Nuts and bolts of the endocrine system

Question 1

Hormones are…..
involved in…
forming part of ……systems

Answer 1

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

Question 2

Hormones are…..
involved in…
forming part of ……systems

Answer 2

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

Question 3

Generally outline the path of a hormone

Answer 3

Hormone –> interstitual space –> blood stream/lymphatic system

Question 4

State the three determents of the affect of hormones

Answer 4

1. Number of molecules available (concentration)
2. Number of receptor available
3. Affinity hormone-receptor

Question 5

Give an example for the following hormone types (and their origins):

1. Steroid:
2. Peptide:
3. Amine:

Answer 5

1. oestradiol, testosterone (from ovaries, testes, adrenal cortex-mesodermal origin)
2. ADH, oxytocin, insulin (from thyroid (endorm), adrenal medulla- ectodermal origin)
3. adrenaline, NA, DA (adenohypophysis - ectodermal orgin; thyroid/parathyroid, pancreas- endodermal origin; scattered endocrine cells in epithelium of GIT and lungs)

Question 6

Why is the hypophysis (pituitary gland) describes as a compound gland?

Location?
Function?
Size?
Blood supply?
Venous drainage?
Control?

Answer 6

• 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

Question 7

What is the benefit of having a portal vein system in the pituitary gland?

Answer 7

! Provides a route for neurosecretory substances released from hypothalamus to also reach anterior lobe

Question 8

Consider the thyroid gland

Appearance?
Location?
Germ layer origin?
Function?
Blood supply?
Venous drainage?
Control?

Why must care be taken during cricothyrotomy?

Answer 8

• 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

Question 9

Consider the parathyroid glands

Appearance? Location?
Germ layer origin?
Function?
Blood supply?
Venous drainage?
Innervation?

Why must care be taken during thyroidectomy?

Answer 9

• 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

Question 10

Generally outline the path of a hormone

Answer 10

Hormone –> interstitual space –> blood stream/lymphatic system

Question 11

State the three determents of the affect of hormones

Answer 11

1. Number of molecules available (concentration)
2. Number of receptor available
3. Affinity hormone-receptor

Question 12

Medullary functions/ secretions?

Answer 12

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)

Question 13

Why is the hypophysis (pituitary gland) describes as a compound gland?

Location?
Function?
Size?
Blood supply?
Venous drainage?
Control?

Answer 13

• 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

Question 14

What is the benefit of having a portal vein system in the pituitary gland?

Answer 14

! Provides a route for neurosecretory substances released from hypothalamus to also reach anterior lobe

Question 15

Consider the thyroid gland

Appearance?
Location?
Germ layer origin?
Function?
Blood supply?
Venous drainage?
Control?

Why must care be taken during cricothyrotomy?

Answer 15

• 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

Question 16

Consider the parathyroid glands

Appearance? Location?
Germ layer origin?
Function?
Blood supply?
Venous drainage?
Innervation?

Why must care be taken during thyroidectomy?

Answer 16

• 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

Question 17

Consider the adrenal glands

Appearance? Location?
Germ layer origin?
Blood supply?
Venous drainage?
Control?

Why must care be taken during thyroidectomy?

Answer 17

• 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

Question 18

What is the relevance that the blood vesseld supplying the medulla traverse the cortex?

Answer 18

Hormones produced by cortical cells influence activity of cells in medulla, cortisol mediates NA conversion to adrenaline.

Question 19

Cortex secretions?

Answer 19

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

Question 20

Medullary secretions?

Answer 20

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)

Question 21

Describe the innervation of the blood vessels and chromaffin cells of the cortex and medulla

Answer 21

Preganglionic symp fibres:

1. synapse at coeliac ganglia, postganglionic fibres supply blood vessels supplying medulla and cortex
2. ramify around cells of medulla

Medulla is under direct control from ANS (symp) –> FAST RESPONSE
C

Question 22

What is the overall structure of endrocrine glands?

Answer 22

Functional unit consists of cuboidal secretory cells with a lumen (pituitary and parathyroid glands cells have no lumen!)

Secretory cells supported by myoepithelial cells

Question 23

Is the pancreas exocrine or endrocrine?

