Lab Exercise 33
Endocrine System
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Major Endocrine Organs
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Figure 16.1
Hormones
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Hormones – chemical substances
secreted by cells into the extracellular
fluids
 Regulate the metabolic function of
other cells
The precise response depends on the
type of the target cell
Target Cell Specificity
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Hormones circulate to all tissues but only
activate cells referred to as target cells
Target cells must have specific receptors
to which the hormone binds
Gross Anatomy -Hypophysis
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Pituitary gland – two-lobed organ that secretes
nine major hormones
Neurohypophysis – posterior lobe (neural
tissue) and the infundibulum
 Receives, stores, and releases hormones
from the hypothalamus
Adenohypophysis – anterior lobe, made up of
glandular tissue
 Synthesizes and secretes a number of
hormones
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Pituitary (Hypophysis)
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Figure 16.6
Pituitary-Anterior Lobe
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There is a vascular connection, the
hypophyseal portal system, consisting
of:
 The primary capillary plexus
 The hypophyseal portal veins
 The secondary capillary plexus
Adenophypophyseal
Hormones
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The six hormones of the
adenohypophysis:
 Abbreviated as GH, TSH, ACTH,
FSH, LH, and PRL
Activity of the
Adenophypophysis
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The hypothalamus sends a chemical
stimulus to the anterior pituitary
 Releasing hormones stimulate the
synthesis and release of hormones
 Inhibiting hormones shut off the
synthesis and release of hormones
Activity of the
Adenophypophysis
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The tropic hormones
 Stimulates an endocrine gland instead
of a target organ. They are:
 Thyroid-stimulating hormone (TSH)
 Adrenocorticotropic hormone (ACTH)
 Follicle-stimulating hormone (FSH)
 Luteinizing hormone (LH)
Thyroid Stimulating
Hormone (Thyrotropin)
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Stimulates the normal development and
secretory activity of the thyroid
Triggered by hypothalamic thyrotropinreleasing hormone (TRH)
Adrenocorticotropic
Hormone (Corticotropin)
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Stimulates the adrenal cortex to release
corticosteroids
Triggered by hypothalamic corticotropinreleasing hormone (CRH) in a daily
rhythm
Gonadotropins
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Gonadotropins – follicle-stimulating
hormone (FSH) and luteinizing hormone
(LH)
 Regulate the function of the ovaries
and testes
 FSH stimulates gamete (egg or
sperm) production
 Triggered by the hypothalamic
gonadotropin-releasing hormone
(GnRH)
Functions of Gonadotropins
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In females
 LH promotes synthesis and release of
estrogens and progesterone
In males
 LH stimulates synthesis of
testosterone by the testes
Adenohypophysis- Growth
Hormone (GH)
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Stimulate most cells, but target bone and
skeletal muscle
Promote protein synthesis and
encourage the use of fats for fuel
Dwarfism, gigantism, acromegaly
Prolactin (PRL)
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In females, stimulates milk production by
the breasts
Regulated by the hypothalamic prolactinreleasing hormone (PRH) and prolactininhibitory hormone (PIH)
Pituitary - Posterior Lobe
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The posterior lobe is a downgrowth of
hypothalamic neural tissue
Has a neural connection with the hypothalamus
(hypothalamic-hypophyseal tract)
Nuclei of the hypothalamus synthesize oxytocin
and antidiuretic hormone (ADH)
These hormones are transported to the posterior
pituitary
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The Posterior Pituitary and
Hypothalamic Hormones
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ADH stimulates reabsorption of water from the
urine
 Produced by the supraoptic nuclei of the
hypothalamus
Oxytocin stimulates smooth muscle contraction
in breasts and uterus
 Produced by the paraventricular nuclei of the
hypothalamus
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Thyroid Gland
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Consists of two lateral lobes connected by the
isthmus
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Thyroid Gland
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Figure 16.8
Thyroid Hormone
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Consists of two related iodine-containing
compounds
 T4 – thyroxine has four iodine atoms
 T3 – triiodothyronine; has three iodine
atoms
Effects of Thyroid Hormone
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TH is concerned with:
 Increasing metabolic rate
 Heat production
 Cellular oxidation
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Hyperthyroidism
Hypothyroidism
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Calcitonin
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Produced by the parafollicular, or C,
cells
Lowers blood calcium levels
Antagonist to parathyroid hormone
(PTH)
PART 2
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Parathyroid Glands
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Tiny glands embedded in the posterior
aspect of the thyroid
PTH (parathormone) increases the level
of calcium in the blood
Parathyroid Glands
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Figure 16.11
Effects of Parathyroid Hormone
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PTH release increases Ca2+ in the blood
as it:
 Stimulates osteoclasts to digest bone
matrix
 Enhances the reabsorption of Ca2+
and the secretion of phosphate by the
kidneys
 Increases absorption of Ca2+ by
intestinal mucosal
Hyperparathyroidism
Hypoparathyroidism
Effects of Parathyroid Hormone
