7. T issue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. T he study of tissue is known as histology or, in connection with disease, histopathology.
12. Meristematic tissue: Cells of this tissue continue to divide throughout the life of the plant. Some of these cells lose their ability to divide and become part of other tissues.
13. A longitudinal section through a growing shoot tip showing apical meristematic tissue. Note that the cells are small, have dense cytoplasm, and are very tightly packed. High power view of a longitudinal section of the Coleus apical meristem. The apical meristem is a dome-shaped mass of dividing cells at the tip of the shoot. The apical meristem will produce the three primary meristems: protoderm, procambium, and ground meristem. These three meristems in turn will produce new cells that will differentiate into the epidermis, primary vascular tissues, and ground tissues (pith and cortex).
14. A longitudinal section through a root tip. The meristematic tissue is located just above the root cap. This too is apical meristem; division of these cells followed by cell elongation results in the root growing in length. It is a cross section of a dicot stem. Focus on the two large vascular bundles in the center of the slide. The xylem tissue is stained red. Just above the xylem is a layer of meristematic tissue, the vascular cambium. The phloem tissue is found outside of the vascular cambium.
15. This is a high-power view of a cross-section showing a lateral meristem, the vascular cambium, in the same plant shown in previous slide. Again, the xylem tissue is stained red, and the large cells on the top of the slide are phloem. The green brick-like cells between the xylem and phloem is the area in which the vascular cambium is located. The new cells produced by the cambium are initially like those of the cambium itself, but, as they grow and mature, their characteristics slowly change as they differentiate into other tissues. The vascular cambium is a single layer of cells within this brick like region; it is responsible for the growth in diameter of a stem. The tissues produced by the vascular cambium are secondary tissues.
16. Permanent tissue: Cells of this tissue have lost their ability to divide and they have a specialized structure to perform specific functions. Based on the type of cells present in the tissue, the Permanent tissue is divided into two categories: Simple Permanent Tissue and Complex Permanent Tissue. While the simple permanent tissue consist of only one type of cells (eg. Parenchyma), the complex permanent tissue consists of more than one type of cells (eg. Xylem and phloem)
17. Types of parenchyma : i) Chlorenchyma :Certain parenchymatous tissue contain chloroplast and synthesize food by the process of photosynthesis. ii) Aerenchyma: In aquatic plants parenchymatous cells have air cavities between them to store air, such a tissue is called Aerenchyma. It provides buoyancy to the aquatic plants so that they can float in water. Simple Permanent Tissues Parenchyma Structure :It is the fundamental tissue composed of thin walled, living cells whose cell wall is composed of cellulose. Small intercellular spaces are present between the cells. Location and function : It occurs in all soft parts of plants and is meant for storage of food and to provide turgidity to softer parts of plants. Parenchyma
18. Collenchyma in Transverse Section Showing Wall Thickenings 1. Cell Wall 2. Wall Thickenings 3. Protoplasm 4. Vacuole Collenchyma Structure : This tissue is composed of somewhat elongated cells with cell walls that are irregularly thickened at corners due to deposition of cellulose or pectin. They may be oval, circular or polygonal. Very little intercellular spaces are present. Location : It occurs below the epidermis of stem and petiole (stalk of the leaf) and around veins. Function : This tissue provides mechanical support and flexibility and in some cases it may possess chloroplasts to perform Photosynthesis. The stem and leaves are able to bend easily and then come back to their original position due to the presence of collenchyma.
19. Sclerenchyma Structure : It is a tissue of dead and thick walled cells, having no intercellular spaces. The thickenings are of cellulose or lignin or both. Several unlignified areas called pits often develop on walls. Location : This t issue is usually found in the hard and stiff parts of the plant like seed coat, husk of coconut, in the stem around vascular bundles, veins of leaves and hard covering of fruits and nuts. Function : It is the chief mechanical tissue in plants and is able to bear push, pull, strain and shearing forces. It provides strength to plant parts and also protects the delicate parts of the plants. They are of two types: fibres and sclereids.
