WINDSOR UNIVERSITY SCHOOL OF MEDICINE

1. WINDSOR UNIVERSITYSCHOOL OF MEDICINE HOMEOSTATIC REGULATION Dr.Vishal Surender.MD.

2. Learning Objectives • Definition of physiology • Review of organ systems • Explain homeostasis • Discuss the relationship between external and internal environments • List the main body fluid compartments, their constituents and their relationship to each other • Define equilibrium and steady state • Give examples of homeostatic mechanisms • Explain negative feedback • Define controlled variable, sensor, comparitor and set point and give examples of each in a negative feedback loop • Discuss factors that may change set points • Define redundancy and hierarchy with respect to hemoestatic control mechanisms • Explain positive feedback • Explain feed-forward regulation

3. Physiology defined • Physiology is the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes.

4. Organization of the human body Organisms (Human body) Organ systems Organs Tissues Cells

5. Organ Systems in Review • Integumentary • Musculoskeletal • Respiratory • Digestive • Reproductive and Urinary • Circulatory • Nervous and Endocrine • Immune

6. Organ Systems in Review The integration between systems of the body

7. Body Fluid Compartments 20%

8. Blood Plasma 3 L Interstitial 11 L Intracellular 28 L Transcellular 1 L Compartments and their Relationship • most cases substances within the plasma must pass through the interstitial fluid before entering cells. • Therefore the interrelationships between these 4 compartments are crucial in underlying whole body homeostasis.

9. External and Internal Environments “all the vital mechanisms, however varied they may be, have only one object, that of preserving constant the conditions of life in the internal environment.” Claude Bernard (1857) • The Basis of • Physiological Regulation • A Stable Internal • Environment Is Essential for Normal Cell Function

10. Environments Variable Outside Inside Temperature -10 and +40 °C 37 °C PO2 160 mm Hg PaO2 95 mm Hg PCO2 0.23 mm Hg 40 mm Hg pH 7.4 pH ?/variable . • stability of the internal environment is the primary condition for a free and independent existence-By controlling its internal environment the organism is no longer at the mercy of the environment .

11. To summarize: Homeostasis is the maintenance of a steady state of the internal environment of the body.

12. Body Fluid Constituents [Na+] = 145 [K+] = 4.5 [Cl-] = 116 [Protein] = 0 mM Osmolality 290 mOsm [Na+] = 142 [K+] = 4.4 [Cl-] = 102 [Protein] = 1 Osmolality 290 mOsm [Na+] = 15 [K+] = 120 [Cl-] = 20 [Protein] = 4 Osmolality 290 mOsm Cellular Plasma Interstitial • substances aren’t in equilibrium, but there is a balance • there is a difference between the basic constituents of the body-fluid compartments. This means that homeostasis is not about reaching equilibrium, but about maintaining a steady-state. Since the system is not necessarily in equilibrium energy expenditure is required to maintain a steady state.

13. Homeostasis & Controls • Successful compensation • Homeostasis reestablished • Failure to compensate • Pathophysiology • Illness • Death

14. Feedback( flow of information along a closed loop)– Negative or Positive • Negative – change is sensed and action taken to prevent further change e.g-regulation of secretion of hormones. • Positive – change is sensed and action taken to amplify change (usually associated with a discrete end point, e.g. birth, ovulation)

15. Homeostatic Mechanisms • Most homeostatic mechanisms are based on negative feedback • specific terms that are used to describe the processes involved- Controlled Variable Sensor Comparator, set point Effectors

16. Blood Pressure Regulation Blood Loss Baroreceptor (sensor) Brain (comparitor) Cardiovascular control center – compares BP to set point and adjusts vascular tone and cardiac output accordingly Vasoconstriction ↑ Cardiac Output (effectors) Blood Pressure (controlled variable)

17. Blood Glucose -ve Feedback b-cell Variable Blood Glucose Insulin secretion Glucose b-cell Cells

19. Cutaneous Blood Vessels Anticipation of exercise and during exercise Sympathetic outflow increases to maintain blood pressure

20. Cutaneous Blood Vessels Anticipation of strenous exercise Sympathetic outflow increases to maintain blood pressure Hypothalamus detects heat increase And inhibits sympathetic outflow Vasodilation helps to divert blood flow to the skin For heat loss

21. Cutaneous Blood Vessels With extreme exercise the need to control Blood pressure takes priority and the Vessels constrict Hypothalamus detects heat increase And inhibits sympathetic outflow Vasodilation helps to divert blood flow to the skin For heat loss

22. Contraction oxytocin Positive Feedback All steps in this process produce an increase in the next step leading to a loop of stimulation. The positive feedback loop is broken when the baby is expelled from the uterus and hence the step involving pressure against the cervix has been removed.

23. Feed-forward Control • Anticipation of change – gets body ready for change • e.g. heart rate and ventilation can increase even before exercise begins • Or salivation and digestive enzyme production begins before a meal is eaten

24. Redundancy • Homeostatic mechanisms are important – therefore often there is more than 1 control mechanism • If 1 mechanism fails – then there is a backup system (e.g. ATP/adenosine in airway surface liquid secretion or control of cutaneous blood vessels by both cardiovascular control center and temperature control center) • Or blood pressure (next slide)

25. Hypovolemic Shock B.P. falls Angiotensinogen in blood Kidney Juxtaglomerular cells Aortic arch Carotid sinus Renin Activity drop Angiotensin I Medulla oblongata Hypothalamus Posterior Pituitary Sympathetic output ACE ADH Adrenal Cortex Kidney Salt water conservation Blood Vessels Heart rate contractility Angiotenin II Aldosterone LUNG Inc. B.P. Inc. vasc. resistance Inc. volume

26. Summary I • Homeostasis – maintenance of a stable internal environment • Steady state – unchanging with time • Equilibrium – when parameters are maintained in an energetically favorable situation • Redundancy – more than 1 system to control a variable (backup systems)

27. Summary II • Negative feedback – feedback causes a perturbation to be minimized or reversed with view to keeping parameter at a set point • Positive feedback – amplification of a deviation (usually defined end point)