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Where is the thyroid gland located?
- Located in the trachea-larynx area
- Composed of 2 lobes that consist of 2 types of cells
What are a single layer of epithelial cells arranged spherically to create a follicle?
What 2 types of cells make up the thyroid gland?
- Follicular cells
- Parafollicular cells
What hormones do the follicular cells make and secrete?
- T4, L-thyroxine
- T3, L-triiodothyronine
- rT3, reverse T3 biologically inactive
Where are the hormones stored in when made by the follicular cells?
Stored in the lumina of follicle
What secretes calcitonin?
What is calcitonin involved with?
What is the function of the thyroid hormones?
Thyroid hormones aid in regulation of several metabolic functions including O2 consumption and heat production, growth, sexual maturity, and protein and carb metabolism
What releases thyrotrophin-releasing hormone (TRH) and stimulates anterior pituitary to secrete thyroid stimulating hormone?
What is a polypeptide hormone that originates in the anterior pituitary gland and regulates synthesis and release of thyroid hormones?
TSH (thyroid stimulating hormone)
How is the secretion of TSH regulated?
- Free T3 (FT3)
- Free T4 (FT4)
How are thyroid hormones circulated in the blood?
- Bound to:
- Thyroxine-binding globulin (TBG)
- Thyroxine-binding prealbumin
- Thyroxine-binding albumin
Which thyroid hormone is more metobolically potent in the tissues?
What is the principal carrier protein for the thyroid hormones?
TBG (thyroxine-binding globulin)
What can cause tissue destruction and analysis is generally directed to measurement of antithyroid peroxidase antibodies (TPOAbs); Also, detected in Hashimoto thyroiditis and in Graves disease?
Thyroid antimicrosomal antibodies (TMAbs)
Enlarged thyroid gland (goiter)
Impaired speech and memory
Increase serum cholesterol and LDL
Decreased: TT3, TT4, FT3, FT4
What is the term for an advanced form of hypothyroidism?
What is important to remember about congenital hypothyroidism/cretinism?
- If untreated in the 1st 3 months of life, irreversible neurological and mental deficiency occurs
- Newborn screening is required in the US
Most common cause of primary hypothyroidism, chronic autoimmune thyroiditis
Has TPOAb, TMAb, TgAb present
Increased: TT3, TT4, FT3, FT4
What is the term for Increased serum levels of thyroid hormones?
What is the term for a life-threatening complication of uncontrolled thyrotoxicosis?
Most common cause of thyrotoxicosis
Exhibits diffuse toxic goiter
Autoimmune disorder with TRAb and TSI present
What is the term that refers to a normal functioning thyroid gland in the presence of an abnormal concentration of TBG?
When is euthyroid seen?
- Estrogen therapy
What is the calculation for the free T4 index?
Free T4 index (FT4I) = TT4 x THBR
THBR (thyroid hormone binding ratio)
Where are the 4 parathyroid glands located and composed of?
- Located bilaterally on or near the thyroid gland capsule
- Composed of chief cells and oxyphil cells
What do chief cells synthesize, store, and secrete?
Parathyroid hormone (PTH)
In the blood, what is the half-life of PTH?
What is the function of PTH?
- Regulation of calcium and phosphate
- Has direct action on bone and kidney
- Has indirect action on the intestines through Vit D
In the kidneys, how does PTH work?
- PTH increases calcium reabsorption in the distal tubule
- Decreases reabsorption of phosphate in the proximal tubule
- Result is phophaturia
In the intestines, how does PTH work?
PTH promotes absorption of calcium and phosphate by stimulating increased production of 1,25 (OH)2D
In bone, how does PTH work?
- PTH stimulates bone resorption (alters osteoclasts) or bone formation
- Elevated PTH increases bone resorption
Name the different forms of the PTH hormone
- Intact PTH
- N-terminal PTH
- Mid-molecule PTH
- C-terminal PTH
What is the reference range of PTH?
How does the measurement of PTH during surgery help the surgeon?
- Measurement of PTH during surgery for ademona resection of the parathyroid glands assists the surgeon in determining completeness of the resection based on the rapid fall of PTHA baseline should be drawn, then one 10 min post-excision - that should be 50% or less of the baseline
What is the clinical significance of hyperparathyroidism?
- Primary hyperparathyroidism: caused by parathyroid adenoma (tumor), parathyroid carcinoma, or hyperplasia
- Secondary hyperparathyroidism: caused by vitamin D deficiency or chronic renal failure
What are the causes of hypoparathyroidism?
- Autoimmune disease
- Inborn errors of metabolism
- Unintentional removal during thyroid surgery
What is secreted by the stomach in response to the vagus and food entering the stomach?
What is the function of gastrin?
Gastrin stimulates secretion of gastric HCl and pancreatic enzymes
What causes a decrease in gastrin secretion?
Acidification of the antrum of the stomach
Has increased gastrin level accompanied by gastric hyperacidity
Caused by: Gastrinomas, Duodenal tumor that secrete gastrin, Pancreatic endocrine tumor that secrete gastrin
How is serotonin synthesized and what secretes it?
- Synthesized from tryptophan
- Secreted by the enterochromaffin cells in the gastrointestinal tract
What is the function of serotonin?
Serotonin is a smooth muscle stimulant and vasoconstrictor that is transported by platelets
How is serotonin metabolized?
Liver metabolizes serotonin to 5-hydroxyindole acetic acid (5-HIAA)
What is included in the endocrine function of the pancreas?
Islets of Langerhans secrete insulin, glucagon, gastrin, and somatostatin into the blood
What is the included in the exocrine function of the pancreas?
Digestive fluid containing bicarbonate and digestive enzymes is made in the acinar cells and secreted into the duodenum
How is the secretion of the digestive fluids regulated?
Regulated by the vagus nerve and the endocrine hormones cholecystokinin and secretin
Where is insulin synethsized and when is it secreted?
- Synthesized in the islets of Langerhans by the beta-cells
- Secreted into the blood when the blood glucose level is elevated
What is the function of insulin?
- Insulin lowers glood glucose
- Insulin affects glucose metabolism by promoting glycogenesis and lipogenesis while inhibiting glycogenolysis
What inhibits insulin?
- Certain drugs (Thiazide, dilantin, diazoxide)
What is the cause and result of hyperinsulinemia?
- Caused by insulinomas (insulin producing tumors of the beta cells of the pancreas)
- Resulting in hypoglycemia
What is the cause and result of hypoinsulinemia?
- Caused by lack of insulin or ineffective insulin
- Resulting in diabetes mellitus
Where is glucagon synthesized at and when is it secreted in the blood?
- Synthesized in the islets of Langerhans by the alpha-cells
- Secreted in to the blood when the blood glucose level is low; exercise, stress, and amino acids
How does glucagon increase blood glucose?
Promoting glycogenolysis in the liver and gluconeogenesis
What inhibits the secretion of glucagon?
Inhibited by insulin
What is the clinical significance of hyperglucagonemia?
Associated with glucagon-secreting tumors of the pancreas (tumors are malignant and have usually metastasized by the time they are diagnosed)