The skeletal system is composed of bones and associated tissues that provide structure, protection, movement, and mineral storage. Bones are living tissues composed of cells, collagen fibers, and minerals. There are four types of bones - long, short, flat, and irregular - with different structures adapted to their functions. Bones develop through intramembranous or endochondral ossification and are remodeled throughout life by bone cells.
Bone tissue is a specialized form of connective tissue composed of cells and a mineralized extracellular matrix. The matrix is made up of collagen fibers and hydroxyapatite crystals that give bone its rigidity. There are two types of bone tissue: compact bone which forms the dense outer layer, and spongy or cancellous bone which is found at the ends of long bones and has a spongy, mesh-like structure. Bones develop through two processes - intramembranous ossification which forms flat bones, and endochondral ossification where cartilage is replaced by bone to form most other bones including long bones.
1. Muscle tissue is one of four primary tissue types and is divided into three main categories: skeletal, cardiac, and smooth muscle. Skeletal muscle is attached to bones and allows voluntary movement.
2. Skeletal muscle contains bundles of fibers surrounded by connective tissues. Within the fibers are myofibrils composed of thin actin filaments and thick myosin filaments that slide past each other to cause muscle contraction.
3. Contraction is triggered when a motor neuron stimulates the neuromuscular junction, causing calcium release and the myosin heads to interact with and pull on the actin filaments. The strength of contraction depends on factors like overlap of filaments and stimulation frequency.
This document provides an overview of muscle tissue histophysiology. It discusses the structural unit of muscle tissue as muscle fibers. It describes the organization of skeletal muscles into myofibrils, sarcomeres, and myofilaments. It explains the sliding filament theory of muscle contraction and how calcium targets activate myofilament sliding. It also discusses dystrophin's role in muscle fiber stability and protection from contraction damage. Smooth muscle tissue types and their roles in organs like the GI tract and blood vessels are outlined. The molecular organization of filaments and caveolae structures in smooth muscle are briefly touched on.
Connective tissue is the tissue that connects or separates, and supports all the other types of tissues in the body. Like all tissue types, it consists of cells surrounded by a compartment of fluid called the extracellular matrix (ECM). However connective tissue differs from other types in that its cells are loosely, rather than tightly, packed within the ECM.
1) The document discusses the three types of muscular tissue - skeletal, cardiac, and smooth muscle.
2) Skeletal muscle is striated, voluntary muscle attached to bones. It contains bundles of fibers surrounded by connective tissue. Microscopically, it contains myofibrils with repeating dark A and light I bands.
3) Cardiac muscle is striated and involuntary. Microscopically, its branching fibers are joined end to end at intercalated discs.
4) Smooth muscle is non-striated and present in organs like blood vessels. Microscopically, its spindle-shaped cells are arranged in bundles and layers connected by gap junctions.
The skeletal system has several important functions:
1. It provides structure and support for the body, protects internal organs, and allows for movement through muscle attachment points.
2. Bones store minerals like calcium and aid in mineral homeostasis. Certain bones also produce blood cells.
3. The skeletal system is composed of bones, cartilage, ligaments, and tendons. Bones are living tissues with osteogenic cells, osteoblasts, osteocytes, and osteoclasts. They have an extracellular matrix containing collagen and minerals like hydroxyapatite.
This document provides an introduction to the field of histology. It defines histology as the study of tissues and organs under the microscope. The document discusses the types of microscopes used in histology, including light and electron microscopes. It also covers basic histological techniques like staining and the structures that different stains highlight. The four basic tissue types - epithelial, connective, muscular and nervous tissues - are introduced along with examples of systemic histology looking at specific organ systems.
Cartilage is a specialized connective tissue composed of chondrocytes embedded in an extracellular matrix. It is avascular and provides structure, support, and acts as a shock absorber. There are three main types of cartilage - hyaline cartilage found in joints, elastic cartilage in the ear, and fibrocartilage in intervertebral discs. Hyaline cartilage contains collagen type II and glycosaminoglycans that allow it to withstand compression. Elastic cartilage contains elastic fibers that give it flexibility. Fibrocartilage contains collagen types I and II and connects bones together.
Connective tissue is one of the four main tissue types found throughout the body. It is the most abundant tissue and develops from mesoderm during embryonic development. Connective tissue consists of cells embedded within an extracellular matrix of fibers and ground substance. The major fibers are collagen, elastic, and reticular fibers. Connective tissue provides structure, strength, and binding properties to organs and varies depending on the composition and organization of its cellular and extracellular components.
This document provides an overview of bone anatomy and physiology. It defines bone, describes its various functions, and classifications including by position, shape, development, and structure. The document discusses the composition of bone, including its organic and inorganic components. It describes the anatomy of bone including its blood and nerve supply. Finally, it provides details on the histology of bone, the different cell types involved in bone formation and resorption, and the processes of ossification and bone remodeling throughout life.
