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By the end of this section, you will be able to:
  • Describe the location and structure of the parathyroid glands
  • Describe the hormonal control of blood calcium levels
  • Discuss the physiological response of parathyroid dysfunction

The parathyroid glands    are tiny, round structures usually found embedded in the posterior surface of the thyroid gland ( [link] ). A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. The function of one type of parathyroid cells, the oxyphil cells, is not clear. The primary functional cells of the parathyroid glands are the chief cells. These epithelial cells produce and secrete the parathyroid hormone (PTH)    , the major hormone involved in the regulation of blood calcium levels.

Parathyroid glands

Part A of this diagram shows the four, small, disc-shaped parathyroid glands embedded in the posterior surface of the thyroid gland. Part B shows a micrograph of parathyroid tissue. The tissue is largely composed of cube-shaped chief cells encircling a central blood vessel. A few larger and darker-staining oxyphil cells are embedded within the many chief cells.
The small parathyroid glands are embedded in the posterior surface of the thyroid gland. LM × 760. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

View the University of Michigan WebScope at (External Link) to explore the tissue sample in greater detail.

The parathyroid glands produce and secrete PTH, a peptide hormone, in response to low blood calcium levels ( [link] ). PTH secretion causes the release of calcium from the bones by stimulating osteoclasts, which secrete enzymes that degrade bone and release calcium into the interstitial fluid. PTH also inhibits osteoblasts, the cells involved in bone deposition, thereby sparing blood calcium. PTH causes increased reabsorption of calcium (and magnesium) in the kidney tubules from the urine filtrate. In addition, PTH initiates the production of the steroid hormone calcitriol (also known as 1,25-dihydroxyvitamin D), which is the active form of vitamin D 3 , in the kidneys. Calcitriol then stimulates increased absorption of dietary calcium by the intestines. A negative feedback loop regulates the levels of PTH, with rising blood calcium levels inhibiting further release of PTH.

Parathyroid hormone in maintaining blood calcium homeostasis

This diagram shows the role of parathyroid hormone in maintaining blood calcium homeostasis. When blood calcium concentration drops, chief cells of the parathyroid gland release parathyroid hormone (PTH). PTH affects bone, the kidneys and the intestines. In regards to bone, PTH inhibits osteoblasts and stimulates osteoclasts. This results in compact bone being broken down, as illustrated by an osteoclast burrowing into the surface of a bone. The break down releases calcium ions into a nearby blood vessel. The osteoblasts are inactive in this stage. In regards to the kidneys, PTH stimulates kidney tubule cells to recover waste calcium from the urine. PTH also stimulates kidney tubule cells to release calcitrol. This is illustrated with a cross section of a kidney tubule, showing the cells of the tubule wall. Urine is running to the left of the tubule wall cells while an artery is to the right. The right edge of the tubule wall cells and the left edge of the artery are separated by a small region of interstitial space. The cells are removing calcium from the urine and pumping it into the interstitial fluid, after which the calcium enters the artery. The cells are also pumping calcitrol into the blood vessel. In regards to the intestine, PTH stimulates the intestines to absorb calcium from digesting food. A cross section of an intestinal cell is shown, which is cube-shaped but with finger-like projections on the intestinal lumen side (top). Beneath the intestinal cell is an artery. Calcitrol is leaving the artery and entering the intestinal cell, stimulating it to absorb calcium from food in the intestinal lumen. The effects of PTH on bone, the kidneys and the intestines all cause blood calcium levels to increase. High calcium concentrations in the blood stimulate the parafollicular cells in the thyroid to release calcitonin. Calcitonin reverses the effects of PTH by stimulating osteoblasts and inhibiting osteoclasts in bone tissue. This is illustrated by calcium ions leaving a blood vessel and traveling to osteoblasts on a section of compact bone. The osteoblasts are thickening the compact bone layer while, in this stage, the osteoclasts are inactive.
Parathyroid hormone increases blood calcium levels when they drop too low. Conversely, calcitonin, which is released from the thyroid gland, decreases blood calcium levels when they become too high. These two mechanisms constantly maintain blood calcium concentration at homeostasis.

Abnormally high activity of the parathyroid gland can cause hyperparathyroidism    , a disorder caused by an overproduction of PTH that results in excessive calcium reabsorption from bone. Hyperparathyroidism can significantly decrease bone density, leading to spontaneous fractures or deformities. As blood calcium levels rise, cell membrane permeability to sodium is decreased, and the responsiveness of the nervous system is reduced. At the same time, calcium deposits may collect in the body’s tissues and organs, impairing their functioning.

In contrast, abnormally low blood calcium levels may be caused by parathyroid hormone deficiency, called hypoparathyroidism    , which may develop following injury or surgery involving the thyroid gland. Low blood calcium increases membrane permeability to sodium, resulting in muscle twitching, cramping, spasms, or convulsions. Severe deficits can paralyze muscles, including those involved in breathing, and can be fatal.

When blood calcium levels are high, calcitonin is produced and secreted by the parafollicular cells of the thyroid gland. As discussed earlier, calcitonin inhibits the activity of osteoclasts, reduces the absorption of dietary calcium in the intestine, and signals the kidneys to reabsorb less calcium, resulting in larger amounts of calcium excreted in the urine.

Chapter review

Calcium is required for a variety of important physiologic processes, including neuromuscular functioning; thus, blood calcium levels are closely regulated. The parathyroid glands are small structures located on the posterior thyroid gland that produce parathyroid hormone (PTH), which regulates blood calcium levels. Low blood calcium levels cause the production and secretion of PTH. In contrast, elevated blood calcium levels inhibit secretion of PTH and trigger secretion of the thyroid hormone calcitonin. Underproduction of PTH can result in hypoparathyroidism. In contrast, overproduction of PTH can result in hyperparathyroidism.

