CELL Biology HIS samenvatting
Histology (B_HISTOLOGY)
Vrije Universiteit Amsterdam
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CELL BIOLOGY - HISTOLOGY HEX CODES TITLE / CHAPTERS: #ADDDCE SUB PARAGRAAF: #E6B TERMEN? : #70AE HISTOLOGY HC EPITELIA AND GLAND 4. 1 TO 4. 3
4-1 Identify the four major types of tissues in the body, and describe their roles. 4-2 Discuss the types and functions of epithelial tissue 4-3 Describe the relationship between structure and function for each type of epithelium HC CONNECTIVE TISSUE 4. 4 TO 4. 7 AND 6. 3 TO 6. 6 4-4 List the specific functions of connective tissue, and describe the three main categories of connective tissue 4-5 Compare the structures and functions of the various tpes of connective tissue proper, and the layers of connective tissue called fasciae 4-6 Describe the fluid connective tissue blood and lymph, and explain their relationship with interstitial fluid in maintaining homeostasis. 4-7 Describe how cartilage and bone function as supporting connective tissues 6-3 Identify the cell types in bone, and list their major functions.
6-4 Compare the structures and functions of compact bone and spongy bone. 6-5 Compare the mechanisms of endochondral ossification and intramembranous ossification. 6-6 Describe the remodelling and homeostatic mechanisms of the skeletal system. HC MUSCLE TISSUE 4. 9 AND 10. 1 TO 10. 4 AND 10. 9 AND 10. 10 4-9 Describe the three types of muscle tissues and the special structural features of each type 10-1 Identify the common properties of muscle tissues and the primary functions of skeletal muscle. 10-2 Describe the organization of muscle at the tissue level. 10-3 Describe the characteristics of skeletal muscle fibres, and identify the components of a sarcomere. 10-4 Identify the components of the neuromuscular junction, and summarize the events involved in the neural control of skeletal muscle contraction and relaxation.
10-9 Identify the structural and functional differences between skeletal muscle fibres and cardiac muscle cells. 10-10 Identify the structural and functional differences between skeletal muscle fibres and smooth muscle cells, and discuss the roles of smooth muscle tissue in systems throughout the body. HC NEURAL TISSUE AND 4. 10 and 12. 1 to 12. 3 4-10 Discuss the basic structure and role of nervous tissue. 12-1 Describe the anatomical and functional divisions of the nervous system 12-2 Sketch and label the structure of a typical neuron, describe the functions of each component, and classify neurons on the basis of their structure and function 12-3 Describe the locations and functions of the various types of neuroglia DIGESTIVE SYSTEM 4. 8 and 24. 1 , 24. 3 and figure 24 - 21 4- 8 Explain how epithelial and connective tissues combine to form 4 types of tissue membranes, and specify the functions of each.
24- 1 Identify the organs of the digestive system, list their major functions, describe the histology of the digestive tract, and outline the mechanisms that regulate digestion. 24- 3 Describe the structure and functions of the pharynx and the esophagus.
HC EPITHEILA 4. 1 TO 4. 3
4. 1 THE FOUR TISSUE TYPES ARE EPITHELIAL,
CONNECTIVE, MUSCLE, AND NERVOUS
Cells that work together form tissues;
A collection of specialized cells and cell products that carry out a limited number of functions. Basic tissue types are functionally organized in organs.
The study of tissues = histology. Histologists recognize four basic types of tissue:
- Epithelial tissue o Covers exposed surfaces. o Lines internal passageways and chambers, and forms glands.
- Connective tissue: o Fills internal spaces, o Provides structural support for other tissues, transports material within the body, and stores energy.
- Muscle tissue: o Is specialized for contraction o Include the skeletal muscles of the body, muscle of the heart, and the muscular walls of hollow organs.
- Nervous tissue: o Carries information from one part of the body to another in the form of electrical impulses.
Embryonic origin
Cell types that are part of the same basic tissue type can look very different. They still share the same embryonic origin.
Embryology & germ layers
- Ectoderm: nervous tissue, skin
- Endoderm: digestive tissue, lung
- Mesoderm: muscle, connective tissue (from mesenchyme)
- 2 EPITHELIAL TISSUE COVERS BODY SURFACES, LINES INTERNAL SURFACES, AND SERVES OTHER ESSENTIAL FUNCTIONS.
