A&P Chapter 7: Skeletal System

Bones

Organs composed of many tissues (bone, cartilage, dense connective, blood, and nervous). Vary in size and shape.

Major functions of bones

PROTECTION, support, body movement, blood cell formation, mineral storage

Bone shapes

Long bones, short bones, flat bones, irregular bones

Long bones

Taller than they are wide, have expanded ends

• ex. femur

Short bones

Cube-like, length=width. Includes sesamoid (round) bones, which are embedded in tendons

• ex. ankle bone, tarsal bones

Flat bones

Plate like with broad surfaces

• ex. sternum

Irregular bones

Variety of shapes and most are connected to several other bones

• ex. vertebrae

11 parts of a long bone

Epiphysis, Diaphysis, Metaphysis, Articular Cartilage, Periosteum, Compact, Spongy, Traveculae, Medullar cavity, Endosteum, Bone marrow

Epiphysis

End of a long bone

Diaphysis

Middle portion/shaft of a long bone

Metaphysis

Between diaphysis and epiphysis, widening part of long bone

Articular cartilage

Hyaline cartilage that covers the ends of bones in synovial joints

Periosteum

Dense connective tissue covering the surface of a bone.

Compact bone

Makes up bone that protects diaphysis; it is the wall of diaphysis

Spongy bone

Makes up epiphysis; has air spaces where red bone marrow is found. Somewhat flexible

Trabeculae

Branching bony plates that makes up spongy bone. It's spaces reduce the bones weight

Medullar cavity

Hollow chamber in disphysis; contains marrow

Endosteum

Lines spaces, cavity

Bone marrow

Red or yellow, lines medulla cavity, found in spongy bone spaces

Appositional growth

Bone gets wider, stronger, and thicker to support excess body weight

Epiphyseal plates

Growth plates; growth/length of long bone

Osteocytes

Mature bone cells

Lacunae

Chambers that contain osteocytes

Canaliculi

Tiny passageways where osteocyte cell processes exchange nutrients and wastes

What is the extracellular matrix of bone mainly composed of?

Collagen fibers- provides resilience (flexibility/strength

Inorganic salts- hardness

Osteons

Cylinder shaped units that make up compact bone

Intramembranous Ossification

Flat skull bones, clavicles, sternum, and some facial bones form between sheets of primitive connective tissue

Endochondrial Ossification

Long bones and most of skeletons are forming from hyaline cartilage models

Intramembranous bones

Broad, flat bones that originate within sheet like layers of connective tissue.

• ex. flat bones of the skull, clavicles, sternum, and some facial bones (mandible, maxilla, zygomatic)

Endochondral bones

Begin as masses of hyaline cartilage and is most bones of the skeleton.

• ex. femur, humerus, radius, tibia, phalanges, vertebrae

Growth at the Epiphyseal Plate process:

Osteoclasts break down the calcified matrix then osteoblasts invade and replace the cartilage with bone tissue

Bone length growth and when it stops

As long as the cartilage cells in the epiphyseal plate remain active, it can continue to grow. When ossification centers meet, and epiphyseal plate ossifies, bone can no longer grow in length.

How can a bone increase in thickness?

By depositing compact bone on the outside, under the periosteum.

Bone homeostasis

It is continuous bone remodeling throughout life, involving opposing processes of resorption and deposition on the surfaces of the endosteum and periosteum.

How do resorption and deposition maintain bone homeostasis?

Osteoclasts remove old bone (resorption) and osteoblasts form new bone (deposition), replacing 10–20% of the skeleton each year.

Major factors that affect bone development, growth, and repair

Nutrition (vitamins D, A, C), sunlight exposure, hormone levels, and physical exercise

How vitamin D affects bone development, growth, and repair:

Needed for calcium absorption. Deficiency causes rickets/osteomalacia

How vitamin A affects bone development, growth, and repair:

Regulates osteoblast/osteoclast activity; deficiency slows bone development.

How vitamin C affects bone development, growth, and repair:

Required for collagen; deficiency leads to fragile bones

How growth hormones affects bone development, growth, and repair:

Stimulates cartilage cell division; too little=dwarfism, too much= gigantism/acromegaly.

