What is Physiology?
Physiology is the study of the normal functions of the living things: their various systems & the different organs that make up the systems!
- We shaver when we are cold ?
Why
- TO HELP WARM UP BECAUSE SHIVERING GENERATES HEAT
How
- INVOLUNTARY REPETITIVE CONTRACTION OF THE SKELETAL MUSCLES GENERATES HEAT
The Physiologists explain WHY and HOW the processes occur.
Organization of the Human Body
Body Systems (11 systems)
ALL SYSTEMS ARE INERCONNECTED & ALL PHYSIOLOGICAL SYSTEMS ARE INTERDEPENDENT!
- Themes in Physiology:
- Structure and function are related.
- Living organisms need energy.
- Information flow coordinates body functions.
- Homeostasis maintains Internal stability.
INTERNAL ENVIRONMENT OF THE BODY
IF EACH CELL IS ABLE TO SURVIVE ON IT’S OWN, THEN WHY CAN’T THEY SURVIVE WHEN THE BODY DIES?
The cells in a multicellular organism cannot live and function without contributions from the other body cells because the vast majority of cells are not in direct contact with the external environment.
WHAT IS EXTRACELLULAR FLUID (ECF)?
WHAT IS INTRACELLULAR FLUID (ICF)?
WHAT IS PLASMA?
The fluid contained within all body cellsis called intracellular fluid (ICF).
The fluid outside the cells is called extracellular fluid (ECF).
THE ECF IS THE INTERNAL ENVIRONMENTOF THE BODY!
ICF is inside the cells.
ECF is outside the cells.
As humans, the environment we live in is the external environment;
Our cells live in the body’s internal environment.
DOES A UNICELLULAR ORGANISM HAVE AN INTERNAL ENVIRONMENT?
Unicellular organisms do NOT have an internal environment as they are cells placed directly in their external environment. Their cell membranes are in direct contact with the outside.
Therefore, in the humans, all cells live in the Extracellular fluid (ECF) which is essentially the Internal environment of the body, also called the milieu interieur
(A term coined by the Physiologist Claude Bernard).
WHAT IS HOMEOSTASIS?
Maintenance of nearly constant conditions in the internal environment despite changes in the external environment is called Homeostasis.
It is a state of balance in the body.
Examples: Maintenance of body temperature & glucose levels in the body.
- The word “Homeostasis” was coined by the American Physiologist Walter Cannon in 1929.
- He said that Homeostasis was a condition that: “may vary, but which is relatively constant.” Homeostasis means “keeping things the same” but “not keeping everything the same”.
- For Homeostasis, you need:
- a VARIABLE which is a regulated condition of the ECF that is monitored & kept relatively constant {e.g. Blood pressure}
- a SENSOR that measures the value of the regulated variable {e.g. Baroreceptors},
- a SET POINT which is the normal range of the value for the regulated variable {A Blood Pressure of 120/80 mmHg} ,
- a CONTROL CENTER which interprets the error if there is a difference b/w the set point and the value of the variable {CNS & Endocrine system} and
- an EFFECTOR that brings about the change to take the variable back to the Set Point {cardiac muscle).
- Regulated Variables in the Human Body:
- Oxygen
- Carbon dioxide
- Na+ion
- K+ion
- H+ion
- Ca2 +ion
- Glucose
- Blood pressure
- Blood volume
- Blood Osmolarity
- Core body temperature
- Questions you should ask about any homeostatically regulated system…
- What and where is the sensor?
- What and where is the control center?
- What and where is the effector(s)? How do they alter their activities so as to produce a response?
- Does the response lead to a change in the regulated variable/stimulus consistent with error signal reduction (negative feedback)?
TYPES OF CONTROL SYSTEMS IN THE BODY These are brought into action after a change has been detected.
NEGATIVE FEEDBACK LOOP
If some variable becomes excessive or deficient (moves away from the set point), the control system initiates a series of changes that returns the system to the set-point from where it started.
Thus, the changes occur opposite to the direction of the stimulus.
Examples of Control Systems of the body aiding in Homeostasis using Negative Feedback:
- Body temperature Regulation (Failure of Homeostasis results in Heat Stroke or Hypothermia)
- Blood Pressure Regulation (Failure of Homeostasis results in Hypertension or Hypotension)
- Blood Glucose Regulation (Failure of Homeostasis results in Diabetes Mellitus)
- Potassium ion concentration (Failure of Homeostasis results in Hyperkalemia or Hypokalemia)
- Oxygen and Carbon Dioxide in the Blood (Failure of Homeostasis results in Hypoxia & Hypercapnia)
POSITIVE FEEDBACK LOOP
If some variable becomes excessive or deficient, the control system causes more of the same initiating stimulus so that the condition worsens and the system moves further away from the homeostasis.
So, response occurs in the direction of the stimulus or change, thus, enhancing or exaggerating it.
E.g. person bleeds, heart weakens, can’t pump enough blood, heart weakens further as less blood reaches it. Thus, the initiating stimulus causes more of the same.
Positive feedback is better known as “vicious cycle”.
HOWEVER, IT CAN BE USEFUL IN SOME INSTANCES.
Example of Positive Feedback Cycle BLOOD CLOTTING
Why do most control systems of the body operate by negative feedback rather than positive feedback?
It is because positive feedback leads to instability rather than stability, and, in some cases, can cause death.
Adaptive Control
Adaptive control is delayed negative feedback. Also contains feed forward mechanisms.
•A good example of Adaptive control is correction of motor movements of parts of the body.
•A good example of feed forward mechanism is salivating at sight of food or shivering before jumping into a pool or increased breathing before starting exercise. All these activities are anticipatory changes that prepare one for the upcoming activity, before the activity actually starts.
QUESTION 1
What are the 3 different types of control systems working to bring about homeostasis in the body.
Give one example of each.
- Negative Feedback:
-Temperature Regulation
-Blood Pressure Regulation - Positive Feedback
-Childbirth
-Blood Clotting - Feed Forward
-Salivation on sight of food
-Release of Insulin from pancreas as soon as food is placed in the mouth.
QUESTION 2
Exposure to a hot environment causes the body to sweat. The hotter the environment, the greater the sweating.
Two students are arguing about it. Student A says that it is Positive Feedback while student B insists that it is Negative Feedback.
Who do u agree with and Why?
QUESTION 3
What factors are homeostatically maintained?
QUESTION 4
Compare Negative and Positive Feedback systems?