chapter 22 the digestive system

Define retroperitoneal

abdominal organs partly or completely outside peritoneal cavity

Define mesenteries

areas where visceral peritoneum folds over on itself around certain organs, particularly small intestine 1. support & bind these organs together & keep small intestine in particular shape that fits within abdominopelvic cavity 2. also house blood vessels, nerves, & lymphatic vessels, anchoring them in place

define mastication

chewing

define emulsification

coat lipids in duodenum and physically break them apart into smaller pieces

define alimentary canal

continuous tube through which food passes directly

define enterogastric reflex

decrease vagal activity & acid secretion

describe peritoneal cavity

found between the outer parietal peritoneum & visceral peritoneum contains serous fluid

organs of the alimentary canal

mouth pharynx esophagus stomach small intestine large intestine

describe the structure of esophagus

muscular tube about 25 cm (10 in) long found posterior to trachea

Define accessory organs

not part of alimentary canal but assist in digestion in some way 1. food generally does not come in direct contact with this type of organ, although teeth and tongue are exceptions

define intraperitoneal

organs located entirely within peritoneal cavity

Define chyme

pummels food in to liquid

list the two types of cells in a salivary gland

serous cells mucus cells

Define bolus

soft mass of chewed food ready to be swallowed

define deglutition

swallowing

organs in accessory organs

teeth tongue salivary gland liver gallbladder pancreas

list three pairs of salivary gland

three pairs of salivary glands, secrete saliva, a fluid containing water, enzymes, mucous & other solutes, through a duct into oral cavity - submandibular -sublingual -parotid gland

explain motility of the stomach in terms of its churning function

- after a meal, smooth muscle layers of stomach begins to produce waves of peristalsis a. peristalsis propels bolus to pylorus where small amounts of chyme are propelled through pyloric sphincter into duodenum b. remainder of chyme is pushed backward into stomach where peristaltic waves churn and mix chyme, and process repeats

describe roles the proximal portions of the large intestine

- consists of ascending and transverse colon B. is primary site of water and electrolyte absorption and bacterial activity

explain motility of the stomach in terms of emptying function

- control movement of chyme into duodenum; different materials pass though pyloric sphincter at different rates a. liquids move rapidly from stomach to duodenum with essentially no delay b. solids must be converted to a nearly liquid state before they are able to enter small intestine c. control of gastric emptying is critical because duodenum must mix incoming chyme thoroughly before it moves to rest of small intestine; two reasons 1. chyme as acidic, and duodenum must mix it with bicarbonate ions to avoid damaging intestinal mucosa 2. chyme is generally very concentrated and must be diluted with water from pancreatic juice to prevent chyme from drawing water into intestinal lumen by osmosis

Describe the histology of the stomach

- has four tissue layers as rest of alimentary canal; exceptions: 1. additional oblique layer of smooth muscle allows stomach to perform churning a. pummels food into liquid called chyme 2. mucosa of stomach is heavily indented to form deep structures called gastric pits a. contains columnar cells and numerous goblet cells, both of which secrete a think mucus that lines & protects cells of the stomach from its own secretions 3. gastric gland contain both endocrine and exocrine cells a. secrete hormones & an acidic gastric juice

describe the process of deglutition

- specialized type of propulsion that pushes a bolus of food from oral cavity through pharynx and esophagus to stomach -swallowing relies on coordinated actions of upper alimentary canal, including soft palate, pharynx & esophagus; tongue also plays a role in this process

describe the major functions of the digestive system

- take food into body & break down into its component nutrients so that they can be used by body cells -playing a critical role in fluid, electrolyte, and acid-base homeostasis by taking in water and electrolytes via diet and delivering them to blood -ingesting vitamins and minerals -producing hormones -excreting metabolic wastes

the three phases of deglutition

- voluntary phase: tongue pushes bolus toward oropharynx - pharyngeal phase: bolus enters oropharynx; soft palate & epiglottis seals off nasopharynx and larynx - esophageal phase: peristaltic waves move bolus down esophagus

roles of the gastroesophageal sphincter

-at esophagus inferior end is another specter called _______ - regulates passage of bolus into stomach - also prevents contents of stomach from re-entering esophagus

roles of the upper esophageal sphincter

-at the junction of pharynx and esophagus , muscularis externa is modified into a sphincter called _______ - controls passage of bolus into esophagus

describe roles the distal portions of the large intestine

-consists of descending and sigmoid colon, rectum and anal canal C. performs a small amount of absorption, primarily of water but its main role is to store fecal material until it is ready to be expelled during defecation

