Please answer the two learning goals on the attach file (need a three to four paragraphs in length) (300 words minimum) & reply to three peers.

Purpose of the Activity

In this activity you will now apply theory to practice. You will now integrate the study of cell anatomy into the further study of dental histology. You have read chapter 7: Overview of the Cell. We now ask ourselves, How does this apply to Dental Hygiene? You have watched the Meiosis, Mitosis and comparison videos which introduced you to the cell cycle phases. Please describe the four phases of mitosis and its connection with the oral cavity and healing. What are some clinical considerations one must understand with mitosis and oral histology. Please read chapter 7 Dental Histology- Cell Overview. In this first 7+minute video: Meiosis - introduces you to how meiosis works. The second 8+minute video: Mitosis describes mitosis's role in healing. The last video is 6+ minutes compares Meiosis and Mitosis.

Learning Goals

Describing the cell cycle phases
Identifying the importance of mitosis in healing of the oral cavity tissue
Outline the cell cycle, describing the phases of mitosis that are involved.

Assignment Instructions

1.Write your initial discussion post

This assignment is asking you to participate in a discussion and apply what you have learned to our profession as dental hygienist. Please answer the two learning goals above, offering a initial post that is three to four paragraphs in length. (300 words minimum) Please post word count at bottom of original discussion.

Reply to Peers

Please reply to 3 peers minimum- Offering constructive feedback- Do you have any suggestions or advice?
Answer any questions you were ask from your initial post.

Youtube links : please watch them

https://www.youtube.com/watch?v=VzDMG7ke69g

https://www.youtube.com/watch?v=f-ldPgEfAHI

https://www.youtube.com/watch?v=zrKdz93WlVk

CH.7 reading: Dental Histology- Cell Overview

CELL PROPERTIES

As an introduction to Unit 3, the microscopic organization of the body is discussed in this chapter. Histology (hi-stol-uh-jee) is the study of the microscopic structure and function of cells and the associated tissue. Another term for histology is microanatomy because the dimensions of the anatomic structures studied are on a microscopic scale; see Appendix B for information on the units of measurement used. A dental professional must have a clear understanding of the basic structural unit of the body, the cell and its components as well as understanding the larger concepts involved in the histology of tissue, such as those found in the oral cavity. This chapter gives an overview of the cell and its various components and then Chapter 8 presents a review of basic tissue types in the body. A discussion of the histology of each of the tissue types within the oral cavity follows in later chapters of Unit 3 along with clinical considerations related to histology.

The smallest living unit of organization in the body is the cell because each cell is capable of performing any necessary functions without the aid of other cells (Figs. 7.1 and 7.2, Table 7.1). Each cell has a cell membrane, cytoplasm, organelles, and inclusions. Thus, every cell is a world unto itself like a small gated community or walled city surrounded by a boundary, having

that make it almost self-sufficient.

Cells also interact with one another similar to how a city interacts with other cities. Cells with similar characteristics of form and function are grouped together to form a tissue, which is analogous to how states or provinces are then formed from cities having a common goal (see Table 7.1). Thus, a tissue is a collection of similarly specialized cells, which are most often surrounded by extracellular materials. Various tissue types are then bonded together to form an organ, a somewhat independent body part that performs a specific function or functions, similar to countries formed from like-minded states or provinces.

Organs can further function together globally as a system. Cells in a tissue undergo cell division to reproduce and replace the dead tissue cells. As a result of the division process, two daughter cells that are identical to each other and to the original parent cell are formed. This process consists of different phases, which are discussed later in this chapter in regard to the different components of the cell.

However, cells also interact with the extracellular environment in many ways. Cells can perform exocytosis (ek-soh-sahy-toh-sis), which is an active transport of material from a vesicle within the cell out into the extracellular environment. Exocytosis occurs when there is fusion of a vesicle membrane with the cell membrane and subsequent expulsion of the contained material.

