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Bio.590-3.Cmprtments
Integrative Physiology Ch. 3 - Compartmentation: Cells and Tissues
| Question | Answer |
|---|---|
| Advantages of compartmentalization | Compartments separate biological processes that might otherwise conflict with one another (e.g. lysosomes) |
| Disadvantages of compartmentalization | Barriers between compartments make it difficult to move needed materials from one compartment to another. This is overcome by means of specialized mechanisms that transport selected substances across membranes |
| Anatomically the body is separated into three major body cavities: | (1) the cranial cavity (commonly referred to as the skull), (2) the thoracic cavity (AKA thorax), and (3) abdominopelvic cavity |
| The cavities are separated from each other by… | …bones and tissues, and they are lined with tissue membranes |
| Cranial cavity | Contains the brain, out primary control center |
| Thoracic cavity | Bounded by the spine and ribs on top and sides, with the muscular diaphragm forming the floor. |
| The thoracic cavity surrounds the… | …heart, which is enclosed in a membranous pericardial sac, and the two lungs, enclosed in separate pleural sacs |
| Abdominopelvic cavity | The abdomen and pelvis form this continuous cavity. A tissue lining called the peritoneum lines the abdomen and surrounds the organs within it. |
| Organs contained within the abdominopelvic cavity | Abdomen: stomach, intestines, liver, pancreas, gallbladder, spleen. Pelvis: reproductive organs, urinary bladder, and the terminal portion of the large intestine. Outside abdominal/pelvic cavities: kidney |
| Where are the kidneys located? | The kidneys lie outside the abdominal cavity, between the peritoneum and the muscles of the back, just above waist level |
| Lumen | The interior of any hollow organ is called its lumen. A lumen may be wholly or partially filled with air or fluid. E.g. the lumen of blood vessels is filled with blood |
| The lumen of the digestive system is… … why? | …continuous with the body’s external environment. Why? Because the material inside the lumen is not truly part of the body’s internal environment until it crosses the wall of the organ |
| When is E. coli harmful? | Only if there is a rupture in the digestive tract and it crosses into the internal environment. |
| Functionally the body has three fluid compartments: | (1) intracellular fluid (ICF), (2) extracellular fluid (ECF), and (3) interstitial fluid |
| Intracellular fluid (ICF) | The fluid within the cells |
| Extracellular fluid (ECF) | Fluid outside of the cells. This fluid can be further subdivided to: plasma (the fluid portion of the blood within the circulatory system) and the interstitial fluid (the fluid between the circulatory system and the cells |
| Membrane definition | Technically a membrane has two definitions: either to a tissue (e.g. mucous membrane) or to a phospholipid-protein boundary layer (e.g. cell membrane) |
| Two synonyms for the term cell membrane | Plasma membrane and plasmalemma |
| General functions of the cell membrane | Physical isolation; regulatory exchange with environment; communication between cell and environment; and structural support |
| Secretion | The process by which a cell releases a substance into the extracellular space |
| All biological membranes consist of | A combination of lipids and proteins plus a small amount of carbohydrate |
| The ratio of protein to lipid | Varies widely, depending on the source of the membrane. Generally, the more metabolically active a membrane is, the more proteins it contains |
| The fluid mosaic model of a biological membrane | The commonly illustrated model of a membrane showing a double layer of phospholipid molecules with various proteins embedded within the membrane and assorted bound carbohydrates |
| Hydrophilic vs. hydrophobic orientation of the phospholipids | Hydrophilic heads face the aqueous solutions, the hydrophobic tails are hidden within the membrane |
| Thickness of a cell membrane | Relatively uniform: about 8nm |
| Three types of lipids make up the cell membrane: | phospholipids, sphingolipids, and cholesterol |
| In what three structures can the phospholipid layer arrangement be found? | The phospholipid bilayer, the micelle, and the liposome |
| Micelles | Small droplets with a single layer of phospholipids arranged so that the interior of the micelle is filled with hydrophobic fatty acid tails. Micelles are important in the digestions and absorption of fats in the digestive tract |
| Liposomes | Larger spheres with bilayer phospholipid walls. This arrangement leaves a hollow center with an aqueous core that can be filled with water-soluble molecules. |
| Today liposomes are being used as… | …a medium to deliver drugs through the skin. |
| Biologists think that _____ was the precursor to the first living cell | A liposome-like structure |
| Sphingolipids | Phospholipids = the major membrane lipid, but some also have significant sphingolipids. They also have fatty acid tails, but their heads may either be phospholipids or glycolipids. They’re slightly longer than phospholipids |
| What function does the lipid cholesterol serve in membranes? | They help make membranes impermeable to small water-soluble molecules and keeps membranes flexible over a wide range of temperatures |
| Membranes proteins are __% of all proteins coded in our DNA | 33% (1/3) |
| Each cell has between __ and __ different types of proteins inserted into its membranes | 10; 50 |
| Three categories of membrane proteins | Integral proteins, peripheral proteins, and lipid-anchored proteins |
