Epithelium Study Guide

Overview of Absorption Disorders

Do You Have SIBO Symptoms? Here Is ALL You Need to Know!
Meanwhile, motilin also plays a role in increasing the production of pancreatic polypeptide and somatostatin. The cardiac sphincter, at the end of esophagus, regulates the movement of food from esophagus to stomach. Food in the GI tract is called a bolus ball of food from the mouth down to the stomach. Extrinsic outside nerves come to the digestive organs from the unconscious part of the brain or from the spinal cord. The serosa or serous membrane secretes the serous fluid. The Neglected Endocrine Organ".

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Intestinal gas

These sensory cells are normally replaced every days by division and differentiation of stem cells , which is handy since they are exposed and easily damaged e. In addition to sensory cells, the elongated cells of the taste bud include support cells , which are sometimes rather pretentiously called sustentacular cells from the same root as "sustain".

Stem cells are normally visible in taste buds as shorter cells with round nuclei which appear at the basal end of the tastebud. Although all cells are general-purpose metabolic factories, most mature cell types are functionally specialized to play one particular role in the economy of the larger body.

In contrast, hepatocytes of the liver are remarkable for the breadth of their "specialization". Among other functions, hepatocytes: The cellular structure of hepatocytes is correspondingly rich. Instead of displaying a concentration of one particular organelle, hepatocytes have lots of everything -- lots of mitochondria , lots of ribosomes , lots of Golgi bodies , lots of endoplasmic reticulum both rough and smooth , lots of stored glycogen , lots of lysosomes , lots of plasma membrane with microvilli on the free surface.

They even have lots of nucleus yes, hepatocytes may be polyploid and commonly have two full-size nuclei. When an introductory biology book illustrates "the cell", the representative example is often a hepatocyte -- because hepatocytes offer splendid and numerous examples of most cellular organelles.

In appearance, hepatocytes are boxy cuboidal cells with one or two large euchromatic nuclei and with abundant, grainy cytoplasm that stains well with both acid and basic dyes reflecting the abundance of various cellular constituents. Because individual liver cells have an indefinite lifespan, they may accumulate abundant lipofuscin yellow-brown "wear-and-tear" pigment , especially with advancing age. Hepatocytes are arranged into cords , in which each hepatocyte is attached to its neighbors in a two-dimensional sheet.

On either side of the cord, each hepatocyte faces the space of Disse , across which it communicates freely with adjacent sinusoids. Hepatocytes are epithelial , but their epithelial nature is expressed in a rather peculiar way. An ordinary epithelial cell sits on its basal surface, has an apical surface exposed to the external space, and is attached to its neighbors along its lateral surface. In principle, h epatocytes follow this same plan -- but they have a unique topology. A typical hepatocyte has two basal surfaces , on opposite ends of the cell where it faces the sinusoids on either side of the cord in which it resides.

The apical surface of a hepatocyte occurs along a band around the cell's middle, half-way between the opposing basal surfaces. It is across this surface that bile is secreted. These bile canaliculi form a network encircling each hepatocyte and sealed within the hepatic cord. Along this network which is shaped like chicken-wire , bile can seep toward the periphery of the lobule and hence into the proper bile ducts which are found only portal areas.

Bile canaliculi are barely visible in routine microscopic preparations, at sites where the boundary between adjacent hepatocytes has been cut neatly and perpendicularly.

They can be clearly demonstrated with special stains. The lateral surfaces of a hepatocyte take the form of two broad bands which wrap around the cell between the two basal surfaces, separated by the narrow band of apical surface.

These lateral surfaces attach the cell to its neighbors within the cord , with junctional complexes sealing off and separating the bile canaliculi at the apical surface from the plasma-containing space of Disse at the basal surfaces. Endothelial cells are simple squamous cells which line the entire vascular system including lymphatic channels.

Endothelial cytoplasm is inconspicuous in routine light microscopy. Typically only the nuclei are visible, at the boundary between the lumen and the wall of a vessel.

