Chapter 9: The Digestive System

The accessory organs of digestion originate from which primary germ layer?

As outgrowths of the gut tube, the accessory organs of digestion arise from embryonic endoderm.

Digestive track overview

Begins with the oral cavity followed by pharynx which is a share pathway for both food entering the digestive system and air entering the respiratory system from the pharynx food enters the esophagus which transports it to the stomach from the stomach food travels to the small and then large intestine waste products of digestion to enter the rectum where feces are stored until an appropriate time of release the salivary glands, pancreas, liver and gallbladder help to provide the enzymes and lubrication necessary to aid in the digestion of food

How do bile and pancreatic lipase work together to digest fats?

Bile accomplishes mechanical digestion of fats, emulsifying them and increasing their surface area. Pancreatic lipase accomplishes chemical digestion of fats, breaking their ester bonds.

What are the main components of bile?

Bile is composed of bile salts (amphipathic molecules derived from cholesterol that emulsify fats), pigments (especially bilirubin from the breakdown of hemoglobin), and cholesterol.

Where is bile synthesized? Where is bile stored? Where does bile carry out its digestive function?

Bile is synthesized in the liver, stored in the gallbladder, and serves its function in the duodenum.

Production of bile by liver

Bile production is one of the most significant jobs of the liver vis-à-vis the digestive system. bile is composed of bile salts, pigments, and cholesterol. Bile salts are amphipathic molecules that can emulsify fat in the digestive system. The major pigment in bile is bilirubin, which is a byproduct of the breakdown of hemoglobin. Bilirubin travels to the liver, where it is conjugated (attached to a protein) and secreted into the bile for excretion. If the liver is unable to process or excrete bilirubin (due to liver damage, excessive red blood cell destruction, or blockage of the bile ducts), jaundice or yellowing of the skin may occur.

Pancreatic juices

CCK also promotes the secretion of pancreatic juices into the duodenum Pancreatic juices are a complex mixture of several enzymes in a bicarbonate-rich alkaline solution. This bicarbonate helps to neutralize acidic chyme, as well as provide an ideal working environment for the digestive enzymes, which are most active around pH 8.5. Pancreatic juices contain enzymes that can digest all three types of nutrients: carbohydrates, fats, and proteins.

List at least one pancreatic enzyme that digests each of the three major classes of biomolecules:

Carbohydrates: pancreatic amylase proteins: trypsin, chymotrypsin, carboxypeptidases A and B fats: pancreatic lipase

Which of the following biomolecules does NOT drain in to the liver before arriving at the right side of the heart?

Cholecalciferol (Vitamin D) While the capillaries from the intestine come together to form the portal vein, which drains to the liver, the lacteals come together to form the thoracic duct, which drains directly into the left subclavian vein. Therefore, fat-soluble compounds do not pass through the liver before reaching the right heart. Only (A), vitamin D, is fat-soluble.

Glucagon and Ghrelin

Glucagon: pancrease Ghrelin: stomach and pancreas stimulate feelings of hunger

Six products that stomach secretes

HCl (kills microbes, denatures proteins, and converts pepsinogen into pepsin) Pepsinogen (cleaved in the stomach to pepsin; an enzyme that partially digests proteins) Mucus (protects mucosa) Bicarbonate (protects mucosa) Water (dissolves and dilutes ingested material) Intrinsic factor (required for normal absorption of vitamin B12)

Synthesis of proteins by the liver

In addition to bile production, processing of nutrients, and detoxification and drug metabolism, the liver also synthesizes certain proteins necessary for proper body function. These proteins include albumin, a protein that maintains plasma oncotic pressure and also serves as a carrier for many drugs and hormones, and clotting factors used during blood coagulation.

Absorption of water in small intestine

In addition to fats, carbohydrates, amino acids, and vitamins, the small intestine also absorbs water. Much of the water in chyme is actually the result of secretions. The average person may consume up to two liters of fluid per day, but secretions into the upper gastrointestinal tract may total up to seven liters of fluid per day. In order to maintain proper fluid levels within the body, much of this fluid must be reabsorbed by osmosis. As solutes are absorbed into the bloodstream, water is drawn with them, eventually reaching the capillaries. Water passes not only transcellularly (across the cell membrane), but also paracellularly (squeezing between cells) to reach the blood.

