CH 22 The Digestive System
Define and account for the alkaline tide.
As H is pumped from the cell and HCO3 (bicarbonate ion) accumulates within the cell,HCO3 is ejected through the basal cell membrane into the capillary blood. As a result, blood draining from the stomach is more alkaline than the blood serving it. This phenomenon is called the alkaline tide.
State the role of bile in digestion and describe how its entry into the small intestine is regulated
Bile is a fat emulsifier. Bile does not usually enter the small intestine until the gallbladder contracts when stimulated by cholecystokinin.
Describe the enzymes that breakdown the components of the cheeseburger?
In the mouth, salivary amylase in saliva begins chemical breakdown of starch. In the stomach pepsin beings to breakdown proteins. Additionally, lingual lipase is released by the minor salivary glands to digest some triglycerides in the stomach. In the small intestine enzymes from pancreas and brush border enzymes attached to microvilli membranes complete digestion of all classes of foods.
Describe how entry of pancreatic juice into the small intestine is regulated.
Pancreatic juice is regulated by neural stimuli and, more importantly, hormones (cholecystokinin and secretin). When no digestion is occurring, the hepatopancreatic sphincter (guarding the entry of bile and pancreatic juice into the duodenum) is closed and the released bile backs up the cystic duct into the gallbladder, where it is stored until needed
Consider the following dental formula: 2I, 1C, 2PM, 3M
Primary: 2I (incisors), 1C (canine), 2M (molars)Permanent: 2I, 1C, 2PM (premolars), 3M
which components of the cheeseburger are digested in which regions of the digestive systems?
Some absorption occurs in the duodenum, but the majority takes place in the other two sections of the small intestine: the jejunum and the ileum. As the food travels down the gut, the smaller molecules are absorbed through the lining of the intestine and into the circulatory system (for carbohydrates and proteins) or into the lymphatic system (for fats). By the time the food makes its way through the 20+ feet of small intestine, almost all of the nutrients have been absorbed and all that you have left is undigestible material (such as fiber) and bile salts.
What is deglutition
The action or process of swallowing. Its a complicated process that involves 22 separate muscle groups. It has 2 major phases: 1.) the buccal phase (occurs in mouth & is voluntary) 2.) The pharyngeal-esophageal phase (involuntary)
Describe stimuli and controls of digestive activity
The digestive system creates an optimal internal environment for its functioning in the lumen of the GI tract, an area that is technically outside of the body •Digestive activities within the GI tract are triggered by mechanical and chemical stimuli. •Controls of the digestive activity are both extrinsic and intrinsic (nervous and hormonal).
List the major functions of the large intestine.
The large intestine absorbs water from indigestible food residues and eliminates the latter as feces
Describe the alimentary canal with its accessory organs:
The organs of the digestive system can be grouped into: 1.) alimentary canal 2.) accessory organs The alimentary canal (gastrointestinal tract ‑ G.I.) is a continuous, coiled, hollow, muscular tube that winds through the ventral body and is open Cal both ends. It digests food and absorbs the fragments through its lining into the blood. Organs include: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus Accessory digestive organs include: teeth, tongue, gallbladder, salivary glands, liver, pancreas. The accessory digestive glands produce saliva, bile, and enzymes.
Define splanchic circulation.
The splanchnic circulation serves the digestive system and includes those arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation (p. 856
What are deciduous teeth
baby teeth, temporary teeth and now more commonly primary teeth, are the first set of teeth in the growth development of humans and other diphyodont mammals.
How many teeth do humans have
most adults have 32 teeth. Among these teeth are 8 incisors, 4 canines, 8 premolars, and 12 molars (including 4 wisdom teeth).
Define retroperitoneal and name the retroperitoneal organs.
•Retroperitoneal organs - organs not suspended by a mesentery. include most of the pancreas and parts of the small and large intestine.
Hormones produced by the stomach
Gastrin: CCK: Secretin
Describe the role of the large intestine in the mechanical breakdown of food
No further food breakdown occurs in the large intestine. The large intestine harvests vitamins made by the bacterial flora and reclaims most of the remaining water and some of the electrolytes (Na+ and chloride) *Major function are propulsive activities that force fecal material toward the anus and eliminate it from the body.
Describe the swallowing reflex Buccal Phase
Occurs in the mouth and is voluntary. We place the tip of the tongue against the hard palate and then contract the tongue to force the bolus into the oropharynx.
