Thyroid cartilage Health Dictionary

A hard but pliant substance forming parts of the skeleton – for example, the cartilages of the ribs, of the larynx and of the ears. Microscopically, cartilage is found to consist of cells arranged in twos or in rows, and embedded in a ground-glass-like material devoid of blood vessels and nerves. The end of every long bone has a smooth layer of hyaline cartilage on it where it forms a joint with other bones (articular cartilage), and in young persons up to about the age of 16 there is a plate of cartilage (epiphyseal cartilage) running right across the bone about 12 mm (half an inch) from each end. The latter, by constantly thickening and changing into bone, causes the increase in length of the bone. (See also BONE.) In some situations there is found a combination of cartilage and ?brous tissue, as in the discs between the vertebrae of the spine. This ?bro-cartilage, as it is known, combines the pliability of ?brous tissue with the elasticity of cartilage. (For cartilages of the knee, see KNEE.)... cartilage

A rare disease that accounts for around 1 per cent of all cancers, cancer of the THYROID GLAND usually presents as an isolated hard nodule in the neck. The rate at which the nodule grows depends upon the patient’s age and type of cancer cell. Pain is not usually a feature, but the increasing size may result in the tumour pressing on vital structures in the neck – for example, the nerves controlling the LARYNX (resulting in hoarseness) and the PHARYNX (causing di?culty in swallowing). If more than one nodule is present, they are likely to be benign, not malignant. Treatment is by surgical removal after which the patient will need to take THYROXINE for the rest of his or her life. Radioactive iodine is usually given after surgery to destroy any residual cancerous cells. If treated early, the outlook is good.... thyroid cancer

A highly vascular organ situated in front of the neck. It consists of a narrow isthmus crossing the windpipe close to its upper end, and joining together two lateral lobes which run upwards, one on each side of the LARYNX. The gland is therefore shaped somewhat like a horseshoe, each lateral lobe being about 5 cm (2 inches) long and the isthmus about 12 mm (••• inch) wide, and it is ?rmly bound to the larynx. The weight of the thyroid gland is about 28·5 grams (1 ounce), but it is larger in females than in males and in some women increases in size during MENSTRUATION. It often reaches an enormous size in the condition known as GOITRE (see also THYROID GLAND, DISEASES OF).

Function The chief function of the thyroid gland is to produce a hormone (see HORMONES) rich in iodine – THYROXINE, which controls the rate of body METABOLISM. Thus, if it is de?cient in infants they fail to grow and suffer LEARNING DISABILITY, a condition formerly known as CRETINISM. If the de?ciency develops in adult life, the individual becomes obese, lethargic, and develops a coarse skin, a condition known as hypothyroidism (see under THYROID GLAND, DISEASES OF). Overactivity of the thyroid, or hyperthyroidism, results in loss of weight, rapid heart action, anxiety, overactivity and increased appetite. (See THYROID GLAND, DISEASES OF – Thyrotoxicosis.)

The production of the thyroid hormone is controlled by a hormone of the PITUITARY GLAND – the thyrotrophic hormone.... thyroid gland

Two crescentic layers of ?bro-cartilage on the outer and inner edges of the knee-joint, which form hollows on the upper surface of the tibia in which the condyles at the lower end of the femur rest. The inner cartilage is especially liable to be displaced by a sudden and violent movement at the KNEE.... semilunar cartilages

... thyroid gland, diseases of

See XIPHOID PROCESS.... xiphoid cartilage

A group of blood tests used to evaluate the function of the thyroid gland and to detect or confirm any thyroid disorder. The thyroid hormones T3 and T4 are measured, as well as thyroid-stimulating hormone (TSH), the pituitary gland hormone that stimulates the thyroid gland.... thyroid-function tests

Disorders of the thyroid gland may cause hyperthyroidism, hypothyroidism, or enlargement or distortion of the gland. Myxoedema, Graves’ disease, and Hashimoto’s thyroiditis are common disorders. Goitre may sometimes occur with no accompanying abnormality of thyroid function. In rare cases, the gland is absent at birth, producing severe cretinism. Sometimes it develops in an abnormal position in the neck, causing, in rare cases, difficulty in swallowing or breathing.