What is the difference between mechanical and chemical digestion?

Mechanical digestion, such as chewing, physically breaks down food into smaller pieces. Chemical digestion involves hydrolysis of bonds and breakdown of food into smaller biomolecules.

Trace the path of food through the body, starting with ingestion and ending with excretion of feces:

Oral cavity (mouth) → pharynx → esophagus → stomach → small intestine → large intestine → rectum → anus

What are the main enzymes found in saliva and what do they do

Salivary amylase (ptyalin): which digests starches into smaller sugars (maltose and dextrin) Lipase: digest fats

Absorption of fat in small intestine

Short-chain fatty acids will follow the same process as carbohydrates and amino acids by diffusing directly into the intestinal capillaries. These fatty acids do not require transporters because they are nonpolar, so they can easily traverse the cellular membrane. Larger fats, glycerol, and cholesterol move separately into the intestinal cells but then reform into triglycerides. The triglycerides and esterified cholesterol molecules are packaged into chylomicrons. Rather than entering the bloodstream, chylomicrons enter the lymphatic circulation through lacteals, small vessels that form the beginning of the lymphatic system. These lacteals converge and enter the venous circulation at the thoracic duct in the base of the neck, which empties into the left subclavian vein.

Absorption of carbohydrates and proteins in the small intestines

Simple sugars, such as glucose, fructose, and galactose, and amino acids are absorbed by secondary active transport and facilitated diffusion into the epithelial cells lining the small intestine Then, these substances move across the epithelial cell membrane into the intestinal capillaries. Blood is constantly passing by the epithelial cells, carrying the carbohydrate and amino acid molecules away. This creates a concentration gradient such that the blood always has a lower concentration of monosaccharides and amino acids than inside the epithelial cells. Thus, simple carbohydrates and amino acids diffuse from the epithelial cells into the capillaries. The absorbed molecules then go to the liver via the hepatic portal circulation.

Key concept:

The chemical digestion of carbohydrates is initiated in the mouth, but is completed in the small intestine. Salivary amylase (active in the mouth) and pancreatic amylase (active in the small intestine) have the same function.

What are the four fat-soluble vitamins?

The fat-soluble vitamins are A, D, E, and K.

Key concept: liver

The functions of the liver include processing and synthesis of nutrients (glycogenesis and glycogenolysis, storage and mobilization of fats, gluconeogenesis), production of urea, detoxification of chemicals, production of bile, and synthesis of albumin and clotting factors.

Gall bladder

The gallbladder is located just beneath the liver and both stores and concentrates bile. Upon release of CCK, the gallbladder contracts and pushes bile out into the biliary tree. The bile duct system merges with the pancreatic duct, before emptying into the duodenum. The gallbladder is a common site of cholesterol or bilirubin stone formation. This painful condition causes inflammation of the gallbladder. The stones may also travel into the bile ducts and get stuck in the biliary tree. In some cases, stones can get caught just before entering the duodenum, resulting in blockage of not only the biliary tree, but the pancreatic duct as well, causing pancreatitis.

Bacteria and the intestine

The large intestine—and even the small intestine—is home to many different species of bacteria. In fact, 30 percent of the dry matter in stool consists of bacteria. Most of these bacteria are anaerobes, but the cecum is also home to many aerobic bacteria. The presence of bacteria in the colon represents a symbiotic relationship: the bacteria are provided with a steady source of food, and the byproducts produced by the bacteria are beneficial to humans. For example, bacteria in the gut produce vitamin K, which is essential for the production of clotting factors, and biotin (vitamin B7), which is a coenzyme for many metabolic enzymes.

List at least four functions of the liver:

The liver processes nutrients (through glycogenesis and glycogenolysis, storage and mobilization of fats, and gluconeogenesis), produces urea, detoxifies chemicals, activates or inactivates medications, produces bile, and synthesizes albumin and clotting factors.

