36 Questions
What is the effect of PTH on osteoblast deposition of calcium?
Inhibition
What is the name of the hormone produced by chief cells?
All of the above
What is the function of PTH in the small intestine?
Increase calcium absorption
What is the result of PTH activation on vitamin D?
Stimulation of vitamin D release
What is the effect of PTH on phosphate ion reabsorption?
Inhibition of phosphate ion reabsorption
How many amino acids does parathyroid hormone consist of?
84
What is the approximate size of a parathyroid gland?
The size of a grain of rice
What is the primary function of parathyroid hormone?
Regulating calcium levels in the blood
What is the role of chief cells in the parathyroid gland?
Producing parathyroid hormone
What is the function of oxyphil cells in the parathyroid gland?
Unknown
How are the chief cells arranged in the parathyroid gland?
In tightly-packed nests around small blood vessels
What is the effect of parathyroid hormone on the kidney?
Increasing calcium ion reabsorption
What surrounds the cells in the parathyroid gland?
A fibrous capsule (connective tissue framework)
How many parathyroid glands are present in the body?
Four
What is the first step in the regulation of PTH direct pathway?
Low serum calcium ions level is sensed by the Calcium sensory receptors
What is the result of the increased transcription of mRNA in the regulation of PTH direct pathway?
Release of PTH from the Chief cells
What is the role of the Chief cells in the regulation of PTH direct pathway?
Releasing PTH
What is the effect of PTH on Ca++ level in the regulation of PTH direct pathway?
It increases Ca++ level
What are the target organs of PTH in the regulation of PTH direct pathway?
Bone and Kidneys
Is Calcitonin involved in the regulation of PTH direct pathway?
No, it is not involved in the regulation of PTH direct pathway
What is the number of amino acids in Pre-Pro PTH synthesized in the RER?
115
What is the enzyme responsible for removing 25 amino acids from Pre-Pro PTH?
Signal peptidase
What is the number of amino acids in PTH after removal of 6 amino acids by Clipase?
84
Where are PTH receptors found in the kidney?
Renal tubules
What is the role of PTH in the small intestine?
It has no direct role
What type of receptor is the Parathyroid Ca++ receptor?
G protein-coupled receptor
What is the mechanism of regulation of PTH?
Negative feedback mechanism
How many pathways are involved in the regulation of PTH?
2
What is the primary function of parathyroid hormone in regulating calcium levels?
To increase calcium levels when they are too low
What is the target tissue/organ of parathyroid hormone?
Bones, kidneys, and intestine
What is the chemical class of parathyroid hormone?
Peptide
What is the condition characterized by the parathyroid glands producing too little parathyroid hormone?
Hypoparathyroidism
What is the term for the condition where the parathyroid glands produce too much parathyroid hormone due to a kidney transplant?
Tertiary hyperparathyroidism
What is the primary cause of secondary hyperparathyroidism?
Something in the body causing the parathyroid glands to produce extra PTH
What is one of the functions of parathyroid hormone in regulating phosphate ion levels?
To regulate phosphate ion levels in serum
What is the effect of parathyroid hormone on blood calcium levels?
It raises blood calcium levels
Study Notes
Parathyroid Gland
- The parathyroid gland is a small, pea-sized gland located in the posterior side of the thyroid gland, with each gland weighing approximately 30 mg and measuring 3-4 mm in diameter.
- There are four parathyroid glands, each about the size of a grain of rice.
- The parathyroid gland secretes parathyroid hormone (PTH), which is an essential regulator of calcium levels in the blood.
Types of Cells in Parathyroid Gland
- There are two main types of cells in the parathyroid gland: oxyphil cells and chief cells.
- Oxyphil cells are the larger cells containing numerous mitochondria, but their function is unknown.
- Chief cells produce parathyroid hormone (PTH).
Histological Structure of Parathyroid Gland
- The chief cells are arranged in tightly-packed nests around small blood vessels.
- The oxyphil cells are larger and contain numerous mitochondria.
- All cells are surrounded by a fibrous capsule (connective tissue framework) that supports them.
Parathyroid Hormone and Target Organs
- Parathyroid hormone acts on three target organs: kidney, small intestine, and bone.
- In the kidney, PTH increases calcium reabsorption, decreases urinary calcium excretion, and inhibits phosphate reabsorption.
- In the small intestine, PTH increases calcium absorption.
- In bone, PTH increases blood calcium by inhibiting osteoblast deposition and stimulating osteoclast removal of calcium.
Structure and Synthesis of Parathyroid Hormone
- Parathyroid hormone (PTH) is a linear polypeptide consisting of 84 amino acids.
- PTH is synthesized as a pre-prohormone in the rough endoplasmic reticulum (RER) of chief cells, which is then converted to pro-PTH and further cleaved to produce the final 84-amino acid PTH molecule.
Parathyroid Hormone Receptors
- PTH receptors are found in target organs, including bones (osteocytes, osteoblasts) and kidneys (renal tubules).
- PTH receptors are not present in the intestine, but instead, PTH activates vitamin D in the kidney to increase calcium absorption from the small intestine.
- Parathyroid Ca++ receptors are G-protein coupled receptors located on the plasma membrane of parathyroid chief cells and kidney tubule cells.
Regulation of Parathyroid Hormone
- PTH is regulated through a negative feedback mechanism involving two pathways: direct and indirect.
- The direct pathway involves the interaction between Ca++ levels and PTH secretion, where low serum calcium levels stimulate PTH secretion.
Function of Parathyroid Hormone
- The main function of parathyroid hormone is to regulate calcium levels by increasing calcium levels when they are too low.
- PTH also activates vitamin D in the kidney and regulates phosphate ion levels in the serum.
Parathyroid Gland Disorders
- Hyperparathyroidism occurs when the parathyroid hormone level is higher, either due to primary, secondary, or tertiary hyperparathyroidism.
- Hypoparathyroidism occurs when the parathyroid glands do not produce enough PTH.
This quiz covers the structure and function of the parathyroid gland, including its location, size, and role in regulating calcium levels.
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