A&P 1 notes.docx - Muscle tissue enables us to move(Figure...

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Unformatted text preview: Muscle tissue enables us to move (Figure 1.3). The cells that make up muscle tissue are specialized for muscle contraction. Connective tissue (Figure 1.4) offers support and protection of body organs and includes bones, tendons, blood, and ligaments. Connective tissue cells are specialized to bind tissues together and play a supportive role. Nervous tissue (Figure 1.5) is responsible for the communication between the cells of the body by forming a system of electrical impulses that communicate very rapidly. Nerves are like the “wiring” of the body. Skeletal System: (Figure 1.7) Serves as the framework for the muscular system and supports the body organs. The skeletal system also provides protection for internal organs and houses blood cells as well as stores minerals. The skeletal system provides the framework for which the muscles attach. . Muscular System: (Figure 1.8) Allows for movement of the body. Muscles attach onto bones to bring movement to the skeletal system. Groups of muscles contract and relax in complex coordination to allow us to perform all our daily activities. Nervous System: (Figure 1.9) Provides internal communication among the cells of the body. Our nervous system uses electrical impulses to communicate within the body and enable the body to respond to the internal and external environments Endocrine System: Made up of glands (Figure 1.11) that make hormones which regulate the reproductive system and the metabolism of the body. Cardiovascular System: (Figure 1.13) Made up of blood vessels which move blood, oxygen and nutrients throughout the body. Lymphatic System: (Figure 1.14) Responsible for immunity and fighting off disease. The lymphatic system is also a part of the circulatory system. It has a complex network of vessels and nodes that allow for the excess fluid to drain back to the heart. Respiratory System: (Figure 1.15) Involved in excretion of the waste CO2 which is a byproduct of metabolism. The respiratory system also keeps the blood supplied with oxygen. Urinary System: (Figure 1.16) Involved in excretion of waste from the body. The urinary system also intricately regulates the water and electrolyte balance in the blood. The cardiovascular system, digestive system and urinary system help to move nutrients and waste through the body. The actual ability to remove waste from the body is known as excretion and is carried out by the digestive, urinary, and respiratory systems. The body can be divided into two regional terms: the axial and the appendicular parts of the body. The axial part (Figure 1.27) makes up the axis of the body and includes the head, neck and trunk. The appendicular part (Figure 1.28) of the body consists of the appendages or limbs that are attached to axis of the body as well as the pelvic and pectoral (shoulder) girdles that serve as a point of attachment. The ventral body cavity is anterior and is the larger of the two cavities. Within the ventral cavity are the thoracic cavity and the abdominopelvic cavity. The ventral cavity houses the visceral organs. The thoracic cavity is protected by the ribs and the muscles found within the chest (Figure 1.32). The thoracic cavity is further divided into the lateral pleural cavities which each contain a lung and the pericardial cavity which surrounds the heart. The pericardial cavity also encloses the thoracic organs which are the esophagus and trachea. The pericardial cavity also contains what is called the mediastinum. The thoracic cavity is divided from the abdominopelvic cavity by the diaphragm. The diaphragm is a dome shaped muscle that is vital to the breathing mechanism (Figure 1.33). The pelvic cavity (Figure 1.35) lies in the bony pelvis and houses the bladder, reproductive organs and the rectum. The organs of the abdominal cavity are very vulnerable to injury because the walls of the abdominal cavity are formed only by the muscles in the trunk of the body. There is no bone for protection. The bony pelvis provides more protection for the pelvic organs. The oral cavity contains the mouth, teeth and tongue (Figure 1.37). This cavity is continuous with the digestive cavity and extends all the way to the anus. Another cavity we will discuss is the nasal cavity (Figure 1.37) which is located within and posterior to the nose. The nasal cavity is part of the respiratory tract. The orbital cavities in the skull house the eyes The two basic types of cells are prokaryotic and eukaryotic cells. Bacteria are prokaryotic cells. Prokaryotic cells (Figure 1.42) are considered simple cells for three reasons. 1) They are typically smaller than eukaryotic cells. Most are between 1-10 μm (micrometers) in size (about 1/30,000 of an inch); therefore, they are just visible with the light microscope. 2) The DNA of a prokaryotic cell is not enclosed in a nuclear membrane (prokaryotic means “before the nucleus”). 