Skeleton Histology and Axial Skeleton PDF

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WEEK 2 - LECTURE 2 Wednesday, 28 February 2018

7:33 pm

The skeleton is made of two types of connective tissue: 1. Cartilage 2. Bone tissue

WHY DO WE NEED A SKELETON? 1. 2. 3. 4. 5. 6.

Support for the body Protection a. E.g. cranial cavity is protected by skull, ribs protect lungs etc Movement Mineral storage a. Calcium, phosphorus etc Blood cell production (made in the bone marrow) Energy storage

HISTOLOGY OF THE SKELETON The skeleton is formed primarily from connective tissues • All connective tissues contain cells and extra-cellular matrix Typically, the matrix contains; • Fibres (e.g. made of collagen) • Ground substance between the cells & fibres •

Cartilage and bone tissues are different types of supportive connective tissues

CONNECTIVE TISSUES OF THE SKELETON: CARTILAGE Cartilage is a supportive connective tissue. 3 types: • Hyaline cartilage ○ Supports bones ○ Linking bones together • Fibrocartilage ○ Provides a framework before the bones form ○ Tougher than hyaline • Elastic cartilage P iti di h b lik l t

t

th

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Positioned in areas where bones are likely to come together E.g. tibia and femur

Provides the basic template for the fetal skeleton before bone formation begins Helps bind or protect (e.g. absorbing shock) many structures of the adult skeleton Has the general properties of rubber and can bear weight while remaining flexible

All connective tissues contain cells & extra-cellular matrix. In cartilage; 1. CELLS are called chondrocytes; a. -cyte indicates a mature cell (chondrocytes create the cartilage) b. Chondro- usually related to cartilage c. Chondrocytes found in spaces called lacunae 2.

The MATRIX contains; a. Ground substance composed of proteoglycans which create flexible and resilient structures i. Gives the material a rubbery consistency; a capacity to resist shock b. Manu collagenous fibres (for tensile strength)

matrix

lacunae

cell HYALINE CARTILAGE • The most abundant cartilage in the skeleton • An important component of many joints • Located at the epiphyses (ends) of long bones, anterior ends of ribs & airways • Also called articular cartilage and also costal cartilage • Cartilage can also link bones together

Hyaline Cartilage Histology The histology of hyaline cartilage is characterised by cells and a matrix that appears "glass-like". Collagenous fibres are not visible.

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Matrix is glass like, contains collagenous fibres which give resistance to the structure (hard to distinguish under the microscope unlike fibro cartilage)

FIBROCARTILAGE • Strongest of the cartilages ○ Has many collagenous fibres (very tough) • Located in pad-like structures such as the knee menisci, intervertebral disks and pubic symphysis • Located in structures where there is a lot of stress on the joint; a lot of pulling and stretching; joint under pressure • Collagenous fibres are visible under the microscope

ELASTIC CARTILAGE DLFK Do some googling yo

CONNECTIVE TISSUES OF THE SKELETON: BONE TISSUE Bone is a hard connective tissue that is the major structural component of bones: • Is a living tissue • Consists of cells and a mineralised matrix ○ Cells; § Osteoblast - cell that builds bone (deposits new bone matrix components) □ When osteoblasts become trapped in the matrix that they secrete, they become osteocytes § Osteocyte - mature cell that maintains bone (located in the lacunae) □ Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste through gap junctions § Osteoclast - cell that breaks down bone ○ Matrix contains: § Minerals and salts (helps bone to resist compression) § Many collagenous fibres (which give it strength) • The strength and rigidity of the matrix allows bones to support other organs of the body MATRIX OF THE BONE TISSUE

MATRIX OF THE BONE TISSUE !

Approximately " of bone matrix (non-cellular component) is collagenous fibres • Provides strength and flexibility # "

Approximately of bone matrix is inorganis matter • •

5% calcium phosphate salt (Hydroxyapetite) 10% calcium carbonate

Inorganic salts in bone tissue resist compression and allow bones support weight without sagging. In general sense, the matrix of bone tissue can be compared to steel reinforced concrete. The inorganic ground substance (salts) is like concrete and can resist compression. Collagenous fibres are like steel beams that give strength and some flexibility to the structure. COMPACT & CANCELLOUS (SPONGY) BONE Bone can be classified according to the organisation of the matrix; 1. Compact (Cortical/ Dense) bone i. Looks like marble a. Makes up the dense outer layer of bones b. Makes up the shaft of long bones c. Main structural unit is the osteon 2. Spongy (Cancellous/ Trabecular) Bone i. Looks like sponge a. Consists of interconnecting plates of bone called trabeculae i. Provides spaces where blood and bone marrow are made b. Contains spaces filled with bone marrow COMPACT BONE (CORTICAL/DENSE) Appears solid when viewed without magnification Contains repeating structural elements (osteons); • A group of lamellae (hollow cylinders) surrounding a central (Haversian) canal ○ Made of hollow cylinders inside of each other

