• Brief anatomy
• Organization of the bones
• Types of bones
• About joints – Fibrous joints – Cartilaginous joints
– Synovial joints or diarthrosis and its types
BRIEF ANATOMY Bone Development
I am a specialized connective tissue. By providing a rigid skeleton, I give the all-important shape to the human beings. I am proud to be entrusted the job of protecting vital structures like brain, lungs and heart.
I am the largest store-house of the all-important mineral, calcium in the body. I am also concerned with hemopoiesis. I give attachment to the muscles and enable them to act on the joints by acting as a lever for their action. I am made-up of 30 percent organic material (mainly type I collagen) and 70 percent mineral (calcium hydroxyapatite).
Remember the functions of bone
• Protection of vital organs
• Support to the body
• Hemopoiesis
• Movement and locomotion
• Mineral storage
How do I start developing?
My development begins with the condensation of the mesenchyme in the embryo. There are certain exceptions like the vault of the skull (membranous ossification), the
clavicle (mixed ossification) and the mandible (Meckel’s cartilage). From this condensation, I rapidly form a cartilaginous model. Between the cartilaginous bone and plates, I form small clefts for the future joints. During this period of 12 weeks, I am particularly vulnerable to teratogenic influences.
As early as the fifth week of intrauterine life, I develop a primary centre of ossification, which gradually replaces this cartilage model to bone by a process of endochondral ossification. During the late fetal stages or early few years of life, I develop secondary centers of ossification.
Growth plate, which keeps the primary and secondary centers of ossification separated from each other until skeletal maturity, helps me grow longitudinally and I increase my width from the growth of the thickened periosteum. In addition, I keep remodeling myself from the fetal stage to the adult stage. Only the rate varies (50%
during the first two years of life and 5% per year thereafter until adulthood).
Remember
• Bone development starts as a condensation of mesenchyme.
• Later a cartilaginous model develops.
• There are two types of ossification—endochondral and membranous.
• There are three types of bone cells.
About Osteon
Now let me tell you how exactly I am made-up of internally. I am made-up of many units called
“osteon”. I have three types of cells, osteoblasts that form the bone, osteoclasts which remove the bone and are concerned with remodeling, osteocytes, which are the resting cells. These cells are present in the lamellae, which surround concentrically the
Volkmann’s canal (which has the nutrient vessel) and each lamellae is interconnected by the canaliculi through which the nutrients pass. Osteoblasts lay down uncalcified matrix, which is subsequently calcified as true bone. These various osteons amalgamate to form large haversian systems, loosely woven in the medullary bone and densely packed in the cortical shell (Fig. 2.1).
Now having known my intrinsic structure, you will be interested to know that I have two major portions, medulla and the cortex.
About Medulla
Medulla is my softer counterpart and has the dual role of structure and storage. It stores more than 95 percent of body’s calcium and is a storehouse for other minerals too. The other important component of the medulla is the marrow between the medullary bone lattices. This is the source from where the RBCs and WBCs originate. Initially present throughout, it confines itself to the metaphyseal regions of the long bones and in some flat bones like pelvis, rib, etc. as age advances and is replaced by a fatty white marrow.
The medulla plays the structural role by its trabecular organization along maximal lines of stress and clearly identifies itself into compression and traction trabeculae.
About Cortex
Cortex gives me the remarkable strength, which you all admire particularly during compression. Its periosteal cover allows remodeling throughout life.
It also gives attachments to ligaments, tendons and muscles through the Sharpe’s fibers.
Remember about medulla
• Softer portion.
• Stores 95 percent of body calcium.
• Marrow is the other important component.
• Also plays a structural role.
About General Structure
Now let me explain to you my general structure. I have an epiphysis and epiphysis plate (which disappears with growth), metaphysis and diaphysis (Fig. 2.2).
Epiphysis is an expanded portion at the end develops usually under pressure and forms a support for the joint surface. It is easily affected by deve-lopmental problems like epiphyseal dysplasias, trauma, overuse, degeneration and damaged blood supply. The result is distorted joints due to avascular necrosis and degenerative changes.
Growth plate (physis) though mechanically weak it helps longitudinal growth. It responds to growth and sex hormones. It is affected by conditions like
Fig. 2.1: Bone cross-section showing its internal structure Fig. 2.2: General structure of a long bone
osteomyelitis, tumor, slipped epiphysis resulting in short stature or deformed growth or growth arrest.
Metaphysis is concerned with remodeling of bone.
