Download The Endocrine System

Exercise 18
The Endocrine System
laboratory Objedives
On completion of the activities in this exercise, you will be able to:
Describe the difference between an endocrine gland and an
exocrine gland.
• Discuss how a hormone affects a target cell.
Explain the functional relationship between the endocrine
system and the nervous system.
Identify the locations of the endocrine glands in the hu­
man body.
• Describe the anatomical relations of the endocrine glands to
adjacent structures.
List the hormones produced by the various endocrine
glands and describe their functions.
Describe the microscopic structure of the endocrine glands.
Materials
Anatomical models:
• Human brain
• Human torso
Human sklills
Compound light microscopes
• Prepared microscope slides:
• Pituitary gland
• Thyroid gland
• Parathyroid gland
• Thymus
• Pancreas
• Adrenal gland
• Ovary
• Testis
he endocrine system consists of a diverse collection of
organs and tissues that contain endocrine glands.
These glands secrete chemicals known as hormones
into nearby blood capillaries. Once in the circulatory system,
hormones can be transported to target cells at some distant
location. At the target cell, a hormone binds to a specific re­
ceptor. Once this occurs, the target cell will respond to the
hormone's chemical message. Hormones can in!1uence a target
cell's metabolic activities by regulating the production of spe­
cific enzymes or critical structural proteins. This can be ac­
complished by promoting or inhibiting specific genes in the
nucleus or by controlling the rate of protein synthesis. Hor­
mones can also activate or deactivate an enzyme's activity by
altering its three-dimensional structure.
Endocrine glands represent one of the two types of glands
found in the body. The second type, exocrine glands, secrete
substances into ducts , which transport the secretions into the
T
lumina (internal cavities) of organs, into body cavities, or to
the surface of the skin. Sweat glands and sebaceous glands,
which you studied in Exercise 6, are examples of exocrine
glands.
The endocrine system operates in conjunction with the nerv­
ous system to maintain homeostasis and to ensure that bodily
functions are carried out efficient'ly. This functional relationship
is sometimes expressed as a neuroendocrine effect in which
nerve impulses can affect the release of hormones and, in turn,
hormones can regulate the !1ow of nerve impulses.
As you learned earlier, the nervous system performs its
functions by conducting electric impulses along nerve fibers
and releasing neurotransmitters across synapses to nearby tar­
get cells. Neural responses occur quickly but do not last for
long periods of time. Endocrine responses are not as rapid as
neural responses but can persist for several hours to several
days , and are equally effective in regulating physio l ogical
activities.
WHAT"S IN A WORD The word hormone is derived from the
Greek word hormao, which means "to provoke" or "set in mo­
tion. " Hormones released by endocrine glands influence their
target organs by "setting in motion" or promoting a specific
function.
Gross Anatomy
of the Endocrine System
An overview of the endocrine system is illustrated in Figure IS.1.
Some structures have an exclUSively endocrine function. They in­
clude the pituitary gland, pineal gland, thyroid gland,
parathyroid glands, and adrenal glands. In addition, the en­
docrine system includes several other organs that produce hor­
mones but also perform nonendocrine functions. They include
the hypothalamus, thymus gland, pancreas, testes, ovaries,
heart, stomach, small intestine, and kidneys.
ACTIVITY 18.1 Examining
Gross Anatomy
of the Endocrine System
Endocrine Organs Located in the Head
1. Obtain a model of a midsagittal section of a human brain.
2. Identify the pineal gland, located along the roof of the
third ventricle (Figure 18.2). Melatonin, the hormone se­
creted by this gland , is believed to control daily sleep­
ing-waking patterns and other cyclical phYSiological
processes (circadian rhythms).
327
EXER C ISE E IGHTEEN
Figure 18.1 Overview of the endocrine
system. The human endocrine system co ntains
a diverse array of orga ns scattered thro ughout
th e body.
HYPOTHALAMUS
PINEAL GLAND
Production of ADH,
oxytocin, and
regulatory hormones
Melatonin
PARATHYROID GLANDS
(on posterior surface of
thyroid gland)
PITUITARY GLAND
Anterior lobe:
ACTH , TSH , GH , PRL, FSH, LH , and MSH Posterior lobe:
Release of oxytocin
andADH
Parathyroid hormone (PTH)
THYROID GLAND
Thyroxine (T 4)
Triiodothyronine (T 3)
Calcitonin (CT)
ADIPOSE TISSUE
Leptin
Resistin
PANCREATIC ISLETS
Insulin, glucagon
ADRENAL GLANDS
Each adrenal gland is
subdivided into:
GONADS
Adrenal medulla:
Epinephrine (E) Norepinephrine (NE) Adrenal cortex:
Cortisol , corticosterone, aldosterone, androgens Testes (male): Androgens (especially testosterone), inhibin
Ovaries (female): Estrogens, progestins, inhibin
Figure 18.2 Endocrine structures
in the brain. Cranial structures that
produce hormones include the hypo­
thalam us, pi tu itary gland, and pineal
gland.
