Homeostasis Part 2 Lecture PDF

Introduction to Organ Systems, Homeostasis, Biological Communication and Control - Part 2 Prof Stefan du Plessis Objectives Control Systems and Homeostasis: Define Physiological control systems Explain the difference between Local control and Reflex control Describe the properti...

Introduction to Organ Systems, Homeostasis, Biological Communication and Control - Part 2 Prof Stefan du Plessis Objectives Control Systems and Homeostasis: Define Physiological control systems Explain the difference between Local control and Reflex control Describe the properties of Homeostatic Reflex Pathways Define the primary components of a reflex pathway response loop Discuss Feedback loops and distinguish between, Negative feedback (Homeostatic), Positive Feedback (Non-homeostatic) and Feedforward Biological Rhythms and setpoints Control Systems and Homeostasis The important concept to remember is that the body monitors its internal state and try to keep it stable. i.e. certain key functions must stay within a particular operating range (not too far from its setpoint) and the body takes action to correct disruptions that threaten its normal function through physiological control mechanisms Control Systems All control systems have 3 components (in its simplest form) Integrate information and initiates an appropriate response Homeostasis and Controls Control Pathways Maintain homeostasis via Control Pathways There are 2 basic patterns of control mechanisms: Local control (Simplest form) Paracrines & autocrines Long-distance / reflex control Nervous Endocrine Cytokines  Control Pathways Local Control Reflex Control Simplest form of control More complex system Restricted to the Changes are cell/tissue involved widespread/systemic Nearby cell(s) sense the change in vicinity and Any long-distance pathway respond by usually that uses the nervous releasing a chemical. and/or endocrine system Response is restricted to Expand on the three area where the change components of response took place loop e.g. Tissue O2 decrease - cells secrete chemical – diffuses e.g. Baroreceptors sense blood pressure is to low – relay to vascular smooth muscle cells - leading to vasodilation information to brain via afferent neurons – respond via ANS and increase HR and peripheral resistance Example: Steps in a reflex Pathway Reflex Control Response Loop Stimulus – disturbance that sets the pathway in motion Sensor/receptor – continuously monitor environment for specific parameter Integrating centers are Afferent path – when activated by usually part of the change the sensor sends input signal nervous or endocrine system to integrating center Integration center – compares input signal with the setpoint or desired value Efferent path - output signal that Output signals may be chemical, electrical or travels to target combination of both Effector - target cell/tissue that carries out the appropriate response to bring variable back within limits Types of Receptors Feedback Loops Feedback loops modulate the response Negative: are homeostatic Response slows stimulation Return to optimal range Responds to an altered output by restoring itself towards a predetermined set point Positive: are NOT homeostatic Stimulation drives more stimulation Responds to a disturbance by moving variables farther away from the initial set point Feedforward control prepares body for change Can anticipate changes and prompt the system to act before the alterations begin to affect it Setpoint Homeostatic range oscillates around setpoint Each regulated variable has a normal range within which it can vary without triggering correction Setpoint Setpoints vary between individuals and can change over time Setpoints can be changed to accommodate different physiological requirements Inheritance Acclimatization – adaptation to a given set of environmental conditions Biorhythms – regulated variables that change predictably and create repeating cycles e.g. circadian rhythm for blood pressure, body temperature, metabolic processes Negative Feedback Opposes or removes the signal Designed to keep the system at or near a setpoint Can restore the normal state, but cannot prevent the original stimulus Negative Feedback Positive Feedback Reflex pathway that is not homeostatic Response reinforces stimulus, rather than decreasing or removing it The response sends the regulated value even farther away from its normal value (out of control/ballistic) Requires intervention outside the loop to stop the response Positive Feedback Feedforward Control Reflexes that predict a change is about to occur and starts the response loop in anticipation of the change e.g. Salivation reflex Cephalic phase Cannon’s Postulates – Properties of Homeostatic Control Systems The role of the nervous system in preserving the fitness of the internal environment. The concept of tonic level of activity (e.g. volume button). The concept of antagonistic controls - different signals that have opposing effect. (systems that are not under tonic control are usually under antagonistic control) The concept that chemical signals have different effects in different tissues of the body. Tonic Control Antagonistic One Ligand - Different Effects The target cell response depends on its receptors (isoforms) or its associated intracellular pathways, not on the ligand. Objectives Biological Communication: Outline and compare the different mechanisms of