General osteology
-
Upload
jamil-anwar -
Category
Health & Medicine
-
view
2.311 -
download
0
description
Transcript of General osteology
General osteology
DR. JAMIL ANWAR
Plan of the lecture1. General concepts about skeleton
2. Bone as an organ
3. Functions of the skeleton
4. Classification of bones
5. Types of bone ossification
6. Development of bones
The Skeletal System! Our First System
Cells (Osteocytes)
Tissues (Osseous Tissue)
Organs (Bones)
Systems (Skeletal)
THE LOCOMOTOR APPARATUS – ITS COMPONENTS AND FUNCTIONAL ROLE
The skeleton is a complex of hard structures that is of mesenchymal origin and possesses a mechanical significance. The term skeleton comes from a Greek word meaning “dried up”.
NB: All the bones and articulations of the body make up the passive part of the locomotor apparatus.
The skeleton
The science concerned with the study of bones is termed osteology.
The skeletal system of an adult is composed of approximately 206 bones. Each bone is an organ of the skeletal system.
For the convenience of study, the skeleton is divided into axial and appendicular parts.
The axial skeleton The axial skeleton
consists of 80 bones that form the axis of the body and which supports and protects the organs of the head, neck, and trunk.
Skull Auditory ossicles Hyoid bone Vertebral column Thoracic cage
The appendicular skeleton
The appendicular skeleton is composed of 126 bones of the upper and lower limbs and the bony girdles, which anchor the appendages to the axial skeleton.
The shoulder girdle (the scapula and clavicle)
The upper limb (the humerus, ulna, radius and bones of the hand)
The pelvic girdle (the hip bone) The lower limb (the femur, tibia,
fibula and bones of the foot)
BONE AS AN ORGANSTRUCTURE OF A BONE AND STRUCTURE OF THE PERIOSTEUM
Bone (osis) is one of the hardest structures of the body. It possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is pinkish-white externally, and red within.
Types of bone tissueThere are two types of bone tissue:
a) compact bony tissue
b) spongy bony tissue
The names imply that the two types differ in density, or how tightly the tissue is packed together.
There are three types of cells that contribute to bone homeostasis.
a) osteoblasts are bone-forming cell
b) osteoclasts resorb or break down the bone
c) osteocytes are mature bone cells.
An equilibrium between osteoblasts and osteoclasts maintains the bone tissue.
OSSIFICATION
OSTEOBLASTSFORM NEW BONE
MATRIX
COLLAGENSTERNGTH
CALCIUM DEPOSITION
OSTEOCYTES
MAINTAIN BONE
OSTEOCLASTS
MAINTAIN SHAPE
Structure of bone On examining a cross section of
any bone, it is composed of two kinds of bony tissue:
Compact tissue, it is dense in texture and it is always placed on the exterior of the bone.
Cancellous tissue consists of slender fibers and lamellae, which join to form a reticular structure and it is placed in the interior of the bone
Macromicroscopic structure of bone
The morphofunctional unit of the bone is the osteon, or Haversian system.
The osteon consists of a system of bony lamellae arranged concentrically around a canal, which is called Haversian canal and this canal contains nerves and vessels. The bone lamellae consist of osteocytes, their lacunae, and interconnecting canaliculi and matrix.
The spongy bone tissue Spongy (cancellous) bone is
lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply.
The spongy bone tissue It may appear that the
trabeculae are arranged in a haphazard manner, but they are organized to provide maximum strength similar to braces that are used to support a building. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.
The periosteum
Externally bone is covered by
periosteum (except articular
surfaces). The periosteum
adheres to the surface of the
bones.
It consists of two layers closely
united together:
a) The outer layer fibrous layer
b) The inner layer or bone-forming layer (cambial)
Structure of the periosteum The periosteum is rich in
vessels and nerves, and it contributes to the nutrition and growth of the bone in thickness. Nutrients are conveyed by blood vessels penetrating in great number the outer (cortical) layer of the bone from the periosteum through numerous vascular openings (foramina nutricia).
The interior of each long tubular bone of the limbs presents a cylindrical cavity named marrow cavity and it is lined with the medullary membrane called endosteum.
Chemical Composition of Bone
Functions of the skeletal system
1. Support - framework for the body 2. Protection - skull, vertebrae, ribcage 3. Leverage - bones are levers, joints are
fulcrums 4. Mineral storage – (calcium) 5. Lipid Storage – (yellow marrow) 6. Blood cell formation - hematopoiesis
Functions of the skeleton
Biological functions
Mechanical functions
Biological functions of the skeleton
a) Haemopoiesis
b) Mineral storage.
Bone marrow
The bony compartments contain bony marrow, medulla ossium. Two types of bone marrow can be distinguished:
red bone marrow white bone marrow The white or yellow marrow fills up the medullary
cavities of the shafts of the long tubular bones. The red marrow is located within the cancellous
tissue and extends into the larger bony canals (Haversian canals) that contain blood vessels.
