Skeletal Physiology

Types of Bones

A) Long bones are easily identified by their extended longitudinal axes and expanded and often uniquely shaped articular ends. Examples are the femur of the thigh and the humerus of the arm.B) Short bones are often described as cube-or box-shaped structures, which are about as broad as they are long. Examples are the wrist (carpals) and ankle (tarsal) bones.C) Flat bones are generally broad and thin with a flattened and often curved surface. Examples are certain bones of the skull, the shoulder blades (scapulae), ribs, and breastbone (sternum).D) Irregular bones are often clustered in groups and come in various sizes and shapes. An example is the kneecap (patella).

The Long Bone

a) Diaphysis: main shaft like portion.b) Epiphyses: both ends of a long bone.c) Articular cartilage: thin layer of hyaline cartilage that covers articular or joint surfaces of epiphyses.d) Periosteum: dense, white fibrous membrane that covers bone except at joint surfaces, where articular cartilage forms the covering.e) Medullary (or marrow) cavity: a tube like hollow space in the diaphysis of a long bone.f) Endosteum: a thin epithelial membrane that lines the medullary cavity of long bones.

Bones Cont.

It consists of cells, fibers, and extracellular material also known as matrix. Its extracellular components are hard and calcified. In bone the extracellular material, or matrix, predominates. The rigidity of bone enables it to serve supportive and protective functions. As a tissue, bone is ideally suited to its functions, and the concept that structure and function are interrelated is apparent in this tissue. It has a tensile strength nearly equal to cast iron but at less than one third the weight. Bone is organized so that its great strength and minimal weight result from the interrelationships of its structural components.

The Haversian System

Lamellae- Concentric, cylinder-shaped layers of calcified matrix.Lacunae- Small spaced containing tissue fluid in which bone cells lie imprisoned between the hard layer of the lamellae.Canaliculi- Ultrasmall canals radiating in all directions from the lacunae and connecting them to each other and into a larger canal (The Haversian Canal)Haversian Canal- extends lengthwise through the center or each Haversian System; contains blood vessels, lymphatic vessels, and nerves from the haversian canal; nutrients and oxygen move through canaliculi to the lacunae and their bone cells

Cells in Bones

Osteoclasts: Osteoclasts are large cells that dissolve the bone. They come from the bone marrow and are related to white blood cells. They usually have more than one nucleus and are found on the surface of the bone mineral.Osteoblasts: Osteoblasts are cells that form new bones. They come from bone marrow and are related to structural cells. They only have one nucleus and they produce new bone called “osteoid” which is made of bone collagen and other proteins. They also control calcium and mineral deposition. They are found on the surface of new bone. Old osteoblasts are called lining cells that regulate the passage of calcium in and out of the bone. They also respond to hormones that create protein that activate osteoclasts.Osteocytes: These cells are found inside the bone that come from osteoblasts. Some turn into osteocytes while the new bone is being formed. These cells can sense pressures or cracks in the bone and help direct where the osteoclasts will dissolve the bone.

Homeostatic Functions

1.Support: Bones are the supporting framework in the body and contribute to shape, alignment, and positioning of the body parts. This involves homeostasis because without support we would have nothing to hold our weight. We would be a glob of blood and organs.

2.Protection: Bones protect the body from the external environment. Bones also protect the structures that they enclose. Without protection from bones we would easily get hurt because there would be nothing to prevent objects from hurting our organs or easily crushing our internal parts. By having protection we can endure more difficult tasks and participate in more rigorous activities.

3.Movement: Muscles are anchored to bones. As the muscles move, they pull on bones, producing movement. Without movement it would be hard to maintain our body temperature because we wouldn't be able to get warm when it’s cold or get cold when it’s hot.

4.Mineral Storage: Bones serve as the major place for calcium, phosphorus, and other minerals. Homeostasis of blood calcium concentration depends a lot on changes in the rate of calcium movement between the blood and bones. For example, if blood calcium moves faster out of the blood into bones and more slowly in the opposite direction, blood calcium concentration decreases. This is essential for healthy survival.

5.Hematopoiesis: Hematopoiesis is another word for blood cell formation. This is the vital process carried on by red bone marrow. This is important because it keeps the body in balance. It helps regulate differences in the body such as infections or fevers.

Intramembranous and Endochondral bone

Intramembranous Bone (flat bones): Membranous bones first look like flat, membrane-like layers. These layers have a continuing flow of nutrient blood supply from blood vessels that are formed between the layers. In the beginning, connective tissue cells situate themselves among the layers and then form into osteoblasts which are bone-forming cells. Osteoblasts remove calcium from the blood and put it in the bone matrix. As a result, layers of spongy bone form around the original cartilage. Later, spaces among the spongy bone fill with bone matrix to become compact bone. The osteoblasts keep depositing calcium supplements into the matrix until it is completely surrounded by it. After, the osteoblasts are considered to be in the lacunae and are called osteocytes. Broad, flat skull bones are examples of intramembranous ossification.

Intramembranous and Endochondral bone

Endochondral bone(long bones). This ossification forms bone by replacing a cartilaginous model that is earlier in embryonic development. These models first undergo changes as the connective tissue gets bigger, destroying surrounding matrix. Soon after, connective tissue cells die. As the cells die, a periosteum is formed on the outside of the developing structure. Next, blood vessels and other cells rush into the dying tissue. Once a significant amount of spongy bone is formed, growth in the cartilage bones occurs. Thickness in cartilage bones is done by intramembrous ossification. Beneath the layer of periosteum, compact bone is formed and hardened with the help of osteoblasts filling portions of the spongy bone with calcium phosphate crystals. Sometimes the compact bone is formed on the surfaces of existing bone tissue and osteoblasts must get rid of them. The crystals are then delivered to blood and tissues.

Similarities

Similarities: Both processes create bone and sometimes the creation of bone requires both endochondral and intramembranous ossification. When both processes are used, mesenchyme cells develop into chondroblasts and increase in number by cell division. The chondroblasts get bigger and excrete a matrix which hardens due to presence or inorganic minerals. Then, chambers form within the matrix and osteoblasts and blood-forming cells enter these chambers. The osteoblasts then secrete minerals to form the bone matrix

Bone Fracture Repair

1. Fracture has occured2. Formation of a fracture hematoma3.Formation of an internal and external callus4.Bone remodeling completes

Types of Cartilage

Hyaline Cartilage- the most common type of cartilage, it appears gelatinous and glossyElastic Cartilage- cartilage with elastic, as well as collagenous fibers; provides elasticity and firmnessFibrocartilage-cartilage with the greatest number of collagenous fibers; strongest and most durable type of cartilage

Types of Cartilage

Hyaline CartilageFibrocartilage

Elastic Cartilage