Exam 3 - Digestive System Flashcards
Functions of digestive system
1) Ingestion and mastication
2) Propulsion and mixing
3) Secretion
4) Digestion
5) Absorption
6) Elimination
Ingestion and mastication
Function of digestive system
Ingestion is intake of solids and liquids
Mastication is process where teeth chew food in the mouth to begin the process of digestion. Vital that solid foods are mechanically broken down to increase total surface area for digestion
Propulsion and mixing
Function of digestive system
Propulsion is movement of food from one end of the digestive tract to the other. Propulsive movements are swallowing a bolus, peristalsis or propelling of material through most of digestive tract, and mass movements or contractions that move material in large intestine to anus.
Mixing is the movement of food back and forth in the digestive tract, without forward movement. Mixing contractions blend food with digestive fluids in stomach and small intestine. Mixing contractions include mixing waves, or gentle waves in stomach that churn food with gastric secretions, and segmental contractions, which mix food particles in small intestine
Secretion
Function of digestive system
Secretions added to lubricate, liquefy, buffer, and digest the food as it moves through digestive tract. Mucus, secreted along the entire digestive tract, lubricates the food and the lining of the tract. Mucus coats and protects epithelial cells of the digestive tract from mechanical abrasion, stomach acid, and digestive enzymes. Secretions contain large amounts of water, which liquefies the food, making it easier to digest and absorb. Liver secretions make digestion and absorption of lipids possible. Enzymes secreted by oral cavity, stomach, small intestine, and pancreas break down large food molecules into smaller molecules that can be absorbed by the intestinal wall
Digestion
Function of digestive system
Breakdown of large organic molecules into their individual components. Large molecules must be digested into individual components to be absorbed by digestive tract. Carbohydrates are broken into monosaccharides. Proteins are broken into amino acids. Triglycerides are broken into fatty acids and glycerol. Minerals, water, and vitamins are not broken down before they’re absorbed
Mechanical digestion involves mastication and mixing of food
Chemical digestion is accomplished by digestive enzymes secreted along the digestive tract
Absorption
Function of digestive system
Movement of molecules out of digestive tract and into the blood or the lymphatic system. Mechanism by which absorption occurs depends on the type of molecule involved. Molecules pass out of digestive tract by diffusion, facilitated diffusion, active transport, symport, or endocytosis
Elimination
Function of digestive system
Process by which the waste products of digestion are removed from the body. During this process, which primarily occurs in large intestine, water and salts are absorbed, changing the material in the digestive tract from liquefied to semisolid. These semisolid waste products, called feces, are stored in the distal large intestine, and then eliminated by the process of defecation
Organs of digestive system
1) Oral cavity, including tongue, teeth, and salivary glands as accessory organs
2) Pharynx
3) Esophagus
4) Stomach
5) Small intestine, consisting of duodenum, jejunum, and ileum, with the liver, gallbladder, and pancreas as accessory organs
6) Large intestine, including cecum, colon, rectum, anal canal, and anus
Histology of digestive tract
Digestive tract consists of four major tunics, or layers. These are present throughout all areas of digestive tract, from esophagus to anus
1) Mucosa
2) Submucosa
3) Muscularis
4) Serosa or adventia
Mucosa
Innermost tunic consists of three separate layers:
1) Inner mucous epithelium: Nonkeratinized stratified squamous epithelium in the mouth, oropharynx, esophagus, and anal canal, and simple columnar epithelium in the remainder of the digestive tract
2) Lamina propria: A loose connective tissue
3) Muscularis mucosae: A thin outer layer of smooth muscle
Submucosa
Beneath mucosa lies submucosa
Thick connective tissue layer
