The Bones, Cartilage and Joints

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Hyaline Cartilage

Lots of collagen fibers, but you can't see them on a stained slide. Used for firm support but pliable for cushioning. Most abundant type of cartilage in the body; found in the articular cartilage of the joints, tip of the nose, coastal cartilage of the ribs, the rings of the trachea, and the embryonic cells.

Elastic Cartilage

Similar to hyaline's structure, but also has a lot of elastic fibers, allowing it to stretch and rebound to original position. Found in the ear and the epiglottis.

Fibrocartilage

Very thick bands of collagen fibers going in the same direction, forming collagen bundles. Compressible, good at resisting tension and stretching. Strong support. Found in intervertebral discs, pubic symphysis, and the meniscus of the knee joint.

Extracellular Matrix

Contains ground substance and fibers. Mostly made of water.

Proteoglycans

Protein/car complexes that draws water into the matrix, helping give it viscosity, they repel each other, which enhances its cushioning properties.

Perichondrium

membrane of connective tissue containing blood vessels surrounding the outside of cartilage. It keeps everything, mainly the water, contained.

Appositional growth

Growth from the outside; cells in perichondrium secrete chondroblast cells, adding new cartilage to the outside.

Interstitial growth

Growth from within; cells inside the cartilage divide and make new matrix.

Five bone functions

Support body weight, movement, protection, mineral storage, and blood cell formation.

Periosteum

Membrane on outside of the bone. Contains dense irregular connective tissue.

Perforating/Sharpey's fibers

Attach periosteum tightly to the surface of the bone. It is the attachment point for ligaments and tendons.

Endosteum

Membrane of connective tissue, collagen fibers, osteoblasts, osteoclasts which all line the cavities inside the bone.

Long bone

Length is greater than the width. Hollow, light, and just as strong as solid bones

Medullary Cavity

Inside diaphysis, filled with yellow marrow

Spongy Bone

Made of trabeculae, which all attach together. Spaces inside are red marrow (hematopoietic tissue - produce blood)

Epiphyseal line

Between diaphysis and epiphysis, very compact. Only present in adults; remnant of epiphyseal plate.

Epiphyseal plate

Growth plate made of cartilage. Around 18-21 years, plate ossifies, stopping bone growth.

Osteocyte

Mature bone cell that maintains and repairs. Trabaculae line up in patterns where there is a lot of stress, like the hip bone.

Organic components of bone

Cells inside bones (osteocytes, blasts, and clasts).

Osteoid

Part of the organic portion of the matrix of the bone. Composed of ground substance and cartilage fibers, like collagen. Collagen fibers extend up through bone in different directions, like concrete or fiberglass, which allows bones to be stronger and resist breaking.

Inorganic components of bone

Mineral portion from your diet, makes up 2/3 of the matrix. Stores calcium and phosphorus, which are critical to bone health.

Ossification

Converting cartilage to bone.

Osteogenesis

Formation of bone.

Intramembranous ossification

In the skull and clavicle, like the frontal, parietal, occipital, and temporal.. These continue to grow after birth up until 2 years old. This allows the baby's head to flex/expand during childbirth, and helps with expansion/growth of skull.

Endochondral ossification

All long bones (besides clavical), vertebrae, and facial bones. Cartilage replaces bone. Starts in the middle of the diaphysis then continues to the ends. Epiphysis ossifies independently, leaving a cartilage gap.

gH hormone

Regulates post-natal growth

Sex hormones

At puberty produce rapid bone growth. Around age 18-21, the growth plates ossify and stop bone growth.

Growth zone

(epiphyseal side of growth plate) - made of cartilage. Cells are chondroblasts that are divided through mitosis. As they divide, they push cartilage upward, which pushes the epiphysis up as well.

Transformation zone

Cartilage cells die and the matrix starts to calcify, laying down calcium deposits. This is when cartilage starts to transform into bone.

Osteogenic zone

Replace cartilage with bone. Osteoclasts break down osteocartilage bone, and new spongy bone is produced by osteoblasts.

Bone Changes timeline

About 5-7% of bone mass gets recycled every 3-4 years. Compact bone is fully replaced every 10 years.

Bone Remodeling Unit

Travels along the surface of the bone, finds damage, fixes and replaces it. Osteoblasts deposit bone where strength is needed or where there is damage. Bone deposition is stimulated by activity; the elderly move less, so they have weakening bones

Four requirements for bone deposition

Activity, calcium, phosphate, and vitamin D.

Two ways osteoclasts remove bone

1. Secrete lysosomal enzymes, which chew up organic portion of the bone
2. Produce hydrochloric acid, which eats away the mineral part of bone

Two reasons to remodel

Regulation of calcium and mechanical stress

Negative Feedback

Most common homeostatic mechanism that forces a variable to change in a way that opposes and initial change, ex. As temp drops, the thermostat kicks on to bring heat back up.

Positive Feedback

Less common, ex. as temp goes down, the AC is turned on, also seen in labor contractions.

