Chapter 44 - Osmoregulation and the Excretory SystemThere are FIVE major concepts this chapter covers
  1. Osmoregulation balances the uptake and loss of water and solutes.
  2. An animal's nitrogenous wastes reflect its phylogeny and habitat.
  3. Diverse excretory systems are variations on tubular theme
  4. The nephron is organized for stepwise processing of blood filtrate.
  5. Hormonal circuits link kidney function, water balance, and blood pressure.

Osmoregulation helps regulate the water uptake and the water loss. In case you forgot water enters and leaves the cell through osmosis. (water entering the cell through the selectively permeable membrane because of solute concentrations)

*This picture shows the selectively permeable membrane when it functions. You can see how it changes based on how hypertonic and hypotonic the water is. When there is a lower solute concentration there is a higher free water concentration. On the flip side the higher the solute concentration is the lower free water concentration is*
Key Vocabulary in Concept 44.1
  • Osmoregulation: process that all animals control solute concentrations and balance water gain and loss
  • Excretion: process that rids the body of nitrogenous metabolites and other waste products
  • Osmolarity: when two solutions separated by the membrane differ in osmotic pressure
  • Isoosmotic: when two solutions between the selectively permeamble membrane have the same osmolarity
  • Osmoconformer: isoomotic with its surroundings
  • Osmoregulator: controls its internal osmolarity independent of its enviornment
  • Stenohaline: individuals that cant colerate substantial changes in outside osmolarity
  • Euryhaline: individuals that can adapt to sudden changes in external osmolarity
  • Anhydrobiosis: when a normal aquatic animal can survive without water, this is an adaption
  • Transport Epithelium: one or more layers of specialized epithelial cells that regulate solute movements

Concept 44.1 Summary
  • All animals need osmoregulation, without it the cells can burst (too much water intake), or shrivel up and die (if too much water is lost)
  • When 2 solutions between the selectively permeable membrane are the SAME molarity they are isoosmotic
  • When 2 solutions are DIFFERENT molarities the one with the higher concentration is hyperosmotic, and the more diluted solution is hypoosmotic

*THE TOP PICTURE'S left side shows the hyperosmotic side, and you can see the water movement through the membrane from the hypoosmotic side. The bottom picture shows normal osmoregulation (top left), what happens in hyperosmotic conditions (the shriveling in top right), and in the center what happens when there is a a hypoosmotic condition (where the cell bursts)*
  • Animals can balance water through two ways, being an osmoconformer or an osmoregulator
  • Osmoconformers are mainly invertebrate marine animals that live in saltwater, they have an internal osmolarity is the same as its enviornment, so they don't gain or lose water
  • Osmoregulators are animals that can live in freshwater and terrestrial habitats, with a different osmloarity than seawater. To survive in a hypoosmotic environment they have to discharge extra water, hyperosmotic environment they have to take in water.
  • Most animals can't survive extreme changes in water concentrations, they are called stenohaline
  • Animals that can survive in extreme changes are euryhaline
  • Most vertebrate marine animals in saltwater are osmoregulators, EX: Cod fish, which constantly loses/gains water by drinking seawater, and use their kidneys and gills to get rid of excess salt.
  • Freshwater animals face hyperosmotic solutions, and its a probelm because the lost salts through diffusion, to solve this problem they drink hardly any water, and pee very diluted urine. They gain salt back by eating. EX: salmon - do the same thing as the marine animals, then change their habits to be more like freshwater animals.
  • Anhydrobiosis allows temporary water based animals to survive out of water, by dehydrating from 85% water to 2%
  • To maintain a stable osmolarity it takes energy from our metabolism
  • The reason why if we drink salt water and get dehydrated is because it takes double the fresh water to excrete the salt.

Key Vocabulary in Concept 44.2
  • Ammonia: a very toxic NH3 produced by nitrogen fixation or as a metabolic waste product of protein and nucleic acid metabolism
  • Urea: mammals excrete urea as a nitrogeneous waste, and its made from the liver and combines ammonia with carbon dioxide
  • Uric Acid: nontoxic nitrogeneous waste

Concept 44.2 Summary
  • Most animals excrete wastes that are diluted in water, and reflects the water balance in the animal
  • Proteins and nucelic acids can be broken down for energy or change into carbs, fats, or enzymes to remove nitrogen in the form of ammonia
  • Organisms excrete wastes such as ammonia, urea, or uric acid.
  • If an animal excretes ammonia they need a lot of water to dilute it because of its toxicity, most commonly found in aquatic mammals since it can be diffused through the body surface
  • Most land animals and some aquatic animals excrete urea, and it has a low toxicity
  • Animals transport urea through the circulatory system, and it helps animals retain as much water as possible
  • The main negative effect of urea is the energy it takes to produce it from ammonia.
  • Uric Acid is excreted by incects, birds, and reptiles. It is nontoxic and doesnt need to be diluted in water.
  • The downside of uric acid is the fact that it takes MORE energy than urea takes, it takes ATP for synthesis of the ammonia
  • The type of waste an animal makes reflects its enviornment, diet, and its energy budget it can spare

