Endocrine System and Nutritional and Metabolic Diseases

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Endocrine System and Nutritional and Metabolic Diseases

Functions of the Endocrine System

The endocrine and nervous systems work together and separately to achieve the delicate physiological balance necessary for survival, termed homeostasis. Whereas the nervous system uses electrical impulses and chemicals termed neurotransmitters, the endocrine system secretes chemical messengers called hormones into the bloodstream. Hormones play a major role in the regulation of metabolism (the conversion of energy), and nutritional disorders may be a cause or result of endocrine dysfunction. The term neuroendocrine, as in the term neuroendocrine tumors, is a recognition of the close relationship between the two systems. Nervous stimulation of the posterior lobe of the pituitary (neurohypophysis) causes secretion of hormones ADH and oxytocin.

Anatomy and Physiology

The endocrine system is composed of several single and paired ductless glands that secrete hormones into the bloodstream. The hormones regulate specific body functions by acting on target cells with receptor sites for those particular hormones only. See Figure 15-1 for an illustration of the body with the locations of the endocrine glands.

Pituitary Gland

The pituitary gland, also known as the hypophysis, is a tiny gland located behind the optic nerve in the cranial cavity in a depression in the sphenoid bone called the sella turcica. The infundibulum, named for its funnel-like appearance, is the structure that attaches the pituitary to the hypothalamus directly superior to it in the brain. Sometimes called the master gland because of its role in controlling the functions of other endocrine glands, the hypophysis is composed of anterior and posterior lobes, each with their own function.

The anterior lobe, or adenohypophysis, is composed of glandular tissue and secretes hormones in response to stimulation by the hypothalamus. The hypothalamus sends hormones through blood vessels, which cause the adenohypophysis either to release or to inhibit the release of specific hormones. The adenohypophysis has a wide range of effects on the body, as Figure 15-2 and the table below illustrate.

The posterior lobe (neurohypophysis) of the pituitary gland is composed of nervous tissue. The hormones that it secretes are produced in the hypothalamus, transported to the neurohypophysis directly through the tissue connecting the organs, and released from storage in the posterior lobe by neural stimulation from the hypothalamus. The two hormones released by this lobe are antidiuretic hormone (ADH) and oxytocin (OT). See the following table and Figure 15-2 for the hormones secreted by the neurohypophysis and their effects.

Adenohypophysis Hormones and Their Effects

Adenohypophysis Hormones Effect
Adrenocorticotropic hormone (ACTH) Stimulates the adrenal cortex to release steroids.
Gonadotropic hormones (include follicle-stimulating hormone [FSH], luteinizing hormone [LH], and interstitial cell-stimulating hormone [ICSH]) FSH stimulates the development of gametes in the respective sexes. LH stimulates ovulation in the female and the secretion of sex hormones in both the male and the female. ICSH stimulates production of reproductive cells in the male.
Growth hormone (GH) (also called human growth hormone [hGH] or somatotropin hormone [STH]) Stimulates growth of long bones and skeletal muscle; converts proteins to glucose.
Prolactin (PRL) (also called lactogenic hormone) Stimulates milk production in the breast.
Thyrotropin (also called thyroid-stimulating hormone [TSH]) Stimulates thyroid to release two other thyroid hormones.

Neurohypophysis Hormones and Their Effects

Neurohypophysis Hormones Effect
Antidiuretic hormone (ADH) (also called vasopressin) Stimulates the kidneys to reabsorb water and return it to circulation; is also a vasoconstrictor, resulting in higher blood pressure.
Oxytocin (OT) Stimulates the muscles of the uterus during the delivery of an infant and the muscles surrounding the mammary ducts to contract, releasing milk.

Thyroid Gland

The thyroid gland is a single organ, but is divided into right and left lobes that are joined by a thin structure termed the isthmus (Fig. 15-3). It is located in the anterior part of the neck and is bounded by the trachea behind it and the thyroid cartilage above it. It regulates the metabolism of the body and normal growth and development, and controls the amount of calcium (Ca) deposited into bone. The thyroid gland is composed of small sacs, called follicles, that absorb iodine. The sacs are surrounded by follicular cells that produce triiodothyronine (T3) and thyroxine (T4). Parafollicular cells in the thyroid produce and secrete calcitonin, which controls the amount of calcium in the blood. Thyroid-stimulating hormone (TSH), released by the anterior pituitary gland, causes the thyroid to release T3 and T4.

Thyroid Gland Hormones and Their Effects

Thyroid Gland Hormone Effect
Calcitonin Regulates the amount of calcium in the bloodstream.
Tetraiodothyronine (also called thyroxine [T4]) Increases cell metabolism.
Triiodothyronine (T3) Increases cell metabolism.

Adrenal Glands (Suprarenals)

The adrenal glands, also called the suprarenals, are paired, one on top of each kidney. Different hormones are secreted by the two different parts of these glands: the external portion called the adrenal cortex and an internal portion called the adrenal medulla.

The adrenal cortex secretes three hormones that are called steroids.