What are the major functions of the digestive tract
1.) Ingestion 2.) Propulsion 3.) Mechanical breakdown 4.) Digestion 5.) Absorption 6.) Defecation
Describe the swallowing reflex Pharyngeal Esophageal Phase
Involuntary. Once food enter the pharynx all routes except the desired one are closed off. Wavelike peristaltic contracts create pressure waves that propel food through the pharynx and into the esophagus. Solid foods pass from the oropharynx to the stomach in about 8 seconds.
Describe the mechanisms of chewing and swallowing
•Mastication, or chewing, begins the mechanical breakdown of food and mixes the food with saliva (p. 866). •Deglutition, or swallowing, is a complicated process that involves two major phases (p. 866; Fig. 23.13). 1.The buccal phase is voluntary and occurs in the mouth where the bolus is forced into the oropharynx. 2.The pharyngeal-esophageal phase is involuntary and occurs when food is squeezed through the pharynx and into the esophagus.
Explain how gastric secretion and stomach motility are regulated
•Neural and hormonal mechanisms •Stimulatory and inhibitory events occur in three phases: 1.Reflex phase (cephalic): few minutes prior to food entry: smell/taste 2.Gastric phase: 3-4 hours after food enters the stomach 3.Intestinal phase: brief stimulatory effect as chyme enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones): not too much now!
Describe what happens to a cheeseburger as it passes through the digestive system:
.) Ingestion: taking food into the mouth 2.) Propulsion: includes swallowing (voluntary) and then peristalsis (involuntary process) which involves alternating waves of contraction and relaxation of muscle in the organ walls. 3.) Mechanical breakdown: chewing, mixing food with saliva by the tongue, churning food in the stomach and segmentation. Segmentation mixes food with digestive juices and makes absorption more efficient. 4.) Digestion: a series of catabolic steps in which enzymes secreted into the lumen of the alimentary canal breakdown complex food molecules 5.) Absorption: is the passage of digested end products from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph. 6.) Defecation: Large intestine eliminates indigestible substances from the body via the anus
Describe the process of absorption of breakdown products of foodstuffs that occurs in the small intestine.
1.Large fat globules are emulsified (physically broken up into smaller fat droplets) by bile salts in the duodenum. 2.Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which "ferry" them to the intestinal mucosa. 3.Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons. 4.Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals. They are carried away from the intestine by lymph.
Describe embryonic development of the digestive system.
1.The epithelial lining of the developing alimentary canal forms from the endoderm with the rest of the wall arising from the mesoderm. 2.The anteriormost endoderm touches the depressed area of the surface ectoderm where the membranes fuse to form the oral membrane and ultimately the mouth. 3.The end of the hindgut fuses with an ectodermal depression, called the proctodeum, to form the cloacal membrane and ultimately the anus. 4.By week 8 the alimentary canal is a continuous tube stretching from the mouth to the anus.
How much fluid enters the digestive tract each day and where does it come from?
About 9 liters of fluid pass through the GI system each day, and only about 2 liters are ingested, the rest represent secretions from the system itself. About half, 3.5, liters is secreted from the exocrine glands, the salivary glands, the pancreas and the liver, the other half is secreted by the epithelial cells of the of the digestive tract it self.
What happens to nucleic acids in the digestive tract
Absorption: active transport via membrane carriers Absorbed in villi and transported to liver via hepatic portal vein Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines
Describe the role of the small intestine in the mechanical breakdown of food
As chyme slowly enters the duodenum, Carbohydrates and proteins are only partially digested. No fat digestion has taken place. Duodenum: is a segment of intestine between the stomach and the jejunum that is very active in digestion where many different enzymes mix from the stomach, liver, gallbladderand pancreas. Jejunum: The mucous membrane on the inner surface of the jejunum is covered with hair-like projections termed villi. These are instrumental in the absorption of nutrients such as proteins, carbohydrates, amino acid, sugar, fatty acid particles, vitamins, minerals, electrolytes and water. It is interesting to note that the villi in the jejunum are longer than those in the duodenum and the ileum. The surface are of the jejunum is also increased due to large circular folds called plicae circulares present in the submucosa. Ileum: absorbs mainly vitamin B12, other water soluble vitamins, bile salts, and nutrients that were not absorbed in the jejunum. More specifically, the absorption of the vitamins takes place at the terminal ileum - the last part of the ileum. Removal of this portion of the ileum will necessitate supplementary vitamin B12 doses for rest of the life.
