The cell and tissues
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The document discusses the structure and function of cells and tissues in the human body. It defines a cell as the smallest unit of life that can function independently. It then describes the main components of cells, including the cell membrane, cytoplasm, organelles like mitochondria and the nucleus. It explains how cells carry out functions and reproduce through mitosis. It also outlines the four main types of tissues - epithelial, connective, nervous and muscular tissue - and provides details on the characteristics and roles of each type.
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- Bases of all life Smallest unit of matter that can live independently and reproduce itself Exist in all shapes and sizes Elongated Square Star-shaped Oval All have many different functions Tissue is formed from a group of cells The study of the structure and form of cells and tissues is called histology
- Protoplasm – a slightly thick, colourless jelly-like substance Made up of 70% water and Compounds of Organic and inorganic salts Carbohydrates Lipids (fatty substances) Nitrogenous substances – amino acids obtained from protein
- Cytoplasm – jelly protoplasm inside the cell but outside the nucleus contains several different structures and substances: Mitochondria organelles – also referred to as the ‘power houses’ of the cell give the cell its energy supply cell survives upon chemical reactions that take place within the mitochondria results in an energy release and the formation of ATP ATP = Adenosine triphosphate ATP is the main energy transporters within the cell Extract energy from fuels such as glucose in the presence of oxygen to produce a molecule called ATP Provides energy for the cell Ribosomes ‘ Protein factories’ of the cell Produce enzymes and other protein compounds Protein is used for the growth, regeneration and repair of a cell
- Endoplasmic reticulum Network of membranes that forms the ‘circulatory system’ of a cell Rough Endoplasmic Reticulum – named so because of the Ribosomes present on its surface, is most prevalent and transports the protein made by the Ribosomes throughout the cell Smooth Endoplasmic Reticulum – less widespread and involved in lipid and steroid production Golgi apparatus Formed at one end by vesicles which bud off from the endoplasmic reticulum At the other end vesicles are released into the cell This process forms a communication network from deep within cells to its membrane Golgi vesicles are also used to make Lysosomes Lysosomes Organelles containing digestive enzymes which destroy worn-out parts of a cell and bacteria They break down parts of the food allowing them to be used for energy transfer within the cell
- Vacuoles Spaces between the cytoplasm Contain waste materials or secretions formed by the cytoplasm Used for storage or digestion purposes in different kinds of cells Function and importance vacuoles varies greatly according to the type of cell Greater prominence in the cells of plants, fungi than those of animals and bacteria. In general, the functions of vacuole include: Isolating materials that might be harmful or a threat to the cell Contain waste products Maintain internal hydrostatic pressure or turgor within the cell Maintaining an acidic internal pH Containing small molecules Exporting unwanted substances from the cell Centrioles Paired, rod-like organelles that lie at right angles to each other Made of fine tubules which play an important role in mitosis Centrosome Dense areas of cytoplasm containing the Centrioles It is an organelle that serves as the main microtubule organizing centre (MTOC) of the animal cell as well as a regulator of cell-cycle progression.
- Nucleus Centre of the cell, Controls every organelle within the cytoplasm, Processes of growth, repair and reproduction Contained within a nuclear membrane – its special protoplasm is called nucleoplasm Contains DNA, which carries the cells genetic code and chromatin, the material needed to form chromosomes Contains nucleoli, chromatin and nucleoplasm all enclosed by the nuclear membrane Chromatids A chromatid is one of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division Centromere The point where two chromatids join in the chromosome A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come in contact. It is involved in cell division as the point of mitotic spindle attachment.
- Nucleolus The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Small body within the nucleus (usually 1-2 per nucleus) Programmes the formation of ribosomes which then move into the cytoplasm of the cell and produce protein Chromatin Chromatin is the combination of loosely coiled strands of DNA and proteins Prior to cell division - chromatin becomes more tightly coiled, making up chromosomes Chromosomes Chromosomes consist of two chromatids Made up of connected strands of DNA molecules, known as genes. A gene is therefore part of the length of DNA molecule Carry inherited information which makes sure that when cells divide the ‘daughter cells’ are identical to the ‘parent cells DNA – organised into functional units called genes which control cell activities and inheritance
- Nucleoplasm Specialised protoplasm, in which the nucleoli and Chromatin/chromosomes are suspended along with Nutrients and other necessary chemicals
- The cell membrane is made up of three parts phospholipids proteins carbohydrates The cell membrane - acts like a fence - which only certain things can enter - isolates the inside of the cell from its external environment Regulates molecules - only the molecules that the cell needs can enter through the phospholipid bilayer into the cells. Helps in the exchange of harmful products that cannot be used Allows the healthy products into the cell that it needs to use This gate keeping activity is called selective permeability The cell membrane is really thin. Approximately 11,000 membranes stacked on each other equals the thickness of one piece of paper.