*This picture shows what goes in to make an amino group, and how it divides to show what ammonia in fish's chemical makeup is, and mammals' urea makeup, and birds' uric acid makeup*
Key Vocabulary in Concept 44.3
Filtration: extraction of water and small solutes including metabolic wastes from the body fluids
Filtrate: cell free fluid excreted from the body fluid by the excretory system
Reabsorbtion: recovery of solutes and water from filtrate
Secretion: discharge of wastes from the body into the filtrate
Protonnephridia: a network of tubes lacking internal openings in flatworms
Metanephridium: excretory organ found in many vertebrates that consists on tubes with internal and extrenal openings
Malpighian Tubule: insects organ that empties into the digestive tract that
Retnal Artery: carries blood to the kidney
Retnal Vein: drains blood from the kidneys
Ureter: where urine exits through, its a duct and we have two
Urinary Bladder: urine from uterers drain into the bladder
Urethra: tube that urine passes through during urination
Renal Cortex: outer portion of the vertebrate kidney
Renal Medulla: inner portion of the vertebrate kidney, beneath the renal cortex
Nephron: tubular excratory unit of the vertebrate kidney
Glomerulus: ball of capillaries surrounded by Bowman's capsule in the nephron and is the site of filtration in the vertebrate kidney
Bowman's Capsule: a cup-shaped receptacle in the kidney and is the expanded segment of the nephron where filtrate enters from the blood.
Proximal Tubule: in the kidney, the portion of a nephron downstream from Bowman's capsule that helps refine filtrate
Loop of Henle: the hairpin turn, with a descending and ascending limb, between the proximal and distal tubules of the vertebrate kidney; functions in water and salt reabsorption
Distal Tubule: in the kidney, the portion of a nephron that helps refine filtrate and empties it into a collecting duct
Collecting Duct: the location in the kidney where processed filtrate, called urine, is collected from the renal tubes
Renal Pelvis: funnel-shaped chamber that holds processed filtrate from the kidney's collecting ducts and is drained by the ureter
Cortical Nephrons: in mammals and birds, a nephron with a loop of Henle located almost entirely in the renal cortex
Juxtamedullary Nephrons: in mammals and birds, a nephron with a loop of Henle that extends far into the renal medulla
Afferent Arteriole: in the kidney, the blood vessel supplying a nephron
Efferent Arteriole: in the kidney, the blood vessel draining a nephron
Peritubular Capillaries: tiny blood vessels that form a network surrounding the proximal and distal tubules in the kidney
Vasa Recta: the capillary system in the kidney that serves the loop of Henle

Concept 44.3 Summary
  • The excretory system provides homeosasis, they control waste and body fluid composistion
  • Body fluid (blood for example) goes through steps. The first step goes into contact with the selective permeable membrane. Our blood pressure drives filtration, and the water, salt, and sugar from the filtrate.
  • Filtrate later turns into waste
  • Reabsorption save valuable solutes, Secretion rids the body of uneeded solutes
  • Excretion is a large network of tubes working together to exchange water and solutes
  • Protonephridia forms tubes that only have one opening (in flatworms) they have flame bulbs on the ends. When the heart beats in a worm it draws water and soultes from the fluid through the flame bulb, and releases filtrate to excrete, typically through the mouth
  • Earthworms are metanephridia, they have a bladder that opens to the outisde. Soultes return to the blood through the capillaries. They maintain their osmoregulation through thier skin.
  • Insects have organs called malpighian tubules come out from dead end tips in the circulatory fluid that opens into the digestive tract, they dont have a filtration step.
  • The tubules secrete solutes into the lumen, then through osmosis goes to the rectum.
  • Kidneys help with osmoregulation and excretion, and are made of tubules also
  • Kindeys get blood through the retnal artery and lose blood through the retnal vein, they receive 25% of the blood exiting the heart
  • Urine exits through the uterer and into the urinary bladder and exits through the urethra
  • Urine is regulated by sphincter muscles that open and close
  • Mammalian kidneys have a rental cortex and a rental medulla with tons of blood vessels
  • Nephrons consist of a ball called the glomerulus, and on the end of it is the Bowman's capsule surrounding it
  • Filtration happens in the glomerulus and the Bowman's capsule
  • Filtrate then goes though the poximal tubule, loop of henle, distal tubule, to the collecting duct
  • The ducts then empties into the renal pelvis to the uterer
  • Nephrons are lined by a transport epithelium that makes urine out of filtrate, they get blood by the afferent arteriole
  • TONS of sugars, water, and vitamins pass through the nephrons, to get reabsorbed into the blood

