Tissues and Skeletal System

• Tissue: Group of cells closely associated that have a similiar structure & perform a related function
• Four Types:
• Epithelium - Covering
• Connective - Support
• Muscle - Movement
• Nervous - Control

* Most organs contain all four types

• * Tissues are made up of sheets of cells
• * Two broad classes of epithelial tissues:
• Simple Epithelium: One layer or cell shape
• -Squamous (squashed/flattened) (lining of blood vessels) Exchange of nutrients, wastes & gases
• -Cuboidal (Cubed) (Walls of glands) Secretes & reabsorbs water & small molecules
• -Columnar (rectangular - possess cilia) (lining of the intestines and uterus) Absorbs nutrients, secretes mucus

• Stratified Epithelium: Multiple layers and cell shapes
• * Classified based on the shape of the uppermost layer of cells (squamous, cubodidal, columnar)
• * Transitional Stratified Epithelial: Cells of transitional stratified epithelial tissues can change their shape and can change the number of cell layers when changed

• • Tight junctions: Leak proof seal between neighboring cells
• ◦ In the intestines, this prevents digestive enzymes from escaping into the blood stream
• • Desmosomes: places where cells are anchored to one another
• ◦ Important in muscle and skin tissues
• • Gap junctions: Channels between cells

• • Microvilli: Finger-like projections of the plasma membrane
• ◦ Increase surface area for absorption
• ◦ Example: Small intestine
• •Cilia: Oar-like proteins
• ◦ Moves mucus over epithelial surfaces
• ◦ Example: Respiratory tubes

• • Universal throughout the body
• • Underlies epithelial tissue
• ◦ Never exposed to the environment outside of the body
• • Cells are suspended in a complex structure called the Extracellular Matrix
• ◦ The extracellular matrix is made up of two parts:
• ▪ Fibers (three different types):
• • Collagen gives structure
• • Reticular fibers give order
• • Elastin provides elasticity
• ▪ Ground Substance: Jelly-like material that fills in the gaps
• ~~~~~~~~~~~~~~~
• • Functions:
• ◦ Protect organs (bone & cartilage are connective tissues)
• ◦ Surround and interconnect tissues
• ◦ Transport materials (blood is a connective tissue)
• ◦ Store energy (fat tissue is a connective tissue)

• • Fibroblasts are responsible for the production and maintenance of the fibers & ground tissue
• ◦ Immune Cells
• • Macrophages (“big eaters”): Engulf parasites
• • Plasma cells: Produce large amounts of antibodies
• • Mast cells: Involved in wound healing
• • Neutrophils: First cells to arrive at the site of an infection
• ◦ Produce a net which traps and kills bacteria
• ◦ Principle component of pus (gives pus its white color)

• • Composed of the body’s bones and associated ligaments, tendons, and cartilages.
• • Functions:
• ◦ Support
• ▪ The bones of the legs, pelvic girdle, & vertebral column support the weight of the erect body
• ▪ The mandible (jawbone) supports the teeth
• ▪ Other bones support various organs and tissues
• • Protection
• ◦ The bones of the skull protect the brain, while vertebrae protect the spinal cord
• ◦ Ribs and sternum (breastbone) protect the lungs and heart
• • Movement
• ◦ Skeletal muscles are attached to bones and use them as levers to move the body
• ◦ Reservoir for minerals and adipose tissue
• ▪ 99% of the body’s calcium is stored in bone
• ▪ 85% of the body’s phosphorous is stored in bone
• ▪ Adipose tissue is found in the marrow of certain bones
• • Hematopoiesis: Blood cell formation
• ◦ All blood cells are made in the marrow of certain bones

• ▪ Forms long axis of the body
• ▪ Includes the bones of the skull, vertebral column, and rib cage.
• ▪ These bones are involved in protection, support, and carrying other body parts.
• ▪ Bones of the Axial Skeleton
• • Skull: Frontal bone, zygomatic, temporal bone, maxilla, mandible
• • Vertebrae: Cervical (with atlas, axis & hyoid bone), thoracic, lumbar, sacral, coccyx,cartilage discs
• • Ribs: True, false, floating, manubrium, sternum, xiphoid process

• ▪ Bones of upper & lower limbs and the girdles (shoulder bones and hip bones) that attachthem to the axial skeleton.
• ▪ Involved in locomotion and manipulation of the environment
• ▪ Bones of the Appendicular Skeleton
• • Shoulder: Scapula, clavicle, humerus
• • Lower Arm: Radius, ulna, carpus, metacarpus, phalanges
• • Hip: Ischium, ilium, pubis, pubic symphysis, femur
• • Lower Leg: Patella, tibia, fibula, tarsals, metatarsals, phalanges, calcaneus

