Download Biology 218 – Human Anatomy - RIDDELL

Biology 218 – Human Anatomy
RIDDELL
Chapter 23 Adapted form Tortora 10th ed.
LECTURE OUTLINE
A. Comparison of Nervous and Endocrine Systems (see Table 23.1): (p. 704)
1. The nervous and endocrine systems together coordinate functions of all body systems.
2. The nervous system controls homeostasis via nerve impulses that trigger release of
neurotransmitter molecules which act on other neurons, muscle cells, or gland cells.
3. The endocrine system controls homeostasis by secreting hormones, i.e., messenger
molecules, into the bloodstream for delivery to virtually all body cells.
4. The nervous and endocrine systems act as a coordinated supersystem called the
neuroendocrine system: some neurons stimulate or inhibit the release of hormones and
some hormones promote or inhibit the initiation of nerve impulses.
5. The nervous system causes muscles to contract and glands to secrete either more
or less of their product; the endocrine system affects virtually all body tissues by
altering metabolic activities, regulating growth and development, and influencing
reproductive processes.
6. Nerve impulses typically produce their effects within several milliseconds and the effects
are relatively brief in duration; hormones may take seconds to hours to produce their
effects and these effects are generally longer in duration.
7. Endocrinology is the science concerned with the structure and functions of the endocrine
glands and the diagnosis and treatment of disorders of the endocrine system.
B. Endocrine Glands Defined (p. 705)
1. The body contains two types of glands:
i. exocrine glands (e.g., sudoriferous, sebaceous, and mucous glands) secrete their
products into ducts which deliver the secretions into body cavities, into the lumen
of an organ, or to the outer surface of the body
ii. endocrine glands secrete their products, called hormones, into the surrounding
interstitial fluid from which they diffuse into capillaries to be carried away by the
blood
2. The endocrine glands (e.g., pituitary, thyroid, and adrenal glands) collectively form the
endocrine system; there are several organs of the body (e.g., hypothalamus, thymus,
pancreas, stomach, skin, heart, etc.) that contain endocrine tissue but are not endocrine
glands exclusively.
C. Hormones (p. 705)
1. Although hormones are delivered by the bloodstream throughout the body, hormones
affect only certain target cells.
2. Target cells for a particular hormone are those cells that have the appropriate receptor
molecules (proteins or glycoproteins) that can bind to the hormone.
3. The number of receptor molecules in a target cell may increase or decrease in order to
increase or decrease, respectively, the sensitivity of that target cell to a particular hormone.
4. The amount of hormone secreted by endocrine cells, usually in short bursts, is regulated to
maintain homeostasis and prevent overproduction or underproduction of that hormone.
D. Hypothalamus and Pituitary Gland (p. 707)
1. The hypothalamus is the major integrating link between the nervous and endocrine
systems.
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2. The hypothalamus receives input from numerous sources and, in addition to many other
functions, exerts control over the pituitary gland and is itself a crucial endocrine gland; the
hypothalamus and pituitary gland together play important roles in regulation of virtually all
aspects of growth, development, metabolism, and homeostasis.