describe the peritoneal membrane

-largest serous membrane in body 1. consist of following two layers: a. outer parietal peritoneum lines inner surface of body wall b. visceral peritoneum, or serosa- where parietal peritoneum meets abdominal organs, its folds in on itself forms outer tissue layer of such organs

describe the function of saliva

-moistening, lubricating, & cleansing oral mucous - lysozyme & IgA deter growth pf pathogenic bacteria in oral cavity - mechanical digestion, achieved by moistening and helping to mix ingested food into a bolus so it can be swallowed -chemical digestion, achieved by actions of salivary amylase - many food molecules dissolve in water of saliva & these molecules then stimulate taste receptors on tongue

explain what serous cells produce

-secrete a water based fluid with enzymes & other solutes - generally released just before or during eating

explain what mucous cells produce

-secrete mucous primarily involved in keeping oral mucosa moist - released continually

describe function of esophagus

-transports a bolus from pharynx to stomach - esophageal mucosa contains esophageal glands which secrete mucus to lubricate bolus as it passes through esophagus - primary functions of ______________ are propulsion & a small amount of secretion of mostly mucus

cells and function of gastric glands

1. enteroendocrine cells secrete hormones that influence digestion a. gastrin stimulates acid secretion 2. chief cells secrete pepsinogen a. when pepsinogen encounters an acidic pH, it becomes pepsin 1. begins protein digestion in stomach 3. parietal cells secrete hydrochloric acid (HCI) a. responsible for acidic pH of gastric juice b. acid activates pepsinogen, destroys many disease-causing organisms, and stimulates parietal cell production of chemical intrinsic factor; required for intestinal absorption of vitamin B12 4. mucous neck cells secrete acidic mucus a. prevents neutralization of acid produced by parietal cells

explain the process of enzymatic hydrolysis reactions of nutrient ,molecules

1. explains why so much water is secreted with fluids 2. water molecules are key components of reactions that chemically break down food molecules 3. digestive enzymes speed up these reactions by a process known as enzymatic hydrolysis

gallbladder pathway of bile flow

1. gallbladder to release bile into cystic duct 2. cystic duct joins common hepatic duct to form common bile duct 3. common bile duct joins main pancreatic duct near duodenum to form hepatopancreatic ampulla 4. ampulla is surrounded by a ring of smooth muscle called hepatopancreatic sphincter a. controls emptying of bile and pancreatic fluids into duodenum 5. contents of hepatopancreatic ampulla empty into duodenum at major duodenal papilla

other liver functions

1. liver excretes bilirubin; a waste product that results from breakdown of hemoglobin by spleen a. some remains in blood and is excreted by kidneys 2. nutrient metabolism- processes nutrients obtained from diet 3. detoxification- detoxifies substances produced by body and substances that we eat or drink, some of which are harmful to body 4. excretion- directly excretes bilirubin in bile along with other substances liver processes, particularly certain antibiotics; also modifies substances so that they can be excreted by kidneys

explain two types of digestion

1. mechanical digestion, in which food is physically broken into smaller parts a. all nutrients go through same mechanisms of mechanical digestion 2. chemical digestion, in which chemical bonds between food molecules are broken a. chemical digestion varies for each nutrient because digestive enzymes are specific for a single type of bond in a single type of nutrient

describe the functions of bacteria within the large intestine

1. produce vitamins- such as vitamin K, which is necessary for blood clotting 2. metabolize undigested materials 3. deter growth of harmful bacteria 4. stimulate immune system- during infancy, normal flora induce immune tolerance to their own antigens at same time, they stimulate development of mucosa-associated lymphoid tissue (MALT) and production of antibodies to pathogens

describe the acid secretion function of the stomach including the three regulatory phase

