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Tissue Level of organization

Tissue

· Tissues are the group of call having similar structure which together to perform a specific function.

· Four general categories of animal tissue

§ Epithelial Tissue

§ Muscle Tissue

§ Nerve Tissue

§ Connective Tissue

Epithelial tissue

· Found on a body surface either internal or external

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Tightly packed cells

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Free border or free surface

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Rest on a basement membrane

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Nonvascular

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Function –

§ First line Protection from environment.

§ Coverage.

§ Secretion and excretion.

§ Absorption.

§ Filtration.

Classifying epithelial tissue

· Simple squamous epithelium –

§ Appearance in thin scales,

§ Nuclei of squamous cell tend to appear flat, horizontal, and elliptical, mirroring the form of the cell.

§ Prevent rapid passage of chemical compound is necessary such as the lining of capillaries and small air sacs of lungs.

§ Composing the mesothelium which secretes serous fluid to lubricate internal body cavity.

· Simple cuboidal epithelium –

§ Cell appears round.

§ Nucleus located center of the cell.

§ Involved in secretion and absorption of molecules requiring active transport.

§ Observed in the lining of kidney tubules and ducts of glands.

· Simple columnar epithelium –

§ Nucleus tends to elongated and located in the basal end of the call.

§ Composed of simple columnar epithelium cells with cilia on their apical surfaces.

§ Involved in secretion and absorption of molecules requiring active transport.

§ Forms a majority of digestive tract and some port of female reproductive organs.

§ Found in lining of fallopian tube and part of respiratory system, where cilia helps remove particulate matter.

· Stratified squamous epithelium –

§ Consist of squamous epithelial cell arrange in layers upon a basal membrane.

§ Apical cells appears squamous, while basal layer contains either columnar or cuboidal cell.

§ Most common type of stratified epithelium in human body.

§ Found in nearly every organs which come in to close contact with outside environments such as respiratory, digestion, excretory and reproductive systems.

§ Top layer may be covered with dead cell containing keratin e.q. skin.

§ Provides protection against mechanical stress, chemical abrasions, and even radiation.

§ Protect the body from desiccation and water loss.

· Stratified cuboidal epithelium –

§ Composed of multiple layers of cube shaped cells

§ Superficial layer is made up of cuboidal cells, other layers can be other type cells.

§ Found in certain glands and ducts such as conjunctiva, pharynx, anus and male urethra.

§ Rare in human body.

§ Makes multiple membrane junction between adjacent cells.

§ Creates an impermeable barrier between two distinct surfaces in the body.

§ Barriers act like a filter, forcing nutrients and water to pass through the cell.

· Stratified columnar epithelium –

§ Composed of column shaped cell arranged in multiple layers.

§ Found in certain glands and ducts such as conjunctiva, pharynx, anus and male urethra.

§ Rare in human body.

§ The main function is protections, it protects the underlying tissue and internal organs against several physical and microbial damages.

§ Protect the conjunctiva and other eye structure.

· Pseudostartified columnar epithelium –

§ Appears to be stratified but consist of a single layer of irregularly shaped and different size epithelium.

§ All cell are in contact with basal lamina, although some do not reach the apical surface.

§ Found in respiratory tract, where some of cell have cilia.

§ Nuclei of neighboring cell appear at different level then clustered in basal end.

§ The arrangement give the appearance of stratification.

§ Heterogeneous epithelia they include additional type of cell interspersed among the epithelial cells.

Muscle tissue

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Muscle tissue is specialized for contraction.

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Calls are elongated, and are also known as muscle fibers.

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Contain the contractile proteins actin and myosin, which interact to shorten and elongate the cells.

Types of muscle tissue:

1.
Skeletal Muscle

· Attached to bones, and contraction of these muscles generates body movements.

· The skeletal muscle fibers are long and cylindrical, with multiple peripherally located nuclei.

2. Cardiac Muscle

· Present in the heart.

· Cells are striated, but the striations are much less obvious than in skeletal muscle tissue.

· The cells are shorter than skeletal muscle fibers, have a single nucleus and are often branched.

· Individual cells are connected via gap junctions and desmosomes.

3. Smooth muscle

· Found in the walls of hollow organs, such as the G.I. tract, blood vessels, and the urinary bladder.

·Contractions of these muscles propel fluid or materials through the organs (food through the GI tract, blood through blood vessels, urine pushed out of bladder).

· Smooth muscle cells are not striated; they have a single nucleus, and have tapered ends.

· In blood vessels there is a layer of smooth muscle deep to the epithelial layer.

· It is thicker on the artery than on the vein, but can be seen in both.

Nervous tissue

Specialized for communication and composes the brain, spinal cord, and peripheral nerves.

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Consists of two major cell types: neurons and glial cells.

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Neurons communicate with each other via electrical and chemical signals.

