NEUROENDOCRINE SYSTEM

HORMONES IN ANIMALS

Neuroendocrine system is a complex system of tissues and organs that uses chemical and electrical signals to coordinate body activities, and respond to the changes in the internal and external environment.

Hormone

• chemical produced by a gland
• released into blood
• carried by circulatory system to all tissues of body
• affects only specific target tissue(s)

Question: What mechanism could account for a hormone affecting only specific tissues, when it is carried to all tissues of the body?

EXAMPLES OF HORMONE EFFECTS & ROLE IN HOMEOSTASIS

Blood calcium level - important for normal nerve, muscle, heart and enzyme function

• normally 9 - 11 mg/100 ml blood
• cells of parathyroid gland detect and respond to a drop in blood Ca
• release parathyroid hormone
• causes break down of bone
• also causes reabsorption of Ca in kidney
• also causes increased absorption of Ca in intestine

Question: What is the controlled variable?

Question: What is the set point?

Question: What is the stimulus?

Question: Why would breaking bone down be helpful in this situation?

Question: What is (are) the effector(s) in this situation?

Question: How is this an example of a negative feedback system?

Control of blood sodium levels - important for fluid volume, blood pressure, muscle, nerve and enzyme function

Experimental approach

Initial observations

• if Na too high, results in increased excretion of Na in urine
• if Na too low, results in decreased excretion of Na in urine

Experimental question - How does kidney respond in correct manner? Chemical signal from some other organ?

Experimental design = removal and replacement

1. Remove various organs individually; observe effect on Na loss in urine

• parathyroidectomy - no effect
• thyroidectomy - no effect
• adrenalectomy - great loss of Na in urine; animal consumes excessive salt

Question: What do you conclude from the removal stage of the experiment? Is this proof of your conclusion? Why or why not?

2. Replacement - Prepare extract made from adrenal gland and inject into adrenalectomized animals

• little Na lost in urine
• normal salt appetite

Question: How does this result affect your previous conclusion?

Question: How could this approach be refined to pinpoint precisely what part of the adrenal gland, and what chemical in the adrenal gland, is controlling the kidney's Na excretion?

Control of blood glucose levels - important for maintaining correct fuel levels, especially to brain; normally about 100 mg/ 100 ml plasma

See Figure 45.11, p.906

insulin - produced & released by pancreas in response to elevated blood glucose

• causes uptake of glucose by most cells of the body (brain & active skeletal muscle do not need insulin to take up glucose)
• causes liver to store glucose as glycogen

Question: When would blood glucose most likely be elevated?

Question: How would the responses listed above affect the level of glucose in the blood?

glucagon - produced & released by pancreas in response to lowered blood glucose

• causes liver to break glycogen down into glucose
• causes synthesis of glucose from amino acids

Question: When would blood glucose most likely be low?

Question: How would the responses listed above affect blood glucose?

NOTE: The balance of glucagon and insulin help to maintain blood glucose within a normal range under most conditions.

diabetes mellitus, type I

• pancreas produces little or no insulin
• occurs mostly in children

Question: How would the lack of insulin affect cells' ability to take up glucose? Blood glucose?

Question: What would cells use as a substrate for cellular respiration? What effects would this have on body mass?

Question: What would happen to the levels of fatty acids in the blood? What effects might this have?

Question: Glycolation of proteins refers to the attachment of sugars to proteins. Tissues that are especially susceptible to damage from glycolation are the lens of the eye, and the inner lining of blood vessels, especially to the extremities. What effects would this have on a person with untreated diabetes mellitus?

Question: What is the treatment for diabetes mellitus?