Digestive System

Identify the pancreatic acini and discuss their functions.

Acinar cells are the exocrine (exo=outward) cells of the pancreas that produce and transport enzymes that are passed into the duodenum where they assist in the digestion of food.

Identify the structure of a gastric gland including the location of the chief (zymogenic) cells, parietal cells, and mucous cells, and discuss the functions of each.

G-cells: sense presence of food and release the hormone gastrin(only functions when in acid) which activates chief and parietal cells Parietal cells: secrete HCl/hydrochloric acid Chief Cells: secrete enzymes that digest proteins and fats. Mucous Cells: protect stomach from acidity

Describe the major functions of the digestive system.

Ingest food/nutrients Mechanically and chemically digest food Propel food Absorb nutrients into bloodstream Eliminate wastes

Name the lobes of the liver

Left Right Caudate (extension of right lobe...superior, next to hepatic vein) Quadrate (extension of right lobe...inferior, next to gallbladder)

Identify the mesentery proper and explain its function.

Mesentery: anchors intestines to dorsal wall of body cavity Omentum: anchors stomach

Identify, and describe the histological structure and the function of, each of the four layers of the wall - the mucosa, the submucosa, the muscularis externa, and the serosa (visceral peritoneum).

Mucosa=inner layer, closest to lumen, composed of epithelial tissue, secretes digestive enzymes, mucus and hormones, absorbs end products of digestion and protects against infectious disease...has three sublayers: epithelium, lamina propria(connective tissue) and muscularis mucosae Submucosa=outside of mucosa, composed of dense connective tissue, contains blood and lymph vessels Muscularis externa=outside of submucosa, composed of smooth muscle (outer: longitudinal and inner:circular), responsible for mixing/segmentation and peristalsis/moving of food Serous Membrane: outermost, visceral peritoneum

Describe regional specializations in the histological structure of the alimentary canal and relate these specializations to the functions of the particular organs in which they are located.

Oral cavity Pharynx Esophagus Stomach Small intestine Large intestine The accessory digestive organs are the tongue, salivary glands, pancreas, liver, and gallbladder.

Identify the hepatic duct, cystic duct, gallbladder, common bile duct, sphincter of the hepatopancreatic ampulla and discuss the roles of those structures in the flow of bile.

Bile flows out of the liver through the left and right hepatic ducts, which come together to form the common hepatic duct. This duct then joins with a duct connected to the gallbladder, called the cystic duct, to form the common bile duct. The common bile duct enters the small intestine at the sphincter of Oddi/hepatopancreatic sphincter (a ring-shaped muscle), located a few inches below the stomach. About half the bile secreted between meals flows directly through the common bile duct into the small intestine. The rest of the bile is diverted through the cystic duct into the gallbladder to be stored. In the gallbladder, up to 90% of the water in bile is absorbed into the bloodstream, making the remaining bile very concentrated. When food enters the small intestine, a series of hormonal and nerve signals triggers the gallbladder to contract and the sphincter of Oddi to relax and open. Bile then flows from the gallbladder into the small intestine to mix with food contents and perform its digestive functions. After bile enters and passes down the small intestine, about 90% of bile salts are reabsorbed into the bloodstream through the wall of the lower small intestine. The liver extracts these bile salts from the blood and resecretes them back into the bile.

Explain the Valsalva maneuver and the effects it has on the process of defecation and on the cardiovascular system.

The Valsalva maneuver is a particular way of breathing that increases pressure in the chest. The Valsalva maneuver is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth, pinching one's nose shut while pressing out . This will increase blood pressure and increase heart rate. This contraction of expiratory chest muscles, diaphragm, abdominal wall muscles, and pelvic diaphragm exerts pressure on the digestive tract. In result, it helps defecate.

Define emulsification.

The breakdown of fat globules in the duodenum into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol. (if you are without a gallbladder, avoid fats because bile salts are stored here and bile salts help emulsify fats)

Describe the structure and discuss the function of the cardiac and pyloric sphincters.

The cardiac sphincter prevents acidic contents of stomach going back up into the esophagus. The pyloric sphincter regulates output to the small intestine. The upper esophageal sphincter (UES) is a bundle of muscles at the top of the esophagus. The muscles of the UES are under conscious control, used when breathing, eating, belching, and vomiting. They keep food and secretions from going down the windpipe. The lower esophageal sphincter (LES) is a bundle of muscles at the low end of the esophagus, where it meets the stomach. When the LES is closed, it prevents acid and stomach contents from traveling backwards from the stomach. The LES muscles are not under voluntary control.

