Anatomy Lecture 5 - Cartilage and Bone

In osteons, only osteocytes in close proximity to blood vessels in the central canal in have direct access to oxygen and nutrients. Which structures in the osteon allow osteocytes in lacunae to pass along oxygen and nutrients to the outer lamellae so that all cells are nourished?

Canaliculi

Describe the structure of cartilage, including chondroblasts, chondrocytes, lacunae, extracellular matrix, and perichondrium.

Chondroblasts - build extracellular matrix, once built around them become condrocytes and maintain the matrix, lacunae is the void where the cell sits, extracellular matrix is the collagen and elastin fibers that surround cells, peridchonrium surrounds cartilage areas (dense, irregular connective tissue). Avascular, hard to heal

During intramembranous ossification, bone develops directly from sheets of mesenchymal (undifferentiated) connective tissue. Which of the following would you expect to develop from intramembranous ossification?

Clavicle

Discuss the different types of bone fractures and how bone fractures are repaired.

Closed (simple) - skin not broken Open (compound) - tears skin (risk of infection) Transverse - cuts shaft transversely Oblique - at an angle Spiral - fractured with twisting motion Comminuted: many pieces broken between two large segments Impacted - one side driven into other (compression) Greenstick - partially fractured, but bone bent so not snapped Fracture hematoma, internal callus/external callus forms (cartilage), cartilage replaced with spongy bone, remodeling/compact bone develops on outside of fracture.

Describe the composition of bone matrix, including both organic and inorganic components.

Collagen fibers where inorganic salt crystals adhere (calcium phosphate/carbonate -> hydroxyapatite, fluoride, sulfate, magnesium hydroxide)

Diagram a typical long bone. Label the following: compact bone, spongy bone, diaphysis, proximal epiphysis, distal epiphysis, metaphysis, epiphyseal line, epiphyseal plate, apophysis, articular cartilage, medullary cavity, endosteum, periosteum, yellow bone marrow, red bone marrow, and nutrient foramen. State the function of each labeled structure.

Compact: outer surface Spongy: inner surface Diaphysis: shaft of bone, compact bone Proximal/distal epiphysis: proximal and distal ends of bone Metaphysis: area that contains epiphyseal plate/line Epiphyseal line/plate: A plate of hyaline cartilage that allows for interstitial growth or longitudinal growth in children. When done growing, become epiphyseal line and is ossified Apophysis: bony outgrowths that lack their own growth center and serve as attachment sites for ligaments or tendons (tubercles, spines, crests, etc) Articular cartilage: reduces friction and acts as a shock absorber where bones meet other bones (hyaline) Medullary Cavity: middle cavity in bone, filled with yellow marrow (Fat storage) Endosteum: delicate membrane lining medullary cavity. Bone growth, repair and remodeling occur here Periosteum: Outer membrane, contains blood vessels, nerves, lymphatic vessels, tendons and ligament attach to periosteum Red bone marrow: Hematopoeisis, in spongy bone Nutrient Foramen: holes where arteries enter

Epiglottis is formed by...

Elastic cartilage

What structure is located in the metaphysis of adults?

Epiphyseal line

Intervertebral discs are formed by...

Fibrocartilage

What is the function of the osteoblast

Forms bone matrix by synthesizing and secreting osteoid.

A patient comes into your clinic with an oblique fracture in the femur. After setting the bone and applying a cast, you expect the healing process to follow this sequence:

Hematoma; cartilage callus; bony callus; bone remodel

Articular Cartilage is formed by...

Hyaline cartilage

Costal cartilage is formed by...

Hyaline cartilage

Describe the composition, function and distribution of hyaline cartilage, fibrocartilage, and elastic cartilage.

Hyaline cartilage - strong and flexible, in fetal skeleton, most common type, short and dispersed collagen fibers and contains large amounts of proteoglycans in its ground substance. Smooth and clear under microscope. Respiratory system (larynx, trachea and bronchi), costal cartilage and nose and makes up the articular cartilages, epiphyseal plate = hyaline Fibrocartilage is tough and acts as an excellent shock absorber because it has thick bundles of collagen fibers dispersed through its matrix. The intervertebral discs, symphysis pubis, and menisci of the knee and jaw joints contain fibrocartilage. Elastic cartilage - contains elastic fibers, gives rigid support as well as elasticity, the external ear contains elastic cartilage, as does the epiglottis.

Growth hormone is a hormone that causes body growth, especially in bone. When someone secretes too much growth hormone as a child (and the epiphyseal plates have not yet closed), bones grow longer. When someone secretes too much growth hormone as an adult (after the growth plates have closed), bones grow wider. What are these two types of bone growth called?

Interstitial growth; appositional growth

Summarize the processes of intramembranous and endochondral ossification. Name the bones formed by each process.

