This lesson will provide an overview on some fundamentals of bones, including:
Bones are the basic the building blocks of the skeletal system. A bone is a connective tissue of cells and fibers covered by a membrane called the periosteum. The periosteum is a two-layered connective tissue that is found on the outside of all bones; it supports, nourishes, and protects the bones of the body.
Two types of cells are important in bone growth and bone structure:
This type of cell is found in the second layer of the periosteum, and is responsible for building bone. An osteoblast builds bone tissue by secreting collagen fibers that bind to calcium; this combination forms the tough tissue matrix of bone. The area around it will mineralize (requiring calcium); when mineralized, it becomes an osteocyte. Osteocytes are mature bone cells and will no longer form bone matrix.
An osteoclast is a cell that breaks down bone tissue by secreting hydrochloric acid into the tissue spaces, dissolving the bond between calcium and collagen.
Why do we have cells that build bone, and cells that break down bone?
Both these types of bone cells are important for a process called bone remodeling. Bone remodeling allows your body to maintain calcium levels; you need certain levels of calcium in your blood. If calcium levels in your blood are too low, osteoclasts will break down bone and release calcium into the blood. Osteoblasts will help build bone if there's excess calcium in the blood. This helps keep bones resilient.
There are two types of bone tissue, and their names give you an idea of what they're like:
1. Spongy Bone
Spongy bone is thin beams of compact bone that are found in the ends of long bones and within flat bones. Spongy bone is porous and lighter in weight. It is basically made up of tiny flattened struts that are fused together in a web. It is a fairly strong type of bone.
2. Compact Bone
Compact bone tissue consists of many osteons and a dense tissue matrix; cells of the osteons surround central canals called Haversian canals, found in the shafts of long bones and the periphery of spongy bone. Compact bone forms in circular layers, and each of the circular layers is called an osteon.
The osteon is the functional unit of bone; it is circular in nature and contains a hollow central canal (Haversian canal) that is surrounded by bone cells (osteocytes). In this hollow canal is room for blood vessels and nerves. Blood vessels will carry substances to and from osteocytes.
Bones also contain two types of bone marrow:
1. Yellow Bone Marrow
In adults, most bone marrow is actually yellow bone marrow, which serves as fat storage.
2. Red Bone Marrow
This type of bone marrow produces red blood cells and white blood cells, but most adults do not have a lot of red bone marrow. It can be found in a few flat bones within your body.
Bone marrow is a substance that is found within the hollow areas of bone. Red marrow is found within the spongy bones, and yellow marrow is found in the shaft (diaphysis) of long bones.
Question: If you don’t have a lot of red bone marrow, and you were in some sort of accident, how would your body compensate for major blood loss?
Answer: Your bone marrow would need to produce more red blood cells to replace the blood that you've lost. Yellow bone marrow can actually convert back to red bone marrow if necessary.
Periosteum is the two-layer membrane found on the outside of the bone. Inside the bone, there are two different types of bone tissue— spongy bone and compact bone. The bone shaft is the center part of the bone where both yellow and red bone marrow are found.
The cartilage model is the model that is used to describe how bone is manufactured from embryonic cartilage. Over time, the cartilage that composes bone will be turned into actual bone by osteoblasts. The building of bone starts from the middle of the bone, and works its way outward.
The epiphyseal plate is a part of the bone that's made of cartilage, and separates the shaft from the epiphysis. The epiphysis is the enlarged ends of long bones that contains spongy bone and yellow bone marrow. The exceptions are the head of the humerus and femur, which contain red marrow.
A bone of a developing embryo will be made of cartilage. Then the osteoblasts are going to become active. They will form a bony collar, and then the bone will start to mineralize. From there, it will grow outwards. Blood vessels will start to invade, more bone tissue will form, and bone remodeling will continue to take place— building more bone from the middle outwards. Then secondary bone-forming centers will appear at the end.
The human growth hormone, HGH, prevents the epiphyseal plate from calcifying until the person is done growing.
This diagram shows how a bone develops over time.
The structure of bone includes several different components. Bone is covered and protected by a membrane called the periosteum. There are two types of cells needed for bone growth and development: osteoblasts, which build bone, and osteoclasts, which break down bone. Inside the bone are spongy bone and compact bone tissue. Bone also contains bone marrow, both yellow and red. Yellow bone marrow serves as fat storage and can convert to red bone marrow when needed. Red bone marrow produces red and white blood cells. The Function of bone is to give support and protection to our bodies and organs.
The cartilage model describes the process of bone growth and development. Bones begin as cartilage. The bone-forming areas at the ends work their way out from the middle of the bone. The epiphyseal plate is the cartilage plate that separates the epiphysis (the end of the bone) from the shaft.
Keep up the learning and have a great day!
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND
A connective tissue of cells and fibers covered by a membrane called the periosteum.
A substance that is found within the hollow areas of bone, red marrow is found within the spongy bones and yellow marrow is found in the shaft (diaphysis) of long bones.
The model that is used to describe how bone is manufactured from embryonic cartilage.
A type of bone tissue that consists of many osteons and a dense tissue matrix; cells of the osteons surround central canals called Haversian canals; found in the shafts of long bones and periphery of spongy bone.
Enlarged ends of long bones that contains spongy bone and yellow bone marrow, except the head of the humerus and femur (contains red marrow).
A cell that builds bone tissue by secreting collagen fibers that bind to calcium; this combination forms the tough tissue matrix of bone.
A cell that breaks down bone tissue by secreting hydrochloric acid into the tissue spaces; dissolves the bond between calcium and collagen.
The functional unit of bone, is circular in nature and contains a hollow central canal (Haversian canal) that is surrounded by bone cells (osteocytes).
A two layered connective tissue that is found on the outside of all bones; it supports, nourishes and protects bones of the body.
Thin beams of compact bone that are found in the ends of long bones and the middle of spongy bone; is porous and lighter in weight.