Digestive sysytem Flashcards
What are the 4 main processes of the digestive system.
Ingestion: Taking in food and liquids into the mouth often large insoluble pieces.
Mechanical processing: crushing and shearing that makes materials easier to propel along the GI tract. Also increases their surface area so are more susceptible to enzymatic attack. Swirling,mixing and churning of the stomach and intestine are also examples of mechanical digestion.
Digestion: breaking down the large pieces of food into smaller soluble subunits of food. Eg. carbohydrates into small soluble sugars. So that they can pass across the digestive epithelium and be transported to the bodies cells.
Secretion: is the release of water, acids, enzymes, buffers and salts by the epithelium of the digestive tract and by glandular organs.
Absorption: organic substrates, electrolytes, vitamins and water must then be absorbed into the (interstitial fluid) blood and/or lymphatic system from the lumen. Not all is absorbed and so eliminated as waste such as fibre. Water is also absorbed into the blood.
Excretion: The removal of indigestible waste material from the anus as faeces.
GI tract (alimentary canal) is a single tube that runs from the mouth all the way to the anus. Accessory organs also involved in the digestive system, but not make up the GI tract. The size of the lumen differs throughout the GI tract which relates to its function at a particular location within the tract. The GI tract lining protects the body/other organs from the bacteria that may have been ingested in the food and from the acid and enzymes involved in digestion. The structure of the layers of tissue of the GI tract are the same throughout but varies slightly depending on location.
The catabolic reactions require two essential ingredients: (1) oxygen, (2) organic molecules such as carbohydrates, fats and proteins, that can be broken down by intracellular enzymes.
Describe the anatomical layout of the digestive system
Order of GI tract and food travel:
The oral cavity (mouth), pharynx, oesophagus, stomach, small intestine (duodenum, jejunum, ileum (which is the longest section)) and large intestine (Starting from the right caecum, acending colon, transverse colon, descending colon, sigmoid colon (goes posterior to the rectum)), rectum and anus. The omentum is a fatty covering that folds down over and covers the abdominal cavity.
Accessory organs: teeth, tongue, and various glandular organs, such as salivary glands, liver and pancreas, which secretes into ducts emptying into the digestive tract. Include water, enzymes, buffers and other components to aid in the preparation of organic and inorganic nutrients for absorption across the epithelial of the GI tract.
Gallbladder: Storage and concentration of bile.
Liver: Secretion of bile (important for lipid digestion), storage of nutrient and many other vital functions.
Pancrease: Exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones.
Describe the process of movement of the digestive materials.
The smooth muscle along the digestive tract shows rhythmic cycles of activity due to the presence of pacesetter cells. These cells undergo spontaneous depolarisation and their contraction triggers a wave of contraction that spread through the entire muscular sheet. Peristalsis describes this process. And mechanical processing is called segmentation.
Peristalsis: the circular muscles contract behind the bolus of food, while circular muscles ahead relax. Longitudinal muscles ahead contract shortening the adjacent segments, followed by another wave of circular muscle contractions that propel the food forward.
Describe the layers of the GI tract
The lumen is surrounded by a mucosa, submucosa, muscular layer, outer serosa or adventitia.
Mucosa: Mucus membrane simple layer of tissue secretes mucus and is lined in mucus. Protects underlying cells and acts as a lubricant ease passage of food material.
In areas that are subject to a lot of mechanical stresses such as in the oral cavity, pharynx and oesophageous the mucosa is made of stratified cells and is thicker.
However the mucosa layer is thin in areas associated with absorption such as the small intestines and most of the large intestine. The mucosa is composed of a simple cuboidal epithelium, one layer of cells thick sitting on a basement membrane. these contain goblet cells, as well as enterendocrine cells that secrete hormones to coordinate the activities of the digestive tract and the accessory glands.
The lamina Propria: Under the muscosa there is a layer of tissue containing blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells, and scattered areas of lymphoid tissue. In most areas of the GI tract the lamina propria contains a narrow band of smooth muscle and elastic fibers, called the musclaris muscosae. This contains circular and longitudinal smooth muscle layers.
The submucosa: layer of dense irregular connective tissue. It contains large blood vessels and lymphatic vessels and lymphatic nodules that are involved in the immunological response. In some areas of the submucosa there are exocrine glands that secrete buffers and enzymes into the lumen of the digestive tract. Along its outer margin there is a network of intrinsic nerve fibers and scattered neurons, called the submucosal plexus. Add more here….
The muscularis externa: Like the muscularis mucosae the muscularis externa also has a circular and longitudinal layer of smooth muscle. they play an essential role in mechanical processing and movement of materials along the GI tract, and are coordinated via the enteric nervous system (myenteric plexus) . The stomach also has an additional layer of muscle that runs obliquely.
The serosa: Loose connective tissue that secretes small volumes of serous. Viceral peritoneal. Allows movement of the intestine (GI tract) over each other. There is no serosa in the oral cavity, pharynx, oesophagus and rectum where dense networks of collagen fibers firmly attach the GI tract to adjacent structures called an adventita.
Describe the visceral and parietal peritoneal membranes function
Parietal (perimeter on the outside)
Describe the visceral and parietal peritoneal membranes function
Parietal (perimeter on the outside), Visceral inside. Between these two membranes there is a potential space of peritoneal cavity containing serous fluid. this allows lengths of bowels of bowel to move relative to one another.
organs that are within the parietaneal space are describe as being intraperitoneal. Got to 14mins in the video.
