Basic Tissues: Bone

Basic Tissues

Bones

Classifications of Bones

1. Developmental Classification

• Intramembranous

• Intacartilagenous

• Membranocartilagenous

2. Regional Classification:

• Axial Bones

• Appendicular bones

3. Classification according to size and shape:

• Long bones

• Long-Short bones

• Short bones

• Flats Bones

• Irregular bones

4. Miscellaneous Classification

• Sesamoid bones

• Supernumery bones

• Accessory bones

• Pneumatic bones

• Wormian bones

5. Structural classification:

1. Compact (haversian) bone:

• Well developed Haversian lamellae (cylindrical lamellae) are present

• Lamellae consist of collagen fibers, lying in a calcified material

• Bone cells lie scattered between the lamellae

• Examples: Shafts of long bones

outer and inner table of skull bones

b. Spongy (cancellous) bone:

• Lamellae are arranged flat, Haversian system is not seen.

• Examples: Ends of long bones

Diploe of skull

Parts of a developing long bone:

1. Diaphysis

• Shaft of long bone.

• Ossification center is called primary ossification center.

• Ossification center appears in 7th week of intra-uterine life.

B. Epiphysis:

• Ends of long bones

• Ossification center is called secondary ossification center.

• Ossification center appears after birth at the age of 1 or 2 years except lower end of femur where is appears in 9th month of IU life.

Types of epiphysis:

1. Pressure epiphysis:

• Develop in the vicinity of site of articulation at 1-2 years of age.

• Example: ends of long bones of limbs

2. Traction epiphysis:

• Develop at the site of attachment of certain tendons at puberty

• Example: Tuberosities of humerus

• Trochanters of femur

3. Atavistic epiphysis:

• Are independent bones phylogenetically which become part of other bones

• Example: coracoid process of scapula

C. Metaphysis:

• Actively growing part of diaphysis (shaft) close to epiphyseal cartilage

• Highly vascular

• Responsible for growth in length

4. Epiphyseal Cartilage:

• Cartilaginous tissue present between epiphysis and diaphysis

• After the completion of growth, it becomes ossified and is represented by epiphyseal line in adult bone

• Completion of growth of long bone usually occurs at between 17-20 years of age.

Blood Supply of Bones

1. Adult long bones:

Most of the pores present in the bones are for veins.

Arterial supply comes from:

1. Periosteal arteries:

• Are numerous.

• Supply the compact bone of shafts and spongy bone of the ends.

b. Nutrient artery:

• enters the bone through the nutrient foramen.

• Gives a number of branches which are ascending and descending. The branches are called “nutritiae”.

• Its branches also pass through Volkman’s canal and haversian canals

• It anastomoses with periosteal and end blood vessels

• It supplies a little more than bone marrow.

c. Arteries at the ends of long bones:

These may arise from:

• Peri-articular anastomsis (juxta epiphyseal arteries of Lexer). These pierce the bone at metaphysis.

• From the artery passing over that region. These pierce the bone at epiphyseal cartilage.

2. Immature long bones:

• Have additional epiphyseal and metaphyseal arteries

• Arise from periosteal arteries present at the ends of long bones.

3. Short bones:

• Only periosteal arteries.

4. Flat bones:

• Periosteal arteries

• Nutriens artery

• Anastomose with each other

5. Irregular bones:

Supplied by periosteal arteries

6. Skull bones:

Supplied by:

• periosteal arteries
• Middle meningeal artery

Histologic Structure

• Two components:

  • Cells

  • Intercellar substance

    • Fibres

    • Ground substance

Bone cells

1. Osteoblasts:

• Are bone forming cells which synthesize and secrete unmineralized bone matrix called “Osteoid”.

• Also secrete an enzyme “Alkaline phosphatase” which causes mineralization of osteoid.

• Active osteoblasts

  • are cuboidal in shape, each having a large spherical nucleus, usually eccentric in position.

  • Cytoplasm is markedly basophilic

  • On E/M, basophilia is due to presence of large quantity of RER.

