Cell Development - Stages of Cell Division, Tissue Development, Epithelization, Sense of Touch - Essay Example

Our Senses and how we Perceive the World Name Course Tutor Date Abstract Cells show a lot of variation in their sizes and structures. Consequently, they have two main parts. These are nucleous and cytoplasm. The two main parts are enclosed in a cell membrane, which is sometimes called plasma membrane. On the other hand, tissues are organizational level of the cell, which is intermediate between a complete organism and cells Tissue can be simply described as an assemblage of cells with similar origin and also in togetherness, which are synchronized to perform a specific function. When multiple tissues come together in a functional grouping they form an organ. This paper established that cell development entails cell growth and division. Cell development and growth can be demonstrated in well equipped laboratory by growing them in cell cultures. As per the cell principle, the new cells always arise from the pre existing cells and this is evident by cell division process, which also transfers genetic information. Tissue development and repair always occur when the existing tissue structure has been tampered with for instance, in case of an injury, which may later develop into a wound. Wound healing process can be aggregated by several factors, which include bloodstream levels of hormones like oxytocin. The paper also obtained that cells group and specializes into tissues, which in turn group and specialize into organs. The tissues are developed to serve a particular function. For instance, when a person is injured, new tissues have to be developed to occupy the worn out parts of the body. When it comes to senses, different tissues are developed to help in sensing different stimuli in the environment. In this paper, the development of worn out tissues and skin tissues are discussed. Key words; plasma membrane, Wound healing, growth factors, mitosis, meiosis. INTRODUCTION The study of cells is known as cytology. Cells always display some variations as far as their sizes and structures are concerned. In this case, they have two main parts namely the nucleous and cytoplasm. These two parts are enclosed in a cell membrane or sometimes called plasma membrane. Plasma membrane has got various features, which make it fit for cell survival. First, it is extremely thin. This reduces the distance through which substances diffuse. Second, the plasma membrane possesses some folding. The folding increases the surface area for diffusion. Third, the plasma membrane is porous and permeable selectively. This means that it is in a position to control what enters and leaves the cell making it its major function. On the other hand is the cytoplasm is located just in between the nucleous and the cell membrane. The cytoplasm constitutes a platform for most metabolic activities in the cell. Cytoplasm contains a clear fluid known as cytosol, which is derived from the name cytoplasm. Cytosol houses the cell organelles. The organelles include Endoplasmic reticulum, Mitochondria, nucleolus, Golgi apparatus. Endoplasmic reticulum constitutes interconnected channels that connect to other cell organelles. There two types of endoplasmic reticulum. These are rough and smooth endoplasmic reticulum. Rough endoplasmic reticulum plays a role in the manufacturing of ribosomes (Braun & Anderson, 2007). Ribosomes are found on the surface of this organelle. Second, there is smooth endoplasmic reticulum. This is the site where lipid is synthesized. Mitochondrion on the other hand is a double layered membranous organelle that has a folded inner layer known as cristae. Lysosome plays a major role in cell lysis. Here, they participate in destroying worn out cells by using enzymes to digest them. Nucleous is an organelle located at the core of the cell and has a membrane that is permeable. The membrane is called nucleous membrane. The cellular genetic materials are found in this organelle. Last, there is the Golgi apparatus. These are membranous sacs that mainly package and transport proteins (Vunjak-Novakovic & Freshney, 2006). At the second level of cell organization, we have tissues. These are organizational level of the cell, which is intermediate between a complete organism and cells A tissue can be simple described as an assemblage of cells with similar origin and which in togetherness, perform specific function. When multiple tissues come together in a functional grouping they form an organ. Histology is defined as the study of tissues. This study is called histopathology when a disease is involved. Tissues found in animals are categorized in four major types which include; epithelial tissue, Connective tissue, Nervous tissue and Muscle tissue Epithelial tissue has their main functions of lining the body cavities. The tissue tends to cover the body surfaces and also form glands. There exist three main types of the epithelium. These types are columnar, squamous and cuboidal epithelium. Epithelium can be categorized into two: simple or stratified. The main difference between these two categories is the number of cell layers present. Consequently, simple epithelium possesses one layer of cells while the stratified one has got more than one or several cellular layers. Epithelial cells aid in myriad of functions, which include materials movement in and out of the animal’s body, product secretion and protection of the internal environment from the external one (Braun & Anderson, 2007). Connective tissues are equally essential body tissues as per their functions. In other words, they offer support; they bind, aid blood formation, store fat and also fill the space. There is a non cellular