Chapter 10-10

General Adaptation Syndrome (GAS)

A wide variety of stress-causing factors produce the same basic pattern of hormonal and physiological adjustments. These responses are part of the _____, AKA the stress response. This has three phases: the alarm phase, the resistance phase, and the exhaustion phase.

Alarm Phase (Fight or Flight)

An immediate response to stress, or crisis. The dominant hormone is epinephrine, and its secretion is part of a generalized sympathetic activation.

Stress

Any condition, physical or emotional, that threatens homeostasis is a form of ________. May be (1) physical, such as illness or injury, (2) emotional, such as depression or anxiety, (3) environmental, such as extreme heat or cold, or (4) metabolic, such as starvation.

Resistance Phase

Begins if a stress lasts longer than a few hours. Glucocorticoids (GCs) are the dominant hormones of the resistance phase. GCs and other hormones act to shift tissue metabolism away from glucose, thus increasing its availability to neural tissue.

Insulin

Growing cells need adequate supplies of energy and nutrients. Without _______, the passage of glucose and amino acids across plasma membranes stops or is drastically reduced.

Permissive Effects

Hormones can have a _______ on other hormones. In such cases, one hormone must be present if a second hormone is to produce its effects. For example epinephrine has no apparent effect on energy consumption unless thyroid hormones are also present in normal concentrations.

Integrative Effects

Hormones may also produce different but complementary results in a given tissue or organ. These integrative effects are important in coordinating the activities of diverse physiological system.s The differing effects of calcitriol and parathyroid hormone on tissues involved in calcium metabolism are an example.

Thyroid Hormones

Normal growth also requires appropriate levels of ______. If these hormones are absent during fetal development or for the first year of life, the nervous system fails to develop normally. Developmental delay results. If thyroxine concentrations decline later in life but before puberty, normal skeletal development does not continue.

Parathyroid Hormone (PTH) and Calcitriol

Promote the absorption of calcium for building bone. Without adequate levels of both hormones, bones can enlarge but will be poorly mineralized, weak, and flexible. For example, rickets is a condition typically resulting from inadequate production of calcitriol due to vitamin D3 deficiency in growing children. As a result, the lower limb bones are so weak that they bend under the body's weight.

Exhaustion Phase

The body's lipid reserves are sufficient to maintain the resistance phase for weeks or even months. But when the resistance phase ends, homeostatic regulation breaks down and the _______ begins. Without immediate corrective actions, the ensuing failure of one or more organ systems will prove fatal.

Growth Hormone (GH)

The effects of GH on protein synthesis and cellular growth are most apparent in children. GH supports their muscular and skeletal development. In adults, GH helps to maintain normal blood glucose levels and to mobilize lipid reserves in adipose tissues. GH is not the primary hormone involved, however. An adult with a GH deficiency but normal levels of thyroxine, insulin, and glucocorticoids will have no physiological problems.

Reproductive Hormones

The presence or absence of sex hormones (androgens in males, estrogens in females) affects the activities of osteoblasts in key locations and the growth of specific cell populations. Androgens and estrogens stimulate cell growth and differentiation in their target tissues, but the targets differ. The differential growth induced by each accounts for gender-related differences in skeletal proportions and secondary sex characteristics.

Synergistic Effects

The two hormones may have additive effects, in which case the net result is greater than the effect that each would produce acting alone. In some cases the net result is greater than the sum of their individual effects. An example of such a synergistic effect is the glucose-sparing action of GH and glucocorticoids.

Antagonistic Effects

The two hormones may have antagonistic (opposing) effects, as is the case for parathyroid hormone and calcitonin, or insulin and glucagon.

Multiple Hormone Instructions

When a cell receives instructions from two different hormones at the same time, four outcomes are possible: antagonistic effects, synergistic effects, permissive effects, and integrative effects.