Q1 LONG ANSWER 10M ★ High-yield

Classify bones with examples. Describe the parts of a long bone and its blood supply. Add a note on the types of epiphysis.

Anatomy · 1st Professional — Pre-Clinical

Definition and Functions

Bone is a specialised connective tissue in which the matrix is impregnated with calcium salts, chiefly hydroxyapatite, giving it hardness and rigidity.

Support — the framework of the body
Protection — skull for brain, thorax for heart and lungs, pelvis for viscera
Movement — acts as levers for muscles
Mineral store — 99% of body calcium and 85% of phosphate
Haematopoiesis — red marrow
Fat storage — yellow marrow

Classification BY Shape

Type	Description	Examples
Long	Length exceeds breadth; has a shaft and two ends	Humerus, femur, tibia, radius
Miniature long	One end only has an epiphysis	Metacarpals, metatarsals, phalanges
Short	Cuboidal; length equals breadth	Carpals, tarsals
Flat	Two plates of compact bone with cancellous bone between	Skull vault, scapula, ribs, sternum
Irregular	Complex shape	Vertebrae, hip bone, maxilla
Sesamoid	Develops in a tendon	Patella (the largest), pisiform, fabella
Pneumatic	Contains air sinuses	Maxilla, frontal, ethmoid, sphenoid, mastoid
Accessory (sutural, Wormian)	Inconstant extra bones in sutures	Along the lambdoid suture

Classification BY Development

Type	Precursor	Examples
Membranous	Directly from mesenchyme	Skull vault (frontal, parietal), maxilla, most of mandible
Cartilaginous (endochondral)	Preformed in hyaline cartilage	All long bones, base of skull, vertebrae
Membrano-cartilaginous	Both routes	Clavicle, mandible, occipital, temporal, sphenoid

The clavicle is the first bone to ossify (5th–6th week) and the last to complete ossification (about 25 years)
It is also the only long bone to ossify in membrane

Parts of a Long Bone

Part	Description
Diaphysis	The shaft; ossifies from the primary centre; a tube of compact bone around the medullary cavity
Epiphysis	The end; ossifies from a secondary centre; cancellous bone with a thin compact shell
Metaphysis	The growing end of the diaphysis, adjacent to the epiphyseal plate; the most vascular part
Epiphyseal plate	Hyaline cartilage between epiphysis and metaphysis; the site of growth in length
Periosteum	Fibrous covering; its osteogenic layer gives growth in thickness and repairs fracture

Types of Epiphysis

Type	Function	Examples
Pressure	Takes part in a joint and transmits weight	Head of femur, head of humerus, condyles
Traction	Provides attachment for muscle; does not take part in a joint; ossifies later	Greater and lesser trochanters, tubercles of humerus, mastoid
Atavistic	A separate bone in lower animals, fused in man	Coracoid process, posterior tubercle of talos
Aberrant	Not always present	Head of the first metacarpal; base of the other metacarpals

Growing End and the Law of Ossification

The end that ossifies first is the last to fuse, and is the growing end.

Bone	Growing end	Note
Humerus	Upper end	Contributes about 80% of growth
Radius and ulna	Lower end	—
Femur	Lower end	The lower femoral epiphysis is the first to appear, at birth — used in medicolegal age estimation
Tibia and fibula	Upper end	—

Mnemonic — "To the elbow I go, from the knee I flee" describes the direction of the nutrient artery, which points away from the growing end
So in the upper limb the nutrient foramen points toward the elbow; in the lower limb away from the knee

Blood Supply of a Long Bone

Nutrient artery — the principal supply; enters the shaft obliquely through the nutrient foramen and supplies the inner two-thirds of the diaphysis and the marrow
Periosteal arteries — supply the outer one-third of the cortex; numerous where muscles attach
Metaphyseal and epiphyseal arteries — supply the ends; the metaphysis is richly vascular with sluggish flow
Juxta-epiphyseal arteries

Applied Aspects

Acute osteomyelitis in children characteristically begins in the metaphysis, because blood flow there is slow and the capillary loops are hairpin-shaped, allowing organisms to settle
Fracture through the epiphyseal plate (Salter–Harris injury) may arrest growth and cause deformity or shortening
Ossification centres are used to estimate age in medicolegal practice — the lower femoral epiphysis at birth, and fusion of the iliac crest at about 21 years
Avascular necrosis follows interruption of a single end-arterial supply — head of femur, scaphoid, talus, lunate
The periosteum is richly innervated, which is why fractures and subperiosteal collections are so painful, while the bone itself is relatively insensitive

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