Week 3 Flashcards
What does the skeletal system consist of?
The skeletal system consists of bones, cartilage, joints and ligaments. Its divided into the axial and appendiceal skeleton.
The axial skeleton consists of vertebrae, ribs, pelvic bones and ribs.
The appendiceal skeleton consists of the long bones of the upper and lower limbs, and also the small tubular bones of the hands and feet.
What are 2 the bone types?
Hay flat bones, eg ribs and pelvic bones, and long bones, eg humerus and femur.
Long bones are divided into the epiphyses, metaphyses and diaphysis. After puberty, the epiphyses becomes fused with the metaphyses.
What does bone consist of?
Bone consists of mineralised bone matrix and bone cells. These develop and maintain adequate structure through modeling and remodeling.
Bone is mostly matrix, which is predominantly Type 1 collagen together with other non-collagenous proteins. This is fully mineralised in adult bone.
Unmineralised bone matrix is called osteoid. The bone cells are osteoblasts, osteocytes and osteoclasts.
What is the function of bones?
The function of bones is:
to provide structural support eg axial skeleton
to protect vital internal organs eg skull, ribs
to enable locomotion eg long bones of upper and lower limbs
to store calcium, and participate in calcium homeostasis
What are the bone types at microanatomic levels?
At a microanatomic level, hay cortical and cancellous bone. Bone also exist as 2 forms, woven bone and lamellar bone.
Woven bone is immature and rapidly produced, eg in the neonate or in the early stages of fracture repair. The collagen fibres are randomly arranged which can be seen under polarized light.
This is then remodelled into stronger lamellar bone, composed of sheets or lamellae of parallel collagen which is visualized under polarized light. Almost all bones in healthy adults are lamellar.
Describe the bone diagram shown, focusing on cortical bone
Cortical bone made of osteons lies on the outer portion of long bones and vertebrae.
W/in the lacunae hay osteocytes. These are differentiated osteoblasts. Tienen a cell body and cell processes that connect with other osteocytes. The cell processes are in canaliculi.
Cortical bone is covered by fibrous connective tissue called periosteum.
The medullary cavity (centre) of bones is cancellous bone, with intervening marrow.
What is cortical bone composed of?
Cortical bone is composed of osteons. These are long parallel columns.
They’re made up of concentric rings of bone, lamellae, around a central channel containing blood and lymphatic vessels. These channels are the Haversian canals
Describe cancellous bone
Cancellous bone is a network of bony plates or struts called trabeculae. These connect with each other and to the endosteum of cortical bone.
In adults, the spaces between the trabeculae are filled with either haemopoetic bone marrow or adipose tissue.
What cells are found in bones?
The cells found in bone are:
Osteoblasts
Osteocytes
Osteoclasts
Describe osteoblasts and osteocytes
Osteoblasts synthesise bone matrix. They lie on the surface of bone. When actively synthesizing bone matrix they appear as cuboidal cells w small nuclei. When inactive, they look like flat bone-lining cells.
Osteocytes are buried w/in cortical and cancellous bone. They’re terminally differentiated osteoblasts. They lie w/in lacunae and their cell processes connect with other osteocytes via cell processes that are in canaliculi.
The function of osteocytes is mechanosensation
Describe osteoclasts
Osteoclasts resorb bone. They are large cells, often multinucleate.
Found on bone surface, often in eroded surfaces or depressions that they have created.
Describe cartiliage
Cartilage consists of chondrocytes set in proteoglycan-rich matrix. This is how its solid, but flexible. Chondrocytes synthesize and secrete cartiliage’s extra-cellular matrix material.
Chondroblasts form areas of cartilage by the proliferation of the chondroblasts which lay down the cartilage matrix. Once the cartilage is laid down the chondroblasts become less active and are chondrocytes.
Cartilage forms a low friction cover for bones where joints are formed. Joints have fibrous tissue around them which hold the bones together and make a space/cavity around the whole joint.
What are the types of cartiliage?
Hyaline cartilage - Type II collagen. Created as a temporary skeleton for bone formation. Most common type, found in the nasal septum, larynx and tracheal rings, most articular surfaces of joints.
Fibrocartilage - Type I & Type II collagen. Is found in intervertebral discs and tendon attachment to bones.
Elastic cartilage - Type II collagen and elastic fibers. Found in the ear, epiglottis, parts of the laryngeal cartilage rings and larynx.
Briefly outline endochondral ossification
Endochondral ossification: mesenchymal cells differentiate into chondrocytes that build a hyaline cartilage model, which then turns into woven bone. This woven bone is remodelled into lamellar bone.
In endochondral ossification, cartilage growth follows appositional and interstitial growth. Explain these terms
In appositional growth, mesenchymal cells differentiate into chondrocytes which secrete new matrix along surfaces to widen the cartilage.
In interstitial growth, chondrocytes secrete new matrix within the cartilage, lengthening it.
Explain osteoporosis.
Osteoporosis: total amount of bone is reduced, but the bone is fully and normally mineralised.This results in poorly connected thinner trabeculae.
This diminishes structural bone integrity, so the bone fractures on minimal trauma.
Describe and explain osteomalacia.
In osteomalacia, the total amount of bone is preserved, but the amount of mineralized bone is reduced, and hay increased amount of osteoid or unmineralised bone matrix.
