6 Bones and Skeletal Tissues Flashcards
The human skeleton initially consists of ____________, which in most places are eventually replaced by bone
Cartilages
Where are the few cartilages that remain in adults found?
Mainly in regions where flexible skeletal tissue is needed (ex. the external ear, tip of the nose, rib cage, surrounding the respiratory tract)
What kind of tissue are skeletal cartilages primarily composed of?
Cartilage tissue (a type of connective tissue)
Describe the basic structure of cartilage tissue
- Very resilient (has the ability to spring back to its original shape after being compressed)
- Avascular, contains no blood vessels or nerves
- Contains cells called chondrocytes, enclosed in small cavities (lacunae) within an extracellular matrix containing a jellylike ground substance and fibers
What is the of the membrane that surrounds cartilage?
Perichondrium
What cells are found in cartilage?
Chondrocytes
What is the perichondrium?
The perichondrium is a layer of dense irregular connective tissue that surrounds cartilage, acting as a reinforcement to resist outward expansion when the cartilage is compressed. It also contains blood vessels that nourish the cartilage cells (chondrocytes)
What limits the thickness of cartilage?
Since cartilage is avascular, the thickness of cartilage is limited by the distance nutrients can diffuse through the matrix to reach the cells (chondrocytes)
How are chondrocytes nourished?
Cartilage tissue is avascular, so chondrocytes rely on the diffusion of nutrients through the jellylike extracellular matrix from blood vessels in the surrounding perichondrium. This limits the thickness of cartilage
Compare/contrast cartilage and bone
What are the three types of cartilage?
1) Hyaline cartilages
2) Elastic cartilages
3) Fibrocartilages
What are hyaline cartilages?
- Look like frosted glass when freshly exposed
- The most abundant skeletal cartilages
- Chondrocytes are spherical
- Only fiber type in their matrix is fine collagen fibers (which are undetectable microscopically)
- Include: articular cartilages (cover the ends of most bones at moveable joints), costal cartilages (connect the ribs to the sternum), respiratory cartilages (form the skeleton of the larynx (voice box) and reinforce other respiratory passageways), and nasal cartilages, which support the external nose
What are elastic cartilages?
- Resemble hyaline cartilages, but contain more stretchy elastic fibers
- Better able to stand up to repeated bending
- Found in only two skeletal locations: the external ear and the epiglottis (flap that bends to cover the opening of the larynx each time we swallow)
What are fibrocartilages?
- Highly compressible with great tensile strength
- Consist of roughly parallel rows of chondrocytes alternating with thick collagen fibers
- Occur in sites that are subjected to both pressure and stretch, such as the padlike cartilages (menisci) of the knee and the discs between the vertebrae
Where in the body are hyaline cartilages located?
- Covering the ends of most bones at moveable joints (articular cartilages)
- Connecting the ribs and the sternum (costal cartilages)
- In the larynx and reinforcing other respiratory passageways like the trachea, bronchi (respiratory cartilages)
- In the external nose (nasal cartilages)
Where in the body are elastic cartilages located?
- External ear (pinna)
- Epiglottis
Where in the body are fibrocartilages located?
- Between vertebral discs
- Meniscus (padlike cartilage in knee joint)
- Pubic symphysis
What are the two types of growth exhibited by cartilage? Which of these does bone exhibit?
- Appositional growth: Cartilage-forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue
- Interstitial growth: the lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within
Bone only exhibits appositional growth; CANNOT exhibit interstitial growth
Interstitial growth is only possible in cartilage because unlike bone (which has a hard matrix), cartilage has a more flexible matrix that can accomodate mitosis, making it the ideal tissue to lay down the embryonic skeleton and to provide for new skeletal growth
Under certain conditions—during normal bone growth in youth and during old age, for example—cartilage can become calcified (hardened due to deposit of calcium salts). Note, however, that calcified cartilage is not bone; cartilage and bone are always distinct tissues.
Which type of cartilage is most plentiful in the adult body?
Hyaline cartilage is the most plentiful in the adult body
What two body structures contain flexible elastic cartilage?
The epiglottis and external ear cartilages are flexible elastic cartilage.
Cartilage grows by interstitial growth. What does this mean?
Interstitial growth is growth from within
What are the 7 important functions of bones?
1) Support: Bones provide a framework that supports the body and cradles its soft organs. For example, bones of lower limbs act as pillars to support the body trunk when we stand, and the rib cage supports the thoracic wall
2) Protection: The fused bones of the skull protect the brain. The vertebrae surround the spinal cord, and the rib cage helps protect the vital organs of the thorax.
3) Anchorage: Skeletal muscles, which attach to bones by tendons, use bones as levers to move the body and its parts. As a result, we can walk, grasp objects, and breathe. The design of joints determines the types of movement possible.