How are glucose and amino acids transported across the mucosa
Carb Absorption: The Na+K+ pump stores energy that drives glucose and galactose uptake by creating a steep concentration gradient for Na+ entry into intestinal cells. As Na+ moves across the membrane through a membrane co-transporter protein, it drives glucose against its concentration gradient into the cells. **Fructose enters the cell by facilitated diffusion. **Monosaccharides exit across membrane via facilitated diffusion on the GLUT2 sugar transporter. Amino Acids: Proteins are digested to amino acids. The amino acids are then absorbed by active transport into the absorptive cells and move their opposite side. The amino acids leave the epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts.
Describe the role of the stomach in the mechanical breakdown of food
Further degrades food both physically and chemically. HCl produced by the stomach glands chemically breaks down proteins and food is converted into a creamy paste called chyme thats delivered to the small intestine. PEPSIN being the most important protein-digesting enzyme produced by the gastric mucosa. The only stomach function essential to life is the secretion of Intrinsic factor which is required for intestinal absorption of B12... needed to produce red blood cells.
Describe the tissue composition and the general function of each of the four layers of the alimentary canal.
Histology of the Alimentary Canal •Mucosa is the innermost, moist, epithelial membrane that lines the entire digestive tract. It secretes mucus, digestive enzymes, and hormones; absorbs digestive end products into the blood; and protects against infectious disease. •Submucosa is a moderately dense connective tissue layer containing blood and lymphatic vessels, lymphoid follicles, and nerve fibers. •Muscularis externa typically consists of smooth muscle and is responsible for peristalsis and segmentation. •Serosa, the protective outer layer of the intraperitoneal organs, is the visceral peritoneum.
Describe the roles of teeth in the mechanical breakdown of food
Masticate or chew by opening and closing our jaws, moving them from side to side while using our tongue to move the food between our teeth. In the process our teeth tear and grind the food, physically breaking it down into smaller fragments.
Name the cell types responsible for secreting the various components of gastric juice and indicate the importance of each component in stomach activity.
Mucous neck cells, found in the upper, or "neck," regions of the glands, produce a thin, soluble mucus Parietal cells - found mainly in the middle region of the glands, simultaneously secrete hydrochloric acid (HCl) and intrinsic factor. Although the parietal cells appear spherical when viewed with a light microscope, they actually have three prongs that bear dense microvilli (they look like fuzzy pitchforks!). This structure provides a huge surface area for secreting H and Cl into the stomach lumen. HCl makes the stomach contents extremely acidic (pH 1.5-3.5), a condition necessary for activation and optimal activity of pepsin. The acidity also helps in food digestion by denaturing proteins and breaking down cell walls of plant foods, and is harsh enough to kill many of the bacteria ingested with foods. Intrinsic factor is a glycoprotein required for vitamin B12 absorption in the small intestine. Chief cells occur mainly in the basal regions of the gastric glands. The chief cells produce pepsinogen, the inactive form of the protein-digesting enzyme pepsin. Chief cells also secrete insignificant amounts of lipases (fat-digesting enzymes). Enteroendocrine cells - ("gut endocrine"), typically located deep in the gastric glands, release a variety of chemical messengers directly into the interstitial fluid of the lamina propria.
Describe how fats, carbohydrates and proteins are digested and absorbed?
Proteins: The chemical side of digestion for proteins starts in the stomach where enzymes such as pepsin begin to break the proteins down into tinnier sections of amino acids. Carbs- Digestion for carbs begins in the mouth with the secretion of saliva from the salivary glands which breaks down complex sugars like starch into simple sugars like glucose. not much occurs enzyme wise in the stomach for carbs. next the they reach the small intestine where the pancreas secretes a slurry of enzymes simply referred to as the pancreatic juices but the main one that deals with carbs is carboxypeptidase. Also in the intestinal enzymes of the alkaline mucosal membranes in the small intestine help to digest carbs. These enzymes include: maltase, lactase and sucrase. All of the breaking down forms simple sugars that can easily diffuse into the blood stream or by products like the indigestible carb cellulose which is the fiber in your diet Fats- Bile emulsification to small fat droplets Enzymes: lipases, colipases & phospholipases Triglycerides monoglycerides & free fatty acids
How are the digested components of the cheeseburger absorbed by the digestive tract?
Stomach: absorbs a few fat-soluble substances (aspirin, alcohol, some drugs) Small Intestine: breakdown products of carbs, proteins, fat and nucleic acid digestion plus vitamins, electrolytes, and water are absorbed by active and passive mechanisms. Large Intestine: absorbs most remaining water, electrolytes (largely NaCl), and vitamins produced by bacteria.