Intramembranous: Clavicles up on fetus do this, develops from sheets of mesenchymal connective tissue. In ossification center, osteoblasts appear and secrete osteoid, become osteocyte, and ossifies connective tissue. Last bones to finish intramembranous ossification are flat bones of face (After adolescent growth spurt). Endochondral: Everything else - bone replacing hyaline cartilage, takes a lot longer. First chondrocytes form cartilage, then perichondrium appears. As it grows, inside cells die from lack of nutrients and disintegrate, but blood vessels invade cavities and bring osteogenic cells. Those become osteoblasts, which secrete bone matrix, slowly killing off the other cartilage cells. A primary ossification center emerges in periosteal collar. Later, a secondary ossification center occurs in epiphyseal region. Eventually almost all ossifies, except plate and articular cartilage

In compact bone, osteons are composed of ________.

Lamellae

Summarize how bones grow length-wise and width-wise during childhood.

Length: Interstitial/longitudinal growth at epiphyseal plate. Epiphyseal side grows cartilage, diaphysis side ossifies it, making bone grow longer. Eventually stops and becomes epiphyseal line. Width - Appositional growth - Osteoblasts work to put new bone beneath periosteum and osteoclasts eat away wall of medullary cavity

Identify the characteristics of long, short, flat, irregular, and sesamoid bones. Be able to classify bones of the body

Long bones: A long bone is one that is cylindrical in shape, being longer than it is wide. Keep in mind, however, that the term describes the shape of a bone, not its size. Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges). Long bones function as levers; they move when muscles contract. Short bones: A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. Short bones in the human skeleton are the carpals of the wrists and the tarsals of the ankles. Short bones provide stability and support as well as some limited motion. Flat bones: The term "flat bone" is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved. Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. Flat bones serve as points of attachment for muscles and often protect internal organs. Irregular bones: An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones. Sesamoid bones: A sesamoid bone is a small, round bone that forms in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. Sesamoid bones protect tendons by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees. The patellae (singular = patella) are the only sesamoid bones found in common with every person.

Briefly discuss the process of bone remodeling and the cells involved in remodeling.

Osteoclasts break down old/damaged bone and release calcium, Osteoblasts build new osteoid matrix and make new bone.

Differentiate between osteogenic cells, osteoblasts, osteocytes and osteoclasts in terms of function and location

Osteogenic - divide and become osteoblasts Osteoblasts - build bones (secretes osteoid), periosteum and endosteum Osteocytes - bone cells (maintain bone), in diaphysis and ossifying the epiphyseal plate, maintain mineral concentration Osteoclasts - break down bones, originate from macrophages and monocytes, found on surfaces of the bones

Describe the following bone disorders: osteomalacia (rickets), osteopetrosis, and osteoporosis.

Osteomalacia: Inadequate mineralization of bones = low bone density, rickets, soft bones/bowed legs (vitamin D/calcium deficiency) Osteopetrosis: Over mineralization of bones, osteoclasts can't break down bone, osteoblasts keep making bone. Really dense but brittle, can cause anemia, foramina decrease in size and have pressure on them. Osteoporosis: Decrease in bone density as you age, affects femur, vertebrae, and wrists. Women lose mass more quickly. Prevention is best: calcium/vitamin D diet

Given a cross section of compact bone (microscopic view), label the following: osteon, concentric lamellae, central canal, osteocytes, lacunae, canaliculi and perforating canal. Explain the functions of each of the labeled structures.

Osteon: Circles of lamallae around the central canal, one unit of the bone Concentric Lamallae: Rings in osteon (like tree rings) Central Canal (Haversian): Main canal where blood vessels, nerves, and lymphatic vessels run Osteocytes: in between lamallae the osteocytes are nestled in the lacunae Lacunae: Holes where osteocytes live Perforating canal (Volkmann's): Runs at right angles to central canal, extends to the periosteum and endosteum Canaliculi: small canals running off of perforating canal/central canal, brings nutrients to individual osteocytes and carries waste away

An 80-year old woman arrives in your emergency department after she slipped and fell out of her bathtub. You determine that she broke her proximal femur. Upon further examination you notice low bone density. What is your most likely secondary diagnosis?

Osteoporosis

What is the function of the osteocyte?

Primary cell of mature bone

In this dissection, _____ is the area where red blood cells, white blood cells, and platelets are all produced.

Red marrow

Diagram a typical flat bone, labelling the following: compact bone, spongy bone, red bone marrow, endosteum, periosteum

See long bones for greater detail

The patella is classified as a ______ bone.

Sesamoid

Explain the major functions of cartilage and bone

Structural support, hematopoeisis, movement, protection, mineral storage, energy storage, shock absorber, stretches

Given a diagram of spongy bone (microscopic view), label the following: trabeculae, lamellae, osteocytes, lacunae, canaliculi, and endosteum.

Trabeculae: criss-crossing beams in matrix, protects red marrow, lightweight structure Lamellae: cross-cut of trabeculae shows rings like osteon, those are lamellae Osteocytes: bone cells snuggled in lacunae Lacunae: gaps in lamellae that house osteocytes Canaliculi: tiny channels that bring nutrients and remove wastes Endosteum: membrane that surrounds the trabeculae, houses osteoblasts

What is the function of the osteogenic cell?

Undifferentiated stem cell, only cell that divides, can become osteoblast

What type of tissue is the periosteum made from?

What type of tissue is the periosteum made from?

The periosteum is ________ to compact bone, and spongy bone is _______ to compact bone.

superficial; deep