Epithelial tissues: tissue existing of cells that are tightly connected to each other. It’s derived from one of the 3 primary germ layers. There are 2 types of epithelial tissue:
- Covering epithelia (skin)
Several successive layers (basal lamina and reticular lamina) A collagen matrix Proteoglycans (intracellular cement) o The BM adheres to the basal surface and to the underlying tissues to establish the cell’s border and resist stretching.
- Cellularity o Epithelia are made almost entirely of cells bound closely together by interconnections known as cell junctions. In other tissue types the cells are often widely separated by extracellular materials.
- Regeneration o Epithelial cells that are damaged or lost at exposed surface are continuously replaced through stem cell divisions in the epithelium.
Apical domain:
- Often has microvilli; to increase surface area
- Sometimes cilia; movement of liquid, sensory function.
Specializations of epithelial cells
Individual epithelial cells may be specialized for
- The movement of fluids of the epithelial surface, providing protection and lubrication
- The movement of fluids through the epithelium, to control permeability
- The production of secretions that provide physical protection or act as chemical messengers
The specialized epithelial cell is often divided into 2 functional regions which means the cell has a strong polarity.
- The apical surface; where the cell is exposed to an internal or external environment
- Basolateral surfaces, which include both the base (basal surface), where the cell attaches to underlying epithelial cells or deeper tissues, and the sides (lateral surfaces), where the cell contacts its neighbours.
Microvilli are especially abundant on epithelial surfaces where absorption and secretion take place, such as along portions of the digestive system and kidneys.
Motile cilia are characteristics of surfaces covered by a ciliated epithelium. The synchronized beating of the cilia moves substances of the epithelial surface.
Maintaining the integrity of epithelia
To be effective as a barrier, epithelium must form complete cover or lining. 3 factors help maintain the physical integrity of an epithelium:
- Intercellular connections
- Attachment to basement membrane
- Epithelial maintenance and repair
1 ; Intercellular connections
Cells in epithelium are firmly attached to one another, and epithelium as unit is attached to extracellular fibres of the superficial basal lamina of the basement membrane.
Intercellular connections involve either extensive areas of opposing plasma membranes or specialized attachment sites called cell junctions.
- Large areas of opposing plasma membranes are interconnected by transmembrane proteins called cell adhesion molecules (CAMs), which bind to each other and to extracellular materials. o CAMs on basolateral surface of epithelium help bind the cell to the underlying basement membrane.
- Membranes of adjacent (aangrensende) cells may also be bonded by thin layer of proteoglycans that contain polysaccharide derivatives known as glycosaminoglycans (GAGs) – help promote cell adhesion.
Cell junctions are specialized areas of plasma membrane that attach cell to another cell or to extracellular materials.
Three most common types of cell junctions are:
- Gap junctions
- Tight junctions
- Desmosomes
Gap junctions:
Have two cells are held together by two embedded interlocking transmembrane proteins called connexons.
- 2 aligned connexons form a narrow passageway that lets small molecules and ions pass from cell to cell. o Gap junctions are common among epithelial cells; where movement of ions helps coordinate functions such as the beating of cilia. They are also common in other tissue
Tight junctions:
- They encircle the apical regions of epithelial cells and round whole cell.
The basal labyrinth is a huge membrane convolute at the basal cell domain, consisting of infoldings of the basal plasma membrane and interdigitating basal ridges of neighbouring cells.
- Both lead to a tremendous increase of the basolateral surfaces of the epithelial cells.
2 ; Attachment to the basement membrane
Not only do epithelial cells hold onto one another, they also remain firmly connected to the rest of the body. They HAVE to be attached to other cells, or else they will die. The inner surface of each epithelium is attached to a two-part basement membrane composed of a basal lamina and a reticular lamina.
The layer closer to epithelium, the basal lamina,
- is an amorphous (vormloos),
- is synthesized by epithelium, ill-organized layers thought to function as a selective filter.
- Part of the basal membrane;
Lamina reticularis; synthesized by connective tissue
- It is secreted by the adjacent layer of epithelia cells.
- The basal lamina restricts the movement of proteins and other large molecules from the underlying connective tissue into the epithelium.
The deeper portion of the basement membrane, the reticular lamina, consists mostly of the reticular fibres and ground substance. This layer gives the basement membrane its strength.
- Also acts as a filter that determines what substances can diffuse between the adjacent tissues and the epithelium.
Attachments between the fibres of the basal lamina and those of the reticular lamina hold the 2 layers together, and hemi attach the epithelial cells to the composite basement membrane.
3 ; Epithelial maintenance and repair
Epithelial cells lead hard lives lol. Exposed to disruptive enzymes, toxic chemicals, pathogenic bacteria, physical distorition, and mechianical abrasion.
