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Diagram of spongy bone

This illustration shows the spongy bone within the proximal epiphysis of the femur in two successively magnified images. The lower-magnification image shows two layers of crisscrossing trabeculae. The surface of each is dotted with small black holes which are the openings of the canaliculi. One of the trabeculae is in a cross section to show its internal layers. The outermost covering of the lamellae is called the endosteum. This endosteum surrounds several layers of concentric lamellae. The higher-magnification image shows the cross section of the trabeculae more clearly. Three concentric lamellae are shown in this view, each possessing perpendicular black lines. These lines are the canaliculi and are oriented on the round lamellae similar to the spokes of a wheel. In between the lamellae are small cavities called lacunae which house cells called osteocytes. In addition, two large osteoclasts are seated on the outer edge of the outermost lamellae. The outermost lamellae are also surrounded by groups of small, white, osteoblasts.
Spongy bone is composed of trabeculae that contain the osteocytes. Red marrow fills the spaces in some bones.

Aging and the…

Skeletal system: paget’s disease

Paget’s disease usually occurs in adults over age 40. It is a disorder of the bone remodeling process that begins with overactive osteoclasts. This means more bone is resorbed than is laid down. The osteoblasts try to compensate but the new bone they lay down is weak and brittle and therefore prone to fracture.

While some people with Paget’s disease have no symptoms, others experience pain, bone fractures, and bone deformities ( [link] ). Bones of the pelvis, skull, spine, and legs are the most commonly affected. When occurring in the skull, Paget’s disease can cause headaches and hearing loss.

Paget's disease

This illustration shows the normal skeletal structure of the legs from an anterior view. The flesh of the legs and feet are outlined around the skeleton for reference. A second illustration shows the legs of someone with Paget’s disease. The affected person’s left femur is curved outward, causing the left leg to be bowed and shorter than the right leg.
Normal leg bones are relatively straight, but those affected by Paget’s disease are porous and curved.

What causes the osteoclasts to become overactive? The answer is still unknown, but hereditary factors seem to play a role. Some scientists believe Paget’s disease is due to an as-yet-unidentified virus.

Paget’s disease is diagnosed via imaging studies and lab tests. X-rays may show bone deformities or areas of bone resorption. Bone scans are also useful. In these studies, a dye containing a radioactive ion is injected into the body. Areas of bone resorption have an affinity for the ion, so they will light up on the scan if the ions are absorbed. In addition, blood levels of an enzyme called alkaline phosphatase are typically elevated in people with Paget’s disease.

Bisphosphonates, drugs that decrease the activity of osteoclasts, are often used in the treatment of Paget’s disease. However, in a small percentage of cases, bisphosphonates themselves have been linked to an increased risk of fractures because the old bone that is left after bisphosphonates are administered becomes worn out and brittle. Still, most doctors feel that the benefits of bisphosphonates more than outweigh the risk; the medical professional has to weigh the benefits and risks on a case-by-case basis. Bisphosphonate treatment can reduce the overall risk of deformities or fractures, which in turn reduces the risk of surgical repair and its associated risks and complications.

Blood and nerve supply

The spongy bone and medullary cavity receive nourishment from arteries that pass through the compact bone. The arteries enter through the nutrient foramen    (plural = foramina), small openings in the diaphysis ( [link] ). The osteocytes in spongy bone are nourished by blood vessels of the periosteum that penetrate spongy bone and blood that circulates in the marrow cavities. As the blood passes through the marrow cavities, it is collected by veins, which then pass out of the bone through the foramina.

In addition to the blood vessels, nerves follow the same paths into the bone where they tend to concentrate in the more metabolically active regions of the bone. The nerves sense pain, and it appears the nerves also play roles in regulating blood supplies and in bone growth, hence their concentrations in metabolically active sites of the bone.

Diagram of blood and nerve supply to bone

This illustration shows an anterior view if the right femur. The femur is split in half lengthwise to show its internal anatomy. The outer covering of the femur is labeled the periosteum. Within it is a thin layer of compact bone that surrounds a central cavity called the medullary or marrow cavity. This cavity is filled with spongy bone at both epiphyses. A nutrient artery and vein travels through the periosteum and compact bone at the center of the diaphysis. After entering the bone, the nutrient arteries and veins spread throughout the marrow cavity in both directions. Some of the arteries and veins in the marrow cavity also spread into the spongy bone within the distal and proximal epiphyses. However, additional blood vessels called the metaphyseal arteries and the metaphyseal veins enter into the metaphysis from outside of the bone.
Blood vessels and nerves enter the bone through the nutrient foramen.