23. Epidermis and Bark The protective tissues The epidermis usually consists of a single-layered group of cells that covers plants leaves, flowers, roots and stems. It forms a boundary between the plant and the external world. Bark is formed from the meristem that appears later in the life cycle of a plant. Woody stems and some other stem structures produce a secondary covering called the secondary meristem or periderm or cork cambium that replaces the epidermis as the protective covering. The periderm replaces the epidermis, and acts as a protective covering like the epidermis. Cells produced on the outside by periderm form the cork. Cells of have suberin in their walls to protect the stem from drying and pathogen attack. Older cork cells are dead, as is the case with woody stems. As the stem grows, the cork cambium produces new layers of cork which are impermeable to gases and water.
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25. Periderm is found on the surface of woody plants; it includes the cork cells on the surface of older woody stems. The periderm replaces the epidermis in plants that have secondary growth. The cork cells are dead; it is their waterproofed cell walls that function as the protective outer covering of plants. Meristematic cells within the periderm (cork cambium, the other lateral meristem) produce the cork cells. type of surface tissue, the outer bark or periderm (stained red in this slide).
30. Multicellular (large) organisms function more efficiently if cells become specialized for specific functions. There are types of tissues found : Connective Tissue Muscular Tissue Nervous Tissue Epithelial Tissue and Cell Junctions While also the system in Organism : Integumentary System Organ System Homeostasis *Sponges do not have tissues.
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41. Connective Tissue: - Cells - Extracellular Matrix Characteristics Of Connective Tissue: Cells - widely spaced in the extracellular matrix Components of extracellular matrix: - Water - Ground substance: semisolid gel containing Tissue fluids, salts & Glycoconjugates two types Proteoglycans – core protein – GAG (Glycoproteins) is attached five – Chondrotin sulphate, dermatan sulphate, keratan sulphate & heparan sulphate. Glycoproteins – shorter branched oligosaccharides - Fibronectin & laminin - Fibres Collagen fibres (white fibres) widely distributed Elastic fibres (yellow fibres) found in the lungs, blood vessels Reticular fibres are fine collagen fibres found in spleen and liver
48. Connective Tissue Continued SUPPORTIVE TISSUE aids in the formation of bone and cartilage. Due to its solid matrix, this tissues cells usually occupy small cavities known as LACUNAE . There are three different types of cartilage: HYALINE CARTILAGE is constructed of a whitish matrix with thin collagen fibers. This type of cartilage is found at the end of bones, in the trachea, and in the nose. Similar to Hyaline, ELASTIC CARTILAGE contains more elastic fibers which yields more flexibility. Elastic cartilage is found in the outer ear area, the voice box (larynx), and the epiglottis. Lastly, the FIBROCARTILAGE consists of very durable collagen fibers which can endure pressure/weight and absorb shock. Fibrocartilage is found in the joint of the pubic bones, spinal disks, and in knee cartilage. Picture from http://en.wikipedia.org/wiki/Fibrocartilage Supportive Connective Tissue Fibrocartilage Hyaline Cartilage Picture from http://www.victoriacollege.edu/dept/bio/Belltutorials/Histology%20Tutorial/Basic%20Tissues/Connective%20Tissue.html#Elastic%20CT
49. Connective Tissue Continued BONES are the firmest connective tissue which is constructed of a hard matrix and collagen fibers. Bones get some of their structure from OSSEOUS TISSUE , which lends to the cylindrical shape of them (OSTEONS) . Long and dense COMPACT BONES have rings of hard matrix in the osteons. At the ends of long bones is a lighter structure known as SPONGY BONE . This material has a separated formation permitting space for marrow and blood vessels. Bone Pictures from http://en.wikipedia.org/wiki/Bone#Compact_bone and Human Biology by Sylvia S. Mader Page 63 Spongy Bone Compact Bone
50. Connective Tissue Continued Fluid BLOOD: Plasma liquid with formed elements (red and white blood cells, and platelets). Bloods duties include carrying oxygen and nutrients throughout the body to other tissues fluid and circulates heat. RED BLOOD CELLS transport oxygen throughout the body by loosely binding the oxygen with the cells HEMOGLOBIN , an iron containing structure. Red blood cells do not contain a nucleus. On the other hand, WHITE BLOOD CELLS contain a nucleus and are larger in size. Also, they have a more translucent appearance. White blood cells help to fight infections by either consuming the pathogens through phagocytosis or creating antibodies to fight infections. PLATELETS are present in bone marrow where they aid in the reconstruction of broken blood vessels. Platelets are pieces of cells. LYMPH: Yellowish fluid containing white blood cells. Lymph originates from tissue fluid and is cleansed in the LYMPH NODES which is lymphatic tissue on a lymphatic vessel. Picture of elements found in blood Picture from Human Biology by Sylvia S. Mader page 64
52. Loose Areolar Connective Tissue - numerous cells and blood vessels - abundant ground substance, flexible, not resistant to stress - Found in - under epithelial surfaces, around blood vessels & glands
53. The 5 primary components of the superficial fascia (loose irregular areolar connective tissue): 1. Fibroblasts 2. Collagen Fibers 3. Elastic Fibers 4. Tissue Fluid 5. Fat In contrast to the overlying dermis and the underlying deep fascia, the superficial fascia may be distinguished by the presence of fat
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58. Epithelial tissue covers the whole surface of the body. It is made up of cells that are closely packed and are composed of one or more layers. This tissue is specialised to form the covering or lining of all internal and external body surfaces. Epithelial tissue that occurs on surfaces on the interior of the body is known as endothelium. Epithelial tissue (a) Squamous. (b) Cuboidal. (c) Columnar. (d) Stratified squamous. (e) Pseudostratified. (f) Transitional.