Describe the defecation reflex and the function of the internal and external anal sphincters.

The defecation reflex occurs when the internal anal sphincter relaxes and the external anal sphincter contracts. Waves of muscular contraction (known as peristalsis) in the walls of the colon move fecal matter through the digestive tract towards the rectum. Then our feces gets excreted.

Describe the structure and discuss the function of the ileocecal valve and the internal and external anal sphincters.

The ileocecal valve is a sphincter muscle situated at the junction of the ileum (last portion of your small intestine) and the colon (first portion of your large intestine). Its function is to allow digested food materials to pass from the small intestine into your large intestine. Internal anal sphincter External anal sphincter

Identify the pancreatic islets and discuss their functions.

The islets of Langerhans are the endocrine (endo= within) cells of the pancreas that produce and secrete hormones such as insulin and glucagon into the bloodstream. The pancreatic hormones, insulin and glucagon, work together to maintain the proper level of sugar (glucose) in the blood. Blood sugar is used by the body for energy.

With respect to monosaccharides, peptides and amino acids, and fatty acids and monoglycerides: List the organs and specific structures involved in the absorption of each of these types of nutrient.

All carbohydrates are absorbed in the form of monosaccharides. The small intestine is highly efficient at this, absorbing monosaccharides at an estimated rate of 120 grams per hour. All normally digested dietary carbohydrates are absorbed; indigestible fibers are eliminated in the feces. Active transport mechanisms, primarily in the duodenum and jejunum, absorb most proteins as their breakdown products, amino acids. Almost all (95 to 98 percent) protein is digested and absorbed in the small intestine. About 95 percent of lipids are absorbed in the small intestine. Bile salts not only speed up lipid digestion, they are also essential to the absorption of the end products of lipid digestion. Short-chain fatty acids are relatively water soluble and can enter the absorptive cells (enterocytes) directly.

Identify the location and discuss the relative length and the functions of the duodenum, jejunum, and ileum.

Duodenum: about 15 inches long, branches off from the stomach, ducts from the pancreas and gallbladder connect here, most intestinal enzymes secreted here, not much absorption of nutrients here Jejunum: about 8 feet long, absorbs nutrients, mixes enzymes due to its muscular structure(peristalsis and segmentation), food moves quickly, located inferior to transverse colon and branches off of duodenum Ilium: located inferior to jejunum, last bit of small intestine, about 10 feet long, less muscular so food slows down and nutrients get absorbed, peyer's patches only found here

Identify the structures of the stomach and the function of the organ overall

Esophagus Cardia Fundus Body Three layers in muscularis externa: longitudinal, circular and oblique The ridges inside the stomach (mucosal layer) are called rugae: they increase surface area Pylorus Lesser curvature Greater Curvature Duodenum Function=The gastric glands in the stomach secretes acid and enzymes that digest food. The stomach muscles contract periodically, churning food to enhance digestion. Gastric juices also help kill bacteria that might have been eaten.

Identify the hepatic artery, hepatic portal vein, and hepatic vein and discuss the function of each of those blood vessels.

Hepatic portal Vein:Delivers deoxygenated, nutrient rich blood from digestive system Hepatic artery: Contains oxygenated blood from aorta

Identify the histological components of a liver lobule (hepatocytes and the components of a hepatic triad) and discuss the function of each.

Hepatocytes: liver cells, produce bile, which then passes through the bile ducts to be stored in the gallbladder. When food containing fats reaches the duodenum,Hepatocytes metabolize hemoglobin, the red oxygen-carrying pigment of red blood cells, into the components heme and globin. Globin protein is further broken down and used as an energy source for the body. The iron-containing heme group cannot be recycled by the body and is converted into the pigment bilirubin and added to bile to be excreted from the body. Bilirubin gives bile its distinctive greenish color. Intestinal bacteria further convert bilirubin into the brown pigment stercobilin, which gives feces their brown color, absorb fatty acids from digested lipids Sinusoids: permeable capillaries Central Vein: receive the blood mixed in the liver sinusoids and return it to circulation via the hepatic veins. Kupffer cells: macrophages that engulf pathogens Bile caniculi: channels for bile...drain into bile ducts of liver

Define chemical and mechanical digestion.

