Skeletal System

Chapter 7

The Skeleton

• Support• Storage• Strength• Attachment scaffold for tendons, ligaments

and muscle• Blood cell production

Types of Bone• Long Bones – long, as in the arm (radius, ulna,

humerus) and thigh (femur)• Short Bones – cube-like, as in wrists (carpal)

and ankles (tarsal)• Flat Bones – plate-like, as in ribs, scapulae,

some skull bones (parietal)• Irregular Bones – vertebrae, facial bones• Round or Sesamoid Bones – small, round,

reside in tendons and next to joints – Knee cap or patella is an example

Long Bones

Short Bones

Flat Bones

Irregular Bones

Sesamoid Bones

Parts of a Long Bone

Parts of a Long Bone1. Epiphysis – wider, thicker region at the ends of

long bones. This usually forms a joint (articulates) with another bone. Mostly made of spongy bone

2. Diaphysis – the long bone shaft between two epiphyses

3. Periosteum – the tough, vascular, fibrous covering that is firmly attached to bone and continues into tendons and ligaments. Helps form and repair bone.

Parts of a Long Bone

4. Spongy Bone (cancellous bone) • mostly found in the epiphyses• Composed of loosely packed bone matrix

with gaps arranged in branching bony plates called trabeculae.

• Spongy bone is surrounded by a thin layer of compact bone.

Parts of a Long Bone6. Compact Bone

• found in the wall of the bone, especially in the diaphysis

• Exists as a rigid long tube with a hollow called the medullary cavity that is surrounded by a thin layer of spongy bone

• The thin layer of spongy bone is further lined with a thin membrane called endosteum, which contains bone-forming cells

• The medullary cavity lined by the endosteum is filled with soft connective tissue called marrow (usually yellow; red marrow is usually found in spongy bone)

• densely packed matrix, having no gaps

Red vs. Yellow Marrow• Red blood cells, platelets and most white blood cells form in

red marrow; some white blood cells develop in yellow marrow. The color of yellow marrow is due to the much higher number of adipocytes. Both types of bone marrow contain numerous blood vessels and capillaries.

• At birth, all bone marrow is red. With age, more and more of it is converted to the yellow type. Adults have on average about 2.6 kg of bone marrow, with about half of it being red.

• Red marrow is found mainly in the flat bones such as hip bone , breast bone, skull, ribs, vertebrae and shoulder blades, and in the cancellous ("spongy") material at the proximal ends (epiphysis) of the long bones such as femur and humerus.

• Yellow marrow is found in the hollow interior of the middle portion of long bones (diaphysis).

A Journey into Compact Bone

(Haversian System)

Inside an Osteon

(Volkman’s canal)

(Haversian System)

Bone Development and Growth

• The skeletal system begins to develop in the first few weeks of gestation

• Bones develop from connective tissue such as cartilage. They can form in two ways:– Bone can develop in sheet-like layers of

connective tissue. These types of bone are called Intramembranous bone.

– Bone can also develop from hyaline cartilage. These bones are called Endochondral bone.

Intramembranous Ossification

1. Unspecialized (primordial or primitive) connective tissue cells form membrane-like layers at sites of future bones

2. These primordial cells are supplied with O2 and nutrition through a dense network of blood vessels and the primordial cells actually form layers around the blood vessels

3. The primordial cells grow large and specialize into osteoblasts (bone-forming cells)

4. Osteoblasts secrete bone matrix around themselves, creating spongy bone along the blood vessels

5. Further along in development some spongy bone can become more dense and form compact bone

Endochondral Ossification1. Hyaline cartilage is what exists in the place of endochondral

bone early in development2. Chondrocytes reside in lacunae and keep growing – their

lacunae grow as well3. The matrix of the cartilage begins to disintegrate and the

chondrocytes die4. As cartilage decomposes, a periosteum develops all round5. Blood vessels and primordial connective tissue cells invade the

decomposing sites6. Invading primordial cells differentiate into osteoblasts and start

forming spongy bone in place of the cartilage (just like intramembranous bone formation)

7. Once the osteoblasts are completely trapped in their bony matrix, they are called osteocytes

8. Osteoblasts from the periosteum deposit compact bone around the spongy bone forming in the diaphysis – this thickens the bone

Most bones of the human skeleton are endochondral bones

Endochondral Ossification, cont’d.

