Human Morph Lecture 6 (Skeletal System)

What are the components of the skeletal system?

Bones of skeleton, cartilage, ligaments, other CT

Bones

Primary organs of the skeletal system, rigid framework of the body, many other functions

Types of Bone

Compact bone and spongy bone

Compact Bone

Dense or cortical bone; 80% of bone mass

Spongy Bone

Cancellous or trabecular bone; located internal to compact bone; appears porous; 20% of bone mass

Cartilage

Semirigid CT, more flexible than bone

Types of Cartilage

Hyaline cartilage and fibrocartilage

Hyaline cartilage

Attaches ribs to sternum, covers ends of some bones, within growth plates, model for bone formation

Fibrocartilage

Weight-bearing cartilage that withstands compression; intervertebral discs, pubic symphysis, menisci of knee

Structures composed of dense regular CT

Ligaments and tendons

Ligaments

Bone to Bone

Tendons

Muscle to Bone

Bones perform several basic functions

Support and protection; levers for movement; hematopoiesis (blood cell production, occurs in red bone marrow CT); storage of mineral and energy reserves (calcium and phosphate)

Bone- combination of tissue type

Primarily connective and nervous tissue

Connective Tissue in Bone

Compact and spongy bone, dense irregular CT, reticular CT, blood

Nervous Tissue in Bone

Detects and monitors sensory stimuli about status of bone

Classification of Bones

Long bones, short bones, flat bones, irregular bones

Long Bones

Greater in length than width; femur, humerus

Short bones

Length nearly equal to width; carpals and tarsals

Flat bones

Flat, thin surfaces, may be slightly curved; for example cranial bones

Irregular Bones

Elaborate, sometimes complex shapes; for example vertebrae

Anatomy- long bone

Diaphysis, Medullary Cavity, Epiphysis, Metaphysis, Epiphyseal Plate, Periosteum, Endosteum

Diaphysis

Elongated, usually cylindrical shaft; provides leverage and weight support; Compact bone with thin spicules of spongy bone extending inward

Medullary (marrow) cavity

Hollow, cylindrical space within the diaphysis; contains red bone marrow in children; contains yellow bone marrow in adults

Epiphysis

Knobby region at each end of long bone; long bone has both proximal and distal epiphysis; articular cartilage covers surface

Proximal Epiphysis

End of bone closest to body trunk

Distal Epiphysis

End furthest from trunk; composed of outer layer of compact bone and inner region of spongy bone

Articular Cartilage

Covers joint surface of epiphysis; thin layer of hyaline cartilage; reduces friction & absorbs shock in moveable joints

Metaphysis

Region where bone widens and transfers weight between the diaphysis and epiphysis

Epiphyseal plate

Located within metaphysis; growth plate; thin layer of hyaline cartilage; provides for lengthwise bone growth; in adults, the epiphyseal line, is the remanent of the epiphyseal plate

Coverings and linings of bone

Periosteum and Endosteum

Periosteum

Tough sheath covering outer surface of bone; outer fibrous layer of dense irregular CT; inner cellular layer; attached to bone by numerous collagen fibers (perforating fibers)

Outer fibrous layer of dense irregular CT in Periosteum

Protects bone from surrounding structures; anchors blood vessels and nerves to bone structure; attachment site for ligaments and tendons

Inner cellular layer in Periosteum

Includes osteoprogenitor cells, osteoblasts

Endosteum

Covers all internal surfaces of bone within medullary cavity; thin layer of CT containing osteoprogenitor cells and osteoblasts

Blood Supply in Bones

Bone highly vascularized (e.g. in regions of spongy bone); nutrient foramen

Nutrient foramen

Small opening or hole in brone; artery entrance and vein exit here

Nerve supply

Accompany blood vessels through forament; innervate bone, periosteum, endosteum, marrow cavity; mainly sensory nerves

Anatomy- other bone classes

Short, flat and irregular bones differ from long bones

How do short, flat and irregular bones differ from long bones

External surface composed of compact bone covered by periosteum; interior composed of spongy bone; no medullary cavity

Diploë

Spongy bone in flat bone of skull

Bone marrow

Soft CT of bone; red bone and yellow bone marrow

Red bone marrow (myeloid tissue)

Hematopoietic (lood cell forming); Reticular CT, developing blood cells, and adipocytes

Red Bone Marrow in Children

Located in spongy bone and medullary cavity of long bones

Red Bone Marrow in Adults

Located only in selected areas of axial skeleton; skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus and femur

Yellow Bone Marrow

Product of red bone marrow degeneration as children mature; fatty substance; may convert back to red bone marrow during severe anemia (condition w/reduced erythrocytes); Facilitates production of additional erythrocytes

Anatomy- Bone CT

Bone CT( osseous CT); primary component of bone; bone is composed of cells and extracellular matrix; cells of bone

4 Types of Cells found in Bone CT

Osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

Osteoprogenitor cells

Stem cells derived from mesenchyme; Cellular division yields another stem cell and a “committed cell” (matures to become an osteoblast); located in periosteum and endosteum

Osteoblasts

Form from osteoprogenitor stem cells; Synthesize and secrete osteoid; Become entrapped within the matrix; differentiate into osteocytes

Osteoid

Initial semisolid organic form of bone matrix; later calcifies

Osteocytes

Mature bone cells derived from osteoblasts; detect stress on bone & trigger new bone formation

Osteoclasts

Large, multinuclear, phagocytic cells; derived from fused hematopoietic cells; ruffled border increases SA exposed to bone; Located within/adjacent to a depression/pit on bone surface; Involved in bone resorption (breakdown of bone)

Resorption lacunan

depression/pit on bone surface

Composition of bone matrix

Organic components and inorganic components

Organic components of bone matrix

Osteoid produced by osteoblasts contains collagen proteins & semisolid ground substance of proteoglycans and glycoproteins; gives bone tensile strength by resisting streching; contributes to bone flexibility

Inorganic components of bone matrix

Salt crytstals, calcium phosphate; Interacts with calcium hydroxide (forms crystals: hydroxyapatite); other substances incorporated into crystals (ex sodium & magnesium; crystals deposit around collagen fibers; harden matrix and account for rigidity of bones

Bone formation

Begins with secretion of osteoid; calcification occurs; process requires Vitamin D & C, calcium and phosphate for calcification

Calcification

Deposition of hydroxyapatite crystals (Ca and phosphate ions precipitate out, form crystals)

Vitamin D in bone formation

Enhances Ca absorption from GI tract

Vitamin C in bone formation

Required for collagen formation

Bone resorption

Bone matrix is destroyed by substances released from osteoclasts; proteolytic enzymes released from lysosomes within osteoclasts; calcium and phosphate dissolved by HCl; freed Ca and phosphate ions enter blood; occurs when blood calcium is low

Proteolytic enzymes in bone resorption

Chemically digest organic matrix components