BIOL 0800 Reading- Chapter 15 Flashcards Preview

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Flashcards in BIOL 0800 Reading- Chapter 15 Deck (228):
1

What acid is in the stomach?

HCl

2

What is pepsin?

Protein-digesting enzymes in the stomach

3

What two molecule types are typically not digested well by acid in the stomach?

Polysaccharides and fats

4

How much absorption of organic nutrients occurs in the stomach?

Virtually none

5

Where does most absorption of nutrients occur?

In the small intestine

6

What is the duodenum?

The initial segment of the small intestine

7

What is the jejunum?

The second segment of the small intestine

8

What is the ileum?

The third, longest segment of the small intestine

9

What are the three segments of the small intestine?

Duodenum, jejunum, ileum

10

What two organs secrete substances into the duodenum?

Pancreas and liver

11

How does the pancreas contribute to digestion?

Secretes digestive enzymes and a fluid rich in HCO3- to neutralize the acidic chyme

12

What does the liver do?

Secretion of bile to break down fast

13

What does the gallbladder do?

Stores secreted bile

14

What are the four layers of the GI wall?

Mucosa, submucosa, muscularis externa, serosa

15

What are the three layers of the mucosa?

Epithelium, lamina propria, muscularis mucosa

16

What is the submucosa?

Major blood and lymphatic vessels, submucosal plexus

17

What is the submucosal plexus?

Network of neyrons

18

What is the muscularis externa?

Circular muscle and myenteric plexus

19

How do circular muscles work?

Fibers oriented in circulate pattern around the tube so that contraction produces a narrowing of the lumen

20

What is the myenteric plexus?

Second network of neurons: innervated by nerves from the autonomic NS and has neurons that project to the submucosal plexus

21

What kinds of nerves innverate the myenteric plexus?

Autonomic nervous system

22

What is the serosa?

Thin layer of connective tissue to connect outer surface of tube to abdominal wall

23

What is a lacteal?

Single, bind-ended lymphatic vessel that is at the center of each villi

24

Most of the fat absorbed in the small intestine goes where?

Through the lacteals, to be emptied through the lymphatic systme into the thoracic duct

25

What is the hepatic portal vein?

The vein through which absorbed nutrients drain from the small intestine to the vena cava

26

What does the hepatic portal vein allow?

Material absorbed into the intestinal capillaries to be processed by the liver before entering general circulation: detox

27

What biological accounts for the liver's function as detox?

Hepatic portal vein: carries intestinally absorbed material through liver before returning it to capillary circulation

28

What are Peyer's patches?

Patches in the SI to secrete inflammatory mediators (cytokines) to alter motility of harmful substances not destroyed by acidity

29

What happens to amylase in the stomach?

It gets inactivated! Oh no!

30

What are the products of salivary and pancreatic amylase?

Maltose and short, branched glucose

31

What happens to carbs after salivary and pancreatic amylase converts them into maltose/short glucose?

Broken down, along with sucrose and lactose, into the three monosaccharides (glucose, fructose, galactose) in the brush border

32

Where are carbs completely broken into monosaccharides?

In the brush border of the small intestine

33

How does fructose get reabsorbed from the brush border?

Facilitated diffusion visual glucose transporter GLUT

34

How do glucose and galactose get reabsorbed from the brush border?

Secondary active transport coupled to Na via sodium-glucose cotransporter SGLT

35

How do all three monsaccharides get transported from the epithelium to the interstitial fluid?

GLUT transporters' facilitated diffusion

36

Where does protein digestion begin?

Stomach with pepsin

37

What substances digest protein in stomach vs SI?

Pepsin in stomach, trypsin and chymotrypsin in SI

38

What organ secretes trypsin and chymotrypsin into the SI for protein digestion?

Pancreas

39

What happens after pepsin/trypsin/chymotrypsin partially fragment proteins in the stomach/SI?

