Histology Exam 1: Introduction To The Cell

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Simple Diffusion

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Fat soluble molecules and small, uncharged molecules.

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Carrier Protein

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Small, water-soluble molecules (highly selective).

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Channel Protein

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Water-soluble molecules (regulated by membrane potential). Highly selective.

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Pinocytosis

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Nonspecific ingestion of fluids & small proteins via small vesicles (especially numerous in endothelial cells lining blood vessels).

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Phagocytosis

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The ingestion of large particles (i.e. cell debris, bacteria, etc..). Ingestion is mostly by macrophages or histiocytes (members of the mononuclear phagocyte system). Receptors on the surface of the macrophages recognize non-antigen binding domains of antibody molecules coating the surface of the invading microorganism.

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Receptor Mediated Endocytosis

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Allows the entry of specific molecules into the cell. Receptors are usually located in specific regions of the cell membrane and are called cargo receptors.

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What are the types of endocytosis?

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Pinocytosis, phagocytosis, and receptor-mediated endocytosis.

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Lysosomes

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Membrane-bound digestive organelles rich in hydrolytic enzymes (synthesized by the RER, modified by the Golgi, and packed into the lysosomes). They are "recycling plants" and practice autophagy (internal house cleaning and removal of worn out cytoplasmic components).

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Give examples of commonly phagocytosed material.

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Bacteria, cell debris, Hemosiderin (hemoglobin breakdown product), carbon particles, and asbestos fibers.

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Rough Endoplasmic Reticulum (RER)

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Has cisternae and ribosomes and functions in protein synthesis. Cells with large amounts of RER have a blue-staining (basophilic) cytoplasm when stained with H&E (lots of RER=ergastoplasm). It is continuous with the outer layer of the nuclear envelope.

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Smooth Endoplasmic Reticulum (SER)

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Has cisternae but not ribosomes. It functions in lipid metabolism and is important in the detoxification of exogenous compounds (via P-450 mixed function oxidase system).

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Golgi Apparatus

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An organelle well developed in secretory cells that functions in post-translational sorting and packaging of proteins. It does not stain with H&E or Wright’s stain.

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Peroxisomes

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Membrane-bound, intracellular, spherical organelles that contain catylase and other oxidative enzymes. They function in beta oxidation of fatty acids. Oxidative reactions result in H2O2 formation (which is highly toxic). Peroxisomal catylase regulates the amount of intracellular H2O2, protecting cells that contain a lot of these enzymes (e.g. the liver).

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What are examples of non-membranous organelles?

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Examples: nucleolus, microtubules, actin filaments, intermediate filaments, centrioles, and ribosomes.

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Function of Actin Filaments

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They provide mechanical support, anchor membrane proteins, aid in motility, and function in the intracellular track system.

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Intermediate Filaments

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Rope-like structures that provide resistance to shearing forces and anchoring connections to desmosomes.

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Nucleus

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The largest “inclusion” within the cell, its envelope is formed by two membranes. It is filled with chromatin on H&E sections.

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Chromatin

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A complex of DNA and proteins (histones). There are 3 feet of DNA in average nucleus. It stains with “basic” dyes.

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Nucleolus

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It is involved in the synthesis of ribosomal RNA, is prominent in cells actively secreting protein, and functions in the regulation of the cell cycle and in cell differentiation.

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Euchromatin

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Diffuse, fine granular chromatin with lots of uncoiled DNA found in cells undergoing active transcription.

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Heterochromatin

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Clumped, course granular chromatin with mostly coiled DNA found in cells with a low level transcription.

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Necrosis

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Cell "murder" resulting in inflammation. It is seen with exposure to toxins, infectious agents, and in mechanical injury.

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Apoptosis

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Cell "suicide" that does not cause inflammation. It is associated with intrinsic and extrinsic signaling.

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Name organelles that can be seen with a light microscope.

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Examples: the nucleolus, centrioles, the nucleus, mitochondria, and the Golgi apparatus.

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Categories of Organelles

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Include: membrane systems of the cell, membrane-limited compartments (which perform metabolic, synthetic, and energy-requiring/generating functions), and non-membranous structural components.

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Cell (Plasma) Membrane

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Composed chiefly of phospholipids, cholesterol, and protein molecules arranged in a bi-layer manner. Cholester and other hydrophobic lipids are located on the interior. There are ~5 million lipids per micrometer (they are moving around and partially stabilized by cholesterol).

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Integral Proteins

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Protein molecules that are embedded in (and pass completely through) the plasma membrane. They play an essential role in regulation, metabolism, and the integration of cells.

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Peripheral Proteins

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Proteins that attach to the surface of the plasma membrane (via strong ionic interactions).

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Glycocalyx

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The collective term for glycoproteins or glycolipids formed when carbohydrate molecules attach to the surface proteins or lipids of the plasma membrane.

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Function of Glycocalyx

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Determines the configuration of cell surface receptors upon which the life of the cell depends (carries a code equally important to the genetic code).

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Ion Pumps

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Transport sodium and potassium across the cell membrane.

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Cell Channels

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Allow the passage of water, small ions, and molecules across the cell membrane.

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Membrane Receptors

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Recognize and bind specific molecules (ligands) vital to communication between cells and essential to multicellular organisms.

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Give some examples of molecules that can bind to membrane receptors.

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Examples: hormones, neurotransmitters, inflammatory mediators, and bacterial toxins.

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Structural Proteins/ Linker Proteins

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Anchor cells to each other in addition to the extracellular matrix using connections with the intracellular cytoskeleton.

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What are the three general ways molecules move into and out of cells?

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Simple diffusion, via carrier proteins, and using channel proteins.

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Endosomes (General)

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Membrane-bound structures associated with endocytosis. They may be temporary or stable. The two types are early and late endosomes.

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Early Endosomes

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Found near the cell membrane and important in the sorting and recycling of proteins internalized by various endocytic pathways. Many of these structures re-fuse with the cell membrane.

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Late Endosomes

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Structures formed from early endosomes that travel deeper into the cytoplasm and eventually develop into lysosomes. They are important in regulating the amount of transporter proteins to and from the plasma membrane.

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Give examples of enzymes carried by lysosomes.

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Examples: Acid phosphatase, glucuronidase, ribonuclease, lipase, and collagenase. * These all degrade engulfed cellular material.

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Primary Lysosomes

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Enzyme-containing vesicles that fuse with phagosomes to form secondary lysosomes or phagolysosomes.

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Autophagy

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The removal, digestion, and reprocessing of damaged and worn-out organelles.

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Heterophagy

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The process by which lysosomes ingest and breakdown material from the external environment (typically performed by specialized phagocytic cells called macrophages).

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Lysosomal Storage Diseases

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Occur when there is a malfunction of lysosomes or their digestive enzymes. They result in an accumulation of substrates within the cell which ultimately impairs cell function.

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Phase I Reactions

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Metabolic processes using oxidative enzymes associated with the detoxification of exogenous (non-polar) compounds. They (usually) modify toxic molecules to a less toxic (polar) substance which is then cleared from the body.

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Phase II Reactions

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Associated with direct conjugation of exogenous (polar) molecules to glucuronic acid, sulfate, or methyl groups. The result is always formation of a less toxic product.