Understanding Homeostasis

Definition of Homeostasis

• homeo means "same" and stasis means "standing"
• Term to describe the constant state of the internal environment.
• Is a state of balance in the body.
• Homeostatic mechanisms refer to activities that help to maintain hemostasis.

What is Homeostasis?

• Body cells function optimally in the correct environment.
• Correct temperature
• Correct water levels
• Correct glucose concentration
• The body is equipped with mechanisms designed to keep cells in a constant environment.

Homeostasis Characteristics

• Ability to maintain a relatively stable internal environment in a dynamic external environment
• Internal environment of the body is always in a dynamic state of equilibrium.
• Chemical, thermal, and neural factors work together to maintain.
• Homeostatic system maintains its structure and functions by dynamic equilibria strictly regulated by interdependent regulation mechanisms
• The system reacts to environmental changes through modifications of equal size and opposite direction to those that created the change

Summary of Homeostasis

• Body’s internal environment comprises extracellular fluid.
• Organ systems' job is to maintain a stable internal environment.
• Numerous variables require homeostatic maintenance within the body
• Loss of homeostasis for just one variable may trigger changes in others
• Example: a consideration is the swing in blood glucose level over the course of day

General Characteristics of Homeostatic Control Systems

• Denotes the stable condition of the internal environment.
• Stability results from operation of compensatory homeostatic control systems.

Homeostasis Control System Components

• Reflexes
• Local homeostatic responses
• Intercellular chemical messengers

Reflex Arc Components

• A reflex arc pathway may be neural or hormonal and consists of a receptor, afferent pathway, integrating center, efferent pathway, and effector.

Intercellular Communication

• Essential to reflexes and local response as well as is achieved by neurotransmitters, hormones, paracrine and autocrine agents
• Intercellular communication through either gap junctions or cell-bound messengers is less common

Homeostasis and Body Conditions

• Conditions in the body must remain within a narrow range.
• This involves keeping the internal environment within set ranges/limits.

Mechanism of Homeostasis

• Thermoregulation maintains a steady body temperature under a variety of conditions.
• Systems involved include:
  • Muscular
  • Integument (skin)
  • Respiratory
  • Circulatory
  • Nervous (hypothalamus in brain)
  • Endocrine (hormones, feedback)

Body Temperature

• The living processes in the cells depend on the activity of enzymes
• Enzymes function in specific conditions, such as those of temperature and pH
• Changing conditions affects the function of the enzymes
• Change may lead to the death of the cells or, ultimately, the whole organism
• Internal environment requires regulation and kept constant regulated and kept constant.
• Human body temperature varies between 36.1 – 37.8 °C with average 36.8°C.

Internal Communication

• Body requires good internal communication for it to be maintained with the aid of the endocrine and nervous systems
• Feedback inhibition will limit the actuation of a system and shut it down when a certain substance is too high such as water, glucose, salt, heat and CO2
• When there is too little of this product, the system will "turn back on."

Home Heating System

• Homeostatic mechanisms reestablish homeostasis when there is an imbalance.
• In a home heating system:
  • When the temperature of a room decreases below a set point, the thermostat electrically starts the furnace.
  • As the temperature of the room rises to the set point, the thermostat shuts down the furnace.
  • As the room cools, step one is repeated.
• System Components
  • The Sensor detects the stress.
  • Control Center receives information from the sensor and sends a message to the Effector.
  • The Effector receives the message from the control center and produces the response, which reestablishes homeostasis.

Homeostatic Control Mechanisms

• Variable produces a change in the body
• Three interdependent components of control mechanisms
  • 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

Thermostatic heating system Components

• Variable is the characteristic of the internal environment controlled by a mechanism like internal temperature
• Sensor detects the change in the variable, feeds this information to the Integrator in the control center like a thermometer
• Integrator puts together and records the data to create the setpoint
• Effector is the mechanism that has the effect of this variable, such as a furnace

Review of Homeostasis

• Temperature changes are detected by the thermometer
• This relays the temp back the thermostat
• The thermostat is then set to an ideal that is signaled to the furnace
• The furnace then either heats or cools the area back to the ideal set point
• An example would be shutting down when the temp is recorded above the set temp

Temperature Regulation

• Set point refers to a single value that the body works to maintain, this includes:
• Levels of water, carbs, oxygen, acidity etc.
• Processes that reduce discrepancies from the set point are known as negative feedback.
• Adaptive way in which the body changes its set point based on current environment

Temperature Regulation as a Biological Priority

• Body temperature regulation is a key biological priority
• Takes up about two-thirds of our energy/kilocalories per day
• Basal metabolism refers to the energy that is required to maintain body temperature while at rest

Homeostatic Regulation of Body Temperature

• Heat receptors in the skin is the sensors for hyperthermia, in the body.
• Sends stress signals to the hypothalamus which acts as the control center
• Effectors such as increased activity of sweat glands and increased blood flow to the skin are activated
• This causes perspiration and cooling of the skin
• When a stress is low enough to be considered shut down the mechanism, processes such as sweating are reduced.

Feedback Systems

• Positive
• Negative

Cellular Relay Race

• Cellular relay race for homeostasis
• Stimulus to receptor to integrating center to effector to response to stimulus

Negative Feedback Control

• Animals/Humans must have bodily constraints within a tolerable limit to maintain proper function
• Use of negative feedback control which brings about a reaction from receptors and effectors to make sure that conditions are still favorable
• The shift within a variable brings about a change that moves the direction against the original one, stabilizing the overall system

Negative Feedback

• Is an occurrence when feedback from an integrator results in a reversal of the change in direction.
• Negative feedback tends to stabilise a system by correcting deviations from the set point

Homeostatic Control Mechanisms

• Input: Information sent along afferent pathway to a control center.
• Change detected by a receptor (sensor).
• Stimulus: Produces a change in a variable.
• Output: Information sent along efferent pathway to an effector.
• Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis.

