Chapter 7: Bone Functions, Classification, and Gross Anatomy

Functions of Bone and the Skeletal System

• Levers for Movement

  • Bones serve as attachment sites for skeletal muscles and other tissues, such as ligaments and skin.

  • Muscles attached to the skeleton contract and exert a pulling force on the skeleton, which functions as a system of levers.

  • Bones alter the direction and magnitude of forces generated by skeletal muscle contractions.

  • Potential movements range from powerful contractions required for running and jumping to delicate, precise movements needed to perform tasks like removing a splinter from a finger.

• Hematopoiesis

  • Etymology: Hematopoiesis ($\text{he'ma-to-poy-e'sis}$) derives from $haima$ (meaning blood) and $poiesi$ (meaning making).

  • Definition: The biological process of blood cell production.

  • Location: Occurs within the red bone marrow of spongy bone connective tissue.

  • Cellular Components: Red bone marrow contains stem cells responsible for forming blood cells and platelets.

• Storage of Mineral Reserves

  • The majority of the body's mineral reserves of calcium and phosphate are stored within and subsequently released from bone connective tissue.

  • When calcium or phosphate is needed by the body, bone connective tissue is broken down to release these minerals into the bloodstream.

  • Calcium: An essential mineral required for:

  • Muscle contraction.

  • Release of neurotransmitters from nerve cells.

  • Blood clotting.

  • Phosphate: A crucial component required for:

  • Structural composition of adenosine triphosphate (ATP), other nucleotides, and phospholipids.

  • Structural composition of the plasma membrane.

• Storage of Energy Reserves

  • Chemical energy is stored in adipocytes (fat cells).

  • These energy reserves are located within the shafts of some adult bones in the form of yellow bone marrow.

Classification of Bones by Shape

Bones appear in various shapes and sizes suited to their specific functions. They are categorized into four major classes based on shape: long bones, short bones, flat bones, and irregular bones.

• Long Bones

  • Proportions: Characterized by a length that is greater than their width.

  • Structural Feature: Possess an elongated, cylindrical shaft known as the diaphysis.

  • Frequency: Represents the most common bone shape in the body.

  • Locations:

  • Upper limbs: Arm, forearm, palm, and fingers.

  • Lower limbs: Thigh, leg, sole of the foot, and toes.

  • Size Variation: Range significantly in size, from the small long bones of the fingers and toes to the large long bones of the thigh (femur) and leg.

• Short Bones

  • Proportions: Have a length nearly equal to their width.

  • Standard Examples: Carpals (wrist bones) and tarsals (foot bones).

  • Sesamoid Bones:

  • Defined as small, sesame seed-shaped bones that develop along the tendons of some muscles.

  • Classified structurally as short bones.

  • The patella (kneecap) is the largest sesamoid bone in the body.

• Flat Bones

  • Proportions & Structure: Feature flat, thin surfaces that may be slightly curved.

  • Functions: Provide extensive surface areas for muscle attachment and protect underlying soft tissues.

  • Examples:

  • Roof of the skull (e.g., frontal bone).

  • Scapulae (shoulder blades).

  • Sternum (breastbone).

  • Ribs.

• Irregular Bones

  • Structure: Exhibit elaborate, complex shapes that do not fit into any of the long, short, or flat bone categories.

  • Examples:

  • Vertebrae.

  • Hip bones (ossa coxae).

  • Skull bones such as the ethmoid bone and sphenoid bone.

Gross Anatomy of Bones

• Overview & Structural Components

  • Long bones consist of specific regional anatomy including the diaphysis, vascular structures, and nerve supplies.

  • Other bone classes (short, flat, and irregular) share foundational tissue types with long bones but differ in macroscopic organization.

  • Bones are highly dynamic tissues requiring dedicated vascular supply (vascularization) and nerve connections (innervation) to support nutrient delivery, mineral exchange, metabolic regulation, and pain/stretch sensation.

Questions & Discussion

• Question: What two minerals are stored in bone, and what are their functions in the body?

  • Response: The two minerals stored in bone are calcium and phosphate. Calcium is required for muscle contraction, neurotransmitter release from nerve cells, and blood clotting. Phosphate functions as a structural component of ATP, other nucleotides, phospholipids, and the cellular plasma membrane.

• Question: What are several examples of flat bones in the body?

  • Response: Examples of flat bones include the bones forming the roof of the skull (such as the frontal bone), the scapulae (shoulder blades), the sternum (breastbone), and the ribs.