THE SKELETAL SYSTEM:
BONE TISSUE 6
B O N E T I S S U E A N D H O M E O S T A S I S Bone tissue is continu
growing, remodeling, and repairing itself. It contributes to homeostasis
body by providing support, protection, the production of blood cells, and th
age of minerals and triglycerides. •
A bone is composed of several different tissues working together: bone or o
tissue, cartilage, dense connective tissues, epithelium, adipose tissue
nervous tissue. For this reason, each individual bone in your body i
sidered an organ. Bone tissue, a complex and dynamic living
continually engages in a process called remodeling
construction of new bone tissue and breaking
of old bone tissue. The entire framewo
bones and their cartilages, along with
ments and tendons, constitutes the sk
system. In this chapter we will surv
various components of bones to
you understand how bones form
age, and how exercise affects thei
sity and strength. The study of
structure and the treatment of bone
ders is called osteology (os-tē-OL
osteo- bone; -logy study of).
,176 CHAPTER 6 • THE SKELETAL SYSTEM: BONE TISSUE
FUNCTIONS OF BONE ing the parts of a long bone, such as the humerus (the arm bon
shown in Figure 6.1a. A long bone is one that has greater leng
AND THE SKELETAL SYSTEM than width. A typical long bone consists of the following par
OBJECTIVE 1. The diaphysis (dı̄ -AF-i-sis growing between) is t
• Describe the six main functions of the skeletal system. bone’s shaft or body—the long, cylindrical, main portion
Bone tissue makes up about 18% of the weight of the human the bone.
body. The skeletal system performs several basic functions: 2. The epiphyses (e-PIF-i-sēz growing over; singular
epiphysis) are the proximal and distal ends of the bone.
1. Support. The skeleton serves as the structural framework for
the body by supporting soft tissues and providing attachment 3. The metaphyses (me-TAF-i-sēz; meta- between; singul
points for the tendons of most skeletal muscles. is metaphysis) are the regions between the diaphysis and the ep
physes. In a growing bone, each metaphysis contains an epiph
2. Protection. The skeleton protects the most important inter-
seal (growth) plate (ep-i-FIZ-ē-al), a layer of hyaline cartila
nal organs from injury. For example, cranial bones protect the
that allows the diaphysis of the bone to grow in length (d
brain, vertebrae (backbones) protect the spinal cord, and the rib
scribed later in the chapter). When a bone ceases to grow
cage protects the heart and lungs.
length at about ages 18–21, the cartilage in the epiphyseal pla
3. Assistance in movement. Most skeletal muscles attach to is replaced by bone; the resulting bony structure is known as t
bones; when they contract, they pull on bones to produce move- epiphyseal line.
ment. This function is discussed in detail in Chapter 10.
4. The articular cartilage is a thin layer of hyaline cartila
4. Mineral homeostasis (storage and release). Bone tissue covering the part of the epiphysis where the bone forms an arti
stores several minerals, especially calcium and phosphorus, ulation (joint) with another bone. Articular cartilage reduc
which contribute to the strength of bone. Bone tissue stores friction and absorbs shock at freely movable joints.
about 99% of the body’s calcium. On demand, bone releases
5. The periosteum (per-e--OS-te--um; peri- round) su
minerals into the blood to maintain critical mineral balances
rounds the external bone surface wherever it is not covered
(homeostasis) and to distribute the minerals to other parts of the
articular cartilage. It is composed of an outer fibrous layer
body.
dense irregular connective tissue and an inner osteogenic lay
5. Blood cell production. Within certain bones, a connective that consists of cells. Some of the cells of the periosteum enab
tissue called red bone marrow produces red blood cells, white bone to grow in thickness, but not in length. The periosteum al
blood cells, and platelets, a process called hemopoiesis protects the bone, assists in fracture repair, helps nourish bo
-
(hēm-ō-poy-E -sis; hemo- blood; poiesis- making). Red tissue, and serves as an attachment point for ligaments and te
bone marrow consists of developing blood cells, adipocytes, fi- dons. It is attached to the underlying bone through perforatin
broblasts, and macrophages within a network of reticular fibers. (Sharpey’s) fibers, thick bundles of collagen fibers that exte
It is present in developing bones of the fetus and in some adult from the periosteum into the extracellular bone matrix.