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61. Epithelial Tissue EPITHELIAL: Constant layer of firmly packed cells. SIMPLE EPITHELIA: Single layer of cells attributed from three cell types. SQUAMOUS EPITHELIUM is a layer found in lungs and blood vessels. It is made of compacted cells and aids in protection. CUBOIDAL EPITHELIUM is a layer of cubed cells found in glands, lining the ovaries and kidney tubules. Cuboidal epithelium aids in absorption. COLUMNAR EPITHELIUM are rectangular shaped cells with the nuclei at the bottom. It is found lining the digestive area and aids in absorption. Pictures from Human Biology by Sylvia S. Mader pages 68-69
62. Epithelial Tissue Continued PSEUDOSTRATIFIED COLUMNAR EPITHELIUM lines the trachea and aids in ejecting impurities. Mucus helps to trap particles and cilia carries it to the throat area. TRANSITIONAL EPITHELIUM lines organs which stretch. Found in bladder, urethra and ureters. STATIFIED EPITHELIA is found in the nose, mouth, esophagus, anal canal and vagina linings. The cells are stacked into layers which offer protection. GLANDULAR EPITHELIA is any epithelium which secretes products. A cell or a group of cells that secrete products are known as GLANDS . Secretion to an outer surface is done by EXOCRINE GLANDS , whereas ENDOCRINE GLANDS secrete products internally through the bloodstream. Pictures from Human Biology by Sylvia S. Mader page 69 and http://en.wikipedia.org/wiki/Transitional_epithelium Transitional epithelia of bladder
63. Muscular tissue Muscles of the body are made up of elongated muscle cells also known as muscle fibre. The movement of the body is brought about by the contraction and relaxation of contractile protein present in muscle cells. These contractile proteins are actin and myosin.
64. Muscular Tissue SKELETON MUSCLE: Found where muscles attach to bone and aid in movement. The fibers are long cylinder shapes that are formed by the combining of cells, resulting in multiple nuclei. SMOOTH MUSCLE: Found in the walls of blood vessels and some internal organs. Aids in the transfer of substances. CARDIAC MUSLE: Found in heart walls. Its function is to pump blood. Pictures from Human Biology by Sylvia S. Mader page 65
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67. All living cells have the ability to react to stimuli. Nervous tissue is specialised to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus . Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialised nerve cells called neurons . Nervous Tissue
68. Neurons have many different shapes and sizes. However, a typical neuron in a human consists of four major regions: a cell body, dendrites, an axon , and synaptic terminals. Like all cells, the entire neuron is surrounded by a cell membrane. The cell body is the enlarged portion of a neuron that most closely resembles other cells. It contains the nucleus and other organelles (for example, the mitochondria and endoplasmic reticulum ). The dendrites and axon are thin cytoplasmic extensions of the neuron. The dendrites, which branch out in treelike fashion from the cell body, are specialized to receive signals and transmit them toward the cell body. The single long axon carries signals away from the cell body. In humans, a single axon may be as long as 1 meter (about 3 feet). Some neurons that have cell bodies in the spinal cord have axons that extend all the way down to the toes.
