Nat Sci ii Lecture #5: Homeostasis

1. Nat Sci ii Lecture #5:Homeostasis Josephine B. Guerrero, MD Asst. Professor, DB, CAS, UPM

2. Homeostasis • A state of balance and order achieved by an open system relative to set points • Set points or Norms • May be internal or external • Often occurs in a range • May be viewed in the level of the: • Cell • Organism • Population

4. Regulation of Homeostasis • Requires: • Input • Processing • Response • Feedback Loops: • Negative Feedback • Positive Feedback

5. Negative Feedback • Any deviation from the set point or norm is negated or opposed to bring back the condition to the previous • The result is that the set point is re-established and the system regains homeostasis

6. Negative Feedback Loop Upper Limit Set Point Lower Limit

8. Positive Feedback • Any deviation from the set point or norm is duplicated or continued • The result is a condition that is farther from the set point and often a “vicious cycle” that is detrimental to the re-establishment of homeostasis

9. Illustration of a positive feedback loop Upper Limit Set Point Lower Limit

12. Homeostasis at the cellular level

13. The Cell Membrane • Selectively permeable • Primarily responsible for the regulation of fluid and solute concentration in cells to maintain the integrity of the cell in terms of form and function

14. Transport Processes Across the Cell Membrane • Passive Transport • Diffusion • Simple Diffusion • Facilitated Diffusion • Osmosis • Active Transport

15. Driving Forces • Concentration gradient • Hydrostatic Pressure • Osmotic or Oncotic Pressure • Pumps

16. Simple Diffusion

17. Simple Diffusion

18. Facilitated Diffusion

19. Osmosis

20. Osmosis in RBCs

21. Turgor Pressure in Plant Cells

22. Active Transport

23. Endocytosis • Phagocytosis • “cell-eating” • Solid particulate matter are taken into the cell • Pinocytosis • “cell-drinking” • Liquid droplets are taken into the cell

24. Exocytosis • Exit of substances from cell • Membrane of secretory vesicle becomes part of the cell membrane

25. Homeostasis at the Organismic Level

26. Osmoregulation in Unicellular Organisms

27. Osmoregulation in Multicellular Organisms

28. Human Excretory System

29. The Nephron • Processes: • Filtration • Absorption • Secretion • Product: • Urine composed of water, electrolytes, urea (nitrogenous waste)

31. Nervous Control

32. Human Nervous System

33. Components • CNS • Brain • Spinal cord • PNS – cranial and spinal nerves exiting the CNS • SNS – Somatic Nervous System • ANS – Autonomic Nervous System

34. Functions

35. Parts of the Brain

36. Parts of the Cerebrum

37. Sagittal Section of the Brain

39. Cranial Nerves

40. Spinal Cord

41. Reflexes • Simplest neural circuit • Automatic, rapid, predictable, involuntary responses to stimuli

42. Autonomic System

43. Endocrine System

44. Glands • Autocrine • Paracrine

45. Endocrine

46. Hypothalamic-Pituitary Axis

47. Hormones, Targets and Functions

48. Hormones, Targets and Functions

49. Hormones, Targets and Functions

50. Hormones in Plants • Auxins – for cell elongation, differentiation, root growth, fruit development • Cytokinin – stimulates cell division, delays aging of leaves • Giberellins – cell and stem elongation, seed germination, flowering, fruit formation • Abscissic Acid – slows growth, induces seed dormancy, stress hormone • Ethylene – ripening of fruits, senescence • Brassinosteroids – act like auxins