Chapter 31: Mechanisms of Endocrine Control Porth

Define paracrine

Hormone acts on cell that produced it

The easiest way to measure hormone levels during a specific period are by either blood samples or urine tests to measure ______ or ______.

metabolites, hormone levels

In an adult with acromegaly, a growth hormone-secreting tumor is suspected. What diagnostic test would be used for this client?

A growth hormone (GH) suppression test. A suppression test may be useful to confirm this situation.

When hormones act locally rather than being secreted into the bloodstream, their actions are termed what?

Autocrine and paracrine. When hormones act locally on cells other than those that produced the hormone, the action is called paracrine. Hormones also can exert an autocrine action on the cells from which they were produced.

The endocrine system is closely linked with both the immune system and the nervous system. What neurotransmitter can also act as a hormone?

Epinephrine. Neurotransmitters such as epinephrine can act as neurotransmitters or as hormones.

Define hormones

Highly specialized organic molecules produced by endocrine organs that exert their action on specific target cells

Many hormones are measured for diagnostic reasons by using the plasma levels of the hormones. What is used today to measure plasma hormone levels?

Radioimmunoassay methods. Real progress in measuring plasma hormone levels came up more than 40 years ago with the use of competitive binding and the development of radioimmunoassay methods.

Define hypophysis

The hypothalamus and the pituitary gland

How does negative feedback regulate hormone levels?

The level of hormones in the body is regulated by negative feedback mechanisms. Sensors detect a change in the hormone level and adjust hormone secretion so that body levels are maintained within an appropriate range. When the sensors detect a decrease in hormone levels, they initiate changes that cause an increase in hormone production; when hormone levels rise above the set point of the system, the sensors cause hormone production and release to decrease the level.

Hormones can be synthesized by both vesicle-mediated pathways and non-vesicle-mediated pathways. What hormones are synthesized by non-vesicle-mediated pathways?

Androgens and estrogens. Hormones that are synthesized by non-vesicle-mediated pathways include the glucocorticoids, androgens, estrogens, and mineralcorticoids - all steroids derived from cholesterol.

To prevent the accumulation of hormones in our bodies, the hormones are constantly being metabolized and excreted. Where are adrenal and gonad steroid hormones excreted?

Bile and urine. Unbound adrenal and gonadal steroid hormones are conjugated in the liver, which renders them inactive, and then excreted in the bile or urine. Adrenal and gonadal steroid hormones are not excreted in the feces, cell metabolites, or the lungs.

What is the structure of a hormone?

Hormones are divided into three categories: (1) Amines and amino acids (2) Peptides, polypeptides, proteins, and glycoproteins (3) Steroids. The first category, the amines, includes norepinephrine and epinephrine, which are derived from a single amino acid, and the thyroid hormones, which are derived from two iodinated tyrosine amino acid residues. The second category, the peptides, polypeptides, proteins, and glycoproteins, can be as small as only to contain three amino acids, and as large and complex to consist of approximately 200 amino acids. The third category consists of the steroid hormones, which are derivatives of cholesterol.

What is a hormone?

Hormones generally are thought of as chemical messengers that are transported in body fluids. They are highly specialized organic molecules produced by endocrine organs that exert their action on specific target cells. Hormones do not initiate reactions but function as modulators of cellular and systemic responses. Most hormones are present in body fluids at all times, but in greater or lesser amounts depending on the needs of the body.

Describe the global role of the anterior pituitary hormones.

Hormones produced by the anterior pituitary control body growth and metabolism (growth hormone, GH), function of the thyroid gland (thyrotropin, TSH), glucocorticoid hormone levels (corticotropin, ACTH), function of the gonads (follicle-stimulating hormone, FSH, and luteinizing hormone, LH), and breast growth and milk production (prolactin). Melanocyte-stimulating hormone, which is involved in the control of pigmentation of the skin, is produced by the par intermedia of the pituitary gland.

Define second messenger

Intracellular signal

_____ hormones attach to intracellular receptors and form a hormone-receptor complex that travels to the cell nucleus.

Lipid-soluble

The hormone levels in the body need to be kept within an appropriate range. How is this accomplished for many of the hormones in the body?

Negative feedback loop. The level of many of the hormones in the body is regulated by negative feedback mechanisms.

What are the main types of cell membrane receptors and how do they exert their effects?

