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The Human Digestive System What is digestion? The process of breaking down foods into molecules the cells of the body can use. Where does digestion occur? The gastrointestinal tract (AKA- alimentary canal) Muscular tube approx. 9 meters long! Organs of the Alimentary Canal and their accessory organs Mechanical vs. Chemical Digestion Mechanical Digestion= The physical breakdown of food into smaller pieces Chemical Digestion= Breaking the bonds in food to change the chemical nature of it Mouth (Buccal Cavity) Mechanical Digestion (mastication) - Teeth break down food - Tongue manipulates food against the hard palate (bony roof of mouth) and contains bumps (papillae) that provide friction for moving food around. - The frenulum connects the tongue to the floor of the mouth. Mouth cont. Chemical Digestion - Salivary glands that line the mouth produce saliva. - Saliva moistens food particles, binds them together, allows tasting, helps to cleanse the mouth and teeth, and begins carbohydrate digestion. - Saliva is a mixture of water, mucus and an enzyme called amylase (breaks down carbs). - The mucus lubricates and holds the food together forming a ball called a “bolus”. INTERESTING FACT: Halitosis results when food particles accumulate in the mouth and bacteria flourish. Saliva helps wash away these food particles. Three pairs of Salivary Glands 1-1.5 L / day for digestion lubrication (swallowing) moistening (tasting) Parotid – lateral side of face, anterior to ear – watery saliva Submandibular – floor of mouth Sublingual – inferior to tongue – thick saliva Pharynx The pharynx connects the nasal and oral cavities with the larynx and esophagus and is divided into a nasopharynx (top portion), oropharynx (middle portion), and largyngopharynx (bottom portion). Sensory receptors in the pharynx sense food, which triggers swallowing reflexes. Esophagus When food is swallowed it passes Peristalsis the pharynx and into the esophagus. The esophagus is a muscular tube approx. 10 inches long. What type of muscle lines the esophagus? Contractions and relaxations of these muscles move the bolus down the esophagus. This process is called- PERISTALSIS Peristalsis is very effective= Can drink upside down Cardiac Sphincter • Circular muscle that opens to allow food to pass from the esophagus into the stomach. • What if the cardiac sphincter doesn’t work properly? Gastroesophageal reflux disease- GERD A condition in which the liquid content of the stomach regurgitates (backs up or refluxes) into the esophagus. The liquid can inflame and damage the lining of the esophagus. The regurgitated liquid usually contains acid and pepsin that are produced by the stomach. Achalasia The term achalasia means "failure to relax" and refers to the inability of the cardiac sphincter to open and let food pass into the stomach. Also, the muscle that lines the esophagus does not contract properly. As a result, patients with achalasia have difficulty in swallowing food. Stomach The stomach is divided into the cardiac, fundus, body, and pylorus regions. E CS SI C PS P B F Stomach • Mechanical Digestion in Stomach - The stomach is lined with smooth muscle. This lining is folded and the folds are called rugae. Smooth muscle of the stomach twists and turns the stomach, physically breaking down food. - If the stomach is empty, then it growls. This is due to the sounds made by the contractions of the muscles. A Real Stomach!!! Stomach cont. Chemical Digestion - Innermost lining of the stomach is a mucous membrane that has openings called gastric pits. - Gastric pits are the openings through which secretions are released into the stomach. - These secretions (called gastric fluid) include: mucus, pepsinogen (breaks down proteins), and hydrochloric acid. - The mucous coating of the stomach protects it from the acid. If it breaks down = ULCER! - Food usually stays in the stomach for 3-4 hours. - The mixture produced from mechanical/chemical digestion is called chyme (fats, sugars, vitamins, minerals, and proteins). Small Intestine Pyloric sphincter = Circular muscle that opens to allow chyme into the small intestine from the stomach. It allows approx. 