Download Lecture Notes - Fullfrontalanatomy.com

Chapter 25
I.
The Endocrine System
Student Notes
The Endocrine System (pp. 712–714, Figs. 25.1–25.2).
A. The endocrine system is composed of several ductless glands that release hormones directly into
the blood or lymph; hormones trigger physiological changes in target cells throughout the body (p.
712).
B. The endocrine system controls and integrates the functions of other systems in the body and
closely interacts with the nervous system (p. 712).
C. Endocrine organs are small and widely separated from each other in the body; mostly endocrine
cells are epithelial in origin, but others are hormone-secreting neurons, muscle cells, and
fibroblast-like cells (p. 721, Fig. 25.1).
1. The primary (“pure”) endocrine glands are the pituitary, thyroid, parathyroid, adrenal,
and pineal glands (p. 712).
2. Endocrine cells also are located in the gonads, pancreas, kidney, alimentary canal, heart,
thymus, and skin (p. 712).
D. Hormones are messenger molecules that signal changes in target cells (pp. 712–714).
1. Classes of hormones are either amino acid derivatives (amines, peptides, or proteins), or
lipid-based steroids (p. 712).
2. Basic hormone action incorporates circulation throughout the entire body and contact
with specific target cells (pp. 712–713).
3. Control of hormone secretion is regulated by three major types of stimuli: humoral,
neural, or hormonal feedback (pp. 713–714, Fig. 25.2).
II.
The Major Endocrine Organs (pp. 714–724, Fig. 25.3, and Table 25.1).
A. The major endocrine glands of the body are the pituitary gland, thyroid gland, parathyroid glands,
adrenal glands, pineal gland, pancreas, thymus, and gonads (p. 714, Fig. 25.3).
B. The pituitary gland is suspended from the diencephalon of the brain and secretes at least nine
major hormones; the pituitary has two basic divisions: the adenohypophysis and the
neurohypophysis (pp. 714–719 and 724, Fig. 25.3, and Table 25.1).
1. The adenohypophysis has three divisions; the largest is the pars distalis with five cell
classes that secrete seven different protein hormones (pp. 714–716, Figs. 25.4–25.5, and
Table 25.1).
2. Hypothalamic control of hormone secretion from the adenohypophysis is exerted by
peptide hormones called releasing hormones (factors) (pp. 716–717).
3. The neurohypophysis secretes two hormones and is structurally part of the brain (pp.
717–719, Fig. 25.6).
C. The thyroid gland is located in the anterior neck; it secretes two hormones (p. 719, Fig. 25.7).
D. The parathyroid glands usually lie on the posterior aspect of the thyroid gland and secrete a
hormone, parathormone, which is essential for life (pp. 719–720, Fig. 25.8).
E. The adrenal (suprarenal) glands are located on the superior surface of the kidneys; each adrenal
gland is two glands in one: the adrenal medulla and the adrenal cortex (pp. 720–722, Fig. 25.9).
1. The adrenal medulla is part of the autonomic nervous system (Chapter 15) and secretes
amine proteins that enhance the “fight, flight, or fright” response (pp. 720 and 442, Fig.
25.9).
2. The adrenal cortex secretes a variety of hormones, all of which are lipid-based steroid
hormones (pp. 720–721, Fig. 25.9).
3. Structure of steroid-secreting cells incorporates many distinctive ultrastructural features
including abundant smooth ER and no secretory granules at all (p. 722, Fig. 25.10).
F. The pineal gland lies on the roof of the diencephalon and secretes the hormone melatonin, which
helps regulate circadian rhythms (p. 722, Figs. 25.1 and 13.15).
G. The pancreas is located in the posterior wall of the abdominal cavity; it functions as a dual organ in
that it secretes digestive enzymes as well as hormones (pp. 722–723, Fig. 25.11).
H. The thymus, an important organ of the immune system, secretes thymic hormones that are
essential for the production of T lymphocytes (p. 723, Fig. 25.1).
I. The gonads (testes and ovaries) are the main source of the steroid sex hormones (p. 723).
III.
Other Endocrine Structures (p. 725).
A. Endocrine cells occur within various organs of the body including the heart, the gastrointestinal
tract and its derivatives, the placenta, the kidneys, and the skin (p. 725).
IV.
Disorders of the Endocrine System (pp. 725–727, Figs. 25.12–25.13).
A. Most disorders of the endocrine glands involve either a hypersecretion (oversecretion) or a
hyposecretion (undersecretion) of a given hormone (pp. 725–727).
B. Pituitary disorders include gigantism, acromegaly, pituitary dwarfs, and diabetes insipidus (p.
725).
C. A disorder of the pancreas, diabetes mellitus, is caused by either by insufficient insulin or
resistance of body cells to the effects of insulin (pp. 725–726).
D. Disorders of the thyroid gland include Graves’ disease, adult hypothroidism, and endemic goiter
(p. 726, Fig. 25.12).
E. Disorders of the adrenal cortex include Cushing’s disease and Addison’s disease (pp. 726–727,
Fig. 25.13).
V.
The Endocrine System Throughout Life (pp. 727–728, Fig. 25.14).
A. The endocrine glands have diverse developmental origins from all three germ layers (pp. 727–728,
Fig. 25.14).
B. Some hormonal secretions change little with aging but others, such as GH, DHEA, and the sex
hormones show marked drops in secretion with age (pp. 727–728).