Notice how the fibres are all aligned. In this type of tissue, the collagen fibres are densely packed, and arranged in parallel. This type of tissue is found in ligaments which link bone to bone at joints and tendons connections between bones or cartilage and muscle.
These are powerfully resistant to axially loaded tension forces, but allow some stretch. Classification of Connective Tissue What is connective Tissue? The other specialised types of connective tissue are covered in other topics.
Loose connective Tissue. Dense Irregular Connective Tissue. Marrow adipose tissue composition in adults with morbid obesity. Effects of estrogen therapy on bone marrow adipocytes in postmenopausal osteoporotic women. Osteoporos Int. Increased marrow adiposity in premenopausal women with idiopathic osteoporosis. Short-term effect of estrogen on human bone marrow fat. Bone marrow fat accumulation after 60 days of bed rest persisted 1 year after activities were resumed along with hemopoietic stimulation: the Women International Space Simulation for Exploration study.
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Troglitazone treatment increases bone marrow adipose tissue volume but does not affect trabecular bone volume in mice. Calcif Tissue Int. Strain-specific effects of rosiglitazone on bone mass, body composition, and serum insulin-like growth factor-I. Rosiglitazone inhibits bone regeneration and causes significant accumulation of fat at sites of new bone formation. Pioglitazone increases bone marrow fat in type 2 diabetes: results from a randomized controlled trial.
Eur J Endocrinol. Caloric restriction leads to high marrow adiposity and low bone mass in growing mice. Metformin affects cortical bone mass and marrow adiposity in diet-induced obesity in male mice. J Cell Physiol. Bone marrow fat accumulation accelerated by high fat diet is suppressed by exercise. High bone mass in adult mice with diet-induced obesity results from a combination of initial increase in bone mass followed by attenuation in bone formation; implications for high bone mass and decreased bone quality in obesity.
Mol Cell Endocrinol. Fibroblast growth factor 21 promotes bone loss by potentiating the effects of peroxisome proliferator-activated receptor gamma. Ghrelin and des-octanoyl ghrelin promote adipogenesis directly in vivo by a mechanism independent of the type 1a growth hormone secretagogue receptor. The skeletal cell-derived molecule sclerostin drives bone marrow adipogenesis.
Regulation of Wnt signaling during adipogenesis. J Biol Chem. Wnt6, Wnt10a and Wnt10b inhibit adipogenesis and stimulate osteoblastogenesis through a beta-catenin-dependent mechanism. Inhibition of adipogenesis by Wnt signaling. Science —3. Patients with high bone mass phenotype exhibit enhanced osteoblast differentiation and inhibition of adipogenesis of human mesenchymal stem cells.
Mechanical loading down-regulates peroxisome proliferator-activated receptor gamma in bone marrow stromal cells and favors osteoblastogenesis at the expense of adipogenesis. Mechanical strain inhibits adipogenesis in mesenchymal stem cells by stimulating a durable beta-catenin signal.
Mechanically induced focal adhesion assembly amplifies anti-adipogenic pathways in mesenchymal stem cells. Stem Cells — Vanadate impedes adipogenesis in mesenchymal stem cells derived from different depots within bone.
Parathyroid hormone directs bone marrow mesenchymal cell fate. Influences of teriparatide administration on marrow fat content in postmenopausal osteopenic women using MR spectroscopy.
Climacteric — Human osteoblasts derived from mesenchymal stem cells express adipogenic markers upon coculture with bone marrow adipocytes. Differentiation —5.
Adipogenic RNAs are transferred in osteoblasts via bone marrow adipocytes-derived extracellular vesicles EVs. BMC Cell Biol. Microvesicles released from rat adipocytes and harboring glycosylphosphatidylinositol-anchored proteins transfer RNA stimulating lipid synthesis.
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A novel serum protein similar to C1q, produced exclusively in adipocytes. Leptin and the regulation of body weight in mammals.
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Functional characterization of human mesenchymal stem cell-derived adipocytes. Biochem Biophys Res Commun. Human bone marrow adipocytes support complete myeloid and lymphoid differentiation from human CD34 cells.
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Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes. Endocrinology —8. Leptin deficiency produces contrasting phenotypes in bones of the limb and spine. Leptin treatment prevents type I diabetic marrow adiposity but not bone loss in mice. Daily leptin blunts marrow fat but does not impact bone mass in calorie-restricted mice. J Endocrinol. Leptin receptor promotes adipogenesis and reduces osteogenesis by regulating mesenchymal stromal cells in adult bone marrow.
Scherer PE. Adiponectin: basic and clinical aspects. Paradoxical decrease of an adipose-specific protein, adiponectin, in obesity. Hyperadiponectinaemia in anorexia nervosa. Clin Endocrinol. Notch signaling enhances osteogenic differentiation while inhibiting adipogenesis in primary human bone marrow stromal cells. Exp Hematol. Disruption of the Fgf2 gene activates the adipogenic and suppresses the osteogenic program in mesenchymal marrow stromal stem cells.
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Bonekey Rep. CREB mediates brain serotonin regulation of bone mass through its expression in ventromedial hypothalamic neurons. Genes Dev. The anatomical distribution, clinical associations and potential functions of bone marrow adipose tissue MAT. The image of the skeleton is adapted from Kricun Skeletal radiology 14 1 , pp. With permission of Springer. Increased bone marrow adiposity BMA is associated with lower bone mineral density and increased skeletal fragility, for example in osteoporosis, ageing and oestrogen deficiency.