How sex hormones (estrogen & testosterone) affects bone development, growth, and repair:

Promotes bone formation

Fractures

Classified by cause and nature of break

2 types of fractures

Simple (closed): protected by uninjured skin (or mucous membrane)

Compound (open): bone is exposed to the outside through opening of skin (or mucous membrane)

Hematopoiesis

Blood cell formation that occurs in red bone marrow.

Red bone marrow

Produces RBC, WBC, and platelets. With age, some of it is replaced by yellow bone marrow, which stores fat & does not produce blood cells

Inorganic salt storage

About 70% of the bone matrix consists of inorganic mineral salts. Loss of bone mineralization leads to osteoporosis

Fragility fracture

Occurs after a fall from less than standing height and signals low bone density

Prevention of fragility fractures

1. 30 minutes of exercise per day

2. Get enough calcium and vitamin D

3. No smoking

Number of bones in body

206; some people have extra, some lack certain bones

Divisions of the skeleton

Axial & Appendicular

Axial Skeleton

Consists of 80 bones

• skull, middle ear bones, hyped bones, vertebral column, thoracic cage

Appendicular Skeleton

126 bones

• pectoral girdle, upper limbs, pelvic girdle, lower limbs

Skull

Typically composed of 22 bones. Cranium (8 bones) and facial skeleton (14 bones) make up the skull

• cranium enclosed and protects the brain

• facial skeleton forms face shape

Fontanels (soft spot of infantile skull)

Fibrous membranes that connect cranial bones where intramembranous ossification is incomplete.

Functions of fontanels

Allow the skull to compress during birth and provide space for the infant’s brain to grow and expand.

Vertebral Column

Forms vertical axis of skeleton. Consists of many vertebrae separated by cartilaginous intervertebral discs, and connected by ligaments. Supports head, trunk, and spinal cord.

• 33 separate bones in infant, 26 in adult

4 curvatures of vertebral column

Cervical (secondary, 7), Thoracic (primary, 12), Lumbar (secondary, 5), Sacral (primary, 5)

• 4 fused coccygeal vertebrae form coccyx

What does a typical vertebra contain?

Body, Pericles, laminae, spinous process, transverse process, vertebral foramen, facets, superior and inferior articular processes

Cervical vertebra

There are 7 cervical vertebrae; they are the smallest, have transverse formamina, and bifid spinous processes on C2-C6. C7 is the vertebral prominens.

What are the roles of C1 (Atlas) and C2 (Axis)?

Atlas (C1): supports the head.

Axis (C2): allows the atlas (and head) to pivot around the dens.

Thoracic vertebrae

There are 12 thoracic vertebrae in chest region. Larger than cervical vertebrae, articulate with ribs, long & pointed spinous process.

Lumbar vertebrae

There are 5 lumbar vertebrae in small of back. They have large bodies, thick, short, nearly horizontal spinous processes, are weight bearing, located in the small of the back

Sacrum

Triangular structure, at base of vertebral column. Typically 5 fused vertebrae,

Coccyx

AKA tailbone. Usually consists of 4 fused vertebrae that typically fuse between ages 25 and 30.

Disorders of vertebral column

Herniated or ruptured disc, kyphosis, scoliosis, lordosis, compression fractures

Thoracic cage

Includes the ribs, thoracic vertebrae, sternum, and costal cartilages. It supports the shoulders and arms, protects organs in the chest and upper abdomen, and helps with breathing.

Ribs

Humans have 12 pairs of ribs

• True ribs: first 7 pairs; join the sternum directly by their costal cartilages

• False ribs: remaining 5 pairs.

  • vertebrochondral ribs- upper 3 pairs of false ribs

  • floating ribs- lower 2 pairs of false ribs.

Structure of a rib

• Shaft: main portion; long and slender

• Head: posterior end; articulates with vertebrae

• Tubercle: articulates with vertebra

• Costal cartilage: hyaline cartilage; connects rib to sternum

Sternum

AKA breastbone. Articulates with costal cartilages and clavicles. Has 3 parts:

1. Manubrium: upper part

2. Body: middle part

3. Xiphoid process: bottom part

Pectoral girdle

Consists of 2 clavicles (collarbones) and 2 scapulae (shoulder blades). Supports upper limbs

Clavicles

S-shaped bones that connect the manubrium to the scalpulae, keeps the shoulder blades in place while allowing them to move freely

Scapulae

Includes the spine, supraspinous fossa, infraspinous fossa, acromion process, caracoid process, glenoid fossa (cavity) which helps form the shoulder joint

Upper limb

Framework of upper arm, forearm, hand. Includes the humerus, radius, ulna, carpals, metacarpals, phalanges

Humerus

Only bone in the upper arm. Key parts include the head, anatomical & surgical necks, greater & lesser tubercles, deltoid tuberosity, capitulum (lateral condyle) and trochlea (medial condyle), lateral & medial epicondyles, coronoid fossa, and olecranon fossa.

