PHS 201 Homeostasis PDF

PHS 201 INTRODUCTORY PHYSIOLOGY, EXCITABLE TISSUE AND AUTONOMIC NERVEOUS SYSTEM TOPIC HOMEOSTASIS LECTURER MR EPHRAIM IME EKANEM  Homeostasis  Homeo = same; stasis = standing  Homeostasis is the condition in which the...

PHS 201 INTRODUCTORY PHYSIOLOGY, EXCITABLE TISSUE AND AUTONOMIC NERVEOUS SYSTEM TOPIC HOMEOSTASIS LECTURER MR EPHRAIM IME EKANEM  Homeostasis  Homeo = same; stasis = standing  Homeostasis is the condition in which the internal environment of the body remains relatively constant despite changes in the external environment. OR  Homeostasis is the process of maintaining a controlled, stable internal environment. OR  Homeostasis refers to the body's ability to regulate physiologically its inner environment to ensure its stability in response to fluctuations in the outside environment.  Homeostasis must be maintained for normal body functioning and to sustain life.  The concept was first articulated by [Frenchman] Claude Bernard in 1860s.  The term homeostasis was coined by Walter Cannon (1932) Homeostatic imbalance  A disturbance in homeostasis resulting in disease Factors Affecting Homeostasis  Metabolic activities constantly taking place inside the body as a result of unwanted chemicals are produced.  Secondly, the external environment or the conditions in which an organism lives may vary greatly even over a brief period. Temperature, acidity , salts , water etc are some of the external factors to which an organism must adjust in order to survive.  Two Major Systems Involved In Homeostasis  Autonomic Nervous System: sends messages to the appropriate organs.  Endocrine System: secretes chemical messengers so the change can be corrected. Regulation of the Body Functions Regulation- the ability of an organism to maintain a stable internal conditions in a constantly changing environment Three types:  Chemical (hormonal) Regulation- a regulatory process performed by hormone or active chemical substance in blood or tissue.  It response slowly, acts extensively and lasts for a long time.  Nervous Regulation- a process in which body functions are controlled by nerve system.  Pathway: nerve reflex  Types: unconditioned reflex and conditioned reflex  Example: baroreceptor reflex of arterial blood pressure  Characteristics: response fast; acts exactly or locally, last for a short time  Autoregulation: a tissue or an organ can directly respond to environmental changes that are independent of nervous and hormonal control  Characteristics: Amplitude of the regulation is smaller than other two types.  Extension of the effects is smaller than other two types. Homeostasis & Controls Successful compensation Homeostasis reestablished Failure to compensate Pathophysiology Illness Death Basic Components Of A Feedback System Receptor  Responds to changes in the environment (stimuli)  Sends information to control center Control Center  Determines set point  Analyzes information  Determines appropriate response Effector  Provides a means for response to the stimulus.  Control centers in the brain play roles in regulating physiological parameters and keeping them within the normal range.  As the body works to maintain homeostasis, any significant deviation from the normal range will be resisted and homeostasis restored through a process called a feedback loop HOMEOSTATIC MECHANISMS  Homeostasis is achieved through negative or positive feedback mechanism. TYPES OF HOMEOSTATIC FEEDBACK MECHANISMS / REGULATION Negative feedback regulation / mechanisms. Positive feedback regulation / mechanisms. Negative feedback regulation / mechanisms  Includes most homeostatic control mechanisms.  Shuts off the original stimulus, or reduces its intensity.  Negative feedback loops are the body’s most common mechanisms used to maintain homeostasis. COMPONENTS OF A NEGATIVE FEEDBACK LOOP Stimulus Condition Receptors Control Centre Effector Response Variables Controlled By Negative Feedback Regulation / Mechanisms Include:  Nutrients  Temperature  Water  Ions, Na+, Ca+, Cl-  pH  Blood volume  Blood pressure  Oxygen  Carbon dioxide  Red blood cells Components of blood pressure negative feedback loop  Stimulus: Drop in blood pressure  Condition: Constant blood pressure  Receptors: Carotid artery receptors  Control Centre: Brain  Effector: Cardiovascular system  Response: Increased blood pressure Homeostatic Regulation of Body Temperature through Negative Feedback Hyperthermia (Stress) Heat receptors in the skin (Sensors) Hypothalamus (Control Center) Increased activity of sweat gland (Effectors) Increased blood flow to the skin (Effectors) Perspiration(sweat) evaporates cooling the skin (Effect) Stress is reduced shutting down mechanism Homeostatic Regulation of Body Temperature Through Negative Feedback Using A Neural Pathway  Many homeostatic mechanisms use a nerve pathway in which to produce their effects.  These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors. Homeostatic Regulation of Blood Sugar through Negative Feedback Hyperglycemia (Stress) Pancreas-beta cells (Sensors and Control Center) Insulin is released into blood Liver and Muscle cells take up glucose from the blood (Effectors) Blood glucose is reduced (Effect) Stress is reduced shutting down mechanism Negative Feedback Via a Hormonal Pathway Regulation of Blood Sugar  Hormones play an important role in many homeostatic pathways.  Hormones are produced by endocrine glands.  They enter the blood after being produced and travel throughout the body.  However, hormones have their effect on specific target tissues. Positive Feedback Regulation / Mechanisms Homeostatic systems utilizing positive feedback exhibit two primary characteristics: 1. Time limitation – Processes in the body that must be completed within a constrained time frame are usually modified by positive feedback. 2. Intensification of stress – During a positive feedback process, the initial imbalance or stress is intensified rather than reduced as it is in negative feedback. Typical Positive Feedback Stress Sensor Control Center Intensifies Effector Homeostatic Regulation of Child Birth through Positive Feedback  The first contractions of labor (the stimulus) push the baby toward the cervix (the lowest part of the uterus).  The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching (the sensors).  These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream.  Oxytocin causes stronger contractions of the smooth muscles in the uterus (the effectors), pushing the baby further down the birth canal.  This causes even greater stretching of the cervix.  The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born, the stretching of the cervix halts thereby stopping the release of oxytocin. Homeostatic Regulation in Coagulation through Positive Feedback BLOOD CLOTTING Positive feedback “mini-loops” are built into pathway to speed up production of chemicals needed to form the clot. Entire sequence of clotting is a negative feedback pathway: Harmful Effects of Positive Feedback Positive feedback can be harmful. Two specific examples of these harmful outcomes would be: 1. Fever can cause a positive feedback within homeostasis that pushes the body temperature continually higher.  If the temperature reaches 45 degrees centigrade cellular proteins denature bringing metabolism to a stop and death. 2. Chronic hypertension can favour the process of atherosclerosis which causes the openings of blood vessels to narrow.  This, in turn, will intensify the hypertension bring on more damage to the walls of blood vessels. Feed-Forward Control Concept:  A direct effect of stimulus on the control system before the action of feedback signal occurs.  Here the direct effect of the stimulus is termed disturb signal or interfere signal.  Example: Shivering before diving into the cold water Significance Of Feedback-Forward  Adaptive feedback control.  Makes the human body to foresee and adapt the environment promptly and exactly.  It prepares the body for the change. ASSIGNMENT 1. Define 'homeostasis'. 2. What are the components of a homeostatic system? 3. Using blood glucose as an example explain how negative feedback works in the restoration of blood glucose levels after ingesting carbohydrates. 4. Using blood pressure as an example identify the following: sensor or receptor; control center; effector; variable. 5. Using falling blood pressure as an example explain how negative feedback works.