Tunic contains nerves, blood vessels, lymphatic vessels, and small glands
A network of neurons and glial cells in the submucosa forms a portion of the enteric nervous system. Axons from submucosal plexus extend to cells in epithelial intestinal glands, stimulating their secretion
Esophagus and stomach lack a submucosal plexus, but the plexus is extensive throughout the rest of the digestive tract
Muscularis
Muscular layer
Consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Two exceptions are the upper esophagus, where the muscles are skeletal, and the stomach, which has three layers of smooth muscle
Between two muscle layers is second portion of enteric nervous system called myenteric plexus. Controls motility of intestinal tract
Serosa or adventitia
Fourth layer is either a serosa or an adventitia, depending on the structure of the layer
Serosa: Parts of digestive tract located within the peritoneal cavity have a serosa as the outermost layer. This serosa, or serous membrane, is called the visceral peritoneum. It consists of a thin layer of connective tissue and a simple squamous epithelium
Adventitia: When the outer layer of the connective tissue covering that blends with the surrounding connective tissue. These areas include the esophagus and the retroperitoneal organs
Glands associated with digestive tract
1) Unicellular mucous glands in the mucosa
2) Multicellular glands in the mucosa and submucosa
3) Multicellular glands (accessory glands, such as pancreas) outside the digestive tract
Neural regulation of digestive system
Most nervous regulation of digestive tract is under local control by the enteric nervous system. Enteric nervous system is extensive network of neural tissue and consists of submucosal plexus and myenteric plexus. Both plexuses are within walls of digestive tract. This network of neurons and associated glial cells is a division of the autonomic nervous system
Chemical regulation of digestive system
Two major ENS neurotransmitters are acetylcholine and norepinephrine. Acetylcholine stimulates and norepinephrine inhibits digestive tract motility and secretions.
Serotonin stimulates digestive tract motility
Gastrin and secretin are secreted by endocrine cells in digestive system and are carried through the blood to target organs of the digestive system or to target tissues in other systems. These hormones help regulate many digestive tract functions, as well as the secretions of associated glands, such as the liver and the pancreas
Paracrine chemicals, such as histamine, are released locally within the digestive tract, where they influence the activity of nearby cells. These localized chemical regulators help local reflexes within the ENS control local digestive tract environments, such as pH levels
Structure of esophagus
Esophagus has thick walls containing the four tunics of the digestive tract: mucosa, submucosa, muscularis, and adventitia. Muscularis has an outer longitudinal layer and an inner circular layer. Esophagus differs by having skeletal muscle fibers in the superior one-third, a mixture of skeletal and smooth muscle fibers in the middle one-third, and smooth muscle fibers in the inferior one-third. Upper esophageal sphincter and a lower esophageal sphincter, at the upper and lower ends of the esophagus, respectively, regulate the movement of materials into and out of the esophagus. Mucosal lining of esophagus is nonkeratinized stratified squamous epithelium. Numerous mucous glands in the submucosal layer produce a thick, lubricating mucus, which passes through ducts to the surface of the esophageal mucosa
Three swallowing phases
1) Voluntary phase: A bolus of food is formed i the mouth and pushed by the tongue against the hard palate, until it is forced toward the posterior part of the mouth and into the oropharynx
2) Pharyngeal phase: Reflex initiated by the stimulation of tactile receptors in the area of the oropharynx. Vestibular folds and vocal cords close, and the epiglottis is tipped posteriorly, so that the epiglottic cartilage covers the opening into the larynx, and the larynx is elevated. These movements prevent food from passing into the larynx.
