D312 ANATOMY AND PHYSIOLOGY I - Set 2 - Part 1

Correct Answer: Eight bones

Option c is correct because the diaphysis is the tubular shaft of a long bone, containing the medullary cavity filled with yellow marrow in adults, making it the central structural region described. Option a is incorrect because the epiphysis refers to the wider ends of a long bone that are filled with spongy bone and red marrow, not the central shaft region. Option b is incorrect because the metaphysis is the transitional zone between the diaphysis and epiphysis where the growth plate is located, not the main shaft itself. Option d is incorrect because the epiphyseal line is a remnant of the growth plate found in mature bones and is a marking rather than a structural shaft region.

Correct Answer: Cell-to-cell communication among osteocytes

Option a is correct because canaliculi are the tiny channels that connect osteocytes in their lacunae, enabling direct communication and nutrient exchange between cells within compact bone tissue. Option b is incorrect because new bone matrix production is primarily carried out by osteoblasts located on bone surfaces, not through the canaliculi communication network between osteocytes. Option c is incorrect because bone resorption is the job of osteoclasts, which break down bone tissue independently of the canaliculi network that connects osteocytes together. Option d is incorrect because calcium storage occurs within the mineralized bone matrix itself and does not depend on the patency of the canaliculi connecting osteocytes.

Correct Answer: Its cells receive nutrients from surrounding marrow

Option d is correct because spongy bone is organized into trabeculae without osteons, and its osteocytes receive nutrients directly from blood vessels in the surrounding red marrow spaces. Option a is incorrect because while periosteum covers outer bone surfaces and supplies some blood, it does not explain why spongy bone internally lacks its own Haversian canal system. Option b is incorrect because osteoclast concentration does not determine whether a bone tissue type needs dedicated blood vessel channels, as osteoclasts are involved in resorption processes. Option c is incorrect because spongy bone is found in many bone types including the epiphyses of long bones, not exclusively in flat bones as this option suggests.

Correct Answer: The inner osteogenic layer

Option b is correct because the periosteum has two layers, and its inner osteogenic layer specifically contains osteoblasts for bone formation and osteoclasts for bone resorption and repair. Option a is incorrect because the dense irregular outer layer of the periosteum provides structural protection and anchoring but does not house the osteoblasts and osteoclasts responsible for remodeling. Option c is incorrect because the endosteum lines the internal medullary cavity of bones and is a separate structure from the periosteum that covers the external bone surface. Option d is incorrect because hyaline cartilage caps are found at articular surfaces of bones at joints and are not part of the periosteum's layered structure.

Correct Answer: Longitudinal bone growth has ceased

Option a is correct because the epiphyseal plate is a zone of active hyaline cartilage enabling lengthwise growth, and its replacement by the epiphyseal line signals that bone elongation has stopped. Option b is incorrect because the medullary cavity remains intact throughout skeletal maturity and does not collapse when the growth plate closes and becomes the epiphyseal line marker. Option c is incorrect because the closure of the epiphyseal plate does not trigger conversion of compact bone into spongy bone, as these tissue types maintain their distinct locations. Option d is incorrect because the periosteum remains attached to bone surfaces throughout life and is unrelated to the epiphyseal plate closure that marks the end of growth.

Correct Answer: Axial: skull, vertebral column, thoracic cage

Option d is correct because the axial skeleton contains eighty bones and comprises three main components: the skull, the vertebral column, and the thoracic cage protecting central organs. Option a is incorrect because the appendicular skeleton contains one hundred twenty-six bones of the limbs and girdles and does not form the central protective axis of the body. Option b is incorrect because while the axial skeleton does include cranial and facial bones, the pelvic girdle belongs to the appendicular skeleton, not the central axial framework. Option c is incorrect because the appendicular skeleton does not include the skull or vertebral column, and this answer incorrectly assigns axial components to the appendicular division.

Correct Answer: Sagittal suture joining the two parietal bones

Option c is correct because the sagittal suture runs along the midline at the top of the skull, specifically uniting the left and right parietal bones that form most of the upper lateral cranium. Option a is incorrect because the coronal suture runs transversely across the skull separating the frontal bone from the parietal bones, not along the midline between the two parietals. Option b is incorrect because the lambdoid suture extends downward and laterally from the sagittal suture junction, connecting the occipital bone to the parietal and temporal bones posteriorly. Option d is incorrect because the squamous suture is located on the lateral side of the skull, joining the temporal bone to the parietal bone, not running along the superior midline.