Answer 23

Both

Question 24

What does neuroendocrine mean?

Answer 24

Neural stimulation of endocrine cells to secrete hormones e.g. the medulla of adrenal gland is stimulated by preganglionic fibres of the ANS

Question 25

What are the clinical manifestations of endocrine disease?

Answer 25

1. Hormone overproduction/underproduction 2. Tumour/mass lesion which can be: - non functional --> pressure effect - associated over production

Question 26

State the cell types found in the adenohypophysis (anterior pituitary gland) and their reaction to dyes How can we identify specific cells?

Answer 26

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

Question 27

For each adenohypophysis cell, provide the hormone and target organ 1. Somatotroph 2. Lactotroph 3. Corticotroph 4. Gonadotroph 5. Thydotroph

Answer 27

1. GH, Bones 2. Prolactin, Breasts, 3. ACTH, adrenal glands 4. FSH, Ovaries, testes LH, Ovaries, testes 5. TSH, thyroid gland

Question 28

What drug has the opposite effect of ADH?

Answer 28

Alcohol

Question 29

Describe pituitary adenomas

Answer 29

- 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

Question 30

Which hormones does the thyroid gland secrete? Why is iodine important for this? What happens in a lack of iodine?

Answer 30

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

Question 31

Describe the appearance of a normal thyroid gland? Other features?

Answer 31

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

Question 32

State 5 pathological states of the thyroid gland and whether they produce too uch, too little or just enough thyroid hormone/

Answer 32

1. Goitre- Euthyroid 2. Graves disease- Hyperthyroid 3. Hashimoto's disease- Hypothyroid 4. Adenoma- Euthyroid 5. Cancer- Euthyroid

Question 33

Why is it important to assess the radiology of a patients goitre before thyroidectomy?

Answer 33

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

Question 34

What is Grave's disease?

Answer 34

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: 1. Infilitrative opthalmopathy- accumulation of soft tissue and inflammatory cells behind the eye leading to proptosis (protruding eyes) 2. Infiltrative dermopathy- thickening and induration of the skin on the anterior shin --> pre-tibial myxoedema

Question 35

What does Graves's look like microscopically?

Answer 35

The colloid has "soap bubble" appearance due to hyperacivity

Question 36

What is Hashimoto's Thyroiditis?

Answer 36

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

Question 37

What does Hashimoto's look like microscopically?

Answer 37

Prominent lymphocytic infiltration The gland is irregular with a solid cut surface

Question 38

Follicular adenomas are.... There are 4 thyroid carcinomas. Give their names, prevalence and description

Answer 38

Benign tumour of the thyroid follicular cells 1. Papillary (75-85%); increased risk of lymph node metastasis 2. Follicular (10-20%); increased metastasis to bone, lung and liver 3. Medullary (5%); arises from C cells, 20% with MEN2 syndrome 4. Anaplastic (<5%) older patients, poorer prognosis

Question 39

What do parathyroid glands do ? Histological appearance? Pathology?

Answer 39

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

Question 40

What colour does a normal adrenal gland appear in the lab? WhY?

Answer 40

Orange/yellow Cells are rich in lipid

Question 41

For each zone of the adrenal cortex, which hormones are secreted?

Answer 41

Zone glomerulosa - Mineralocorticoid - Aldosterone * *for absorption of sodium Zone fasciculata - Glucocorticoids - Cortisol and cortisterone - Sex hormones Zone reticularis - 17 ketosteroids - sex hormones

Question 42

How does the histology differ between the cells of the adrenal cortex?

Answer 42

ZG- Closely packed round cells ZF- Clear cells arranged in cords ZR- Smaller, darker staining cells

Question 43

Adrenocortical hyperactivity and adrenocortical insufficiency are both examples of adrenal gland pathology. What causes them?

Answer 43

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

Question 44

How does the histological appearance of the adrenal medulla differ to that of the cortex?

Answer 44

Adrenal medulla cells are neuroendocrine- darker staining that the cortex cell - "Looser"

Question 45

What is a phaechromocytoma? Why is is describe as a 10% tumour?

Answer 45

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 ```