Principles of Hormonal Control Systems

Hormone Structures and Synthesis

Amine Hormones Peptide Hormones Steroid Hormones Hormone Transport in the Blood Hormone Metabolism and

Excretion Mechanisms of Hormone Action Hormone Receptors Events Elicited by Hormone-Receptor Binding

Pharmacological Effects of Hormones

Inputs That Control Hormone Secretion

Control by Plasma Concentrations of Mineral Ions or Organic Nutrients Control by Neurons Control by Other Hormones Control Systems Involving The Hypothalamus and Pituitary Posterior Pituitary Hormones The Hypothalamus and Anterior Pituitary

Candidate Hormones

Types of Endocrine Disorders

Hyposecretion Hypersecretion Hyporesponsiveness and Hyperresponsiveness

SUMMARY KEY TERMS REVIEW QUESTIONS CLINICAL TERMS THOUGHT QUESTIONS

Vander et al.: Human I II. Biological Control I 10. Principles of Hormonal I I © The McGraw-Hill

Physiology: The Systems Control Systems Companies, 2001 Mechanism of Body Function, Eighth Edition

The endocrine system is one of the body's two major communication systems, the nervous system being the other. The endocrine system consists of all those glands, termed endocrine glands, that secrete hormones. As described in Chapter 6, endocrine glands are also called ductless glands to distinguish them from all other (exocrine) glands. Hormones, as noted in Chapter 7, are chemical messengers that enter the blood which carries them from endocrine glands to the cells upon which they act. The cells influenced by a particular hormone are the target cells for that hormone.

Table 10-1 summarizes, for reference and orientation, the endocrine glands, the hormones they secrete, and the major functions the hormones control. The endocrine system differs from most of the other organ systems of the body in that the various glands are not anatomically continuous; however, they do form a system in the functional sense. The reader may be puzzled to see listed as endocrine glands some organs—the heart, for instance—that clearly have other functions. The explanation is that, in addition to the cells that carry out the organ's other functions, the organ also contains cells that secrete hormones. This illustrates the fact that organs are made up of different types of cells.

Note also in Table 10-1 that the hypothalamus, a part of the brain, is considered part of the endocrine system too. This is because the chemical messengers released by certain neuron terminals in both the hypothalamus and its extension, the posterior pituitary, do not function as neurotransmitters affecting adjacent cells but rather enter the blood, which carries them to their sites of action.

Table 10-1 demonstrates that there are a large number of endocrine glands and hormones. One way of describing the physiology of the individual hormones is to present all relevant material, gland by gland, in a single chapter. In keeping with our emphasis on hormones as messengers in homeostatic control mechanisms, however, we have chosen to describe the physiology of specific hormones and the glands that secrete them in subsequent chapters, in the context of the control systems in which they participate. For example, the pancreatic hormones are described in Chapter 18, which is on organic metabolism, parathyroid hormone in Chapter 16 in the context of calcium metabolism, and so on.

The aims of the present chapter are therefore limited to presenting: (1) the general principles of endocrinology—that is, a structural and functional analysis of hormones in general that transcends individual glands; and (2) an analysis of the hypothalamus-pituitary hormonal system. The control systems for the hormones of this particular system are so interconnected that they are best described as a unit to lay the foundation for subsequent descriptions in other chapters.

Before turning to these presentations, however, several additional general points should be made concerning Table 10-1. One phenomenon evident from this table is that a single gland may secrete multiple hormones. The usual pattern in such cases is that a single cell type secretes only one hormone, so that multiple hormone secretion reflects the presence of different types of endocrine cells in the same gland. In a few cases, however, a single cell may secrete more than one hormone (for example, the secretion of follicle-stimulating hormone and luteinizing hormone by the anterior pituitary).

Another point of interest illustrated by Table 10-1 is that a particular hormone may be produced by more than one type of endocrine gland. For example, somatostatin is secreted by endocrine cells in both the gastrointestinal tract and the pancreas and is also one of the hormones secreted by the hypothalamus.

Finally, as emphasized in Chapter 7, a chemical messenger secreted by an endocrine gland cell is often also secreted by other cell types and serves in these other locations as a neurotransmitter or paracrine/autocrine agent. For example, prolactin is secreted not only by the anterior pituitary but by at least 12 other cell types where it is thought to exert a huge number of paracrine/autocrine functions.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Principles of Hormonal Control Systems CHAPTER TEN

Principles of Hormonal Control Systems CHAPTER TEN

TABLE 10-1 Summary of the Hormones

Site Produced (Endocrine Gland)

Hormone

Major Function* Is Control of:

Adipose tissue cells

Leptin

Food intake; metabolic rate

Androgens Aldosterone

Organic metabolism; response to stress; immune system Sex drive in women Sodium, potassium, and acid excretion by kidneys

