Animal, Plant & Soil Science

Lesson C2-3The Skeletal System

Objectives Examine the skeletal system, and

describe its functions.

Identify the components of bone, discuss the three cell types found in bones, and discuss how bones are classified.

Objectives Differentiate between moveable and

immoveable joints.

Discuss the chemical process in the formation of bones and calcification.

Identify and recall the names of bones found in livestock and companion animals.

What is the skeletal system, and what are its functions? In mammals the skeletal system consists

of bones, teeth, joints, and structures that connect bones to other bones or muscles (e.g., ligaments, tendons, and cartilage).

The skeletal system gives animals shape and has the following functions.

What is the skeletal system, and what are its functions? A. Support: Many bones of the body

provide support, but this is especially true of the long bones. For example, the long bones

in legs help support the trunk. Bones other than long bones

also provide support. For example, the first vertebra

supports the skull.

What is the skeletal system, and what are its functions? B. Protection: A vital function of the

skeletal system is the protection of vital internal organs. The skull protects the brain, and the rib cage

protects the heart, lungs, and abdominal organs.

C. Movement: In combination with the muscular system, the skeletal system provides for bodily motion. Skeletal muscles are attached to bones by

tendons that act as a lever to move bones.

What is the skeletal system, and what are its functions? D. Mineral storage: The outer layers of

bony tissues are used for the storage of minerals (primarily calcium and phosphorus). Deposits and

withdrawals of mineral ions from bone are continuous, which helps to maintain blood levels of calcium and phosphorus.

What is the skeletal system, and what are its functions? E. Blood-cell formation: The inner core of

bone is a soft tissue called bone marrow. Red marrow is a major site of blood cell and

platelet formation. F. Energy storage: Yellow marrow is found

in the shaft of long bones and other mature bones. Yellow marrow consists mostly of fat and

serves as an energy reserve.

What are bone components? What are the three cell types found in bones? How are bones classified? Bones are composed of inorganic and

organic materials and are classified by shape.

A. Sixty-five percent of bone is inorganic, primarily calcium phosphate, which gives bone its hardness and rigidity.

B. The organic component consists of the three cell types found in bones and osteoid, which is primarily collagen and gives bone its high tensile strength.

What are bone components? What are the three cell types found in bones? How are bones classified? The three cell types found in bones are

osteoblasts, osteocytes, and osteoclasts. 1. The osteoblasts form a bone matrix by

secreting collagen, become enclosed in the matrix, and develop into osteocytes.

2. Osteocytes are the principle bone cells that maintain daily cellular activities (e.g., exchange of nutrients and wastes with blood).

What are bone components? What are the three cell types found in bones? How are bones classified?

3. Whereas osteoblasts deposit bone, osteoclasts secrete enzymes that digest bone.

Bone is a living tissue that is continually remodeled in response to the body’s need for calcium and for repairing damaged tissue.

Osteoclasts are important in the development, growth, maintenance, and repair of bone.

What are bone components? What are the three cell types found in bones? How are bones classified? C. Bones are classified by

shape as long, short, flat, sesamoid, and irregular.

1. Long bones are cylindrical in shape and consist of a shaft with two ends. Found in limbs, long bones

typically support body weight and act as levers.

The femur, or thighbone, is an example of a long bone.

What are bone components? What are the three cell types found in bones? How are bones classified 2. Short bones are cube-like

in that they are nearly equal in length and width. Short bones are found in the

knee and hock and help to absorb the shock of impact.

What are bone components? What are the three cell types found in bones? How are bones classified 3. Flat bones are typically thinner and

usually curved. Flat bones (e.g., ribs, scapula, and some

bones in the skull) surround and protect vital organs.

What are bone components? What are the three cell types found in bones? How are bones classified 4. Sesamoid bones are small and

embedded in tendons. The patella (knee cap) is the only human

sesamoid bone. 5. Irregular bones have a variety of shapes

and sizes. Vertebrae and some bones in the skull are

examples of irregular bones.

What is the difference between a moveable and an immoveablejoint? A joint, or articulation, is the union of

bone or cartilage. The classification of

joints is based on joint structure and mobility.

Joints are classified as fibrous, cartilaginous, or synovial.

What is the difference between a moveable and an immoveablejoint? A. Fibrous joints include those

united by connective tissue or fused bone. Fibrous joints, or fixed joints,

typically do not permit any type of movement.

An example of this type of joint is found in the skull.

What is the difference between a moveable and an immoveablejoint? B. Cartilaginous joints allow only slight

movement; these are joints in which the bones are connected with cartilage. An example of a cartilaginous joint is the area

between vertebrae. This area has a pad of

cartilage that separates and cushions vertebrae.

