Lecture 2 - Bones / Skull

Question 1

Are the bones of the skeleton organs? Yes/No…Why?

Answer 1

Yes. this is because the bones of the skeleton contain several tissue types: nervous tissue in the nerves, blood tissue in the blood vessels, cartilage in articular cartilages, and epithelial tissue lining the blood vessels.

Question 2

What are the 6 functions of the bones?

Answer 2

Support
Movement
Protection
Mineral Storages
Blood cell formation and energy storage
Energy metabolism

Question 3

How do bones provide support?

Answer 3

The bones provide a hard framework to support the weight of the body. For example the legs are pillars supporting the the trunk of the body in a standing person.

Question 4

How do bones provide movement?

Answer 4

Skeletal muscle attaches to the bones by tendons and use bones as levers to move the body and its parts. As a result, humans can walk, grasp objections and move the rib cage to breathe.

Question 5

How do bones provide protection?

Answer 5

The bones of the skull provide a case for the brain. The vertebrae surrounds the spinal cord to protect it and the rib cage protects organs of the thorax.

Question 6

How do bones provide mineral storage?

Answer 6

Bone serves as reservoirs for minerals the most important being calcium and phosphate. They are stored and distributed as ions through the bloodstream to all parts of the body when needed.

Question 7

How do bones provide blood formation and energy storage?

Answer 7

Bones contains red and yellow marrow. The red marrow makes blood cells and the yellow marrow is a site of fat storage with little or no role in blood cell formation.

Question 8

How do bones provide energy metabolism?

Answer 8

Bone producing cells, osteoblasts, secrete a hormone which influences blood sugar regulation and energy metabolism. This hormone, osteocalcin, stimulates pancreatic secretion which lowers the blood sugar level (insulin). This hormone also causes fat cells to store less fat and secretes a hormones that increases the insulin sensitivity of cells.

Question 9

What is bone tissue?

Answer 9

Like other connective tissue, bone tissue consists of cells separated by the extracellular matrix. The bone tissue is composed of organic and inorganic components. The organic components are cells, fibres and ground substances. The inorganic components are the mineral salts that invade the bony matrix making the bone tissue hard. Bone does contain small amounts of tissue fluid although bone contains less water than other connective tissues.

Question 10

What are the organic substances of the the bone tissue?

Answer 10

The collagen fibres can be compared to steel rods which provide tensile strength.

Organic substances of bone tissue account for 35% of the total tissue mass. These organic substances especially collagen, contribute the flexibility and tensile strength that allow bone to resist stretching and twisting. Collagen is remarkably abundant in bone tissue.

Question 11

What are the inorganic substances of the bone tissue?

Answer 11

Mineral salts can be compared to sand and rock in concrete which provides compressional strength.

The inorganic substances of bone tissue accounted to 65% of the mass of the tissue. These substances consists of hydroxyapatites, or mineral salts, primary calcium phosphate. These mineral salts are present as tiny crystals that are in and around the collagen fibrils in the extracellular matrix. The crystals pack tightly which provides the bone with exception al hardness enabling it to resist compression.

Question 12

What are long bones?

Answer 12

Long bones are elongated bones which are longer than they are wide. They have a shaft and 2 distinct ends. Most limb bones are long bones. These bones are named for their elongated shape and not their overall size. The bones in the fingers and toes are long bones even though they are small.

Question 13

What are short bones?

Answer 13

They are roughly cube shaped which occur in the wrist and ankle. Sesamoid bones are special types of short bones that form in tendons. For example the kneecap (patella). Sesamoid bones size and number vary in different people.

Question 14

What are flat bones?

Answer 14

Flat bones are thin, flattened and somewhat curved. Most cranial bones of the skull are flat as are the ribs, sternum (|breastbone), and scapula (shoulder blade).

Question 15

What are irregular bones?

Answer 15

Bones that have various shapes and do not fit into the other bone categories. Examples are the vertebrae and the hip bones.

Question 16

What are compact and spongy bones?

Answer 16

Almost all the bones of the skeleton have a dense outer layer which looks smooth and solid to the naked eye. This external layer is called compact bone.

Internal to this is the spongy bone also called trabecular bone - a honeycomb of needle-like or flat pieces called trabeculae. In this network, the spaces between the trabeculae are filled with red and yellow bone marrow.

Question 17

What is the diaphysis and epiphyses?

Answer 17

The diaphysis or shaft forms the long axis of the bone (the length of the bone).

The epiphyses are the bone ends. The joint surface of each of the epiphysis is covered in a thin layer of hyaline cartilage called the articular cartilage.

Between a diaphysis and each epiphyses of an adult long bone is an epiphyseal line. A remnant of the epiphyseal plate, commonly called the growth plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone.

Question 18

Explain blood vessels in the bones.

Answer 18

Unlike cartilage, bones are well vascularised with 3%-11% of the body’s blood in skeleton bones at any given time.

The main vessels serving the diaphysis is the nutrient artery and nutrient vein. Together these run through a hole in the diaphysis called the nutrient foramen. The nutrient artery branches inwards to supply the bone marrow and spongy bone. Then branches extend outwards to supply the compact bone. Epiphyses arteries and veins do the same for each epiphysis.

Question 19

What is the medullary cavity?

Answer 19

All bones consist of large amounts of spongy bone. However, at the very centre of the diaphysis, there is no bone tissue and this is called the medullary cavity or marrow cavity in which yellow bone marrow is filled in.

Lined by endosteum.

Question 20

What is periosteum?

Answer 20

Periosteum (around the bone) is a connective tissue membrane which covers the entire exterior of the bone except the epiphyses of the bone where articular cartilages occur.

The periosteal membrane 2 sublayers: a superficial layer of dense irregular connective tissue which resists tension placed on the bone during bending, and a deep layer that borders the compact bone which is osteogenic containing both osteoblasts (bone producing cells) and osteoclasts (bone destroying cells).

During growth or deposition, the osteogenic cells differentiate into osteoblasts. These osteoblasts are what produce the layers of bone tissue which encircles the perimeter of the bone. This is called circumferential lamellae.

Periosteum is richly supplied with nerves and blood vessels, which is why there is profuse bleeding when a bone breaks.

The periosteum is secured to the underlying bone by perforating collagen fiber bundles (Sharpey’s Fibers), thick bundles of collagen that run from the periosteum to the bone matrix.