Lec3 - Nuts and Bolts of the Endocrine System Flashcards
The endocrine system is a:
System of hormone secreting glands
The endocrine system is essential for:
Normal growth and development
Adaptation to internal and external environment
Contribute to the process of sexual reproduction
The nervous system and the endocrine system interact at the:
hypothalamus
e.g. in the regulation of temperature, circadian rhythms and hunger etc
Characteristics of the hormones affecting other cells’ metabolism
Number of molecules of hormone available
Number of receptors available
Affinity of hormone to receptor
Name the chemical classifications of some hormones
Steroid e.g. testosterone, oestrogen
Peptide/ protein e.g. oxytocin, ADH, insulin
(Amine e.g. adrenaline, noradrenaline and dopamine)
NO = nitric oxide is both a neurotransmitter and hormone
Name the sources of the hormone types
Steroid hormones: adrenal cortex, ovaries and testes (from embryonic mesodermal tissue)
Protein/peptide: adenohypophysis (from ectodermal tissue of the oral cavity)
Thyroid, parathyroid, pancreas (from the endodermal origin of GI tract)
Amine: thyroid, adrenal medulla (from ectodermal origin)
What is meant by diffuse neuroendocrine system?
Scattered nerve cells with endocrine function
Where is the pituitary gland located?
In the SELLA TURCICA of the sphenoid bone
What is the function of the pituitary gland?
It produces hormones which influence the activity of the other endocrine glands
What part of the pituitary gland is the adenohypophysis?
The anterior portion - the glandular part; outpouching of ectoderm of oral cavity - Ratke’s pouch
What part of the pituitary gland is the neurohypophysis?
The posterior portion - the neural part - down growth from the diencephalon of the brain
What is the blood supply to the pituitary gland?
Superior hypophyseal artery
Inferior hypophyseal artery
The superior and inferior hypophyseal arteries are branches of which artery?
Internal carotid
The superior hypophyseal artery supplies:
the median eminence &
upper part of the stalk/infundibulum
The inferior hypophyseal artery supplies:
the neurohypophysis &
lower part of the stalk/ infundibulum
The arteries that supply the median eminence and stalk/infundibulum end as what?
Capillary plexuses
The capillary plexuses in the median eminence and stalk ending are drained by:
portal veins
The portal veins then pass to:
The anterior lobe of the pituitary gland where they form a secondary plexus
What is the significance of the portal veins which run from the capillary plexuses in the median eminence and stalk ending to the anterior lobe of pituitary?
It provides a route for the neurosecretory substances released from the hypothalamus to also reach the anterior lobe
What controls hormone release from both adenohypophysis and neurohypophysis
Signals from the hypothalamus
What is the shape and location of the thyroid gland?
A bilobed gland in the neck (4x2 cms in size) weighing ~30g
What is the point of connection of the two lateral lobes called?
ISTHMUS - lies anterior to the trachea
What the upper and lower limits of the lobes of the thyroid gland?
From just below the oblique line of the thyroid cartilage to the 5/6th tracheal ring, immediately anterior to the trachea
What type of tissue is the thyroid gland derived from?
Endoderm
How does the thyroid gland develop?
It develops as a growth from the floor of the pharynx, near the base of the tongue
What is the role of the thyroid gland?
Essential role in regulating tissue metabolism, growth and development
What is secreted by the thyroid gland?
T3 - triiodothyronine
T4 - thyroxine
What is the arterial supply to the thyroid gland?
Superior thyroid artery from the external carotid
Inferior thyroid artery from the subclavian artery
What are the veins that drain the thyroid gland?
From an extensive plexus, the blood drains into the internal jugular and brachiocephalic veins
What type of surgery of the thyroid gland do you need to be careful with and why?
Cricothyrotomy - damage to the recurrent pharyngeal nerve from the vagus
How many parathyroid glands are there?
4 - 2 superior and 2 inferior
What is the location of the parathyroid glands?
Embedded in the capsule of the thyroid gland in the posterior aspect
How big are the parathyroid glands?
