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Chapter 5: A Scaffold to Build On: The Skeleton Summary

Functions of the skeletal system

  1. Protection: The skeleton shields internal organs that are delicate. It protects the organs from damage during motion. An example is a brain that is protected by the cranium.
  2. Movement: The skeletal system provides a surface onto which muscles can be anchored to enable movement. the joints act as fulcrums, bones as levers, and muscles apply force.
  3. Support: The vertebral column supports the whole body weight. The support of the upper body comes from the clavicle. This bone attaches the upper region of the body to the axial skeleton.
  4. Storage of minerals: The bones serve as a store for phosphorus, calcium, and magnesium to maintain a constant concentration of the mineral in the bloodstream.
  5. Formation of blood cells: Many blood cells are formed in the red marrow within long bones ends. three blood cells are formed in the bone marrow: leukocytes, erythrocytes, and thrombocytes.

Types of bones

  1. Long bones: These are bones that form the weight possessing regions of the skeleton. They include bones in legs and arms.
  2. Short bones: These are bones with a blocky like structure and promotes a wide range of movement. They include the tarsals and carpals.
  3. Flat bones: These are bones that protect soft tissues. They include pelvic girdle, skull, scapulae, and sternum.
  4. Irregular bones: These bones are found in a variety of sizes and shapes. They are useful for attachment of tendons, ligaments, and tensions. An example is a patella.

Bone formation process

  • Ossification is the process in which bones are formed.
  • Osteoblasts are the cells that produce mature bone cells called osteocytes.
  • Osteoclasts are cells that digest the bone.

Types of ossification

  • Endochondral ossification: It takes place when minerals calcify on the cartilage produced from the developing fetus which starts at week five of conception.
    • This process occurs in the presence of parathyroid hormone and vitamin D.
    • Bold entering the cartilage brings osteoblast that attaches onto the cartilage.
    • The diaphysis first forms a spongy bone along with the cartilage.
    • The epiphyses then follow to form secondary ossification centers.
    • An epiphyseal plate is then formed from where bone length growth occurs.
  • Intramembranous ossification: The process occurs along with a membrane template.
    •  In the fetus, the formation of the mandible and the skull starts as a membrane.
    • Osteoblasts from blood bind to the membrane and ossify outwards from the center.
    • Skullbone edges do not ossify fully to allow hed molding during birth.

The axial skeleton

  • It has 33 bones found in the vertebral column.
  • They are laid in four curvatures:
    • The cervical curvature has 7 vertebrae.
    • The thoracic curvature contains 12 vertebrae.
    • The lumbar curvature has 5 vertebrae.
    • The pelvic curvature has 5 fused vertebrae.

The sternum

The sternum contains three parts:

  • Manubrium: This is the region that articulates with the clavicle.
  • Body: It is the central part of the sternum that forms the breastbone bulk.
  • Xiphoid process: This forms the lower sternum part where abdominal muscles and diaphragm attach.

Articulating joints

  • Joint articulation refers to any bone union that either moves freely or not at all.
  • Types of joints include the following:
    • Fibrous joints: These joints are joined by fibrous tissue to form a synarthrosis articulation.
    • Cartilaginous joints: the joint is in two forms. They include the following:
      • Synochondrosis articulation which is composed of rigid cartilage that restricts movement.
      • Symphysis joints are formed where bones are fused with cartilage leading to slight movement under pressure.
    • Synovial joints: These are freely moving joints. They have a synovial cavity filled with a fluid released from synovial membranes to caution the joints and release pressure.

Types of synovial joints

  • Gliding joints: They are formed in flat surfaces that slide across each other.
  • Hinge: they allow right-angle movement along one plane.
  • Pivot: They involve joints where one bone rotates on a constantly fixed bone.
  • Condyloid: Formed where a bone head fits into a depression on another bone.
  • Saddle: they contain a saddle-like shape.
  • Ball and socket joint: This is joints involving bones with round heads that fit into a cup-like depression on another bone.
Type of joint movement
  • Flexion
  • Extension
  • Abduction
  • Adduction
  • Rotation
  • Pronation
  • Eversion
  • Circumduction.
  • Supination

Revision

Name five functions of bones.
The functions of the skeletal system are:
To offer a framework that supports body structures and gives shape to the body. To protect delicate internal organs and tissues. To provide attachments for muscles and act as levers in conjunction with muscles to produce movements. To manufacture blood cells in the red bone marrow. To store minerals such as calcium phosphate, calcium carbonate, magnesium, and sodium.

