While ligaments are used to connect a bone to another bone, tendons are used to attach muscles to bones. Tendons are made of collagen and are able to withstand great amounts of tension.

Joints refer to the general articulation between two bones can house several different structures. Tendons and ligaments often play key roles in joint mobility and stability. Fascia is the region of connective tissue found between and around muscles and can help anchor them to other nearby muscles or organs.

Tendons are formed at the ends of muscles, and are a compact version of muscle. The tendon connects the muscle to the bone to allow flexing and extension motions, transferring the force of muscle contraction to the bone to cause movement. Ligaments connect bone to bone and provide further support to the bones and skeleton by stabilizing joints.

The skeletal system is comprised of bones, bone marrow, ligaments, and cartilage. The skeletal system is responsible for a number of functions. Most prominently, the bones bear the weight of the body, provide attachment points for muscles, and are responsible for locomotion. Bones also serve as stores for calcium and phosphorus. Red bone marrow is responsible for producing erythrocytes and the cells of the immune system, while yellow bone marrow plays a key role in fat storage.

The bones can be broken into two main categories: the axial skeleton and the appendicular skeleton. The bones that make up the axial skeleton are the vertebral column, thoracic cage, hyoid bone, and the skull. The appendicular skeleton is made of the upper and lower limbs, the pelvic girdle, and the pectoral girdle.

Cartilage serves to provide cushioning between bones, and ligaments are essential for maintaining stability.

Functions of the skeletal system include support, protection, mineral storage, and hematopoiesis. The structure of bones and their coordinated function with muscles, ligaments, and tendons allow for movement and support of the body. They also provide protection of vital organs, such as the rib cage surrounding the heart and pelvis protecting reproductive organs. Calcium and phosphate are stored in the hydroxyapatite matrix of the bone and hematopoiesis, the generation of red blood cells, takes place in red bone marrow, which houses hematopoietic stem cells.

Several systems coordinate thermoregulation, but ultimately this function is performed by the muscles. Muscles are responsible for most ATP usage in the body. Break down of ATP releases heat, which is why we shiver when we are cold. Regulation of blood flow and actions of the integumentary system also contribute to thermoregulation in other manners.

The correct answer is osteons. An osteon (or haversian system) is the fundamental unit of most compact bone. Osteons are formed during the process of bone remodeling, but are not one of the three types of cells involved in bone homeostasis.

Bone homeostasis involves the development, growth and remodeling of bones. The three cell types responsible for these processes are osteoblasts, osteocytes and osteoclasts. Each cell type refers to a different process:

• osteoblasts = bone forming cells
• osteocytes = mature bone cells
• osteoclasts = break down and reabsorb bone

All of these layers make up hyaline cartilage. The superficial layer is distinguished by the parallel (relative to the articular surface) arrangement of it's collagen fibers. The middle zone is characterized by the oblique orientation of its fibers. The deep zone has collagen fibers that are oriented perpendicularly to the articular surface. The calcified layer connects directly to the underlying (subchondral) bone.

The ends of long bones, called epiphyses, contain spongy bone. Spongy bone contains red bone marrow, which is the site of erythropoiesis.

The shaft of the long bone is the diaphysis and houses yellow bone marrow, which mainly functions for fat storage. Articular cartilage is found on the exterior of the bone and helps to lubricate and provide cushioning for joints. Lacunae are small gaps in the hydroxyapatite matrix that house osteocytes. The Haversian canal runs through the center of an osteon and serves to house the blood vessels and nerves associated with bone.

The bone marrow makes new red blood cells in a process called erythropoiesis. This is stimulated by the kidneys detecting decreased levels of oxygen in the blood stream. They then release a hormone called erythropoietin which stimulates the bone marrow to make more erythrocytes or red blood cells.

The correct answer is red marrow.

Hematopoiesis is the formation of blood cells, which is a function of red marrow. Red marrow forms red blood cells, white blood cells and blood platelets. The process beings with a stem cell that proliferates (reproduces rapidly), differentiates (becomes a specialized cell) and replicates (duplicates).

The other choices are all parts of bones, but have different functions/characteristics besides hematopoiesis. While red marrow contains the red and white blood cells and blood platelets, yellow marrow consists of mostly fat cells. Compact bones are hard and contain closely packed osteons that form a solid mass. The periosteum is the connective tissue covering the surface of a bone. Spongy bones are less dense than compact bone and are lighter than compact bones. It contains plates (trabeculae) of bone and cavities that contain the red marrow.

While humoral immunity and cell-mediated immunity play different roles in the immune system, both systems require helper T-cells. B-lymphocytes must interact with helper T-cells in order to differentiate into plasma and memory B-cells, initiating the humoral immune response. Helper T-cells are also necessary for activating cytotoxic and suppressor T-cells in cell-mediated immunity.

Basophils are not involved in adaptive immunity of any type; they are responsible for inflammation and certain other processes in innate immunity.