bones, such as the hip bones, ribs, breastbone, vertebrae (back-
6. The medullary cavity (MED-u--lar-e- ; medulla- marro
bones), skull, and ends of the bones of the arm and thigh. Blood
pith) or marrow cavity is a hollow, cylindrical space within t
cell production is considered in detail on page 693.
diaphysis that contains fatty yellow bone marrow in adults.
6. Triglyceride storage. Yellow bone marrow consists mainly
7. The endosteum (end-OS-te--um; endo- within) is a th
of adipose cells, which store triglycerides. The stored triglyc-
membrane that lines the internal bone surface facing t
erides are a potential chemical energy reserve. In a newborn,
medullary cavity. It contains a single layer of cells and a sm
all bone marrow is red and is involved in hemopoiesis. With
amount of connective tissue.
increasing age, much of the bone marrow changes from red to
yellow. CHECKPOINT
3. Diagram the parts of a long bone, and list the functions
CHECKPOINT
of each part.
1. What types of tissues make up the skeletal system?
2. How do red and yellow bone marrow differ in
composition and function?
HISTOLOGY OF BONE TISSUE
STRUCTURE OF BONE OBJECTIVE
OBJECTIVE • Describe the histological features of bone tissue.
• Describe the structure and functions of each part of a long
We will now examine the structure of bone at the microscop
bone.
level. Like other connective tissues, bone, or osseous tiss
We will now examine the structure of bone at the macroscopic (OS-ē-us), contains an abundant extracellular matrix that su
level. Macroscopic bone structure may be analyzed by consider- rounds widely separated cells. The extracellular matrix is abo
, HISTOLOGY OF BONE TISSUE
Figure 6.1 Parts of a long bone. The spongy bone tissue of the epiphyses and metaphysis contains red bone marrow, and
the medullary cavity of the diaphysis contains yellow bone marrow (in adults).
A long bone is covered by articular cartilage at its proximal and distal epiphyses and by periosteum around
the diaphysis.
Articular cartilage
Proximal
epiphysis Spongy bone Proximal
epiphysis
Red bone marrow
Metaphysis Spongy bone
Epiphyseal line
Metaphysis
Compact bone
Endosteum
Compact bone Medullary cavity
in diaphysis
Periosteum
Medullary cavity (b) Longitudinally sectioned femur (thigh bone)
Diaphysis
Nutrient artery in
nutrient foramen
Humerus
Femur
Functions of Bone Tissue
1. Supports soft tissue and provide
Metaphysis attachment for skeletal muscles.
2. Protects internal organs.
3. Assists in movement along with
skeletal muscles.
Distal
epiphysis 4. Stores and releases minerals.
Articular cartilage
5. Contains red bone marrow, which
produces blood cells.
6. Contains yellow bone marrow, w
(a) Partially sectioned humerus (arm bone)
stores triglycerides (fats).
? What is the functional significance of the periosteum?
25% water, 25% collagen fibers, and 50% crystallized mineral lagen fibers of the extracellular matrix, they crystallize a
salts. The most abundant mineral salt is calcium phosphate tissue hardens. This process, called calcification (kal-si-fi
[Ca3(PO4)2]. It combines with another mineral salt, calcium shun), is initiated by bone-building cells called osteo
hydroxide [Ca(OH)2], to form crystals of hydroxyapatite (described shortly).