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Figure 16.12
Adrenal (Suprarenal) Glands
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Adrenal glands – paired, pyramidshaped organs atop the kidneys
Structurally and functionally, they are
two glands in one
 Adrenal medulla – neural tissue that
acts as part of the SNS
 Adrenal cortex – glandular tissue
Adrenal Cortex
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Synthesizes and releases steroid hormones
called corticosteroids
Different corticosteroids are produced in each
of the three layers
 Zona glomerulosa – mineralocorticoids
(chiefly aldosterone)
 Zona fasciculata – glucocorticoids
(chiefly cortisol)
 Zona reticularis – gonadocorticoids
(chiefly androgens)
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Aldosterone
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Electrolyte balance in extracellular fluids
Stimulates reabsorption of Na+ by the
kidneys
Stimulates secretion of K+ by the kidney
Glucocorticoids (Cortisol)
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Help the body resist chronic stress by:
 Keeping blood sugar levels relatively
constant
Cortisone, hydrocortisone,
corticosterone:
 Rises in blood glucose, fatty acids,
and amino
Gonadocorticoids
(Sex Hormones)
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Most gonadocorticoids secreted are
androgens (male sex hormones), and
the most important one is testosterone
Androgens contribute to:
 The onset of puberty
 The appearance of secondary sex
characteristics
 Sex drive in females
Adrenal Medulla
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Secrete epinephrine and norepinephrine
Secretion of these hormones causes:
 Blood glucose levels to rise
 Blood vessels to constrict
 The heart to beat faster
 Blood to be diverted to the brain,
heart, and skeletal muscle
Pancreas
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Mixed gland, which has both exocrine and
endocrine cells
Acinar cells produce an enzyme-rich juice used
for digestion (exocrine product)
Pancreatic islets (islets of Langerhans) produce
hormones (endocrine products)
The islets contain two major cell types:
 Alpha () cells that produce glucagon
 Beta () cells that produce insulin
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Insulin and Glucagon
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Glucagon major target is the liver, where
it promotes:
 Release of glucose to the blood from
liver cells
Insulin:
 Lowers blood glucose levels
 Enhances transport of glucose into
body cells
Gonads: Female
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Paired ovaries in the abdominopelvic
cavity produce estrogens and
progesterone and the ova
Estrogen:
 Appearance of secondary sexual
characteristics
 Breast development and cyclic
changes in the uterine mucosa
Gonads: Female
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Progesterone:
 Cycling changes of the uterine lining
 Keeps pregnancy
 Prepares breast for lactation
Gonads: Male
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Testes located in an extra-abdominal
sac (scrotum) produce testosterone
Testosterone:
 Initiates maturation of male
reproductive organs
 Causes appearance of secondary
sexual characteristics and sex drive
 Is necessary for sperm production
 Maintains sex organs in their
functional state
Pineal Gland
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Small gland hanging from the roof of the
third ventricle of the brain
Secretory product is melatonin
Melatonin is involved with:
 Day/night cycles
 Physiological processes that show
rhythmic variations (body temperature,
sleep, appetite)
Thymus
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Lobulated gland located deep to the
sternum
Secrete thymosins
These hormones are essential for the
development of the T lymphocytes (T
cells) of the immune system
Microscopic anatomy of the
glands
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Thyroid gland
 Follicles – simple squamous or
cuboidal cells
• Colloid – contain thyroglobulin, T3
and T4
 Parafollicular cells (C cells)
• Between follicles
• Secrete calcitonin
Microscopic anatomy of the
glands
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Parathyroid
 Fibrous capsule surrounds the organ
 Chief cell
• Small cells, round nuclei, arranged
in clusters, secret PTH
 Oxyphil cells
• Lager than chief cells
• Scattered
• Unknown function
Microscopic anatomy of the
glands
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Pancreas
 Exocrine acini
• Darker cells
 Endocrine with Islets of Langehans
• Beta cells – located at the center
and secrete insulin
• Alpha cells – located at the
periphery and secrete glucagon
Microscopic anatomy of the
glands
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Anterior Pituitary gland
 Chromophils
• Acidophils- reddish-brown. GH and
PRL
• Basophils – deep-blue. Tropic
hormones
 Chromophobes
• Do not take collor (Pale)
• Controversial role
Microscopic anatomy of the
glands
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Posterior pituitary gland
 Nerve fibers
 Pituicytes (glial cells)
Microscopic anatomy of the
glands
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Adrenal gland- cortex
 Zona glomerulosa
• outermost, spherical clusters of
cells, secrete mineralocorticoids
 Zona fasciculate
• Next layer, cells arranged in parallel
cords, secrete glucocorticoids
 Zona reticularis
• Inneremost, cells arranged in
branches, produces mainly sex
hormones
Microscopic anatomy of the
glands
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Adrenal gland – medulla
 The core of the gland
 Modified neurons
 Secrete E and NE
Microscopic anatomy of the
glands
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Ovary
 Vesicular follicle
• Ovum
Microscopic anatomy of the
glands
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Testes
 Seminiferous tubules
• Produce sperm
 Interstitial cells
• Between seminiferous tubules.
• Secrete testosterone
Cat’s Glands to Identify
Thyroid
 Thymus
 Pancreas
 Adrenal
 Gonads
 Testes
 Ovaries
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