CASE 9

Question 1

THYROID

• located _________ to the larynx on each side of and _________ to the trachea
• composed of lots of follicles — follicles are lined with _______ epithelial cells that secrete into the interior of the follicles
• the secretory fluid in the follicles is called colloid
• the main component of colloid is _________

Answer 1

• inferiorly
• anteriorly
• cuboidal
• thyroglobulin

Question 2

what does the thyroid secrete?

Answer 2

thyroxine (T4), triiodothyronine (T3), and calcitonin

Question 3

what is thyroid secretion controlled by?

Answer 3

thyroid secreting hormone (TSH) from the anterior pituitary gland

Question 4

what is iodide trapping?

Answer 4

the basal membrane of the thyroid actively pumps the iodide into the follicular cells of the thyroid gland through Na+/I= symporter

Question 5

what stimulates iodide trapping?

Answer 5

TSH

Question 6

what is the effect on iodide trapping when the thyroid gland becomes more active?

Answer 6

more iodide is actively transported into the follicle cell

Question 7

what catalysed the oxidation of iodide ions?

Answer 7

peroxidase enzyme

Question 8

what is iodide oxidised to?

Answer 8

iodine

Question 9

where is peroxidase enzyme located?

Answer 9

either located in the apical membrane of the follicle cells or attached to it

Question 10

what is the organification of thyroglobulin

Answer 10

the binding of iodine with the thyroglobulin molecule

Question 11

what is tyrosine iodised to and then converted to?

Answer 11

1. tyrosine is first iodised to monoiodotyrosine (MIT)
2. MIT is then converted to diiodotyrosine (DIT)

Question 12

what forms T3 and T4?

Answer 12

thyroxine = 2 coupled DIT molecules — T4. thyroxine remains part of the thyroglobulin molecule

triodothyronine (T3) = coupling of one MIT + one DIT — T3

Question 13

effects of thyroid hormone on mitochondria

Answer 13

increase mitochondrial activity — increases the size and number of mitochondria. the total membrane SA of the mitochondria also increase in proportion to the increased metabolic rate — more ATP production and cellular function

Question 14

what effect does TH have on ion active transport?

Answer 14

increases ion active transport — increases NaK ATPase activity

Question 15

what growth does TH promote?

Answer 15

• promote growth in growing children
• promotes growth of brain during foetal development and first few years of life

Question 16

what effect does TH have on cholesterol, phospholipids and triglycerides levels? effect of hypothyroidism?

Answer 16

lowers levels (even though TH increases FFAs)

not enough TH —> excess deposition of fat in the liver

Question 17

vitamins and TH

Answer 17

increases need for vitamins (therefore vitamin def can occur when there is excess TH)

Question 18

effect of TH on heart and blood flow

Answer 18

increases blood flow, cardiac output, HR, heart strength (arterial pressure remains normal) (SBP elevates in hyperthyroidism and diastolic pressure decreases)

Question 19

hyper vs hypo thyroidism on GI motility

Answer 19

TH increases GI motility therefore:

hypothyroidism - constipation
hyperthyroidism - diarrhoea

Question 20

where is thyrotropin releasing hormone (TRH) released from? where does it then go?

Answer 20

• secreted by nerve endings in the median eminence of the hypothalamus
• from the median eminence, the TRH is then transported to the anterior pituitary by the way of the hypothalamic-hypophysial portal blood

Question 21

what does calcitonin do?

Answer 21

decreases plasma Ca conc

Question 22

where is calcitonin made and secreted from?

Answer 22

C cells, lying in the interstital fluid between the follicles of the thyroid gland

Question 23

what effect does increased plasma Ca conc have on calcitonin secretion?

Answer 23

increases calcitonin secretion

Question 24

parathyroid hormone secretion is stimulated by what?

Answer 24

low Ca conc

Question 25

how does calcitonin decrease blood Ca ion conc?

Answer 25

1. immediate effect — decrease the absorptive activities of osteoclasts thus shifting the balance in favour of deposition of calcium in the exchangeable bone calcium salts 2. prolonged effect — decrease the formation of new osteoclasts

Question 26

how does parathyroid hormone (PTH) control extracellular calcium and phosphate concs?

Answer 26

by regulating: - intestinal reabsorption - renal excretion - exchange of these ions between the ECF and bone

Question 27

what does excess action of the parathyroid gland cause?

Answer 27

excess PTH release - rapid absorption of Ca slats form the bones — hypercalcaemia in ECF

Question 28

how does PTH increase Ca and phosphate absorption from the bone?

Answer 28

1. rapid phase — results from activation of osteocytes to promote calcium and phosphate absorption 2. slow phase — results from proliferation of the osteoclasts, followed by greatly increased osteoclast reabsorption of the bone itself

Question 29

what is the most common cause of endogenous hyperthyroidism?

