1. Homeostasis
Chapter 9

2. Homeostasis Physiological state of the body
Internal physical and chemical conditions are maintained within a tolerable range
Includes
Temperature, hormone levels, pH, pressure, concentrations of glucose and other solutes in the blood

3. Internal Environment Extracellular fluid
Interstitial fluid – fills the spaces between cells and tissues (e.g. plasma)
Consists of water, sugars, salts, FA, AA, coenzymes, hormones, neurotransmitters, waster products
Regulates flow of chemicals and allows cells to function properly
Lymphatic system transports fluid throughout the body

4. Internal Environments
Changes in Extracellular Fluid has negative effects on cellular function
Body uses organ systems to regulate internal conditions
Nervous system
Endocrine system
Muscular system
Integumentary system
Excretory system
Reproductive system

5. Nervous System Brain, spinal cord, peripheral nerves, sensory organs
Receives sensory data from the environment
Informs body of external conditions
Transmits signals throughout the body

6. Endocrine System Pituitary, thyroid, pancreas, adrenal (glands)
Regulates levels of hormones and other chemicals

7. Excretory System Kidneys, bladder, urethra, ureters
Rids the body of waste
Maintains clean internal environment

8. Integumentary System Skin, sweat glands, hair, nails
Maintains a constant body temperature

9. Immune System
White blood cells
Protects/fights infection

10. Digestive System Liver Breaks down amino acids
Detoxifies harmful chemicals (alcohol)
Manufactures important proteins

11. Homeostatic Mechanisms
Respond to internal and external conditions
Feedback systems – Positive/Negative
Help bring the body back into balance
Breathing rate, heart rate, internal temperature, blood glucose levels

12. Negative Feedback
Reduces the output or activity of an organ or system back to its normal range
Include 3 elements
Sensor
tissues or organs - detects change
Integrator - hypothalamus
control centre – compares conditions from environment with to optimal conditions in the body
Set points – ranges of values which need to be maintained
Effector
returns measured condition back to set point – response
Antagnositc effectors – produce opposite effect of change detected

18. Hypothalamus Body’s thermostat Maintains body temperature
Optimal body temperature – 35⁰ ⁰
Body temp falls → vasoconstriction in skin/shivering→ reduced blood flow→ less thermal energy lost to environment → body temp increases
Body temp rises → blood vessels dilate/induce vasodilation/sweating → increase blood flow→ increase thermal energy loss to environment→ body temp decreases
Signals from hypothalamus make us aware of our own temperature

19. Positive Feedback Mechanisms
Increases change in environmental condition
Does not result in homeostasis
Cause system to become unstable
“fight or flight” response
reproduction
fever
Positive feedback mechanisms operate within negative feedback mechanisms
Allows body to be brought back into balance

21. Thermoregulation Internal temperature regulation
Negative feedback mechanism
Thermoreceptors – compare external temp with internal set point
Trigger responses (2)
Rate of exothermic reactions in body (metabolism)
Rate of thermal energy exchange through surface of body

23. Mechanisms of Thermal Energy Exchange
Occurs at the surface where body comes into contact with the external environment
Exchange of thermal energy occurs through 1 of 4 mechanisms
Conduction
Convection
Radiation
Evaporation
All of these mechanisms act
simultaneously

24. Conduction
Flow of thermal energy between molecules that are in direct contact

25. Convection
Transfer of thermal energy within a fluid (liquid or gas)

26. Radiation
Thermal energy is transferred electromagnetically

27. Evaporation
Absorbs thermal energy from skin via water/sweat

28. Homeotherms
Animals that maintain a stable internal temperature regardless of external conditions
Includes
Poikilotherms
Endotherms
Ectotherms

29. Poikilotherms Fish, amphibians, reptiles, and most invertebrates
Body temperature varies with and often matches the temperature of the external environment

30. Endotherms Warm blooded animals (mammals, birds)
Homeotherms that use internal physiological mechanisms (metabolism) to generate thermal energy and maintain body temp
Remain fully active over a wide range of temperatures
Need a constant supply of energy

32. Ectotherms Cold blooded animals (reptiles, amphibians, fish)
Homeotherms that use external sources of energy to absorb thermal energy and regulate body temperature
Temperature fluctuates with environmental temperature
Inactive when temp are too low
Undergo thermal acclimatization
Gradual adjustment to seasonal temp

33. Torphor, Hibernation, Estivation
Adaptations to survive extreme climates by conserving energy
Torphor
Sleeplike state
Metabolic rate and body temperature drop in response to daily temp (nocturnal animals, hummingbird)
Hibernation
State of inactivity over an extended period of time
Estivation
Seasonal torphor – environment is hot and water is scarce

34. Water Balance
Extracellular fluid needs to maintain a constant volume (~15L) of water and balance of solute within the body
Mechanism
Osmosis

35. Osmosis
Water molecules move from a high concentration to a region of lower concentration across a selectively permeable membrane
Osmotic pressure
Results from a difference in water concentration gradient between the two sides of the selectively permeable membrane
Hyperosmotic
Hypoosmotic
Isoosmotic

36. Hyperosmotic Solution with higher concentration of solute molecules
Water tends to move to this side

37. Hypoosmotic Solution with lower concentration of solute molecules
Water tends to move from this solution

38. Isoosmotic
Solution with the same solute and water concentrations

39. Osmoregulation
Process of actively regulating the osmotic pressure of bodily fluids
Extracellular fluid = intracellular fluid (isoosmotic)
[solute] remains the same
[water] remains the same