Fragments broken down by carboxypeptidase from pancreas and aminopeptidase from SI epithelium

40

Where are carboxypeptidase and aminopeptidase produced?

In the pancreas and the epithelium of the SI

41

What do carboxypeptidase and aminopeptidase do?

Break down protein fragments in the SI into AAs

42

How do free aas enter the epithelial cells of the SI?

Secondary active transport coupled to Na+ cotransporters: different transporters for different aas

43

Can short chains of aas be absorbed to the SI epithelium?

Yes: couples to hydrogen ion gradient

44

What happens to di and tripeptides that were transported into the epithelial cells of the SI coupled to hydrogen ion gradient?

Broken down into single amino acids and leave through facilitated diffusion

45

What enzyme is responsible for fat digestion?

Lipase

46

Where is lipase produced?

In the pancreas

47

What does lipase do?

Breaks a triglyceride into a monoglyceride and two fatty acids

48

What are the main emulsifying agents in digestion?

Phospholipids ingested or secreted in bile, and bile salts

49

What is colipase?

Protein secreted by pancreas to lodge on lipid droplets to bind the lipase enzyme

50

What are micelles?

Very small emulsion droplets: bile salts, monoglycerides and fatty acids: with polar side out and nonpolar side in

51

How do micelles increase absorption?

Continuously break down and reform, keep the lipids emulsified, while also allowing small amounts of broken-down lipids into the fluid to cross the membrane into the epithelial cells

52

What happens to monoglycerides and fatty acids in the epithelial cells?

Resynthesized into triglycerides for passage through to the interstitial fluids

53

Why is it advantageous that lipids leave the epithelial cells for the interstitium as triglycerides rather than fatty acids and monoglycerides?

Maintains the concentration gradient so that monoglycerides and fatty acids keep diffusing into the epithelium

54

What are chylomicrons?

Small extracellular fat droplets released by the smooth ER when the triglycerides were reformed

55

Where do chylomicrons go after formation?

To the lacteals! Because those have big pores and let the chylomicrons out easily

56

How are fat soluble vitamins absorbed? (ADEK?)

Same way as fats: broken into micelles

57

How are water soluble vitamins absorbed?

Through diffusion or mediated transport, EXCEPT for B12

58

Why is B12 tricky for absorption?

It's a large charged molecule

59

How is B12 absorbed?

Binds to an intrinsic factor protein, which binds to sites on epithelial ileum for endocytosis

60

Where is intrinsic factor for B12 produced?

Acid-secreting cells of the stomach

61

What is the most abundant solute in chyme?

Na+

62

How does water absorption occur in the small intestine?

Wherever there's a water concentration gradient created by actively transported solutes (Na+)

63

What solutes are absorbed with Na+ to cause water diffusion?

Cl- and HCO3-

64

What happens to iron in the small intestine?

Acitvely transported into epithelial cells, mostly bound into ferritin (intracellular iron storage) to be released to the blood side onto transferrin

65

How does the body control storage of iron?

Increased transcription of gene for ferritin: increased binding of iron in SI epithelial cells, so increased iron storage and reduced release into the bloodstream

66

What are four luminal stimuli to initiate GI reflexes?

Wall distension, chyme osmolarity, chyme acidity, and chyme concentration of specific digestion products: monosac, Fas, peptides, aas, etc.

67

What is the enteric NS?

GI's own nervous system: submucosal plexus and myenteric plexus

68

How does activity in one half of the enteric NS affect the other?

Interrelated because the axons of one synapse with the neurons of the other

69

In which direction can impulses conduct along plexuses of the enteric NS?

Both directions: stimulation at one plexus point can affect other areas, like SI to stomach and lower intestinal tract muscle

70

What is the difference in influence of myenteric vs submucosal plexus?

Submucosal is mostly for secretory activity, and myenteric is mostly for smooth muscle activity

71

What kinds of neurons are in the enteric NS?

Adrenergic and cholinergic neurons; and neurotransmitter-releasing neurons

72

What are the main effectors of enteric NS neurons?