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They have nucleated cell bodies and two types of elongated cellular processes: dendrites which receive signals, and axons – which send signals.

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Glial cells are the support cells of nervous tissue.

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Maintaining proper ion concentrations in the fluid surrounding neurons,

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Generating myelin (an insulating material that surrounds some axons),

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Cleaning up debris.

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The large neurons with their elongated cellular processes and the smaller, more numerous glial cells.

Connective Tissue

· Tissue that connects, separates and support all type of tissue in body.

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Connective tissues vary widely in their form and function, but they are all characterized by the presence of extracellular matrix.

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The extracellular matrix is nonliving material composed of protein fibers and ground substance.

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The protein fibers are composed of collagen (which gives strength) or elastin (which gives flexibility).

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The number and type of fibers differs between the various types of connective tissue.

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The ground substance fills the spaces between the cells and the fibers.

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It contains interstitial fluid (tissue fluid) and large polysaccharide molecules.

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The consistency of the ground substance can vary from liquid to gel‐like to a solid.

Type of connective Tissue

1. Dense connective tissue

· Fewer cells then loose

· ECM is densely packed with collagen fibers

· Arrangement of fibers there are two sub type

§ Dance regular connective tissue – collagen aligned parallel to each other, provide unidirectional resistance to stress.

§ Dance irregular connective tissue – collagen fiber randomly interwoven, forming three dimensional network resistance to distension in all direction. Usually located in capsule and wall of organs, dermis and glands.

2. Loose connective tissue

· Also called areolar connective tissue

· Flexible

· Not very resistance to mechanical stress

· Almost equal amount of cells, fibers and ground substance

· Binding other tissue type together for joining tissue with organs

· Most widely distributed type of connective tissue found in lining of body surface

3. Specialized connective tissue

1. Reticular connective tissue

· Produced by modified fibroblasts called reticular cells.

· Similar to dance connective tissue, it produced reticular fiber arranged in an interlaced network.

· Reticular fibers are thinner, compose a more delicate mesh, with reticular cell remaining bonded to the fibers.

· Supports the stroma of body organs especially lymphoid.

· Filter lymph and provide passage and attachment of WBC.

2. Cartilage

· Avascular Connective Tissue

· Connect bones at joint

· Comprises wall of upper respiratory airways and external ear.

· Surrounded by pericardium

· Pericardium is reach in blood vessels and supply to cartilage.

· Chief call called chondrocytes.

· EMC makes cartilage flexible in various degree but resistance to mechanical stress.

· Three type-

§ Hyaline Cartilage – most represented type, rich in collagen ii molecule, found on articular surface of joint, wall of upper respiratory airways and medial ends of ribs.

§ Elastic Cartilage – most elastic fibers, found in the wall of external ear, cuneiform cartilage in the larynx and epiglottis.

§ Fibrocartilage – mainly collagen I molecules, comprises articular discs, such as intervertebral disc, pubic symphysis and knee menisci.

3. Bone

· Comprises the body skeleton.

· Produced by osteoblasts, osteocytes and osteoclasts.

· Osteoblasts produce cell matrix

· Dormant osteoblast called osteocytes.

· Osteoclasts absorb bone matrix.

· Synchronized of these call is necessary for recovery of fracture bone and general wellbeing.

· Allow to serve as storage site for calcium and phosphate.

· Composed of cells within an extracellular matrix of fibers and ground substances.

· Extracellular bone matrix is mineralized and arranged in circular layers known as lamellae.

· Lamellae circumvent around a central canal which provide passage of neurovasculature.

4. Blood

· Specialized connective tissue within circulatory system.

· It has cellular and extracellular components.

· Extracellular matrix of blood known as blood plasma.

· Blood cell carried by plasma are erythrocytes (RBC), leukocytes (WBC), and thrombocytes (Platelets).

· Produced in bone marrow in the process of haematopoiesis.

5. Adipose Tissue

· Energy storing connective tissue.

· Consist of Adipocytes, cell filled with lipids.

· Small amount of ECF made up of few collagen fiber for keep cell together.

· Two type of adipose tissue –

§ Brown Adipose Tissue – each cell contain multiple fat drops, surrounding centrally positioned nucleus. Usually found in baby for energy storage and serve as thermogenesis.

§ White Adipose Tissue – predominant found in adults, store energy, cushions and protect organs and secreting Hormones. Distributed in visceral and parietal fats

· Visceral fats surround and support body organs, such as eyeball and kidney.

· Parietal fats aggregations embedded in the connective tissue of the skin, topically in the abdominal, back and thigh.

6. Embryonic connective tissue

· Found in early embryos and umbilical card.

· Chief call are mesenchymal cells.

· Divided into mesenchyme embryos) and mucoid connective tissue (Umbilical card).

· Mesenchyme originates from mesoderm, one of the three layers of embryos.

· Matures into other type of connective tissue, muscles, vessels, mesothelium and urogenital system.