A genetic disorder may impair the thyroid’s ability to secrete hormones and goitre may result. Thyroid infection is uncommon and leads to thyroiditis. Viral infection can cause extreme pain and temporary hyperthyroidism. Hormonal changes during puberty or pregnancy may cause a degree of goitre temporarily. Hyperthyroidism due to excessive production of by the pituitary gland is rare but can occur as a result of a pituitary tumour.

Because iodine is necessary for the production of thyroid hormone, its deficiency may lead to goitre. Severe iodine deficiency in children may cause myxoedema. (See also thyroid cancer.)

thyroid hormones The 3 hormones produced by the thyroid gland are thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, and calcitonin, which helps to regulate calcium levels in the body.... thyroid gland, disorders of

Techniques, such as radionuclide scanning and ultrasound scanning, that are used to provide information about the location, anatomy, and function of the thyroid gland.... thyroid scanning

either of the two pyramid-shaped cartilages that lie at the back of the *larynx next to the upper edges of the cricoid cartilage.... arytenoid cartilage

a cartilage that connects a *rib to the breastbone (*sternum). The first seven ribs (true ribs) are directly connected to the sternum by individual costal cartilages. The next three ribs are indirectly connected to the sternum by three costal cartilages, each of which is connected to the one immediately above it.... costal cartilage

the cartilage, shaped like a signet ring, that forms part of the anterior and lateral walls and most of the posterior wall of the *larynx.... cricoid cartilage

a type of *cartilage in which elastic fibres are distributed in the matrix. It is yellowish in colour and is found in the external ear.... elastic cartilage

see xiphoid process.... ensiform cartilage

the most common type of *cartilage: a bluish-white elastic material with a matrix of chondroitin sulphate in which fine collagen fibrils are embedded.... hyaline cartilage

a cartilaginous bar in the fetus around which the *mandible develops. Part of Meckel’s cartilage develops into the malleus (an ear ossicle) in the adult. [J. F. Meckel, the Younger (1781–1833), German anatomist]... meckel’s cartilage

one of a pair of crescent-shaped cartilages in the knee joint situated between the femur and tibia.... semilunar cartilage

a rarely seen but well-documented alteration in the shape of the nails resembling *clubbing but unique to Graves’ disease (see thyrotoxicosis). It is often associated with formation of new bone seen on X-rays of the hands and wrists, which is said to resemble bubbles along the surface of the bones.... thyroid acropachy

autoantibodies directed against the cells of the thyroid gland, which serve as a marker of autoimmune thyroid disease. There are two main types: antibodies directed against the thyroid peroxidise (TPO) enzyme; and anti-thyroglobulin, directed against the thyroid colloid (see thyroid gland). The highest level of thyroid antibodies is found in *Hashimoto’s disease.... thyroid antibodies

(thyroid storm) a life-threatening condition due to an acute and severe exacerbation of previously undiagnosed or inadequately treated *thyrotoxicosis. It often follows infections, childbirth, nonthyroid surgery, or trauma but can occur without an obvious cause. The presenting features are a fever, severe agitation, nausea and vomiting, diarrhoea, and abdominal pains. An accelerated heart rate and irregularity of the heart rhythm can cause heart failure, and psychotic episodes or coma can result. Blood tests will reveal hyperthyroidism and may also show altered liver function, high blood sugar, high calcium levels, a high white blood cell count, and often anaemia. Treatment is with intravenous fluids, oxygen, antithyroid drugs (such as *carbimazole or *propylthiouracil), high-dose iodide solution (see Lugol’s solution), high-dose steroids, and beta blockers. The patient must be cooled and given antipyretics, such as paracetamol. Any underlying cause must also be treated.... thyroid crisis

an iodine-containing substance, synthesized and secreted by the thyroid gland, that is essential for normal metabolic processes and mental and physical development. There are two thyroid hormones, *triiodothyronine and *thyroxine, which are formed from *thyroglobulin. Lack of these hormones gives rise to *cretinism in infants and *myxoedema in adults. Excessive production of thyroid hormones gives rise to *thyrotoxicosis.... thyroid hormone

(TSH, thyrotrophin) a hormone, synthesized and secreted by the anterior pituitary gland under the control of *thyrotrophin-releasing hormone, that stimulates activity of the thyroid gland. Raised levels of TSH are found in primary *hypothyroidism. Normal or low TSH levels in the presence of a low serum thyroxine are found in secondary hypothyroidism and the *euthyroid sick syndrome.... thyroid-stimulating hormone

see thyroid crisis.... thyroid storm