| Integral proteins | AKA transmembrane proteins, extend across the cell membrane. They’re tightly bound into the membrane with their 20-25 NONPOLAR (hence hydrophobic) amino acids in the alpha-helix formation |
| Transmembrane proteins are classified into families based on | How many transmembrane segments they have. There can be as many as 12 or as little as 1 |
| What’s special about transmembrane proteins with multiple segments? | They have loops of peptide chains that extend into cytoplasm and extracellular fluid. Carbohydrates attach to the extracellular loops, and phosphate groups attach to the intracellular loops (phosphorylation) |
| Peripheral proteins | They don’t span the entire membrane; instead they attach themselves loosely to the transmembrane proteins or to the polar heads of the phospholipids. They can be removed without destroying the membrane. |
| Peripheral proteins include | Enzymes and some structural binding proteins that anchor the cytoskeleton to the cell membrane |
| Lipid-anchored proteins | Proteins covalently bound to lipid tails that insert themselves into the bilayer. Many lipid-anchored proteins are found in association with membrane sphingolipids, leading to the formation of lipid rafts |
| Lipid rafts | The longer tails of sphingolipids elevate over their phospholipid neighbors to create what look like “rafts” floating on a sea of phospholipids (pg 61). |
| What is the lipid-anchored protein that’s almost always found in association with lipid rafts? | Placental alkaline phosphatase |
| Can all membrane proteins move freely (laterally, that is) throughout the membrane? | No, some integral proteins are anchored to cytoskeleton proteins and therefore immobile. |
| Why are immobile integral proteins important? | The ability of the cytoskeleton to restrict the movement of integral proteins allows cells to develop polarity, in which different faces of the cell have different proteins and therefore different properties |
| Most membrane carbohydrates are | Glycolipids and glycoproteins |
| Where are glycolipids and glycoproteins found? | They’re found exclusively on the external surface of the cell, where they form a protective layer known as the glycocalyx |
| Membrane sugars’ role in the immune response | ABO blood groups are determined by the number and composition of sugars attached to membrane sphingolipids |
| There is estimated to be over ___ different types of cells in the human body | 200 |
| Differentiation | During differentiation, only selected genes are activated, transforming the cell into a specialized unit |
| Internally, the cell is divided up into the ____ and the ____ | Cytoplasm; nucleus |
| Cytoplasm | Consists of a fluid portion called cytosol; insoluble particles called inclusions; and membrane-bound structures collectively known as organelles |
| Cytosol | AKA intracellular fluid; a semi-gelatinous fluid separated from the extracellular fluid by the cell membrane. It contains dissolved nutrients and proteins/ions/waste products |
| Inclusions | Particles of insoluble materials. Some are stored nutrients. Others are responsible for specific cell functions and these structures are sometimes called the nonmembranous organelles. Suspended in the cytosol |
| Organelles | “Little organs” – are membrane-bounded compartments that play specific roles in the overall function of the cell. E.g. lysosomes act as the cell’s digestive system. |
| Examples of inclusions | Ribosomes, proteasomes, vaults, protein fibers (cytoskeleton), lipid droplets (nutrients), glycogen granules (nutrients), centrioles, centrosomes, cilia, flagella |
| Ribosomes | Small, dense granules of RNA and protein that manufacture proteins under the direction of the cell’s DNA. |
| Fixed ribosomes | Ribosomes attached to the cytosolic surface of organelles |
| Free ribosomes | Ribosomes suspended free in the cytosol |
| Polyribosomes | Some free ribosomes form groups of 10 to 20 known as polyribosomes |
| A ribosome that is fixed for one minute may… | …release and become a free ribosome the next |
| Proteasomes | Hollow protein cylinders with a protein cap on each end. They’re “nanomachines” that function as the cell’s site for protein degradation |
| Vaults | Made of RNA and proteins and, like proteasomes, are hollow barrel-shaped particles, but their function is still uncertain. One vault protein is associated with tumors’ resistance to certain cancer-treating drugs |
| The three families of cytoplasmic protein fibers | Classified by diameter and protein composition: actin fibers, AKA microfilaments (thinnest); intermediate filaments (somewhat larger), made of myosin or keratin etc; and microtubules (largest) made of tubulin |
| Two general purposes for insoluble protein fibers | Structural support (from the cytoskeleton) and movement (with the help of motor protein enzymes) |
| The centrioles, cilia, and flagella are made from | The largest of the cytoplasmic protein fibers, the microtubules |
| Short summary: Microfilaments | Composed of actin protein (globular) Functions: cytoskeleton; associates with myosin for muscle contraction |
| Short summary: Intermediate filaments | Composed of myosin; neurofilament protein; or keratin; etc. (filaments). Functions: cytoskeleton; hair and nails; protective barrier of skin; myosin forms thick filaments for muscle contraction |
| Short summary: Microtubules | Composed of tubulin (globular). Functions: Movements of cilia, flagella, and chromosomes; intracellular transport of organelles; cytoskeleton |
| Centrosome | The cell’s microtubule-organizing center. It assembles tubulin monomers into microtubules. The centrosome contains two centrioles, each one is a cylindrical bundle of 27 microtubules, arranged in nine triplets |
