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Lecture 24. Biology 1108 Chapter 44: Control of the Internal Environment. Learning Objectives (1 of 3). Contrast Osmoregulation in salt water & fresh water fish Ectotherms and endotherms Define Homeostasis Discuss “Goose bumps”. Learning Objectives (2 of 3). Contrast:

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Lecture 24

Biology 1108

Chapter 44: Control of the Internal Environment


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Learning Objectives (1 of 3)

  • Contrast

    • Osmoregulation in salt water & fresh water fish

    • Ectotherms and endotherms

  • Define

    • Homeostasis

  • Discuss

    • “Goose bumps”


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Learning Objectives (2 of 3)

  • Contrast:

    • Ammonia excretion in fish, birds, mammals

  • Recall:

    • Maximum amount of water lost to sweat

    • Functions of liver, kidneys

    • Function of each part of the excretory system

  • Discuss:

    • Seasonal dehydration

      • Water bear survival

      • Stone Mountain fairy shrimp


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Learning Objectives (3 of 3)

  • Some words to define:

    • Trehalose

  • Identify ALL urinary system parts


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Homeostasis

  • This chapter: “Control of the Internal Environment”

  • Homeostasis = maintenance of stability

  • For today, 2 types of internal control:

    • Temperature (thermoregulation)

    • Chemical (osmoregulation)


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Thermoregulation

  • Maintenance of a certain body temperature

  • Two basic types of animals

    • Endotherms vs. Ectotherms


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Ectotherms

  • Most of body heat comes from outside

  • Often must use behavior to regulate heat gain/loss

    • Reptiles bask in sun or on hot rock

    • Fish find water suitable for body temp

      • Trout prefer cold

      • Bass prefer somewhat warmer


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Endotherms

  • Most of heat comes from metabolism

  • Examples:

    • Birds

    • Mammals

    • Great white sharks


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Endotherms: Limiting Heat Loss

  • Most endotherms must limit heat loss

    • Thick body fat

    • Feathers in birds

    • Fur in mammals

    • Counter current exchange


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“Goose Bumps”

  • Each hair follicle has a tiny muscle

    • When cold, muscles raise hairs

    • Insulating air is trapped

    • Works better for furry mammals

      • We still have it as vestige of our evolutionary history

  • Birds have similar strategy


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Counter Current Heat Exchange

  • Limits heat loss through blood

  • Where is it found?

    • Great white shark

    • Penguin legs


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How it works:

  • Veins and arteries close together

  • Thermal energy flows from warmer to colder

    • Outgoing blood warms incoming blood

    • Heat stays towards body’s center



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Endotherms: Cooling

  • Sometimes cooling necessary

  • Increased blood flow to skin helps

    • Elephants dilate ear arteries & flap

    • Humans flush

  • Sweating causes evaporative cooling


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Osmoregulation

  • Control of internal chemical environment

    • Ex: Enzymes require certain pH & salinity to work properly

  • Saltwater & freshwater fish must have opposite strategies for osmoregulation!


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Hypotonic vs. Hypertonic

  • Just remember to ask, “How is the outside?”

    • If less concentrated, then environment is hypotonic (lower in salt)

    • If more concentrated, then environment is hypertonic (higher in salt)


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Freshwater Fish: Ion Balance

  • Constantly loses ions to hypotonic (lower salt) environment

    • Sodium Na+

    • Calcium Ca+

    • Chloride Cl-

  • To compensate:

    • Gills absorb ions from water

    • Digestive system absorbs ions from food


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Freshwater Fish: Water Balance

  • In danger of having too much water

    • These fish must avoid drinking

    • Kidneys produce copious, dilute urine


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Saltwater Fish: Ion Balance

  • Fish at risk of having too many ions

  • To compensate, gills constantly expel ions


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Saltwater Fish: Water Balance

  • Environment is hypertonic (salty)

    • Will rob fish of water

  • To compensate:

    • Saltwater fish drink lots!

    • Produce very little, but concentrated urine


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Question:

  • Let’s say you’re dehydrated

  • Which is absorbed by your body more quickly:

    • A sports drink?

    • Plain water?


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Dehydration from Sweating

  • Body sweats to cool skin

  • Up to 2 liters per hour during heavy exercise!

    • 2% loss affects performance

    • Excess loss reduces blood flow to skin, sweating stops

      • At 5%, heat stroke can occur


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Seasonal Dehydration

  • Problematic for aquatic or moisture-requiring organisms

  • Strategies

    • Lay desiccation-resistant eggs

    • Evolve to tolerate drought


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Stone Mountain Fairy Shrimp

  • Endangered species

    • Stone Mountain, GA is only home!

    • Live in ephemeral (temporary) pools

  • All adults die when pool dries up

  • Eggs resistant to dessication

    • Can survive for years


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Water Bears Survive Dehydration!

  • Can lose 95% of body moisture!

    • Homeostasis requirement relaxed

    • Remain inactive for decades

    • Rehydrate in minutes

  • Water bears = Phylum Tardigrada


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More Amazing Feats:

  • Temperature: -270°C to 150°C

  • Pressure: 6000atm = 10km under sea!

  • Pure alcohol!

  • Websites

    • Nature

    • Tardigrade Animations


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Dehydration in Nematodes

  • Some nematodes can survive dessication

    • Normally, cell membranes would collapse, proteins would break down

    • Nematodes have special sugar (trehalose) which prevents damage

    • Trehalose used to preserve some protein-based pharmaceuticals



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Nitrogenous Wastes

  • Proteins have many nitrogen-containing amino groups

    • In waste products, they become ammonia

      • Very toxic!

  • Body must eliminate ammonia!


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Eliminating Ammonia

  • Ammonia is chemically simple

  • Fish excrete ammonia directly through gills, directly to water

  • Terrestrial animals must convert ammonia to less toxic chemicals


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Terrestrial Animals: Urea

  • Mammals make urea

    • Water soluble (excreted in urine)

    • Disadvantage: energy cost (more complex)


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Terrestrial Animals: Uric Acid

  • Birds, reptiles make uric acid

    • Not water soluble (excreted as white paste)

    • Highest energy cost (most complex)


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Excretory System

  • We have 2 kidneys

    • Filters blood, producing urine

    • Each has 80 km of tubing!

      • Tubing has semipermeable membrane

      • Sorts waste molecules out of blood


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Overview of Excretory System

  • Contrast ureter vs. urethra

    • Ureter connects kidneys to bladder

    • Urethra (with an A) connects bladder to outside (think, AHHHH!)


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Anatomy of the Kidney

  • Contrast cortex (outer surface) vs. medulla (inner parts)

  • Note that renal pelvis collects urine


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Anatomy of the Nephron

  • Contrast filtrate vs. urine

    • Filtrate removed from blood by Bowman’s capsule

      • Has valuable solutes, glucose

    • Urine is filtrate after refining by the rest of the nephron

      • Returns solutes, glucose to blood stream


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Nephron Details

  • Filtrate goes from glomerulus, to proximal tuble, loop of Henle, distal tubule

    • Becomes more concentrated on journey


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Dialysis

  • If kidneys fail, patient must receive blood-cleansing treatment, or death will occur

  • Dialysis machine has pump, semi-permeable tubing, dialyzing solution

    • Treatments expensive

    • Three times a week, 4-6 hours each time


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Liver

  • Many homeostatic functions, including:

    • Changing ammonia into urea

    • Converting alcohol & drugs into inactive wastes

    • Regulation of blood glucose levels


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