biological communication in the body by referring to: Short distance communication -- Cell-Cell Communication, Contact dependent, Gap junctions, Paracrine, Autocrine, Juxtacrine, Intracrine Long distance communication -- Electrical or Chemical/Neural Hormonal Short- or Long-distance communication -- Cytokines Cell-to-Cell Communication Human body compose of 75 trillion cells Cells may be only 1m up to meters apart Need to communicate rapidly and convey huge amount of information to each other Only two types of physiological signals: Electrical = changes in RMP Chemical = molecules secreted into ECF Cells receiving these signals = Target cells Cell-to-Cell Communication Our bodies use various basic methods of cell-to-cell communication: Short Distance Gap junctions Juxtacrine or Contact-dependant signals Intracrine Local communication (autocrine and paracrine) Long-distance communication Cell-to-Cell Communication Gap junctions Direct cell-to-cell communication Union of membrane-spanning proteins (connexins) Transfer chemical & electrical signals >20 Isoforms – allowing movement of various ions and small molecules (AA, ATP, cAMP) Cell-to-Cell Communication Contact-dependent signals/Juxtacrine Requires cell-to-cell contact (surface molecule on one cell bind to membrane protein on another) Immune system, growth and development Cell adhesion molecules acts as receptors in cell-to- cell signaling and is linked to cytoskeleton and intracellular enzymes CAMs transfer signals in both directions across cell membrane Cell-to-Cell Communication Intracrine Refers to a hormone that acts inside a cell, regulating intracellular events. The cell stimulates itself by cellular production of a factor that acts within the cell. Cell-to-Cell Communication Local cell-to-cell communication Chemical signals distributed by diffusion in Interstitial fluid Restricted to adjacent cells as diffusion is limiting factor Two types: Autocrine signals – chemical signal that acts on cell that secreted it Paracrine signals – chemical signal that acts on cells in immediate vicinity e.g. cytokines – regulatory peptides, eicosanoids - lipid derived signal molecules Cell-to-Cell Communication Long distance communication: Hormones Signal Chemicals Made in endocrine cells Transported via blood all over body Only cells with receptors can react (Target cells) Cell-to-Cell Communication Long distance communication: Neurotransmitter Electrical signal travels down axon - then translated into chemical signal Chemical signal then secreted by neuron = neurocrine Neurotransmitter = diffuse to target cell across narrow extracellular space and have rapid response Neuromodulator = if neurocrine acts more slowly as a paracrine or autocrine signal Cell-to-Cell Communication Long distance communication: Neurohormone Electrical signal travels down axon - then translated into chemical signal Chemical signal then secreted by neuron = neurocrine Neurohormone = if neurocrine diffuse into blood for distribution. Cell-to-Cell Communication Cytokines Variety of regulatory peptides All nucleated cells secrete cytokines in response to stimuli Control cell development, cell differentiation and immune response Mode of action During development and differentiation they act as autocrine/paracrine During stress and inflammation they may act on distant targets (transported through circulation) Cytokines Hormones Act on broad spectrum of cells Specific target cells Not produced by specialized cells Produced by specialized cells (glands) Most peptide/protein hormones are Made on demand made in advance and stored Intracellular Communication (Signal Transduction) Signal pathway First messenger Second messenger Concept Checks: Extended Matching Communication Communication Communication Property Method Property ? Electrical signal Autocrine ? Chemical signal ? Both electrical and chemical signal Cytokine Gap Junction You see a car speeding towards you and jump out of the way. Do you think the internal signal to jump have Hormone been transmitted by a paracrine signal? Provide 2 reasons to explain why or why not. Neurohormone Neurotransmitter Paracrine Concept Checks What is a synonym for a reflex control pathway? Provide an example of a variable that is controlled by local control? Give 7 basic steps of reflex control pathway Provide an example of a variable that is controlled by Compare local control to reflex (long distance) control long distance control? Homeostasis tries to maintain variables within a range and if variable moves out of range, there is a response. Describe this response. Concept Checks What is the drawback of having only a single control What is acclimatization? system (a heater) for maintaining aquarium water temperature in some desired range? What is a feedback loop? What is tonic control? What is a positive feedback loop? What is antagonistic control? Concept Checks What is negative feedback control? What is feedforward control? Is positive feedback a common method for maintaining Give an example of Negative feedback. homeostasis? What is the difference between tonic control and antagonistic control? Define Set Point. Concept Checks What is the pathway of a simple neural reflex? What is an example of a simple neural reflex? What is the pathway of a simple endocrine reflex? What is an example of a simple endocrine reflex? What is the pathway of a neurohormone reflex? What is an example of a neurohormone reflex?