Calcitonin

Hormone from the thyroid gland, which blocks resorption of bone and stimulates calcium deposition to the bone, taking calcium out of the blood stream and into the bone.

PTH

When calcium levels decrease, parathyroid hormones secrete this, stimulating osteoclasts to chew up bone and release calcium into the blood.

Wolff's Law

Bone remodels in response to the demands and stresses placed upon them. Bones will get stronger when stressed, and are removed where not needed so that the bones don't get too heavy.

Non-displaced fracture

bone ends retain normal position

Displaced fracture

bone ends fall out of normal alignment

Complete break

bone is broken all the way through

Closed/Simple break

Bone ends do not puncture skin

Open/Compound break

Bone ends do puncture skin

Transverse break

Fracture goes straight across, perpendicular to long axis of the bone

Linear break

fracture is parallel to long axis of bone

Oblique break

occurs at an angle to the bone

Greenstick fracture

incomplete breakage like a snapping of a twig

Comminuted fracture

bone fragments into 3 or more pieces

Spiral fracture

twisting of the bone (torsion) like when skiing

Compression

Bone gets crushed, common in osteoporosis

Epiphyseal fracture

Weak spot in the growth plates; fracture in children that occurs in the growth plate. 15% of all childhood fractures. Usually heals without lasting effects. When blood flow to epiphyseal plate is disrupted, then retardation of bone growth occurs. Also, if there is severe damage to the plate (shifted, shattered, etc.), it could lead to a deformity in bone growth.

Stress fracture

Overuse injuries, exceeding body's ability to deal with stress. Micro fractures start to add up, exceeding the body's ability to repair. Often seen in the military (marching). This can also lead to muscle fatigue, which is a contributing factor to stress fractures because they are stress absorbers. When the muscles become tired, bones are forced to do more shock absorbing. These fractures are painful, but are non-displaced and can heal easily.

Closed reduction

Dr. fixes fracture/realigns bone by hand

Open reduction

Dr. realigns bone surgically

Osteomalacia and Rickets

They are "soft bones"; cannot mineralize organic bone once made. Produces pain when weight is put on the bones and causes bending (bow legs). Rickets are a bigger problem in kids because they are still growing. At epiphyseal plate, the cartilage can't be mineralized on the bottom, which is a point of weakness on the bone. It is caused by malnutrition, insufficient calcium, phosphorus, and vitamin D, improper absorption, or inadequate sunlight in the diet.

Osteoporosis

Group of diseases where resorption of bone happens faster than deposition, leading to bone loss. Fractures very easily because it is weak. Commonly found in the vertebrae, hips of the elderly (lack of activity) and post-menopausal women

Osteogenesis Imperfecta (OI)

Genetic weakening of the bones. Bones are very easily fractured from little applied force. Other symptoms: early hearing loss, bluish coloration to the whites of the eyes. Victims ay have hundreds of fractures over their lifetime. About 20,000 people in the U.S. have it (rare). Cause - genetic mutation affecting the production of collagen fibers; bones are like glass. They either have less collagen that they should have, or the collagen is not structured properly

Fibrodysplasia Ossificans Progressiva (FOP)

Rare genetic disorder where bones form in places they shouldn't - replaces muscles, tendons, ligaments, and other connective tissues, and soft tissue. Makes the victim immobile and look like a statue. Big toe points inward. Normal life for the first few years, then the symptoms begin before age 10. Manifests itself at site of injuries and bruises (appears in response to tissue damage).

Heterotopic ossification

Formation of bone in the wrong place.

Achondroplasia

Most common form of dwarfism; bone growth disorder. AA is fatal, only is Aa when they have the disease. It affects the rates at which epiphyseal bones grow and don't ossify correctly.

Herniated disc

Very painful and common - intervertebral disc that has broken, which is supposed to provide cushioning between the vertebrae, like a get pad.

Nucleus pulposus

Gelatinous material that absorbs shock in the intervetebral disc (center)

Anulous fibrousis

Collar of fibrocartilage that resists expansion/escaping of the gel (outer).

Differential growth

As long as bones grow, developmental changes occur. Head grows relatively slow so that it will be normal size later on because it is so big at birth. The limbs grow faster than the head.

Fibrous joint

Bone ends are attached by collagen fibers. Movement depends on how long the fibers are.

Suture

Fibrous joint; connection between flat portions of the skull. Collagen fibers anchor to the periosteum of adjacent bones. Synarthroses because the fibers are very short. Protects the brain from compression. Synostosis - bony connection

Syndesmosis

Fibrous joint; bones are connected by larger fibers, a ligament. Variable in length; could be synarthrosis or amphiarthroses.

Gomposis

Fibrous joint; "peg in socket" joint - only example is your teeth (pegs); alveolar socket -ligaments connect tooth to the bone

Cartilaginous joint

Bone ends are united by cartilage.

Symphysis

bone ends covered by hyaline, but in between the hyaline is fibrocartilage; used for shock absorption. Amphiarthroses, ex. Pubic symphysis

Synostosis

hyaline cartilage. Synarthroses. Examples: epiphyseal plates, and cartilage in between ribs and sternum

Synovial joints

Distinct articular joint capsule filled with fluid. Most joints fall into this category. Highly mobile. Richly supplied by nerves, which monitor joint position. Reflexes are present. Also richly supplied with blood, which makes up most of the fluid in the cavity.

