telencephalon (cerebral hemispheres) + diencephalon
midbrain = mesencephalon = tectum + cerebral peduncles
• brain stem = the brain minus the cerebrum and cerebellum.
• BRAIN STEM = the stalk of the brain connecting the cerebral
hemispheres with the spinal cord and compromising the
midbrain (mesencephalon), pons and medulla ablongata.
• ????//// DIENCEPHALON IS CONSIDERED PART OF BRAIN STEM BY
• The hypothalamus forms the floor of the 3rd ventricle.
• It includes, from before backwards,
• the optic chiasma, the tuber cinereum, the infundibular
stalk (leading down to the posterior lobe of the
pituitary), the mamillary bodies and the posterior
• In each of these there is a number of cell masses or nuclei and a fibre
pathway—the medial forebrain bundle—which runs throughout the
length of the hypothalamus and serves to link it with the midbrain
posteriorly and the basal forebrain areas anteriorly.
• Sherrington described the hypothalamus as the head ganglion of the
• It is largely concerned with autonomic activity and can be divided into
a posteromedial sympathetic area and an anterolateral area concerned
with parasympathetic activity
The hypothalamus (continue)
• The hypothalamus plays an important part in endocrine
control by the formation of releasing factors or
• These substances, following their secretion into the
hypophyseal portal vessels, influence the production
by the cells of the anterior pituitary of adrenocorticotrophin
(ACTH), follicle-stimulating hormone, luteinizing hormone,
prolactin, somatotrophin, thyrotrophin and melanocyte-
• The hormones oxytocin and vasopressin (anti-diuretic
hormone, ADH) are produced by neurones in the
hypothalamus and released at their axon terminals in the
Clinical features (skip)
1) Lesions of the hypothalamus may result in a
variety of autonomic disturbances, e.g.
somnolence (somnolentia), disturbances of temperature
regulation and obesity, as well as a variety of endocrine
abnormalities, e.g. hypogonadism and hypothyroidism.
2) Damage to the supraoptic nuclei or the
infundibular stalk leads to diabetes insipidus.
The thalamus and 3rd ventricle in coronal section.
The pineal gland
• The pineal gland rests between the two superior
colliculi (corpora quadrigemina) and is attached
by a stalk to the posterior dorsal thalamus.
• It secretes melatonin and has an important role
in setting the circadian rhythm.
• (When calcified, the pineal gland is easily identified on skull
radiographs. It may then give the important radiological sign of
lateral displacement by a space-occupying lesion of the cerebral
hemisphere). The latter is a radiological finding you can skip it.
• The small, red, pinecone–shaped pineal gland, or epiphysis
cerebri, is part of the epithalamus. The pineal gland contains
neurons, glial cells, and special secretory cells called pinealocytes .
• Pinealocytes synthesize the hormone melatonin which is
derived from molecules of the neurotransmitter serotonin.
• Melatonin slows the maturation of sperm, oocytes, and
reproductive organs by inhibiting the production of a
hypothalamic releasing factor that stimulates FSH and LH
• Collaterals from the visual pathways enter the pineal gland and
affect the rate of melatonin production.
• Melatonin production rises at night and declines during the day.
This cycle is apparently important in regulating circadian rhythms,
our natural awake-asleep cycles.
• This hormone is also a powerful antioxidant that may help protect CNS
tissues from toxins generated by active neurons and glial cells.
The sphenoid Bone / Sella Tursica
• The general shape of the sphenoid has been compared to a giant
bat with its wings extended. The wings can be seen most clearly
on the superior surface .
• A prominent central depression between the wings cradles the pituitary
gland below the brain. This recess is called the hypophysial fossa, and the
bony enclosure is called the sella turcica .
• The anterior clinoid processes are posterior projections of the lesser wings of
the sphenoid. The tuberculum sellae forms the anterior border of the sella turcica; the
dorsum sellae forms the posterior border.
• A posterior clinoid process extends laterally on either side of the dorsum sellae.
• The lesser wings are triangular in shape, with the superior surfaces
supporting the frontal lobe of the brain.
• The inferior surfaces form part of the orbit and the superior part of the superior
orbital fissure, which serves as a passageway for blood vessels and cranial nerves of the
The pituitary gland (hypophysis cerebri)
• This is an example of a ‘two in one’ organ of which nature is so keen;
compare the two glandular components of the suprarenal cortex and
medulla, and the exocrine and endocrine parts of the pancreas, testis and
• The pituitary comprises a larger anterior and smaller posterior lobe,
the latter connected by the hollow infundibulum (pituitary stalk) to the
tuber cinereum in the floor of the 3rd ventricle.