What is the difference between a moveable and an immoveablejoint? C. Synovial joints are freely movable

joints in which the bones are held together (at the joints) by ligaments.

Within the joint is synovial fluid, which lubricates the joint and permits it to move freely and without friction.

Types of synovial joints include ball-and-socket, hinge, and pivot.

What is the difference between a moveable and an immoveablejoint? 1. Ball-and-socket joints allow movement

in all directions. For example, the ball of the femur fits into the

socket on the hip bone. 2. A hinge joint allows movement in one

axis. The knee and elbow joints are

examples of hinge joints. Hinge joints work similarly to a

hinged door in that they primarily allow movement in one direction.

What is the difference between a moveable and an immoveablejoint? 3. A pivot joint is found between the first

and second vertebrae. It allows the head to be turned in more than

one direction. A pivot joint allows

rotation around a point.

What is the chemical process in the formation of bones andcalcification? As mentioned previously, bone is a living

tissue that is continually remodeled in response to the body’s need for calcium and for repairing damaged tissue.

In addition, bone is capable of growth. Bone begins development long before

birth as cartilage, which is a firm but pliable tissue found in mature animals at the ends of long bones and between vertebrae.

What is the chemical process in the formation of bones andcalcification? Cartilage is also found in ears and noses. It is found in higher proportions in younger

animals because most cartilage is transformed into bone as animals grow and age.

The process of transforming cartilage into bone is called endochondral ossification.

Even after ossification, bones are ever changing due to growth and remodeling.

What is the chemical process in the formation of bones andcalcification?

A. Bones grow in length but they also grow in thickness through a process called appositional growth. Growth in length occurs in long

bones at the ends between the epiphysis and diaphysis.

Long bones have two epiphysis (enlarged ends) and one diaphysis (shank).

The area of growth is called the growth plate, or epiphysial–diaphysial cartilage, and is where cartilage is formed in layers.

What is the chemical process in the formation of bones andcalcification?

The layers gradually become bone through calcification, and a new layer of cartilage is formed.

Calcification is the deposition of calcium salts that harden, which is a process that continues until adulthood.

Once the cartilage is replaced by bone, bone growth stops.

Thus, animal growth stops, except for fattening.

What is the chemical process in the formation of bones andcalcification? B. Once a bone has been formed, it is

continuously being remodeled. Bone remodeling involves the action of

osteoblasts, osteoclasts, and two hormones: the parathyroid hormone and calcitonin.

The parathyroid hormone (PTH) is secreted by the parathyroid gland when blood calcium levels are low.

PTH stimulates the osteoclast cells, which causes the digestion or resorption of bone.

What is the chemical process in the formation of bones andcalcification?

As a result, Ca++ is released into the bloodstream. Calcitonin is secreted by the thyroid gland when blood calcium levels are high.

Calcitonin inhibits bone resorption and increases osteoblast activity, which causes a deposition of bone matrix.

What are the names of bones commonly found in livestock andcompanion animals? There are many bones found in livestock

and companion animals that share the same names as human bones.

Veterinarians, livestock producers, and even pet owners benefit from knowing the names of these common bones.

What are the names of bones commonly found in livestock andcompanion animals? A. The bone that surrounds and protects

the brain is known as the skull. Similarly, bones that surround and protect the

spinal cord are known as vertebrae. There are five types of vertebrae, beginning

near the skull with cervical and followed by thoracic, lumbar, sacral, and coccygeal.

B. The two bones that make up the jaw are known as the mandible and maxilla. The maxilla is positioned above the mandible.

What are the names of bones commonly found in livestock andcompanion animals? C. The shoulder blade is called the scapula. In the front arm (or wing) of an animal, the large

single bone above the joint is called the humerus.

Below the joint contains two bones: the ulna and the radius.

The front foot bones are known as the carpals and metacarpals, while the rear foot bones are known as the tarsus and metatarsus.

The rear leg of the animal has a structure similar to the front leg.

The large, single leg bone is called the femur, and the two smaller leg bones below the knee joint are the tibia and fibula.

What are the names of bones commonly found in livestock andcompanion animals? D. Ribs are bones that surround and

protect the heart and lungs, the most vital internal organs. There are normally many ribs, surrounded with

muscle and connective tissue to give the chest cavity movement and protection.

E. Many other bones throughout the animal body each serve a specific function. Depending on the animal, hundreds of bones

can be found throughout the body.

Review What is the skeletal system, and what are

its functions?

What are bone components? What are the three cell types found in bones? How are bones classified?

What is the difference between a moveable and an immoveable joint?

Review What is the chemical process in the

formation of bones and calcification?

What are the names of bones commonly found in livestock and companion animals?