Endocrine Glands and Specialised cells

• The endocrine system is a chemical messenger system comprising of feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs

  Contrasted to exocrine glands, which secrete hormones to the outside of the body (eg salivary gland, sweat gland)
• PITUITARY

  • Pea-shaped gland, measuring about 1 – 1.5cm in diameter.
  • Lies in the hypophyseal (pituitary) fossa of the sella turcica of the sphenoid bone.
  • Attached to the hypothalamus by a stalk called the infundibulum.
  • Anterior lobe (adenohypophysis). Posterior lobe (neurohypophysis).
• Pituitary

  Produces hormones:

  • Central diabetes insipidus caused by deficiency of vasopressin
  • Gigantism/acromegaly caused by excess of growth hormone in childhood/adulthood
  • Hypothyroidism - deficiency of TSH
  • Hyperpituitarism, increased secretion of one or more hormones normally produced by pituitary gland
  • Hypopituitarism, decreased secretion of one or more hormones normally produced by pituitary gland
  • Panhypopituitarism, decreased secretion of most of the pituitary hormones
  • Pituitary adenomas, mostly benign tumours that occur in the pituitary gland
• THYROID

  • Located anteriorly in the neck at the level of the C5 – T1 vertebrae.
  • Lies anterolateral to the larynx and trachea.
  • The isthmus lies anterior to the 2nd – 3rd tracheal rings and unites the two lobes of the thyroid gland.
• The thyroid consists of follicles

  Follicular cells

  • Thyroxine T4
  • Triiodothyronine T3

  Parafollicular cells (less)

  • Calcitonin – calcium homeostasis
• Arterial supply of the thyroid:

  • superior thyroid
  • ascending pharyngeal
  • Lingual
  • facial
  • occipital
  • posterior auricular
  • maxillary
  • superficial temporal
• Nerves of the thyroid

  • Superior, middle and inferior cervical (sympathetic) ganglia
  • Via cardiac, superior and inferior plexuses which accompany arteries
  • Vasomotor control of blood supply
  • Endocrine secretion regulated by pituitary hormones
  • TSH
• Lymphatic drainage of thyroid

  Prelaryngeal, pretracheal, paratracheal nodes to superior and inferior deep cervical nodes

  Brachiocephalic lymph nodes and thoracic duct
• Thyroid conditions

  • Hypothyroidism
  • Hyperthyroidism
  • Graves’ disease
  • Hashimoto’s thyroiditis
  • Goitre - Non neoplastic non inflammatory enlargement due to iodine deficiency
  • Carcinoma - Papillary, follicular, medullary. Multiple neoplastic syndromes (MEN)
• Thyroid surgery complication - Potential to cause unilateral vocal cord paralysis. Patients with this typically complain of new-onset hoarseness, changes in vocal pitch, or noisy breathing (stridor)
• Parathyroid gland

  • Consists of two pairs of glands (four) – right and left, superior and inferior parathyroid glands. The exact number can vary between different people.
  • Lie on the posterior surface of the thyroid gland outside its capsule.
  • The superior parathyroid gland lies above the point of entry of the inferior thyroid artery into the thyroid gland.
  • The inferior parathyroid gland lies below the point of entry of the inferior thyroid artery into the thyroid gland.
• Nerve supply of the parathyroid gland

  Nerve fibres supplying the parathyroid gland are derived from the thyroid branches of the cervical (sympathetic) ganglia.

  These are vasomotor fibres and not secretomotor, because secretions are hormonally regulated.
• Lymphatic vessels of parathyroid drain with those of the thyroid gland into the deep cervical and paratracheal lymph nodes.
• Blood supply of parathyroid

  Branches of the inferior thyroid arteries.

  The veins drain into the thyroid plexus of veins of the thyroid gland and trachea.
• Histology of parathyroid

  The Chief or Principal cell - more numerous, secretes parathyroid hormone (PTH)

  The Oxyphil cells - functions not well known but may secrete parathyroid hormone in cancer of the parathyroid gland.
• Primary hyperparathyroidism results from a hyperfunction of the parathyroid glands themselves. The oversecretion of PTH is due to a parathyroid adenoma, parathyroid hyperplasia, or rarely, a parathyroid carcinoma. This disease is often characterized by the quartet, stones, bones, groans, and psychiatric overtones, referring to the presence of kidney stones, hypercalcemia, constipation, and peptic ulcers, as well as depression, respectively
• Secondary hyperparathyroidism is due to physiological (i.e. appropriate) secretion of parathyroid hormone (PTH) by the parathyroid glands in response to hypocalcemia (low blood calcium levels). The most common causes are vitamin D deficiency (caused by lack of sunlight, diet or malabsorption) and chronic kidney failure.
• Tertiary hyperparathyroidism: raised PTH and raised serum calcium. It is differentiated from primary hyperparathyroidism by a history of chronic kidney failure and secondary hyperparathyroidism
• Adrenal gland

  “Suprarenal” gland

  Between superior medial kidneys and diaphragm in perinephric fat

  Fascia connected to diaphragm

  Thin fascia separates from kidneys

  Right

  • “Pyramidal” in shape
  • Related to IVC and liver

  Left

  • Crescent shaped
  • Related to spleen, stomach, pancreas
• Blood supply of adrenal gland

  Arterial supply

  • Abundant
  • Superior suprarenal artery
  • From inferior phrenic artery
  • Middle suprarenal artery
  • From abdominal aorta
  • Inferior suprarenal artery
  • From renal artery

  Venous drainage

  • Right suprarenal to IVC
  • Left suprarenal to left renal vein
• Adrenal Cortex

