Diaphysis: It resembles the shaft of a long bone. The centre of ossification appears in the 7th week of Intrauterine life. The ossification centre is called primary ossification centre.
It resembles the ends of a long bone. The centre of ossification usually appears after birth at the age of one or two years except the lower end of femur where the secondary centre of ossification appears in the 9th month of Intrauterine life.
Types of Epiphysis:
Pressure epiphysis: They develop in the vicinity of site of articulation during 1st and 2nd year of development.
i.Head of humerus.
ii.Condyles of humerus.
Five paired long bones of limbs always have pressure epiphyses at both ends.
2) Traction epiphysis: They develop in the site of attachment of certain tendons at the time of puberty.
i.Tuberosities of humerus
ii.Trochanters of femur
Atavistic epiphysis: These are Phylogenetically independent bones which have become part of other bones, coracoid process of scapula.
Metaphysis:
They actively growing part of shaft close to epiphyseal cartilage is called Metaphysis. It is highly vascular and is responsible for growth in length.
Epiphyseal Cartilage :
It is a plate of cartilagenous tissue present between epiphysis and diaphysis.
After the completion of growth, it is also ossified and is represented by epiphyseal line in adult bone. Completion of growth in long bones usually occurs between the age of 17-19/20 year.
BLOOD SUPPLY OF BONES:
Majority of the pores present in the bone are meant for veins mainly. Adult long bone derives its blood supply from following sources :-
Periosteal arteries: They are numerous and supply the compact bone of the shaft and spongy bone of the ends.
Nutrient artery:
It enters the bone through nutrient foramen and reaches the medullary cavity. It gives a number of branches which are descending and ascending. It anastomoses with periosteal and end-blood vessels. Its branches also pass through Volkman’s canal and Haversian canals.
It supplies little more than bone marrow. The branches of nutrient artery are called “nutritiae.”
Arteries at the end of long bones: These arise from two
Sources:
a)Peri-articular anastomosis (circulus vasculosus). These vessels are called juxta epiphyseal vessels of lexer.
b)From the artery passing over that region.
These arteries (a & b) pierce the bone at metaphysis and epiphyseal cartilage respectively.
BLOOD SUPPLY OF IMMATURE LONG BONE
Here additional Epiphyseal and Metaphyseal arteries are present. Epiphyseal artery surrounds the periphery of epiphyseal cartilage and Metaphyseal artery supplies the metaphysis – growing portion of diaphysis. These arteries are derived from periosteal arteries which are situated at the ends of the long bone.
(C)BLOOD SUPPLY OF SHORT BONES
These are only supplied by Periosteal arteries.
(D)BLOOD SUPPLY OF FLAT BONES
These are supplied by two types of arteries which anastomose with each other. These arteries are :-
i)Periosteal arteries.
ii)Nutrient artery.
The veins follow the arteries:
(E) BLOOD SUPPLY OF IRREGULAR BONES
Periosteal arteries enter the bone at the origin of transverse ness and they supply both compact and spongy bone.
The smaller veins unite to form two large veins. These veins leave the body of vertebrae at their posterior surface.
(F) ARTERIES OF SKULL BONES
These are supplied by two types of arteries:
i)Periosteal arteries
ii)Middle meningeal artery
Veins start from diploic venous sinuses present in diploic bone (spongy bone). They drain into dural sinuses; veins of skull and scanty.
All bones are supplied by both medullated and non-medullated nerve fibres. These nerves enter the bone through nutrient foramen and periosteum.
The nutrient foramen has direction against the growing end. “Towards the Elbow we go; from the knee we flee.
In the humerus bone the nutrient foramen is directed towards the elbow and upper end of the bone is the growing end.
In the femur bone ‘the nutrient foramen is directed upwards, and the lower end of the bone is the growing end.
GROSS STRUCTURE OF LONG BONE:
It is tubular structure which has two expanded ends and a long shaft of body. The shaft is hollow and has a cavity filled with bone marrow called marrow cavity or medullary cavity. The walls of the cavity are very hard and thus make the shaft very strong with minimum expenditure of material. Usually the shaft has three borders and three surfaces.
The ends are articular, smooth and covered by hyaline cartilage. They may be either concave or convex and expanded.
The long bone is preformed in hyaline cartilage and ossified by replacement of cartilage by a very complicated process. The primary centre of ossification for the shaft appears during intrauterine life. The secondary centres of ossification appear usually after birth.
The nutrient foramen is present in the middle of the shaft and is directed away from the growing end.
Longitudinal section of a long bone shows following features:
1. The ends are composed of spongy bone covered by hyaline cartilage, and are the active sites of blood formation.
The shaft shows following features:-
It is covered by a fibro-vasculo-cellular membrane called periosteum. The periosteum is connected to the underlying cortical bone by periosteal collagenous fibres which penetrate the cortical bone. They are especially developed at the site of attachment of muscles. These periosteal collagenous fibres are called perjorating fibres of Sharpey.
