ELC 1 Flashcards by Andrew Macdonald

How do paracrine hormones act?

1.1/1.2

A cell produces a signal to induce changes in nearby cells, altering the behavior of those cells. Binding of a paracrine factor to its respective receptor initiates signal transduction cascades, eliciting different responses.

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What class of hormone is insulin? What type of receptor is the insulin receptor?

(1.1/1.2)

Peptide Hormone. Tyrosine Kinase receptor.

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TorF
AC activation and inhibition by GPCR both result in cAMP production

(1.1/1.2)

F- AC activation leads to cAMP production to act as secondary messengers. AC inhibition results in enhanced cAMP breakdown by Phosphodiesterase activation (PDE).

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Which endocrine organ secretes melatonin, the “hormone of darkness”?

(1.1)

Pineal gland- regulates circadian rhythm

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What two hormones are released by the neurohypophysis (posterior pituitary)?

(1.1/1.2)

Oxytocin and Vasopressin. Note that these aren’t produced by the posterior pituitary itself, they are produced in the hypothalamus and released into the systemic circulation by neuronal terminals in posterior pituitary.

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TorF
The hypothalamic-hypophyseal portal system exists for both the anterior and posterior pituitary.

(1.1/1.2)

F- the posterior pituitary doesn’t receive portal vessels from the hypothalamic stalk, instead the stalk contains icons from neurosecretory neuronal cells in the hypothalamus. Only the anterior pituitary receives the H-H portal system from capillaries in the hypothalamus.

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What are the embryological origins of parafollicular cells and follicular cells?

(1.3)

Parafollicular cells are derived from neural crest cells.

Follicular cells are endoderm derived

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Where does the thyroid gland migrate from during development?

(1.3)

The foramen caecum- the attachment site of the thyroglossal duct to the root of the tongue.

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Which of the following about action of thyroid hormones on target cells is true:

a) 3’5’ Monodeiodinase activity on the target cell surface removes the 5’ iodine converting T4 to T3.
b) Only T3 can enter the target cell either by diffusion or carrier mediate transport.
c) Thyroid hormone receptor binds thyroid hormone and binds to thyroid response element
d) Thyroxin-binding globulin binds both T3 and T4 in blood plasma

(1.3)

a) False- 3’5’ monodeiodinase activity is inside the cytoplasm of target cell.
b) False- BOTH T3 and T4 can enter the cell.
c) False- thyroid hormone receptor + retinoid X receptor (RXR) both bind TRE on DNA.
d) True

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Which of the following about the HPT axis is true?

a) TRH released by the hypothalamus reaches the thyrotrophs in the anterior pituitary via the long portal vessels.
b) TRH binds to a tyrosine kinase receptor on the thyrotroph membrane, thus triggering the DAG/IP3 pathway leading to increased intracellular Ca2+
c) TSH released by thyrotrophs act on parafollicular cells of the thyroid gland
d) TSH stimulates a GPCR to activate DAG/IP3 pathway

(1.3)

a) true
b) False- TRH binds to a GPCR and the rest is true.
c) False- TSH acts on follicular cells of thyroid gland
d) False- TSH receptor is a GPCR that activates the AC pathway and raises [cAMP]

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What two neurohormones inhibit TSH release?

1.3

Somatostatin and Dopamine- released by hypothalamic neuron

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Parafollicular cells secrete _________ in response to _____________

(1.3)

Parafollicular cells secrete calcitonin in response to increased blood calcium.

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PTH is released by _______ cells in response to ___________

1.3

PTH is released by chief cells in response to decreased plasma calcium

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What are the 7 steps of thyroid hormone synthesis?

1.3

Trapping of iodine in follicular cell due to upregulation of NIS
Iodide leaves the cell and is oxidised to iodine
Iodination of thyroglobulin in follicular lumen
Conjugation of tyrosines to form T4 and T3 linked to thyroglobulin
Endocytosis of iodinated thyroglobulin into the follicular cells from colloid
Proteolysis of thyroglobulin form T4 and T3.
Secretion of T4 and T3 into circulation

Also, TSH exerts growth factor effect- hyperplasia within thyroid gland

memory: T I I C E P S

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Which steps of the thyroid hormone synthesis pathway are upregulated by TSH?

(1.3)

All but step 2- movement of iodide out of cell

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Which of the following is false:

a) The main hormone secreted by the thyroid follicle cells is T4 (90%)
b) T3 is ~10 times more potent in its cellular biological activity than T4
c) most of the secreted T4 is converted to T3 in peripheral tissues
d) ~99.5% of T3 and T4 is unbound in plasma
e) there can be an increase or decrease in circulating levels of TBG but normal free T3/T4.

(1.3)

d) is false- <0.5% of unbound T3 and T4 in plasma, almost all of it is bound to TBG

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Oestrogen ________ TBG levels (eg in pregnancy).

Androgenic steroids and glucocorticoids ______ TBG levels.

