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LabsHistology & JointsTissues are collections of specialised cells, i. a group or layer of cell that work together toperform a specific function.Epithelial tissue or epithelium is specialised to protect, absorb and secrete substances, aswell as detect sensations. It covers and protects surfa...

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Labs Histology & Joints Tissues are collections of specialised cells, i.e. a group or layer of cell that work together to perform a specific function. Epithelial tissue or epithelium is specialised to protect, absorb and secrete substances, as well as detect sensations. It covers and protects surfaces both inside and outside the body, forms a barrier to the outside world and controls absorption. Epithelium forms most of the surface of the skin, and the lining of the intestinal, respiratory, and urogenital tracts. Epithelium also lines internal cavities and passageways such as the chest, brain, eye, inner surfaces of blood vessels, and heart and inner ear. Connective tissues are specialised to provide support and hold the body tissues together. They form capsules around organs and separate muscles, arteries, veins and nerves from one another. They store compounds such as fats and minerals and cushion the organs they surround. Connective tissue cells of the immune system and blood play a major role in protecting the body against toxins and microorganisms, whereas bones protect underlying structures. Connective tissue is also involved in the transportation of gases, nutrients, enzymes and hormones. It differs from the other three tissue types in that it consists of cells separated from each other by abundant extracellular matrix. Muscular tissue is specialised for its ability to contract. Muscle cells are elongated and referred to as muscle fibres. When a stimulus is received at one end of a muscle cell, a wave of excitation is conducted through the entire cell so that all parts contract in harmony. Muscles contract to move the entire body, to pump blood through the heart and blood vessels, and to decrease the size of hollow organs. Nervous tissue is characterised by its ability to conduct electrical impulses (action potential) and convey information from one area of the body to another. Nervous tissue is found in the brain, spinal cord and nerves. There are two types of nervous tissue – neurons and neuroglia. Neurons transmit the impulses and neuroglia provides physical support for the neural tissue, controls tissue fluids around the neurons, and helps defend the neurons from invading organisms.

Epithelial tissues Skin is a highly complex organ – the largest in the body – and an example of keratinised stratified squamous epithelium. It consists of the epidermis (outer layers of cells) overlying the connective tissue of the dermis. Deep to this is the hypodermis or superficial fascia, consisting of loose areolar and adipose tissue. The thickness of the skin varies with body location. The deepest layers consist of living cells and the outer layers are composed of anucleated (no nucleus) dead cells containing the protein keratin. The epidermis of thick skin has 5 strata: 

Stratum corneum – keratin-packed dead cells

   

Stratum lucidum – clear layer of dead cells (found in soles & palms) Stratum granulosum – thin middle layer, initiates keratinisation (cell death) Stratum spinosum – spiny prickle cells that interlock to support the skin Stratum basale – single layer of cells that divide continuously

Pseudostratified epithelium is a modification of simple epithelium that rarely occurs as squamous or cuboidal epithelia and, as such, is known as pseudostratified columnar epithelium. All of the cells in this epithelium make contact with the basement membrane and are thus a single layer. However, the nuclei of the cells are not always aligned in the same plane so it gives the appearance (pseudo = false) of having many layers. This type of epithelium is found in the lining of the trachea, nasal cavities, auditory tubes, pharynx and lung bronchi. Transitional epithelium is modified stratified epithelium consisting of multiple layers of epithelial cells which can contract and expand. This type of epithelium is found in the urinary bladder, ureters, superior urethra and gland ducts of the prostate. Epithelium often functions as a protective covering, and as such is able to regenerate. Epithelium is avascular, meaning that nutrients must reach epithelial cells by diffusion (from blood vessels in tissues beneath the basement membrane) or from absorption (from the external environment). Epithelial tissue has a high degree of cellularity, meaning that it has many cells that are joined together, minimizing any extracellular material. Epithelial cells themselves are polarised, meaning that they have both an apical (outward-facing) and basal (basement membrane-facing) surface. The epithelium of the skin provides protection against physical and chemical damage, and pathogens. Sensory organs in the skin also allow it to detect sensation. The digestive epithelium has important roles in digestion and absorption. The epithelium of the olfactory mucosa is important to our ability to detect smell. The epithelium of the glomerulus is important for filtering blood to produce urine. Various other functions are carried out by epithelia elsewhere in the body. Squamous epithelial cells are thin, and smooth on the free surface. Areas that require physical protection and strength tend to be stratified, and areas that secrete or transport products tend to be simple. Lamina propria – made of loose connective tissue with no glands, it is connected to the basement membrane of the stratified squamous epithelial tissue in the vagina and the skin. Squamous epithelium characteristics    

