Chapter 7: SKELETAL SYSTEM
7.1 Introduction
- Bones, the organs of the skeletal system, support and protect softer tissues, provide
points of attachment for muscles to enable body movement, house blood-producing cells,
and store inorganic salts.
7.2 Bone Structure
- Bone classification:
- Bones may be classified according to their shape--long, short, flat, or irregular.
- Parts of a Long Bone
- At each end of a long bone is an expanded portion called an epiphysis, which
articulates (forms a joint) with another bone.
- The epiphysis that is nearest the attachment to the trunk of the body is
called the proximal epiphysis.
- The epiphysis that is farthest from the trunk of the body is called the distal
epiphysis.
- The shaft of the bone, between the epiphysis, is called the diaphysis.
- The wall of the diaphysis is mainly composed of tightly packed tissue
called compact bone, also called cortical bone.
- Compact bone has a continuous extracellular matrix with no gaps.
- The epiphyses, in contrast, are composed largely of spongy
bone, also called cancellous bone, with thin layers of
compact bone on their surfaces.
- A tough covering of dense connective tissue called the periosteum, completely
encloses the bone, except for the articular cartilage on the bone’s ends.
- The periosteum is firmly attached to the bone, and periosteal fibers are
continuous with the connecting ligaments and tendons.
- The periosteum also helps form and repair bone tissue.
- Compact bone in the diaphysis of a long bone forms a tube with a hollow
chamber called the medullary cavity, that is continuous with the spaces of the
spongy bone.
- Microscopic Structure
- Bone cells called osteocytes occupy very small, bony chambers called lacunae.
- The lacunae are within the bony matrix of the lamellae, which form
concentric circles around central canals (Haversian canals).
- In compact bone, osteocytes and layers of extracellular matrix are clustered
around a central canal and form a cylinder-shaped unit called an osteon
(Haversian system). Many osteons together form the substance of compact bone.
7.4 Bone Function
- Bones shape, support, and protect body structures.
- Aid in body movements, house tissue that produces blood cells, and store inorganic salts.
- Support, Protection, and Movement
- Bones give shape to structures such as the head, face, thorax, and limbs.
- They also support and protect.
- For example, the bones of the lower limbs, pelvis, and backbone support
the body’s weight.
, - The bones of the skull protect the eyes, ears, and brain.
- Bones of the rib cage and shoulder girdle protects the heart and lungs,
whereas the bones of the pelvic girdle protects the lower abdominal and
internal reproductive organs.
- Bones and muscles interact to cause limbs and other body parts to move.
- Blood Cell Formation
- The process of blood cell formation is called hematopoiesis.
- Two types of marrow: red and yellow.
- Red marrow functions in the formation of red blood cells, white blood
cells, and blood platelets.
- The color comes from the oxygen-carrying pigment hemoglobin in
the red blood cells.
- Yellow marrow, which stores fat, replaces much of the red marrow when
someone ages.
- Storage of Inorganic Salts
- Vital metabolic processes require calcium.
- Bones store calcium.
- The extracellular matrix of bone tissue is rich in calcium salts, mostly in
the form of calcium phosphate.
7.5 Skeletal Organization
- Two major portions: an axial skeleton and the appendicular skeleton.
- The axial skeleton consists of the bony and cartilaginous parts that support and protect
the organs of the head, neck, and trunk.
- Skull. The skull is composed of the cranium, or brain case, and the facial bones.
- Vertebral Column. The vertebral column, or spinal column (backbone), consists
of many vertebrae separated by cartilaginous intervertebral discs. Near the distal
end of the vertebral column, five vertebrae fuse, forming the sacrum, which is part
of the pelvis. The coccyx, a small, rudimentary tailbone composed of four fused
vertebrae, is attached to the end of the sacrum.
- Thoracic Cage. The thoracic cage protects the organs of the thoracic cavity and
the upper abdominal cavity. It is composed of twelve pairs of ribs, which
articulates posteriorly with the thoracic vertebrae. The thoracic cage also includes
the sternum, or breastbone, to which most of the ribs attach anteriorly.
- The appendicular skeleton consists of the bones of the upper and lower limbs and the
bones that anchor the limbs to the axial skeleton.
- Pectoral girdle. Part of the skeleton that supports and attaches the upper limbs.
The pectoral girdle is formed by the scapula, or shoulder blade, and a clavicle, or
collarbone, on both sides of the body. The pectoral girdle connects the bones of
the upper limb to the axial skeleton and aids in upper limb movements.
- Upper limbs. Each upper limb consists of a humerus, or arm bone, two forearm
bones—a radius, and an ulna—and a hand.
- The humerus, radius, and ulna articulate with each other at the elbow joint.
At the distal end of the radius and ulna is the hand. There are eight carpals,
or wrist bones. The five bones of the palm are called metacarpals, and the
fourteen bones of the fingers are called phalanges.
