Comparing Different Cells
All cells in the human body are made when a sperm cell and an egg cell fuse together.

Cell which have adapted to a specific function are known as specialized cells. These cells are grouped together to form tissues. When tissues combine together, they form organs and organ systems.

Stem cells are defined by their potential to differentiate in a range of specialized cells.
At fertilization, a zygote is formed when two haploid gametes fuse together. The single cell will develop into a brand new organism, which includes external tissues such as the placenta. It is a totipotent stem cell.

The zygote develops into a blastocyst, after a few divisions. The outer layer of cells forms the placenta, whereas the inner mass of cells develops into an embryo

The inner cells can differentiate into any part of the new embryo, but it cannot now form part of the placenta. They are pluripotent stem cells.

As the embryo develops, some cells differentiate fully and therefore no longer are classed as stem cells, but are classed as specialized body or somatic, cells. Other develops into more specific forms of stem cells, which are multipotent stem cells.

Multipotent cells lie dormant in the body’s tissues throughout adult life. These are now known as adult stem cells. For example, haematopoietic cells in bone marrow divide to replace lost or damaged blood cells.

The tree types of stem cells are:
1. Embryonic Stem Cells: these include those which are found within the embryo, the foetus or the umbilical cord blood. Embryonic stem cells can give rise to about any cell in the human body; however this depends on when they were harvested.
2. Adult Stem Cells: these can be found in infants, children and adults. They exist in tissue that has already developed such as those in the heart, kidney and the brain.
3. Induced Pluripotent Stem Cells (IPSC): these are adult differentiated cells which have been “programmed” experimentally into stem cell-like state.

There are four main groups of specialized tissue which makes up the human body.

Epithelial Tissue

It covers the whole of the body surface, which is made up of cells that are closely packed together and are arranged .The internal and external body surfaces’ covering/lining is made up from epithelial tissue, as this is what it is specialized to do.
They are packed closely together tightly so that there are almost no intercellular spaces and there is only a small amount of intercellular substance. No matter what type it is, it is usually separated underlying tissue by the basement membrane (this is the provider of structural support of the epithelium and also bids it to the neighbouring structures).
There are two types of epithelial tissue.
1. Simple Epithelium: this can then be subdivided depending on the shape and function of its cells. a) SQUAMOUS (PAVEMENT) EPITHELIUM: - These appear to be thin and flat plates. - The shape of it nucleus resembles the form of the cell; it also helps to identify the epithelium type. - For example, they tend to have horizontal, flattened, elliptical nuclei because of the thin and flattened form of the cell. - Cavity linings such as mouth, blood vessels, heart and lungs are made from these, and they also make up the outer layers of the skin. [pic][pic]

b) SIMPLE CUBOIDAL EPITHELIUM - In shape, cuboidal cells are roughly square or cuboidal. - However, each of these cells has a spherical nucleus, in the centre of the cell. - Cuboidal epithelium found in kidney tubules lining, glands and in the gland ducts.
[pic] [pic] c) SIMPLE COLUMNAR EPITHELIUM - These occur in one or more layers. - The cells are elongated and shaped like columns. - The cell’s nuclei are also elongated and are usually found located near the cells base. - They form the stomach and intestines lining. - Some however, are specialized for sensory reception.
[pic] [pic] d) CILIATED COLUMNAR EPITHELIUM - These are similar to the simple columnar epithelium. - However, they have addition to them, which is that these have fine hair-like outgrowth cilia on their free surfaces. - The cilia are capable of rapid, rhythmic and wavelike beatings in a certain way. - This movement then causes mucus, which goblet cells secrete to flow/stream in that direction. - Ciliated epithelium is usually found in air passages, like in the nose. - It can also be found in other areas such as the uterus and fallopian tubes in females. [pic] [pic] e) GLANDULAR EPITHELIUM - This is columnar epithelium but with goblet cells. - Some parts of this consist of a large number of goblet cells, meaning that there are few epithelial cells left. - Columnar and cuboidal epithelial cells often become specialised as glad cells. - These are then able to synthesise and secrete certain substances such as enzymes, hormones, milk, mucus, sweat, wax and saliva.
[pic][pic]
2. Stratified Epithelium: this is where linings of the body have to endure wear and tear. The epithelia which are made up of several layers of cells are called stratified epithelium. The cells at the top are flat and scaly, which it may or may not be keratinised. [pic]