The adrenal medulla is the inner portion of the adrenal gland. It produces sympathomimetic hormones that stimulate the fight-or-flight response to stress, similar to the action of the sympathetic nervous system.

Adrenal Cortex Hormones and Their Effects

Adrenal Cortex Hormones Effect
Glucocorticoids (e.g., cortisol [hydrocortisone]) Respond to stress; have antiinflammatory properties.
Mineralocorticoids (e.g., aldosterone) Regulate blood volume, blood pressure, and electrolytes.
Sex hormones (e.g., estrogen, androgen) Responsible for secondary sex characteristics.

Adrenal Medulla Hormones and Their Effects

Adrenal Medulla Hormones (Catecholamines) Effect
Dopamine Dilates arteries and increases production of urine, blood pressure, and cardiac rate. Acts as a neurotransmitter in the nervous system.
Epinephrine (also called adrenaline) Dilates bronchi, increases heart rate, raises blood pressure, dilates pupils, and elevates blood sugar levels.
Norepinephrine (also called noradrenaline) Increases heart rate and blood pressure and elevates blood sugar levels for energy use.


The pancreas, located inferior and posterior to the stomach, is a gland with both exocrine and endocrine functions (Fig. 15-4). The exocrine function is to release digestive enzymes through a duct into the small intestines. The endocrine function, accomplished through a variety of types of cells called islets of Langerhans, is to regulate the level of glucose in the blood by stimulating the liver. The two main types of islets of Langerhans are alpha and beta cells. Alpha cells produce the hormone glucagon, which increases the level of glucose in the blood when levels are low. Beta cells secrete insulin, which decreases the level of glucose in the blood when levels are high. Insulin is needed to transport glucose out of the bloodstream and into the cells. In the absence of glucose in the cells, proteins and fats are broken down, causing excessive fatty acids and ketones in the blood. Normally, these hormones regulate glucose levels through the metabolism of fats, carbohydrates, and proteins. See Figure 15-5 for a diagram explaining the effects of insulin and glucagon.

Pineal Body

The pineal body (gland) is located in the center of the brain, functioning to secrete the hormone melatonin, thought to be responsible for inducing sleep.


image Exercise 2:

Endocrine Anatomy and Physiology

Fill in the blanks.

1. The pituitary gland, the __________________, is called the master gland because of its control over other endocrine glands.

2. The pituitary gland is stimulated by the __________________________________________________________.

3. The anterior lobe of the pituitary gland is also known as the ______________________________________.

4. The thyroid gland is responsible for regulation of the body’s _________________________ and controls the amount of __________________ deposited into bone.

5. Adrenal glands are named for their location above the ____________________________________________.

6. The inner part of the adrenal gland is the adrenal __________________, whereas the outer part of the adrenal gland is the adrenal _____________________________________________________________________.

7. The endocrine function of the pancreas regulates glucose in the blood through the hormones ___________________________________________________ and ________________________________________________.

8. Fatty acids and __________________ are produced if glucose cannot pass out of the bloodstream into the cells to be metabolized.

9. The thymus gland is located in the __________________ above the heart and is responsible for stimulating key cells in the __________________ response.

10. The __________________ gland is located in the center of the brain, functioning to secrete the hormone ______________________, thought to be responsible for inducing __________________________.

Combining Forms for the Anatomy and Physiology of the Endocrine System

Meaning Combining Form
adrenal gland adren/o, adrenal/o
calcium calc/o, calc/i
cortex cortic/o
gland aden/o
glucose, sugar gluc/o, glyc/o, glycos/o
gonads gonad/o
ketone ket/o, keton/o
kidney ren/o, nephr/o
lobe lob/o
medulla medull/o
pancreas pancreat/o
parathyroid gland parathyroid/o
pituitary gland hypophys/o, pituitar/o, pituit/o
thalamus thalam/o
thymus gland thym/o
thyroid gland thyr/o, thyroid/o
to secrete crin/o
turning trop/o

Prefixes for the Anatomy of the Endocrine System

Prefix Meaning
endo- within
exo- outward
hypo- under, deficient
supra- above

Suffixes for the Anatomy of the Endocrine System

Suffix Meaning
-al pertaining to
-crine to secrete
-us, -is structure


Most of the pathology of the endocrine system is the result of either hyper– (too much) or hypo– (too little) hormonal secretion. Developmental issues also play a role in determining when the malfunction occurs and what the results will be.

Terms Related to Signs and Symptoms of Endocrine Disorders (RØØ-R99)

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Term Word Origin Definition
anorexia an- no, not, without
orex/o appetite
-ia condition
Lack of appetite. Anorexia nervosa is an eating disorder.
glycosuria glycos/o sugar, glucose
-uria urinary condition
Presence of glucose in the urine. May indicate diabetes mellitus. Also called glucosuria.
hyperalimentation hyper- excessive, above
aliment/o nutrition
-ation process of
An excessive intake of food. May be used to describe overeating.
hyperglycemia hyper- excessive, above
glyc/o glucose, sugar
-emia blood condition
Excessive glucose in the blood.
ketonuria keton/o ketone
-uria urinary condition