Human Growth & Endocrine System Overview

Human Growth & Endocrine System

• Human growth is the organized addition of new tissue, occurring from infancy to adulthood.
• Growth involves the lengthening of the skeleton (especially long bones and the spine) and the increasing size of soft tissues.
• The process begins at conception and completes during adolescence, when growth plates fuse.

Growth Mechanisms

• Growth is an increase in the size of a tissue or organism due to hypertrophy (increase in cell size) and hyperplasia (increase in cell number).
• The extracellular matrix around cells also increases in size.

Control of Growth

• Growth patterns are not linear, differing throughout development, like in neonates, infants, and puberty.
• Major factors influencing growth include genetics, adequate diet, and the absence of chronic diseases/stressful environments.

Allometric Growth

• Allometric growth describes differential growth of body parts.
• Body proportions change between infancy and adulthood, with a visible change in proportions as an individual ages from newborn to adult.

Growth Patterns Over Time

• A graph shows the relative growth of different body parts (head, lymphoid tissue, reproductive organs) as a percentage of total growth over time from birth to 15 years.

Structure of Long Bones

• Long bones are made up of spongy bone, medullary cavity, compact bone, diaphysis (shaft), epiphysis, metaphysis, and growth plates.

Bone Elongation and Calcification

• Chondrocytes rapidly divide in the proliferation zone increasing cartilage.
• New cartilage pushes older cartilage towards the diaphysis, lengthening the bone.
• Chondrocytes enlarge and the cartilage matrix calcifies.
• Osteoblasts invade and replace calcified cartilage with bone.

Epiphyseal Lines

• When long bones stop growing around ages 18-25, the epiphyseal cartilage disappears.
• The epiphyseal plate is visible in X-rays as epiphyseal lines.
• Bone can no longer lengthen once the growth plates fuse.

Growth Hormone (GH)

• GH is a 191 amino acid protein hormone.
• It has a half-life of 19 minutes and is secreted in pulses.
• Secretion is greatest in newborns and decreases at 4 years of age, then bursts during puberty after which it again decreases.
• Secreted by somatotrophs in larger quantities than other pituitary hormones.

Pulsatile Secretion of GH

• GH secretion fluctuates throughout the day.
• High levels during sleep and after strenuous exercise.

Pathway of GH Control

• GH release is regulated by a complex feedback loop.
• Stimuli, like GHRH and somatostatin, from the hypothalamus regulate the anterior pituitary. The pituitary then regulates GH levels.
• GH stimulates the liver to produce IGF-1. IGF-1 then further regulates GH secretion.

Factors Affecting GH

• Various factors like glucose, free fatty acids, and hormones like glucocorticoids affect GH secretion.
• Ghrelin, a peptide hormone, is shown to stimulate GH release.
• Various molecules called growth hormone secretagogues (GHS) also stimulate GH release.

Actions of Ghrelin

• Ghrelin stimulates appetite, gastric motility, and acid secretion.
• Affects reproductive function, glucose and lipid metabolism, and cardiovascular function.
• Has anti-inflammatory effects, and stimulates bone formation and cell proliferation.

Explore the stages and mechanisms of human growth, from infancy to adulthood. This quiz highlights the control factors, allometric growth, and key influences that shape development. Test your understanding of how genetics and nutrition impact growth patterns.