Histology Chapter 5 - Connective tissue

Types of Antibodies

->Ig stands for immunoglobulins -> Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells (WBC). ->There are 5 types of heavy chain constant regions in antibodies. The 5 types - IgG, IgM, IgA, IgD, IgE - (isotypes) are classified according to the type of heavy chain constant region, and are distributed and function differently in the body. IgG is the main antibody in blood.

Common characteristics

-All CT share same characteristics despite the variety: ->Develop from the same embryonic tissue(mesoderm) ->Composed of many different types of cells within the tissue, majority of it is ECM -> Contains extracellular matrix ->Great variation in the amount of blood supply (vascularization) ->Composed of cells, fibers and ground substance ->Most diverse and abundant tissue

Bone

-Bone is specialised CT composed of: a. intercellular calcified material b. bone matrix c. three cell types: 1) Osteocytes which are found in cavities (lacunae) within the matrix 2)Osteoblasts which synthesise the organic components of the matrix 3)Osteoclasts which are multinucleated giant cells involved in the resorption and remodelling of bone tissue

Cells in Matrix

-Cells in CT make and maintain the ground substance and fibers -Each type of CT have immature and mature forms of these cells -Immature cells have suffix "-blast" - actuveky produce matrix -Mature cells have suffix "-cyte" - maintain health of matrix, reverting to blasts to regenerate matrix after injury.| ->Fibroblasts - makes CT / fibers ->Chondroblasts - makes cartilage ->Osteoblasts - makes bone ->Hematopoeitic stem cells - makes blood

Cartilage

-Characterised by ECM enriched with glycosaminoglycans (GAG) and proteoglycans, macromolecules that interact with collagen and elastic fibers -variation in the composition of these matrix components produce 3 types of cartilage adapted to local bio mechanical needs -Cartilages is specialised form of CT in which the firm consistency of the ECM allows the tissue to bear mechanical stresses without permanent distortion -Another function of Cartilage is to support soft tissue. -> because it is smooth surfaced and resilient, cartilage is: 1-Shock-absorbing 2-sliding area for joints 3- facilitates bone movement -cartilage is also essential for the development and growth of lone bones before and after birth

Chondrocyte

-Chondrocyte function depends on a proper hormonal balance -The synthesis of sulfated GAG is accelerated by growth hormone, thyroxin, and testosterone and is slowed by cortisone, hydrocortisone and estradiol -Cartilage growth depends mainly on the hypophyseal growth hormone somatotropin ->This hormone does not act directly on cartilage cells but promotes the synthesis of somatomedin C in the liver. ->Somatomedin C acts directly on cartilage cells, promoting their growth.

Fibrocartilage

-Contains bundles of collagen in the matrix that are usually more visible under microscopy -full of collagen type I -Hard -Found in the pubic symphysis, intervertebral disc, and menisci of the knee Function: -Support and fusion -Shock absorption

Extracellular Matrix (ECM)

-ECM is the substance that connective cells are embedded within -Made of non-living material called ground substance: -> can be liquid, gel-like, semi-solid or hard -> texture depends on amount of cell adhesion proteins ->proteoglycans which traps water forming a gel. ->More proteins, more solid ground substance -Contains fibers that provide great strength or flexibility or both -Extracellular matrices consist of different combinations of protein fibers and ground substance -Allows CT to bear weight, mechanical abuse - protects

Periosteum and Endosteum

-External and internal surfaces of bone are covered by layers of bone-forming cells and CT called periosteum and endosteum. -Periosteum consists of an outer layer of collagen fibers and fibroblasts -The inner, more cellular layer of the periosteum is composed of fibroblast like cells called osteoprogenitor cells.

Hyaline cartilage

-Fine collagen fibers embedded in a gel-type matrix -Occasionally chondrocytes inside lacunae -Lack of collagen type I -Soft -Found in embryonic skeleton, at the ends of long bones, in the nose and in respiratory structures Function: -Flexibility -Provides support -allows movement at joints

Storage and mobilization of lipids con't

-Growth hormone , glucocorticoids, prolactin, corticotropin, insulin and thyroid hormone also have roles at various stages in the metabolism of adipose tissue -AT(adipose tissue) also functions as a secretary organ -It synthesises several molecules that are carried by the blood or remain attached to the endothelium of capillaries around adipose cells (e.g. lipoprotein lipase) -Leptin, a protein produced by adipose cells. Several cells in the brain and other tissues have receptors for laptin.