Cells are flat and scalelike Nuclei are centrally located Nuclei are disk-shaped Cytoplasm

Stratified squamous epithelium is thick, which reflects its protective function. It is found in areas of the body that may be exposed to a lot of abrasion or friction. Simple squamous epithelium is thin to facilitate processes like diffusion and filtration. It is also smooth and may secrete lubricating substances. These characteristics reduce friction between the body cavity or organ that the epithelium lines, and its content. Cuboidal epithelium characteristics    

Cells are cubelike Large nuclei Nuclei are centrally located Nuclei are spherical

Simple cuboidal epithelium is located in the kidney tubules, ducts of small glands, and in areas where secretion occurs in these small glands. Stratified cuboidal epithelium is located in large sweat glands, mammary glands, and salivary glands. The main functions of simple cuboidal epithelium are secretion and absorption, and for stratified cuboidal epithelium is secretion and protection. Simple cuboidal epithelium can withstand more abrasion than simple squamous epithelium. Columnar epithelium characteristics    

Cells are elongated Cells may be ciliated or smooth May be dispersed with other cell types, such as goblet cells Nuclei are elongated

Pseudostratified columnar epithelium is ciliated and studded with mucus-producing goblet cells. The mucus traps harmful particles, which are then swept away by cilia. Pseudostratified columnar epithelium is notably found in the respiratory tract, where it keeps dust and harmful particles out of the lungs. Simple columnar epithelium – lining of the intestines that is specialised for absorption, and can withstand a significant amount of abrasion. Stereocilia – nonmotile, specialised cellular projections that act as mechanoreceptors. They appear as a wispy, irregular border of filaments on the lumen-side (apical) surface of the pseudostratified columnar epithelium. Found in the inner ear. Microvilli – short, cellular projections on the lumen-side (apical) surface of cells. Found in the small intestine. Cilia – motile, specialised cellular projections that facilitate fluid movement across the epithelium. The border that cilia form is thicker than that created by microvilli. Smooth columnar epithelium specialises in secretion and absorption. Ciliated columnar epithelium plays important roles in the protection of tissues and transport of substances.

Keratins are tough and fibrous proteins. They form intermediate filaments that give structure to epithelial cells. Keratinisation refers to the formation of keratin. Found in nails. Epithelial disease – cervical cancer The pap (Papanicolaou) smear is a means of screening the morphology of epithelial cells from the cervix of the uterus in order to check for abnormal pre-cancerous cells before they undergo changes into cancer cells. To achieve early detection sexually active women should be screened every 2-3 years and often more frequently if the woman has had many different partners. Changes in shape, growth and the number of cells is monitored. Epithelial disease – skin cancer There are two types  

Malignant melanoma (MM) Non-melanoma skin cancer (NMSC)

Malignant melanomas are relatively rare, but has seen a rise in cases in recent years. They develop from the melanocytes or pigment cells in the skin. More common in fair skinned, blonde-haired, blue-eyed populations exposed to short sharp excesses of sun exposure accompanied by severe sunburn. NMSC is 10 times more common and only occasionally fatal. Rates greater in white than non-whites and linked to cumulative effects of sun. Two types known – basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). BCC’s are the most common, they rarely metastasise. They begin as small nodules with pearly borders, often on face and scalp; may become ulcerous after months or years. SCC’s occur anywhere, but more on face and back of hands exposed to sun. They appear as persistent red lesions. Metastasises – spread of cancer to other parts of the body often occurs along the paths of blood vessels and nerves and can affect any organ.

