Cell membrane – encloses the contents of the cell and regulates the flow of substances into and out of the cell. Mitochondrion – this feature produces a substance called adenosine triphosphate (ATP) which is the carrier of energy in all cells. Centriole – these two features made of hollow tubules play a key role in cell division. Ribosomes – these small, granular features of the cell play a key role in the assembly of proteins. Chromosome – During cell division, DNA, the genetic material duplicates and forms linked coils called chromosomes.

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Endoplasmic reticulum – this organelle helps to transport materials through the cell. Rough reticulum is the site of attachment for ribosomes; smooth reticulum is the site of fat production. Nucleolus – this is a small structure inside the nucleus that plays an important role in ribosome production. Nucleus – this is the cells control centre and it mainly contains chromatin, a granular material composed of DNA, the cells genetic material and proteins. The inner nucleus is made up of RNA and proteins.

The nucleus is surrounded by the nuclear envelope, a two-layered membrane with pores. Golgi complex – A stack of flattened sacs receives and processes protein that has been dispatched by the endoplasmic reticulum. The proteins are modified and released at the cell membrane. P2 There are four main types of tissue: epithelial, connective, muscle and nervous. [pic] Epithelial tissue is found in skin and in diverse forms has special functions in other areas of the body.

The main types are: simple epithelium, a single layer of squamous (flat), cuboidal (cube like), or columnar (tall) cells; stratified epithelium, with two or more layers; pseudostratified epithelium, which looks stratified but has only one layer of columnar cells that have surface hairs (cilia) or secrete mucus; and transitional epithelium, which is multi layered and flexible. [pic] Connective tissue – the most common type of connective tissue is loose connective tissue. It holds organs in place and attaches epithelial tissue to other underlying tissues.

Adipose – tissue is a form of loose connective tissue that stores fat. Cartilage – is a form of fibrous connective tissue that is composed of closely packed collagenous fibres in a rubbery gelatinous substance called chondrin. The skeletons of sharks and human embryos are composed of cartilage. Cartilage also provides flexible support for certain structures in adult humans including the nose, trachea and ears. Bone – is a type of mineralised connective tissue that contains collagen and calcium phosphate, a mineral crystal. Calcium phosphate gives bone its firmness. Blood – is considered to be a type of connective tissue.

Even though it has a different function in comparison to other connective tissues it does have an extracellular matrix. The matrix is the plasma and erythrocytes, leukocytes and platelets are suspended in the plasma. [pic] There are 3 main types of muscle tissue. The striated muscle – is attached to and brings about the movement of the various bones of the skeleton. The whole muscle, such as the biceps, is enclosed in a sheath of connective tissue, the epimysium. Striated muscles function in pairs to bring about the co-ordinated movements of the limbs, jaws, eyeballs, etc.

It is directly liked to the breathing process. The non striated muscle – is involuntary. It is made up of thin-elongated muscle cells, fibres. These fibres are pointed at their ends and each has a single, large, oval nucleus. Non striated muscle forms the muscle layers in the walls of hollow organs such as the digestive tract, the walls of the bladder, the uterus, and the walls of the blood vessels. The non striated muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and intestines.

The muscle of the arteries contracts and relaxes to regulate the blood pressure and the flow of blood. Cardiac muscle – The cardiac muscle tissue is only found in the walls of the heart. Cardiac muscle tissue shows some of the characteristics of smooth muscle and some of skeletal muscle tissue. The spaces between the different fibres of the cardiac muscle are filled with areola connective tissue which contains blood capillaries to supply the tissue with the oxygen and nutrients. Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart.

It causes the rhythmical beating of the heart, circulating the blood and its contents throughout the body. [pic] There are two types of nervous tissue. Neurones – are nerve cells. They carry information as tiny electrical signals. There are three different types of neurones, each with a slightly different function. Sensory neurones carry signals from receptors to the spinal cord and brain. Relay neurones carry messages from one part of the CNS to another. Motor neurones carry signals from the CNS to effectors. Neuroglia – are cells that support and protect neurons.

Astrocytes have numerous processes that give the cell a star-shaped appearance. Astrocytes maintain the ion balance around neurons and control the exchange of materials between blood vessels and neurons. Oligodendrocytes have fewer processes than astrocytes. They wrap these cytoplasm processes around neurons to create an insulating barrier called a myelin sheath. Microglia are phagocytic macrophages that provide a protective function by engulfing microorganisms and cellular debris. Ependymal cells line the fluid-filled cavities of the brain and spinal cord. These types of neuroglia are found in the CNS.

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