Mechanical digestion: physical act of breaking down the food by non-chemical means. Mechanical digestion begins in the mouth by the physical act of mastication/chewing Chemical digestion: breakdown of food in the mouth, stomach and intestines through the use of acids and enzymes.

List the organs and structures of the digestive system that function in chemical and mechanical digestion and explain the details of the process for each.

Mouth and Stomach are mechanical digestion organs With the use of teeth, the mouth breaks down food when we chew. In the stomach, segmentation (the back and forth mixing of food) results in breakdown of food. Chemical digestion occurs in the stomach were Hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.

Describe the location of the parotid, submandibular, and sublingual glands and their respective ducts.

Parotid gland: anterior to the ear and external to the masseter muscle...parotid duct opens into the vestibule next to the second upper molar Submandibular gland: medial to the body of the mandible...duct opens at the base of the lingual frenulum Sublingual gland: anterior to submandibular gland under the tongue..opens via 10-12 ducts into the floor of the mouth

Identify the location and discuss the functions of the cecum,appendix and the large intestine, rectum, and anus.

The main functions of the cecum are to absorb fluids and salts that remain after completion of intestinal digestion and absorption and to mix its contents with a lubricating substance, mucus. The internal wall of the cecum is composed of a thick mucous membrane, through which water and salts are absorbed. Function of appendix is unknown. One theory is that the appendix acts as a storehouse for good bacteria, "rebooting" the digestive system after diarrheal illnesses. Ions and nutrients released by gut bacteria and dissolved in water are also absorbed in the large intestine and used by the body for metabolism. The dried, condensed fecal matter is finally stored in the rectum and sigmoid colon until it can be eliminated from the body through the process of defecation. The anus controll the expulsion of feces, unwanted semi-solid matter produced during digestion,

Explain the processes involved in absorption of each type of nutrient.

The monosaccharides glucose and galactose are transported into the epithelial cells by common protein carriers via secondary active transport (that is, co-transport with sodium ions). The monosaccharides leave these cells via facilitated diffusion and enter the capillaries through intercellular clefts. The monosaccharide fructose (which is in fruit) is absorbed and transported by facilitated diffusion alone. The monosaccharides combine with the transport proteins immediately after the disaccharides are broken down. The type of carrier that transports an amino acid varies. Most carriers are linked to the active transport of sodium. Short chains of two amino acids (dipeptides) or three amino acids (tripeptides) are also transported actively. However, after they enter the absorptive epithelial cells, they are broken down into their amino acids before leaving the cell and entering the capillary blood via diffusion. Despite being hydrophobic, the small size of short-chain fatty acids enables them to be absorbed by enterocytes via simple diffusion, and then take the same path as monosaccharides and amino acids into the blood capillary of a villus.

Identify the pancreatic duct and the hepatopancreatic sphincter and discuss their roles in the flow of pancreatic enzymes.

The pancreatic duct: this large duct carries the digestive enzymes down the length of the pancreas, from the tail to the head section, and into the duodenum. The common bile duct also runs through the head section of the pancreas, carrying bile from the liver and gallbladder into the small intestine. The bile duct and pancreatic duct usually join just before entering the duodenum and share a common opening into the small intestine. The Hepatopancreatic sphincter: opens to allow bile and pancreatic juice to flow through, and then closes again. If hepatopancreatic sphincter is open, bile goes straight from liver to duodenum. If closed, bile stores into the gallbladder.

List the structures involved in the process of deglutition/chewing and explain how they function, including the changes in position of the glottis and larynx that prevent aspiration.

Tongue Hard Palate Soft Palate Pharyngeal muscles Esophagus Gastroesophageal junction When we swallow, the epiglottis covers the larynx so the food goes into the esophagus. Humans need to elevate the larynx and move it anteriorly during swallowing to prevent aspiration. This motion causes the epiglottis, which is sandwiched between the base of the tongue and framework of the larynx to protect the lower airway. The vocal folds themselves also participate in prevention of aspiration during swallowing by closing the glottis.

Identify and discuss the histology and functions of the villi and microvilli.

Villi: small "fingers" of epithelium Microvilli: microscopic projections on membranes of mucosal cells (sometimes referred to as "brush border") All three increase surface area to allow for more absorption to take place in the small intestine.