UNIT 8 - HOMEOSTASIS

What is Homeostasis?

condition where body’s internal environment is maintained relatively constant

• ensures normal physiological functioning in a range

• must continuously strive

What is the purpose of Homeostasis?

ensures all biological processes (chemical / enzymatic reactions, etc) occur normally and at the appropriate rate

What happens if Homeostasis is disrupted?

causes stress, illness and or death

What are the three conditions essential for Normal Functioning?

1. proper amounts of nutrients, gases, water, and salts

2. optimal temperature for normal biochemical reactions + molecular structure

3. optimal pressures for various fluid pressures in body

What makes up the Internal Environment of the body?

generally 60% fluid

• 2/3 intracellular fluid (ICF)

• 1/3 extracellular fluid (ECF)

  • 80% interstitial fluid

  • 20% plasma

What is the Extracellular Fluid (ECF)?

fluid that is outside the cells

• separated from fluid inside cells via cell membrane

• found in blood, lymph, tissues, joints, eyes, brain, etc

What makes up the Extracellular Fluid?

1. interstitial fluid (mainly between cells)

2. plasma (blood minus the cells; less presence)

the blood vessel walls separate these two components

How do these fluids flow between compartments?

• plasma exchanges materials with intracellular via circulatory system

• interstitial exchanges materials with intracellular

• fluid is also exchanged between extracellular compartments

• interstitial fluid can return to the circulatory system via lymphatic system

What is a Stress?

any condition that causes imbalance / variation in body’s normal internal environment

• example: any condition that threatens / disrupts homeostasis maintaining

What are examples of Internal Factors?

• low O2 concentrations

• variation in ambient temperature

• infection

What are examples of External Factors?

• variation in blood pressure

• variation in blood sugar levels

• variation in O2 and CO2 levels

What is the Feedback Loop?

1. factor / stimulus occurs

2. receptor detects state of factor + reports to control center

3. control center recieves report + makes decision and sends command to effector

4. effector brings about a change

5. homeostasis is returned

What is a Positive Feedback system?

the positive feedback loop will result in an increase of a stress

• very rare + can potentially cause damage

• specific situations where it is essential in restoring homeostasis

What is one example of a Positive Feedback?

child birth:

1. contractions force baby into cervix

2. increases the stretching of cervix

3. nerve cells in cervix send nerve impulses

4. brain interprets input + releases oxytocin

5. muscles in uterus wall contract forcefully; baby’s body stretches cervix more

6. birth decreasses cervix stretching, returns to homeostasis

What is Negative Feedback?

the system responds to decrease a stress

• most common for maintaining homeostasis

• examples: blood pressure control, temperature regulation, blood sugar levels, blood O2 and CO2 levels

How does the control of Blood Pressure work in a Negative Feedback system?

1. stimulus disrupts homeostasis by increasing BP

2. baroreceptors in certain blood vessels send nerve impulses

3. brain interprets and sends nerve impulses to heart + blood vessels

4. a decrease in heart rate decreases BP

5. homeostasis is returned when BP is normal

How does the skin regulate hot temperatures?

• stimulus: excessive heat

• receptors: thermoreceptors

• control centre: hypothalamus

• effectors: nervous stimulation to skin

• response: sweat gland secretion; vasodilation in skin + reduced muscle tone

• stimulus ends: heat loss

How does the skin regulate cold temperatures?

stimulus: excessive cold

receptors: thermoreceptors

control centre: hypothalamus

effectors: nervous stimulation to skin

response: “goosebumps,” vasoconstriction in skin, shivering

stimulus ends: heat gain