Thyroid gland, Regulation, and Insulin/Adrenal

Thyroid gland secretes

Thyroxine - made in follicle epithelial cells

Calcitonin - made in cells between the follicles

Thyroxine production

Thyroglobulin is made in and secreted in the lumen of the follicle then iodinated, stored, and processed by the follicle epithelial cells and turned into T₃ and T₄

Follicles are activated by

Thyrotropin (TSH) secreted by the anterior pituitary so that thyroxine production starts

Thyrotropin (TSH) production is activated by

Thyrotropin releasing hormone (TRH) from the hypothalamus activates the TSH producing pituitary cells in the anterior pituitary

The production of T₃ and T₄ is regulated by _____

Negative feedback loop

Is thyroxine water soluble or lipid soluble

Lipid soluble

Conditions/ diseases caused by thyroxine imbalance

Cretinism

Goiter

Cretinism

Insufficient thyroxine in a human fetus or growing child

• results in physical and mental retardation

Goiter causes

Hyperthyroidism and Hypothyroidism

Goiter - hyperthyroidism

Graves disease - autoimmune disease

• Antibodies on follicle cells keep the thyroid gland active causing excess thyroxine

symptoms: High metabolic rate, usually hot, buildup of fat behind the eyeballs (causing eye to bulge)

Goiter - hypothyroidism

Iodine deficiency

• with too little iodine the follicle cells can’t produce thyroxine

• Thyroglobulin is still made but it is not turned into thyroxine

symptoms: low metabolism, intolerance to cold, general physical and mental sluggishness

Mechanisms for regulation of Calcium levels 

• Deposition or reabsorption of bone

• Excretion or retention of Ca by kidneys

• Absorption of Ca from digestion tract

Too much Calcium

depressed nervous system (muscle weaken including heart)

Too little Calcium

Overexcited nervous system (muscle spasms and seizures)

Calcitonin

Released by Thyroid land

• regulated bone turnover by decreasing the activity of osteoclasts

Osteoclasts

Break down bone and release Ca into the blood

Osteoblasts

Take up Ca and deposit it in new bone

Parathyroid hormone (PTH)

Secreted by the parathyroid glands

• works on bone and kidney

  • increases osteoclasts

  • stimulates kidney to reabsorb Ca

• Blood Ca levels control synthesis and release of PTH

• Acts on kidneys to eliminate phosphate in urine

Calcitriol

Made from Vitamin D (Calciferol)

PTH activates conversion of Calciferol (Vit D) to Calcitriol

• Increases gut absorption of Ca from food

Release of phosphate from bone is stimulated from

PTH (parathyroid hormone)

Increases in Ca and phosphate in the blood can result in ______

Precipitation of calcium and phosphate salts

Kidney stones are

Ca deposits

Diabetes mellitus (type 1) cause

lack of insulin

How does insulin enable glucose intake by the cells

Insulin controls Glucose transporters.

Transporters inside the cell move to the cell membrane and facilitate glucose uptake.

Without insulin transporters remain in the cells cytoplasm

Islets of Langerhans

Endocrine cells in the pancreas that secrete different hormones

• Beta cells

• Alpha cells

• Delta cells

Pancreas beta cells produce:

Insulin

Pancreas alpha cells produce:

Glucagon

Pancreas delta cells produce:

Somatostatin

type 2 diabetes causes

Low production of insulin or ​Insensitivity to insulin​

When blood glucose levels drop__

alpha cells release glucagon

Glucagon does what?

Stimulates liver to convert glycogen to glucose

Somatostatin

Paracrine functions

• inhibits insulin and glucagon release

• slows digestion to increase nutrients absorption

Hypothalamic somatostatin

growth hormone inhibiting hormone (GHIH)

• inhibits release of growth hormone and thyrotropin