| Why are centrosomes important in cell division? | In cell division, the centrioles direct the movement of DNA strands. If cells have lost their ability to undergo cell division, such as mature nerve cells, they lack centrioles |
| How to centrosomes appear under the microscope? | It appears as a region of darkly staining material close to the cell nucleus. |
| Cilia | Short hairlike structures protruding from the cell surface. It’s a continuation of the cell membrane and its core contains nine pairs of microtubules surrounding a central pair |
| Basal body | The portion of the cilia where the microtubules terminate. |
| How do cilia move? | They beat rhythmically back and forth when the microtubule pairs in their core slide past each other with the help of the motor protein dynein. |
| Function of cilia? | Their movement creates currents that sweep fluids or secretions across the cell surface. Ciliated cells are found mostly in the upper airways and part of the female reproductive tract |
| Flagella | Has the same microtubule arrangement as cilia but are much longer. Flagella are found on free-floating single cells, and in humans the only flagellated cell is the sperm cell. There is only one projection unlike cilia |
| The movement and function of flagella | Flagella bend and move by the same basic mechanism of cilia. They function to push cells through fluid, e.g. sperm. |
| The cytoskeleton is a… | …Flexible, changeable three-dimensional scaffolding of actin microfilaments, intermediate filaments, and microtubules that extends throughout the cytoplasm |
| Are cytoskeleton fibers permanent? | Some are, but most are synthesized or disassembled according to the cell’s needs. |
| Five important functions of the cytoskeleton | (1) cell shape, (2) internal organization, (3) intracellular transport, (4) assembly of cells into tissues, and (5) movement |
| Cytoskeleton function: cell shape | The protein scaffolding provides mechanical strength to the cell and in some cells plays an important role in determining the shape of the cell |
| Microvilli | Fingerlike extensions of the cell membrane that increase the surface area for absorption of materials |
| Cytoskeleton function: internal organization | Cytoskeletal fibers stabilize the positions of organelles |
| Cytoskeleton function: intracellular transport | The cytoskeleton helps transport materials into the cell and within the cytoplasm, serving as an intracellular railroad track for moving organelles. This is crucial in the nervous system where material must be transported very far |
| Cytoskeleton function: assembly of cells into tissues | Protein fibers of the cytoskeleton connect with protein fibers in the extracellular space, linking cells to one another (providing a means of communication) and to supporting materials outside the cells (mech. strength) |
| Cytoskeleton function: movement | Cytoskeleton helps cells move, e.g. white blood cells squeezing out of blood vessels, nerve cells that elongate, cilia and flagella obviously, motor proteins that use ATP to “walk” along cytoskeletal fibers to transport material |
| Motor proteins | Proteins that are able to convert stored energy into directed movement. |
| Three groups of motor proteins associated with the cytoskeleton: | Myosins, kinesins, and dyneins. Note: all three use ATP to propel themselves along cytoskeleton fibers |
| Myosins | Bind to actin fibers and are best known for their role in muscle contraction |
| Kinesins and dyneins | Associated with movement along microtubules. Dyneins’ association with the microtubule bundles of cilia and flagella help create their whiplike motion |
| The composition of most motor proteins | Multiple protein chains arranged into three parts: two heads that bind to the cytoskeleton fiber, a neck, and a tail portion that is able to bind “cargo”, such as an organelle that needs to be transported through the cytoplasm |
| How much ATP does the movement of motor proteins require? | Each “step” (the alternate binding of the heads to the cytoskeleton fiber) requires one ATP. |
| Four major groups of organelles | Mitochondria, the ER, the Golgi complex, and lysosomes/peroxisomes |
| Mitochondria | Small elliptical organelles with a double wall. The outer wall defines its shape; the inner wall is folded into leaflets called cristae. |
| The different compartments within mitochondria | The inner portion: mitochondrial matrix which contains ribosomes, enzymes, granules, and DNA; between the inner and outer membrane: the intermembrane space which is an important region for ATP production. |
| Mitochondria are the site of most… | …ATP production; hence its name: the “powerhouse” of the cell. |
| The number of mitochondria in a cell depends on… | …the cell’s energy needs. Cells such as skeletal muscle cells, which require a lot of energy, have many mitochondria relative to cells with low energy needs such as adipose cells |
| Two unique characteristics of mitochondria | (1) they have their own unique DNA and RNA, called the mitochondrial DNA and matrix RNA; and (2) their ability to replicate (aided by their DNA) even when the cell to which they belong isn’t undergoing cell division |
| Mitochondrial replication takes place by… | …budding, during which small daughter mitochondria pinch off an enlarged parent. |
| Note regarding exercising and mitochondria | Exercising muscle cells leads to an increase in mitochondria in the cells to handle the increased energy requirements |
| Endoplasmic reticulum (ER) | A network of interconnected membrane tubes that are a continuation of the outer membrane surrounding the cell nucleus. The name “reticulum” is derived from Latin for “net” referring to the tube’s net-like appearance |
| Two forms of ER | The rough RER and smooth SER |
