EXAM 3: Chapter 40 Water and Electrolyte Balance in Animals

Biological Science Eighth Edition

Chapter 40: Water and Electrolyte Balance in Animals

Overview

  • Proper levels of:

    • Heat

    • Water

    • Electrolytes

Chapter Roadmap

Objectives

  • Understanding the challenges different habitats pose regarding water and electrolyte balance.

  • Examining how animals control concentrations of water and electrolytes in their bodies.

Topics Covered

  • Diffusion

  • Osmosis

  • Transport across membranes

  • Marine fishes

  • Freshwater fishes

  • Terrestrial insects

  • Terrestrial vertebrates; specifically the mammalian kidney

Body Temperature

Types of Thermoregulation

  • Endothermy vs. Ectothermy:

    • Endotherms produce their own heat.

    • Ectotherms rely on environmental heat.

  • Homeothermy vs. Heterothermy:

    • Homeotherms maintain a constant body temperature.

    • Heterotherms allow body temperature to fluctuate.

Water and Electrolyte Balance

  • Varies among:

    • Marine organisms

    • Freshwater organisms

    • Terrestrial organisms

Homeostasis

Definition

  • Homeostasis: Maintaining a fairly constant internal environment, including:

    • Body temperature

    • Water/salt balance

    • Blood pressure

    • pH

    • Blood glucose, etc.

Mechanism

  • Achieved by division of labor among cells and tissues, but requires energy.

  • Responses can be:

    • Negative feedback: Counteracts deviations from set points.

    • Positive feedback: Drives conditions further from set points, rarer than negative feedback.

Importance of Homeostasis

Reasons for Maintaining Homeostasis

  1. Enzymatic Function:

    • Enzymes catalyze energy conversion reactions, functioning best within narrow ranges of temperature and pH.

  2. Diffusion Rates:

    • Both temperature and solute concentration impact diffusion rates within body tissues.

Feedback Mechanisms

Negative Feedback Loop Example

  • Blood Glucose Regulation:

    • Pancreas monitors blood glucose levels.

    • When glucose is high:

    • Insulin is secreted.

    • Causes uptake/storage of glucose, lowering blood glucose levels.

    • When glucose is low:

    • Glucagon is secreted.

    • Stimulates conversion of glycogen to glucose, raising blood glucose levels.

Positive Feedback Example

  • Oxytocin in Childbirth:

    • Stimulates contractions of the uterus.

    • Stretching of the uterus increases production of oxytocin, enhancing contractions.

Variation in Body Temperature Regulation

Endotherms and Ectotherms

  • Endotherms:

    • Small birds, most birds, mammals

  • Heterotherms:

    • Mole-rats, bees, some insects, a few fish

  • Homeotherms:

    • Most terrestrial and marine invertebrates, amphibians, reptiles

  • Ectotherms:

    • Rely on environmental heat; body temperature varies with environmental temperature.

Mammal Body Temperature Regulation

Mechanisms to Regulate Heat
Heat-Loss Centers Activated:

  1. Blood vessels near the skin dilate, increasing blood flow and heat loss.

  2. Sweat glands stimulated, leading to evaporation and heat loss.

  3. Respiratory centers stimulated, resulting in panting and heat loss.

Heat-Gain Centers Activated:

  1. Blood vessels near the skin constrict, reducing blood flow and heat loss.

  2. Shivering generates heat in muscles.

  3. Chemical signals increase cellular respiration and heat production.

Countercurrent Heat Exchangers

Summary

  • Adaptations that conserve body heat.

  • Critical for species living in cold environments.

Adaptations for Preserving Core Body Temperature

Examples of Physiological Adaptations

  • Many desert animals can tolerate high body heat during the hottest part of the day.

  • Torpor and Hibernation: Temporary reduction in body temperature and metabolism.

  • Naked Mole Rats: Exhibit a variation in body temperature with environmental temperature.

Osmoregulation and Excretion

Definitions

  • Osmoregulation:

    • The process by which organisms control the concentration of water and solutes within their bodies.

  • Electrolytes and Water Movement:

    • Electrolytes move by diffusion; water moves by osmosis.

Key Processes
Diffusion

  • Movement of uncharged substances down concentration gradients.

Osmosis

  • Movement of water down its concentration gradient across a semipermeable membrane.

Osmoregulation in Marine and Freshwater Fishes

Marine Fishes

  • Experience severe osmotic stress due to lower tissue Na+ and Cl- concentrations compared to seawater.

  • Solutions:

    • Na+ and Cl- enter through gills.

    • Retain urea and other soluble compounds in blood plasma.

    • Excrete NaCl using specialized rectal glands with sodium/potassium pumps.

Freshwater Fishes

  • Hypertonic to their environment; water tends to enter their bodies.

  • Must actively transport ions back into their bodies to maintain homeostasis.

Water and Electrolyte Balance in Animals

Mechanisms in Terrestrial Animals

  • Obtain water through food/drinking.

  • Conservation methods include:

    • Producing concentrated urine.

    • Reabsorbing water in kidneys, particularly in the Loop of Henle.

  • Different adaptations like salt glands for excretion of surplus salts (mammals and birds).

Kidneys and Nitrogenous Waste

Mammalian Kidneys

  • Contain approximately 1 million nephrons.

  • Blood volume averages 5 - 6 L with 2000 L passing through kidneys daily. - About 180 L filtered through glomerulus resulting in 1-2 L urine produced daily.

Nitrogenous Waste Management

  • Breakdown of Amino Acids and Nucleic Acids: Converts to Ammonia (NH3), which is toxic.

  • Different strategies for nitrogenous waste removal:

    • Fish release ammonia directly (requires lots of water).

    • Mammals convert ammonia to urea.

    • Birds, reptiles, insects convert ammonia to uric acid, which is energy-intensive but results in little water loss.

Loop of Henle

Structure

  • Three main regions:

    • Descending Limb: Highly permeable to water, impermeable to solutes.

    • Thin Ascending Limb: Impermeable to water, permeable to Na+ and Cl-.

    • Thick Ascending Limb: Active transport of Na+ out of the nephron.

Function

  • Creates osmotic gradients essential for water reabsorption in nephron loops, particularly beneficial for desert-dwelling mammals with longer loops.

Hormonal Regulation of Water Reabsorption

Antidiuretic Hormone (ADH)

  • Regulates the permeability of the collecting duct to water.

    • High ADH levels increase permeability, leading to more water reabsorption.

    • Low ADH levels decrease permeability, resulting in less water reabsorption.

Key Concepts Recap

  • Importance of water/electrolyte balance for animals.

  • Differences between osmoconforming and osmoregulating animals.

  • Various adaptations for osmoregulation in saltwater, freshwater, and terrestrial habitats.

  • Functions of kidneys (nephrons) and Malpighian tubules in excretion and osmoregulation.

  • Differences in nitrogenous waste production between vertebrate groups; energy and water implications of waste management.

  • Diverse kidney structures and mechanisms across vertebrate species adapted for specific environmental challenges.

Summary Questions

  1. How do marine bony fishes resist osmotic loss of water and gain electrolytes?

  2. Explain how salmon can adapt their osmoregulation between freshwater and saltwater environments.

  3. Discuss the role of nephrons in kidneys and describe differences in their structure and function across different vertebrate groups.

  4. Assess how hormonal regulation affects water balance in the body.