It is the cancellous portion and heals readily. It gives attachment to ligament and tendons. It is vulnerable to develop osteomyelitis, dysplasias and tumors resulting in distorted growth and altered bone shapes.
Diaphysis is a significant compact cortical bone which is strong in compression and which gives origin to muscles. It forms the shafts of the bones.
Healing is slow when compared to metaphysis.
In remodeling, it can remodel angulations but not rotation. It may develop fractures, dysplasias, infection and rarely tumors.
Remember Parts of a bone
• Epiphysis
• Physis (growth plate)
• Metaphysis
• Diaphysis
ORGANIZATION OF THE BONES
We are 206 in number and are grouped into two subdivisions namely:
1. Axial skeleton—80 bones (Table 2.1).
2. Appendicular skeleton—126 bones (Table 2.2).
Axial skeleton forms the upright axis of the body and the appendicular skeleton forms the appendages and girdles that attach them to the axial skeleton (Fig. 2.3).
Out of this 206, some of us are short and some are long. We have different shapes. The shape and size depend upon the functions attributed to us.
TYPES OF BONES (FIGS 2.4A TO C)
Long bones These serve as levers for the muscle action, e.g. femur, tibia, etc (Fig. 2.4C).
Short bones These are generally cube-shaped and are found in areas where limited movements are required (Fig. 2.5). Their primary role is to provide strength.
Flat bones These consist of parallel layers of compact bone separated by a thin layer of cancellous bone tissue, e.g. scapula, skull, etc (Fig. 2.4A).
Irregular bones These have a peculiar and irregular shape and are unique in their appearance and functions, e.g. pelvic bones (Fig. 2.4B).
Table 2.2: Bones of the appendicular skeleton Shoulder girdle
• Clavicle 2
• Scapula 2
Upper extremities
• Humerus 2
• Ulna 2
• Radius 2
• Carpals 16
• Metacarpals 10
• Phalanges 28
Hip girdle
• Metatarsals 10
• Phalanges 28
Total 126
Table 2.1: Bones in the axial skeleton Skull
• Cranium 8
• Face 14
Vertebral column
• Cervical vertebrae 7
• Thoracic vertebrae 12
• Lumbar vertebrae 5
• Sacrum 1 (5 fused bones)
• Coccyx 1 (3-5 fused bones)
Sternum 1
Ribs 24 (12 pairs)
Hyoid 1
Fig. 2.3: Organization of bones: Axial and appendicular skeleton
Sesamoid bones: These are small, rounded or triangular bones, which develop within the substance of a tendon or fascia. Their name is
derived from their resemblance to “sesame seeds”, e.g. patella (largest and most definitive of the sesamoid bones).
Remember Types of bones
• Long bones
• Short bones
• Flat bones
• Irregular bones
• Sesamoid bones
The above bones are arranged in two groups
• Axial—80 bones
• Appendicular—126 bones
Thus, my duty is to serve you to the best of my ability, so that you lead a healthy skeletal life. Much depends on you in keeping me in a proper shape.
You need to take good nutritious diet rich in calcium and vitamins to keep me healthy. Proper exercises, protection against injuries and infection enhance my efficiency in serving you, but there are certain inherent problems in me in which you can do precious little. Congenital problems, hormonal problems, metabolic problems, tumor conditions, etc. are some of these.
However, the above problems are troublesome I develop them infrequently. Nevertheless, the problem that poses a serious threat to my integrity is injuries due to trauma. As a child, you are more playful and more prone to fall and this breaks me quite often. As an adult, you are more prone for road traffic accidents (RTAs) and this subjects me to a plethora of different varieties of forces causing many complexes, grotesque and bizarre breaks.
Though you pride in the fast-paced life of yours, I grieve at my misfortune and at my vulnerability to these vast array of incriminating forces, which overcome me putting you out of action for months.
As you age, my faithful friends, proteins and minerals gradually desert me. I cannot provide you the same strength as earlier. In this phase, even trivial forces (pathological fractures) easily overcome me. I am sad that I cannot provide you the same privileges as before but I hope you can realize that I am not being unfaithful to you, but I am made helpless by situations beyond anybody’s control.
ABOUT JOINTS
A joint exists where two or more skeletal compo-nents— whether bone or cartilage, come together to meet. Without joints in between the bones, your whole body would be rigid and immobile. The existence of these joints makes movement of the body parts possible. Joints are classified into three major groups:
FIBROUS JOINT OR SYNARTHROSIS
These are immovable joints, e.g. sutures of the skull.