| Rough ER | Has a granular appearance due to rows of ribosomes dotting its cytoplasmic surface. It’s the main site for the synthesis of proteins. After being assembled the proteins are sent into the RER lumen and chemically modified |
| Smooth ER | The main site for the synthesis of fatty acids, steroids, and lipids. Phospholipids are produced, cholesterol is modified into steroid hormones (e.g. testosterone) |
| The smooth ER of the liver | Detoxifies or inactivates drugs |
| The smooth ER in skeletal muscle | A modified version of the smooth ER in skeletal muscle cells stores calcium ions (Ca^2+) to be used in muscle contraction |
| Golgi complex | Consists of a series of hollow curved sacks stacked on top of each other. The Golgi complex receives proteins made on the rough ER, modifies them, and packages them into vesicles. |
| Two kinds of vesicles | Secretory and storage |
| Secretory vesicles | Contain proteins that will be released from the cell |
| Storage vesicles | Contents of storage vesicles never leave the cytoplasm. |
| Lysosomes | Small spherical storage vesicles that appear as membrane-bound granules in the cytoplasm. They use powerful enzymes to break down bacteria or old organelles, such as mitochondria, into their component molecules |
| Why are the contents of cells not destroyed by lysosomal enzymes | The enzymes are only activated by very acidic conditions (100x the cytoplasm). When pinched off the Golgi the lysosomes’ pH are neutral, around 7-7.3. The lysosomes slowly accumulate H+ and become more acidic |
| Are the enzymes of lysosomes always kept within the organelle? | Most of the time, but occasionally lysosomes release their enzymes outside the cell to dissolve extracellular support material, such as the hard calcium carbonate of the bone, or to atrophy muscle from lack of use |
| Lysosomal storage diseases | Inherited conditions in which lysosomes lack some of the required enzymes and are thus ineffective |
| Tay-Sachs disease | Infants with Tay-Sachs have defective lysosomes that fail to break down glycolipids. Accumulation of glycolipids in nerve cells causes nervous system dysfunction including blindness and loss of coordination. Poor prognosis |
| Peroxisomes | Storage vehicles even smaller than lysosomes. They contain a different set of enzymes with their function being to degrade long-chain fatty acids and potentially toxic foreign molecules |
| Where does the name “peroxisome” come from? | They get their name from the fact that the reactions that take place inside them generate hydrogen peroxide (H2O2), a toxic molecule. The peroxisomes then convert H2O2 to O2 and H2O with the enzyme catalase. |
| Peroxisomal disorders | They disrupt the normal processing of lipids and can severely disrupt neural function by altering the structure of nerve cell membranes |
| Nuclear envelope | A two-membrane structure that separates the nucleus from the cytoplasmic compartment |
| Nuclear pore complexes | Large protein complexes with a central channel. Ions and small molecules move freely through this channel when it is open, but large molecules such as proteins and RNA must be transported via a process that requires energy |
| The benefit of nuclear pore complexes | They allow the cell to restrict DNA to the nucleus and also to restrict various enzymes to either the cytoplasm or the nucleus |
| Chromatin | Randomly scattered granular material composed of DNA and associated proteins |
| Nucleoli | Region in the nucleus where the genes and proteins that control the synthesis of RNA for ribosomes are located |
| Note: Pap test | AKA pap smear. A screening test to detect potentially pre-cancerous or cancerous processes in the endocervical canal. It can prevent cervical cancer. A speculum is used in the vaginal canal to obtain cervical cells |
| Note: liposomes in medicine | The centers of liposomes are filled with drugs or fragments of DNA (for gene therapy). They’re then applied to the skin or injected. A new area of research is in “immunoliposomes” that use antibodies to recognize cancer cells |
| Note: dysplasia | A change in the size and shape of cells that is suggestive of cancerous changes |
| The cells in any tissue are held together by | Cell junctions and by other support structures |
| Tissues range in complexity from… | …simple tissues containing only one cell type, such as the lining of blood vessels, to complex tissues containing many cell types and extensive extracellular material, such as connective tissue |
| The cells of most tissues work… | …together to achieve a common purpose |
| Histology | The study of tissue structure and function |
| Histologists describe tissues by what features? | (1) the shape and size of the cells, (2) the arrangement of the cells in the tissue (in layers, scattered, and so on), (3) the way cells are connected to one another, and (4) the amount of extracellular material present in the tissue |
| Four primary tissue types in the human body | Epithelial, connective, muscle, and neural |
| Extracellular matrix | Usually just called matrix – It is extracellular material that is synthesized and secreted by the cells of a tissue. It many functions ranging from holding cells together to growth and development to cell death |
| The composition of matrix | It varies from tissue to tissue, but always has two basic components: proteoglycans (glycoproteins) and insoluble protein fibers (e.g. collagen, fibronectin, and laminin – they provide strength and anchor cells to the matrix) |
| The amount of extracellular matrix in a tissue is… | …highly variable. Nerve and muscle cells have very little matrix while connective tissues (cartilage, bone, etc) have extensive matrix that occupies as much volume as their cells |
