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1 Pineal gland
2 Adenohypophysis
3 Neurohypophysis
4 Thalamus
5 Superior colliculi
6 Inferior colliculi
7 Medial geniculate nucleus
8 Cerebral peduncle
9 Medulla oblongata
10 Falx cerebri
11 Corpus callosum
12 Pons
13 Cerebellum
14 Sphenoid sinus
15 Occipital bone
16 Atlas
17 Axis
18 Soft palate
19 Nasopharynx
20 Tongue
21 Middle cerebellar
peduncle
22 Fourth ventricle
Dissection of brainstem and diencephalon
Posterior view
Sagittal section of brainstem and diencephalon in situ
Medial view
The pineal gland, a small reddish-gray body covered with pia
mater, is a midline epithelial outgrowth of the embryonic midbrain positioned in a depression between the two superior
Pineal Gland
colliculi on the midbrain’s dorsal surface. The distal end of this outgrowth becomes a small mass of
secretory cells that resemble the shape of a pine cone. It is from this appearance that it derives its
name. The pia mater sends septa into the pineal gland that divide it into cords of secretory cells that
are intermingled with numerous blood capillaries. The secretory cells of the pineal gland, called pinealocytes, have arm-like processes that contact both neighboring capillaries and the ependymal cells
that line the third ventricle. Hormonal secretions produced in the body of the cell are moved through the
arm-like processes where they are released by exocytosis into the capillaries and cerebrospinal fl uid.
Projecting into these cords of tissue are sympathetic postganglionic neurons from the superior cervical
sympathetic ganglion. The gland plays a role in integrating photoperiod and affecting circadian rhythms.
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1 Thymus
2 Thymic cortex
3 Thymic medulla
4 Trabeculae
5 Capsule
6 Maturing T cells
7 Epithelioreticular cell
8 Thymic corpuscle
9 Right lung
10 Left lung
Thymus in situ
Anterior view
The thymus is one of the primary lymphoid organs, but it also has an
endocrine component. The thymus provides the specialized environment for the precursor T cells to develop, differentiate, and undergo
Thymus
clonal expansion. This bilobed organ sits just posterior to the superior sternum along the
midline. It spans from the top of the sternum, sometimes even projecting into the inferior cervical
region, to the level of the fourth costal cartilages and sits anterior to the top of the heart and its
great vessels. It has an outer fi brous capsule that sends fi brous septa, connective tissue walls,
into the organ forming small lobular subregions. The thymus was once thought to diminish in
size with age, but in actuality it does not. Because of its high content of lymphoid tissue and a
rich blood supply, it has a reddish appearance in a living body. With age, however, fatty infi ltrations replace the lymphoid tissue and it takes on more of the yellowish color of the invading fat.
This gives it the false appearance of a reduction in size. The thymus produces hormones that
promote the maturation of T cells and may help retard the aging process.
Photomicrograph of thymus
50x
Photomicrograph of thymus
400x
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1 Right lobe of thyroid gland
2 Left lobe of thyroid gland
3 Isthmus of thyroid gland
4 Thyroid follicle
5 Follicular cell
6 Thyroglobulin (TGB)
7 Parafollicular (C) cell
8 Trachea
9 Fibromuscular membrane of trachea
10 Esophagus
11 Thyroid cartilage
12 Cricoid cartilage
13 Cricothyroid muscle
14 Brachiocephalic artery
15 Common carotid artery
16 Subclavian artery
17 Aortic arch
18 Vagus nerve
19 Thyrohyoid muscle
Thyroid gland in situ
Anterior view
Photomicrograph of thyroid gland
240x
Transverse section of thyroid gland
Inferior view
The thyroid gland is a bilobed organ positioned in the anterior
neck. This highly vascular organ consists of two lateral lobes of
endocrine tissue joined in the middle by a narrow portion of the
Thyroid Gland
gland called the isthmus. It is red-brown in color and is enveloped by a thin layer of connective tissue. This
connective tissue capsule sends extensions into the gland that divide the vascular and epithelial core into
masses of irregular shape and size. The epithelial cells within the compartments of the thyroid gland form
the secretory tissues of the organ. The major thyroid secretory cells are arranged into hollow spheres,
each of which forms a functional unit called a follicle. In a microscopic section the follicles appear as rings
of follicular cells enclosing an inner lumen fi lled with colloid, a substance that serves as an extracellular
storage site for thyroid hormones. Interspersed in the interstitial spaces between the follicles are other
secretory cells, the C cells, so called because they secrete the peptide hormone calcitonin.