9. In long bones endochondral ossification begins in the middle of the diaphysis – this is called the primary ossification centerprimary ossification center

10. The epiphyses remain cartilaginous and continue to grow

11. Eventually, spongy bone forms from the cartilage in the epiphyses – this is called the secondary ossification centersecondary ossification center

12. The primary ossification center (diaphysis) and the secondary ossification centers (epiphyses) are separated from each other by a band of cartilage called the Epiphyseal Epiphyseal plateplate

Growth at the Epiphyseal PlatesThe chondrocytes in this plate are arranged in 4 layers

• The first layer - layer closest to the end of the epiphyses contain resting chondrocytes – they do not actively grow. This layer also attaches the epiphyseal plate to the spongy bone tissue of the epiphysis

2. The second layer contains chondrocytes dividing mitotically. As they divide and form cartilaginous matrix around them, the epiphyseal plate thickens

3. As the cells divide, the older chondrocytes enlarge and thicken the plate even more – this forms the third layer

a. This activity lengthens the boneb. Osteoblasts invade the growing plate and deposit a calcified

matrix around the older cells. The old cartilage cells die.

4. The fourth layer is basically made up of dead chondrocytes trapped in a calcium matrix

Layers of the Epiphyseal Plate

(1st Layer – resting chondrocytes)

(2nd Layer – chondrocyte mitosis)

(3rd Layer- chondrocytes enlarging)

(4th Layer)

http://medocs.ucdavis.edu/CHA/402/labsyl/01/10.htm

Spongy bone and red marrow

Growth at the Epiphyseal Plates, Growth at the Epiphyseal Plates, cont’d.cont’d.

• Eventually, the fourth layer of the epiphyseal Eventually, the fourth layer of the epiphyseal plate is invaded by cells called osteoclasts, plate is invaded by cells called osteoclasts, which are large, multinucleated cells that are which are large, multinucleated cells that are created from the fusion of white blood cells created from the fusion of white blood cells called monocytescalled monocytes

• Osteoclasts dissolve the calcified matrix with Osteoclasts dissolve the calcified matrix with lysosomes and phagocytize it lysosomes and phagocytize it

• That allows bone-forming osteoblasts to invade That allows bone-forming osteoblasts to invade the area and deposit bone matrixthe area and deposit bone matrix

• Osteoclasts also invade the center of the Osteoclasts also invade the center of the diaphysis and dissolve some of the matrix. This diaphysis and dissolve some of the matrix. This forms the medullary cavityforms the medullary cavity

Growth Arrest• The growth and ossification of the diaphysis and the

epiphysis continues until the two ossification centers meet.

• Once the sites meet, bone growth is no longer possible in that area

• Some hyaline cartilage remains at the end of epiphyses as articular cartilage

• Children have epiphyseal plates in their bones – Children have epiphyseal plates in their bones – indicating the possibility of further growthindicating the possibility of further growth

Hydroxyapatite (a type of calcium phosphate)

Composition of Bone

Calcium

Potassium

Sodium

Magnesium

Carbonate

Phosphate

Collagen

33% Organic (protein)components

67% inorganic components

Bone Growth and Repair• Balanced nutrition, adequate exposure to

sunlight, hormones and exercise all contribute to bone growth and repair– Calcium and phosphate salts– Vitamin D3 (Cholecalciferol) – helps in calcium

absorption and is found in eggs, milk and foods fortified with it

– Vitamin A is needed for osteoblast and osteoclast activity

– Vitamin C is needed for collagen development, so a lack of it will inhibit bone development

– Vitamin K and B12 are needed for protein synthesis in bones

Bone Growth and Repair• Growth hormone from the pituitary gland in the

brain stimulates division of chondrocytes in epiphyseal plates– Lack of it will cause pituitary dwarfism– Too much will cause pituitary gigantism– Some adults acquire an excess of growth hormone

and develop an exaggerated growth of certain body parts like the jaw and hands – this is called acromegaly

• Male and female hormones (estrogen and testosterone) becomes active at puberty and promote bone growth

• Physical exercise stimulates bone growth – this is called hypertrophy and lack of exercise causes bone loss – called atrophy

All through life, osteoclasts reabsorb bone and octeoblasts replace bone

• When blood calcium levels are low, parathyroid hormone stimulates osteoclasts to break down bone tissue, releasing calcium from bone matrix into blood

• When there is too much calcium in the blood, the thyroid gland releases calcitonin which stimulates osteoblasts to pick up calcium from blood and store it in bone matrix – thus forming new bone tissue

• Too much calcium in the blood also inhibits osteoclast activity

Calcium Resorption and Deposition

Bone and Joint Pathology

1) Rheumatoid arthritis - autoimmune disease, affects smaller joints (e.g., hands)

2) Osteosarcoma - malignant bone tumor 3) Osteoporosis - porous bones 4) Gout - deposition of sodium urate crystals 5) Osteoarthritis - wear and tear arthritis, major

joints (e.g., knees)

Arthritis

• The most common form of arthritis, osteoarthritis is also known as degenerative joint disease and occurs following trauma to the joint, following an infection of the joint or simply as a result of aging. There is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis.

