Chapter 18

The Endocrine System

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Endocrine System Overview

• Uses hormones as control agents

• Hormones = chemical messengers released into the blood to regulate specific body functions

• EndocrinologyEndocrinology = the study of hormones and the endocrine organs

Nervous System vs. Endocrine System

• rapid• action potentials &

neurotransmitters • brief

• slower• hormones circulated

throughout the body in the blood

• all body cells exposed; only target cells with receptors respond

• hormones persist for seconds/hours/days

The Chemistry of Hormones

2 main chemical classes of hormones:

• Proteins

• Steroids (synthesized from cholesterol)

Mechanisms of Hormone Action

• Changing membrane permeability by opening or closing ion channels

• Enzyme activation or deactivation

• Induction or suppression of secretory activities

• Stimulation of mitosis and meiosis

Positive vs. Negative Feedback

• Positive feedback: “more gets you more”

• Negative feedback: “more gets you less”

MajorEndocrine Glands

I. Hypothalamus

II. Pituitary gland

III. Thyroid gland

IV. Parathyroid glands

V. Pancreas

VI. Adrenal glands

VII. Gonads

VIII. Pineal gland

I.Hypothalamus• Links the NS with ES• Secretes important hormones

which are stored and released from posterior Pituitary gland:

1. Oxytocin

2. Antidiuretic hormone (ADH)

• Both are made in the hypothalamus and released by the pituitary gland.

II. Pituitary Gland = “The Master Gland”

• Stimulates all other endocrine glands

• Two parts: posterior and anterior

Posterior Pituitary:1. Antidiuretic hormone (ADH) –

promotes retention of water by kidneys

2. Oxytocin (OT) – responsible for contractions during labor and milk ejection

Anterior Pituitary Gland1. Growth hormone (GH) – promotes growth2. Prolactin (PRL) – stimulates milk

production

3. Follicle-stimulating hormone (FSH) – stimulates secretion of estrogen, development of follicle cells in ovaries, sperm maturation

4. Luteinizing hormone (LH) – promotes ovulation, secretion of estrogen, progesterone and testosterone

5. Thyroid-stimulating hormone (TSH) – triggers secretion of thyroid hormones

6. Adrenocorticotropic hormone (ACTH) – stimulates production of glucocorticoids

III. Thyroid Gland• Located under larynx (voice box)• Produces thyroid hormones & calcitonin• Thyroid hormones - increase metabolic

rate, oxygen consumption and body heat production

• Calcitonin - ↓calcium concentration in body fluids (inhibits osteoclasts and stimulates calcium excretion)

Thyroid Gland Pathologies

Hypothyroidism Hyperthyroidism – Grave’s disease

IV. Parathyroid Glands

• 4 small glands on the posterior surface of the thyroid gland

• Produce parathyroid hormone

• Parathyroid hormone - ↑ calcium concentration in body fluids (stimulates osteoclasts, inhibits osteoblasts, reduces urinary excretion of calcium, & stimulates formation of calcitriol)