69. A nerve is an enclosed, cable-like bundle of axons (the long, slender projections of neurons). A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons.
70. Nervous Tissue Nerve tissue consists of Neurons and Neuroglia. NEURONS: A cell consisting of dendrites, a body and axon. DENDRITES are branches off the cell body that receive signals. The CELL BODY contains a nucleus and cytoplasm. An AXON carries out nerve impulses from the body. NEUROGLIA: Cells found in nervous tissue. Neuroglia support neurons through nourishment. Picture from Human Biology by Sylvia S. Mader Page 66 Axon Dendrites
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72. Integumentary System : Skin and other organs SKIN: Covers the body, protects tissues, prevents H 2 O loss, regulates temperature, and protects against diseases from entering the body. The skin contains two sections, the epidermis and the dermis. Certain cells can produce Vitamin D with the help of UV radiation. EPIDERMIS: Stratified squamous epithelium. Stem cells get new epidermal cells for skin renewal. Picture from Human Biology by Sylvia S. Mader Page 71 Epidermis Dermis Subcutaneous layer SUBCUTANEOUS LAYER : Constructed of adipose and loose connective tissue. Offers protective layer against external abuse. DERMIS: Thick fibrous (collagen and elastic) tissue under the epidermis. Allows movement and flexibility without tearing. Blood vessels deliver nutrients to the skin while regulating body temperature. Contains sensory receptors. Nails, hair follicles, and sweat glands are accessory organs of skin.
101. changes in epidermal cell shape during keratinisation and three specialised cells within the epidermis: m = melanocyte; L = Langerhans cell; M = Merkel cell (associated with nerve ending).
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109. The sebaceous gland is indicated by the arrow. Note how its duct is unbranched and how it empties into a hair follicle.
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114. Notice the hair shaft, hair follicle, papilla, and the multiple sebaceous glands.
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116. The arrow indicates an arrector pili muscle. In this picture, you should also try to identify the shaft, root, follicle, hair papilla, and sebaceous gland.
118. SKIN, vertical section. Epidermis with keratinized cells, hair in hair follicles, sebaceous glands. Thick dermis.
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121. Organ System Overview Continued DORSAL CAVITY: Contains the Cranial Cavity and the Vertebral Cavity. CRANIAL: Brain VERTEBRAL: Spinal Cord VENTRAL CAVITY: Contains the Thoracic Cavity, Abdominal Cavity, and Pelvic Cavity. THORACIC: Heart, lungs, and esophagus ABDOMINAL: Stomach, Liver, Spleen, Pancreas, Gallbladder, and Intestines PELVIC: Reproductive organs A muscle known as DIAPHRAM separates the thoracic and abdominal cavities. Four Types of Body Membranes MUCOUS: Loose fibrous epithelial tissue which lines the interior respiratory, digestive, urinary, and reproductive systems. Goblet cells secrete mucus to from bacterial or virus penetration. SEROUS: Thoracic cavity and lungs are covered by pleurae, heart is covered by pericardial sac, and the abdominal cavity is covered by the peritoneum. The abdominal organs are attached to the wall by mesentery (double layer peritoneum). Membranes remain lubricated by watery secretion. SYNOVIAL: Loose connective tissue lines cavities of joints and secrete lubricative solution to keep bones moving freely. MENINGES: Protective tissue which covers the brain and spinal cord.
122. Organ System Overview Continued Thoracic Cavity Abdominal Cavity Ventral Cavity Dorsal Cavity Picture from Human Biology by Sylvia S. Mader Page 77
123. Homeostasis: The body’s capacity to physically regulate its internal environment is known as HOMEOSTASIS . All systems work together to help maintain homeostasis. The normal conditions upheld in a cell or organism is known as Homeostasis. For example, the organ systems of humans all work together to perform certain functions such as absorbing nutrients and oxygen, and excreting waste. Picture from Human Biology by Sylvia S. Mader Page 79 They also adjust their processes to maintain regularity such as sweating when the body temperature starts to rise.