1.occurs continuously throughout day between meals, at what is known as basal rate 2. during eating, secretion can be divided into three phases a. cephalic phase- mediated by sight, smell, taste, or even though food under direction of CNS 1. prepares stomach to receive food by increasing release of hydrogen ions into it b. gastric phase- begins when food enters stomach 1. presence of food or partially digested proteins stimulates acid secretion due to gastrin c. intestinal phase- responsible for only 10% of remaining acid secretion after which it inhibits further acid secretion 1. triggered by presence of partially digested proteins in fluid entering duodenum releases more gastrin 2. stimulatory effect of intestinal phase is brief; as chyme enters duodenum, declining pH & presence of lipids trigger enterogastric reflex 3. secretin & gastric inhibitory peptide (GIP) from duodenum reduce acid secretion

describe the composition of saliva

A. consist primarily of water, electrolytes such as sodium, chloride, & potassium ions; & variable amounts of mucus also contains: - salivary amylase- fist digestive enzyme that ingested food encounters; catalyzes beginning at carbohydrate digestion -enzyme lysozyme catalyze perforation of bacterial plasma membrane; allows bacteria- killing substances in saliva to enter & kill bacteria - secretory IgA- antibody immunoglobulin A or IgA; binds specific antigens on pathogens and mediates their destruction - bicarbonate ions function is to neutralize any acid from stomach that regurgitates into esophagus

discuss the basic functions of the oral cavity, teeth & tongue

A. digestive system begins with this cavity where four different digestive processes occur: ingestion, secretion, chemical & mechanical digestion, & propulsion B. it is part of alimentary canal it also houses two accessory organs teeth & tongue C. three pairs of accessory organ, salivary gland, are located in & around this cavity 1. turns ingested food into moist, chewed mass called bolus D. posterior oral cavity, pharynx, & esophagus then delivers bolus to stomach through process of swallowing or deglutition E. teeth masticate, or chew, ingested food , grinding it into small pieces 1. mastication aids digestion by increasing overall surface area of food, giving digestive enzymes more places to catalyze reactions of chemical digestion F. tongue is involved during ingestion phase of digestion 1. movement of tongue during chewing helps turn food into bolus 2. tongue also pushes the food against hard palate during chewing, which assists in mechanical digestion, & also push bolus posteriorly during swallowing

describe motility in small intestine during fasting

A. during fasting, small intestine exhibits slow, rhythmic contractions along its length in a pattern called migrating motor complex 1. contractions clear any remaining material, including leftover food and secretions 2. requires about 2 hours to push digesting food from duodenum to ileocecal valve 3. controlled by both ENS and a hormone called motilin; produced by cells in duodenal mucosa

describe the pancreas and its digestive function

A. for digestive system: secretes enzymes that are released into ducts of pancreas that empty into alimentary canal; makes pancreatic juice B. pancreatic juice- collective secretions of pancreatic acinar and duct cells 1. consists of water and multiple digestive enzymes and other proteins 2. duct cells also secrete bicarbonate ions, a base, which make pancreatic juice alkaline a. alkaline juice helps neutralize acidic chyme that enters duodenum from stomach; protects duodenum from damage by acid 3. its digestive enzymes, secreted by acinar cells are crucial in chemical digestion a. catalyze reactions that digest carbohydrates, proteins, lipids, and nucleic acids c. pancreatic secretion occurs at a basal rate between meals; during eating, pancreatic secretion rises due to parasympathetic and hormonal stimulation

describe the six basic processes of the digestive system

A. ingestion: bring food & water into digestive system 1. occurs via mouth under normal conditions B. secretion: digestive organs contain both endocrine and exocrine glands that secrete a variety of substances, such as; mucus, enzymes, acid, hormones- to aid other digestive processes C. propulsion: process that allows ingested food and liquids pass from one digestive organ to next 1. propulsion is accomplished largely by rhythmic contractions of the smooth muscle of alimentary canal called peristalsis; aided by mucus secreted by multiple organs D. digestion: food breakdown E. absorption: movement of digested food particles through wall of alimentary canal into blood and lymphatic vessel 1. water, electrolytes, vitamins are also absorbed into blood in same manner F. defecation: exit of certain ingested materials are not digestible or usable by body 1. defecation also provides body with a way to eliminate certain metabolic wastes

describe the structure of small intestine

A. internally three progressively smaller types of folds; most absorption that occurs takes place in this region 1. folds increase surface area available for absorption that occurs takes place in this region B. circular folds: largest type of folds: visible with naked eye as ridges in wall 1. folds also slow down transit of chyme through small intestine cells (enterocytes) more time to absorb nutrients C. smaller two types of folds are not visible to naked eye 1. mucosa folds into projections called villi a. each villus consists of a layer of enterocytes surrounding central core of blood capillaries and a lymphatic vessel called lacteal b. between villi mucosa indents to form intestinal crypts 1. house glands with enteroendocrine cells and mucus-secreting goblet cells 2. smallest folds, microvilli, are found in plasma membrane of enterocytes a. each enterocyte has as many as 3000 microvilli; gives cell appearance of a bristle brush border b. digestive enzymes produced and secreted by enterocytes catalyze reactions that break down disaccharides and peptides

