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Chapter 18
The Endocrine
System
.
Endocrine System Overview
• Uses hormones as control agents
• Hormones = chemical messengers released
into the blood to regulate specific body
functions
• Endocrinology = the study of hormones and
the endocrine organs
Nervous System
• rapid
• action potentials &
neurotransmitters
• brief
vs.
Endocrine System
• 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”
Major
Endocrine 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 Gland
1. Growth hormone (GH) – promotes growth
2. 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)
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