Correct Answer: Thirty bones per side

Option a is correct because one upper extremity includes the humerus, radius, ulna, eight carpals, five metacarpals, and fourteen phalanges, totaling exactly thirty bones per side. Option b is incorrect because twenty-six bones per side underestimates the true count by omitting several carpal or phalangeal bones from the standard upper extremity bone inventory. Option c is incorrect because thirty-two bones per side overestimates the actual number, adding extra bones that are not part of the standard upper extremity skeletal anatomy. Option d is incorrect because twenty-eight bones per side also underestimates the total, likely miscounting the number of carpal bones or phalanges in the standard upper extremity count.

Correct Answer: The mandible, with fourteen facial bones

Option b is correct because the mandible is the only movable bone in the adult skull, forming the lower jaw, and the facial skeleton contains fourteen bones including paired and unpaired bones. Option a is incorrect because the maxilla forms the upper jaw and is a fixed bone fused to the rest of the skull, making it incapable of the independent movement described in the question. Option c is incorrect because the hyoid bone is not part of the skull at all and is classified separately as it sits in the neck region without direct bony articulation to the skull. Option d is incorrect because the vomer is a fixed unpaired facial bone that forms the inferior part of the nasal septum and has no capacity for independent movement.

Correct Answer: The pelvic girdle with two coxal bones

Option d is correct because the pelvic girdle, made of two coxal or hip bones, specifically transfers weight from the axial skeleton to the lower limbs and protects pelvic organs. Option a is incorrect because the pectoral girdle connects the upper limbs to the axial skeleton and does not transfer body weight to the lower limbs or protect pelvic structures. Option b is incorrect because the thoracic cage protects the heart, lungs, and great vessels in the chest but does not transfer weight to the lower limbs or shield pelvic organs. Option c is incorrect because while the vertebral column transmits weight vertically, it is not a girdle structure and does not independently protect pelvic organs the way the coxal bones do.

Correct Answer: Hinge joint allowing flexion and extension

Option a is correct because hinge joints like the elbow are uniaxial synovial joints that permit movement in only one plane, specifically flexion and extension, matching the described movement pattern. Option b is incorrect because ball-and-socket joints like the hip and shoulder are multiaxial joints allowing the widest range of motion in multiple planes, not just one. Option c is incorrect because pivot joints allow rotational movement around a single axis, such as turning the head, which does not match the bending and straightening pattern described. Option d is incorrect because saddle joints permit biaxial movement in two planes, allowing more freedom than the single-plane flexion and extension described in the scenario.

Correct Answer: Ligaments connect bone to bone, tendons connect muscle to bone

Option c is correct because ligaments are fibrous connective tissue that connect bone to bone and stabilize joints, while tendons connect muscle to bone to transmit contractile force. Option a is incorrect because this answer reverses the definitions, as tendons connect muscle to bone and ligaments connect bone to bone, not the other way around. Option b is incorrect because cartilage is a cushioning connective tissue found at joint surfaces and in structures like the nose and ear, not a bone-to-bone connector like ligaments. Option d is incorrect because fascia is a general connective tissue wrapping that surrounds muscles and organs, and it does not serve the specific bone-to-bone connecting function of ligaments.

Correct Answer: Ball-and-socket joint then hinge joint

Option d is correct because the ball-and-socket joint is the most mobile synovial joint allowing multiaxial movement, while the hinge joint is uniaxial and only permits flexion and extension. Option a is incorrect because a pivot joint allows only rotational movement around one axis and a saddle joint allows biaxial movement, neither matching the multiaxial-to-uniaxial pattern described. Option b is incorrect because this answer lists the joints in reverse order of mobility, placing the least mobile hinge joint first and the most mobile ball-and-socket joint second. Option c is incorrect because a saddle joint allows biaxial movement and a pivot joint allows only rotation, so neither represents the full multiaxial freedom described for the first patient.

