of Principles Biology II Osmoregulation and Excretion This lecture will cover Chapter 44. Read the chapter quickly before coming to class. Become familiar with the following parts of the nephron and their abbreviations; also be able to trace the movement of materials through these parts from the blood to outside the body. Bowman's capsule (BC) Collecting duct (CD) Distal tubule = distal convoluted tubule (DCT) Loop of Henle (LH): ascending limb Loop of Henle (LH): descending limb Proximal tubule = proximal convoluted tubule (PCT)
Osmoregulation and Excretion
Chapter 44 Regulation of internal environment
Water (by controlling solute concentrations) Ions (including H+) Wastes
Organs
Kidneys and kidney like organs in nephridia Epithelial tissues: skin, gills, digestive tract
I. Wastes
Most important: nitrogenous
From breakdown of proteins and amion acids More produced by endotherms
Three forms
Ammonia
Highly toxic, highly water soluble Most aquatic organisms Synthesis does not need much energy
Urea
Less toxic, can be stored at higher concentrations Less water needed to remove Requires energy to produce Mammals (event aquatic mammals), terrestrial amphibians, and sharks
Uric acid
Non-toxic, but not water soluble Little water needed to remove Requires much energy to produce Birds, most reptiles (related to shelled egg) Bird poop the white stuff is uric acid. It can be made and set aside and wont affect the embryo
Wastes can vary with environment
II. Water
Roles: chemical reactions, solvent, bulk flow, temperature control Control: exchange with environment
Enters body: food, drink, skin, gills Leaves body: urine, feces, skin, gills, evaporation (skin, lungs, airways, mouth)
Moves across cell membranes by diffusion (osmosis: depends on solute concentrations)
NO active transport
Strategies 1. Osmoconformers
Most marine invertebrates Do not control water exchange
Composition of internal environment is the similar to the external (stable) down side is that when the outside changes drastically the internal will too and can be lethal.
2. Osmoregulators
Vertebrates Control water exchange Body composition differs from environment
Regulation permits life in more environments
Energy costs
a. Freshwater
Low solute (dilute) environment
Greater water concentration outside animal
Problem: gain water through surfaces, gills Fishes
Remove water through dilute urine Kidneys retain solutes Gain solutes through active transport by gills (from environment)
b. Marine
High solute environment
Greater water concentration inside animal
Problem: lose water through surfaces, gills Bony fishes
Drink sea water (adds a problem brings in too much salt) Kidneys save water and removes salts Lose salt through active transport by gills
Chondrichthyans
Do not drink
Keeps salt intake low Salts removed by kidney and rectal glands
Water source?
High levels of organic solutes (urea) in body Draw in water by osmosis
c. On land
Water loss by evaporation, in feces, and in urine (needed to remove wastes) Strategies
Reduce loss by waterproofing
Exoskeleton of insects Mucous in some amphibians Thickened skin in amniotes
Reduce exposure to heat (be nocturnal, hide) Use metabolic water Reduce loss in airways Kidneys that conserve water while removing wastes
Birds Mammals (greatest in marine mammals)
Salt glands in some reptiles and birds
III. Excretory Systems
Regulate water (volume and concentration) and remove wastes Excretory organs: found in Bilateria
Basic structure: tubules (nephridia)
Connected to outside Internal portions exchange materials with body fluids
A. Common processes
Filtration
Water and solutes enter from body fluids
Blood, coelomic fluid, hemolymph Movement due to pressure
Cross a layer
Not very selective: all except cells and proteins Advantage pass get rid of harmful things very easy doesn't require Disadvantage allows good things to pass
Result: filtrate
Filtrate is modified by active transport (water follows sodium ion which is active transport)
Much water and needed solutes reabsorbed
Glucose, some ions, amino acids Returned to body
Other materials secreted into tubules
Excess ions and toxins
Process are selective, controlled Result: urine
Proper volume and concentration
B. Vertebrate kidney 1. Nephron structure
Nephron tubules Blood vessels
Afferent arteriole Golmerulus: surrounded by Bowman's capsule Efferent arteriole Peritubular capillaries Vein
2. Nephron function a. Glomerular filtration
Materials move from glomerulus to BC (Bowman's capsule)
Due to pressure Reduced if afferent arteriole constricts (situation: fight or flight, low blood pressure)
Move through
Openings in glomerular capillaries Slits in BC
Do not pass through
Blood cells, platelets, most proteins
Pass through
Water, small toxins Wastes, toxins Needed materials
Product = (ultra-)filtrate: equivalent to blood plasma minus cells and proteins About 20% of plasma is removed from the blood Amount produced = Glomerular filtration rate (GFR) = 180 liters/day
99% is returned to blood later
b. Modification of filtrate
Exchange of materials between peritubular capillaries and PCT, LH, DCT, CD
Secretion
From capillaries to tubules by active transport Materials are removed from body
Toxins, drugs K+, H+, ammonium (NH4+)
Reabsorption
From tubules to capillaries
Mostly in PCT
Materials are saved
Sugar and amino acids
Fully reabsorbed from filtrate
Needed by body; not found in urine
How? Active transport
Limited number of binding sites
If substance is excessive, not all reabsorbed materials will be found in urine
Diabetes mellitus
Insulin deficiency
Sugar does not enter cells Too much sugar in blood: hyperglycemia High sugar levels in filtrate Not all will be reabsorbed
Glycosuria Also: large urine volume (why? Because takes in more water due to high solute concentrations.)
sugar in urine
How is glycosuria possible with normal blood sugar levels?
Salts & water
Kidneys save ions and water Na+ actively transported; negative ions and water
Nitrogenous wastes
Have uses in body, but harmful in high concentrations Kidneys reabsorb some, excrete excess
c. Control urine volume & concn
Loop of Henle (figure 44.15)
Sets up high solute region in kidney Draws out water from collecting duct
Makes urine more concentrated
ADH: antidiuretic hormone
Secreted by posterior pituitary in response to low blood volume or low water concentration in blood (example: dehydration)
Response: DCT and CD become more permeable to water Result? More water Will move out and enter the body increases blood volume and pressure lowers urine volume, more concentrated in solute concentration
If body has too much water
Less ADH secreted DCT and CD are less permeable to water More water stays in urine: high volume and low solute concentration (diuresis) Body loses excess water
Application: diuretic drugs
Increase urine formation and excretion
Can reduce blood volume and blood pressure
Alcohol: inhibits ADH release Caffeine: inhibits sodium re-absorption
3. Diversity
Variation in need and ability to concentrate urine
Mammals: greatest ability to concentrate
Especially desert and marine forms: long Loops of Henle
Birds: can concentrate
LH not as long as in mammals Uric acid waste
Reptiles: cannot concentrate urine
Water is reabsorbed in cloaca Uric acid waste
Freshwater fishes and amphibians
Produce much dilute urine Kidneys with many nephrons
Marine bony fishes
Need to save water retain water Fewer/smaller nephrons, small/no glomerali
Regulation within individuals (READ vampire bats)