Digestive system

Bile

- A mixture secreted by the liver to accomplish the emulsification of lipids in the small intestine. A yellow-brown or yellow-green alkaline solution (pH 7.6 to 8.6), bileis a mixture of water, bile salts, bile pigments, phospholipids (such as lecithin), electrolytes, cholesterol, and triglycerides. The components most critical to emulsification are bile salts and phospholipids, which have anonpolar (hydrophobic) region as well as a polar (hydrophilic) region. The hydrophobic region interacts with the large lipid molecules, whereas the hydrophilic region interacts with the watery chyme in the intestine. This results in the large lipid globules being pulled apart into many tiny lipid fragments of about 1 μm in diameter. This change dramatically increases the surface area available for lipid-digesting enzyme activity. This is the same way dish soap works on fats mixed with water.

Bile salt

- Acts as emulsifying agents, so they are also important for the absorption of digested lipids. While most constituents of bile are eliminated in feces, bile salts are reclaimed by the enterohepatic circulation. Once bile salts reach the ileum, they are absorbed and returned to the liver in the hepatic portal blood. The hepatocytes then excrete the bile salts into newly formed bile. Thus, this precious resource is recycled.

Pancreas function

- An exocrine and endocrine gland the excretes enzymes to break down the proteins, lipids, carbohydrates, and nucleic acids in food. Secretes the hormones insulin and glucagon to control blood sugar levels throughout the day.

Circular folds

- Beginning near the proximal part of the duodenum and ending near the middle of the ileum, these folds facilitate absorption. Their shape causes the chyme to spiral, rather than move in a straight line, through the small intestine. Spiraling slows the movement of chyme and provides the time needed for nutrients to be fully absorbed.

Bile storage

- Bile is stored in the gallbladder until it is needed for digesting fatty foods in the duodenum of the small intestine.

Structures of the Stomach

- Cardia ( cardiac region): The ponit where the esophagus connects to the stomach and through which food passes into the stomach. - Fundus: Located inferior to the diaphragm. Stores both undigested food and gases that are released during the process of chemical digestion. - Body: mid portion of the stomach - Pylorus : connects the stomach to the duodenum - Pyloric atrium: connects to the body of the stomach - Pyloric Sphincter: located at the latter point of connection and controls stomach emptying. - Ruga: A large fold that when there is an absence of food, the stomach deflates inward, and it mucosa and submucosa fall in to it. - Inner oblique smooth muscle layer gives the muscularis the ability to vigorously churn and mix food.

Lower Esophageal Sphincter

- Controls the movement of food from the esophagus to the stomach.

Upper Esophageal Sphincter

- Controls the movement of food from the pharynx to the esophagus.

Liver Function

- Filter the blood coming from the digestive tract, before passing it to the rest of the body. Detoxifies chemicals and metabolizes drugs. As it does so, it secretes bile that ends up back in the intestines.

Intestinal Glands

- In addition to the three specialized absorptive features just discussed, the mucosa between the villi is dotted with deep crevices that each lead into a tubular; formed by cells that line the crevices.

Jejunum

- Most of the nutrients present in food are absorbed by the here before being passed on to the ileum for further absorption.

Digestive organs

- Mouth: Ingests food, chews and mixes food, begins chemical breakdown of carbohydrates, moves food into the pharynx, and begins breakdown of lipids via lingual lipase. - Pharynx: Propels food from the oral cavity to the esophagus. - Esophagus: Propels food to the stomach. - Stomach: Mixes and churns food with gastric juices to form chyme, begins breakdown of proteins, releases food into the duodenum, as chyme, absorbs some fat-soluble substances (ex. alcohol and aspirin) - Small intestine: Mixes chyme with digestive juices, propels food at a rate slow enough for digestion and absorption, absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, mineral, and water. performs physical digestion via segmentation. - Large intestine: further breaks down food residues, absorbs most residual water, electrolytes, and vitamins produces by enteric bacteria, propels feces toward rectum, and eliminates feces.

Stomach cells

- Mucous cells: Secrete an alkaline mucus that protects the epithelium against shear stress and acid. protects from the corrosive nature of gastric acid. - Parietal cells: Hydochloric acid - Chief cells: Secrete pepsin, a proteolytic enzyme. - G cells: Secrete the hormone gastrin

Esophagus

- Muscular tube that connects the pharynx to the stomach. 25.4 cm in length, located poserior to the trachea, remains in a collapsed form when not engaged in swallowing. Runs straight through the mediastinum of thorax. To enter the abdomen, the esophagus penetrates the diaphragm through an opening called the esophageal hiatus.

Gastric Pits

- Narrow channel formed by the epithelial lining of the stomach mucosa.

