WEEK10 - module 4. Principles of Homeostasis

Learning objectives 

 

-Describe a simple negative feedback system that allows control over room temperature, incorporating the terms effector, sensor, set point, stimulus, and variable. 

 

: When room temperature increases or decreases, sensor(thermometer) detects the variable(temp) as the stimulus and sends the afferent signal to the integration center(thermostat). Then the efferent signal is sent to the effector(heater) to adjust the temperature by turning on or off. When the effector brings the temperature back to the set point, it sends the negative feedback to the stimulus. 

 

-Describe what would happen if changes in room temperature generated positive feedback loops

: If the room temperature generates positive feedback loops, it increases or decreases temperature inlimitely. It increases the deviation from the set point. 

 

-Describe two common examples of positive feedback that are non-pathological, commenting on their duration

: blood clotting and (oxytocin -milk production/ child birth)

 

-Blood clotting :

When the blood vessels are destroyed, the damaged tissue releases factors that bring platelets to the site of the wound. As the plateletes are gathered, the chemicals released by platelets attract more plateletes to the site. This positive feedback ends when the damaged tissue is healed

 

-Oxytocin : child birth : 

When the cervix stretches (stimulus), sensory neuron around it send the signal to the hypothalamus. It secretes oxytocin via posterior pituitary gland. Oxytocin stimulates myometrium in the uterus to contract. When the uterus is contracted, cervix stretches more (positive feedback) and the stimulus ends when the baby comes out.

 

-Oxytocin : milk ejection :

When the baby suckles the nipple, sensory neurons around it send the signal to the hypothalamus. Hypothalamus secretes oxytocin via posterior pituitary gland. Oxytocin stimulates myoepithelial cells in the mammary gland, which let down milk. 

 

 

-Homeostatic mechanisms rely on measuring variables in blood, but are primarily concerned with the ECF, i.e. the condition of fluid that surround cells. Explain this.

Internal millieu

: The homeostasis is controlled by the vital mechanism such as cardiac out put, renal function, respiratory function and etc. And those organ system detect the ECF to operate. So the control and creation of ECF composition is depended on the organ system. ECF composition is called internal millieu for that reason. 

 

-Homeostatic variables oscillate: describe what this means using body temperature as an example – differentiate this from changes in set point, again referring to body temperature. 

Osciliation and the homeostasis

: Osciliation occurs when the variable fluctuates around the set point. When the stimulus makes the variable to heat the bottom , negative loop turns on and the variable is adjusted to the level near to the set point. 

When the body temperature decreases, sensors such as nerve endings (shell) and hypothalamus(core) sense it and send the stimulus to the hypothalamus (control center of thermoregulation). It then sends signals to effectors (such as smooth muscles on the blood vessels and skeletal muscles) and make the body temperature increase. This whole process and fluctuation around the set point is osciliation.

 

 

-Use either body temperature or plasma cortisol levels to illustrate what a diurnal (or circadian) rhythm is and explain the variation in the set-point observed.

 

Circadian rhythm

: Normally osciliation refers to the fluctuation of the variables (around fixed set point) and the circadian rythm explains that the set point is not always fixed, and it can move in 24hr cycle.

Our set point of the body temperature is the lowest in the day time and our cortisol level is at peak in the morning. Set points change as our body demands change. 

 

-Walter Cannon is known as the ‘father of homeostasis’ because he realized or described what?

: He figured out that control of variables,homeostasis is a result from not only one agent but numerous effectors.

 

-Variables corrected by homeostasis in biological systems show something termed error – what does this mean and relate this to the concept of gain. 

: Gain = correction/ error.

Error represent how well the homeostasis works on our body. when there's a stress toward body, homeostasis (negative feedback) adjust/correct the level of stimulus (= correction) and bring it near the set point. Gap between the original set point and adjusted/ corrected point is called error. 

 

 

 

PPT

Design a Homeostatic System

Stimulus : dropping room temperature 

Control center (thermostat)

Signal wire turns heater on

Effector(heater): heater on

Response : temperature rises

Receptor-sensor (thermometer in thermostat) : set pont

 

Stimulus : rising room temperature

Control center (thermostat)

Signal wire turns heater off

Effector(heater) : heater off

Response : temperature drops

Receptor-sensor (thermometer in the thermostat) : set point

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A general Homeostatic System

 

1. Imbalance in homeostasis are detected as a stimulus by the receptors. 

2. Receptor/ the sensor sends the signal to the control center with the afferent pathway.

3. Control center recieves the signal and send the signal to the effector with the efferent pathway.

4. Effector feeds back with the response and brings it back to the balance in homeostasis.

-> In this way, homeostasis is maintain in variables.