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○ All have the same centre (concentric) Run parallel to axis of long bones ○ Provides reinforcement Contain collagenous fibres in criss-crossing arrangements for structural reingorcement Blood vessels and nerves gain access from Haversian and Volkmann's canals (Volkmann's are the horizontal ones) ○ Blood vessels and nerves inside the bone tissue Canaliculi link osteocytes to blood supply

BONE HISTOLOGY

Compact Bone Histology

SPONGY BONE (CANCELLOUS/TRABECULAR) Spongy bone is a porous lattice of bony struts called trabeculae • Trabeculae oriented along lines of stress • Strong but light ○ (not as strong as compact but still strong) • Bulk of the spongy bone is empty space filled with red bone marrow ○ Between the trabeculae are cavities which contain red marrow (source of new blood cells) Found in abundance in short, flat and irregular bones. Spongy Bone Histology

BONE MEMBRANES Periosteum Double-layered protective membrane lining external surface of bones • Outer layer of fibrous connective tissue ○ Bones have to be connected to things otherwise they are useless: help bones attach to things • Inner osteogenic (bone forming) layer containing osteoblasts and osteoclasts (allows bone remodelling to occur) • Anchored to bone by Sharpey's fibres Endosteum • Delicate (more delicate than the periosteum) membrane covering internal surfaces of bone • Contains osteoblasts and osteoclasts ○ (contains the cells for regeneration)

BONE CLASSIFICATIONS Bones can be classified on the basis of their shape. • Long: ○ Found primarily in the upper and lower limbs ○ Length is greater than their breadth; most common bone shape; they may be small or large. For example the phalanges of the toes and fingers do not appear particularly long due to their small size but their dimensions are such that they classify as long bones. • Flat ○ Relatively thin; many flat bones are curved rather than flat • Short ○ E.g. bones in the wrist - looks pebbly

E.g. bones in the wrist looks pebbly Essentially cuboid in shape; the length, width, and height of each short bone are approximately equal; no medullary cavity is present ; sesamoid bones are short, seed-like bones contained within tendons or joint Irregular ○ Weird shape ○ Bones which do not fulfil the above criteria are classified as irregular bones ○ Sultural (Wormian) bones are small irregular bones located between the flat bones of the skull that are not named and are highly variable between individuals ○ ○

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LONG BONES GROSS ANATOMY OF LONG BONES • Epiphysis (plural is epiphyses) ○ An expanded head at each end of a long bone • Diaphysis ○ Elongated cylindrical central portion composed of compact bone (shaft) • Epiphyseal growth plate ○ For immature bones A l t f h li til th t t th di h i f

A plate of hyaline cartilage that separates the diaphysis from the epiphysis in immature long bones (absent in adult bone) Spongy Bone ○ Found in abundance in the deeper portions of the epiphyses Compact bone ○ Forms the wall of diaphysis and the outer edges in the epiphyses Medullary cavity ○ Fat tissues (yellow marrow) Periosteum ○ Contain cells for bone regeneration Nutrient foramen ○ A hole where nutrients can enter Endosteum ○ Contain cells for bone regeneration Epiphysis ○ The shape of this determines the type of movement is possible Articular cartilage ○ Protects of the bone ○

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STRUCTURE OF LONG BONES Diaphysis • Tubular shaft that forms the axis of long bones • Composed of compact bone surrounding a medullary cavity • Yellow marrow (fat) contained in medullary cavity Epiphyses • Expanded ends of long bones • Exterior is compact bone, interior is spongy bone • Joint surface lined with articular (hyaline) cartilage ○ Exists when there is connection between two bones for protection • In immature bones, the epiphyseal plate separates the diaphysis from the epiphyses Epiphysis of a Long Bone

Diaphysis of a Long Bone

SHORT, FLAT, AND IRREGULAR BONES STRUCTURE OF SHORT, FLAT AND IRREGULAR BONES Thin plates of periosteum-lined compact bone on the outside endosteum-lined spongy bone (diploë) on the inside • Outer shell of compact bone and inside of spongy bone ○ A sandwich of compact bone and spongy bone in red bone marrow between the trabeculae

BONE FORMATION Before week 8, the embryonic skeleton is composed of fibrous membranes and hyaline cartilage • Bones formed from templates of fibrous membrane and hyaline cartilage After this time, the foetal skeleton begins to ossify (form bone). Regions of the premature skeleton that are first to ossify called primary ossification centres