124. Homeostasis Continued NEGATIVE FEEDBACK: The internal environment stays fairly stable due to negative feedback mechanisms through sensors and the control center. When a change occurs, a sensor will notify the control center which release an effect to overturn the change. POSITIVE FEEDBACK: When the internal environment senses stimulation from nerve impulses, the brain sends positive signals to not only keep the stimulation going, but to make it stronger. Example of Negative Feedback Cycle
148. Allografting Definition: The transfer of organs or tissue from human to human or from cadaver to human As there are more and more people every year waiting for donor organs and tissues, allografting transplantation has become quite common. Allografting transplantation has many applications.
152. From which animals are we able to transplant organs 1. The Chimpanzee: Its DNA sequence differs from ours by only 2% 2. The Baboon: Its organs are too small for a large adult human 3. The Pig: Surprisingly similar too our anatomy and physiology
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164. Tissue Engineered Heart Valves (TEHV) Heart valve disease occurs when one or more of the four heart valves cease to adequately perform their function, thereby failing to maintain unidirectional blood flow through the heart Surgical procedures or total valve replacement are necessary Adapted from http://z.about.com/d/p/440/e/f/19011.jpg
165. Tissue Engineered Blood Vessels (TEBV) From An Introduction to Biomaterials. Ch 24. Fig.4 Ramaswami, P and Wagner, WR. 2005. Atherosclerosis, in the form of coronary artery disease results in over coronary artery bypass graft procedures. Many patients do not have suitable vessels due to age, disease, or previous use. Synthetic coronary bypass vessels have not performed adequately to be employed to any significant degree
177. www.millenium-biologix.com/Html/00_ScientificInformationCartiGraft.htm Autologous de novo cartilage formed on Skelite™ tissue engineering scaffold (grown in vitro ), illustrating the configuration of the implant that provides functional cartilage tissue at the articular surface. The presence of functional cartilage tissue represents a major advance over current cell therapy techniques. Cell therapy involves the implantation of cells that still have to make new cartilage in vivo at the defect site under very challenging conditions. The histology image on the right shows that cells are healthy and growing, while attaching themselves to the Skelite™ and beginning to differentiate into mature cartilage.
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183. Works Cited Amarin. Lipophilic Platform – Plasma Membrane. Accessed 4 Feb 2008. < http://www.amarincorp.com/science_and_technology/lipophilic_platform.452.399.html >. "Bone." Wikipedia, The Free Encyclopedia . 6 Feb 2008, 05:32 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Bone&oldid=189439576 >. "Cell." Wikipedia, The Free Encyclopedia . 1 Feb 2008, 15:34 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Cell_%28biology%29&oldid=188815215 >. "Cell nucleus." Wikipedia, The Free Encyclopedia . 1 Feb 2008, 01:41 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Cell_nucleus&oldid=188933496 >. "Eukaryote." Wikipedia, The Free Encyclopedia . 1 Feb 2008, 21:56 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Eukaryote&oldid=189118974 >. "Fibrocartilage." Wikipedia, The Free Encyclopedia . 27 Oct 2007, 13:26 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Fibrocartilage&oldid=167424710 >. "Fibrous connective tissue." Wikipedia, The Free Encyclopedia . 7 Dec 2007, 11:12 UTC. Wikimedia Foundation, Inc. 2 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Fibrous_connective_tissue&oldid=176345853 >. Mader, Sylvia S. Human Biology . New York: The McGraw-Hill Companies, Inc, 2008. Pages 41-82. Menlo School. Cytoskeleton. Accessed 5 Feb 2008. < http://sun.menloschool.org/~birchler/cells/animals/cytoskeleton/ >. "Mitochondrion." Wikipedia, The Free Encyclopedia . 22 Jan 2008, 18:59 UTC. Wikimedia Foundation, Inc. 6 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Mitochondrion&oldid=186166731 >. "Osmosis." Wikipedia, The Free Encyclopedia . 4 Feb 2008, 21:04 UTC. Wikimedia Foundation, Inc. 5 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Osmosis&oldid=189106016 >. "Transitional epithelium." Wikipedia, The Free Encyclopedia . 23 Jan 2008, 07:06 UTC. Wikimedia Foundation, Inc. 3 Feb 2008 < http://en.wikipedia.org/w/index.php?title=Transitional_epithelium&oldid=186300028 >. Victoria College. Biology Department - Connective Tissues. Accessed 5 Feb 2008. < http://www.victoriacollege.edu/dept/bio/Belltutorials/Histology%20Tutorial/Basic%20Tissues/Connective%20Tissue.h tml>.