 

Negative feed back occurs when the response  feeds back to the stimulus and it brings back to the homeostasis.

 

 

 

 

 

 

 

 

 

Why Homeostasis is Important

-Biochemical processes in cells are sensitive to temp, pH, concentrations of nutrients molecules.

-The external environment of cells is the ECF (descrived as the internal milieu of the body)

-Conditions within the ECF must be kept stable, within a range of tolerable values, or biochemical operations inside and outside cells crash

-Nervous and endocrine systems are involved in directing homeostatic responses. These feedback systems are operating constantly, every second of every day of every year.

-Disease can often be best thought of as disruption to homeostasis.

 

Our body uses enzymes to maintain our body functions. They are made up of protein which is easily damaged by temperature change, pH and other factors. 

 

 

 

 

 

 

 

 

 

 

History

Claude Bernard (mid 1800's)

-The "father" of homeostasis, recognized that organ system of body (kidney, heart etc) create and control composition of " internal millieu" and that this constancy is required for cells of the body to operate

" It is the fixity of the internal environment that is the condition of free and independent life.. all the vital mechanisms, however varied they may be, have only one object, that of preserving constant the conditions of the internal milieu"

-By "vital mechanisms" he meant things like cardiac output, renal function, respiratory function etc.

 

 

Walter Cannon (early 20th century)

-American physiologist who first defined the principles of homeostatic control mechanisms

-Determined that numerous agents/processes act together (show integrated activity) to control particular variables (ex. blood pressure, body temp)

-Take thermoregulation for example, 

Skin, nerve, muscle, blood flow, catecholamine levels, water balance, renal function conscious and unconscious CNS decisions..

are all involved, acting in an integrated fashion to help control body temperature (just one important homeostatic variable)

 

 

 

 

 

 

 

 

 

Gain

 

error = 38-37.5

correction = 37.5?

gain = 37.5/ 0.5 = ???

 

 

 

 

 

 

 

 

 

 

Circadian Rhythms

-Set points of some controlled variables are not constantly fixed over time, but can vary, often with a diurnal rhythm, also known as a circadian rhythm (approx. 24hr daily cylcle)

 

-Examples are core body temperature & cortisol secretion

 

-Set points may also change because of changing physiological conditions or demands, eg fever or because of chronic (ie. prolonged) insult, eg established by hypertension

 

Circadian Rhythms

-Cortisol levels, Core body temperature

 

 

 

 

 

 

 

 

 

 

 

Oscillations

-An efficient homeostatic system that has low tolerance for change will respond quickly and minimises the size (amplitude) of the osciliations

-A less efficient homeostatic system that hass high tolerance for change will respond more slowly and the oscillations will be bigger.

 

Can you think of a physiological homeostatic system with low tolerance and one with high tolerance for change?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Self-paced quiz

 

-When the variable crushes the balance in homeostasis, the receptor/sensor detect the changes as a stimulus and send the signal to the control center with an afferent pathway.

-Control center recieves the signal and sends the signal with an efferent pathway to the effector, which are mostly glands and organs. 

-Receptors/effectors react to that signal, which is sent from the control center, and bring about changes to alter the  imbalance to the balance in homeostasis. Negative feedback stops the reaction of receptors/effectors when the body reaches its set-point.

-The set-points are not fixed, and can vary. Oscillation occurs between the range of set-point and the negative feedback.

Osciliation and circadian rythm

Osciliation normally refers to the fluctuation of the variable around the 'fixed' set point. However, set-points are not always fixed, and they are also constantly moving within the physiologial tolerance limits. It is referred to  Circadian/diurnal rythm. It normally happens in 24hrs cycle as a respond to the change in the body demands.

For example, cortisol and core body temperature have the circadian rythm. The level of cortisol is at peak in the morning when we get up. And the core body temperature is normally low in the early morning.

 

 

 

 

 

Summary