The document discusses the gross and microscopic anatomy of long bones. Grossly, long bones are composed of a diaphysis or shaft made of compact bone covered by periosteum. The epiphyses at the ends are made of thin compact bone enclosing spongy bone. Articular cartilage provides a smooth, slippery joint surface. Microscopically, osteocytes are found in lacunae surrounding central haversian canals, communicating through canaliculi and perforating canals.
The document discusses the microstructure of the cardiovascular system. It begins by outlining the learning objectives which are to understand the histology of the heart including its structure, muscles, and conduction system. It then describes the layers of the heart walls including the endocardium, myocardium, and epicardium. It explains the specialized cardiac muscle cells and conduction system. Finally, it discusses the histological features of arteries, veins, and capillaries focusing on their layers and differences between vessel types.
There are two types of bone ossification: intramembranous and endochondral. Intramembranous ossification forms bones like the skull and clavicles directly in connective tissue. Endochondral ossification replaces cartilage with bone to form long bones. This process begins with mesenchymal cells forming cartilage, which then undergoes interstitial and appositional growth. Osteoblasts eventually deposit bone matrix around the calcified cartilage, forming trabeculae and replacing the cartilage with bone from the primary ossification center outward.
Bone tissue is a type of specialized connective tissue composed of cells and an extracellular matrix. The matrix is made up of collagen fibers and hydroxyapatite crystals that give bone its rigidity. There are three main cell types involved in bone tissue: osteoblasts which form new bone, osteocytes embedded in the matrix, and osteoclasts which resorb bone. Bone has two types of internal structures - compact bone which is dense and cancellous bone which is spongy. Bone tissue is continuously remodeled through the actions of osteoblasts and osteoclasts throughout life.
The document defines bone and its microscopic structure. It discusses the three types of bone cells - osteoblasts that build bone, osteocytes embedded in the bone matrix, and osteoclasts that resorb bone. Compact bone contains concentric osteons surrounded by lamellae, while spongy bone has a honeycomb structure of trabeculae. The periosteum and endosteum surround bone and provide osteoblasts. Bone formation occurs through intramembranous ossification where mesenchymal cells directly form bone, or endochondral ossification where cartilage is replaced by bone.
Cartilage is a connective tissue composed of cells called chondrocytes embedded in an extracellular matrix. There are three main types of cartilage - hyaline, elastic, and fibrocartilage. Hyaline cartilage is found in joints, respiratory airways, and growing bones. It contains type II collagen and proteoglycans that allow it to bear mechanical stress and provide cushioning. Chondrocytes maintain the extracellular matrix by synthesizing its components. Cartilage grows through both interstitial and appositional growth and has limited ability for repair due to its avascular nature.
This document provides an overview of bone histology. It defines bone as a mineralized connective tissue composed of bone matrix and three cell types: osteoblasts, osteocytes, and osteoclasts. It describes the microscopic structure of compact and spongy bone, including osteons, central canals, lamellae, and trabeculae. It explains the functions of osteoblasts in bone formation, osteoclasts in bone resorption, and osteocytes in bone maintenance. Finally, it discusses the periosteum and endosteum, which cover the external and internal bone surfaces and provide nutrition and new osteoblasts.
A seminar presentation on the histology of the large intestineEmmanuel Uchenna
Ebere Uchenna Emmanuel presented a seminar on the histology of the colon for their Anatomy course. The presentation covered the divisions and layers of the large intestine, including the mucosa, submucosa, muscularis externa, and serosa. Key histological features of the colon mentioned were the lack of villi and plicae circulares, and a smooth interior surface. Clinical correlates discussed were colitis, colonoscopy for screening for colon cancer, and colon cancer itself.
Skeletal muscle tissue functions include movement, posture maintenance, joint stabilization, and heat generation. The main types of muscle tissue are skeletal, cardiac, and smooth muscle. Skeletal muscle is striated and voluntary, attaching to bones and moving the skeleton. Cardiac muscle is only found in the heart walls and has involuntary, rhythmic contractions. Smooth muscle lacks striations and controls involuntary functions like digestion and blood flow. All muscle tissues contain contractile filaments that slide past each other to cause shortening, but the tissues differ in organization, fiber type, and control.
Connective tissue is composed of cells, fibers and a semi-solid matrix. It comes in several types including loose connective tissue, dense connective tissue, cartilage, bone, and fluid connective tissue like blood and lymph. Connective tissue functions include binding other tissues together, forming protective sheaths around organs, storing fats, and producing blood cells and antibodies. The major cell types are fibroblasts, adipocytes, chondroblasts and osteoblasts. Fibers within the matrix include collagen, elastic and reticular fibers. Ground substance provides structure and includes proteins and polysaccharides.
The skeletal system provides structure and protection for the body. It is made of bones connected by ligaments at joints, and bone marrow inside bones produces blood cells. The skeleton changes over one's lifetime from a flexible newborn skeleton with over 300 bones to the 206 bone adult skeleton. Bones are constantly being built and repaired by osteoblasts and osteoclasts throughout life.
