Lecture 2 -- Pituitary and Thyroid Gland

What are the two components of the pituitary gland?

Anterior pituitary and posterior pituitary

What are the other name of posterior pituitary gland?

Neurohypophysis

What is another term for the anterior pituitary?

Adenohypophysis

What is the role of the hypothalamus in pituitary function?

Paraventricular nerve (PVN) and Supraoptic nerve (SON) in hypothalamus synthesis hormone e.g. oxytocin and ADH → These hormone store in posterior pituitary gland and release from posterior pituitary gland when needed

What is the structure that connects the posterior pituitary gland to the brain?

infundibulum

What is a capillary portal system in pituitary gland?

2 capillaries bed involved
→ Artery → Capillaries bed 1 → Portal vessel → Capillaries bed 2 → Vein → Target organ

What is the difference between the negative feedback systems of the posterior pituitary gland and the anterior pituitary gland?

The posterior pituitary gland has a complex negative feedback system involving two hormones, while the anterior pituitary gland typically involves one hormone

What does intermediate lobe of pituitary gland release?

Melanocyte stimulating hormone (MSH)

In terms of hormonal feedback, what does short-loop feedback and long-loop feedback indicate?

→ Short-loop feedback = Simulating hormone inhibit the release of releasing hormone
→ Long-loop feedback = The actual hormone inhibits the release of both releasing and tropic hormones.

Where is thyroid gland?

Below the laryngeal cartilage and sit each side of the trachea

Can thyroid gland easily be palpated?

No unless the animals are experiencing hyperthyroidism.
→ Cats are more likely to experience hyperthyroidism and may have an enlarged thyroid that can be palpated
→ In healthy animals, the thyroid gland is generally not easily felt during a routine examination.

What triggers the thyroid gland to release thyroid hormones?

→ Hypothalamus produce TRH → TRH passes through the capillary portal system release to anterior pituitary gland → Anterior pituitary gland releases TSH → TSH goes through the bloodstream and reaches the thyroid gland → Thyroid gland produces thyroid hormone

Which ion is critical for thyroid hormone synthesis?

Iodine.

How is the thyroid hormone produced in thyroid gland?

→ Iodine from the diet
→ Absorb into the bloodstream
→ Enter the follicular cells of thyroid gland via Na/I symporter
→ Thyroidglobulin then become iodinated
→ Droplet of colloid re-enters back to the follicle cells via pinocytosis
→ It then bind to lysosome
→ T3 + T4 then cleave of from thyroidglobulin
→ Become lipophilic and secreted into the bloodstream
→ 99% of thyroid hormone are bind with protein in blood

Body produce more T4 than T3 BUT T3 is more potent and biologically active than T4

→ When T4 and T3 reaches the target organs, they are released from protein
→ T4 can be converted into rT3 (inactive) or T3
→ T3 exert its effects (Increase metabolic rate in various tissues except brain, spleen and gonads)

What role do follicular cells of the thyroid play?

Produce thyroidglobulin colloid that is required to make the thyroid hormone

What kind of protein do thyroid hormones bind to?

20-30% of thyroid hormones bind to albumin; 70-80% bind to TBG (thyroxine-binding globulin)

What is T3 and T4?

T3 is triiodothyronine and T4 is thyroxine, both are thyroid hormones.

What happens when thyroid hormone levels are high?

TRH and TSH release is inhibited, leading to less thyroid hormone production.

How long can thyroid hormone be stored in the colloid?

Typically lasts 2-3 months.

How long can protein bound thyroid hormone in the blood last for?

several days

What is the primary biological activity of T3 compared to T4?

T3 is 3 to 5 times more biologically active than T4.

What effects does thyroid hormone have?

1. Increases metabolic rate in almost all tissues except brain, spleen and gonads

2. Leads to increased O2 consumption + thermogenesis (Increased the amount of heat being created)

3. Required for normal growth and development because it increases protein synthesis and increases cell division

What are the symptoms of hyperthyroidism

1. Increase HR

2. Become flurry

3. Find some colder place

4. Irritating

5. Increase food intake

What is the role of a carrier protein?

-> Stop the biological action of any thyroid hormone before it reaches the target cells

What is the difference in volume and activity between free T3 and free T4?

More T4 is produced
T3 is more biologically active and potent