HOMEOSTASIS
Physiology
Study of functions of living things
Classified by organ or organ system being studied
2 approaches to explain body function
Emphasis on mechanism (how) - explanations in terms of cause and effect
Emphasis on purpose of body functions - explanations are in terms of meeting bodily need
Can specialize in levels of organisms other than systematic
Anatomy
Study structure of body
Physiological mechanisms possible through structural design
Structure determines what functions can occur. so if structure changes so must function
Structural levels
Tissue level
Organ level
Cellular level
Organ system level
Chemical level
Organism level
Body functions are integrated
Body parts work together
Proper functioning of 1 part = proper functioning of another
External environment
External side of epithelial body barrier
Air in lungs, urine in bladder
Internal environment
Immediate environment of cells
Includes tissue fluid and plasma
Body fluids and compartments
Body divided into compartments
Compartments contain fluids
Compartments separated by epithelial membranes
Membranes semi permeable
Transport between membranes
Total body water (TBW)
Consists of water and dissolved materials
Includes solutions within cells and solutions surrounding cells
Body fluid compartments
Intracellular fluid (ICF)
Fluid contained within all body cells
Extracellular fluid (ECF)
Fluid environment in which cells live
2 components (plasma and interstitial fluid)
Homeostasis
Maintenance of relatively stable physical and chemical conditions within specific limits
Dynamic steady state
Compensatory physiological changes minimizes changes from steady state
Temp, volume and composition regulated
Requires organ system integration
Disruption = disease and death
Cells in multicellular organisms
Can't directly exchange nutrients and waste products with external environment
Exchange made via internal envronment
Factors critical for cell survival must be regulated
Homeostatically regulated factors
Conc of nutrients, O2, CO2, waste products, water salts and electrolytes
pH
Plasma volume and bp
Temp
Molecular basis for stable internal environment
Proteins require specific shape for efficient function
Conformation affected by: pH, temp, ion conc
Protein function diminished or lost if conformation changed - manifests as disease conditions
Stable internal environment maintains protein conformation
Terms
Regulated variables - aspect which is maintained within a range
Negative feedback - regulated variable decreases, system responds to make it increase and is self correcting
Set point - expected value of regulated variable
Error signal - difference between the value of set point and value of regulated variable
Components
Receptors - sensors that detect stimuli (thermo, chemo, baro)
Integrating center - orchestrates appropriate response, many found in brain
Effectors - responsible for body responses
Signals
Allows components to communicate
Input signals is from a receptor to integrating center
Output signal is from integrating center to effector
Chemical messages sent via neurons
Roles of organ systems in homeostatic regulation
Table 1 - 1 on power point
Maintain homeostasis by:
Detecting deviations from normal in the factor that requires regulation
Integrating info with other relevant info
Making appropriate adjustments to restore homeostasis
Control systems
Intrinsic regulation
Extrinsic regulation
Auto
Built in / inherent in organs
Serves only in the organ they occur in
Cell, tissue, organ or organ system adjusts its activities automatically in response to environmental change
Systemic / reflex
Mechanisms initiated outside organ to alter organs activity
Results from activities of nervous system and / or endocrine system
Coordinated response - controls / adjusts activities of many other systems simultaneously
Forward feedback - response reinforces stimulus, sending variables farther from set point
Feed forward - response made in anticipation of change
Imbalance
Disturbance of homeostasis
Increases risk of disease
Control systems become less efficient
Contributes to changes associated with aging
If negative feedback mechanisms become overwhelmed, destructive positive feedback mechanisms may take over
Malfunctions of body systems result in homeostatic imbalance - unstable internal environment, cell function disrupted leads to pathology
Ageing - control system less efficient, internal environment less stable, increased risk of illness