Homeostasis - Lecture Notes PDF

Homeostasis HEAL0002 David Woolford  Learning Objectives The importance of homeostasis in the human EXPLAIN body DESCRIBE Two ways the body maintains homeostasis The purpose of a negative feedback loop in DEFINE homeostasis What is...

Homeostasis HEAL0002 David Woolford  Learning Objectives The importance of homeostasis in the human EXPLAIN body DESCRIBE Two ways the body maintains homeostasis The purpose of a negative feedback loop in DEFINE homeostasis What is Homeostasis?  Origins Concept first recognised by Claude Bernard (1813- 1878) a French physiologist. Term Homeostasis introduced in1926 by Walter Cannon (1871-1945) an American Scientist Etymoly – Ancient Greek From Homoios – Meaning Simillar And Stasis Meaning To Stand still  Homeostasis In order for the body to function properly its internal environment needs to remain relatively stable. This ranges from the levels of nutrients and fluids to pressure and levels of gasses within the body. Homeostasis refers to the ability of the body to maintain a constant internal environment by making small internal adjustments to compensate for large external disturbances. Its all about balance! 7  Group Exercise In groups list some of the physiological factors within the body that need to be finely balanced….. No Google or looking at the next slide!!  Examples of physiological factors requiring Homeostasis Temperature pH Concentration of Water/Ion balance waste products Energy requirements Gas Exchange Volume/pressure  So why is this important? In order to function properly the bodies cells, tissues and organs have a narrow range of temperature, pH, levels of nutrients in which they can survive. Internal environment consists of water and dissolved substances outside of the cells – extracellular Separated from the inside of the cell by the cell membrane Certain components can cross over the membrane  Importance continued Therefore maintaining the balance of this internal environment is essential to the health of cells, tissues and organs. Homeostasis is so important that it requires most of our metabolic energy.  How are these regulated? Shivering Kidney Function Breathing Sugar levels Calcium levels in bone Lymphatic system – fighting infection But how is this relevant to us as clinicians?  Relevance? The maintenance of homeostasis underpins every physiological process in the body. It underpins the sensations and responses such as thirst, hunger, pain etc that our patients may experience An understanding of the control processes and what may go wrong helps us to understand common diseases, conditions and the effects of trauma. It helps explain the effects (good and bad) and reasons for why we give the drugs we do and the interventions we perform. Examples of therapeutic drugs?  Common therapeutic drugs Oxygen Maintenance of Blood 02 Sodium Chloride 0.9% fluid levels Aspirin Maintenance of internal Glucose fluid Reduces clotting Salbutamol Raises blood glucose Relaxes smooth muscle and helps open airways  So how does one achieve balance? In order to achieve homeostasis homeostatic control mechanisms are required These are processes by which the bodies internal environment are controlled  Homeostatic control mechanisms Self-regulating control systems that the body uses to maintain homeostasis The body uses homeostatic mechanisms to keep body levels within a normal range so it can function properly; normal ranges can vary from one individual to the next. Example: Regulation of body temperature in a manner like the functioning of a home heating/cooling thermostat Example: Regulation of blood pressure by pressure- sensitive receptors and muscle cells in the blood vessels 18  Homeostatic mechanisms - 3 main components Receptors Control Centres that includes a set point Effectors 19  Receptors Receptors detect changes within the internal environment Receptors can be cells, proteins or channels within cell walls Can be chemo, thermo, baroreceptors amongst others They initiate a response which is received by the control centre.  