3) Esophageal phase: Responsible for moving food from the pharynx to the stomach. Muscular contractions in the wall of the esophagus occur in peristaltic waves. As peristaltic waves and food bolus approach stomach, the lower esophageal sphincter in the esophagus relaxes. Presence of food in the esophagus stimulates the myenteric plexus, which controls the peristaltic waves. Food in esophagus also stimulates tactile receptors, which stimulates contractions and reinforces peristaltic contractions of skeletal and smooth muscles within the esophagus
Anatomy characteristics of the stomach
Stomach is divided into four regions:
1) Cardia: Esophagus empties into cardia of the stomach at the gastroesophageal opening. Lower esophageal sphincter surrounds opening
2) Fundus: Left of the cardia, and superior to cardiac opening
3) Body: Largest part of stomach, which turns to the right, creating a greater curvature and a lesser curvature. Body narrows to form funnel-shaped pylorus
4) Pylorus: Wider part of funnel, toward the body of the stomach, is the pyloric antrum. Narrow part of funnel is the pyloric canal. Pyloric canal opens through the pyloric orifice into the small intestine. Pyloric orifice is surrounded by the pyloric sphincter, a relatively thick ring of smooth muscle that helps regulate the movement of gastric contents into the small intestine
Histology of the stomach
Serosa, or visceral peritoneum, is the outermost tunic of the stomach. Consists of an outer layer of simple squamous epithelium and an inner layer of connective tissue
Muscularis of stomach consists of three layers
1) Outer longitudinal layer
2) Middle circular layer
3) Inner oblique layer: Unique to the stomach wall. Helps generate strong stomach contractions that physically break down ingested blood into smaller particles.
Deep to muscularis are submucosa and mucosa, which are arranged in large folds called rugae when the stomach is empty. These folds allow the mucosa and submucosa to stretch, and the folds disappear as the stomach volume increases as it is filled
Mucous lining of the stomach is simple columnar epithelium
Secretions of the stomach
1) Hydrochloric acid
2) Intrinsic factor
3) Mucus
4) Digestive enzymes (pepsinogen and gastric lipase)
Functions of stomach secretions
Once food enters the stomach, it is mixed with stomach secretions to form a semifluid material called chyme. The primary function of the stomach is to store and mix chyme
Hydrochloric acid: Kill bacteria that are ingested with essentially everything humans put into their mouths
2) Intrinsic factor: Glycoprotein that binds with vitamin B12, making the vitamin more readily absorbed in the ileum of the small intestine
3) Mucus: Thick layer of mucus lubricates and protects epithelial cells of the stomach wall from the damaging effect of the acidic chyme and pepsin. Irritation of the stomach mucosa stimulates the secretion of a greater volume of mucus
4) Digestive enzymes: Chief cells within gastric glands secrete pepsinogen and gastric lipase. Pepsinogen is converted into pepsin by hydrochloric acid. Pepsin breaks apart proteins into smaller peptide chains. Gastric lipase is a lipase, which can digest lipids even in an acidic environment
Regulation of stomach secretion
Nervous and hormonal mechanisms regulate gastric secretions
Neural mechanisms: Reflexes integrated within the medulla oblongata and local reflexes integrated within the ENS
Hormonal mechanisms: Chemical messengers that regulate stomach secretions include hormones gastrin, secretin, and cholecystokinin, as well as paracrine chemical messenger histamine
Regulation of stomach secretion is divided into three phases:
1) Cephalic
2) Gastric
3) Intestinal phase
Gastric movement regulation
Regulation of stomach secretion is divided into three phases:
1) Cephalic: Stomach secretions are increased in anticipation of incoming food. Stimuli influence gastric secretions
2) Gastric: When most of the stimulation of secretion occurs. Stomach secretion produces the greatest volume of gastric secretion. Gastric secretion is inhibited when pH of stomach contents falls below 2. Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors
3) Intestinal phase: Stomach secretion decreases. Secretin is released and inhibits gastric secretions by inhibiting both parietal and chief cells. Cholecystokinin inhibits gastric secretions. Acidic chyme entering duodenum triggers a decrease in stomach acid secretion. Too much fat takes time to digest, so stomach holds onto chyme longer. A lot of fat means physically break down fat or chemically break down fat
Characteristics that account for large surface area of the small intestine
The lining of the small intestine has three structural modifications that increase its surface area about 600-fold to allow for more efficient digestion and absorption of food
1) Circular folds: Mucosa and submucosa form a series of folds called circular folds, which run perpendicular to the long axis of the digestive tract
2) Villi: Tiny, fingerlike projections of the mucosa form numerous villi. Each villus is covered by simple columnar epithelium and contains a blood capillary network and a lymphatic capillary called a lacteal