Chapter review

A hollow medullary cavity filled with yellow marrow runs the length of the diaphysis of a long bone. The walls of the diaphysis are compact bone. The epiphyses, which are wider sections at each end of a long bone, are filled with spongy bone and red marrow. The epiphyseal plate, a layer of hyaline cartilage, is replaced by osseous tissue as the organ grows in length.

Bone matrix consists of collagen fibers and organic ground substance, primarily hydroxyapatite formed from calcium salts. Osteogenic cells develop into osteoblasts. Osteoblasts are cells that make new bone. They become osteocytes, the cells of mature bone, when they get trapped in the matrix. Osteoclasts engage in bone resorption. Compact bone is dense and composed of osteons, while spongy bone is less dense and made up of trabeculae. Blood vessels and nerves enter the bone through the nutrient foramina to nourish and innervate bones.

Questions & Answers

what is the difference between a vaccine and a antiserum
Silver Reply
An antiserum contains antibodies already produced and is used to pass on immune responses. A vaccine contains a substance that stimulates the production of antibodies to create an immune response.
A vaccine a preparation of antigens for one (or more) diseases that is given to stimulate active immunity and protect against the disease (s). while an antiserum either neutralizes the "infection " or stimulates your immune system to attack an infection.
what is deoxyribonucleic acid
Carlene Reply
A negatively charged molecule; polymer of nucleotides found in the nucleus of a cell ... DNA.
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to maintain certain biological activities of cell
jeeni Reply
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Shaili Reply
caused by two different agents.. malaria is caused by Culex mosquito in birds and Anopheles in humans.. while dengue fever is caused by Aedes mosquito
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Shaili Reply
system that defends the body against invading microbes n pathogens... (white blood cells makes immune system)
what is interferon's ?
maya Reply
interferon is any group of glycoproteins, produce by the immune system.
what is immune system
the difference between human biology and principles of biology
Henry Reply
human biology is the studying of stucture and of function of the body and the principles of how humans interacts with men, animal and plants around them and the social activities that take place.
human biology is the studying of human body structures function in the way of interacting physical and internal. while biology is the study of living and non living things.
what is Mitosis/Meiosis? What are the similarities and differences?
Abayomi Reply
differences: occurence... one in somatic n other in germ cells no of daughter cells.. 2 and in meisis 4. genetic recombination... only occurs in meiosis during crossing over no. of chromosomes.. remains same in mitosis n reduced to half in meiosis major phases... similar karyokinesis n cytokinesis
karyokinesis... divided into prophase.. meta.. ana.. and telophase... in meiosis.. further division into meiosis 1 and meiosis11 so phases are named as pro1..meta1..ana1..and telo1
differences among phases.. prophase.. other changes similar.. but diff occur in meiosis where synapsis, crossing over,chiasmata formation and tetrad form metaphase... in mitosis chromosomes align at equatorial plate.. in meiosis homologouy chromosomes align at equatorial plate.
anaphase.. in mitosis chromatids gets separated in meiosis chromosomes gets separated.. meiosis 11 is similar to mitosis except that during interkinesis.. duplication in S phase doesnt occur
What is the difference between prokaryotic and eukaryotic organisms
AAlfred Reply
Prokaryotic cell are unicellular, lacks a membrane bound organelles ... e.g bacteria and archea. Eukaryotic cells are multicellular, membrane bound organelles ... e.g Animals, Plants, Fungi, Algae.
what are organelles
Lorella Reply
Organelles are specialized structures in the that perform a specific function. Examples: mitochondrial , Golgi apparatus, etc.
Organelles are specialized structures in the cell that perform a specific function. Examples: mitochondrial, ribosomes, etc.
what connect bone to bone
Rebecca Reply
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Isaya Reply
it don't have any function
what is a joint
Rebecca Reply
A joint is a place where two bones meet or articulate.
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