Radius

Lateral bone of the forearm, shorter than the ulnar. Located on thumb side of forearm. Key parts include: head, radial tuberosity, styloid process, and ulnar notch. It helps form the elbow and wrist joints.

Ulna

Medial bone of the forearm. Includes the OLECRANON PROCESS which helps straighten the arm; aka “funny bone”. It helps form the elbow and supports forearm movement.

Hand

Made up of:

• Carpal (wrist) bones (8): Scaphoid, Lunate, Triquetrum, Pisiform, Hamate, Capitate, Trapezoid, Trapezium

• Metacarpals (palm, 5)

• Phalanges (fingers bones, 14): Proximal, Middle, Distal

Pelvic girdle

Consists of 2 coxal (hip) bones. The pelvis = pelvic girdle + sacrum + coccyx.

• Functions: supports the trunk, protects internal organs, transmits weight to lower limbs, and provides attachment for lower limbs.

Hip bones

AKA coxal bones. Each hip bone consists of 3 fused bones:

1. Ilium (largest, top): Iliac crest, iliac spines, greater sciatic notch

2. Ischium (L-shaped, bottom): Supports weight while sitting, ischial spines, ischial tuberosity

3. Pubis (front): Pubic symphysis, pubic arch, acetabulum (for femur head), obturator foramen

True Pelvis

(lower, lesser). Inferior to pelvis brim. Bounded by sacrum & coccyx (back), lower ilium, ischium, and pubis (sides/front); forms the lower pelvic cavity.

False Pelvis

(greater, upper). Above the pelvic brim; bounded by lumbar vertebrae (back), iliac bones (sides), abdominal wall (front); supports abdominal organs.

Main differences between the female and male pelvis

• Female pelvis: Functions as a birth canal, iliac bones more flared, broader hips, wider pelvic cavity, greater pubic arch angle, more space between ischial spines/tuberosities, sacral curvature shorter and flatter.

• Male pelvis: Heavier, less flared, narrower hips and pelvic cavity.

Lower limb

Forms framework of each thigh, leg, and foot. Includes the femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.

Femur

AKA thigh bone. Longest bone of the body. Key parts include: head, fovea capitis, neck, greater and lesser trochanters, linea aspera, medial & lateral condyles, and medial & lateral epicondyles. It connects the hip to the knee and supports body weight.

Patella

AKA kneecap. A flat sesamoid bone in the quadriceps tendon, located on the front of the knee. It helps with lever action during lower limb movement.

Tibia

AKA shin bone. The larger leg bone, medial to fibula. Key parts: proximal condyles, tibial tuberosity (for patellar ligament), anterior crest, and medial malleolus.

Fibula

A long, slender bone on the lateral side of the tibia. Key parts: head and lateral malleolus. It is non-weight bearing and provides muscle attachment.

Foot

• Tarsals (ankle, 7): Calcaneus, Talus, Navicular, Cuboid, Lateral, Intermediate, Medial cuneiforms

• Metatarsals (palm of foot, 5) make up the arch of the foot

• Phalanges (toes, 14): Proximal, Middle, Distal

• Calcaneus: large heel bone

• Talus: lies inferior to the tibia, and allows the foot to pivot up and down

Life span changes

• Decrease in height begins at about age 30

• Calcium levels fall

• Bones become brittle and more prone to fracture

• Hip & Vertebral compression fractures become common

Low blood calcium

The parathyroid gland releases parathyroid hormone (PTH), which breaks down bone to release calcium, restoring normal blood calcium levels.

High blood calcium

The thyroid gland releases calcitonin, which stimulates osteoblasts to deposit calcium in bones, lowering blood calcium to normal.