Nuts and bolts of the endocrine system Flashcards
Hormones are…..
involved in…
forming part of ……systems
mediator molecules
sexual reproduction, normal growth and development, adaptation to internal and external environment
endocrine and nervous (neuroendrocrine) - these two systems interact at the hypothalamus
NO is an example of a neuroendocrine transmitter
Hormones are…..
involved in…
forming part of ……systems
mediator molecules
sexual reproduction, normal growth and development, adaptation to internal and external environment
endocrine and nervous (neuroendrocrine) - these two systems interact at the hypothalamus
NO is an example of a neuroendocrine transmitter
Generally outline the path of a hormone
Hormone –> interstitual space –> blood stream/lymphatic system
State the three determents of the affect of hormones
- Number of molecules available (concentration)
- Number of receptor available
- Affinity hormone-receptor
Give an example for the following hormone types (and their origins):
- Steroid:
- Peptide:
- Amine:
- oestradiol, testosterone (from ovaries, testes, adrenal cortex-mesodermal origin)
- ADH, oxytocin, insulin (from thyroid (endorm), adrenal medulla- ectodermal origin)
- adrenaline, NA, DA (adenohypophysis - ectodermal orgin; thyroid/parathyroid, pancreas- endodermal origin; scattered endocrine cells in epithelium of GIT and lungs)
Why is the hypophysis (pituitary gland) describes as a compound gland?
Location? Function? Size? Blood supply? Venous drainage? Control?
- Compound as it has 2 origins: adenohypophysis - glandular outpouch of ectoderm of oral cavity, neurohypophysis- neural, downgrowth from diencephalon)
- Sella turcica, sphenoid bone
- Produces hormones that influence acitivity of other endocrine glands
- no larger than a pea
- Superior hypophyseal supplies median eminence, upper part of stalk; inferior hypophyseal supplies neurohypophysis, lower part of stalk
- Capillary plexuses drained by portal veins –> anterior lobe of pituitary –> veins form secondary plexus
- Controlled by signals from the hypothalamus
What is the benefit of having a portal vein system in the pituitary gland?
! Provides a route for neurosecretory substances released from hypothalamus to also reach anterior lobe
Consider the thyroid gland
Appearance? Location? Germ layer origin? Function? Blood supply? Venous drainage? Control?
Why must care be taken during cricothyrotomy?
- Bilobed in neck, 30g (2 lateral lobes connected by an isthmus that course anterior to the trachea)
- Below oblique line of thyroid cartilage to 5/6 tracheal ring; immediately anterior to trachea
- Endoderm origin, develops as growth from floow or pharynx
- Function: regulates tissue metabolism, growth and development
- Blood supply: superior thyroid (from external carotid) and inferior thyroid (from subclavian)
- Venous drainage: (from an external plexus) into IJV and BCV
-Control: hypothalamus –> thyrotrophin releasing hormone / hypophysis –> TSH
Recurrent nerve (from vagus) damage –> loss of speech
Consider the parathyroid glands
Appearance? Location? Germ layer origin? Function? Blood supply? Venous drainage? Innervation?
Why must care be taken during thyroidectomy?
- 4 glands (2 superior, 2 inferior) embedded in capsule of thyroid. Very small (rice), 40mg
- Develop from cells originating from 3rd/4th pharyngeal pouches (migrate caudally with the thymus, inferior parathyroids travel further)
- Secrete parathyroid hormone - regulates calcium and phosphate levels within homeostasis
- Blood supply: Primarily, inferior thyroid (+sup)
- Venous drainage: Sup+ middle + inf thyroid
- Innervation: middle and inf cervical ganglion
If parathyroid glands removed–> blood [Ca2+] drops –> muscles (including those involve din respiratory and laryngeal) go into tetanic contraction –> death
Generally outline the path of a hormone
Hormone –> interstitual space –> blood stream/lymphatic system
State the three determents of the affect of hormones
- Number of molecules available (concentration)
- Number of receptor available
- Affinity hormone-receptor
Medullary functions/ secretions?
Chromaffin cells (secretory cells) develop from same embryonic tissue as symp. ganglia. Stimulation of them causes secretion of adrenaline and small amounts of NA ie catecholamines into adjacent circulation
Modified symp. ganglia (ANS)
Function: fight or flight response (HR, BP, increased b/g,SM of viscera)
Why is the hypophysis (pituitary gland) describes as a compound gland?
Location? Function? Size? Blood supply? Venous drainage? Control?
- Compound as it has 2 origins: adenohypophysis - glandular outpouch of ectoderm of oral cavity, neurohypophysis- neural, downgrowth from diencephalon)
- Sella turcica, sphenoid bone
- Produces hormones that influence acitivity of other endocrine glands
- no larger than a pea
- Superior hypophyseal supplies median eminence, upper part of stalk; inferior hypophyseal supplies neurohypophysis, lower part of stalk
- Capillary plexuses drained by portal veins –> anterior lobe of pituitary –> veins form secondary plexus
- Controlled by signals from the hypothalamus
What is the benefit of having a portal vein system in the pituitary gland?
