MEH Thyroid Flashcards
Where do you find the thyroid gland in relation to the thyroid cartilage (Adams apple)?
Posterior. It’s on the cricoid cartilage
2/3rd ring of trachea
The two lobes are joined by an …
Isthmus
Where do you find the parathyroid glands?
On the posterior of the thyroid gland.
These are distinct glands
What do the thyroid glands produce (2)?
What do the parathyroid glands produce (1)?
Thyroid hormone (T4/Thyroxine/tetraiodothyronine) and (T3/triiodothyronine) produced in the follicular cells
Calcitonin is produced in the parafollicular cells. It reduces the calcium in the blood and offsets the effects of parathyroid hormone
Parathyroid (chief cells) produce parathyroid hormone
Where is thyroid hormone produced?
In the thyroid follicles
Thyroid follicles are made up of thyroid cells that form a circle with COLLOID (a deposit of thyroglobulin)
What is the important enzyme involved in thyroid hormone production?
What 3 reactions does it cause?
THYROID PEROXIDASE
1) Oxidation of Iodide to iodine
2) Addition of Iodine onto tyrosine residues on thyroglobulin
3) Coupling of MIT/DIT to form thyroid hormones within thyroglobulin protein
Name 3 foods were you find iodine?
Fish
Iodised salt
Milk (not organic), cheese,
Eggs
Name the transporter that gets iodide into the centre of the thyroid follicles.
1)
2)
Sodium Iodide symporter
Pendrin
T3 v T4
Which is more biologically active?
Which is more commonly secreted
Where is T4 converted to T3 in the body?
How is T3/4 carried in the blood?
T3
T4 = 90%
Liver and Kidney
Thyroxine-binding globulin
In the thyroid axis which does the hypothalamus produce?
What does the _________ pituitary produce?
Thyroid releasing hormone (TRH) - Rolf Harris is RELEASED from prison)
Thyroid stimulating hormone released from the ANTERIOR PITUITARY
What two hormones are released from the POSTERIOR pituitary?
Vasopressin (ADH)
Oxytocin
In the thyroid hormone axis.. What has a positive feedback effect and what has a negative feedback effect?
Positive
TRH +> Ant Pituitary
TSH +> Thyroid Glands
T3/4 +> Target organs
Negative
TSH -> Hypothalamus
Thyroid hormone -> Ant pituitary and hypothalamus
TSH is a trigger for Thyroid hormone release. What type of GPCR does it activate
Gas and Gaq
PKA, PKC, Ca2+ all stimulate the synthesis and release of thyroid hormone
What are the 3 general effects of thyroid hormone
1) Increase Basal metabolic rate and heat production
- Increase mitochondria size and number
- Stimulating respiratory chain enzymes
2) Stimulate Metabolic pathways
- Lipid metabolism (Lipolysis and B-oxidation of fatty acids)
- Carbohydrate metabolism (stim insulin-dependent entry of glucose to cells, Increase gluconeogenisis and glycogenolysis
3) Sympathomimetic effects
Thyroid hormone effects of CVS? (2)
Increase CO (HR and force of contraction) Peripheral vasodilation
Thyroid hormones effect on nervous system?
Increase myelination
What type of receptor are thyroid hormone receptors?
Nuclear receptors
Is thyroid hormone lipid soluble?
Yes
Does thyroid hormones repress or relive repression of gene transcription?
Relieves repression
What is a goitre?
Is it caused by hypo or hyperthyroidism?
A goitre is a enlargement of the thyroid gland
Caused by both Hypo and hyper
Name 5 symptoms of HYPOTHYROIDISM?
Obesity Lethargy (lack of energy)/Tiredness Intolerance to cold Bradycardia Constipation Slow reflexes Dry skin Alopecia
MENORRHAGIA
Name a disease that can cause HYPOTHYROIDISM
Hashimotos disease
Autoimmune - destruction of thyroid follicles
Most common disease of thyroid gland
More common in women
Goitre may or may not be present
Hypothyroidism in
Infants.. causes?
Adults..causes?
Infants - cretinism
Adults - myxedema (dermatologenous display of hypothyroid symptoms - puffy skin, muscle weakness, slow speach, mental deterioration, intolerance to cold
What is the main cause of hyperthyroidism
Graves’ disease
Name 5 symptoms of hyperthyroidism?
Tachycardia Weight loss Heat intolerance Fatigue and weakness Increased bowel movements Sweating and tremor Hyper-reflexive Breathlessness
What is Graves’ disease?
Autoimmune disease that causes a toxic multinodular goitre
Caused by the production of THYROID STIMULATING IMMUNOGLOBULIN (TSI)
TSI continually stimulates Thyroid hormone secretions
+T3, +T4, –ve TSH
Graves’ disease
Name a drug used to treat hypo/hyper thyroidism?
CARBIMAZOLE - block thyroid hormone
It’s a pro-drug and gets converted into its active form of Methimazole
How can you distinguish between a goitre and a thyroglossal duct cyst?
A thyroglossal duct cyst moves up on tongue protrusion
When can physiological goitres occur?
Menarche (first period)
Pregnancy
Menopause
What is the commonest cause of goitres globally?
1st?
2nd?
Iodine deficiency
Multinodular goitre (can become toxic, then causes hyperthyroidism). MOST COMMON IN THE UK
