Chapter 17: The Endocrine System

anterior pituitary

Hormones produced by the ________ (in response to releasing hormones) enter a secondary capillary plexus, and from there drain into the circulation.

renin angiotensin aldosterone

A decline in blood flow to the kidneys stimulates them to release the enzyme renin, triggering the ________ (RAAS) system, and stimulating the reabsorption of sodium and water.

**endocrine system**

uses just one method of communication: chemical signaling.

**endocrine gland**

is the major player in this system.

endocrine system

As the body ages, changes occur that affect the ________, sometimes altering the production, secretion, and catabolism of hormones.

glucose levels

Reduces blood ________.

**exocrine system**

whose glands release their secretions through ducts.

**paracrine factor**

which is a chemical that induces a response in neighboring cells.

The endocrine system uses just one method of communication

chemical signaling

When fetal development is complete, the peptide-derived hormone oxytocin (tocia

= "childbirth") stimulates uterine contractions and dilation of the cervix

There are three regions

the pars distalis is the most anterior, the pars intermedia is adjacent to the posterior pituitary, and the pars tuberalis is a slender "tube" that wraps the infundibulum

The gonadotropins include two glycoprotein hormones

follicle-stimulating hormone (FSH) stimulates the production and maturation of sex cells, or gametes, including ova in women and sperm in men

In the colloid, peroxidase enzymes link the iodine to the tyrosine amino acids in thyroglobulin to produce two intermediaries

a tyrosine attached to one iodine and a tyrosine attached to two iodines

The cortex itself is divided into three zones

the zona glomerulosa, the zona fasciculata, and the zona reticularis

The liver is responsible for secreting at least four important hormones or hormone precursors

insulin-like growth factor (somatomedin), angiotensinogen, thrombopoetin, and hepcidin

The pituitary gland arises from two distinct areas of the ectoderm

the anterior pituitary gland arises from the oral ectoderm, whereas the posterior pituitary gland arises from the neural ectoderm at the base of the hypothalamus

**Peptide and Protein Hormones**

Peptide hormones consist of short chains of amino acids, whereas protein hormones are longer polypeptides.

**Steroid Hormones**

are derived from the lipid cholesterol

**second messenger**

Initiate a signaling cascade that is carried out by a molecule called a

**cyclic adenosine monophosphate (cAMP)**

The second messenger used by most hormones is

**permissive effect**

in which the presence of one hormone enables another hormone to act.

**synergistic effect**

in which two hormones with similar effects produce an amplified response.

a**ntagonistic effect**

in which two hormones have opposing effects.

**pituitary gland**

(or hypophysis), a bean-sized organ suspended from it by a stem called the **infundibulum** (or pituitary stalk).

**oxytocin**

(tocia- = “childbirth”) stimulates uterine contractions and dilation of the cervix.

**osmoreceptors**

—specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.

**antidiuretic hormone (ADH)**

In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors signal the posterior pituitary to release

**Anterior Pituitary**

originates from the digestive tract in the embryo and migrates toward the brain during fetal development.

**hypophyseal**

portal system, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation.

**growth hormone (GH)**

also called somatotropin—a protein hormone produced and secreted by the anterior pituitary gland.

**insulin-like growth factors (IGFs)**

GH indirectly mediates growth and protein synthesis by triggering the liver and other tissues to produce a group of proteins called

**pituitary dwarfism**

Abnormally low levels of GH in children can cause growth impairment—a disorder called__ (also known as growth hormone deficiency).

**thyroid-stimulating hormone**

The activity of the thyroid gland is regulated by **___** (TSH), also called thyrotropin.

**adrenocorticotropic hormone (ACTH)**

also called corticotropin, stimulates the adrenal cortex (the more superficial “bark” of the adrenal glands) to secrete corticosteroid hormones such as cortisol.

**follicle-stimulating hormone (FSH)**

stimulates the production and maturation of sex cells, or gametes, including ova in women and sperm in men.

**Luteinizing hormone (LH)**

triggers ovulation in women, as well as the production of estrogens and progesterone by the ovaries.

**Prolactin**

promotes lactation (milk production) in women.

**thyroid gland**

is located anterior to the trachea, just inferior to the larynx.

**colloid**

The follicles are made up of a central cavity filled with a sticky fluid called

**parathyroid glands**

are tiny, round structures usually found embedded in the posterior surface of the thyroid gland.

**parathyroid hormone (PTH)**

the major hormone involved in the regulation of blood calcium levels.

**hyperparathyroidism**

a disorder caused by an overproduction of PTH that results in excessive calcium reabsorption from bone.

**zona glomerulosa**, the **zona fasciculata,** and the **zona reticularis**

The cortex itself is divided into three zones:

**adrenal cortex**

as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation.

**adrenal medulla**

is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons.

**adaptation syndrome (GAS)**

The body responds in different ways to short-term stress and long-term stress following a pattern known as the general

**alarm reaction**

Stage one of GAS is called the

**stage of resistance**

If the stress is not soon relieved, the body adapts to the stress in the second stage called the

**stage of exhaustion**

individuals may begin to suffer depression, the suppression of their immune response, severe fatigue, or even a fatal heart attack.

**mineralocorticoids**

because of their effect on body minerals, especially sodium and potassium.

**Aldosterone**

is the major mineralocorticoid.

**pineal gland**

a tiny endocrine gland whose functions are not entirely clear.

**pinealocyte**

cells that make up the pineal gland are known to produce and secrete the amine hormone **melatonin,** which is derived from serotonin.

**testosterone**

primary hormone produced by male testes

**inhibin**

which inhibits the secretion of FSH from the anterior pituitary gland.

**estrogens**

The primary hormones produced by the ovaries are

**progesterone**

which contributes to regulation of the menstrual cycle and is important in preparing the body for pregnancy as well as maintaining pregnancy.

**pancreas**

is a long, slender organ, most of which is located posterior to the bottom half of the stomach.

**pancreatic islets**

clusters of cells formerly known as the islets of Langerhans secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).

**alpha cell**

produces the hormone glucagon and makes up approximately 20 percent of each islet

**beta cell**

produces the hormone insulin and makes up approximately 75 percent of each islet.

**delta cell**

accounts for four percent of the islet cells and secretes the peptide hormone somatostatin.

**PP cell**

accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone.

**atrial natriuretic peptide (ANP)**

In response, specialized cells in the wall of the atria produce and secrete the peptide hormone

**Skeleton**

Although bone has long been recognized as a target for hormones, only recently have researchers recognized that the skeleton itself produces at least two hormones.

**Adipose Tissue**

produces and secretes several hormones involved in lipid metabolism and storage.

**leptin**

a protein manufactured by adipose cells that circulates in amounts directly proportional to levels of body fat.

**Skin**

The skin functions as an endocrine organ in the production of the inactive form of vitamin D3, cholecalciferol.

**Thymus**

is an organ of the immune system that is larger and more active during infancy and early childhood, and begins to atrophy as we age.

**thymosins**

that contribute to the development and differentiation of T lymphocytes, which are immune cells.

**Liver**

is responsible for secreting at least four important hormones or hormone precursors: insulin-like growth factor (somatomedin), angiotensinogen, thrombopoetin, and hepcidin.