  • Cytoplasm also contains a large golgi apparatus located in the central region of cell.

  • Active osteoblasts also have many finger like cytolasmic processes that bring them in contact with neighbouring osteobalsts

• Inactive osteoblasts (aka bonelining cells)

  • are fusiform (spindle shaped), with slightly basophilic cytoplam and small darkly staining nucleus.

2. Osteocytes:

• Are mature bone cells

• Are derived from osteoblasts which have secreted bone around them.

• Are flat almond shaped cells

• Have faintly basophilic cytoplasm, which contains small amount of RER and a small golgi apparatus.

• Osteocytes lie within small cavities, the Lacunae, in the bone matrix.

• Neighboring lacunae communicate with each other by narrow channels called Canaliculi.

• Fine cytoplasmic processes from each osteocyte extend for some distance into canaliculi and make contact with similar processes from neighboring cells.

• Gap junctions are present where these cytoplasmic processes meet. These junctions allow intercellular flow of ions and small molecules, providing a mechanism by which nutrients and metabolites can be exchanged between blood vessels and distant osteocytes

3. Osteoclasts:

• Are bone-resorbing cells

• Are multinucleated gaint cells, 50-150μm in diameter.

• Each cells has about 30 or more nuclei

• Are mostly found close to bone surface, where they are located in shallow concavities called Howship’s Lacunae. These cavities are produced by erosion of underlying bone

• Nuclei are away from bone surface

• E/M shows that cytoplasm of an osteoclast contains many golgi complexes, abundant mitochondria and many lysosomes.

• The surface of osteoclast which lies in contact with bone surface shows deep infoldings of plasma membrane with formation of irregular cytoplasmic processes. This surface is called “Ruffled border”.

• Surrounding the ruffled border is a cytoplasmic zone called Clear Zone which lacks cytoplasmic processes and is devoid of oraganelles

• Clear zone contains actin filaments which enable the osteoclasts to anchor itself to bony surface.

• In this way, a closed Subosteoclastic compartment is created between the ruffled border and the bone that is undergoing resortion. Osteoclasts seceret H+ ions and hydrolytic enzyms into this compartment.

• Resorption of bone matrix by osteoclasts involves 2 processes:

a. Initial dissolution of minerals: H+ ions secreted by osteoclasts create acidic mircoenvironment which increases the solubility of bones mineral salts resulting in release in re-entry of bone minerals (mainly Ca, PO4) back into blood stream.

b. Subsequent enzymatic degradation of collagen: by lysosomal hydrolases released by osteoclasts into subosteoclastic compartment.

Functions of osteoclasts:

1. Resorption bone matrix causing bone remodelling during bone growth and bone repair.

2. Calcium hemostasis

   1. Calcitonin lowers blood calcium level because it suppresses the process of osteoclastic resorption.

   2. Parathormone accelerates this process, so they raise blood calcium level.

Cell Surface

Cell Surface

Basement Membrane

• Sheetlike structure that underlies all the epithelia

• Consists of:

  • Basal lamina

    • Composed of: type IV collagen, glycoproteins, and proteoglycan

  • Reticular lamina

    • Composed of delicate reticular fibrers

• Functions:

  • Forms a barrier between epithelium and connective tissue. Normally:

    • Lymphocytes pass through it during immune surveillance

    • Cancer cells pass through it during invasion

  • Serves as filter (e.g. renal glomuruli)

  • Plays a role in regeneration (epithelial, nervous and muscle cells use it as a scaffolding during regeneration)

  • 
    

Lateral Surface specializations

A. Zonula occludens (Tight Junction):

• Formed by fusion of opposed cell membranes

• Extends completely around the apical cells to seal the underlying intercellular clefts from contact with outside environment

• May be leaky or tight

• Can be rapidly formed & disassembled e.g. in leukocyte migration across endothelium

B. Zonula Adharens (Intermediate Junction):

• Band like junction that serves in the attachment of adjacent epithelial cells.