Digestive function of the large intestine: Chemical digestion

- Occurs because of bacteria in the lumen of the colon. A process called sacccharolytic fermentation: bacteria breaks down remaining carbohydrates, results in discharge of hydrogen, carbon dioxide, and methane gases the create flatus/gas.

Duodenum

- Receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine. Many chemical secretions from the pancreas, liver and gallbladder mix with the chyme in the duodenum to facilitate chemical digestion.

Salivary glands

- Secrete saliva - Moisten and lubricate the lining of the mouth and pharynx. - Moisten, soften, and dissolve food - Clean the mouth and teeth - Salivary amylase breaks down starch

Gastrin

- Stomach: Increases secretions by gastric gland; promotes gastric emptying. - Small intestine: Promotes intestinal muscle contraction. - ileocecal valve: Relaxes valve - Large intestine: Triggers mass movement.

Drainage of digestive enzymes

- The entry of acidic chyme into the duodenum stimulates the release of secretin, which in turn causes the duct cells to release bicarbonaterich pancreatic juice. The presence of proteins and fats in the duodenum stimulates the secretion of CCK, which then stimulates the acini to secrete enzyme-rich pancreatic juice and enhances the activity of secretin.

Small intestine

- Where 90% digestion occurs and also the absorption of food.

Villi

- Within the circular folds are small (0.5-1 mm long) hairlike vascularized projections called villi (singular = villus) that give the mucosa a furry texture. There are about 20 to 40 villi per square millimeter, increasing the surface area of the epithelium tremendously. The mucosal epithelium, primarily composed of absorptive cells, covers the villi. In addition to muscle and connective tissue to support its structure, each villus contains a capillary bed composed of one arteriole and one venule, as well as a lymphatic capillary called a lacteal. The breakdown products of carbohydrates and proteins (sugars and amino acids) can enter the bloodstream directly, but lipid breakdown products are absorbed by the lacteals and transported to the bloodstream via the lymphatic system.

Microvilli

- are much smaller (1 μm) than villi. They are cylindrical apical surface extensions of the plasma membrane of the mucosa's epithelial cells, and are supported by microfilaments within those cells. Although their small size makes it difficult to see each microvillus, their combined microscopic appearance suggests a mass of bristles, which is termed the brush border. Fixed to the surface of the microvilli membranes are enzymes that finish digesting carbohydrates and proteins. There are an estimated 200 million microvilli per square millimeter of small intestine, greatly expanding the surface area of the plasma membrane and thus greatly enhancing absorption.

Digestive function of the large intestine: Mechanical digestion

- begins when chyme moves from the ileum into the cecum, an activity regulated by the ileocecal sphincter. Right after you eat, peristalsis in the ileum forces chyme into the cecum. When the cecum is distended with chyme, contractions of the ileocecal sphincter strengthen. Once chyme enters the cecum, colon movements begin. 3 types of movement: 1) haustral contraction: slow moving. 2) peristalsis: muscular contractions and relaxations that propel food through the GI tract. 3) mass movement: strong waves that start midway through the transverse colon quickly force the contents toward the rectum. occurs 3-4 times a day while eating or afterward

Liver Structure

- divided into two primary lobes: a large right lobe and a much smaller left lobe. In the right lobe, some anatomists also identify an inferior quadrate lobe and a posterior caudate lobe, which are defined by internal features.

Defecation reflexes

- eliminates feces from the rectum. a parasympathetic reflex mediated by the spinal cord. It contracts the sigmoid colon and rectum, relaxes the internal anal sphincter, and initially contracts the external anal sphincter. The presence of feces in the anal canal sends a signal to the brain, which gives you the choice of voluntarily opening the external anal sphincter (defecating) or keeping it temporarily closed. If you decide to delay defecation, it takes a few seconds for the reflex contractions to stop and the rectal walls to relax. The next mass movement will trigger additional defecation reflexes until you defecate.

Pancreas structure

- elongated 12-15 cm long organ consisting of head, body and tail. It is located posterior to stomach with its head in the curve of duodenum. The body and tail extends laterally. The tail touches the spleen.

Bile in fat digestion

- emulsifies fats: breaks them down to small droplets for a larger surface area. increases the rate of which fat is digested by lipase. neutralizes the acid production in the stomach to provide ideal alkaline conditions for enzymes in the small intestine.

Structure of large intestine

- it is more than twice the diameter of the small intestine, about 3 inches. - Cecum: sac-like structure that is suspended inferior to the ileocecal valve. Receives the contents of the ileum, and continues the absorption of water and salt. - Colon: Reabsorbs fluids and process waste products from the body and prepare for its elimination. 4 parts descending, ascending, transverse, and sigmoid. -Rectum: connects colon to anus. when anything comes into your rectum, sensors send a message to your brain. - Anal canal: Opens to the exterior of the body at the anus. Plays a role in fecal continence.