BONE REMODELLING Intramembranous Ossification • Produces mostly flat bones of the skull • Bone develops from a fibrous membrane ○ Osteoblast will infiltrate it and create bone Endochondral Ossification • Produces most bones of the skeleton below the skull • Uses hyaline cartilage "bones" as template material • Epiphyseal plate facilitates lengthwise growth of long bones until puberty

BONE REMODELLING CONT •

Bone is a dynamic living tissue that is constantly broken down and reformed to physical and hormonal factors throughout life. § This turnover allows the bone structure to meet changing physical stresses in the skeleton

Bone Resorption 1. Osteoclasts degrade organic matrix 2. Solubilise mineral matrix Bone Deposition 1. Osteoblasts secrete organic matrix 2. Mineralisation follows

1. 2. 3.

Osteoclasts chew their way through, removing the bone tissue Osteoblast will come in from the endosteum and the periosteum to regenerate the bone tissue After depositing new bone matrix components, osteoblasts will become trapped in the matrix they secreted and become osteocytes

When osteoblasts become trapped in the matrix that they secrete, they become osteocytes. Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi, which are used for exchange for nutrients and waste through gap junctions.

HISTOLOGY OF OSTEOPOROSIS •

Osteoclasts breaking down too fast so that osteoblasts do not have time to deposit new matrix composition (imbalance between bone resorption and new bone formation) ○ Creates gaps: weakens the bone

GENERAL SURFACE FEATURES OF BONES Bones exhibit a variety of surface features which represent; 1. 2.

3.

Articular surfaces (help form joints) Points of attachment for a. Muscles b. Joint capsules c. Ligaments Routes for nerves and blood vessels

Condyles of femur

SURFACE FEATURES OF BONES: ARTICULATIONS 1

Condyle:

1.

Condyle: a. A rounded knob that articulates with another bone b. Large, smooth, rounded articular oval process

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Head: a. Prominent expanded end of bone b. Large, round ended of a bone e.g. head of the humerus

3.

Facet: a. Smooth flat, slightly convex or concave surface b. Small articular surface, often flattened; e.g. Superior articular facet of the vertebra

4. Trochlea a. Smooth, pulley-like process (resembles or acts like a pulley) or surface; e.g. Trochlea of humerus

5. Malleolus a. Triangular, rounded bony prominence; provides site for muscle and ligament attachment whilst acting as articular surface (a bony projection with a shape likened to a hammer head); e.g. Medial malleolus of tibia

6. Fovea a. Pit; often acts an articulating site and can be called a facet in

these cases; e.g. Costal fovea of a vertebra

7. Notch a. Deep depression or U or V-shaped cut into bone surface; not always articular - may provide opening or passageway for nerves or blood vessels; e.g. Trochlear notch of ulna (articular) and suprascapular notch of scapula (no-articular)

SURFACE FEATURES OF BONES: PROJECTIONS 1. Process a. Marked bony prominence, often elongated; sometimes used as an articulating surface; i. E.g. Corocoid process of the scapula

2. Eminence a. A bony prominence, not as prominent as a process; i. E.g. Intercondylar eminence of the tibia

3. Spine a. Slender, elongated process that may be pointed i. E.g. Iliac spines of hip bone

4. Tuberosity a. Rough elevated surface b. Large slightly raised prominence; usually rough i. E.g. Radial tuberosity of radius

5. Tubercle a. Small rounded process/prominence i. E.g. Conoid tubercle of clavicle

6. Trochanter a. Large processes on a femur b. Blunt prominent roughened process; only found on the femur i. E.g. Greater trochanter of femur

7. Crest a. Narrow ridge b. Narrow or sharp ridge-like projection, often roughened i. E.g. Iliac crest of hip bone

8. Epicondyle a. Projection superior to a condyle b. Non-articular projection that extends from or lies adjacent to a condyle i. E.g Medial epicondyle of the humerus

9. Fossa a. Shallow and often broad depression or pit-like recess i. E.g. Supraspinous fossa of the scapula b. Can also provide site for articulation i. E.g. Glenoid fossa of the scapula

SURFACE FEATURES OF BONES: OPENINGS AND SPACES 1. Meatus a. Canal-like passage b. Canal or tube like passageway through a bone or between bones i. E.g. External auditory meatus of the skull

2. Foramen a. Circular opening in bone usually for blood vessels and/or nerves i. E.g. Foramen magnum of the skull

3. Fissure a. Slit like opening

4. Sinus a. Large cavity within a cranial bone i. E.g. Frontal sinus of frontal bone

5. Canal a. Passageway through a bone; often interchangeable with the term meatus but often shorter than a meatus

i.