One possibility is that bone marrow adipocytes share the same skeletal stem cell precursor as bone-forming osteoblasts, in which case MAT accumulation might occur at the expense of osteoblast development.
Is MAT accumulation therefore bad for bone health? Unfortunately, it is too early to tell. Although increased MAT may be associated with elevated fracture risk, increased MAT is not always associated with bone loss.
The potential impact of MAT on skeletal tumour development also remains to be fully understood. Given the public health challenges posed by osteoporosis, skeletal cancers and ageing-associated diseases, elucidating these functions of MAT is a major goal of ongoing research. The key function of bone marrow is in blood cell production, so it is unsurprising that many of the earliest studies of MAT were pursued from a haematological perspective.
Cuboidal epithelial cells are cube-shaped with a single, central nucleus. They are most-commonly found in a single layer, such as a simple epithelia in glandular tissues throughout the body where they prepare and secrete glandular material. They are also found in the walls of tubules and in the ducts of the kidney and liver.
Cuboidal epithelia : Simple cuboidal epithelial cells line tubules in the mammalian kidney where they are involved in filtering the blood. Columnar epithelial cells are taller than they are wide: they resemble a stack of columns in an epithelial layer.
They are most-commonly found in a single-layer arrangement. The nuclei of columnar epithelial cells in the digestive tract appear to be lined up at the base of the cells. These cells absorb material from the lumen of the digestive tract and prepare it for entry into the body through the circulatory and lymphatic systems. Columnar epithelia : Simple columnar epithelial cells absorb material from the digestive tract.
The nuclei line up at the base of the cells. Goblet cells secret mucous into the digestive tract lumen. Columnar epithelial cells lining the respiratory tract appear to be stratified. However, each cell is attached to the base membrane of the tissue and, therefore, they are simple tissues. The nuclei are arranged at different levels in the layer of cells, making it appear as though there is more than one layer.
This is called pseudostratified, columnar epithelia. This cellular covering has cilia at the apical, or free, surface of the cells. The cilia enhance the movement of mucous and trapped particles out of the respiratory tract, helping to protect the system from invasive microorganisms and harmful material that has been breathed into the body.
Goblet cells are interspersed in some tissues such as the lining of the trachea. The goblet cells contain mucous that traps irritants, which, in the case of the trachea, keep these irritants from getting into the lungs. Pseudostratified columnar epithelia : Pseudostratified columnar epithelia line the respiratory tract.
They exist in one layer, but the arrangement of nuclei at different levels makes it appear that there is more than one layer. Transitional or uroepithelial cells appear only in the urinary system, primarily in the bladder and ureter.
These cells are arranged in a stratified layer, but they have the capability of appearing to pile up on top of each other in a relaxed, empty bladder. As the urinary bladder fills, the epithelial layer unfolds and expands to hold the volume of urine introduced into it; the lining becomes thinner.
In other words, the tissue transitions from thick to thin. Connective tissue is found throughout the body, providing support and shock absorption for tissues and bones. Connective tissues are composed of a matrix consisting of living cells and a non-living substance, called the ground substance. The ground substance is composed of an organic substance usually a protein and an inorganic substance usually a mineral or water. The principal cell of connective tissues is the fibroblast, an immature connective tissue cell that has not yet differentiated.
This cell makes the fibers found in nearly all of the connective tissues. Fibroblasts are motile, able to carry out mitosis, and can synthesize whichever connective tissue is needed. Macrophages, lymphocytes, and, occasionally, leukocytes can be found in some of the tissues, while others may have specialized cells.
The matrix in connective tissues gives the tissue its density. When a connective tissue has a high concentration of cells or fibers, it has a proportionally-less-dense matrix. The organic portion, or protein fibers, found in connective tissues are either collagen, elastic, or reticular fibers. Collagen fibers provide strength to the tissue, preventing it from being torn or separated from the surrounding tissues.
Elastic fibers are made of the protein elastin; this fiber can stretch to one and one half of its length, returning to its original size and shape. Elastic fibers provide flexibility to the tissues. Reticular fibers, the third type of protein fiber found in connective tissues, consist of thin strands of collagen that form a network of fibers to support the tissue and other organs to which it is connected.
Loose connective tissue, also called areolar connective tissue, has a sampling of all of the components of a connective tissue. Loose connective tissue has some fibroblasts, although macrophages are present as well. Collagen fibers are relatively wide and stain a light pink, while elastic fibers are thin and stain dark blue to black.
The space between the formed elements of the tissue is filled with the matrix. The material in the connective tissue gives it a loose consistency similar to a cotton ball that has been pulled apart.
Loose connective tissue is found around every blood vessel, helping to keep the vessel in place. The tissue is also found around and between most body organs. In summary, areolar tissue is tough, yet flexible, and comprises membranes. Loose connective tissue : Loose connective tissue is composed of loosely-woven collagen and elastic fibers. The fibers and other components of the connective tissue matrix are secreted by fibroblasts.
Fibrous connective tissues contain large amounts of collagen fibers and few cells or matrix material. The fibers can be arranged irregularly or regularly with the strands lined up in parallel.
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