The document discusses homeostasis and control systems in the human body. It explains that various internal variables like blood sugar, body temperature, and pH levels must stay within certain ranges to maintain homeostasis. When changes occur internally or externally, feedback systems work to regulate monitors, coordinating centers, and regulators to return levels to the normal range. Negative feedback is the most common type of response that works to reverse changes, while positive feedback reinforces changes. Multiple organ systems interact together to continuously monitor and adjust conditions to uphold homeostasis.

1. HOMEOSTASIS &
CONTROL SYSTEMS

2. Objectives
• H - Explain the importance of maintaining a constant
internal environment
Guiding Question
• How do the different systems interact together to maintain
homeostasis?

3. Important variables are regulated within
the body:
• Blood sugar
• Fluid balance
• Body temperature
• Oxygen levels
• Blood pressure
• pH
• These variables must stay within certain ranges
• Changes in the external environment can cause shifting within
these ranges

4. Homeostasis
• The process by which a constant internal environment is
maintained despite changes in the external environment.
• Body maintains a constant balance, or steady state,
through a series of monitored adjustments.
• This balance requires constant monitoring and feedback
about body conditions

6. Components of a Control System:
Component Function
Monitor Detects a change
Coordinating Centre Receives a message from the
monitor
Directs a response via a regulator
Regulator Carries out the response initiated by
the coordinating centre

8. Hypothalamus & Pituitary Glands
• Hypothalamus:
• Often serves as the coordinating centre to either tell the pituitary to
work more or work less depending on the message
• Receives messages from monitors
• Initiates a hormonal/nervous response
• Attempts to keep the body within accepted ranges
• Pituitary:
• Master gland
• Receives communications from hypothalamus and tells other
glands what to produce

10. How to Maintain Homeostasis
• Via use of feedback systems
• Two types of feedback systems:
• Negative feedback
• Positive feedback

11. The clapping game
• Player 1: Clap half the number of player 3’s claps.
• Player 2: Clap twice the number of player 1’s claps.
• Player 3: Clap twice the number of player 2’s claps.

12. The clapping game
• Player 1: Clap half the number of player 3’s claps, unless
you hear “Inhibit”, then clap a quarter the number of
player 3’s claps.
• Player 2: Clap twice the number of player 1’s claps.
• Player 3: Clap twice the number of player 2’s claps.
• Player 4: When player 3 claps 8 times or more, say
“Inhibit”

13. Negative Feedback
• Change in condition triggers a response to reverse the
change
• e.g. Body’s response to increase in temperature
• Most responses are under this category

14. Positive Feedback
• Change in conditions triggers to response, and reinforces
the change
• Less common in biological systems
• e.g. uterine contractions during birth of baby, mosquito bites, drug
addictions

15. Ben’s Story
• Work on the following module about how the body
maintains homeostasis and how all systems interact
• http://ats.doit.wisc.edu/biology/ap/ho/ho.htm

16. Internal Factors to Monitor
1. Temperature:
• Liver and muscle contractions are primarily responsible for
generating heat within the body.
• When the temperature of the body is greater than the
surroundings, the skin loses heat.
• Evaporation is also a means of cooling down the body
temperature and getting rid of excess heat.
• The brain also produces a lot of heat.
• The system of blood vessels comprising the head, allow the excess
heat to escape and cool the head off.

17. 2. Osmoregulation:
• The body makes sure that the water content within the
body does not become too diluted or too concentrated.
• Kidneys help by removing excess ions from the blood.
This is then excreted as urine and affects blood pressure
3. Sugar:
• The pancreas secretes two hormones essential to
regulating blood sugar levels (glucagon and insulin).
• ↑ sugar levels = pancreas ↑ insulin = glucose is stored as
glycogen = ↓ blood sugar levels
• Reverse is true when blood sugar is low

18. 4. Calcium:
• ↓ calcium regulation = detection bh receptors in
parathyroid gland.
• This releases PTH which ↑ blood calcium levels by
release of calcium from bones.
• Thyroid gland releases calcitonin, which helps lower
calcium levels by absorption of calcium into the bones.
• 5. Balance of Fluids:
• adequate balance of fluids within the body includes both
the gain as well as loss of fluids.
• Antidiuretic hormone (ADH) and aldosterone are two
major hormones that help maintain a fluid balance.

20. ORGAN SYSTEMS:
Their Role in Maintaining Homeostasis

23. • The proper functioning of the body requires all systems to
work together and in proper condition.
• Many diseases can affect the various organs and organ
systems of the body.
• When homeostasis within the body cannot be maintained
it can lead to death.

24. A person is stuck in icy water and
loses heat faster than they can
generate it. Their body temperature
drops below 35°C
Enzymes become less active.
Exergonic reactions that release
heat become less active.
The body cools down.
Less heat is released.

25. A person loses 2+ litres of blood in an accident
Arterial blood pressure falls
Flow of blood to
the heart
vessels
decreases
The heart pumps less blood
The heart weakens

26. Baroreceptors signal
the medulla that the
blood pressure is too
high
The medulla signals
the heart to
decrease rate,
which decreases
cardiac output.
The medulla
signals blood
vessels to dilate
(vasodilation)
This also decreases
venous return, which
decreases cardiac
output.
This lowers
blood pressure.

27. Baroreceptors signal
the medulla that
blood pressure is
too low.
The medulla signals
the heart to increase
rate, which
increases cardiac
output.
The medulla signals
blood vessel to
constrict
(vasoconstriction).
This also increases
venous return which
increases cardiac
output.
This raises
blood pressure.

28. Brain stimulates
pituitary gland to
secrete oxytocin
Nerve impulse from
cervix transmitted to
brain.
Head of fetus pushes against cervix
Oxytocin carried in
bloodstream to
uterus
Oxytocin
stimulates
uterine
contractions and
pushes fetus
towards cervix.

29. Kidneys detect reduced
O2 carrying capacity of
blood
When less O2 is delivered
to the kidneys they
secrete erythropoietin
into the blood
Erythropoietin
stimulates red blood
cell production
(erythropoiesis) by
bone marrow
Increased O2 carrying
capacity of blood stops
erythropoietin secretion
Additional red
blood cells
(erythrocytes)
increase O2
carrying capacity
of blood

30. Fever!

31. • What sets body temperature? what can change the set
point for body temperature?
• How does stress affect body temperature?
• How is fever different from a simple rise in body
temperature?
• What role might fever play in fighting infection?
• Why does the body sweat when a fever breaks?

32. Hypothermia