Key Vocabulary in Concept 44.4
Aquaporin: a channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane
Countercurrent Multiplier Systems: a countercurrent system in which energy is expended in active transport to facilitate exchange of materials and generate concentration gradients

Concept 44.4 Summary
  • Reabsorption in the proximal tube is crucial for recycling ions, water and valuable nutrients
  • NaCl in the filtrate diffuses into the cells of the transport epithelium where Na+ goes into the interstitial fluid.
  • This drives the passive transport of Cl-
  • As the salt moves along from filtrate to interstitial fluid, water follows by osmosis, salt then goes to the peritubular capillaries
  • Processing of filtrate in the proximal tubule helps maintain a relatively constant pH level
  • The acidity of the filtrate is proportional to the amount of ammonia cells
  • Proximal tubules also reabsorb 90% of the buffer bicarbonate to also help pH balance
  • Reabsorption continues for water in the descending limb of the loop of Henle
  • Aquaporin proteins  make numerous water channels so that epithelium can transport freely
  • Filtrate undergoes water loss while also increasing solute concentration at every major step down the loop of Henle
  • The ascending limb has many channels for ions but not water
  • Ascending limb has 2 specialized regions: thin segment near the loop tip and a thick segment next to the distal tube
  • NaCl diffuses out as it moves up, helps maintain the osmolarity of the interstitial fluid in the medulla
  • Epithelium actively transports NaCl into the interstitial fluid
  • The distal tubule regulates the K+ and NaCl concentration
  • The collecting duct carries filtrate to the renal pelvis, hormone control helps the urine concentration
  • kidneys help to reabsorb salts without allowing water to follow osmosis, to dilute urine
  • Different mammals can have different urine osmolarity, the reflect the environment
  • Variations in nephron structure help the kidneys be able to maintain osmoregulation
  • longer loops of Henle means animals live in the desert because they need to recycle more water



This picture shows the anatomy of the kidney This picture shows the journey through the tubes. The descending limb of loop has water channels to help filtrate. The ascending loop has lots of ion channels to help dilute filtrate. It then passes through the ureter to the bladder

Key Vocabulary in Concept 44.5
Antidiuretic Hormone (ADH) - promotes water retention
Renin-Angiostensin-Aldosterone System (RAAS): a hormone cascade pathway that helps regulate blood pressure and volume
Juxtaglomerular Apparatus (JGA): a specialized tissue in nephrons that releases the enzyme renin in response to a drop in blood pressure or volume
Angiotensin II: a peptide hormone that stimulates constriction of precapillary arterioles and increases reabsorption of NaCl and water by the proximal tubules of the kidney, increasing the blood pressure and volume
Aldosterone: a steroid hormone that acts on tubules of the kidney to regulate the transport of sodium ions (Na+) and potassium ions (K+)
Atrial Natriuretic Peptide (ANP): a peptide hormone secreted by cells of the atria of the heart in response to high blood pressure. ANP's effects on the kidney alter ion and water movement and thereby reduce blood pressure

Concept 44.5 Summary
  • water and salt balance drive the rate of urea production, kidneys adjust accordingly
  • Vampire bats drink as much blood as possible, and to avoid being too heavy to fly the kidneys adjust and excrete large volumes of urine, and help them lose up to 24% of their body weight.
  • The ADH is made in the hypothalamus and stored in the pituitary gland
  • ADH mainly goes to the distal tubules and collecting ducts to make the epithelium more permeable
  • Large volumes of water lead to less ADH used, resulting in large quantities of very dilute urine
  • Alcohol disrupts ADH regulation leading to excessive dehydration due to extreme urinary water loss
  • RAAS consists with JGA that supplies blood to the arteriole which helps with blood pressure
  • JGA releases renin (enzyme) that starts chemical reactions to cleave plasma proteins to make angiotensin II
  • Angiotensin II regulates blood pressure by constricting arterioles, and releases aldosterone
  • Aldosterone helps absorb more Na and water to increase blood pressure and volume
  • ANP helps increase blood volume and blood pressure, ANP is released to initiate JGA and reduces aldosterone, it works on a system of checks and balances

Helpful Links

Information/questions/test on Kidneys

Overview of Digestive System

Complete outline of Chapter 44

Video of Digestive System

Video on How Kidneys Work