Key concept: bile

The major components of bile are bile salts, which emulsify fats; pigments (especially bilirubin, from the breakdown of hemoglobin); and cholesterol.

What effect does the parasympathetic nervous system have on the digestive system? What effect does the sympathetic nervous system have?

The parasympathetic nervous system increases secretions from all of the glands of the digestive system and promotes peristalsis. The sympathetic nervous system slows peristalsis.

What are the three sections of the small intestine, in order? What are the three sections of the large intestine, in order?

The small intestine consists of the duodenum, jejunum, and ileum. The large intestine consists of the cecum, colon, and rectum.

Villi, microvilli and lacteal

The small intestine is lined with villi, which are small, fingerlike projections from the epithelial lining, Each villus has many microvilli, drastically increasing the surface area available for absorption. In addition, at the middle of each villus there is a capillary bed for the absorption of water-soluble nutrients and a lacteal, a lymphatic channel that takes up fats for transport into the lymphatic system.

What are the two circulatory vessels in a villus? What biomolecules are absorbed into each?

The two circulatory vessels are capillaries and lacteals. The capillary absorbs water-soluble nutrients like monosaccharides, amino acids, short-chain fatty acids, water-soluble vitamins, and water itself. The lacteal absorbs fat-soluble nutrients, like fats, cholesterol, and fat- soluble vitamins.

Salivary glands in the real world

There are three pairs of major salivary glands: the parotid, submandibular, and sublingual glands. Other microscopic salivary glands are scattered throughout the upper digestive system. While the parasympathetic nervous system is responsible for promoting salivation, the sympathetic nervous system has some input into the glands as well. The sympathetic nervous system increases the viscosity of saliva, which is why dry mouth and even a tacky sensation in the mouth occurs during a fight-or-flight response.

Absorption of vitamins by small intestine

Vitamins are also absorbed in the small intestine. Vitamins can be categorized as either fat- soluble or water-soluble. Because there are only four fat-soluble vitamins (A, D, E, and K), these can be easily memorized. All other vitamins (B complex and C) are water-soluble. Fat-soluble vitamins dissolve directly into chylomicrons to enter the lymphatic circulation. Failure to digest and absorb fat properly, which can be due to pathologies in the liver, gallbladder, pancreas, or small intestine, may lead to deficiencies of fat-soluble vitamins. The water-soluble vitamins are taken up, along with water, amino acids, and carbohydrates, across the endothelial cells of the small intestine, passing directly into the plasma.

Vibrio cholera causes a severe infection in the intestines, leading to massive volumes of watery diarrhea—up to 20 liters per day. Given these symptoms, does cholera likely impact the small intestine or the large intestine?

While the large intestine's main function is to absorb water, the small intestine actually absorbs a much larger volume of water. Thus, massive volumes of watery diarrhea are more likely to arise from infections in the small intestine than in the large intestine.

Pancreas exocrine function

acing cells that make up the bulk of the pancreas are responsible for this produce pancreatic juices which are bicarbonate rich alkaline secretions containing many digestive enzymes that work on all three classes of biomolecules

In an experiment, enteropeptidase secretion was blocked. As a direct result, levels of all of the following active enzymes would likely be affected EXCEPT:

aminopeptidase Aminopeptidase is a brush-border peptidase secreted by the cells lining the duodenum; it does not require enteropeptidase for activation. Both trypsinogen and procarboxypeptidases A and B are activated by enteropeptidase, eliminating (A) and (D). Once activated, trypsin can activate chymotrypsinogen; if trypsinogen cannot be activated, then chymotrypsinogen will not be activated either, eliminating (C).