Medical application

-Hypertrophic obesity = Excessive weight gain in adulthood, characterized by expansion of already existing fat cells -Hyperplastic obesity = Excessive weight gain in childhood, characterized by the creation of new fat cells. Obese people have same cells as normal people but the cells increase in size - this is called hypertrophy Hyperplasia is the increase of number of cells

Multilocular adipose tissue - brown fat tissue

-Important mainly in the first months of postnatal life, when it produces heat and thus protects the newborn against cold -Greatly reduced in adulthood -Multilocular tissue cells are polygonal and smaller than cells of unilocular adipose tissue -Their cytoplasm contains a great number of lipid droplets of various sizes, a spherical and central nucleus, and numerous mitochondria with abundant long cristae. -Function: ->main function is to produce heat ->Cells of this tissue receive direct sympathetic innervation

Bone matrix

-Inorganic matter represents about 50% of the dry weight of bone matrix -Calcium and phosphorus are especially abundant, but bicarbonate, citrate, magnesium, potassium, and sodium are also found

Types of CT

-Loose (areolar) CT -> delicate thin layer between tissues; present in all mucous membranes -Adipose tissue -Dense CT-> Tendons/ ligaments -Hyaline cartilage-> nose/ end of long bones/ribs -Elastic cartilages -> outer ear, epiglottis -Fibrocartilage -> between vertebrae, knee joints, pubic joint -Bone -> skeletal system -Blood -> bloodstream

Multilocular adipose tissue - brown fat tissue con't

-Neurotransmitter activates the hormone sensitive lipase present in adipose cells -> promoting hydrolysis of triglycerides to fatty acids and glycerol -Liberated fatty acids are metabolized with a consequent increase in oxygen consumption and heat production -> elevating the temperature of the tissue and warming the blood passing through it -Heat production is increased -> because the mitochondria in cells of this tissue have a transmembrane protein called thermogenin in their outer membrane.

Bone disease

-Osteoporosis -Osteoarthritis -Osteosarcoma

Laptin

-Participates in the regulation of the amount of adipose tissue in the body and in food ingestion -It acts mainly in the hypothalamus to decrease food intake and increase energy consumption -Acts as chemical messenger -High leptin = full appetite -Low leptin = hungry -Mostly in females because of a hormone called histamine -When hungry, the body uses the fat on the retroperitoneal

Thermogenin

-Permits the back flow of protons previously transported to the intermembranous space without passing through the adenosine triphosphate (ATP) synthetase system in the mitochondrial globular units -Consequently, energy generated by proton flow is not used to synthesize ATP but it dissipated as heat -Warmed blood circulates the body, heating the body and carrying fatty acids not metabolised in the adipose tissue. -Other organs use these fatty acids

Fractures

-Simple/closed: bone breaks cleanly, but does not penetrate skin -Compound/open: broken ends of bone protrude through tissue and skin -Comminuted bone fragments into many pieces -Compression: bone is crushed (due to porous bone) -Depressed: broken bone is pressed inward (e.g. in skull) -Colles': posterior displacement of distal end of radius (extension)

Osteology

-Study of osseous structures Functions: -Support -Protection -Movement -Mineral homeostasis -Hemopoiesis: blood cell formation -Storage of adipose tissue: yellow marrow

Fibroblasts

-Synthesizes collagen, elastin, glycosaminoglycans, proteoglycans and multiadhesive glycoproteins -Are most common cells in connective tissue and are responsible for the synthesis of extracellular matrix Types: 1-Active: ->cells with intense synthetic activity are morphologically distinct from the quiescent fibroblasts that are scattered within the matrix they have already synthesized. 2-Fibrocyte: ->Inactive form

Bone con't

-The exchanges between osteocytes and blood capillaries depend on communication through the canaliculi which are thin, cylindrical spaces that perforate the matrix.

Elastic cartilage

-Treadlike network of elastic fibers within the matrix -Found in external ear, auditory tubes, epiglottis Function: -Give support -Maintains shape -Allows flexibility

Medical application of multilocular adipose tissue

-Unilocular adipocytes can generate very common benign tumours called Lipomas -Malignant adipocyte-derived tumours (liposarcomas) are not frequent in humans

Unilocular adipose tissues

-Unilocular adipose cells are spherical when isolated but are polyhedral in adipose tissue, where they are closely packed -Each cell appears in standard microscope preparation as a thin ring of cytoplasm surrounding the vacuole left by the dissolved liquid droplet"the signet ring cell"

Storage and mobilization of lipids

-Unilocular adipose tissue is a large depot of energy for organism -lipid stored in adipose cells are chiefly triglycerides i.e. esters of fatty acids and glycerol -Fatty acids stored by these cells have their origin in dietary fats that are brought to adipose tissue in the form of chylomicron triglycerides. -In triglycerides synthesized in the liver and transported to adipose tissue in the form of very low density lipoproteins (VLDL) -Synthesis of free fatty acids and glycerol from glucose to form triglycerides in adipose cells

