Chapter 19 - Endocrine System

How does the endocrine system differ from the nervous system

The endocrine system provides long-term regulation using hormones released into the bloodstream, while the nervous system provides rapid, short-term control using electrical signals and neurotransmitters

What do endocrine cells secrete

Hormones

What are hormones

Chemical messengers released into the bloodstream that regulate target cells and organs

How is endocrine activity regulated

By endocrine reflexes triggered by humoral, hormonal, or neural stimuli, often through negative feedback

What are the four chemical classes of hormones

Amino acid derivatives, peptide hormones, steroid hormones, eicosanoids

Which class includes steroid hormones

Steroid hormones

Which class includes peptide hormones

Peptide hormones

How does the hypothalamus control endocrine activity

By secreting regulatory hormones that control the anterior pituitary and producing ADH and oxytocin for release by the posterior pituitary

Which pituitary lobe is controlled by regulatory hormones

Anterior pituitary

Which pituitary lobe releases ADH and oxytocin

Posterior pituitary

What is the pituitary gland also called

Hypophysis

Name the two lobes of the pituitary gland

Anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis)

Which hormones are released by the posterior pituitary

Antidiuretic hormone (ADH) and oxytocin

Which hormones are released by the anterior pituitary

ACTH, TSH, GH, PRL, FSH, LH, and MSH

What is the function of the hypophyseal portal system

Transports regulatory hormones directly from the hypothalamus to the anterior pituitary

Why is the hypophyseal portal system important for anterior pituitary regulation

It allows rapid and precise control of hormone secretion without dilution in systemic circulation

Where is the thyroid gland located

On the anterior surface of the thyroid cartilage of the larynx

What hormones does the thyroid gland secrete

Thyroxine (T4), triiodothyronine (T3), and calcitonin

What is the function of T3 and T4

Regulate metabolism, growth, and development

Which thyroid hormone regulates calcium homeostasis

Calcitonin

What are thyroid follicles

Spherical structures lined with follicular cells that produce thyroid hormones

What is stored in the colloid

Thyroglobulin

What cells produce thyroid hormones

Follicular (thyrocyte) cells

What cells produce calcitonin

Parafollicular (C) cells

What hormone stimulates TSH release

Thyrotropin-releasing hormone (TRH)

What hormone directly stimulates the thyroid gland

Thyroid-stimulating hormone (TSH)

Where are the parathyroid glands located

On the posterior surface of the thyroid gland

What hormone do the parathyroid glands secrete

Parathyroid hormone (PTH)

What is the function of PTH

Increases blood calcium levels and regulates calcium homeostasis

Where is the thymus located

In the mediastinum, superior to the heart

What does the thymus secrete

Thymosins

How does the thymus change with age

It atrophies and becomes smaller with age

Where are the suprarenal (adrenal) glands located

On top of the kidneys

What are the two main regions of the adrenal glands

Adrenal cortex and adrenal medulla

What hormones are produced by the adrenal cortex

Mineralocorticoids, glucocorticoids, and androgens

What hormones are produced by the adrenal medulla

Epinephrine and norepinephrine

What hormones are produced by the kidneys

Renin, erythropoietin, and calcitriol

What hormones are produced by the heart

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)

What do kidney and heart hormones regulate

Blood pressure, blood volume, and red blood cell production

What endocrine cells are found in the pancreas

Alpha, beta, delta, and F cells

Which pancreatic cells secrete insulin

Beta cells

Which pancreatic cells secrete glucagon

Alpha cells

Which pancreatic cells secrete somatostatin

Delta cells

What hormones are produced by the testes

Androgens (testosterone) and inhibin

What hormones are produced by the ovaries

Estrogens, progestins, inhibin, and relaxin

What does inhibin do

Inhibits FSH secretion

What hormone does the pineal gland secrete

Melatonin

What is the function of melatonin

Regulates circadian rhythms and sleep–wake cycles

When is melatonin production highest

At night

How does aging affect hormone levels

Hormone levels increase at puberty and decline with aging, especially during menopause, while most endocrine functions show relatively few changes