Muscle cells and exocrine glands

73

What kinds of neurons, sympathetic or parasympathetic, innervate the plexuses of the enteric NS?

Both! Allow CNs to influence motility and secretory activity of GI tract

74

What are the two types of neural0reflex arcs?

Short reflexes and long reflexes

75

What is a short reflex?

From receptors through nerve plexuses to effector cells

76

What is a long reflex?

From receptors to CNS by afferent nerves, then back to nerve plexus and effector cells through autonomic neurons

77

Where do hormones for regulating GI activity come from?

Cells scattered in the stomach and SI

78

What stimulates endocrine cells to secrete regulatory hormones to the GI tract?

Chyme: if it touches the endocrine cell on the luminal side, the endocrine cell will secrete hormones to the basolateral side into the blood to reach target cells by circulation

79

What are the four GI hormones?

Secretin, cholecystokinin (CCK), gastrin, and glucose-dependent insulinotropic peptide (GIP)

80

What are the two generalizations of GI hormones?

They participate in feedback control to regulate one aspect of the GI environment, and they affect multiple kinds of target cells

81

What triggers CCK secretion into the blood from the SI?

Fatty acids and amino acids in the SI

82

What happens when CCK is released into the blood after being triggered by fatty acids and amino acids?

Stimulates the pancreas to increase digestive enzyme secretion; causes gallbladder to contract and deliver bile salts

83

What is potentiation?

How secretin (stimulates pancreatic bicarb secretion) and CCK (weak stimulus for pancreatic bicarb secretion) TOGETHER cause major secretion of bicarb: whole is greater than sum of parts

84

Why does potentiation for secretin and CCK exist?

Because even though CCK is a weak stimulus for bicarb secretion from the pancreas, it amplifies the stimulation of secretin

85

What is the point of potentiation?

Small changes in plasma concentration of one GI hormone can have large effects on the actions of other GI hormones

86

What is leptin?

Peptide hormone: released from adipose cells, influences good intake and metabolic rate; induces satiety

87

What is ghrelin?

Peptide hormone: released from stomach during fasting; induces hunger

88

What are incretins?

GI hormones that alter insulin secretion from pancreatic islet cells

89

Which of the four main GI hormones is an incretin?

GIP: glucose-dependent insulinotropic peptide

90

What are the three phases of neural and hormonal control of the GI system?

Cephalic, gastric, and intestinal

91

Gastrin: what kind of hormone, where produced, stimuli for release?

Peptide; stomach; AAs, peptides in stomach, parasympathetic nervous

92

CCK: what kind of hormone, where produced, stimuli for release?

Peptide; SI; AAs , FAs in SI

93

Secretin: what kind of hormone, where produced, stimuli for release?

Peptide, SI; acid in small intestine

94

GIP: what kind of hormone, where produced, stimuli for release?

Peptide; SI; glucose, fat in SI

95

What factors inhibit gastrin release?

Acid in stomach; somatostatin

96

Gastrin: how does it affect stomach acidity and motility?

Stimulates

97

CCK: how does it affect stomach acidity and motility?

Inhibits

98

Secretin: how does it affect stomach acidity and motility?

Inhibits

99

How does CCK affect the pancreas activity?

Stimulates enzyme secretion; potentiates secretin's effect on bicarb release

100

How does secretin affect pancreas activity?

Stimulates bicarb release; potentiates CCK's effect on enzyme secretion

101

How does GIP affect pancreas activity?

Stimulates insulin secretion

102

How do secretin and CCK affect liver activity?

Secretin stimulates bicarb secretion, and CCK potentiates it

103

How does CCK affect gallbladder activity?

Stimulates gallbladder contraction

104

How does CCK affect the sphincter of Oddi?

Relaxes it

105

How does gastrin affect the SI and LI?

Stimulates ileum motility, and mass movement of LI

106

What is the cephalic phase on GI regulation?