| Note: cartilage (e.g. in meat) | Connective tissue found in ears, joints, etc. It’s comprised of specialized cells called chondroblasts that produce large amounts of matrix composed of collagen, proteoglycans, and elastin fibers |
| Cell adhesion molecules (CAMs) | Membrane-spanning proteins responsible for both cell junctions and for transient cell adhesions. E.g. they allow white blood cells to escape circulation by clinging to damaged blood vessels. |
| Major CAMs | Cadherins, integrins, immunoglobin superfamily CAMs, and selectins |
| Cadherins | Found in cell-cell junctions such as adherens junctions and desmosomes. They connect with one another across the intercellular space. Calcium-dependent. |
| Integrins | Primarily found in cell-matrix junctions. They are membrane proteins that can also bind to signal molecules in the cell’s environment and transmit info to the cytoplasm thus also functioning in cell signaling |
| Immunoglobulin superfamily CAMs | NCAMs (nerve-cell adhesion molecules). Responsible for nerve cell growth during nervous system development |
| Selectins | Temporary cell-cell adhesions |
| Cell junctions can be categorized into three categories | Gap junctions, tight junctions, and anchoring junctions |
| Gap junctions | The simplest cell-cell junctions. They create cytoplasmic communication bridges (via connexins) between adjoining cells so that the chemical and electrical signals pass rapidly from one cell to the next allowing cell-cell communication |
| Connexins | Cylindrical proteins that interlock (in gap junctions) to create passageways that look like hollow rivets with narrow channels through their centers. |
| Tight junctions | Occluding (“to close up”) junctions designed to restrict the movement of material between the cells they link. Adjacent cells partially fuse together with the help of proteins called claudins and occludins |
| Examples of barriers created by tight junctions | Intestinal tract and kidney: prevent most substances from moving between the external and internal environments. Blood-brain barrier: prevents substances in the blood from reaching the extracellular fluid of the brain |
| Anchoring junctions, e.g. desmosomes | Attach cells to each other (cell-cell) or to the matrix (cell-matrix). Cell-cell anchoring junctions are created by CAMs called cadherins. Cell-matrix junctions use integrins. Due to interlocking cadherins they look like zippers |
| Example of anchoring junction | The strong protein linkage between layers of skin which resist stretching and twisting. Note: If the cadherin proteins sheer, fluid will accumulate in the resulting space and the layers will separate, resulting in a blister |
| Paracellular pathway | Movement of materials between cells is known as the paracellular pathway. Anchoring junctions are like a picket fence and allow for the paracellular pathway; tight junctions are like a brick wall and do not. |
| Cell-cell anchoring junctions take the form of either… | …adherens junctions or desmosomes |
| Adherens junctions | Link actin fibers in adjacent cells together. |
| Desmosomes | Attach to intermediate filaments in the cytoskeleton. They are the strongest cell-cell junctions. |
| How can desmosomes be recognized? | They can be recognized (in electron micrographs) by the dense glycoprotein bodies, or plaques, that lie just inside the cell membranes in the region where the two cells connect |
| Spot desmosomes vs. belt desmosomes | Desmosomes may be small points of contact between two cells (spot desmosomes) or bands that encircle the entire cell (belt desmosomes) |
| Two types of cell-matrix anchoring junctions | Hemidesmosomes and focal adhesions |
| Hemidesmosomes | Strong junctions that anchor intermediate fibers of the cytoskeleton to fibrous matrix proteins such as laminin. |
| Focal adhesions | They tie intracellular actin fibers to different matrix proteins such as fibronectin |
| Pemphigus | A disease in which the body attacks some of its own cell junction proteins. |
| The role of anchoring junctions in cancer | Cancer cells lose their anchoring junctions because they have fewer cadherin molecules. Once they’re released, they secrete proteases which destroy the surrounding matrix and escape the tissues and enter the bloodstream |
| Epithelial tissues (AKA epithelia) | Protect the internal environment of the body and regulate the exchange of materials between the internal and external environments. These tissues cover exposed surfaces, such as the skin, and line internal passageways |
| Any substance that enters or leaves the internal environment of the body must… | …cross an epithelium |
| Epithelia typically consist of… | One or more layers of cells connected to one another, with a thin layer of matrix lying between the epithelial cells and their underlying tissues. This matrix layer is called the basal lamina |
| Basal lamina | AKA the basement membrane is composed of a network of collagen and laminin filaments embedded in proteoglandins. They hold the epithelial cells to the underlying cell layers. |
| The cell junctions in epithelia | They’re variable. They’re classified as either “leaky” or “tight” depending on how easily substances pass from one side to the other. |
| Leaky epithelia | In leaky epithelia, anchoring junctions allow molecules to cross the epithelia by passing through the gap between two adjacent cells. E.g. capillaries where all dissolved materials except large proteins can pass |
| Tight epithelia | Adjacent cells are bound to each other by tight junctions that create a barrier, preventing substances from traveling between adjacent cells. To cross, substances must enter the cells and go through them. E.g. kidney cells |