Cerebral hemisphere
~------;-,,=f-~-------':k-----.lb,.----::l;.-----~,--,.L-
Corpus callosum
Thalamus
-r:::::t-t-tk~~s:=---I=-='::--=~---=~~--=:=..J,- Pineal gland
Hypothalamus
_~...,!~~...,L:q~=d::=--_ _
Infundibulum
Pituitary
­ - - ­- - - - - ­+
Medulla oblongata
----
--
Midbrain
--=:~~:i_-- Cerebellum
TI-I
(Figure lS.3). The anterior lobe produces several hor­
mones (Table lS.l ) that regulate the activities of other
structures, including other endocrine glands, through­
out th e body. The pos terior lobe, as described earlier,
stores and secretes the two hypothalamic hormones,
ADH and oxytocin (Table lS.2 ) .
CLINICAL CORRELATION
Melatonin production and secretion increase during periods of darkness and decrease during periods of light. This fluctuati on in activity is believed to be the underlying cause of seasonal af­ fective disorder. This condition brings about unusual changes in mood, sleeping pattern, and appetite in some people living at high latitudes where periods of darkness are quite long during winter months. 3. Locate the hypothalamus, just inferior to the thalamus
(Figure IS.2). It produces a number of releasing hormones
that increase, and inhibiting hormones that reduce , the pro­
duction and secretion of hormones in the anterior pituitary
(Table IS. 1). The hypothalamus also releases antidiuretic
hormone (ADH), which acts on the kidneys to reduce water
loss, and oxytocin, which stimulates smooth muscle con­
tractions, most notably labor contractions in the uterus and
contractions in reproductive glands and ducts of both sexes
during intercourse. ADH and oxytocin are transported along
axons to the posterior lobe of the pituitary gland, where they
are stored and eventually released.
4. Identify the pituitary gland, or hypophysis, which is di­
rectly connected to the hypothalamus by a stalk of tissue
called the infundibulum (Figure lS.2). It lies within the
sella turcica of the sphenoid bone (F igure lS.3a). Obtain
a human skull and identify the sella turcica along the floor
of the cranial cavity.
The pituitary gland is divid ed into two distinct re­
gions: the anterior lobe and the posterior lobe
E 1\ OOCRI N E SYS TEM
WHAT' S IN A WORD The term pituitary is derived from the
Latin word pitllita, which means phlegm or thick mucous secre­
tion. The Renaissance anatomist , Andreas Vesalius, gave the pi­
tuitary its name because he mistakenly thought that it produced
a mucous secretion related to the throat. When the true function
of the pituitary was determined , some 200 years later, it was
given a ne,v name, the hypophysis, which is the Greek word for
"undergrowth ". This is probably a be tter name for th e gland
since it describes its position suspended from the inferior surface
of the hypothalamus.
Endocrine Organs Located in the Neck
1. Obtain a torso or head and neck model.
2. Locate the thyroid gland, which is composed of two elon­
gated lobes located on each side of the trachea, just infe­
rior to the thyroid cartilage. The isthmus of the thyroid
travels across the anterior surface of the trachea and con­
nects the two lobes (Figure lS.4a). The thyroid gland pro­
duces the hormones thyroxine (T 4 ) and triiodothyronine
(T 3), which regulate cell metabolism , general growth and
development, and the normal development and matura­
tion of the nervous system. It also produces calcitonin
that reduces the levels of calcium ions in body fluids.