Initiated when receptors in head stimulated by sight/smell/taste/chewing

107

What kinds of neurons are involved in the cephalic phase?

Parasympathetic fibers in vagus nerves: activate neurons in GI plexus to affect secretory/contractile activity

108

What is the gastric phase of GI regulation?

Initiated by four stimuli: gastric distension, acidity, AAs, and peptides formed during digestion

109

What kind of neurons are involved in the gastric phase?

Short and long neural reflexes; also affected by gastrin release

110

What is the intestinal phase of GI regulation?

Initiated by stimuli in intestinal tract: distension, acidity, osmolarity, digestive products

111

What kinds of neurons are involved in the intestinal phase?

Short and long neural reflexes; also affected by the four gastric hormones (secretin, gastrin, CCK, GIP)

112

What four stimuli initiate the gastric phase?

Gastric distension, acidity, AAs, and peptides

113

What four stimuli initiate the intestinal phase?

Gastric distension, chyme acidity, chyme osmolarity, and chyme concentration of digestive products

114

How is chewing initiated?

Somatic nerves to skeletal muscles; mechanoreceptors in gums/hard palate/tongue --> reflexive inhibition of jaw muscles to cycle between contraction/relaxation

115

What are the three pairs of salivary glands?

Parotid, sublingual, and submandibular

116

How do sympathetic and parasympathetic nerves affect salivation?

Both stimulate salivary secretion, but parasympathetic has a great response

117

What nerve stimulation causes swallowing?

Mediated by pressure receptors in pharynx: afferent impulses to swallowing center in medulla oblongata of brainstem; elicits swallowing by efferent fibers to muscles in pharynx/esophagus/respiratory muscles

118

Why does pressure want to push contents into the esophagus down from the pharynx and up from the stomach?

Because there's higher pressure in the pharynx (Patm)and in the stomach-end of the esophagus (supra Patm) than in the esophagus (sub Patm)

119

Why isn't contents pushed into the esophagus because of pressure differences?

Because of esophageal sphincters

120

How does the composition of the two esophageal sphincters differ?

Upper is skeletal muscle, lower is smooth muscle

121

Why can we swallow when upside down or without gravity?

Because peristaltic waves constitute the esophageal phase of swallowing

122

What kind of nervous input allows the esophageal phase of swallowing?

Somatic nerves for upper sphincter, and autonomic nerves for lower sphincter; afferent fibers from esophagus to the swallowing center

123

Where is the swallowing center?

Medulla oblongata of brainstem

124

How does the lower esophageal sphincter stay closed even without swallowing?

Underneath the diaphragm: the abdominal pressure is the same on the esophagus and stomach

125

Why is there sometimes heartburn in late pregnancy?

The fetus pushes the esophagus up above the diaphragm: no pressure maintenance for esophagus and stomach, so higher pressure on the stomach forces the sphincter open and allows gastric contents into the esophagus

126

What is the fundus vs antrum of the stomach?

Upper and lower parts

127

What substances are secreted by the body of the stomach?

Pepsinogen, mucus, and HCl

128

Which half of the stomach has a thicker layer of smooth muscle?

The antrum: secrete less acid, but more gastrin

129

What half of the stomach secretes less acid, but more gastrin?

The antrum

130

What are parietal cells?

On gland wall: secrete acid and intrinsic factor (for B12)

131

What are chief cells?

On gland wall: secrete pepsinogen

132

Which cells secrete acid/intrinsic factor vs pepsinogen?

Parietal for acid/IF and chief for pepsinogen

133

What are canaliculi?

Invaginations of the luminal membrane of parietal cells: increase surface area to maximize secretion

134

What are enteroendocrine cells?

In the antrum: secrete gastrin

135

What are enterochromaffin-like cells?

Release paracrine agent histamine

136

What are D cells?

Secret somatostatin

137

How is HCl produced in the stomach?

H/K ATPases pump H+ into lumen (K+ pumped out, but diffuses back in), and Cl- pumped in through Cl-/HCO3- countertransport, and then diffuses into lumen

138

Where are the H+/K+ pumps in the stomach located?

In the parietal cells

139

How does increased acid production occur?

By increased H+/K+ pump proteins being added to the parietal cell (fused from intracellular vesicles) to increase the number of pumps: like aquaporins for water permeability in the nephron!

140

What four chemical messengers regulate H+/K+ pump increases?

Gastrin, ACh, histamine, and somatostatin

141

What three kinds of cells are responsible for producing three of the four chemical messengers that increase acid production?

Enteroendocrine (gastrin), ECL (histamine), and D cells (somatostatin)

142

Which of the four chemical messengers that affect acid production is inhibitory?

Somatostatin booooooooo

143

Why is histamine really important for increasing acid production?

Potentiates the effect of gastrin and ACh

144

What nervous system action mediates ACh release in parietal cells to stimulate H+/K+ pump addition to increase acid production?

Parasympathetic stimulation to stomach's enteric system

145

How does H+ affect gastrin and somatostatin secretion?

Inhibits, because already acidic enough; Stimulates, to reduce acid production

146

Why does protein stimulate acid secretion?

Peptides stimulate acid secretion; protein is a buffer for H+, so protein decreases the H+ concentration, which decreases secretion inhibition

147

How does duodenum acidity affect acid secretion? Why?

High duodenum acidity inhibits acid secretion by the stomach; because the activity of bile salts and enzymes is negatively impacted by acidity

148

What are enterogastrones?

Hormones released by the intestinal tract that reflexively inhibit gastric activity: secretin and CCK

149

When is pepsinogen converted to pepsin?

During exposure to low pH in the stomach; faster when pH is lower

150

Why is it important for digestive enzymes to be zymogens?

Produced in inactive form: protects substrates from digestion, prevents damage to cells

151

Why is pepsinogen neutralized in the SI?

The bicarb neutralizes the H+

152

Why does pepsinogen secretion parallel acid secretion?

Because most of the factors that stimulate/inhibit acid secretion do the same for pepsinogen

153

Why can the stomach "expand?"

Because the smooth muscles relax when food is about to enter: receptive relaxation

154

How is receptive relaxation mediated?

Parasympathetic nervous input to enteric nerve plexuses; coordination provided by afferent input from stomach via vagus nerve and swallowing center in medulla oblongata; mediated by NO and serotonin from enteric neurons

155

What two substances from the enteric neurons mediate receptive relaxation?

NO and serotonin

156

What happens when the weak peristaltic wave reaches the thick antrum?

Gets stronger and produces powerful contraction to mix luminal contents and close the pyloric sphincter

157

What is the pyloric sphincter for?

Closing the gap between the antrum and duodenum: only allows a small amount of chyme to enter the SI per peristaltic wave and contributes to mixing through backsplash

158

What generates peristaltic waves in the stomach?

Pacemaker cells in longitudinal smooth muscle: spontaneous depo-repo cycles

159

What is basic electrical rhythm of the stomach?

The spontaneous depo-repo cycles of the stomach's smooth muscle that create peristalsis

160

How are the slow waves of peristalsis conducted throughout the stomach?

Through gap junctions in the stomach's longitudinal muscular layer, as well as through the stomach's circular muscular layer

161

What determines the frequency and strength of stomach contractile peristalsis?

Frequency determined by basic electric rhythm; Strength determined by number of action potentials generated at the peak of the slow-wave cycle , which is determined by neural and hormonal input to antral smooth muscle

162

What factors inhibit gastric emptying?

Duodenum distension, presence of fat/acid/hypertonic solutions in the duodenum (also inhibit acid and pepsin secretion in the stomach) = prevents OVERFILLING of duodenum

163

How does autonomic nerve fiber input affect gastric motility?

Input to stomach activated by CNS: increased in parasympathetic activity increases gastric motility

164

How do parasympathetic and sympathetic input influence gastric motility?

