<< Chapter < Page Chapter >> Page >

A third hormone, calcitonin, is produced by parafollicular cells of the thyroid either releasing hormones or inhibiting hormones. Calcitonin release is not controlled by TSH, but instead is released when calcium ion concentrations in the blood rise. Calcitonin functions to help regulate calcium concentrations in body fluids. It acts in the bones to inhibit osteoclast activity and in the kidneys to stimulate excretion of calcium. The combination of these two events lowers body fluid levels of calcium.

Parathyroid glands

Most people have four parathyroid glands ; however, the number can vary from two to six. These glands are located on the posterior surface of the thyroid gland, as shown in [link] . Normally, there is a superior gland and an inferior gland associated with each of the thyroid’s two lobes. Each parathyroid gland is covered by connective tissue and contains many secretory cells that are associated with a capillary network.

The parathyroid glands are round structures located on the surface of the right and left lobes of the thyroid gland. In the illustration shown, there are two parathyroid glands on each side, and one is located above the other.
The parathyroid glands are located on the posterior of the thyroid gland. (credit: modification of work by NCI)

The parathyroid glands produce parathyroid hormone (PTH). PTH increases blood calcium concentrations when calcium ion levels fall below normal. PTH (1) enhances reabsorption of Ca 2+ by the kidneys, (2) stimulates osteoclast activity and inhibits osteoblast activity, and (3) it stimulates synthesis and secretion of calcitriol by the kidneys, which enhances Ca 2+ absorption by the digestive system. PTH is produced by chief cells of the parathyroid. PTH and calcitonin work in opposition to one another to maintain homeostatic Ca 2+ levels in body fluids. Another type of cells, oxyphil cells, exist in the parathyroid but their function is not known. These hormones encourage bone growth, muscle mass, and blood cell formation in children and women.

Adrenal glands

The adrenal glands are associated with the kidneys; one gland is located on top of each kidney as illustrated in [link] . The adrenal glands consist of an outer adrenal cortex and an inner adrenal medulla. These regions secrete different hormones.

The adrenal glands are lumpy, irregular structures located on top of the kidneys.
The location of the adrenal glands on top of the kidneys is shown. (credit: modification of work by NCI)

Adrenal cortex

The adrenal cortex    is made up of layers of epithelial cells and associated capillary networks. These layers form three distinct regions: an outer zona glomerulosa that produces mineralocorticoids, a middle zona fasciculata that produces glucocorticoids, and an inner zona reticularis that produces androgens.

The main mineralocorticoid is aldosterone, which regulates the concentration of Na + ions in urine, sweat, pancreas, and saliva. Aldosterone release from the adrenal cortex is stimulated by a decrease in blood concentrations of sodium ions, blood volume, or blood pressure, or by an increase in blood potassium levels.

The three main glucocorticoids are cortisol, corticosterone, and cortisone. The glucocorticoids stimulate the synthesis of glucose and gluconeogenesis (converting a non-carbohydrate to glucose) by liver cells and they promote the release of fatty acids from adipose tissue. These hormones increase blood glucose levels to maintain levels within a normal range between meals. These hormones are secreted in response to ACTH and levels are regulated by negative feedback.

Questions & Answers

How do mermaid reproduce?
Ini-odu Reply
what is a microscope
Faith Reply
Can i get access to Functional Approach Biology
Bako Reply
How does the synthesis of organic compounds in photosynthetic bacteria differ from that in: green plants ,chemosynthetic bacteria?
Bako
green plants uses photons or light from the sun for synthesis of food but chemosynthetic autotrophs uses chemical subtances for synthesis of organic materials
Ebenezer
what is zygote?
Obialor Reply
a foetus gotten from the fusion of the male and female gamete
Akinpelu
Important of bacteria to human
Ebben Reply
how does meiosis produced
Kauzi Reply
Meiosis happens in sex cells only. And produces 4 nonidentical sex cells.
Eric
what are structure of the cell
wana Reply
what did Darwin say about evolution
Hope Reply
effect of planning beans of using fertilizer
Elizerbeth Reply
what do we mean by transgenic organisms?
FADILAT Reply
what is or are the functions of the Islets of Langarhaans
FADILAT
They are the regions of the pancreas that contains the endocrine cell
Iyadi
is the studly of life
Aisha Reply
what is biology
Asunta Reply
is the study of living organism and their interection with one another and their environment.
Belbon
what is soil
Mukisa Reply
the top layer of the earth in which plant's, tree's
Ahmad
type of soil
Asunta
function of cell wall
Nthati Reply
function of cell wall
Asunta
To protect the cell from bursting
Maurice
to protect the cell from bursting
Deborah
to protect all other internal components of the cell
Olaoye
What is escherichia coli
Tumise Reply
It's an example of gram negative Bacteria
Abdulrasheed

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask