chapter 24: digestive system Flashcards
1
Q
anatomy of the digestive system
A
digestive tract and accessory organs
2
Q
digestive tract
A
gastrointestinal (GI) tract; alimentary canal; a tube from the mouth to the anus
includes oral cavity, pharynx, esophagus, stomach, small intestine, large intestine
3
Q
accessory organs
A
includes glands that secrete substances into digestive tract
includes the tongue, teeth, salivary glands, liver, gallbladder, pancreas
4
Q
functions of the digestive system
A
ingestion and mastication, propulsion and mixing, secretion, digestion, absorption, elimination
5
Q
propulsion and mixing
A
consists of swallowing, peristalsis, and mass movements
6
Q
swallowing
A
deglutition; moves food and liquid (bolus) from the oral cavity into the esophagus
7
Q
peristalsis
A
moves material though the digestive tract
1) wave of circular smooth muscle relaxation moves ahead of bolus or chyme allowing digestive tract to expand
2) wave of contraction of circular smooth muscles behind bolus or chyme propels it through the digestive tract
3) mixing done by mixing waves in stomach and segmental contractions in the small intestine
8
Q
mass movements
A
in the large intestine
9
Q
secretion
A
lubricates, liquefies, digests, protects
consists of mucus, water, enzymes
10
Q
mucus (secretion)
A
secreted along the entire tract;
lubricates food and lining;, coats lining; provides protection from mechanical digestion, acid, and digestive enzymes
11
Q
water (secretion)
A
liquefaction makes food easier to digest and absorb
12
Q
enzymes (secretion)
A
chemical digestion
13
Q
digestion
A
mechanical and chemical; digestion of carbohydrates, proteins, lipids, nucleic acids
14
Q
absorption
A
movement from the tract into the blood or lymph
15
Q
elimination
A
waste products (feces) is removed from the body through defecation
16
Q
process of peristalsis
A
1) muscular contractions with a wave of relaxation of circular muscles in front of the bolus
2) a wave of strong contraction of circular muscles behind the bolus, which forces the bolus along the digestive tract
17
Q
segmental contractions
A
1) mass of bolus within the tract begins at one location
2) segments of the tract alternate between contraction and relaxation
3) mass of bolus spreads out (dilutes) in both directions
18
Q
histology of the digestive tract
A
mucosa, submucosa, muscularis, serosa
19
Q
mucosa
A
innermost layer of digestive tract
extends into lamina propria in places to form intestinal glands or crypts
specialized cells include mechanoreceptors for peristalsis and chemoreceptors fro chemical digestion
20
Q
mucosa composition
A
mucous epithelium: nonkeratinized stratified squamous epithelium in the mouth, oropharynx, esophagus, anal canal, and simple columnar epithelium in the rest of the gastrointestinal tract
lamina propria: loose connective tissue
muscularis mucosae: smooth muscle
21
Q
submucosa
A
thick connective tissue layer with nerves, blood vessels, lymphatics, and small glands
22
Q
submucosal plexus (meissner plexus)
A
network of neurons and glial cells of the enteric nervous system that control the release of intestinal gland secretion
note: esophagus and stomach lack submucosal plexus
23
Q
muscularis
A
2 to 3 layers of smooth muscle (circular and longitudinal layers); contains myenteric plexus between layers
24
Q
myenteric plexus (auerbach plexus)
A
controls movement along the gastrointestinal tract; interstitial cells form a network of pacemakers to promote rhythmic contraction
enteric nervous system: submucosal and myenteric plexuses
25
serosa (adventitia)
connective tissue; serosa along the visceral peritoneum and adventitia along the outer layer
26
local nervous regulation of the digestive system
enteric nervous system (ENS); sensory, motor, interneurons
coordinates peristalsis and regulates local reflexes
27
general nervous regulation of the digestive system
coordination with the central nervous system; parasympathetic primarily
may initiate reflexes because of sight, smell, or taste of food
28
sympathetic input of general nervous regulation of the digestive system
inhibits muscle contraction, secretion, and decrease of blood flow to the digestive tract
29
neurotransmitters (chemical regulation of the digestive system)
acetylcholine stimulates while norepinephrine inhibits; serotonin stimulates digestive motility
30
_____ percent of the body's serotonin is found in the digestive tract (microbiota)
95
31
gastrin and secretin
part of the chemical regulation of the digestive system
32
paracrine chemicals (chemical regulation of the digestive system)
example: histamine
help local reflexes in the enteric nervous system control conditions of the digestive tract internal environment (example: pH levels)
33
peritoneum (serosa)
double layered, continuous serous membrane; visceral peritoneum and parietal peritoneum; retroperitoneal
34
visceral peritoneum
covers the organs
35
parietal peritoneum
covers the interior surface of the body wall
36
retroperitoneal
certain organs covered by the peritoneum on only one surface; considered behind the peritoneum
found in the kidneys, pancreas, duodenum
37
peritonitis
inflammation of the peritoneum
38
mastication
involves chewing and mastication reflex
39
chewing
incisors and canines bite or cut off food; premolars and molars grind food
muscles involved: masseter, temporalis, medial and lateral pterygoids
40
mastication reflex
medulla oblongata controls basic movements involved in chewing; conscious override from the cerebrum
41
what are the three pairs of salivary glands?
parotid (largest), submandibular, sublingual (smallest)
42
what are additional salivary glands (aside from the main three)?
palate, cheek, lip
43
saliva
produce amylase; function in gustation
44
swallowing involves what structure?
pharynx, esophagus, sphincters
45
pharynx (swallowing)
pharyngeal constrictors in oropharynx and laryngopharynx contribute to swallowing; epiglottis covers the larynx to keep food and drinks out of it
46
esophagus (swallowing)
transports food to the stomach; passes through the diaphragm
47
hiatal hernia
widening of the hiatus of the diaphragm
48
what are the swallowing phases?
voluntary, pharyngeal, esophageal
49
voluntary swallowing (phase one)
bolus of food is moved by the tongue from the oral cavity to the pharynx
50
pharyngeal swallowing (phase two)
reflex is controlled by the medulla oblongata
soft palate elevates, upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, and food is pushed into the esophagus by pharyngeal constrictors
51
esophageal swallowing (phase three)
stretching of the esophagus causes the enteric nervous system to initiate peristalsis of the muscles in the esophagus
52
stomach mucosa epithelial lining
simple columnar with goblet cells
53
protective properties of the stomach mucosa
mucus layer traps bicarbonate underneath to neutralize it (ph from 1 to 2); epithelial cells are connected by tight junctions; gastric glands are impermeable to gastric juice
54
gastric pits
extend deep into the stomach mucosa
consists of gastric glands, enteroendocrine cells, neck cells, parietal cells, chief cells, and chyme
55
gastric glands
secrete gastric juice for chemical digestion
56
enteroendocrine cells
secrete histamine and gastrin; some secrete somatostatin to inhibit gastrin and insulin secretion
57
neck cells
produce mucus
58
parietal cells
associated with HCl and intrinsic factor (allows for the uptake of vitamin B12)
59
chief cells
secrete pepsinogen and gastric lipase
60
pepsinogen is converted to pepsin via _____ (protein digestion_
hydrochloric acid (HCl)
61
chyme
slurry of mechanical and chemical digestion
62
regulation of stomach secretions: cephalic phase
1) taste or smell of food; tactile sensations of food in mouth or thoughts of food stimulate the medulla oblongata
2) parasympathetic action potentials carried by the vagus nerve to to the stomach where the enteric plexus neurons are activated
3) postganglionic neurons stimulate secretion by parietal and chief cells (HCl and pepsin) and stimulate the secretion of gastrin and histamine
4) gastrin is carried through circulation back to the stomach where it and histamine stimulate further secretion of HCl and pepsin
63
regulation of stomach secretions: gastric phase
1) distention of the stomach activates action potentials carried by the vagus nerves to the medulla oblongata (reflex)
2) medulla oblongata stimulates further secretions of the stomach
3) distention stimulates local reflexes to amplify the stomach secretions
4) gastrin is carried through the blood and back to the stomach where it stimulates secretions with the aid of histamine
64
regulation of stomach secretions: intestinal phase
1) chyme in duodenum; pH less than one with lipids that inhibit gastric secretions
2) sensory input to the medulla oblongata from the duodenum inhibits motor input from the medulla oblongata to the stomach, and stops secretion of pepsin and HCl
3) local reflexes inhibit gastric secretions
4) secretin and cholecystokinin produced in the duodenum decreases gastric secretion with the help from the enterogastric reflex
65
during the gastric phase, increased acid levels in the stomach trigger what?
decrease in additional acid secretion
66
during the intestinal phase, acidic chyme entering the duodenum triggers what?
decrease in stomach and acid secretion
67
negative-feedback loops (control of gastric secretions)
ensure that acidic chyme entering the duodenum is neutralized
this is because digestion of food by the pancreas and small intestine are inhibited by acid; there is also a prevention of peptic ulcer formation
68
movements in the stomach
1) weak contractions cause mixing waves to thoroughly mix food with stomach secretions to form chyme
2) fluid chyme is pushed toward the pyloric sphincter and solid chyme moves back toward the body of the stomach
3) stronger contraction cause peristaltic waves, forcing chyme toward and through the pyloric sphincter
4) fluid chyme is pushed toward the pyloric region while solid chyme squeezes past peristaltic constriction toward the body of the stomach
5) each peristaltic contraction is sufficiently strong enough to cause partial relaxation the pyloric sphincter and pump, increasing motility and emptying
69
what occurs when the stomach empties too quickly?
efficiency of digestion and absorption decreases; acidic chyme can damage duodenum and cause peptic ulcers
70
what occurs when the stomach empties too slowly?
stomach wall can be damaged by acid, causing gastric ulcers
71
what is a major stimulus for both secretions and motility?
distention of the stomach (increase in motility = increase in emptying)
72
what is the effect of hormonal and neural mechanisms with the duodenum?
decrease in gastric secretions and motility; prevents relaxation of the pyloric sphincter
73
enterogastric reflex and cholecystokenin
major inhibitors of gastric motility; reduce the rate of stomach emptying
74
_____-rich chyme stays in the stomach longer
fat
75
_____-rich chyme moves through the stomach quickly
carb
76
voting mechanism
form of stomach emptying; associated with emetic center in the medulla oblongata
77
small intestine
primary site for digestion and absorption of nutrient and water
structures: duodenum, jejunum, ileum
78
what structures of the small intestine are major sites of nutrient and water absorption?
duodenum and jejunum
79
anatomy (and histology) of the small intestine
circular folds, villi, microvilli
80
circular folds (plicae)
folds of the mucosa and submucosa perpendicular to the long axis
81
villi
finger-like projections of the mucosa; each covered by simple columnar epithelium; contains blood capillary network and lacteal
82
microvilli
cytoplasmic extensions on the apical surface of simple columnar cells of villi
function to increase surface area of the brush border
83
what are the different cell types of epithelial lining?
absorptive, goblet, granular, endocrine
84
absorptive cells
produce digestive enzymes and absorb digested food; contains microvilli
85
goblet cells
produce protective mucus
86
granular cells (paneth cells)
may help protect against bacteria
87
endocrine cells
produce regulatory hormones
88
intestinal glands
tubular glands in the mucosa as the base of villi
89
duodenal glands
tubular mucous glands of the submucosa that open into the base of intestinal glands
90
small intestine
major site of nutrient absorption; gradual decrease in diameter and thickness of the intestinal wall; number of circular folds and number of villi are farther way from the stomach
91
features of the small intestine
major and minor duodenal papillae, peyer's patches, ileocecal junction
92
major and minor duodenal papillae
openings to ducts from the liver and/or pancreas
93
peyer's patches
lymphatic nodules of the mucosa and submucosa
94
ileocecal junctions
contains a rings of smooth muscle (ileocecal sphincter) and a one-way ileocecal valve
95
secretions of the small intestine
fluid primarily composed of water, electrolytes and mucus
96
mucus (secretion of the small intestine)
protects against digestive enzymes and stomach acids (can lead to peptic ulcers)
secreted by the duodenal glands, intestinal glands, and goblet cells
97
electrolytes and water (secretion of the small intestine)
keep chyme in aqueous solution to facilitate chemical digestion
98
digestive enzymes (secretion of the small intestine)
bound to the membranes of absorptive cells (called brush border enzymes)
99
disaccharidases
break down disaccharides to monosaccharides
100
peptidases
hydrolyze peptide bonds
101
movement in the small intestine
mixing and slow propulsion over short distances
segmental contractions mix while peristalsis propels
generally takes about 3 to 5 hours for chyme to move from the pyloric sphincter to the ileocecal junction
102
ileocecal sphincter
remains slightly contracted until peristaltic waves reach the sphincter; then relaxes to allow chyme to move into the cecum
103
cecal distention
causes local reflex; ileocecal valve constricts
prevents more chyme from entering the cecum; increases digestion and absorption in the small intestine by slowing the progress of chyme; prevents backflow
104
functions of the liver
bile production, nutrient storage, processing of nutrients, detoxification, synthesis of new molecules
105
bile production (liver function)
for digestion and excretion; bile salts (bilirubin), bile pigments, cholesterol, fats, fat-soluble hormone, lecithin
neutralizes and dilutes stomach acid
106
bile salts
emulsify lipids and solubilize cholesterol; are reabsorbed in the ileum (95%)
107
secretin
from the duodenum; stimulates bile secretion, increasing H2O and HCO3- content of the bile
108
nutrient storage (liver function)
glycogen, fat, vitamins (A, B12, D, E, K), copper, iron
hepatic portal blood comes to the liver from the small intestine
109
processing of nutrients (liver function)
amino acids to energy producing compounds (ATP); transforms unusable nutrients to usable substances; hydroxylation of vitamin D that becomes active in the kidney
110
detoxification (liver function)
hepatocytes remove ammonia and convert it to urea (urine); hepatic phagocytic cells remove damaged red and white blood cells, bacteria, and debris
111
synthesis of new molecules (liver function)
albumins, fibrinogen, globulins, heparin, clotting factors, cholesterol
112
gallbladder
saclike structure for bile storage (rugae, inner muscularis, outer serosa)
bile arriving constantly from the liver is stored and concentrated
113
what is the gallbladder stimulated by?
cholecystokinin (CCK) and the vagus nerve
114
gallstones
precipitated cholesterol that blocks cystic duct; can occur because of drastic dieting
115
flow into and out of the liver
1) hepatic artery carries oxygenated blood from the aorta through the porta of the liver and blood from the hepatic artery branches enters the hepatic sinusoids and supplies hepatocytes in the hepatic cords with oxygen
2) hepatic portal vein carries nutrient-rich, deoxygenated blood from the intestines through the porta of the liver and blood form the hepatic portal vein branches enter the hepatic sinusoids to supply hepatocytes in the hepatic cords with nutrients
3) blood in the hepatic sinusoids coming from the hepatic artery and hepatic portal vein picks up plasma proteins, processed molecules, and waste products produced by hepatocytes of the hepatic cords