• Often lies basal to zonula occludens, surround the perimeter below zonula occludens.

C. Desmosomes:

• Small discrete attachment

• Formed by juxtaposition of two disk-shaped plaques (desmolakins) in the cytoplasm of each adjacent cell.

• Tonofilaments (intermediate filaments) radiate away from the plaques

• Are common in lining membranes
  

D. Gap Junction (Nexus):

• Are subject to wear and tear
• Are considered spot welds that hold cells together

• Area of communication between adjacent cells.

• Allow very small particles and ions across a small intercellular gap within the junction. This allows conduction of electrical impulses

• Consists of a hexagonal lattice of tubular proteins, connexons which form hydrophilic channels connecting cytolplasm of adjacent cells.

Apical Surface Specialization

A. Microvilli:

• Are apical cell surface evaginations of cell membranes

• Core of each microvillus contains actin microfilaments.

• Is anchored to the terminal web in cytoplasm which itself is anchored to zonula adharens

• Function: increase the cell surface area available for absorption.

B. Stereocilia:

• Are elongated microvilli

• Found at the apices of cells lining the epididymis, ductus deferens and hair cells

C. Cilia:

• Are apical cell surface projections that contain microtubules

• Are inserted on centriole-like basal bodies present below the membrane surface

• Contain two central microtubules surrounded by a circle of nine peripheral microtubule doublets.

• The peripheral doublets are fused so that they share a common tubule wall and form 2 subunits, A & B.

• Adjacent doublets are linked to one another by Nexin links

• A pair of dynein arms is attached to each A subtubule.

• The arms bind to ATP and rearrange themselves so that a binding site for the B tubule on the tip of arm is exposed.

• B tubule interacts with the binding site, causing arm to snap back and movement to occur.

• Each cycle of a dynein arm slides adjacent doublets by 10 nm past each other.

• Function: cilia move back and forth to propel fluid and particles in one direction. Important in clearing mucus from the respiratory tract.

D. Flagella:

• Are longer than cilia but have the same microstructure

• Example: sperm

INTRODUCTION:

INTRODUCTION:

Who is the founder of anatomy?

• Hippocrates

Different stages of life.

Life before Birth:

• Ovum:

  • Fertilization to end of 1st week

• Embryo:

  • 2nd to 8th week

• Fetus:

  • 3rd month till birth

Life after Birth

• Neonate:

  • Birth to 1 month

• Infant:

  • Up to 1 year

• Toddler:

  • Up to 2 1/2 years

• Preschool child:

  • 2 ½ to 6 years

• Latency (School age):

  • 7-11 years

• Adolescence:

  • 11-20 years

    • Early adolescence- 11-14 years

    • Middle adolescence- 14-17 years

    • Late adolescence- 17-20

• Early adulthood:

  • 20-40 years

• Middle adulthood:

  • 40-65 years

• Late adulthood (old age):

  • 65 years +

DEFINITIONS

Anatomy:

• Consideration of various structures which make up the human body

• Greek word that means "to cut up" or "to dissect"

• Structure can be investigated by:

  • Dissection

  • Miscodissection

  • Light microscopy

  • Electron microscopy

  • Radiology etc etc.

Divisions of Anatomy:

• Systematic Anatomy:

  • Anatomy of various structures studied system-wise

• Topographic (Regional) Anatomy:

  • Anatomy of various structures as they in relation to one another in different regions of body

• Surface Anatomy:

  • Identification of various structures in the living person by inspection and palpation

  • OR anatomy as it occurs on and projects to the external surface of the body

• Radiologic (radiographic) anatomy:

  • Study of the structure of the body with the help of imaging techniques

• Cross-sectional Anatomy:

  • Study of the structure of the body with the help of cross-sections of various regions

  • anatomy viewed in the transverse (horizontal) plane of the body

• Neuroanatomy:

  • Study of nervous system

• Developmental anatomy:

  • Study of the biological processes that extend from fertilization to the formation of the adult anatomy.

