UNIT IV: The Skeletal System

Overview

This unit introduces the structure and function of the skeletal system, focusing on bones, cartilage, and their roles in movement and protection. The following notes summarize key concepts relevant to Anatomy & Physiology students.

Cartilage in the Skeletal System

Structure and Function of Cartilage

• Cartilage is a resilient, flexible connective tissue that forms the initial skeleton in the human embryo. Most cartilage is later replaced by bone, except in areas requiring flexibility.

• Chondrocytes are the primary cells of cartilage, residing in small spaces called lacunae within a jelly-like extracellular matrix.

• Skeletal cartilage is composed mainly of water, making it highly resilient and able to withstand compression.

• Cartilage is avascular (contains no blood vessels) and lacks nerves.

• The perichondrium is a dense connective tissue layer surrounding cartilage, providing nutrients and resisting outward expansion.

Types of Cartilage

• Hyaline cartilage: Most abundant; provides support, flexibility, and resilience. Found in articular surfaces of joints, costal cartilage (ribs), respiratory structures (larynx, trachea), and nasal cartilage.

• Elastic cartilage: Similar to hyaline but contains more elastic fibers. Found in the external ear and epiglottis.

• Fibrocartilage: Contains thick collagen fibers, providing great tensile strength. Located in intervertebral discs, pubic symphysis, and menisci of the knee.

Example: The meniscus in the knee is made of fibrocartilage, allowing it to absorb shock during movement.

Functions of Bones

Main Functions

• Support: Bones provide a framework that supports the body and cradles soft organs.

• Protection: Bones protect vital organs, such as the brain (skull), spinal cord (vertebral column), and thoracic organs (rib cage).

• Movement: Bones act as levers for muscles, enabling movement.

• Mineral Storage: Bones store minerals, especially calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Formation (Hematopoiesis): Occurs in red bone marrow, producing red and white blood cells and platelets.

• Triglyceride (Fat) Storage: Yellow bone marrow stores fat, serving as an energy reserve.

• Hormone Production: Bones produce osteocalcin, a hormone that helps regulate insulin secretion, glucose homeostasis, and energy expenditure.

Example: During periods of low blood calcium, bone tissue is broken down to release calcium into the bloodstream.

Summary Table: Types of Cartilage and Their Locations

Additional info:

• Cartilage is essential for the growth and development of the skeletal system, serving as a precursor to bone in the embryo and providing flexible support in adults.

• Bone functions are often summarized as: support, protection, movement, mineral storage, blood cell formation, fat storage, and hormone production.