Homeostasis

1. Homeostasis Chapter 9 http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/homeo/homeosts.shtml

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 - 37.8⁰ • 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

40. The Excretory System • Main functions (with the help of osmoregulation) • Concentrate wastes and expel them from the body • Regulate fluids and water within the body • Organs included • Kidney • Adrenal gland • Ureter • Urinary bladder • Urethra

41. Removal of Metabolic Waste

42. Kidneys • Removes waste • Balances blood pH • Maintain body’s water balance • Blood is supplied to kidney via renal artery • Re-enters circulatory system via renal vein

43. Nephrons • Functional unit of the kidney (1 000 000 per kidney) • Regulate water balance • Conduct excretion • Different sections of the nephron have specialized functions in formation of urine and conservation of water • http://www.youtube.com/watch?v=oXcEAH_yesY

44. Urinary Bladder • Renal pelvis connects the kidney to the ureter which fills the bladder • Holds ~300mL-400mL of urine before exiting the urethra

45. Deamination • Occurs in the liver – breakdown of protein • Removal of amino group from amino acid • Creates ammonia NH₃ (toxic to body) • Urea Cycle • Ammonia reacts with bicarbonate and 2 ATP molecules to form urea • Transported to kidneys where excretion occurs via blood

46. Bicarbonate Buffer System • Maintains pH of blood (acid-base homeostasis)

47. Formation of Urine • Ultimate goal – conserve water, balance salts, concentrate wastes • Urine – hypoosmotic to surrounding body fluids - water tends to move from urine into the body fluids • 3 Feature of nephron interact to achieve ultimate goal • Arrangement of loop of Henle • Difference in permeability • Concentration gradient of molecules and ions • 3 processes interact to achieve formation of urine • Filtration • Reabsorption • Secretion

48. Formation of Urine: Overall Process

49. Filtration • Begins at Bowman’s capsule (selectively permeable membrane) • Receives water, ions, glucose, AA and urea from glomerulus • Difference of pressure allows for transfer of molecules and ions into capsule • 1400L of blood pass through kidneys every day • Bowman’s capsule filters ~180L from blood • ~1.5L is excreted as urine daily

50. Reabsorption • Occurs as fluid from Bowman’s capsule enters proximal convoluted tubule, Loop of Henle and distal convoluted tubule • Water, ions and nutrients are transferred back into interstitial fluid and peritubular capillaries via passive and active transport • Microvilli inside tubules increase surface area • Difference in solute concentration allows water to move across the membrane and back into interstitial fluid via osmosis (aquaporins)