The uptake of materials from the extracellular environment into the cell is endocytosis (en-doh-sahy-toh-sis). Endocytosis can take place as an invagination of the cell membrane. Endocytosis can also take the form of phagocytosis (fag-uh-sahy-toh-sis), which is the engulfing and then digesting of solid waste and foreign material by the cell through enzymatic breakdown of the material (discussed later in this chapter). CELL ANATOMY

The cell membrane (or plasma membrane) surrounds the cell (see Figs. 7.1 and 7.2). Despite its fragile microscopic structure, it is a tough and resourceful "gatekeeper" for the cell's interior. The usual cell membrane is an intricate bilayer, consisting mostly of phospholipids and proteins.

The phospholipids serve mostly as a diffusion regulator. The proteins of the cell membrane serve as structural reinforcements as well as receptors for specific hormones, neurotransmitters, and immunoglobulins (or antibodies). The cell membrane is associated with many of the mechanisms of intercellular junctions and other functions of the cell.

The cytoplasm (sahy-tuh-plaz-uhm) includes the semifluid part contained within the cell membrane boundary as well as the skeletal system of support or cytoskeleton (discussed later in this chapter). The cytoplasm contains not only a number of structures but also cavities or vacuoles (vak-yoo-ohlz).

79 ORGANELLES

The organelles (awr-guh-nels) are metabolically active specialized structures within the cell (see Figs. 7.1 and 7.2). The organelles allow each cell to function according to its genetic code. Organelles also subdivide the cell into compartments. The major organelles of the cell include the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, and the cytoskeleton. Nucleus

The nucleus (noo-klee-uhs) (plural, nuclei [noo-klee-ahy]) is the largest, densest, and most conspicuous organelle in the cell when it is examined microscopically (Fig. 7.3; see Figs. 7.1 and 7.2). A nucleus is found in all cells of the body except mature red blood cells and most cells have a single nucleus. However, some cells are multinucleated, such as osteoclasts or skeletal muscles (see Figs. 8.15 and 8.18).

The main nucleic acid in the nucleoplasm is deoxyribonucleic acid

(DNA), in the form of chromatin (kroh-muh-tin), which looks like diffuse stippling when the cell is viewed at lower power microscopically. In an actively dividing cell, the chromatin condenses into visible and discrete rodlike chromosomes (kroh-muh-sohms) (see Table 7.2). Each chromosome has a centromere (sen-truh-meer), a clear constricted area near the middle. Chromosomes then become two filamentous or threadlike chromatids (kroh-muh-tids) as daughter chromosomes joined by a centromere during cell division. After cell division, major segments of the chromosomes again become uncoiled and dispersed among the other components of the nucleoplasm as before.

The nucleus is the cell's "data bank" because it stores the genetic code. From its sequence of nucleotides in the chromatin, the DNA and ribonucleic acid (RNA) contain instructions for everything the cell is and will become. Thus, they control all functions the cell performs. The nucleus is also the "command center" of the cell, controlling the other organelles in the cell; it is influenced by what occurs inside the cell as well as outside the cell. Only certain genes are "turned on" to participate in the production of specific proteins at any particular time.

The chemical messages that result in genes switching on or off in the nucleus come from the cytoplasm, where in turn, they are generated as a result of interaction between the surface membrane and the environ-ment. Although genes contain the total range of the cell's possibilities, the cellular environment dictates which of these possibilities for differ-entiation, growth, development, and specialization will be expressed. As would be expected, the nucleus is constantly active. Before cell division, new DNA must first be synthesized with every single gene rep-licated. These genes, linked into chromosomes, are then separated into duplicate sets during cell division. In the nucleus, three very important types of RNA are produced, the messenger RNA (mRNA) molecules, which are complementary copies of distinct segments of DNA, and transfer RNA (tRNA) molecules, which are capable of specifically binding to and transporting amino acid units for protein synthesis as well as ribosomal RNA (rRNA) molecules, which will be discussed later.

In addition to all the activity associated with cell division, the genes on the DNA selectively direct the synthesis of thousands of enzymes and other integral and cytoplasmic proteins as well as any secretory products.

This process involves transcription of information from various parts of the DNA molecules into new strands of mRNA, which carry the encoded instructions into the cytoplasm for processing through the process of translation, which involves tRNA, rRNA, and amino acids.

