Question

in which stage of human development pituitary gland shows highest activity

Answer 1

Human growth is far from being a simple and uniform process of becoming taller or larger. As a child gets bigger, there are changes in shape and in tissue composition and distribution. In the newborn infant the head represents about a quarter of the total length; in the adult it represents about one-seventh. In the newborn infant the muscles constitute a much smaller percentage of the total body mass than in the young adult. In most tissues, growth consists both of the formation of new cells and the packing in of more protein or other material into cells already present; early in development cell division predominates and later cell filling.

Pituitary growth hormone, a protein with molecular weight of 21,600 and of known amino-acid composition, is secreted by the pituitary gland throughout life. Exactly what its function is in the adult is not clear, but in the child it is necessary for growth; without it dwarfism results. During fetal life it seems not to be necessary, though normally present. It is not secreted at a constant rate all day but in small bursts of activity. Secretion by the pituitary is controlled by a substance sent to it from an adjacent part of the brain. The normal stimulus for secretion is not certain, but a sharp and “unnatural” lowering of blood sugar will cause growth hormone to be secreted, and this is used as a test. The hormone decreases the amount of fat and causes protein to be laid down in muscles and viscera. Children who lack it are fat as well as small; when given it by injection, they lose fat and grow rapidly.

The hormone is peculiar in being species-specific; that is, only growth hormone from human glands is active in man. Supplies of the hormone for treating children who need it are obtained at autopsy, and supply has been limited by this. Recombinant DNA technology shows possibilities in increased manufacture of this hormone in the laboratory.

Answer 2

The pituitary is an organ dual of origin. The anterior lobe (adenohypophysis) is epithelial in origin, whereas the posterior lobe (neurohypophysis) derives from the neural ectoderm. Precise spatial and temporal co-ordination of transcription factor expression in both structures is critical for pituitary formation and the differentiation of hormone-producing cells. Disruption of this regulation, for instance by mutation, can lead to numerous developmental disorders. We provide an overview of the molecular drivers of pituitary organogenesis and illustrate the anatomy and histology of the mature pituitary, comprising adenohypophysis (anterior lobe), neurohypophysis (posterior lobe), pars intermedia and infundibulum (pituitary stalk).

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