Connective tissues Loose CT consists of relatively few protein fibres that form a lacy network, with numerous spaces filled with ground substance. It surrounds blood vessels and nerves, holds organs in place and attaches epithelial tissue to other underlying tissues. Loose (areolar) CT often found between structures and provides cushion, shock absorbance, and support to organs, nerves and blood vessels. It also facilitates diffusion of essential nutrients. Dense CT has a relatively large number of protein fibres that form thick bundles which fill nearly all the ECM. Dense regular CT has protein fibres orientated mainly in one direction, found in tendons and ligaments. Dense irregular CT contains protein fibres randomly orientated, or in an arrangement where fibres in one layer are orientated in one direction with the adjacent layer fibres orientated at right angles to that. Found in areas that undergo strong forces in multiple directions such as deep layers of the skin to help anchor the more superficial layers.

Cartilage is usually found in close association with bone. It is a type of CT which is tough, semi-transparent and flexible. The ground substance of the extracellular matrix (ECM) consists mainly of the glycoprotein chondroitin sulphate. The cartilage cells (chondrocytes) lie scattered in the matrix. There are three types of cartilage – hyaline cartilage, fibrocartilage, & elastic cartilage. Bone is composed of cells and mineralised ECM. There are 4 types of bone cells – osteoprogenitor, osteoblasts, osteocytes, & osteoclasts. The organic matter is composed of glycoproteins and type I collagen fibres. Inorganic salts, predominantly hydroxyapatite, form the mineral component of bone ECM. Blood has a fluid ECM which allows it to flow rapidly through the body transporting oxygen, carbon dioxide, hormones, nutrients, waste products and other materials. There are three types – red blood cells, white blood cells, platelets. Haemopoietic tissue is found in bone marrow which is the soft connective tissue in the cavities of bone. Red marrow is found mainly in the flat bones, such as the pelvis, sternum, cranium, ribs, vertebrae and scapulae, and in the cancellous (“spongy”) material at the epiphyseal ends of long bones such as the femur and humerus. Yellow marrow is found in the medullary cavity – hollow interior of the middle portion of long bones. Cell type Fibroblast

Fibrocyte Adipocyte Mast cell

Macrophage Blood cells

Function Cells that produce collagen and other fibers. Found throughout connective tissue close to fibers. Cells that help maintain fibers. Fat cell (white or brown) that stores energy. Cushions surrounding structures. Produce anti-inflammatory chemicals (for example, histamine) in response to allergens. Especially numerous in the connective tissue of the dermis (skin) and in the mucosal lamina propria (nasal cavity). Initiates immune response and destroys pathogens via phagocytosis. Erythrocytes (red blood cells) deliver oxygen and carbon dioxide around the body. Platelets produce antibodies in response to antigens. Leukocytes (white blood cells) contribute to the immune response, produce chemicals that help mediate allergic response, and help destroy parasites.

The suffix –blast refers to an immature cell. These cells often produce building materials for other cells. The suffix –cyte refers to a mature cell that helps to maintain structure off a tissue.

Reticular connective tissue provides a 3D mesh-like scaffold that supports soft organs like the liver, spleen, lymph nodes, bone marrow, and glands. Reticular connective tissue is typically located in bone marrow, the liver, the pancreas, adrenal glands, and all lymphoid organs (except the thymus). Think of tissue that requires a flexible mesh framework that will support cells with specific functions related to that organ. Elastic connective tissue helps structures like the aorta, larger arteries, and some vertebral ligaments spring back to their original shape after being stretched. Elastic connective tissue is found surrounding larger arteries. Think of structures that need to "rebound" and return to their original shape after being stretched. The elasticity od arterial walls allows the pulse pressure wave to travel along the artery, and to bounce back to its original shape afterwards. This aids in the pumping of blood around the body. Ligaments contain more elastin fibres and are stretch more than tendons. Lung disease The respiratory system’s prime function, to oxygenate blood and remove CO2, requires that air is brought into close approximation with blood. The tract includes a system of airways to rapidly transport air from the exterior to the air sacs where gaseous exchange occurs. The system is potentially vulnerable to spread infection and to pollutants – dusts, fumes and particularly cigarette smoke. Emphysema – alveoli and terminal bronchioles become enlarged and the delicate tissue damaged and destroyed. Oedema – excessive accumulation of fluid occurs in the interstitial spaces and alveoli