Adrenal medulla

Epinephrine Norepinephrine

Organic metabolism; cardiovascular function; response to stress

Gastrointestinal tract

Gastrin Secretin

Cholecystokinin

Glucose-dependent insulinotropic peptide (GIP)f Motilin

Gastrointestinal tract; liver; pancreas; gallbladder

Gonads: Ovaries: female

Estrogen Progesterone Inhibin Relaxin

Reproductive system; breasts; growth and development; influences gametes FSH secretion

? Relaxation of cervix and pubic ligaments

Testes: male

Testosterone Inhibin

Müllerian-inhibiting hormone

Reproductive system; growth and development; sex drive; influences gametes FSH secretion

Regression of Mullerian ducts

Heart

Atrial natriuretic factor (ANF, atriopeptin)

Sodium excretion by kidneys; blood pressure

Hypothalamus

Hypophysiotropic hormones: Corticotropin releasing hormone (CRH) Thyrotropin releasing hormone (TRH) Growth hormone releasing hormone (GHRH) Somatostatin (SS)

Gonadotropin releasing hormone (GnRH)

Dopamine (DA, also called prolactin-

inhibiting hormone, PIH) Posterior pituitary hormones

Secretion of hormones by the anterior pituitary Secretion of adrenocorticotropic hormone (stimulation) Secretion of thyroid-stimulating hormone (stimulation) Secretion of growth hormone (stimulation) Secretion of growth hormone (inhibition) Secretion of luteinizing hormone and follicle-

stimulating hormone (stimulation) Secretion of prolactin (inhibition)

See posterior pituitary

Kidneys

Renin (an enzyme that generates angiotensin)

Erythropoietin

1,25-dihydroxyvitamin D3

Aldosterone secretion; blood pressure Erythrocyte production Plasma calcium

Leukocytes, macrophages, endothelial cells, and fibroblasts

Cytokines* (these include the interleukins, colony-stimulating factors, interferons, tumor necrosis factors)

Immune defenses

Liver and other cells

Insulin-like growth factors (IGF-I and II)

Cell division and growth

Glucagon

Somatostatin

Organic metabolism; plasma glucose

Parathyroids

Parathyroid hormone (PTH, PH, parathormone)

Plasma calcium and phosphate

Pineal

Melatonin

? Sexual maturity; body rhythms

Vander et al.: Human I II. Biological Control I 10. Principles of Hormonal I I © The McGraw-Hill

Physiology: The Systems Control Systems Companies, 2001 Mechanism of Body Function, Eighth Edition

PART TWO Biological Control Systems

TABLE 10-1 Summary of the Hormones (continued)

Site Produced (Endocrine Gland)

Hormone

Major Function* Is Control of:

Pituitary glands: Anterior pituitary

Growth hormone (GH, somatotropin)

Thyroid-stimulating hormone (TSH, thyrotropin) Adrenocorticotropic hormone (ACTH, corticotropin) Prolactin

Gonadotropic hormones: Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) ß-lipotropin and ^-endorphin

Growth, mainly via secretion of IGF-I; protein, carbohydrate, and lipid metabolism

Thyroid gland

Adrenal cortex

Breast growth and milk synthesis; may be permissive for certain reproductive functions in the male

Gonads (gamete production and sex hormone secretion)

Unknown

Vasopressin (antidiuretic hormone, ADH)

Milk let-down; uterine motility Water excretion by the kidneys; blood pressure

Placenta

Chorionic gonadotropin (CG)

Estrogens

Progesterone

Placental lactogen

Secretion by corpus luteum See Gonads: ovaries See Gonads: ovaries Breast development; organic metabolism

Thymus

Thymopoietin

T-lymphocyte function

Thyroid

Thyroxine (T4) Triiodothyronine (T3) Calcitonin

Metabolic rate; growth; brain development and function Plasma calcium

Multiple cell types

Growth factors* (e.g., epidermal growth factor)

Growth and proliferation of specific cell types

°This table does not list all functions of the hormones.

+The names and abbreviations in parentheses are synonyms.

*Some classifications include the cytokines under the category of growth factors.

§The posterior pituitary stores and secretes these hormones; they are made in the hypothalamus.

°This table does not list all functions of the hormones.

+The names and abbreviations in parentheses are synonyms.

*Some classifications include the cytokines under the category of growth factors.

§The posterior pituitary stores and secretes these hormones; they are made in the hypothalamus.

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Responses

  • fausto
    What are hormonal control mechanisms?
    7 years ago
  • niklas
    What are 10 organs that secrete hormones?
    7 years ago
  • kalimac took
    Does adipose tissue participate in gamete production?
    7 years ago
  • efrem demsas
    What are the body's 2 major control systems?
    7 years ago
  • VIRGINIA
    How hormones control body functions?
    7 years ago
  • RANDY
    Which chemical messengers are secreted by endocrine glands and enter the blood?
    6 years ago

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