Table 18.1 Hormones Produced by the Anterior Pituitary
Hormone
Target Effect
Hypothalamic regulatory hormone
Thyroid stimulating
hormone (TSH)
Thyroid gland
Promotes secretion of thyroid hormones
Thyrotropin-releasing hormone (TRH)
Adrenocorticotropic
hormone (ACTH)
Adrenal cortex
Promotes secretion of glucocorticoids
Corticotropin-releasing hormone (CRH)
Follicle cells in ovaries
Gonadotropin-releasing hormone (GnRH)
Interstitial cells in testes
Promotes estrogen secretion and follicle
development
Promotes sperm maturation
Promotes ovulation, corpus luteum
formation, and progesterone secretion
Promotes testosterone secretion
Prolaction
Mammary glands
Stimulates milk production
Prolactin-releasing factor (PRF); prolactin-inhibiting
hormone (PIH)
Growth hormone
All cells
Growth, protein synthesis, lipid
mobilization, and catabolism
Growth hormone-releasing hormone (GH-RH);
Growth hormone-inhibiting hormone (GH-IH)
Melanocytes
Increased melanin synthesis
Melanocyte stimulating hormone-inhibiting
hormone (MSH-IH)
Pars distalis
Gonadotropins
a. Follicle stimulating
hormone (FSH)
b. luteinizing hormone
(lH)
Sustentacular cells in testes
Follicle cells in ovaries
Pars intermedia
Melanocyte stimulating
hormone (MSH)
EXERCISE EIGHTEEN
Anterior
lobe
Median
eminence
Infundibulum
Diaphragma
sellae
Mamillary
body
-i;;;~~s~~~
Anterior
lobe
Posterior
lobe
-----sPhenoid
(sella turcica)
Secretes other
pituitary hormones
(a) Secretes
MSH
Releases ADH
and oxytocin
(b)
Figure 18.3 Anatomy of the pituitary gland. a) Diagram of the anterior and posterior lobes of the pituitary
gland. Note that it is connected to the hypothalamus by the infundibulum. b) light micrograph of th e anterior
and posterior lobes of the pituitary (lM x 100).
Table 18.2 Honnones Secreted by the Posterior Pituitary
Hormone
Target
Effect
Hypothalamic regulatory hormone
Antidiuretic
hormone (ADH)
Kidneys
Reabsorption of water; elevation of blood volume
and pressure
None; transported along axons from hypothalamus
to posterior pituitary
Oxytocin (OT)
Uterus, mammary glands
labor contractions; milk ejection
Same as above
Ductus deferens,
prostate gland
Contractions of ductus deferens and prostate
gland
3. Typically there are two pairs of parathyroid glands em­
bedded on the posterior surfaces of the thyrOid gland
lobes (Figure IS.Sa). These glands may not be illus­
trated on the models in your lab. If not, locate them in
an illustration. They produce parathyroid hormone
(PTH), which opposes the action of calcitonin by in­
creasing the concentration of calcium ions in body
fluids.
Endocrine Organs Located in the Thoracic Cavity
1. Remove the anterior body wall from a torso model so that
the contents of the thoracic cavity are exposed (Figure IS.6).
2. Note that the heart is located in the central region of the tho­
racic cavity, known as the mediastinum. If blood volume is
elevated above normal , cardiac muscle cells in the heart wall
secrete natriuretic peptides. These hormones act on the
kidneys to promote the loss of sodium ions and water.
WHAT' S IN A WORD Natriuretic peptides promote natriuresis,
or the excretion of sodium in the urine. The term nau"iuresis is de­
rived from two Greek words: natrium, meaning "sodium" (the
chemical s)'lnbol for sodium is Na) , and Ollron, meaning "urine".
3. The thymus gland is located just posterior to the sternum.
If it is present on the models in your lab, observe how it
covers the superior portion of the heart and extends supe­
riorly into the base of the neck. The thymus produces a
group of hormones called thymosins that promote the
maturation of T-lymphocytes , a type of white blood cell
THE EN DOCR t N E SYSTEM
Thyroid cartilage
of larynx
ll~fS~~~~ulr---- Hyoid bone
Superior
thyroid vein
~~....WH"'---~· Superior
thyroid artery
Right lobe
of thyroid
gland
Internal
jugular vein
Cricoid cartilage
of larynx
Middle
thyroid vein
Left lobe of
thyroid gland
Common carotid
artery -------,~-4~
Thyrocervical-trunk
Trachea
Isthmus of
thyroid gland
--------"""""..
Inferior
thyroid artery
---j~~~~~~~J~
Inferior
thyroid
veins
clavicle
OUtiineOf~
sternum
Follicle
cells
(a)
Cuboidal
epithelium
of follicle
C cell
Follicle
cavities
C cell
Tlhyroglobulin stored in
colloid of follicle
(b)
Thyroid
follicle
(e)
Figure 18.4 Anatomy of the thyroid gland. a) Diagram of the thyroid gland, illustrating its relationship with
neighboring structures; b) diagram; and c) light micrograph, illustrating the microscopic structure of the thyroid gland
(lM x 200).
that coordinates the body's immune response. The thymus
is relatively large in newborns and young children. After
puberty, the size of the thymus is gradually reduced, and
the glandular tissue is replaced by fat and fibrous connec­
tive tissue . Exercise 23 presents the structure and function
of the thymus in greater detail.
Endocrine Organs Located in the Abdominopelvic Cavity
1. On a torso model, remove the digestive organs from the
abdominopelvic cavity to expose the structures along the
posterior wall. The stomach and small intestine produce
several hormones that are important for regulating diges­
tive activities, which will be discussed later when you
study the digestive system.
