Anatomy Unit 3 -- Digestive System
Identify the two major cell types in the epithelial lining of the large intestine and their functions.
--outer longitudinal layer of muscularis externa is in three thickened strips *2 types of cells* 1) Absorptive Cells: microvilli, absorb water & electrolytes 2) Goblet Cells: produce mucus
Describe two functions of the colon/large intestine
1) Absorption of Water & Electrolytes (& vitamins) 2) Production of Vitamins --also production of feces
Describe the anatomy of the ducts that carry the secretions to the small intestine .
1) Cystic duct contains bile from the gall bladder 2) Hepatic duct contains bile from the liver 3) Join together to form the common bile duct 4) Common bile duct combines with the pancreatic duct to secrete bile and digestive enzymes into the small intestine
Identify the three segments of the small intestine. Describe a distinguishing feature of each segment and its functional significance
1) Duodenum -- contain Brunner's glands which are mucous glands in the submucosa that secrete bicarbonate-rich mucus to neutralize acids 2) Jejunum -- increased number of plicae circularis 3) Ileum -- peyer's patches are lymphoid nodules in the submucosa, secondary lymphoid organs
Describe the two cell types in the epithelium of the small intestine and their functions.
1) Enterocytes --secrete enzymes into the lumen and absorb nutrients and water 2) Enteroendocrine cells --secrete hormones into the blood stream, only in the crypts *simple columnar epithelium w/microvilli*
Identify the three glands which empty into the small intestine. Describe the secretion(s) of each gland.
1) Liver: produces bile, processes absorbed substances 2) Gall Bladder: stores bile 3) Pancreas: produces digestive enzymes and pancreatic juice
Describe the four layers present in the wall of the digestive tract. * SUBMUCOSA*
1) Loose CT & Blood Vessels 2) *Submucosal Plexus*
Explain the three main functions of the stomach.
1) Mechanical Digestion & Propulsion 2) Chemical Digestion 3) Storage of Food 4) Absorption (a little)
What are the four layers present in the wall of the digestive tract?
1) Mucosa 2) Submucosa 3) Muscularis Externa 4) Serosa *lumen is the in the middle of all layers collectively*
Describe the layers of the esophagus in detail
1) Mucosa -- stratified squamous epithelium 2) Muscularis Externa --upper third is skeletal muscle --middle third is mixed muscle --lower third is smooth muscle
Describe the muscularis externa layer of the stomach. Explain the functional significance of its unique organization.
1) Outer longitudinal 2) Inner circular 3) Innermost oblique The functional significance is that the stomach has three muscle layers instead of the usual two. This is because it allows for churning and peristalsis to take place.
What are the predominant cell types at the gastric glands of the gastric mucosa?
1) Parietal Cells — produce HCl 2) Chief Cells — produce pepsinogen Pepsinogen + HCl = Pepsin —> zymogen that degrades food proteins into peptides.
Name and describe the three levels of folding in the lining of the small intestine. Explain the functional significance of this extensive folding.
1) Plicae Circularis "Circular Folds" --folds in the submucosa --covered with villi 2) Villi --folds in mucosa --covered w/intestinal cells containing microvilli 3) Microvilli --folds in cell membrane *These levels of folding together increase SA for secretion & absorption by 600 times*
What are the glands that are associated with the digestive tract?
1) Salivary Glands (3 of them) 2) Liver 3) Gall Bladder 4) Pancreas
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *ABSORPTION*
Absorption is the movement of molecules across the gastrointestinal (GI) tract into the circulatory system. Most absorption happens in small intestine.
Explain the course of venous blood leaving the small and large intestines.
All capillaries of the gut tract drain into: splenic vein, superior mesenteric vein, inferior mesenteric vein. The portal vein receives all the venous drainage from the gut.
Describe what an ulcer is and explain what causes ulcers.
An ulcer is an erosion of the stomach mucosa. It is caused by baceria called Heliobacter pylori. The bacteria damages the mucus layer, allowing acid to reach the mucosa. Treatment is 2 weeks of antibiotics. It was initially thought stress was the main reason for ulcers.