3. The pituitary gland or hypophysis:
i. is about 1-1.5 cm in diameter and lies in the sella turcica of the sphenoid bone
ii. is attached to the hypothalamus by the infundibulum
iii. has two anatomically and functionally separate portions:
a. anterior pituitary gland (anterior lobe) accounts for about 75% of the
total weight of the gland and contains many glandular epithelial cells
that form the glandular part of the pituitary gland; in the adult, it
consists of the pars distalis and the pars tuberalis
b. posterior pituitary gland (posterior lobe), consisting of the pars
nervosa and the infundibulum, contains axons and axon terminals of
neurons whose cell bodies are located in the supraoptic and
paraventricular nuclei of the hypothalamus
- the axon terminals in the posterior pituitary gland are associated
with specialized neuroglia called pituicytes
iv. has a third region called the pars intermedia that atrophies during fetal
development
4. Anterior Pituitary Gland (Anterior Lobe) or Adenohypophysis:
i. Secretion of anterior pituitary hormones is regulated by releasing hormones and
inhibiting hormones that are delivered from the neurosecretory cells of the
hypothalamus by a hypophyseal portal system of blood vessels:
a. superior hypophyseal arteries that form the primary plexus at the base
of the hypothalamus
b. hypophyseal portal veins that pass down outside of the infundibulum to
form a secondary plexus in the anterior pituitary; anterior pituitary
hormones are carried away by the anterior hypophyseal veins for
distribution to target tissues throughout the body
ii. Five types of anterior pituitary cells secrete seven major hormones:
a. somatotrophs secrete human growth hormone (hGH) or somatotropin
which stimulates several tissues to secrete insulinlike growth factors,
hormones that stimulate general body growth and regulates aspects of
metabolism
b. thyrotrophs secrete thyroid-stimulating hormone (TSH) or thyrotropin
which regulates activities of the thyroid gland
c. gonadotrophs secrete follicle-stimulating hormone (FSH) and
luteinizing hormone (LH) which affect activities of the ovaries and testes
d. lactotrophs secrete prolactin (PRL) which stimulates milk production
e. corticotrophs secrete adrenocorticotropic hormone (ACTH) or
corticotropin which stimulates the adrenal cortex to secrete
glucocorticoids; some corticotrophs also secrete melanocyte-stimulating
hormone (MSH) which is thought to affect brain activity and skin
pigmentation
f. the 5 different types of secretory cells can be classified according to their
staining reactions into basophils, acidophils and chromophobes.
iii. Some of the anterior pituitary hormones are tropic hormones or tropins, i.e.,
hormones that influence another endocrine gland.
iv. Table 23.2 provides a summary of anterior pituitary gland hormones and their
actions.
5. Posterior Pituitary Gland (Posterior Lobe) or Neurohypophysis:
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i.
ii.
RIDDELL
The posterior pituitary does not synthesize hormones but it does store and release
two hormones synthesized in the hypothalamus.
The posterior pituitary consists of:
a. pituicytes
b. axon terminals of hypothalamic neurosecretory cells whose cell bodies
are located in the paraventricular and supraoptic nuclei of the
hypothalamus
- axons of these cells form the hypothalamohypophyseal tract which
extends from the hypothalamus to the posterior pituitary
- the cell bodies of these cells produce:
1. oxytocin (OT) which enhances uterine contractions during
labor and stimulates milk ejection
2. antidiuretic hormone (ADH), also called vasopressin,
which decreases urine volume and increases blood pressure
- these hormones are delivered in secretory vesicles to and stored in the
axon terminals until nerve impulses that are delivered to the axon
terminals trigger exocytosis to release the hormones into nearby
capillaries
iii. Blood is supplied to the posterior gland by inferior hypophyseal arteries that
drain into the capillary plexus of the infundibular process; from this plexus,
hormones pass into the posterior hypophyseal veins for delivery to target cells in
other tissues.
iv. Table 23.3 provides a summary of posterior pituitary gland hormones and their
actions.
E. Thyroid Gland (p. 711)
1. The butterfly-shaped thyroid gland is located just below the larynx.
2. It has right and left lateral lobes, located on either side of the trachea, that are connected
by an isthmus that lies in front of the upper end of the trachea; a small pyramidal-shaped
lobe sometimes extends upward from the isthmus.
3. It contains thyroid follicles; the wall of each follicle consists of two types of cells:
i. numerous follicular cells which secrete:
a. thyroxine or tetraiodothyronine or T4
b. triiodothyronine or T3
- these two hormones are collectively called the thyroid hormones
- these hormones regulate the rate of metabolism, growth, and
development
ii. less numerous parafollicular cells or C cells which secrete calcitonin
- calcitonin influences calcium homeostasis by decreasing blood calcium
concentration
4. The thyroid gland receives its blood supply from the superior and inferior thyroid arteries;
blood is drained by the superior, middle, and inferior thyroid veins.
