1. 8.1 Human Body Systems and Homeostasis

2. Organization of Living Things
The trillions of cells in your body can be organized into approximately 100 different types of cells.
  Cells that perform a common function are organized into tissues, which are organized into organs. Organs work together in systems.
Cells-> Tissues->Organs->Body Systems
Smooth muscle cells make up smooth muscle tissue. Smooth muscle tissue lines the inside of the urinary bladder, an organ that is part of the excretory (urinary) system.

3. Human Body Systems Human body systems perform the following functions:
transport materials in the body via circulatory (blood, nutrients, oxygen, cellular waste), lymphatic (fat and excess tissue fluid), and immune systems
add or remove substances from blood
communicate with the brain and spinal cord
Continued…

4. Human Body Systems cont’d
enable the body to move through the muscular and skeletal systems
allow responses from external and internal stimuli
secrete chemicals for messaging between
produce sex hormones

5. Homeostasis Some of the variables controlled are:
Homeostasis - the tendency of the body to maintain a relatively constant internal environment. It is dynamic. It allows for fluctuations throughout the day and night.
Some of the variables controlled are:
-temperature
-blood glucose concentration
-blood pH
-blood pressure
-heart rate

6. Feedback Systems
Homeostasis is continuously disturbed by external or internal stimuli. Body systems constantly monitor changes and maintain homeostasis through both negative and positive feedback systems. A feedback system consists of:
a sensor- detects changes & sends signals to the control centre
a control centre- sets the range of values within which a variable should be maintained, receives info. from sensors & sends signals to effectors
an effector-responds to signals from a control centre to effect change in a variable

7. Negative Feedback Systems
The body works to reverse a change detected in a variable so that the variable is brought back to within a normal range.
*Most variables are maintained by negative feedback loops.
EX. Body temperature is maintained by a negative feedback system.

8. Example: Thermoregulation
Decreasing body temperature:
As you sweat and the perspiration evaporates from your skin, it requires heat
When your blood vessels dilate (vasodilation), more blood is brought to surface of skin, resulting in heat loss
Increasing body temperature:
When you shiver, muscles contract repeatedly, which increases heat production
When your blood vessels constrict (vasoconstriction), heat loss through the skin is decreased

9. Positive Feedback Systems
Strengthening or increasing a change in a variable. Ex: Contractions during childbirth
This loop has a definitive cut-off point to stop amplification of the response.
Contractions during childbirth are regulated by a positive feedback system.