The intracellular signal system is termed the second messenger, and the hormone is considered the first messenger. The most widely distributed second messenger is cyclic adenosine monophosphate (cAMP). Adenylate cyclase is functionally coupled to various cell surface receptors by the regulatory actions of G proteins. The second major cell surface receptor involves the binding of a hormone or neurotransmitter to a surface receptor acts directly to open an ion channel in the cell membrane. The influx of ions, then, serves as an intracellular signal to convey the hormonal message to the interior of the cell.

An 87-year-old woman has come to the clinic for a routine physical examination. She says she has no complaints and is concerned only about a 20-pound weight gain in the past 2 years. She says that she is not as active as she used to be. She also mentions that she has fallen several times and now has a large bruise on her right hip. With the client's weight gain over the past 2 years and her decrease in activity level, the nurse would expect what test to be ordered to either rule out or confirm type II diabetes in this client?

The nurse would expect an assessment of insulin function through a blood glucose level.

Imaging has proven useful in both the diagnosis and follow-up of endocrine disorders. Two types of imaging studies are useful when dealing with endocrine disorders, isotopic imaging and nonisotopic imaging. What is an example of isotopic imaging?

Thyroid scan. Isotopic imaging includes radioactive scanning of the thyroid.

Define half-life of a hormone

Time it takes for the body to reduce the concentration of the hormone by one-half

Sometimes the measurement of hormone is done through a urine sample. What is an advantage of measuring hormone levels through a urine sample rather than a blood sample?

Urine samples are easily obtained. The advantages of a urine test include the relative ease of obtaining urine samples and the fact that blood sampling is not required.

The functions of the endocrine system are closely linked with those of the _____ system and the _____ system.

nervous, immune

Hormones produce their effects through interaction with ______, which in turn are linked to one or more effector systems within the cell.

high-affinity receptors

The endocrine system uses chemical substances called ____ as a means of regulating and integrating body functions.

hormones

The synthesis and release of anterior pituitary hormones is regulated by the action of releasing or inhibiting hormones from the ______, which is the coordinating center of the brain for endocrine, behavioral, and autonomic nervous system function.

hypothalamus

When hormones act locally on cells other than those that produced the hormone, the action is called ______.

paracrine

The structure of hormone _____ varies in a manner that allows target cells to respond to one hormone and not to others.

receptors

Define hormone response element

Activate or suppress intracellular mechanisms such as gene activity.

The hypophysis is a unit formed by the pituitary and the hypothalamus. These two glands are connected by the blood flow in what system?

Hypophyseal portal system. The hypothalamus and the pituitary (i.e. hypophysis) form a unit that exerts control over many functions of several endocrine glands as well as a wide range of other physiologic functions. These two structures are connected by blood flow in the hypophyseal portal system, which begins in the hypothalamus and drains into the anterior pituitary gland, and by the nerve axons that connect the supraoptic and paraventricular nuclei of the hypothalamus with the posterior pituitary gland.

The pituitary gland has been called the _____ because its hormones control the functions of many target glands and cells.

master gland

An 87-year-old woman has come to the clinic for a routine physical examination. She says she has no complaints and is concerned only about a 20-pound weight gain in the past 2 years. She says that she is not as active as she used to be. She also mentions that she has fallen several times and now has a large bruise on her right hip.The nurse knows that this client is at risk for osteoporosis because of her decrease in activity. What test would the nurse expect to be ordered to either confirm or rule out osteoporosis in this patient?

The nurse would expect a dual electron x-ray absorptiometry (DEXA) to be ordered as the nurse knows that this test is used routinely for the diagnosis and monitoring of osteoporosis and metabolic bone diseases.

How do tissues regulate a hormone's affect?

The response of a target cell to a hormone varies with the number of receptors present and with the affinity of these receptors for hormone binding. The number of hormone receptors on a cell may be altered for any of several reasons. Antibodies may destroy or block the receptor proteins. Increased or decreased hormone levels often induce changes in the activity of the genes that regulate receptor synthesis. For example, decreased hormone levels often produce an increase in receptor numbers by means of a process called up-regulation; this increases the sensitivity of the body to existing hormone levels. Likewise, sustained levels of excess hormone often bring about a decrease in receptor numbers by down-regulation, producing a decrease in hormone sensitivity.

Hormones that are released into the bloodstream circulate either as _____ molecules, or as hormones _______ to transport carriers.

free, bound

Define autocrine

Hormone affecting neighboring cells

Hormones also can exert an ______ action on the cells from which they were produced.

autocrine