Human Growth and Endocrine System

Human Growth - Role of Endocrine System

• Human growth is the organized addition of new tissue, occurring from infancy to adulthood. It includes lengthening of the skeleton (especially long bones and spine) and increasing size of soft tissues.
• The process starts at conception and finishes in adolescence with growth plate fusion.
• Growth is an increase in the size of a tissue or organism due to hypertrophy (increased cell size) and hyperplasia (increased cell number). It also involves increased extracellular matrix around cells.

Control of Growth

• Human growth is not linear, with different growth patterns evident in neonates, infants, and during puberty.
• Major factors influencing growth include genetics, adequate diet, and the absence of chronic illness or stressful environments. While hormones play a role in growth, other factors are influential.

Allometric Growth in Humans

• Allometric growth is differential growth of body parts.
• Body proportions change between infancy and adulthood.

Growth Patterns Over Time

• A graph shows relative growth patterns of lymphoid tissue, head size, and reproductive organs over time from birth. The relative growth of a human as a whole is also shown.

Structure of Long Bones

• Long bones consist of spongy bone, medullary cavity, compact bone, epiphysis, metaphysis, and diaphysis (shaft).

Bone Elongation and Cartilage Expansion

• Bone elongation is driven by chondrocyte proliferation and cartilage expansion, pushing older cartilage towards the diaphysis.
• Chondrocytes enlarge, and the matrix calcifies.
• Osteoblasts then invade and replace the calcified cartilage with bone.

Epiphyseal Lines

• Long bone growth stops between ages 18-25.
• The epiphyseal plate closes, marking the end of bone lengthening at that point. This is visible on X-rays as an epiphyseal line.

Growth Hormone (GH)

• GH is a protein hormone, species-specific.
• Its half-life is 19 minutes.
• It's secreted in a pulsatile fashion by somatotrophs (in larger quantities than other pituitary hormones).
• Secretion is greatest in newborns, decreases by 4 years, then bursts again during puberty.

Pulsatile Secretion of GH

• GH secretion is not constant but happens in pulses.
• Patterns can change with sleep and periods of strenuous exercise.

Pathway of GH Control

• GH release is regulated by a complex pathway involving the hypothalamus, anterior pituitary, liver, and other factors.
• Factors include short-loop and long-loop feedback, as well as ultra-short-loop feedback loops. Other factors also play a role in the pathway.

Factors Influencing GH Release

• Various hormones, including ghrelin, thyroid hormones, glucocorticoids, sex steroids, and others influence GH release positively or negatively.
• Free fatty acids, glucose and other factors also influence GH release.

Ghrelin and GH

• Endorphin-derived peptides were shown to stimulate GH release.
• Growth hormone secretagogues (GHS) stimulate GH release through the IP3 pathway.
• GH receptor was cloned in 1996 and the natural ligand was identified in 1999 as ghrelin.

Actions of Ghrelin

• Ghrelin influences appetite, food intake, gastric motility, acid secretion, and reproductive function, as well as glucose and lipid metabolism. It also has cardio-vascular effects, influences endocrine effects on exocrine pancreatic secretion and bone, and modulates cell proliferation.

This quiz explores the role of the endocrine system in human growth from infancy to adulthood. It covers aspects such as the control of growth patterns, factors influencing growth, and the concept of allometric growth. Test your knowledge on how hormones and environment play a part in growth and development.