Skeletal System — Set 2

Correct Answer: A. Immovable joints

• **Immovable joints** = Sutures are fibrous joints (synarthroses) where the adjacent skull bones are tightly bound by Sharpey's fibres; no movement is possible, providing rigid protection for the brain. • **Key fact** — In infants, sutures are wider and the gaps are called fontanelles (soft spots), which allow the skull to compress slightly during birth and expand rapidly during early brain growth; they fuse completely by about age 2. • Major skull sutures include the coronal (frontal + parietals), sagittal (between two parietals), and lambdoid (parietals + occipital). • 💡 Option B (Synovial joints) is wrong because synovial joints have a fluid-filled cavity and are freely movable, the opposite of sutures; Option C (Slightly movable joints) is wrong because amphiarthroses like the pubic symphysis allow slight movement — sutures allow none; Option D (Freely movable joints) is wrong because diarthroses like the shoulder move freely, unlike sutures.

Correct Answer: A. Humerus

• **Humerus** = The humerus is the single long bone of the upper arm, running from the shoulder (where it forms the ball of the ball-and-socket joint with the scapula) down to the elbow (where it articulates with the radius and ulna). • **Key fact** — The radial nerve runs in the spiral groove of the humerus, so a mid-shaft fracture of the humerus can cause wrist drop due to radial nerve damage — a classic exam association. • The humerus provides attachment to major muscles of the shoulder (deltoid) and the arm (biceps, triceps, brachialis). • 💡 Option B (Ulna) is wrong because the ulna is one of the two forearm bones; Option C (Femur) is wrong because the femur is the thigh bone in the lower limb; Option D (Radius) is wrong because the radius is the other forearm bone on the thumb side.

Correct Answer: D. 33

• **33** = At birth the human vertebral column has 33 individual vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. • **Key fact** — In adults, the count reduces to 26 because the 5 sacral vertebrae fuse into one sacrum and the 4 coccygeal vertebrae fuse into one coccyx — but at birth all 33 exist as separate bones. • The cervical vertebrae are the smallest and most mobile; the lumbar are the largest and bear the most body weight. • 💡 Option A (30) is wrong because no standard anatomy recognises 30 vertebrae at any stage; Option B (22) is wrong because 22 is the number of skull bones; Option C (26) is wrong because 26 is the adult count after sacral and coccygeal fusion, not the birth count.

Correct Answer: C. Shoulder joint

• **Shoulder joint** = The glenohumeral (shoulder) joint is a ball-and-socket joint where the rounded head of the humerus (ball) fits into the shallow glenoid cavity of the scapula (socket), allowing movement in all planes — flexion, extension, abduction, adduction, rotation, and circumduction. • **Key fact** — Because the socket is very shallow to allow maximum mobility, the shoulder is the most commonly dislocated joint in the body; stability depends mainly on the rotator cuff muscles rather than bony congruence. • The hip joint is the other major ball-and-socket joint, but it is far more stable because the acetabulum is much deeper. • 💡 Option A (Knee joint) is wrong because the knee is primarily a hinge joint allowing flexion and extension; Option B (Wrist joint) is wrong because the wrist is an ellipsoid (condyloid) joint; Option D (Elbow joint) is wrong because the elbow is a hinge joint.

Correct Answer: B. Knee cap

• **Knee cap** = The patella is a triangular sesamoid bone embedded in the quadriceps tendon at the front of the knee; because it sits over and protects the knee joint, it is universally called the 'knee cap.' • **Key fact** — As a sesamoid bone, the patella develops within a tendon (not from a separate ossification centre like most bones) and its function is to increase the mechanical advantage of the quadriceps by holding the tendon away from the joint axis, multiplying the extension force by about 30%. • The patella is the largest sesamoid bone in the human body. • 💡 Option A (Wrist bone) is wrong because wrist bones are called carpals; Option C (Ankle bone) is wrong because the ankle bone is the talus; Option D (Elbow cap) is wrong because no sesamoid caps the elbow — the bony point of the elbow is the olecranon process of the ulna.

