Body Fluid Regulation and Excretion. Chapter 36

Transcription

1 Body Fluid Regulation and Excretion Chapter 36

2 Excretion The excretory system monitors the concentration of body fluids and removes harmful or waste substances from the body Water, nutrients and minerals that exit the body through excretion, exhaling, or evaporation must be replaced in equal amounts Excretion occurs differently in aquatic and terrestrial animals

3 Aquatic Excretion The fluids of aquatic animals are nearly isotonic to seawater o Removing waste through osmosis is difficult Even if they live in salt water, fish have unusually low amounts of salt Fish are at risk of constant dehydration (yep, fish get dehydrated) unless they regulate their waste content Cartilaginous fish build waste as a mixture of ammonia and urea, a combination so toxic it would be deadly to terrestrial animals The high amount of solutes ensures the organisms are isotonic with the high salt concentrations of their environments

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5 Terrestrial Excretion Animals that live near the sea are usually able to drink saltwater, reducing the likelihood of dehydration Some organisms prevent dehydration by secreting high levels of nitrogenous waste Others, like camels, have large amounts of mucus which collect air/water during exhalation Either by removing waste at a high rate or preventing water loss, organisms are able to conserve water Humans accomplish water conservation by adjusting the amount of water in their waste urine.

6 Waste Products Ammonia is the main excretory chemical in fishes o Ammonia is formed by Amino groups removed from amino acids in digestion. o Ammonia requires high amounts of water to safely flush out, but little energy to form. Amphibians and mammals excrete urea as their main chemical component o Amino groups require more energy to convert to urea, but it requires less water expenditure Reptiles, birds and insects excrete uric acid, o Uric Acid requires the most ATP for conversion but is released with almost no water loss Thus, waste removal requires either lots of water or lots of energy, or a little of both. It all depends on your environment

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8 Excretory System Other non-human excretory systems o Planarian organisms contain flame cells which contain cilia that expel molecules from the body o Annelids (such as earthworms) have nephridia in each body segment Nephridia are similar to flame cells, but contain capillaries that reabsorb any nutrients hiding in the waste before excretion o Insects contain malphighian tubules. MT s are similar to flame cells, except they are also able to reabsorb water in watery or humid environments

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12 Human Excretory System Kidneys o Kidneys filter out waste materials from blood and produce a chemical called urine. o Urine collects inside the renal pelvis inside the kidney and is carried to the bladder through the ureter. o Each kidney contains millions of tubules called nephrons, where the kidney forms urine. o Nephrons are vascular tissue made up of multiple filtering cells

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15 Human Excretory System Urine requires three distinct processes 1) Glomerular filtration at the glomerular capsule (GET EVERYTHING OUT) o Glomerular filtration is the movement of molecules from arteries through the glomerular wall due to blood pressure o This filtrate removes everything from the blood except large plasma proteins and blood cells o All the nephrons in the body filter 5 liters of blood in about 40 minutes 2) Tubular Reabsorption (BRING GOOD STUFF BACK) o Water needs to be reabsorbed back into the blood o Nephrons pump Na + and Cl - ions into the blood, which osmotically attracts water out of the nephron and into the blood.

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17 Human Excretory System o At the same time, carrier proteins allow recognized nutrients (glucose, amino acids, etc) to reenter the bloodstream o Proteins monitoring the blood glucose level are selective about the amount of glucose returning to blood or staying in urine. (Kidneys assume everything is bad and filter everything out of the blood. Then, they receive information about which nutrients they need and re-filter it back in. 3) Tubular Secretion (GET OUT AGAIN!) o Larger plasma molecules such as uric acid, hydrogen, ammonia and penicillin are all removed in this tube. o This is the last stop before urine. They won t have a chance to accidentally be reintroduced to blood in step two if they re removed here.

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19 Urine Antidiuretic hormone (ADH) released by the pituitary affects water re-absorbtion ADH is released into the distal tubule of the nephron when the pituitary senses a low amount of water in the blood The ADH attracts water back into the collecting duct and carries it to mix with urine o ADH gives off a heavy greenish-yellow pigment. Hence, urine is more colored when an organism is dehydrated Aldosterone is a hormone that triggers the return of 99% of sodium back to the blood. o Sodium is needed for Na + /K + exchange in nerve cells and for maintaining osmosis in blood