Epithelial tissues have many functions. ➢ Protection – epithelial cells from the skin protects ant underlying tissues from harmful chemicals, from injury etc. ➢ Sensation – sensory stimuli enters specialised epithelial cells. ➢ Secretion – when in the glands, epithelial tissues are specialised to secrete certain chemical substances. ➢ Absorption – certain cells that line the small intestines absorb nutrients from the digestion of food. ➢ Excretion – in the kidneys, they excrete was products from the body and reabsorb the needed materials from the urine. Sweat is also excreted from the body by sweat glands. ➢ Diffusion – simple epithelium encourages gas, liquid and nutrients to diffuse. This is because they form a thin lining, they are also ideal for gas diffusion. ➢ Cleaning – ciliated epithelium helps of the removal of particles of dust and other foreign bodies, which are in or blocking, the air passages. ➢ Reduces Friction – the epithelial cells that line the whole circulatory system reduced friction between blood and the blood vessel walls.

Connective Tissue

They function to support the body and also to bind and functions all tissue types. Connective tissue provides a skeleton that plays an important role in locomotion. Connective tissue is described as large amounts of intercellular substance.
They are reasonably few cells, but they are widely separated from each other. These are the importance for the secretion of large amounts of intercellular ground substance (matrix).
There are three divisions of connective tissue. 1. Cartilage: it is found in close contact with the bone in the body. It is tough, elastic, flexible and also semi-transparent. Its ground substance is mainly consistent of glycoprotein material and chondroitin. It is then covered by a fibrous membrane which is dense and is known as the perichondrium.

[pic]

There are three types of cartilage. a) HAYLINE CARTILAGE: It is semi-transparent and is a bluish-white colour. Even though it is very strong it is also flexible and elastic. This type consists of living cells are known as chondrocytes. These are located far apart in the lacunae (these are fluid filed spaces). It is in the trachea, larynx, and the nose tip. It is also the connection between the ribs and the breast bone. You will also be able to find it at the ends of the bones where joints are formed. It has many funcions: ➢ Reduces Friction at Joints – as a result of the smooth surface, it provides a sliding area which reduces the friction, and therefore making it easier for bone movement. ➢ Movement – it joins bones firmly together, in a way that only a certain amount of movement is possible. ➢ Support – c-shaped cartilaginous rings in the windpipes helps in keeping the tubes open. ➢ Growth – it is responsible for the longitudinal growth of bone in the neck regions of the long bones. [pic]

b) WHITE FIBROCARTILAGE: This is an extremely tough tissue. The bundles direction is dependent on the stresses acting on the cartilage. The collagenous bundles are in a parallel direction to the cartilage. Fibrocartilages are discs which are found between the vertebrae between pubic bones, these are in front of the pelvic girdle and also around the edges of the articular cavities. It has many functions: ➢ Shock absorber – cartilage between the adjacent vertebrae absorbs the shocks that will damage and jar the bones whilst we run or walk. ➢ Provides Sturdiness without Impeding Movement – it forms a joint which is firm between the bones, but it allows for a reasonable degree of movement. ➢ Deepens Sockets – in articular cavities, they deepen the sockets to make dislocation less possible

c) ELASTIC CARTLIAGE: This is similar to hyaline cartilage. However it is different because the matrix contains a full network of yellow branched elastic fibres. The fibres run in all directions through the matrix. You can find this in the ear lobe, epiglottis and in larynx parts. It has many functions: ➢ Maintaining its Shape – in the ear, this type of cartilage helps the maintenance of the shape and the flexibility of the organ ➢ Support – it strengthens and supports these structures.
[pic]

2. Bone: bone tissue occurs in the different bones that we have in our body. It consists of living cells with large amounts of ground substance/matrix. It consists of a shaft and a thickened end at each end. It has many functions: ➢ Support – skeleton forms a supportive framework. This gives the body its shape and rigidity. ➢ Locomotion – the bone tissue forms a system of levers to which the voluntary muscles are attached. ➢ Protection – the bones protects soft and delicate organs on the body. For example, the skull protects the brain. ➢ Manufacturing Blood Cells – red blood cells are made in the red bone marrow. This is located in the spongy tissue at the ends on long bones. ➢ Homeostasis – bones help to maintain a constant level of calcium in the blood.

