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Integrative Physiology Ch. 3 - Compartmentation: Cells and Tissues

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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