Very small - like a grain of rice and weight 40mg
How do the parathyroid glands develop?
Develop from endoderm tissue, mostly from cells originating from the 3rd/4th pharyngeal pouches and migrate caudally with the thymus
What is the role of the parathyroid glands?
To secrete parathyroid hormone
To regulate calcium and phosphate levels in homeostasis
Why must the parathyroid glands be preserved during thyroidectomy?
Because if removed, the blood calcium levels all and muscles including respiratory and laryngeal go into tetanic contraction leads to death
What is tetanic contraction and why does it occur?
Sodium and calcium compete for entry into cells
If calcium is removed, sodium is able to enter the cell freely, the cell becomes more positive, reaches threshold and action potentials are constantly fired. This causes constant contraction of muscle and they don’t relax
VAN of the parathyroid glands
Veins: superior, middle and inferior thyroid veins
Arteries: primarily inferior thyroid arteries (but also superior)
Nerves: from middle and inferior cervical ganglions
What is the location of the adrenal glands?
Superior pole of the kidneys - T12 and retroperitoneal
What are the shapes of the adrenal glands?
Right is pyramidal
Left is semilunar
What is the function of the adrenal glands?
Hormone release in response to stress
What is the origin of the adrenal glands?
Cortex derived from mesoderm
Medulla derived from neural crest cells
What is the function of the cortex?
To secrete corticosteroids
Cells adjacent to the capsule secrete MINERALOCORTICOIDS e.g. ALDOSTERONE - function to maintain electrolyte balance
Deeper part of cortex secretes GLUCOCORTICOIDS e.g. HYDROCORTISONE - affect metabolism and electrolyte balance
Inner part of cortex secretes ADRENAL ANDROGENS e.g. TESTOSTERONE
What are the secretory cells of the medulla?
Chromaffin cells
Where do chromaffin cells develop from?
The same embryonic tissue as the sympathetic ganglia
What is the medulla regarded as?
Modified sympathetic ganglion (ANS)
What does the medulla secrete?
Adrenaline and smaller amounts of noradrenaline (catecholamines)
What effect does secretion of adrenaline and noradrenaline from the medulla have?
“Fight or flight” response - affects heart rate, metabolism, blood pressure and smooth muscle of viscera
What is the arterial supply to the adrenal glands?
Superior suprarenal artery (from the inferior phrenic artery)
Middle suprarenal artery (from aorta)
Inferior suprarenal artery (from renal)
What controls the thyroid gland?
The hypothalamus releasing Thyrotrophin releasing hormone (TRH)
Pituitary gland releasing Thyroid stimulating hormone (TSH)
Describe the arterial supply to the cortex and medulla of the adrenal gland
The arteries branch before they enter the capsule, and the rami supply the cortex and medulla
Cortical arteries give rise to a SUBCAPSULAR PLEXUS and turn into CORTICAL SINUSOIDS that distribute blood to cortical cells
How many sources of blood does the medulla receive?
Two
What are the two sources of blood received by the medulla
- The rami from the branched arteries (superior, middle and inferior suprarenal arteries) supplying the cortex and medulla
- The medullary arteries which pass through the cortex to supply the medulla
What is the significance of the two sources of blood to the medulla?
The hormones secreted by cortical cells can influence the activity of the cells in the medulla
e.g. cortisol mediates NA conversion to adrenaline
What is the venous drainage of the adrenal glands?
Adrenal veins drain into the IVC (on the right)
or renal vein (on the left hand side)
The activity of the adrenal glands is under the control of?
The hypothalamus & pituitary - ACTH
Sympathetic division of the ANS - coeliac plexus and splanchnic nerves
How does the release of ACTH affect the adrenal glands?
