57. Disturbances in the function of the pituitary gland.

Growth hormone excess

Gigantism

• Growth hormone excess occurring before puberty and before fusion of the epiphyses of the long bones results in gigantism
• Excessive secretion of GH by somatotrope adenomas causes gigantism in the prepubertal child
• It occurs when the epiphyses are not fused and high levels of IGF stimulate excessive skeletal growth

Acromegaly

• When GH excess occurs in adulthood or after the epiphyses of the long bones have fused, the condition is referred to as acromegaly
• Acromegaly results from excess levels of GH that stimulate the hepatic secretion of IGF-1 → causes most of the clinical manifestations of acromegaly
• The most common cause of acromegaly is a somatotrope adenoma, followed by excess secretion of GHRH by hypothalamic tumours, ectopic GHRH or GH secretion by non endocrine tumours
• Clinical manifestations
• Insidious onset
• Pronounced enlargement of the hands and feet, a broad and bulbous nose, a protruding lower jaw→ due to enlargement of the small bones of the hands and feet and of the membranous bones of the face and skull
• Slanting forehead → facies leonina (face looks like a lion)
• Skin is rough and sweaty
• Deepened voice due to enlargement of the cartilaginous structures in the larynx
• Obstructive lung disorders → GH constricts the bronchioles
• Kyphosis
• Arthralgias (joint pain) due to bone overgrowth, and degenerative arthritis
• Metabolic effects
• Increased release of FFA from adipose tissue → increased concentration of FFA in body fluids
• Enhances formation of ketones and the utilisation of FFA for energy instead of carbohydrates and proteins
• Decreased glucose uptake by skeletal and adipose tissue
• Increased glucose production by the liver
• Increased insulin secretion → GH-induced insulin resistance→ glucose intolerance → pancreatic beta cells secrete more insulin → beta cells become overstimulated and “burn out”
• Increased reabsorption of phosphates by the kidneys → stimulates PTH → secondary PTH and osteoporosis