Endocrine | 17.4 & 17.5

What gland is the largest endocrine gland/organ and is butterfly-shaped?

Thyroid gland

Location of the thyroid gland?

Located anterior to the trachea, just inferior to the larynx

What is the middle region that connects the left and right lobes of the thyroid gland?

The Isthmus

What is the colloid?

The center of thyroid hormone production

• Surrounded by a wall of epithelial follicle cells

The tissue of the thyroid gland is composed mostly of?

Thyroid follicles

• The follicles are made up of a central cavity filled with a sticky fluid called colloid

What is the function of the Thyroid Gland?

• Secretes hormones needed for growth and metabolism

What is the thyroid gland’s essential and unique component in which production is dependent on?

Iodine

• Without iodine, we can not make thyroid hormones

Hormones from the thyroid glands made up of Follicular cells?

• Thyroglobulin

• Triiodothyronine (T3)

• Tetraiodothyronine/Thyroxine (T4)

Hormones from the thyroid glands made up of Parafollicular cells (C cells)?

• Calcitonin

Is T3 more potent that T4?

Yes

• Many cells convert T₄ to T₃ through the removal of an iodine atom.

Functions of the Thyroid hormones?

• Increase basal metabolic rate (BMR)

• Help maintain normal body temperature

• Stimulate protein synthesis

• Increase the use of glucose and fatty acids for ATP production

• Upregulate beta (β) receptors that attach to catecholamines

• Work with hGH and insulin to accelerate body growth

Calcitonin is released in response to a rise in?

Blood calcium levels.

• Decreases blood calcium levels

What are Catecholamines?

Group of hormones

• Norepinephrine

• Epinephrine

• Dopamine

How does calcitonin decrease the blood calcium levels?

• Inhibiting the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix

• Increasing osteoblastic activity

• Decreasing calcium absorption in the intestines

• Increasing calcium loss in the urine

Thyroid-stimulating hormone (TSH) regulates?

The release of T₃ and T₄ from the thyroid gland

Regulation of TH Synthesis if there are low blood levels of T₃ and T_4?

• Release of thyrotropin-releasing hormone (TRH) from the hypothalamus.

• Triggers secretion of TSH from the anterior pituitary.

• TSH stimulates the thyroid gland to secrete T₃ and T₄

• Increased Basal metabolic rate of body cells and rise in body temperature

Regulation of TH Synthesis if there are high blood levels of T₃ and T_4?

• Hypothalamus stops TRH release

• Anterior Pituitary gland stops TSH release

• No T3 or T4 is made

The levels of TRH, TSH, T₃, and T₄ are regulated by a negative feedback system in which?

Increasing levels of T₃ and T₄ decrease the production and secretion of TSH.

Goiter (enlargement of the thyroid gland) and hypothyroidism (cretinism) is caused by?

Hypothyroidism

Exophthalmos (excess thyroid hormones, as in Grave’s disease) is caused by?

Hyperthyroidism

What is the second messenger in many signaling pathways, and is essential for muscle contraction, nerve impulse transmission, and blood clotting?

Calcium

What are the two types of follicle cells in the Thyroid gland?

• Follicular Cells

• Parafollicular Cells

  • C-cells

What are tiny, round structures usually found embedded in the posterior surface of the thyroid gland?

The parathyroid glands

What are the two cells of the parathyroid gland?

• Chief cells

• Oxyphil cells

How many parathyroid glands are there?

Typically four, but it ranges form 2-6

Function of oxyphil cells?

Unclear

Function of Chief cells?

The primary functional cells of the parathyroid glands

• These epithelial cells produce and secrete the parathyroid hormone (PTH), the major hormone involved in the regulation of blood calcium levels.

What separates the thyroid and parathyroid glands?

A thick connective tissue capsule

What are the two hormones that regulate calcium?

• Calcitonin

• Parathyroid Hormone (PTH)

• Two mechanisms that constantly maintain blood calcium concentration at homeostasis

In response to low blood calcium levels, the parathyroid glands produce and secrete?

Parathyroid hormone (PTH)

Parathyroid hormone (PTH) overall effect?

Increases blood calcium levels

• Secretes enzymes that degrade bone and release calcium into the interstitial fluid.

• Causes the release of calcium from the bones by stimulating osteoclasts

• Inhibits osteoblasts, the cells involved in bone deposition, thereby sparing blood calcium.

What are the effects due to the release of Parathyroid hormone (PTH) on bones?

• Inhibits Osteoblasts

• Stimulates Osteoclasts

• Bone is broken down, which releases calcium ions into the blood

What are the effects due to the release of Parathyroid hormone (PTH) on the kidneys?

• Stimulates kidney tubule cells to recover waste calcium from the urine

• Stimulates kidney tubule cells to release calcitrol

What are the effects due to the release of Parathyroid hormone (PTH), which leads to the release of calcitriol in the intestines?

• Stimulates the intestine to absorb calcium from the digestion of food

Effects of calcitonin on bones?

• stimulates osteoblasts

• Inhibits osteoclasts

• Calcium is removed from the blood and used to build bone

• excess calcium goes to bones

• Makes bones

• Stimulates calcium salt deposit in bone

What is Calcitriol?

Active form of Vitamin D

What else is Calcium important for?

• Muscle Contraction

• Blood Clotting

• Etc.

Goiter is caused by?

• iodine deficiency

• Hashimoto’s Disease

• Grave’s disease

• Thyroid nodules

• Thyroid Cancer

• Pregnancy

• Inflammation

What is Hashimoto’s disease?

An autoimmune disorder where the immune system mistakenly attacks the thyroid gland, leading to its damage and reduced hormone production

• causes goiter