Tissues and Healing Notes PDF

# Tissues and Healing ## Introduction - The document discusses the structure of plant and animal cells and how these cells divide to form new cells. - It then focuses on how these cells become specialized to carry out specific functions. - Large multicellular organisms are made up of millions of...

# Tissues and Healing ## Introduction - The document discusses the structure of plant and animal cells and how these cells divide to form new cells. - It then focuses on how these cells become specialized to carry out specific functions. - Large multicellular organisms are made up of millions of cells that were all made by repeated mitotic divisions starting with the first cell (zygote). - Early in development most cells look the same. - However, not all cells continue dividing. - Cells differentiate, becoming specialized to carry out special functions. - Cells start to form tissues. ## Definition of a Tissue A tissue is a group of similar cells that have been grouped together to perform a particular function. ## Plant Tissues Some examples of plant tissues include: | Tissue | Description | |---|---| | Epidermal tissue | Consisting of cells forming the outer covering of roots, stems and leaves. | | Xylem Tissue | Consisting of long tube-like cells which transport water up the plant. | | Phloem tissue | Consisting of cells specialized to carry food made in the leaves to other parts of the plant. | | Photosynthetic tissue | Made of cells with thin walls and many chloroplasts. | | Supporting tissue | Cell walls are strengthened or thickened in some way. There are several different types of supporting tissue. | | Storage Tissue | Made up of cells with thin walls and many chloroplasts. | ## Animal Tissues Some examples of animal tissues include: | Tissue | Description | |---|---| | Epithelial tissues | These are covering tissues which are found lining the inside or outside of structures in the body. | | Connective tissues | These include ligaments, tendons, adipose (fat) tissue and areolar connective tissue and blood. | | Skeletal Tissues | Bone tissue and the different types of cartilage. | | Nerve Tissue | Makes up the nerves, brain and spinal cord. | | Muscle Tissue | There are three types of muscle tissue - striated/striped/voluntary muscle, smooth muscle/involuntary muscle and cardiac/heart muscle. | ## Other Levels of Organsation - Different tissues are grouped together to form organs. - An organ is a group of tissues working together to carry out a function. - For example, the stomach is made up of epithelial tissue, muscle tissue, connective tissue, nerve tissue and blood tissue. - The stomach is an organ. - Other organs include the heart, kidneys, lungs, etc. - Organs work together to form systems. - The stomach does not work alone. - It is part of the **digestive system** which includes the mouth, salivary glands, oesophagus, intestines, liver etc. - Other systems include the excretory system, respiratory system, blood circulatory system, and nervous system. ## Animal Tissues - Epithelial Tissues - Epithelium are covering or lining tissues. - They can be divided into two main types: - Simple Epithelium: Consisting of a single layer of cells. - Compound Epithelium: Made up of many layers of cells. - In all epithelia the cells rest on a basement membrane. - This membrane is made of collagen fibres in a jelly substance. - The cells of the epithelium are held together by a cement-like **intercellular substance**. ### Epithelia - Types #### 1. Squamous Epithelium - Made up of extremely flat and thin cells. - Cells bulge where the nucleus is found. - Cells fit quite closely together. - Membranes may be irregular. - Found where exchange of substances takes place such as the lining of blood capillaries and linings of the air sacs (alveoli) of the lungs. - Consists of a single layer of cells. - Flattened cells speed up the rate of diffusion. #### 2. Cuboidal Epithelium - Cells are cubical in shape. - The nucleus of each cell is spherical in shape. - Found in sweat glands, thyroid glands and the liver, as well as the kidney tubules. - Cells are glandular, secreting substances. - May be involved in absorption. - The free surface is covered in finger-like foldings of the cell membrane called **microvilli**. - This surface is also called a **brush border**. - Microvilli increase surface area for absorption. #### 3. Columnar Epithelium - Made of column-shaped cells. - Nuclei are large and slightly oval in shape. - May have a **brush border of microvilli**. - Most of the alimentary canal is lined with columnar epithelium. - Designed for digestion and absorption. - May have goblet cells that produce mucus. - Cells are important for protection as mucus lubricates the surface, keeps it moist, and prevents enzymes and stomach acids from damaging the lining. - Cells may also have a brush border of microvilli to increase the surface area for absorption. #### 4. Ciliated Epithelium - Columnar (sometimes cuboidal) epithelium. - Has hair-like cilia on its free surface. - Designed for moving fluids along tubes in the body. - Found lining the trachea and bronchi. - Protects the lungs from infections. - Goblet cells produce mucus that traps foreign particles. - Cilia move rhythmically, moving mucus up the air tubes and