Name the organic and inorganic matter found in bones.
Organic matter of bones consists of bone cells, blood vessels, connective tissue, and marrow. Inorganic matter consists of calcium phosphate and calcium carbonate.

Name two types of bone tissue and indicate where they are found.
Two types of bone tissue are cancellous or spongy tissue and dense or compact tissue. Dense bone tissue is found on the outer portion of the bone just under the periosteum. Cancellous tissue is found on the interior of flat bones and in the ends of long bones.

Which covering protects the bone?
The periosteum covers and protects bone.

How are the bones nourished?
Bones receive their nourishment through blood vessels that enter through the periosteum into the interior of the bone. Bone marrow also aids in the nutrition of the bone.

Name he various shapes of bones found in the body. Give an example of each.
Flat bones, such as the skull; long bones, such as the legs; short bones, such as the fingers; and irregular bones, such as the vertebrae of the spine.

Name two kinds of marrow and where each is found.
Yellow bone marrow is found in the medullary cavity of the long bones. Red bone marrow is located in the ends of the long bones and in flat bones. In infants and young children, red marrow also occupies the cavities of long bones.

What is the function of red bone marrow?
Red bone marrow is the site of blood cell synthesis.

What are the two main parts of the skeleton?
The main parts of the skeleton are the axial skeleton and the appendicular skeleton.

Name three classifications of joints and differentiate between them.
The three classifications joints are synarthrotic joints such as those in the skull, which are immovable; amphiarthrotic joints, which have limited motion; and diarthrotic joints, which are freely movable.

Which structure cushions the bones at the joints?
Articular cartilage cushions bones at the joints.

Which structure connects and supports the bones at the joints?
Bones are supported at the joints by ligaments.

Which fluid lubricates the joints?
Joints are lubricated by synovial fluid or synovium.

Approximately how many bones are found in the human body?
There are approximately 206 bones in the adult human body.

Why must the skeletal system be considered in the practice of massage therapy?
The form or outline of the bones must be carefully followed and the limitations of the range of movements be considered when practicing massage therapy. Knowing the names of bones serves as a guide in recalling the names of related structure connected with the body part being massaged.

List five types of movable joints and give an example of each.
Pivot joints, as in the neck between the atlas and the axis. Hinge joints include the elbows, knees, and two distal joints of the fingers. Ball and socket joints are in the hips and shoulders. Gliding joints, as in the spine or hand. Saddle joints. as in the wrist, thumb, ankle.

What is a fracture?
A fracture is a break or rupture of a bone.

What is a sprain? Describe the difference between the three classes of sprains.
A sprain is an injury to a joint that results in the stretching or tearing of the ligaments. In a class I sprain, the ligament, some discomfort, and minimal loss of function. In a class II sprain, the ligament is torn, with some loss of function. In a class III sprain, the ligaments are torn, and there is internal bleeding and severe loss of function.

What is arthritis? What are the three most common types of arthritis?
Arthritis is an inflammatory condition of the joints often accompanied by pain and changes of bone structure. The three most common types of arthritis are rheumatoid arthritis, osteoarthritis, and gouty arthritis.

What is osteoporosis? Which precautions must be observed when massaging a person with osteoporosis?
Osteoporosis literally means porous bones and is a condition in which minerals are drawn out of the bones, leaving them brittle and weak. When massaging a person with osteoporosis, the therapist must not use heavy pressure or forceful joint movements, either of which could fracture the weakened bones.

Describe three abnormal curves of the spine.
Three abnormal curves of the spine are as follows: kyphosis is an exaggerated convex curve usually associated with the thoracic spine. Lordosis is an exaggerated concave curve usually associated with the lumbar spine. Scoliosis is an abnormal lateral curve of the spine.

T/F: Appositional growth occurs within the epiphyseal plate.
False

Indicate whether each statement is true or false.
1) The most significant age-related changes in the skeletal system affect quality and quantity of bone matrix.

  1. Bone mass is at its highest around the age of 30, and men typically have denser bones than women.
  2. Compact bone is lost first as lamellae become thinner and weaker.
  3. A slow loss of the internal spongy bone begins at about age 40 and increases after age 45.
    1) True
    2) True
    3) False
    4) False

Which step in the formation of calcitriol is regulated by parathyroid hormone?
Conversion of calcidiol to calcitriol

T/F: If you are not getting adequate calcium in your diet, calcitonin will be secreted, which stimulates osteoclasts to resorb bone and thereby increases calcium levels in the blood.
False

The secondary ossification center in a long bone is located in the
epiphysis.