The only way the epithelium can maintain its structure over time is by the continual division of stem cells. Most epithelial stem cells are located near the basement membrane, in a relatively protected location.
4. 3 CELL SHAPE AND NUMBER OF LAYERS DETERMINE THE
CLASSIFICATION OF EPITHELIA
An epithelium is classified based on
- Ecto, endo, mesodermal
- The shape of the cells
- Number of cell layers (called strata)
Epithelial cells have 3 basic shapes:
- Squamous
- Cuboidal
- Columnar
To classify by shape, we look at both the apical surface and the basement membrane. Once determined one of these three; then look at number of cell layers; there are two options
Simple
When one layer of cells cover the basement membrane making layer a simple epithelium and they are necessarily thin;
- Cells have same polarity; distance nucleus to BM doesn’t change from one cell to another. o Because of this; fragile and not able to provide mechanical protection. o Therefore only located in protected areas inside the body like compartments and passageways. o Also in regions in which secretion or absorption occurs because the thinness is an advantage; reduces time required for material to cross epithelial barrier.
Stratified
Several layers of cells cover basement membrane.
- Are generally located in areas that are exposed to mechanical or chemical stresses
Squamous epithelia:
- Cell in squamous epithelium are thin, flat and irregular in shape
A simple squamous epithelium is body’s most delicate type of epithelium;
- Located in protected regions where absorption or diffusion takes place
- Where a slick, slippery surface reduces friction.
Simple SE that lines body cavities enclosing the lungs, heart and abdominal organs is called a mesothelium. The SSE that lines the inner surface of the heart and all blood vessels is called an endothelium.
Epithelia: gland tissue
- Often invagination of epithelial tissue
- Parenchyma (gland cells) and stroma (connective tissue)
- Often presence of secretion vesicles.
Many epithelia contain gland cells that are specialized for secretion; these are known as glandular epithelium. Collection of epithelial cells that produce secretions are called glands.
There are 2 main types of glands, classified by where they deliver their secretions.
- Endocrine glands; release their secretions into the blood,
- Exocrine glands release their secretions directly onto an epithelial surface or into passageways called ducts that open onto an epithelial surface.
Most do either one, but few complex organs; including digestive tract and pancreas produce both kinds of secretions.
Endocrine glands / ductless glands.
- Produces hormones; they enter bloodstream for distribution throughout body. o Hormones regulate or coordinate activities of various tissues, organs and organ systems.
- Think of; thyroid gland, thymus and pituitary gland.
- They may also be present outside in lining of digestive tract.
Exocrine glands
- Secretions; which are discharged onto an epithelial surface.
- Most ExS reach surface through tubular ducts, which empty onto skin surface or onto epithelium lining an internal passageways that communicates with the exterior.
- Think of enzymes entering digestive tract, perspiration on skin, tears in eyes and mil produced by mammary glands.
We classify ExG from 3 perspectives;
- Structure of glands
- How glands secrete products
- What those products are.
Gland structure:
In epithelia that have independent, scattered gland cells, the individual secretory cells are called unicellular glands.
Multicellular glands include glandular epithelia and aggregation of gland cells that produce exocrine or endocrine secretions.
Unicellular exocrine glands
- Consist of single cells called goblet cells that are specialized for secretion. Like mucous cells; they secrete mucin; mixes with water to form mucus. Location determines if goblet or mucous cells.
- Goblet cells are scattered among absorptive cells in the columnar epithelium of the small and large intestines. Mucous cells are scattered among other epithelial tissues.
The simplest multicellular exocrine gland
- is a secretory sheet, in which gland cells form an epithelium that releases secretions into an inner compartment. o Think of mucin-secreting cells that line the stomach protect that organ from its own acids and enzymes by continuously secreting mucin.
- Most other multicellular EG are in pockets set back form epithelial surface. Their secretions travels through one or more ducts to the surface. o Think of salivary glands; they produce mucins and digestive enzymes
Three characteristics are useful in describing the structure of multicellular exocrine glands.
- Structure of duct
- Gland is simple if it has single duct that does not divide on its way to gland cells.
- Gland is compound if duct divided one or more times on its way to the gland cells.
- Shape of the secretory portion of the gland
- Glands whose glandular cells form tubes are tubular; tubes may be straight or coiled.
- Those that form blind pockets are alveolar or acinar.
- Glands whose secretory cells form both tubes and pockets are called tubule-alveolar and tubule-acinar.