(1.3)

Increase

Decrease

What happens to plasma concentrations of T3/T4, TSH and TRH in hypothyroidism with the following causes:

Primary failure of thyroid gland
Secondary to hypothalamic failure
Lack of dietary iodine

(1.3)

T3/T4 levels low, TSH and TRH high - goitre present
T3/T4 levels low, TSH low and/or TRH low - no goitre present
T3/T4 levels low, TSH levels high - goitre present

Which of the following about thyroid dysfunction is correct?

a) in Graves’ disease, there is abnormally high T3/T4 and low TSH
b) in Graves disease there is no goitre present
c) one cause of hypothyroidism is secondary to excess hypothalamus and pituitary secretion
d) hypersecreting thyroid tumour can lead to excess T3/T4 levels and high TSH

(1.3)

a) true - TSI stimulates excess thyroid hormone release
b) false - goitre present due to overstimulation by TSI
c) false - excess hypothalamus and ant pituitary secretion will lead to hyperthyroidism
d) false - excess Thyroid hormone production will negatively feedback on TSH (and TRH levels) so reduce TSH

Which of the following is NOT a clinical manifestation of hyperthyroidism?

a) thyroid stare and lid lag
b) Weight loss, sweating and heat intolerance
c) osteoporosis
d) bradycardia
e) low serum lipids and hyperglycaemia.

(1.3)

d) false- tachycardia is common due to increased demand for O2 and increased cardiac contractility. (can lead to AF in 10-20% or palpitations)

Which of the following about Hypothyroidism is true?

a) Hypothyroidism is less common than hyperthyroidism.
b) common causes of hypothyroidism are Hashimoto’s thyroiditis and Iodine deficiency
c) Hypothyroidism is more common in men than in women
d) some common clinical manifestations of hypothyroidism include ophthalmology, heat intolerance, tachycardia, weight loss and smooth skin

(1.3)

a) false- hypothyroidism is one of the most common of all endocrine disease, even more common than Grave’s disease. Affects 1-2% of all adults.
b) true
c) false- more common in women
d) false- this is for hyperthyroidism. Common features of hypothyroidism rarely include eye conditions, but include peripheral edema, cold intolerance, bradycardia, weight gain and coarse, dry skin and hair

Which of the following about the parathyroid gland is false?

a) The parathyroid gland is responsible mainly for secreting PTH and maintaining calcium homeostasis
b) Parathyroid gland lies behind thyroid gland and is embryologically related to thyroid.
c) parathyroid hormone is a peptide hormone that is stored in secretory granules
d) secreted PTH has a half-life of 2-4 minutes and is cleared by the liver and kidney
(1. 3)

b) false- the parathyroid gland is derived from the 3rd and 4th pharyngeal pouches. The thyroid gland is derived from pharyngeal endoderm, not from pharyngeal pouches

Which of the following about calcium receptor is false?

a) the calcium receptor is a GPCR which sense calcium
b) increased serum calcium inhibits secretion and release of performed PTH
c) it is expressed in high levels in parathyroid gland
d) increased Mg2+ leads to paralysis of parathyroid gland
e) only 1.5 hours of PTH stores in parathyroid gland

(1.3)

d)false- decreased Mg2+ leads to paralysis of parathyroid gland

TorF

PTHrP is a tumour product which has the effect of causing hypocalcaemia

F- PTHrP can activate PTH receptors causing hypercalcaemia. Can progress to bone metastases.

Which of the following are true about Thyroid Nuclear medicine? 1. Wolf-Chaikoff effect may lead to hypothyroidism and reduced uptake on scan 2. Jod-Basedow phenomenon reduces thyroid function (1.4)

1. true- shutdown of NIS leads to reduced thyroid function which may lead to hypothyroidism 2. False- accelerates thyroid function which may lead to hyperthyroidism and increased uptake on scene.

Which radiotracer used in nuclear medicine, Sodium 99mcTc pertechnetate and Iodine-131, are taken up by thyroid cancer cells and therefore is useful for imaging of thyroid cancer? (1.4)

Iodine-131 taken up- used in therapy of overactive thyroid and imaging of thyroid cancer. Sodium 99mcTc pertechnectate is not taken up by thyroid cancer cells.

Which of the following histological findings is false? a) Grave's disease is associated with hyperplastic follicular epithelium with swelling of the colloid b) Hashimoto's thyroiditis has lymphocytic infiltration with follicle formation (1.5)

a) false- leads to hyper plastic epithelium but infolding and scalloping of colloid.

Which of the following is false? a) multinodular goitre (benign hyperplasia) can progress to follicular carcinoma (malignant) b) Follicular adenoma is a benign neoplasm that has well-formed fibrous capsule without capsular invasion. c) Follicular carcinoma is more common than papillary carcinoma d) follicular carcinoma can have capsular and vascular invasion leading to metastasis e) adenocarcinoma of the pancreas is most commonly found in the pancreatic head (60%) (1.5)

c) false- papillary carcinoma is more common (75-85% vs 10-20%)

At which location is TSH (thyroid stimulating hormone) synthesised and released? 1) hypothalamus. 2) pars distalis. 3) pars intermedia. 4) pars nervosa. 5) thyroid gland. (quiz and anat prac)

2) Pars distalis TSH is synthesised and released by the anterior pituitary (pars distalis) under the control of TRH from the hypothalamus.