In these, there are three varieties:
Syndesmosis: This is characterized by a dense fibrous membrane that binds the articular bone surfaces very closely and tightly to each other, e.g. distal tibiofibular joint.
Figs 2.4A to C: Types of bones: (A) Flat bone, (B) Irregular bone, and (C) Long bone
Fig. 2.5: Foot is an assembly of short bones of various sizes
Sutures: True sutures are found in the skull. Here the adjoining bone margins are united into rigid, jagged interlocking processes, e.g. sagittal suture of the skull.
Gomphosis: Here a conical peg or projection that fits into a socket, e.g. teeth and sockets of jawbones.
Figs 2.6A to G: Different types of joints: (A) Hinge joint, (B) Pivot joint, (C) Plane joint, (D) Ellipsoid joint, (E) Saddle joint, (F) Bicondylar joint and (G) Ball and socket joint
CARTILAGINOUS JOINTS OR AMPHORTHOSIS These are slightly movable joints with either hyaline or fibro cartilage in between. Two varieties are described:
Synchondroses: Here hyaline cartilage is posed in between, e.g. articulations between rib and sternum.
Symphysis: Here the fibrocartilage is interposed in between and is usually found in the midline of the body, e.g. pubic symphysis.
SYNOVIAL JOINTS OR DIARTHROSIS
These form the majority of the joints in the body.
They have between the bones, a synovial or joint cavity. They form the most mobile joints in the body and hence are more prone for injuries.
It consists of a fibrous joint capsule that helps to hold the articulating bones together. The synovial membrane lines the joint space and secretes the synovial fluid. This fluid serves to lubricate the joints and provides nourishment for the articular cartilage.
The articular cartilage is formed by the hyaline cartilage, which is a unique type of connective tissue formed by specialized cells called chondrocytes.
Types of Synovial Joints
Uniaxial joints: These permit movement in only one plane and one axis (Figs 2.6A to G). In this, there are two types:
Hinge joints: Here movement takes place around a horizontal axis, e.g. elbow joint.
Pivot joints: Here movement takes place around a vertical axis that permits rotation, e.g. atlantoaxial joint.
Biaxial joints: Here movement occurs in two planes and two axes that are at right angles to each other.
Two types are described:
Saddle joint: Here the articular surface is concave in one direction and convex in the other while the articular surface of the opposing bone is exactly the opposite, e.g. carpometacarpal joint at the base of the thumb.
Condyloid joint: In this, an oval condyle fits into an elliptic socket or cavity, e.g. radiocarpal joints.
Multiaxial joints: Here there are two or more axes of rotation and movement takes place in three or more planes. Two varieties are described:
Ball and socket joint: In this a ball-shaped head of one fits into a concave socket of another bone. Of all the joints in the body, these provide the widest, most free range of movements in almost any direction or plane, e.g. hip joint, shoulder joint, etc. (see Fig 2.6G).
Gliding joints: These are numerous, gliding move-ments occur in all planes, e.g. joints between the carpal and tarsal bones, and all the joints between the articular processes of the vertebrae (see Fig. 2.6C).
INTRODUCTION
Birth asphyxia accounts for about 19% of the 5 million neonatal deaths that occur each year worldwide.
American Academy of Pediatrics (AAP) and American Heart Association (AHA) developed a neonatal resuscitation program which has shown to protect and prevent harmful effects on the vital organs of the body due to perinatal asphyxia and ischemia (Fig. 3.1).
BASICS OF ASPHYXIA
APNEA
The asphyxiated infant passes through following series of events:
Rapid breathing and fall in heart rate
Primary apnea
Irregular gasping respiration, further fall in heart rate and drop in blood pressure
Secondary apnea
Most infants in primary apnea will resume breathing, when stimulated. Once in secondary apnea, infants are unresponsive to stimulation.
Apnea at birth should be treated as secondary apnea of unknown duration and resuscitation should begin at once.
CLEARING ALVEOLAR FLUID
The first few breaths of a normal infant are usually adequate to expand the lungs and clear the alveolar lung fluid.
The pressure required to open the alveoli for the first time may be two to three times that for normal breaths.
Problems in lung fluid clearance occur with:
Apnea at birth
Weak initial respiratory effort caused by:
prematurity
depression by asphyxia, maternal drugs, or anesthesia.
PULMONARY CIRCULATION
At birth, pulmonary blood flow increases as the lung arterioles open up and blood is no longer diverted through the ductus arteriosus.
With asphyxia, hypoxemia and acidosis cause further pulmonary vasoconstriction and maintain the fetal pattern of circulation.