5-15 ml in at a time. The lengthy small intestine receives secretions from the pancreas and liver. The small intestine functions to complete digestion of the nutrients in chyme, absorb the products of digestion, and transport the remaining residues to the large intestine. If stretched out, the small intestine is 21 feet long! It is held together by a thin tissue layer called mesentery. The 3 parts of the small intestine include: 1st = Duodenum (10 inches) 2nd= Jejunum (8 feet) 3rd= IIleum (13 feet) Mesentery of Small Intestine: Liver and Gall Bladder Liver - Large brownnish-red organ to the right of the stomach - Makes bile (important in fat digestion) Gall bladder - Stores the bile made by the liver - Bile travels from the liver to the gall bladder through the common hepatic duct and cystic duct. - When chyme is present in the small intestine (duodenum), the gall bladder releases bile through the cystic duct to the common bile duct which dumps into the small intestine at the duodenum. Human Digestion: Small Intestine Gall Bladder Removal Why? Quick video of a removal Pancreas The pancreas secretes pancreatic fluid into the small intestine (duodenum). This helps breakdown the chyme. Pancreatic fluid leaves the pancreas through the pancreatic duct. The pancreatic duct joins the common bile duct just before it enters the small intestine. Absorption in the Small Intestine Digestion products are absorbed into the circulatory system through blood and lymph vessels. The lining of the jejunum and illeum has extensions called villi that increase surface area. Inside the villi are capillaries and lacteal (lymph vessels). Fatty acids enter lacteals Other substances diffuse into capillaries and carried to cells of the body Celiac Disease Celiac disease is when the small intestine lining (villi) is damaged and absorption of nutrients is hindered. The damage is due to a reaction to eating gluten, which is found in wheat, barley, rye, and possibly oats. The immune system incorrectly attacks villi because of the gluten they are absorbing. Large Intestine Once the remaining food enters the large intestine, it moves toward the anus by contractions of the smooth muscle in the lining of the large intestine. The large intestine consists of the cecum (pouch at the beginning of the large intestine), colon (ascending, transverse, descending, and sigmoid regions), the rectum, and the anal canal. As the matter moves through the large intestine, water is absorbed into the capillaries in the lining. This makes the matter more solid. The solid material is called feces. Large Intestine What is Feces?? Feces is composed of undigested material, water, electrolytes, mucus, and bacteria. The color of feces is due to the action of bacteria on bile pigments. The odor of feces is due to the action of bacteria. What can we learn from our poop? Color, smell, consistency, curvature? What goes in must come out! Diverticulitis Diverticulosis happens when pouches (diverticula ) form in the wall of the colon . If these pouches get inflamed or infected (with feces), it is called diverticulitis. Diverticulitis can be very painful. Doctors aren't sure what causes diverticula in the colon. They think that a low-fiber diet may play a role. Without fiber to add bulk to the stool, the colon has to work harder than normal to push the stool forward. The pressure from this may cause pouches to form in weak spots along the colon. Diverticulitis happens when feces get trapped in the pouches (diverticula). This allows bacteria to grow in the pouches. This can lead to inflammation or infection. Facts at a Glance The average person eats 3 pounds of food a day. That's 1,095 pounds a year! An adult stomach holds 5 cups. 35 million glands produce acid in the stomach. The acid can dissolve a razor blade in one week! The body uses energy efficiently. (900 miles to the gallon!) Our own food breakdown factory! Why do we need our urinary system? • To remove (excrete) metabolic waste from the bloodstream and carry it out of the body in the form of urine – Metabolism: Cells breaking down compounds for energy • To regulate the water content in the body Functions of the organs of the human urinary system Kidneys- Where blood is filtered and urine is produced Ureter- Narrow tube connected to each kidney that carries urine to the urinary bladder Urinary bladder- A muscular sac that stores urine and contracts to release urine Urethra- The tube that carries urine from the bladder out of the body Organs of the human urinary system Kidney Renal vein Renal artery Ureter Urinary bladder Urethra