Cecum

an outpocketing that accepts fluid exiting the small intestine through the ileocecal valve and is the site of attachment of the appendix

Hormones involved with feeding behavior

antidiuretic hormone (ADH or vasopressin), aldosterone, glucagon, ghrelin, leptin, cholecystokinin

Bile salts

are derived from cholesterol. they are not enzymes and do not directly perform chemical digestion (the enzymatic cleavage of chemical bonds) play an important role in the mechanical digestion of fats and ultimately facilitate the chemical digestion of lipids have hydrophobic and hydrophilic regions allowing them to serve as a bridge between aqueous and lipid environments (like soaps) in small intestine they emulsify fats and cholesterol into micelles. micelles increase the surface area of the fats, increasing the rate at which lipase can act. Without bile, fats would spontaneously separate out of the aqueous mixture in the duodenum and would not be accessible to pancreatic lipase, which is water- soluble. --- Ultimately, proper fat digestion depends on both bile and lipase. Bile gets the fats into the solution and increases their surface area by placing them in micelles (mechanical digestion). Then, lipase can come in to hydrolyze the ester bonds holding the lipids together (chemical digestion).

Peptidases -aminopeptidase -dipeptidase -enteropeptidase -procrboxypeptidases A and B

break down proteins aminopeptidase is a peptidase secreted by glands in the duodenum that removes the N-terminal amino acid from a peptide dipeptidases cleave the peptide bonds of dipeptides to release free amino acids Unlike carbohydrates, which must be broken down into monosaccharides for absorption, proteins can be broken down into di- and even tripeptides and can be absorbed across the small intestine wall. Enteropeptidase (enterokinase) is an enzyme critical for the activation of trypsinogen, a pancreatic protease to trypsin (trypsin then initiates an activation cascade). can also activate procaboypeptidases A and B to active form

Pancreatic Amylase

breaks down large polysaccharides into small disaccharides and is therefore responsible for carbohydrate digestion

Pancreatic lipase

capable of break-ing down fats into free fatty acids and glycerol

Salivary amylase

capable of hydrolyzing starch into smaller sugars (maltose and dextrin)

Three main energy sources

carbohydrates, fats, and proteins

Lipase

catalyzes the hydrolysis of lipids

Pharynx

cavity that leads from the mouth and posterior nasal cavity to the esophagus connects not only to the esophagus but also to the larynx which is a part of the respiratory tract 3 parts: -nasopharynx (behind the nasal cavity) -oropharynx (at the back of the mouth) -laryngopharynx (above the vocal cord) food is prevented from entering the larynx during swallowing by the epiglottis, a cartilaginous structure that folds down to cover the laryngeal inlet. failure of this can lead to choking

Mastication

chewing helps to increase the surface area-to-volume ratio of the food creating more surface area for enzymatic digestion as it passes through the gut tube also moderates the size of food particles entering the lumen of the alimentary canal; food particles that are too large create an obstruction risk in tract

Sphincters

circular Smooth muscles around the canal that can contract to allow compartmentalization of function

Enteric nervous system

collection of one hundred million neurons that govern the function of the gastrointestinal system neurons are present in the walls of the digestive tract and trigger peristalsis in order to move materials through the system can function independently of the brain and spinal cord and is heavily regulated by the ANS

Gastric juice

combination of secretions from the chief and parietal cells kills most harmful bacteria (except helionbacter pylori) infection with which is usually asymptomatic but can cause inflammation (ulcers and even certain gastric cancers) acidic env. helps to denature proteins and can break some intramolecular bonds that hold food together HCl of parietal cells secrete intrinsic factor

Bile

complex fluid composed of bile salts, pigments and cholesterols

Pyloric glands

contained in the mucosa of the stomach contain G cells that secrete the peptide hormone gastrin

Many medications have anticholinergic side effects, which block the activity of parasympathetic neurons throughout the body. Older individuals may be on many such medications simultaneously, exacerbating the side effects. Which of the following would NOT be expected in an individual taking medications with anticholinergic activity?

diarrhea The parasympathetic nervous system has many roles in the digestive system. It promotes motility of the gut tube and secretion from glands. Therefore, blocking the parasympathetic nervous system would likely result in dry mouth (from reduced secretion of saliva), slow gastric emptying (from decreased peristalsis), and decreased gastric acid production (from reduced HCl secretion from the parietal cells in the gastric glands), eliminating (A), (C), and(D). (B) is the correct answer because we would expect constipation in such an individual, not diarrhea: slowed motility through the colon would lead to increased water reabsorption, making the feces too firm and causing constipation.

