Homeostasis Part 4 PDF

HOMEOSTASIS PART4/4 Dr Anna Maceri School of Nursing and Midwifery Commonwealth of Australia Copyright Act 1968 WARNING This material has been reproduced and communicated to you by or on behalf of Western Sydney University under Part VB of the Copyright Act 1968 (the Act). The material in this commu...

HOMEOSTASIS PART4/4 Dr Anna Maceri School of Nursing and Midwifery Commonwealth of Australia Copyright Act 1968 WARNING This material has been reproduced and communicated to you by or on behalf of Western Sydney University under Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. HOMEOSTASIS q q q q q q State of internal balance. Body is constantly working to maintain homeostasis. Internal conditions are always changing (dynamic equilibrium) Narrow range. When body leaves homeostasis, feedback systems are activated to return back to homeostasis. Examples: Body temperature, blood pressure, blood sugar levels. 3 MAIN COMPONENTS Receptors Sensors that detect the stimulus occurring to the body. Control Centre Effectors Analyses the information sent from the receptors, compares to the set point and determines a response. Cell or organ that produces a response under the instruction by the control centre. FEEDBACK PATHWAYS q Negative Feedback - Responds to reduce or stop the undesirable initial stimulus. q Most homeostatic control systems are negative feedback systems. q Body temp, blood pressure, blood sugar levels. q Positive Feedback - Responds to enhance or continue the initial stimulus. q Less common. q Childbirth, breast feeding, blood clotting. BODY TEMPERATURE REGULATION Example of negative feedback pathway q Hypothalamus - control centre for body temperature o o o q 37 C = average optimal temperature (35.8 C – 38.2 C range) q Enzyme reactions within the body vital for survival. q Elevated body temp destroys enzymes. Why do we sweat when hot? Why do we shiver when cold? INCREASED BODY TEMPERATURE 3. Effectors Blood vessels in skin - vasodilate Sweat glands in skin - sweat Convey message via neurons 2. Control Centre Hypothalamus o 37 C Convey message via neurons 1. Receptors Thermoreceptors in skin detect increase skin temperature INCREASED BODY TEMPERATURE BLOOD VESSELS IN SKIN Vasodilate - increase blood vessel diameter. Blood flow closer to skin surface. Heat is transferred onto skin surface. Heat is lost from the skin surface by heat exchange mechanisms (conduction, convection, radiation). SWEAT GLANDS IN SKIN Produce sweat onto skin surface. Heat transferred into the sweat. Heat is removed as the sweat evaporates. DECREASED BODY TEMPERATURE Convey message via neurons 3. Effectors Skeletal muscles – shiver Blood vessels in skin - vasoconstrict 2. Control Centre Hypothalamus o 37 C Convey message via neurons 1. Receptors Thermoreceptors in skin detect decrease in skin temperature. DECREASED BODY TEMPERATURE BLOOD VESSELS IN SKIN Vasoconstrict - decrease blood vessel diameter. Decreased blood flow near skin surface- pale skin. Heat is conserved to warm the body and not lost onto skin surface. SKELETAL MUSCLES Muscles rapidly contract (shivering). Shivering generates heat. Heat warms body. CHILDBIRTH Example of positive feedback Release of oxytocin from Pituitary gland Message sent to brain Receptors in cervix detect stretch Oxytocin causes uterus to contract Head of fetus presses on cervix SUMMARY POSITIVE FEEDBACK NEGATIVE FEEDBACK Stimulus Receptors Enhance the stimulus Control Centre Effectors Response Reduce the stimulus