Chapter 44 - Osmoregulation & Excretion

Question 1

Describe osmolarity.

Answer 1

The concentration of a solution expressed as the total number of solute particles per liter.

Question 2

Describe osmoregulation.

Answer 2

The regulation of solute concentration and water balance by a cell or organism.

Question 3

Define isoosmotic, hypoosmotic, and hyperosmotic.

Answer 3

• If two solutions have the same osmolarity they are described as isoosmotic.
• When two solutions differ, the one with the greater concentration of solutes is said to be hyperosmotic…
• The one with the more dilute solution is hypoosmotic.

Question 4

Describe osmoconformers vs. osmoregulators.

Answer 4

• To be an osmoconformer is to be issosmotic with your surroundings.
• To be an osmoregulator is to control internal osmolarity independent of your surroundings.

Question 5

Describe osmoregulation in terms of different environments : Problems & solutions of different animals, osmolarity of different animals and their urine.

Answer 5

• In marine environments the animal is hypoosmotic to water; tends to lose water and gain salt. Drinks water, excretes salt through active transport by gills, small volume of urine produced, urine slightly less concentrated than body fluids.
• In freshwater environments the animal is hyperosmotic to water; tend to gain water and lose salt. Does not drink water, intakes salt throuugh active transport by gills, large volume of urine produced, urine less concentrated than body fluids.
• In terrestrial vertebrates body water is lost to air. Drinks water, intakes salt by eating, loses water and salt. Moderate volume of urine produced, urine more concentrated than body fluids.

Question 6

Describe nitrogenous wastes produced by different animals.

Answer 6

• Aquatic animals, including most body fishes excrete ammonia
  
  • Not as energetically demanding, but is more toxic.
  • But, doesn’t matter because animals usually live in large aquatic environments.
• Mammals, most amphibians, sharks, and some bony fishes excrete urea
  
  • More expesnive to make, but is less toxic.
  • Some animals can switch between producing ammonia and urea (amphibians).
  • Endotherms produce more nitrogenous wastes (because they eat more), especially carnivores (protein diet).
• Reptiles, birds, insects, and land snails excrete uric acid.
  
  • Very expensive to make, but less toxic.
  • Important because when developing in shells as a baby need a less toxic environment.

Question 7

Describe types of excretory systems.

Answer 7

• Protonephridia
  
  • ex: flatworms
  • network of “dead-end” tubules
  • Tubes capped by units called flame bulbs which contain cilia that beat to draw in water/solutes from interstitial fluid through bulb.
  • Processesd filtrate move out the tubules into external envionment through nephridiopores.
  • Osmoregulation only, no excretion
• Metanephridia
  
  • ex: segmented worms
  • Ciliated funnel draws fluid from adjacent anterior segment into collecting tubule, which includes a bladder with an opening to the outside through nephridiopores.
  • Osmoregulation and excretion
• Malpighian tubules
  
  • Ex: terrestrial arthropods
  • Removes nitrogenous wastes from hemolymph and dumps into digestive system where uric acid is excreted with feces.
  • Functions in osmoregulation; no filtration, just secretion, and reabsorption still occurs.
• Kidneys
  
  • Ex: vertebrates & other chordates
  • Specialized organ composed of network of tubules, which is part of a more complex system.

Question 8

Describe kidney structure & function.

Answer 8

• A pair of kidneys connected to renal artery & vein
• Kidney → Ureter → Urinary bladder → Urethra
• Each kidney has outer renal** cortex and inner renal medulla.
  
  • Within are excretory tubulues (nephrons) which collect urine for the renal pelvis which passes it to the urinary bladder.

Question 9

Describe cortical vs. juxtamedullary nephrons.

Answer 9

• Cortical nephrons consist of 85% of total nephrons in the human kidney.
  
  • Reach only a short distance into the medulla
• Juxtamedullary neprons compose the remainder and extend deep into medulla.
  
  • Are essential for production of urine that is hyperosmotic to body fluids.

Question 10

Describe the parts of the nephron, the process of filtration, & pathway of filtrate.

Answer 10

• Each nephron begins with a ball of capillaries called the glomerulus contained inside Bowman’s capsule.
• Blood pressure forces fluid from the blood in the capillaries into Bowman’s capsule forming filtrate. Composed of salts, nutrients, wastes, etc. selective by size. Proteins, RBCs are too big to pass.
• Blood enters glomerulus through afferent arterial, and exits through efferent arterial.
• The filtrate passes through the proximal tubule, the loop of Henle, the distal tubule ending at the collecting duct.
• In the proximal tubulue, reabsorption of potassium (K⁺), sodium chloride (NaCl), water (H2O), amino acids, glucose and bicarbonate (HCO₃^-) occurs.
  Uric acid and organic acids (drugs & toxins) are secreted. (“Does most of the reabsorption and secretion”)
• In the loop of Henle water is further reabsorbed in the descending limb, and additional sodium chloride in the ascending limb, therefore leaving a higher concentration of urea, waste products. (“Sets up the ratio for concentration”)
• In the distal tubulue additional bicarbonate (HCO₃^-), water and NaCl is reabsorbed. Some K⁺ and H⁺ ions are secreted. (“Does the fine tuning”)
• In the collecting duct some final reabsorption of urea, NaCl and some water.
• Finally excretion occurs consisting of water, NaCl, K⁺, HCO₃-, creatinine and urea.
• The main way the nephron absorbs water is by the movement of NaCl, which water follows by osmosis.

Question 11

Describe how the loop of Henle, collecting duct, ADH, NaCl, & urea contribution to urine concentration.

Answer 11

• The loop of Henle sets up concentration gradient of NaCl via countercurrent exchange.
• Collecting duct uses it to controle urine
  
  • Regulated by anti-diuretic hormone (ADH)

Question 12

Describe variations in vertebrate kidneys.

Answer 12

• Desert animals and marine mammals would have long nephrons with more juxtamedullary nephrons.
• Marine fish have fewer nephrons and decreased filtration rates.
• Freshwater mammals would would have shorter corticol nephrons.
  Freshwater fish would have lots of nephrons.
• Reptiles have only cortical nephrons and produce uric acid.
• Birds have shorter loops and produce uric acid.
• Amphibians have lots of nephrons; when living in water urine is dilute and salt is taken up via skin, when living on land water is reabsorbed in bladder.

Question 13

Describe hormonal regulation of kidney function (in terms of ADH & RAAS only)

Answer 13

• Anti-diuretic hormone (ADH) responds to changes in blood; increased concnetration of blood results in increased ADH.
  
  • Reabsorption of water in distal tibules and collection ducts occur by increasing number of aquaporins.
  • More concentrated urine is produce.
  • Works via negative feedback loop.
  • Alcohol is a diuretic and inhibits ADH, producing lots of urine (dehydration = hangover)
• Renin-Angiotensis-Aldosterone System (RAAS) responds to changes in blood pressure or volume detected by JGA of afferent arteriole.
  
  • JGA releases enzyme called renin which forms angiotensisn II which is a vasoconstrictor working to increase blood pressure and decrease blood flow to kidneys
  • This causes relase of aldosterone (from adrenal glands) increasing reabsorption of NaCl & water in distal tubules therefore increasing blood pressure & blood volume.