The fluid part within the nucleus is the nucleoplasm (noo-klee-uh-plaz-uhm), which contains important molecules used in the construction of ribosomes, nucleic acids, and other nuclear materials. The nucleus is surrounded by the nuclear envelope (noo-klee-er), a membrane similar to the cell membrane, except that it is double layered The nuclear envelope is associated with many other organelles of the cell. The nuclear envelope may be pierced by nuclear pores, which act as avenues of communication between the inner nucleoplasm and the outer cytoplasm. The number and distribution of these nuclear pores vary with the cell type, with the level of cell activity, and with states of differentiation level of the same cell type.

Contained in the nucleus is the nucleolus (noo-klee-uh-luhs), a prominent and rounded nuclear organelle that is centrally placed in the nucleoplasm when the cell is examined microscopically (see Fig. 7.3).

The nucleolus mostly produces RNA and the nucleotides of the two other types of RNA. Without a nucleolus, no protein synthetic activity would occur within the cell; the nucleolus acts similarly to a "city hall" in managing the activity within the cell. The roles of the nucleolus and ribosomes with rRNA in protein synthesis are discussed later.

Mitochondria

The mitochondria (mahy-tuh-kon-dree-uh) are the most numerous organelles in the cell. They are associated with energy conversion and thus are the "power stations" for the cell (see Figs. 7.1 and 7.2). They are a major source of adenosine triphosphate (ATP) and thus are the site of many metabolic reactions. Microscopically mitochondria resemble small bags with a larger bag fitted inside because each bag is folded back on itself. These inner folds exist to increase the surface area for more dense packing of the particular proteins and enzyme molecules involved in aerobic cellular respiration. Internal to the folds, mitochondrial DNA, calcium and magnesium granules, enzymes, electrolytes, and water are present in a matrix. A matrix is a surrounding medium to a structure as discussed in Chapter 6.

Most of a cell's energy comes from mitochondria, produced by two of the pathways of aerobic cellular respiration. These involve both the Krebs cycle (or citric acid cycle) with its multienzyme system as well as the hydrogen pathway, which uses the electron transport chain of enzymes. Besides supplying energy, mitochondria help with the balance of the concentration of water, calcium, and other ions in the cytoplasm.

Cells with high levels of mitochondria are also known for high levels of activity, such as with "young" fibroblasts in healthy oral mucosa; the reverse is noted with the cellular changes encountered with inflammatory periodontal disease having lower levels of mitochondria in the

"older" fibroblasts (see Chapter 8). This may also explain the possible interrelationship between two prominent inflammatory diseases, periodontal disease and cardiovascular disease (CVD). Ribosomes

The ribosomes (rahy-buh-sohms) are the tiny sphere-shaped organelles in the cell (see Fig. 7.2). The ribosomes are produced in the nucleolus from RNA and protein molecules and are assembled in the cytoplasm. They function as mobile "protein factories" for the cell; their location changes based on the type of protein being made for the cell. They can be within mitochondria, free in the cytoplasm, or bound to membranes, either to the outer nuclear membrane or onto the surface of the rough endoplasmic reticulum (discussed next).

Ribosomes can also be found singly or in clusters within the cell. As many as 30 separate ribosomes may be attached sequentially to a single molecule of mRNA, with each ribosome making its own protein copy as it works its way along the length of the mRNA transcript. Within these ribosomes, free amino acids are being joined together according to the particular order specified by the mRNA transcript corresponding to the sequence of the required protein chain.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) (en-duh-plaz-mik) is so referred to because it is more concentrated in the cell's inner or endoplasmic region as compared to the peripheral or ectoplasmic region (see Figs. 7.1 and 7.2). The ER consists of parallel membrane-bound channels.

All the membranes of the ER interconnect, forming a system of channels and folds microscopically, and are continuous with the nuclear envelope like a "highway" system for the cell.

The ER can be classified as either smooth or rough, which is determined by the absence or presence of ribosomes, giving each a differing outer microscopic texture structure as well as differing in function. The smooth ER (SER), which is free of ribosomes, appears microscopically smooth in surface texture. The rough ER (RER) as discussed earlier is dotted with ribosomes on its outer surface, which makes it appear microscopically rough.