away from the lungs. - Also found in the oviducts, Eustachian Tube. #### 5. Stratified Epithelium - Compound epithelium because it is made of many layers of cells. - The epidermis of the skin is a stratified epithelium. - The bottom layer of cells sits on the basement membrane. - These cells divide rapidly. - As cells move away they become flattened and impregnated with the protein called keratin. - Cells on the outside are dead and scale-like (cornified). - Makes an effective protective covering for the skin. - Found lining the vagina and oesophagus. - Regions are kept moist and the outer layers do not become cornified (impregnated with keratin). ## Connective Tissues - These are a wide variety of tissues that bind and support different tissues or organs of the body. - For example, they bind the skin to the underlying tissues like muscles and they form sheaths around organs. - Usually made up of cells and fibres embedded in an intercellular matrix. ### Types of Connective Tissue #### 1. Areolar Connective Tissue - Found around most of the organs of the body. - Connects the skin to the structures underneath. - Forms a sheath around many blood vessels and nerves. - Holds the different parts of the body together. - Matrix is slightly jelly-like fluid. - Cells and fibres are found scattered in the matrix. - Two types of fibres are found: - **White (collagen) fibres**: Made of the protein collagen and thicker and less elastic than elastin fibres. They are, however, still very flexible. Give tissue strength. - **Yellow elastic (elastin) fibres**: Made of the protein elastin, thinner and more elastic than collagen fibres. Tend to be branched. Allow tissue to stretch. - Fibroblasts: small, flattened, spindle-shaped cells producing collagen. They usually lie very close to the fibres - Macrophages: larger cells varying in shape that engulf bacteria and other foreign particles to fight infection. - Mast cells: small oval cells that are involved in the histamine reaction. #### 2. White Fibrous Tissue (Tendon) - Joins muscle to bone. - Needs to be strong. - Made up mainly of white collagen fibres running parallel to each other. - There is very little matrix and most of the cells are fibroblasts. #### 3. Yellow Elastic Tissue (Ligaments) - Joins bone to bone at joints. - Needs to be very elastic. - Made up of a network of branched elastin fibres. - There is very little matrix, but many scattered fibroblasts. #### 4. Adipose Tissue (Fat) - Is almost entirely made of **fat cells**. - Fat cells are almost completely filed with fat, the nucleus being pushed against the side of each cell. - There is no intercellular matrix and virtually no fibres. - Blood vessels form a network through the tissue. - Stores excess energy (fat). - Protects organs like the heart and kidneys. - May act as a shock absorber and an insulator against heat loss. ## Skeletal Tissues - Tissues that form the skeleton of the body. - Made up of cells and fibres embedded in an intercellular matrix. ### Cartilage - Hard, rubbery and flexible tissue. - Can be compressed slightly. - Protects the ends of bones at joints. - Gives structure to parts of the body that need some flexibility. - Acts as a shock absorber in the skeleton. - Intercellular matrix is firm and rubbery. - Known as **chondrin**. - **Chondroblasts** make the matrix and become enclosed in compartments called **lacunae** once the matrix is made. - **Chondrocytes** are chondroblasts enclosed in lacunae. - Edge of cartilage tissue usually has many fibres and fibroblasts. - This region is called the **perichondrium**. #### Types of Cartilage - Hyaline cartilage: fairly elastic and compressible and is found at the ends of bones, the nose, and forms the C-shaped rings which keep the trachea (windpipe) open. - Yellow elastic cartilage: contains many elastin fibres which makes it much more flexible and elastic and gives support to areas like the ear (pinna) and the epiglottis. - White fibrous cartilage: has many white collagen fibres in the matrix. This forms a very tough kind of cartilage which gives cushioning between bones that take a great deal of stress, for example, the discs between the vertebrae of the backbone. ### Bone Tissue - Makes up the skeleton of most vertebrates. - Strong and non-flexible so muscle can attach to it. - Surrounds and protects some important parts of the body (eg. the brain and spinal cord). - Matrix is hard and consists mainly of inorganic salts containing calcium, phosphorus and magnesium. - These elements are therefore very important for a healthy skeleton. - May also be some collagen fibres embedded in the matrix. - **Osteoblasts** are the bone cells and are found in compartments called **lacunae**. - They are responsible for making the matrix. - **Lamellae**: Concentric rings of matrix around a central canal called a **Haversian canal**. - Lacunae are arranged in rings. - **Haversian canal**: contains an artery and vein and minute canals called **canaliculi** link all lacunae with one another and with the Haversian canal. - One Haversian canal with its concentric rings of matrix and lacunae is known as a **Haversian System**. - Bone tissue is made up of many Haversian Systems which are linked with one another. - May have an outer covering made of many fibres and some blood vessels