Hormones and Homeostasis

Homeostasis Maintaining a stable internal environment

despite unstable external conditions Examples of systems with homeostasis

Blood pH Maintained around 7.4 Uses buffers

Carbon dioxide concentration Uses chemoreceptors in the walls of certain blood

vessels Blood glucose level Body temperature Water balance

Endocrine System Consists of endocrine glands that

produce hormones Hormones are put into the blood stream Only cells with special receptors will

accept the hormones Called target cells

Helps maintain homeostasis

Important Hormones Thyroxin

Produced by the thyroid gland Regulates metabolism in the cell Regulates body temperature

Leptin Produced by adipose tissue Increased fat increases leptin secretion Should decrease appetitie

Some people are leptin desensitized Melatonin

Produced by the pineal gland Regulates sleep cycles Melatonin pills can be used to help induce sleep in children and

when jet lagged from travel

Negative Feedback Loop Control of a process by the result or effect of

the process Requires

Sensors to measure the current situation A center in the brain that knows the optimum

value of the situation A way of bringing the situation to the optimum

value When this occurs the center turns off the mechanism

used to bring it to optimum Action changes things so that action is no longer needed

Negative Feedback Loop

Blood glucose regulation Done with hormones located in the islets of langerhans (in the

pancreas) Contain chemoreceptors which are sensitive to the levels of

glucose in the blood Levels rise after a meal Levels drop after exercise

If blood levels are too low The alpha cells will release glucagon Protein hormone that travels to all parts of the body but with the liver

being the target Liver cells respond by converting glycogen into glucose Will also convert amino acids to glucose

If blood levels are too high Beta cells will release insulin Protein hormone released into the blood Makes muscle cells absorb glucose Makes liver cells turn glucose into glycogen In fat tissues glucose is turned into fat

Diabetes A metabolic disorder where the person does not produce enough

insulin or the body does not properly react to insulin Type I

No insulin or an insufficient level is produced by the beta cells Caused by the bodies producing antibodies to the insulin or the beta cells Treatment

Injection of insulin Pancreas transplant

Type II Insufficient levels produced or cells of the body become less sensitive to

it Unknown causes but might be

Obesity Increase in age Family history

Treatment Reduced carbohydrate intake Increased physical activity Weight loss medication

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