Explain the dental formula and differentiate clearly between deciduous and permanent teeth.
The dental formula is a shorthand way of indicating the numbers and relative positions of the different types of teeth in the mouth. This formula is written as a ratio, uppers over lowers, for one-half of the mouth. (2I,1C,2PM,3M)/(2I,1C,2PM,3M) X 2=32 teeth Primary Dentition consists of the deciduous teeth (decid = falling off), also called milk or baby teeth. Permanent Teeth enlarge and develop, the roots of the milk teeth are resorbed from below
What is the role of the gall bladder?
The gallbladder is a small storage organ located inferior and posterior to the liver. Though small in size, the gallbladder plays an important role in our digestion of food. The gallbladder holds bile produced in the liver until it is needed for digesting fatty foods in the duodenum of the small intestine. Bile in the gallbladder may crystallize and form gallstones, which can become painful and potentially life threatening.
Describe the role of the gallbladder
The gallbladder stores and concentrates bile that is not needed immediately for digestion.
Describe the histologic anatomy of the liver.
The liver is composed of sesame seed-sized structural and functional units called liver lobules. Each lobule is a roughly hexagonal (six-sided) structure consisting of plates of liver cells, or hepatocytes, organized like bricks in a garden wall. The hepatocyte plates radiate outward from a central vein running in the longitudinal axis of the lobule.
What is the role of the pancreas in digestion
The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar.
Describe the regulation of defecation. Feces forced into the rectum by mass movements stretch the rectal wall and initiate the defecation reflex.
This spinal cord-mediated parasympathetic reflex causes the sigmoid colon and the rectum to contract, and the internal anal sphincter to relax. As feces are forced into the anal canal, messages reach the brain allowing us to decide whether the external (voluntary) anal sphincter should be opened or remain constricted to stop feces passage temporarily. If defecation is delayed reflex contractions end within a few seconds, and the rectal walls relax.With the next mass movement, the defecation reflex is initiated again—and so on, until the person chooses to defecate or the urge to defecate becomes unavoidable.
What is the role of the liver in digestion?
its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. In addition, the liver is the body's chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs.
List and define the major processes occurring during digestive system activity.
•Digestive Processes Ingestion is the simple act of putting food into the mouth (p. 853). Propulsion moves food through the alimentary canal and includes both swallowing and peristalsis (p. 853; Fig. 23.3). Mechanical digestion is the physical process of preparing the food for chemical digestion and involves chewing, mixing, churning, and segmentation (pp. 853-854). Chemical digestion is a series of catabolic steps in which complex food molecules are broken down to their chemical building blocks by enzymes (p. 854). Absorption is the passage of digested end products from the lumen of the GI tract through the mucosal cells into the blood or lymph (p. 854). Defecation eliminates indigestible substances from the body via the anus as feces
Describe abnormalities of the gastrointestinal tract at different stages of life.
•GI tract motility declines, digestive juice production decreases, absorption is less efficient, and peristalsis slows, resulting in less frequent bowel movements and often constipation. •Diverticulosis, fecal incontinence, and cancer of the GI tract are fairly common problems in the elderly.
Describe the gross and microscopic anatomy and the basic functions of the mouth, pharynx, and esophagus.
•Mouth is a stratified squamous epithelial mucosa-lined cavity with boundaries of the lips, cheeks, palate, and tongue The lips and cheeks have a core of skeletal muscle covered externally by skin that helps to keep food between the teeth when we chew and plays a small role in speech. The palate forms the roof of the mouth and has two parts: the hard palate anteriorly and the soft palate posteriorly. The tongue is made of interlacing bundles of skeletal muscle and is used to reposition food when chewing, mix food with saliva, initiate swallowing, and help form consonants for speech. Salivary glands produce saliva, which cleanses the mouth, dissolves food chemicals for taste, moistens food, and contains chemicals that begin the breakdown of starches. The teeth tear and grind food, breaking it into smaller pieces. •Pharynx - oropharynx and laryngopharynx provides a common passageway for food, fluids, and air (p. 864). •Esophagus - provides a passageway for food and fluids from the laryngopharynx to the stomach where it joins at the cardiac orifice
State the role of pancreatic juice in digestion.
•Pancreatic juice consists mainly of water and contains enzymes that break down all categories of foodstuffs and electrolytes. •Secretion of pancreatic juice is regulated by local hormones and the parasympathetic nervous system.
List the end products of protein, fat, carbohydrate, and nucleic acid digestion.
