ENDOCRINE SYSTEM
PAPER
ARRANGED
IN PARTIAL FULFILLMENT
Histology
that
guided by Dra. Amy Tenzer, M.S and Dra. Nursasi
Handayani, M.Si
Arranged by:
6th Group
Class A - Offering A
1.
Rizqa Rhadiyah (100341400689)
2.
Rulyana Salma
Rosadha (100341400687)
3.
Sari Rahma Putri (100341400696)
4.
Septi Darlia
Putri (100341400693)
5.
Silfia Anggraeni (100341400697)
6.
Tutut Indria
Permana (100341400716)
The Learning University
UNIVERSITY OF MALANG
FACULTY OF MATHEMATICS AND NATURAL SCIENCES
DEPARTMENT OF BIOLOGY
December 2011
PREFACE
Gratitude
Praise presence writer
prayed God Almighty, because of the blessing
of his paper, entitled “ENDOCRINE SYSTEM” this
in turn can be resolved.
The paper is organized
to fulfill the
task of Histology course that guided by Dra. Amy Tenzer, M.S dan
Dra. Nursasih Handayani, M.Si.
Furthermore,
we say great thank to:
1. Dra.
Amy Tenzer, M.S dan Dra. Nursasih Handayani, M.Si guided
course as lecturers
and assistant lecturers
are always accompanied and guided us in
preparing this paper.
2. Students
Biology offering A years of 2010.
3. All those who have helped in
the process of preparing this paper.
A part
from all the shortcomings
of writing this paper, both in composition and
writing the wrong,
the author pleaded for forgiveness and hope that the writing of this paper is useful especially for
writers and the
readers.
We as authors are aware that the writing of this paper is still far from perfection, and therefore, We always expect criticism and constructive suggestions from you for improvements in the preparation of the next paper.
We as authors are aware that the writing of this paper is still far from perfection, and therefore, We always expect criticism and constructive suggestions from you for improvements in the preparation of the next paper.
Finally,
may Allah Swt. always gives His guidance to anyone who loves science
and education. Amin Ya Robbal Alamin.
Malang, December 2011
The writers
CONTENTS
Cover .................................................................................................................. i
Preface ................................................................................................................ ii
Contents .............................................................................................................. iii
Chapter I
Introduction
1.1 Background ...................................................................................... 1
1.2 Problem Formulas ............................................................................. 2
1.3 Objectives ......................................................................................... 2
Chapter II
Discussion
2.1 Hypophysis or Pituitary Gland ......................................................... 4
2.2 Hypothalamus–the Controller of the Pituitary ................................. 10
2.3 Adrenal Gland .................................................................................. 11
2.4 Thyroid Gland .................................................................................. 14
2.5 Parathyroid Gland ............................................................................ 21
2.6 Pineal Gland (Epiphysis Cerebri) ...................................................... 24
Chapter III
Conclusion
3.1 Conclusions ....................................................................................... 27
3.2 Suggestions ....................................................................................... 27
References
CHAPTER I
INTRODUCTION
1.1 Background
The two great integrating forces of the body are the
nervous and endocrine system. Both systems respond to variations in the
external and internal environments of the body. They react by sending messages
to various parts of the body that cause the organism to adjust to the
environmental changes. Thus, both of these systems are homeostatic mechanisms
because they help maintain a constant, steady state in the various physiologic
system of the body. (Telford, 1995)
While the
nervous system can send signal at great speed, e.g. 130 m/sec, the endocrine
system respond much more slowly because its messengers, the hormones, must
travel via the blood stream, usually to some distant organ or tissue. Although
some hormonal effects occur in seconds, others may take days before they begin,
and then they may continue for days, months, or even a lifetime. (Telford,
1995)
The secretion of an endocrine gland is termed a
hormone. The function of hormones is to control the activity levels of the
co-called target tissues or organs. To provide this vital function, the
hormones may alter the chemical reactions within the cell; alter the
permeability of the plasma membrane to specific substance; and elaborate some
other specifics cellular mechanism. They may have permissive, synergistic or
inhibitory relationships. A permissive relationship is where the presence of
one hormone is essential for another hormone to evoke its special respond. A
synergistic relationship is complementary or cooperative. (Telford, 1995)
Based on the fact above, we know that endocrine system
have a big role in the human body. In this paper, we will discuss about the
histological structure of endocrine system that consists of endocrine glands
and endocrine organs.
1.2 Problem Formulas
1.
How is the
histological structure of hypophysis or pituitary gland?
2.
How is the
histological structure of hypothalamus-the controller of the pituitary?
3.
