
vitamins---------------------------------------------->		vitamins

A person might be diabetic if they have glucose in their urine.
If your total glomerular filtrate= 125 ml per min.= 184 liters per day. 99% is reabsorbed and 1% (.5 liters) is urine.

Filtration pressure controls the rate:

increase blood pressure through the glomerulus and you increase your filtration.
decrease blood pressure and you decrease filtration.

Function of the Kidneys: See figure 42.11

Small molecules are pushed across the thin walls of the glomerulus to the inside of the Bowman's capsule; bloodstream that enters the glomerulus is divided into two paths; nonfilterable blood components that are retained and leave the glomerulus in the bloodstream and filterable components that pass across and leave the glomerulus in the urine stream. Flow of materials in the human kidney. Figure 42.11

Antidiuretic hormone controls your hydration.

used for the conservation of water
- stays in the kidneys
- alcohol inhibits this hormone *this is the reason for a hangover (dehydration)

In PTC, reabsorption of solutes, via active transport. Then in the descending are water is given off. Up the ascending limb sodium and chlorine are pumped, but by active transport. The urine is concentrated and in the collecting duct, water is reabsorbed; so, is some of the urea.
- This process is controlled by the ADH hormone (vasopressin). Alcohol inhibits ADH - anti-diuretic- hormone and therefore more water is released from the kidneys. ADH controls the reabsorption of water in the collecting ducts.

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