Okay, so the next chapter we're going to discuss is the tissue level of organization. Now that we understand and have discussed in detail cells, we're going to examine tissues. Tissues are groups of cells that are similar in structure and function. There's different types of tissue that we will examine: epithelial tissue, connective tissue, muscle tissue, and nerve tissue. For each of the tissue types that we will examine along with the subtypes, you should be able to identify the types and arrangement of the cells, whether there's an intracellular matrix (if it's absent or present and its composition, and the function), and body locations of the various tissues. Now histology studies tissues just like cytology is the study of cells. and we will study tissues both in lecture and in labs and in lab. You will use a compound light microscope to examine tissues in further detail. There's three types of embryonic germ layers from which all adult tissues are derived: 1) endoderm which gives rise to the functional linings of the digestive and respiratory tracts as well as to the associated accessory glands and organs like your liver stomach and pancreas. 2) Mesoderm which gives rise to the components of the skeletal musculature muscular and circulatory systems and 3) ectoderm which gives rise to the epidermis of the skin and all of the components of the nervous system. Now there is various types of cell junctions that connect tissues together. There are tight junctions, gap junctions, and anchoring junctions. Each of these junctions might have different types of tissue or cell to cell connections possibly allowing for either no substances to pass through or they might allow for communication between tissues and cells like gap junctions which are found in cardiovascular tissue for example. So let's start with epithelial tissue. Now epithelial tissue is found in rows, sheets, or tubes composed of squamous, cuboidal, or columnar cells which form the outer skin as we've already discussed and protects secretes and absorbs. Now there is some particular characteristics of epithelial tissue that you must be familiar with. Epithelial tissue is avascular meaning it has no blood vessels so the cells are fed by the underlying connective tissue blood vessels. It is regenerative. Mitosis constantly replaces from the basal layer or basement membrane of connective tissue. It is innervated, it is full of nerves. It has a variety of cell to cell connections and it also is polarity, meaning it has an apical and a basal surface. The apical surface may bear microvilli is composed of closely packed cells and the apical surface can also have cilia like in the lining of the trachea. You can see that epithelial tissue can be arranged in different forms. It can either be simple, composed of one cell layer, stratified composed of multiple cell layers, or pseudostratified where the cells are arranged in various groupings with the nucleus not in the center of the cell but found in various locations throughout the cell. So let's examine the different types of epithelial tissue starting with columnar and the other thing to think about with epithelial tissue is the classification is going to be based on the number of cell layers again simple one cell layer stratified multiple cell layers. So squamous squamous is thin flat scale like cells with a centralized nucleus and this would be found in columnar so you can have simple columnar, simple squamous, or simple cuboidal. Cuboidal is a three dimensional square commonly found in the kidney. Squamous is commonly found in the cheek lungs and walls of capillaries. Columnar is taller than they are wide with the nucleus low in the cell this type of epithelial cell can be ciliated or non ciliated and it's found in the digestive and rest Vittoria systems now one thing to keep in mind if the the--all 2xu is stratified it's named according to the apical layer of cells stratified epithelium is shown here and again you can have squamous cuboidal and columnar stratified squamous epithelium is composed of several cell layers the basal cells are cuboidal or columnar and metabolically active the surface cells are flattened squamous hence the name stratified squamous functions to protect underlying tissues in areas of the body that are subject to abrasion there is two types keratinized and non-keratinized keratinized the surface cells are full of keratin and dead non-keratinized type you might find in the esophagus mouth or vagina the keratinized variety forms the epidermis of the skin cuboidal stratified cuboidal is very rare in the body it's found in some sweat and mammary glands and it's typically two cell layers thick stratified columnar also has a limited distribution in the body with small amounts found in the pharynx some glandular ducts and the male urethra now there is additional types of epithelial tissue like pseudo stratified ciliated columnar epithelium and it's a single layer of cells with differing Heights some not stretching to the free surface the nuclei are seen at different levels and it may contain mucous secreting cells which are goblet cells it functions in secretion particularly of mucus and propulsion of mucus via ciliary action location the non ciliated type might be in male's sperm carrying ducts and ducts of large glands the ciliated type might be found in the trachea and most of the upper respiratory tract transitional epithelium resembles both stratified squamous and stratified cuboidal the basal cells are generally cuboidal or