Osteogenesis Imperfecta• Osteogenesis imperfecta (OI) literally means imperfectly

formed bones. People with OI have an error (mutation) in the genetic instructions on how to make strong bones. As a result, their bones break easily.

• One of the genes that tells the body how to make a specific protein (type I collagen) is defective in people with OI. Type I collagen is a major component of the connective tissues in bones, ligaments, teeth, and the white outer tissue of the eyeballs (sclera). As a result of the defect, the body may not produce enough type I collagen or it may produce poor quality collagen. The result in both cases is the same: fragile bones that break easily. However, the bones heal at a normal rate.

Osteogenesis Imperfecta

Osteoporosis • Osteoporosis is a term that means "porous

bones." It is a skeletal disease affecting women and men. Osteoporosis is a condition in which bones have lost minerals—especially calcium—making them weaker, more brittle, and susceptible to fractures (broken bones). Any bone in the body can be affected by osteoporosis, but the most common places where fractures occur are the back (spine), hips, and wrists.

• Women are 4 times as likely than men to develop it – usually after menopause

Bone Movement

More Joints

Fractures

BONES OF THE SKULL

How many bones?

• There are 22 bones in the skull– 8 bones form the cranium– 14 bones make up the face

• 21 of the 22 bones are immobile and interlocking

• The 22nd, is the mandible (a facial bone) - the only movable bone

Cranial Bones - 8The cranium protects the brain

• 1 Frontal bone – contains frontal sinuse• 2 Parietal bones (held together by the sagittal suture)• 1 Occipital bone (Back of skull and base of cranium)• 2 Temporal bones • 1 Sphenoid bone – contains spenoid sinuses, sella

turcica, optic canal, foramen ovale, foramen rotundum and foramen spinosum

• 1 Ethmoid bone – contains superior nasal conchae, middle nasal conchae, perpendicular plate, crista galli, cribiform plate, ethmoid sinuses, olfactory foramina

Facial Bones• 2 Maxillary bones (upper jaw) – contains

maxillary sinuses• 2 Palatine bones• 2 Zygomatic bones• 2 Lacrimal bones• 2 Nasal bones• 1 Vomer• 2 Inferior nasal conchae• 1 Mandible – contains mental foramen, ramus,

coronoid process, alveolar arch, mandibular foramen

SinusesCavities in bones

• 2 Frontal sinuses (Cranium)• 2 Sphenoid sinuses (Cranium)• 2 groups of Ethmoid sinuses (Cranium)• 2 Maxillary sinuses (Face)

Foramina of Skull

1. Anterior Palatine Foramen2. Palatine Process of Maxilla3. Palatine4. Greater Palatine Foramen5. Lesser Palatine Foramen6. Pterygoid Processes of Sphenoid7. Zygomatic Process8. Squamous Part of Temporal Bone9. Mandibular Fossa10. Styloid Process11. Stylomastoid Foramen12. Mastoid Process13. Mastoid Foramen14. Superior Nuchal Line15. External Occipital Protruberance16. Median Nuchal Line17. Inferior Nuchal Line18. Foramen Magnum19. Condyloid Canal20. Occipital Condyle21. Hypoglossal Canal22. Jugular Foramen23. Carotid Canal24. Foramen Spinosum25. Foramen Ovale26. Foramen Lacerum27. Vomer28. Transverse Palatine Suture29. Median Palatine Suture

Infantile Skull• Not completely developed at birth – leaves

room for growth and molding• Fibrous membranes called Fontanels connect

cranial bones– Anterior fontanel-closes last (by end of year 2)– Posterior fontanel – closes in month 2 after birth– Sphenoid fontanel – closes in 3 months after birth– Mastoid fontanel – closes at the end of the 1st year

The Vertebral Column

The Vertebral Column• Extends from skull to pelvis• Made of bone called vertebrae

that are separated by discs of fibrocartilage

• Provides support as well as movement

• An adult has 26 bones in the column– 7 cervical– 12 thoracic– 5 lumbar– sacral (These are 5 fused vertebrae

and counted as 1)– coccyx region (These are 4 fused

vertebrae and counted as 1)

Convex anteriorly

Convex anteriorly

Concave anteriorly

Concave anteriorly

(PELVIC)

Curvatures

• A normal column has four curvatures which offer strength and resiliency – Cervical curvature –secondary - develops

when baby learns to hold head up– Thoracic curvature– Lumbar curvature – secondary - develops

when child learns to stand up– Pelvic curvature

Abnormal Curvatures

1) Kyphosis – Exaggerated thoracic curvature

2) Lordosis – Exaggerated lumbar curvature

3) Scoliosis - lateral bending of the vertebral column

Kyphosis and Lordosis

This condition is also called swayback

This condition is also called roundback

Scoliosis – Abnormal Curvature• Congenital scoliosis is caused by defects in

the spine present at birth. This form of scoliosis is also accompanied by other disorders of various organs.

