Medical Histology
Instructor: Dr. Sherry Stewart
Course Creator: Dr. Sherry Stewart
Designer: Catherine Gilabert
30. ENDOCRINE SYSTEM - PITUITARY GLAND
OBJECTIVES
1. List and compare the 3 types of systems that
control the body.
2. Differentiate between endocrine and exocrine
glands.
3. List and describe different types of hormones.
4. Describe the embryologic origin of the 2 major
parts of the hypophysis (neurohypophysis and
adenohypophysis).
5. List and describe the parts of the
adenohypophysis.
6. Describe the structure of the neurohypophysis
and its relationship to the hypothalamus. What
2 hormones are secreted by the
neurohypophysis?
7. Describe the staining characteristics of the
cells in the pars distalis. Name the hormone(s)
produced by each type of cell.
8. Describe the hypophyseal portal system.
LECTURE OUTLINE
I. Introduction
II. Hypophysis
a. Adenohypophysis
b. Neurohypophysis
III. Pineal Gland
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I. Introduction
There are 3 types of systems that control the body:
1. Nervous system - nerve-to-nerve and nerve to target cells; involves finite control by
directly linking the signal with the target cells. Response is rapid and specific,
but short-lasting.
2. Endocrine system (not shown in the above diagram) - chemical signals (hormones)
are released and carried locally or throughout the body by the blood stream.
Response is slower, specific for a specific receptor on a target cell, and
longer-lasting than the nervous system.
3. Neuroendocrine system - neurons release hormones (neurotransmitters in this
case) directly into blood where they are carried to the target cell.
What are hormones?
Hormones are complex chemical substances synthesized and secreted by endocrine
cells. They enter and travel in the vascular system, have an action on the target cell,
and then are destroyed.
1. Paracrine –
produced and
have action
within the
same tissue.
2. Autocrine –
produced and
have action on
the cell of origin.
3. Juxtacrine – never secreted by the cell of origin – remains in the cell membrane (cellto-cell hormone communication)
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There are several different classifications of hormones:
1. Steroid Hormones –
derivatives of cholesterol;
examples are androgens,
testosterone, estrogen,
progesterone,
glucocorticoids; examples of
organs that secrete them
are the testes, ovaries and
adrenal cortex. They
interact with receptors
INSIDE the cell (cytoplasm
and nucleus).
2. Peptide and Protein
(hydrophilic) Hormones –
secreted by cells in the
hypothalamus, hypophysis,
parathyroid gland,
pancreas and cells
scattered in the GI tract
and lungs. They interact
with membrane
receptors.
Examples:
a. peptides (oxytocin)
b.polypeptides
(insulin, growth
hormone)
c. glycoproteins
(protein hormones such as FSH)
3.Biogenic amines – neurotransmitters, serotonin, histamine, melatonin
4. Prostanoids – long chain fatty acids (arachadonic acid, prostaglandins
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The endocrine system consists of distinct glands or tissues that secrete hormones that
specifically stimulate or otherwise cause a change in metabolic activity in target tissues
or organs. The endocrine system performs the role of communication and regulation.
Primary Endocrine Organs:
1. Pituitary Gland (hypophysis cerebri)
2. Pineal Gland (epiphysis cerebri)
3. Thyroid Gland
4. Parathyroid Gland
5. Adrenal Gland
Secondary Endocrine Organs:
1. Kidney
2. Testes
3. Ovaries
4. Pancreas
5. Stomach
6. Intestines
7. Thymus
8. Heart
9. Placenta
Characteristics of Endocrine
Glands:
• Epithelial in origin
• Ductless
• Highly vascular
• Produce hormones
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II. Hypophysis (pituitary gland)
The hypophysis consists of 2
parts:
1. Adenohypophysis
(pink) (anterior lobe) –
“glandular” pituitary;
derived from infolding
epithelium lining the
mouth cavity.
2. Neurohypophysis (light
blue) (posterior lobe)–
“neuro” pituitary;
neurosecretory tissue
derived from
outpocketing of the brain.
The pituitary gland is located at the base
of the brain and is “connected” to it by the
infundibular stalk. As the epithelium from
the mouth invaginates toward the brain
(this is called Rathke’s pouch), a remnant
of its lumen may remain in varying
amounts. This “opening” is called the
hypophyseal cleft (or “cystic cavities” in
the human).
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Since nervous tissue is quite different from glandular tissue,
the 2 sections of the hypophysis can be distinguished even
at very low powers. The hypophyseal cleft is often a good
histological landmark.
A. Adenohypophysis
The cells of the adenohypophysis are glandularlooking and the tissue is highly vascular
(typical of most endocrine tissues).
The adenohypophysis is divided into 3 parts:
1. Pars distalis (“distal part”) – largest of
the 3 parts; produces trophic hormones, i.e.
hormones that stimulate the production of other
hormones. The cells in the pars distalis are
under the regulation of hormones in the
hypothalamus (at the base of the brain).
Stimulating (releasing) and inhibiting
hormones from the hypothalamus regulate
the release of hormones in the pars distalis;
thus it is a “2-hormone” system.
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This “2-hormone” system requires that 2
capillary beds be linked by vessels (portal
veins). Here, it is a venous linkage; thus
this is an example of a portal system. It is
called the hypophyseal portal system.