Questions & Answers

type 2 is controled by diet
Chloe Reply
Diet and life style
Paias
Diet how? maybe eating food containing less sugar?
BTS
what is hypotension
regina Reply
hypotension is when the blood pressure is less than 60/50
Mursal
hypo means low so it implies low blood pressure
Isaac
ok
Mursal
what is mild DKA
Mursal
mild diabetic ketoacidosis is when there is high level of sugar in the blood and the ketone bodies build up in the body ,is a type 1 which can lead to type 2
Isaac
what is the normal range for blood pressure?
BTS
120 over 80
Danielle
low blood pressure; opposite of high blood pressure which is hypertension
Regina
what if your a type 2 diabetic and you have no way to get meds due to no insurance what is some good over the counter medications to take?
Ashley
type 2 diabets is controlled by diet not meds.type 1 is contolled by insulin.
Chloe
type 1 diabets cant be controlled type 2 can be controlled.type 1 is worse than type 2 diabets.
Chloe
type 2 is purely a lifestyle disease, eat healthy, fresh, natural unprocessed real foods.
Danielle
sometime , we already eat diabetic diet than the results of blood sugar level not turn good , what is the reason ?
Muhammad
What is a "diabetic diet" though? Be specific. Juvenile diabetes and/or Type 1 diabetes is something that one can be born with, this needs medical diagnosis and intervention.
Danielle
what i mean by diabetic diet is we take fiber-rich food like vegetables,nut and also fish.
Muhammad
ok, no cause a doctor told me I needed metformin and my suger won't go under 300
Ashley
what is the difference between plasma and serum
Gloria Reply
Plasma contains fibrinogen while serum doesn't
Kateregga
plasma ----- fibrinogen = serum
Sneha
In what time stomach empty it's content in to doudemun? what is chyme?
Sneha Reply
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Chemical digestion---Mixtures of the food with the gastric acid Mechanical digestion--- churning of the food in the stomach making it become more involved into chyme
Mercy
absorption takes place in the small intestine because of the presence of the villi
Enada
name the muscles supplied redina nerve
Appu Reply
mechanism of hormone releasing by gland
said Reply
why is muscle tissue not considered to be a type of connective tissue?
Ezel Reply
A Skeletal muscles consist of numerous muscles cells called Muscle Fibers . Three layers of connective tissues surrounded these fibers to make the muscles tissues
Manisha
that's wny connective tissues is not considered as muscles fibers
Manisha
there are 4 types of tissues : epithelial, connective tissue, nervous tissue and muscle tissue, each one has its own properties. The main function of connective tissue is nutrition, it supplies nutrientes to epithelial tissues that are responsible for protection.
Ariete
Muscle tissue has properties that allow movement, the function here is movement and not nutrition like connective tissue.
Ariete
In what time stomach empty it's content in to doudemun?
Sneha
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Does absorption take place in stomach? what are the absorption in the stomach by which cell?
Sneha
mechanism of hormone controlling releasing by gland
said
please can someone explain renin angiotensin aldosteron system for me
okolie
name the joint present between epichysif and diachysif
JAYKISHAN Reply
what is arteries
JAYKISHAN
oxygenated blood carrying vessels
Karanpreet
I think oxygenated blood carrying pulmonary vein
Omaryare
ya this stetment is right 4 pulmonary vein carrying the oxygenated blood
Sneha
What is the relation between cold and clammy skin and disorders that cause poor perfusion?
Tyrone Reply
name the instruments used to measure the gas volume and flow in pulmonary function test
Preethi Reply
Spirometer
Ravi
In a spirometry test, While you are sitting, you breath into a mouthpiece that is connected to an instrument called a spirometer . The spirometer records the amount and the rate of air that you breath in and out over a period of time. When standing, Some numbers might be slightly different.
Ravi
tq soo much
Preethi
u most wlcm
Ravi
what is signal transduction?
Bahle
Signal Transduction (Also know as cell signaling) is the transmission of molecular signal from a cell exterior to its interior.Signals receive by cells must be transmitted effectively into the cell to ensure an appropriate response. This step is initiated by cell - surface receptors.
Ravi
i know now didn't know
Cypline
that's great respond
Feng
what is histological anatomy?
Thelma Reply
what is histological anatomy?
Thelma
the study of form of structure seen under the microscope
Metinah
is the branch of biology which studies the microscopic anatomy of biological tissues.
Jeffrey
it's the study of the microscopic anatomy of cells and tissues in the plants and it's carried out by examining a thin slice of tissues under a microscope light / or an electronic microscope
Manisha
is the study of anatomy in a microscopic level
simon
thank you
Thelma
what are the significance differrences can be donated between the female and male skeleton..
charles
What is Ions and Ionic bonds
Ravi Reply
2 less stable atoms
Hope
Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively
Hope
what is osmosis
Brown Reply
it's out Body Fluid.
Sa
high pressure to low pressure flow
Sneha
Osmosis is the movement of solvent from a region of lower solute concentration to a region of higher solute concentration through a semi- permeable membrane.
Ravi
how many types of tissue
ABBAKARR Reply
4, that is muscle tissue, connective, nerve and epithelial tissue
Mapesho
We have four types of tissue these are ,epithelial tissue,nerve tissue,muscle tissue and connective tissue
Samboat
function of labia minora
temba
why is a graph of plasma [glucose] superimposed
Sefai Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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