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1. Homeostasis
Regulation of the
Internal Milieu
Wade Haaland
BioEd Online

2. What is Homeostasis?

Refers to a state of constancy in a system.

In its normal, or resting, state, a system often is said
to be in homeostasis.

When events occur that disrupt the normal state, the system is
able to respond and restore homeostasis.

Physiologists use the term homeostasis to refer to
maintaining a constant internal environment.

A homeostatic system makes adjustments to lessen the
internal impact of major external disturbances.

Example: During exercise, sweating increases to
maintain a constant internal temperature.
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3. The Internal Milieu
The “internal milieu” is the internal environment of an organism,
or the extracellular fluid environment.
The fluid environment surrounds cells, exchanges nutrients
and wastes, and acts as a buffer.
The cell is the simplest unit of life.
Cells make up body systems; body systems maintain homeostasis;
and homeostasis is necessary for healthy cells.
Each cell contributes to the maintenance of homeostasis and each
is cell is dependent on the overall maintenance of homeostasis.
The cell needs a constant internal environment.
Cells obtain nutrients from, and remove wastes to, the internal
milieu.
Cells have specialized functions that contribute to
homeostasis.
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4. History of Homeostasis

Claude Bernard (1813-1878)

French physiologist

Developed the concept of the internal milieu.

Recognized that many animals regulate their
internal environment even if the external
environment changes.

Walter Cannon (1871-1945)

Coined the term “Homeostasis” in 1926.

Realized the importance of the autonomic nervous
system in maintaining a constant internal
environment.
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5. Homeostasis

Organism’s Internal Regulation

Examples of physiological conditions requiring homeostasis:

Temperature

Concentration of Waste Products

Gas Exchange

pH

Energy Requirements

Water/Ion balance

Volume/Pressure

“Regulators” use behavioral and physiological mechanisms to
buffer external changes and thus, maintain a constant internal
environment.

“Conformers” adjust the internal environment in reaction to
external changes.
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6. Necessary Components of a Homeostatic System

Receptor

Control Center

Effector
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7. Homeostatic Mechanism
Negative-Feedback Regulation
The homeostatic mechanism
Positive-Feedback Regulation
Birthing contractions
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8. Glucose Homeostasis Chart
Liver breaks down
glycogen to create glucose
Raises blood-glucose
Glucose uptake by
muscle/fat tissue
Lowers blood-glucose
Result
GlucagonInsulinEffector
-cell of the pancreas-cell of the pancreasControl Center
Glucose transporterGlucose transporterReceptor
Low Blood Sugar
Do not meet energy
requirements of cell
High Blood Sugar
Toxic
Condition
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9. -cells release
glucagon
stimulate glycogen
breakdown and
gluconeogenesis
-cells release
insulin
stimulate glucose
uptake by
peripheral tissues
Glucose Homeostasis
Lower Blood Glucose
Higher Blood Glucose
Food
Between meals
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10. Disruption of Homeostasis

Injury

Punctured Lung

Illness

Flu

Disease

Diabetes

Death
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11. Type 1 Diabetes Mellitus
High blood glucose
Detected by -cells
-cells release insulin
Peripheral cells
respond to insulin by
taking up glucose
Lower blood glucose
Normal Glucose Metabolism Type 1 Diabetes
High blood glucose
Detected by -cells
-cells release insulin
Peripheral cells
respond to insulin by
taking up glucose
Lower blood glucose
-cells destroyed by
autoimmune reaction
These steps do
not happen
because the
- cells have
been destroyed
Blood glucose remains high
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12. Type 2 Diabetes Mellitus
Time
Peripheral Tissue Insulin
Resistance v. Time
R
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R
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Time
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I
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P
r
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t
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o
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-cell Insulin
Production v. Time
Disease
Progression
A
g
e
Birth
Normal Glucose
Homeostasis
Pre-Diabetic
Diabetic
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13. Glucose Homeostasis Research Timeline

1552 BC: Ebers Papyrus in ancient Egypt. First known written description of diabetes.

1
st
Century AD: Arateus — “Melting down of flesh and limbs into urine.”

1776: Matthew Dobson conducts experiments showing sugar in blood and urine of diabetics.

Mid 1800s: Claude Bernard studies the function of the pancreas and liver, and their roles in
homeostasis.

1869: Paul Langerhans identifies cells of unknown function in the pancreas. These cells later are
named “Islets of Langerhans.”

1889: Pancreatectomized dog develops fatal diabetes.

1921: Insulin “discovered” — effectively treated pancreatectomized dog.

1922: First human treated with insulin. Eli Lilly begins mass production.

1923: Banting and Macleod win Nobel Prize for work with insulin.

1983: Biosynthetic insulin produced.

2001: Human genome sequence completed.
1552BC 1
st
Century AD 1776 1869 188918
th
Century 1921-23 1983 2001
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14. Current/Future Research in Diabetes

Current

Clinical Trials: physiological traits of patients/response to
therapeutics

Genetic Approaches: candidate genes; family-based studies;
genome-wide scans

Animal Models: developing gene-knockout models; large-
scale mutagenesis studies to produce diabetic phenotypes

Microarray Analysis: analysis of gene expression in tissues

Future

Continued utilization of human genome sequence data

Sequencing multiple ethnicities

-cell transplantation
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15. Conclusion
“Homeostasis” is the ability of the body to maintain a
constant internal environment by making small internal
adjustments to compensate for large external
disturbances.
Injuries, illness, disease and death can disrupt
homeostasis.
Diabetes causes disruption of glucose homeostasis. It is
only one example of the potentially severe problems
caused by disrupting homeostasis.
Science is actively pursuing a broader, more detailed
understanding of homeostatic mechanisms and the
consequences of their disruptions.
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