Negative Feedback

• Cooling and Heating are components to negative feedback.
• In cooling vasodilation occurs to release heat.
• Sweating(Diaphoresis) can also occur to cool down.
• The cooling is triggered by the hypothalamus when external factors are in play.
• In heating, shivers are triggered which generate heat.
• In order to conserve heat vasoconstriction occurs.
• The hypothalamus is the trigger for this cycle when external actors are in play as well.

Homeostasis and the Environment

• An example of Homeostasis is humans shivering in response to cooling
• Homeostasis allows organisms to remain balanced with certain environments
• Not maintaining these balances can kill the organism

Negative Feedback Systems

• Systems when in the negative, send signals that shuts off the original stimulus
• Example is regulation of blood glucose levels

Negative Feedback Loop Requirements

• Sensor to detect changes needed in certain variable
• Comparator to be a reference point for the sensor to compare to
• Effector which determines direction of signal to restore levels

Dueling Hormones

• What goes up, must come down in insulin and glucagon
• Insulin is produced by beta-cells of the pancreas to trigger the use of glucose by the body, to lower blood glucose, while glucagon is produced by alpha cells, to increase blood sugar
• Insulin facilitates the transport of glucose into target cells
• Signals the liver to break down glycogen into simple glucose to increase the levels

Dueling Mechanisms

• Thermoregulation is one of the many dueling mechanisms in the body.
• It is where sweating assists the body in cooling vs. shivering which assists with warming processes.
• Blood pressure uses a dueling mechanism of Vasoconstriction vs. vasodilation.
• Osmoregulation uses Hypotonic vs. hypertonic dueling mechanisms.

Hire-Wire Artist Model

• Model of homeostasis
• Demonstrates body's responses to maintain a position of equilibrium.
• Variable: position of body
• Setpoint: directly over the wire
• Sensors: nerve receptors (eyes, inner ears, muscle stretch receptors, etc.)
• Integrator: brain
• Effectors: skeletal muscles
• High-wire artist uses negative feedback to maintain relatively constant position on wire.

Positive Feedback

• Ability to maintain the direction of a stimulus and can accelerate its effect
• Accelerates a process leading to explosive effects
• Involves no means of stopping

Positive Feedback Mechanisms

• Homeostatic systems that exhibit two primary Characteristics:
• Time Limitation - Processes in the body are completed within a constrained time frame.
• Intensification of stress – The initial imbalance or stress is intensified rather than reduced Typical Process
• Stress -Sensor - Control Center - Effector

Positive Feedback Control Details

• Is a Biochemical control in which the accumulation of a substance will trigger the accumulation of an enzyme, further increasing the accumulation of the substance
• The trigger works in information that further accelerates the stimulus of the response from increasing levels of a trigger

Blood Clotting and Positive Feedback

• An example of homeostasis related to blood clotting is a break or tear in a blood vessel
• This tear triggers the feedback cycle which entails the release of chemicals that attract more platelets to that site
• The resulting process seals the wound in a positive feedback loop until the cycle ends

Hyperthermia

• Causes a positive feedback within homeostasis because it pushes the body temperature continually higher
• If the temperature reaches 45 degrees centigrade (113 degrees Fahrenheit), cellular proteins denature bringing metabolism to a stop, and leads to death

Chronic Hypertension

• Favors the process of atherosclerosis
• Process can narrow blood vessels
• Intensifies the hypertension, which causes even more damage to the walls of blood vessels

Feedback Control Comparison

• Negative feedback: promotes stability
• Feed-forward: anticipates change, and prepares for them
• Positive feedback: promotes a change in one direction that in many instances can cause distress or death to subject

Feed Forward Regulation

• Anticipates changes in regulated variable
• Improves the speed of the body's homeostatic responses
• Minimizes fluctuations in the level of the variable being regulated
• Works in conjunction with feedback system

Temperature Sensitive Nerve Cells Example

• A temperature shift can trigger a negative loop in order to accommodate the change in the body
• Addition of additional nerve cells, such as in the skin, may take an effect.
• Other bodily effects are the measure of a change, such as an opened door in order to automatically turn on the heater

Limitations of Negative Feedback

• Feedback control must occur after a variable is disturbed
• The correction will be incomplete without a measurement being applied to the magnitude fo error
• Overcorrection can cause oscillations
• These disadvantages will be overriden by proper regulatory measures
• Insulin regulation
• Release of insulin causes glucose levels to decrease

Advantages of Homeostasis

• Has benefits of survival due to the animal's adapting to changing environment, such differences stepping outside.
• Body maintains a norm that attempts to stay at an even level
• Can only work with extreme situations by disabling negative feedback; treatment must ensue

Acclimatization

• Refers to how and organism can adapt to certain events or changes
• The improvement happens, given the exposure without any changes in genetic features, it may be irreversible

Biological Rhythms

• Provides a feed forward component to control systems for homeostasis .
• Rhythms are internally driven by pacesetters within the brain that get adjusted by cues, such as light.
• Without these adjustments, the body will free run.

Resetting of Set Point Details

• External environment changes can displace variable from set point
• Set points can adjust within the body through new values such as a response to high body temperature
• The elevated temperature is maintained and adaptive so infection stops because elevated temperature inhibits pathogens to proliferate.

Balance of Chemical Substances Balance

• Chemical body homeostasis will be achieved through matching inputs and outputs
• Overall balance will shift through negative or positive states

Homeostatic Imbalance

• Disturbance/Destruction in overall equilibrium
  • Results in over-correction of of negative feedback