Disaccharidases -maltase -isomaltase -lactase -sucrase

digest disaccharides maltose digests maltose, isomaltase digests is-maltose, lactase digests lactose and sucrase digests sucrose bacteria in the intestines are then able to hydrolyze that disaccharide producing methane gas as a byproduct undigested disaccharides can have an osmotic effect and pull water into the stool causing diarrhea

Pepsin

digests proteins by cleaving peptide bonds near aromatic amino acids, resulting in short peptide fragments activated by acidic environment and is most active at low pH its activity at low pH is unique as most human enzymes are most active at physiological pH (7.4_

Brush-border enzymes -disaccharidases -peptidases

disaccharidases (maltase, isomaltase, lactase and sucrase) and peptidases (including dipeptidase) present on the luminal surface of cells lining the duodenum and break down dimers and trimer of biomolecules into absorbable monomers

Colon

divided into ascending, transverse, descending, and sigmoid portions main function is to absorb water and salts such as NaCl from the undigested material left over from the small intestine small intestine absorbs much more water than colon so the colon primarily concentrates the remaining material to form feces too little or too much water absorption can cause diarrhea or constipation

Small intestine

duodenum jejunum ileum up to seven meters long

Chemical digestion

enzymatic cleavage of chemical bonds, such as the peptide bonds of proteins or glycosidic bonds of starches

Sucrase

enzyme brush-border enzyme, breaks down sucrose into monosaccharides

Dipeptidase

enzyme bush border enzyme, breaks down dipeptides into free amino acids

Enteropeptidase

enzymes activates trypsinogen which initiates an activation cascade

Saliva

functions in chemical digestion and aids in mechanical digestion by moistening and lubricating food contains salivary amylase (ptyalin) and lipase

Autonomic Nervous System and Digestion

heavily regulates enteric nervous system parasympathetic division is involved in stimulation of digestive activities, increasing secretions from exocrine glands and promoting peristalsis -we often feel sleepy and lethargic after eating a big meal because of this system sympathetic division is involved in the inhibition of these activities. -during periods of high sympathetic activity, blood flow is decreased to the digestive tract and gut motility slows significantly

Stomach

highly muscular organ with a capacity of approx. two liters located in the upper left quadrant of the abdominal cavity underneath the diaphragm uses hydrochloric acid and enzymes to digest food which create a fairly harsh environment mucosa is quite thick to prevent auto digestion 4 main divisions: -fundus and body which contain mostly gastric gland -antrum and pylorus which contain mostly pyloric glands Lesser curvature: the internal curvature of the stomach Greater curvature: the external curvature Rugae: the lining of the stomach is thrown into folds called this the stomach is mainly an organ of digestion and few substances are absorbed directly from it (alcohol and aspirin)

Secretin

hormone increases pancreatic secretions, especially bicarbonate; reduces HCl secretion; decreases mobility

Cholecystokinin

hormone recruits secretions from gall bladder and pancreas; promotes satiety

Gastrin

induces the parietal cells in the stomach to secrete more HCL and signals the stomach to contract, mixing its contents

Swallowing

initiated in the muscles of the oropharynx which constitute the upper esophageal sphincter peristalsis squeezes, pushes and propels the bolus toward the stomach as the bolus approaches the stomach, a muscular ring known as the lower esophageal sphincter (cardiac sphincter) relaxes and opens to allows the passage of food

Salivary glands

innervated by parasympathetic nervous system like all digestive tract glands presence of food in the oral cavity triggers a neural circuit that ultimately leads to increased parasympathetic stimulation of these glands salivation can also be triggered by signals that food is near such as smell of sight

Jejunum and Ileum

involved in apportion of nutrients lined with villi and microvilli

Digestion

involves the breakdown of food into its constituent organic molecules; starches and other carbohydrates into monosaccharides lipids into free fatty acids and glycerol and proteins into amino acids carbs and strach -) monosaccharides lipids -) free fatty acids and glycerol proteins -) amino acids

Absorption

involves the transport of products of digestion from the digestive tract into the circulatory system for distribution to the body's tissues and cells