Bones and its structure in detail with two different form of bone formationbhartisharma175
It consist of detail content about different types of bone cells, two different type of bone formation and structure of long bone. easy to understand for students. language is simple.
The skeletal system is composed of bones and associated tissues that perform several essential functions:
1. Support - Bones provide structural support for the body and protection for internal organs.
2. Movement - Skeletal muscles use bones as levers to enable movement of the body.
3. Mineral storage - Bones store minerals like calcium and phosphorus.
There are over 200 bones in the human body that are classified as long, short, flat, or irregular. Bones are living tissues composed of cells like osteoblasts, osteocytes, and osteoclasts embedded in an organic bone matrix and inorganic minerals. Compact bone forms the dense outer layer while spongy bone composes the inner layer. Long bones have
Bones provide structure, protect organs, allow movement, and store minerals. There are several bone types classified by shape. Long bones have a shaft and two ends, while short, flat, and irregular bones vary in shape. Bone tissue contains cells, water, collagen fibers, and minerals. Growth and remodeling is regulated by hormones and nutrients. Bones develop from cartilage templates in a multi-step process beginning before birth and continuing into early adulthood.
The skeletal system is composed of 206 bones that serve important biological and mechanical functions. The axial skeleton includes 80 bones that form the axis of the body and protect organs like the brain, while the appendicular skeleton has 126 bones that make up the limbs and their attachments. Bones are living organs composed of compact and spongy tissues, cells like osteoblasts and osteoclasts, and minerals including calcium that provide structure and strength. The skeleton supports the body, protects organs, allows for movement through leverage, and stores minerals and produces blood cells in the bone marrow. Bones are classified by their shapes including tubular, flat, irregular, and sesamoid.
The skeletal system consists of 206 bones that make up two divisions: the axial skeleton and appendicular skeleton. The axial skeleton includes the skull, vertebral column, and thorax, while the appendicular skeleton includes the upper and lower limbs. Bones can be classified by their shape as long, short, flat, or irregular. Each bone has specific structures including compact and spongy bone, periosteum, endosteum, and markings for muscle attachments. Bones provide structure, protection, movement, mineral storage, and blood cell production. They continuously remodel in response to hormones and mechanical stresses.
Cartilage and bone are connective tissues that provide structure and support. There are three types of cartilage - hyaline, fibro, and elastic - each with different compositions and locations in the body. Bones contain bone tissue as well as other tissues. Bones function to provide structure, protect organs, allow movement via muscle attachment, produce blood cells, and store minerals and energy. There are four classes of bones - long, short, flat, and irregular - with different shapes and locations. Bones grow and remodel through both interstitial and appositional growth.
The musculoskeletal system is made up of bones, cartilage, ligaments, tendons and muscles, which form a framework for the body. Tendons, ligaments and fibrous tissue bind the structures together to create stability, with ligaments connecting bone to bone, and tendons connecting muscle to bone.
The musculoskeletal system Anatomy and physiologykajal chandel
The musculoskeletal system is made up of bones, cartilage, ligaments, tendons and muscles, which form a framework for the body. Tendons, ligaments and fibrous tissue bind the structures together to create stability, with ligaments connecting bone to bone, and tendons connecting muscle to bone.
Bone provides structure and support to the body through its skeleton framework. It has several important functions including support, protection, movement, mineral storage, and energy storage. Bone is composed of cells, collagen fibers, and hydroxyapatite crystals that calcify and harden it. There are 206 bones in the adult human skeleton that are divided into the axial skeleton (skull, vertebral column, ribs) and appendicular skeleton (limbs). Bones can be classified based on their location, size, shape and internal structure. Long bones are found in the limbs and have a shaft and expanded ends. Bone tissue is either compact or spongy and contains osteocytes, osteoblasts, and osteoclasts that allow bone to
Bone is a complex living tissue that provides structure, protection, and support. There are several types of bone tissue - cortical bone is dense and hard, forming the outer shell, while cancellous bone is spongy and light. Bones also contain bone marrow, which produces blood cells. Bones are made of an organic collagen matrix and inorganic hydroxyapatite crystals. They contain various bone cells that maintain the balance between bone formation and resorption. Bones come in different shapes suited to their functions, including long bones in the arms and legs, flat bones in the skull, and irregularly shaped bones.
The document discusses the structure and function of long bones. It describes the key parts of long bones including the diaphysis, epiphyses, articular cartilage, periosteum, medullary cavity, compact and spongy bone. It also discusses bone formation through intramembranous and endochondral ossification as well as homeostasis and functions of bone such as support, protection, movement, blood cell formation, and storage of inorganic salts.
There are four main types of bones: long bones, short bones, flat bones, and irregular bones. Long bones have a shaft and two articulating ends, examples being the femur and humerus. Short bones are cube-shaped like wrist and ankle bones. Flat bones are broad and thin, found in the skull, shoulder blades, ribs, and sternum. Irregular bones come in various shapes and sizes, like the patella. Bones are made up of cells, fibers, and extracellular matrix. They provide structure, protection, movement, mineral storage, and blood cell formation to the body. Bone formation occurs through two processes - intramembranous ossification which forms flat bones, and endochondral oss
This document provides an introduction to osteology, the study of bones. It defines osteology and discusses the classification, structure, and microscopic features of bones. The key points covered are:
1. Bones are classified based on their position in the body as either axial or appendicular, and based on their shape as long, short, flat, irregular, or sesamoid.