  • Corticosteroids and androgens

  3 zones

  Zona glomerulosa (Mineraloocorticoids)

  • Aldosterone
  • Kidneys retain Na and water and excrete K to

  increase blood pressure and volume

  • ACTH transient control
  • Angiotensin II when BP drops

  Zona fasciculata (Glucocorticoids)

  • Cortisol, corticosterone, cortisone
  • ACTH
  • Cortisol enhances activity of glucagon and catecholamine
  • Enhances metabolism

  Zona reticularis

  • Androgens
• Adrenal Medulla

  Chromaffin cells - Secrete catecholamines:

  • Adrenaline and noradrenaline
• Adrenal conditions

  • Phaeochromocytoma
  • -Paraganglioma – catecholamine secreting tumour
  • -Hypertension
  • Neuroblastoma
  • -Adrenal medulla
  • -Childhood cancer
  • Cushing’s Syndrome
  • -Glucocorticoid excess
  • —Disease – ACTH-producing pituitary adenoma-
  • Conn’s Syndrome
  • -Hyperaldosteronism
  • Adrenal cortical insufficiency
  • -Primary or secondary
  • -Addison’s disease
  • -Adrenal crisis
  • Congenital adrenal hyperplasia
  • -Androgen excess
  • Haematoma
  • -Severe stress/sepsis
  • -Trauma
  • Metastases
  • -Rich blood supply
• Pancreas

  • Exocrine secretion
  • Pancreatic juice from acinar cells
  • Into pancreatic ducts and duodenum
  • Endocrine secretions
  • From pancreatic islet cells of Langerhans
  • Glucagon (A cells) and insulin (B cells)
  • Glucose metabolism
  • Somatostatin (D cells) and pancreatic polypeptide (F cells)
  • Modulate action on glucagon and insulin secretion
• Ovaries

  • Oestrogen and progesterone
  • Inhibin
• Testes

  Testosterone

  Inhibin
• Identify the location of the thyroid glands on the body

  Located anteriorly in the neck at the level of the C5-T1 vertebrae

  Lies anterolateral to the larynx and trachea

  The isthmus lies anterior to the 2nd-3rd tracheal rings and unites the two lobes of the thyroid gland
• Describe the structure of the thyroid gland

  Has two lobes (left and right) and a pyramidal lobe in about 50% of persons.

  Has fibrous capsule and made up of thyroid follicles

  Wall of the follicles consists mainly of follicular cells and few parafollicular cells in between the follicles
• Outline the vasculature of the thyroid gland

  • highly vascularised
  • right and left superior thyroid arteries - first branch of the external carotid arteries
  • right and left inferior thyroid arteries - largest branch of thyrocervical trunks of the subclavian arteries
  • unpaired thyroid ima artery from brachiocephalic trunk
  • superior thyroid veins
  • inferior thyroid veins
  • veins form thyroid plexus of veins
  • superior and inferior thyroid veins accompany arteries
• lymphatic vessels of thyroid drain into:

  • prelaryngeal nodes, which drain into the superior deep cervical lymph nodes
  • pretracheal and paratracheal nodes, which drain into inferior deep cervical lymph nodes
  • some lymphatic vessels may drain into brachiocephalic lymph nodes of thoracic duct
• secretions of thyroid gland

  follicular cells secrete thyroid hormones

  thyroxine (tetraiodothyronine/T4)

  triiodothyronine (T3)

  parafollicular cells secrete hormone calcitonin for calcium homeostasis
• Nerve supply of thyroid

  Derived from superior, middle and inferior cervical (sympathetic) ganglia.

  Reach thyroid through cardiac, superior and inferior thyroid peri-arterial plexuses that accompany thyroid artery

  Vasomotor fibres, not secretomotor, because secretions are hormonally regulated
• Describe location of parathyroid gland

  Two pairs of glands - right and left superior and inferior parathyroid glands. Number can vary.

  Posterior surface of thyroid outside its capsule

  Superior parathyroid gland lies above point of entry of inferior thyroid artery into thyroid

  Inferior parathyroid gland lies below point of entry of inferior thyroid artery into thyroid
• Describe structure of parathyroid gland

  Two kinds of cells.

  Chief or Principal Cell - more numerous, secrete PTH

  Oxyphil Cell - functions not well known but may secrete PTH in cancer of parathyroid gland
• Blood supply of parathyroid

  Branches of inferior thyroid arteries

  Also superior thyroid arteries, thyroid ima artery or laryngeal artery, tracheal and oesophageal arteries.

  Veins drain into thyroid plexus of veins of thyroid and trachea

  Lymphatic vessels drain with thyroid into deep cervical and paratracheal lymph nodes
• Nerve supply of parathyroid

  Derived from thyroid branches of cervical (sympathetic) ganglia

  Vasomotor, not secretomotor, because secretions are hormonally regulated
• Two histological parts of adrenal gland and their embryological origins

  outer cortex, derived from intermediate mesoderm

  inner medulla, derived from neural crest cells
• Identify specialised cells within medulla and secretions

  chromaffin cells (like postsynaptic sympathetic ganglion neurons)

  secrete catecholamines

  adrenaline and noradrenaline
• Blood supply of adrenal gland

  Superior and inferior suprarenal arteries from phrenic arteries

  Middle suprarenal arteries from abdomina aorta

  right suprarenal vein drains into inferior vena cava

  left suprarenal vein often joined by inferior phrenic to drain into left renal vein
• Describe some of the adrenal gland associated pathologies

  • phaeochromocytoma
  • neuroblastoma
  • cushing's syndrome
  • conn's syndrome
  • suprarenal cortical insufficiency