3) Microvilli: Most of the cells that make up the surface of the villi have numerous cytoplasmic extensions called microvilli, which further increase the surface area. The combined microvilli on the entire epithelial surface form the brush border
4) Mucosal epithelium: Simple columnar. Absorptive cells, goblet cells, enteroendocrine cells, intraepithelial lymphocytes
Functions of the cells of the duodenal mucosa
Mucosa of the small intestine is simple columnar epithelium with four major cell types:
1) Absorptive cells: Cells with microvilli that produce digestive enzymes and absorb digested food
2) Goblet cells: Produce a protective mucus
3) Granular cells: May help protect the intestinal epithelium from bacteria
4) Endocrine cells: Produce many regulatory hormones. For example, the hormone secretin and cholecystokinin stimulate hepatic and pancreatic secretions
Secretions of small intestine
Mucosa of the small intestine produces secretions that contain primarily mucus, as well as electrolytes and water that lubricate and protect the intestinal wall:
1) Mucus is secreted from duodenal glands, intestinal glands, and goblet cells. It protects the wall of the intestine from the irritating effects of the acidic chyme and from the digestive enzymes that enter the duodenum from the pancreas. Secretions are released from the duodenal glands in response to Vagus nerve, stimulation, the hormone secretin, and chemical or tactile irritation of the duodenal mucosa. Chemical and tactile stimulation of mucosa also stimulate goblet cells to produce mucus
2) Secretion of electrolytes and water from intestinal epithelium keeps the chyme in an aqueous solution, which facilitates the digestive process by pancreatic enzymes and small intestine enzymes
Anatomy of liver
Largest internal organ of the body
Right-upper quadrant of the abdomen, tucked against the inferior surface of the diaphragm. Consists of four lobes:
1) Right lobe
2) Left lobe
3) Caudate lobe
4) Quadrate lobe
Right and left lobes are separated by connective tissue septum, the falciform ligament. The caudate and quadrate lobes can be seen inferior view, along with the porta hepatis. The gallbladder is a small sac on the inferior surface of the liver that stores bile. Porta hepatis is on the inferior surface of the liver, where blood vessels and nerves enter and bile ducts and lymphatic vessels leave the liver. Blood flows into the liver via the hepatic portal vein and the hepatic artery. Bile flows out of the liver via two hepatic ducts, one each from the right and left lobes, and exit the liver at porta hepatis
Histology of the liver
Divided into hepatic lobules
Hepatic lobules are hexagon-shaped regions surrounded by connective tissue septa and defined by a portal triad at each corner and a central vein in the center of the lobule
Portal triad: Contains three structures, which are hepatic portal vein, hepatic artery, and hepatic duct
Liver ducts
1) Common hepatic duct: Right and left hepatic ducts unite to form a single common hepatic duct
2) Cystic duct: From gallbladder and joins common hepatic duct to form the common bile duct. Bile can flow from gallbladder through cystic duct into common bile duct, or it can flow back up the cystic duct into the gallbladder
3) Hepatopancreatic ampulla: Joins common bile duct and pancreatic duct together. Empties into duodenum at major duodenal papilla. Smooth muscle sphincter surrounds common bile duct where it enters the hepatopancreatic ampulla
3) Accessory pancreatic duct: Empties pancreatic secretions in the duodenum at the minor duodenal papilla. Eventually combines to enter duodenum
Functions of liver
Hepatocytes of the liver perform five functions:
1) Bile production for digestion and excretion: Produces bile, which is a solution that contains bile salts, bile pigments, cholesterol, lipids, lipid-soluble hormones, and lecithin. It neutralizes stomach acid and emulsifies lipids. Alkaline pH of bile helps neutralize acidic chyme
2) Storage of nutrients: Remove glucose from blood and store it in the form of glycogen. Also store lipids, vitamins, copper, and iron. Storage function is usually short-term. Hepatocytes help maintain blood glucose levels within very narrow limits
3) Processing of nutrients: Liver can convert some nutrients into others. Hepatocytes can break down the amino acids and cycle many of them through metabolic pathways so they can be used to produce ATP, lipids, and glucose. Hepatocytes can also transform substances that cannot be used by most cells into more readily usable substances
4) Detoxification: Liver forms a major line of defense by altering the structure of many of harmful substances to make them less toxic or to make their elimination easier. For example, ammonia is turned into urea
5) Synthesis of new molecules: Liver can produce own new compounds, including plasma proteins and clotting factors, which are released into the blood. Liver is a major site of cholesterol synthesis
Structure of gallbladder
On inferior surface of liver. Cystic duct connects the gallbladder to the common bile duct.
