Human Growth and Endocrine System

Study Notes

Human growth is the organized addition of new tissue, occurring from infancy to adulthood. It involves lengthening of the skeleton (especially long bones) and an increase in size of soft tissues.
Growth begins at conception and is largely complete in adolescence.
Growth is an increase in size of a tissue or organism, caused by either hypertrophy (increase in cell size) or hyperplasia (increase in cell number), or an increase in extracellular matrix.
Growth patterns are not linear, differing throughout development, including neonate, infant, and puberty stages.
Major factors influencing growth include genetics, adequate diet, and the absence of chronic disease or environmental stress.

Allometric growth refers to how different body parts grow at different rates. This leads to changes in body proportions from infancy to adulthood.

GH is a 191 amino acid protein hormone.
Its half-life is 19 minutes.
It is secreted in a pulsatile fashion.
Secretion is greatest in newborns, decreases at around age four, and then increases again during puberty.
GH is released from somatotrophs in larger amounts than other pituitary hormones.

GH secretion is controlled by a complex feedback loop involving the hypothalamus and anterior pituitary gland, as well as the liver and tissues.
The hypothalamus releases GHRH and somatostatin, which stimulate or inhibit GH.
The pituitary gland releases GH based on these factors.
The liver and other tissues release IGF-1, which provides long-loop feedback.

Various factors influence GH release, including hormones (like GHRH and somatostatin), nutrients (such as glucose, fatty acids), and stress.

Endorphin-derived peptides stimulate GH release.
Growth hormone secretagogues (GHS) stimulate GH release through the IP₃ pathway.
The GHS receptor was discovered in 1996.
Ghrelin is the natural ligand of the GHS receptor, discovered in 1999.

Ghrelin affects appetite, gastric motility, reproductive function, glucose/lipid metabolism, and cardiovascular system.
It also stimulates endocrine and exocrine pancreatic secretion, bone formation, and cell proliferation.
It has anti-inflammatory effects.

Long bones are composed of diaphysis (shaft), epiphysis (ends), and metaphysis, containing growth plates.
Growth plates are cartilage responsible for bone lengthening.
When growth stops, the growth plate is replaced by epiphyseal line.

Growth is a controlled process influenced by genetics, diet, hormones, and environmental factors.
The endocrine system plays a critical role in controlling the rate and pattern of growth.