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203: The endocrine system > Anatomy > Flashcards

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Location of the hypophysis

Encased in the sphenoid bone
- Sella turcica

Inferior to the hypothalamus
- Connected by the infundibulum

Posterior to the optic chiasm


Structure of hypophysis

Divided into
- Neurohypophysis, posterior--> Neural down-growth of the diencephalon

- Adenohypophysis, anterior--> Outpouch of ectoderm, Rathke's pouch (oral cavity)


Function of the hypophysis

Master gland
- Secretes hormones to to all glands, control their secretion.


Arterial supply to the hypophysis

Superior and Inferior hypophyseal artery
- From ICA

Superior supplies
- Median eminence
- Upper infundibulum

Inferior supplies
- Neurohypophysis
- Lower infundibulum

Arteries supplying the infundibulum and median eminence end as capillary plexus as the anastomose.


Venous drainage of the hypophysis

Portal system

Capillary plexus at the stalk ending and median eminence drain into portal veins.
- Form secondary capillary plexus at the anterior pituitary.
- Allows substances from the hypothalamus to reach the anterior pituitary.


Compare hormonal from neurotransmission

Hormonal---> Release of hormones
- Much slower
- Transported every in the body via circulatory system

Neurones-->Neural impulse, using neurotransmitters
- Very fast (1-2ms)
- Act locally from pre to postsynaptic neurones, microns apart


Thyroid location

Anterior to the trachea
- Lateral to thyroid cartilage

Recurrent laryngeal nerves passes deep to the posteromedial surface of the lobes.


Type of endocrine glands [3]

Discrete- separate and distinct. Only secretes hormones
- Hypophysis
- Thyroid and parathyroid
- Adrenal

Larger glands- both exocrine and endocrine function
- Pancreas
- Kidney
- Ovaries/ testes
- Placenta

Diffuse neuroendocrine
- Nerve cells with endocrine function


Anatomy of thyroid

Two lobes joined by the isthmus
- Covers 5-6 cartilage rings
- Covers cricoid and lower cartilage


Arterial supply of the thyroid

Superior thyroid
- From external carotid

Inferior thyroid
- From thyrocervical trunk (subclavian)


Venous drainage of the thyroid gland

Plexus drains into the superior, middle and interior thyroid veins.

Thyroid veins drain into
- Internal jugular (superior and middle)
- Brachiocephalic (inferior)


Development of the thyroid

Endodermal origin
- From the floor of the pharynx, near the base of the tongue


Thyroid function

Release of thyroid hormones that regulate growth and development- T3, T4
- Under the control of TRH and TSH from the hypothalamus and anterior pituitary



Incision in the cricothyroid membrane to establish patent airway.


Parathyroid location

Deep to the lateral lobes of the thyroid
- Posterior aspect of the thyroid capsule.

Can also be located elsewhere between the carotid bifurcation and the mediastinum.


Parathyroid origin

Third pharyngeal pouch
- inferior parathyroid

Fourth pharyngeal pouch
- Superior parathyroid

The pouches grow caudally towards the thymus to their adult positions.


Anatomy of the parathyroid gland

2 pairs- 4 altogether
- Superior and inferior
- Very small- 40mg, size of the grain of rice.


Arterial supply of the parathyroid

Mainly inferior thyroid artery
- From Thyrocervical trunk (subclavian)

Superior thyroid
- From external carotid


Venous drainage of parathyroid

Superior, middle and thyroid veins
- Drains into Internal jugular and brachiocephalic


Nervous supply of the parathyroid

Middle and inferior cervical ganglion.


Function of the parathyroid

Composed predominantly of epithelial chief cells
- Secretes PTH

PTH regulates blood calcium and phosphate levels.


Parathyroid implication of thyroidectomy

Parathyroid MUST be conserved
- Unless calcium and phosphate regulation is disrupted.

Leads to hypocalcaemia--> Tetanic contraction---> death.


Adrenal gland location

Superior to kidneys
- At T12 level
- Retroperitoneal


Adrenal gland gross anatomy
- Shape
- Layers
- Size

Left gland---> Semilunar

Right gland---> Pyramidal

- Outer capsule
- Cortex
- Medulla

- 3.5-5g


Adrenal gland orgin

Medulla---> Neural function
- Neural crest origin

Cortex---> Exocrine
- Mesodermal orgin


Adrenal medulla function

Release of catecholamines
- NA and ADR from chromaffin cells

Cells act are modified sympathetic post-ganglionic

Release of catecholamines= fight or flight
- Raised HR, BP
- Relaxation of SM viscera.


Adrenal cortex function

Release of adrenal corticosteroids and adrenal androgens
- Glucocorticoids, from zona fasciculata---> Maintains blood glucose concentration
- Mineralocorticoids, from zona glomerulosa---> Maintains Na+ levels

Secretion of hormones under the control of ACTH, RAS.


Adrenal medulla ANS

Receives direct preganglionic fibres from the sympathetic trunk
- Allows fast fight-or-flight response

Impulse--->release of Ach--> Chromaffin cells---> Release of NA, ADR

Also receives post-ganglionic fibres from coeliac ganglion
- Supplies blood vessels that penetrates the cortex


Arterial supply of the adrenal gland

Superior suprarenal artery
- From Inferior phrenic

Middle suprarenal
- From aorta

Inferior suprarenal
- From renal

Arteries branch before entering capsule

- Arteries branch into subcapsular plexus---> sinusoids

- Arteries pass through cortex, into medulla---> Cortical activity can influence medulla


Venous drainage of the adrenal glands

Adrenal veins
- Drain into IVC (R)
- Drain into left renal vein (L)