Using the hypophyseal cleft for orientation, the
pars distalis is the large glandular area labeled
“d.” The pars intermedia is labeled "i", and the
neurohypophysis is labeled "n". The "c"
indicates the hypophyseal cleft.
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Histologically, three cells types can be distinguished in the pars distalis.
1. acidophils (black arrows) – stain red;
produce growth hormone (GH) and
prolactin (PR).
2. basophils (green arrows) – stain blue;
produce adrenocorticotropic hormone
(ACTH), thyroid stimulating hormone
(TSH), follicle stimulating hormone
(FSH) and luteinizing hormone (LH).
3. chromophobes (blue arrows) – clear;
may be precursors to acidophils and
basophils.
Use this H&E slide to review the cell types
and name the hormones they secrete
(black arrows = acidophils; green arrow =
basophil).
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Let’s use an example to go through how this
system works. Your text gives an example for
TSH, I’ll use LH (luteinizing hormone).
Essentially, LH is important in
maturation of ova (eggs), ovulation
and development of the corpus
luteum. In males, it stimulates the
secretion of testosterone by
testicular interstitial cells. For
ovulation to occur, the
hypothalamus (1) must produce
LH-releasing factor (LRF). It is
picked up in the capillary bed (2) in
the infundibular stalk, carried by
the portal veins through the pars
tuberalis, and is released into the
pars distalis (3) to stimulate the
release of LH by the basophils.
The LH, in turn, is emptied into the
capillary bed in the pars distalis
and carried to its target organ, the
ovary. This whole system is highly
regulated and is sensitive to
negative feedback.
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2. Pars intermedia
The pars intermedia (“intermediate part”) is
easy to locate using the hypophyseal cleft as a
landmark. It lies across the cleft from the pars
distalis and adjacent to the neurohypophysis.
The cellularity of the glandular pars
intermedia distinguishes it from the
adjacent, relatively acellular,
neurohypophysis.
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Note the pars intermedia and the
neurohypophysis. The predominant cell type of the
pars intermedia is a nonspecific basophil. These
cells most likely produce melanocyte stimulating
hormone (MSH) and possibly ACTH.
Even without the hypophyseal
cleft, it is relatively easy to
distinguish the pars distalis
(D), pars intermedia (I) and
neurohypophysis (N).
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3. Pars tuberalis (“tubular part”)
The pars tuberalis wraps around the
infundibulum (part of the neurohypophysis) to
create the infundibular stalk, much the same as
wrapping your hand around a pipe.
The pars tuberalis contains the portal system, and thus appears very vascular. The
slides below show low power (left) and high power (right) views of the pars tuberalis.
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The stimulating and releasing hormones
produced in the hypothalamus are released
in the median eminence (MI) (part of the
neurohypophysis in the infundibulum that
connects the pituitary with the
hypothalamus). Capillary loops (arrows)
from the pars tuberalis (T) pick up the
stimulating and releasing hormones and
transport them to the pars distalis in the
portal system.
The function of the pars tuberalis has not
been clearly established. There are
weakly basophilic cells present, which
undoubtedly produce hormones.
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B. Neurohypophysis
Recall that the
neurohypophysis is an
outpocketing of the
brain/hypothalamus.
The main component of the neurohypophysis is the
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Pars nervosa - Adjacent to the adenohypophysis, the pars nervosa is the site
where hormones from the hypothalamus are released to capillary beds. There
are no secretory cells in the pars nervosa.
Even at low power, the pars nervosa can be
distinguished from the pars distalis. PN = pars
nervosa, PD = pars distalis, C = hypophyseal cleft
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Observe that the pars nervosa (PN) is very
vascular but contains few cells. Cells are
fibroblasts, mast cells, endothelial cells or
pituicytes. Pituicytes probably act as glial
cells in the pars nervosa. PD = pars distalis,
C = hypophyseal cleft; PI = pars intermedia
There are 2 different cell types in the
hypothalamus producing 2 different
hormones, which are released in the pars
nervosa. These are really neuroendocrine
cells as they are neurons emptying
hormones into the blood. These cells are
located in 2 different sites in the
hypothalamus: the paraventricular
nucleus and the supraoptic nucleus.
The 2 hormones released by these cells are:
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1. oxytocin – suckling
stimulus releases
oxytocin; stimulates
contraction of
contractile cells in the
mammary glands for
“milk letdown” (ejection
of milk from the glands);
stimulates uterine
smooth muscle
contraction at
parturition (birth).
2. antidiuretic hormone
(ADH) – targets the
kidney; concentrates
urine by stimulating the
removal of water from
urine in the collecting
ducts; decreases rate of
perspiration; increases
blood pressure by
preserving blood volume and by stimulating contraction of smooth muscle in the
walls of arterioles.
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Overall view of major endocrine system components
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III. Pineal Gland
•
•
•
•
Dorsal outgrowth of
diencephalon.
Pinealocytes secrete melatonin.
Affects circadian rhythms,
sexual behavior and
reproduction.
“Brain sand”: copora arenacea=
deposits of calcium salts and
debris (normal).
That’s enough for a brief overview.
BONEHEAD QUIZ !!
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