Three tunics form the gallbladder wall:
1) Inner mucosa folded into rugae that allow the gallbladder to expand
2) A muscularis, which is a layer of smooth muscle that allows the gallbladder to contract
3) An outer covering of serosa
Function of the gallbladder
Function is to store and concentrate bile. Liver continually secretes bile, which flows to gallbladder. While bile is in gallbladder, water and electrolytes are absorbed. Thus, bile salts and pigments become 5-10 times more concentrated than when secreted by the liver. Bile is released from the gallbladder by contractions stimulated by cholecystokinin and by vagal stimulation. In this way, large amounts of concentrated bile are dumped into small intestine shortly after a meal
Stimulates the release of bile
1) Parasympathetic nerve impulses: Parasympathetic stimulation through the Vagus nerves increases bile secretion from the liver
2) Cholecystokinin: Released from duodenum to increase bile in digestive tract. Stimulates gallbladder contractions to release bile into duodenum
3) Secretin: Released from duodenum to increase bile in the digestive tract. Stimulates bile secretion from the liver, primarily by increasing the water and HCO3 content of bile
Anatomy of pancreas
Composed of both endocrine and exocrine tissues that perform several functions. The pancreas is located behind the stomach. The head of the pancreas is nestled within the curvature of the duodenum. The body and tail extend to the spleen
Histology of pancreas
Endocrine part of pancreas consists of pancreatic islets, or islets of Langerhans. They produce three hormones:
1) Insulin: Controls the blood levels of nutrients, such as glucose and amino acids
2) Glucagon: Controls the blood levels of nutrients, such as glucose and amino acids
3) Somatostatin: Regulates insulin and glucagon secretion and may inhibit growth hormone secretion
Pancreatic ducts
1) Intercalated ducts: Secretions from pancreas first flow into these ducts
2) Intralobular ducts: Connects intercalated ducts and interlobular ducts
3) Interlobular ducts: Connects intralobular ducts to main pancreatic duct. Leaves lobules to join interlobular ducts between lobules
4) Pancreatic duct: Joins common bile duct at the hepatopancreatic ampulla to the interlobular ducts
Function of pancreatic secretions
Pancreatic juice
Delivered to the small intestine through the pancreatic ducts, where it functions in digestion
1) An aqueous component: Rich in bicarbonate ions (HCO3). Actively secreted by columnar epithelial cells that line the smaller ducts of the pancreas. Contains Na+, K+, and water. HCO3 ions of the aqueous pancreatic juice neutralize the acidic chyme that enters the small intestine from the stomach. Neutralized pH caused by pancreatic secretions in duodenum stops digestion, is required for functions of pancreatic and brush-border enzymes, and prevents damage to the duodenum by the acid from the stomach
2) An enzymatic component: Contains enzymes that digest all major classes of food. This enzyme-rich secretion is produced by acinar cells of pancreas. Without enzymes produced by pancreas, lipids, proteins, and carbohydrates cannot be adequately digested. Three major proteolytic enzymes:
1) Trypsin
2) Chymotrypsin
3) Carboxypeptidase
Pancreatic acini: Clusters of secretory cells that contain zymogen granules that secrete digestive enzymes
Inactive enzymes: Trypsinogen activated to trypsin and procarboxypeptidase activated to carboxypeptidase
Active enzymes: Amylase (carbohydrates), lipase (fats), nuclease (RNA and DNA), but they require ions or bile for optimal activity
Regulation of pancreatic secretion
