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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

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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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 1 Frontal lobe

 2 Parietal lobe

 3 Temporal lobe

 4 Insular lobe

 5 Lateral ventricle

 6 Third ventricle

 7 Cerebral aqueduct

 8 Fourth ventricle

 9 Septum pellucidum

10 Falx cerebri

 11 Tentorium cerebelli

12 Anterior lobe of cerebellum

13 Posterior lobe of cerebellum

Frontal section of head at anterior aspect of auricle

Anterior view

The brain sections on this and the following page depict aspects of brain anatomy

that are not evident on the external views of the brain, and the association of the

brain with surrounding structures of the head. Each section is approximately 2

Brain Sections

14 Flocculus

15 Superior vermis

16 Superior cerebellar peduncle

17 Cerebral peduncle

18 Pituitary gland

19 Pons

20 Olive

21 Corpus callosum

22 Caudate nucleus

23 Internal capsule

24 Putamen

25 External capsule

26 Body of fornix

27 Globus pallidus

28 Medial thalamic nucleus

29 Lateral thalamic nucleus

30 Dentate gyrus

31 Circular gyrus

32 Optic chiasm

33 Facial nerve

34 Vestibulocochlear nerve

35 Vertebral artery

36 Middle cerebral artery

37 Internal carotid artery

38 Anterior cerebral artery

39 Superior sagittal sinus

centimeters thick and is an anterior view of three sections in succession. The fi rst section begins at the anterior aspect of

the ear and the last section is just posterior to the ear.

40 Sigmoid sinus

41 Internal jugular vein

42 Tympanic cavity

43 Cochlea

44 Sphenoid sinus

45 Mastoid air cells

46 Mandibular condyle

47 Occipital condyle

48 Atlas

49 Axis

50 Lateral pterygoid muscle

51 Medial pterygoid muscle

52 Sternocleidomastoid muscle

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Frontal section of head through

middle of auricle

Anterior view

Frontal section of head just postrior to auricle

Anterior view

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Sagittal section of braining revealing the ventricular system

Medial view, arrows show path of cerebrospinal fluid

Developmentally the entire central nervous system forms from the

hollow neural tube. As development proceeds and the wall of the

neural tube becomes increasingly thicker, the hollow lumen of the tube

Ventricular System

undergoes changes in relative size and shape throughout different regions of the changing central nervous system. As a

result of this developmental history, there remains a hollow interconnected center throughout the entire central nervous

system. This hollow core forms the ventricular system. Beginning within the cerebral hemispheres are the large paired lateral

ventricles. Each lateral ventricle has a C-shape like its corresponding hemisphere. The lateral ventricles communicate via

the interventricular foramina with a midline cavity, the third ventricle. The third ventricle sits within the core of the diencephalon where the right and left thalamus form its lateral walls. From the third ventricle a narrow channel, the aqueduct of the

midbrain or cerebral aqueduct, passes through the core of the midbrain. This narrow channel expands in the region of the

pons and cerebellum to form the fourth ventricle. The fourth ventricle tapers through the medulla to enter the spinal cord as

the central canal. Within the four ventricles of the brain convoluted aggregations of capillaries, called a choroid plexus, project into the cavity of the ventricle. These capillary projections are the principal site for the production of cerebrospinal fl uid.

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 1 Lateral ventricle

 2 Interventricular foramen

 3 Third ventricle

 4 Cerebral aqueduct

 5 Fourth ventricle

 6 Median aperture

 7 Choroid plexus

 8 Corpus callosum

 9 Caudate nucleus

10 Septum pellucidum

 11 Fornix

12 Frontal lobe

13 Parietal lobe

14 Occipital lobe

15 Temporal lobe

16 Cingulate gyrus

17 Hypothalamus

18 Thalamus

19 Pineal gland

20 Midbrain

21 Superior colliculus

22 Inferior colliculus

23 Pons

24 Medulla oblongata

Floor of lateral ventricles

Superior view

Roof of lateral ventricles

Inferior view

Fourth ventricle

Posterolateral view

25 Cerebellum

26 Falx cerebri

27 Internal carotid artery

28 Middle cerebellar peduncle

29 Trochlear nerve

30 Vestibulocochlear nerve

31 Vagus nerve

32 Accessory nerve

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Dissection of cranial and spinal dura mater

Posterior view

Dura removed to expose leptomeninges

Posterior view

Within the cranium and vertebral column, the meninges form a protective encasement for the

tissue of the brain and spinal cord. There are three meningeal membranes, the tough outer

connective tissue pachymenix, the dura mater, and the epithelial inner leptomeninges, the

Meninges

arachnoid mater and pia mater. Between the leptomeningeal layers there is a fl uid compartment called the subarachnoid

space. Cerebrospinal fl uid, secreted from the choroid plexuses of the ventricles, exits the ventricles to fi ll this compartment.

The cerebrospinal fl uid forms a hydraulic shock absorber and suspension system for the brain and spinal cord. In addition

to protecting the central nervous system, the meninges support many of the blood vessels that are associated with the brain.

Within the cranium the subdivisions of the dura mater split to form large venous channels, the dural venous sinuses, which

drain all the tissues of the cranial vault, and these splits also form strong, fi brous septa that separate different parts of the brain.