Describe the four layers present in the wall of the digestive tract. * MUSCULARIS EXTERNA*
At least 2 layers of smooth muscle 1) Inner circular layer 2) Outer longitudinal layer Then there is the *Myenteric Plexus*which is between the two layers
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *CHEMICAL DIGESTION*
Chemical digestion involves breaking down the food (using enzymes) into simpler nutrients that can be used by the cells. Chemical digestion begins in the mouth when food mixes with saliva.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *DEFECATION*
Defecation, also called bowel movement, the act of eliminating solid or semisolid waste materials (feces) from the digestive tract
Explain the cause of diarrhea and why it can be such a dangerous condition
Diarrhea is an increase in the volume of stool or frequency of defecation. It is can be caused by viruses, bacteria, or other syndromes. Normally, the lower small intestine and colon should absorb water from the liquid undigested food to a solid stool. But with diarrhea, the absorption doesn't happen and there is increased amounts of water in the stool or the undigested food passes too quickly through the small intestine and colon for enough water to be removed. It can cause severe dehydration because of the water and salt loss form the body. In infants, it can be deadly.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *DIGESTION*
Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma.
Describe where fats, carbohydrates, proteins, and toxins go after they are absorbed into the wall of the digestive tract.
Fats are absorbed across intestinal epithelium and into lacteals --> travel through lymph --> venous circulation via thoracic duct. Proteins, carbs, and toxins are absorbed across intestinal epithelium and into the blood capillaries --> the hepatic portal vein --> liver for processing and detoxification. They do not enter the general circulation until after the liver checks them out.
Explain two mechanisms by which gut motility is generated
Gut motility is generated within the gut itself by pacemaker cells (smooth muscle) and by the enteric nervous system.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *INGESTION*
Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth into the gastrointestinal tract, such as through eating or drinking.
What is the enteric nervous system?
It is made of 2 plexuses (nerve cell bodies and fibers) 1) Submucosal Plexus -- controls mucosal glands and muscle 2) Myenteric Plexus -- controls muscularis externa It is regulated by the ANS and sends info back to the CNS.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *MECHANICAL DIGESTION*
Mechanical digestion involves physically breaking the food into smaller pieces. Mechanical digestion begins in the mouth as the food is chewed.
What are the predominant cell types at the surface of the gastric mucosa?
On the surface, the gastric mucosa contains epithelial cells.
Describe the four layers present in the wall of the digestive tract. *SEROSA*
Outermost layer made up of loose connective tissue
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *PERISTALSIS*
Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed. Next, peristalsis continues in the small intestine and concludes in the large intestine.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *PROPULSION*
Propulsion is the movement of food along the digestive tract. Propulsion takes place pretty much everywhere along the digestive tract by means of swallowing and peristalsis.
Describe the two structures which are important for the control of defecation
Rectum 1) Internal Anal Sphincter -- involuntary smooth muscle 2) External anala sphincter -- voluntary skeletal muscle
Explain why these epithelial cells of the small intestine are so severely affected by chemotherapy and radiation treatments.
Since these cells turn over 5-7 days, these are easily damaged by chemotherapy and radiation because they target cells that are dividing rapidly.
Describe two ways in which smooth muscle cells are connected to each other. Explain the functional significance of those connections.
Smooth muscle have a physical connection by dense bodies and then it has a electrical connection by gap junctions.
Briefly describe each process performed by the digestive system. Know where each of these processes occurs in the gastrointestinal tract. *SWALLOWING*
Swallowing is taking a substance through the mouth and pharynx and into the esophagus. It is a combination of a voluntary act and series of reflex actions.
Describe the source of the blood supply to the digestive tract.
The blood supply to the gut comes from *the abdominal aorta* which is made up of the celiac trunk, superior mesenteric artery, and the inferior mesenteric artery 1) Celiac Trunk: supplies blood to stomach, liver, spleen, gall bladder, and pancreas 2) Mesenteric Arteries Superior: small intestine, first half of large intestine Inferior: last half of large intestine
Locate the esophagus. Describe the structure of its muscularis externa layer and the significance of the configuration of this muscle layer.
