Key concepts Test 2 Flashcards
Making of skeletal structures
Neural crest/mesoderm undergoes mesenchymal condensation, starts from centre and grows out (intramembranous ossification -> skull/mandible/clavicle) for bone or into cartilage. The cartilage template leads to persistent cartilage of joints or is removed and turned into bone
What is intramembranous ossification and where does it occur?
Intramembranous ossification is a type of bone development in which bone tissue is created directly from mesenchymal tissue without a cartilage template. This process primarily occurs in the flat bones of the skull, mandible, and clavicle. It is crucial for the formation of the cranial bones of the skull, the clavicles, and facial bones.
< 8 weeks in development
Key steps of intramembranous ossification
Mesenchymal stem cells in the connective tissue aggregate and differentiate into osteoblasts.
Osteoblasts secrete osteoid, the organic bone matrix made of collagen and other proteins.
The osteoid matrix calcifies (hardens) when the deposited calcium salts crystallize. Bony spicules are formed
Calcified areas form trabeculae, the spongy bone which eventually fuses to form the compact bone. Spicules join trapping BV
The surface layers of undifferentiated mesenchymal cells at the periphery of the bone develop into the periosteum, which contains the bone’s blood vessels and nerves.
Endochondral ossification
Endochondral ossification is a process by which bone tissue is created from pre-existing cartilage models. This is the predominant method for the formation of the bones in the body, particularly the long bones like femur, tibia, and humerus.
> 8 weeks in development
Endochondral ossification process
- Chondrocytes mature, forming future bone, small struts calcify and enlarged chondrocytes die and leave cavities within the cartilage
- Blood vessels grow around the edge or the cartilage. Perichondrium convert to osteoblasts.
- BVs penetrate cartilage and fibroblasts migrate from BVs and differentiate into osteoblasts producing spongy bone at the centre.
- Remodelling occurs, bone shaft becomes thicker, cartilage near epiphysis is replaced by shafts of bone
- Capillaries and osteoblasts migrate into the epiphysis creating secondary ossification centres. Spherical growth
- Epiphyses filled with spongy bone, articular cartilage remains exposed to joint cavity, is reduced to thin superficial layer. Epiphyseal cartilage separates epiphysis from diaphysis.
Process of chondrogenesis
Skeletogenic mesenchymal cell develops into a condensed prechondrocyte by TGBFb and Wnt
Condensed prechondrocyte develops into an early chondrocyte by Sox9 and Sox5/6 which is from Wnt/b-catenin and Bmp respectively
How do long bones grow in length?
Long bones grow in length by the process of endochondral ossification at the epiphyseal plates. New cartilage is continuously formed on the epiphyseal side of the plate while the diaphyseal side of the plate ossifies, adding length to the bone.
Structural levels of collagen type I: collagen synthesis
Synthesis of pro-alpha chain containing Gly-X-Y repeats.
Self-assembly of three pro-alpha chains.
Procollagen triple helix formation followed by secretion into the ECM.
Cleavage of propeptide
Self-assembly into FIBRIL (see banding pattern in the EM)
Aggregation of collagen fibrils to form a collagen FIBRE
Scurvy
Vit C deficiency
Essential for production of lysyl hydroxylase, the enzyme that catalyses the hydroxylation of proline and lysine. Absence of Vit C - collagen doesn’t formed its coiled structure. Most prominent in areas with high collagen turnover (periodontal ligament)
Symptoms include rotten teeth, bleeding from all mucous membranes and bowed legs
Osteogenesis Imperfecta
Genetic disease - mutation int two genes that encode collagen type I.
Symptoms include brittle bones, weak tendons (tendinosis), abnormal skin, teeth and healing
Stickler syndrome
Type I - autosomal dominant inherited mutations in the COL2A1 gene
Type II defective formation of collagen type II
Flattened facial appearance, nearsightedness, varying hearing loss, osteoarthritis, joint pain
Aging and osteoporosis
Lose mineral and bones become less dense. Bone resorption outpaces bone formation resulting in decreased bone mass. Density and quality of bone is reduced.
Increased osteoclast activity and reduced osteoblast activity. Loss of calcium from the body and hormonal changes post menopause
Articular cartilage resist load by
Experiences compression with low amounts of tension & shear at articular surface.
Articular cartilage is a specialised form of hyaline cartilage, found at end of bones within synovial joints
Transition from a gel-like pliable tissue into the hard, ossified bone, with an intermediate of calcified cartilage acting as a protective cushion
Osteoarthritis
Affects all tissues of the joint. Presents as degeneration of articular cartilage. Low grade inflammation which is thought to contribute to ECM breakdown and viscous cycle begins.
