Thyroid and Parathyroid Gland

Question 1

Thyroid gland structure

Answer 1

• inferior to Adam’s apple
• largest purely endocrine organ
• consists of two lobes connected by the isthmus
• composed of spherical follicles

Question 2

Spherical follicles

Answer 2

• hollow structures that store colloidal material
• follicular cells secrete thyroglobulin (precursor)
• follicle cavity stores thyroid hormone precursor, colloid, composed of thyroglobulin and iodine
• parafollicular cells (C cells): secrète calcitonin

Question 3

Thyroid hormone

Answer 3

• either T4 (thyroxine), the majority which some transforms into T3s (triiodothyronine)
• affects nearly every cell in the body
• binds to intracellular receptors (initiates transcription)

Question 4

Thyroid hormone effects

Answer 4

• increase in basal metabolic rate (metabolism, promotes oxidation of glucose)
• regulates growth and development (critical for normal development)
• maintains BP (by increasing the number of adrenergic receptors (NE & E) in blood vessels)
• regulated by the release stimulated by the TSH (high levels of feedback on the hypothalamus and AP)

Question 5

Hypothyroidism

Answer 5

-myxedema: low metabolic rate, associated to cold, lethargy, and sluggishness
-goieter: myxedema caused by iodine shortage
>follicular cells produce colloid, but cannot add iodine
>TSH stimulates TH production but only results in more colloid build up, leading to thyroid swelling
-crenitism: developmental consequences

Question 6

Hyperthyroidism (Grave’s disease)

Answer 6

• increases metabolic rate
• sudden weight loss
• rapid, irregular heartbeat
• sweating
• nervousness, irritability
• ex) Grave’s disease

Question 7

Calcitonin (humoral response)

Answer 7

-released from C cells in response to heightened [Ca2+]
-no known physiological role
-at high doses, it prevents bones from
>osteoclasts activity inhibition
>Ca2+ uptake stimulation into bone matrix
-antagonistic to parathyroid hormone

Question 8

Parathyroid Glands location

Answer 8

• usually four glands posterior to the thyroid

- secretes parathyroid hormone

Question 9

Function of parathyroid glands

Answer 9

-controls Ca2+ balance
(falling Ca2+ triggers its release, rising causes inhibition)
-hypercalcemic hormone (when there’s an increased [Ca2+] in blood
>stimulates osteoclasts (which eats bones for Ca2+ absorption)
>enhances Ca2+ reabsorption in kidneys
>promotes activation of Vit D (by increasing Ca2+ absorption in the intestinal mucosa