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Describe the location of Epithelial Tissue
It covers or lines all body surfaces, Forms the parenchyma (secretory portion) of glands and their ducts
List the six main characteristics of Epithelial Tissue
Avascular, Renewable, Metaplasia, Close cell proximity, Polarity, Basal surface rests on Basement membrane
Explain the concept of Polarity in terms of Epithelial Cells
Polarity describes the structural and function asymmetry of a cell. Cells also exhibit intracellular polarity in terms of the arrangement of organelles. Outwardly, each cell has an apical domain, Lateral domain, and Basal domain.
What are the five main functions of Epithelial Tissue?
Transport, Receptor, Absorbance, Protection, Secretion
Describe the Apical Domain of an Epithelial Cell
Top portion that often contains specific enzymes, ion channels, or carrier proteins. Many exhibit special structural modifications such as microvilli, stereocilia, cilia, and flagella.
Describe the Lateral Domain of an Epithelial Cell
The side portion of the cell which is characterized by the presence of cell adhesion molecules responsible for joining the cells together through three different types of junctions: Occluding, Anchoring, and Communicating.
Describe the three types of Cell Junctions
Zonula Occludens form a barrier between two cells due to a localized sealing of the plasma membrane. Anchoring junctions include Zonula adherens and Macula adherens. Zonula adherens involve the E-cadherin-catenin complex that connects the two cells. Macula adherens rely on desmogleins and desmocollins. Communicating Junctions allow for cell-to-cell communication. Ions, signal molecules, and metabolites may pass through pores to adjacent cells. These junctions are formed by connexin proteins and the pores open and close in response to calcium ions
Describe the Basal Domain of an Epithelial Cell
This region is primarily concerned with attachment to the extracellular matrix and has three main specializations: Cell-to-ECM junctions, NaKATPase, and the presence of basal Lamina. Cell-to-ECM junctions use focal adhesion (zonula adherens - actin) and Hemidesmosomes (macula adherens - intermediate filaments) to attach the cell to the basal lamina. NaKATPase is found on this layer due to its close proximity to blood vessels. The basal lamina is the layer above the connective tissue matrix and is composed of collagen, laminins, and proteoglycans
What are the five main functions of the Basal Lamina?
structural attachment, compartmentalization, filtration, tissue scaffolding, regulation and signaling
Identify and Describe the two major types of Glands
Exocrine glands secrete their products onto a surface directly or through epithelial ducts. Endocrine glands lack a duct system and secrete products into the connective tissue
What are the main three classifications (and their sub classifications of exocrine glands?
Main: structure, product, mode of secretion
----- Number of cells (single vs. multicellular)
----- Duct system (simple/unbranched vs. compound (branched)
----- Secretory portion (tubular, acinar/alveolar, mixed)
------ Merocrine - no loss of cytoplasm
------ Apocrine - some loss of cytoplasm
------ Holocrine - apoptosis of cell
What are the nine main types of Connective Tissue?
Loose and dense collagenous, Reticular, Elastic, Mucous, Adipose, Bone, Cartilage, Blood
Describe the characteristics of the CT fiber, collagen
Collagen is the most abundant structural component and is found in every type of connective tissue. It has tremendous tensile strength. In terms of structure, every third AA is glycine and it has a high number of proline and lysine residues-- all three AAs are usually hydroxylated leading to sugar attachment. Collagen is a triple helical molecule made up of three alpha chains.
Describe the characteristics and give the locations of the four main types of collagen.
Type I collagen is the most abundant and widespread. It is able to form thick fibers and bundles. It occurs in tendons and ligaments as well as in the bones, dermis, and capsules of organs
Type II collagen is found in the cartilage matrix in adults
Type III collagen is structurally similar to Type I, but is more heavily glycosylated. It forms thinner fibrils and it supports smooth muscle cells, nerve cells, and adipocytes. It is the major fiber component of hemopoietic tissues
Typ IV collagen is found in the basal lamina and it doesn't form fibers or fibrils
Describe the synthesis process of collagen
Pro-alpha chains are synthesized in the rER then discharged to the cisternae where posttranslation modifications occur. These modifications include hydroxylation of proline and lysine and subsequent glycosylation causing a globular structure to form. Disulfide bonds and chaperone protein hsp47 stabilize and help the triple helix to form. The resulting Procollagen molecule is then passed to the Golgi where it starts to aggregate. Aggregates are transported via vesicles to the cell surface and excreted. Procollagen peptidase cleaves the secreted molecule to produce a mature collagen molecule. The mature collagen molecules can align to form collagen fibrils.