The periosteum of the shaft is continuous with the articular capsule (joint capsule) near the ends.
The periosteum is sensitive due to rich nerve supply which is derived from the nerves supplying the muscles attached to the bone. However the sensitivity is increased in those areas where the periosteum is supplied by cutaneous nerves, tibia bone.
a)Underneath the periosteum the cortical bone or cortex is composed of compact bone.
c)The marrow cavity or medullary cavity is lined by endosteum and contains a gelatinous material called bone marrow.
There are two types of bone marrow:
1.Yellow bone marrow:
It is a yellowish gelatinous fibro-fatty mass present in the medullary cavity.
2.Red bone marrow:
It is a red gelatinous mass consisting of haemo- poietic tissue. It is engaged in erythropoiesis. It is found in:
i)the ends of long bones.
ii)The bodies of vertebrae.
iii)The sternum.
iv)The flat bones of the skull.
- The yellow marrow can be converted into red marrow if need arise.
- The marrow cavity is absent in clavicle bone and ribs.
TERMS USED FOR SURFACE MARKINGS ON A. DRIED BONE:
Various small holes are present on the surface of a bone. They are called foramina (singular is formen). They are much numerous near the ends are meant for passage of blood vessels.
In the middle of the shaft a promir ent foramen is present which leads into a canal and directed away from tle growing end of the bone. It is called a nutrient foramen, through which utrient artery supplies the bone.
The attachments of muscles, tendons and ligaments produce different types of markings on the bone. The fleshy fibres of muscle produce no marking on the bone while the fibrous elements like tendons and ligaments produce various types of markings which are evident at puberty.
These markings can be discussed as follows:-
I.ELEVATIONS:
The raised area is called an elevation. These are further subdivided into followings according to shape and degree of prominence:
A)Linear elevations
These are of following types:
- Line,Gluteal lines of the Hip bone.
- Spiral line of Femur.
- Oblique line of Radius.
FACETS:
Spine, e.g., Anterior superior iliac spine of Hip bone. Process, e.g., Styloid process of ulna.
Small, smooth and flat areas of the bone are termed as facets, e.g., Articular facets are flat and covered by articular cartilage.
1.The articular facets may show following variations:
2.They may be rounded like the heads of humerus and femur.
3.They may be knuckle-like, e.e.g, condyles of Femour. The lower end of humerus is a modified condyle.
4.They may be pulley-shaped like Trochlea of humerus.
DEPRESSIONS:
They are of following types:
A) Pit or fovea:It is very small and shallow depression, e.g., Fovea of head of Femur.
B) Fossa:It is a slightly large and deep depression.
C)Iliac fossa of Hip bone.
D)Olecranon fossa of Humerus.
Notch or Incisura:
It is a depression bridged by a ligment, e.g., supra scapular notch of scapula.
Groove or sulcus:
i)It is a depression with some length, e.g.,
ii)Radial groove of Humerus.
iii)Inter tubercular sulcus of Humerus.
Foramen:
It is a perforated depression or a hole in the bone, e.g., Nutrient foramen; Foramina are common in skull.
F) Canal or Meatus: It is a foramen with some length.
i)External auditory meatus.
ii) Pterygoid canal.
iii)Hypoglossal canal.
iv)Stylomastoid canal.
Every canal has an opening at each end called the orifice or ostium.
CARTILAGE
DEFINITION:
The cartilage is a phylogenetically old type of connective tissue, with wide spread distribution in vertebrates, which is characterized by the presence of rigid but flexible matrix.
GENERAL FEATURES:
1.It is usually covered by a fibro-vasculo-cellular membrane called perichondrium.
2.It has high tensile strength and resistance to compressive and shearing forces.
3.It is avascular, i.e., it lacks exchange blood vessels.
4.Its metabolic rate is low.
5. It has no lymphatics and nerves.
TYPES:
Regeneration is not so much effective especially in articular cartilage which lacks perichondrium. It is composed of:
1. Cells (chondroblasts & chondrocytes).
2. Matrix (consists of ground substance and connective tissue fibres).
Depending upon the nature of matrix there are three types of cartilage :
- Hyaline
- Elastic
- Appearance
Bluish white, translucent and homogenous.
Yellow; Elastin fibres prominent in the matric.
| Distribution | Cartilage Type | Details |
|---|---|---|
| Most Abundant | Embryonic Cartilage | |
| ii. Articular Cartilage | ||
| iii. Costal Cartilage | ||
| iv. Tracheal Cartilage | ||
| v. Bronchial Cartilage | ||
| Rare | i. Pinna | |
| ii. Epiglottis | ||
| iii. Auditory Tube | ||
| White Fibro-cartilage | White, opaque and collagen fibers are more abundant in the matrix. | |
| Less Abundant | i. Intervertebral Disc | |
| ii. Intra Articular Disc |