How is the
histological structure of adrenal gland?
4.
How is the
histological structure of thyroid gland?
5.
How is the
histological structure of parathyroid gland?
6.
How is the
histological structure of pineal gland (epiphysis cerebri)?
1.3 Objectives
1.
To know the
histological structure of hypophysis or pituitary gland.
2.
To know the
histological structure of hypothalamus-the controller of the pituitary.
3.
To know the
histological structure of adrenal gland.
4.
To know the
histological structure of thyroid gland.
5.
To know the
histological structure of parathyroid gland.
6.
To know the
histological structure of pineal gland (epiphysis cerebri).
CHAPTER II
DISCUSSION
Endocrine system consists of endocrine glands that
have no functional duct system. Endocrine system and nervous system is has
relationship. Both systems respond to variations in the external and internal
environments of the body. They react by sending messages to various parts of
the body that cause the organism to adjust to the environmental changes.
(Telford, 1995)
The secretion of an endocrine gland is termed a
hormone. The function of hormones is to control the activity levels of the
co-called target tissues or organs. The endocrine gland in vertebrate is
consisting of hypophysis or pituitary gland, adrenal gland, thyroid gland,
parathyroid gland and pineal gland. (Tenzer, 1993)
The parenchymal cells of endocrine glands have the
following features in common:
1.
They have a rich
blood supply. At least one surface of each endocrine cell abuts onto a
fenestrated capillary. Such a relationship facilitates the entry of the
hormones into the surrounding interstitial spaces.
2.
They have no
functional duct system. Therefore, endocrine are also called ductless gland.
3.
Cells usually
are arranged in blocks, islets, plates, or cords.
4.
Except for the
neurosecretory cells of the hypothalamus, all endocrine cells are epithelial in
origin, supported by delicate connective tissue stroma.
5.
Cells are
usually polyhedral in shape with a prominent spherical nucleus.
6.
Organelles are
very numerous, especially the mitochondria, Golgi complexes, secretory
vesicles, and endoplasmic reticulum. (Telford, 1995)
7.
Based on the
secretory cell that arranged the endocrine glands there are two type; sinusoid
type with secretory cell that consist of squamous or cuboidal shape (almost all
of endocrine gland have this type); and follicle type with secretory cell that
arranged in vesicles and called follicles (in thyroid gland). (Tenzer, 1993)
2.1 Hypophysis
or Pituitary Gland
The pituitary gland, or hypophysis (Gr. hypo, under, + physis,
growth), weighs about 0.5 g in adults and has dimensions of about 10 x 13 x 6
mm. It lies below the brain in a cavity of the sphenoid bone–the sella turcica.
The hypophysis is often called the “master or chief gland” of the endocrine
system. The pituitary is actually a servant of the brain, since nearly all of
its hormonal secretions are controlled by signals emanating from the
hypothalamus. The hypophysis plays a major role in integrating the endocrine
and nervous systems in control of many of our physiological processes.
(Telford, 1995)
Type
of hormones
All of the pituitary hormones are polypeptides divided
into two general categories:
1.
Some hormones
act directly and modulate the function of other endocrine glands. These are so
called trophic hormone that influence the growth, development, and nutrition of
specific target glands. These pituitary-dependent endocrine glands include
thyroid, which responds to the thyroid stimulating hormone (TSH); the gonads,
which react to the follicle-stimulating hormone (FSH) and to the luteinizing
hormone (LH) equivalent to interstitial cell stimulating (ICSH) of the testis;
and the adrenal cortex, which is stimulated by the adrenocorticotrophic hormone
(ACTH).
2.
The other
classification contain those hormone that act directly on nonendocrine tissues
or organs. They are somatotropin (STH) or growth hormone (GH), which acts
mostly in skeletal structure; prolactin or lactogenic hormone, which triggers
milk production; antidiuretic hormone (ADH) or vasopressin, which concentrates
the urine in the kidney, allowing resorption of water; oxytocin, which aids
contraction of the uterine muscles during parturition; and the
melanocytes-stimulating hormone (MSH), which controls melanin dispersal in the
skin of certain lower animals. (Telford, 1995)
Development
The hypophysis has a dual origin. The glandular part, adenohypophysis, is derived from oral ectoderm as an upward outpocketing of the roof of the oral
cavity, called Rathke’s pouch. Simultaneusly, the nervous part, the
neurohypophysis, arises from neural ectoderm as a tubular downgrowth (the
infundibulum) of the floor of the third ventricle of the primitive brain.