called the **periosteum**. ## Muscle Tissue - Makes up 40% of a mammal's body mass. - Responsible for contraction and movement. - Made up of highly specialised cells or fibres held together by connective tissue. #### Types of Muscle Tissue - **Striated/Striped (Voluntary) Muscle**: - Moves the skeleton. - Also called skeletal muscle. - Muscle fibres have stripes running across them. - Contracts quickly, creating fast movement. - Fatigues quickly. - **Smooth/Involuntary Muscle**: - Fibres are not striated. - Found around the gut, blood vessels and various other structures of the body. - Responsible for automatic movements like peristalsis. - Contracts more slowly but fatgues slowly. - **Cardiac Muscle**: - Makes up the heart. - Fibres are branched and striped. - Involuntary. - Contracts slowly and rhythmically. - Doesn't fatigue. ## Nerve Tissue - Made up of special nerve cells called **neurons**. - Transmit electrical impulses to and from the brain and spinal cord. ## Blood Tissue - A tissue that is mainly responsible for transporting substances and distributing heat around the body. - Transports oxygen, carbon dioxide, food (nutrients), wastes and hormones. - Defends the body by forming blood clots and fighting disease. - Average adult man has approximately 5½ litres of blood. ### Composition of Blood - A typical connective tissue. - Made up of cells floating in a fluid matrix called blood plasma. #### 1. Blood Plasma - Mostly water in which many other substances are dissolved. - Includes: - glucose - amino acids - salts - hormones - wastes (urea) - plasma proteins - antibodies #### 2. Red Blood Cells (Erythrocytes) - Smallest but most numerous. - About 5 million in 1 cubic mm of blood. - Round, flattened, disc-shaped structures. - Sometimes referred to as being **biconcave discs**. - Main function is the transport of oxygen and, to a lesser extent, carbon dioxide. - Filled with a special iron-containing red pigment called **haemoglobin** which is responsible for carrying this oxygen. - This is what gives them the red colour. - Made in the bone marrow of some bones such as ribs, vertebrae and some limb bones. - Have no nucleus and a limited life of approximately 120 days. - Broken down in the liver and spleen. - The iron from haemoglobin is saved to be used to make new haemoglobin. - Cells are replaced at a very rapid rate (about 9000 million per hour). #### 3. White Blood Cells (Leucocytes) - Slightly larger than red blood cells. - Have a nucleus. - Fight infection. - Divided into two main groups. ##### Types of White Blood Cells - **Granulocytes**: have many small granules in the cytoplasm. - Their nuclei are divided into a number of sections (lobes). - They fight disease by flowing around and engulfing foreign particles. - This method of feeding is called **phagocytosis** and the cells are said to be **phagocytic**. - **Agranulocytes**: have very little cytoplasm because the nucleus is large and almost fills the entire cell. - **Lymphocytes**: Fight disease by making antibodies that destroy foreign organisms. - Most agranulocytes are lymphocytes. - **Monocytes**: Phagocytic and destroy foreign organisms by engulfing them. - All granulocytes, monocytes and some lymphocytes are made in bone marrow, but some lymphocytes are made in lymph glands. #### 4. Blood Platelets (Thrombocytes) - Small fragments of cells without a nucleus. - Formed in the bone marrow. - Involved in blood clotting. - When platelets are exposed to air (such as when a wound occurs,) they release substances that cause plasma protein (fibrin) to change into longer fibres. - Fibres form a tangled mesh over the wound that traps red blood cells and platelets. - This dries up to form a scab to plug the wound. ## Immunity - White blood cells fight disease by destroying foreign germs, like bacteria and viruses. - The body recognises certain proteins called **antigens** on the disease causing agent. - White blood cells are then called into action. - This is known as the **immune reaction** which leads to **immunity**. ### Types of Immunity - **Natural Immunity**: Acquired when the body comes into contact with a foreign antigen. - **Natural active immunity**: Antibodies are formed and destroyed by the immune system. - **Natural passive immunity**: Antibodies are passed from the mother to the child, before or after birth (in milk). - Generally quite short-lived, because the antibodies are used up and not replaced. ### Acquired Immunity - Small amounts of an antigen can be injected into an organism so that the body can learn how to make the antibody before the active antigen arrives. - This done by giving an injection (vaccination) with a harmless form (made safe in some way) of the antigen (vaccine). - The body then has the ability to make the antibody before the harmful form of the antigen enters the body. - If the person comes into contact with the active antigen, the body will destroy the antigen without experiencing the symptoms of the disease. - This is known as **acquired active immunity**. - **Acquired passive immunity**: Antibiotics are injected into another individual. - These antibodies are then extracted from the other organism and injected into a person. - Gives temporary immunity and prevents the person from getting the disease. - Immunisations are done