5. The thyroid gland is innervated by postganglionic fibers from the superior and middle
cervical sympathetic ganglia; the preganglionic fibers of these ganglia emerge from the
second through seventh thoracic segments of the spinal cord.
6. Table 23.4 provides a summary of thyroid gland hormones and their actions.
F. Parathyroid Glands (p. 713)
1. There is usually one superior and one inferior parathyroid gland attached to the posterior
surface of each lateral lobe of the thyroid gland, i.e., usually 4 in total.
2. The parathyroid glands contain two types of cells:
i. numerous principal cells which secrete parathyroid hormone (PTH) or
parathormone
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RIDDELL
- this hormone increases blood calcium and magnesium levels,
decreases blood phosphate levels, and promotes the formation of
calcitriol, which is the active form of vitamin D
ii. less numerous oxyphil cells whose function is currently unknown
3. The parathyroid glands receive their blood supply from the superior and inferior thyroid
arteries; blood is drained by the superior, middle, and inferior thyroid veins.
4. The parathyroid glands are innervated by the thyroid branches of cervical sympathetic
ganglia.
5. Table 23.5 provides a summary of parathyroid hormone actions.
G. Adrenal Glands (p. 715)
1. The two adrenal (suprarenal) glands lie superior to the two kidneys.
2. Each gland is differentiated into two regions:
i. large, peripherally located adrenal cortex which is subdivided into three zones:
a. outer zona glomerulosa that secretes mineralocorticoids which affect
mineral (especially sodium and potassium) levels in the blood
b. middle zona fasciculata that secretes glucocorticoids which affect
glucose metabolism
c. inner zona reticlaris that secretes minute amounts of weak androgens
ii. small, centrally located adrenal medulla which consists of chromaffin cells;
these cells:
a. are innervated by sympathetic preganglionic neurons
b. are specialized sympathetic postganglionic neurons that secrete about
80% epinephrine or adrenaline and about 20% norepinephrine (NE) or
noradrenaline
- both hormones have sympathomimetic effects
3. The adrenal glands receive their blood supply from several superior, the middle, and the
inferior suprarenal arteries; blood is drained by the right and left suprarenal veins.
4. The adrenal medullae are innervated by preganglionic fibers from the thoracic splanchnic
nerves.
5. Table 23.6 provides a summary of adrenal gland hormones and their actions.
H. Pancreas (p. 717)
1. The pancreas is both an endocrine gland and an exocrine gland.
2. It is a flattened organ located posterior and slightly inferior to the stomach.
3. It consists of three regions: head, body, and tail.
4. Scattered among the exocrine portions (acini) of the pancreas are tiny clusters of
endocrine tissue called pancreatic islets or islets of Langerhans.
5. The pancreatic islets contain four types of cells:
i. alpha (or A) cells which secrete glucagon
- glucagon increases blood glucose concentration
ii. beta (or B) cells which secrete insulin
- insulin decreases blood glucose concentration
iii. delta (or D) cells which secrete somatostatin
- somatostatin inhibits the secretion of glucagon and insulin
iv. F cells which secrete pancreatic polypeptide
- this hormone inhibits secretion of somatostatin and pancreatic
digestive
enzymes
6. The pancreas receives its blood supply from the superior and inferior pancreaticoduodenal
arteries and from the splenic and superior mesenteric arteries; blood drains into the splenic
vein and the superior mesenteric vein.
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RIDDELL
7. The pancreas is innervated by autonomic nerves derived from the celiac and superior
mesenteric plexuses; included are preganglionic vagal, postganglionic sympathetic, and
afferent fibers (but note that pancreatic secretion is controlled primarily by the intestinal
hormones secretin and cholecystokinin).
8. Table 23.7 provides a summary of pancreatic hormones and their actions.
I.
