Endocrinology

There are many valuable resources for endocrinology, but also some gaps. Please let us know if you would like to recommend something.

Overview

The endocrine system consists of several glands, in different parts of the body, that secrete hormones directly into the blood rather than into a duct system. Hormones have many different functions and modes of action; one hormone may have several effects on different target organs, and, conversely, one target organ may be affected by more than one hormone. Although every organ system secretes and responds to hormones (including the brain, lungs, heart, intestine, skin, and the kidney), the clinical specialty of endocrinology focuses primarily on the endocrine organs, meaning the organs whose primary function is hormone secretion. These organs include the pituitary, thyroid, parathyroids, adrenals, ovaries, testes, and pancreas.

Pathophysiology

Endocrinology is the study of chemical communication systems that provide the means to control a huge number of physiological processes. Like other communication networks, endocrine systems contain transmitters, signals and receivers that are called, respectively, hormone producing cells, hormones and receptors. Understanding hormone secretion and action is key to the study of Endocrinology. From here, the various individual endocrine organs can be studied in more detail, and the feedback loops and pathology can be understood. Endocrine systems are now known to interact with nervous and immune system are the role of genetics in endocrinology is emerging. There are a number of very good resources here covering aspects of pathophysiology, some of which extend into clinical areas.

Clinical Endocrinology

Hormones influence or control a wide range of physiological activities, such as growth, development, puberty, level of alertness, sugar regulation and appetite, bone growth, etc. Problems with hormones and the way they work contribute to some of the major diseases of mankind; for example, diabetes, thyroid conditions, pituitary conditions, some sexual problems, some neurological problems, appetite and obesity, bone problems, cancer, etc.

Clinical Endocrinology is a wide-ranging specialty but for simplicity we have divided it up according to the main endocrine organs. There are many general resources (covering all subjects); we have provided links to the appropriate sub-speciality pages, and inserted some topic specific resources.

In this section we concentrate on the diagnosis and management of disease. At the end we provide links to sites discussing clinical cases, and providing self assessment.

The Endocrine Pancreas

The Endocrine Pancreas secretes hormones (insulin and glucagon), which are mainly responsible for blood glucose control. This will be discussed in more detail in our separate diabetes pages.

The Thyroid Gland

Thyroid disease is very common and can present with over or under production of thyroid hormones, a neck lump or a goitre. In the UK, autoimmune disease is the most common cause of thyroid abnormality, although multi-nodular goitre is a growing problem in older populations. Medication, coincident illness, viruses, and pregnancy can all interfere with thyroid status. On a worldwide scale, goitre due to iodine deficiency is a common problem. Students often find interpretation of thyroid function tests difficult and there are resources here to help with this and other aspects of clinical management of thyroid disease. The types and treatment of thyroid cancer is also covered here.

The Adrenal Gland

The adrenal gland is located above the kidney and produces a number of key hormones . It is separated into two distinct structures, the adrenal cortex and medulla. The cortex mainly produces cortisol (zona fasciculata), aldosterone (zona glomerulosa), and androgens (zona reticularis), whilst the medulla chiefly produces epinephrine and norepinephrine, secreted in the flight or fight response.

The main pathological conditions affecting the adrenal gland are tumours which are usually benign, but occasionally malignant. They are either secretory (aldosterone (Conn’s tumours), catcholamine (Phaochromocytoma), androgen or cortisol producing) or non-functioning. Incidental adenomas are increasingly common because of widespread use of modern imaging techniques. Enzymatic defects such as seen in congenital adrenal hyperplasia lead to widespread adrenal hormone dysfunction requiring careful management. There is also a growing interest in the role of idiopathic adrenal hyperplasia, which is emerging as a common cause of secondary hypertension.

The Parathyroid glands, Calcium, Vitamin D and Bone

Plasma calcium levels are dictated by many factors including diet , GI absorption, renal and liver function, drug interactions, bone health, and levels of Vit D/ parathyroid hormone. Chronic hyperparathyroidism or vitamin D deficiency can have profound secondary effects on bone, which will demineralised secondary to hormone stimulus or in attempt to retain the plasma calcium status quo. It is important when investigating a person with calcium problems to assess all these potential causes and consider consequences.

Hyperparathyroidism (in younger patients) and malignancy in older patients are the most common cause of hypercalcaemia. Whilst immediate management may be similar, long term management differs greatly. Vitamin D deficiency is an increasing problem and may have more serious implications for long term health than previously thought. Osteoporosis is a common multifactorial disease, that is diagnosed on the basis of bone density (using DEXA scanning). Treatment for osteoporosis is aimed at reducing fracture risk and includes medication and lifestyle measures.

These and other common diseases of calcium and vitamin D metabolism will be described in detail in the resources below:

Reproductive Endocrinology /Gonads

Reproductive Endocrinology may be managed by gynaecologists or endocrinologists (or both). Common referrals in women include: abnormalities of pubertal development, amenorrhea, abnormal menstruation, infertility, premenstrual syndrome, menopause and hormone replacement. Polycystic ovarian syndrome is the largest referral problem with a growing prevalence in line with the obesity epidemic. In men, testosterone deficiency, erectile dysfunction and infertility are the commonest issues.

Pituitary Disease

The pituitary is an endocrine gland about the size of a pea located below the hypothalamus in a small bony cavity called the sella turcica. The pituitary gland secretes hormones usually under the control of hypothalamic regulators. Pituitary hormones stimulate other endocrine glands, and are regulated by ‘feedback loops’.

The pituitary is divided into anterior and posterior lobes . The anterior pituitary secretes ACTH (stimulating adrenal steroid production), TSH (stimulating thyroxine production), LH and FSH which control gonadal function and prolactin (which impact on menstrual function and control lactation). The posterior pituitary releases oxytocin (best known for its role in induction of labour), and ADH (also known as vasopressin) which regulates salt and water balance.

Any brain condition that results in damage to the pituitary gland or it’s blood supply may cause hormonal disturbance. Conditions affecting the pituitary gland directly include tumours (ademonas) (most of which are benign), which are categorised as non-functioning or functioning. Functioning tumours produce excess hormone leading to Acromegaly (GH excess), Cushings disease (ACTH excess), Amenorrhoea/ lactation/ gynaecomastia (prolactin excess), Thyrotoxicosis (TSHoma). Pituitary hormone deficiency may result from destruction of the pituitary gland by pathological causes or secondary to treatment of an adenoma/ craniopharyngioma or may be due to a primary syndromes such Isolated Growth Hormone deficiency/ hypophysitis- leading to Diabetes Insipidus.

Endocrine Syndromes

There are a number of rare but well characterised endocrine sydromes, many of which now have well defined genetic causes. These include multiple endocrine neoplasia (MEN) types 1 and 2 ,and the polyglandular syndromes which are predominantly auto-immune in nature.

Endocrinology in systemic disease

The endocrine system may be disregulated in many common systemic diseases ranging from hypertension to heart failure and renal disease. Hypo-natraemia is one of the commonest endocrine referrals from general medical wards. Some of the resources below touch on aspects of endocrinology in systemic disease and also covers other endocrine disease originating outwith the classical endocrine organs such as neuro-endocrine tumours/ carcinoid.

Clinical Case Scenarios and Self Assessment

There are a number of websites with clinical case scenarios that span different areas of endocrinology. These are great for consolidating knowledge and understanding the clinical and management implications. They are also good practice material for clinical examinations. There is also some self assessment material (mainly in MCQ format).