2. Bones are composed of compact cortical bone and cancellous spongy bone. Long bones specifically have a diaphysis and two epiphyses.
3. Bones are living tissues with osteoblasts, osteoclasts, and osteocytes that remodel the matrix of collagen fibers, hydroxyapatite crystals,
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The skeletal system has three main functions: providing structure and shape to the body, protecting vital organs, and allowing for bodily movement. It is made up of 206 bones that form the axial skeleton (skull, vertebrae, ribs, sternum) and appendicular skeleton (limbs and girdles). Bones are living tissues composed of compact bone, spongy bone, bone marrow, and various bone cells. They provide structure through their interaction with muscles, tendons, and ligaments at joints like the ball-and-socket hip. The skeletal system also plays roles in blood cell production and mineral storage.
The skeletal system consists of bones and cartilage which provide structure, protect organs, allow movement, store minerals, produce blood cells, and store fats. The skeleton is divided into the axial skeleton which includes the skull, vertebral column, ribs, and sternum, and the appendicular skeleton including the pectoral girdle, upper limbs, pelvic girdle, and lower limbs. Bones are made of organic and inorganic components and contain osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts. Joints connect bones and allow movement, with synovial joints providing the most mobility.
The document summarizes the skeletal system, including its main components, functions, classification of bones, bone structure, development and growth. It discusses the two divisions of the skeleton - axial and appendicular. It also describes the different types of joints, their classification and movements allowed. The skeletal system provides structure and support to the body, protects internal organs, allows movement, stores minerals and enables blood cell formation. It consists of bones organized into an internal axial skeleton and external appendages.
The document summarizes key aspects of the skeletal system, including:
1. Bones develop from cartilage early in development and continue changing in structure throughout life.
2. There are 206 bones in the human body classified as either axial or appendicular based on location and role.
3. Bones are living tissues composed of both organic and inorganic materials and have distinct structures depending on their shape and role.
4. Bones continuously remodel through the processes of deposition and resorption to maintain strength and mineral homeostasis.
The skeletal system includes bones, cartilage, ligaments, and connective tissues that provide structure and support to the body. Bones are composed of compact bone on the outer surface and spongy bone on the inner surface. Red bone marrow is found within bones and produces red blood cells, white blood cells, and stem cells. There are several classifications of bones based on shape including long, short, flat, irregular, and sesamoid. Bones develop through two processes - intramembranous ossification and endochondral ossification. The skeletal system allows for support, protection of organs, storage of minerals, blood cell production, and movement.
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Bone tissue
1. Skeletal System Composed of the body’s bones and associated ligaments, tendons, and cartilages. Functions: Support The bones of the legs, pelvic girdle, and vertebral column support the weight of the erect body. The mandible (jawbone) supports the teeth. Other bones support various organs and tissues. Protection The bones of the skull protect the brain. Ribs and sternum (breastbone) protect the lungs and heart. Vertebrae protect the spinal cord.
2. Skeletal System Functions: Movement Skeletal muscles use the bones as levers to move the body. Reservoir for minerals and adipose tissue 99% of the body’s calcium is stored in bone. 85% of the body’s phosphorous is stored in bone. Adipose tissue is found in the marrow of certain bones. What is really being stored in this case? ( hint – it starts with an E ) Hematopoiesis A.k.a. blood cell formation. All blood cells are made in the marrow of certain bones.
3. Bone Classification There are 206 named bones in the human body. Each belongs to one of 2 large groups: Axial skeleton Forms long axis of the body. Includes the bones of the skull, vertebral column, and rib cage. These bones are involved in protection, support, and carrying other body parts. Appendicular skeleton Bones of upper & lower limbs and the girdles (shoulder bones and hip bones) that attach them to the axial skeleton. Involved in locomotion and manipulation of the environment.
4. Bone Classification 4 types of bones: Long Bones Much longer than they are wide. All bones of the limbs except for the patella (kneecap), and the bones of the wrist and ankle. Consists of a shaft plus 2 expanded ends. Your finger bones are long bones even though they’re very short – how can this be? Short Bones Roughly cube shaped. Bones of the wrist and the ankle. Femur Carpal Bones
5. Bone Classification Types of bones: Flat Bones Thin, flattened, and usually a bit curved. Scapulae, sternum, (shoulder blades), ribs and most bones of the skull. Irregular Bones Have weird shapes that fit none of the 3 previous classes. Vertebrae, hip bones, 2 skull bones ( sphenoid and the ethmoid bones). Sternum Sphenoid Bone
6. Bone Structure Bones are organs. Thus, they’re composed of multiple tissue types. Bones are composed of: Bone tissue (a.k.a. osseous tissue). Fibrous connective tissue. Cartilage . Vascular tissue. Lymphatic tissue. Adipose tissue. Nervous tissue.