Storage and Mobilization of lipids

-in response to body needs, lipids are not mobilized uniformly in all parts of the body. -Subcutaneous, mesenteric, and retroperitoneal deposits are the first to be mobilised, whereas adipose tissues in the hands, feets, and retroorbital fat pads resists long period of starvation -After such period of starvation, unilocular adipose tissue loses nearly all its fat and contains polyhedral or spindle-shaped cells with very lipid droplets

CT prper Structures

-made of Variety of cells, fibers and grounds substances ->types of depends on use Cells found in connective tissue proper: -Fibroblasts- give rise to protein fibers -Macrophages, Lymphocytes - antibody producing cells -Adipocytes -> fat cells -Mast cells -> vertebrate body cells that produces histamine and other molecules that trigger the inflammatory response. -Stem cells / Mother cells Fibers: -Collagen -> very strong and abundant, long and straight -Elastic -> branching fibers with a wavy appearance (when relaxed) -Reticular - Form a network of fibers that form a supportive framework in soft organs like spleen and liver. (Reticuloendothelial system)

Bone con't

-some osteoblasts are gradually surrounded by newly formed matrix and become osteocytes. -During matrix synthesis, osteoblasts have the ultra-structure of cells actively synthesizing proteins for export -Osteoblasts are polarized cells -Matrix components are secreted at the cell surface, which is in contact with older bone matrix, providing a layer of new matrix called osteoid, between the osteoblast layer and the previously formed bone. -This process, bone apposition, is completed by subsequent deposition of calcium salts into the newly formed matrix .

Component of Connective tissue (CT) or Supportive tissue

1-Cells 2-Matrix: -Protein fibers -Ground substance They vary according to the tissue

Types and functions

1-Loose connective tissue: fat, areolar ->insulation, protection 2-Dense connective: Ligaments and tendons ->binding and support 3-Cartilage -> protection, support 4-Bone ->support 5-Blood ->transportation -Maintain the form of organs through out the body -Gives metabolic support to cells as medium for diffusion of nutrients and waste products

Loose connective tissue

1. Areolar CT: -Consists of all 3 types of fibers, several types of cells, and semi-fluid ground substance -Found in subcutaneous layer and mucous membranes, and around blood vessels, nerves and organs Function: -Strength -Support -Connection -Elasticity

Loose Connective tissue con't

2. Adipose tissue: -Consists of adipocytes; "signet ring" appearing fat cells. -Store energy in the form of triglycerides(liquid) -Found in subcutaneous layer, around organs and in the yellow marrow of long bones Function: -Support -Protects -Insulates -Serves as energy reserve

Loose connective tissue Type

3. Reticular CT: -Consists of fine interlacing reticular fibers and reticular cells -Found in liver, spleen, and lymph nodes Function: -Forms the framework (stroma) of organs -binds together smooth muscle tissue cells

Antigen and Antibody

Antibodies, also called immunoglobulins, are large Y-shaped proteins which function to identify and help remove foreign antigens or targets such as viruses and bacteria. Antigens are large molecules, usually proteins, on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, and foreign particles. Any substance capable of triggering an immune response is called an antigen.

Matrix fibers

Collagen Fibers: -Large fibers made of protein collagen -are typically the most abundant fibers. -Promote tissue flexibility Elastic Fibers: -Intermediate fibers made of protein elastin -Branching fibers that allow for stretch and recoil Reticular Fibers: -Small delicate, branched fibers that have same chemical composition of collagen -Forms structural framework for organs such as spleen and lymph nodes

Fibril forming collagen

Collagen Type I: ->Thick, highly picrosirius, birefringent, fibers ->found in skin, tendon, bone, dentin ->function: resistance to tension Collagen Type II: -> loose aggregates of fibrils, birefringent ->found in cartilage, vitreous body ->function: Resistance to pressure Collagen Type III: ->Thin, weakly birefringent, argyrophilic(silver binding) fibers ->found in skin, muscle, blood vessels, frequently together with type I ->function: Structural maintenance in expansible organs

Types of bone

Compact bone (Osteon): -External layer -Called lamellar bone (group of elongated tubules called lamella) -Majority of all long bones -Protection and strength (wt. bearing) -Concentric ring structure -Blood vessels and nerves penetrate periosteum through horizontal openings called perforating (Volkmann's) canals.

Cartilage con't

Consists of: 1) Chondrocytes 2)ECM- composed of fibers and ground substance -Chondrocytes synthesize and secrete the ECM, and the cells themselves are located in matrix cavities called Lacunae Types of cartilage: 1. Hyaline cartilage 2. Fibrocartilage 3. Elastic cartilage

Ectoderm

Ectoderm: ->The ectoderm generates the outer layer of the embryo, and it forms from the embryo's epiblast. ->The surface ectoderm develops into: epidermis, hair, nails, lens of the eye, sebaceous glands, cornea, tooth enamel, the epithelium of the mouth and nose. ->The neural crest of the ectoderm develops into: peripheral nervous system, adrenal medulla, melanocytes, facial cartilage, dentin of teeth. ->The neural tube of the ectoderm develops into: brain, spinal cord, posterior pituitary, motor neurons, retina.