! Provides a route for neurosecretory substances released from hypothalamus to also reach anterior lobe
Consider the thyroid gland
Appearance? Location? Germ layer origin? Function? Blood supply? Venous drainage? Control?
Why must care be taken during cricothyrotomy?
- Bilobed in neck, 30g (2 lateral lobes connected by an isthmus that course anterior to the trachea).
- Below oblique line of thyroid cartilage to 5/6 tracheal ring; immediately anterior to trachea
- Endoderm origin, develops as growth from floow or pharynx
- Function: regulates tissue metabolism, growth and development
- Blood supply: superior thyroid (from external carotid) and inferior thyroid (from subclavian)
- Venous drainage: (from an external plexus) into IJV and BCV
-Control: hypothalamus –> thyrotrophin releasing hormone / hypophysis –> TSH
Recurrent nerve (from vagus) damage –> loss of speech
Consider the parathyroid glands
Appearance? Location? Germ layer origin? Function? Blood supply? Venous drainage? Innervation?
Why must care be taken during thyroidectomy?
- 4 glands (2 superior, 2 inferior) embedded in capsule of thyroid. Very small (rice), 40mg
- Develop from cells originating from 3rd/4th pharyngeal pouches (migrate caudally with the thymus, inferior parathyroids travel further)
- Secrete parathyroid hormone - regulates calcium and phosphate levels within homeostasis
- Blood supply: Primarily, inferior thyroid (+sup)
- Venous drainage: Sup+ middle + inf thyroid
- Innervation: middle and inf cervical ganglion
If parathyroid glands removed–> blood [Ca2+] drops –> muscles (including those involve din respiratory and laryngeal) go into tetanic contraction –> death
Consider the adrenal glands
Appearance? Location? Germ layer origin? Blood supply? Venous drainage? Control?
Why must care be taken during thyroidectomy?
- Right (pyramidal), left (semi-lunar)
Retroperitoneal from superior pole of kidney, 2-3cm x 1, 3.5-5g - Cortex derived from mesoderm; medulla derived from neural crest cells
- Blood supply: superior (from inf. phrenic), middle (aorta) and inferior suprarenal arteries
- Arteries branch before entering capsule and the rami supply the cortex and medulla of gland
- Cortical arteries give rise to subcapsular plexus and in turn to cortical sinusoids that distribute blood to cortical cells
- Medullary arteries pass through cortex to supply medulla
- Venous drainage: adrenal veins, drain into IVC (R) or renal vein (L)
- Hypothalamus (ACTH release from hypophysis) symp division of ANS (fast response at medulla): coeliac plexus, splanchnic nerves
What is the relevance that the blood vesseld supplying the medulla traverse the cortex?
Hormones produced by cortical cells influence activity of cells in medulla, cortisol mediates NA conversion to adrenaline.
Cortex secretions?
Cells subjacent to capsule secrete mineralcorticoids e.g. aldosterone function to maintain electrolyte balance
Deep cortex = glucocorticoids e.g. hydrocortisione affect metabolism and electrolyte balance
Produces adrenal androgens e.g. testosterone
Medullary secretions?
Chromaffin cells (secretory cells) develop from same embryonic tissue as symp. ganglia
Modified symp. ganglia (ANS)
Secretes adrenaline and small amounts of NA ie catecholamines
Function: fight or flight response (HR, BP, SM of viscera)
Describe the innervation of the blood vessels and chromaffin cells of the cortex and medulla
Preganglionic symp fibres:
- synapse at coeliac ganglia, postganglionic fibres supply blood vessels supplying medulla and cortex
- ramify around cells of medulla
Medulla is under direct control from ANS (symp) –> FAST RESPONSE
C
What is the overall structure of endrocrine glands?
Functional unit consists of cuboidal secretory cells with a lumen (pituitary and parathyroid glands cells have no lumen!)
Secretory cells supported by myoepithelial cells
Is the pancreas exocrine or endrocrine?
Both
What does neuroendocrine mean?
Neural stimulation of endocrine cells to secrete hormones e.g. the medulla of adrenal gland is stimulated by preganglionic fibres of the ANS
What are the clinical manifestations of endocrine disease?
- Hormone overproduction/underproduction
- Tumour/mass lesion which can be:
- non functional –> pressure effect
- associated over production
State the cell types found in the adenohypophysis (anterior pituitary gland) and their reaction to dyes
How can we identify specific cells?
Acidophils - take up acidic dyes
Basophils - take up basic dyes
Chromophobe - no specific staining techniques
**ACTH is secreted by both chromophobes and basophils (no specific pattern for hormones)
Immunocytochemistry assists in identifying specific cells e.g. antibodies to GF
For each adenohypophysis cell, provide the hormone and target organ
- Somatotroph
- Lactotroph
- Corticotroph
- Gonadotroph
- Thydotroph
- GH, Bones
- Prolactin, Breasts,
- ACTH, adrenal glands
- FSH, Ovaries, testes
LH, Ovaries, testes - TSH, thyroid gland
What drug has the opposite effect of ADH?