(Telford, 1995)
|
Figure of pituitary gland. (Source: Mescher, 2010)
Adenohypophysis (Anterior Pituitary)
The component of the adenohypophysis
develop from Rathke’s pouch. The greatly thickened anterior wall of the pouch
becomes the pars distalis (anterior lobe). The narrow fusion region between the
two anlagen develops into the pars intermedia (intermedia lobe), while the
superior lateral extensions of the pouch warp around the upper stalk of the
infundibulum like a collar. These extensions become the pars tuberalis, which
is actually an extension of the pars distalis. (Telford, 1995)
1.
Pars Distalis
The pars
distalis accounts for 75% of the adenohypophysis and is covered by a thin
fibrous capsule. The main components are cords of epithelial cells interspersed
with fenestrated capillaries. Fibroblasts are present and produce reticular
fibers supporting the cords of hormone-secreting cells. Common stains suggest
two broad groups of cells in the pars distalis based on staining affinity:
chromophils and chromophobes.
a.
Chromophils are secretory cells in which
hormone is stored in cytoplasmic granules. They are also called basophils and
acidophils according to their affinity for basic and acidic dyes, respectively.
Subtypes of basophilic and acidophilic cells are identified by TEM or more
easily by immunohistochemistry and are named for their specific hormones or
target cells. Acidophils include the somatotropic and mammotropic cells, while
the basophilic cells are the gonadotropic, corticotropic, and thyrotropic
cells. Somatotropic cells typically constitute about half the cells of the pars
distalis in humans, with thyrotropic cells the least abundant.
b.
Chromophobes stain weakly, with few or no
secretory granules, and also represent a heterogeneous group, including stem
and undifferentiated progenitor cells as well as any degranulated cells
present. Each granular cell makes one kind of hormone, except gonadotropic
cells which produce two proteins and corticotropic cells, in which the major
gene product, proopiomelanocortin (POMC), is cleaved posttranslationally into
the smaller polypeptide hormones adrenocortical trophic hormone (ACTH) and -lipotropin (-LPH). Hormones
produced by the pars distalis have widespread functional activities; they
regulate almost all other endocrine glands, milk secretion, melanocyte
activity, and the metabolism of muscle, bone, and adipose tissue.
(Mescher, 2010)
|
Figure components of pars distalis. (Source: Mescher,
2010)
Secretory
cells of the pars distalis
Cell Type
|
Stain Affinity
|
% of Total Cells
|
Hormone Produced
|
Main Physiologic Activity
|
Somatotropic cell
|
Acidophilic
|
50
|
Somatotropin
(growth hormone, GH)
|
Acts on growth of long
bones via insulin-like growth factors synthesized in liver
|
Mammotropic cell
(or actotropic cell)
|
Acidophilic
|
15–20
|
Prolactin (PRL)
|
Promotes milk
secretion
|
Gonadotropic cell
|
Basophilic
|
10
|
Follicle-stimulating
hormone (FSH) luteinizing hormone (LH) in the same cell type
|
FSH promotes
ovarian follicle and development and estrogen secretion in women and
spermatogenesis in men. LH promotes ovarian follicle maturation and
progesterone secretion in women and interstitial cell androgen secretion in
men.
|
Thyrotropic cell
|
Basophilic
|
5
|
Thyrotropin (TSH)
|
Stimulates thyroid
hormone synthesis, storage, and liberation
|
Corticotropic cell
|
Basophilic
|
15–20
|
Adrenal corticotropin (ACTH)
Lipotrophins
|
Stimulates secretion of adrenal cortex hormones
Lipid metabolism regulation
|
2.
Pars Tuberalis
The pars
tuberalis is a funnel-shaped region surrounding the infundibulum of the neurohypophysis.
Most of the cells of the pars tuberalis are basophilic gonadotropic cells that
secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
(Mescher, 2010)
3.
Pars Intermedia
The pars
intermedia is a thin zone of basophilic cells between the pars distalis and the
pars nervosa of the neurohypophysis, which is often invaded by these basophils.
The pars intermedia develops from the dorsal wall of the hypophyseal pouch and
usually contains colloid-filled cysts that represent remnants of that
structure's lumen. During fetal life parenchymal cells of this region, like the
corticotropic cells of the pars distalis, express POMC. However in these cells
POMC is cleaved by a different protease to produce smaller peptide hormones,
including two forms of melanocyte-stimulating hormone (MSH), -LPH, and -endorphin. MSH
increases melanocyte activity and cells of the pars intermedia are often
referred to as melanotropic cells, but the overall physiological significance
of this region remains uncertain, especially in adults.