Describe the degradation of collagen
The degradation of collagen occurs through two main methods: Proteolytic Degradation and Phagocytic Degradation. Proteolytic Degradation occurs outside the cells and uses degradative enzymes called MMPs. Phagocytic Degradation occurs inside the cell and uses macrophages and fibroblasts
Describe the characteristics of reticular fibers
Reticular fibers are composed of type III collagen and are very highly glycosylated. They are found supporting smooth muscle, nerve cells, and adipocytes. They are also present in hemopoietic tissue. Structurally, they are thin fibers that allow for scaffolding for immune cells which helps in filtration
Describe the characteristics of elastic fibers
Elastic fibers are able to return to their original shape after being stretched. This is important for structures such as vocal cords and arteries. They are composed of the protein elastin which contains hydrophobic AA residues along with special AAs - desmosine and isodesmosine which help with crosslinking.
Describe the characteristics of Ground Substance
Ground substance is composed of proteoglycans and glycoproteins. Proteoglycans have glycosaminoglycans covalently bound to them. Two main types of glycoproteins are Fibronectin (mediates attachment of cells to the ECM) and Laminin (mediates attachment of epithelial cells to the basal tissue)
What are the five major classes of GAGs?
Identify the cells of Connective Tissue
Connective Tissue is made up of Fixed (native) and Wandering cells. Fixed cells include fibroblasts, reticular cells, and adipose cells. Wandering Cells include Macrophages, Mast cells, and plasma cells
Describe Fibroblast cells
Fibroblasts synthesize collagen/fibers and maintain the major components of the ECM. It also regulates glycosylation.
Describe Reticular cells
Reticular cells are found exclusively in the hemopoetic and lymphoid tissue. They make reticular fibers and phagocytose antigenic material and cellular debris. They serve as APCs to the immune system
Describe Adipose cells
Adipose cells are specialized to store neutral fat and produce a variety of hormones
Macrophages are phagocytic cells derived from monocytes in the bloodstream. They are part of the nonspecific immune response. Specialized macrophages include Kupffer cells (liver), Microglial cells (nervous tissue), and Dust cells (lungs)
Describe the Characteristics and Location of Loose (areolar) Connective Tissue
Areolar tissue contains loosely arranged fibers and abundant cell types. It appears very disorganized. It has a moderately viscous ground substance. In terms of location, this tissue surrounds and suspends vessels and nerves and is primarily located beneath the epithelia. It is very well vascularized so it is able to convey nutrients to the epithelial tissue.
Describe the Characteristics and Location of Dense Connective Tissue
Dense Connective tissue is further divided into regular and irregular forms.
The irregular form is abundant in fibers, and has a few cells (mostly fibroblasts). It is vascular and appears disorganized. It is made up of type I collagen and can transmit force in any direction. In terms of location, it covers organs and tissues
The regular form is ordered and densely packed. It is avascular. The pattern and directionality is obvious in the orientation of its fibroblasts. It is composed of type I collagen and can transmit force in one direction. It is found in the tendons, ligaments, periostium, pericardium.
Describe the Characteristics and Location of Reticular Connective Tissue
This tissue is made up of Reticular fibers / Type III collagen fibers. Reticular fibers serve as scaffolding for lymphocyte cells. It performs a filtration function within the lymph node or spleen
Describe the Characteristics and Location of Elastic Connective Tissue
This tissue is made up of elastic fibers and is located in large arteries
Describe the Characteristics and Location of Mucous Connective tissue
This tissue is chiefly composed of Hyaluronic Acid. It yields fairly readily to pressure, but is able to resume its original shape. It is located in the umbilical cord and the center of intervertebral discs
Describe the two main hormones that effect of Connective Tissue
Cortisol is made by the adrenal glands and inhibits connective tissue fiber synthesis and responses by connective tissue cells
Thyroxin is made by the thyroid glands and corresponds to GAG levels. Low levels of thyroxin cause GAGs to accumulate which attract sodium which attract water which causes swelling (Myxedema)
What is a nutritional effect of Connective Tissue?