•Protein 1. Amino acids are absorbed by cotransport with sodium ions. 2. Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells. 3. Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. •Fat 1. Fatty acids and monoglycerides enter the intestinal cells via diffusion. 2. Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells, and the resulting chylomicrons are extruded by exocytosis. 3. The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct. 4. Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein. •Carbohydrate 1. Monosaccharides (simple sugars), the monomers of carbohydrates, are absorbed immediately 2. Glucose and galactose are absorbed via cotransport with sodium ions. 3. Fructose passes via facilitated diffusion. 4. All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. •Nucleic Acid 1. Units enter intestinal cells by active transport via membrane carriers. 2. Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein.
Describe the composition and functions of saliva, and explain how salivation is regulated.
•Saliva is largely water—97 to 99.5%—and therefore is hypoosmotic. As a rule, saliva is slightly acidic (pH 6.75 to 7.00), but its pH may vary. Its solutes include electrolytes (Na,K,Cl, PO43, and HCO3) the digestive enzymes salivary amylase and lingual lipase (both optimally active at an acid pH); the proteins mucin (mu sin), lysozyme, and IgA; and metabolic wastes (urea and uric acid). When dissolved in water, the glycoprotein mucin forms thick mucus that lubricates the oral cavity and hydrates foodstuffs. •The intrinsic salivary glands secrete saliva continuously in amounts just sufficient to keep the mouth moist.But when food enters the mouth, the extrinsic glands are activated and copious amounts of saliva pour out. The average output of saliva is 1000-1500 ml per day. Salivation is controlled primarily by the parasympathetic division of the autonomic nervous system.When we ingest foods, chemoreceptors and mechanoreceptors in the mouth send signals to the salivatory nuclei in the brain stem
Describe the function of the digestive system, and differentiate between organs of the alimentary canal and accessory digestive organs
•The digestive system takes in food, breaks it down into nutrient molecules, absorbs these molecules into the bloodstream, and then rids the body of the indigestible remains. •Digestive system organs fall into two main groups: the alimentary canal and the accessory organs (pp. 852-853). The alimentary canal, or gastrointestinal (GI) tract, is the continuous muscular digestive tube that winds through the body digesting and absorbing foodstuff; its organs include: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Accessory digestive organs aid digestion physically and produce secretions that break down foodstuff in the GI tract; the organs involved are the teeth, tongue, gallbladder, salivary glands, liver, and pancreas.
Describe the location and function of the peritoneum.
•The visceral peritoneum covers the external surfaces of most of the digestive organs, and the parietal peritoneum lines the body wall of the abdominopelvic cavity. •The peritoneal cavity is located between the visceral and parietal peritoneums and is filled with serous fluid. •Mesentery is a double layer of peritoneum that extends to the digestive organs from the body wall. It allows blood vessels, lymphatics, and nerves to reach the digestive organs, and holds the organs in place as well as stores fat.
Identify structural modifications of the wall of the stomach that enhance the digestive process.
•contains four tunics •fibers run obliquely; allows to mix, churn, move food along but pummel the food, physically breaking down into smaller fragments and to ram the food into the small intestine •lining epithelium is simple columnar epithelium composed entirely of mucous cells
List the enzymes involved in chemical digestion; name the foodstuffs on which they act.
•salivary amylase - Chemical digestion of carbohydrates begins in the mouth, where salivary amylase breaks large polysaccharides into smaller fragments. •Pepsin - secreted by the chief cells, begins the chemical digestion of proteins in the stomach. •Rennin - is produced in infants and breaks down milk proteins. •Pancreatic enzymes - such as trypsin and chymotrypsin, further break down proteins in the small intestine. •The brush border enzymes - carboxypeptidase, aminopeptidase, and dipeptidase work on freeing single amino acids in the small intestine. •Lipases are secreted by the pancreas and are the enzymes that digest fats after they have been pretreated with bile.
Differentiate between the roles of the various cell types of the intestinal mucosa.
•simple columnar absorptive cells=nutrient and electrolyte absorption •crypt epithelial cells= secretory cells the secrete intestinal juice •specialized cell types: absorptive cells, goblet cells, enteroendocrine cells, paneth cells
Identify and describe structural modifications of the wall of the small intestine that enhance the digestive process.
•the mucousa and submucousa are modified to reflect the intestines functions in the digestive pathway •epithelium= simple columnar absorptive cells bound by tight junctions (responsible for nutrient and electrolyte absorption) intestinal crypts= secretory cells the secrete intestinal juice (serve as a carrier fluid for absorbing nutrients from chyme)