[pic]

3. Blood:

[pic]

a) BLOOD PLASMA: It is a yellowish, strae-coloured liquid. It is 90% water. Dissolved substances make up the other 10%. Of this 10% the following are the most important: 2% is organic constituents, 7% are plasma proteins, and then you have inorganic salts and ions; secretions; dissolved gases and antibodies. They have many functions: ➢ Plasma transports all the various types of blood around the body. ➢ It transports food and nutrients to various tissues in the body from the digestive system. ➢ Transportation of waster products from the tissues. ➢ Fibrinogen is important in blood clotting ➢ Transports hormones to their targeted organs where a specific function is bought out. ➢ Albumen and globulin regulates the cells water content and extracellular body fluids. ➢ Globulin brings about antibodies which gives us the immunity that we have to various diseases. ➢ If there is a proper balance of ions, it allows the normal functioning of the nerve, muscles etc. to take place.

[pic] b) ERYTHROCYTES (RED BLOOD CELLS): These are small, round, bi-concave discs that float in the blood plasma. They are yellowish in colour but when in large numbers they are red. They are also soft, flexible and elastic, so they can easily move through narrow blood capillaries. The have many functions: ➢ They are the transportation of oxygen in the blood from the lungs to all tissues and cells in the body. ➢ They help transport carbon (IV) oxide from tissues to the lungs. ➢ It is important in regulating the acid-base balance of the blood. ➢ It helps when there are blood clots. [pic]

c) LEUKOCYTES (WHITE BLOOD CELLS): These are larger than erythrocytes and have a definite nucleus. They don’t have a regular shape and are nearly colourless. There are five types which then can be divided into two groups: granular white blood cells and non-granular white blood cells. White blood cells have two principals, these are neutrophils (most abundant and produced in the red bone marrow) and lymphocytes (produced by the spleen, tonsils and lymph nodes and are the smallest of the white blood cells). It had many functions: ➢ Neutrophils: ▪ Active in phagocytosis and defends us against viruses that are harmful as well as bacteria and other foreign intruders. ▪ They play a role in wound healing and repairing worn out and damaged tissues. ▪ Prevents infections from spreading to other tissues in the body. ➢ Lymphocytes contribute to the synthesis and distribution of antibodies in and around the blood. The B-cells are responsible for humeral or antibody immunity and the T-cells for cellular immunity.

[pic] d) BLOOD PLATELETS: These are plate-like discs which are sml in size and also colourless. They are not true cells however they are cytoplasmic fragments of large cells, these are found in red bone marrow. If a tissue is damaged, the platelets leave the blood vessels and release a substance. The substance transforms soluble fibrinogen in the plasma to a network or fibrin threads. It has one function: ➢ They play an important role in the initiating process of blood clotting and in the plugging up and sealing of damaged blood vessels and forms tissues.

[pic]

Muscle Tissue

They have the ability to relax and contract.
There are three type of muscle tissue: 1. Smooth Muscle Tissue: This is made up of thin and elongated muscle cells and fibres. Each of these fibres are interlaced with each other, this is to form sheets/layers of muscle tissues rather than bundle of muscle tissues. It is an involuntary tissue. They have two functions: ➢ They control slow involuntary movements ➢ The arteries muscles contracts and regulate the blood pressure and blood flow of the body.

[pic] [pic]

2. Skeletal Muscle Tissue: This is the most abundant. They are attached to being out the movement of various bones of the body. During its contraction, the acting filaments stride inwards. For this to take place, energy is need, this is supplied by the mitochondria of the cells. The contraction is very quick and is very forceful. It has two functions: ➢ They function in pairs. This brings out the coordinated movements of the limbs, tunic jaws, eyelids etc. ➢ They are involved directly in the process of breathing. [pic] [pic] 3. Cardiac Muscle Tissue: It is unique as you can only find it the walls of the heart. Its fibres have cross-striations and contain numerous amounts of nuclei. It is involuntary. It differs from striated muscle as: ➢ They are shorter in size ➢ Striations are not as obvious ➢ There is only one nucleus present in the centre of each cardiac fibre. ➢ The adjacent fibres branch out but are also linked to each other by muscle bridges. The have two functions: ➢ They play an important role in the contraction of the atria and ventricles of the heart. ➢ They cause the beating of the heart, circulating the blood and its contents throughout the body as a consequence. [pic][pic]