1) Parasympathetic stimulation through Vagus nerve also stimulates the secretion of enzyme-rich pancreatic juices. Sympathetic impulses inhibit secretion. Effect is greatest during cephalic and gastric phases of stomach secretion
2) Both hormonal and neural mechanisms control secretion of pancreatic juice. The hormones secretin and cholecystokinin are released from the duodenum in response to specific stimuli. Each hormone stimulates secretion of a specific type of pancreatic juice. Secretin stimulates secretion of HCO3 rich aqueous juice. An acidic chyme in the duodenum stimulates the release of secretin
3) Cholecystokinin stimulates the secretion of the enzyme-rich pancreatic juice. Cholecystokinin stimulates the release of bile from the gallbladder, which aids in the digestion of lipids. The major stimulus for the release of cholecystokinin is the presence of fatty acids and other lipids in the duodenum
Anatomy of large intestine
Large of intestine is portion of digestive tract extending from the ileocecal junction to the anus. It consists of four parts:
1) Cecum: Proximal end of large intestine, where it meets small intestine at the ileocecal junction
2) Colon: Consists of four parts, ascending colon, hepatic flexure, transverse colon, splenic fixture, descending colon, sigmoid colon. Mucosal lining of the large intestine consists of simple columnar epithelium. Has numerous, straight, tubular glands called crypts
3) Rectum: Straight, muscular tube that begins at the distal end of the sigmoid colon and ends at the anal canal. Mucosal lining of the rectum is simple columnar epithelium, and the muscular tunic is relatively thick, compared with the rest of the digestive tract
4) Anal canal: Begins at the inferior end of the rectum and ends at the anus. Smooth muscle layer of the anal canal is even thicker than that of the rectum and forms the internal anal sphincter at its superior end. Skeletal muscle forms the external anal sphincter at the inferior end of the canal. The epithelium of the superior part of the anal canal is simple columnar, and that of the inferior part is stratified squamous
Mesocolon: Anchors transverse and sigmoid colons
Secretions of large intestine
Major secretion product of the large intestine is mucus. Mucus is secreted from numerous goblet cells scattered along the length of the mucosa of the large intestine. There are numerous crypts lined almost entirely with goblet cells. Little enzymatic activity is associated with secretions of the large intestine. Mucus lubricates the wall of the large intestine and helps fecal matter stick together. Tactile stimuli and irritation of the large intestine wall trigger local enteric reflexes that increase mucous secretion
Functions of large intestine
Chyme is converted to feces
Formation of feces involves the absorption of water and salts, secretion of mucus, and extensive action of microorganisms. Large intestine stores the feces until they are eliminated by defecation
Packages what cannot be absorbed
Regulation of defecation
During defecation, the contractions that move feces toward the anus must be coordinated with the relaxation of the internal and external anal sphincters. Parasympathetic reflexes are responsible for most of the defecation reflex. Internal and external anal sphincters prevent defecation
Regulation of digestion
1) Mechanical and chemical stimuli: Stretch, osmolarity, presence of substrate in lumen stimulate receptors. Autonomic reflexes
2) Intrinsic control: Short reflex. Regulation of digestion. Local enteric nerve plexi
3) Extrinsic control: Long reflex. Regulation of digestion by the central nervous system works through the local enteric nerve plexi
4) Local enteric nerve plexi: Affect smooth muscle of organ wall or gland
Stomach mucosa
Epithelial lining: Simple columnar with goblet cells (mucous)