Endoderm, Mesoderm

Endoderm: ->The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube except part of the mouth and pharynx and the terminal part of the rectum Mesoderm: ->The formation of a mesoderm leads to the development of a coelom. ->The mesoderm forms: muscle (smooth and striated), bone, cartilage, connective tissue, adipose tissue, circulatory system, lymphatic system, dermis, genitourinary system, serous membranes, and notochord.

True CT cells

Fibroblasts: secretes both fibers and ground substance of the matrix (wandering -> meaning always moving) Macrophages: Phagocytes that develop from monocytes (wandering or fixed) Plasma cells: Antibody secreting cells that develop from B Lymphocytes (wandering) Mast cells: Produces histamine that helps dilate small blood vessels in reaction to injury (wandering) Adipocytes: Fat cells that store triglycerides, supports, protect and insulate (fixed)

CT proper structure con't

Ground substance: -Along with fibers, fills the extracellular space -Ground substance help determine functionality of tissue.

Multilocular adipose tissue con't

Histogenesis of multilocular adipose tissue: -multilocular adipose tissue develops differently from unilocular adipose tissue -No formation of multilocular adipose tissue after birth -One type of adipose tissue is not transformed into another

Matrix ground substance

Hyaluronic Acid: -Complex combination of polysaccharides and proteins found in "true" or proper CT Chondroitin sulfate: -Jellylike ground substance of cartilages, bone, skin and blood vessels Other ground substance: -Dermatin sulfate, keratin sulfate, and adhesion proteins

Classifications

Loose CT: -Areolar -Reticular -Adipose Dense CT: -Regular -Irregular -Elastic

Bone formation

Ossification occurs in two ways: 1-Intramembranous ossification 2-Endochondral ossification -Both method above lead to the same bone formation but are different methods of getting there.

Bone con't

Osteoblasts: -are responsible for synthesis of the organic components of bone matrix (type I collagen, proteoglycans, and glycoproteins) -Deposition of the inorganic components of bone also depends on the present of viable osteoblasts -Are exclusively located on the surfaces of bone tissue, side by side, in a way that resembles simple epithelium. -When actively engaged in matrix synthesis, osteoblasts have a cuboidal to colimnar shape and basophilic cytoplasm -When their synthesising activity declines, they flatten, and cytoplasmic basophilic declines

Bone con't

Osteoclasts: -Are very large, branched motile cells -Secretes collagenase and other enzymes and pumps protons into a sub-cellular pocket promoting the localized digestion of collagen and dissolving calcium salt crystals. -Osteoclasts activity is controlled by cytokines and hormones. -Osteoclasts have receptors for calcitonin, a thyroid hormone, but not for parathyroid hormone -Osteoblasts have receptors for parathyroid hormone and, when activated by this hormone, produces a cytokine called osteoclast stimulating factor.

Bone con't

Osteocytes: -Derive osteoblast -lie in the lacunae situated between lamellae of matrix -only one osteocyte is found in each lacuna -The thin, cylindrical matrix canaliculi house cytoplasmic processes of osteocytes. -Processes of adjacent cells make contact via gap junctions, and molecules are passed via these structures from cell to cell.

Cells in matrix con't

Other cells present: -White blood cells (macrophages, plasma cells) - responsible for immune response -Mast cells - responsible for inflammation following injury or infection

Fractures con't

Smith's: anterior displacement of distal end of radius (flexion) Transverse: break occurs across the long axis of a bone -Impacted: broken bone ends are forced into each other -Spiral: ragged break as a result of excessive twisting of bone -Epiphyseal: break occurring along epiphyseal line/plate -Greenstick: bone breaks incompletely -Pott's: malleolus of tibia and fibula break

Types of bone con't

Spongy bone (cancellous bone): -internal layer -Latticework of bone tissue (haphazard arrangement) -Made of trabeculae -Filled with red and yellow bone marrow -Osteocytes get nutrients directly from circulating blood -Short, flat and irregular bone is made of mostly spongy bone

Adipose tissue types

Type: 1 - Unilocular adipose tissue (yellow): -Almost all adipose tissue in adults is of this type -Found throughout the human body except eyelids, penis, scrotum, entire auricle of external ear except for the lobule. -Age and sex determine the distribution and density of adipose deposits -Regulated by sex hormone and adrenocortical hormones -> which controls the accumulation of fat and are largely responsible for male or female body contour