Skeletal System

Monday, October 10, 2022

Functions of skeletal system:

• Shape & form (support)

• Movement (muscles use bones as levers)

• Protections by encasing organs fully or partially

• Mineral storage of calcium and phosphate, lots of minerals

• Blood cell formation/hematopoiesis occurs in some bones

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Classification of bones:

Axial skeleton: straight line of the skeleton, vertebral column

• Skull, Vertebrae, Ribs 

Appendicular skeleton: appendages

• Limbs, Shoulders, Hips

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Unique shape of each bone fulfills a particular need/function

Bones are also classified by shape

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Long bones:

• Longer than they are wide
• Has a shaft and two ends
• Bones = clavicle/collarbone, limbs, fingers (except patella, wrist, and ankle)

Short bones:

• Cube shaped
• Sesamoid: bone formed in tendon (patella/kneecap, pisiform)
• Bones = wrist (carpels) and ankles (tarsals)

Flat bones:

• Thin, flattened
• May be curved
• Bones = sternum, scapula, ribs and most skull bone

Irregular bones:

• Complicated shape

• Bones = vertebrae, sacrum, mandible, hyoid, coccyx, most facial bones, and hip bones(ilium, ischium, pubis)

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Skeletal cartilages:

• Human skeleton is initially made of cartilage

• Most cartilage is replaced by bone

• Cartilage remains in areas where flexibility is needed

• Cartilage

  • Avascular (no blood cells)
  • No nerves

• Chondrocytes: cells that make up cartilage

• Typical growth ends during adolescence (skeleton stops growing)

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Types of cartilage:

Hyaline: most common;  in the skeleton, these cartilages include …

• Articular(where ever the 2 bones meet)
• Costal (rib cage)
• Respiratory (voice box)
• Nasal (front of the nose)

Elastic: found only in external ear and in epiglottis; most flexible

Fibrocartilage: occur at sites of high pressure (knee, between vertebrae, etc)

Tuesday, October 11, 2022

Joints:

Any site where 2+ bones meet

Main functions:

• Help us move

• Hold skeleton together

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Fibrous joints:

• Sutures: between skull bones; interlocking joints; keeps bone together; stops movement

• Syndesmosis: bones connected by ligaments; mainly for supporting movement

• Gomphosis: peg in socket; only found in the tooth and gum; through the root of the tooth

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Cartilaginous joints:

• Synchondrosis: chondro = cartilage; bar/plate of hyaline cartilage; unites bones
• Symphysis: surface of bones covered with fibrocartilage

Synovial joints: 

• Plane
  • Flat articular surfaces; slides on top of one another(front, back, side to side); allow slipping or gliding movements; (notebook on table; planes in math)
  • Ex: vertebrae, thumb carpals
• Hinge
  • Opens and closes, uniaxial joints (permits flexion and extension)
  • Ex: elbow, phalanges
• Pivot
  • One bone locked in place and another bone can move around that bone; rounded bone end protrudes into sleeve of bone or ligament
  • Ex: atlas and axis(head rotation), radius and ulna(forearm rotation)
• Condyloid
  • Oval surface fits into depression; convex and concave; biaxial(permit angular motions); like swings- front to back, side to side, swing
  • Ex:  radiocarpal; metacarpophalangeal; bottom finger joint to the hand
• Saddle
  • Each articular surface has a concave and convex surface; biaxial
  • Ex: thumb only
• Ball-and-socket
  • Being able to make full circles; spherical head articulates with a cuplike socket; multiaxial(permit most freely moving)
  • Ex: shoulder, hip

Thursday, October 13, 2022

Bone structure:

Bones contain: nervous tissue, cartilage, fibrous connective tissue, muscle, epithelial tissue

• Bones contain various different tissue: this makes them organs

Bone is made of:

• Compact bone: dense outer layer

• Spongy bone: internal layer; pattern in which spongy bone is layered is trabeculae: small honeycomb of needle-like bone

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Long bone

• Diaphysis (shaft)
  • Long axis of bone; thick collar of compact bone; surrounds marrow cavity
  • In adults: yellow bone marrow cavity = contains fat  (yellow marrow)
• Epiphysis (bone end)
  • Exterior = compact bone; Interior = spongy bone
  • Joint surface covered with a articular cartilage
  • In adults: epiphyseal line = between diaphysis and epiphysis; remnant of growth plate

Short, flat, and irregular bones

• No marrow cavity, no shaft, no epiphysis
• Ribs, skull, etc
• Contain red bone marrow between trabeculae
• Flat bones: spongy bone = diploe (stiff sandwich of compact - spongy - compact)

Tuesday, October 18, 2022

Long bone:

Periosteum: 

• Externa; surface of entire bone (except joint surfaces) rich with nerve fibers, lymph vessel, and blood vessels
  • Outer layer = dense irregular connective tissue
  • Inner layer = osteoblasts and osteoclasts
• Anchoring point for tendons and ligaments
• Sharpey’s fibers: secures periosteum to the underlying bone by perforating bone

Short, flat, and irregular: thin plates covering compact bone

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Endosteum: 

• Delicate connective tissue that covers trabeculae of spongy bone
• Lines canals of compact bone
• Contains osteoblasts and osteoclasts