Parasympathetic increases, sympathetic decreases

165

Why does hypertonic duodenum lumen inhibit gastric emptying?

Too hypertonic lumen means too much water into the intestine: lowers blood volume and causes circulatory complications; intestinal distension can cause vomiting

166

What is the difference in secretion of bicarb and digestive enzyme from the pancreas?

Bicarb is secreted from epithelial cells lining the pancreatic duct, and digestive enzymes are secreted from the pancreatic end of the duct system

167

How is bicarb secreted by the pancreas?

Like H+ is secreted by the stomach except in reverse: H+ transported out of the cells by H+/K+ pump into blood, and bicarb secreted into the lumen

168

What is enterokinase?

Enzyme in the luminal plasma of intestinal epithelial: proteolytic enzyme that splits peptide from pancreatic trypsinogen to form trypsin

169

What is trypsin?

Proteolytic enzyme; activates pancreatic zymogens by splitting off a peptide; also digests ingested protein

170

Why does pancreatic secretion increase during a meal?

Stimulation by secretin (for bicarb) and CCK (enzymes)

171

Which four pancreatic enzymes digest proteins?

Trypsin, chemotrypsin, elastase (break peptide bonds) and carboxypeptidase (split terminal AA from carboxyl end of protein)

172

What pancreatic enzyme digests fast?

Lipase: splits triglyceride into monoglyceride and two FAs

173

What pancreatic enzyme digests carbs?

Amylase (splits polysaccharides into glucose and maltose)

174

What pancreatic enzymes digest nucleic acids?

Ribonculease and deoxyribonuclease

175

What is the major stimulus for bicarb release from the pancreas?

Acidity in the duodenum: BECAUSE its function is to neutralize the acid

176

What is the major stimulus for digestive enzyme release from the pancreas?

Presence of FAs and AAs in the duodenum

177

How do luminal acid and FAs activate their own digestion?

Act of afferent nerve endings in the intestinal wall to initiate reflexes to the pancreas to secrete enzyme and bicarb

178

What kind of nerve input leads to increased pancreatic secretion during the cephalic and gastric stimuli?

Parasympathetic

179

What are hepatic lobules?

Functional units of the liver

180

What is a portal triad?

Branches of the hepatic artery/portal vein/bile duct at the periphery of each hepatic lobule

181

From which two sources does the liver receive blood supply?

Hepatic portal vein (blood from SI to process absorbed nutrients), and hepatic arteries (bring oxygenated blood from aorta)

182

How does blood leave lobules?

Blood drains into central veins that merge for form hepatic veins to empty into vena cava

183

What are hepatic sinusoids?

Capillaries surrounding hepatocytes

184

What are bile caniculi?

Small hepatocyte ducts that converge to form the common hepatic duct for bile transport

185

What are the six main ingredients of bile?

Bile salts, lecithin, bicarb, cholesterol, pigments, and trace metals

186

What is lecithin?

A phospholipid in bile: synthesized by liver: solubilize fat in the SI

187

What happens to most of the bile salts in the intestine?

Absorbed by specific Na+ coupled transporters in the ileum, then transported through the portal vein to the liver

188

In what portion of the SI are bile salts absorbed?

Ileum, through Na+ coupled transporters

189

What drives the uptake of bile salts from portal blood into the hepatocyte, after it's been absorbed from the ileum by Na+ coupled transporters into the portal vein?

Secondary active transport coupled to Na+

190

What is enterohepatic circulation?

The recycling pathway of bile salts from the liver to SI to liver

191

What is the predominant bile pigment?

Bilirubin: extracted from blood from damaged erythrocytes; yellowish color to bile and urine

192

What are the two types of cells that product bile components, and which do they produce?

Hepatocytes (bile salts, cholesterol, lecithin, and pigments) and epithelail cells of bile ducts (bicarb)

193

How does the liver produce cholesterol?

By extracting it from the blood or making it itself; when bile salts need to be replenished, reduces blood concentration of cholesterol

194

When is bile secretion greatest?