The two lobes are connected by a narrow zone termed the pars intermedia.
The pituitary lies in the cavity of the pituitary fossa covered over by the
diaphragma sellae, which is a fold of dura mater.
This fold has a central aperture through which passes the infundibulum.
Below is the body of the sphenoid, laterally lies the cavernous sinus and its
contents separated by dura mater, with intercavernous sinuses
communicating in front, behind and below.
The optic chiasma lies above, immediately in front of the infundibulum.
• The anterior lobe is extremely cellular and
consists of chromophobe, eosinophilic and
• The pars intermedia contains large colloid
vesicles reminiscent of the thyroid.
• The posterior lobe is made up of nerve fibers
whose cell stations lie in the hypothalamus.
• The posterior lobe is a cerebral diverticulum.
• The anterior lobe and the pars intermedia
develop from Rathke’s pouch in the roof of
the primitive buccal cavity.
• Occasionally a tumour grows from remnants
of the epithelium of this pouch
• These tumours are often cystic and calcified.
Clinical features (skip)
• Tumours of the pituitary, as well as forming intracranial space-
occupying lesions, may have two special features; their endocrine
disturbances and their relationship to the optic chiasma.
• Chromophobe adenoma is the commonest pituitary tumour. As it
enlarges it expands the pituitary fossa (sella turcica) and this may be
• Compression of the optic chiasma produces the very rapid typical
• The tumour itself is non-secretory and gradually destroys the normally
• The patient develops hypopituitarism with loss of sex characteristics,
hypothyroidism and hypoadrenalism.
• In childhood there is an arrest of growth.
• As the tumour extends there may be involvement of the
hypothalamus with diabetes insipidus and obesity
Clinical features (skip)
• The eosinophil adenoma secretes the pituitary growth
hormones. If it occurs before puberty, which is unusual,
it produces gigantism; after puberty it results in
• The basophil adenoma is small, produces no pressure
effects and may be associated with Cushing’s syndrome,
although this more often results from hyperplasia or
tumour of the suprarenal cortex.
• Pituitary tumours may be approached through a frontal bone flap or, using the fibre-
optic endoscope, through the nasal cavity and sphenoid sinus.
• The close relationship of the pituitary to the sphenoid sinus makes it possible to insert
fibre-optic instruments into the pituitary gland by a transnasal, transsphenoidal
approach. This is now the preferred approach to surgery of pituitary tumours.
The descent of the thyroid, showing possible sites of ectopic thyroid tissue or
thyroglossal cysts,and also the course of a thyroglossal fistula.
(The arrow shows the further descent of the thyroid which may take place retrosternally
into the superior mediastinum.)
The Thyroid Gland
• The thyroid is made up of :
1. The isthmus—overlying the 2nd and 3rd rings of the trachea;
2. The lateral lobes— each extending from the side of the thyroid
cartilage downwards to the 6th tracheal ring;
3. An inconstant pyramidal lobe projecting upwards from the isthmus,
usually on the left side, which represents a remnant of the embryological
descent of the thyroid.
• The gland is enclosed in the pretracheal fascia,
• covered by the strap muscles
• overlapped by the sternocleidomastoids.
• The anterior jugular veins course over the isthmus. When the
thyroid enlarges, the strap muscles stretch and adhere to the gland. so
that, at operation, they often appear to be thin layers of fascia.
The Thyroid Gland (continue)
• On the deep aspect of the thyroid lie the larynx and
trachea, with the pharynx and oesophagus behind and
the carotid sheath on either side.
• Two nerves lie in close relationship to the gland;
in the groove between the trachea and oesophagus lies
the recurrent laryngeal nerve and deep to the upper
pole lies the external branch of the superior laryngeal
nerve passing to the cricothyroid muscle.
Three arteries supply and three veins drain the thyroid gland:
• the superior thyroid artery
arises from the external carotid and passes to the upper pole;
• the inferior thyroid artery
arises from the thyrocervical trunk of the 1st part of the subclavian artery and passes behind the
carotid sheath to the back of the gland;
• the thyroidea ima artery
is inconstant; when present, it arises from the aortic arch or the brachiocephalic artery;
• the superior thyroid vein
drains the upper pole to the internal jugular vein;
• the middle thyroid vein
drains from the lateral side of the gland to the internal jugular;
• the inferior thyroid veins (often several)
drain the lower pole to the brachiocephalic veins.