(Mescher. 2010)
|
Figure
of pars intermedia. (Source: Mescher, 2010)
Neurohypophysis
(Posterior Pituitary)
The neurohypophysis develops from the
neural anlage.
1.
The pars nervosa arises from the large, bulbous distal end,
2.
The infundibulum (pituitary stalk) from the medial portion, and
3.
The median eminence from the expanded proximal portion.
The latter is a part of hypothalamus,
located in the floor of the third ventricel of the brain. The porterios lobe is
formed by the fusion of pars nervosa with pars intermedia. (Telford, 1995)
The pars nervosa, unlike the adenohypophysis, does not contain secretory cells. It is
composed of neural tissue, containing some 100,000 unmyelinated axons of
secretory neurons situated in the supraoptic and paraventricular nuclei of the
hypothalamus. Also present are highly branched glial cells called pituicytes
that resemble astrocytes and are the most abundant cell type in the posterior
pituitary. (Mescher, 2010)
|
Figure
of pars nervosa: neurosecretory bodies and pituicytes. (Source: Mescher, 2010)
2.2 Hypothalamus–the
controller of the pituitary
The hypothalamus occupies only a small area at the
base of the brain, posterior to the optic chiasma, and includes the
infundibulum and the mammillary bodies. It has an important role in the control
of pituitary secretions. Attached to the brain by the infundibulum, the
pituitary has extensive neural and vascular connections with the hypothalamus
that are used for communication between the two organs. Although the pituitary
synthesizes a considerable number of hormones, their release or inhibition is
triggered by signals from the hypothalamus. (Telford, 1995)
The pars nervosa functions as a temporary reservoir
for the neurosecretions of the hypothalamus, oxytocin and vasopressin (ADH).
These hormones are produced by neurosecretory cells (neurons) whose cell bodies
are located in the supraoptic and paraventricular nuclei of the hypothalamus.
(Telford, 1995)
In contrast, hormones from the pars distalis of the
pituitary are controlled by a series of releasing and inhibitory factor
(hormones) synthesized by neurons in unidentified loci (nuclei) within the
hypothalamus. Unlike the pars nervosa,
the pars distalis does not have nervous connection with the hypothalamus.
Instead the releasing and inhibiting factors pass to the adenohypophysis by way
of a portal venous system. (Telford, 1995)
In the pars intermedia, the principal hormone produced
is MSH-melanocyte-stimulating hormone. All releasing factors of the
hypothalamus appear to be peptides of comparatively low molecular weights. (Telford,
1995)
Hypothalamic hormones regulating the anterior
pituitary
Hormone
|
Chemical
Form
|
Functions
|
Thyrotropin-releasing
hormone (TRH)
|
3-amino acid
peptide
|
Stimulates
synthesis and release of both thyrotropin (TSH) and prolactin
|
Gonadotropin-releasing
(GnRH)
|
10-amino acid
peptide
|
Stimulates the
release of both FSH and LH hormone
|
Somatostatin
|
14-amino acid
|
Inhibits release of
both somatotropin (GH) and thyrotropin (TSH)
|
Growth
hormone–releasing hormone(GHRH)
|
40- or 44-amino
acid polypeptides (2 forms)
|
Stimulates
synthesis and release of somatotropin (GH)
|
Dopamine
(prolactin-inhibiting hormone)
|
Modified amino acid
|
Inhibits release of
prolactin
|
Corticotropin
releasing hormone (CRH)
|
41-amino acid
polypeptide
|
Stimulates
synthesis of POMC and release of both -lipotropin (-LPH) and
corticotropin (ACTH)
|
Thus, these neurosecretory cells forge a link between
the two great integrating mechanisms of the body: the nervous and endocrine
systems. (Telford, 1995)
2.3 Adrenal
Gland
The adrenal
glands are a pair of organs located near the poles of the kidneys, immersed in
the fat tissue. These glands are 2 pieces, yellowish and outside (extra)
peritoneal. Right part and form a pyramid-shaped cap (attached) on the upper
pole right kidney. While the left is shaped like a crescent, attached to the
center pole of the kidney from the top to the left renal hilum. In human
adrenal glands 4-6 cm long, 1-2 cm wide, and 4-6 mm thick. Together adrenal
glands weighed approximately 8 g, but the weight and size vary with age and
physiological state of individuals. The gland is surrounded by dense connective
tissue collagen tissue containing fat. In addition each gland is wrapped by a
capsule of connective tissue that is thick and form a septum / septa into the
gland.
Adrenal
cortical steroids synthesize molecules that are sorted into three groups namely
glucocorticoid hormones, and androgens mineralkortikoid with zones / layers of
different producers.
