Which of the following is the result of increased concentration of red blood cells on blood pressure?

a. Acetylcholine: This is the primary neurotransmitter at neuromuscular junctions. It binds to receptors on muscle cells (specifically nicotinic acetylcholine receptors) and triggers an action potential, leading to muscle contraction.

b. Calcium: While calcium ions are essential for muscle contraction, they are not neurotransmitters. Instead, they play a role in the release of acetylcholine from the nerve terminal and in the contraction process within muscle cells.

c. Adenosine triphosphate (ATP): ATP is the primary energy carrier in cells but is not a neurotransmitter. It is crucial for muscle contraction, as it provides the energy for various steps in the contraction cycle.

d. Sodium: Sodium ions are involved in generating action potentials and depolarizing muscle cells, but they are not neurotransmitters.

a. Cartilage: Cartilage is a type of connective tissue found at the ends of bones in joints. It provides a smooth, elastic surface that cushions the bones and reduces friction during movement.

b. Tendon: Tendons are tough, fibrous bands that connect muscles to bones. They do not reduce friction at joints.

c. Fibrillin: Fibrillin is a protein component of connective tissue, but it's not a specific structure like cartilage and doesn't directly reduce friction in joints.

d. Osteocytes: Osteocytes are mature bone cells. They are not located at joints and don't play a role in friction reduction.