Endocrine Diseases

Most endocrine glands are controlled by hormones produced in the anterior pituitary, themselves under control of substances produced in the hypothalamus. A variety of stimuli control pituitary and hypothalamic hormone release, especially feedback control from hormone levels from the target glands. Levels of pituitary hormones show a circadian rhythm.

Endocrine diseases can be broadly classified as:

Hormone excess

Hormone deficiency

Hormone resistance

Effects of non-functioning tumours

Pituitary Gland

The pituitary has two parts; the anterior (adenohypophysis) and the posterior (neurohypophysis).

Anterior Pituitary (Adenohypophysis)

The blood supply is via a portal system from the hypothalamus bringing peptides which stimulate or inhibit pituitary hormone production. The cells producing each hormone can be identified by immunohistochemistry (for stored hormone) or in situ hybridisation (for mRNA).

Posterior Pituitary

This is composed of neural tissue and secretes two hormones made in the hypothalamus (oxytocin and antidiuretic hormone).

Note

1. ACTH (39 amino acids long) is synthesised as part of a large molecule proopiomelanocortin (POMC) from which other molecules including melanocyte stimulating hormone (MSH) are derived.

2. Hypothalamic releasing hormones have been found for TSH (TRH), LH/FSH (GnRH), ACTH (CRH) and GH (GHRH); somatostatin inhibits release of GH.

Pituitary Hyperfunction

In most cases, this is associated with pituitary adenoma.

Pituitary adenomas are divided on the basis of size into macroadenomas (>10 mm) and microadenomas (<10 mm).

Small tumours present only if they produce excess hormones, while larger tumours may cause pressure effects (e.g. on optic chiasma, page 141) or with hypopituitarism due to destruction of normal pituitary. Occasionally haemorrhage into a pituitary adenoma causes raised intracranial pressure (pituitary apoplexy).

Gigantism and Acromegaly

These are both the result of excess production of growth hormone by a somatotroph (acidophil) adenoma. Gigantism arises in children before the epiphyses have fused; acromegaly occurs in adult life.

Gigantism

The excess growth hormone induces skeletal growth, the bones retaining their normal shape and relative proportions. Fusion of epiphyses is delayed, but eventually occurs and the features of acromegaly appear.

Acromegaly

There is overgrowth of bone and soft tissue.

Clinical signs

Features coarsened: nose enlarged.

Prognathic (projecting jaw).

Irregular bone formation – interferes with joint function – leads to osteoarthritis.

Limbs enlarged.

Pain due to nerve compression is common. Glucose tolerance is diminished and diabetes occurs in 10%. High blood pressure with cardiac hypertrophy and extensive atheroma is common, and the patient may die in cardiac failure. There is a 2–3 fold increased risk of colonic cancer.

Hypopituitarism

Failure of pituitary secretion may affect one or several hormones. Causes include:

This syndrome occurs in women and is due to ischaemic necrosis of the pituitary following post-partum haemorrhage. The normally low pressure in the pituitary portal vascular supply increases the susceptibility of the gland. The results vary with the extent of necrosis and may include the following:

In time, the peripheral endocrine organs – thyroid, adrenals, ovaries – show atrophy.

In childhood, growth hormone deficiency is a cause of dwarfism. Skeletal growth is diminished with retarded sexual development but normal intelligence. Hypothalamic GHRH deficiency may be responsible.

Note: Some individuals treated with human growth hormone have developed Creutzfeld–Jacob disease (p.555).

In adults, GH deficiency leads to lethargy, diminished muscle mass, obesity and premature atheroma.

Thyroid Gland – Underactivity

The thyroid gland is under the control of the pituitary thyroid-stimulating hormone (TSH p.623).

T₄ can be regarded as a prohormone, which is converted to active T₃ by deiodination in liver, muscle and kidney.

Adults – Myxoedema

Clinical signs

Basal metabolic rate reduced, weight gain.

Body temperature falls, cold intolerance.

Lethargy and apathy.

Appetite reduced.

Constipation.

Respiratory and heart rates reduced.

Diminished libido.

Lack of ovulation.

Skin thickened, non-pitting oedema due to increase in mucopolysaccharide ground substance.

Hair brittle, dry and falls out.

Blood cholesterol is raised.

TSH secretion is increased.

T₃ and T₄ blood levels low.

Causes

1. Autoimmune thyroiditis

(a) Atrophic form – so-called primary myxoedema – the commonest cause of hypothyroidism

(b) Hashimoto’s disease.

2. Severe iodine deficiency.

3. Dyshormonogenesis – inborn errors in the formation of thyroid hormones.

4. Anti-thyroid drugs, e.g. lithium

5. Excessive surgical resection of thyroid gland.

6. Treatment with radioiodine.

7. Hypopituitarism → reduced TSH.

Pathological changes in primary myxoedema

Children – Cretinism

Infants normal at birth, but abnormality appears within weeks.

Clinical Signs

Changes are irreversible unless treatment is given early. Two forms are recognised:

(1) endemic and

(2) sporadic cretinism.

Thyroid Gland – Overactivity

Thyroid Hyperfunction

Excessive quantities of circulating thyroid hormone (T₃ and T₄) cause thyrotoxicosis. Three types of thyroid lesion can give rise to thyrotoxicosis.

1. Graves’ disease (exophthalmic goitre) >80%.

2. Toxic nodular goitre 10%.

3. Toxic adenoma <5%.

Graves’ Disease (Exophthalmic Goitre)

Clinical signs:

Graves’ Disease

In some cases there are foci of thyroiditis with lymphocytes and plasma cells.

Other changes:

1. Patches of myxoedema – usually on pre-tibial aspect of legs.

< div class='tao-gold-member'>

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Like this:

Like Loading...

Related

Related posts:

1. Healing
2. Musculo-skeletal System
3. Liver, Gall Bladder and Pancreas
4. Neoplasia

Stay updated, free articles. Join our Telegram channel

Join