Nervous Tissue

They are made to react to stimuli and to conduct impulses to various body organs. Nerve tissues are made up of neurones. These neurones are then stimulated and transmit impulses very rapidly.
A motor neurone has many processes (dendrites). A single process, the axon, leaves at the other end. Dendrites are usually short and divided whilst axons are very long and they don’t branch freely. Impulses are then transmitted in one direction.
[pic]
There are three classifications of neurones:
1. Unipolar Neurones: Snesory neurones only have a single process/fibre, which divides close to the body of the cell into two main bracnhes. They are known as unipolar neurones because of their structre.
2. Multipolar Neurones: These are motor neurones which have numerous processes.
3. Bi-Polar Neurones: These are spindle shaped. They have a dendrite at one end and an axon at the other end.

[pic] Nervous tissues have many functions: ➢ They allow an organism to sense stimuli in both environments (internal and external). ➢ The stimuli is analysed and interegated to provide appropriate, coordinated responses in vairous organs. ➢ Sensory neurones conduct nerve impulses from sense organs and receptors to the central nervous system (CNS). ➢ Connector neurones supply the connection between the afferent and efferent neurones as well as different parts of the CNS. ➢ Somati motor neurones transmit the impulses from the CNS to a muscle which then reacts to the initial stimulus. ➢ Autonomic motor/efferent neurones transmits impulses to the involuntary muscles and glands. ➢ [pic]

References

❖ INFORMATION • http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/ • http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/Epithelial.htm • http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/Connective.htm • http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/muscle.htm • http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/nervous.htm • http://science.howstuffworks.com/life/cellular-microscopic/stem-cell1/htm