2. Locate the elongated pancreas that stretches across the pos­
terior bod wall between the duodenum (first part of the
small intestine) and the spleen. The head of the pancreas is
that portion which is nestled within the C-shaped curvature
of the duodenum on the right side (Figure 18.7a). Moving
to the left , the body of the pancreas is the main portion of
the organ. It. gives rise to an elongated tail that extends to
the left toward the spleen. Although the pancreas is largely
composed of exocrine glands that produce digestive en­
zymes , scattered throughout are regions of endocrine tissue
EXERCISE EIGHT EEN
Figure 18.5 Anatomy of the
parathyroid glands. a) Diagram
showing the position of th e four
parathyroid glands along the posterior
wall of the thyroid gland; b) light mi­
crograph of a region similar to the
area enclosed by the rectangular box
in (a). Portions of both the para thy­
roid and thyroid glands are shown
(lM x 100); c) light micrograph of a
region of the parathyroid gland simi­
lar to the area enclosed by the rec­
tangular box in (b). Principa l (chief)
cells and oxyphil cells are present
(lM
(a) Thyroid gland, posterior view
x 400).
(e) Principal
(chief) cells
Oxyphil
cells
matostatin regulates the secretion of both insulin and
glucagon. Pancreatic polypeptide inhibits muscular contrac­
tions in the wall of the gallbladder and controls the pancre­
atic production of digestive enzymes.
Trachea ------"'-..,.;,,::~_\I+.:....
--T-----~-----THYMUS
Right - -----;,,<---- - - IJ-.
lobe
.......,.------+----Left
lobe
Figure 18:6 Endocrine structures in the thoracic cavity. The heart pro­
duces natriu re tic peptldes and the thymus produces thymosins.
known as the pancreatic islets (islets of Langerhans;
Figures 18.7b and c) . The two main hormones produced by
the islet cells are glucagon and insulin , which regulate
blood glucose levels. Glucagon elevates blood glucose levels
by promoting the breakdown of glycogen, the synthesis of
glucose from fats and proteins, and the release of glucose
into the blood. Insulin lowers blood glucose levels by pro­
moting glucose uptake into most cells. Additionally, in
skeletal muscles and in the liver, insulin increases glucose
storage by stimulating the production of glycogen. Two
other hormones, somatostatin and pancreatic polypep­
tide (PP), are also produced by the pancreatic islets. 50­
CLINICAL CORRELATION
Normally, any glucose that is filtered out of the blood by the kid­
neys is reabsorbed back into the blood. Thus, glucose is usually
not present in urine. However, an individual with diabetes mel­
litus has glucose levels that are well above normal, a condition
called hyperglycemia, and the kidneys cannot reabsorb the ex­
cess. As a result, glucose will be present in the urine. There are
two main types of diabetes mellitus. Type I diabetes accounts for
5% to 10% of all cases in the United States. It usually develops
in children or young adults and destroys the pancreatic cells that
produce insulin. It can be treated by daily administration of in­
sulin, supplemented by a carefully monitored dietary plan. Type II
diabetes is far more common, making up 90% to 95% of all
cases. In addition, a strong correlation exists between type II dia­
betes and obesity. People with type II dia betes produce normal
amounts of insulin but cannot utilize the hormone effectively.
This could be due to the production of defective insulin mole­
cules or the lack of insulin receptors on target cells. Careful di­
etary control, weight reduction, and other lifestyle changes (e.g.,
regular exercise) are the best treatments for this form of the dis­
ease. Diabetes is a long-term, progressive disorder that has po­
tentially serious systemic effects. It can contribute to blindness
heart disease, stroke, kidney failure, circulatory problems resul~ing
in limb amputations, and nerve damage. It is also one of the
leading causes of death in the United States.
THE EN DOCRINE SYSTEM
Figure 18.7 Anatomy of the
pancreas. a) Diagram showing the
Ducts --+=;---~
Connective
tissue septum
-+--=0-­
Exocrine cells ~--i-'\-=,,;"""":-="':'--:~~
in pancreatic
acini
Endocrine cells
in pancreatic islet
Pancreatic
duct
Lobules
1\
Body o f
pancreas
.".---!=-­
relationship of the pancreas to the
duodenum ; b) diagram; and c) light
micrograph illustrating the light mi­
croscopic strudure of the pancreas.
The pancreatic islets are the en­
docrine portions of the pancreas
(lM X 100).
~Tailof
r
o
I
p~ncreas
(h)
Pancreatic islet -~~~~~4'~
(endocrine)
Pancreatic acini
(exocrine)
Duct-~~~~~~II~~~~~ (e)
3. The adrenal (suprarenal) glands are pyramid-shaped struc­
tures resting on the superior margins of the kidneys
(Figure IS.Sa). Fibrous connective tissue attaches the ad­
rena'! glands to the connective tissue capsule that sur­
rounds the kidneys. If possible, remove the anterior
portion of one adrenal gland and observe its internal
structure. Identify the inner adrenal medulla and the
outer adrenal cortex (F igure IS .Sb). The adrenal cortex
produces three categories of hormones.