As we know, the adrenal cortex has
three layers / zones namely:
·
Zona glomerulosa to produce hormones
mineralkortikoid.
·
Zone fasikulata to produce
glucocorticoid hormones (along with the zone reticularis).
·
Zona reticularis untuk
memproduksi homon androgen. (Tenzer,
1993)
Figure of adrenal gland
structure. (Source: Mescher, 2010)
Structure and Function of Adrenal
Glands
Located
in the upper pole of both kidneys. Known also as suprarenalis gland because it
is situated above the kidneys. And sometimes also referred to as a child gland
attached to the kidney because the kidney. The adrenal gland consists of two
layers of the cortex and the medulla. Both support the survival and welfare,
but only the cortex that are essential for life.
Cortex
adrenal
Adrenal cortex is essential for survival. Loss of
adrenocortical hormones can cause death. Adrenal cortex synthesizes by three
classes of steroid hormones kinds, there are: mineralocorticoids,
glucocorticoids, and gonadokortikoid.
1. Mineralokortikoid
Mineralocorticoid (aldosterone in
humans in particular are) formed in the adrenal cortex glomerulosa zone. These
hormones regulate electrolyte balance by increasing the retention of sodium and
potassium excretion. Physiological activity is further assist in maintaining
normal blood pressure and cardiac output. Mineralocorticoid deficiency
(Addison's disease) leads to hypotension, hyperkalemia, decreased cardiac
output, and in acute cases, shock. Mineralocorticoid excess resulting in
hypertension and hypokalemia. (Tenzer, 1993)
2. Glukokortikoid
Glucocorticoids fasikulata formed in
the zone. Cortisol is the primary glucocorticoid in humans. Cortisol has
effects on the body, among others in: glucose metabolisms (glukosaneogenesis)
which increases blood glucose levels; metabolism of protein, fluid and
electrolyte balance; inflammation and immunity; and to stressors. Sex hormones
of the adrenal cortex to secrete small amounts of sex steroids from the
reticular zone. Generally secreting adrenal androgens and estrogens slightly
compared to the large amounts of sex hormones secreted by the gonads. But the
production of sex hormones by the adrenal glands can cause clinical symptoms.
For example, the release of excess androgens cause virilisme. while the excess
release of estrogen (eg, due to adrenal carcinoma causing gynecomastia and
sodium and water retention. Structure and Function of Gonads gland formed in
the first weeks of gestation and was evident in the fifth week. (Tenzer, 1993)
3. Gonadokortikoid
Gonadokortikoid (sex hormone)
include androgen and estrogen. Both hormones are equivalent to the hormone -
sex hormone produced by the gonads. Gonadokortikoid produced in small amounts
so that under normal circumstances physiological effects can be ignored. In
mammals: generated by the reticular zone. (Tenzer, 1993)
The main
hormone in the synthesis by the tissue aminogenik is epinephrine and
norepinephrine. epinephrine in humans is 80% of the total secretion of these
glands and is more potent than norepinephrine. These hormones usually secreted
in large quantities in response to intense emotions, as well as defense against
stress. The second effect of this hormone-like effects of the sympathetic
nerves, among others, the phase konstrikal blood vessels, hypertension,
increased heart rate, and metabolic effects such as increased blood glucose
levels. (Tenzer, 1993)
2.4 Thyroid
Gland
The word thyroid derived from
thyreos (Greek) that mean shield like. It called thyroid gland because the
structure its two pear-shape lobes resemble to warrior shields. It also called
as thyroid because it located near thyroidea cartilage. (Telford, 1995)
The thyroid gland, located in the
cervical region anterior to the larynx, consists of two lobes united by an
isthmus. Thyroid gland encloses by capsule that containing connective tissue.
Thyroid function is to synthesize the thyroid hormones thyroxine
(tetra-iodothyronine or T4) and tri-iodothyronine (T3), which are important for
growth, for cell differentiation, and for the control of the basal metabolic
rate and oxygen consumption in cells throughout the body. Thyroid hormones affect
protein, lipid, and carbohydrate metabolism. (Tenzer, 1998)
Figure of Thyroid Gland
(Source: Mescher, 2010)
Thyroid Development
Thyroid originates in early embryonic life from the
foregut endoderm near the base of the future tongue. Thyroid development begins
in the fourth week as an epithelial diverticulum growing down from the endodermal
lining of the foregut. The thyroid diverticulum continues to grow in an
inferior direction and its connection to the developing pharynx, the thyroglossal
duct, later regresses. By fetal stages, the thyroid has attained its normal
adult position. The decent of the gland is arrested and thyroid develops within
the base of the tongue. Also, cysts and bit of thyroid tissue may be strewn
along the path of the duct as accessory thyroid. The most constant of this
structure is a superior extension isthmus called pyramidal lobe. (Mescher,
2010)
Figure of Thyroid
Diverticulum Form Figure of Thyroid
gland migrate inferiorly
(Sources : Mescher, 2010)
Figure of Adult
Thyroid Gland (Source: Mescher, 2010)
Histological
Features
The
parenchyma of the thyroid is composed of millions of rounded epithelial
structures called thyroid follicles.