ACTH stimulates secretion/release of corticosteroids
Describe the ANS control of the medulla
The medulla is under direct control of the ANS - sympathetic division & therefore produces a very fast response
Preganglionic sympathetic fibres end in the chromaffin cells of the medulla
The chromaffin cells release catecholamines into adjacent circulation when they receive impulses from the preganglionic sympathetic fibres
Give the definitions of the following words: Endocrine Autocrine Paracrine Neuroendocrine
Endocrine - the action of a hormone on a target organ far away from the secreting cell
Autocrine - the action of the hormone of the secreting cell itself
Paracrine - the action of the hormone on the adjacent cell
Neuroendocrine - neural stimulation of endocrine cells to secrete hormones e.g. medulla of the adrenal gland
What are the clinical manifestations of endocrine diseases?
Depends on whether it is: A hormone overproduction Hormone underproduction OR Tumour/mass/lesion which can be functional or non-functional
What is the difference between a functional and non-functional tumour?
A functional tumour is associated with an overproduction of hormones
A non-functional tumour is associated with a pressure effect on surrounding tissues or structures
What is the overall structure of an endocrine gland?
A functional unit consisting of cuboidal secretory cells with a lumen at the centre
Not all functional endocrine units have a lumen - pituitary and parathyroid gland cells have no lumen
Secretory cells supported by myoepithelial cells
Describe three types of cells of the anterior pituitary gland
Acidophils - take up acidic dyes - stain pink
Basophils - take up basic dyes - stain purple
Chromophobe - no specific staining features
Does the staining pattern relate to a specific hormone secretion?
No - ACTH is secreted by both basophils and chromophobes
Name the types of pathology of the pituitary gland
Pituitary adenoma (benign tumours) - can be functional = secreting hormones causing HYPERPITUITARISM or non-functional = not producing hormones - a pressure effect causing HYPOPITUITARISM
What are the space occupying effects of functional or non-functional adenomas?
Diplopia - double vision Impaired vision because the skull cannot expand to allow for extra space being taken up Headaches Nausea Vomiting
What effect do cancers that metastasise to the brain have?
Space occupying - build up of pressure
What are the names of the two hormones secreted by the thyroid gland?
Triiodothyronine T3
Thyroxine T4
What is the function of T3 and T4?
To stimulate metabolic rate
What is required in order to synthesise T3 and T4?
Iodine
Where is iodine commonly found?
Sea salt
What condition is associated with a lack of iodine?
GOITRE - an enlarged thyroid gland
Why does the thyroid gland enlarge when there is a lack of iodine?
To absorb the maximum amount of iodine
Describe the composition of a ‘normal’ thyroid gland
Thyroid tissue is composed of follicles with variable sized lumina
The follicles contain colloid with an eosinophilic/pink appearance
The follicles are lined with cuboidal cells
The thyroid gland is highly vascular - True or False?
True
What is the purpose of the fenestrations in the endothelial cells lining the capillaries around the thyroid gland?
The fenestrations allow passage of the hormone into the circulation
What type of cells are found between the follicles?
Parafollicular cells or C cells
What is the function of C cells?
C cells secrete calcitonin which promotes reduction of calcium concentration in the blood
Describe the various types of pathology of the thyroid gland and their effects.
Goitre - enlargement of the thyroid gland - can be euthyroid
Grave’s Disease - excess T3 and T4 low TSH - causing hyperthyroidism
Hashimoto’s disease - low T3 and T4 high TSH - aka thyroiditis - causing hypothyroidism
Adenoma - can be euthyroid
Cancer - can be euthyroid
Why does multi-nodular goitre occur?
Multi-nodular just means enlargement of many nodes
Due to a lack of iodine
Goitre due to hyperplasia and hypertrophy of the thyroid cells
The gland enlarges to maximise the amount of iodine absorbed
How can patients with goitre be euthyroid?
Because the enlarged gland means more iodine is absorbed and so overcomes the deficiency - therefore the pt is euthyroid
What gives rise to the irregular appearance of the thyroid gland in goitre?
Fibrosis of the thyroid tissue but the pt is euthyroid
Why is it important to assess the radiology before thyroidectomy surgery?