- Passive Transport Dependent on the permeability of the cell membrane. There are four main kinds Diffusion Osmosis Facilitated diffusion Filtration
- Passive Transport Dependent on the permeability of the cell membrane. Diffusion Diffusion describes the spread of particles through random motion from regions of higher concentration to regions of lower concentration The cell membrane has tiny pores, Proteins and lipids within the membrane allow small to molecules pass Example - oxygen and carbon dioxide ---------------------------------- Osmosis The diffusion of water molecules across a selectively permeable membrane. The net movement of water molecules through a partially permeable membrane from a solution of high water potential to an area of low water potential. A cell with a less negative water potential will draw in water but this depends on other factors as well such as solute potential (pressure in the cell e.g. solute molecules) and pressure potential (external pressure e.g. cell wall). Osmosis may occur when a cell is submerged in water , the water molecules pass through the cell membrane from an area of low solute concentration (outside the cell) to one of high solute concentration (inside the cell) Cell membrane is selectively permeable, so only necessary materials are let into the cell and wastes are left out When the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at the exact same rate; there is no net flow of water through the membrane.
- Dissolution (or dissolving) A few substances can diffuse directly through the lipid bilayer part of the membrane. The only substances that can do this are lipid-soluble molecules such as steroids, or very small molecules, such as H 2 O, O 2 and CO 2 . This is when fatty substances which are too big to pass through the membrane are dissolved into the lipid part of the membrane lipid diffusion is (obviously) a passive diffusion process, no energy is involved and substances can only move down their concentration gradient. Lipid diffusion cannot be controlled by the cell, in the sense of being switched on or off. Filtration Caused by the difference in pressure either side of the membrane The force of a fluid’s weight pushes against a surface and the fluid is thus moved through the membrane This is called hydro-static pressure - The process responsible for the information of urine in the kidneys. Waist products are filtered out of the blood into kidney tubules because of a difference in hydrostatic pressure. (1) The movement of water and solutes across the cell membrane due to hydrostatic pressure from the cardiovascular system . (2) The process of separating suspended particles from the fluid through a porous material in which the fluid can pass while the suspended particles are retained.
- Active transport Active transport is the pumping of substances across a membrane by a trans-membrane protein pump molecule. The protein binds a molecule of the substance to be transported on one side of the membrane, changes shape, and releases it on the other side. Called active transport because energy is used. Glucose and amino acids are both transferred by active transport. The proteins are highly specific, so there is a different protein pump for each molecule to be transported. The protein pumps are also ATPase enzymes , since they catalyse the splitting of ATP -> ADP + phosphate (Pi), and use the energy released to change shape and pump the molecule. Pumping is therefore an active process , and is the only transport mechanism that can transport substances up their concentration gradient.
- Cell reproduction - achieved through - processes called mitosis During which, exact replicas of chromosomes in parent cells are duplicated to form daughter cells Cells are reproduced sexually through meiosis, a process which produces genetic variation Consists of four main stages Prophase Metaphase Anaphase Telophase Interphase The cell carries out normal metabolic activities DNA is reproduced just before mitosis occurs Nuclear protein is synthesised Cell begins to increases in size
- 1 Prophase Centrosomes divide into two Centrioles - then move away from each other - still joined by the spindle-like threads of the centrosome The chromatin in the cell’s nucleus shortens and thickens - forming into visible pairs of rods called chromosomes - made of condensed chromatin and DNA One chromosome consists of two chromatids joined by a centromere The nucleolus disappears 2 Metaphase The nuclear membrane of the nucleus disappears The chromosomes arrange themselves at the centre of the cell, each attached to the spindle by its centromere By the end – each individual chromosome can be seen distinctly as two chromatids starting to pull apart
- 3 Anaphase The centromere stretches - Centrioles are drawn further apart Pairs of chromatids divide and identical halves of the pairs move to each end of the cell At the end – the spindle threads of the Centrioles divide to from new centromeres and the cell membrane begin to constrict in the centre Telophase A new nuclear membrane appears around each set of chromosomes The spindle fibres disintegrate and the centrioles replicate The cell membrane continues to constrict until two cells are formed Forming two daughter cells – they are two identical copies of the original Eventually these two new cells will again duplicate
- Epithelial tissue (or Epithelium) Simple epithelium - usually functions as a covering or lining for organs and vessels Compound epithelium – provides external protection (fingernails) and internal elasticity (lining of the mouth)
- Simple Epithelium Consists of a single layer of cells attached to a basement membrane Goblet cells often found in simple epithelium – secrete mucus Four types of simple epithelium: Squamous Cuboidal Columnar Ciliated Squamous Flattened cells Forms thin, often permeable lining for the heart, blood and lymph vessels, and alveoli of the lungs – allows diffusion and filtration