in this way and need to be given regularly. - The antibodies are not made by the organism itself. ## Plant Tissues - All the tissues that have been discussing so far are found in animals. - Plant cells have cell walls. ### Types of Plant Tissue #### 1. Meristematic Tissue - Actively dividing tissue. - Found in parts of the plant where new cells are being formed, such as the tips of the roots and stems. - Cells are small, tightly-packed, with the nuclei occupying most of the cell. - Cytoplasm is dense because they do not have large vacuoles. - Nuclei may appear disorganized because the cells are in the process of dividing by mitosis #### 2. Parenchyma - Found filling spaces between other tissues. - A packing tissue that maintains the shape and firmness of the plant but is also useful as a storage tissue. - Made up of large rounded cells with very thin cellulose cell walls. They have large vacuoles for storage and may contain many starch grains. - There are usually many air spaces between the cells (intercellular air spaces). - The parenchyma tissue found in the leaves of plants contains many chloroplasts for photosynthesis. - This type of parenchyma tissue is known as **chlorenchyma**. #### 3. Collenchyma - A special type of supporting tissue. - Usually found in the outer parts of stems and in the midrib (main vein) of leaves - Cell walls are made up of cellulose but have extra thickening at the corners of the cells. - Cells are living because cellulose is permeable. #### 4. Sclerenchyma - A special type of supporting tissue. - Cell walls have been thickened all round the cell and they have been impregnated with a special carbohydrate called lignin. - Lignin is an impermeable substance, which provides extra strength. - Essential substances cannot enter or leave the cells. - Once the walls have become completely lignified, the cells inside die, leaving a hollow lumen. - Sclerenchyma cells are long fibres which are packed together to form strengthening rods in stems. - The shells of nuts are also made up of sclerenchyma tissue. #### 5. Epidermal Tissue - The plant's equivalent of epithelium. - Found on the outer surface of leaves and stems. - Cells fit tightly together with the outer surface of the epidermis usually having a waxy covering called a **cuticle**. - Prevents excessive water loss. - Thick in plants living in dry areas. - May have special pores called **stomata** for gaseous exchange. - Opening and closing of the stomatal pores is controlled by **guard cells**. - Stomata are more common in leaves (usually on the lower surface) than in stems. - May have **epidermal hairs (or trichomes)**. - These protect the plant from excessive drying out and protect the epidermis from sap-sucking insects. #### 6. Vascular Tissues - Concerned with transporting substances around the plant. - Two main types are found in vascular bundles in the stem, and the central stele of the root. - **Xylem** - **Phloem** ##### Xylem Tissue - Responsible for transporting water, and the mineral nutrients dissolved in it, from the roots to the leaves. - Main transporting cells are **tracheids and vessels**. - Both are hollow structures because the walls have become impregnated with lignin, which is impermeable. - **Tracheids**: - Long cigar-shaped cells, joined end-to-end and overlapping one another. - The end-walls between the cells are perforated, and there are small holes (called pits) found in their side walls. - This allows water to flow freely from one cell to another. - **Vessels**: - Differ in that the end-walls between the cells have usually broken down completely to form continuous tubes running from the roots to the leaves. - The walls of vessels also have pits. - Walls are often not evenly thickened. - May be thickened in a spiral or annular (series of rings) fashion. - This allows them to be strong but flexible, so that they do not break when the plant bends. ##### Phloem Tissue - Responsible for transporting dissolved organic food made by the plant, from the leaves to other parts of the plant. - Includes parenchyma cells and sclerenchyma fibres, but the most important cells are the **sieve tubes and companion cells**. - **Sieve tubes**: - Long cells, joined end-to-end, with the cross walls between them being perforated with many holes. - These perforated end-walls are called **sieve plates** and they allow larger organic food molecules to move through fairly easily. - The cellulose cell walls of sieve tubes are fairly thin and they are not lignified like xylem vessels. - They are living cells. - Don't have nuclei. - **Companion cells**: - Smaller. - Lie next to the sieve tube cells. - They have large nuclei and dense cytoplasm, and it is thought that they provide the energy for the sieve tubes to stay alive and be active. - A large number of plasmodesmata also connect the two cells. ## Arrangement of Tissues in the Stem - The document illustrates how tissues are arranged to form organs...the stem being an organ of a plant. - The stem is made up of vascular bundles which include: - **Xylem**: For transporting water and mineral nutrients. - **Phloem**: For transporting dissolved organic food. - The vascular bundle is surrounded by parenchyma tissue, collenchyma tissue and sclerenchyma fibres with an epidermis on the outside of the stem.