Anatomy Flashcards
1
Q
What is the pituitary gland?
A
The pituitary gland secretes hormones that control the actions of other endocrine organs and various tissues around the body
2
Q
What is the diencephalon?
A
- Posterior part of the forebrain which consists of the thalamus and hypothalamus
- Forms central core of cerebrum with connections to right and left cerebral hemispheres and midbrain
3
Q
Where is the pituitary gland?
A
- Pea-sized oval structure, suspended from the underside of the brain by the infundibulum (pituitary stalk)
- It sits within the sella turcica of the sphenoid bone, in a small depression called the pituitary fossa
4
Q
What sits anteriorly to the pituitary gland?
A
sphenoid sinus
5
Q
What sits posteriorly to the pituitary gland?
A
posterior intercavernous sinus, dorsum sellae (posterior wall of the sella turcica), basilar artery and the pons
6
Q
What sits superiorly to the pituitary gland?
A
diaphragma sellae (fold of dura mater that covers the pituitary gland), optic chiasm
7
Q
What sits inferiorly to the pituitary gland?
A
sphenoid sinus
8
Q
What sits laterally to the pituitary gland?
A
cavernous sinus
9
Q
What is the anatomical structure of the pituitary gland?
A
Pituitary gland is anatomically and functionally divided into anterior and posterior lobes
10
Q
What are the areas of the anterior lobe of the pituitary gland?
A
Pars distalis, pars tuberalis, pars intermedia
11
Q
What is the embryology of the anterior pituitary lobe?
A
Embryologically, the anterior pituitary is formed from an upgrowth of Rathke’s pouch (ectoderm)
12
Q
What is the function of the anterior pituitary lobe?
A
- Responsible for synthesis and release of most pituitary hormones
- Trophic: TSH, ACTH, FASH, LH
- Non-trophic: GH and prolactin
13
Q
describe the histology of the anterior pituitary lobe?
A
- Acidophils and basophils are divided into different classes of cells which have different secretory products and target organs
- Anterior pituitary also contains one type of chromophobe (cells stain weakly) - largely non-functional
14
Q
Describe the anatomical and functional structure of the posterior pituitary lobe.
A
- Pars nervosa
- Extension of neural tissue that consists of modified glial cells and axonal processes
15
Q
What is the embryology of the posterior pituitary lobe?
A
Embryologically begins as an outpouching of the third ventricular floor
16
Q
What is the function of the posterior pituitary lobe?
A
Releases ADH and oxytocin (synthesised in the hypothalamus)
17
Q
Describe the histology of the posterior pituitary lobe.
A
Consists of non-myelinated axons of neurosecretory neurons
18
Q
How are hormones secreted by the anterior pituitary?
A
- Hypothalamic neurons secrete either releasing hormones (stimulate anterior pituitary to release hormones) or release-inhibitory hormones (prevent anterior pituitary from releasing hormones)
- Hypophyseal portal veins transport hypothalamic hormones to 2nd capillary bed in the anterior pituitary
- There is an increase or decrease in the level of hormone production by the anterior pituitary
- Hormones travel to the hypophyseal veins into the SVC and then enter systemic circulation
19
Q
What is the Dural venous sinuses and what is the anatomy?
A
- The dural venal sinuses are venous channels within the dura mater that drain most venous blood from the cranial cavity (including brain) into the internal jugular veins at jugular foraminae in the floor of the posterior fossa
- There are eleven venous sinuses in total
- The cavernous sinus drains the ophthalmic veins and can be found on either side of the sella turcica
20
Q
What is the dura mater?
A
The entire cranial cavity is lined internally
21
Q
What is diaphragma sellae?
A
tough sheet of dura mata forming roof (diaphragm) over pituitary fossa
22
Q
What is the tentorium cerebelli?
A
tough sheet of dura mater ‘tenting’ over cerebellum in posterior cranial fossa but with central gap to permit brainstem to pass through
23
Q
Where does the temporal lobe of the brain?
A
lies in the middle cranial fossa
24
Q
How can a pituitary tumour affect the vision?
A
- Pituitary gland lies immediately inferior to optic chiasma (formed from right and left optic nerves CN II)
- Any expanding lesion from the pituitary or hypothalamus which expands upward through the diaphragma sellae can produce visual field defects by pressure on the chiasma
It can result in bitemporal hemianopia
25
What other structures are at risk from a pituitary tumour other than the optic nerve?
Lateral extension of pituitary lesions may involve the vascular and nervous structures of the cavernous sinus and may rarely reach the temporal lobe of the brain
The pituitary is encased in a bony box, therefore any lateral, anterior, or posterior expansion must cause bony erosion
26
What are the surgical accesses to the pituitary fossa?
- **Transcranial approach:** subfrontal (inferior to frontal lobe)
- **Transsphenoidal approach:** via nasal cavities and sphenoid sinus
- Requires surgical fracture of the nasal septum and floor, and roof of sphenoid sinuses
- Lefort I down-fracture approach provides better surgical access in more complicated cases
27
What are the functions of the fascial compartments of the neck?
- The fascial compartments of the neck surround layers and prevent the spread of infection
- Pus that collects in the retropharyngeal space can travel down to the mediastinum
28
What are the platysma muscles and how are they innervated?
