Chapter 45 (2)

In response to an internal or environmental stimulus, __ cells secrete a part hormone. The hormone travels in the __ to target ells, where it interacts with its specific receptors. __ within target cells rings about a physiological response. Finally, the response leads to a reduction in the stimulus and the pathway shuts off.

Example of homeostasis: Acidic stomach contents released into teh __ (first part of s. intestine) serve as stimulus. Low __ in the smal intestine stimulates certain endocrine cells of the __,c alled __ cells, to secrete the hormone __.

__ enters the bloodstream and reaches target cells in the __, a gland locatred behind the stomach, causing them to release __, which raises the pH in the __. The patway is self-limiting because the response to __ (bicarbonate release) reduces the stimulus (low pH).

A feedback loop connecting the response to the initial stimuls is characteristic of control pathways. For __ and many other hormones, the response pathway involves __, a loop in which the response reduces the initial stimulus. By decreasing or abolishing hormone signaling, __ regulation prevents excessive pathway activity. __ are an essential part of many hormone pathways especially those involved in maintaining homeostasis.

True or False:
Because fat is a major fuel for cell resp., and a key source of carbon skeletons for biosynthesis, maintaing blood fatconcentrations near this set point (90 mg/100 mL) is a critical bioenergetic and homeostatic function.
True False

Two antagonistic hormones, __ and __ regulate the concentraiton of glucose in the blood. Each hormone operates in a simple endocrine pathway regulated by negative feeedback.

When blood glucose rises above hte set point, release of __ triggers uptake of glucose from the blood, decreasing the blood glucose concentration.

When blood glucose drops below the set point, the release of __ promotes the release of glucose into the blood, increasing the blood glucose concentration. Because __ and __ have opposing effects, the combined activity of these wo hormones tightly controls the concentraiton of glucose int he blood.

__ and __ are produced int eh pancres. Scattered throughout the pancreas are clusters of endocrine cells known as the __. Each islet has __, which make glucagon, and __ which make insulin. Like all hormones, __ and __ are secreted into the interstitial fluid and enter hte circulatory system.

Overall, hormone-secreting cells make up only 1-2% of hte mass of the pancreas. Other cells in the pancreas produce and secrete __ ions and digestive enzymes. These secretions are released into small ducts that empty into the __, which leads to the small intestine. Thus, the pancreas is both an __ gland and an __ gland with functions in the endocrine and digestive systems.

__ lowers bllod glucose levels by stimulating nearly all body cells outside the brain to take up glucose from the blood. __ also decreases blood glucose by slowig glycogen breakdown in the liver and inhibiting the conversion of amino acids and glycerol from fats to glucose.

__ influences blood glucose levels through its effects on target cells in the liver. The liver, skeletal muscles, and adipose tissues store large amonts of fuel. the liver and muscles store sugar as glycogen, whereas cells in adipose tissue convert sugars to fat. Of these tissues, only those in the liver are sensitive to __. When the blood glucose level decreases to or below the set point, __ signals the liver cells to increase glycogen hydrolysis, convert amino acids and glycerol to glucose, and release glucose into the bloodstream. The net effect is to restore the blood glucose level to the set point.

The antagonistic effects of __ and __ are vital to managing fel storage and consumption by body cells.

For both hormones, the __ is a critical target.

Nutrients absorbed by blood vessels of the small intestine are transported directly to the lvier by the __. W/in theliver, __ and __ regultte nutrient processig in ways that support glucose homeostasis.

However, glucose homeostasis also relies on responses to __ and __ elsewhere in the body as well as responses to other hormones- __ and __.

A disruption in glucose homeostasis can be quite serious, affecting the heart, blood vessels, eyes and kidneys. One such disorder, __, is caused by a deficiency of insulin or a decreased response to insulin target tissues.

True or False:
Blood glucose levels rise, but cells are unable to take up enough glucose to meet metabolic needs. Instead, fat becomes the main substrate for cellular respiration. In severe cases, acidic metabolites formed during fat breakdown accumulate in the blood, threatiening life by lowering blood pH and depleting sodium and potassium ions from the body.
True False

In peope with __, the high levels of glucose in bllood exceeds hte capacity ofhte kidneys to reabsorb this nutrient. Glucose that remains in the flitrate is excreted. For this reason, the presence of sugar in urine is one test for htis disorder.

As glucose is concentrated n the urine, more water is excreted along with it resulting in excessive volumes of urine. __ refers to the copious urination; and __ refers to the presence of ugar in urine.
__ is a rare disorder of kidney function that results in large volumes of dilute urine but no major disruption in glucose metabolism.

There are two types of __. Each is marked by high blood glucose, but with very different causes.

__, or insulin-dependant diabters, is an autoimmune disorder in which the immune system destroys the beta cells of hte pancreas. __, which usually appears during childhood, destroys the person's ability to produce insulin. Treatment consists of insulin, typically injected sveral times daily. In the past, insulin was extracted from animal pancreases, but now human insulin can be obtained from genetically engineered bacteria, a relatively inexpensive source. Stem cell research may someday provide a cure for __ by generating replacement beta cells that restore insuilin rpoduction by the pancreas.

__, or non-insulin dependent diabtes is characterized by a failure of target cells to respond normally to insuin, which is produced but target cells fail to take up glucose from the blood. And blood glucose levesls remain elevated.

Although heredity can play a role in __, excess body weight and lack of exercise significantly increase the risk. This form of diabetes generally apepears after the age 40, but even children who are overweight and sedentary can develop the disease. More than 90% of people with diabetes have __. Many can control their blood glucose levels with regular exercise and a healthy diet; some require edications. Nevertheless, __ is the seventh most common cause of death in the US and a growng public health problem worldwide.