Excretion AP Biology Unit 6

Osmolarity Osmolarity = moles of osmotically active particles per liter of solvent 1 M Glucose = 1 Osmolar solution 1 M NaCl = 2 Osmolar solution 2 osmotically active particles because NaCl dissociates to become Na+ and Cl- in water

Question… What would happen if your body did not maintain proper osmolarity? You would either have an excess of water (bloated) or too little water (dehydrated) Cells wouldn’t have the correct balance of solutes and H2O  won’t function properly

Osmoconformers Animals whose internal osmolarity changes in relation to their external environment Equilibrate with the environment There are limits to this– too high or too low will cause death Marine invertebrates Ex. Brine Shrimp (Artemia)

Osmoregulators Animals who can maintain their internal osmolarity at a particular level regardless of the external environment Ex. Fish, humans, lots of other animals 

Question… How does the environment one lives in affect how osmoregulation takes place? Depending on the environment one lives in, osmoregulation can be very different

Saltwater Fish Challenge: Prevent too much water from leaving the body (to go into the outside environment) Higher osmolarity outside compared to inside of body Solution…

Freshwater Fish Challenge: Prevent too much water from coming into the body from the outside Higher osmolarity inside body compared to outside Solution…

Birds: Salt Glands Many birds who live by the sea may take in sea water along with the food they eat Get rid of the extra salt in by excreting it through nasal salt glands  sneeze or shake off the salt droplets

Nitrogen Waste Nitrogenous wastes are a type of metabolic waste that must be removed from the body. Carbohydrates broken down into CO2 and H2O Fats broken down into CO2 and H2O Proteins and Nucleic Acids broken down into NH2 groups (urea, ammonia, uric acid)

continuously excreted (keep internal levels low) OR Ammonia Ammonia is the most common nitrogen waste Toxic at certain concentrations To prevent toxicity to the animal ammonia must be continuously excreted (keep internal levels low) OR Converted to a nontoxic molecule (urea or uric acid) before excretion

Excretion in Aquatic Animals For most aquatic animals, excreting ammonia is not an issue - why? Ammonia is highly soluble in H2O, diffuses away rapidly (won’t stay concentrated around them) Aquatic animals continuously lose ammonia from their bodies through diffusion across their gill membranes

Ammonotelic Animals that excrete nitrogen waste mostly as ammonia are ammonotelic Ex. Aquatic invertebrates, bony fish

Question… Why don’t terrestrial animals and some aquatic animals just excrete dilute ammonia in liquid? Since ammonia is toxic even at fairly low levels, it would have to use a lot of water to dilute it Too much water loss = dehydration

Ureotelic Animals that excrete nitrogen waste mostly as urea are ureotelic Ex. Mammals (us!), amphibians, sharks, rays, some bony fish

Uricotelic Animals that excrete nitrogen waste mostly as uric acid are uricotelic Helps conserve H2O because it isn’t very soluble in water  semi solid Ex. Birds, reptiles, insects, some amphibians

Excretory Process The main steps in producing urine (fluid waste) are: Filtration Selective Reabsorption Secretion

Filtration nonselective process in which water and small solutes are filtered across a membrane into the excretory system Small solutes include salts, nitrogen wastes, sugars, amino acids Filtrate = liquid produced from this step

Selective Reabsorption Useful/”good” molecules are reabsorbed back into the body from the excretory system by active transport Sugars, amino acids, some salts

Secretion More waste (toxins, extra salts, etc) are transported into the filtrate By active transport Selective reabsorption and secretion also causes water to move in /out of filtrate Urine = whatever is left of the filtrate after it has completed all 3 steps

Nephrons The filtering units in the mammalian excretory system are the nephrons. Random fact: there are approximately 1 million nephrons in each kidney

Major structures of the nephron Glomerulus Bowman’s Capsule Proximal Tubule Loop of Henle Distal Tubule Collecting Duct

Summary of Urine Creation Urine is created as solutes are taken out of blood due to: The differences in osmolarity in the tubules and the surrounding tissues Differences in permeability in the tubule membranes Random fact: each day you create approximately 2-3 liters of urine

Glomerulus & Bowman’s Capsule Glomerulus = dense ball of capillaries High pressure blood from arteries flows into the glomerulus substances are filtered from the glomerulus into Bowman’s capsule due to the high pressure Everything small enough gets across (red blood cells, proteins too big to fit through)

Selective Reabsorption In the proximal tubule, many useful solutes are reabsorbed back into the body fluid Glucose, amino acids, salts, some water

Loop of Henle The main function of the is to reabsorb water from the urine Ascending limb reabsorbs NaCl into the surrounding tissue; NOT permeable to H2O Descending limb IS permeable to H2O H2O flows out of filtrate due to osmosis (high salt concentrations all around) Descending limb Ascending limb

Loop of Henle As NaCl is actively transported out osmolarity decreases As H2O is reabsorbed from the filtrate, the osmolarity in the solution increases As NaCl is actively transported out osmolarity decreases

Question… Desert animals (kangaroo rats) usually have long loops of henle, while freshwater animals (beavers) have relatively short loops of henle. How does the environment one lives in relate to the length of the loop of henle? Loop of henle is for water reabsorption. Living in a drier area means you need to save more water from urine  need a longer loop to do this

Distal tubule More secretion and reabsorption takes place in the distal tubule

Collecting Duct More water is reabsorbed in the collecting duct  urine is concentrated Pathway of urine: kidney  ureter  bladder  urethra

Control of Excretion Processes Antidiuretic hormone (ADH) increases the permeability of the collecting ducts to increase the reabsorption of water Urine is concentrated further Also called vasopressin

Control of Excretory Processes Aldosterone also increases salt and water reabsorption in the distal tubule Usually a response to low blood pressure/volume The last step in a series of reactions involving other hormones

Interfering with ADH Caffeine and alcohol are diuretics substances that cause more frequent urination Caffeine and alcohol interfere with the actions of ADH  more urine produced Alcohol = prevents ADH from being secreted Caffeine = prevents ADH from binding to receptors on collecting duct