| Structurally, epithelial tissues can be divided into two general types: | (1) sheets of tissue that lie on the surface of the body or that line the inside of tubes and hollow organs, and (2) secretory epithelia that synthesize and release substances into the extracellular space |
| How do histologists classify sheet epithelia | By the number of cell layers in the tissue and by the shape of the cells in the surface layer. Two types of layering: simple and stratified. Three cell shapes: squamos, cubiodal, and columnar. |
| Simple layering | Characterized by one cell thick |
| Stratified layering | Characterized by multiple cell layers |
| Squamos cell shape | Epithelium that consists of think, flattened cells |
| Cuboidal cell shape | Epithelium shaped like a cube |
| Columnar cell shape | An epithelium shaped like a column; some have cilia |
| Five functional types of epithelia (as opposed to the structural definitions above) | Exchange, transporting, ciliated, protective, and secretory |
| Exchange epithelia | Simple squamos and leaky. Made of thin flattened cells that allow gases (CO2 and O2) to pass across. It lines the blood vessels and lungs, the two major sites of gas exchange. AKA endothelium when in heart/blood vessels |
| Transporting epithelia | Actively and selectively regulate the exchange of nongaseous materials, such as ions and nutrients, between the internal and external environments. Line the digestive system and kidney |
| Absorption vs. secretion in transporting epithelia | Movement from external to internal environments across the epithelium = absorption. The other way around = secretion. |
| Transporting epithelia: cell shape | Much thicker than exchange epithelia. They act as both a barrier and entry point. It’s composed of simple epithelia, but they can be either cuboidal or columnar |
| Transporting epithelia: membrane modifications | Apical membrane: the surface facing the lumen has microvilli that increase the surface area (by at least 20x) available for transport. Basolateral membrane: on side facing extracellular fluid, may also have folds |
| Transporting epithelia: cell junctions | Firmly attached to adjacent cells by moderately tight to very tight junctions. Thus, for material to cross they must move into the cell on one side and move out of the cell on the other |
| Transporting epithelia: cell organelles | Most cells that transport materials have numerous mitochondria to provide energy for transport processes |
| Are the properties of all transporting epithelia constant? | No, they differ depending on where they’re located. E.g., the epithelia in the large intestines have different absorption properties than those in the small intestine. Hormones can also change the epithelia’s behavior |
| Ciliated epithelia | Nontransporting tissues that line the respiratory system and parts of the female reproductive tract. The surface of the tissue facing the lumen is covered with cilia beating in a coordinated fashion, moving fluid/particles |
| Injury to ciliated epithelia | Can stop cilia movement. E.g. Loss of cilia function contributes to a higher incidence of respiratory infection in smokers, when the mucus that traps bacteria can no longer be swept out of the lungs. |
| Shape of ciliated epithelia | Cuboidal to columnar |
| Protective epithelia | Prevents exchange between internal and external environments and protect areas subject to mechanical or chemical stresses. They’re stratified, and flattened on surface layers while polygonal in deeper layers |
| Protective epithelia are strengthened by… | …the secretion of keratin, the same insoluble protein abundant in hair and nails. |
| Examples of where protective epithelia is found in the body | The epidermis, linings of the mouth, pharynx, esophagus, urethra, and vagina are all protective epithelia |
| Life span of the cells in protective epithelia | Because they’re subject to irritating chemicals, bacteria, and other destructive forces, they have a short life span. In deeper layers the cells are produced continuous, displacing older cells at the surface. |
| Secretory epithelia | They’re composed of cells that produce and secrete a substance. They may be scattered among other epithelial cells or group together to form a multicellular gland. Simple to stratified and columnar to polygonal |
| Two types of secretory glands: | Exocrine and endocrine |
| Exocrine glands | Release their secretions into the body’s external environment. E.g. the surface of the skin or intestine. Most excrete their products through open tubes known as ducts. |
| Examples of exocrine glands | Sweat glands, mammary glands, salivary glands, the liver, and pancreas. |
| Exocrine glands produce two types of secretions: | Serous secretions and mucous secretions. |
| Serous secretions | Watery solutions, most of which containing enzymes. Examples: Tears, sweat, and digestive enzyme solutions. |
| Mucous secretions | Sticky solutions containing glycoproteins and proteoglycans |
| Goblet cells | Single exocrine cells that produce mucus. |
| Function of mucus | Acts as a lubricant for food to be swallowed, as a trap for foreign particles and microorganisms inhaled or ingested, and as a protective barrier between the epithelium and the environment |
| Do secretory glands only contain one type of secretory cell? | Not all; some contain both types. Some may produce both serous and mucous secretions, e.g. salivary glands produce mixed secretions |
| Endocrine glands | Ductless glands that release hormones into the body’s extracellular compartment. Hormones enter the blood for distribution to other parts of the body. |
| Some of the best known endocrine glands | Pancreas, thyroid, gonads, and pituitary gland. |