• Mineralcorticoids, such as aldosterone, act on the kid­
neys to conserve water and sodium ions , and to secrete
potassium ions.
• Glucocorticoids, such as cortisol, act on many cells to
conserve glucose by utilizing fatty acids and proteins as
an energy source (glucose-sparing effect), and they
function as anti-inflammatory agents by inhibiting ce\1ls
in the immune system.
• Androgens (gonadocorticoids) are male sex hormones
that are produced in small quantities and converted to
estrogens (female sex hormones) when they enter the
blood. The function of adrenal androgens is not clear.
The adrenal medulla releases two hormones ,
epinephrine and norepinephrine, in response to sympa­
thetic nervous system activation, contributing to the fight­
or-flight response. The effects include increased hekrt rate,
blood pressure, and respiratory rate , and decreased diges­
tive activity.
CLINICAL CORRELATION
Glucocorticoids are steroid hormones. Because of their inflam­
matory effects, these chemicals, or derivatives of them, are used in prescription and over-the-counter "steroid creams" to treat skin rashes such as poison ivy. In addition, many college and professional athletes are given cortisone injections to reduce the inflammation that occurs at an injured joint. These injections are effective in reducing injury-related pain, but they do little in repairing damaged tissue. Thus, an athlete who re­
ceives a series of cortisone injections might misinterpret a re­
duction in pain for complete recovery, return to normal activity prematurely, and possibly cause a more serious injury. 4. Locate the kidneys (Figure l S.Sa) . Although they are
mostly involved with waste removal, they also have en­
docrine functions. Under the influence of parathyroid hor­
mone , the kidneys release a hormone called calcitriol,
which acts on the sma ll intestine to increase absorption of
calcium and phosphate. The kidne ys also release
erythropoietin (EPO) , which stimulates red blood cell
production in bone marrow.
5. The gonads include the ovaries in females and the testes in
males . On a female model, locate the ovaries along the lat­
eral wall of the pelvic cavity (Figure IS.9a). They produce
the female sex hormones called estrogens. On a male
model , locate the testes. They originate in the abdominal
cavity near the kidneys, but descend into the scrotum ,
EXERC ISE EIGHT EEN
Figure 18.8 Anatomy of the ad­
renal gland. a) Diagram showing the
relationship of the adrenal gland to
the kidney and neighboring blood ves­
sels; b) diagram showing the two re­
gions of the adrenal gland-the inner
ad renal medulla and the outer adre­
na l cortex; c) light micrograph illustrat­
ing the microscopic strudure of the
adrenal gland. Notice that the ad renal
cortex is divided into three distind
zones, whi ch are illustrated in the
three insets at higher magnification
- -'-:::---- Cortex
--"..---\----- Left adrenal
(suprarenal) gland
~....,,--~-Medulla
Suprarenal
arteries
Left suprarenal
vei n
(lM x 400) .
Superior --..... ___•
mesenteric
artery
_ _JJIIII.. "~-----"""r Left
(b)
renal artery
....~-:::--"""""!~+- Left renal vein
~
Abdominal
aorta
--~- Left kidney
Inferior
vena cava
(a)
Ad renal cortex
Zona
reticu laris
Adrenal medulla
(e)
Cells of
zona
reticularis
Zona
fasciculata
Cells of
zona
fasciculata
Zona
glomerulosa
Cells of
zona
glomerulos
-
- - -
-
-
THE E N DOCRINE SYSTEM
Figure 18.9 Anatomy of the
ovary. a) Midsagittal section of the
Ovary
female pelvic cavity, showing the re­
lationship of the ovary to neighboring
structures; b) diagram illustrating the
structure of the ovary in cross sec­
tion; c) light micrograph illustrating
the microscopic structure of the
ovary. Notice the developing follicles
in the cortex of the ovary. The follicu­
lar cells that surround the egg pro­
duce female sex hormones
Urinary
bladder
(lM x 40).
Vagina
(a)
i~~I~!im~~I~11
Egg cells """
(oocytes)
Cortex
Corpus
luteum
Medulla
(c)
(b)
which is outside the body cavity (Figure 18.10a) . The
testes produce male sex hormones (androgens), of which
testosterone is the most important. The sex hormones
control the development and maturation of sex cells (egg
and sperm) , maintain accessory sex organs, and support
secondary sex characteristics.
Endocrine glands are surrounded by an exten­
sive network of blood capillaries. Suggest a rea­
son why this anatomical relationship is significant.
