Ch. 26 Digestion
What are four functions of HCl in the stomach?
1.) activates pepsin from protein digestion; 2.) breaks down limited amt of plant cell walls; 3.) converts ferric to ferrous; 4.) destroys pathogens
What are three general substances in pancreatic juice?
1.) enzymes; 2.) zymogens; 3.) sodium bicarbonate
Explain the four histological layers of the GI tract.
1.) mucosa: stratified squamous in mouth, upper esophagus, and anus, anywhere else is simple columnar, contains own layer of smooth muscle called muscular mucosae; 2.) submucosa: connective tissue, bld vessels, nerve plexuses, MALT located here; 3.) muscle layers: inner circular smooth muscle and outer longitudinal smooth muscle layer for most of GI tract, myenteric nerve plexus controlling smooth muscle; 4.) adventitia/serosa: adventitia = areolar CT outside peritoneum, serosa = covered by visceral peritoneum
Explain five functions of the liver.
1.) remove hormones and toxins; 2.) make bile; 3.) secrete albumins, lipoproteins clotting factors and hormones; 4.) metabolism of nutrients; 5.) enzyme activation
Describe the phases of deglutition.
1.) voluntary phase: bolus of food is pushed by tongue against hard palate and moves toward oropharynx; 2.) pharyngeal involuntary phase: soft palate and uvula close nasopharynx, larynx elevates so epiglottis closes laryngeal opening; 3.) esophageal involuntary phase: peristaltic contractions of esophagus move bolus towards stomach
Explain how the chloride shift relates to events in the stomach.
H+ and Cl- have to enter separately into lumen of stomach, so Cl- shift allows Cl- to enter lumen while HCO3- enters bld
What substances makes the pH so low in the stomach? Why is this necessary?
HCl, to digest proteins
In general, what is a sphincter? Specifically, where is the LES, cardiac sphincter and pyloric sphincter? What is the role of these sphincters?
a ring of muscle that closes a tube; LES: end of esophagus and beginning of stomach, prevents acid from going up esophagus; cardiac sphincter: upper portion of stomach, prevents acid from going up esophagus; pyloric sphincter: by pyloris and beginning of duodenum, allows food from stomach to small intestine
What nutrient are made in the large intestine by bacteria?
biotin and vitamin K
Contrast bolus and chyme in terms of the substances each contain and where each is found in the digestive tract.
bolus: chewed food mixed with saliva, found in mouth and esophagus; chyme: food mixed with stomach juices, found in pyloris,
Explain the function of bile. What causes the gallbladder to secrete?
breaks down fats; cholecystokinin (CCK) causes gallbladder to release bile
Where and how (mechanism of action) are fatty acids, monoglycerides, monosaccharides, and amino acids absorbed?
diffusion for fatty acid and monoglycerides; monosaccharides and amino acids thru active transport in hepatic portal vein
What is the difference between the digestive tract and the digestive system? Include examples of organs or glands in each.
digestive tract: long tube which digesting food is passing; digestive system: accessory organs and GI tract
Where does most nutrient chemical digestion and absorption occur? Be specific for each nutrient.
duodenum is most chemical digestion, most nutrient absorption is jejunum; amino acids and monosaccharides in small intestine, fatty acids and monoglycerides in lymphatic system
Define: enterocytes, brush border, microvilli, villi.
enterocytes: simple columnar cells that line lumen of small intestine, make enzymes; brush border: formed by microvilli; microvilli: increase surface area, appear as brush border; villi: contains bld vessels and lacteal, increase surface area
Explain the role of the epiglottis and the uvula.
epiglottis: prevents food from entering trachea; uvula: prevents food from entering nasal cavity
Explain how the pancreas is exocrine and remember how it is endocrine.
exocrine: substances released thru duct, 99% of functionality is exocrine; endocrine: hormones released into bld, 1% function endocrine
Explain the roles of gastrin, CCK, and secretin as discussed in class.
gastrin: stimulates activity in stomach; CCK: causes gallbladder to contract; secretin: causes decrease in secretory activity of stomach
What are the functions of the greater omentum and the mesentery proper?