columnar and the surface cells are dome-shaped or squamous like depending on the degree of organ stretch transitional epithelium functions because it stretches readily and permits distinction of for example your urinary organs and it's found lining the ureters urinary bladder and part of the urethra now there's also glandular epithelium a gland is one or more cells that makes and secretes an aqueous fluid and they're classified by the site of product release and the relative number of cells that form the gland now the site of product release can either be endocrine or exocrine endocrine is released into the interstitial fluid and you will talk about endocrine glands in more detail an A&P to particularly when you study the endocrine system the exocrine glands are more numerous than endocrine glands and they secrete their products into ducts or the secrete can be released on to body surfaces like the skin examples would include mucus sweat boil and salivary glands there's also different modes of secretion Marek Rhine and holocron Marek Rhine the products are secreted by exocytosis like the pancreas sweat and salivary glands holocron the products are secreted by the rupture of the glands like the sebaceous glands and then a brine you have cytoplasmic loss of the gland and those would be mammary glands as an example now glands may also be unicellular or multicellular multicellular exocrine glands are composed of a duct and a secretory unit the duct type can be simple or compound and they can have different types of structures of their secretary units like tubular alveolar for tubular alveolar so here are some examples of the different types of glandular epithelium and the secretions modes of secretions that we just discussed and you can see whether it's a small portion pinched off via a secretory vessel vesicle or a portion or the whole cell ruptures and dies now connective tissue is the next type of tissue connective tissue is very abundant and widely distributed and there's four classes that we will go over connective tissue proper cartilage bone tissue and blood connective tissue has a matrix and the matrix can contain fibers elastin which are yellow and allow for stretch collagen which are white and provides strength and reticular which is mesh light and consists of networks the matrix can also contain a ground substance or glue and here's the different types of connective tissue connective tissue proper which can be further subdivided into loose or dense fluid connective tissue and supporting connective tissue the major functions of connective tissue are binding and support protection insulation and transportation and connective tissues have varying degrees of vascularity and their cells are separated by a nonliving extracellular matrix that is the ground substance and fibers meesa chyme is embryonic connective tissue which gives rise to all other connective tissue types now the different types of connective tissue are shown here loose connective tissue and dense connective tissue are two forms of connective tissue proper loose connective tissue consists of areolar adipose and reticular dense connective tissue consists of dense regular dense irregular and elastic areolar connective tissue is very abundant in the body it has a gel-like matrix with all three fiber types it contains cells fibroblasts macrophages mast cells and some white blood cells it functions to wrap and cushion organs and also because of its macro Fache it can phase phagocytized bacteria so it plays an important role in inflammation it's located widely distributed under the epithelia of the body and found packaging and surrounding organs and capillaries adipose tissue the matrix is similar to areolar but very sparse closely packed cells called adipocytes or fat cells it functions to provide reserves of food fuel insulates against heat loss and supports and protects organs it's located in the skin and the hypodermis around kidneys and eyeballs within your abdomen and ingress reticular tissue consists of a network of reticular fibers in a loose ground substance and the fibers function to form a soft internal skeleton that supports other cell types it's located in lymph organs lymph nodes bone marrow and spleen dense regular connective tissue has primarily parallel collagen fibers a few elastic fibers and the major cell type is the fibroblast it attaches muscles to bones or to muscles bones to bones and can withstand great tensile stress when pulling force is applied in one direction it's located in tendons and most ligaments dense irregular connective tissue has an irregularly arranged collagen fibers and some elastic fibers and the major cell type is the fibroblast it functions to withstand tension exerted in many directions and provides structural strength it's found in fibrous capsules of organs and joints dermis of the skin and submucosa of the digestive tract blood is a type of liquid connective tissue and the cells include both red and white blood cells the matrix is a plasma liquid and it functions to transport respiratory gases nutrients waste and other substances and you will study blood and lymph in more detail in a and p2 supporting connective tissue consists of cartilage and bone there's three types of cartilage heileen elastic and fiber cartilage cartilage contains chondrocyte cells these are cells that sit in small pools called lacunae and they tend to have a fried egg appearance the matrix is semi solid but flexible hylene cartilage is found in the fetal skeleton and