EXERCISE EIGHTEEN
Figure 18.10 Anatomy of the
testis. a) Midsagittal section of the
male pelvic cavity. In the adult male,
the testes are located in the scrotal
sac, outside the body cavity. b) low­
power light micrograph showing
cross sections of seminiferous
tubules in a testis (lM x 100) .
c) High-power light micrograph and
corresponding diagram of a single
seminiferous tubule, similar to the
tubule enclosed by the box In (b).
The interstitial cells produce testos­
terone (lM x 200).
Pubic - ---7.-:---;-;..:;:,;;:.­
symphysis
fj{-7;ti-- -­
-"-'-=.-;---7--Semi nal vesicle
+T.r---'-=;.s~=-:-:--'----;'=--:-'------ Prostate
gland
Spongy urethra --:i-.~-f. ':
Ductus deferens
Ejaculatory duct
Bulbourethral gland
Anus
EpididymiS
External urethral
orifice
Scrotum
(a)
c:'!!~-'-t-;?
Developing
sperm cells
(b)
Microscopic Anatomy
of the Endocrine System
The cells of endocrine glands possess the following common
features.
• The cells are usually cuboidal or polyhedral (many sides)
with a large, spherical nuclei.
• With the exception of the hypothalamus , all endocrine cel'ls
are derived from epithelial tissue.
• The cells are typically arranged in clusters, small islands
(islets) , or cords.
• Endocrine cells form glands that lack a system of ducts .
Hormones are secreted directly into the surrounding
tissue spaces and eventually gain entry into the blood
circulation.
• Endocrine cells have an extensive blood supply, and all of them
have at least one surface that is directly adjacent to a capillary.
As you study the microscopic anatomy of the various en­
docrine organs, be aware of these similarities as well as the unique
features that characterize each structure.
ACTIVITY 18.2
Examining Microscopic Anatomy
of Endocrine Organs
Pituitary Gland
1. Obtain a slide of the pituitary gland (hypophysis).
2. View the slide with the scanning or low-power objective
lens. Depending on your slide preparation, adjacent brain
and bone tissue may also be present.
TH E EN DOCRI N E SYSTEM
• Vl1hat region of the brain would you expect to see on
your slide 7 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
• What skull bone would you expect to be present?
3. Move the slide so that the pituitary gland is centered.
Identify the darker staining anterior lobe (adenohypoph­
ysis) and the lighter staining posterior lobe (neurohy­
pophysis or pars nervosa). If possible , identify the
infundibulum that connects the pituitary gland to the hy­
pothalamus (Figure IS.3a).
4. Observe the anterior lobe of the pituitary with high power.
The anterior lobe is a true endocrine gland because it con­
tains several types of endocrine cells that produce and se­
crete hormones (Table IS. 1). Identify the following
regions of the anterior lobe (Figure lS.3b).
• The pars distalis consists of glandular epithelial cells
arranged in cords or clusters. Notice that these ceUs
have a cuboidal shape and possess well-defined nuclei.
As you scan the slide , you will see that the cells vary
conSiderably in their staining properties. The different
colors that you observe in these cells depend on the
staining technique used to prepare your slide. Neverthe­
less, this variability reflects the fact that the pars distalis
contains several cell types, each responsible for produc­
ing a specific hormone (Table IS. I).
• The pars intermedia is a narrow band of tissue between
the pars distalis and the posterior lobe. In the fetus ,
young children, and pregnant women, the cells in this
region produce melanocyte-stimulating hormone
(Table IS. I). In most adults, this region of the anterior
pituitary is normally inactive.
• The pars tuberalis is an extension of the anterior lobe
that wraps around the infundibulum , then spreads along
the inferior margin of the hypothalamus. If the in­
fundibulum and hypothalamus are present on your slide, •
look for the pars tuberalis hugging their outside borders.
CLINICAL CORRElATION
Growth hormone (GH), secreted by the pars distalis, pro­
motes protein synthesis in virtually all cells. It is particularly im­
portant for the growth and development of muscle, cartilage,
and bone. Inadequate production (hyposecretion) of GH before
puberty leads to a condition called pituitary dwarfism. Peo­
ple with this disorder have normal body proportions, but abnor­
mally short bones due to reduced activity at the epiphyseal
plates. Pituitary dwarfism can be successfully treated before pu­
berty by administering synthetic GH.
Two other abnormalities are caused by excessive secretion
(hypersecretion) of GH. Gigantism is the overproduction of GH
before bone fusion. Individuals with this disorder have normal
body proportions but excessively long limbs and can reach
heights up to 8.5 ft. Acromegaly is caused by excessive GH
production after bone fusion . In this condition, bones cannot
lengthen, but instead become thicker and denser, particularly in
the face, hands, and feet. Both gigantism and acromegaly are
usually caused by a tumor in the pars distalis and can be
treated by its surgical removal.
