Digestive, Excretory & Urinary Systems Digestive, Excretory & Urinary Systems DIGESTION & ITS ORGANS

Gastrointestinal Tract  Is the pathway along which the process of digestion occurs  Digestion is the process of breaking down food into molecules that the body can use  It begins at the mouth and ends at the anus  It is divided into several distinct organs which are directly involved in the digestive process  There are additional organs, not part of the system that aid in digestion by providing secretions

Digestion  Includes the:  Mechanical & chemical breakdown of food into nutrients  Absorption of nutrients  Elimination of waste

The Mouth  The location of the mechanical phase of digestion  Incisors and molars cut & grind up your food  The tongue keeps food between your chewing surfaces  Chemical digestion also begins here  Salivary glands produce saliva: a mixture of water, mucus, & salivary amylase

Parts of the Mouth  Teeth  Tongue  Soft Palate  Hard Palate  Salivary glands  Pharynx

Salivary Glands  3 types:  Parotid  Sublingual  Submandibular  All produce saliva & salivary amylase whose function is to break down starch into maltose

Next step of Digestion  After food has been thoroughly chewed, moistened, and rolled into a ball: bolus  It is then forced into the pharynx by swallowing action  The bolus passes into the esophagus and gets pushed down through a series of rhythmic muscular contractions & relaxations: peristalsis

Peristalsis

Esophagus  Is a muscular tube approx. 25 cm long that runs form the back of the mouth to the stomach

Esophagus

Step 3 of Digestion  Takes place in the stomach  By now the bolus is now fairly well minced and turned into a pulpy mass as it passes into the stomach  The mechanical action of the muscles in the stomach constrict and relax in a continuous motion blending, whipping, and stirring the stomach's contents into chyme  Chyme is a pulpy substance that can be handled by the small intestine.

Stomach  Is involved in both mechanical & chemical digestion  Located in the upper left side of the abdominal cavity & just below the diaphragm  It is an elastic bag that is J-shaped, when full and lies in folds when empty  It looks like a deflated balloon when empty, but when full, it becomes about a foot long and six inches wide  It is able to hold about two quarts of food and drink.

Stomach Continued  The function of the stomach is best described as a food processing unit and a storage cistern  Various chemicals in the stomach like the digestive enzymes interact to break down the food  Digestive enzymes of the stomach include: pepsin, rennin, & lipase  Hydrochloric acid creates suitable environment for the enzymes and assists in the digestion  A watery mucus provides a protective lining for the muscular walls of the stomach so it will not be digested by the acid or enzymes

Mechanical Digestion In detail  As food enters the stomach, the esophageal sphincter closes to prevent food from reentering the esophagus  Food remains in the stomach for 3-4 hours  Muscle contractions churn the contents, breaking them down and mixing them with gastric fluid

Stomach Anatomy  The stomach is composed of six tissue layers  From the outside in they are:  Serosa  Muscularis  Submucosa  Lamina muscularis  Mucosa  Gastric surface

Stomach Anatomy  The walls of the stomach have several layers of smooth muscle  Circular  Longitudinal  Diagonal  These muscles work together to churn the contents of the stomach

Internal Stomach Anatomy  The inner lining of the stomach is a thick, wrinkled mucous membrane composed of epithelial cells  Inside of this membrane are small openings called gastric pits  Gastric pits: are open ends of gastric glands, which release secretions from special cells  These secretions make up the acidic digestive fluid

Stomach Wall Anatomy

4 Major Secretory Cells 1. Chief cells  Produces pepsinogen  When pepsinogen enters the low pH environment of the stomach it becomes the digestive enzyme pepsin  Pepsin is responsible for digesting proteins

4 Major Secretory Cells 2. Parietal cells  Produce HCl (hydrochloric acid)  Antacids work by block the receptors which control HCl secretion  Also produce intrinsic factor, which binds to and allows B12 absorption in the intestines

4 Major Secretory Cells 3.G-cell  secretes gastrin hormone  gastrin activates gastric juice secretion & gastric smooth muscle “churning”  gastrin also activates the gastroileal reflex which moves chyme from the ileum to the colon in the intestines

4 Major Secretory Cells 4.Mucus cells  Produce mucus which protects against acids and digestive enzymes

Chemical Digestion  Is done by gastric fluid which contains water, mucous, & digestive enzymes  Pepsin digests proteins by breaking them into short amino acid chains known as peptides  HCl provides the necessary low pH of 1.5 to 2.5 to active the enzymes, dissolve minerals, and kill bacteria

Chemical Digestion  Peristalsis forces chyme out of the stomach and into the small intestine through the pyloric sphincter  Each time the pyloric sphincter opens, approx. 5 to 15 ml of chyme moves into the small intestine  Chemical digestion continues in the small intestine

Accessory Organs to Digestion  The liver, gallbladder, & pancreas are accessory organs to the process of digestion  They perform several important functions including the production of secretions  They do not come directly in contact with food

The Liver  Is located to the right of the stomach  Not only an organ but the largest gland of the body  Its main functions are to filter and process nutrient-rich blood & aid in digestion  Additional functions include:  Storing glucose as glycogen  Regulates lipid metabolism: such as making cholesterol  Making proteins  Breaking down toxins  Secretes & makes bile

Bile  Is a bitter, alkaline, brownish-yellow or greenish-yellow fluid  It aids in the emulsification, digestion, and absorption of fats  Made up of bile salts & bilirubin  Bilirubin is the main pigment of bile

Gallbladder  Is a cm, dark green saclike organ found underneath the liver  Also known as the cholecyst  Its functions include:  Store & release bile (50 mL)  Stimulate the release of cholecystokinin

Pancreas  Lies beneath the stomach  It is an organ & a gland  It has several functions  It produces several enzymes & secretions

Pancreas Functions  Acts as in endocrine gland by producing hormones to regulate blood sugar levels, specifically insulin  Two roles in the digestive system:  Produces sodium bicarbonate to neutralize stomach acid  Produces enzymes to break down carbohydrates, lipids, proteins & nucleic acids

Pancreas Enzymes  Pancreatic amylase -breaks down carbohydrates  Pancreatic lipase -breaks down lipids  Trypsin-comes from the precursor trypsinogen, and digests proteins  Chymotrypsin-comes from the precursor Chymotrypsinogen, and digests proteins  Nucleases: digests nucleic acids  DNAase  RNAase