7.1 Introduction
- Bones, the organs of the skeletal system, support and protect softer tissues, provide
points of attachment for muscles to enable body movement, house blood-producing cells,
and store inorganic salts.
7.2 Bone Structure
- Bone classification:
- Bones may be classified according to their shape--long, short, flat, or irregular.
- Parts of a Long Bone
- At each end of a long bone is an expanded portion called an epiphysis, which
articulates (forms a joint) with another bone.
- The epiphysis that is nearest the attachment to the trunk of the body is
called the proximal epiphysis.
- The epiphysis that is farthest from the trunk of the body is called the distal
epiphysis.
- The shaft of the bone, between the epiphysis, is called the diaphysis.
- The wall of the diaphysis is mainly composed of tightly packed tissue
called compact bone, also called cortical bone.
- Compact bone has a continuous extracellular matrix with no gaps.
- The epiphyses, in contrast, are composed largely of spongy
bone, also called cancellous bone, with thin layers of
compact bone on their surfaces.
- A tough covering of dense connective tissue called the periosteum, completely
encloses the bone, except for the articular cartilage on the bone’s ends.
- The periosteum is firmly attached to the bone, and periosteal fibers are
continuous with the connecting ligaments and tendons.
- The periosteum also helps form and repair bone tissue.
- Compact bone in the diaphysis of a long bone forms a tube with a hollow
chamber called the medullary cavity, that is continuous with the spaces of the
spongy bone.
- Microscopic Structure
- Bone cells called osteocytes occupy very small, bony chambers called lacunae.
- The lacunae are within the bony matrix of the lamellae, which form
concentric circles around central canals (Haversian canals).
- In compact bone, osteocytes and layers of extracellular matrix are clustered
around a central canal and form a cylinder-shaped unit called an osteon
(Haversian system). Many osteons together form the substance of compact bone.
7.4 Bone Function
- Bones shape, support, and protect body structures.
- Aid in body movements, house tissue that produces blood cells, and store inorganic salts.
- Support, Protection, and Movement
- Bones give shape to structures such as the head, face, thorax, and limbs.
- They also support and protect.
- For example, the bones of the lower limbs, pelvis, and backbone support
the body’s weight.
, - The bones of the skull protect the eyes, ears, and brain.
- Bones of the rib cage and shoulder girdle protects the heart and lungs,
whereas the bones of the pelvic girdle protects the lower abdominal and
internal reproductive organs.
- Bones and muscles interact to cause limbs and other body parts to move.
- Blood Cell Formation
- The process of blood cell formation is called hematopoiesis.
- Two types of marrow: red and yellow.
- Red marrow functions in the formation of red blood cells, white blood
cells, and blood platelets.
- The color comes from the oxygen-carrying pigment hemoglobin in
the red blood cells.
- Yellow marrow, which stores fat, replaces much of the red marrow when
someone ages.
- Storage of Inorganic Salts
- Vital metabolic processes require calcium.
- Bones store calcium.
- The extracellular matrix of bone tissue is rich in calcium salts, mostly in
the form of calcium phosphate.
7.5 Skeletal Organization
- Two major portions: an axial skeleton and the appendicular skeleton.
- The axial skeleton consists of the bony and cartilaginous parts that support and protect
the organs of the head, neck, and trunk.
- Skull. The skull is composed of the cranium, or brain case, and the facial bones.
- Vertebral Column. The vertebral column, or spinal column (backbone), consists
of many vertebrae separated by cartilaginous intervertebral discs. Near the distal
end of the vertebral column, five vertebrae fuse, forming the sacrum, which is part
of the pelvis. The coccyx, a small, rudimentary tailbone composed of four fused
vertebrae, is attached to the end of the sacrum.
- Thoracic Cage. The thoracic cage protects the organs of the thoracic cavity and
the upper abdominal cavity. It is composed of twelve pairs of ribs, which
articulates posteriorly with the thoracic vertebrae. The thoracic cage also includes
the sternum, or breastbone, to which most of the ribs attach anteriorly.
- The appendicular skeleton consists of the bones of the upper and lower limbs and the
bones that anchor the limbs to the axial skeleton.
- Pectoral girdle. Part of the skeleton that supports and attaches the upper limbs.
The pectoral girdle is formed by the scapula, or shoulder blade, and a clavicle, or
collarbone, on both sides of the body. The pectoral girdle connects the bones of
the upper limb to the axial skeleton and aids in upper limb movements.
- Upper limbs. Each upper limb consists of a humerus, or arm bone, two forearm
bones—a radius, and an ulna—and a hand.
- The humerus, radius, and ulna articulate with each other at the elbow joint.
At the distal end of the radius and ulna is the hand. There are eight carpals,
or wrist bones. The five bones of the palm are called metacarpals, and the
fourteen bones of the fingers are called phalanges.