5. The posterior lobe of the pituitary gland , or pars
nervosa, is actually an extension of the brain. It is not a
true endocrine gland because it does not produce its own
hormones. Vi ew the posterior lobe with high power
(Figure 18.3b) and notice that most of this structure con­
tains axons, which originate from neuron cell bodies in
the hypothalamus. Antidiuretic hormone and oxytocin,
produced in the hypothalamus , travel along these axons
and are released from axon terminals in the posterior lobe .
Thyroid Gland
1. Obtain a slide of the thyroid gland.
2. View the slide "vith the scanning or low-power objective
lens. Notice that the thyroid has a distinctive structure ,
consisting of numerous thyroid follicles of various sizes
(Figures 18.4b and c) .
3. Use the high-power objective lens to examine the thyroid
follicles more closely. Notice that each follicle consists of a
central follicle cavity surrounded by a single layer of
cuboidal follicle cells (Figures 18.4b and c).
4. Inside the follicle cavities, identify a lightly staining mate­
rial known as colloid. Follicle cells produce a globular
protein known as thyroglobulin and secrete it into the
colloid for storage. Thyroglobulin is later used to synthe­
size the thyroid hormones thyroxin (T 4) and triiodothyro­
nine (T )).
5. In the regions of connective tissue between the follicles,
identify the parafollicular cells (C cells), which produce
calcitonin. They usually appear in small clusters and are
characterized by their pale or lightly stained cytoplasm
and large nuclei (Figures lS.4b and c).
Parathyroid Gland
1. Obtain a slide of the parathyroid gland.
2. View the slide with the scanning or low-power objective
lens. Since the parathyroid glands are embedded in the
posterior wall of the thyroid gland , your slide may display
tissue from both structures (Figure lS.5b).
3. Center an area of parathyroid tissue and switch to high
power. The darkly stained cells that fill the field are
principal (chieO cells, which produce parathyroid
hormone. If you look carefully, you should notice that
these cells are arranged in a curvilinear fashion
(Figure lS.5c).
4. A second cell type, the oxyphil cells are found only in
human parathyroid glands. If you are viewing a human
parathyroid , attempt to locate these cells (Figure lS.5c).
They are larger, stain lighter, and are far fewer than the
principal cells. The function of the oxyphil cells is un­
known.
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EXERCIS E EIGHTEEN
Pancreas
1. Obtain a slide of the pancreas .
.., View the slide with the low-power objective lens and iden­
tify the pancreatic acini. Each acinus contains a cluster of
cuboidal cells (pancreatic acinar cells), arranged around
a central lumen (Figures lS.7b and c). The acinar cells are
the exocrine portion of the pancreas, and produce diges­
tive enzymes. Observe that the darkly stained acinar cells
comprise the vast majority of the pancreas.
3. Scattered among the pancreatic acini, identify the islands
of lighter staining cells. These are the pancreatic islets or
islets of Langerhans (Figures lS.7b and c), which are the
endocrine portion of the pancreas. The pancreatic islets
contain four ce ll types. On your slides, you will probably
be unable to identify the different cell types.
However, each type is responsible for producing a spe­
cific hormone, as follows:
•
•
•
•
Alpha cells produce glucagon.
Beta cells produce insulin.
Delta cells produce somatostatin.
F cells produce pancreatic polypeptide (PP).
Adrenal Gland
1. Obtain a slide of the adrenal gland.
2. View the slide with the scanning or low-power objective
lens and identify the outer adrenal cortex and the inner
adrenal medulla (Figure lS.Sb).
3. Center the adrenal cortex and switch to high power. Iden­
tify the following three cellular layers (Figure lS.Sc ).
• The zona gomerulosa is the outermost layer and is cov­
ered by a connective tissue capsule (the capsule may not
be present on your slide). It comprises 10% to 15% of
adrenal cortical volume. Notice how the cells in this
layer are arranged in small circular clusters. These cells
produce mineralcorticoids.
• The zona fasciculata is the middle layer and makes up
75% to 7S% of the volume of the adrenal cortex. As you
move the slide into this region , notice that the cells are
larger and more lightly stained than those in the previ­
ous layer. The lighter staining is due to the large supply
of lipids in the cytoplasm. Observe that the cells in this
layer are organized into stacks or columns, rather than
clusters. These cells manufacture glucocorticoids.
• The zona reticularis is the smallest (7% to 10% of the
total cortical volume) and innermost layer of the adrenal
cortex . As you move into this layer, notice that the cells
are more deeply stained and form an irregular, intersect­
ing network. The cells in this layer produce a small
amount of androgens.