describe the liver functions that pertain to digestion

A. main digestive function is to produce bile 1. bile: a liquid that contains multiple components, including water, electrolytes, and organic compounds 2. bile serves two critical function a. required for digestion and absorption of lipids b. mechanism by which liver excretes wastes and other substances that kidneys cannot excrete 3. liver produces bile continually but generally does not secrete it at a basal rate

describe the function of the small intestine

A. main processes occur in small intestine: secretion, digestion, absorption, and propulsion 1. enterocytes produce multiple digestive enzymes, hormones and mucus 2. enzymes are responsible for bulk of chemical digestion 3. after nutrients are digested chemically, they are absorbed across enterocytes into either blood or lymph, along with water, vitamins and other substances 4. also mixes and propels its contents along its length and into large intestine

briefly explain regulation of motility by the endocrine and nervous system

A. movement of the alimentary canal is a key process in every region of canal B. each type of motility is regulated by nervous system and/or endocrine system C. nervous system regulation of motility consist of nerves of autonomic nervous system, or ANS 1. enteric nervous system, or ENS is a self-contained branch of autonomic nervous system that extends from esophagus to anus

describe the histology of large intestine

A. mucosa of large intestine lacks villi and its cells lack microvilli 1. these structural adaptations reflect fact that nutrient absorption is not large intestine primary function B. mucosa is rich with goblet cells that secrete protective and lubricating mucus

describe the role of the pharynx in regards to digestion

A. only oropharynx & laryngopharynx are part of alimentary canal B. oropharynx houses two sets of tonsils- palatine tonsils and lingual tonsils 1. tonsils perform defensive functions; protect remainder of alimentary canal from any pathogens that enter body via oral and nasal cavities C. primary function of pharynx is propulsion in form of swallowing, during which bolus passes through pharynx and into esophagus

describe the function of large intestine

A. receives material from small intestine that was not digested or absorbed and is a passageway for feces and fecal matter to exit body B. active in absorbing water and electrolytes 1. critical for maintaining fluid, electrolyte and acid-base homeostasis C. secretion (primarily in form of mucus), propulsion and defecation D. houses numerous bacteria that perform important functions such as synthesizing vitamins

describe the function of the gallbladder

A. stores bile, concentrates if (removing water) and releases it when stimulated

describe motility in small intestine during eating

B. during eating: peristalsis and segmentation 1. peristalsis is accomplished by alternating contracts of longitudinal and circular layers of smooth muscle in muscularis externa a. primary function is to propel chyme toward ileum and ultimately through ileocecal valve to cecum 2. segmentation also known as intestinal churning, involves contractions of only circular layer of smooth muscle a. produces a squeezing motion b. primary functions are mechanical digestion and mixing chyme with intestinal and pancreatic enzymes as well as bile

explain the motility of the stomach in terms of its receptive function

B. motility enables stomach to receive food from esophagus, churn incoming bolus into chyme, and control rate at which chyme empties into small intestine. 1. receptive function- when food or liquid is swallowed, gastroesophageal sphincter and smooth muscle of fundus and body of stomach relax to allow stomach to fill a process known as receptive relaxation

explain the role of bile

B. one of bile's main compounds is bile salts 1. bile salts are amphiphilic, meaning they have both polar and nonpolar part a. allows bile salts to interact with both lipids and watery environment of small intestine 2. coat lipids in duodenum and physically break them apart into smaller pieces a. process know as emulsification 3. mechanical digestion necessary for chemical digestion and absorption of lipids 4. bile also contains varying amounts of materials that liver excretes, including cholesterol, waste products, and toxins such as heavy metals

explain the motility of large intestine

D. two main types of motility of proximal segment: 1. type of segmentation (churning) a. circular muscle of each haustrum contracts repeatedly; swirls material around in haustrum b. aids in water and electrolyte absorption primarily controlled by local neurons of ENS; triggered by stretch 2. propulsive motion known as a mass movement (mass peristalsis) a. during a mass movement, multiple haustra undergo peristalsis: propels their contents toward distal large intestine b. mass movement occurs three to four times per day, and appear to be triggered by food consumption; initiates reflexes controlled by ENS E. distal large intestine is much less motile than proximal large intestine 1. when mass movements force fecal material into normally empty rectum, it initiates parasympathetic-medicated defecation reflex