An abnormal increase in the size of the thyroid gland is called a goiter. A goiter can be caused by too little secretion of thyroid hormone, or from hyperthyroidism. Depending on the stage, goiters can be undetectable to the eye, or quite obvious.

Hypothyroidism is characterized by large weight gain, slow heart rate, and slowing of movement, speech, and thoughts. Hyperthyroidism generally includes the contrasting symptoms, such as weight loss, rapid heart rate, and tremor. Addison's disease involves the hyposecretion of steroid hormones from the adrenal gland and does present with some of the same symptoms as hypothyroidism, but may include nausea, diarrhea, and craving for salty foods. The parathyroid is a major regulator of calcium and phosphate levels via parathyroid hormone. Its effects are to increase blood calcium. 

Hypocalcemia is defined as low levels of calcium in the blood. Hypercalcemia is defined as elevated levels of calcium in the blood. The body's corrective response to hypocalcemia may involve secretion of parathyroid hormone and/or activation of vitamin D.

Cushing's syndrome is an endocrine disorder characterized by the oversecretion of glucocorticoids. It is often caused by a pituitary tumor that oversecretes adrenocorticotropic hormone (ACTH) or by a cortisol-secreting tumor of the adrenal gland. Addison's disease involves the opposite cause (hyposecretion of glucocorticoids and mineralocorticoids from the adrenal gland).

Hyposecretion of glucocorticoids is found in Addison's syndrome. Addison's syndrome is often caused by autoimmune conditions, infection, cancer, or tuberculosis. Cushing's syndrome is caused by the opposite (hypersecretion of cortisol).

Insulin deficiency in type I diabetes is caused by loss of pancreatic beta cells in the islets of Langerhans. It is an autoimmune disorder which results in destruction of beta cells via T-cells. This occurs in genetically-predisposed people, and is treated with insulin therapy. Alpha cells secrete glucagon, and gamma cells secrete somatostatin. 

Vitamin D deficiency can lead to a condition called rickets, which is a disease of growing bone. The skin is involved in vitamin D production. Vitamin D3 is produced by UV radiation of substances in the skin. When vitamin D levels are low, the absorption of calcium, phosphorus, and other minerals is impaired. This ultimately leads to bone-softening diseases such as rickets and/or osteomalacia, in which the bones may bow.

Seasonal affective disorder (SAD) may be caused by too much melatonin secretion resulting from increased hours of darkness. Melatonin is a hormone that is regulated by the light-dark cycle and plays a role in the circadian rhythm (the body's biological clock). 

Grave's disease is an autoimmune condition which causes the body to produce antibodies that bind to thyroid stimulating hormone (TSH) receptors, and mimic the effect of TSH. This results in the overproduction of the thyroid hormone, which leads to hyperthyroidism. Addison's disease is not an autoimmune disease, and involves the hyposecretion of steroid hormones from the adrenal glands. Cushing syndrome is a combination of signs and symptoms caused by prolonged hypercortisolism. Myasthenia gravis may be caused by an autoimmunity malfunction, and involves the inactivation of acetylcholine receptors on the postsynaptic cell of the neuromuscular junction. This results in muscle weakness. Systemic lupus erythematous is an autoimmune disease in which the body mistakenly attacks healthy cells of many different internal organs.

Hypothyroidism is a condition in which too little thyroid hormone is secreted into the blood. There are various causes of hypothyroidism including atrophy of the gland, autoimmune destruction, and lack of dietary iodine. Myasthenia gravis is usually an autoimmune disease that affects skeletal muscles. Diabetes mellitus type I is an autoimmune disease that results in the destruction of the pancreatic beta-cells. Treatment involves insulin therapy. Diabetes insipidus is an endocrine disorder that is caused by decreased levels of antidiuretic hormone.