Notas del editor
Biological substitutes that mimic tissues
No shearing. Fully Immobile.
E.g. patient needing a CABG has atherosclerosis and has associated disease which may be varicose veins which cannot be used for grafting. Burns patient needs skin graft but not enough available from own body
Immune response in graft rejection can be hyperacute (mins/hours) polymorphonuclear invasion after cytotoxic antibodies encounter foreign antigens. Causes vascular deterioration. acute (days/months) mononuclear exudate of inflammation that is reversible if treated quickly. chronic (months/years after good function); slow deterioration. Can be confused with recurrence of previous disease. ABO and rhesus crossmatching required, then HLA tissue typing before transplant.
Can hyperacute or acute. Again, vascular system affected because antibodies attack endothelial cells and trigger complement causing micro thrombi so rejection. More genetic differences between species so greater immune response. Diseases: prions such as bovine BSE to human CJD. PERV porcine endogenous retrovirus, porcine tissues decell in use e.g. heart valves but infection risk unknown. Ethics and religion: rearing animals for sacrifice; animal parts inside body.
Most important is off the shelf availability
Myskin in sheffiled. Dermagraft. Clinically: Used to induce wound healing in diabetic foot ulcers, burns. In the lab: studying disease processes e.g. psoriasis, melanoma.
Porcine ureter – advantages: natural, long without branches Many other models, including wrapping cell sheets around a mandrel
Developed by synergraft. Trials were stopped due to early deaths occuring in children. Leaflets did not re-endothelialize in vivo like they had in specifically controlled conditions in vitro. Collagen matrix which was not supposed to be antigenic caused inflammatory response which led to fibrosis around the valve. Synergraft have also developed a bovine ureter-based arteriovenous shunt to be used in patients on renal dialysis. Reduces the risks of infection associated with multiple needle puncture sites.
Collagen matrix decellularised and implanted in sections of urethra in patients with strictures. Stayed patent and functional for up to 7 years. Ideal off-the-shelf availability with autologous cell seeding.
Bladder dysfunction causes not only urinary problems but can also affect renal function. PGA scaffold with autologous urothelial cells seeded, anastamosed to native bladder and covered with omentum. Improved symptoms.
Bovine. Renal cells cloned, seeded onto a membranous scaffold. Urine collected in sub cut. Bags and analysed. Cells shown to have the capacity to filter, reabsorb and secrete. There was no immune response that was expected in using mitochondrial DNA of oocytes in cloning renal cells.
Chondrocytes seeded into matrices made e.g. from PGA or fibrin glue. Useful in patients with cartilage defects or impingent in the knee joint. Picture: lamb model: biodegradable tube seeded with mesenchymal stem cells collected from amnion to fix congenital tracheal defect in lamb. Convenient because trachea not needed before birth so implantation carried out in utero.
TE came to the forefront of research when it emerged as a positive alternative to current surgical and scientific methods. When hurdles became more obvious, interest dwindled. Now scientists are finally getting over some of these problems with pioneering new ideas. Safety – e.g. how do you monitor the patency of a graft after implantation into a patient?
Typical pore size 100 micrometers. Has to allow movement of cells through it so cells don’t aggregate and die. Natural: collagen, fibrin which can be extracted and purified from animals/humans. Can be supplemented with GAGs like hyaluronic acid. Natural materials and no cells so no immune response and less risk of infection Synthetic: PLA, PGA. Foreign so risk of infection but allow precise engineering of properties like mechanical strength, pore size, rate of degradation Hybrids: natural with natural, synthetic and natural, synthetic and synthetic. Can have best of both, improved properties. E.g. getting same burst pressure as native arteries. Niklason et al used smooth muscle cells and PGA, very high burst pressure but not natural. Compromises.
Commercial eg Skin: Myskin in sheffield.
Adult stem cells – could become any cell type within the organ of origin. Embryonic: before differentiation into 3 embryonic tissues so could become any tissue. Blessing because can make them become any tissue. But disadvantage is that their differentiation in vivo is difficult to control. Teratogenic Eg. Stem cells used for a corneal transplant might form wrong cell type eg hair, teeth. Ethics: creating embryos for sacrifice.
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