Ch. 6 Bones and Skeletal Tissues

Marieb - Human Anatomy & Physiology 11th Edition

Marieb, Hoehn11th EditionHuman Anatomy & PhysiologyISBN: 9780136874034Not the one you use?Change textbook

Marieb, Hoehn 11th Edition

Ch. 6 Bones and Skeletal Tissues

Problem 17

Chapter 6, Problem 17

Why do you think wheelchair-bound people with paralyzed lower limbs have thin, weak bones of the leg and thigh?

Verified step by step guidance

Understand that bones require mechanical stress or weight-bearing activity to maintain their density and strength, a concept known as Wolff's Law.

Recognize that in wheelchair-bound individuals with paralyzed lower limbs, the legs and thighs do not experience normal weight-bearing forces due to lack of movement and muscle contractions.

Identify that the absence of mechanical stress leads to decreased stimulation of bone-forming cells (osteoblasts) and increased activity of bone-resorbing cells (osteoclasts), resulting in bone loss or osteoporosis.

Connect that this bone loss manifests as thinner, weaker bones in the legs and thighs because the skeletal system adapts to the reduced functional demand.

Conclude that maintaining bone strength requires regular mechanical loading, which is absent in paralyzed limbs, explaining the observed bone thinning and weakness.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bone Remodeling and Mechanical Stress

Bone remodeling is a continuous process where bone tissue is broken down and rebuilt. Mechanical stress from weight-bearing activities stimulates bone formation, maintaining bone density and strength. Without regular stress, bones lose mass and become weaker.

Effects of Immobilization on Bone Health

Immobilization or lack of movement, such as in wheelchair-bound individuals, reduces mechanical loading on bones. This leads to decreased bone formation and increased bone resorption, causing bones to become thin, fragile, and prone to fractures.

Impact of Paralysis on Musculoskeletal System

Paralysis of lower limbs results in muscle atrophy and reduced stimulation of bones due to inactivity. The lack of muscle contractions and weight-bearing activities diminishes bone strength and density, contributing to weaker bones in the legs and thighs.

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Related Practice

Textbook Question

Compare bone to cartilage tissue relative to its resilience, speed of regeneration, and access to nutrients.

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Textbook Question

Compare and contrast controls of bone remodeling exerted by hormones and by mechanical and gravitational forces, including the purpose of each control system and changes in bone architecture that might occur.

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Textbook Question

(a) During what period of life does skeletal mass increase dramatically? Begin to decline?

(b) Why are fractures most common in elderly individuals?

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Textbook Question

Describe the process of new bone formation in an adult bone. Use the terms "osteoid seam" and "calcification front" in your discussion.

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Textbook Question

Mrs. Abbruzzo brought her 4-year-old daughter to the doctor, complaining that she didn't 'look right.' The child's forehead was enlarged, her rib cage was knobby, and her lower limbs were bent and deformed. X rays revealed very thick epiphyseal plates. Mrs. Abbruzzo was advised to increase dietary amounts of vitamin D and milk and to get the girl outside to play in the sun. Considering the child's signs and symptoms, what disease do you think she has? Explain the doctor's instructions.

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Textbook Question

Yolanda is asked to review a bone slide that her professor has set up under the microscope. She sees concentric layers surrounding a central cavity. Is this bone section taken from the diaphysis or the epiphyseal plate of the specimen?

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