Each follicle consists of a simple epithelium and a central lumen filled with a
gelatinous substance called colloid.
The thyroid is the only endocrine gland in which a large quantity of secretory
product is stored. Moreover, the accumulation is outside the cells, in the
colloid of the follicles, which is also unusual. In humans there is sufficient
hormone in follicles to supply the body for up to three months with no
additional synthesis. Thyroid colloid contains the large glycoprotein thyroglobulin, the precursor for the
active thyroid hormones.
The
thyroid gland is covered by a fibrous capsule from which septa extend into the
parenchyma, dividing it into lobules and carrying blood vessels, nerves, and
lymphatics. Follicles are densely packed together, separated from one another
only by sparse reticular connective tissue. This stroma is very well
vascularized with an extensive network of fenestrated capillaries closely
surrounding the follicles, which facilitates molecular transfer between the
follicular cells and blood.
Figure:
A low-power micrograph of thyroid gland shows the thin capsule (C), from which
septa (S) with the larger blood vessels, lymphatics, and nerves enter the gland
(Source: Mescher, 2010)
In each
follicle wall contain 2 kinds of cells
Follicular
cells range in
shape from squamous to low columnar and the follicles are quite variable in
diameter. The size and cellular features of thyroid follicles vary with their
functional activity. Active glands have more follicles of low columnar
epithelium. Glands with mostly squamous follicular cells are considered
hypoactive. (Mescher, 2010)
The follicular epithelial
cells have typical junctional complexes apically and rest on a basal lamina.
The cells exhibit organelles indicating active protein
synthesis and secretion, as well as phagocytosis and digestion. The nucleus is
generally round and in the center of the cell. Basally the cells are rich in
rough ER and apically, facing the follicular lumen, are Golgi complexes,
secretory granules filled with colloidal material, large phagosomes and
abundant lysosomes. The cell membrane of the apical pole has a moderate number
of microvilli. Mitochondria and other cisternae of rough ER are dispersed
throughout the cytoplasm. (Telford, 1995)
It is also found inside the
basal lamina of the follicular epithelium or as isolated clusters between
follicles. Parafollicular cells, derived from neural crest cells migrating into
the area of the embryonic foregut, are usually somewhat larger than follicular
cells and stain less intensely. They have a smaller amount of rough ER, large
Golgi complexes, and numerous small (100–180 nm in diameter) granules
containing polypeptide hormone. These cells synthesize and secrete calcitonin, one function of which is
to suppress bone resorption by osteoclasts. Calcitonin secretion is triggered
by elevated blood Ca2+ levels.
Figure
of Follicle in Thyroid Gland (Source: Wilkins, 2006)
N :
nuclei, F: follicle, CT: Connective tissue, FC: Follicular cell, PF:
Parafollicular cell, Cl: Coloid
Summary of
Follicular and Parafollicular Cell
Character
|
Follicular
|
Parafollicular
|
Hormone
|
Thyroxin and triodothyronine
|
Calcitonin
|
Target organ or tissue
|
All tissue and organs
|
Bone
|
Natural of hormones
|
Amino acid
|
Polypeptide
|
Function
|
Stimulates general oxidative
metabolism, growth and development
|
Inhibit excessive blood calcium
|
Table
summary of follicular and parafollicular cell
(Source:
Telford, 1955)
Regulation of
Thyroid Gland
The
major regulator of the anatomic and functional state of thyroid follicles is
thyroid-stimulating hormone (TSH; thyrotropin), which is secreted by the anterior
pituitary. TSH increases the height of the follicular
epithelium and stimulates all stages of thyroid hormone production and release.
Thyroid hormones inhibit the release of TSH, maintaining an adequate quantity
of T4 and T3 in the organism. TSH receptors are abundant
on the basal cell membrane of follicular cells. Secretion of TSH is also
increased by exposure to cold and decreased by heat and stressful stimuli.