Alcohol
Describe pituitary adenomas
- Benign tumours arising from anterior lobe
- Can be function or non-functional. Productive adenomas cause hyperpituitarism. Non-producive adenomas cause hypopituitarism
- Space occupying effect of both types cause: headaches, vomiting nausea and diplopia, impaired vision (bitemporal hemianopia)
- Constitute 10% of intra-cranial neoplasms
Which hormones does the thyroid gland secrete?
Why is iodine important for this? What happens in a lack of iodine?
Thyroxine (T4) and Triiodothyronine (T3) which stimulate metabolic rate
Synthesis of these hormones requires iodine
Sea salt is rich in iodine. Lack of iodine leads to an enlarged thyroid gland –> goitre. This happens to absorb maximum concentration of iodine.
Goitre is due to hyperplasia and hypertrophy. The increase in size overcomes the hormone deficiency and the patients are euthyroid
Describe the appearance of a normal thyroid gland?
Other features?
35-45g
Bilobed with isthmus
Composed of follicles with variable-sized lumina
Follicles contain colloid with eosinophillic/pink appearance. They are lines by cuboidal cells
- Highly vascularised
- Endothelial cells lining the captillaries are fenestrated allowing passage of hormones into circulation
- Para-follicular cells (C cells) found between the follicles which secrete calcitonin which promotes reduction of calcium concentration in the blood
State 5 pathological states of the thyroid gland and whether they produce too uch, too little or just enough thyroid hormone/
- Goitre- Euthyroid
- Graves disease- Hyperthyroid
- Hashimoto’s disease- Hypothyroid
- Adenoma- Euthyroid
- Cancer- Euthyroid
Why is it important to assess the radiology of a patients goitre before thyroidectomy?
Multi-nodular goitre compressing the trachea removal can lead to tracheomalacia –> cardiac arrest
The trachea collapses due to it becoming flaccid and therefore obstructs the airway
What is Grave’s disease?
Autoimmune disease where the TSH receptor is stimulated by auto-antibodies
Diffuse enlargement of the thyroif gland goitre due to hyperplasia of thyroid cells
Leads to:
- Infilitrative opthalmopathy- accumulation of soft tissue and inflammatory cells behind the eye leading to proptosis (protruding eyes)
- Infiltrative dermopathy- thickening and induration of the skin on the anterior shin –> pre-tibial myxoedema
What does Graves’s look like microscopically?
The colloid has “soap bubble” appearance due to hyperacivity
What is Hashimoto’s Thyroiditis?
Autoimmune disease
- Progessive depletion of thyroif cells by inflamation and replaced by fibrosis.
- Decreased T3/T4
- Increased TSH
- Most common cause of hypothyroidism in areas where iodine is readily available
What does Hashimoto’s look like microscopically?
Prominent lymphocytic infiltration
The gland is irregular with a solid cut surface
Follicular adenomas are….
There are 4 thyroid carcinomas. Give their names, prevalence and description
Benign tumour of the thyroid follicular cells
- Papillary (75-85%); increased risk of lymph node metastasis
- Follicular (10-20%); increased metastasis to bone, lung and liver
- Medullary (5%); arises from C cells, 20% with MEN2 syndrome
- Anaplastic (<5%) older patients, poorer prognosis
What do parathyroid glands do ?
Histological appearance?
Pathology?
Secrete PTH
- Control the levels of calcium in the blood
- Decrease in blood calcium stimulates PTH secretion
Chief cells with no lumen
Highly vascularised
Adenoma- involves one gland
Hyperplasia- involves all four glands
** Both cause hypercalcaemia
What colour does a normal adrenal gland appear in the lab? WhY?
Orange/yellow
Cells are rich in lipid
For each zone of the adrenal cortex, which hormones are secreted?
Zone glomerulosa
- Mineralocorticoid
- Aldosterone
- *for absorption of sodium
Zone fasciculata
- Glucocorticoids
- Cortisol and cortisterone
- Sex hormones
Zone reticularis
- 17 ketosteroids
- sex hormones
How does the histology differ between the cells of the adrenal cortex?
ZG- Closely packed round cells
ZF- Clear cells arranged in cords
ZR- Smaller, darker staining cells
Adrenocortical hyperactivity and adrenocortical insufficiency are both examples of adrenal gland pathology.
What causes them?
Adrenocortical hyperactivity:
- Due to hyperplasia, adenoma, cancer (rare)
- Cushing’s syndrome (excess cortisol)
- Conn’s Syndrome (excess aldosterone)
- Adrenogenital syndrome (excess androgenes)
Adrenocortical insufficiency
- Addison’s disease
How does the histological appearance of the adrenal medulla differ to that of the cortex?
Adrenal medulla cells are neuroendocrine- darker staining that the cortex cell
- “Looser”
What is a phaechromocytoma?
Why is is describe as a 10% tumour?
Tumour of the adrenal medulla
- Cause of treatable hypertension (0.1-0.3%)
- Due to high levels of catecholamines
- Precipitous increase in BP, tachycardia, palpitations, headache, sweating, tremor and sense of apprehension
- Complications of high BP : CCF, IHD, arrrhythmias, CVA
10% familial (MEN2) 10% extra-adrenal 10% bilateral 10% malignant 10% arise in childhood