The patient might arrest even after successful thyroidectomy due to tracheomalacia
What is tracheomalacia?
softening of the trachea which collapses and obstructs the airways
What do you do to prevent cardiac arrest during or after a thyroidectomy?
Intubate the patient
What causes Grave’s disease?
Autoantibodies which stimulate TSH receptors
What is Grave’s disease?
Diffuse enlargement of the thyroid gland - goitre due to hyperplasia of thyroid cells
What characteristic appearance does a Grave’s disease thyroid gland have following thyroidectomy?
Vascular surface
What characteristic appearance does the colloid have in Grave’s Disease and why?
The colloid has a ‘soap bubble’ appearance due to hyperactivity
Name two associated consequences of Grave’s Disease
Infiltrative opthalmopathy - accumulation of soft tissue and inflammatory cells behind the eye leading to proptosis
Infiltrative dermopathy - thickening and induration of the skin on the anterior shin - pre-tibial myxoedema
What is Hashimoto’s thyroiditis?
An autoimmune disease where the immune system destroys its own thyroid tissue
There is progressive depletion of thyroid cells by inflammation & replaced by fibrosis
What happens to T3, T4 and TSH in Hashimoto’s thyroiditis?
Low T3/T4 and high TSH because the negative feedback is disrupted
Name the four main types of thyroid carcinoma
- Papillary carcinoma (75-85%) increased risk of lymph node metastasis
- Follicular carcinoma (10-20%) increased metastasis to bone, lung and liver
- Medullary (5%) - arises from C cells; 20% as with MEN2 syndrome (multiple endocrine neoplasm)
- Anaplastic (<5%) - older patients & poor prognosis
What is a follicular adenoma?
A benign tumour of the thyroid follicular cells - where the follicular cells join together
What do parathyroid glands secrete?
Parathyroid hormone (PTH)
What is the function of PTH?
To control levels of calcium in the blood - a decrease in blood calcium stimulates PTH secretion
Describe the types of pathology of the parathyroid glands
Parathyroid adenoma - involving one gland
Parathyroid hyperplasia - involving all four glands
Both cause hypercalcaemia
The adrenal glands consist of the adrenal cortex and medulla which are embryonically, morphologically and functionally distinct. True or false?
True
What colour are normal adrenal glands and why?
Orange/yellow because the cells are rich in lipids
Describe the different causes of adrenocortical hyperactivity
Adrenal hyperplasia, adenoma or cancer (rare)
Cushing’s syndrome
Conn’s syndrome
Adrenogenital syndrome
What is Cushing’s syndrome?
Where there are excessive levels of cortisol
What is Conn’s syndrome?
Excess levels of aldosterone
What’s is adrenogenital syndrome?
Excess androgens
Describe a cause of adrenocortical insufficiency
Addison’s disease
What are the two types of adrenal cortex adenoma?
Functional adrenal cortex adenoma - can cause Cushing’s or Conn’s Syndrome
Non-functional adrenal cortex adenoma
What is the function of the cells of the adrenal medulla?
To secrete catecholamines in response to intense emotional reaction - fight or flight hormones
Secretion of catecholamines (noradrenaline, adrenaline, cortisol) results in:
vasoconstriction, increased heart rate, increased blood glucose - part of organism’s defence to stress
Why do adrenal medulla cells stain darker than cortical cells?
Because medullary cells are neuroendocrine cells
What is a phaeochromocytoma?
Adrenal medulla tumour
0.1 -0.3% cause of treatable hypertension
Why are phaeos called 10% tumours?
Because: 10% are familial as part of the MEN2 syndrome 10% are extra adrenal 10% are bilateral 10% are malignant 10% arise in childhood
What occurs as a result of a phaeo?
Due to high levels of catecholamines, there is a precipitous increase in BP, tachycardia, palpitations, headache, sweating, tremor and sense of apprehension
What are complications of increased BP?
Congestive cardiac failure (CCF)
Ischaemic heart disease (IHD)
Cardiac arrhythmias
Cerebrovascular accident (CVA)
