Bones 1 & 2 Flashcards
What type of tissue is cartilage and what is its function
Specialised connective tissue with a support function (e.g. shock absorbing or tough/flexible)
What type of cells are in cartilage
Chondrocytes
What makes up the matrix of cartilage (general)
Type II collagen
Elastin
Proteoglycans (GAGs)
Others depending on type
Chondroblast
Immature chondrocytes
Vaguely describe the development of chondrocytes
Derived from embryonic mesenchyme (spindle) that turn into rounder clusters of chondroblasts surrounded by a layer of perichondrium (mesenchyme derived fibroblastic cells & collagen)
Interstitial Growth
Cell division resulting in the growth of a tissue type
Appositional Growth
Growth by forming new layers on the surface of pre-existing layers
Does cartilage grow by interstitial or appositional growth and how
Both
Interstitial - Limited division of chondroblasts in ECM
Appositional - New chondroblasts from perichondrium
Lacuna of cartilage
The cavities in the matrix that chondrocytes are contained in
What percentage of cartilage ECM is water
70%
**DONT REMEMBER
Composition of proteoglycans
GAGs attached to a core protein
Role of proteoglycan aggreggates
Providing compressive strength as a flexible cushioned surface in collagen
Types of Cartilage
Hyaline Cartilage
Elastic Cartilage
Fibrocartilage
Composition of Hyaline Cartilage
non ground substance
Type II collagen only
Broad location of hyaline cartilage
Smooth glistening (glassy) articular surfaces - Articular ends of long bones, Ventral rib cartilage, tracheal rings
Composition of Elastic Cartilage
non-ground substance
Type II Collagen + Elastin
Broad location of Elastic Cartilage
non-ground substance
End of nose, Ears, Larynx
Composition of Fibrocartilage
Type II & Type I collagen -strong
Broad location of Fibrocartilage
Intervertebral disks, Insertions of ligaments & tendons, Joint capsules, Sternoclavicular joint
What type of cartilage is the epiglottis
Elastic Cartilage
Hyaline cartilage at joints
Resists compression due to elasticity & stiffness of proteoglycans
Tensile strength due to collagen & hydrogel ground substance
Describe vascularity of cartilage and consequence
Most is avascular, limiting repair & regeneration when damaged
Presence of perichondrium at articular surfaces of joints and why
No perichondrium so no source of new chondroblasts
This would introduce friction otherwise
Reversibility of cartilage atrophy
Reversible but time consuming
What type of tissue is bone
Specialised connective tissue
What ions does bone act as a reservoir for
Calcium & Phosphate
Composition of bone
Cell & extracellular matrix
Where does haematopoiesis occur
Bone marrow
Energy need of bone (vaguely) and why
High
It is constantly adapting, remodelling and also performing roles like haematopoiesis
What is the inside of bone like
Spongy/Strandy
Osteoid
Unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue
Layers of Bone
Compact Bone - Dense outer shell
Cancellous/Trabeculae Bone - Inner spongy part
Epiphysis
Expanded end of the long bones in animals
Diaphysis
Shaft or central part of a long bone
Periosteum
Membranous tissue that covers the surfaces of bones
Describe the structure of a bone
Blood vessels within the compact bone
Concentric lamellae with osteocytes in lacunae connected via canaliculi all within a single trabecula
Role of trabecular bone
Reduces weight
Provides space for marrow
Struts are arranged to provide maximum stress resistance
Where might trabecular bone be found
Wrists
Vertebrae
Femoral Neck
Osteoporosis
Thinning of cortical/compact and trabecular bone; thinned trabeculae prone to fracture
Which sex is more affected by osteoporosis
Females
**Due to effect of oestrogen on bone density
Parts of bone matrix
Organic/Osteoid - Strong
Inorganic - Hard
Organic bone matrix
Produced by osteoblasts
Collagen I
Tensile & Compressive strength
Role of non collagenous proteins in organic bone matrix
Mediating mineral deposition
Inorganic bone batrix
Calcium Phosphate
Deposited in organic matrix
66% of dry weight of bone
Provides hardness of bone
Osteogenesis Imperfecta
Brittle Bone Disease
Congential disease of defective collagen chain in bone causing a fragile skeleton (think of a poor organic bone matrix)
Development of Bone cells
Derived from mesenchymal stem cells that differentiate into osteoprogenitor cells or chondroblasts
Osteoprogenitors differentiate into osteoblasts which lay down the organic bone matrix, mediates mineralisation of osteoid and becomes an osteocyte when syrrounded by mineralised bone
Role of osteocytes
Maintaining matrix of bone
What does osteoid secrete
Collagen & Matrix vesicles which contain enzymes/proteins to control Ca and PO4 availability so that mineral is precipitated
Immature osteoid
Woven bone with haphazard fibre arrangement that is mechanically weak (foetal development/fracture repair)
Mature osteoid
Lamellar bone; remodelled woven bone with regular parallel collagen - strong
Adult bone
Arranged as osteons aligned with direction of force
Arrangement of Bones and Osteocytes
Osteocytes in concentric rings surrounding a blood vessel
Lamella
Canaliculi
Microscopic canals between the lacunae of ossified bone that radiate from osteocytes
Role of osteocytes
Maintaining matrix
Allowing nutrient diffusion through canaliculi
Response to tiny currents generated during bone deformity
Osteoclasts
Cells that exist purely to destroy bone (only cell with this role in the body)
Bone resorbing cell that takes up calcium when needed e.g. for heart
Also for clearing bone when needed for growth or remodelling
Phagocytic in nature
Nucleation of osteoclasts
Multinucleate mobile cell