(Mescher, 2010)
Figure of Thyroid Gland Regulation (Source: Saul, 2011)
Production,
storage, and release of thyroid hormones involve an unusual,
multistage process with both an exocrine phase and an endocrine phase in the follicular
cells. Both phases are promoted by TSH and can be occurring in the same cell.
The major activities of this process include the following:
This large glycoprotein has
no hormonal activity itself but contains 140 tyrosyl residues used to make
thyroid hormone. As part of the exocrine phase of cellular activity,
thyroglobulin is released from large vesicles at the apical surface of the cell
into the lumen of the follicle.
·
The
uptake of
circulating iodide is accomplished in follicular cells by the Na/I
symporter or cotransporter in the basolateral cell membrane, which allows for
30-fold concentration of dietary iodide in the normal thyroid relative to the
plasma. Low levels of circulating iodide trigger synthesis of the Na/I
symporter, increasing the uptake of iodide and compensating for the lower serum
concentration.
·
At
the apical surface of the cells, iodide is transferred to the follicular lumen
by the anion transport protein pendrin and there it undergoes
oxidationto active iodine by
membrane-bound thyroid peroxidase at the cell surface.
·
In
the lumen tyrosine
residues of thyroglobulin are iodinated covalently with either one or
two iodine atoms. Following this, two iodinated tyrosines, still part of
thyroglobulin, are conjugated by oxidative coupling reactions to form T3
or T4.
·
Immediately
or after a delay, in the endocrine phase of the process the follicular cells
take up the iodinated thyroglobulin in colloid by endocytosis or pinocytosis.
T4 and T3, freed in this manner from thyroglobulin, then cross the
cell membrane and basement membrane, and are taken up into the capillaries.
Nearly
all of both thyroid hormones are carried in blood tightly
bound to plasma proteins. T4 is the more abundant compound, constituting 90% of
the circulating thyroid hormone. Both molecules bind the same intracellular
receptors of target cells, but T3 is two- to tenfold more active than T4. The
half-life of T3 is 1.5 days in comparison with a week for T4. Both thyroid
hormones increase the number of mitochondria and their cristae and stimulate
mitochondrial protein synthesis. (Mescher, 2010)
2.5 Parathyroid
Gland
The parathyroid glands are four small oval
masses. They are located on the back of the thyroid gland, one at each end of
the upper and lower poles, usually embedded in the larger gland's capsule. The
parathyroid glands are derived from the pharyngeal pouches the superior glands
from the fourth pouch and the inferior glands from the third pouch. Their
embryonic migration to the developing thyroid gland is sometimes misdirected so
that the number and locations of the glands are somewhat variable. Up to 10% of
individuals may have parathyroid tissue attached to the thymus, which
originates from the same pharyngeal pouches.
Figure of parathyroid gland.
(Source: Mescher, 2010)
Each parathyroid gland is contained
within a capsule which sends septa into the gland, where they merge with
reticular fibers that support elongated cordlike clusters of secretory cells.
With increasing age many secretory cells are replaced with adipocytes, which
may constitute more than 50% of the gland in older people.
Two types of cells are present in
parathyroid glands: chief (or principal) cells and oxyphil cells. The chief cells are
small, cuboidal cell with relatively large, dark nuclei, slightly acidophilic
cytoplasm. The cells are arranged in clumps or cords that border on a
capillary. Ultrastructurally the cytoplasm is seen to be filled with
irregularly shaped granules 200–400 nm in diameter. These are secretory granules
containing the polypeptide parathyroid
hormone (PTH), a major
regulator of blood calcium levels. These are much larger than the principal
cells and are characterized by acidophilic cytoplasm filled with abnormally
shaped mitochondria. Some oxyphil cells show low levels of PTH synthesis,
suggesting these cells are transitional derivatives from chief cells. The
actively secreting chief cells reveal a prominent enlarged golgi complex, rER,
small oval mitochondria, and an abundance of small dense, membrane bound
secretory granules that located at or near cell membrane. In the active chief
cells are several small golgi bodies and considerable accumulation of glycogen
and lipofuscin granules. The parathyroid hormone is synthesized by the chief
cells.
CC (Chief
Cells), OC (Oxyphils Cells), BV
(Blood Vessels),CT (Connective
Tissue), N (Nuclei). (Source: Wilkins, 2006)
The figure of Chief cells. (Source: Telford, 1995)
The
figure of Oxyphil cells. (Source: Telford, 1995)
The
less numerous cell type is the oxyphil or acidophil cells. They do not occur in
all animals and in humans perhaps do not appear until puberty but increase in
number with age. Oxyphils are larger than chief cell. They have a smaller, more
condensed nucleus, and the abundant cytoplasm has a large number of fine
eosinophilic granules. These granules to be mitochondria with prominent
cristae. There is no known function for oxyphil, but they secrete parathormone
in individuals who have oxyphils tumors.