Liver

located in the upper right quadrant of the abdomen and contains two unique structures for communicating with the digestive system bile ducts: connect the liver with both the gallbladder and small intestine. bile is produced in the liver and travels down the ducts where it may be stored in the gall bladder or secreted in the duodenum liver receives all blood draining from the abdominal portion of the digestive tract through the hepatic portal vein. this nutrient rich blood can be processed by the her before draining into the inferior vena cava on its way to the right side of the heart. (ex. For example, the liver takes up excess sugar to create glycogen, the storage form of glucose, and stores fats as triacylglycerols. The liver can also reverse these processes, producing glucose for the rest of the body through glycogenolysis and gluconeogenesis and mobilizing fats in lipoproteins.) live detoxifies both endogenous compounds (made in the body) and exogenous compounds (brought in from env.)

Gastric glands

mucosa of stomach contains these respond to signals from the vagus nerve of the parasympathetic nervous system which activated by the brain in response to the sight, taste and smell of food three different types of cells: -mucous -chief -parietal

Esophagus

muscular tube that connects the pharynx to the stomach top third is composed of skeletal muscles, bottom third is composed of smooth muscle, middle is a mix of both top is under somatic (voluntary) control, bottom is under autonomic nervous control

Anus

opening through which wastes are eliminated and consists of two sphincters: internal and external anal sphincter The external sphincter is under voluntary control (somatic), but the internal sphincter is under involuntary control (autonomic).

Accessory organs of digestion

organs that originate as outgrowths of endoderm from the gut tube during development

Intracellular digestion

part of metabolism involves the oxidation of glucose and fatty acids for energy

Cholecystokinin (CCK)

peptide hormone secreted in response to the entry of chyme (specifically amino acids and fat in the chyme) into the duodenum stimulates the release of both bile and pancreatic juices and also acts in the brain where it promotes satiety

Secretin

peptide hormone that causes pancreatic enzymes to be released into the duodenum regulated the pH of the digestive tract by reducing HCl secretion from parietal cells and increasing bicarbonate secretion from the pancrease secretin is all an enterogastrone, a hormone that slows motility through the digestive tract. slowing of motility allows increased time for digestive enzymes to act on chyme (especially fats)

Anatomy of the pancreas

pg. 534

Oral cavity

plays a role in both mechanical and chemical digestion of food mechanical (mastication): breaking up of large food particles into smaller pieces using teeth, tongue and lips chemical: breakdown of chemical bonds in the macromolecules that make up food. relies on enzymes from saliva produced by the three pairs of salivary gland -minimal chemical digestion in mouth as food does not stay here long

Mucous cells

produce the bicarbonate-rich mucus that protects the muscular wall from harshly acidic (pH=2) and proteolytic environment of the stomach

Intrinsic factor

produced by parietal cells it is a glycoprotein involved in the proper absorption of vitamin B12

A two-week-old male infant is brought to the emergency room.His mother reports that he has been unable to keep any milk down; shortly after he nurses, he has sudden projectile vomiting. During exam, an olive-shaped mass can be felt in his upper abdomen. It is determined that there is a constriction in the digestive system that prevents food from reaching the small intestine from the stomach. Which structure is most likely the site of the problem?

pyloric sphincter The question is basically asking us to identify the structure that lies between the stomach and the small intestine. This is the pyloric sphincter; the presentation given in the question is a classic example of what is called pyloric stenosis, in which the pyloric sphincter is thickened and cannot relax to permit chyme through. The cardiac sphincter, (A), lies between the esophagus and the stomach. The ileocecal valve, (C), lies between the ileum of the small intestine and the cecum of the large intestine. The internal anal sphincter, (D), lies at the end of the rectum.

