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Julian Davis
Julian Davis

Ductless Gland

Ductless glands are glands that secrete their product directly onto a surface rather than through a duct. Examples are the goblet cells in the epithelial surface of the digestive, respiratory, urinary and reproductive systems. Many endocrine glands are also ductless glands, as they secrete the hormones they produce directly into the blood or lymph system so it will be circulated to the entire body. The pineal gland, the thymus gland, the pituitary gland, the thyroid gland, the spleen, and the two adrenal glands are all ductless glands.

ductless gland

The endocrine system, along with the nervous system, functions in the regulation of body activities. The nervous system acts through electrical impulses and neurotransmitters to cause muscle contraction and glandular secretion. The effect is of short duration, measured in seconds, and localized. The endocrine system acts through chemical messengers called hormones that influence growth, development, and metabolic activities. The action of the endocrine system is measured in minutes, hours, or weeks and is more generalized than the action of the nervous system.

The endocrine glands do not have ducts to carry their product to a surface. They are called ductless glands. The word endocrine is derived from the Greek terms "endo," meaning within, and "krine," meaning to separate or secrete. The secretory products of endocrine glands are called hormones and are secreted directly into the blood and then carried throughout the body where they influence only those cells that have receptor sites for that hormone.

A gland is an organ which produces and releases substances that perform a specific function in the body. There are two types of gland. Endocrine glands are ductless glands and release the substances that they make (hormones) directly into the bloodstream. These glands form part of the endocrine system and information on them is included in this website. There is another type of gland called an exocrine gland (e.g. sweat glands, lymph nodes). These are not considered part of the endocrine system as they do not produce hormones and they release their product through a duct. Information on these glands is not included on this website.

The adrenal glands are small structures attached to the top of each kidney. The human body has two adrenal glands that release chemicals called hormones into the bloodstream. These hormones affect many parts of the human body.

(English pronunciations of ductless gland from the Cambridge Advanced Learner's Dictionary & Thesaurus and from the Cambridge Academic Content Dictionary, both sources Cambridge University Press)

The pineal is a small endocrine gland present in the diencephalon region of the brain. It helps in the release of melatonin, which has an influence on our sleep patterns. This melatonin also has an influence on the melanocytes and melanotropes present in the skin.

The pituitary gland is a small endocrine gland with a weight of 0.5 to 1 gram and a diameter of 1 cm. It is situated in the sphenoid bone at the base of the skull. It is connected with the hypothalamus by the hypophyseal stalk or pituitary stalk. The hypothalamus links the nervous and endocrine systems through the pituitary.

Parathyroid glands are four small glands present as pairs in each lobe of the thyroid gland. The gland produces the parathyroid hormone (PTH) which regulates the level of calcium ions (Ca2+) in the blood. PTH regulates calcium levels along with calcitonin by promoting the breaking of bones, reabsorption by the renal system and absorption of calcium ions from food. The normal bone destruction by osteoclasts in bone resorption is triggered indirectly by PTH.

The thymus gland is a lymphoid organ positioned between the two lungs behind the sternum. Structurally, it is a two-lobed gland forming a major part of the immune system. The peptide hormone called thymosine secreted by the thymus gland produces T-lymphocytes for the cell-mediated immunity and antibodies for humoral immunity. On arrival of puberty, the human thymus becomes much smaller and starts to disintegrate which in turn reduces the production of thymosins. This is why immunity in old individuals is generally weaker than immunity in infants.

Adrenal glands are two triangular-shaped glands present at the top of each kidney. The outer cortex part secretes a hormone generally known as corticosteroids while the inner medulla produces hormones generally known as catecholamines.

Gonads are the reproductive glands which include both male and female sex organs. The male gonad also called testes, is the primary centre which produces androgen. Testosterone is an important hormone among them. They are responsible for the secondary sexual characteristics of puberty and other hormonal regulations.

Chemical messengers are the substances involved in cell signalling that are mainly secreted from endocrine glands. Some of them are secreted by nerve endings and the cells of several other tissues also. All these chemical messengers carry certain signals to the target cells. They may be hormones or hormone-like substances.