| Are all hormones produced by cells grouped together in endocrine glands? | No, there are also isolated endocrine cells that occur scattered in the epithelial lining of the digestive tract, the tubules of the kidney, and in the walls of the heart |
| Epithelial structure of exocrine vs. endocrine glands | Both types of glands initially grow downward into the supporting tissue. Exocrine glands remain connected via a duct, while the duct disappears for endocrine glands which thus only have connection to the blood stream. |
| Connective tissues | Provide structural support and sometimes a physical barrier that helps defend the body from foreign invaders such as bacteria. They have an extensive matrix containing scattered cells that secrete and modify the matrix |
| Connective tissues include… | …the blood, the support tissues for the skin and internal organs, and cartilage and bone |
| The matrix of connective tissue | It’s a “ground substance” of proteoglycans and water in which insoluble protein fibers are arranged. It’s variable depending on the type of connective tissue, ranging from the watery matrix of blood to bone. |
| Connective tissue cells embedded in the matrix can either be _____ or _____ | Fixed or mobile |
| Fixed connective tissue cells | They remain in one place. They’re responsible for local maintenance, tissue repair, and energy storage |
| Mobile connective tissue cells | They move from place to place. They’re primarily responsible for defense. |
| Is the distinction between mobile and fixed cells absolute? | No, there is at least one cell type that exists as both fixed and mobile forms |
| Although the matrix is nonliving… | …the connective tissue cells are constantly modifying it by adding, deleting, or rearranging molecules. |
| Naming scheme of connective tissue cells. | The suffix –blast signifies that the cell is either growing or actively secreting matrix. The suffix –clast indicates that the cell is actively breaking down the matrix. The suffix –cyte indicates that the cell is doing none of the above. |
| Fibroblast | Connective tissue cells that secrete collagen-rich matrix |
| Three cell types found in bone | Osteoblast, osteocyte, osteoclast |
| Four types of fiber proteins found in the matrix | Collagen, elastin, fibrillin, and fibronectin |
| Collagen | The most abundant protein in the human body (1/3 dry weight) and the most diverse, with 12 different variations. It’s found almost anywhere connective tissue is found, including skin and bones. |
| How strong is collagen | Individual collagen molecules pack together to form collagen fibers flexible but inelastic fibers whose strength per unit weight exceeds that of steel. |
| Elastin | A coiled, wavy protein that returns to its original length after being stretched. This property is known as elastance. |
| Fibrillin | Very thin, straight fibers that combine with elastin to form filaments and sheets of elastic fibers. |
| Elastin and fibrillin are important in | Elastic tissues such as the lungs, blood vessels, and skin |
| Fibronectin | Connects cells to the matrix at focal adhesions. They also play a role in wound healing and in blood-clotting |
| Types of connective tissue (7) | (1) loose connective tissue, (2) dense, irregular connective tissue, (3) dense, regular connective tissue, (4) adipose, (5) blood, (6) cartilage, (7) bone |
| Loose connective tissue | The elastic tissues that underlie skin and provide support for small glands. Cell type: fibroblasts. |
| Dense connective tissues | Provide strength or flexibility. E.g. tendons, ligaments, and the sheaths surrounding muscles and nerves. Collagen fibers are the dominant type. Cell type: fibroblasts. |
| Tendons | Attach skeletal muscles to bones. They cannot stretch |
| Ligaments | Connect one bone to another. They consist of elastic fibers in addition to collagen fibers and as a result can stretch (to a limited degree that is) |
| Adipose tissue | Made up of adipocytes, AKA fat cells. Adipocytes can contain either white fat or brown fat. |
| An adipocyte of white fat | Typically contains a single enormous lipid droplet that occupies most of the volume of the cell. This is the most common form of adipose tissue in adults. |
| An adipocyte of brown fat | Composed of adipose cells that contain multiple lipid droplets rather than a single large droplet. It’s almost entirely absent in adults but plays a role in regulating temperature in infants |
| Blood | Unusual connective tissue that is characterized by its watery matrix, consisting of a dilute solution of ions and dissolved organic molecules. It lacks insoluble protein fibers but contains a large variety of soluble proteins |
| Cartilage | Found in the nose, ears, knees, and windpipe. It’s solid, flexible, and lacks a blood supply (and thus heals slowly because it can only receive its nutrients via diffusion). Cell type: chondroblasts |
| Bone | The matrix of bone is “calcified” because it contains mineral deposits, primarily calcium salts, such as calcium phosphate. They give the bone strength and rigidity. Cell types: osteoblasts and osteoclasts |
| Note: new procedures to replace damaged cartilage | Extract chondrocytes from patient, reproduce them in vitro, and then surgically implant them into the damaged tissue. The chondrocytes will secrete matrix and repair damaged cartilage |
| The third and fourth of the body’s four tissue types—muscle and neural—are collectively called the _____. Why? | The “excitable tissues” because of their ability to generate and propagate electrical signals called action potentials |