• As well as these named branches, numerous small vessels pass to the thyroid from the pharynx
Development of Thyroid Gland
• Thyroid gland develops mainly from the thyroglossal duct.
• Parafollicular cells are derived from the caudal pharyngeal
complex (from 4th and 5th pharyngeal pouch).
• After formation of the pharyngeal arches, the medial ends of
the two mandibular arches are separated by
• Tuberculum impar =
A midline structure in the floor of the pharynx.
• Immediately the tuberculum impar the epithelium of the
floor of the pharynx shows a thickening.
• This thickening is soon depressed to form a diverticulum
called the thyroglossal duct.
Development of Thyroid Gland (continue)
• The site of the diverticulum is now seen as a depression called
the foramen caecum.
• The diverticulum grows down in the midline into the neck.
• Its tip bifurcates.
• Proliferation of the cells of this bifid end gives rise to the
• Two lobes of the thyroid gland.
• The developing thyroid gland comes into intimate contact with
The caudal pharyngeal complex and fuses with it.
• Cells arising from this complex are believed to give origin to the
parafollicular cells of the thyroid.
The Parathyroid Glands
The normal sites of the parathyroid glands (posterior aspect).
The relationship of the recurrent laryngeal nerve to the thyroid gland and the inferior thyroid
artery. (a) The nerve is usually deep to the artery but
(b) may be superficial to it or (c) pass through its branches.
Normal and abnormal sites of the parathyroid glands (lateral view).
The Parathyroid Glands
• These are usually four in number, a superior and
inferior on either side;
• however, the numbers vary from two to six.
• 90% are in close relationship to the thyroid,
• 10% are aberrant, the latter invariably being the
• Each gland is about the size of a split pea and is of
a yellowish-brown colour.
The Parathyroid Glands (continue)
• The superior parathyroid is more constant in position than the inferior gland.
• It usually lies at the middle of the posterior border of the lobe of the thyroid
above the level at which the inferior thyroid artery crosses the recurrent
• The inferior parathyroid is most usually situated below the inferior artery
near the lower pole of the thyroid gland.
• The next commonest site is within 1cm of the lower pole of the thyroid
• Aberrant inferior parathyroids may descend along the inferior thyroid veins
in front of the trachea and may even track into the superior mediastinum in
company with thymic tissues.
• Less commonly, the inferior gland may lie behind and outside
the fascial sheath of the thyroid and be found behind the
oesophagus or even in the posterior mediastinum.
• Only on extremely rare occasions are the glands actually
completely buried within thyroid tissue.
• The superior parathyroids differentiate from the 4th
• The inferior gland develops from the 3rd pouch
in company with the thymus,
• As the thymus descends, the inferior
parathyroid is dragged down with it.
• It is thus easily understood that the inferior
parathyroid may be dragged beyond the thyroid into
The derivatives of the branchial pouches. The inferior parathyroid migrates downwards from
the 3rd pouch whereas the superior parathyroid (4th pouch) remains stationary.
Clinical Features (skip)
1. These possible aberrant sites are, of course, of
great importance in searching for a parathyroid
adenoma in hyperparathyroidism.
2. The parathyroids are usually safe in subtotal
thyroidectomy because the posterior rim of the
thyroid is preserved. However, they may be
inadvertently removed or damaged, with
resultant tetany due to the lowered serum
The Suprarenal Glands
• The suprarenal glands are retroperitoneal, cap the upper poles of the
kidneys and lie against the crura of the diaphragm.
• The left is related anteriorly to the stomach across the lesser sac,
• the right lies behind the right lobe of the liver and tucks medially
behind the inferior vena cava.
• Each gland, weighing only 3 to 4 g,
• Each gland has three arteries supplying it:
• direct branch from the aorta; branch from the phrenic artery; branch
from the renal artery.
• The single main vein drains from the hilum of the gland
into the nearest available vessel—the inferior vena cava on the right, the
renal vein on the left.
The Suprarenal Glands
• The suprarenal gland comprises a cortex and medulla, which
represent two developmentally and functionally independent
endocrine glands within the same anatomical structure.
• The medulla is derived from the neural crest (neuroectoderm)
whose cells also give rise to the sympathetic ganglia.
• The cortex, on the other hand, is derived from the mesoderm.
• The suprarenal medulla receives preganglionic sympathetic fibres
from the greater splanchnic nerve and secretes adrenaline and
• The cortex secretes the adrenocortical hormones.
• The pancreas lies retroperitoneally in roughly the transpyloric plane.
• For descriptive purposes it is divided into head, neck, body and tail.
• The head lies in the C-curve of the duodenum and sends out the
uncinate process which hooks posteriorly to the superior mesenteric
vessels as these travel from behind the pancreas into the root of the
• Posteriorly lie the inferior vena cava, the commencement of the portal
vein, aorta, superior mesenteric vessels, the crura of diaphragm,
• coeliac plexus, the left kidney and suprarenal gland.
• The tortuous splenic artery runs along the upper border of the
• The splenic vein runs behind the gland, receives the inferior
mesenteric vein and joins the superior mesenteric to form the portal
vein behind the pancreatic neck.
• To complete this list of important posterior
relationships, the common bile duct lies either in
a groove in the right extremity of the gland or
embedded in its substance, as it passes to open
into the second part of the duodenum.
• Anteriorly lies the stomach separated by the
• To the left, the pancreatic tail lies against the
hilum of the spleen.
• The blood supply
• Blood is supplied from the splenic and the
• the corresponding veins drain into the portal
• The lymphatics
• The lymphatics drain into nodes which lie along
its upper border, in the groove between its head
and the duodenum,
and along the root of the superior mesenteric vessel.
Cell of the Pancreas
• Pancreatic islets, accounts for only 1% of the
pancreatic cell population.
• There are two million islets in the normal
1. Alpha cells ------- Glucagon.
2. Beta cells --------- Insulin.
3. Delta cells -------- somatostain.(GHIH)
4. F cells ------------ PP (pancreatic polypeptide)
• The pancreas develops from a larger dorsal diverticulum
from the duodenum and a smaller ventral out pouching
from the side of the common bile duct.
• The ventral pouch swings round posteriorly to fuse with
the lower aspect of the dorsal diverticulum, trapping the
superior mesenteric vessels between the two parts.
• The ducts of the two formative segments of the pancreas
• that of the smaller takes over the main pancreatic
flow to form the main duct,
• leaving the original duct of the larger portion of the
gland as the accessory duct.
Testis and Epididymis
• The left testis lies at a lower level than the right within the scrotum;
• rarely, this arrangement is reversed.
• Each testis is contained by a white fibrous capsule, the tunica albuginea, and each
is invaginated anteriorly into a double serous covering,
• the tunica vaginalis, just as the intestine is invaginated anteriorly into the
• Along the posterior border of the testis, rather to its lateral side, lies the
epididymis, which is divided into an expanded head, a body and a pointed tail
• Medially, there is a distinct groove, the sinus epididymis, between it and the testis.
The epididymis is covered by the tunica vaginalis except at its posterior margin
which is free or, so to say, ‘extraperitoneal’.
• The testis and epididymis each bear at their upper extremities a small stalked
body, termed respectively the appendix testis and appendix epididymis (hydatid of
• The appendix testis is a remnant of the upper end of the paramesonephric
(Müllerian) duct; the appendix epididymis is a remnant of the mesonephros.
• These structures, being stalked, are liable to undergo torsion.
• The testicular artery arises from the aorta at the level of
the renal vessels.
• It anastomoses with the artery to the vas, supplying the vas
deferens and epididymis, which arises from the inferior
vesical branch of the internal iliac artery.
• This cross-connection means that ligation of the testicular
artery is not necessarily followed by testicular atrophy.
• The pampiniform plexus of veins becomes a single vessel,
the testicular vein, in the region of the internal ring.
• On the right this drains into the inferior vena cava,
• on the left into the renal vein.
Lymph Drainage + Nerve Supply
• The lymphatic drainage of the testis obeys the usual rule; it
accompanies the venous drainage and thus passes to the para-
aortic lymph nodes at the level of the renal vessels.
• Free communication occurs between the lymphatics on either
• there is also a plentiful anastomosis with the paraaortic
intrathoracic nodes and, in turn, with the cervical nodes,
• so that spread of malignant disease from the testis to the
nodes at the root of the neck is not rare.
• Nerve supply
• T10 sympathetic fibres via the renal and aortic plexus.
• These convey afferent (pain) fibres—hence referred pain from
the testis to the loin.
Structure of the Testis
• The testis is divided into 200–300 lobules each containing
one to three seminiferous tubules.
• Each tubule is some 2 feet (62 cm) in length when teased
out, and is thus obviously coiled and convoluted to pack
away within the testis.
• The tubules anastomose posteriorly into a plexus termed
the rete testis from which about a dozen fine efferent ducts
arise, pierce the tunica albuginea at the upper part of the
testis and pass into the head of the epididymis,which is
actually formed by these efferent ducts coiled within it.
