Homeostasis & Controls PDF

Homeostasis & Controls Successful compensation Homeostasis reestablished Failure to compensate Pathophysiology Illness Death 1  Regulation: The ability of an organism to maintain a stable internal conditions in a constantly changing environment...

Homeostasis & Controls Successful compensation Homeostasis reestablished Failure to compensate Pathophysiology Illness Death 1  Regulation: The ability of an organism to maintain a stable internal conditions in a constantly changing environment –Three types: 1. Hormonal Regulation 2. Nervous Regulation 3. Autoregulation  Regulation of the Body Functions The three regulations have coordinated and acts as one system, “feedback control system”. Control System in the Human Body Feedback Control. -Feed-forward control Feedback Control – Feedback: Output (feedback signal) from controlled organ returns to affect or modify the action of the control system. – Feedback control mechanism consists of two forms: Negative feedback control. Positive feedback control 3 Negative feedback The feedback signals from controlled system produces effect opposite to the action of the control system. The opposite effect is mainly “inhibitory action”. 4 Negative Feedback: Inhibitory Stimulus triggers response to counter act further change in the same direction. Negative-feedback mechanisms prevent small changes from becoming too large. 5 Homeostasis: Control Mechanisms The variable produces a change in the body The three interdependent components of control mechanisms are: – Receptor – monitors the environments and responds to changes (stimuli) – Control center – determines the set point at which the variable is maintained – Effector – provides the means to respond to the stimulus Negative Feedback In negative feedback systems, the output shuts off the original stimulus Prevents sudden and severe changes within the body. Example: Regulation of blood glucose levels 6 Homeostasis: Control Mechanisms 3 Input: Control center 4 Output: Information sent Information sent along along afferent Efferent pathway to pathway to Receptor (sensor) Effector 2 Change detected by receptor 5 Response of effector feeds 1 Stimulus: back to influence magnitude Produces of stimulus and returns change variable to homeostasis in variable Variable (in homeostasis) 7 Homeostasis: Negative Feedback  Positive feedback  The feedback signal or output from the controlled system increases the action of the control system  Examples:  Blood clotting  Micturition  Defecation  Na+ inflow in genesis of nerve signals  Contraction of the uterus during childbirth (parturition) 9 Positive Feedback: Stimulatory. Stimulus trigger mechanisms that amplify the response and reinforces the stimulus. 10  Importance: Enhance the action of original stimulus or amplify or reinforce change promote an activity to finish Vicious circle - can lead to instability or even death 11  Feed-forward control Concept: Direct effect of stimulus on the control system before the action of feedback signal occurs. – 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 (prepare the body for the change). 12  Feed-forward control Significance of Feedback-forward : – Adaptive feedback control. – Makes the human body to foresee and adapt the environment promptly and exactly (prepare the body for the change). 13  Types of Ion Channels Leakage (non-gated) channels are always open nerve cells have more K+ than Na+ leakage channels as a result, membrane permeability to K+ is higher explains resting membrane potential of -90mV in nerve tissue. Gated channels open and close in response to a stimulus results in neuron excitability – voltage-gated open in response to change in voltage – ligand-gated open & close in response to particular chemical stimuli (hormone, neurotransmitter, ion) – mechanically-gated open with mechanical stimulation 14 15 16 17  Electrical potentials exist across the membranes of almost all cells of the body. In addition, some cells, such as nerve and muscle cells, are capable of generating rapidly changing electrochemical impulses at their membranes, and these impulses are used to transmit signals along the nerve or muscle membranes. In glandular cells, macrophages, and ciliated cells, local changes in membrane potentials also activate many of the cells’ functions 18 Resting Membrane Potential of Nerves The resting membrane potential of large nerve fibers when not transmitting nerve signals is about –90 millivolts. That is, the potential inside the fiber is 90 millivolts more negative than the potential in the extracellular fluid on the outside of the fibre. 19  Factors that determine the level of resting potential 1-Active Transport of Sodium and Potassium Ions Through the Membrane—The Sodium- Potassium (Na+-K+) Pump All cell membranes of the body have a powerful Na+-K+ that continually pumps sodium ions to the outside of the cell and potassium ions to the inside. This is an electrogenic pump because more positive charges are pumped to the outside than to the inside (three Na+ ions to the outside for each two K+ ions to the inside), leaving a net deficit of positive ions on the inside; this causes a negative potential inside the cell membrane. 20 2-Leakage of Potassium and Sodium Through the Nerve Membrane. A channel protein in the membrane through which potassium and sodium ions can leak, called a potassium-sodium (K+-Na+) ―leak‖ channel. These channels are far more permeable to potassium than to sodium, normally about 100 times as permeable. This differential in permeability is exceedingly important in determining the level of the normal resting membrane potential. 21  Relation of the Diffusion Potential to the Concentration Difference—The Nernst Potential The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane is called the Nernst potential for that ion The magnitude of this Nernst potential is determined by the ratio of the concentrations of that specific ion on the two sides of the membrane. 22  Nernst Equation Nernst equation, can be used to calculate the Nernst potential for any univalent ion at normal body temperature (37°C): 23 Calculation of the Diffusion Potential When the Membrane Is Permeable to Several Different Ions Goldman-Hodgkin-Katz equation, gives the calculated membrane potential on the inside of the membrane when two univalent positive ions, sodium (Na+) and potassium (K+), and one univalent negative ion, chloride (Cl–), are involved. 24 25 26 27