Set point and Control Centre The set point is the particular physiological value (required for cells to operate at their optimum) around which the normal range fluctuates. E.g. Body temperature – 37 degrees C Control centres located in the brain and other parts of the body process information received from stimuli from within the body indicating change. If these changes exceed the set point the control centre stimulates effectors  Effectors Effectors – often muscles or glands receive stimuli from the control centre The effectors then respond in a variety of ways such as contraction/relaxation/release of hormones. This response aims to effect a return to the set point or homeostasis Components of Homeostatic Mechanisms  Homeostatic mechanisms how they work 2 main processes that control how homeostatic mechanisms work. Negative Feedback Positive Feedback 24  Negative Feedback A mechanism by which a deviation in a variable from its set point is corrected. (Too hot/cold. Not enough O2, too much CO2). Negative feedback is the most common homeostatic mechanism. When receptors detect a change, stimuli are sent to the control centre and if the set point is exceeded, the effectors are stimulated initiate a response to return conditions toward normal ranges. Receptors constantly send information to the control centre As the variable returns toward its set point, stimulation of the effectors by the control centre is gradually reduced thus preventing over-correction. A Thermostat as an Example of Negative Feedback 26  Which systems contribute to homeostatic temperature control? Take 5 minutes have a think. 27  The body has detected a change outside of the usual limits…now what? Negative Feedback Loop  Homeostatic temperature control Responses to Cold Environmental Temperature: Thermoreceptors detect drop in body temperature Send nerve signals to control center in brain Blood vessels in skin constrict, to prevent heat loss through the skin, and conserve heat Certain muscles are caused to contract involuntarily (shivering) to produce body heat Body is warmed, and body temperature returns toward normal  Homeostatic Temperature Control Responses to Warm Environmental Temperature: Thermoreceptors detect rise in body temperature Send nerve signals to control center in brain Sweat glands are activated to secrete sweat, which cools the skin Blood vessels in skin dilate to lose heat to the outside  Too cold Too hot Process Vasoconstriction Vasodilation Arterioles Get narrower Get wider Blood flow in skin Decreases Increases capillaries Heat loss from skin Decreases Increases Vasoconstriction Vasodilation  Further Examples of Negative Feedback Control of blood pressure Metabolism Blood glucose levels Production of red blood cells  Regulation of Blood Glucose Negative feedback Fat (adipose) cells Glycerol & fatty acids lipids Blood Pancreatic Liver cells Blood Glucose  insulin  cell Glucose Glycogen Glucose  other cells (not brain) Glucose storage Blood glucose returns to normal levels Blood Pancreatic Liver cells Blood Glucose  glucagon  cell Glycogen Glucose Glucose  Negative feedback 34 Positive Feedback  Positive Feedback Positive feedback intensifies a change in the bodies physiological condition rather than reversing it. A deviation from the normal range or set point results in further effector activity and change away from that normal range rather than the effector being turned off. Usually produce unstable conditions that do not seem compatible with homeostasis. However, have specific functions and are short  Positive Feedback Loops Rare but we have 2: – Clotting of Blood – Uterine contractions during Labour Make a situation more EXTREME  Examples Blood Clotting Child Birth 38  Positive Feedback Loops - Blood clotting leads to increased blood clotting, which stops bleeding - During childbirth uterine contractions stimulate the release of increasing amounts of oxytocin which result in stronger uterine contractions. This progresses the labour. 39 Childbirth 40  Key points Negative Feedback Mechanism- Takes the variable back to normal Positive Feedback Mechanism- Takes the variable away to help get back to normal. 41  Nervous and Endocrine system Homeostasis is maintained by - Autonomic nervous system - Endocrine system Autonomic nervous system = concerned with rapid changes. Endocrine system = hormonal and concerned with slower, more precise changes. 42  To be completed by next week Visit the additional resources for this weeks lecture Complete the weekly quiz Find and anatomy and physiology book and complete self-study on this weeks topic Questions?  References and Further Reading Waugh, A. and Grant, A. (2018) Ross & Wilson Anatomy and Physiology in Health and Illness. 13th edition. London: Elsevier Ltd. Tortora, G.J. and Derrickson, B. (2017) Tortora’s Principles of Anatomy and Physiology. 15th edition. John Wiley & Sons. Moore, K.L., Dalley, A.F. and Agur, A.M.R. (2018) Clinically Oriented Anatomy. 8th edition. Philadelphia: Wolters Kluwer. Marieb, E.N. and Hoehn, K. (2019) Human Anatomy and Physiology. 11th edition. Harlow: Pearson Education Limited. 45