Haemopoiesis function
The bone marrow provides haemopoiesis function and biological protection of the organism. It takes part in nutrition, development and growth of the bone. The red marrow concerned with haemopoiesis and bone formation, has an active role in the healing of fractures. Red marrow predominates in infants and in children, with growth of child the red marrow is gradually replaced by yellow marrow.
NB: The bones of the embryo and new-born contain only red marrow.
Haemopoiesis function
The red bone marrow of an adult produces white blood cells, red blood cells, and platelets.
In an infant, the spleen and liver produce red blood cells, but as the bones mature, the bone marrow performs this task.
It is estimated that an average of 1 million blood cells are produced every second by the bone marrow to replace those that are worn out and destroyed by the liver.
Mineral storage
The inorganic matrix of bone is composed primarily of minerals calcium and phosphorus. These minerals give bone rigidity and account for approximately two-thirds of the weight of bone.
About 95% of the calcium and 90% of the phosphorus, within the body, are stored in the bones and teeth.
In addition to calcium and phosphorus, lesser amounts of magnesium and sodium salts are stored in bones.
Mechanical functions of the skeleton
a) Support
b) Protection
c) Body movement
Support (weight bearing)
The skeleton forms a rigid framework to which are attached the soft tissues and organs of the body.
Protection function
Protection is assured by the property of the bones to form body cavities which protects the vital important organs.
The skull and vertebral column enclose the central nervous system.
The thoracic cage protects the heart, lungs, great vessels, liver and spleen.
The pelvic cavity supports and protects pelvic organs.
Even the site where blood cells are produced is protected within the central portion of certain bones.
Body movement Bones serve as anchoring
attachments for most skeletal muscles. In this capacity, the bones act as levers, with the joints functioning as pivots, when muscles, which are regulated by the nervous system, contract to cause the movement.
Classification of bones by shapeTubular bones
a) Long tubular bones humerus, radius, ulna, femur, tibia, fibula
b) Short tubular bones metacarpal, metatarsal bones and phalanges
Classification of bonesSpongy bones
a) Long spongy bones sternum, ribs, etc
b) Short spongy bones carpal and tarsal bones
c) Sesamoid bones knee-cap pisiform bone, etc.
Classification of bonesFlat bones
Skull bones Bones of the vault of the
skull
Girdle bones The scapula The hip bone, etc.
Classification of bonesMixed bones
The vertebrae are mixed, or irregular bones (their bodies are referred to spongy bones, but their arches and processes are referred to flat bones).
Bone formation (osteogenesis)
Osteogenesis occurs throughout life but in different ways 1. embryo responsible for laying down of bony
skeleton (ossification well started by 8th week) 2. bone growth continues until early adulthood 3. remodeling & repair continues for life• Ossification - The process of replacing other
tissues with bone (endochondral and intramembranous)
Calcification - The process of depositing calcium salts Occurs during bone ossification and in other
tissues
2 types of ossification
1. Intramembranous (dermal ossification) Formation of most of the flat bones of the skull and the
clavicles from a fibrous membrane Fibrous connective tissue membranes are formed by
mesenchymal cells
2. Endochondral Formation of bone in hyaline cartilage
Both lead to the same type of bone Both begin with migration of mesenchymal cells from c.t. to
areas of bone formation No blood supply chondroblasts Blood supplyosteoblasts
Intramembranous Ossification: Step 1
Mesenchymal cells aggregate: differentiate into
osteoblasts begin ossification
at the ossification center
develop projections called spicules
Intramembranous Ossification: Step 2
Blood vessels grow into the area: to supply the
osteoblasts Spicules connect:
trapping blood vessels inside bone
Intramembranous Ossification: Step 3
Spongy bone develops and is remodeled into: osteons of compact bone periosteum or marrow cavities
Endochondral Ossification
Begins in the second month of development
Uses hyaline cartilage “bones” as models for bone construction
Requires breakdown of hyaline cartilage prior to ossification
Endochondral Ossification: Step 1
Chondrocytes in the center of hyaline cartilage: enlarge form struts and calcify die, leaving cavities in
cartilage
Endochondral Ossification: Step 2
Blood vessels grow around the edges of the cartilage
Cells in the perichondrium change to osteoblasts: producing a layer of
superficial bone around the shaft which will continue to grow and become compact bone .
Endochondral Ossification: Step 3
Blood vessels enter the cartilage: bringing fibroblasts that
become osteoblasts spongy bone develops at
the primary ossification center
Endochondral Ossification: Step 4
Remodeling creates a marrow cavity: bone replaces cartilage
at the metaphyses
Endochondral Ossification: Step 5
Capillaries and osteoblasts enter the epiphyses: creating secondary
ossification centers
Endochondral Ossification: Step 6
Epiphyses fill with spongy bone: cartilage within the
joint cavity is articulation cartilage
cartilage at the metaphysis is epiphyseal cartilage
Primary centers of ossification
In the second month of the intrauterine life, the primary points of ossification appear first, in the shafts, or diaphyses of tubular bones, and in the metaphyses.