How do the developmental origins differ between the adenohypophysis and neurohypophysis? (anat prac)

The pituitary is unique in that it has dual ectodermal origin- the adenohypophysis arises from the ectoderm and the neurohypophysis arises from the neuroectoderm

What is the arterial supply of the pituitary? | anat prac

superior hypophyseal arteries inferior hypophyseal arteries both branches of the internal carotid artery (note- as opposed to thyroid gland supplied by external carotid arteries.

What level of spine is the thyroid gland located? | Anat prac

C5-T1, isthmus cross at 2nd to fourth rings of tracheal cartilage.

10% of the population have a thyroid Ima artery to supply the thyroid as well as the superior and inferior thyroid arteries (branches of the external carotid and subclavian respectively). Which artery does the thyroid ima branch from? (anat prac)

the brachiocephalic trunk

A low intake of dietary iodine is most likely to result in which of the following conditions? 1) Grave's disease. 2) Thyrotoxicosis. 3) Goitre. 4) Hyperthyroidism. 5) Hypopituitarism. (quiz)

3. In response to low iodine, the thyroid gland undergoes hyperplasia and cells hypertrophy in an attempt to produce more thyroid hormone, this often results in goitre. Hyperthyroidism suggests high levels of thyroid hormone, which would not be seen in the case of an iodine deficiency.

Iodide is transported into thyrocytes simultaneously with which ion? 1) Sodium. 2) Potassium. 3) Magnesum. 4) Chloride. 5) Calcium.

1. The NIS (sodium-iodide symporter) transports iodide and sodium into the cell simultaneously.

Iodide is added to tyrosyl residues on which molecule during the synthesis of thyroid hormone? 1) Serum albumin. 2) Thyroxine binding globulin (TBG). 3) Thyroxine binding pre-albumin (TBPA). 4) Thyroglobulin (TG). 5) Growth hormone binding protein (GHBP).

4. TG has four tyrosyl residues that can be iodinated in the lumen of the thyroid follicle.

Thyroid hormone pools provide storage for the supply of thyroid hormone for approximately how long? 1) 7 minutes. 2) 7 hours. 3) 7 days. 4) 7 weeks. 5) 7 years.

3. Stored thyroid hormone and circulating thyroid hormone pools provide a supply of thyroid hormone for 7 to 10 days.

Which of the following correctly describes the thyroid hormone receptor? 1) It is a seven transmembrane G-protein coupled receptor. 2) It is a tyrosine kinase receptor. 3) It is a cAMP activated receptor. 4) It is an intracellular receptor. 5) It is an extracellular, soluble receptor.

The thyroid hormone receptor is structurally similar to a steroid receptor (intracellular) that binds T3 with a greater affinity than T4.

T3 enhances adrenergic responses in cardiac and skeletal muscle by which of the following mechanisms? 1) stimulating the release of epinephrine (adrenaline) from the adrenal medulla. 2) depolarising sympathetic nerve ganglia adjacent to the adrenal medulla. 3) stimulating the production of beta-adrenergic receptors in these tissues 4) stimulating the production of alpha-adrenergic tissues in these tissues. 5) inhibiting the release of acetylcholine that antagonises epinephrine (adrenaline) actions in these tissues.

Beta-adrenergic receptors are up-regulated in cardiac and skeletal muscle, adipose tissue and lymphocytes by the action of T3.

Which bone cells resorb bone under the influence of parathyroid hormone (PTH)? 1) Osteocytes. 2) Chondrocytes. 3) Osteoblasts. 4) Chondroblasts. 5) Osteoclasts.

5. Osteoclasts secrete lysosomal enzymes and acid to break down hydroxyapetite, the calcium phosphate component of bone. This action releases calcium into the circulation maintaining calcium homeostasis under the influent of PTH.

Which of the following correctly describes the calcium receptor? 1) a seven transmembrane G-protein coupled receptor. 2) a tyrosine kinase receptor. 3) a heat-shock protein activated receptor. 4) an intracellular receptor. 5) an extracellular, soluble receptor.

1. The calcium receptor is a G-protein coupled receptor that transduces its signal via the cAMP second messenger system

Which secretory endocrine gland is calcitonin synthesised in, and released from? 1) Hypothalamus. 2) Pituitary gland. 3) Parathyroid gland. 4) Pancreas. 5) Thyroid gland.

5. C-cells (parafollicular cells) of the thyroid gland have calcium receptors, which control the synthesis and release of calcitonin within these cells, antagonising the actions of parathyroid hormone.