3) Prokaryotic cells do not contain many of the internal membrane-bounded organelles of eukaryotic cells. Like eukaryotic cells, however, prokaryotic cells do contain a plasma membrane and ribosomes. Ribosomes are composed of ribonucleic acid (RNA) and synthesize proteins for use by the cell; they are not surrounded by a membrane. Membranes provide a location for metabolic processes to occur. Because prokaryotes lack organelles with membranes, the plasma membrane of a prokaryotic cell is often folded inward to create numerous folds where metabolic processes take place. The Cell The cell is the basic unit of life. A cell is the smallest unit that can carry out all activities we associate with life. When provided with essential nutrients and an appropriate environment, some cells can be kept alive and growing for many years. By contrast, no isolated part of a cell is capable of sustained survival. There are both uni-cellular organisms such as bacteria and protists and multi-cellular organisms like human beings. Biologists realized by the middle of the nineteenth century that cells are the basic living units of organization and function in all organisms and that all cells come from other cells. This is called the cell theory and was established through the work of German scientists, Schleidan, Schwann and Virchow. Most cells are small enough that they cannot be seen with the eye alone; they require magnification with a light microscope, a device which passes light through a thin sample of the cell medium and then through a magnifying lens to be seen by the human eye. Few cells are as big as one millimeter (mm) in diameter (which is about 1/25th of an inch) and are large enough to be seen by the human eye. Think, for example, of a frog’s egg. Organelles (parts within a cell) and the biomacromolecules (proteins, lipids, carbohydrates and nucleic acids) from which they are composed are too small to be seen without the aid of a microscope. Organelles are to a cell what an organ is to a human. Organelles can be used for energy conversion and for synthesis of needed compounds. Why are cells so small? Cells must take in food and other materials and rid itself of waste. Everything that enters or leaves a cell must pass through its plasma membrane. Figure 1.41 shows the plasma membrane of a cell. The plasma membrane surrounds all cells and contains specialized “pumps” and “gates” that regulate the passage of materials into and out of the cell. Figure 1.41 Structure of a cell membrane (phospholipid bilayer with embedded proteins) As a cell grows, the surface area to volume ratio changes. (Table 1) Cells need to remain relatively small because as a cell expands the amount of surface area relative to the volume of the cell decreases. The smaller cell is more active because relative to its volume, its surface area is larger than a bigger cell. With a larger surface area (relative to its volume) this allows the metabolic processes to occur faster. Metabolic processes such as diffusion (transportation of particles across the membrane) can all occur faster. Cells (like those of the intestinal wall) and organelles (like the mitochondria) that are actively carrying out biochemical processes have adaptations (like numerous folds) in addition to their small size which greatly increase their surface area. Table 1 Comparing smaller vs. larger cells example: Compare cube A to cube B. While cube B is clearly larger than cube A, its surface area relative to its volume is less than the smaller cell. The two basic types of cells are prokaryotic and eukaryotic cells. Bacteria are prokaryotic cells. Prokaryotic cells (Figure 1.42) are considered simple cells for three reasons. 1) They are typically smaller than eukaryotic cells. Most are between 1-10 μm (micrometers) in size (about 1/30,000 of an inch); therefore, they are just visible with the light microscope. 2) The DNA of a prokaryotic cell is not enclosed in a nuclear membrane (prokaryotic means “before the nucleus”). 3) Prokaryotic cells do not contain many of the internal membrane-bounded organelles of eukaryotic cells. Like eukaryotic cells, however, prokaryotic cells do contain a plasma membrane and ribosomes. Ribosomes are composed of ribonucleic acid (RNA) and synthesize proteins for use by the cell; they are not surrounded by a membrane. Membranes provide a location for metabolic processes to occur. Because prokaryotes lack organelles with membranes, the plasma membrane of a prokaryotic cell is often folded inward to create numerous folds where metabolic processes take place. Figure 1.42 Prokaryotic cell Most people think of bacteria as causing diseases. An example is botulism, a type of food poisoning which can lead to paralysis and sometimes death. This bacterium, Clostridium botulinum, can form a dormant, extremely durable cell called an endospore which is released by the bacterium under adverse conditions. During the canning process, food must be heated to boiling for 3 to 4 minutes to kill any highly heat-resistant endospores which might be