Chapter 18: The Endocrine System

What is the endocrine system?

A system of glands that secrete hormones to help maintain homeostasis

What two systems work together to maintain homeostasis?

The endocrine system and nervous system

What do endocrine glands secrete?

Hormones

Where do endocrine glands release hormones?

Into the bloodstream

What are target cells or target organs?

Specific cells or organs stimulated by hormones

How are endocrine glands different from exocrine glands?

Endocrine glands secrete into the bloodstream; exocrine glands secrete into ducts

What is endocrinology?

The study of the endocrine system and hormones

What are the major functions of the endocrine system?

Maintaining homeostasis and regulating metabolism, reproduction, growth, and development

How does the nervous system regulate body functions?

Through rapid nerve impulses

How does the endocrine system regulate body functions?

Through hormone release

Which system responds faster, nervous or endocrine?

Nervous system

Which system has more widespread effects, nervous or endocrine?

Endocrine system

What are hormones?

Chemical substances secreted by glands that regulate metabolic activities of cells and organs

What are the three major classes of hormones?

Amino acid-based hormones, steroid hormones, and eicosanoids

What are amino acid-based hormones?

Hormones ranging from small amino acids to large proteins; most human hormones belong to this class

What are steroid hormones derived from?

Cholesterol

Which hormones are steroid-based?

Gonadal and adrenocortical hormones

What are eicosanoids?

Hormones released by cell membranes involved in inflammation and allergic reactions

What are examples of eicosanoids?

Leukotrienes and prostaglandins

Are hormones specific to target cells and organs?

Yes

Which nervous system division helps regulate hormone secretion?

Autonomic nervous system

What feedback system regulates most hormone release?

Negative feedback

How do hormones influence body activities?

Alter membrane permeability, stimulate protein production, activate/deactivate enzymes, induce secretions, and stimulate mitosis

Where is the pituitary gland located?

In the sella turcica of the sphenoid bone

What connects the pituitary gland to the hypothalamus?

Infundibulum

What regulates most pituitary hormone release?

Hypothalamus

What are the two lobes of the pituitary gland?

Adenohypophysis and Neurohypophysis

What is another name for the adenohypophysis?

Anterior pituitary

Why is the adenohypophysis called the master gland?

Because its hormones stimulate other endocrine glands

What is somatotropin?

Growth hormone (GH)

What does growth hormone do?

Stimulates growth of cartilage, bone, muscle, and fat by promoting mitosis

What regulates growth hormone release?

Growth hormone releasing factor and growth hormone inhibiting factor from the hypothalamus

What is gigantism?

Hypersecretion of growth hormone before adulthood

What is acromegaly?

Excess growth hormone secretion in adults

What is pituitary dwarfism?

Deficiency of growth hormone

What is thyrotropin hormone (TSH)?

Hormone that stimulates thyroid gland secretion

What is ACTH?

Hormone that stimulates adrenal gland secretion and stress responses

What are gonadotropins?

FSH and LH

What do FSH and LH regulate?

Growth and development of sex organs and female menstrual cycle

What is prolactin (PRL)?

Hormone that stimulates breast development and milk production

What stimulates prolactin release?

Estrogen

What stimulates additional prolactin release after childbirth?

Infant suckling

What is galactorrhea?

Milk production in a non-nursing woman or male, often due to a pituitary tumor

What is the neurohypophysis?

Posterior pituitary that stores hormones produced by the hypothalamus

What two hormones are stored in the neurohypophysis?

Oxytocin and ADH

What does oxytocin do?

Stimulates uterine contractions, regulates blood pressure, and aids milk ejection

What does ADH do?

Regulates water balance and reduces urine output

How does alcohol affect ADH?

Inhibits ADH secretion

What is diabetes insipidus?

Disorder caused by impaired ADH production, secretion, or function

What are signs of diabetes insipidus?

Extreme thirst and excessive pale urine

Where is the thyroid gland located?

In the neck below the larynx on either side of the trachea

What connects the two lobes of the thyroid gland?

Isthmus

What structures make up the thyroid internally?

Follicles

What are the two major thyroid hormones?

Thyroxine (T4) and Triiodothyronine (T3)

What is another name for T3 and T4 collectively?

Thyroid hormone (TH)

What do thyroid hormones do?

Regulate metabolism and heat production

What does calcitonin do?

Lowers blood calcium by stimulating osteoblast activity

What is a goiter?

Enlarged thyroid gland

What commonly causes a goiter?

Iodine deficiency

What is Graves disease?

Autoimmune hyperthyroidism

What are signs of Graves disease?

Increased metabolism, sweating, heat intolerance, weight loss, rapid heart rate, and exophthalmos

What is hypothyroidism?

Reduced thyroid hormone production

What is hypothyroidism called in adults?

Myxedema

What are symptoms of hypothyroidism?

Weight gain, lethargy, low metabolism, and mental sluggishness

What is congenital hypothyroidism?

Hypothyroidism present at birth

What can untreated congenital hypothyroidism cause?

Mental retardation

Where are the parathyroid glands located?

On the posterior surface of the thyroid gland

How many parathyroid glands are usually present?

Four

What hormone is secreted by the parathyroid glands?

Parathyroid hormone (PTH)

What does PTH do?

Raises blood calcium levels

How does PTH increase calcium levels?

Stimulates osteoclast activity

Where are the adrenal glands located?

On top of the kidneys

What are the two major regions of the adrenal gland?

Cortex and medulla

What does the zona glomerulosa secrete?

Mineralocorticoids

What does the zona fasciculata secrete?

Glucocorticoids and gonadocorticoids

What does the zona reticularis secrete?

Androgens

What are mineralocorticoids?

Hormones that regulate electrolyte balance

What is the most abundant mineralocorticoid?

Aldosterone

What does aldosterone regulate?

Sodium levels

What is aldosteronism?

Hypersecretion of aldosterone

What are symptoms of aldosteronism?

High blood pressure, poor vision, and weak muscles

What are glucocorticoids?

Hormones that regulate energy metabolism and stress responses

What hormone regulates glucocorticoid secretion?

ACTH

What is the most common glucocorticoid?

Cortisol

What does cortisol do?

Regulates fat breakdown and glucose release

What is Cushing's syndrome?

Hypersecretion of cortisol

What are symptoms of Cushing's syndrome?

Moon face, trunk obesity, acne, and buffalo hump

What is Addison's disease?

Deficiency of cortisol

What are symptoms of Addison's disease?

Fatigue, hypoglycemia, sweating, and bronzed skin

What are gonadocorticoids?

Sex hormones produced by the adrenal cortex

What cells make up the adrenal medulla?

Chromaffin cells

What hormones are secreted by the adrenal medulla?

Epinephrine, norepinephrine, and dopamine

What is another name for epinephrine and norepinephrine?

Adrenaline

What role do epinephrine and norepinephrine play?

Fight-or-flight responses

Which adrenal medulla hormone is released in the greatest amount?

Epinephrine

What does dopamine do?

Increases urine output and relaxes blood vessels

Where is the pancreas located?

Below and behind the stomach

Why is the pancreas considered a dual organ?

It has digestive and endocrine functions

What do acinar cells do?

Produce digestive enzymes

What are the islets of Langerhans?

Endocrine cell clusters in the pancreas