in the adult it forms part of the ribs ends of long bones larynx and trachea it functions to support and reinforce and has resilient cushioning properties while resisting compressive stress elastic cartilage is similar to heileen cartilage but has more elastic fibers in its matrix it's flexible it functions to maintain the shape of a structure while allowing great flexibility and its location is the external ear and the epiglottis fiber fiber cartilage the matrix is similar but similar to but less than that inhaling cartilage you have thick cuddly collagen fibers that predominate and it's found in the disks of vertebrae pads of knees and pubic joint it functions to provide tensile strength with the ability to absorb compressive shock bone is a fairly rigid type of connective tissue with some Bend ability it has a hard calcified matrix containing many collagen fibers the mature bone cells are osteocytes which reside in the lacunae bone is also very well vascularized bone functions in support and protection by enclosing the soft protecting the organs beneath it providing a lever for the muscles to act on storing calcium and other minerals and fat and the marrow inside bones is the site for blood cell formation now there's different types of connective tissue cells fibroblast cells which synthesize connective tissue fibers adipocytes which store lipids and blood cells cells that are mitotically active in secretory generally end in blasts so fibroblasts for example mature cells and insights like osteocytes or chondrocytes osteocytes and bone and chondrocytes in cartilage and again the matrix of connective tissue can consist of the three fiber types as shown here collagen reticular and elastic and here's the different types of connective tissue that we just went through again for each you should be able to identify a description of the tissue its function and body location you should also know the cells and the matrix intracellular matrix whether it is absent or present and also its composition so you can see areolar connective tissue with the out of the site cells the mature cell adipose tissue with the adipocyte cells reticular with the reticular fibers dense connective tissue dense regular a regular repeating pattern of collagen fibers dense irregular you see that we have an irregular repeating pattern of collagen fibers both containing fibroblasts nuclei fibroblast cells cartilage heileen elastic and fibrocartilage hylene mostly collagen fibers elastic more elastic fibers and fiber cartilage rows of collagen fibrocartilage will have a wavy type of appearance when examined under the microscope and remember in cartilage it is the chondrocytes which is the mature cell that sits in the lacunae that's space or cavity bone vascularized matrix of ground substance with calcium salts and collagen and there's different types of bone that we will examine later on spongy bone which has a trabeculae or lattice type network and compact bone which is a repeating pattern of osteons the sure sell again with bone is the osteo site which sits in the lacunae the periosteum surrounds it fluid connective tissue both blood and lymph which you will examine in more detail and A&P too but again there is a definite cell type and the matrix is liquid in this case and muscle tissue muscle to tissue also contains specialized cells but it has different types of protein microfilaments like actin myosin troponin and tropomyosin that you will study later on skeletal muscle has cylindrical cells and the striations that you see in skeletal muscle or arts are alternating dark and light striped bands of protein skeletal muscle is multi nucleated and it functions in voluntary movement locomotion facial expression voluntary control examples might be your triceps biceps quadriceps smooth muscle has tapered cells with a large central nucleus no striations and is found in the walls of hollow organs such as the stomach uterus and blood vessel walls smooth muscle functions to propel substances or objects along internal passageways and again it's under involuntary control mostly found in the walls of hollow organs cardiac muscle is located in the atria and ventricles in walls of the large vessels of the heart it contains branch cells striations one central nucleus per cell it all contains intercalated discs which are a thickening of the cell membrane and allows for communication between the cells cardiac muscle functions - as it contracts to propel blood into the circulation and is under involuntary control nervous tissue nervous tissue consists of neurons and neural glial cells neurons are highly specialized cells with a cell body which contains a nucleus organelles and produces neurotransmitters and cell membrane extensions called axons and dendrites which conduct nervous impulses we will study the nervous system later on in the course neuroglial cells are small packed cells in between neurons for support and nourishment of neurons and also can function to clean up cellular debris or dead cells nervous tissue is found in both your central and peripheral nervous system and again we will study it in more detail later including the various types of neuroglial cells some of which are shown here like the microglial cell and oligodendrocyte so for each of the different tissue types again make sure you know the function location and description including the fibers cell type and matrix whether it's present or absent and what it consists of this concludes our look at the tissue level of organization