Howships Lacuna
Pits left behind after work of osteoclasts
How do osteoclasts work
Sucking onto the bone and:
Organic: They secrete proteinases that degrade the organic matrix & collagen I
Inorganic: Pumping out H+ and essentially melting bone
How to stimulate/reduce osteoclasts activity
Stimulate: Parathyroid hormone from parathyroid gland
Reduce: Calcitonin secretion from thyroid
Bone Remodelling
Constant
Enables response
What direction is new trabecula made and how are osteoclasts involved
In bone remodelling, new trabeculae are made in the direction of the force that the bone endures
Osteoclasts take away bone from places where there is less force in order to maintain a healthy weight
**SEEN WHEN TAKING UP A NEW SPORT
Osteopetrosis
Marble/stone-bone
Rare group of inherited conditions causing defective bone remodelling due to the inability of osteoclasts to excrete sufficient H+
Brittle and easily fractured
Clinical effects of osteopetrosis
Fractures, spinal nerve compression, recurrent infection due to reduced bone marrow cavity
Hepatosplenomagaly due to haematopoiesis outside bone
Treatment of osteopetrosis
Bone marrow transplant to provide heathy osteoclast precursors
Relationship between osteoblasts and osteoclasts
ParaThyroid Hormone (PTH) doesn’t actually directly interact with osteoclasts; instead PTH stimulates osteoblasts which have specialised receptors
Osteoblasts activate a ligand on their membrane which docks onto a receptor on osteoclast membranes, allowing them to do their shit
Osteoprotegrin
Protein which prevents resorption by binding to the ligand on osteoblast surface which normally activates osteoclasts (RANKL)
What ratio determines bone resorption
RANKL:Osteoprotegrin
Factors affecting likelihood of contracting osteoporosis
Disuse/Lack of activity Genetic Factors Nutrition Hormones (e.g. menopause) Aging
What is a condition which sees higher osteoclast activity
Osteoporosis
Types of bone development in the embryo
Intramembranous
Endochondral
**BOTH INVOLVE REPLACING A CONNECTIVE TISSUE TEMPLATE
Intramembranous Bone Embryological Development
Sheets of mesenchymal stem cells differentiate into osteoblasts in centres of ossification which merge to form trabecular bone that is remodelled
Remaining mesenchyme makes bone marrow and periosteum
Where can bone made intramembranously be found
Flat bones of skull, maxilla & mandible
Endochondral Bone Embryological Development
Bone is formed onto a temporary cartilage model
Blood supply to shaft of bone causes osteoblast differentiation - primary centre of ossification
Following this the ends of the bone also diferenitate, allowing a long bone to eventually form
Where can bone made endochondrally be found
Long Bones
Remnant left behind by endochondral ossification
Epiphyseal cartilage
Chondrocyte into Bone conversion in endochondral ossification
proliferating chondrocytes grow until eventually they get close enough to the centre and big enough where they die and turn into bone cells
Proliferating chondrocytes eventually stop proliferating, stopping growth
What direction do the femur growth plates towards
Away from the knee (growth plates nearest knee are fastest growing)
**From the knee I flee
What direction do the humerus growth plates towards
Towards the elbow (growth plate towards elbow, growth plates of proximal humerus and distal radius are fastest growing)
**To the elbows I grow
Ossification times of carpal bones
Predictable sequence used for predicting bone age
Capitate & Hamate Triquetral Lunate Scaphoid & Trapezium & Trapeziod Pisiform
Cap hurts three lovers - Scorpios, Trainers and Trapeze performers
How do bones grow width-wise
Bone is laid out on the outside while it is removed on the inside
e.g. on skull where space is made for the brain as it grows
Achondroplasia
Dwarfism
Congenital bone disease causes by mutation on fibroblast growth factor receptor 3 (activation mutation)
This activation inhibits chondrocute proliferation, affecting growth plates
Long bone growth is stunted
Back has an inword curve, legs are bowed and extremities stunted (especially proximal)
Substances that influence bone contribution to calcium homeostasis
PTH
Calcitonin
Vitamin D
Role of PTH in Ca Homeostasis
Increases blood Ca while regulating Phosphate
Releases calcium from bone by indirectly stimulating osteoclasts
PTH also stimulates Vit D which enhances Ca uptake in gut
Also increases Ca & PO4 reabsorption from bone (more Oc, less Ob)
Conserving Ca in kidney while reducing reabsorption of PO4
Role of Calcitonin in Ca Homeostasis
Decreasing blood Ca
- By inhibiting osteoclast activity
- By reducing Ca reabsorption in kidney
Metabolic Bone Disease
Result from imbalance between bone formation and resorption
Four Main Metabolic Bone Diseases
Osteoporosis
Rickets and Osteomalacia (lack of Vit D, inadequate bone mineralisation)
Paget’s disease (overactive osteoclasts, overactive osteoblasts respond making heavy, weak and metabolically demanding bone)
Hyperparathyroidism (PTH overstimulation of osteoclasts)
**DONT MEMORISE THE SPECIFICS THIS IS EXTRA INFORMATION
Bone Fracture Repair until hyaline cartilage
- Periosteum is breached, haematoma and blood clot forms
- Replaced by vascular collagenous tissue (granulation tissue) which becomes increasingly fibrous: fibrous granulation tissue
- Replaced by hyaline cartilage: Firm, flexible provisional callus
Bone Fracture Repair after hyaline cartilage
- Osteoprogenitor cells from peri & endosteum differentiate onto osteoblasts & lay down new woven bone: Bony callus
- Site completely bridge by bone: Bony Union
- Slowly remodelled to form oriented lamellar bone