WHAT'S IN A WORD The three zones of the adrenal cortex are
named according to the organization of the cells in each layer.
The term glomerulosa is derived from the Latin word glomus,
which means "a baH". The cells in the zona glomerulosa are
arranged in a spherical fashion . The term fasciclIlata has its ori­
gins from the Latin word fasciculus, which refers to "a bundle or
corel". The name describes the columns of cells in the zona fas­
ciculata. The word reticularis comes from the Latin term
reticulatus, which means "netlike", ancl is suggestive of cell ar­
rangment in the zona reticularis.
4. Switch back to low power, locate the adrenal medulla , and
center this region in the field of view.
5. With high power, observe the cells in the adrenal medulla
(Figure lS.Sc). This region consists of loosely arranged
polyhedral cells with large round nuclei. An extensive net­
work of capillaries travels between the cells and a large
medullary vein (or veins), which drains the entire adre­
nal gland. may be identified. The endocrine cells in the
adrenal medulla resemble cells found in sympathetiC gan­
glia, and their secretory activity is promoted by pregan­
glionic sympathetic nerve fibers . The majority of the cells
produce epinephrine, and a smaller number synthesize
norepinephrine.
Ovary
1. Obtain a slide of the ovaries from a human or another mammalian species. The ovaries are the primary sex or­
gans in the female. 2. View the slide with the scanning or low-power objective
lens. Identify the two regions of the ovary (Figures lS.9b
and c).
• The outer cortex contains the ovarian follicles at vari­
ous stages of development. Each follicle contains a de­
veloping egg cell, known as an oO(:yte.
• The inner medulla is a region of loose connective tis­
sue with numerous blood vessels, nerves, and lym­
phatics.
3. Scan the cortex and identify follicles at various stages of
development (Figure lS.9c). In each developing follicle,
identify the egg cell and the multiple layers of follicular
cells that surround it. The follicular cells produce the fe­
male sex hormones known as estrogens.
Testis
1. Obtain a slide of the testes from a human or another mam­
malian species. The testes are the primary sex organs in
the male.
2. View the slide with the scanning or low-power objective
lens. Scan along the edge of the section and observe the fi­
brous connective tissue covering called the tunica albug­
inea. Connective tissue partitions derived from the tunica
albuginea divide the testes into lobules.
3. Within each lobule of the testes are three or four
seminiferous tubules. As you scan the slide under low
power, the tubules can be observed throughout the field of
view. Each tubule is surrounded by connective tissue and
contains several layers of cells surrounding a central lu­
THE ENDOCRI N E SYSTEM
men (Figure IS. lOb) . Because of the plane of section, the
lumen may not be evident in some tubule profiles.
4. Observe a seminiferous tubule under high power (Figure
lS.10c). Most of the cells in the walls of the tubules are
sperm cells in various stages of development. Collectively,
these cells are called spermatogenic cells. As the sperm
cells form , they move from the base to the lumen of the
seminiferous tubules. Observe these various cells on the
slide. Note that as you view the cells in the tubule walls,
from base to lumen, their appearance changes progressively.
5. Scan the slide under high power and observe areas of
connective tissue between seminiferous tubules. These in­
terstitial areas contain the interstitial (Leydig) cells
(Figure IS.10c), which produce the male sex hormone ,
testosterone.
Based on your microscopic observations in the
previous activity, identify structural similarities
and differences in the various endocrine organs. Focus your at­
tention on the arrangement and structure of the glandular cells
in each structure.
Similarities:
Differences:
Exercise 18 Review Sheet
The Endocrine System
Name _______________________________________
LabSectio" ________----_______________________
Date ________________________________________
1. Discuss the differences between an endocrine gland and an exocrine gland.
2. Target cells respond to inputs from both the nervous system and the endocrine system.
In general , how does a neural response differ from an endocrine response?
3. What is meant by a neuroendocrine effect?
4. Explain how the hypothalamus influences the function of the anterior lobe of the pitu­
itary gland.
5. Describe the functional relationship between the hypothalamus and the posterior lobe
of the pituitary.
Questions 6-12: Match the hormone in column A with its function in column B.
A
B
6. Insulin
a. Regulates cell metabolism
7. Oxytocin
b. Lowers blood glucose levels
8. Aldosterone
c. Promotes sperm development
9. Epinephrine
d. Elevates b'lood calcium levels
10. Testosterone
e. Promotes uterine contractions during labor
II. Thyroxine
f. Promotes egg development
12. Parathyroid hormone
g. Acts on the kidneys to conserve water and sodium
h. Lowers blood calcium levels
i. Promotes the fight-or-flight response
j. Elevates blood glucose levels