Accessory Organs

- liver: produces bile salts, which emulsify lipids, aiding their digestion and absorption. - Gallbladder: stores, concentrates, and releases bile. - Pancreas: produces digestive enzymes and bicarbonate.

Gastroileal reflex

- long reflex that increases the strength of segmentation in the ileum

Digestive of food Mouth:

- mechanical digestion includes chewing and swallowing. - Chemical digestion of carbohydrates and fats

Digestion of food Small Intestine:

- mechanical digestion includes mixing and propulsion, primarily by segmentation - chemical digestion of carbohydrates, fats, polypeptides, and nucleic acids - absorption of peptides, amino acids, glucose, fructose, fats, water, minerals, and vitamins

Digestion of food Stomach:

- mechanical digestion includes peristaltic mixing and propulsion. - chemical digestion of proteins and fats -absorption of lipid- soluble substances such as alcohol and aspirin

Digestion of food Large Intestine

- mechanical digestion includes segmental mixing and propulsion -no chemical digestion (except bacteria) -absorption of ions, water, minerals, vitamins, and organic molecules

Gastrocolic reflex

- propulsive movement in the colon activated by the presence of food in the stomach.

Bilirubin

- the main bile pigment, is a waste product produced when the spleen removes old or damaged red blood cells from the circulation. These breakdown products, including proteins, iron, and toxic bilirubin, are transported to the liver via the splenic vein of the hepatic portal system. In the liver, proteins and iron are recycled, whereas bilirubin is excreted in the bile. It accounts for the green color of bile. Bilirubin is eventually transformed by intestinal bacteria into stercobilin, a brown pigment that gives your stool its characteristic color! In some disease states, bile does not enter the intestine, resulting in white ('acholic') stool with a high fat content, since virtually no fats are broken down or absorbed.

Large intestine

- the terminal part of the alimentary canal. The primary function of this organ is to finish absorption of nutrients and water, synthesize certain vitamins, form feces, and eliminate feces from the body.

Salivary Glands

-To produce saliva, which begins digestion and lubricates food for swallowing. - submandibular glands: are in the floor of the mouth, secrete saliva into the mouth through the submandibular ducts. - Sublingual gland: lie below the tongue, used the lesser sublingual ducts to secrete saliva into the oral cavity. - Parotid gland: lie between the skin and the messeter muscle. neat the ears. The secrete saliva into the mouth through the parotid duct, which is near the second upper molar.

ileum

-absorb vitamin B12, bile salts, and whatever products of digestion were not absorbed by the jejunum

Components of Saliva

95.5% water, the remaining 4.5% is a complex mixture of ions, glycoproteins, enzymes, growth factor, and waste products. - enzyme salivary amylase: initiates the breakdown of carbohydrates.

Accessory digestive organs

Aid in the breakdown of food.

Function of the digestive system

Break down the foods you eat, release their nutrients, and absorb those nutrients into the body.

Layers of the digestive tract

Mucosa: Inner Layer- mucus-secreting membrane lining all body cavities or passages that communicate with the exterior. - Sub Mucosa: tissue layer under the mucosa; dense irregular connective tissue; contains blood vessels, lymphatic vessels, nerve fibers. - Serosa: outer layer or convering of the alimentary canal, made of visceral peritoneum; its function is protection and secretion of serous fluid to reduce friction. - Muscularis: consists of a circular inner muscular layer and a longitudinal outer muscular layer. The circular muscle layer prevents the food from going backwards and the longitudinal layer shortens the tract. The coordinated contractions of these layers is called peristalsis and propels the bolus, or balled-up food, through the GI tract.

Gastric Gland

Secrete a complex digestive fluid referred to as gastric juice. * Fundic glands *Cardic glands: located at the beginning of the stomach. secrets mucus, which coats and protects it from self-digestion by helping to dilute acids and enzymes. *Pyloric glands: in terminal portion of the stomach.coats and protects it from self-digestion by helping to dilute acids and enzymes.

Alimentary Canal Organs / GI Tract

The function of these organs is to nourish the body. Begins at the mouth and terminates at the anus.

Hepatocytes

work non-stop, but bile production increases when fatty chyme enters the duodenum and stimulates thesecretion of the gut hormone secretin. Between meals, bile is produced but conserved. The valve-like hepatopancreaticampulla closes, allowing bile to divert to the gallbladder, where it is concentrated and stored until the next meal.