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The Alimentary Canal The human digestive system consists of the alimentary canal and its accessory glands. It’s a long tube starting from the mouth and ending at the anus. Humans digest all their food extracellularly, that is outside of their cells. If you laid out your alimentary canal from end to end, how long would it be ? a) Same as your height b) As long as a sports car c) As wide as a tennis court Click here for answer 9 meters ! As wide as a tennis court ! Mouth Esophagus Stomach Small Intestine Large Intestine Anus Mouth The mouth opens into a cavity called the oral cavity. This cavity is surrounded by upper and lower jaws bearing teeth. A thick muscular tongue is present on the floor of the mouth cavity. It manipulates food during chewing and swallowing. In mammals, it bears taste buds to sense the taste of food. Upper lip Teeth Tongue Lower lip Diagram of the Human Alimentary Canal Large Intestine - about 1.5 Esophagus - a 25 cm long tube Intestine -gland the longest m Small long, and divided into that opens into the stomach. Liver - the largest in the tube in colon the human body. About caecum, and rectum. human body. Divided into left and 7 Also called the food pipe. The m long, divided into the divided Stomach -awhich ablind 'J’-shaped right lobes, are further Caecum –and pouch, about wall of the esophagus is highly duodenum, the jejunum and the structure, divided into three Gall bladder a hollow pearinto sub lobes. The ducts from the 6 cm long. The vermiform muscular and no digestion ileum. regions: cardiac, fundic and right and left lobes, calledis hepatic shaped sac that stores bile appendix (2-7 cm long) occurs in it. Duodenum -esophagus the initial short part, Pancreas -to the second largest ducts, join form the common pyloric.The opens into produced by the liver. attached to it. somewhat C-shaped, and 25 gland after liver. Itwhich isabout hepatic duct. the This hepatic duct joins the cardiac stomach, is Colon is further divided into and cm long. It receives bile duct carrot-shaped and lies below and the cystic duct from the gall bladder surrounded by cardiac sphincter. the ascending colon, the pancreatic duct. The concave to form a bile duct.middle TheThe bile duct and behind the stomach. head of The part in the is the portion articulates the pancreas. transverse colon, the pancreatic ductisofencircled the pancreas join the pancreas by the fundic stomach. The pyloric Jejunum – the part in the middle; descending colon and touches sigmoid, together toand form a common bile and duodenum its tail stomach opens into the small about 2.5 m colon. long. ie, S-shaped pancreatic duct which opens into the spleen. Anus - the opening through Ileum the final coiled part, by intestine which is12 surrounded duodenum small intestine. Rectum -ofathe tube cm long which undigested about 3.6m long. It liesfood between pyloric sphincter. that opens into the anus. thematter arches (faeces) of the large intestine. is egested out from the body. Digestion Begins in the Mouth Digestion begins in the mouth with the mechanical action of teeth and the chemical action of digestive enzymes present in the saliva. The enzyme, salivary amylase, breaks starch into the sugar, maltose. Saliva lubricates the contents of the mouth. The tongue manipulates food into a bolus/mushy ball as it is chewed and initiates the swallowing process. Starch Salivary Amylase Maltose Role of Salivary Glands in Digestion The salivary glands secrete saliva. This fluid moistens food particles, helps bind them, and begins the chemical digestion of carbohydrates. Saliva is also a solvent, dissolving foods so they can be tasted, and it helps cleanse the mouth and teeth. There are two types of secretory cells, within a salivary gland: Serous cells – Produce Amylase Mucous cells – Produce mucus Why do you think bread tastes sweet when you chew it? Saliva converts bread, containing starch, into maltose Role of Teeth in Digestion Teeth are an important feature of almost all vertebrates. Mammals are characterized by differentiation of teeth for various functions. Moving from front to rear of the mouth, the types of teeth are: Incisors - Tearing Canines - Gripping Premolars - Grinding Molars - Grinding Esophagus (The Food Pipe) On the way to the stomach After being chewed and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wavelike muscle movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability to eat or drink even when we're upside-down. No digestion occurs in the esophagus. Cardiac stomach Esophagus Stomach Pyloric stomach Fundic stomach Digestion in the Stomach The stomach has branched and tubular glands present on its wall. Proteins Lipids The secretions of these glands are collectively called gastric juice, which is a mixture of Gastric secretory products of three Lipase types of glands secreting Pepsin hydrochloric acid, protein digesting enzyme and mucus. In acidic medium of gastric juice Fatty Peptones (pH 1 - 3), the protein digesting acids enzyme, pepsin, breaks down proteins into peptones (partial hydrolyzed protein). Gastric lipase partially breaks down lipids/fats. Role of the Liver Liver produces a fluid called bile. Bile is released in the duodenum of the small intestine via the bile duct. Bile breaks down fats into smaller fatty acids and glycerol. Excess bile is stored in the gall bladder. Fats Bile Fatty acids & Glycerol What causes our feces/poop to be yellowish-brown in color ? BILE ! Gall bladder Liver Role of the Pancreas The pancreas produces pancreatic juice, which Proteins Fats Starch contains the following enzymes: Trypsin and Chymotrypsin: Breaks down large proteins into Lipase Amylase Trypsin partially digested proteins. Pancreatic Lipase: Breaks down fats into fatty acids and glycerol. Fatty acids Peptones Maltose & Pancreatic Amylase: Glycerol Breaks down starch into maltose. Digestion in the Small Intestine The partially digested food containing proteins, Peptones carbohydrates and fats enter the small intestine. It is here that the intestinal juice, succus entericus, complete the digestion of proteins into amino acids, carbohydrates into glucose and fats into fatty acids and glycerol. Fats Carbo hydrates Intestinal juice Succus entericus Amino acids Fatty acids & Glycerol Glucose Absorption in the Small Intestine Bicarbonate ions secreted by the small intestinal wall makes the medium alkaline. Inside, the wall of the small intestine is provided with numerous long finger-like projections called villi, which increase the surface area of the inner lining of the intestine. This enhances the intestinal wall’s absorption capacity for nutrients that are then sent to the bloodstream. Stomach Small Intestine The Large Intestine/Colon In the large intestine, some of the water and chemicals like sodium are absorbed from the food by the walls of the intestine. Very little digestion goes on in the colon, as compared to the small intestine. Many microbes present in it (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) help in the digestion process. Undigested food matter is stored in the rectum and finally sent out via the anus. Colon Small Intestine Rectum Anus Caecum Summary Starch Maltose Amylase Proteins Peptones No digestion Peptones Fats occurs Carbohydrates Trypsin,Chymotrypsin Fats Succus entericus Fatty acids Fats Bile Fatty acids Proteins LipasePeptones Pepsin Maltose LipidsStarch Partially digested fats Amino acidsAmylase Fatty acids Glucose Lipase