Answer 29

Grave’s dosease

Question 30

Grave’s disease is characterised by what triad of clinical findings?

Answer 30

1. hyperthyroidism due to diffuse, hyper functional enlargement of the thyroid 2. infiltrative ophthalmopathy with resultant exophthalmos (protrusion f eyeball) 3. pretibial myxoedema

Question 31

what antibodies are present in Grave’s disease?

Answer 31

TSH receptor

Question 32

what is the most common cause of hypothyroidism in areas of the world where iodine levels are sufficient?

Answer 32

Hashimoto thyroiditis — THIS DISEASE DESCRIEBS PATIETNS WITH GOITRE AND INTENSE LYMPHOCYTIC INFILTRATION OF THE THYROID

Question 33

what disease is characterised by the gradual thyroid failure due to autoimmune destruction of the thyroid?

Answer 33

hashimoto thyroiditis

Question 34

what antibodies are present in hashimoto thyroiditis?

Answer 34

antibodies against thyroid peroxidase, thyroglobulin and TSH receptors

Question 35

how does a goitre develop?

Answer 35

- low iodine levels - decreased synthesis and secretion of TH - compensatory increase in TSH - follicular cell hypertrophy and hyperplasia - growth and enlargement of thryoid gland (goitre)

Question 36

where are the different types of B-receptors located?

Answer 36

B1 = mainly in heart and kidneys B2 = lungs, GIT, liver, uterus, vascular smooth muscle, skeletal muscle B3 = adipocytes

Question 37

what does B1 stimulation by adrenaline/noradrenaline result in?

Answer 37

heart — increases cardiac conduction velocity and automaticity kidneys — renin release d

Question 38

what does stimulation of B2 receptors cause?

Answer 38

smooth muscle relaxation/bronchodilation induces tremor in skeletal muscle increases glycogenolysis in liver and skeletal muscle

Question 39

what does B3 stimulation cause?

Answer 39

lipolysis

Question 40

what is an adverse effect of blockade by beta blockers at B1, especially at macula densa?

Answer 40

inhibits renin release — decreases release of aldosterone, causing hyponatraemia and hyperkalaemia

Question 41

what are the effects on glucose levels by blockade of B2 receptors?

Answer 41

hypoglycaemia because B2 adrenoreceptors normally stimulate glycogenolysis (hepatic glycogen breakdown) and pancreatic release of glucagon

Question 42

what is pronanolol?

Answer 42

non-selective B blocker

Question 43

in the zona glomerulosa, early action of what enzyme steers away from sex steroid precursors to aldosterone or cortisol?

Answer 43

HSD3B2

Question 44

what enzyme does the zona fasciculata contain for the production of cortisol?

Answer 44

CYP11B2

Question 45

describe CYP17A1 enzyme

Answer 45

- in zona reticulosa - allows for the production of sex steroid precursors (androstenedione)

Question 46

Answer 46

Question 47

what is the ratio of production of T3:T4 ?

Answer 47

1:20 — lots more thyroxine

Question 48

half life of T3 vs T4?

Answer 48

longer for T4 - 4 days T3 - a day

Question 49

what is more of a long term measure?

Answer 49

TSH (similar to HbA1c)

Question 50

subclinical hypothyroidism

Answer 50

TSH high and T4 normal

Question 51

subclinical hyperthyroidism

Answer 51

TSH low and T4 normal

Question 52

what would be seen if someone takes a load of thyroxine in one go?

Answer 52

high T4/3 and a normal TSH (takes longer)

Question 53

what is sick euthyroid syndrome?

Answer 53

low TSH and T4 — common in hospital inpatient . abnormal thyroid levels in patients with non-thyroid related illnesses

Question 54

what long term health effects can you get from hyperthyroidism?

Answer 54

atrial fibrillation, osteoporosis

Question 55

another name for primary adrenal insufficiency

Answer 55

addisons disease

Question 56

when does secondary adrenal insufficiency occur?

Answer 56

occurs when the pituitary gland doesn't make enough of the hormone ACTH

Question 57

gad65 antibodies

Answer 57

The glutamic acid decarboxylase 65-kilodalton isoform (GAD65) antibody is a biomarker of autoimmune central nervous system (CNS) disorders and, more commonly, nonneurological autoimmune diseases. Type 1 diabetes, autoimmune thyroid disease, and pernicious anemia are the most frequent GAD65 autoimmune associations.

Question 58

primary vs secondary hypoadrenalism

Answer 58

primary = lack of cortisol AND aldosterone secondary = normal aldosterone but deficient in cortisol (because don’t have any ACTH coming from pituitary gland)