Download Endocrine

Histology
Lab-11-
Ass. Lec.
Wafaa H. M. Alhashimy
Dentistry College
Second Stage
Endocrine system
The endocrine system consists of cells , tissues and organs that synthesize and secrete
hormones directly into blood and lymph capillaries . The complete endocrine glands
include the hypophysis or pituitary glands , thyroid glands , adrenal glands and
parathyroid glands .
Hypophysis (pituitary gland)
is an endocrine gland It is not a part of the brain. It is a protrusion off the bottom of the
hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica)
covered by a dural fold . The pituitary is functionally connected to the hypothalamus
by the median eminence via a small tube called the infundibular stem (Pituitary stalk).
The pituitary gland secretes nine hormones that regulate homeostasis. The pituitary
glands consist of:
1-Adenohypophysis ( anterior pituitary ) has three subdivision :
the pars distalis is the largest part of the hypophysis .
the pars tuberalis: surrounds the neural stalk .
the pars intermedia: is a thin cell layer between the pars distalis and the
neurohypophysis ; it respresents the remnant of the hypophyseal pouch . the pars
intermedia is rudimentary in humans .
2-Neuro hypophysis (posterior pituitary ) has three subdivision :
Pars nervosa : it is largely a collection of axonal projections from the hypothalamus
that terminate behind the anterior pituitary gland. It is where neurohypophysial
hormones are stored and released such as antidiuretic hormone (ADH) and oxytocin.
Infundibular stalk or infundibulum: is bridge the hypothalamic and hypophyseal
systems.
Median eminence : is located in the base the hypothalamus .
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Thyroid glands
The thyroid gland is a unique endocrine organ is found in the neck, below the thyroid
cartilage The isthmus (the bridge between the two lobes of the thyroid) is located
inferior to the cricoid cartilage , its cells are arranged into spherical structures, called
follicles . each follicle is surrounded by reticular fibers and avascular network of
capillaries that allows for easy entrance of thyroid hormones into the blood stream .
the follicular epithelium can be simple sequamous , cuboidal or low columnar ,
depending on the state of activity of the thyroid gland.
Follicles are the srucutueal and functional units of thyroid gland , the cells that
surrounded the follicles , the follicular cells .in addition to follicular cells , the thyroid
gland also contains larger , pale – staining parafollicular cells these cells are found
either peripherally in the follicular epithelium or within the follicle . follicular cells is
producing thyroid hormones, triiodothyronine (T3) and thyroxine (tetraiodothyronine
T4). Parafollicular produces calcitonin, which plays a role in calcium homeostasis.
Parathyroid glands
are located on the posterior surface of the thyroid gland. There are typically four
parathyroid glands. The two parathyroid glands on each side which are positioned
higher are called the superior parathyroid glands, while the lower two are called the
inferior parathyroid glands. cells of the parathyroid glands are arranged into cords or
clumps that are surrounded by a rich network of capillaries . two types of cells are
found in the parathyroid glands , functional chief cells and oxyphil cells .
Name
Staining Quantity Size
parathyroid chief cells darker
oxyphil cells
many
lighter few
Function
smaller manufacture parathormone
larger function unknown.
parathormone (PTH) increases blood calcium levels by stimulating osteoclasts to
break down bone and release calcium. PTH also increases gastrointestinal calcium
absorption by activating vitamin D, and promotes calcium reabsorption by the
kidneys.
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Adrenal glands
Each adrenal gland is surrounded by a dense irregular connective tissue capsule and
is embedded in a dipose tissue around the kidneys . each adrenal gland consists of an
outer cortex and an inner medulla .
Cortex : The adrenal cortex exhibits three concentric zones : the zona glomerulosa ,
zona fasciculate and zona reticularis .
Medulla : The medulla lies in the center of adrenal gland . the cells of the adrenal
medulla , which are also arranged in small cords , are modified postganglionic
sympathetic neurons that synthesize and secrete catecholamines .
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