• • Immovable Joint:
• ◦ Skull, sacroiliac joint, between ribs & vertebrae
• ◦ At birth, the bone formation is incomplete and the bones don't join each other; this allows thebaby to fit through the birth canal
• • Ball and Socket: Provides variety of movement
• ◦ Top of humerus & femur
• • Hinge Joint: Permits back & forth movement
• ◦ Elbow & knee
• • Gliding Joint: Permits back & forth movement
• ◦ Wrist & ankle
• • Pivotal Joint: Permits rotation in one plane
• ◦ Neck & head, radius & ulna
• • Saddle Joint: Up and down motion
• ◦ Thumb
• • In a joint, the contacting surfaces are covered with cartilage. Ligaments hold the bones in a joint toone another. The joints are lubricated by secretions from the ligaments.

• • Long Bones
• ◦ Much longer than they are wide
• ◦ All bones of the limbs except for the patella (kneecap), and the bones of the wrist and ankle
• ◦ Consists of a shaft plus 2 expanded ends
• ◦ Your finger bones are considered long bones even though they’re short
• • Short Bones
• ◦ Roughly cube shaped
• ◦ Bones of the wrist and the ankle
• Flat Bones
• ◦ Thin, flattened, and usually a bit curved
• ◦ Scapulae (shoulder blades), sternum, ribs and most bones of the skull
• Irregular Bones
• ◦ Have weird shapes that fit none of the 3 previous classes
• ◦ Vertebrae, hip bones, 2 skull bones (sphenoid and the ethmoid bones)

• • Bones are organs. Therefore, they’re composed of multiple tissue types.
• • Bones are composed of:
• ◦ Connective tissue
• ◦ Adipose tissue
• ◦ Cartilage/Bone
• ◦ Vascular tissue
• ◦ Lymphatic tissue
• ◦ Nervous tissue
• • Because bone tissue is a type of connective tissue, it consists of cells plus a significant amount of extracellular matrix

• • Osteoblasts: Bone-building cells
• ◦ Synthesize and secrete collagen fibers and other organic components of bone matrix
• ◦ Initiate the process of calcification
• • Osteocytes: Mature bone cells
• ◦ Osteoblasts that have become trapped by the secretion of matrix
• ◦ No longer secrete matrix
• ◦ Responsible for maintaining the bone tissue
• • Osteoclasts: Huge cells derived from the fusion of as many as 50 cells
• ◦ Cells that digest bone matrix
• .............▪ This process is called bone resorption and is part of normal bone growth, development,maintenance, and repair
• ......................• As a child, the amount of bone that you make out paces the amount of bone resorptionthat occurs. As you grow older, the rates of formation and resorption become equal.
• .............▪ Osteoporosis is a condition due to resorption occurring more quickly than formation.

• • Consists of organic and inorganic components
• ◦ 1/3 organic and 2/3 inorganic by weight

• • Organic component
• ◦ Consists of several materials that are secreted by the osteoblasts:
• ▪ Collagen fibers and other organic materials
• ▪ These (particularly the collagen) provide the bone with resilience and the ability to resiststretching and twisting
• • Inorganic component of bone matrix
• ◦ Consists mainly of 2 salts:
• ▪ Calcium phosphate
• ▪ Calcium hydroxide
• ◦ Bone also contains smaller amounts of magnesium, fluoride, and sodium
• ◦ These minerals give bone its characteristic hardness and the ability to resist compression

• • A long bone is essentially a shaft with two expanded ends
• ◦ Diaphysis: The shaft of the bone
• ▪ Consists of a thick collar of compact bone surrounding a central cavity that contains the marrow
• ▪ Two types of marrow
• • Bone marrow: Blood cell production
• • Yellow marrow: Fat storage
• ◦ Epiphysis: An expanded end of the bone
• ▪ Thin layer of compact bone covering an interior of spongy bone
• ▪ Joint surface of each epiphysis is covered with cartilage.
• ▪ The cartilage cushions the bone ends and reduces friction during movement

• • In a child, the marrow cavity of nearly every bone is filled with red bone marrow
• ◦ Red bone marrow looks like blood but with a thicker consistency

• • In young to middle-aged adults, the shafts of the long bones are filled with fatty yellow bonemarrow
• ◦ Yellow marrow no longer produces blood, although in the event of severe or chronic anemia(lack of red blood cells), it can transform back into red marrow

• In adults, red marrow is limited to the axial skeleton, pectoral girdle, pelvic girdle, and epiphyses of the humerus and femur