• Embryology:

  • Study of various changes in developing organism from fertilization of ovum up to the birth

• Gross (macroscopic) anatomy:

  • Study of anatomy with the unaided eye

• Histology (microscopic anatomy):

  • Study of different tissues by various scientific methods using magnification

• Cytology:

  • Study of different type of cells by various biological methods

• Comparative Anatomy:

  • Study of anatomy of different species when compared to one another

• Applied Anatomy:

  • Application of the facts of human anatomy to clinical sciences

• Teratology:

  • Study of developmental abnormalities

• Phylogeny:

  • Evolutionary history of the group to which the organism belongs

• Statistical Anatomy:

  • Study of facts and figures (data) on variations in measurements, structures and relationships of different parts of human body

• Anthropology:

  • Study of mankind

    • Physical: external features and measurements of different races & study of prehistoric remains

    • Racial: percentage difference in form and arrangement of structures among different races

Divisions of Systematic Anatomy:

• Osteology:

  • Study of skeletal system (bones cartilages, associated membrances)

• Arthrology:

  • Study of articular system (joints)

• Myology:

  • Study of muscular system (muscles, fasciae, tendons, synovial sheaths and bursae)

[Locomotor apparatus: skeletal, articular and muscular system]

• Angiology:

  • Study of heart, blood vessels, lymphatics, lymph nodes and other lymphoid tissues

• Neurology:

  • Study of nervous system including:

    • Central nervous system (brain and spinal cord)

    • Peripheral nervous system: (peripheral nerves and their ganglia)

    • Autonomic nervous system (sympathetic and parasympethetic nerves and ganglia)

    • Organs of special senses (eye, ear, nose, tongue)

• Splanchnology:

  • Study of visceral systems except cardiovascular and lympathic systems

    • Respiratory system

    • Digestive system

    • Urinary system

    • Genital system

    • Endocrine system

Divisions of Regional Anatomy

• Head & Neck

• Trunk:

  • Thorax

  • Abdomen

  • Pelvis

• Limbs

  • Upper

  • Lower

• Brain

Anatomical position

• Standing erect

• Eyes looking forward to the horizon

• Arms by the side

• Palms and toes pointing forwards

Planes of the body:

• Medial plane:

  • vertical antero-posterior plane diving the body into right and left halves

• Saggital (paramedian) plane:

  • any vertical antero-posterior plane parallel to the median plane

• Coronal plane:

  • any vertical plane which lies at right angle to the saggital plane

• Transverse (horizontal) plane:

  • any plane at right angle to the above two planes

• Oblique plane:

  • at any other angle

Terms of Relationship

• Anterior:

  • near the front surface of the body

• Posterior:

  • near the back surface of the body

• Superior:

  • near the crown of the body

• Inferior:

  • near the soles of feet

• Cranial:

  • near the head

• Caudal:

  • near the tail

• Medial:

  • near the median plane

• Lateral:

  • away from the median plain

• Proximal:

  • Near the trunk

• Distal:

  • Away from the trunk

• Flexor surface:

  • Anterior surface of upper limb and posterior surface of lower limb

• Extensor surface:

  • Posterior surface of upper limb and anterior surface of lower limb

• Palmar:

  • anterior surface of hand

• Planter:

  • inferior surface of foot

• Superficial:

  • close to skin

• Deep:

  • Away from skin

• Ipsilateral:

  • on the same side of body

• Contralateral:

  • on the opposite sides of body

• Interior:

  • Inner part of the hollow organ

• Exterior:

  • Outer part of the hollow organ

• Invagination:

  • Inward protrusion of a viscus

• Evagination:

  • Outward protrusion of the viscus

• Ventral:

  • Towards the belly (ant)

• Dorsal:

  • Towards the back (post)

• Supine:

  • lying down with face looking anteriorly

• Prone:

  • Lying down with face looking posteriorly

Cell:

Structural unit of a multicellular organism

Tissue:

Combination of various cells performing a certain function

Organ:

Different tissues combine to form an organ

System:

Different organs combine to form a system