• Neuromuscular scoliosis is caused by problems with the nerves or muscles. They are unable to support the spine in its normal position. The most common causes of this type of scoliosis are cerebral palsy (see cerebral palsy entry) and muscular dystrophy (see muscular dystrophy entry).

• Degenerative scoliosis is caused by deterioration of the bony material (discs) that separate the vertebrae. Arthritis in the spinal cord can also lead to degenerative scoliosis.

• In four out of five scoliosis cases, however, the cause is unknown. Such cases are known as idiopathic scoliosis. Children with idiopathic scoliosis have not suffered from related disorders such as bone or joint disease early in life. Some researchers believe that the condition may be inherited, but scientists have yet to find a gene responsible for the disease.

Vertebrae• A single bone of the vertebral column is called a

vertebra.• A typical vertebra is made up of a drum-like part

called the body – a longitudinal row of these bodies support the head and trunk.

• There are intervertebral discs between the rough surfaces of the bodies

• Adjacent bodies are joined by two types of ligaments, one on the anterior side and one on the posterior side– The anterior longitudinal ligaments– The posterior longitudinal ligaments

Vertebral Ligaments

1. Anterior longitudinal ligament 2. Posterior longitudinal ligament

Cervical Vertebrae• These seven bones are the smallest of the vertebrae

that comprise the neck and support the head.

• The first vertebra is the atlas, which appears as a bony ring and supports the head.

• The second vertebra is the axis, with its toothlike dens that pivots within the atlas.

• Features that separate cervical vertebrae from the rest are the bifid spinous processes and transverse foramina.

Notice how the dens of the Axis pivots inside the atlas.

The Shape of the rest of the

Cervical Vertebrae

Cervical vertebrae have

the smallest bodies of all

vertebrae

Spina Bifida

• Often called open spine, spina bifida affects the backbone and, sometimes, the spinal cord. It is among the most common severe birth defects in the United States, affecting 1,500 to 2,000 babies (one in every 2,000 live births)

• Spina Bifida means cleft spine, which is an incomplete closure in the spinal column.

Spina Bifida

Thoracic Vertebrae

Thoracic Vertebrae

• Twelve thoracic vertebrae articulate with the ribs.

• These bones are larger and stronger than the cervical vertebrae.

Lumbar VertebraeThe five massive lumbar vertebrae support the weight of the body. They have the largest bodies of all vertebrae

Body

Sacrum and Coccyx

Sacrum, CoccyxSacrum

• The sacrum is a triangular structure at the base of the vertebral column made up of five vertebrae fused into one bone.

• The spinous processes of these vertebrae fuse to form a ridge of tubercles that have dorsal sacral foramina along their sides.

• On the ventral surface of the sacrum, four pairs of pelvic sacral foramina provide passageways for nerves and blood vessels.

Coccyx

• The coccyx is the lowermost portion of the vertebral column and is composed of four fused vertebrae.

Thoracic Cage

The Thoracic Cage• The thoracic cage includes the ribs, thoracic vertebrae, sternum, and costal

cartilages.• It supports the pectoral girdle and upper limbs, functions in breathing, and

protects thoracic and upper abdominal organs.Ribs • Normally, there are 12 pairs of ribs that attach to the thoracic vertebrae.• The first seven pairs of ribs are true (or vertebrosternal) ribs that join the

sternum directly by their costal cartilages.

• The remaining five pairs are false ribs: the first three pairs are vertebrochondral ribs, and the last two pairs are floating ribs.

• Features of a typical rib include a shaft, costal groove, anterior (sternal) end, head, neck, and tubercle.

– The head articulates with the vertebrae; the tubercle articulates with the transverse process of the thoracic vertebrae.

Sternum • The sternum (breastbone) is located along the anterior midline of the thoracic

cage.• It consists of an upper manubrium, middle body, and lower xiphoid process.