- Relationship between ducts and glandular areas
- Gland is branched if several secretory areas (tubular or acinar) share a duct.
Methods of secretion
Exocrine glands are made up of exocrine cells; which use one of three different methods to secrete their products
- Merocrine secretion
- The product is released from an exocrine cell by secretory vesicles through exocytosis. o Most common methods of exocrine secretion; think of mucin that is also a mercrine secretion.
Exocytosis: release of product on the cellular surface.
Steroids-producing gland
- Extensive smooth endoplasmic reticulum
- Specialized mitochondria o Specific steps in cholesterol synthesis
- No storage of steroids in the cells.
HC CONNECTIVE TISSUE 4. 4 TO 4. 7 AND 6. 3 TO 6. 6
4. 4 – CONNECTIVE TISSUE HAS VARIED ROLES IN THE BODY THAT REFELCT THE
PHYSICAL PROPERTIES OF ITS THREE MAIN TYPES
Connective tissue; a diverse group of supporting tissues. In essence, connective tissue connect the epithelium to the rest of the body. Other types of connective tissue include bone, fat and blood.
- Cells are separated by extracellular matrix
- (Embryonal) precursor tissue: mesenchyme
Connective tissue vary widely in appearance and function, but they all share three basic components:
- Specialized cells
- Extracellular protein fibres
- A fluid known as ground substance
Together, extracellular fibres and ground substance make up the matrix which surrounds the cells. While cells make up bulk of epithelial tissue, the matrix accounts for most of volume of connective tissues.
Connective tissue occurs throughout body but never exposed to outside environment.
- Many are highly vascular and contain sensory receptors that detect pain, pressure, temperature, and other stimuli.
Other functions of CT:
- Supportive connective tissue o Framework for body o Protecting organs o Supporting, surrounding, and interconnecting other types of tissue.
- Metabolic connective tissue o Storing energy o Defending body from invading microorganisms. o Supply of oxygen, nutrients o Transporting fluids and dissolved materials
We classify connective tissue by physical properties; three general categories of CT are
- Connective tissue proper
- Fluid connective tissue
- Supporting connective tissue
Connective tissue proper
- Includes those CT with many types of cells and extracellular fibres in a viscous (syrupy) ground substance.
- This broad category contains a variety of CT that are grouped into loose CT and dense CT. o These grouping are based on number of cell types present, and on relative properties and proportions of fibres and ground substance. o Both adipose tissue, or fat (loose) and tendons (dense) are CT proper, but have very different structural and functional characteristics.
Fluid connective tissues
- Have distinctive populations of cells suspended in a watery matrix that contains dissolved proteins.
- Only two types are blood and lymph.
Supporting connective tissues
- Differ from CT proper in having less diverse cell population and matrix containing much more densely packed fibres.
- Protect soft tissues and support weight of part of all of the body.
- Have 2 types o Cartilage: matrix of cartilage is a gel with characteristics that vary with predominant type of fibre. o Bone : matrix of bone contains mineral depostits, primarily calcium salts that provide rigidity (stijfheid)
Other cells defend and repair damaged tissues; these are more modible and include and are not permanent residents but migrate through healthy CT and collect at sites of tissue injury.
- Macrophages
- Mast cells
- Lymphocytes
- Plasma cells
- Microphages
RESIDENT CELLS:
- Chondroblasts
- Chondrocytes
- Adipocyte
- Fibroblast
- Mesothelial cell
- Endothelial cell
- Osteoblast
- Osteocyte
Fixed and migratory cells of CT proper include following:
--
Fibroblasts
- Are only cells that are always present in CTP and are most abundant fixed residents of CTP
- Secrete hyaluronan (help epithelial cells lock together) In CTP, extracellular fluid, hyaluronan and proteins interact to form proteoglycans that make ground substance viscous. (stroperig)
- Secretes protein subunits that assemble to form large extracellular fibres and just proteins.
Fibrocytes
- are spindle-shaped cells that maintain CT fibres of CTP.
Adipocytes
known as fat cells
(typically), contains a single enormous lipid droplet o Nucleus and other organelles and cytoplasm are squeezed to one side; making sectional view of cell resemble a class ring.
Number of adipocytes varies from one type of CT to another; from one region of body to other and among individuals
Mesenchymmal cells
- Are stem cells that are present in many CT.