The esophagus connects the pharynx to the stomach. Its function is propulsion and peristalsis to push the bolus of food down. It is a muscular tube and is *made up mucosa and muscularis externa.*
Locate the two capillary beds which make up the hepatic portal system. Describe what happens within each capillary bed.
The first capillary bed is the stomach/intestines. In this one, nutrients and toxins enter capillaries within villi. The second one is the liver. In this one, nutrients and toxins leave capillaries within the liver.
Explain which organ will be damaged if too many toxins are absorbed in the digestive tract and why.
The first organ that will be damaged is the liver because it will be overwhelmed by all the toxins in the body. The toxins then might be able to enter the blood and irritate vital organs like the heart, brain, and kidneys if they remain in the circulation too long.
Gall Bladder: location & parts of the tract into which it secretes
The gall bladder is located underneath the liver and secretes storage bile into the duodenum.
What are the predominant cell types at the gastric pits of the gastric mucosa?
The gastric pit contains mucous cells that produce protective mucus. OUTER
Describe the four layers present in the wall of the digestive tract. * MUCOSA*
The internal layer of the mucosa is epithelium. The middle layer is lamina propia which is made up of loose CT, glands, blood vessels, lymphatic's. Finally, the outermost layer is composed of smooth muscle. 1) Muscularis Mucosa 2) Lamina Propia 3) Epithelium
Liver: location & parts of the tract into which it secretes
The liver is located above the stomach and next to it . It secretes bile into the duodenum directly or sent to the gall bladder for storage. The bile is used to emulsify fats.
Explain the roles of the mouth, and tongue in digestion.
The mouth is where ingestion occurs and we can take in food and liquids into the mouth. The tongue aids in mechanical digestion as we chew but also aids in propulsion because we push food into the pharynx using the tongue to initiate swallowing. The tongue is innervated by CN XII
Describe the structures that prevent damage to the stomach lining
The mucus layer protects the stomach lining from damage due to digestive juices.
Pancreas: location & parts of the tract into which it secretes.
The pancreas looks like chewed up gum that is located underneath the stomach and slightly behind it. The pancreas secretes digestive enzymes (amylases, lipases, peptidases) into the duodenum through the pancreatic duct. It also secretes insulin & glucagon into the circulatory system.
Identify which regions of the pharynx are part of the digestive system. Describe the role of the pharynx in digestion.
The pharynx, a tube of skeletal muscle, is made up of 3 parts. 1) Nasopharynx (resp. only) 2) Oropharynx (resp. & digest) 3) Larynxgopharynx (resp. & digestive) The oropharynx and laryngopharynx are the only ones involved in digestion. They help with propulsion and initiating swallowing.
Salivary Glands: location & parts of the tract into which they secrete.
The salivary glands aid in chemical digestion by production of salivary amylase to start breaking down the food. 1) Parotid Gland 2) Sublingual gland 3) Submandibular Gland They are stimulated by salivation -- CN VII & IX
Explain the general functions of the small intestine.
The small intestine is specialized for secretion and absorption by secreting enzymes and absorbing nutrients and water. The enteroendocrine cells also secrete hormones into the blood stream to tell other organs what to do
Describe the structures which prevent food from entering the nasal cavity and trachea during swallowing.
The soft palate (aka the uvula) helps prevent food from entering the nasal cavity and the trachea during swallowing. The epiglottis also helps to direct food to the esophagus/covering the airway.
Identify which two layers of the wall of the digestive tract contain nerve plexuses.
The submucosa and the muscularis externa contain nerve plexuses.
Explain which structure malfunctions to cause GastroEsophageal Reflux Disease (GERD).
When the cardiac sphincter does a shitty job, this causes "heartburn" because the gastric contents can go backward into the esophagus and cause inflammation of the esophagus.