7. All bones consist of a dense, solid outer layer known as compact bone and an inner layer of spongy bone – a honeycomb of flat, needle-like projections called trabeculae . Bone is an extremely dynamic tissue!!!! Above: Note the relationship btwn the compact and spongy bone. Below: Close up of spongy bone.
8. Note the gross differences between the spongy bone and the compact bone in the above photo. Do you see the trabeculae?
10. Bone Structure Bone tissue is a type of connective tissue, so it must consist of cells plus a significant amount of extracellular matrix. Bone cells: Osteoblasts Bone-building cells. Synthesize and secrete collagen fibers and other organic components of bone matrix. Initiate the process of calcification. Found in both the periosteum and the endosteum The blue arrows indicate the osteoblasts. The yellow arrows indicate the bone matrix they’ve just secreted.
11. Bone Structure 2. Osteocytes Mature bone cells. Osteoblasts that have become trapped by the secretion of matrix. No longer secrete matrix. Responsible for maintaining the bone tissue . Yellow arrows indicate osteocytes – notice how they are surrounded by the pinkish bone matrix. Blue arrow shows an osteoblast in the process of becoming an osteocyte. On the right, notice how the osteocyte is “trapped” within the pink matrix
12. 3. Osteoclasts Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell). Cells that digest bone matrix – this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair. Concentrated in the endosteum. On the side of the cell that faces the bone surface, the PM is deeply folded into a ruffled border. Here, the osteoclast secretes digestive enzymes ( how might this occur ?) to digest the bone matrix. It also pumps out hydrogen ions ( how might this occur ?) to create an acid environment that eats away at the matrix. What advantage might a ruffled border confer? Why do we want a cell that eats away at bone? (Hint: bone is a very dynamic tissue.)
13. Here, we see a cartoon showing all 3 cell types. Osteoblasts and osteoclasts are indicated. Note the size of the osteoclast (compare it to the osteoblast), and note the ruffled border. Why is there a depression underneath the osteoclast? What is the name of the third cell type shown here? What do you think the tan material represents?
14. Bone Structure Bone Matrix: Consists of organic and inorganic components. 1/3 organic and 2/3 inorganic by weight. Organic component consists of several materials that are secreted by the osteoblasts: Collagen fibers and other organic materials These (particularly the collagen) provide the bone with resilience and the ability to resist stretching and twisting.
15. Inorganic component of bone matrix Consists mainly of 2 salts: calcium phosphate and calcium hydroxide. These 2 salts interact to form a compound called hydroxyapatite . Bone also contains smaller amounts of magnesium, fluoride, and sodium. These minerals give bone its characteristic hardness and the ability to resist compression. Three-dimensional array of collagen molecules. The rod-shaped molecules lie in a staggered arrangement which acts as a template for bone mineralization. Bone mineral is laid down in the gaps. Note collagen fibers in longitudinal & cross section and how they occupy space btwn the black bone cells.
16. This bone: a. Has been demineralized b. Has had its organic component removed
17. Long Bone Structure Shaft plus 2 expanded ends. Shaft is known as the diaphysis . Consists of a thick collar of compact bone surrounding a central marrow cavity In adults, the marrow cavity contains fat - yellow bone marrow. Expanded ends are epiphyses Thin layer of compact bone covering an interior of spongy bone. Joint surface of each epiphysis is covered w/ a type of hyaline cartilage known as articular cartilage . It cushions the bone ends and reduces friction during movement.
18. Long Bone Structure The external surface of the entire bone except for the joint surfaces of the epiphyses is covered by a double-layered membrane known as the periosteum . Outer fibrous layer is dense irregular connective tissue. Inner cellular layer contains osteoprogenitor cells and osteoblasts. Periosteum is richly supplied with nerve fibers, lymphatic vessels and blood vessels. These enter the bone of the shaft via a nutrient foramen . Periosteum is connected to the bone matrix via strong strands of collagen.
19. Long Bone Structure Internal bone surfaces are covered with a delicate connective tissue membrane known as the endosteum . Covers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone. Contains both osteoblasts and osteoclasts.
20. Structure of Short, Irregular, and Flat Bones Thin plates of periosteum-covered compact bone on the outside and endosteum-covered spongy bone within. Have no diaphysis or epiphysis because they are not cylindrical. Contain bone marrow between their trabeculae, but no marrow cavity. In flat bones, the internal spongy bone layer is known as the diplo ë , and the whole arrangement resembles a stiffened sandwich.
