The Skeletal System
• Humans are invertebrates
o Vertebrates are animals that have a vertebral column (backbone) and rely on
a sturdy internal frame centred on a prominent spine
• Human skeletal system
o The human skeletal system consists of bones, cartilage, ligaments and
tendons that account for about 20% of total body weight
o Cartilage - strong, flexible connective tissue that protects bones and joints
o Ligament - fibrous connective tissue that attaches bone to bone
o Tendon - fibrous connective tissue that attaches muscle to bone
o Bones contain active tissue that consume nutrients, require a blood supply
and change shape or remodel in response to variations in mechanical stress
• Divisions in the skeletal systems - axial skeleton
o
o 80 bones in total
o Bones of the head, neck, back and chest
§ Cranial (8) - Parietal (2), Temporal (2), Frontal (1), Occipital (1),
Ethmoid (1), Sphenoid (1)
§ Facial (skull) (14) - Maxilla (2), Zygomatic (2), Mandible (1), Nasal (2),
Platine (2), Inferior nasal concha (2), Lacrimal (2), Vomer (1)
§ Auditory ossicles (4) - Malleus (2), Incus (2), Stapes (2)
§ Hyoid (1)
§ Vertebral column (26) - Cervical vertebrae (7), Thoracic vertebrae
(12), Lumbar vertebrae (5), Sacrum (1), Coccyx (1)
§ Thoracic cage (25) - Sternum (1), Ribs (24)
• Divisions of the skeletal system - appendicular skeleton
o 126 bones in total
o Bones of the hands, feet, upper extremities, shoulder girdle and pelvic bones
o All bones exist in pairs apart from the pelvic girdle
o Pectoral (shoulder) girdle (4) - Clavicle (2), Scapula (2)
o Upper extremities (60) - Humerus (2), Radius (2), Ulna (2), Carpals (16),
Metacarpals (10), Phalanges (28)
o Pelvic Girdle (2) - ischium, ilium, pubis (fused)
o Lower extremities (60) - Femur (2), Tibia (2), Fibula (2), Patella (2), Tarsals
(14), Metatarsals (10), Phalanges (28)
, o NOTE - Sometimes you might find that various sesamoid bones are not
included in the list, such as the largest of the sesamoid bones, the
patella, that protects the knee joint, and important attachment points for
the ligaments that allow for the extension of the knee
• Role of the skeletal system
o Rigid framework (skeleton) provides body shape, large bones of the lower
limbs support the trunk when standing
o Supports and protects soft organs and soft body parts and helps to protect
against the effect of gravity
o Assist movement with muscles (mechanical lever support)
o Calcium reservoir (Calcium phosphate)
o Maintenance of mineral homeostasis and acid base balance, acts as a
reservoir of growth factors and cytokines
o Red bone marrow - site for formation of RBCs (hematopoiesis), WBCs and
platelets
o Triglyceride storage
o Cytokine - any of a number of substances, such as interferon, interleukin, and
growth factors which are secreted by certain cells of the immune system and
have an effect on other cells
• Dual-energy x-ray absorptiometry (DEXA)
o The most common test for measuring bone mineral density (BMD) and at
various sites that are prone to fracture (hip, spine)
o DEXA uses low level x-rays to scan a person in a supine position
o BMD by DEXA at the hip and spine is generally considered the most reliable
way to diagnose osteoporosis and predict fracture risk
• Anatomy of the bone
o Hole in a bone - foramen - passageway for a nerve or blood vessel
o If the hole is elongated into a tunnel-like passage through the bone, iti is a
canal or meatus
o A depression in a bone is called a fossa
o A lump on the bone is a tubercle or a tuberosity
o Projection from a bone is called a process
• Structure of a bone
o Diaphysis - bone shaft or body
o Epiphyses - distal and proximal ends
o Metaphysis - where diaphysis and epiphysis are joined
o Articular cartilage - covers the epiphysis at a joint
o Periosteum - tough sheath of dense connective tissue covers areas not
covered by articular cartilage
o Medullary cavity - houses the yellow bone marrow
o Endosteum - thin membrane lining the medullary cavity
• Histology of bone (osseous tissue)
o Hematopoietic stem cell - immature cell that can develop into either a white or
red blood cell or a platelet
o Osteogenic (osteoprogenitor) - unspecialised stem cells, undergo cell
division, daughter cells develop into osteoblasts
o Osteoblast - build the matrix of bone and initiate calcification. Osteoblasts
surrounded with matrix become osteocytes
o Osteocyte - mature bone cell, main cells in bone tissue, maintain metabolism