[Ca10(PO4)6 (OH)2]. As the crystals form, they combine with still It was once thought that calcification simply occurred
other mineral salts, such as calcium carbonate (CaCO3), and ions enough mineral salts were present to form crystals. W
such as magnesium, fluoride, potassium, and sulfate. As these know that the process requires the presence of collagen
mineral salts are deposited in the framework formed by the col- Mineral salts first begin to crystallize in the microscopic
BONE TISSUE 6
B O N E T I S S U E A N D H O M E O S T A S I S Bone tissue is continu
growing, remodeling, and repairing itself. It contributes to homeostasis
body by providing support, protection, the production of blood cells, and th
age of minerals and triglycerides. •
A bone is composed of several different tissues working together: bone or o
tissue, cartilage, dense connective tissues, epithelium, adipose tissue
nervous tissue. For this reason, each individual bone in your body i
sidered an organ. Bone tissue, a complex and dynamic living
continually engages in a process called remodeling
construction of new bone tissue and breaking
of old bone tissue. The entire framewo
bones and their cartilages, along with
ments and tendons, constitutes the sk
system. In this chapter we will surv
various components of bones to
you understand how bones form
age, and how exercise affects thei
sity and strength. The study of
structure and the treatment of bone
ders is called osteology (os-tē-OL
osteo- bone; -logy study of).
,176 CHAPTER 6 • THE SKELETAL SYSTEM: BONE TISSUE
FUNCTIONS OF BONE ing the parts of a long bone, such as the humerus (the arm bon
shown in Figure 6.1a. A long bone is one that has greater leng
AND THE SKELETAL SYSTEM than width. A typical long bone consists of the following par
OBJECTIVE 1. The diaphysis (dı̄ -AF-i-sis growing between) is t
• Describe the six main functions of the skeletal system. bone’s shaft or body—the long, cylindrical, main portion
Bone tissue makes up about 18% of the weight of the human the bone.
body. The skeletal system performs several basic functions: 2. The epiphyses (e-PIF-i-sēz growing over; singular
epiphysis) are the proximal and distal ends of the bone.
1. Support. The skeleton serves as the structural framework for
the body by supporting soft tissues and providing attachment 3. The metaphyses (me-TAF-i-sēz; meta- between; singul
points for the tendons of most skeletal muscles. is metaphysis) are the regions between the diaphysis and the ep
physes. In a growing bone, each metaphysis contains an epiph
2. Protection. The skeleton protects the most important inter-
seal (growth) plate (ep-i-FIZ-ē-al), a layer of hyaline cartila
nal organs from injury. For example, cranial bones protect the
that allows the diaphysis of the bone to grow in length (d
brain, vertebrae (backbones) protect the spinal cord, and the rib
scribed later in the chapter). When a bone ceases to grow
cage protects the heart and lungs.
length at about ages 18–21, the cartilage in the epiphyseal pla
3. Assistance in movement. Most skeletal muscles attach to is replaced by bone; the resulting bony structure is known as t
bones; when they contract, they pull on bones to produce move- epiphyseal line.
ment. This function is discussed in detail in Chapter 10.
4. The articular cartilage is a thin layer of hyaline cartila
4. Mineral homeostasis (storage and release). Bone tissue covering the part of the epiphysis where the bone forms an arti
stores several minerals, especially calcium and phosphorus, ulation (joint) with another bone. Articular cartilage reduc
which contribute to the strength of bone. Bone tissue stores friction and absorbs shock at freely movable joints.
about 99% of the body’s calcium. On demand, bone releases
5. The periosteum (per-e--OS-te--um; peri- round) su
minerals into the blood to maintain critical mineral balances
rounds the external bone surface wherever it is not covered
(homeostasis) and to distribute the minerals to other parts of the
articular cartilage. It is composed of an outer fibrous layer
body.
dense irregular connective tissue and an inner osteogenic lay
5. Blood cell production. Within certain bones, a connective that consists of cells. Some of the cells of the periosteum enab
tissue called red bone marrow produces red blood cells, white bone to grow in thickness, but not in length. The periosteum al
blood cells, and platelets, a process called hemopoiesis protects the bone, assists in fracture repair, helps nourish bo
-
(hēm-ō-poy-E -sis; hemo- blood; poiesis- making). Red tissue, and serves as an attachment point for ligaments and te
bone marrow consists of developing blood cells, adipocytes, fi- dons. It is attached to the underlying bone through perforatin
broblasts, and macrophages within a network of reticular fibers. (Sharpey’s) fibers, thick bundles of collagen fibers that exte
It is present in developing bones of the fetus and in some adult from the periosteum into the extracellular bone matrix.