Ribs

Shaft

Lamina

Body

Neck of rib

Facet

Anterior (sternal) end of rib

Articular facet

Spinous Process

Pedicle

Vertebral Foramen

Pectoral Girdle

Made up of four parts:2 clavicles and 2 scapulae

Scapula

The scapulae are flat, triangular bones on either side of the upper back.A spine divides the scapula into unequal portions.The spine leads to the acromion process (articulates with clavicle) and coracoid process (provides attachments for limb and chest muscles).The glenoid cavity articulates with the head of the humerus.

Superior border

Lateral border

Medial border

Clavicle• S-shaped• Medial (Sternal) side

articulates with upper side of manubrium

• Lateral side (acromial) meets the acromion of the scapulae

• Help hold shoulders in place

• Break easily due to the elongated S shape

Upper Limbs1. Humerus

• Extends from scapula to elbow• The “head” fits into the glenoid cavity of scapula• It articulates with the scapulae at its head, with the radius at the capitulum, and

with the ulna at the trochlea.2. Radius

• Located on thumb side of the forearm• Partners up with a slightly longer bone – the ulna• Extends from elbow to wrist and crosses over the ulna

3. Ulna• On the proximal end (elbow end) it has a wrench-like opening called the trochlear

(semilunar) notch which articulates with the trochlea of the humerus• The olecranon process lies above the trochlear notch and the coronoid process

lies below the trochlear notch - these help with movement of upper arm at the elbow

• At the distal end, the “head” articulates with the ulnar nothch of the radius and also is separated by a cartilaginous disc from the triquetrum one of the carpals (wrist)

4. Hand and wrist– The wrist of the hand is made up of eight carpal bones bound into a carpus.– The framework of the hand is made up of five metacarpal bones.– The fingers are composed of three phalanges in each finger except the thumb,

which lacks the middle phalanx.

Humerus

Radius and Ulna

Hand and Wrist

Pelvic Girdle• The pelvic girdle consists of the two coxal bones and the sacrum; it supports

the trunk of thebody on the lower limbs.

• The pelvic girdle supports and protects the lower abdominal and pelvic organs.

• Each Coxal bone is made up of three bones: iilium, ischium, and pubis, that are fused in the region of the acetabulum, the cuplike depression that articulates with the head of the femur.

• The ilium is the largest and most superior portion of the coxal bone and joins the sacrum at the sacroiliac joint.

• Features of the ilium include the iliac crest, and anterior superior iliac spine.• The ischium forms the L-shaped portion that supports weight during sitting.• Fractures of the ischium include the ischial tuberosity and ischial spine.• The pubis comprises the anterior portion of the coxal bones and articulates

at the symphysis pubis which has fibrocartilage.• The large opening, the Obturator Foramen lies within each pubis.• The greater pelvis is above the pelvic brim and the lesser pelvis is below it.• There are structural differences between males and female pelves

Pelvic Girdle

Pelvic Girdle – Male vs. Female

Female

Male

(Fibrocartilage)

The Coxa

The Lower Limb1. Femur

– The femur, or thighbone, extends from the hip to the knee and is the longest bone in the body.

– Its head articulates with the acetabulum; it articulates with the tibia at the medial and lateral condyles.

– Other features of the femur include the fovea capitis, neck, and greater and lesser trochanters.

– The patella (kneecap) is located in the tendon that passes over the knee.

2. Tibia– The tibia (shinbone) supports the weight of the body and articulates

with the femur (medial and lateral condyles) and with the tarsal bones of the foot.

– Its anterior tibial tuberosity is the point of attachment for the patellar ligament.

– Other features of the tibia include the medial malleolus (inner ankle). 3. Fibula

– The fibula is a slender bone lying lateral to the tibia; it does not bear body weight.

– The lateral malleolus forms the lateral ankle.4. Foot and ankle

FemurArticulates with acetabulum of coxal bone

Fibula and Tibia

(Shinbone)(Lies lateral to tibia)

(The lateral malleolus forms the lateral ankle.)

(The medial malleolus forms the

lateral ankle.)

Foot and Ankle• The ankle is composed of seven tarsal bones, forming a

tarsus.

• The talus articulates with the tibia and fibula.

• The calcaneus supports the body weight.

• The instep of the foot consists of five metatarsal bones and provides an arch.

• Each toe is made up of three phalanges, with the exception of the great toe, which lacks a middle phalanx.

Foot and AnkleThe talus articulates with the tibia and fibula.

Foot and Ankle

3 Types of LeversForce Resistance

Pivot

Force

Resistance

ResistancePivot

Pivot

Force

Lever in the Body

• The straightening of the upper limb at the elbow – First class lever ( force-pivot-resistance)

• The mandible being lowered and raised within the temporal bone - Second class lever (force-resistance-pivot)

• Bending of the arm at the elbow – Third-class lever (resistance-force-pivot)

THE END