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1st yr-Med 2022-2023 > GHM L8 > Flashcards

GHM L8 Flashcards

1
Q

sDescribe the anatomy of thyroid gland

A

Butterfly-shaped, bilateral
2 lobes joined by isthmus
Front of neck, around cartilages of larynx

DIAGRAM

Functional units of thyroid gland - Follicles

Follicles contain follicular cells - produce colloid

Colloid (gelatinous proteins) - made of thyroglobulin (Tg), precursor to thyroid hormones (T3 and T4)

Tg facilitates assembly of thyroid hormones
T4 - Thyroxine
T3 - Triiodothyronine
This happens in thyroid follicular lumen

In thyroglobulin, its the tyrosine molecule that becomes modified, tyrosine is modified into T3 and T4

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2
Q

State the function of C cells in the thyroid gland follicles

A

C cells secrete CALCITONIN

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3
Q

State the function of follicular cells

A

Secrete
Tg into colloid with IODINE

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4
Q

Describe the process of TSH stimulation

A

TSH secreted from anterioir pituitary
Stimulates thyroid gland to secrete T3 and T4 - bloodstream

(Follicular cells reabsorb iodinated Tg, degreade it, releasing T3 and T4)

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5
Q

State the functions of T3 and T4

A
  • Homeostasis
    -Cell differentation
    -Growth
    -Metabolism
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6
Q

Describe the process of iodine trapping

A
  1. Iodine from diet (e.g. spinach), travels through bloodstream in form an iodide ion (I-)
  2. I- accumulate in thyroid via active transport
  3. Na+ cotransported with iodide from basolateral membrane
  4. Concentrated in thyroid follicles
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7
Q

What stimulates iodine trapping ?

A

TSH

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8
Q

What region of the thyroid contains the most iodide ions?

A

FOLLICLE

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9
Q

State examples of iodine sources

A
  1. Cow’s milk
  2. DIARY PRODUCTS yoghurt etc
  3. Meat
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10
Q

Describe the function of TPO

A

TPO: thyroperoxidase

  1. TPO found outer-membrane of follicular cells
  2. Catalyses oxidation of I- by H2O2 (adds H2O2) to a reactive iodine intermediate
  3. This intermediate iodises tyrosine - (iodine added to tyrosine to form T3 and T4, t3 - 3 iodines, t4 - 4 iodines)

This whole process is controlled by TSH (upregulates TPO expression)

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11
Q

Where is thyroglobulin synthesised and secreted?

A

ER
Secreted in colloid by exocytosis

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12
Q

Describe the proteolysis of Tg with release of T3 and T4

A

T4 and T4 synthesised + stored within thyroglobulin
Protelysis of modifed thyroglubulin occurs

Modified thyroglublin (Tg) taken back into the folicular cell via endocytosis (phagacytosis), then undergoes proteolytic cleavage (proteolysis) to release + produce the mature T3 and T4 hormones which are then secreted into circulation

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13
Q

State the name of the transporter on the apical side of follilcular cell membrane

A

PENDRIN (I-/Cl-)

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14
Q

State the name of the transporter on the apical side of follilcular cell membrane

A

Na+/I- symporter

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15
Q

What stimulates endocytosis of iodinated Tg back into the cell?

A

Megalin binding to iodinated thyrogloblin
TSH

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16
Q

Which thyroid hormone is more abundant in the body?

A

T4

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17
Q

Where in the body is T4 produced?

A

ONLY THYROID Gland

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18
Q

State the 2 processes producing T3 in the body

A

80% produced from DE-IODINATION of T4 (peripheral tissues)
20% direct thyroid secretion (thyroid gland)

19
Q

State 3 enzymes and locations which de-iodinate T4 into T3

A

Type I Enzyme: Thyroid, pituitary, liver, kidney - 80% MOST
Type II: CNS, pituitary, brown adipose tissue, heart
Type III: Placenta, CNS This deiodinase converts T4 into rT3 which is inactive

20
Q

State the differences between hypothyrodism and hyperthyroidism

A

HYPOthyrodism

-Forgetfullness
-Moodiness
-Irratibility
-THINNING HAIR/HAIR LOSS
-WEIGHT GAIN
-DRY PATCHY SKIN
-HYPERLIPIDEMIA
-PUFFY EYES
-GOITER
-DEEPENING VOICE
-PERSISTANT DRY SORE THROAT
-BRADYCARDIA
-DIFFICULTY SWALLOWING
-INFERTILITY
-HEAVY PERIOID

HYPERthyroidism

-SUDDEN PARALYSIS
-sleepless
-BULGING EYES
-GOITER
-WARM MOST PALMS
-SWEATING
-MUSCLE FATIGUE
-TACHYCARDIA
-WEIGHT LOSS
-FREQUENT BOWEL MOVEMENT
-LIGHT PERIOD
-INFERTILITY

21
Q

Describe 3 types of hypothyroidism

A

Primary: Thyroid destruction MOST COMMON

Secondary: Lesion to anterioir pituitary gland (tumour-CRANIOPHARYNGIOMA) therefore, deficient TSH secretionn + Congenital (less common)