21. Bone Marrow Bone marrow is a general term for the soft tissue occupying the medullary cavity of a long bone, the spaces amid the trabeculae of spongy bone, and the larger haversian canals. There are 2 main types: red & yellow . Red bone marrow = blood cell forming tissue = hematopoietic tissue Red bone marrow looks like blood but with a thicker consistency. It consists of a delicate mesh of reticular tissue saturated with immature red blood cells and scattered adipocytes. Notice the red marrow and the compact bone
22. Distribution of Marrow In a child, the medullary cavity of nearly every bone is filled with red bone marrow. In young to middle-aged adults, the shafts of the long bones are filled with fatty yellow bone marrow. Yellow marrow no longer produces blood, although in the event of severe or chronic anemia, it can transform back into red marrow In adults, red marrow is limited to the axial skeleton, pectoral girdle, pelvic girdle, and proximal heads of the humerus and the femur. Note the compact bone on the bottom and marrow on the bottom.
23. Microscopic Structure of Compact Bone Consists of multiple cylindrical structural units known as osteons or haversian systems . Imagine these osteons as weight-bearing pillars that are arranged parallel to one another along the long axis of a compact bone. The diagram below represents a long bone shaft in cross-section. Each yellow circle represents an osteon. The blue represents additional matrix filling in the space btwn osteons. The white in the middle is the marrow cavity.
24. Osteons Each osteon consists of a single central canal, known as a haversian canal , surrounded by concentric layers of calcified bone matrix. Haversian canals allow the passage of blood vessels, lymphatic vessels, and nerve fibers. Each of the concentric matrix “tubes” that surrounds a haversian canal is known as a lamella . All the collagen fibers in a particular lamella run in a single direction, while collagen fibers in adjacent lamellae will run in the opposite direction. This allows bone to better withstand twisting forces.
25. Running perpendicular to the haversian canals are Volkmann’s canals . They connect the blood and nerve supply in the periosteum to those in the haversian canals and the medullary cavity.
26. Osteons Lying in between intact osteons are incomplete lamellae called interstitial lamellae . These fill the gaps between osteons or are remnants of bone remodeling. There are also circumferential lamellae that extend around the circumference of the shaft. There are inner circumferential lamellae surrounding the endosteum and outer circumferential lamellae just inside the periosteum.
27. Spider-shaped osteocytes occupy small cavities known as lacunae at the junctions of the lamellae. Hairlike canals called canaliculi connect the lacunae to each other and to the central canal. Canaliculi allow the osteocytes to exchange nutrients, wastes, and chemical signals to each other via intercellular connections known as gap junctions .
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29. Here, we have a close up and a far away view of compact bone. You should be able to identify haversian canals, concentric lamellae, interstitial lamellae, lacunae, and canaliculi.
30. Microscopic Structure of Spongy Bone Appears poorly organized compared to compact bone. Lacks osteons. Trabeculae align along positions of stress and exhibit extensive cross-bracing. Trabeculae are a few cell layers thick and contain irregularly arranged lamellae and osteocytes interconnected by canaliculi. No haversian or Volkmann’s canals are necessary. Why?
31. Bone Development Osteogenesis (a.k.a. ossification ) is the process of bone tissue formation. In embryos this leads to the formation of the bony skeleton. In children and young adults, ossification occurs as part of bone growth. In adults, it occurs as part of bone remodeling and bone repair.
32. Formation of the Bony Skeleton Before week 8, the human embryonic skeleton is made of fibrous membranes and hyaline cartilage. After week 8, bone tissue begins to replace the fibrous membranes and hyaline cartilage. The development of bone from a fibrous membrane is called intramembranous ossification . Why? The replacement of hyaline cartilage with bone is known as endochondral ossification . Why?
33. Intramembranous Ossification Some bones of the skull (frontal, parietal, temporal, and occipital bones), the facial bones, the clavicles, the pelvis, the scapulae, and part of the mandible are formed by intramembranous ossification Prior to ossification, these structures exist as fibrous membranes made of embryonic connective tissue known as mesenchyme .
34. Mesenchymal cells first cluster together and start to secrete the organic components of bone matrix which then becomes mineralized through the crystallization of calcium salts. As calcification occurs, the mesenchymal cells differentiate into osteoblasts. The location in the tissue where ossification begins is known as an ossification center . Some osteoblasts are trapped w/i bony pockets. These cells differentiate into osteocytes.
35. The developing bone grows outward from the ossification center in small struts called spicules. Mesenchymal cell divisions provide additional osteoblasts. The osteoblasts require a reliable source of oxygen and nutrients. Blood vessels trapped among the spicules meet these demands and additional vessels branch into the area. These vessels will eventually become entrapped within the growing bone.
36. Initially, the intramembranous bone consists only of spongy bone. Subsequent remodeling around trapped blood vessels can produce osteons typical of compact bone. As the rate of growth slows, the connective tissue around the bone becomes organized into the fibrous layer of the periosteum. Osteoblasts close to the bone surface become the inner cellular layer of the periosteum.
37. Endochondral Ossification Begins with the formation of a hyaline cartilage model which will later be replaced by bone. Most bones in the body develop via this model. More complicated than intramembranous because the hyaline cartilage must be broken down as ossification proceeds. We’ll follow limb bone development as an example.