Secretions of endocrine glands are called hormones. The anterior pituitary secretes growth hormone, thyroid-stimulating hormone, luteinising hormone, adrenocorticotropic hormone (ACTH), etc. Whereas the posterior pituitary secretes hormones like oxytocin and antidiuretic hormone (ADH). The thyroid secretes T3, T4 and calcitonin. The pancreas primarily secretes insulin and glucagon.

The thyroid is an endocrine gland located at the root of the neck on either side of the trachea. It secretes three hormones, namely the T4 or thyroxine, T3 and calcitonin. Tyrosine and iodine are essential for the formation of these thyroid hormones. They primarily stimulate growth in children and increase metabolic rate.

Exocrine glands release (secrete) substances through openings (ducts) onto your body surfaces. Exocrine glands secrete sweat, tears, saliva, milk and digestive juices. A gland is a unit of cells that work together to create and secrete these substances. Exocrine glands can be found in many different organs in your body. They have a variety of functions.

Your liver and pancreas are exocrine glands too. Your liver secretes bile through ducts into your gastrointestinal tract. Your pancreas secretes pancreatic juices through ducts into your gastrointestinal tract. But your liver and pancreas are also considered endocrine glands. They have dual roles. They also secrete hormones directly into your bloodstream.

Endocrine glands are also known as the ductless glands because of the fact that their secretions are released directly into the blood, not to any tubes or ducts. Hypothalamus, Pituitary gland, Pineal body, Thyroid, Parathyroid, Adrenal glands, Pancreas, and Gonads are the major glands that make up the human endocrine system.

Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary glands are neuroendocrine organs.[1]

The pituitary gland hangs from the base of the brain by the pituitary stalk, and is enclosed by bone. It consists of a hormone-producing glandular portion of the anterior pituitary and a neural portion of the posterior pituitary, which is an extension of the hypothalamus. The hypothalamus regulates the hormonal output of the anterior pituitary and creates two hormones that it exports to the posterior pituitary for storage and later release.

The thyroid gland is located in the front of the neck, in front of the thyroid cartilage, and is shaped like a butterfly, with two wings connected by a central isthmus. Thyroid tissue consists of follicles with a stored protein called colloid, containing[thyroglobulin], a precursor to other thyroid hormones, which are manufactured within the colloid.

Calcitonin, produced by the parafollicular cells (C cells) of the thyroid gland in response to rising blood calcium levels, depresses blood calcium levels by inhibiting bone matrix resorption and enhancing calcium deposit in bones.Excessive secretion cause hyperthyroidism and deficiency cause hypothyroidism.

The pancreas, located in the abdomen, below and behind the stomach, is both an exocrine and an endocrine gland. The alpha and beta cells are the endocrine cells in the pancreatic islets that release insulin and glucagon and smaller amounts of other hormones into the blood. Insulin and glucagon influence blood sugar levels. Glucagon is released when the blood glucose level is low and stimulates the liver to release glucose into the blood. Insulin increases the rate of glucose uptake and metabolism by most body cells.

The pineal gland is located in the diencephalon of the brain. It primarily releases melatonin, which influences daily rhythms and may have an antigonadotropic effect in humans.[citation needed] It may also influence the melanotropes and melanocytes located in the skin.[citation needed]

The natural decrease in function of the female's ovaries during late middle age results in menopause. The efficiency of all endocrine glands seems to decrease gradually as ageing occurs. This leads to a generalized increase in the incidence of diabetes mellitus and a lower metabolic rate.

The endocrine glands belong to the body's control system. The hormones which they produce help to regulate the functions of cells and tissues throughout the body. Endocrine organs are activated to release their hormones by humoral, neural, or hormonal stimuli. Negative feedback is important in regulating hormone levels in the blood.

Endocrine disease is characterized by irregulated hormone release (a productive pituitary adenoma), inappropriate response to signalling (hypothyroidism), lack of a gland (diabetes mellitus type 1, diminished erythropoiesis in chronic kidney failure), or structural enlargement in a critical site such as the thyroid (toxic multinodular goitre). Hypofunction of endocrine glands can occur as a result of the loss of reserve, hyposecretion, agenesis, atrophy, or active destruction. Hyperfunction can occur as a result of hypersecretion, loss of suppression, hyperplastic, or neoplastic change, or hyperstimulation. 041b061a72


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