• The efferent ducts fuse to form a considerably convoluted
single tube which constitutes the body and tail of the
Development and Descent of the Testis
• This is important and is the key to several features which are of
• The testis arises from a germinal ridge of mesoderm in the
posterior wall of the abdomen just medial to the mesonephros
• and links up with the epididymis and vas, which differentiate from
the mesonephric duct.
• As the testis enlarges, it also undergoes a caudal migration
according to the following timetable:
• 3rd month (of fetal life) reaches the iliac fossa;
• 7th month traverses the inguinal canal;
• 8th month reaches the external ring;
• 9th month descends into the scrotum.
Development and Descent of the Testis
• Amesenchymal strand, the gubernaculum testis, extends from the caudal
end of the developing testis along the course of its descent to blend into
the scrotal fascia.
• The exact role of this structure in the descent of the testis is not known;
theories are that it acts as a guide (gubernaculum = rudder) or that its
swelling dilates the inguinal canal and scrotum. I
• n the third fetal month, a prolongation of the peritoneal cavity invades the
gubernacular mesenchyme and projects into the scrotum as the processus
• The testis slides into the scrotum posterior to this, projects into it and is
therefore clothed front and sides with peritoneum. About the time of
birth this processus obliterates, leaving the testis covered by the tunica
• Very rarely, fragments of adjacent developing organs —spleen or
suprarenal — are caught up and carried into the scrotum along with the
The testis arises at the level of the mesonephros at the level of L2/3
When searching for secondary lymphatic spread from a neoplasm of the testis,
Rarely, a rapidly developing varicocele (dilatation of the pampiniform plexus of
The testis may fail to descend and may rest anywhere along its course— intra-
abdominally, within the inguinal canal, at the external ring or high in the
Abnormalities of the obliteration of the processus vaginalis lead to a number of
extremely common surgical conditions of which the indirect inguinal hernia is
the most important.
Types of hydrocele. (a) Vaginal hydrocele, (b) congenital hydrocele, (c) infantile hydrocele,
(d) hydrocele of the cord. (The tube at the upper end of each diagram represents the internal
inguinal ring. Yellow = hydrocele, Brown = vas and epididymis)
◊The Fallopian tube, ovary and broad ligament
• The ovary is an almond-shaped organ, 1.5 in (4 cm) long, attached to the back of
the broad ligament by the mesovarium.
• The ovary has two other attachments, the infundibulopelvic ligament, (sometimes
called the suspensory ligament of the ovary), along which pass the ovarian vessels
and lymphatics from the side wall of the pelvis,
• and the ovarian ligament, which passes to the cornu of the uterus.
• The ovary is usually described as lying on the side wall of the pelvis opposite the
• which is a depression bounded by the external iliac vessels in front and the ureter
and internal iliac vessels behind and which contains the obturator nerve.
• However, the ovary is extremely variable in its position and is frequently found
prolapsed into the pouch of Douglas in perfectly normal women.
• The ovary, like the testis, develops from the genital ridge and then descends into
the pelvis. In the same way as the testis, it therefore drags its blood supply and
lymphatic drainage downwards with it from the posterior abdominal wall.
Blood supply, lymph drainage and
• Blood supply
• is from the ovarian artery which arises from the aorta at the level of
the renal arteries.
• The ovarian vein drains, on the right side, to the inferior vena cava,
on the left, to the left renal vein, exactly comparable to the venous
drainage of the testis.
• Lymphatics pass to the aortic nodes at the level of the renal vessels,
following the general rule that lymphatic drainage accompanies the
venous drainage of an organ.
• Nerve supply is from the aortic plexus (T10).
• All these structures pass to the ovary in
the infundibulopelvic ligament
• The ovary has no peritoneal covering; the serosa ends at the
• It consists of a connective tissue stroma containing Graafian follicles
at various stages of development, corpora lutea and corpora
albicantia (hyalinized, regressing corpora lutea, which take several
months to absorb completely).
• The surface of the ovary in young children is covered with a so-
called ‘germinal epithelium’ of cuboidal cells.
• It is now known, however, that the primordial follicles develop in
the ovary in early fetal life and do not differentiate from these cells.
• In adult life, in fact, the epithelial covering of the ovary disappears,
leaving only a fibrous capsule termed the tunica albuginea.
• After the menopause the ovary becomes small and shrivelled; in
old age the follicles disappear completely.