matrix that separates one connective cell from one the other. The matrix might be in different forms, for instance, a bone (solid), loose connective tissues (soft) or blood (liquid).Connective tissue is divided into two broad and main categories, Fibrous Connective Tissue and Loose Connective Tissue (Mangan et al., 2006). Muscle tissue is responsible for the movement of the animal. This is made possible by contraction of individual muscle cells, which are known as muscle fibres. Muscle fibres that occur in animals are grouped into three. These are cardiac, smooth and striated or skeletal muscle fibres. These muscle fibres are multinucleated and the nuclei are present just beneath the plasma membrane (Vunjak-Novakovic & Freshney, 2006). Nervous tissue always functions in integrating stimulus and controlling response to that particular stimulus. The cells found in the nerves are known as neurons. Every neuron has got an axon, a cell body and a number of dendrites. The main function of neurons is to transmit the nerve messages. Nervous tissue is made up of two major types of cells, neurons and glial cells. The so called glial cells surround and are always in contact with the neurons. Neuron can also be described or defined as a functional unit of the nervous system (Braun & Anderson, 2007). Cell Development In our daily normal life thousands of our body cells die. Their death puts our body to task of keeping cell growth and cell death in balance. Cell development entails cell growth and division. Cell development and growth can be demonstrated in well equipped laboratory by growing them in cell cultures. The proliferation of the cell is always controlled by various factors of growth. These factors make the growth possible since they are bound to specific receptors. The receptors are connected to the signaling molecules, which in return pass the information or message from the known receptor to the nucleous. In the nucleous, transcription factors bind to deoxyribonucleic acid, switching on or maybe off protein production that promotes cell division(Sherwood, 2007). In the laboratory set up cells grow in cultures, myriad populations that need to be attended to on a frequent basis so as to notice the required or intended changes in their conditions. As per the cell principle the new cells always arise from the pre existing cells and this is evident by cell division process, which is involved in the transfer of genetic information. All the living organisms display the same cell division process and that solely shows the unity in life among the living organisms. This process is necessary for cell development, reproduction, growth and regeneration (Vunjak-Novakovic & Freshney, 2006). In eukaryotes, the multicellular organisms, the division is mainly of two types, which are mitosis and meiosis. Some primitive animals though exhibit a different cell division known as amitosis whereby the nucleous simply elongates and finally splits into two. For each single cell that is capable of dividing, it posses a cell cycle that consists of three main stages. These stages are interphase, karyokinesis and cytokinesis. These cycles are always of different length and they are dependant on a number of factors. These factors include nature of the cell, food, oxygen and other nutrients. Among the various types of cell divisions, mitosis is the most common one since its so important in regeneration, repair, growth and reproduction. Mitosis takes place in living cells in the body of a living organism thus making to earn the name somatic cell division (Braun & Anderson, 2007). This division can be described as equitional division since the daughter cells will have the same number of chromosomes as the parent cell. Mitosis exhibits three main stages. These are interphase, karyokinesis and cytokinesis. Deoxyribonucleic acid replication and synthesis of food reserves always occur during the interphase. During karyokinesis, several changes occur leading to splitting and separation of chromosomes. There are four main stages involved; prophase, telophase, anaphase and metaphase. Lastly cytokinesis plays a role in dividing cytoplasm thus causing separation of the daughter cells (Yavin & Yavin, 2008). Stages of cell division Interphase is the first stage of the cell division. In this stage the cell organizes itself for division process hence more metabolic activities are carried out within the cell. Interphase is further divided into three phases which are G1, S AND G2. This is where the cell gains its maturity by producing proteins and cytoplasmic organelles. At interphase, there is replication of deoxyribonucleic acid even though there is no formation of clear structure of chromosome. Therefore, there is lack of clear discernment of chromosomes in the nucleous of the cell. The chromosomes appear like loosely coined chromatin. At this point and time, the cell posses small cylindrical organelles known as centrioles, nucleolus which is a protein body found in the nucleous and a nuclear membrane to keep the deoxyribonucleic acid molecules from undergoing mutation (Vunjak-Novakovic & Freshney, 2006). Then follows the prophase stage where the chromatin starts to shorten and condense. This always occurs as a result of coiling. The result of this condensation and shortening is the formation of chromosomes. Centrioles now begin spreading to the directly opposite end sides of the cell and the spindle fibres extend from the centromeres. At this stage of development, the nucleous and the nuclear membrane can now be observed (Evert & Eichhorn, 2006). Prometaphase sets in when each chromosome forms two kinetochores. These are the protein structures present on chromosomes, at the centromere. Each