- Cuboidal Cube-shaped cells Forms lining of kidney tubules as well as some glands – can secrete substances and absorb them Columnar Tall, rectangular cells – resilient Forms lining in very active parts of the body such as the stomach intestines and urethra Ciliated Mostly columnar cells (sometimes combined with Squamous or cuboids cells) Tiny hair-like projections, or cilia, stick out from the cell membrane The cilia work in waves, all move together and in the same direction Help to remove mucus, foreign matter and debris – keeps passageways and linings clear Example – the lining of the respiratory system
- Many layers of cells and no basement membrane Formed from a combination of deep layers of columnar cells plus flatter cells towards the surface Protects and delicate parts of the body Two types of compound epithelium: Stratified Keratinised (dry) has dried out into keratin, Non-keratinised (wet) Transitional
- Stratified Keratinised (dry) – surface layer has dried out into keratin, a fibrous protein which creates a waterproof layer Compound epithelium with dry surface cells; forms a dead layer – hair, nails skin The skin – keratinised, Squamous epithelium The keratinisation prevents deeper layers from dying out and protects them Non-keratinised (wet) Compound epithelium with wet surface cells e.g. inside the mouth, lining of oesophagus, conjunctiva (mucous membrane) of eyes Provides lubrication Transitional Similar to stratified epithelium except that the surface cells are not flattened and thus can change shape Surface cells – cube-shaped Deeper cells – pear-shaped Found in organs that need waterproof and expandable lining e.g. bladder and ureters
- Nervous tissue Arranged in bundles of fibres Composed of nerve cells and neuroglia Have long fibrous processes – called dendrites and axons Capable of transmitting signals to and from the brain – protective Muscular tissue Three types: Skeletal – striated and voluntary – support and movement Smooth - non-striated and involuntary – carry out involuntary movements Cardiac – striated and involuntary – heart muscle to pump blood
- Areolar Loose connective tissue Most general connective tissue Semi-solid and permeable Contains yellow elastic and white fibres, and fibrocytes and mast cells which produce histamine (protection) and heparin (anti-coagulant, prevents clotting) Found all over the body - under the skin, between muscles supporting blood vessels and nerves and in the alimentary canal - (human gastrointestinal tract (GI tract) Adipose Known as fatty tissue Made up of fat cells containing fat globules Found between muscle fibres and under the skin giving the body a smooth, continuous outline Also found in the kidneys and the back of the eyes Protective and insulator properties; helps retain body heat because it is a poor conductor of heat; also a food reserve
- White Fibrous Strongly connective but not very elastic Mainly closely packed bundles of collagen fibres Few cells in rows that run in the same direction Function is connection and protection of parts of the body e.g. ligaments and periosteum of bone, outer protection of organs – around the kidneys, dura of the brain, fascia of muscle and tendons Lymphoid Semi-solid tissue – has some white fibres Majority of cells are lymphocytes and reticular cells which have a disease control function These cells engulf bacteria and destroys it Forms lymphatic system cells and blood cells Protects against disease, found in lymph nodes, thymus, the spleen, the tonsils, wall of the large intestine, appendix and the glands of the small intestine
- Yellow elastic Mainly composed of elastic fibres - has very few cells Enables stretch and capable of considerable extension and recoil Forms lung tissue, bronchi and trachea, arteries, stomach and bladder Bone Hardest structure in the body; Two types – compact and cancellous Compact is dense bone for strength Cancellous for structure bearing and cellular development Composition – 25% water, 30% organic material, 45% inorganic salts Supports and protects the body and all organs, also produces cells in bone marrow
- Blood Fluid connective tissue Contains 45% cells and 55% plasma Cell content is erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets) Transports food and oxygen to all the cells of the body and removes waste from them (erythrocytes), fights infection (leucocytes) and to clot (thrombocytes) Cartilage Firm, though tissue; solid and contains cells called chondrocytes Three types; Hyaline: Bluish – white, smooth; Chondrocytes cells are grouped together in nests in a solid matrix Particularly resilient Connects and protects Found on articular surfaces of joint Bone which forms joints – forms costal cartilages and parts of the larynx, trachea and bronchi
- Hyaline: Bluish – white, smooth; Chondrocytes cells are grouped together in nests in a solid matrix Particularly resilient Connects and protects Found on articular surfaces of joint Bone which forms joints – forms costal cartilages and parts of the larynx, trachea and bronchi Yellow elastic cartilage: Runs through a solid matrix Contains fibrocyte and chondrocytes cells which lie between multidirectional fibres Flexibility – found in areas which movement is needed the pinna (cartilage part of the ear) and epiglottis (flap of elastic cartilage tissue covered with a mucus membrane, attached to the root of the tongue)
- White fibrocartilage While fibres – packed closely in dense masses; contains chondrocytes cells Extremely tough and slightly flexible Absorbs shock Example – forms intervertebral discs as well as the semi-lunar cartilages (menisci) Also found in the knee joint, hip and shoulder sockets