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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

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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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