of the kinetochore is attached to a particular chromatid. The chromosomes then start moving after the structural components of the cell known as microtubules has attached itself to the kinetochores. Metaphase stage picks up from the prometaphase. In this stage the spindle fibres tend to mount themselves to the centromere of the chromosomes. They therefore, align along the middle of the nucleous. Due to this there is a line formed and it is referred as the metaphase plate or also called the equatorial plate. The alignment is so essential in this stage since it will ensure that during the next stage, which is anaphase, when chromosomes separate, each newly formed nucleous will definitely acquire one copy of each chromosome (Braun & Anderson, 2007). Anaphase is the immediate stage after metaphase. Most observable process in this stage is that in which the paired chromosomes separate and move to the opposite side of the cell after the spindle fibers have shorten and centromere splitted. The main purpose of this movement is still unknown, though some studies suggest that this might have been caused by the rapid assembly and breakdown of microtubules. Due to this, there has got to be the separation of the two identical copies of the sister chromosomes (Yavin & Yavin, 2008). Telophase is the last stage of mitotic cell divison. In the telophase stage, there is formation of nuclear membrane around each set of sister chromosomes. This happens after the sister chromosomes have attached themselves at the opposite ends of the pole. Disintegration of spindle fibers also takes place (Vunjak-Novakovic & Freshney, 2006). Cytokinesis though not mitotic phase winds up the whole process of cell division. Cytokinesis entails the splitting of daughter cells apart and this happens with formation of a furrow as the cell is pinched in to two. When all this takes place successfully each daughter cell possesses a complete copy of the genome of its parent cell, actually the number and the quality is similar. On the other hand, we have meiosis, which is type of cell division that is normal or mostly occurs in the reproductive cells only during the sexual reproduction. Meiosis can also be termed as germ cell division. In other words meiosis can be referred to as reductional division. This is because the number of daughter cell is reduced to half(haploid) that of the parent cell. Meiosis is divided into two stages, which are successive. These stages are Meiosis 1 and Meiosis 2. During the first meiotic stage that is meiosis 1,there is formation of two haploid cells with half number of chromosomes but then the deoxyribonucleic acid does not reduce in amount (Evert & Eichhorn, 2006). Tissue Development Tissue development and repair always occur when the existing tissue structure has been tampered with. Therefore, it occurs in case of an injury, which may later develop into a wound. The repair process is also known as cicatrisation. It is a natural process whereby the skin or any or any other organ tissue tends to repair itself mostly after an injury has been inflicted. In the epidermis, which is outermost layer of the skin and the dermis, which is the deepest skin layer, there exists a steady state equilibrium that creates protection from the outside environment. When this protectional barrier is destroyed, the natural tissue formation or wound healing kicks off in a spontaneous manner. Just after the injury of the skin tissue has been kicked off, a myriad of biochemical processes take place in an organized unique manner geared to the repair of damaged tissues. Few minutes after the injury, the platelets, which have their main function as clotting agents, assemble at the site of the injury leading to the formation of a fibrin clot. This process aids in controlling the bleeding. Wound healing process can be aggregated by several factors, for instance, bloodstream levels of hormones like oxytocin. Wound healing process is divided into three main categories. These stages are Inflammation, Proliferation and Remodeling (Braun & Anderson, 2007). Inflammatory Phase Before this phase takes place, clotting has to take place to control the bleeding as said earlier. After the bleeding particular soluble factors such as cytokines and chemokines are released to stimulate the release of cells that carry out phagocytosis on debris, harmful bacteria present and damaged tissue. To add on they release molecules that signal the initiation of the proliferative phase. Just after the blood vessel is broken or breached, the ruptured cell membranes produces the inflammatory factors such as prostaglandins and thromboxanes that mainly act by preventing excess loss of blood and collecting the inflammatory cells and vessels in the said area. The whole collection process can be scientifically termed as vasoconstriction, and it always lasts up to ten minutes or less. It is immediately followed by vasodilation or widening of the blood vessels. This means it takes up to twenty minutes after the injury case (Vunjak-Novakovic & Freshney, 2006). Approximately after one hour of tissue damage or wounding , polymorphonuclear neutrophils (Abbrv PMN’S) set in at the injury site and pose as the predominant cells at the site for around two days after the breaching of the skin and their numbers increase tremendously being high on the second day. Fibronectin kinins play a key role in attracting the polymorphonuclear neutrophils. Neutrophils majorly carry out phagocytosis on debris and also secretes free radicals to kill the bacteria. This is called the respiratory burst. Neutrophils are also engulfed and killed by macrophages after they have accomplished their task in a process referred to as apoptosis(Neels, Thinnes & Loskutoff, 2004). Macrophages play a key role in the wound healing process. They take over from the PMN’s as the principal cells in injury site after two days. The main function of the macrophages at the site is to phagocytize or destroy bacteria and the tissues, which have been damaged and in addition they provide debridement of the damaged tissues by secreting proteases. At around third to fourth day after wounding, the macrophages release growth factors and cytokines. It is also evident that macrophages are highly stimulated by low levels of oxygen and they also act in producing cells that in return stimulate reepithelization of the wound hence the new extracellular matrix is formed at that point and time (Vunjak-Novakovic & Freshney, 2006). Proliferative Phase Profilerative phase always commences even if the inflammatory phase is not yet over thus after two to three days, of which is the time when the fibroblasts start to enter the injured tissue site. It is also noted that the processes in this phase occur in an overlapped time contrary to the other phases. The process of angiogenesis or may also be referred as neovascularization takes place in concurrence with the fibroblast proliferation, especially when there is migration of endothelial cells to the wounded area. The tissues where there has been the occurrence of angiogenesis always tend to appear red in color (Braun & Anderson, 2007). Stem cells of endothelial cells, which originates from parts of blood vessels that are not injured usually develop a protrusion known as a pseudopodia and press through the extracellular matrix directly to the site of the wound in order to establish a new blood vessel for appropriate blood flow. For the endothelial cells to migrate they require collagenases and plasminogen to disintegrate the whole clot and some area of the extracellular matrix. All this makes it possible for proliferation, cell migration and angiogenesis (Vunjak-Novakovic & Freshney, 2006). Granulation tissue functions just as rudimentary tissue. It always start to come out in wound during the inflammatory phase and that is common between two to five days of wounding. This continues to occur until there is a complete coverage of wound bed. Granulation tissue has blood vessels, which are new. There are new fibroblasts, endothelial cells, inflammatory cells, myofibroblasts and a new component of extracellular matrix, which is different from the previous ECM (Neels, Thinnes & Loskutoff, 2004). Epithelization As noted earlier granulation tissue formation into an open wound provides conducive environment for the reepithelization phase to commence. Basal keratinocytes and dermal appendages like sweat glands, hair follicles and sebaceous glands are the major cells that drive the process of reepithelization. Keratinocytes carry out migration without first profilerating. This migration process can take place as early as just few hours after the injury occurrence. Before this migration, these cells become longer, change shape, and flatten thus making them look like ruffles. As this migration continues new epithelial cells ought to be formed at the edges of the wound in order to replace them. Keratinocytes always continue with their migration across the bed of the wound up to the point at which cells of the either sides converge in the middle hence contact inhibition makes them to stop the migration. After this the keratinocytes secrete proteins that in return comes up with new basement membrane (Neels, Thinnes & Loskutoff, 2004). Development of epithelial tissue The epithelial tissue covers most part of the skin. On the other hand, the skin is the sensory organ in the body that covers about 20 square feet of all the total area and is the largest of all the other organs. The skin acts as a protection of the inner tissues and organs from disease causing micro-organism, regulation of body temperature and permission of the sensation of touch, heat and cold. The skin is made up of three layers of tissues. These tissues are epidermis, dermis and subcutaneous tissue (Braun & Anderson, 2007). (a) Epidermis is this is the outer most layer of the skin that enables a waterproof barrier and creates a skin tone. (b) Dermis is a layer of the skin that lies beneath the epidermis. It is composed of rough connective tissues, sweat glands and the hair follicles (c) The deeper subcutaneous tissue is the layer that is made up of fat and connective tissues. People of all works of life have different skin colours. The skin color is determined by melanin which a pigment created by special cells is called melanocytes which are situated in the epidermis. Nerve endings in a skin aids in sensing pain, pressure and temperature. Areas that have more nerve endings in the body are the fingertips and toes; these are the areas that are extremely sensitive to touch. Hair follicles in the skin also play a critical role in enhancing sensation (Vunjak-Novakovic & Freshney, 2006). Sense of Touch According to Gardner in the neurobiology perspective, touch is ‘the special sense by which contact with the body of an organism is perceived in the conscious mind’. These allow one to determine objects size, shape, weight, temperature and whether this causes pain or pleasure. In this case the touch makes individuals get to understand the environment better and shape their perspective towards it. Touch receptors inside a humans body also, allows one to know the shape of the bones, muscles and other soft tissues (Braun & Anderson, 2007). Touch as compared to other senses is the most necessary and interesting, this is noticeable during movements in that it requires one’s sensitive alertness gained though proprioception which is an internal form