BioEd Online Homeostasis Regulation of the Internal Milieu Wade Haaland.

BioEd Online

HomeostasisRegulation of the

Internal Milieu

Wade Haaland

www.BioEdOnline.orgBioEd Online

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.


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.


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.


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.


Necessary Components of a Homeostatic System

Receptor

Control Center

Effector

70 72 74 76 78 80 82 84 86 88 90 92


Homeostatic Mechanism

Negative-Feedback Regulation The homeostatic mechanism

Positive-Feedback Regulation Birthing contractions

70 72 74 76 78 80 82 84 86 88 90 92


Glucose Homeostasis Chart

Liver breaks down glycogen to create glucose

Raises blood-glucose

Glucose uptake by muscle/fat tissue

Lowers blood-glucoseResult

GlucagonInsulinEffector

-cell of the pancreas-cell of the pancreasControl Center

Glucose transporterGlucose transporterReceptor

Low Blood SugarDo not meet energy requirements of cell

High Blood SugarToxic

Condition


-cells release glucagon stimulate glycogen breakdown and gluconeogenesis

-cells release insulin stimulate glucose uptake by peripheral tissues

Glucose Homeostasis

Lower Blood Glucose

Higher Blood GlucoseFood

Between meals


Disruption of Homeostasis

Injury Punctured Lung

Illness Flu

Disease Diabetes

Death


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


Type 2 Diabetes Mellitus

Time

Peripheral Tissue Insulin Resistance v. Time

Rel

ativ

e In

sulin

Res

ista

nce

Time

-ce

ll In

sulin

Pro

duct

ion

-cell InsulinProduction v. Time

Disease Progression

Age

Birth

Normal Glucose Homeostasis

Pre-Diabetic

Diabetic


Glucose Homeostasis Research Timeline

1552 BC: Ebers Papyrus in ancient Egypt. First known written description of diabetes.

1st 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 1st Century AD 1776 1869 188918th Century 1921-23 1983 2001


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


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.

BioEd Online Homeostasis Regulation of the Internal Milieu Wade Haaland.

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