P2.
Outline the structure of the main tissues in the human body.
A tissue is a group of similar cells. An organ contains different tissues, that work together to carry out different functions.
The four main types of tissues are: 1) Epithelial tissue 2) Nervous tissue 3) Muscle tissue 4) Connective tissue

Epithelial Tissues.
This is located on the internal and external body cavities and surfaces, including tubes and channels (ducts), carrying discharge from glands.
They may be made by several layers of cells, which is called compound Epithelia or a single layer is called simple Epithelia. The lower/bottom part of the cell layer is attached to the basement membrane for support/connections. There are nerve supplies to the epithelia but they are provided by diffusion. As they are on the surface, their volume to growth is a lot quicker than other tissues.
Simple Epithelia.
Simple Epithelia is one thick layer of tissue made from cells, it can be one of these three different shapes: 1. Squamous 2. Cuboidal 3. Columnar
Squamous are found in: * Lung alveoli. * Blood capillaries. * Bowman’s capsule of nephrons.
Cuboidal can be found in: * Kidney tubules. * Sweat ducts. * Glands that are like the thyroid gland. * Breast tissue.
Columnar cells are found lining: * The trachea and bronchi. * Villi in the small intestine.
Compound epithelia.
The compound epithelia contain two or more layers of cells. This is so it can protect deeper structures, and the several layers of cells obstruct the passage of materials. The vagina, tongue, mouth and oesophagus are lined by squamous, cuboidal or columnar cells, they slowly start to become flattened by the compression from below as they reach the surface. The lowest layer of cells on the basement membrane keenly divides and pushes the older cells upwards. This type of epithelia is generally a pink colour and is often named mucous membrane.
The skin has an outer layer of epithelium similar in the structure to the stratified epithelium but with the vital count of flattened lifeless cells on the outside, this is known as the epidermis. As the cells do advance from the basement membrane, they gradually become filled with a protein (keratin) and are thought to be keratinised and cornified. This layer is significant to prevent micro-organisms entering deeper structures, and it does have a waterproof effect on the skin.
Nervous Tissues.
The nervous tissue is only found in the nervous system and consists of the brain, spinal cord and nerves. Receiving motivation from both external and internal sources, it serves to create consistency (homeostasis), co-ordination, and communication between the different parts of the body.
Nervous tissue is composed of: * Neurones: A highly particular nerve cells that transmit nervous impulses which are only in the brain and spinal cord. * Neuroglia: Connective tissue cells, combined with neurones in the brain and spinal cord, that offers support and defence.
Muscle Tissue.
Muscle is an excitable tissue because it is capable of responding to stimuli.
Three different types: * Striated (Skeletal). * Non-Striated (Smooth). * Cardiac.
Striated muscle.
Most striated muscle is connected to the bone of the skeleton, although some facial muscles are attached to skin. This type of muscle will contract when it receives nerve impulses controlled by conscious thoughts from the central nerve system.
Each fibre is cylindrical and multinucleate, lies parallel. There might be thousands of fibres in one muscle, depending on its size.
Non-Striated muscle.
Even though this type of muscle contains protein (filaments), they don’t lie in a normal pattern and hence they do not produce banding that is typical of the striated muscle.
Non-Striated muscle tends to have two sheets running in different directions, which is known as antagonistic muscles. In the digestive tract, one of the sheets run in a circle fashion around the intestines, the other runs down the length. The two work together to propel the food contents down the tract.
Cardiac muscle.
Type of muscle that is only found in the four chambers (atria and ventricle) of the heart. It’s said to be myoglobin because it can be rhythmically contract without receiving any messages front the nervous system and it does fluctuate from the other muscles. Under normal healthy circumstances, the muscle cannot be contracted by the myogenically as the atrial or the upper chamber muscle has a different contraction rate to that of a lower ventricular muscles and this could lead to inefficient and uncoordinated heart actions.

Connective tissue.
These tissues lie underneath the epithelia tissues, joining different parts of the internal structure. The function of these tissues are to move materials (blood), give support (areolar and cartilage), and reinforce and defend (bones).
There are five different connective tissues: * Blood. * Cartilage. * Bone. * Areolar. * Adipose.
Blood.
Consists of: * Plasma: Straw coloured fluid with 90% water with dissolved gases and nutrients, waste products, hormones and enzymes. Carries material.

* Components:
Red blood cells- small bi-concave with elastic membrane, no nucleus- haemoglobin- transports oxygen.
White blood cells- larger, nucleated. Less numerous Phagocytes and Lymphocytes- defence mechanism for the body.
Platelets- small disc shaped, no nucleus, clotting mechanism, plasma protein.

Cartilage tissue. The cartilage is smooth, firm, translucent element that helps protect the joining of bones from friction during movement. Cartilage is a major part of the nose and ears (Pinnae). Cartilage does not contain any blood vessels and is nurtured by diffusion from the underlying bone.
Bone.
The bone is the most rigid of the connective tissues.
Two types of bone: * Compacted, hard and thick outer layer. * Cancellous, sponge-like inner layer.
The matrix is composed of: * Calcium salts that are formed round the collagen fibres. * Collagen fibres do provide ability to flex to some extent. * Osteocytes.
The function of the bone tissue is to shape the body, support the body, protect it, make it have movement, blood cell production, mineral and fat storage.
The bones offer support for organs, muscles and soft tissue but not all of the important organs are protected with bone (intestines).
Areolar.
The areolar is located in the dermis of the skin which binds skin to the underlying muscle, the mucous membranes, around organs, the blood vessels and the nerves.
The function of the areolar is to hold the organs in place, it attaches the epithelia tissues to other underlying tissues. Nearly every cell obtains their nutrients from the areolar and release all waste into the areolar connective tissues.
Adipose Tissue.
Adipose tissue is a fatty loose tissue containing numerous adipocytes, each of these adipocytes contains a droplet of triglyceride. These tissues are found all over the body.
Its main role is to store energy in lipids, this is so the body is insulated by these cells. There are two type of adipose cells: * White adipose which store the energy. * Brown adipose which generates body heat.