Pancreas endocrine functions

release of insulin, glucagon and somatostatin; peptide hormones necessary for the maintenance of proper blood sugar levels islets of langerhans are the endocrine cells throughout the organ

Pancreatic peptidases -trypsinogen -chymotrypsinogen -carboxypeptidases A and B

released in their zymogen form but once activated are responsible for protein digestions enteropeptidase produces by the duodenum is the master switch -converts trypsinogen to trypsin which can then activate the other zymogens and also activates procarbboxypeptidases A and B

Duodenum -pyloric sphincter -brush border enzymes -disaccharidases -maltase -isomaltase -lactase -sucrase

responsible for the majority of chemical digestion and has some minor involvement in absorption most of the absorption takes place in jejunum and ileum food enters duodenum from stomach through the pyloric sphincter the presence of chyme in the duodenum causes the release of brush-border enzymes like disaccharidases (maltase, isomaltase, lactase and sucrase) and peptidases (including dipeptidase) the duodenum also secretes enteropeptidase which is involved in the activation of other digestive enzymes from the accessory organs of digestion secretes hormones like secretin and cholecystokinin (CCK) into the bloodstream peptidases are also active here

Peristalsis more

rhythmic contraction of smooth muscle that propels food toward the stomach under normal circumstances this proceeds down the digestive tract However, certain factors such as exposure to chemicals, infectious agents, physical stimulation in the posterior pharynx, and even cognitive stimulation, can lead to reversal of peristalsis in the process of emesis (vomiting).

Peristalsis

rhythmic contractions of the gut tube

Starch is hydrolyzed into maltose by enzymes from the: i. salivary glands ii. brush border iii. pancreas

salivary glands and pancreas Starch is hydrolyzed to maltose by two enzymes: salivary amylase (secreted by the salivary glands) in the mouth and pancreatic amylase (secreted by the pancreas) in the duodenum. Brush-border disaccharidases can further break down maltose, but do not break down starch.

Parietal cells

secrete hydrogen ions into the stomach as hydrochloric acid which cleaves pepsinogen to pepsin

Chief cells

secrete pepsinogen this is the inactive "zymogen" form of pepsin, a proteolytic enzyme

Parietal Cells (secretions and functions)

secretion: HCl, intrinsic factor function: -HCl; decreases pH, kills microbes, denatures proteins, activates pepsinogen to pepsin, carries out some chemical digestion -intrinsic factor: absorption of vitamin B12

Mucous Cells (secretions and functions)

secretion: mucus function: protects lining of stomach, increases pH (bicarbonate)

Chief Cells (secretions and functions)

secretion: pepsinogen function: digests proteins, activated by H+

G Cells (secretions and functions)

secretions: gastrin function: increases HCl production, increases gastric motility

Rectum

serves as a storage site for feces which consists of indigestible material, water, bacteria (E. coli and others) and certain digestive secretions that are not reabsorbed (enzymes and some bile)

Appendix

small fingerlike projection that was once thought to be vestigial may have a role in warding off certain bacterial infections and repopulating the large intestine with normal flora after episodes of diarrhea

leptin and cholecystokinin

stimulate feelings of satiety

Which of the following correctly lists two organs in which proteins are digested?

stomach and small intestine Protein digestion begins in the stomach, where pepsin (secreted as pepsinogen) hydrolyzes specific peptide bonds. Protein digestion continues in the small intestine as trypsin (secreted as trypsinogen), chymotrypsin (secreted as chymotrypsinogen), carboxypeptidases A and B (secreted as procarboxypeptidases A and B), aminopeptidase, and dipeptidases hydrolyze specific parts of the peptide. No protein digestion occurs in the mouth or large intestine.

Extracellular digestion

substances aside from glucose and fatty acids must be extracted from our food these nutrients are obtained from food through the lumen of the alimentary canal

Chyme

the digestion of solid food in the stomach results in an acidic semifluid mixture known as chyme the combined mech and chem digestive activities in the stomach result in a sig increase in the surface area of the now unrecognizable food particles when chyme reaches the small intestine the absorption of nutrients from it can be maximized

Mechanical Digestion

the physical breakdown of large food particles into smaller food particles but does not involve breaking chemical bonds

Ingest

to eat

ADH and Aldosterone in digestion

trigger the sensation of thirst encouraging the behavior of fluid consumption

Large intestine

water absorption larger diameter than small intestine but shorter length three major sections -cecum -colon rectum