Correct Answer: Cartilage with progenitor cells in collagen matrix

Option a is correct because cartilage is a connective tissue with progenitor cells in a collagen-rich matrix, found at joint surfaces and in the nose and ears, and it is largely avascular. Option b is incorrect because ligaments are fibrous connective tissue connecting bone to bone at joints and do not serve as cushioning surfaces at articular areas or form structural support in ears. Option c is incorrect because tendons are dense connective tissue that transmit muscular force to bone and are not found as cushioning surfaces at joints or in structures like the nose. Option d is incorrect because the periosteum is a fibrous membrane covering bone surfaces and contains osteogenic cells for bone repair, not the cushioning connective tissue found at joint surfaces.

Correct Answer: Reducing friction between articulating surfaces

Option b is correct because synovial fluid fills the synovial cavity of freely movable joints and its primary role is to lubricate and reduce friction between the articulating bone surfaces. Option a is incorrect because red blood cell production occurs through hematopoiesis in red bone marrow, not within synovial fluid or the synovial joint cavity itself. Option c is incorrect because connecting muscle to bone is the function of tendons, which are fibrous connective tissue structures, not a role performed by synovial fluid in joints. Option d is incorrect because rigid structural support is provided by the bones themselves and their surrounding ligaments, not by the lubricating synovial fluid inside the joint cavity.

Correct Answer: Skeletal, smooth, cardiac in that order

Option c is correct because striated fibers on bone are skeletal muscle, smooth spindle-shaped cells in vessel walls are smooth muscle, and striated fibers with intercalated discs are cardiac muscle. Option a is incorrect because cardiac muscle has intercalated discs and is found only in the heart, not attached to bone, and this ordering misidentifies the first and third tissue samples. Option b is incorrect because smooth muscle is non-striated and found in hollow organ walls, not the striped bone-attached fibers described as the first sample in the question scenario. Option d is incorrect because the second sample describes smooth non-striated cells in blood vessel walls, not cardiac tissue, making the placement of cardiac as the second sample wrong.

Correct Answer: Endomysium, perimysium, epimysium

Option a is correct because endomysium wraps individual muscle fibers, perimysium wraps bundles of fibers called fascicles, and epimysium wraps the entire muscle from innermost to outermost. Option b is incorrect because perimysium wraps fascicles at the middle level, not individual fibers at the innermost level, so placing it first in the sequence is out of order. Option c is incorrect because epimysium is the outermost wrapping around the entire muscle and should be listed last, not first, in a sequence going from smallest to largest structure. Option d is incorrect because epimysium wraps the whole muscle and should come after perimysium in the sequence, not between endomysium and perimysium as this option suggests.

Correct Answer: Troponin sitting on the actin filaments

Option d is correct because calcium binds specifically to troponin on actin filaments, causing a conformational change that shifts tropomyosin away from myosin-binding sites and enables cross-bridge formation. Option a is incorrect because tropomyosin is the blocking protein that covers myosin-binding sites on actin, and it is moved by troponin's shape change rather than directly binding calcium itself. Option b is incorrect because myosin is the motor protein forming thick filaments that pull on actin during contraction, but it is not the regulatory protein that calcium binds to initiate contraction. Option c is incorrect because actin forms the thin filaments and contains the binding sites for myosin, but it is not the specific regulatory protein that undergoes a shape change upon calcium binding.

Correct Answer: Myofibrils composed of actin and myosin

Option b is correct because myofibrils are the contractile units within each muscle fiber, composed of repeating arrangements of thin actin filaments and thick myosin filaments that generate force. Option a is incorrect because fascicles are bundles of muscle fibers wrapped in perimysium and are not the intracellular contractile units composed of actin and myosin protein filaments. Option c is incorrect because the sarcolemma is the cell membrane of a muscle fiber that conducts action potentials, not a contractile unit made of protein filaments inside the cell. Option d is incorrect because mitochondria are organelles that produce energy for cellular processes and are not the contractile units responsible for the physical pulling force of muscle contraction.

Correct Answer: Skeletal muscle attached to bones

Option c is correct because skeletal muscle is the only voluntary muscle type, meaning a person can consciously decide to contract or relax it for purposeful movements like walking or gripping. Option a is incorrect because cardiac muscle is involuntary and contracts automatically under the control of the heart's intrinsic pacemaker system without any conscious input from the individual. Option b is incorrect because smooth muscle is involuntary and operates automatically in the walls of hollow organs and blood vessels without requiring conscious effort or deliberate thought. Option d is incorrect because neither cardiac nor smooth muscle is under voluntary conscious control, as both function automatically through involuntary neural and hormonal regulatory mechanisms.