The School of Biomedical Sciences Wiki - User contributions [en]

Blood donation

2016-10-18T14:49:46Z

140572629: Created page with "Donating blood can be done every 12 weeks for males and every 16 weeks for females. The blood types are divided by two systems; the Rhesus and the ABO system..."

Donating blood can be done every 12 weeks for males and every 16 weeks for females. The [[Blood types|blood types]] are divided by two systems; the Rhesus and the ABO system, which are determined by the [[Antigen|antigens]] and [[Antibody|antibodies]] contained within the blood. Blood type O- is known as the universal donor as it does not contain any A, B or RhD antigens. However, people who are type O- can only receive O- blood in a transfusion as all other types contain either A, B or RhD antigens, or a combination of the three<ref>NHS Choices, Blood Groups (2015). accessed 18/10/16 http://www.nhs.uk/Conditions/blood-groups/Pages/Introduction.aspx</ref>.

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Water

2015-10-19T14:36:59Z

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Water (Molecular formula: H2O) consists of two [[Hydrogen|hydrogen]] atoms and a single [[Oxygen|oxygen]] [[Atom|atom]]. Each [[Hydrogen|hydrogen]] atom forms a [[Covalent_bond|covalent bond]] with the oxygen. Oxygen has a higher [[Electronegativity|electronegativity ]]than hydrogen due to its two lone pairs of electrons. This causes a region of slight negativity (although not enough to create an ion) on the oxygen compared to the hydrogens. This spatial imbalance of [[Electron|electrons ]]is represented by delta negative (δ-) on the oxygen and delta positive signs (δ+) on the hydrogen atoms<ref>Jim Clark (2000-Last modified February 2015) Chemguide available at http://www.chemguide.co.uk/atoms/bonding/hbond.html 19/10/15</ref>. When water [[Molecule|molecules]] interact with each other, the positively charged region ([[Hydrogen|hydrogen]] atom) of one water [[Molecule|molecule]] forms a weak [[Hydrogen bonds|hydrogen bond]] with the negatively charged region ([[Oxygen|oxygen]] atom) of a second water [[Molecule|molecule]] <ref>Alberts et al., Molecular Biology Of the cell, 5th edition, 2008, Garland Science, New York, pg 51</ref>.  This is a hydrogen bond and although it isn't as strong as a covalent bond, it is highly stable and is responsible for the properties and thus abundance of water on Earth. 

Water is a bent molecule there the distribution of charge is assymetric. As a result of the charged regions in water, water is a [[Polarity|polar]] molecule and can conduct electricity. Water molecules react with molecules in aqueous solution through the formation of [[Hydrogen bonds|hydrogen bonds and]] via ionic interactions. These interactions mean that water is a good  and can dissolve polar molecules and ions. Water has small molecules and maintains its physical state of bein a liquid over a large range of temperatures.It is also highly [[Cohesive|cohesive]]. Networks of [[Hydrogen bonds|hydrogen bonds hold]] the structure of ice and liquid water together. These interactions are responsible for the cohesion of water. Water is involved in many different reactions and can affect several [[Noncovalent bonds|noncovalent bonds with]] its presence. Examples of noncovalent bonds that the presence of water can affect are [[Electrostatic interactions|electrostatic interactions]], [[Hydrogen bonds|hydrogen bonds and]] [[Van der waals forces|van der Waals interactions]]. Furthermore when water cannot react with nonpolar molecules through hydrogen bonding or ionic interactions, the result is the [[Hydrophobic|hydrophobic effect that]] is accompanied by [[Hydrophobic|hydrophobic interactions]].<ref>Berg Jeremy M., Tymoczko John L., Stryer Lubert., (2007) Biochemistry, Sixth Edition, New York, W.H. Freeman and Company. P8-9</ref> 

Humans contain around 40 [[Litre|litres]] of water and both unicellular organisms and multicellular cells live in water. 

Many diseases are associated with water, for example excess water ([http://en.wikipedia.org/wiki/Hyperhydration hyperhydration]), not enough water ([[Dehydration|dehydration]]) and many [[Microorganisms|microorganisms]] use water as a form of transport and spread through water, e.g. [[Cholera|Cholera]]. 

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Dative covalent bond

2015-10-18T22:57:28Z

140572629: Created page with " A dative covalent bond, also called a coordinate bond, is 'a shared pair of electrons between two atoms where the electron pair have been provided by one of th..."

A dative covalent bond, also called a coordinate bond, is 'a shared pair of [[Electron|electrons]] between two atoms where the electron pair have been provided by one of the bonding atoms only'<ref>Gent D and Ritchie R (2008)fckLROCR ChemistryfckLRPearson Education Limited</ref>.

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Phenol

2015-10-18T22:38:32Z

140572629:

Phenol is an [[Organic compound|organic compound]] with the [[Molecular formula|molecular formula]] C6H5OH<ref>http://www.chemguide.co.uk/organicprops/phenol/background.html</ref>. The structure is a [[Benzene|benzene ring]] (molecular formula C6H6) with a [[Hydroxyl group|hydroxyl group]] (-OH) directly attached to a carbon in the benzene ring<ref>Jim Clark 2004, ChemguidefckLRAvailable at: http://www.chemguide.co.uk/organicprops/phenol/background.html#topfckLR18/10/15</ref>. Phenol may undergo chemical reactions with other [[Molecules|molecules]], for example with [[Bromine|bromine]] Br2. It can be toxic in water and it's crystals are pink and white in colour<ref>Deprez Philippe, Chapter 25 Textbook of Chemical Peels, First Editiom http://informahealthcare.com/doi/abs/10.3109/9780203347416.028</ref>. It smells of disinfectant and will cause immediate white blistering if it comes into contact with skin<ref>http://www.chemguide.co.uk/organicprops/phenol/background.html</ref>.

