The thyroid gland is a very vascular endocrine gland which is located in the middle of the lower neck, just below the larynx or the voice box. The shape is typically described as “bow tie” or “H” shaped with one half on each side of the neck. The two lobes are joined by the isthmus. Each lobe of the thyroid is about 4cm long and 1 to 2 cm wide. The name "thyroid" comes from the Greek word which means "shield", because the gland does look like a shield. To view the relative size and location of the thyroid gland, please see the diagram below.
The thyroid gland is one of many endocrine glands and it produces hormones which regulate physiological functions of the body. Thyroxine is one of the hormones produced by the thyroid and it regulates the rate at which the patient’s body metabolizes and carries on its necessary functions.
The human body also has a few other endocrine glands, these include the pancreas, the pituitary, the adrenal glands, the parathyroid glands, the testes, and the ovaries. These organs are always richly supplied with blood and are located in strategic areas.
Diagram 1. Neck exposed to show thyroid gland and adjacent organs.
Functions of the Thyroid Gland.
Thyroxine production is the main hormone produced by the thyroid. Thyroxine contains peptides with iodine. The two most important hormone is tetraiodothyronine (thyroxine or T4). Then, there is another hormone called triiodothyronine (T3). Both of these hormones are essential for life and have many effects on body metabolism, growth, and development.
For the thyroid gland to function properly Iodine must be available. It is the main component of thyroid hormones tetraiodothyronine (thyroxine or T4) and triiodothyronine (T3). In some countries like Canada most common salt (sodium chloride) sold for consumption contains added iodine. In some areas it is also added to the water we all drink. Last but not least, in some countries it is added to bread. It would be an interesting exercise for you to find out if the water you drink and the common salt you consume is iodised or not.
Taking excessive doses of iodine as a nutritional supplement or in foods such as kelp will aggravate any autoimmune thyroid disease your patinet may have. If the thyroid gland enlarges, Goitre is said to occur. This enlargement does not always indicate the presence of disease because goitre can also occur as a result of natural physiological conditions like pregnancy and puberty.
Definition of Peptide: Peptides are two or more complex amino acids chained together by a bond called a "peptide bond." A protein is a long chain of amino acids joined together in this way, and therefore is sometimes referred to as a "polypeptide." Some proteins contain more than one polypeptide chain.
Definition of Hormone: Any number of bodily substances that originates in a gland or an organ, are conveyed to other organic sites and have any of a number of effects on these targets cells. Many substances which are listed as hormones by virtue of their production by glands also function as neurotransmitters eg norepinephrine.
Definition of enzyme: An organic substance which acts as a catalyst which produces chemical changes in other substances without being changed themselves. Enzymes are complex proteins found particularly in the digestive processes that break down complex food substances into simple compounds.
How thyroxin affects body metabolism.
- speeds up chemical reactions
- speeds up oxygen consumption
- affects amount of heat produced
Hypothyrodism is a condition in which the thyroid gland fails to produce sufficient amounts of thyroxine for the body’s need. The most common cause of hypothyroidism is
Hashimoto's thyroiditis, a disease of the thyroid gland where the body's immune system attacks the gland. Congenital (birth) defects, surgical removal of the thyroid gland, irradiation of the gland, and inflammatory conditions can cause hypothyroidism.
Four types of thyroid deficiencies are recognised.
Primary hypothyroidism is a condition resulting from the inability of the thyroid gland to sevrete sufficient amounts of thyroxine. In noramal individuals the sevretion of T3 and T4 is controlled by the pituitary gland and the hypothalamus. The signs and symptoms of hypothyrodism include feeling slow and lethargic. In extreme hypothyrodism myxedema coma may occur. This is a medical emergency.
Secondary hypothyroidism is the failure of the pituitary gland to secrete an adequate amoutn of THS.
Tertiary hypothyroidism results when the hypothalamus fails to release thyroid releasing hormone.
Cretinism is a condition of the thyroid in which a peron is born with a thyroid deficiency since childhood.
Signs and Symptoms of Hypothyroidism.
- The patient’s vital signs will be unusual. Heart rate and body temperature may be lower and the patient may complain of feeling cold, even when the ambient temperature is comfortable to other people
- Most patients with hypothyroidism tend to put on weight because the metabolism is slow. Many of us use this as an excuse for our obesity and over eating habits
- The patient may have a dry and lethargic skin
- Female patients may develop mehorrhagia
- Cold feet and low blood pressure may be present
- Facial expressions may become stolid and mask like, bloating in later stages
- Low levels of energy, tire easily, feeling sleepy most of the time
- Severe constipation.
- Tendency to develop arteriosclerosis
- Memory problems
- Brittle hair an nails
- Cerebral ataxia, muscle aches and weakensses, clumsiness
- All thyroid disorders are much more common in women than in men
Diagnosis and evaluation:
- A sample of blood is taken and the serum thyroxine level is measured. Low levels are indicative of hypothyroidism.
- T3 (radioactive- triiodothyronine uptake) low values suggests hypothyroidism
- fine needle aspiration biopsy,
- thyroid scan,
- ultrasound,
- x-rays and/or CT scan
Hyperthyroidism (Graves' disease) is due to too much thyroid hormone.
Treatment and Management of Hyperthyroidism.
Surgical excision of one or both of the lobes of the thyroid gland, this is done under anaesthesia. This procedure is indicated when the patient is experiencing difficulties with breathing and/or swallowing or the gland has become cancerous. One or both of the lobes may be excised.
If you are the Nurse looking after a patient following thyroidectomy, please pay particular attention to neck swelling and respiratory obstruction. This is most likely to occur a few hours after the patient returns from theatre. Be alert to your patient’s respiratory status at night.
Picture 1. Neck showing enlarged thyroid gland. Patient suffers from Graves disease. (Hyperthyroidism = too much thyroixine production) picture from ghorayeb.com
Vocal cord paralysis and hypocalcaemia are two of the most frequent complications. Hypocalcaemia or low blood calcium is normal when both the lobes of the thyroid have been removed. This is due to the interference with the four tiny glands called parathyroid glands, which are located within or very close to the thyroid gland. Fortunately, hypocalcaemia is usually temporary, may require calcium supplements.
Treatment & management of hypothyroidism.
The goal of treatment and management is to correct the thyroid hormone. A medication known as Levothyroxine is the usual choice of most physicians. This medication needs to be taken daily for the rest of one’s life. If it is not take myxedema crises may occur. The final result may be death.
These lecture notes are for nursing students only and are not suitable for diagnosis or treatment. Please see your physician if you have similar signs and symptoms.