Nervous tissues

Neurons are electrically excitable cells that produce action potentials when they receive electrical or chemical stimulation. They are specialised for the transmission of signals and they communicate with each other through chemical synapses. Cerebrum and cerebellum – the outer cortex of the cerebrum is known as the grey matter due to its grey appearance. Deep to this, the cerebrum appears white. This is due to the high density of myelinated axons running along tracts. Spinal cord – the outer cortex of the spinal cord is composed of white matter as the axons running in tracts reside here. The inner medulla of the spinal cord is composed of grey matter where cells bodies of neurons reside. Purkinjie cell layer – middle layer of the cortex. Composed of large multipolar neurons called purkinjie cells that are important for inhibitory functions. Granular layer – innermost layer of the cortex. Composed of the smallest neuron cell bodies. Molecular layer- outermost layer of the cortex, composed of neuron cell bodies. Medulla – also called white matter. The internal layer of the cerebellum, composed of neuron axons travelling to their location of synapse. Neuron cell body – also termed perikaryon. Location where neurotransmitters are produced

Astrocytes – anchor neurons and capillaries together to hold neurons close to their nutrient supply; form a barrier between neurons and capillaries to help regulate the chemical environment around neurons Microglia – engulf microorganisms and dead neural tissue Ependymal cells – line the ventricles of the brain and central canal of the spinal cord. These cells are important for the production, absorption, and circulation of CSF Oligodendrocytes – produce myelin sheaths that wrap around and insulate nerve fibres, speeding the conduction of electrical signals. They extend several paddle-like projections from the cell body. Each projection forms a myelin sheath around separate axons. Can myelinate part of several axons A tract is a bundle of axons (nerve fibres) that connects one part of the brain with another. Tracts form the white matter of the CNS. In the PNS, this is known as a nerve.

Purkinjie cells are able to inhibit the granule cells. The spinal cord Arachnoid mater – spider web-like layer of the meninges that provides protection and nutritional support to the spinal cord Pia matter – thin connective tissue that is tightly adhered to the surface of the spinal cord Myelinated axon – clear staining due to fatty myelin Unmyelinated axon – darker staining due to absence of fatty myelin Central canal – narrow tubelike space within the spinal cord filled with cerebrospinal fluid Ependymal cell – line the ventricles of the brain and central canal of the spinal cord, produce cerebrospinal fluid.

Cell bodies of somatic motor neurons lie in the anterior (ventral) horn. Axons exit via the ventral roots at each level of the spinal cord. Each axon innervated its target skeletal muscle. Peripheral nerves Endoneurium – a basement membrane that surrounds each axon Perineurium – connective tissue surrounding a bundle of axons Epineurium – dense connective tissue that surrounds an entire nerve

Myelin insulates the axon and reduces the amount of charge lost across the membrane, which greatly increases the conduction speed of an action potential.

Schwann cells form myelin sheaths around nerve fibres in the PNS. They can only wrap around party of one axon. Neurodegeneration is the umbrella term for progressive loss of structure or function of neurons, including death of neurons. Alzheimer's disease is a form of cortical dementia, affecting higher mental functions. Patients experience irreversible global, progressive impairment of brain function, leading to reduced intellectual ability. There is a generalised loss of neurones so that the cortical grey matter is thin and the ventricles appear large due to loss of neural tissue. There is also amyloid plaques (dense, insoluble deposits) and neurofibrillary tangles (aggregates of protein which are hyper phosphorylated and accumulate inside the cells themselves). Huntington's disease affects muscle coordination and leads to cognitive decline and psychiatric problems. It is the most common genetic cause of abnormal involuntary writhing movements called chorea. The disease is caused by an autosomal dominant mutation in either of an individual's two copies of a gene called huntingtin. Selective atrophy of the caudate nucleus with correlated increase in the relative size of the lateral ventricles. There is a loss gamma-aminobutyric acid (GABA). Ischaemia is a condition in which there is insufficient blood flow to the brain to meet metabolic demand. This leads to poor oxygen supply or cerebral hypoxia and thus to the death of brain tissue or cerebral infarction (ischaemic stroke). Cerebral infarction occurs when a blood vessel becomes blocked, or leakage occurs outside the vessel walls. Blunt head injury occurs when the head is accelerated/decelerated rapidly such as in a motor vehicle accident. The brain moves violently within the cranium during the insult and surface contusions and/or diffuse axonal injury result.

Muscle tissues Cardiac muscle is only found in the heart. It controls the pumping of blood through the heart.

Smooth muscle is found in the walls of hollow organs like the digestive system and certain bloo...