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Smooth muscle cell

2014-11-28T12:13:19Z

140572629:

Smooth muscle has elongated spindle shaped cells with a single [[Nucleus|nucleus]]. Unlike [[Skeletal_Muscle|skeletal muscle]], which appears striated when stained and viewed under a light microscope, the contractile filaments in smooth muscle cells aren't arranged in such an ordered, linear way. The contractile proteins are [[Actin|actin]] and [[Myosin|myosin]], the same as in skeletal muscle cells.The amount of myosin in smooth muscle cells is considerably less than in cells of skeletal muscle; the ratio of actin to myosin is about 15:1 for smooth muscle, compared to only 2:1. Smooth muscle cells are located within the walls of tubular or hollow organs or vessels for structural support. These can be divided into subtypes of smooth muscle cells; those in the vascular system, respiratory system, intestines, the eye and reproductive organs.

[[Muscle_contraction|Contraction]] of smooth muscle is controlled by the autonomic nervous system, meaning its movements are primarily involuntary. However, as opposed to skeletal muscle, it can also be controlled by chemical and physical signals. This means that either an action potential is required to cause a change in membrane potential, or the opening of stretch-mediated ion protein channels; they both bring about contraction.

Smooth muscle cell contraction is regulated by the calcium binding protein calmodulin. When there is an increase in calcium ion concentration, calmodulin attaches to caldesmon, which is an actin-binding protein. Caldesmon normally blocks the myosin-binding sites on actin filaments. As calmodulin attaches to caldesmon it releases actin, causing the myosin heads to bind to the actin filaments. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). [[Contraction|Contraction]] is initiated by calcium-regulated phosphorylation of myosin<ref>Walter F. Boron, E. L. (2009). Medical Physiology (2nd ed.). Philadelphia: Saunders Elsevier.</ref>. Apart from calcium ions, smooth muscle activity can also be regulated by external signalling molecules, for example, adrenaline. When adrenaline binds to the receptor and changes its shape, this in turns alters the structure of the G protein that binds to the receptor. This causes an increase of level of cyclic AMP inside the cell, which activates protein kinase. Protein kinase then phosphorylates and inactivates myosin light chain kinase, eventually leading to relaxation of the smooth muscle. Smooth muscle contraction is significantly slower than skeletal muscle contraction. It usually takes nearly a second whereas skeletal muscle takes a few milliseconds<ref>Alberts, B. (2002). Molecular biology of the cell (4th ed.). New York: Garland Science.</ref>. 

=== References ===

<references /> Silverthorn D, Johnson B, Ober W and Silverthorn C. (2012) Human Physiology: An Integrated Approach. 6th Edition

American Physiology Society. Advances in Physiology Education: Smooth Muscle Contraction and Relaxation (2014) Available at: http://advan.physiology.org/content/27/4/201

Smooth muscle cell

2014-11-27T22:32:52Z

140572629:

Smooth muscle does not have [[Actin|actin]] and [[Myosin|myosin]] arranged into arrays like stirated muscle so appears uniformed under a microscope when stained. The content of myosin in smooth muscle cells is considerably less; the ratio of actin to myosin is about 15:1 whereas in striated skeletal muscle cells the ratio is 2:1. A smooth muscle cell is located within the walls of tubular or hollow organs or vessels for structural support. It is involved in physiologically substantial processes within the body including: regulation of blood flow through the vascular system; movement of the iris and expulsive actions of the urinary bladder and the uterus during childbirth. Smooth muscle cells have an elongated spindle shaped cell with a single [[Nuclei|nuclei]]. Smooth muscle contracts using the sliding filament mechanism, where [[Actin|actin]] and [[Myosin|myosin]] slide over each other. This mechanism requires energy which is provided by the hydrolysis of [[ATP|ATP]]. Instead of using troponins, which are used in skeletal muscle cell contraction, smooth muscle cell contraction is regulated by the calcium binding protein calmodulin. When there is an increase in calcium ion concentration, calmodulin attaches to caldesmon, which is an actin-binding protein. Caldesmon normally blocks the myosin-binding sites on actin filaments. As calmodulin attaches to caldesmon it releases actin, causing the myosin heads to bind to the actin filaments. The globular heads that protrude from the myosin molecule bind to the actin filament which forms crossbridges. The myosin moves along the actin and then releases from the actin (also requiring the use of ATP). [[Contraction|Contraction]] is initiated by calcium-regulated phosphorylation of myosin<ref>Walter F. Boron, E. L. (2009). Medical Physiology (2nd ed.). Philadelphia: Saunders Elsevier.</ref>. Apart from calcium ions, smooth muscle activity can also be regulated by external signalling molecules, for example, adrenaline. When adrenaline binds to the receptor and changes its shape, this in turns alters the structure of the G protein that binds to the receptor. This causes an increase of level of cyclic AMP inside the cell, which activates protein kinase. Protein kinase then phosphorylates and inactivates myosin light chain kinase, eventually leading to relaxation of the smooth muscle. Smooth muscle contraction is significantly slower than skeletal muscle contraction. It usually takes nearly a second whereas skeletal muscle takes a few millisecond<ref>Alberts, B. (2002). Molecular biology of the cell (4th ed.). New York: Garland Science.</ref>.  === References === <references></references>