Ovaries and Testes (p. 719)
1. The ovaries are paired oval structures located in the pelvic cavity; they secrete several
hormones:
i. estrogens and progesterone, the female sex hormones, which are responsible
for the development and maintenance of female sexual characteristics
ii. inhibin which inhibits secretion of FSH
iii. relaxin which relaxes the pubic symphysis and helps dilate the cervix just before
the birth of a baby
2. The testes are paired oval structures located in the scrotum; they secrete:
i. testosterone, the male sex hormone, which regulates production of sperm and
stimulates growth and development of male sexual characteristics
ii. inhibin which inhibits secretion of FSH
3. Table 23.8 provides a summary of hormones secreted by the ovaries and testes and their
principal actions.
J. Pineal Gland (p. 720)
1. The pineal gland is attached to the roof of the brain’s third ventricle.
2. It is part of the epithalamus and is covered by a capsule formed by the pia mater.
3. It consists of masses of neuroglia and secretory cells called pinealocytes; it is innervated
by sympathetic postganglionic fibers from the superior cervical ganglia.
4. The pineal gland secrets melatonin which is believed to promote sleepiness and play a
role in setting of the body’s biological clock.
5. The pineal gland receives its blood supply from the posterior cerebral artery; blood drains
into the great cerebral vein.
K. Thymus (p. 720)
1. The thymus plays a major role in immunity and was described in Chapter 16; review the
details of structure and function of the thymus as previously described in Chapter 16.
2. Hormones secreted by the thymus gland include:
i. thymosin
ii. thymic humoral factor (THF)
iii. thymic factor (TF)
iv. thymopoietin
3. These hormones promote the proliferation and maturation of a group of lymphocytes called
T cells.
L. Other Endocrine Tissues (p. 721)
1. In addition to the endocrine glands described above, there are other organs that contain
endocrine cells which secrete hormones; these organs include (see Table 23.9):
i. gastrointestinal tract which secretes:
a. gastrin
b. glucose-dependent insulinotropic peptide (GIP)
c. secretin
d. cholecystokinin (CCK)
ii. placenta which secretes:
a. human chorionic gonadotropin (hCG)
b. estrogens
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c. progesterone
d. human chorionic somatomammotropin (hCS)
iii. kidneys which secrete renin, erythropoietin (EPO) and calcitriol
iv. heart which secretes atrial natriuretic peptide (ANP)
v. adipose tissue which secretes leptin
M. Development of the Endocrine System (p. 721)
1. The pituitary gland (hypophysis) develops from two different regions of the ectoderm:
i. the posterior pituitary gland (neurohypophysis) develops from an outgrowth of
ectoderm called the neurohypophyseal bud, located on the floor of the
hypothalamus
ii. the infundibulum is also an outgrowth of the neurohypophyseal bud and connects
the posterior pituitary gland to the hypothalamus
2.
3.
4.
5.
6.
7.
8.
9.
iii. the anterior pituitary gland (adenohypophysis) develops from an outgrowth of
ectoderm called the hypophyseal (Rathke’s) pouch, located in the roof of the
mouth
The thyroid gland develops as a midventral outgrowth of endoderm called the thyroid
diverticulum, from the floor of the pharynx.
The parathyroid glands develop from endoderm as outgrowths from the third and fourth
pharyngeal pouches.
The adrenal cortex develops from intermediate mesoderm from the same region that
produces the gonads.
The adrenal medulla develops from ectoderm, namely the neural crest.
The pancreas develops from two outgrowths of endoderm from the part of the foregut that
later becomes the duodenum; these two outgrowths eventually fuse to form the pancreas.
The development of the ovaries and testes is described in Chapter 27.
The pineal gland develops as an outgrowth between the thalamus and colliculi from
ectoderm associated with the diencephalon,.
The thymus develops from endoderm of the third pharyngeal pouches.
N. Aging and the Endocrine System (p. 723)
1. Endocrine glands generally atrophy with aging.
2. However, the secretion of only some hormones is decreased, e.g., hGH, thyroid hormones,
cortisol, aldosterone, insulin, and sex hormones.
O. Key Medical Terms Associated with the Endocrine System (p. 726)
1. Students should familiarize themselves with the glossary of key medical terms.
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