• Humans are invertebrates
o Vertebrates are animals that have a vertebral column (backbone) and rely on
a sturdy internal frame centred on a prominent spine
• Human skeletal system
o The human skeletal system consists of bones, cartilage, ligaments and
tendons that account for about 20% of total body weight
o Cartilage - strong, flexible connective tissue that protects bones and joints
o Ligament - fibrous connective tissue that attaches bone to bone
o Tendon - fibrous connective tissue that attaches muscle to bone
o Bones contain active tissue that consume nutrients, require a blood supply
and change shape or remodel in response to variations in mechanical stress
• Divisions in the skeletal systems - axial skeleton
o
o 80 bones in total
o Bones of the head, neck, back and chest
§ Cranial (8) - Parietal (2), Temporal (2), Frontal (1), Occipital (1),
Ethmoid (1), Sphenoid (1)
§ Facial (skull) (14) - Maxilla (2), Zygomatic (2), Mandible (1), Nasal (2),
Platine (2), Inferior nasal concha (2), Lacrimal (2), Vomer (1)
§ Auditory ossicles (4) - Malleus (2), Incus (2), Stapes (2)
§ Hyoid (1)
§ Vertebral column (26) - Cervical vertebrae (7), Thoracic vertebrae
(12), Lumbar vertebrae (5), Sacrum (1), Coccyx (1)
§ Thoracic cage (25) - Sternum (1), Ribs (24)
• Divisions of the skeletal system - appendicular skeleton
o 126 bones in total
o Bones of the hands, feet, upper extremities, shoulder girdle and pelvic bones
o All bones exist in pairs apart from the pelvic girdle
o Pectoral (shoulder) girdle (4) - Clavicle (2), Scapula (2)
o Upper extremities (60) - Humerus (2), Radius (2), Ulna (2), Carpals (16),
Metacarpals (10), Phalanges (28)
o Pelvic Girdle (2) - ischium, ilium, pubis (fused)
o Lower extremities (60) - Femur (2), Tibia (2), Fibula (2), Patella (2), Tarsals
(14), Metatarsals (10), Phalanges (28)
, o NOTE - Sometimes you might find that various sesamoid bones are not
included in the list, such as the largest of the sesamoid bones, the
patella, that protects the knee joint, and important attachment points for
the ligaments that allow for the extension of the knee
• Role of the skeletal system
o Rigid framework (skeleton) provides body shape, large bones of the lower
limbs support the trunk when standing
o Supports and protects soft organs and soft body parts and helps to protect
against the effect of gravity
o Assist movement with muscles (mechanical lever support)
o Calcium reservoir (Calcium phosphate)
o Maintenance of mineral homeostasis and acid base balance, acts as a
reservoir of growth factors and cytokines
o Red bone marrow - site for formation of RBCs (hematopoiesis), WBCs and
platelets
o Triglyceride storage
o Cytokine - any of a number of substances, such as interferon, interleukin, and
growth factors which are secreted by certain cells of the immune system and
have an effect on other cells
• Dual-energy x-ray absorptiometry (DEXA)
o The most common test for measuring bone mineral density (BMD) and at
various sites that are prone to fracture (hip, spine)
o DEXA uses low level x-rays to scan a person in a supine position
o BMD by DEXA at the hip and spine is generally considered the most reliable
way to diagnose osteoporosis and predict fracture risk
• Anatomy of the bone
o Hole in a bone - foramen - passageway for a nerve or blood vessel
o If the hole is elongated into a tunnel-like passage through the bone, iti is a
canal or meatus
o A depression in a bone is called a fossa
o A lump on the bone is a tubercle or a tuberosity
o Projection from a bone is called a process
• Structure of a bone
o Diaphysis - bone shaft or body
o Epiphyses - distal and proximal ends
o Metaphysis - where diaphysis and epiphysis are joined
o Articular cartilage - covers the epiphysis at a joint
o Periosteum - tough sheath of dense connective tissue covers areas not
covered by articular cartilage
o Medullary cavity - houses the yellow bone marrow
o Endosteum - thin membrane lining the medullary cavity
• Histology of bone (osseous tissue)
o Hematopoietic stem cell - immature cell that can develop into either a white or
red blood cell or a platelet
o Osteogenic (osteoprogenitor) - unspecialised stem cells, undergo cell
division, daughter cells develop into osteoblasts
o Osteoblast - build the matrix of bone and initiate calcification. Osteoblasts
surrounded with matrix become osteocytes
o Osteocyte - mature bone cell, main cells in bone tissue, maintain metabolism