Based on their shape, the most common type of bone is the _ bone.
long

Bone-forming cells that produce collagen and proteoglycans and release matrix vesicles are
osteoblasts

Osseous tissue matrix is composed of
calcium phosphate

An osteoblast is an example of an __ component of bone.
organic

What is the role of nerves that supply a bone?
Detect injuries in the bone

Activity of _ results in the formation of hydrochloric acid used to dissolve bone minerals in a process called _.
osteoclasts; mineral resorption

Parathyroid hormone is released from the __ glands.
parathyroid

Match the part of a long bone with its description.
1) hollow, cylindrical space within the diaphysis
2) Layer of cells that covers all the internal surfaces of the bone
3) Dense irregular connective tissue covering the outer surface of bone
4) Contains bone marrow
5) Contains the growth plate
6) Region between diaphysis and epiphysis
(medullary cavity, metaphysis, endosteum, periosteum)
1) Medullar cavity: contains bone marrow; hollow cylindrical space within the diaphysis
2) Metaphysis: Region between diaphysis and epiphysis; contains the growth plate
3) Endosteum: Layer of cells that covers all internal surfaces of the bone
4) Periosteum: Dense irregular connective tissue covering the outer surface of bone

In the epiphyseal plate, the microscopic zone in which chondrocytes undergo rapid cell division and become aligned into longitudinal columns of flattened lacunae is called the
zone of proliferating cartilage

A flat bone of the skull is produced by _ ossification.
intramembranous

Indicate whether each statement is true or false.

  1. Intramembranous ossification is completed by birth.
  2. Within the spongy bone that is formed by intramembranous ossification, there are spaces that contain developing red bone marrow.
  3. The end products of intramembranous bone formation are bones with outer compact bone surfaces and spongy centers.
    1) False
    2) True
    3) True

Complete each sentence by dragging the proper word or phrase into the appropriate position. Not all terms will be used.
1) Sunlight contacting the epidermis converts________________ to vitamin D₃, otherwise known as cholecalciferol.
2) Transported via the blood to the liver, ____ is converted to calcidiol.
3) Calcidiol returns to the blood once again where transport to the kidneys then allows the final conversion to __.
4) Now in the most active form, calcitriol acts to_______ blood calcium by acting on three target organs: 1) small intestines 2) skeleton, and 3) kidneys.
1) 7-dehydrocholesterol
2) cholecalciferol
3) calcitriol
4) increase

A nutrient artery enters the bone at the (two words) _ _.
nutrient foramen

Bone cells that become surrounded by bone matrix and are located in cavities called lacunae are
osteocytes

The anterior pituitary gland secretes _, which stimulates the formation of ____.
growth hormone; somatomedin

Indicate whether each statement is true or false.

  1. Endochondral ossification ceases at two years of age.
  2. The cartilage model used in endochondral ossification becomes surrounded by perichondrium except in the diaphysis.
  3. In long bones, the diaphysis is the site of the primary ossification center.
  4. In mature bone, the only cartilage that remains is the articular cartilage on the epiphyses of bones.
    1) False
    2) False
    3) True
    4) True

During the healing of a bone fracture, the procallus forms dense regular connective tissue and becomes a __ callus, which lasts for at least three weeks.
fibrocartilaginous

__ is(are) found in compact bone, but not spongy bone.
central canals

T/F: Parathyroid hormone is released in response to elevated blood calcium levels and will help the body return to homeostasis.
False

Match the type of ossification with its brief description.
1) ossification that develops from the mesenchyme
2) Begins with a hyaline cartilage model
1) intramembranous ossification
2) endochondral ossification

Video Question: Bone-producing cells are
osteoblasts

Video Question: Compact bone contains concentric, interstitial, and circumferential
lamellae

Video Question: The combination of all of the concentric rings of bone built around a single blood vessel is called a(n)
osteon

T/F: Bone building cells beneath the endosteum lay down bone to form ridges around a blood vessel.
False

T/F: Once a tunnel of bone is formed around a blood vessel, the bone building cells of the periosteum lay down bone in concentric circles that fill in the tunnel.
False

Video Question: Bones in the legs, arms, spine, and pelvis grow
at different rates.

Video Question: Which of the following is not considered a weight-bearing activity?
Choices: running, swimming, jumping rope, walking
Swimming

Video Question: Trusses and arches that help form an internal scaffolding network are found in
trabecular bone.

Video Question: At which of the following ages would calcium loss from bone be more than calcium deposits into bone, even when a high calcium diet is eaten?
Choices: 50 years old, 18 months old, 18 years old, 10 years old
50 years old

Which mineral is most important throughout life to assist in maintaining strong bone?
calcium

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