bones, such as the hip bones, ribs, breastbone, vertebrae (back-
6. The medullary cavity (MED-u--lar-e- ; medulla- marro
bones), skull, and ends of the bones of the arm and thigh. Blood
pith) or marrow cavity is a hollow, cylindrical space within t
cell production is considered in detail on page 693.
diaphysis that contains fatty yellow bone marrow in adults.
6. Triglyceride storage. Yellow bone marrow consists mainly
7. The endosteum (end-OS-te--um; endo- within) is a th
of adipose cells, which store triglycerides. The stored triglyc-
membrane that lines the internal bone surface facing t
erides are a potential chemical energy reserve. In a newborn,
medullary cavity. It contains a single layer of cells and a sm
all bone marrow is red and is involved in hemopoiesis. With
amount of connective tissue.
increasing age, much of the bone marrow changes from red to
yellow. CHECKPOINT
3. Diagram the parts of a long bone, and list the functions
CHECKPOINT
of each part.
1. What types of tissues make up the skeletal system?
2. How do red and yellow bone marrow differ in
composition and function?
HISTOLOGY OF BONE TISSUE
STRUCTURE OF BONE OBJECTIVE
OBJECTIVE • Describe the histological features of bone tissue.
• Describe the structure and functions of each part of a long
We will now examine the structure of bone at the microscop
bone.
level. Like other connective tissues, bone, or osseous tiss
We will now examine the structure of bone at the macroscopic (OS-ē-us), contains an abundant extracellular matrix that su
level. Macroscopic bone structure may be analyzed by consider- rounds widely separated cells. The extracellular matrix is abo
, HISTOLOGY OF BONE TISSUE
Figure 6.1 Parts of a long bone. The spongy bone tissue of the epiphyses and metaphysis contains red bone marrow, and
the medullary cavity of the diaphysis contains yellow bone marrow (in adults).
A long bone is covered by articular cartilage at its proximal and distal epiphyses and by periosteum around
the diaphysis.
Articular cartilage
Proximal
epiphysis Spongy bone Proximal
epiphysis
Red bone marrow
Metaphysis Spongy bone
Epiphyseal line
Metaphysis
Compact bone
Endosteum
Compact bone Medullary cavity
in diaphysis
Periosteum
Medullary cavity (b) Longitudinally sectioned femur (thigh bone)
Diaphysis
Nutrient artery in
nutrient foramen
Humerus
Femur
Functions of Bone Tissue
1. Supports soft tissue and provide
Metaphysis attachment for skeletal muscles.
2. Protects internal organs.
3. Assists in movement along with
skeletal muscles.
Distal
epiphysis 4. Stores and releases minerals.
Articular cartilage
5. Contains red bone marrow, which
produces blood cells.
6. Contains yellow bone marrow, w
(a) Partially sectioned humerus (arm bone)
stores triglycerides (fats).
? What is the functional significance of the periosteum?
25% water, 25% collagen fibers, and 50% crystallized mineral lagen fibers of the extracellular matrix, they crystallize a
salts. The most abundant mineral salt is calcium phosphate tissue hardens. This process, called calcification (kal-si-fi
[Ca3(PO4)2]. It combines with another mineral salt, calcium shun), is initiated by bone-building cells called osteo
hydroxide [Ca(OH)2], to form crystals of hydroxyapatite (described shortly).
[Ca10(PO4)6 (OH)2]. As the crystals form, they combine with still It was once thought that calcification simply occurred
other mineral salts, such as calcium carbonate (CaCO3), and ions enough mineral salts were present to form crystals. W
such as magnesium, fluoride, potassium, and sulfate. As these know that the process requires the presence of collagen
mineral salts are deposited in the framework formed by the col- Mineral salts first begin to crystallize in the microscopic