38. Endochondral Ossification – Step 1 Chondrocytes near the center of the shaft of the hyaline cartilage model increase greatly in size. As these cells enlarge, their lacunae expand, and the matrix is reduced to a series of thin struts. These struts soon begin to calcify. The enlarged chondrocytes are now deprived of nutrients (diffusion cannot occur through calcified cartilage) and they soon die and disintegrate.
39. Endochondral Ossification – Step 2 Blood vessels grow into the perichondrium surrounding the shaft of the cartilage. The cells of the inner layer of the perichondrium in this region then differentiate into osteoblasts. The perichondrium is now a periosteum and the inner osteogenic layer soon produces a thin layer of bone around the shaft of the cartilage. This bony collar provides support.
40. Endochondral Ossification – Step 3 Blood supply to the periosteum, and capillaries and fibroblasts migrate into the heart of the cartilage, invading the spaces left by the disintegrating chondrocytes. The calcified cartilaginous matrix breaks down; the fibroblasts differentiate into osteoblasts that replace it with spongy bone. Bone development begins at this primary center of ossification and spreads toward both ends of the cartilaginous model. While the diameter is small, the entire diaphysis is filled with spongy bone. Notice the primary ossification centers in the thigh and forearm bones of the above fetus.
41. Endochondral Ossification – Step 4 The primary ossification center enlarges proximally and distally, while osteoclasts break down the newly formed spongy bone and open up a medullary cavity in the center of the shaft. As the osteoblasts move towards the epiphyses, the epiphyseal cartilage is growing as well. Thus, even though the shaft is getting longer, the epiphyses have yet to be transformed into bone.
42. Endochondral Ossification – Step 5 Around birth, most long bones have a bony diaphysis surrounding remnants of spongy bone, a widening medullary cavity, and 2 cartilaginous epiphyses. At this time, capillaries and osteoblasts will migrate into the epiphyses and create secondary ossification centers . The epiphysis will be transformed into spongy bone. However, a small cartilaginous plate, known as the epiphyseal plate , will remain at the juncture between the epiphysis and the diaphysis. Articular cartilage Epiphyseal plate
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44. Growth in Bone Length Epiphyseal cartilage (close to the epiphysis) of the epiphyseal plate divides to create more cartilage, while the diaphyseal cartilage (close to the diaphysis) of the epiphyseal plate is transformed into bone. This increases the length of the shaft.
45. As a result osteoblasts begin producing bone faster than the rate of epiphyseal cartilage expansion. Thus the bone grows while the epiphyseal plate gets narrower and narrower and ultimately disappears. A remnant (epiphyseal line) is visible on X-rays (do you see them in the adjacent femur, tibia, and fibula?) At puberty, growth in bone length is increased dramatically by the combined activities of growth hormone, thyroid hormone, and the sex hormones.
46. Growth in Bone Thickness Osteoblasts beneath the periosteum secrete bone matrix on the external surface of the bone. This obviously makes the bone thicker. At the same time, osteoclasts on the endosteum break down bone and thus widen the medullary cavity. This results in an increase in shaft diameter even though the actual amount of bone in the shaft is relatively unchanged.
47. Fractures Despite its mineral strength, bone may crack or even break if subjected to extreme loads, sudden impacts, or stresses from unusual directions. The damage produced constitutes a fracture . The proper healing of a fracture depends on whether or not, the blood supply and cellular components of the periosteum and endosteum survive.
48. Fracture Repair Step 1: Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma , develops. Bone cells at the site become deprived of nutrients and die. The site becomes swollen, painful, and inflamed. Step 2: Granulation tissue is formed as the hematoma is infiltrated by capillaries and macrophages, which begin to clean up the debris. Some fibroblasts produce collagen fibers that span the break , while others differentiate into chondroblasts and begin secreting cartilage matrix. C. Osteoblasts begin forming spongy bone. D. This entire structure is known as a fibrocartilaginous callus and it splints the broken bone.
49. Step 3: Bone trabeculae increase in number and convert the fibrocartilaginous callus into a bony callus of spongy bone. Typically takes about 6-8 weeks for this to occur. Fracture Repair Step 4: During the next several months, the bony callus is continually remodeled. Osteoclasts work to remove the temporary supportive structures while osteoblasts rebuild the compact bone and reconstruct the bone so it returns to its original shape/structure.
50. Fracture Types Fractures are often classified according to the position of the bone ends after the break: Open (compound) bone ends penetrate the skin. Closed (simple) bone ends don’t penetrate the skin. Comminuted bone fragments into 3 or more pieces. Common in the elderly (brittle bones). Greenstick bone breaks incompletely. One side bent, one side broken. Common in children whose bone contains more collagen and are less mineralized. Spiral ragged break caused by excessive twisting forces. Sports injury/Injury of abuse. Impacted one bone fragment is driven into the medullary space or spongy bone of another.
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52. What kind of fracture is this? It’s kind of tough to tell, but this is a _ _ _ _ _ _ fracture .