❖ PICTURES • http://www.google.co.uk/imgres?q=simple+squamous+epithelium+micrograph&hl=en&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=Q_EyABhr58qPUM:&imgrefurl=http://www.medicalhistology.us/twiki/bin/view/Main/EpitheliumAtlas01&docid=V6G-y_aWq7K1TM&imgurl=http://www.medicalhistology.us/twiki/pub/Main/ChapterOneSlides/a28_simple_squamous_epithelium_renal_artery_vein_40x_he_labeled.jpg&w=800&h=643&ei=b0tSUby5CoPR0QX6k4CQDA&zoom=1&iact=hc&vpx=593&vpy=418&dur=2198&hovh=201&hovw=250&tx=142&ty=139&page=1&tbnh=137&tbnw=187&start=0&ndsp=29&ved=1t:429,r:17,s:0,i:130 • http://www.google.co.uk/imgres?q=SIMPLE+CUBOIDAL+EPITHELIUM+micrograph&um=1&hl=en&sa=N&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=DqxRBbsl1iEzrM:&imgrefurl=http://www.mesacc.edu/~saufr37291/anatomy/epithelial_tissue.html&docid=jBwRy5P8r-6gxM&imgurl=http://www.mesacc.edu/~saufr37291/anatomy/images/sc.jpg&w=408&h=367&ei=VU9SUdrYE-G60QXd2oCwBA&zoom=1&iact=hc&vpx=1005&vpy=270&dur=214&hovh=213&hovw=237&tx=173&ty=137&page=1&tbnh=134&tbnw=145&start=0&ndsp=28&ved=1t:429,r:12,s:0,i:118 • http://www.google.co.uk/imgres?q=SIMPLE+COLUMNAR+EPITHELIUM+micrograph&um=1&hl=en&sa=N&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=Ams1PIpBAEi8XM:&imgrefurl=http://www.lima.ohio-state.edu/biology/archive/epithelial_tissue.htm&docid=37eM81ygAncMkM&imgurl=http://www.lima.ohio-state.edu/biology/images/anatomy/Pseudosratified%252520columnar%252520epithelium%252520400X.jpg&w=607&h=480&ei=lU9SUdiUK6u00QWhv4H4CA&zoom=1&iact=hc&vpx=1140&vpy=267&dur=1372&hovh=200&hovw=253&tx=185&ty=133&page=1&tbnh=144&tbnw=195&start=0&ndsp=27&ved=1t:429,r:13,s:0,i:121 • http://www.google.co.uk/imgres?q=glandular+epithelium+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=H7X2I2b2ndoTuM:&imgrefurl=http://www.ouhsc.edu/histology/text%2520sections/epithelium.html&docid=5dbGYWzMSUYHPM&imgurl=http://www.ouhsc.edu/histology/Glass%252520slides/80_03.jpg&w=400&h=297&ei=DudSUc2iMoXY0QXHmYDwDw&zoom=1&iact=hc&vpx=1132&vpy=2&dur=992&hovh=193&hovw=261&tx=132&ty= • http://www.google.co.uk/imgres?q=white+fibrocartilage+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=OplNt8Qw9XFHbM:&imgrefurl=http://www.masterfile.com/stock-photography/image/861-03350768/Human%2520white%2520adipose%2520tissue%2520or%2520white%2520fat%2520tissue,%2520H%26E%2520stain.%2520LM%2520X100&docid=CJNSV6EPKZjTUM&imgurl=http://image1.masterfile.com/em_w/03/35/07/861-03350768w.jpg&w=550&h=388&ei=VvdSUcnfOoLG0QWv64GwBA&zoom=1&iact=hc&vpx=87&vpy=273&dur=1058&hovh=188&hovw=267&tx=145&ty=88&page=1&tbnh=139&tbnw=197&start=0&ndsp=33&ved=1t:429,r:8,s:0,i:106 • http://www.google.co.uk/imgres?imgurl=http://kentsimmons.uwinnipeg.ca/cm1504/15lab42006/lb4pg6_files/image017.jpg&imgrefurl=http://kentsimmons.uwinnipeg.ca/cm1504/15lab42006/lb4pg6.htm&h=323&w=432&sz=26&tbnid=Ifv21_y3i2uh8M:&tbnh=90&tbnw=120&prev=/search%3Fq%3Dhyaline%2Bcartilage%2Bmicrograph%26tbm%3Disch%26tbo%3Du&zoom=1&q=hyaline+cartilage+micrograph&usg=__sXsLfupP7tBR0GaocpXEKa_VxYc=&docid=yYIm3jAf_-khqM&sa=X&ei=9_VSUemwH4e50QW--4HAAQ&ved=0CD8Q9QEwAw&dur=1630 • http://www.google.co.uk/imgres?q=elastic+cartilage+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=mQBI1ySZGbDt_M:&imgrefurl=http://faculty.une.edu/com/abell/histo/histolab3.htm&docid=m7dMu71D0MC7jM&imgurl=http://faculty.une.edu/com/abell/histo/elascart1.gif&w=336&h=252&ei=m_hSUYP8M6KI0AWggIG4Cg&zoom=1&iact=hc&vpx=785&vpy=126&dur=766&hovh=194&hovw=259&tx=98&ty=147&page=1&tbnh=142&tbnw=181&start=0&ndsp=31&ved=1t:429,r:5,s:0,i:97 • http://www.google.co.uk/imgres?imgurl=http://www.biog1105-1106.org/demos/105/unit10/media/bone.gif&imgrefurl=http://www.biog1105-1106.org/demos/105/unit10/unit10slides.html&h=738&w=1296&sz=45&tbnid=oSOUGhWKxY3kPM:&tbnh=82&tbnw=144&prev=/search%3Fq%3Dbone%2Bmicrograph%26tbm%3Disch%26tbo%3Du&zoom=1&q=bone+micrograph&usg=__DecYgxF7PoK6OBwKzbK1Dw7pGBQ=&docid=dBd9KSSj0tn-RM&hl=en&sa=X&ei=4BpTUcO6Hc-n0wXo3YHwBA&ved=0CC8Q9QEwAA&dur=747 • http://www.google.co.uk/imgres?q=blood+plasma+micrograph&um=1&hl=en&sa=N&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=flHya18M1w8FOM:&imgrefurl=http://www.wadsworth.org/chemheme/heme/microscope/plasmacell.htm&docid=1T1P0w2VtJwi5M&imgurl=http://www.wadsworth.org/chemheme/heme/microscope/pix/plasmacell_nw.jpg&w=399&h=299&ei=kh1TUaSkM6720gWW14CQBg&zoom=1&iact=rc&dur=2&page=1&tbnh=133&tbnw=169&start=0&ndsp=29&ved=1t:429,r:0,s:0,i:82&tx=82&ty=70 • http://www.google.co.uk/imgres?imgurl=http://www.optics.rochester.edu/workgroups/cml/opt307/spr06/john/lesoineTEMSEM_files/image006.jpg&imgrefurl=http://www.optics.rochester.edu/workgroups/cml/opt307/spr06/john/lesoineTEMSEM.htm&h=480&w=641&sz=21&tbnid=BypClhbHgGfSHM:&tbnh=90&tbnw=120&prev=/search%3Fq%3Derythrocytes%2Bmicrograph%26tbm%3Disch%26tbo%3Du&zoom=1&q=erythrocytes+micrograph&usg=__0QIwcH2chb6X5B1QdDC9IbW4eeA=&docid=P_hwsTCsCyh1zM&sa=X&ei=2x5TUbGKM5C00QWS6YC4Cg&ved=0CEgQ9QEwBA&dur=1001 • http://www.google.co.uk/imgres?q=leukocytes+micrograph&um=1&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=dy5SpIidr0QDUM:&imgrefurl=http://www.masterfile.com/stock-photography/image/861-03350303/The%2520inside%2520of%2520a%2520vein%2520showing%2520white%2520blood%2520cells%2520or%2520leukocytes.%2520%2520%2520%2520SEM%2520X2685&docid=lib0RWPBemR6xM&imgurl=http://image1.masterfile.com/em_w/03/35/03/861-03350303w.jpg&w=550&h=422&ei=XyJTUdjFDoHJ0AXA8oHAAg&zoom=1&iact=rc&dur=327&page=1&tbnh=141&tbnw=182&start=0&ndsp=31&ved=1t:429,r:0,s:0,i:82&tx=139&ty=87 • http://www.google.co.uk/imgres?q=cardiac+muscle+tissue+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=8Gb6XuS34EkPxM:&imgrefurl=http://biologyonline.us/Online%2520Human%2520Biology/HB%2520Lab/HB%2520Lab%25205/28.htm&docid=qDdRFeH2SyFS9M&imgurl=http://biologyonline.us/Online%252520Human%252520Biology/HB%252520Lab/HB%252520Lab%2525205/images/cardiac_muscle.jpg&w=588&h=382&ei=51lTUfnYC8jV0QXAsYDwAg&zoom=1&iact=hc&vpx=759&vpy=2&dur=3722&hovh=181&hovw=279&tx=144&ty=90&page=1&tbnh=135&tbnw=201&start=0&ndsp=28&ved=1t:429,r:4,s:0,i:94 • http://www.google.co.uk/imgres?q=skeletal+muscle+tissue+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=GHZxJYbAe8-VXM:&imgrefurl=http://home.earthlink.net/~dayvdanls/IHP2.html&docid=pIcY1k0yDPr8mM&imgurl=http://www.unm.edu/~jimmy/skeletal_muscle.jpg&w=540&h=400&ei=MFhTUai3BYWH0AWx3YCwBg&zoom=1&iact=rc&dur=153&page=1&tbnh=142&tbnw=192&start=0&ndsp=28&ved=1t:429,r:7,s:0,i:103&tx=79&ty=115 • http://www.google.co.uk/imgres?q=nervous+tissue+micrograph&hl=en&sa=X&rls=com.microsoft:en-gb&biw=1440&bih=737&tbm=isch&tbnid=XuieFFJeinwZ3M:&imgrefurl=http://dc317.4shared.com/doc/R0Ghe_AP/preview.html&docid=Oi2Xex81aF7bPM&imgurl=http://dc317.4shared.com/doc/R0Ghe_AP/preview_html_7dc28cdd.jpg&w=580&h=731&ei=xV1TUfLACMWc0AWviIDgAg&zoom=1&iact=rc&dur=156&page=3&tbnh=142&tbnw=110&start=69&ndsp=39&ved=1t:429,r:87,s:0,i:349&tx=35&ty=88

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TOTIPOTENT Stem Cells (e.g., zygote)

PLURIPOTENT Stem Cells (e.g. embryonic stem cell)

DECREASING
POTENCY

MULTIPOTENT Stem Cells (e.g., adult stem cell)

SOMATIC Stem Cells (e.g., Red Blood Cells)

White Fibrocartilage