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Photomicrograph of parathyroid gland
240x
1 Superior parathyroid gland
2 Inferior parathyroid gland
3 Left lobe of thyroid gland
4 Right lobe of thyroid gland
5 Isthmus of thyroid gland
6 Pyramidal lobe of thyroid gland
Thyroid and parathyroid glands (exposed on left)
Posterior view
The parathyroid glands are small, oval, light brown glands situated
on the posterior border of the two lateral lobes of the thyroid gland.
The parathyroid glands sit just beneath the connective tissue capsule
Parathyroid Glands
of the thyroid gland. There are four parathyroid glands, two superior and two inferior. The endocrine cells of the parathyroid
glands are called chief or principal cells. The chief cells form interconnecting columns of cells separated by fenestrated
capillaries. The chief cells produce the parathyroid hormone.
7 Chief cell
8 Oxyphil cell
9 Capillary
10 Arteriole
11 Venule
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1 Right suprarenal gland
2 Left suprarenal gland
3 Zona glomerulosa of cortex
4 Zona fasciculata of cortex
5 Zona reticularis of cortex
6 Medulla
7 Capsule
8 Kidney
9 Aorta
10 Inferior vena cava
11 Crura of diaphragm
12 Diaphragm
13 Psoas major muscle
14 Bladder
15 Celiac artery
16 Superior mesenteric artery
17 Ureter
18 Common iliac artery
19 Renal vein and artery
20 Autonomic nerve plexus
Left suprarenal gland
Anterior view
Photomicrograph of suprarenal gland
100x
There are two yellowish suprarenal or adrenal
glands that sit on the superior end of the kidneys.
Each gland is surrounded by a thin connective
Suprarenal Glands
tissue envelope. These highly vascular organs are not symmetrical. The right suprarenal gland is slightly
smaller and forms a fl at tetrahedron or four-sided polygon. The left suprarenal gland, like the left kidney,
is more superior than the right gland and has a semilunar shape that resembles a fl attened stocking hat
placed on the upper end of the kidney. Each suprarenal gland is actually composed of two endocrine
organs, one surrounding the other. The inner portion of the gland, called the suprarenal medulla, forms
approximately 20% of the organ. The medulla secretes catecholamines. The more massive outer part
of the gland, called the suprarenal cortex, secretes a variety of steroid hormones. The two parts of
the gland each have different embryonic origins. The suprarenal medulla forms from the embryonic
mesoderm, and the suprarenal cortex forms from embryonic neural crest cells.
Deep dissection of abdomen
Anterior view
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1 Pancreas
2 Pancreatic islet
3 Beta cell
4 Alpha cell
5 Exocrine acinus
6 Pancreatic duct
7 Gallbladder
8 Common bile duct
9 Duodenum
10 Liver
Pancreas in situ
Anteror view
The pancreas is a retroperitoneal organ that forms as an outgrowth of the
duodenal lining. Situated posterior to the stomach it is pinkish in color and
about 15 cm long, running from the loop of the duodenum on the right to the
Pancreas
spleen on the left. It has four basic regions: a head, neck, body, and tail. The pancreas has two functional parts, the exocrine pancreas and the endocrine pancreas. The endocrine portion of the pancreas
forms as small clusters of cells, the pancreatic islets, distributed among the exocrine acinar cells of the
pancreas. They are far less numerous (approximately 5% of the pancreas) than the cells of the exocrine
pancreas. There are four distinct cell types within the pancreatic islets: alpha or A cells, beta or B cells,
delta or D cells, and F cells. The alpha (20%) and beta (70%) cells constitute the greater part of the
pancreatic islets and produce the hormones glucagon and insulin, respectively. The other 10% of the
islet cells are delta and F cells, which secrete somatostatin and pancreatic polypeptide, respectively.
Photomicrographs of pancreas
200x (left), 640x (right)
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1 Ovary
2 Primordial follicle
3 Primary follicle granulosa cells
4 Secondary follicle granulosa cells
5 Follicular antrum
6 Corpus luteum
7 Primary oocyte
8 Zona pellucidum
9 Corona radiata
10 Uterine tube
11 Uterus
12 Vagina
13 Bladder
14 Urethra
15 Rectum
16 Clitoris
17 Pubic symphysis
18 Parietal peritoneum
Sagittal section of female pelvis
Medial view
The ovaries are ovoid organs about the size of an unshelled almond
and occupy the boundary zone between the abdominal and pelvic
cavities. They consist of a dull white fi brous tissue embedded with
Ovaries
oocytes, the “egg” cells of the female. Surrounding the oocytes are numerous follicular cells
that undergo changes during the female menstrual cycle. The follicular cells are the endocrine
cells of the ovary that produce the female steroidal hormones.
Photomicrograph of ovary
30x
Photomicrograph of mature
ovarian follicle
70x
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