E.g. Optic canal of skull

6. Sulcus a. Shallow and narrow groove; usually elongated i. E.g. Intertubercular sulcus of humerus

THE HUMAN SKELETON The typical adult skeleton consists of 206 bones. These bones are grouped into 2 main divisions. 1

A i l Sk l t

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Axial Skeleton Skull Vertebral column Bony thorax

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Appendicular Skeleton Pectoral girdle Pelvic girdle Bones of the limbs

THE AXIAL SKELETON • •

Central axis of the body Mostly made of irregular and flat bones (dominant bone types found here)

THE AXIAL SKELETON: THE SKULL 22 bones; mostly joined by sutures • 8 Cranial bones surround cranial cavity (contains brain) ○ Protect brain ○ Attachment for head & neck muscles • 14 Facial bones form the framework of the face; supports teeth and form a nasal cavity and orbit ○ Provides openings for food liquid and air ○ Provides attachments for facial and jaw muscles • The skull also houses 6 auditory ossicles of the middle ear ○ (an ossicle is a very small bone, especially one of those in the middle ear)

Note: Bones are symmetrical (only need to learn one side) SKULL FEATURES: CRANIAL FOSSA 3 flattened surfaces that comprise the cranial floor • Anterior fossa: supports frontal lobe of brain • Middle fossa: supports temporal lobes of brain • Posterior fossa: supports cerebellum

The cranial cavity contains the brain. The base of the cranial cavity is divided internally into three basin-like structures which correspond to the contours of the inferior surface of the brain. Cranial bones are defined as those bones which contribute to the walls of the cranial cavity and include the paired temporal bones, the paired parietal bones, the single occipital bone, and parts of the frontal, ethmoid, and sphenoid bones (8 bones in total) SKULL FEATURES: THE NASAL CAVITY Consists of two halves separated by a median partition called the osseous nasal septum. Each half has a roof, a lateral wall, a floor, and a medial wall (consisting of the nasal septum). Cavity posterior to external nose; • Constructed of bone and cartilage • Lined with hair and mucous membranes • Divided into right and left parts by nasal septum (a curtain of bone cartilage) • Helps warm, moisten and purify air ○ Sinus links up to the nasal cavity Constituted by: • Lateral wall of each nasal cavity ○ Mainly made up of the maxilla ○ Deficiency made up by: § Perpendicular plate of palatine bone § Medial pterygoid plate § Labyrinth of ethmoid § Inferior concha • Roof ○ Nasal bone (1/3 to 1/2) ○ Junctions of the upper lateral cartilage and nasal septum • Floor (also the roof of the mouth) ○ Bones of the hard palate

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The horizontal plate of the palatine bone posteriorly Palatine process of the maxilla anteriorly

SUTURES OF THE SKULL Sutures are immovable fibrous joints that form the boundaries between cranial bones. In adulthood, when cranial growth has stopped, the sutures fuse. Sagittal suture • Links the left and right parietal bones Coronal suture • Links the frontal bone to both the parietal bones Lambdoidal suture • Links the occipital bone to parietal bones SUPERIOR VIEW

PARANASAL SINUSES OF THE SKULL The paranasal sinuses are air-filled chambers within bones of the skull that open into the nasal cavity. The sinuses are lined with epithelium that helps humidify and warm inhaled air. Paranasal sinuses significantly contribute to making the skull lighter and provide resonance to the voice. Four bones of the skull contain paired air spaces the paranasal sinuses • Lighten skull/ humidify air • Lined by pseudostratified ciliated columnar (respiratory) epithelium ○ Cleaning system ○ These chambers link to the nasal cavities ○ Give the voice its resonance ○ Contributes to the respiratory system All paranasal sinuses open into the nasal cavity via ducts Named for the bones in which they are located • Frontal (2 or more) • Maxillary (2) • Ethmoidal (many) • Sphenoidal (2)

SKULL FEATURES: THE ORBITS The cavities which contain the eyeballs. Seven bones contribute to each orbit. • •

Bony cavities that encase the eyeballs (the socket for the eye) Formed by parts of 7 bones ○ Frontal bone ○ Sphenoid bone ○ Ethmoid bone ○ Lacrimal bone ○ Palatine bone ○ Zygomatic bone ○ Maxilla

CRANIAL BONES

FRONTAL BONE • Single bine that forms forehead and part of cranium roof • Forms roofs of the orbits • Contains frontal sinuses • Forms most of anterior cranial fossa (provides the seat for the most anterior part of the brain) • •

Superior aspect extends posteriorly from foreh...