They ossify by perichondral and enchondral osteogenesis.
Secondary and accessory points of ossification
The secondary points of ossification appear shortly before birth or during the first years after birth and they develop by encondral osteogenesis.
The accessory points of ossification appear in children, adolescents, and even adults in the appophyses of bones (e.g. tubercles, trochanters, the accessory processes of the lumbar vertebrae).
Blood Supply of Mature Bones 3 sets of blood vessels develop Nutrient artery and vein:
a single pair of large blood vessels enters the diaphysis through the nutrient foramen
Metaphyseal vessels: supply the epiphyseal cartilage
where bone growth occurs Periosteal vessels provide:
blood to superficial osteons secondary ossification centers
Effects of Hormones and Nutrition on Bone1. Growth hormone
Single most important stimulus to the epiphyseal plate (dwarfism/gigantism)
2. Thyroid hormone Moderates growth hormone to insure proper
proportions of growth3. Sex hormones (estrogens & androgens)
A great ‘rush’ at puberty = growth spurt Lead to a breakdown of cartilage that leads
to a closure of plates …steroids!4. Calcitriol
Made in kidneys; synthesis requires cholecalciferol Helps absorb calcium & phosphorus from GI tract
Additional dietary regulators Need adequate calcium, phophorus, magnesium,
flouride, iron, & manganese Calcium is necessary for:
Transmission of nerve impulses Muscle contraction Blood coagulation Secretion by glands and nerve cells Cell division
Vitamin D – absorption of calcium from GI Vitamin C – formation of collagen Vitamin A – stimulates osteoblast activity Vitamins K and B12 - help synthesize bone proteins
Bone Fractures (Breaks)
Bone fractures are classified by: The position of the bone ends after fracture The completeness of the break The orientation of the bone to the long axis Whether or not the bones ends penetrate the skin
Types of Bone Fractures Nondisplaced – bone ends retain their normal position Displaced – bone ends are out of normal alignment Complete – bone is broken all the way through Incomplete – bone is not broken all the way through Linear – the fracture is parallel to the long axis of the bone Transverse – the fracture is perpendicular to the long axis of the bone Compound (open) – bone ends penetrate the skin Simple (closed) – bone ends do not penetrate the skin Comminuted – bone fragments into three or more pieces; common in the
elderly Spiral – ragged break when bone is excessively twisted; common sports
injury Depressed – broken bone portion pressed inward; typical skull fracture Compression – bone is crushed; common in porous bones Epiphyseal – epiphysis separates from diaphysis along epiphyseal line;
occurs where cartilage cells are dying Greenstick – incomplete fracture where one side of the bone breaks and
the other side bends; common in children
The Major Types of Fractures
The Major Types of Fractures
Fracture Repair: Step 1
Bleeding: produces a clot
(fracture hematoma) establishes a fibrous
network Bone cells in the area
die
Fracture Repair: Step 2
Cells of the endosteum and periosteum: Divide and migrate into
fracture zone Calluses stabilize the
break: external callus of
cartilage and bone surrounds break
internal callus develops in marrow cavity
Fracture Repair: Step 3
Osteoblasts: replace central
cartilage of external callus
with spongy bone
Fracture Repair: Step 4
Osteoblasts and osteocytes remodel the fracture for up to a year: reducing bone
calluses
Osteoporosis Bone reabsorption>bone
production Osteopenia begins between
ages 30 and 40 Women lose 8% of bone mass
per decade, men 3% Decrease in bone
massincrease fracture risk Decreased levels of estrogen
primarily Most important cause of fracture
in women>50 35% of bone mass may be gone
by age 70 Vertebrae & femur neck are
most affected
Risk Factors Body build – short
women have less bone mass
Weight – thinner at greater risk
Smoking – decreases estrogen levels
Lack of dietary calcium Exercise – decrease rate
of absorption Drugs – alcohol,
cortisone, tetracycline Premature menopause
Osteopenia
Figure 6–19 The Effects of Osteoporosis on Spongy Bone.
Homeostatic Imbalances Osteomalacia
Bones are inadequately mineralized causing softened, weakened bones
Main symptom is pain when weight is put on the affected bone
Caused by insufficient calcium in the diet, or by vitamin D deficiency
Rickets Bones of children are inadequately mineralized causing
softened, weakened bones Bowed legs and deformities of the pelvis, skull, and rib cage
are common Caused by insufficient calcium in the diet, or by vitamin D
deficiency
Developmental Aspects of Bones
The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms
At birth, most long bones are well ossified (except for their epiphyses)
By age 25, nearly all bones are completely ossified In old age, bone resorption predominates A single gene that codes for vitamin D docking
determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life
THE END