Protective properties:
1) Mucous layer: Traps bicarbonate underneath
2) Epithelial cells connected by tight junctions so acids cant penetrate
3) Gastric glands are impermeable to gastric juices
Gastric pits
Extend deep into mucosa
Contain gastric glands that secrete gastric juices which allows chemical digestion. Enteroendocrine cells: Gastrin, histamine, and many others
Neck cells: Mucous
Parietal cells: HCl and intrinsic factor (allows B12 intake)
Chief cells: Pepsinogen, or pepsin precursor
Pepsinogen activation
Converted to pepsin by HCl
Digests proteins
Rising pH
Highly acidic
pH lowers
Gastric motility
Pyloric valve is closed when peristaltic waves occur within the stomach. When pyloric valve opens slightly, the chyme
Wave every 120 seconds
Movement back and forth hits valves until duodenum can take it
Rate of peristaltic waves: 3 per minute initiated by pacemaker cells
Chyme movement: Delivered in small amounts to duodenum forced back into stomach for further mixing
Gastric emptying
As peristalsis forces chyme into the duodenum, presence of chyme stimulates causes neural enterogastric reflex. Hormonal enterogastrone mechanisms
Resulting inhibition: Gastric secretion and duodenal filling
Carb rich chyme moves through duodenum quickly
Fat rich chyme moves slower, causing it to remain in the duodenum longer
Olestra
Fat substitute
Made of cottonseed
Humans cant digest
Intestinal crypts
Produces intestinal juice
Found within small intestine
High pH
Alkaline
Mostly H2O
Enzyme poor
Mucous
Submucosal modifications of small intestine
Brunner’s glands: Secrete alkaline mucous in duodenum
Peyer’s patches: Lymph tissue in ileum
No gallbladder
Can still eat fat moderately
Liver brings bile directly to duodenum without any storage
Bile composition
Yellow-green
Alkaline
Contains:
1) Bile salts: Cholesterol derivatives
2) Bile pigments
3) Cholesterol
4) Neutral fats
5) Phospholipids
6) Electrolytes
Functions of bile
1) Emulsify fat
2) Facilitate fat and cholesterol
3) Help solubilize cholesterol
Rectal valves
2L of gas in body per day
Allow gas to escape without the release of feces
Appendix
Vestigial?
Plays role in digestive fibers/undigestibles
Bacteria in large intestine
Bacterial flora of large intestine include:
1) Those that survive small intestine
2) Those that enter via anus
These bacteria:
1) Colonize colon
2) Ferment indigestible CHOs, or carbs
3) Release irritating acids and gases
4) Synthesize B complex and K vitamins
Developmental considerations
Embryonic development:
1) Third week: Gut formation; mouth and anus nearly formed
2) Eighth week: Accessory organ formation
Fetal development:
1) Nutrition: Via placenta
2) GI tract: Stimulated by swallowing of amniotic fluid
At birth:
1) Feeding: Most important baby activity. Need high amount of food
2) Enhanced by rooting reflex and sucking reflex
Old age:
1) GI activity declines, absorption less efficient, peristalsis slowed
2) Diverticulosis, fecal incontinence, and cancer of GI tract
Causes of malabsorption of nutrients
1) Anything that interferes with delivery of bile or pancreatic juice
2) Damaged intestinal mucosa (e.g., bacterial infection)
Celiac disease
Malabsorption of nutrients
Gluten-sensitive enteropathy
Gluten damages the intestinal villi and brush border
Treated by eliminating gluten from the diet (all grains but rice and corn)
Digestion in small intestine
As chyme enters duodenum:
1) Carbohydrates and proteins are only partially digested
2) No fat digestions has taken place
3) Chyme is hypertonic and has low pH
Digestion continues in small intestine:
1) Chyme is slowly released into dudeonum
2) Mixing is required for proper digestion
3) Substances required are provided by liver
4) All nutrient absorption takes place in small intestine