Vitamin C is a cofactor for Proline hydroxylase which is needed for collagen synthesis. Without Vitamin C, collagen cannot be synthesized and connective tissue throughout the body is weakened (Scurvy)
Describe the General features of Adipose tissue
Adipose tissue functions as storage for lipids. It is important for metabolism and serves as an important endocrine "organ" because it produces leptin which regulates appetite. Adipose tissue is composed of clusters of adipocytes and has little ground substance. It is further divided into White Adipose tissue and Brown Adipose tissue
Compare and Contrast White and Brown Adipose Tissue
White has adipocytes with a single fat droplet whereas Brown has smaller, multiple fat droplets. Both are highly vascularized. White is distributed throughout the subcutaneous layer whereas Brown is much less common. Both are metabolically active tissue, but brown is much more so and is capable of thermoregulation. White functions through lipogenic influences (dietary abundance, insulin prompts glucose uptake) and lipolytic influences (cortisol raises blood-glucose levels, adrenocortical tropic hormone stimulates release of stored fatty acids, norapenephrin triggers lipases to break down stored fatty acids)
Describe the General Features of Cartilage
Cartilage is firm, solid, and resilient. It is composed of cells (chondrocytes), fibers (type II collagen), and a firm, gel-like ground substance. Cartilage has very few blood vessels and nerves within, but the covering perichondrium supplies vascular needs and contains stem-like cells that will differentiate into new cartilage cells. Depending on the composition of the ground substance, nutrients and oxygen can percolate into the tissue
Describe Hyaline Cartilage
Hyaline Cartilage is composed of type II collagen fibers and its Ground substance contains GAGs (chondroitin sulfate and hyaluronic acid), proteoglycans, proteoglycans aggregates, glycoproteins (fibronectin and chondronectin), and tissue fluid
Hyaline cartilage involves extensive cross-linking among all of the components. Chondrocytes are embedded in spaces of the cartilage matrix known as lacunae.
Hyaline cartilage is able to grow fairly rapidly while retaining a level of rigidity, making it idea fetal skeletal tissue. It also makes up articular cartilage that is present at the ends of large bones and forms the components of the epiphyseal plate. It is the most abundant type of cartilage in the body.
It is located between ribs and sternum, laryngeal cartilage, and trachea
Describe Elastic Cartilage
Elastic cartilage is composed to type II collagen and is identical to Hyaline cartilage with the exception of the presence of Elastic fibers. It is located in the walls of the external auditory canal, the external part of the ear, auditory tubes, and the epiglottis
Fibrocartilage is composed of type I collagen and resembles dense connective tissue (thought to develop from it as well). It contains equal amounts of dermatin sulfate and chondroitin sulfate. It's chondrocytes are arranged in a columnar fashion.
It is located in places where strong mechanical stress occrs such as bone-ligament junctions.
Describe the General Features of Bone Tissue
Bone tissue is composed of cells, fibers, and ground substance. It's main fibrous component is type I collagen. It functions to support and protect. It contains hematopoietic tissue and forms a system of levers and pulleys to facilitate movement with muscles.
There are two types of bone. Spongy bone is inside and has characteristic spaces which assist in scaffolding and storage of red bone marrow. The spaces also decrease the weight of the bone. Compact bone makes up the outer surface and is much stronger
Identify the four main Cells in Bone Tissue
osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts.
Describe Osteoprogenitor cells
Osteoprogenitor cells are associated with the periosteum (outer cover) and the endosteum (inner covering). There are two different types which become osteoblasts and osteoclasts respectively.
Osteoblasts are involved in developing and making bone. They secrete all components of bone matrix. Mature form differentiates into Osteocytes
Osteocytes make up the cellular component of the bone. It is derived from osteoblasts and occupies a lacuna
Osteoclasts are multi-nucleated cells with a ruffled border and are responsible for the resorption of bone. They also occupy lacuna.
Osteoclasts are also very responsive to hormones such as parathyroid hormones that stimulate resorption to regulate blood-calcium levels
What is the purpose of breaking down bones?
Breaking down bones is primarily to release calcium, but also plays a role in repair and reshaping. Bone deposition and resorption is a constant "turnover" process
Identify and Describe the Organic and Inorganic components of Bone Matrix
Bone matrix contains organic and inorganic components.
The organic components include Type I collagen which makes up 95% of the bone and an acidic ground substance composed of proteins, carbs, and some lipids. Specifically, it contains glycoproteins and gamma-carboxyglutamic acid along with chondroitan sulfates and keratin sulfates
The inorganic component is the hydroxyapaptite crystals (calcium salts) that make up 75% of the weight of bones and gives them their hardness
Explain the Calcium Reserve system of Bones
Bones store calcium which is important for muscle contraction, nerve signals, blood clotting, and cell adhesion. Calcium is mobilized through two main mechanisms. The first involves a rapid physical transfer of calcium ions between hydroxyapatite crystals and interstitial fluid along the concentration gradient. (ions leak out). The second involves the parathyroid hormone which stimulates resorption by osteoclasts, inhibits bone deposition by osteoblasts, and reduces calcium excretion by the kidneys.
Deposition of bone is prompted by the hormone Calcitonin counteracts the parathyroid hormone and enhaces osteoblast activity
Describe the nutritional factors of Bone
Deficiencies in protein, calcium, vitamin c, vitamin a, and vitamin D slows bone growth and development. Excess vitamin a increases ossification
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