Correct Answer: D. Marrow

• **Marrow** = Bone marrow is the soft, spongy tissue that fills the internal cavities (medullary cavity and spaces in cancellous bone) of bones; it exists in two forms — red marrow (haematopoietic) and yellow marrow (predominantly adipose/fat tissue). • **Key fact** — In newborns, almost all marrow is red (actively making blood cells); as a person ages, red marrow is progressively replaced by yellow marrow in the long-bone shafts, with red marrow retained mainly in flat and irregular bones in adults. • Bone marrow transplants (stem cell transplants) treat leukaemia and other blood disorders by replacing diseased marrow with healthy donor cells. • 💡 Option A (Cartilage) is wrong because cartilage is a flexible connective tissue covering joint surfaces, not the marrow cavity; Option B (Tendon) is wrong because tendons connect muscle to bone; Option C (Ligament) is wrong because ligaments connect bone to bone at joints.

Correct Answer: C. Sternum

• **Sternum** = The sternum (breastbone) is a flat, dagger-shaped bone in the midline of the anterior chest wall; together with the ribs and costal cartilages it forms the thoracic cage that encases and protects the heart and lungs. • **Key fact** — The sternum has three parts: the manubrium (top), the body (middle, largest), and the xiphoid process (inferior tip); the sternal angle (manubriosternal junction) is a key anatomical landmark at the level of the 2nd rib. • During CPR, compressions are applied to the lower half of the sternum to indirectly compress the heart and maintain circulation. • 💡 Option A (Scapula) is wrong because the scapula is the shoulder blade at the back of the thorax, not the front; Option B (Vertebra) is wrong because vertebrae protect the spinal cord, not the heart and lungs directly; Option D (Clavicle) is wrong because the clavicle is the collar bone connecting the sternum to the shoulder.

Correct Answer: A. 8 bones

• **8 bones** = The carpus (wrist) of each hand is made up of 8 carpal bones arranged in two rows of four: proximal row — scaphoid, lunate, triquetrum, pisiform; distal row — trapezium, trapezoid, capitate, hamate. • **Key fact** — A useful mnemonic: 'Some Lovers Try Positions That They Can't Handle' (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate). The scaphoid is the most commonly fractured carpal bone. • The 8 carpal bones, combined with 5 metacarpals and 14 phalanges, give each hand a total of 27 bones. • 💡 Option B (5 bones) is wrong because 5 is the number of metacarpals (palm bones); Option C (14 bones) is wrong because 14 is the number of phalanges (finger bones) per hand; Option D (7 bones) is wrong because no anatomical grouping in the hand contains exactly 7.

Correct Answer: A. Osteoporosis

• **Osteoporosis** = Osteoporosis ('porous bone') is a metabolic bone disease in which bone mineral density decreases and bone microarchitecture deteriorates, making bones brittle and prone to fractures even with minimal trauma. • **Key fact** — It is most common in post-menopausal women because oestrogen normally inhibits osteoclast activity; after menopause, osteoclasts resorb bone faster than osteoblasts can build it, causing net bone loss. • A T-score of −2.5 or lower on a DEXA scan diagnoses osteoporosis; hip and vertebral fractures are its most dangerous complications. • 💡 Option B (Arthritis) is wrong because arthritis is inflammation of joints, not loss of bone density; Option C (Rickets) is wrong because rickets causes soft bones in children due to vitamin D deficiency, not age-related density loss; Option D (Scurvy) is wrong because scurvy is caused by vitamin C deficiency and affects collagen/connective tissue, causing bleeding gums, not the specific density loss of osteoporosis.

Correct Answer: B. Synovial fluid

• **Synovial fluid** = Synovial fluid is a viscous, egg-white-like fluid secreted by the synovial membrane that lines freely movable (diarthrodial) joints; it lubricates the articular cartilage, reduces friction, absorbs shock, and nourishes the avascular cartilage. • **Key fact** — Synovial fluid gets its name from the Latin 'synovia' (resembling egg white); its viscosity comes from hyaluronic acid produced by synoviocytes, and it also contains lubricin, a glycoprotein that prevents cartilage-to-cartilage adhesion. • In inflammatory conditions like rheumatoid arthritis, the synovial membrane thickens (pannus formation) and produces excess, inflammatory fluid that damages cartilage. • 💡 Option A (Lymph) is wrong because lymph is the fluid in lymphatic vessels that drains interstitial tissue, not joints; Option C (Plasma) is wrong because plasma is the liquid component of blood; Option D (Cerebrospinal fluid) is wrong because CSF cushions the brain and spinal cord inside the CNS, not the joints.