Types of BonesA) Long bones are easily identified by their extendedlongitudinal axes and expanded and often uniquely shapedarticular ends. Examples are the femur of the thigh and thehumerus of the arm.B) Short bones are often described as cube-or box-shapedstructures, 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 andoften 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 invarious sizes and shapes. An example is the kneecap (patella).
The Long Bonea) Diaphysis: main shaft like portion.b) Epiphyses: both ends of a long bone.c) Articular cartilage: thin layer of hyaline cartilagethat covers articular or joint surfaces of epiphyses.d) Periosteum: dense, white fibrous membrane thatcovers bone except at joint surfaces, wherearticular cartilage forms the covering.e) Medullary (or marrow) cavity: a tube like hollowspace in the diaphysis of a long bone.f) Endosteum: a thin epithelial membrane that linesthe medullary cavity of long bones.
Bones Cont.It consists of cells, fibers, and extracellular materialalso known as matrix. Its extracellular componentsare hard and calcified. In bone the extracellularmaterial, or matrix, predominates. The rigidity ofbone enables it to serve supportive and protectivefunctions. As a tissue, bone is ideally suited to itsfunctions, and the concept that structure andfunction are interrelated is apparent in this tissue. Ithas a tensile strength nearly equal to cast iron butat less than one third the weight. Bone is organizedso that its great strength and minimal weight resultfrom the interrelationships of its structuralcomponents.
The Haversian SystemLamellae- Concentric, cylinder-shaped layers of calcifiedmatrix.Lacunae- Small spaced containing tissue fluid in whichbone cells lie imprisoned between the hard layer of thelamellae.Canaliculi- Ultrasmall canals radiating in all directionsfrom the lacunae and connecting them to each other andinto a larger canal (The Haversian Canal)Haversian Canal- extends lengthwise through the centeror each Haversian System; contains blood vessels,lymphatic vessels, and nerves from the haversian canal;nutrients and oxygen move through canaliculi to thelacunae and their bone cells
Cells in BonesOsteoclasts: Osteoclasts are large cells that dissolve the bone. Theycome from the bone marrow and are related to white blood cells. Theyusually have more than one nucleus and are found on the surface ofthe bone mineral.Osteoblasts: Osteoblasts are cells that form new bones. They comefrom bone marrow and are related to structural cells. They only haveone nucleus and they produce new bone called “osteoid” which ismade of bone collagen and other proteins. They also control calciumand mineral deposition. They are found on the surface of new bone.Old osteoblasts are called lining cells that regulate the passage ofcalcium in and out of the bone. They also respond to hormones thatcreate protein that activate osteoclasts.Osteocytes: These cells are found inside the bone that come fromosteoblasts. Some turn into osteocytes while the new bone is beingformed. These cells can sense pressures or cracks in the bone andhelp direct where the osteoclasts will dissolve the bone.
Homeostatic Functions1.Support: Bones are the supporting framework in the body and contribute to shape,alignment, and positioning of the body parts. This involves homeostasis because withoutsupport we would have nothing to hold our weight. We would be a glob of blood andorgans.2.Protection: Bones protect the body from the external environment. Bones also protectthe structures that they enclose. Without protection from bones we would easily get hurtbecause there would be nothing to prevent objects from hurting our organs or easilycrushing our internal parts. By having protection we can endure more difficult tasks andparticipate 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 bodytemperature because we wouldnt be able to get warm when it’s cold or get cold when it’shot.4.Mineral Storage: Bones serve as the major place for calcium, phosphorus, and otherminerals. Homeostasis of blood calcium concentration depends a lot on changes in therate of calcium movement between the blood and bones. For example, if blood calciummoves faster out of the blood into bones and more slowly in the opposite direction, bloodcalcium concentration decreases. This is essential for healthy survival.5.Hematopoiesis: Hematopoiesis is another word for blood cell formation. This is the vitalprocess carried on by red bone marrow. This is important because it keeps the body inbalance. It helps regulate differences in the body such as infections or fevers.
Intramembranous andEndochondral boneIntramembranous Bone (flat bones): Membranous bones firstlook like flat, membrane-like layers. These layers have acontinuing flow of nutrient blood supply from blood vesselsthat are formed between the layers. In the beginning,connective tissue cells situate themselves among the layersand then form into osteoblasts which are bone-forming cells.Osteoblasts remove calcium from the blood and put it in thebone matrix. As a result, layers of spongy bone form aroundthe original cartilage. Later, spaces among the spongy bone fillwith bone matrix to become compact bone. The osteoblastskeep depositing calcium supplements into the matrix until it iscompletely surrounded by it. After, the osteoblasts areconsidered to be in the lacunae and are called osteocytes.Broad, flat skull bones are examples of intramembranousossification.
Intramembranous andEndochondral boneEndochondral bone(long bones). This ossification forms bone byreplacing a cartilaginous model that is earlier in embryonicdevelopment. These models first undergo changes as theconnective tissue gets bigger, destroying surrounding matrix.Soon after, connective tissue cells die. As the cells die, aperiosteum is formed on the outside of the developing structure.Next, blood vessels and other cells rush into the dying tissue. Oncea significant amount of spongy bone is formed, growth in thecartilage bones occurs. Thickness in cartilage bones is done byintramembrous ossification. Beneath the layer of periosteum,compact bone is formed and hardened with the help ofosteoblasts filling portions of the spongy bone with calciumphosphate crystals. Sometimes the compact bone is formed onthe surfaces of existing bone tissue and osteoblasts must get ridof them. The crystals are then delivered to blood and tissues.
SimilaritiesSimilarities: Both processes create bone andsometimes the creation of bone requires bothendochondral and intramembranous ossification.When both processes are used, mesenchyme cellsdevelop into chondroblasts and increase in numberby cell division. The chondroblasts get bigger andexcrete a matrix which hardens due to presence orinorganic minerals. Then, chambers form within thematrix and osteoblasts and blood-forming cellsenter these chambers. The osteoblasts thensecrete minerals to form the bone matrix
Bone Fracture Repair1. Fracture hasoccured2. Formation of afracture hematoma3.Formation of aninternal andexternal callus4.Bone remodelingcompletes
Types of CartilageHyaline Cartilage- the most common typeof cartilage, it appears gelatinous andglossyElastic Cartilage- cartilage with elastic, aswell as collagenous fibers; provideselasticity and firmnessFibrocartilage-cartilage with the greatestnumber of collagenous fibers; strongestand most durable type of cartilage
Types of Cartilage Elastic CartilageHyaline Cartilage Fibrocartilage