| The matrix oc the excitable tissues | Minimal; usually limited to a supportive layer called the external lamina. Some types of muscle and nerve cells are also notable for their gap junctions which play an important role in conducting electrical signals |
| Muscle tissue. What are the three types? | Has the ability to contract and produce force and movement. Three types: cardiac muscle, smooth muscle (which makes up most internal organs), and skeletal muscle (attached to bone and resp. for movement) |
| Neural tissue. Two types | Two types: (1) neurons: carry information in the form of chemical and electrical signals from one part of the body to the other. Concentrated in the brain/spinal cord. (2) Glial cells: AKA neurolgia, are support cells for neurons |
| Cell death occurs in two ways: | Necrosis and apoptosis |
| Necrosis | In necrosis, cells die from physical trauma, toxins, or lack of oxygen when their blood supply is cut off. Necrotic cells swell, their organelles deteriorate, and finally the cells rupture. |
| Apoptosis | Programmed cell death wherein the neighboring cells aren’t disrupted. |
| Describe the process of apoptosis | When the “suicide signal” is initiated, chromatin in the nucleus condenses, the cell pulls away from its neighbors, shrinks, and finally breaks up into tidy membrane-bound “blebs” that are consumed by other cells |
| How does apoptosis play a role during fetal development? | Apoptosis removes unneeded cells, such as half the cells in the developing brain and the web of skin between fingers and toes. |
| Examples of normal occurrences of apoptosis in adults | Cells that are subject to wear and tear from exposure to the outside environment may live only a day or two before undergoing apoptosis. The intestinal epithelium, for example, is replaced every 2-5 days |
| The very earliest cells in the life of a human are said to be… | …totipotent |
| Totipotent | Has the ability to develop into any and all types of specialized cells. Any totipotent cell has the ability to become a functioning organism. |
| After 4 days of development, the totipotent cells of the embryo… | …begin to specialize, or differentiate. As they do so, they narrow their potential fates and become pluripotent. |
| Pluripotent | Pluripotent cells can develop into many different cell types but not all cell types. An isolated pluripotent cell cannot develop into an orgasm. |
| As differentiation continues, pluripotent cells… | …develop into the various tissues of the body. As the cells specialize and mature, many lose the ability to reproduce themselves. Others, called stem cells, retain the ability to divide. |
| Stem cells | Stem cells are cells that are multipotent – that is, they can divide and develop into specialized cells of a particular tissue. E.g. bone marrow stem cells can give rise to blood cells |
| Do nerve and muscle cells have corresponding stem cells? | Yes, but neural and muscle stem cells exist in very small numbers. They cannot replace large masses of dead or dying tissue that result from stroke or heart attacks. |
| One goal of stem cell research | To produce pluripotent or multipotent neural and muscle cells to be implanted to treat degenerative diseases (those in which cells degenerate and die) |
| Researchers hope that adult stem cells will show plasticity, which is… | …the ability to specialize into a cell of a type different from the type for which were destined. |
| Three major challenges of stem cell research | (1) Finding a good source of stem cells, (2) determining the chemical signals that tell stem cells when to differentiate and what type of cell to become, and (3) overcoming cell/tissue rejection |
| Layers of the skin: | Epidermis, dermis, hypodermis |
| Layers of skin: epidermis | The surface is a mat of linked keratin fibers left behind when old epithelial cells die. Beneath that are epidermal cells linked via desmosomes. Beneath that is the basal lamina linked to the epidermal cell by hemidesmosomes |
| Layers of skin: dermis | Loose connective tissue that contains exocrine glands, blood vessels, muscles, and nerve endings |
| Hypodermis | The bottom layer which contains adipose tissue for insulation |
| Hair follicles | Contained in the dermis; they secrete nonliving keratin that constitute hair |
| Sebaceous glands | Exocrine glands in the dermis that secrete a lipid mixture |
| Arrector pili muscles | Muscles in the dermis that pull hair follicles into a vertical position when the muscle contracts, creating “goose bumps” |
| Sweat glands | Secrete a dilute salt fluid to cool the body |
| Apocrine glands | In the hypodermis of the genitalia, anus, axillae (armpit), and eyelids release waxy or viscous milky secretions in response to fear or sexual excitement |
| Phospholipid matrix | The matrix around the keratinocytes on the surface of the epidermis that act as the skin’s main waterproofing agent. |
| Organs | Groups of tissues that carry out related functions. |
| Villi are oriented toward… | …the lumen of the tissue |
| 4 main types of human tissues | Epithelial, connective, muscle, neural |
| Secretion | The process of material, like protein, leaving a cell. (Not the same as excretion) |
| Exocrine secretion | Secretion via ducts |
| Endocrine secretion | Ductless glands |
| 5 types of epithelium | Secretory, exchange, transporting, protective, ciliated |
| Leaky exchange epithelium | Particles move (leak) through pores (e.g. between ECF and blood) |
| What do tight junctions in transport epithelium do? | They force particles to cross THROUGH the cells rather than between them |
| Apical membrane vs. basal lateral sides | Apical = side of the lumen; basal lateral (on the blood side). (“b”asal and “b”lood) |
| Squamos cell carcinoma | Second most common skin cancer |
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