4) hepatic sinusoids empty into the central veins connected to the hepatic veins connected to the inferior vena cava
5) bile produced by hepatocytes in the hepatic cords enter the bile caniliculi connected to the hepatic duct branches
6) hepatic duct branches converge to form left and right hepatic ducts and carry bile out of the liver
116
endocrine (pancreas)
pancreatic islets (islets of langerhans) produce insulin (beta cells), glucagon (alpha cells), and somatostatin
117
exocrine (pancreas)
acinar cells secrete enzymes into the pancreatic duct
118
pancreatic duct
joins common bile duct and enter the duodenum at the hepatopancreatic ampulla controlled by the hepatopancreatic sphincter
119
pancreatic juice
contains H2O and HCO3- which neutralizes acidic chyme, inhibiting pepsin; provides proper pH for enzymes
120
trypsinogen
activated by enterokinase to trypsin
121
chymotrypsinogen
activated by trypsin to chymotrypsin
122
procarboxypeptidase
activated by trypsin to carboxypeptidase
123
pancreatic amylase
carbohydrate digestion
124
pancreatic lipase
lipid digestion
125
deoxyribonuclease and ribonuclease
nucleic acid digestion
126
parasympathetic stimulation (vagus nerve)
causes the release of pancreatic juice
127
secretin (pancreatic secretion)
stimulates the release of HCO3(-)-rich pancreatic juice
128
cholecystokinin (pancreatic secretion)
stimulates the release of enzyme-rich pancreatic juice
129
large intestine
absorption of water and salts; secretion of mucus; extensive action of microorganisms
extends from the ileocecal junction to the anus
structures: cecum, colon, rectum, anal canal
130
in the large intestine, slow motility (18 to 24 hours) occurs as chyme is converted to _____
feces
131
colon
structures: ascending colon (retroperitoneal), hepatic flexure, transverse colon, splenic flexure, descending colon (retroperitoneal), sigmoid colon (joins rectum)
132
mesocolon
anchors transverse and sigmoid colons
133
anal canal
structures: rectal calves, internal anal sphincter, external anal sphincter
134
internal anal sphincter
smooth muscle; involuntary canal
135
external anal sphincter
skeletal muscle; voluntary control
136
hemorrhoids
in anal canal; vein enlargement or inflammation
137
microscopic anatomy of the large intestine
mucosa, anal canal mucosa, superficial venous plexi (associated with anal canal)
138
mucosa
simple columnar epithelium
crypts (lined with goblet cells)
139
anal canal mucosa
stratified squamous epithelium
sinuses (exudes mucous and compresses feces)
140
what is the major secretion of the large intestine?
mucus; parasympathetic stimulation increases the rate of goblet cell secretion
141
microbiota (secretion of the large intestine)
produces acids while antiporters remove acid from epithelial cells that line the large intestine
exchange of bicarbonate ions for chloride ions
exchange of sodium ions for hydrogen ions
water leaves lumen of the colon by osmosis ad sodium and chloride move into the epithelial cells
bacteria produce vitamin K which is passively absorbed
142
microbiota metabolism
produces gas (flatus) from certain carbohydrates
143
feces
water, undigested food (cellulose), microorganisms, sloughed epithelial cells
144
mass movements (motility in the large intestine)
common after meals (especially breakfast); initiated by the enteric nervous system reflexes (gastrocolic and duodenocolic)
145
gastrocolic reflex
initiated by the stomach distention
146
duodenocolic reflex
initiated by the distention of the duodenum
147
mass movements and enteric nervous system mediation
by parasympathetic reflexes, local reflexes, and hormones (cholecystokinin and gastrin), as well as thought or smell of food
148
defecation (motility in the large intestine)
parasympathetic reflex ultimately under conscious control (external anal sphincter)
can be initiated voluntarily through the valsalva maneuver
149
embryonic development
third week: gut formation with mouth and anus nearly formed
eighth week: accessory organ formation
150
fetal development
nutrition via placenta
gastrointestinal tract development stimulated by the swallowing of amniotic fluid
151
at birth, _____ is the most important baby activity
feeding (enhanced by rooting reflex and sucking reflex)
152
effects of aging on the digestive system
decrease in mucus layer, connective tissue, muscles and secretions
increased susceptibility to infections and toxic agents
increase in ulcerations and cancers
gastroesophageal reflux disease (GERD) increases
enamel on teeth things; gingivitis increases
