The Digestive System PDF

The Digestive System  Digestive System includes all the structures that are concerned with bringing food into the body to provide for the needs of the body’s cells. Each cell in an organism relies on a continuous expenditure of energy. Fats, carbs & proteins are broken down during c...

The Digestive System  Digestive System includes all the structures that are concerned with bringing food into the body to provide for the needs of the body’s cells. Each cell in an organism relies on a continuous expenditure of energy. Fats, carbs & proteins are broken down during cellular metabolism & the energy derived from them is used to make ATP.  Digestive System deals with: Mechanical Chemical Ingestion Absorption Elimination Breakdown Breakdown bringing physically large food simple material that nutrients into breaking food molecules nutrients cannot be MakeA Plan the body into smaller (polymers) are (monomers) digested is (mouth) pieces for broken down pass out of the expelled from digestive into monomers digestive tract the body enzymes to & into cells act Anatom y  Salivary glands pharynx mouth esophagus stomach liver gall bladder pancreas large intestine (colon) small intestine appendix rectum mouth = entrance to the digestive system palate uvula tonsils tongue salivary glands  Teeth cut & grind food increase surface area of food improves the rate of digestive reactions canine premolar molar incisor  Tongue This muscular, mobile organ serves many roles: pushes food around and mixes it with saliva gathers food together into a bolus for swallowing used for speech part of the lymphatic system that helps defend the body from infection  Salivary Glands 3 pair: parotid, sublingual, submandibular produce saliva to lubricate food contains salivary amylase, an enzyme that breaks starch into disaccharides makes some antibacterial enzymes parotid dissolves some food sublingual submandibular  Taste Buds Identify the type & quality of the food Food dissolves in saliva & moves into the taste pores. Receptor cells ‘sense’ the taste & pass on the message to attached nerve cells. taste receptor cells sensory taste nerve pore  Pharynx the cavity connecting the mouth & nose to the esophagus & trachea. It is a structure that belongs to both the respiratory & digestive systems.  nasopharynx nasal sinus pharynx palate tongue epiglottis  Epiglottis is a flap of tissue & cartilage that prevents food from entering the trachea. swallowing raises the larynx (voice box) to meet the epiglottis, to conduct food down the esophagus. Prevents food from entering the trachea (airway) and potentially damaging the lungs  Esophagus is a muscular tube that propels food from the mouth to the stomach. circular muscles surrounding it contract in sequence to squeeze the bolus towards the stomach. longitudinal muscles propel the bolus along in a wave-like motion, called peristalsis.  Stomach an expandable, muscular sac, capable of holding 2-4L of food & liquid food in the stomach is a thick, acidic liquid called chyme. it secretes a thick layer of mucin to prevent self-digestion. layers of muscle aid in mechanical breakdown, by churning food.  Stomach Different regions of the stomach are: fundus External muscles ⚬ longitudinal ⚬ circular ⚬ oblique greater curvature lesser curvature  Stomach Gastric folds, or ‘rugae’ line the interior. Rugae allow the stomach to expand after eating and drinking, and increase the surface area for digestion.  Stomach Major functions include: Stores food & gradually releases it to the small intestine at a rate suitable for proper digestion, neutralization & absorption Assists in the mechanical breakdown of food via peristalsis & churning contractions. Glands secrete enzymes such as pepsin & lipase, Secretes mucin & HCl (2L/day @ pH 1.5-2) to facilitate the breakdown of proteins Kills bacteria Absorption of alcohol & aspirin (ASA) directly into blood at the Stomach: sphincters Sphincters are circular muscles that control the passage of materials by opening & closing found in the gastrointestinal tract, urinary system, blood vessels & eyes. the stomach has 2 sphincters: ⚬ cardiac sphincter ⚬ pyloric sphincter  Cardiac sphincter ring of muscle at the junction of the esophagus & stomach, prevents stomach contents from backwashing up & burning (Heartburn)  Pyloric sphincter ring of circular muscle at the junction of the stomach & small intestine, regulates the passage of food out of the stomach Contracts about once every 20 seconds, releasing 1 tsp of chyme out Small Intestine coiled narrow tube, approximately 3m long, with a diameter of 2-5cm 