10.10: Blood and Nerve Supply to the Bones
Bones are dynamic organs that require a rich supply of oxygen and nutrients. Around 5% to 10% of the cardiac output supplies blood to the bones. A typical long bone has three main sources: the nutrient artery, the metaphyseal and epiphyseal arteries, and the periosteal arteries.
Nutrient Artery
The nutrient artery is the main blood vessel that enters the diaphysis via the nutrient foramen. While most long bones have only one nutrient foramen, large bones, such as the femur, may have two. This high-pressure arterial system branches into the main ascending and descending branches that run parallel to the long axis of the bone. They then branch out radially into smaller vessels to supply the bone marrow in the medullary cavity and the inner two-thirds of compact bone.
Metaphyseal and Epiphyseal Arteries
The metaphyseal arteries enter the bone transversely at the metaphyses to supply blood to the spongy bone. These arteries repeatedly divide to form a profuse network of small vessels that supply the trabeculae of the spongy bone. The blood vessels combine and fuse with the dense network that emerges from the main nutrient branches, making the metaphyses the most vascular region of the bone. Another set of arteries, the epiphyseal arteries, enter the epiphyses and branch out to form a network of small vessels that supply the red bone marrow and spongy bone.
Periosteal Arteries
Numerous blood vessels found in the proximity of the periosteum throughout the bone surface enter transversely via Volkmann's canals. This low-pressure system supplies blood to the outer one-third of the compact bone via the Haversian canals of the osteons.
Venous System
Blood from the bone drains away via a network of veins that follow paths similar to the arterial system. The epiphyseal and metaphyseal veins drain out of the epiphyses and metaphyses, respectively. The radial vasculature of the diaphysis collects into one or two nutrient veins, which exit the bone via the nutrient foramen. Blood from the outer compact bone drains via numerous periosteal veins that exit via the periosteum.
Nervous System in Bones
The bone has a rich nerve supply that follows similar paths to the blood vessels. These sensory nerves are particularly abundant in the periosteum of the bone. The nerves detect damage, such as tearing or tension and relay the pain signals to the brain. Thus, bone damage can be very painful, especially damage that affects the periosteum. For example, during a bone marrow biopsy, the patient feels pain as the needle pierces the periosteum. But once it is through and reaches the spongy bone marrow, the degree of pain reduces.