present. Plants, animals, and humans all possess eukaryotic cells. Eukaryotic cells (complex cells) are ten to one hundred times larger than prokaryotic cells, possess a nuclear membrane (eukaryotic means “true nucleus”), and contain many membrane-bound organelles (Figure 1.43). Membranes are important to a complex cell for many reasons, such as the forming of compartments within organelles where reactants are more likely to come into contact or to keep certain compounds away from one another. Membranes also form a work surface where many enzymes can congregate to complete a complex reaction. Ribosomes are often located on the endoplasmic reticulum (ER). The ER is a maze of tightly packed and flattened, saclike structures that form interconnected compartments within the cytoplasm. When ribosomes are located on the endoplasmic reticulum it is called the rough endoplasmic reticulum (RER). The ER (Figure 1.43) is an extension of the outer membrane of the nucleus. After proteins are assembled by the ribosomes, they are modified and transported by the ER. There are two continuous sections to the endoplasmic reticulum. The sections that possess ribosomes appear “bumpy” and are called rough ER (Figure 1.46). Smooth ER has no attached ribosomes and is responsible for the synthesis of lipids. Human liver cells possess extensive amounts of smooth ER. This is where cholesterol, a major component of cell membranes, is formed. Both types of ER possess a large variety of enzymes that catalyze (speed up) chemical reactions. The cytoplasm (cytosol) includes the fluid portion of the cell and all the organelles outside of the nucleus. (Figure 1.43) The Golgi complex (apparatus) (Figure 1.43, Figure 1.46) is named after the scientist that discovered it. The Golgi complex is an organelle made up of a stack of many flattened sacs called cisternae. Parts of the Golgi complex are connected; however, most form separate compartments. The Golgi complex is responsible for receiving lipids and proteins synthesized by the endoplasmic reticulum, altering their structures and shipping them to other parts of the cell. As portions pinch off from the Golgi membrane forming enclosed sacs called vesicles, they and their contents can be transported to other organelles within the cell or exported out of the cell through the cell membrane. This is accomplished through fusion of the vesicles with the plasma membrane of the cell or other membrane-bound organelles. Fusion can occur because all membranes within the cell are structured similarly. The Golgi complex also produces small sacs of digestive enzymes called lysosomes ("lysis" means to disintegrate). The digestive enzymes break down biomacromolecules (proteins, lipids, carbohydrates, and nucleic acids) that originate inside or outside of the cell. Once broken into their building block monomers, these molecules can later be recycled into new biomacromolecules. Lysosomes can also fuse with other vesicles containing harmful bacteria. In this way, the bacteria can be degraded into its components. In the genetic disease known as Tay-Sachs, one of the normally present digestive enzymes inside lysosomes is lacking. Thus, a toxic lipid in the brain cells cannot be broken down. The resulting buildup of lipids in these cells can cause intellectual disability and death. Mitochondria (singular, mitochondrion, Figure 1.47) is the organelle responsible for converting the chemical energy found in food into ATP. ATP stands for adenosine triphosphate. ATP is a high-energy molecule that provides energy for the cell. This process is called aerobic cellular respiration. During cellular respiration oxygen is required to break down food (usually in the form of glucose). Carbon dioxide, water, and ATP are produced. Notice that this is very much like respiration (breathing) in your lungs, but at the cellular level. It is through the lungs that the necessary oxygen is obtained to be used by the cells for respiration. Each mitochondrion is bound by a double membrane (note the inner membrane and outer membrane in Figure 1.47). That means that there are two membranes, one inside the other. There is an intermembrane space between the inner and outer membranes, and a matrix which forms the center of the mitochondrion, bound by just the inner membrane. The inner mitochondrial membrane possesses numerous folds which increases the surface area, allowing ample room for the chemical reactions and enzymes required to transfer the chemical energy in food into ATP. Eukaryotic cells also contain a cytoskeleton (Figure 1.48). The cytoskeleton consists of a network of protein fibers that provide structural support and movement within the cell. We will look at two types of protein fibers that compose the cytoskeleton, both of which can be rapidly assembled and disassembled. 