Endothelial nuclei typically appear thin and dark, in cross section. However, occasionally endothelium lies parallel to the plane of section. In this case the nuclei may appear very large, round, and pale. The term reticuloendothelial system refers to the macrophages of the liver , spleen and lymph nodes i.

The name reflects former confusion about the distinction between endothelial cells and the scattered population of macrophages monocytes, histiocytes. Macrophages can be readily labelled experimentally through their phagocytosis of injected carbon particles.

However, endothelial cells are also labelled by the same procedure. Although endothelial cells are not dramatically phagocytotic, they do shuttle some materials across the endothelial lining via small endocytotic and exocytotic vesicles. Although endothelial cells appear rather uninteresting under the microscope, these are important cells. They are situated at a critical location, between the blood and all other body cells.

They secrete substances which control local blood flow and blood coagulation, and they are active participants in white blood cell emigration during inflammation. Throughout much of the body, the capillary endothelial lining is continuous , with neither large gaps between cells nor holes through cells. Materials pass through the endothelium either by diffusion or via rapid vesicular transcytosis.

In most of the brain, a lack of transcytotic vesicles accounts for the blood brain barrier -- the only substances which cross such a barrier are those which can diffuse through plasma membranes or those for which specific membrane channels exist. In a few special locations -- notably in the sinusoids of the liver , in the glomeruli of the kidney, and in most endocrine glands -- the endothelium is fenestrated i. In the liver, where there is also no basement membrane, the fenestrations permit blood plasma to wash freely over the exposed surfaces of the hepatocytes through the space of Disse.

Kupffer cells are macrophages found in the sinusoids of the liver. This particular population of macrophages are especially significant, with responsibility not only for cleaning bacteria out of the portal blood stream the "dirty" blood" from the intestine , but also for removing worn-out red blood cells and recycling hemoglobin a job shared with macrophages of the spleen.

Kupffer cells are closely associated with the endothelial lining of the liver. Lying along side or draped across the liver sinusoids, the Kupffer cells are not easily distinguished from the endothelial cells. The term reticuloendothelial system refers to the macrophages of the liver, spleen and lymph nodes, i.

Ito cells are stellate cells of the liver , located at intervals within the space of Disse. These cells function as storage sites for fat and vitamin A. Although evidently included within Kupffer's original description of Kupffer cells , Ito cells comprise a distinct cell type proper Kupffer cells are liver macrophages. The protective epithelial cells which line the surface of the stomach including gastric pits are called surface mucous cells. These cells are critical for resisting attack by digestive acid and enzymes.

Any disruption of these cells' function can lead to an ulcer. Not all people with celiac disease experience a rash. In the case of protein malabsorption, a gluten-free diet needs to be followed. You can probably get the protein you need from meat, poultry, fish, eggs and dairy. Carrying excess fluid around can place undue pressure on your heart and lungs.

Diarrhea and weight loss will make you feel sluggish and weak. Books, diets and informational programs about a gluten-free diet abound. Many restaurants now offer dishes that contain no gluten.

Within two weeks of switching to a gluten-free diet, your symptoms will improve. Be sure to visit your physician for a diagnosis before beginning the diet. Video of the Day. Bile and Fat Digestion. Foods to Increase Intestinal Absorption. Action of Bile Salts. Other types of absorption disorders include tropical sprue and Whipple's disease. Tropical sprue is more common in tropical and subtropical areas of the world, including the Caribbean and Southeast Asia.

The exact cause for the condition is unknown, but it may be related to an infection that damages the lining of the small intestine. Symptoms include anemia, diarrhea, weight loss, and malnutrition. Tropical sprue is treated with antibiotics. Whipple's disease is caused by bacteria Tropheryma whippelii that usually infect the small intestine and cause malabsorption. Whipple's disease also can affect other areas of the body e. Patients who have Whipple's disease often experience joint pain and stiffness years before developing intestinal symptoms e.

Treatment involves antibiotics to destroy the bacteria and also may involve intravenous IV; through a vein fluid and electrolyte replacement and dietary supplements. Electrolytes are substances e. If left untreated, Whipple's disease can be fatal.

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