greater momentum: fatty apron of adipose tissue that insulates organs and stores fat; mesentery proper: fan-shaped peritoneum that supports and stabilizes jejunum and ileum
What is the role of the taeni coli?
help bunch of large intestine into sacs called haustra
What is the hepatic portal vein versus the hepatic vein.
hepatic portal vein: transports deoxygenated and nutrient-rich bld from capillary beds of GI tract, spleen, and pancreas; hepatic vein: collects bld from central vein and empty into inferior vena cava
What type of chemical reaction allows foods to be broken down? Describe what occurs in these reactions? What molecule is necessary to speed up the rate of these reactions?
hydrolysis; water is added to break chemical bonds; catalyst?
Explain the type of muscle present in the anal sphincters and the significance of this.
internal: smooth muscle, involuntary control; external: skeletal muscle, voluntary control
Where are microbiota in the GI tract and what benefits do they provide?
large intestine; microbiome makes it possible to make biotin and extract more vitamins
Which accessory organ makes bile and which accessory organ stores bile? Can a person live without the organ that stores bile?
liver; gallbladder; yes
What is the LES and describe its role in acid reflex, GERD and heartburn.
lower esophageal sphincter prevents stomach acid from entering esophagus; if sphincter is not working properly, acid will enter esophagus and cause problems such as acid reflux, heartburn, and GERD
What is a lacteal and which nutrient is first absorbed in a lacteal?
modified lymphatic vessel for fatty acid absorption
What is the common term for each of the following: oral cavity, pharynx, colon
mouth, throat, large intestine
List the organs of the digestive tract in the order in which they occur as food is being digested. Then, describe four accessory organs in terms of their functions.
oral cavity, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (ascending, transverse, descending, sigmoid colon), rectum, anus; 1.) teeth: allow for mechanical digestion, 2.) tongue: swallowing, 3.) salivary glands: create saliva to lubricate food, 4.) liver: produces bile
Explain the role of parietal and chief cells of the stomach.
parietal cells: secrete HCl and intrinsic factor (IF- for vitamin. B 12 absorption); chief cells: secrete pepsinogen which is activated into pepsin by HCl to digest proteins
List the salivary glands and the components of saliva. Include the functions of components as appropriate.
parotid salivary gland, submandibular gland, sublingual gland; saliva: 99.5% water, pH of 6.4-6.8, mucus (lubricates bolus), electrolytes, lysozyme (antimicrobial), IgA (antibody), salivary amylase (chemical digestion of carbs), lingual lipase (chemical digestion of fats)
What relative amounts of saliva are produced by salivary glands?
parotid: 25-30%; submandibular: 60-70%; sublingual: 3-5%
Contrast peristalsis versus segmentation.
peristalsis: moves contents along GI tract by alternating contractions of circular and longitudinal layers; segmentation: localized mixing and churning
Explain the role of rugae and plicae.
rugae: increase surface area of stomach after meal; plicae: small circular folds of small intestine, increase surface area
Why is intrinsic factor necessary and what cells release it?
secreted by parietal cells; needed for vitamin B12 absorption in small intestine
List the parts of the small intestine and the parts of the large intestine.
small: duodenum, jejunum, ileum; large: ascending, tranverse, descending, sigmoid colon
When chyme exits the stomach, what substance increases the pH and from which accessory organ does this originate?
sodium bicarbonate from pancreas
Most parts of the GI tract have two layers of smooth muscle (a circular layer and a longitudinal layer). How does this differ in the stomach?
stomach has 3 layers of smooth muscle (circular, longitudinal, and oblique)
Describe the peritoneum. Then, list GI organs that are intraperitoneal and retroperitoneal.
thin serous membrane that lines anterior abdominal cavity, made of parietal peritoneum, peritoneal cavity, and visceral peritoneum; intraperitoneal: stomach, jejunum, and ileum of small intestine; retroperitoneal: duodenum, pancreas, ascending and descending colon, rectum
Explain the various features that increase surface area in the small intestine.
villi, microvilli, plicae
What nutrient is absorbed in the large intestine?
water