1) Microtubules are hollow cylinders (like a tube) which are involved in the movement of chromosomes during cell division and in the structure of cilia and flagella. Cilia and flagella project from the surface of some cells. The flagellum is usually a long, whip-like structure that propels or pulls a single-celled organism through a watery medium. Flagellum are also found on sperm cells. Cilia are shorter and found in greater number. In humans, ciliated cells are found along the respiratory passageways for trapping and moving debris. In order for the microtubules to perform their job, they generally need to be anchored somewhere in the cell. These anchoring regions are called microtubule-organizing centers (MTOC's). During cell division, microtubules (Figure 1.48) grow outward from the MTOC assisting in the movement of chromosomes into two new cells. Inside the MTOC of animal cells are usually found two centrioles. The centrioles are made up of nine sets of three attached tubules arranged to form a hollow cylinder. Similar structures called basal bodies anchor cilia and flagella. Both centrioles and basal bodies play a role in microtubule assembly. 2) Microfilaments are flexible, solid fibers made up of two intertwined polymer chains of actin molecules. Actin fibers themselves cannot contract but they can generate movement by rapidly assembling and disassembling. During cell division, a ring of actin, associated with another protein, myosin, causes the constriction of the cell to form two daughter cells. In muscle cells actin and myosin slide past one another, shortening the muscle fiber and causing muscle contraction. Most eukaryotic cells are surrounded by a cell coat. The coat is made of polysaccharide (carbohydrate) side chains, that project out from the proteins (glycoproteins), and lipids (glycolipids) that comprise the cell membrane. These side chains allow cells to recognize one another, make contact, and, sometimes, to adhere to one another, such as in forming tissues. Many eukaryotic cells also secrete an extracellular matrix which contains tough protein fibers called collagen (Figure 1.49). Figure 1.49 The outside of eukaryotic cells usually contains a cell coat, made up of carbohydrate chains and other lipids that protrude outside the cell Lastly, is the cell wall (Figure 1.42). Animal and human cells do not possess a cell wall; however, most plants and bacteria do. The thick cell walls in plants contain multiple layers of cellulose fibers. These layers give the cell wall great mechanical strength and provide structural support for the stem, roots, and leaves. In bacteria, the cell wall structure varies among species. Bacterial cell walls do not contain cellulose, but may contain peptidoglycan which is a 3-D mesh-like structure composed of sugars and amino acids ("peptid-" refers to the peptide bonds and "glycan" refers to sugar). Those bacteria possessing a very thick layer of peptidoglycan absorb and retain a violet stain and are called gram-positive, while those that possess a very thin layer of peptidoglycan do not retain the violet stain and are called gram-negative (the staining process was designed by a physician named Christian Gram). The cell wall acts as protection for the bacteria. The antibiotic penicillininterferes with the cell wall structure of gram-positive bacteria, resulting in a fragile cell wall that cannot protect the cell. Animals and humans do not require cell walls as they are often equipped with some form of supportive and/or protective skeleton. Cells can be studied with the use of a microscope. Light microscopes (the least expensive and most common) are also known as compound microscopes because they contain several lenses (Figure 1.50). Because light must pass through the specimen, only thin objects can be observed. Light microscopes have a maximum magnification of about 1000 times. In addition, their resolution (ability to discern fine detail) is only about 500 times that of the human eye. Electron microscopes, however, can magnify up to 250,000 times or more and have a resolution of more than 10,000 times that of the human eye. With a transmission electron microscope, the specimen is cut into extremely thin sections (many times thinner than specimens commonly observed under a light microscope). Each section is passed under an electron beam which forms an image on a photographic plate or fluorescent screen. To see the complete object, it would be necessary to view numerous consecutive sections. Figure 1.50 Image produced by a light microscope A scanning electron microscope produces a 3-D picture of the surface of an object (Figure 1.51). The object is coated with a thin film of gold or other metal. Electrons do not pass through the object, instead particles are emitted as the electrons strike the object. This produces an image of the external features of a specimen that would not otherwise be visible with a scanning electron microscope. Figure 1.51 Image produced from a scanning electron microscope In 1972, the fluid-mosaic model (Figure 1.52) of membrane structure was introduced, which proposes that the membrane is a phospholipid bi-layer in which proteins are either part...
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