The outer layer of the nuclear envelope connects with all the ER in the cell, both smooth and rough. The ER's primary functions are mod-ification, storage, segregation, and finally transport of proteins that the cell manufactures on the ribosomes for use in other sections of the cell or even outside the cell.

Golgi Complex

Once the ER has modified a new protein, it is then transferred to the Golgi complex (gawl-jee) (or Golgi apparatus) for subsequent segregation, packaging, and transport of protein compounds just like a "distribution All the membranes of the ek interconnect, forming a system of channels and folds microscopically, and are continuous with the nuclear envelope like a "highway" system for the cell.

Golgi Complex

Once the ER has modified a new protein, it is then transferred to the Golgi complex (gawl-jee) (or Golgi apparatus) for subsequent segregation, packaging, and transport of protein compounds just like a "distribution center" for the cell (see Figs. 7.1 and 7.2). The Golgi complex is the second largest organelle after the nucleus and is composed of stacks of 3 to 20 flattened smooth-membrane vesicular sacs arranged parallel to one another.

Vesicles of protein molecules from the RER fuse with the Golgi com-plex, transferring protein molecules to be further modified, concen-trated, and packaged by the Golgi complex. After this modification and packaging, the Golgi complex wraps up large numbers of these molecules into a single membranous vesicle and then sends it on its way to the cell's surface to be released by the process of exocytosis. These protein molecules, which include hormones, enzymes, and other secretory products, are released into the extracellular space or into capillaries as these vesicles fuse with the cell membrane. These products that are put together in the Golgi complex can include such substances as mucus secretory product for the salivary glands or insulin for the pancreas.

The modifications by the Golgi complex to the protein molecules include adding carbohydrates, thus forming glycoproteins as it does in the production of mucus. The Golgi complex also may remove part of a polypeptide chain as it does in the case of insulin. The Golgi complex not only prepares proteins for export by exocytosis but also produces a separate organelle, lysosome (discussed next). Lysosomes

The lysosomes (lahy-suh-sohmz) are organelles produced by the Golgi complex and function in both intracellular and extracellular digestion by the cell (see Fig. 7.2). This digestive function is due to their ability to lyse or digest various waste and foreign materials in or around the cell, which occurs during phagocytosis like a "sewer system" for the cell (Fig. 7.4). Lysosomes break down many kinds of molecules using the powerful hydrolytic and digestive enzymes contained within them (see Fig. 8.15). The main hydrolytic enzyme in lysosomes is hyaluroni-dase. Lysosomes are membrane-bound vesicles that develop as a bud that pinches off the end of one of the Golgi complex's flattened sacs.

The enzymes of the lysosomes originally are produced on the RER and then are transported for packaging in the Golgi complex, where the lysosomes originate.

As the substances are broken down into sufficiently small and simple products, the usable material diffuses out of the lysosome into the cell's cytoplasm to be incorporated into new molecules being synthesized, a type of cellular "recycling." Indigestible material remains in the lysosome and becomes a residual body. It either migrates to the cell surface to be released by exocytosis or remains as a remnant in the lysosome and becomes an inclusion (discussed later in this chapter). Although all cells, except red blood cells, are capable of some digestive activity, other cells such as certain white blood cells (e.g., neutrophils) have differentiated to specialize in digestive processes, especially during phagocytosis (see Fig. 8.17). Phagocytosis is very active at the junction between healthy gingival tissue and the tooth surface (see Chapter 10).

Centrosome

The centrosome (sen-truh-sohm) is a dense and somewhat oval-shaped organelle that contains a pair of cylindrical structures, the centrioles (sen-tree-ohlz) (see Fig. 7.2). The centrosome is always located near the nucleus, which is important because it plays a significant role in forming the mitotic spindle apparatus during cell division. There are two centrioles within the centrosome and each is composed of triplets of microtubules arranged in a cartwheel pattern. Without this self-rep-licating centriole-centrosome unit, a cell from the body cannot reproduce (discussed later in this chapter). INCLUSIONS

The cell also contains inclusions (in-kloo-zhuhns), which are metabolically inert substances that are also considered transient over time in the cell (see Fig. 72). These include masses of organic chemicals and often are recognizable microscopically. These inclusions are released from storage by the cell Cytoskeleton

