Human Physiology Questions about tissue/skin and skeletal system! Please fill ou
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Human Physiology Questions about tissue/skin and skeletal system! Please fill out fully for a thumbs up rating!
Human Physiology Question about tissue/skin and skeletal system! Please fill out fully for thumbs up rating! Tissue and Skin (4) Tissue vs. Organ Cell junctions (tight,gap,desmosomes,hemidesmosomes etc) Apical vs. basilar membranes Basic characteristics of epithelium Skeletal (2) Bone structure (diaphyics, epiphysis, medullary space) Osteon structure (osteocytes, collagen, hydroxyapatite, etc) Parathyroid hormoneExplanation / Answer
Cell junctions: They are intercellular bridges that connect cells of a tissue, of multicellular organisms. Cell junctions are generally found between cells of higher organisms. These junctions consist multiprotien complexes and cells communicate through them. Cell junctions are abundantly seen in epithelial cells.
There are different types of cell junctions:
Tight junctions: They are found between epithelial cells of vertebrates only. They regulate movement of water and solutes. Most of the tight junctions are selective for cations, and each type of tight junction in different epithelia is selective for solutes, the selectivity is based on the size, charge, and dipole of the solute.
Tight junctions are composed of proteins. These proteins are classified into four categories:
Regulation proteins: Regulate flow of ions or molecules between cells
Scaffolding proteins: They play important role in signaling by binding to other protein scaffolds associated with signaling
Signaling proteins: They play important role in signal transduction, and thus regulate gene transcription, barrier regulation, and are also involved in assembly of junctions
Regulation proteins: They regulate gene expression, transport and targeting of membrane vesicles
Transmembrane proteins: They are permanently attached to membrane and span or cross the membrane several times. They play the function of ‘loading docks’ for transport of substances across the membranes. They are made of proteins called junctional adhesion molecule, occluding, and claudin.
Anchoring junctions: These junctions help cells to attach to one another and to the extracellular matrix. They are classified into Desmosomes, Hemidesmosomes, and Adherens junctions.
Desomsomes: They rivet cell membrane of one cell to membrane of another cell. They prevent separation of cells. They form a region called plaque on membranes. Adjacent cells are held by the linker protein filaments that extend from plaques and form a zipper like linkage. Keratin filaments are mainly found in the linkage, cadherins act as anchors of the cells to plaque.. Desmosomes are in high number in cells that are prone to mechanical stress.
Hemidesmosomes: They form riveting linkage between cytoskeleton and extracellular matrix components. They tie to intermediate filaments in the cytoplasm, but their transmembrane anchors are integrins.
Gap junctions: they are also called communicating junctions. They allow for direct chemical communication between adjacent cells. They contain a center pore called connnexon. The connexon is made of six connexin proteins, which interact to form a cylinder with a pore in the center. Connexons stretch across the membranes, and when two connexons interact, they form a complete gap junction channel. Gap junctions are mainly concerned with contraction of heart muscle, signal transfer in brain, and skin cells.
Apical and basal membranes refer to cell polarity. It refers to the spatial differences in shape, structure, and functions of cells. Cells exhibit polarity which is required for them to exhibit certain functions like secretion of molecules. Epithelial cells and neurons are typical example of cells that show apical-basal polarity.
Apical surface of a membrane is exposed to the lumen. The micro-villi bearing surface of epithelial cells is typical example of apical surface. It is separated from other surface of membranes by the zonula occludens.
Basal surface of membrane forms the basal and lateral surfaces, it faces towards the interstitium, and away from the lumen. Basal membrane is generally in contact with the basal membrane.
Characters of epithelium: Epithelia form membranes that serve as protective layers, secretory components , and sensory components of the body. The characteristics of epithelia are:
Limited intercellular space: The cells of epithelia are held tightly, with restricted intercellular space. This enables them form an effective barrier.
Ability to form layers: They can form either monolayers or multiple layers, depending on the demand of the function. Where diffusion or filtration is required, they form monolayers with flattened cells. Otherwise, to protect from friction or mechanical damage, they form multiple layers.
Free apical surfaces: Epithelial cells possess free apical surfaces, so that they can participate in absorption, secretion, and excretion functions
Avascular: Epithelial cells lack blood vessels, and so are avascular tissues. They absorb nutrients, and excrete wastes, by diffusion, into the nearby connective tissue blood vessels
Mitotic capability: They have extensive mitotic ability, and thus can replace worn out cells at a faster pace. Repair and regeneration is high in epithelial tissues.
Structure of a bone: A bone is a rigid structure that gives mechanical strength and supports the body. Structure of a typical long bone has the following sections:
Diaphysis: It is the long central shaft of bone. Bone marrow is usually present within the diaphysis, in its middle tubular part. It is made up of cortical bone.
Epiphysis: It forms the larger, rounded, smooth ends of the long bones. Bones join with adjacent bones at diaphysis. It is filled with red bone marrow and is site for hemopoiesis. The regions of epiphyses are divided into pressure epiphysis, traction epiphysis, atavistic epiphysis, and aberrant epiphysis. Each of these preform the function of transmitting weight of body, formation of joints, form fused bones, and deviations from the normal bones, respectively.
Medullary space is the cavity of bone shafts of long bones. It usually contains red and yellow bone marrow and is the site for hemopoiesis. The medullary space has walls composed of spongy bone, and is lined with a thin vascular membrane.
Osteon structure: Osteon is also called Haversian system. It is the basic functional unit of a compact bone. Osteons are cylindrical or roughly cylindrical structures of several millimeters length and diameter of 0.2 mm. An osteon has concentric layers or lamellae of compact bone, that enclose a Haversian canal.
The lamellae are made of osteoblasts. These osteoblasts develop into osteocytes which occupy a specific position or space called lacuna. They make contact with cytoplasmic processes of other osteocytes via a network of small canals called canaliculi. This helps them to exchange nutrients and metabolic waste. The space between osteons is occupied by interstitial lamellae. They are formed due to reabsorption of bone.
Osteoblasts: These are the cells that form the bone or that lay the bone tissue. They get trapped within the bone matrix they secrete, and become differentiated into osteocytes, after extensive proliferation. Osteocytes respond to stress on bones and thus, change the bone density by laying bone mass.
Osteoclasts: The remove bone tissue and are responsible for bone demineralization. Osteoclasts are essential for bone repair, remodeling of bones. They perform the function of bone resorption, that is, they digest the composite of hydrated protein and mineral of bone. Osteoclasts also play an essential role in regulation of calcium level.
Parathyroid hormone: It is secreted by parathyroid glands and is responsible for calcium metabolism in the body. The hormone acts to increase calcium ion concentration in blood. Bone and kidney cells express parathyroid hormone receptor I, and central nervous system contain parathyroid hormone 2 receptor. By binding to these receptors, the hormone regulates the calcium related functions of these organs.
PTH promotes osteoclastic activity in bones, and thus promotes release of calcium from bone. It enhances active reabsorption of calcium from distal tubules and the thick ascending limb of nephrons of bone, and thus increase the calcium concentration in blood. It also enhances absorption of calcium from the intestine, by increasing the production of active Vitamin-D.
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