Slide 1 : Parts of the Alimentary Canal
1. Mouth (Buccal cavity)
The teeth, tongue and chewing action break up the food physically which increases surface area, and they form it into a ball or bolus. The salivary glands secrete saliva, which contains water to dissolve soluble substances, mucus for lubrication, lysozymes to kill bacteria and amylase to digest starch. The food bolus is swallowed by an involuntary reflex action through the pharynx (the back of the mouth). During swallowing the trachea is blocked off by the epiglottis to stop food entering the lungs. digestion in humans
Slide 2 : This is a simple tube through the thorax, which connects the mouth to the rest of the gut. No digestion takes place. There is a thin epithelium, no villi, a few glands secreting mucus, and a thick muscle layer, which propels the food by peristalsis. This is a wave of circular muscle contraction, which passes down the oesophagus and is completely involuntary. The oesophagus is a soft tube that can be closed, unlike the trachea, which is a hard tube, held open by rings of cartilage. oesophagus[food pipe]
Slide 3 : This is an expandable bag where the food is stored for up to a few hours. There are three layers of muscle to churn the food into a liquid called chyme. This is gradually released in to the small intestine by a sphincter, a region of thick circular muscle that acts as a valve. The mucosa of the stomach wall has no villi, but numerous gastric pits (104 cm-2) leading to gastric glands in the mucosa layer. These secrete gastric juice, which contains: hydrochloric acid (pH 1) to kill bacteria (the acid does not help digestion, in fact it hinders it by denaturing most enzymes); mucus to lubricate the food and to line the epithelium to protect it from the acid; and the enzymes pepsin and rennin to digest proteins stomach
Slide 4 : internal structure of stomach
Slide 5 : Liver/Gall Bladder- At this point, our food is hit with more chemicals. The liver makes a chemical called bile but bile is not stored in the liver. Instead it is stored in the gall bladder. When the gall bladder mixes bile with our food, it does an important job: breaking down the fat (from milk, butter, cheeses) into tiny droplets. This fat will supply us with much energy later.
The pancreas also adds a digestive chemical as the food leaves the stomach. This digestive juice works on breaking down the carbohydrates (from breads, potatoes, etc.) and the proteins (from meats, cereals, peanut butter) digestive glands
Slide 6 : The Small Intestine is the real hero of the digestive system. The small intestine is a tube that is about 22 feet long! This is where the real digestion takes place. As the food passes through, it is mixed with the new chemicals and soon our "food" is now digested small enough to be put to use by the body
Slide 7 : This is about 6.5 m long, and can be divided into three sections:
The duodenum (30 cm long). Although this is short, almost all the digestion takes place here, due to two secretions: Pancreatic juice, secreted by the pancreas through the pancreatic duct. This contains numerous carbohydrase, protease and lipase enzymes. Bile, secreted by the liver, stored in the gall bladder, and released through the bile duct into the duodenum. Bile contains bile salts to aid lipid digestion, and the alkali sodium hydrogen carbonate to neutralise the stomach acid. Without this, the pancreatic enzymes would not work. The bile duct and the pancreatic duct join just before they enter the duodenum. The mucosa of the duodenum has few villi, since there is no absorption, but the submucosa contains glands secreting mucus and sodium hydrogen carbonate. small intestine
Slide 8 : The internal surface area is increased enormously by three levels of folding: large folds of the mucosa, villi, and microvilli. Villi are large structures composed of many cells that can clearly be seen with a light microscope, while microvilli are small sub-cellular structures formed by the folding of the plasma membrane of individual cells. Microvilli can only be seen clearly with an electron microscope, and appear as a fuzzy brush border under the light microscope. internal structure of small intestine
Slide 9 : Along the walls of the intestine are thousands of tiny fingers called villi.. Blood vessels (capillaries) in the villi can absorb the tiny food molecules and send them off to the rest of our body through the blood.
Slide 10 : It is inside the small intestine that we absorb most of the nutrients in our food. Although the small intestine has a relatively small diameter, the intestinal walls are covered in wrinkles called rugae, which are themselves covered in millions of finger-like projections called villi, which are themselves studded with millions of smaller projections called microvilli. This provides a surface-area of about the size of a tennis court for nutrient absorption. Inside each villus is a series of lymph vessels (lacteals) and blood vessels (capillaries). The lacteal lymph vessel absorbs digested fat into the lymphatic system which eventually drains into the bloodstream. The blood vessels receive other nutrients and transport them via the hepatic portal vein to the liver. absorption of food
Slide 11 : Large Intestine
This comprises the caecum, appendix, colon and rectum. Food can spend 36 hours in the large intestine (mind you that's if your pretty constipated!), while water is absorbed to form semi-solid faeces. The mucosa contains villi but no microvilli, and there are numerous glands secreting mucus. Faeces is made up of cellulose, cholesterol, bile, mucus, mucosa cells (250g of cells are lost each day), bacteria and water, and is released by the anal sphincter. This is a rare example of an involuntary muscle that we can learn to control (during potty training). LARGE INTESTINE
Slide 12 : The blood vessels receive other nutrients and transport them via the hepatic portal vein to the liver. Here the blood is filtered, toxins are removed and the nutrients are processed. An important task performed by the liver in this context is the regulation of blood glucose levels to provide sufficient energy for the body. Excess glucose is converted in the liver to glycogen in response to the hormone insulin, and stored. Then, when blood glucose levels begin to drop, (eg. between meals), the glycogen is re-converted to glucose in response to messages conveyed by the hormone glucagon. release of energy from food
Slide 13 : Where do cows put all that grass?
Did you know that a cow has four stomachs? Being herbivores, they need space for all that grass to ferment before it moves through their digestive system. The four stomachs give them extra storage, since it takes a lot of grass to feed a one-ton animal. FUN FACTS
Slide 14 : Esophagus-burn doesn’t have the same ring…
Your heart has nothing to do with heartburn. The esophagus has a ring of muscles at the top and bottom. If the bottom ring doesn’t keep the lower part closed between swallows, stomach acid can come up and create a burning sensation. fun facts