During and just after a meal

195

What stimulates secretion of salt solution from bile ducts?

Secretin in response to acid in the duodenum

196

What happens when the sphincter of Oddi is closed?

Bile is shunted into the gallbladder for storage

197

What is the signal for gallbladder contraction and sphincter relaxation?

CCK: because duodenum fat is a trigger for CCK release

198

What is the primary ion for determining the magnitude of fluid secretion in the SI?

Cl-, controlled by hormonal and paracrine signals

199

What amount of fluid secreted by the SI is absorbed back into the blood?

Basically all of it, following the absorption of ions from the lumen to the blood

200

What is peristaltic segmentation?

In the SI: rhythmic contraction and relaxation of the intestine every few centimeters: for mixing and surface area contact

201

What initiates segmentation peristalsis?

Pacemaker cells in circular smooth muscle layer: basic electrical rhythm produces membrane potential oscillations

202

How does the basic electrical rhythm of the SI and stomach differ?

Stomach is constant (3/min), but for SI, the frequency varies along the intestine (as you go along, slower frequency)

203

How does parasympathetic/sympathetic activity affect segmentation force?

Parasympathetic increases, sympathetic decreases

204

What happens when segmentation peristalsis ends?

Peristaltic migrating myoelectrical complex activity (MMC) beings

205

What is MMC activity?

Peristalsis continues for several feet and dies out, then starts again a little further down: moves all material to LI

206

What hormone most likely initiates MMC?

Motilin by enteric and autonomic nervous systems

207

What is the gastroileal reflex?

When segmentation intensity in the ileum increases during gastric emptying

208

What is intestino-intestinal reflex?

When large distension of the intestine, injury, or infection leads to complete motility cessation

209

What are the three parts of the LI?

Cecum, colon, rectum

210

What is the ileocecal valve?

Sphincter between ileum and cecum: circular muscle innervated by sympathetic nerves

211

What kind of nerves innervate the ileocecal valve?

Sympathetic

212

What is the appendix?

Projection from the cecum, nonessential

213

What is the colon?

Three segments: ascending, transverse, descending, sigmoid

214

What is the difference in surfaces of the SI and LI?

Less surface area in LI because shorter, nonconvoluted, lacks villi

215

What are the secretions of the LI?

Mucus, bicarb, and potassium

216

What is the primary function of the LI?

Store and concentrate fecal material before defecation

217

What is the primary absorptive process in the LI?

Reabsorption of water following active transport of Na+ out of the lumen

218

Which way does K+ travel between blood and LI lumen?

Transported from blood to lumen, most likely through cAMP mediated process

219

How does bicarb get secreted into the LI lumen?

By coupling with Cl- absorption form the lumen

220

What happens to fiber in the LI?

Converted into short-chain fatty acids by bacteria, absorbed by passive diffusion (acidity neutralized be presence of bicarb); produces gas

221

How does parasympathetic/sympathetic input affect colonic contractions?

Parasympathetic increases, sympathetic decreases

222

What is a mass movement?

A wave of intense contraction of the LI, usually coinciding with gastroileal reflex (gastric emptying)

223

What is the difference between internal and external anal sphincter?

Internal is smooth muscle, and external is skeletal and under voluntary control

224

What is the defecation reflex?

Neurally mediated: initiated by mass movement of fecal material into the rectum; triggered by rectum distension

225

What happens during the defecation reflex?

Initial contraction of external sphincter with relaxation of internal sphincter, increased sigmoid colon peristalsis

226

Why doesn't the high stomach acidity break down the stomach walls?

Musocal lining is alkalinic, and contains proteins that neutralize the H+ near the membrane; tight junctions prevent leakage to underlying structures; damaged cells are replaced quickly

227

Where is the vomiting center located?

Medulla oblongata of brainstem

228

What is the area postrema?

Outside blood-brain barrier; sensitive to toxins and initiates vomiting