- Respond to local injury or infection by dividing to produce daughter cells that differentiate into fibroblasts, macrophages or other CT
Melanocytes
- Synthesize and store melanin
- Play role in determining skin colour
- Are abundant in CT of eye and dermis of skin but the number differs by body region and among individuals
Macrophages
- Large phagocytic cells scattered throughout matrix
- They engulf damaged cells or pathogens that enter tissues
- Important in mobilizing body’s defences.
- When stimulated, they release chemicals that activate the immune system and attract large numbers of additional macrophages and other cells involved in tissue defence.
- Are either fixed macrophages which spend long periods in a tissue or free macrophages which migrate rapidly through tissues. o In effect; fixed macrophages provide defence that can be reinforced by arrival of free macrophages and other specialized cells.
Mast cell
- Circulate in blood in immature form before they migrate to other vascularized tissues and undergo final maturation.
- Cytoplasm of this cell is filled with granules containing histamine and heparin. o Histamine; released after injury or effection stimulates local inflammation. o Basophilis, bloodcells that enter damaged tissues and enhance inflation process also contain granules of histamine and heparin o Level of heparin in blood is normally low; it is anticoagulant that enhances local blood flow during inflammation and reduces the development of blood clots in areas of slow moving blood.
Lymphocytes
- Type 4 : basal lamina
Synthesis collagen:
- In RER and Golgi
- Secreted via a constitutive route
- Self-assembly of tropocollagen into collagen fibres in the extracellular matrix
Reticular fibres
- arranged differently than collagen fibres and are thinner.
- form branching, interwoven framework; though yet flexible.
- Resist forces applied from many directions because form network rather than share common alignment. o This interwoven network; called stroma, stabilizes the relative positions of functional cells, parenchyma, of organs such as the liver.
- Predominantly in basal membranes and around organs.
Basal membrane
- Basal lamina: synthesized by epithelium o Basal lamina; lamina lucida en densa
- Lamina reticularis: synthesized by fibroblasts.
For adhesion of epithelium to connective tissue
Elastic fibres
- Contain protein elastin and microfibrils
- Synthesized by fibroblasts, chondrocytes and smooth muscle cells.
- After stretching they return to original length.
- Present in elastic dense CT, elastic cartilage and blood vessel walls.
Loose connective tissue
- Are packing materials of body; they fill spaces between organs cushion and stabilize specialized cells in many organs and support epithelia.
- These tissues surround and support blood vessels and nerves, store lipids, and provide a route for diffusion of materials.
- Includes mucous CT in embryos and areolar tissue, adipose tissue and reticular tissue in adults.
Reticular tissue
Organs contain reticular tissues in which reticular fibres form a complex 3d stroma. o Stroma supports functional cells of these organs.
Fibrous framework also found in lymph nodes and bone marrow.
Fixed macrophages, fibroblasts, and fibrocytes are associated with the reticular fibres, but these cells are seldom visible in microscopic sections, because specialized cells with other functions dominate organs.
Dense CT
Fibre create most of volume of dense CT; these tissues are often called collagenous tissues, because fibres are the dominant type of fibre in them. The body has 2 types of dense connective tissues.
- Dense regular CT o Elastic tissue; specialized type
- Dense irregular CT
Dense regular CT
- Collagen fibres are parallel to each other, packed tightly and aligned with forces applied to the tissue.
- Tendons are cords of dense RCT that attach skeletal muscles to bones.
- The collagen fibres run longitudinally along the tendon and transfer the pull of the contracting muscle to the bone. o Ligaments resemble tendons but connect one bone to another or stabilize position fo internal organs
- An aponeurosis is tendinous sheet that attaches a broad, flat muscle to another muscle or to several bones of the skeleton. o It can also stabilize positions of tendons and ligaments. o They are associated with large muscle of skill, lower back and abdomen and with tendons and ligaments of palms of the hands and the soles of the feet o Large numbers of fibroblasts are scattered among the collagen fibres of tendons, ligaments, and aponeuroses
Dense irregular CT
- Form interwoven meshwork in no consistent pattern
- These tissues strengthen and support area subjected to stresses from many directions.
- Layer of DICT gives the deep later of skin; dermis, its strength. Think of cured leather (animal skin)
- It forms a thick fibrous layer called a capsule, which surrounds internal organs such as liver, kidneys, and spleen and encloses the cavities of joints. But there; dense ICT also forms sheath around cartilages (perichondrium) and bones (periosteum).
Elastic tissue
CELL Biology HIS samenvatting
Vak: Histology (B_HISTOLOGY)
Universiteit: Vrije Universiteit Amsterdam
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