4) Mineral Storage: Bone is a reservoir for minerals, most importantly calcium and phosphate. The stored minerals are released into the bloodstream in their ionic form as needed for distribution to all parts of the body. Indeed, “deposits” and “withdrawals” of minerals to and from the bones go on
almost continuously
5) Blood Cell Formation: Most blood cell formation, or hematopoiesis , occurs in the red marrow of certain bones
6) Triglyceride (Fat) Storage: Fat, a source of energy for the body, is stored as yellow marrow in the cavities of long bones
7) Hormone Production: Bones produce osteocalcin, a hormone that helps to regulate insulin secretion, glucose homeostasis, and energy expenditure
How many named bones are there in the adult human skeleton?
206
What are the two major groups of bones in the body based on location?
- The axial skeleton forms the long axis of the body and includes the bones of the skull, vertebral column, and rib cage. Generally speaking these bones protect, support, or carry other body parts
- The appendicular skeleton consists of the bones of the upper and lower limbs and the girdles (shoulder bones and hip bones) that attach the limbs to the axial skeleton. Bones of the limbs help us move from place to place (locomotion) and manipulate our environment
Generally speaking, what major functions do the bones of the axial skeleton perform?
They protect, support, or carry other body parts
Generally speaking, what major functions do the bones of the appendicular skeleton perform?
Locomotion, manipulating the environment
What groups are bones classified into based on shape?
- Long bones: longer than they are wide; have a shaft and two ends that are often expanded; all limb bones except the patella (kneecap) and the wrist and ankle bones are long bones; named for elongated shape, NOT overall size (long bones can be very small like the bones of the finger)
- Short bones: roughly cube shaped; bones of the wrist and ankle; include the sesamoid bones (special type that form in a tendon, ex. the patella)
- Flat bones: thin, flattened, and usually a bit curved; sternum (breastbone), scapulae (shoulder blades), ribs, and most cranial bones of the skull
- Irregular bones: have complicated shapes that fit none of the preceding classes; the vertebrae and the hip bones
Who was Andreas Vesalius?
What type of bone forms the hard, dense outer layer of bones throughout the human body?
Compact bone
What type of bone is composed of light, porous bone enclosing numerous large spaces that give a honeycombed appearance?
Spongy bone (also called trabecular bone)
What is compact bone?
Compact bone, also called cortical bone, is the denser, stronger of the two types of bone tissue. It is found under the periosteum and in the diaphyses of long bones, where it provides support and protection.
What is spongy bone?
Spongy bone, also known as cancellous bone or trabecular bone, is characterized by its spongy, porous, honeycomb-like structure and is typically found at the ends of long bones and sandwiched in the center of flat bones
What are the two major types of bone tissue?
Compact bone and spongy bone
Describe the gross anatomy of short, irregular, and flat bones
- Consist of thin plates of spongy bone (diploe) sandwiched between/covered by outer layers of compact bone
- The compact bone is covered externally by the periosteum and internally by the endosteum
- Bone marrow is scattered throughout cavities of spongy bone; no defined marrow cavity
- Hyaline cartilage covers surfaces where they form movable joints with neighbors
Describe the gross anatomy of long bones
- All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes (periosteum and endosteum)
- Diaphysis: tubular shaft that forms long axis of bone; consists of compact bone surrounding internal medullary cavity that is filled with yellow marrow in adults
- Epiphyses: ends of long bones that consist of compact bone externally and spongy bone internally; articular cartilage covers joint surfaces
- Between diaphysis and epiphysis of adult long bones is epiphyseal line, a remnant of the epiphyseal plate. The epiphyseal plate, commonly called the growth plate, is a disc of hyaline cartilage that grows during childhood to lengthen the bone.
What are perforating fibers? What role do they play?
Perforating fibers are bundles of collagen fibers in the periosteum that pass/penetrate into the outer circumferential lamellae of bone, securing the periosteum to the underlying bone and providing anchoring points for tendons and ligaments
Explain the distribution of red marrow and yellow marrow in the body and how it changes from infancy to adulthood
In infants, the medullary cavity of the diaphysis and all areas of spongy bone contain red bone marrow.
In adults, much of the red marrow, particularly in long bones, has been replaced by yellow marrow.
In most adult long bones, the fat-containing yellow marrow extends well into the epiphysis, and little red marrow is present in the spongy bone cavities.
As a result, red marrow in adults is only found in the cavities between trabeculae of spongy bones in: The flat bones of the skull, as well as the sternum, ribs, clavicles, scapulae, hip bones, and vertebrae; The heads of the femur (thigh bone) and humerus (long bone of the arm)
Compared to long bones (femur and humerus), the red marrow found in the spongy bone of flat bones (such as the sternum) and in some irregular bones (such as the hip bone) is much more active in hematopoiesis. When clinicians suspect problems with the blood-forming tissue, they obtain red marrow samples from these sites. However, yellow marrow in the medullary cavity can revert to red marrow if a person becomes very anemic (has low oxygen-carrying capacity) and needs more red blood cells.