Short, flat, and irregular: covering spongy bone

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Bone cells:

• Osteocytes: maintains bone tissue; are the bone tissue

• Osteoblasts: forms bone matrix; start of the bone

• Osteogenic cells: stem cells; can change into any other type of bone cell

• Osteoclasts: resorbs bones; breakdown the bone to allow new cells to form there

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Hematopoiesis: 

• Production of blood cells
• Long bones: occurs in the head of femur and humerus; closest to the point of attachment so red blood cells are created closer to the trunk where it is needed more
• Flat & irregular: red marrow of diploe is much more active; occurs in sternum, hip, and more
• Yellow marrow can revert to red marrow if red blood cell production is needed

Wednesday, October 19, 2022

Osteons (haversian system): Structural unit of compact bone; group of hollow tubes placed one inside the other; tubes inside of tubes inside of tubes next to tubes inside of tubes 

• Elongated cylinder: lamella (compact bone - lamellar bone)

• Oriented parallel to long axis of the bone

• Tiny weight bearing pillars

• Central canal (haversian canal): runs through core of each osteon; contains nerves and blood vessels

• Volkmann’s canal: right angle to bone axis; connect blood/nerve of the periosteum to central canals and marrow cavity

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Osteocytes: 

• Spider shaped mature bone cells

• Filling the whole between the plates

• Occupy lacunae at lamellar junctions

• Canaliculi: hair like canals; connect lacunar to each other and central canal

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Trabeculae:

• Align along the lines of stress; help bone resist stress

• No osteons are present

• Contains irregularly arranged lamellae

• Osteocytes interconnected by canaliculi

• Nutrients reach spongy bone by diffusion through capillaries in endosteum

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Ossification /osteogenesis: osteo = bones; genesis = formation

• Babies have zero bone when in the womb, it's all cartilage
• Conversion of cartilage to bone; bones start at cartilage
• Bone growth until early adulthood
• Bones altar in thickness, remodeling, and repair

Ossification process:

1. Osteoblasts appear in cartilage

2. Osteoblasts secrete osteoid and osteocytes get trapped in bone

3. Blood vessels weaving into the bone and the periosteum forms

4. Lamellar bone is developed/formed and osteocytes, osteoblasts, and osteoclasts are all present; keeps happening until your bones are fully formed

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Bone growth: 

• Infancy /youth: long bones get longer; all bones grow in thickness; 
• Adolescence: most bones stop growing; females stop growing at around 18; males stop growing at around 21
• Adult: ossification mostly remodeling

Monday, October 24, 2022

Bone growth - hormones:

• Growth hormone: released by pituitary gland; makes you bones grown in length and thickness

• Thyroid hormone: regulates activity of the growth hormone; ensure proper proportions for growth

• Adolescence/puberty: sex hormones promote growth spurt; later, hormones end longitudinal bone growth

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Bone remodeling:

• Regulated by:

  • Blood calcium levels (Ca2+) negative feedback
  • Hormones: PTH (parathyroid hormone) & Calcitonin
  • Response to forces (mechanical or gravitational) on skeleton

• Purpose: repair skeleton damage, prevent accumulation of old bone, obtainstore calcium & phosphorus

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• Occurs when: bone is injured, bone strength needed

• For optimal bone deposit, you need: a lot of things

  • Proteins, vitamin C, D, A, minerals(calcium, phosphorus), blood, nerves, etc.

Wolff’s law:

• Bone grows or remodels in response to the demands placed on it
• For example…
  • Featureless bones of fetus
  • Atrophied bones of bedridden people
  • Thickened bones of weight lifters

Friday, October 28, 2022

Scoliosis:

• “Twisted” disease
• Abnormal lateral curvature of the thoracic vertebrae
• Idiopathic (without a known cause)
• Treatment: physical therapy to strengthen muscles; rod down vertebrae

Lordosis:

• Abnormal curvature of lumbar vertebrae
• “Sway back”
• Idiopathic 
• Treatment: usually fixes itself (in children); may require physical therapy

Kyphosis:

• Exaggerated posterior curvature of thoracic vertebrae

• “Hunchback”

• Treatment: medication(for pain); surgery

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Imbalance:

Osteomalacia: soft bone disease; calcium is not deposited; lack of vitamin D; 

• Rickets: osteomalacia in kids; mostly in children; bowed legs and other bone deformities

Osteoporosis: bone resorption outpaces bone deposit; decreases bone mass; calcium deficiency

• Risk factors: decline in estrogen levels, petite body form, poor diet/exercise, smoking, age

Ostealgia: bone pain; caused by arthritis or fracture

Osteogenic sarcoma: bone cancer; affects osteoblasts; occurs most often in the bones of teenagers during growth spurt; treatment: chemotherapy

Osteonecrosis: bone death; loss of blood supply to a bone; caused by crushed bones or diabetes; pain, limitation of motion, muscle/joint spasm in area

Osteoarthritis: more common; cartilage wears down with movement; primary effect on weight bearing joints(knees, hips, back, nack, shoulder); maintain movement

Rheumatoid arthritis: immune system attacks own joints/body; come with other symptoms (fever, loss of appetite, weight loss); primary effect on smaller joints; limited movement

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