of tactile sense.. Sense of touch in the embryo is the first to develop of all the other senses and continues to work in old age even after the other senses failed. This sense guides the infants in their development to learn about their environment and relationship with other people (Freudenrich, 2006). Through out people’s life time, the sense of touch helps learning, protection from harm, relationship with others and experiencing of pleasure. Sensory neurons are numerous in the skin such that in each square inch of skin there are hundreds of sensory nerve endings according to (Gardner). Each sensory neuron in the skin has a specialized capsule on its peripheral end which is physically linked to the nerve ending of the adjacent skin tissue (Vunjak-Novakovic & Freshney, 2006). The basis of the sense of touch is on mechanical deformations of the skin and soft tissues of the body, this causes change in the shape of the capsule adjoining the nerve ending. The nerve ending, called a mechanoreceptor, detects this change and produces an action potential which is propagated to the rest of the nervous system. The action potential codes for the touch’s location on the skin, the amount of force, and its speed. Other touch receptors in the skin have specific duties of producing action potentials in response to the object’s temperature and to the presence of chemicals on the skin (Evert & Eichhorn, 2006). The sensory neurons sent the signals to the thalamus and the celebral cortex. This is the specific location in the brain at where each sensory neuron synapses are determined and the touch signal interpreted. Sensory neurons arrangement is similar in all human beings but the details of the somatotopic map characterize each individual and are determined largely by experience according to Gardner (Vunjak-Novakovic & Freshney, 2006). The types of touches that people experience throughout their lives affect the development of their nervous tissue, hence the architecture of the brain; this in turn affects one’s interpretation and response to different types of touch. A general statement about neuronal communication is that “repetitive activation of a nervous tissue pathway strengthens those synapses, making it easier to pass information forward” Gardner. This explains that the more a person gets used to a certain type of touch, the nervous tissue becomes active and accurate in interpreting the information being relayed. However, in absence of touch the sensory neurons will become deactivated and the synapses in that neuronal pathway will never strengthen. Through its effect on the development of nervous tissue, hence neuronal pathways and communication, the amount and type of touch an individual receives may have serious effects on behavior and health (Braun & Anderson, 2007). At the start of the twentieth century, psychologists and doctors have come up with a conclusion that affectionate touch is necessary for physical, mental, and emotional development in children. Lack of affectionate touch has been known to have serious consequences in that it causes depression, violence, memory deficits, and illness. One possibility, referred to as Attachment Theory according to Hatfield, has to do with the relationship between affectionate touch and parent-child bonding If a child does not receive adequate affectionate touch because his or her parents are emotionally neglectful, then the child and parents will not form a proper emotional bond. The lack of bonding will, consciously or unconsciously, cause unhappiness and a lack of trust on the child’s part. As a child grows older this will manifest itself as an inability to relate to other people, which will make the child to always remain unhappy and stressed up. This theory has definite merit, but it does not provide a clear cause and effect for touch deprivation and abnormal development (Braun & Anderson, 2007). Conclusion From this discussion, it is clear that cell development occurs through a process of cell division. In this case, a single cell divides and produces a similar cell. For each single cell that is capable of dividing, it posses a cell cycle that consists of three main stages. These stages are interphase, karyokinesis and cytokinesis. These cycles are always of different length and they are dependant on a number of factors. These factors include nature of the cell, food, oxygen and other nutrients. Among the various types of cell divisions, mitosis is the most common one since its so important in regeneration, repair, growth and reproduction. Mitosis takes place in living cells in the body of a living organism thus making it possible to earn the name somatic cell division. Tissues on the other hand are developed according to the duties to be accomplished by the organs of an organism. If there is need to repair worn out tissues, cells will specialize and develop the tissues for healing the wound. If there is need for the body to feel or sense the environment, cells in the skin specialize and develop epithelial tissue as well as nervous tissue, which will function together to enable an organism perceive the environment. References: Braun, C. A., & Anderson, C. M.,2007, Pathophysiology: functional alterations in human health. Philadelphia, Lippincott Williams & Wilkins. Coultas, L., Chawengsaksophak, K. & Rossant,J. 2005, Endothelial cells and VEGF in vascular development Nature 438, 937-945 (15 December 2005) | doi:10.1038/nature04479; Published online 14 December 2005 Disher, D., Janmey, P. &Wang, Y.,2005, Tissue Cells Feel and Respond to the Stiffness of Their Substrate. Science 18 November 2005:Vol. 310 no. 5751 pp. 1139-1143 Evert, R. F., & Eichhorn, S. 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