The interior of the cell is neither liquid nor gel in nature but somewhat between the two types of substances. Within the cell there is a three-di-mensional system of support using cellular scaffolding, the cytoskeleton (CSK) (sahy-tuh-skel-i-tn) (see Fig. 7.2). The components of the CSK include microfilaments, intermediate filaments, and microtubules as a shifting lattice arrangement of structural and contractile components distributed throughout the cell cytoplasm. This design lends basic stability to the cell as a whole, functioning like reinforced girders. It also acts to compartmentalize the cytoplasm, creating preferred "freeways" for the movement of molecules formed by cellular processes.

Both microfilaments (mahy-kruh-fil-uh-muhnts) and microtu-bules (mahy-kroh-too-byoolz) consist of specialized proteins. Micro-filaments are delicate threadlike microscopic structures. Microtubules are slender hollow tubular microscopic structures that may appear individually, doubly, or as triplets. Microtubules assist microfilaments in the maintenance of overall cell shape and in the transport of intra-cellular materials. Additionally, microtubules form the internal framework of cilia and flagella, centrioles, and the mitotic spindle for cell division (discussed later in this chapter).

Certain cells exhibit projections that help move substances along the surface of the cell or are for moving the entire cell in the extracel-lular environment. If the projections on the cell are shorter and more numerous, they are cilia (sil-ee-uh); if the projections are fewer and longer, they are flagella (fluh-jel-uh).

Both the projections of cilia and flagella are useful in human repro-duction. An ovum is propelled within the fallopian tube by cilia, and sperm are propelled by their own flagella (see Fig. 3.1). Structurally, there is no major difference between cilia and flagella except for their relative lengths. Both consist of pairs of multiple microtubules that form a ring around two single microtubules. Cilia are also noted in the respiratory mucosa lining the nasal cavity and paranasal sinuses as they move the mucous coating of these tissue types along the surface (see Fig. 11.20).

The intermediate filaments (fil-uh-muhnts) are of various types of thicker threadlike microscopic structures within the cell. One type of intermediate filaments, the tonofilaments (tohn-oh-fil-uh-muhnts), have a major role in intercellular junctions (discussed later in this chapter).

Another type of intermediate filaments is one that forms keratin, which is found in a calloused type of epithelium located in the oral cavity on the attached gingiva as well as the dorsal surface of the tongue (see Fig. 9.4). mucous coating of these tissue types along the surface (see Fig. un

INCLUSIONS

The cell also contains inclusions (in-kloo-zhuhns), which are metabolically inert substances that are also considered transient over time in the cell (see Fig. 7.2). These include masses of organic chemicals and often are recognizable microscopically. These inclusions are released from storage by the cell and used as demand dictates. Lipids and glycogen can be decomposed for energy from inclusions in the cell. Melanin is stored as inclusions in certain cells of the skin and oral mucosa being responsible for the pigmentation of these tissue types (see Figs. 9.23 and 9.24). Inclusions also include residual bodies, which are spent lysosomes and their digested material.

CELL DIVISION

Cell division or mitosis (mahy-toh-sis) is a complex process involving many of the organelles of the cell (Table 7.2). Mitosis functions during tissue growth or regeneration and its activity is dependent on the length of the individual cell's lifespan. Before cell division, the DNA is replicated during interphase (in-ter-feyz) as part of the cell cycle, which is the cell's "living" time. Interphase has three phases: Gap lor G1 (or initial resting phase that has cell growth and functioning); synthesis or S (or cell DNA synthesis by duplication); and Gap 2 or G2 (or second resting phase that resumes cell growth and functioning).

Following interphase, mitosis occurs with the cell's nuclear material dividing so that the resulting production is of two daughter cells that are identical to the parent cell as well as to each other (see Chapter 3).

Then, at the same time, the other cytoplasmic components of the cell also are divided. The cell division that takes place during mitosis consists of four phases: prophase (proh-feyz), metaphase (met-uh-feyz), anaphase (an-uh-feyz), and telophase (tel-uh-feyz); cell division is followed again by interphase continuing the overall cell cycle (see again Table 7.2).