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Dural sac (above), Leptomeninges (below)

Lateral views

 1 Cranial dura mater

 2 Spinal dura mater

 3 Dural venous sinus

 4 Cranial leptomeninges - arachnoid is superficial to and covering pia mater

 5 Spinal leptomeninges - arachnoid is superficial to and covering pia mater

 6 Middle meningeal artery and branches in dura mater

 7 Superficial middle cerebral vein and tributaries in subarachnoid space

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 1 Falx cerebri

 2 Tentorium cerebelli (cut)

 3 Superior sagittal sinus

 4 Straight sinus

 5 Transverse sinus

 6 Lateral ventricle

 7 Septum pellucidum

 8 Third ventricle

 9 Fourth ventricle

10 Cerebrum

 11 Cerebellum

12 Corpus callosum

13 Choroid plexus

14 Optic chiasm

15 Trigeminal nerve

Head frontal section revealing dural septa

Anterior view

Dissection of cranium

Superoposterior view

Dissection of cranium

Superoposterior view

Meninges

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15 Endocrine System

Like the nervous

system, the endocrine system is a control system within the

body. Th e nervous system administers its control over the

body tissues via long wirelike cells that originate form

complex circuits in the central nervous system. Th is

circuitry receives sensory input, processes this input,

and generates regulatory output. Endocrine control

works in a much diff erent fashion. Th e endocrine

system consists of a number of diff erent glands

that function like radio transmitting stations.

Just as different radio stations send radio

signals of diff erent wavelengths into the air,

endocrine glands distribute diff erent types of

small molecules called hormones throughout

the body via the circulatory system. Th ese

small molecules travel through the blood

stream and are detected by eff ector organs in

diff erent parts of the body, much like radio

waves are detected by radios in diff erent

parts of a city. Eff ector organs have receptor

sites that are specifi c to specifi c hormones.

Th is results in a “lock and key” function at the

eff ector cell. When the hormone binds to the

receptor site, it initiates a regulatory eff ect on

the cell.

Because the hormones are distributed by the

circulatory system, the speed of endocrine

 regulation is slower than that of nervous regulation, many minutes compared to milliseconds.

Also, because of the distribution of the hormones

via the circulatory system, endocrine eff ects can

be  experienced anywhere there are cells with the

 appropriate receptor site. In comparison to the

 nervous system, endocrine distribution is potentially

very widespread. Because the hormone can lock into

the receptor site and not be degraded instantly, the

 duration can be longer lasting than that initiated by a single

nervous impulse.

Find more information

about the endocrine

system in

249

REAL ANATOMY

250

 1 Hypothalamus

 2 Pineal gland

 3 Frontal lobe of cerebrum

 4 Parietal lobe of cerebrum

 5 Occipital lobe of cerebrum

 6 Temporal lobe of cerebrum

 7 Corpus callosum

 8 Thalamus

Sagittal section of brain

Medial view

The hypothalamus occupies the area of the brain

between the third ventricle and the subthalamus. It is

a major intersection between the thalamus, cerebral

Hypothalamus

cortex, and ascending fi ber systems from the spinal cord and brainstem. It is the control center

of the autonomic nervous system and regulates the function of numerous endocrine glands. The

posterior pituitary gland, or neurohypophysis, is an outgrowth of the hypothalamus. Many

factors infl uence the hypothalamus and dictate its controlling infl uence over tissues in the body.

These factors include the nervous input that enters it, temperature, osmotic pressure, and levels

of hormones in the circulating blood that pass through its capillaries.

 9 Midbrain

10 Pons

 11 Cerebellum

12 Medulla oblongata

13 Lateral ventricle

14 Fourth ventricle

15 Mammilary body

16 Spinal cord

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Photomicrograph of anterior pituitary

200x

 1 Pituitary gland

 2 Infundibulum

 3 Adenohypophysis

 4 Neurohypophysis

 5 Parenchyma consisting of

 acidophils, basophils, and

 chromophobes

 6 Capillary with red blood cells

 7 Parenchyma consisting of

 axons and pituicytes

 8 Hypothalamus

 9 Cerebrum

10 Falx cerebri

 11 Midbrain

12 Pons

13 Cerebellum

14 Medulla oblongata

15 Spinal cord

16 Nasal septum

17 Soft palate

18 Tongue

19 Epiglottis

20 Atlas

21 Axis

22 Intervertebral disc

23 Sphenoid sinus

24 Occipital bone

Sagittal section of head and neck with enlarged callout of pituitary gland

Medial view

The pituitary gland, or hypophysis, “hangs” from the base

of the brain via a connecting stalk, the infundibulum,

which connects it to the hypothalamus. The infundibulum

Pituitary Gland

contains numerous nerve fi bers that relay from the hypothalamus to the posterior portion of the pituitary

gland. In addition to this nervous pathway between the hypothalamus and the pituitary, numerous

small blood vessels pass between the two organs. The pituitary gland has two anatomically and functionally distinct lobes, the neurohypophysis (posterior lobe) and the adenohypophysis (anterior lobe).

The posterior lobe arises as an outgrowth of the embryonic brain. It is composed of nervous tissue and

forms a neural link with the hypothalamus through the infundibulum. The anterior lobe arises from the

epithelial lining of the embryonic pharynx. It consists of glandular epithelial tissue and forms a vascular

link with the hypothalamus via the small blood vessels that pass between the two regions.

Photomicrograph of posterior pituitary

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Photomicrograph of posterior pituitary

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