TERTIARY (CENTRAL): Lesion (growth/tumour) of pituitary stalk + hypothalamus (which are above the level of pituitary), therefore, defisient TSH stimulation
(less common than secondary)

22
Q

Primaty hypothyroidism

A
  • Autoimmune disorder
    -Autoimmune antibodies against thyroperoxidase (TPO)
    -Less TPO
    -More TSH to compensate, as TSH upregulates TPO, therefore, TSH high
23
Q

Secondary hypothyroidism

A

Lesions compressing pituitary (adenoma, enuryssm carotid artery) leading to LOW TSH

Another cause: autoimmune
thalassemia = iron overlead
TB, SYPHILIS

TREATMENT:
-SURGERY
-RADIATION at Pituitary

24
Q

Central / Tertiary Hypothyoidism

A
  • Lesion to levels above anterioir pituitary including infundipular stalk + HYPOTHALAMUS
  • Insuficient TSH

CAUSES:

  • CONGENITAL
  • IODINE DEFICIENCY IN PERGNANCY

TREATMENT:

DAILY DOSE OF THYROXINE

25
Q

Describe the causes of hyperthyroidism

A
  1. Grave’s Disease - aka toxic diffuse goiter

-Autoimmune
-Antibodies bind to + activate TSH receptor
-more TSH, more TPO upregulated, more T3 and T4

26
Q

Describe characteristics of hyperthyroidism Grave’s disease

A

EXOPTHALMOS - popping / bulging eyes

WHY?

Autoimmune inflammation of periorbital connective tissue + extraocular muscles

TREATMENT:

Radioidine, surgery, antithyroid drugs

27
Q

State examples of drugs that increase TBG

A

Oral contraceptives (sources of oestrogen)
METHADONE (ANALGESIC)
Clofibrate (reduces cholestrol)
5-flurobacil (cancer)
HEROIN
Tamoxifen (BREAST CANCER)

28
Q

Give examples of conditions which increase TBG

A
  • Pregnancy
  • Infectious / chronic active hepatitis
  • HIV infection
  • Billary cirrhosis
  • Acute intermittent porphyria
  • Genetic factors
29
Q

State the effect of drugs and conditions decreasing and increasing TBG

A

Increase in TBG: Increase T4 and T3 Levels
Decrease in TBG: Decrease T4 and T3 levels

30
Q

State examples of drugs that decrease TBG

A
  1. Glucocorticoids
  2. Androgens
  3. L-asparaginase
  4. Salicylates
  5. Mefenamic acid (anti-inflammatory)
  6. Antiseizure medications
  7. Furosemide
31
Q

State examples of conditions that decrease TBG

A
  • Genetic factors
    -Acute + chronic ilness
32
Q

Give an adaptation of the thyroid gland to its function of hormone production

A

RICH BLOOD SUPPLY

33
Q

Why is T3 more active than T4?

A

T4 pro-hormone for T3
(precursor)

T4 less active than T3
Has reduced of the affinity for nuclear receptor than T3

34
Q

State the enzyme used to convert T4 into T3

A

Monodeiodinase (5’ deiodination)

35
Q

Describe how T4 and T3 play a major role in growth and development

A

Increase protein sytnthesis
Increases ATP synthesis
Increases O2 utilisation
Increases heat production
Increases fat metabolism (therefore, decreases fat store)
-Essental for NORMAL BRAIN DEVELOPMENT

36
Q

Describe how T4 and T3 play a major role in growth and development

A

Increase protein sytnthesis
Increases ATP synthesis
Increases O2 utilisation
Increases heat production
Increases fat metabolism (therefore, decreases fat store)
-Essental for NORMAL BRAIN DEVELOPMENT

37
Q

Describe how thyroid hormone is essential for childhood growth

A

-Increases protein synthesis, ATP synthesis, O2 utilsation, fat metabolism, normal brain development

38
Q

Describe the severity of untreated congenital hypothyroidism

A

aka chronic hypothyrodism

  • incomplete development
    -mental retardation
39
Q

Describe how thyroid hormone stimulates protein synthesis

A

Thyroid hormone binds to nuclear receptors

This modulates gene transcription

Stimulates protein formation

40
Q

Give common symptoms between hypothyrodism and hyperthyroidism

A
  1. Infertility
  2. Goiter
41
Q

Describe the metabolic effects of T3

A

Stimulates lipolysis - release of free fatty acids, glyceol

Stimulates metabolism of cholestrol to bile acids and rapid removal of cholestrol from plasma

Stimulates protein degradation

Converts Carotene to Vit A

42
Q

Describe the location of the parathyroid glands

A
  • 4 small glands
    -Posterior surface of thyroid, also can be in chest
    -Upper pair - superioir parathyroid gland
    -Lower pair - inferioir parathyroid gland
43
Q

State two tyes of cells present in parathyroid gland

A
  1. Chief cells -
  2. Oxyphil cells - larger, stain differently, derivede from chiefc cells, INCREASE IN NUMBER WITH AGE, embedded in MATRIX or STOMA
  3. Adipose cells (if adipose cells present, person older as adipose cells appear with age)
  4. Lots of blood capillaries
44
Q

State where parathyroid hormone is produced

A

Chief cells in parathyroid gland

PTH

1st yr-Med 2022-2023 (57 decks)

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