Human Anatomy Lecture 3: Basic Bone Structures

Bone Classification

• Bones can be classified according to their position in the skeleton into axial and appendicular skeleton
• Axial skeleton consists of skull, mandible, hyoid bone, vertebral column, sternum, and ribs
• Appendicular skeleton consists of shoulder girdles, arms, hands, pelvic girdle, thighs, and legs, and feet
• The skeleton is bilaterally symmetrical and has approximately 206 bones

Bone Types

• Long bones: found in extremities, have a main part (diaphysis), two ends (epiphysis), and a medullary cavity containing bone marrow tissue
• Examples: Femur and humerus
• Short bones: small, cuboidal in shape
• Examples: Tarsals, Carpals
• Flat bones: consist of two layers of compact bone with spongy or cancellous bone in between
• Examples: Sternum
• Irregular bones: have irregular shapes, compact bone surrounding spongy bone in between
• Examples: Vertebrae

Sesamoid Bones

• Developed in tendons of certain muscles at sites of friction or pressure
• Examples: Patella

Pneumatic Bones

• Skull bones having air-filled cavities called air sinuses
• Examples: Frontal sinuses, maxilla sinuses

Bone Marrow

• Soft, gelatinous tissue that fills the medullary cavities, the centers of bones
• Two types: red bone marrow (myeloid tissue) and yellow bone marrow (fatty marrow)
• From birth to early adolescence, the majority of bone marrow is red marrow
• As we grow and mature, increasing amounts of red marrow are replaced by yellow marrow
• Circulating blood cells are produced by a process known as hematopoiesis

Cartilages

• Firm and resilient structure that forms a small part of the skeleton
• A form of connective tissue in which the living cells (chondrocytes) are embedded in the gel matrix
• Three types: hyaline cartilage, white fibro-cartilage, and yellow elastic cartilage

Hyaline Cartilage

• Has great resistance to wear and tear and has a very large amount of amorphous intercellular matrix
• Found at articular surfaces of the joints, epiphyseal plate of growing bones

White Fibro-Cartilage

• Has a large number of collagen fiber bundles embedded in a small amount of matrix
• Found at intra-articular disc of the joints, inter-vertebral discs of the vertebral column

Yellow Elastic Cartilage

• Has a large number of elastic fibers embedded in the matrix
• Stretchable and more resilient than other two forms of cartilage
• Found at cartilage of external auditory meatus, cartilage of auditory tube

Lymphatic System

• Essentially a drainage system that helps rid the body of toxins, waste, and other unwanted materials
• Primary function is to transport lymph, a clear, colorless fluid, throughout the body
• Consists of lymphatic tissues, lymphatic vessels, and lymph nodes

Lymphatic Tissues

• Connective tissue that contains large numbers of lymphocytes, essential for the immunologic defenses of the body
• Organized into organs such as thymus gland, spleen, and tonsils

Lymphatic Vessels

• Consist of a network of fine vessels called lymph capillaries that drain lymph from the tissue spaces
• Capillaries are in turn drained by small lymph vessels
• Lymph vessels have numerous valves along their course

Lymph Nodes

• Small, round or bean-shaped clusters of cells, also called lymph glands
• Examples: axillary lymph nodes, inguinal lymph nodes
• Inside lymph nodes, different types of immune system cells play a vital role to fight off infections and filter the lymph from all foreign particles before it returns to the bloodstream