EXTRACELLULAR MATERIALS

The cells in each tissue type are surrounded by extracellular materi-als, which include both tissue fluid and intercellular substance. Tissue fluid (or interstitial fluid) provides a medium or matrix for dissolving, mixing, and transporting substances and for carrying out chemical reactions. Similar to blood plasma in its content of ions and diffusible substances, tissue fluid contains a small amount of plasma proteins.

Tissue fluid enters the tissue to surround the cells by diffusing through the capillary walls as a filtrate from the plasma of the blood.

Tissue fluid then drains back into the blood as lymph through osmo-sis, via the lymphatics (see Chapter 8). The amount of tissue fluid varies from tissue to tissue, with smaller variations occurring over time within any one tissue. An excess amount can accumulate when an injured tissue undergoes an inflammatory response, leading to edema with its tissue enlargement (see Fig. 10.8).

Intercellular substance (in-ter-sel-yuh-ler) (or ground substance) is a shapeless, colorless, and transparent material in which the cells of a tissue are imbedded; it also fills the spaces between the cells in a tissue. The intercellular substance serves as a barrier to the penetration of foreign materials into the tissue as well as a medium for the exchange of gases and metabolic substances. The surrounding cells produce the intercellular substance and one of its most common elements is hyaluronic acid.

INTERCELLULAR JUNCTIONS

Certain cells in varying tissue are joined by the mechanism of intercel-Jular junctions. These are mechanical attachments formed between cells and also between cells and adjacent noncellular surfaces. With the formation of these intercellular junctions, the cell membranes of different cells come close together but do not completely attach. Higher-power magnification is needed to visualize these attachments, which appear as dense bodies. All intercellular junctions involve some type of intricate attachment device. The attachment device includes an attachment plaque that is located within the cell as well as adjacent ton An intercellular junction between cells is formed by (dez-moh-sohm), such as that present in the superficial lay or oral mucosa (Fig. 7.5). The desmosome appear as such can be likened to a "spot weld" within The desmosomal junctions are also released du then become reattached in new locations as th during repair after an inine ta 4t Jular junctions. These are mechanical attachments formed between cell, and also between cells and adjacent noncellular surfaces. With the for. mation of these intercellular junctions, the cell membranes of different cells come close together but do not completely attach. Higher-power magnification is needed to visualize these attachments, which appear as dense bodies. All intercellular junctions involve some type of intricate attachment device. The attachment device includes an attachment plaque that is located within the cell as well as adjacent tonofilaments.

An intercellular junction between cells is formed by a desmosome (dez-moh-sohm), such as that present in the superficial layers of the skin or oral mucosa (Fig. 75). The desmosome appears to be disc-shaped and as such can be likened to a "spot weld" within the structure of a tissue The desmosomal junctions are also released during tissue turnover and then become reattached in new locations as the cells migrate, such as during repair after an injury to the skin or oral mucosa (see Fig. 83).

Desmosomes can create an artifact when cells in the stratified squamous epithelium are fixed for prolonged microscopic study. The reg ularly plump cells in the prickle cell layer appear prickly or spiky a their outer edges as they still maintain their junctional stronghold from the desmosomes. The individual dehydrated cells have shrunk from the drying fixation chemicals as a result of cytoplasm loss (see Fig, 9.8).

Another type of intercellular junction is formed by a hemidesmo-some (hem-eye-dez-moh-sohm), which involves an attachment of l cell to an adjacent noncellular surface (Fig. 7.6). This type of attachmen is used for attaching the epithelium to connective tissue, such as with the basement membrane in the skin and oral mucosa (see Fig. 8.4).

The attachment device of a hemidesmosome represents half of a des-mosome because it involves a smaller attachment plaque and has tono-filaments from only the cellular side. Therefore it appears as a thinner disc because the noncellular surface cannot produce the other half of the attachment mechanism. Hemidesmosomes are also involved as a mechanism allowing gingival tissue to be secured to the tooth surface by the epithelial attachment (see Figs. 10.6 and 10.7), which is similar to the attachment between the nails and adjoining nail beds.