53. Bone Remodeling Bone is a dynamic tissue. What does that mean? Wolff’s law holds that bone will grow or remodel in response to the forces or demands placed on it. Examine this with the bone on the left.
54. Check out the mechanism of remodeling on the right! Why might you suspect someone whose been a powerlifter for 15 years to have heavy, massive bones, especially at the point of muscle insertion? Astronauts tend to experience bone atrophy after they’re in space for an extended period of time. Why?
55. Nutritional Effects on Bone Normal bone growth/maintenance cannot occur w/o sufficient dietary intake of calcium and phosphate salts. Calcium and phosphate are not absorbed in the intestine unless the hormone calcitriol is present. Calcitriol synthesis is dependent on the availability of the steroid cholecalciferol (a.k.a. Vitamin D) which may be synthesized in the skin or obtained from the diet. Vitamins C, A, K, and B 12 are all necessary for bone growth as well.
56. Hormonal Effects on Bone Growth hormone , produced by the pituitary gland, and thyroxine , produced by the thyroid gland, stimulate bone growth. GH stimulates protein synthesis and cell growth throughout the body. Thyroxine stimulates cell metabolism and increases the rate of osteoblast activity. In proper balance, these hormones maintain normal activity of the epiphyseal plate ( what would you consider normal activity? ) until roughly the time of puberty.
57. Hormonal Effects on Bone At puberty, the rising levels of sex hormones ( estrogens in females and androgens in males) cause osteoblasts to produce bone faster than the epiphyseal cartilage can divide. This causes the characteristic growth spurt as well as the ultimate closure of the epiphyseal plate. Estrogens cause faster closure of the epiphyseal growth plate than do androgens. Estrogen also acts to stimulate osteoblast activity.
58. Hormonal Effects on Bone Other hormones that affect bone growth include insulin and the glucocorticoids . Insulin stimulates bone formation Glucocorticoids inhibit osteoclast activity. Parathyroid hormone and calcitonin are 2 hormones that antagonistically maintain blood [Ca 2+ ] at homeostatic levels. Since the skeleton is the body’s major calcium reservoir, the activity of these 2 hormones affects bone resorption and deposition.
59. Calcitonin Released by the C cells of the thyroid gland in response to high blood [Ca 2+ ]. Calci ton in acts to “ tone down ” blood calcium levels. Calcitonin causes decreased osteoclast activity which results in decreased break down of bone matrix and decreased calcium being released into the blood. Calcitonin also stimulates osteoblast activity which means calcium will be taken from the blood and deposited as bone matrix. Notice the thyroid follicles on the right. The arrow indicates a C cell
61. Parathyroid Hormone PTH increases calcitriol synthesis which increases Ca 2+ absorption in the small intestine. PTH decreases urinary Ca 2+ excretion and increases urinary phosphate excretion. Released by the cells of the parathyroid gland in response to low blood [Ca 2+ ].Causes blood [Ca 2+ ] to increase. PTH will bind to osteoblasts and this will cause 2 things to occur: The osteoblasts will decrease their activity and they will release a chemical known as osteoclast-stimulating factor . Osteoclast-stimulating factor will increase osteoclast activity.
62. Increased PTH release by parathyroid gland Binds to osteoblast causing decreased osteoblast activity and release of osteoclast-stimulating factor OSF causes increased osteoclast activity Decreased bone deposition and increased bone resorption Increased calcitriol synthesis Increased intestinal Ca 2+ absorption Decreased Ca 2+ excretion Increased Blood [Ca 2+ ] Decreased Blood [Ca 2+ ]
63. Clinical Conditions Osteomalacia Literally “soft bones.” Includes many disorders in which osteoid is produced but inadequately mineralized. Causes can include insufficient dietary calcium Insufficient vitamin D fortification or insufficient exposure to sun light. Rickets Children's form of osteomalacia More detrimental due to the fact that their bones are still growing. Signs include bowed legs, and deformities of the pelvis, ribs, and skull. What about the above x-ray is indicative of rickets?
64. Clinical Conditions Osteomyelitis Osteo=bone + myelo=marrow + itis=inflammation. Inflammation of bone and bone marrow caused by pus-forming bacteria that enter the body via a wound (e.g., compound fracture) or migrate from a nearby infection. Fatal before the advent of antibiotics.
65. Clinical Conditions Osteoporosis Group of diseases in which bone resorption occurs at a faster rate than bone deposition. Bone mass drops and bones become increasingly porous. Compression fractures of the vertebrae and fractures of the femur are common. Often seen in postmenopausal women because they experience a rapid decline in estrogen secretion; estrogen stimulates osteoblast and inhibits osteoclast activity. Based on the above, what preventative measures might you suggest?
66. Clinical Conditions Gigantism Childhood hypersecretion of growth hormone by the pituitary gland causes excessive growth. Acromegaly Adulthood hypersecretion of GH causes overgrowth of bony areas still responsive to GH such as the bones of the face, feet, and hands. Pituitary dwarfism GH deficiency in children resulting in extremely short long bones and maximum stature of 4 feet.