36. Thyroid And Adrenal Hormones Flashcards
What are follicular cells?
Where are they found?
Cuboidal epithelial cells
Line the follicles of the thyroid
Where is thyroid hormone stored?
In colloid composed on thyroglobulin
What is secreted by parafollicular cells?
Calcitonin
What is the purpose of thyroglobulin?
It is the site of synthesis and storage of T3 and T4
What form of iodine is transported to the colloid?
Iodine TPO, oxidised form of dietary iodide
How are T3 and T4 formed?
T3 formed by MIT and DIT coupling, T4 formed by 2 DIT
How do T3 and T4 get from the colloid to the blood stream?
By endocytosis of thyroglobulin which is digested to release T3 and T4 which diffuse into the blood
How are thyroid hormones circulated in the blood?
Bound to thyroid binding globulin (99.5%) or free (0.5%)
Why is much of the T4 converted into T3 in the cell?
Nuclear receptors have a higher affinity for T3
How does thyroid hormone binding to DNA affect the cell?
Initiates transcription and formation of multiple mRNAs
What is the main function of thyroid hormone?
Increase metabolic activity of nearly all tissues
Increase BMR, number of mitochondria, Na+/K+ ATPase activity
How does thyroid hormone affect the cardiovascular system?
Increases sympathetic NS activity, ie increases heart rate, contractility, CO, etc
What stimulates TSH production?
Thyrotropin releasing hormone from hypothalamus
How does TSH affect thyroid hormone production?
Increases secretion of T3 and T4
What are the causes of congenital hypothyroidism?
Thyroid dysgenesis, thyroid dyshormonogenesis, thyroid receptor abnormalities, iodine deficiency
What is a sign of thyroid disfunction?
High levels of TSH in babies, suggests thyroid gland is not responding
What drug is used to treat hypothyroidism?
Levothyroxine
Converted into T3 in body
What does the adrenal cortex produce?
What does the adrenal medulla produce?
Steroid hormones
Adrenaline, Noradrenaline, and dopamine
What are the histological layers of the adrenal cortex?
Zona glomerulosa - clusters of small cells. Release aldosterone
Zona fasciculata - large cells in cords. Produces cortisol
Zona reticularis - small randomly arranged cells. produced adrenal androgens
What are the effects of cortisol?
Gluconeogenesis, lipolysis, suppress release of insulin, breakdown of skeletal muscle protein, immune suppression
How is cortisol secretion regulated?
By hormones produced in hypothalamus and anterior pituitary (HPA axis)
What stimulates cortisol release?
CRH from hypothalamus stimulates ACTH from pituitary which stimulates cortisol production in adrenals
When is cortisol secretion highest?
In the early morning, controlled by daylight exposure
What is the role of cortisol in the stress response?
Maintains steady supply of glucose, suppresses immune system and has anti-inflammatory action to prepare for long term damage
What is Cushing’s syndrome?
Prolonged exposure to excess cortisol (not caused by pituitary tumour)
What are the symptoms of Cushing’s disease?
Red moon face, thin extremities, fat around back of neck and abdomen, thin skin, etc.