- Located immediately deep to the skin within the superficial fascia of the neck
- Belong to the muscles of facial expression
- Innervated by CN VII (facial nerve)
29
What is the carotid sheath and where is it located?
- Deep to investing fascia; located anterolaterally in neck posterolateral to thyroid gland
- Tube-like bilateral compartments of deep fascia
- Attach superiorly to base of skull (around jugular foramen and entrance to carotid canal)
- Blend inferiorly with mediastinal fascia
30
What innervates the strap muscles?
- All except thyrohyoid are innervated by the ansa cervicalis of the cervical plexus, which arises from the anterior rami of C1-C3
- Thyrohyoid is innervated by C1, which travels within the hypoglossal nerve
31
Describe the embryology of the thyroid gland
- Thyroid gland begins development in the 4th week of embryogenesis as a midline proliferation of pharyngeal epithelium at junction between the anterior 2/3 and posterior 1/3 of the tongue
- The point of origin in the tongue persists as the foramen caecum
- The thyroid then migrates inferiorly whilst remaining attached to the tongue via the thoracic duct
- Gland reaches its final position in the 7th week of development with the two lobes joined at the isthmus, in front of the trachea
- By 12 weeks, primitive follicles are visible as simple epithelium surrounding a central lumen, and now able to trap iodide and respond to TSH
32
What are the failures of embryological development for the thyroid gland?
- Failure of development - congenital hypothyroidism
- Failure of descent - lingual thyroid
- Excessive descent - retrosternal location in mediastinum
- Failure of thyroglossal duct to regress - thyroglossal duct cyst
33
What is the location and structure of the thyroid gland?
- Usually consists of two lateral lobes (right and left) and isthmus (narrow connecting band)
- Lobes attach to lateral aspects of thyroid and costal cartilages, and to the trachea
- Situated between vertebral levels C5-T1
- Isthmus lies anterior to 2nd or 3rd cartilages of the trachea
- A normal thyroid gland usually weighs ~ 25g
- Clinical notes: due to relationship with larynx and trachea, a lump in the gland (e.g. thyroglossal duct cyst) or enlarged gland (e.g. goitre) will move superiorly then inferiorly with the larynx during swallowing
- Four parathyroid glands are located on the posterior surfaces of the thyroid gland lateral lobes
34
What is the pyramidal lobe?
- Remnant of the thyroglossal duct
- 28-55% prevalence
- Most commonly originates from left lateral lobe
- 9.2% are not connected to the main thyroid gland
- Most attach superiorly to the thyroid cartilage
- May extend as far superiorly as the hyoid bone
35
What is located anteriorly to the thyroid gland?
sternothyroid, superior belly of the omohyoid and sternohyoid (strap muscles)
36
What is located laterally to the thyroid gland?
carotid sheath
37
What is located medially to the thyroid gland?
larynx, pharynx, trachea and oesophagus, external laryngeal and recurrent laryngeal nerves
38
What is the blood supply to the thyroid gland and where is it located?
- **Superior thyroid artery:** arises as the first branch of the external carotid artery
- It lies in close proximity to the external branch of the superior laryngeal nerve (innervates the larynx)
- **Inferior thyroid artery:** arises from the thyrocervical trunk (a branch of the subclavian artery)
- It lies in close proximity to the recurrent laryngeal nerve (innervates the larynx)
39
What is the venous drainage of the thyroid gland?
- Venous drainage is carried by the superior, middle, and inferior thyroid veins, which form a venous plexus around the thyroid gland
- The superior and middle veins drain into the internal jugular vein and the inferior empties into the brachiocephalic vein
40
What is the innervation of the thyroid gland?
- Autonomic nerve supply
- Parasympathetic: vagus nerves
- Sympathetic: superior, middle, and inferior ganglia of the sympathetic trunk
41
What is the lymphatic drainage of the thyroid gland?
The lymphatic drainage of the thyroid is to the paratracheal and deep cervical nodes
42
What are the islets of langerhans in the endocrine pancreas and what do they secrete?
- **⍺ cell (blue):** secrete glucagon which acts to increase blood glucose levels
- **β cell (red):** secrete insulin which acts facilitate the uptake of glucose into body cells
- **ƍ cell (green):** secrete somatostatin which inhibits the exocrine, endocrine and CNS systems
43
What are the adrenal glands? and where are they located?
- Bilateral glands, 4-5 grams each
- Located in the retroperitoneum, superior and medial to the upper pole of the kidneys
- Separated from the kidneys by a fascial septum
- Have two anatomical and functional parts which secrete hormones, the cortex and the medulla
44
How is the adrenal cortex organised?
- Organised into three zones which correlates with function
- Zona glomerulosa - mineralocorticoids e.g. aldosterone
- Zona fasciculata - glucocorticoids e.g. cortisol
- Zona reticularis - sex steroids and glucocorticoids
45
What is the adrenal medulla and how is it innervated?
- Central core of the adrenal gland
- Innervated by pre-sympathetic fibres of sympathetic nervous system
- Neuroendocrine (chromaffin) cells - secrete catecholamines (adrenaline and noradrenaline)
46
What hormones are secreted by the ovary?
It is influenced by the pituitary gland and secretes oestrogen and progesterone