2.6 Pineal
Gland (Epiphysis Cerebri)
The pineal gland, known as the pineal body
or epiphysis cerebri, regulates the daily rhythms of bodily activities. It is a
very small, pine cone-shaped organ in the brain measuring approximately 5–8 mm
in length and 3–5 mm at its greatest width and weighing about 150 mg. The
pineal develops with the brain from neuroectoderm in the roof of the
diencephalon and is found in the posterior of the third ventricle, attached to
the brain by a short stalk.
The pineal gland is covered by
connective tissue of the pia mater, from which emerge septa
containing small blood vessels and subdividing various sized groups of
secretory cells as lobules. The prominent and abundant secretory cells are the pinealocytes, which have slightly
basophilic cytoplasm and large, irregular euchromatic nuclei and nucleoli. Ultrastructurally
pinealocytes are seen to have secretory vesicles, many mitochondria, and long
cytoplasmic processes extending to the vascularized septa, where they end in
dilatations near capillaries, indicating an endocrine function. These cells
produce melatonin, a low
molecular-weight tryptophan derivative. Unmyelinated sympathetic nerve fibers
enter the pineal gland and end among pinealocytes, with some forming synapses.
|
|
Interstinal
Cell
Interstinal cell has an elongated
nucleus that is deeper staining than those of pinealocytes. These cells are
found chiefly dispersed among the clumps of pinealocytes and capillary beds.
They may have long protoplasmic processes with many fine flaments. The
processes surround the pinealocytes as well as sympathetic nerve fiber and
other processes. Microtubule are scarce. Mitochondria are smaller and less
numerous than those parenchymal cells. The interstitial cells has been
identified as a type of astrocyte.
Function
In lower animals it activities has
function :
1. Regulating the reproductive system,
particularly in animals that are seasonal breeders
2. Moderating the timing of various
circadian and diurnal rhythms in many birds and some reptile
The melatonin synthesized in
darkness promotes blanching of the skin in amphibians and reptiles by the
aggregation of melanosomes in
melanocytes
CHAPTER III
CONCLUSION
3.1 Conclusion
Endocrine system
consists of endocrine glands that have no functional duct system. The endocrine
gland in vertebrate is consisting of hypophysis or pituitary gland, adrenal
gland, thyroid gland, parathyroid gland and pineal gland.
1.
The histological
structure of hypophysis or pituitary gland is consist of pars distalis, pars,
intermedia, and pars nervosa.
2.
The histological
structure of hypothalamus-the controller of the pituitary is consists of
neurosecretory bodies and pituicytes.
3.
The histological
structure of adrenal gland consists of two concentric layers: a yellowish
peripheral layer, the adrenal cortex, and a reddish-brown central layer, the
adrenal medulla.
4.
The histological
structure of thyroid gland, the parenchyma of the thyroid is composed of
millions of rounded epithelial structures called thyroid follicles. Each
follicle consists of a simple epithelium and a central lumen filled with a
gelatinous substance called colloid.
5.
The histological
structure of parathyroid gland is contained within a capsule which sends septa
into the gland, where they merge with reticular fibers that support elongated
cordlike clusters of secretory cells.
6.
The histological
structure of pineal gland (epiphysis cerebri), is covered by connective tissue
of the pia mater, from which emerge septa containing small blood vessels and
subdividing various sized groups of secretory cells as lobules.
3.2 Suggestion
It should
be better if adding the more reference and can understand all of the material
in this paper.
REFERENCES
Anonym. 2000. Kelenjar Tiroid. (online) (www.mediastore.com, accessed on 9 December
2011.
Encyclopedia Britannic. 2011. Encyclopedia Britannica. (online) (http://www.britannica.com/EBchecked/topic/594629/thyroid-gland,
accessed on 9 December 2011
Mescher AL, Anthony.2010. Junquira’s Basic Histology Text and Atlas.
USA : McGraw-Hill
Companies
Saul. 2002. Biology in Motion: Thyroid Gland. (online) (www.biologyinmotion.com, accessed on 9 December 2011
Telford, Bridgman. 1995. Introduction to Functional Histology. United States of America :
HarperCollins College Publishers
Tenzer, Amy. 1998. Struktur Hewan Jilid II. Malang: IKIP.
William and
Wilkins. 2006. Interactive Color Atlas of Histology: Student Version 2.0. USA: Lippincott Williams & Wilkins
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