Which statement about mitosis and cytokinesis is TRUE?

The marked structure is the deltoid muscle, a large, thick, triangular muscle covering the shoulder joint and forming the rounded contour of the shoulder. It originates from the lateral third of the clavicle, the acromion, and the spine of the scapula, and inserts on the deltoid tuberosity of the humerus. The deltoid is the primary abductor of the arm at the glenohumeral joint, especially beyond the initial 15 degrees initiated by the supraspinatus. It is also involved in flexion, extension, and rotation of the shoulder depending on the muscle fibers activated.

A. Trapezius: The trapezius is a large, superficial muscle of the upper back extending from the occipital bone to the lower thoracic vertebrae and laterally to the scapula and clavicle. It functions in scapular elevation, retraction, depression, and rotation, contributing to posture and shoulder stabilization. Unlike the deltoid, it does not act directly on the humerus or produce shoulder abduction.

B. Biceps brachii: The biceps brachii is located in the anterior compartment of the upper arm and has two heads originating from the scapula. It primarily functions in elbow flexion and forearm supination. It is not a shoulder muscle and does not form the rounded contour of the shoulder like the deltoid.

C. Deltoid: The deltoid is a multipennate muscle covering the lateral shoulder, forming its rounded contour. It abducts the arm at the shoulder joint and assists in flexion, extension, and rotation depending on fiber orientation. It originates from the clavicle, acromion, and scapular spine and inserts on the humerus. Its superficial position and shoulder-covering shape make it the correct identification.

D. Latissimus dorsi: The latissimus dorsi is a broad, flat muscle of the back that extends from the lower thoracic spine, lumbar fascia, and iliac crest to the humerus. It functions in shoulder extension, adduction, and internal rotation. Compared to the deltoid, it is located posteriorly and inferiorly and does not form the shoulder’s rounded contour.

The cell structure represents cuboidal epithelial cells, which are characterized by their cube-like shape with approximately equal height and width and a centrally located, round nucleus. Cuboidal epithelium is commonly found in glandular tissue and kidney tubules, where it plays an important role in secretion and absorption. Its structural design provides a balance between surface area and cellular volume, allowing efficient metabolic and transport activities.

A. Squamous: Squamous cells are thin, flat, and scale-like in shape with flattened nuclei. They are specialized for diffusion and filtration due to their minimal thickness, as seen in structures like alveoli and capillary endothelium. Unlike cuboidal cells, they are not cube-shaped and are less involved in active secretion or absorption.

B. Cuboidal: Cuboidal cells are roughly square-shaped epithelial cells with centrally placed nuclei. They are well adapted for secretion and absorption due to a higher cytoplasmic volume compared to squamous cells. They commonly line kidney tubules, small ducts of glands, and thyroid follicles. Their equal height and width make them the correct identification.

C. Columnar: Columnar cells are tall, rectangular epithelial cells with nuclei typically located toward the basal region. They are specialized for absorption and secretion and often contain microvilli or cilia depending on location. Compared to cuboidal cells, they are taller than they are wide and are commonly found in the gastrointestinal tract rather than kidney tubules.

D. Stratified: Stratified epithelium refers to multiple layers of epithelial cells rather than a single cell shape. It is classified based on arrangement, not individual cell morphology. Its main function is protection against abrasion in areas like the skin and oral cavity. Unlike cuboidal cells, it does not describe a single cell shape but a tissue organization pattern.