Stiffness, joint swelling, reduced mobility. Joint replacement surgery or exercise needed
How OA progresses
Fibrillations - fraying of collagen
Collagen beneath SZ start to breakdown -> Free PG bring in H2O by bringing in more cations, increasing art cart height
Fissures develop - chondrocytes divide for futile repair and increase matrix prodution
Inflammation occurs - increased collagenase 1 and aggreanase which breaks down matrix
Bone is stiff, has pain and effusion with swelling
Functions of axial skeleton
create a framework that supports and protects organs in the dorsal and ventral body cavities
- house special sense organs for taste, smell, hearing, balance and sight.
- provide an extensive surface area for the attachment of muscles
- permit limited movement
- contain red marrow for blood cell formation
Excessive curvature conditions
Scoliosis = lateral
Kyphosis = sagittal, primarily thoracic
Lordosis = sagittal, primarily lumbar
Motor pathways in the CNS and PNS
Upper motor neuron - cranial nerve nuclei / somatic motor nuclei of brainstem-> skeletal muscle of face, hand and neck
Lower motor nuclei - somatic motor nuclei of spinal cord -> skeletal muscle of lower body
Medial lemniscus pathway
Axons of first order neurons enter spinal cord through dorsal root and ascend the fasciculus cuneatus or grailus
Second order neurons that synapse in the thalamus. Axons decussate here (nucleus cuneatus and gracilus)
It carries axons and synapses in the ventral posterolateral nucleus (VPN) of the thalamus to third order neurons
Brachial plexus
C5-T1
Innervates the upper limb
The root emerging from C5-T1 unite to form the superior, middle and inferior trunks and they divide into posterior and anterior division
Erbs palsy
C5-C6 superior trunk
Musculocutaneous and axillary nerve
Loss of function of shoulder and upper arm - usually permanent -> muscle wasting of upper arm
Klumpke’s Palsy
C8-T1 inferior trunk
Loss of function of the lower arm, wrist and fingers
Functions of skin
Barrier - water loss and entry. Burned can result in dehydration due to loss of barrier
Microorganisms
- physical barrier
- oil of skin is antibacterial (Sebum)
- sweat (slightly acidic - inhibits bacterial growth)
Ultra-violet radiation - melanin
Excretory organ - sweat
Synthesis of Vit D - by action of UV, Ca2+
Sense organ - touch, pressure etc
Papillary layer
Consists of loose connective tissue, blood vessels, cells and sensory receptors.
Allows movement of immune cells to detect bacteria
Dermal papillae - blood vessels nourish all hair follicles, bring nutrients and oxygen to the lower epidermal cell layers
Reticular layer of dermis
Dense, irregular collagen I that surrounds hair follicles, blood vessels and glands.
Contains majority of elastin in dermis
Areas of connective tissue in body
Loose CT
Areolar - skin, intestine
Adipose - skin, intestines
Reticular - liver
Dense CT
Regular - tendon
Irregular - skin, intestine
Cartilage
Hyaline - joints
Fibrocartilage - intervetebral disc
Elastic - ear
Trabecular bone
Found on the inside of mature bone
Especially at the ends of long bones where compressive forces are greatest
Moulded by mechanical forces & stresses
Contains red and/or yellow bone marrow
Compact bone
Found on the outside of mature bones
Solid, hard surface layer
Thickest around the shaft of long bones where tensile & torsional stresses are greatest
Long bones
Length > breadth
Tubular in shape – gives the strongest & lightest combination
Shaft or body (diaphysis, which is usually hollow)
Two expanded ends for articulation (epiphyses)
Leavers
Short bones
Cuboid in shape
Thin layer of compact bone supported by a network of trabecular bone
Found in the wrist & foot
Resist compression
Irregular bones
Usually have extensions of bone creating a variety of irregular shapes
Examples - include facial bones & vertebrae
Attachment - more SA for muscles
Pneumatized bones
Bones with air-filled cavities
Present in the skull
Serves to lighten the skull & add resonance to the voice
Examples – maxilla, ethmoid
Dont have bone marrow
Flat (squamous bones)
Two flat laminae of compact bone with spongy bone (& marrow) in between
Usually protective or reinforcing
Forms walls of cavities, eg skullcap (calvarial) bones, sternum, scapula
Sutural bones
Small flat ‘biscuit’ like joining bones
Typically fuse with the larger flat bones of the skull and disappear in adults
Sesamoid bones
Round or oval nodules
Resemble sesame seeds, hence the name
Develop in certain tendons (postnatal), where the tendon is exposed to pressure
Protect tendon from excessive wear
Can help change the line of pull of muscles, giving them a mechanical advantage
Example – patella (kneecap) – the largest sesamoid bone
Looks like sesame seeds - protects tendons
