Skeletal and Muscle System Notes with PDF
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Human Body Composition
Water Content
- The human body is 60-70% water.
- Babies have a higher water content (75-78% at birth), which decreases to 65-70% after one year.
- Water is the most effective liquid for dissolving substances.
Elemental Composition
- The most abundant element is Oxygen (65%).
- The body is primarily made of six elements:
- Oxygen (65%)
- Carbon (18.5%)
- Hydrogen (9.5%)
- Nitrogen (3.2%)
- Calcium (1.5%)
- Phosphorus (1.0%)
The Skeletal System (Bones)
Total Number of Bones
- An adult human body has 206 bones.
- A baby is born with about 300 bones, which fuse as they grow.
Bone Structure & Composition
- The primary salt found in bones is Calcium Phosphate.
- Bones are made of a mineral called hydroxyapatite, which accounts for up to 50% of bone volume and 70% of its weight.
- Long bones (e.g., leg bones) are hollow and cylindrical.
- The shaft (diaphysis) is made of strong, compact bone and contains yellow bone marrow (stores fat).
- The ends (epiphysis) are filled with a spongy structure and red bone marrow (which produces red blood cells).
- Bones are primarily made of collagen protein, calcium, and phosphorus.
Specific Bone Groups
- Ribs: The body has 12 pairs (24 total) of ribs, forming the rib cage.
- Skull: The human skull is made of 28 bones (excluding the hyoid bone).
- Neurocranium: 8 bones
- Facial Skeleton (Viscerocranium): 14 bones
- Auditory Ossicles (in the middle ear): 6 bones
Individual Bones
- Smallest Bone: The Stapes (in the middle ear).
- Largest Bone: The Femur (in the upper leg).
- Common Bone Names:
- Breastbone: Sternum
- Collarbone: Clavicle
- Knee-cap: Patella
- Shoulder blade: Scapula
Joints & Connective Tissues
- Ligaments are strong, elastic tissues that hold bones together at joints.
- Arthroplasty is a surgical procedure for joint replacement (e.g., hip-joint replacement).
Teeth: Structure & Care
- Teeth are hard, white, and dense, composed of calcium, phosphorus, and other minerals.
- Tooth Enamel is the strongest substance in the human body.
- It is made of hydroxyapatite crystals (calcium phosphate).
- Dental Plaque is a slimy layer on teeth made of bacteria, food particles, saliva, and acids.
- Humans are diphyodont, meaning they develop two sets of teeth:
- 20 milk teeth followed by 32 permanent teeth.
Skin, Hair, and Nails
- Alpha-Keratin is a key structural protein present in the skin, hair, nails, hooves, and horns, providing strength.
- Hair is primarily composed of the protein Keratin.
- Nails are made of layers of dead alpha-keratin cells.
- They lack nerves and blood vessels, so cutting them is painless.
Muscles
- The strongest muscle relative to its weight is the jaw muscle (masseter).
- The jaw muscles can exert a force of up to 200 pounds (90.7 kg) on the molars.
Essential Nutrients for Skeletal Health
- Calcium and Phosphorus: Essential for the formation and strengthening of bones and teeth.
- Fluorine (Fluoride): Essential for strong bones and teeth; helps prevent dental problems.
- Iodine: Not directly involved in bone/teeth formation; its primary role is in regulating the thyroid gland.
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