Fibrous Capsule

External layer of the articular joint capsule in a synovial joint. Dense irregular tissue connected to the periosteum of the bones and helps to hold bones together.

Synovial Membrane

Inner layer of articular joint capsule in synovial joint; lines the capsule covers any non- cartilage joint surfaces. Produces synovial fluid contained within joint capsules

Weeping Lubrication

Pressure forces articular to compress, squeezing fluid out onto the joint cavity, which helps the joint be lubricated under pressure.

Menisci/Meniscus

Pad of fibrocartilage found inside the joint cavity. Found in the knee and your jaw joints; it is put in places where there is a lot of compression and pressure to stabilize the joints.

Bursa

Little sacs of lubricant that can get inflamed.

Tendo-sheaths

Elongated bursa surrounding a tendon, lubricates the tendon and prevents it from rubbing against bone; filled with synovial fluid.

Bony articulation

Fits bones tightly together, creating a tight connection. The shape has influence of the movement. Large articular surface that connects very snuggly, like the acetabulum of the hip. However, most joints do not rely on this for stability.

Ligaments

Connect bone to bone but it could limit the movement if too tight. Bear excessive strain and stretch and might break. Can only stretch 6% of the resting length. Should not be used in isolation because they are not very effective by themselves.

Muscles and their tendons

Most common form of joint stability; especially critical in the knee, shoulder, foot arch, and ankle.

Elbow joint

Move in one plane - hinge joint.

Knee joint

Largest and most complex bone in the body; most frequently injured

Carpal Tunnel Syndrome

Flexor retinaculum (band of tendon across underside of wrist) becomes inflammed, swollen, and painful

Cleft Palate

Easily fixed in surgery. Developmental issue where the 2 sides of the hard palate don't connect. In a baby breast feeding, the milk can aspirate through the nose into the lung, which can cause pneumonia, Surgery is done in the first year of life; before the surgery you can use a prosthetic to prevent milk inhalation.

Shoulder dislocation

forward and downward separation between the humorous and Glenoid surface. Can be put back in place, but the ligaments are permanently stretched, leading to future injuries

Shoulder separation

separation between acromion process of scapula and clavicle; 3 types of severity.

Sprain

stretching and tearing of the ligaments in a joints; most common in the knee, ankle, and lower back. Mild will heal on its own with no permanent damage, though they are slow to heal because of poor blood supply. A complete tear of ligaments requires surgical procedure. Lots of inflammation can degenerate tissue.

Cartilage injury

meniscus is not well supplied by blood. If you tear meniscus it will most likely stay torn. Repair injury with sutures or remove the flappy part. Should not impair mobility, but will impede stability.

Dislocation

bones in the joint come out of alignment; associated with falls or impacts. Some can be popped back in alignment, mild to severe forms. Most common are in the jaw bone, shoulders, fingers, and thumbs.

Bursitis

inflammation of a bursa. Due to impact or friction. Symptoms : pain, swelling. Treatments: anti-inflammatory drugs, rest, icing will all deal with the pain. To deal with the cause (friction), physical therapy can correct it.

Tenosynovitis

inflammation of the tendon sheath due to rubbing or friction. Treatments: anti-inflammatory drugs, rest, icing will all deal with the pain. To deal with the cause (friction), physical therapy can correct it.

Tendonitis

inflammation of a tendon. Common with athletes. Treatments: anti-inflammatory drugs, rest, icing will all deal with the pain. To deal with the cause (friction), physical therapy can correct it.

Arthritis

inflammation/degeneration of joints. There are over 100 different types of this. Extremely common; 1 out of 7 people in the U.S. have this.

Osteoarthritis

most common form, chronic, degenerative, and progressively gets worse. Most common in the elderly. 85% of the U.S. will develop this. The breakdown of cartilage is faster than the repair process, so we lose articular cartilage (covers bone ends). Bones begin to get exposed, causing pain and immobility because the bones rub against each other and erode.

osteophytes

spurs that cause increased pain

crepitus

crunching noise caused by osteoarthritis

Rheumatoid Arthritis

inflamed disease of joints. Appears around age 40-50 or older. 3x more common in women. Tender, stiff, swollen joints. Affects both sides of body at the same time. Flare ups and remissions. Autoimmune. Infection may trigger this disease. Inflammation in the synovial membrane causes excess fluid to gather and swells the joints. Synovial membrane adheres to and erodes the cartilage and the bone. Scare tissue forms, binding the bone together. Creates a bony connection and fuses the bone.

Ankylosis

ossification of a joint no cure but can be controlled by immunosuppressant and can help treat the pain.

Gouty Arthritis (gout)

caused by uric acid. If you produce too much of it, it will accumulate in the blood. Gets deposited in the joints as urate crystals. More common in males because they have more uric acid in the blood. Can lead to fusion of the joint.

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