2 main functions: ⚬ digests small pieces of food from the stomach into small molecules, with help from liver, pancreas & SI lining cells ⚬ absorbs these molecules into the  Small Intestine secretes an alkaline mucin (pH 7.2-9) to neutralize acidic chyme, secretes digestive enzymes, including: ⚬ intestinal amylase - hydrolyzes carbohydrates ⚬ peptidases - hydrolyzes proteins ⚬ lipase - acts on lipids ⚬ lactase - breaks down lactose  Small Intestine Numerous foldings (lumen), projections (villi) & minute projections (microvilli) vastly increase the surface area inside the SI to maximize absorption. microvilli lumen villi  Small Intestine Villi move gently back & forth in chyme movement increases exposure to molecules & facilitates absorption. Rhythmic contractions of circular muscles slosh chyme around & forward Nutrients absorbed include: ⚬ water (75% reabsorbed here by osmosis) ⚬ monosaccharides, ⚬ amino acids & peptides, ⚬ fatty acids,  Small Intestine Each villus has a rich supply of blood capillaries & a lymph capillary (lacteal) Sugars & amino acids diffuse into the blood, while fats diffuse into the lacteal blood capillaries lacteal Small Intestine is divided into 3 unequal sections: ⚬ duodenum (beginning) ⚬ jejunum (middle) ⚬ ileum (end) there is no obvious separation between the sections, though each has a slightly different role  first ~25cm Duodenum curves into a ‘c’ shape monomers digested here bile duct pancreas walls secrete digestive enzymes ducts from liver (gall bladder) & pancreas secrete digestive gall bladder materials duodenum Duodenum duodenum  Jejunum coiled middle section occupies around half of the remaining length of the small intestine has abundant blood vessels, which give it a deep red color absorbs the digested nutrients at jejunum villi & lacteals ileum  Ileum Last section of the small intestine walls are thinner & narrower less blood supply than jejunum absorbs most of the digested nutrients and water jejunum ileum  is the largest organ inside the body, Liver it lies just above & left of the stomach stores carbohydrates in the form of glycogen for energy regulates blood glucose levels synthesizes blood proteins stores iron & vitamins converts toxic ammonia, from amino acid digestion, into urea detoxifies nicotine & alcohol produces BILE, a yellow/green alkaline liquid (pH ~7.6), about 700mL per day Liver: gall bladder Gall bladder is the storage site for bile Bile contains bile salts, bile pigments (bilirubin & biliverdin) & cholesterol. There are NO ENZYMES in bile. Bile reduces the acidity of the gut, helps excrete drugs & dyes from the body, and emulsifies fats. It aids in the dispersal of globs of fat in chyme into microscopic particles, this increasing the  Pancreas a long, lumpy organ behind the stomach. consists mostly of glands that secrete ‘pancreatic fluid’, an enzyme soup containing: ⚬ pancreatic amylase - digests starch & glycogen into maltose ⚬ lipase breaks emulsified fats into fatty acids & glycerol ⚬ sodium bicarbonate – NaHCO3, helps neutralize chyme, protects intestines, provides correct pH for intestinal enzymes. ⚬ trypsin, chymotrypsin, carboxypeptidase - all are proteases that digest proteins & large polypeptides into small  Pancreas Different proteases break polypeptides at different places: ⚬ trypsin at basic amino acids (arg, lys, his) ⚬ chymotrypsin at aromatics (phe, trp, tyr) ⚬ carboxypeptidase at -COOH end.  Pancreas Pancreatic secretions are triggered by: 1) expectation of food 2) smell/taste of food 3) distention of the stomach The pancreas also contains cells that produce hormones to help regulate blood sugar. Large Intestine 1.5m long, 7.5cm diameter Consists of 2 mains parts: ⚬ Colon (most of the L.I.) ⚬ Rectum (last 15cm). At the juncture of the small & large intestine is the appendix – a small sac, with minimal function in humans, a vestigial organ. Leftovers of digestion (H2O, undigested fats, fibre, etc) enter the large intestine Large Intestine secretes mucin to lubricate food remnants reabsorbs salts & water contains a large population of bacteria (E. coli & other coliforms) that live on unabsorbed nutrients, Coliforms help by synthesizing vitamin B12, thiamine, riboflavin & vitamin K (otherwise deficient in a normal diet), which are than absorbed by cells lining the colon Large Intestine No enzymes, no digestion occurs here Feces formed ⚬ 75% water, ⚬ 25% indigestible waste & dead bacteria Feces are brown because of bilirubin. Peristaltic contractions carry feces to the rectum, where it is compacted & stored until defecation. Stretch receptors in rectum stimulate defecation