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MCAT-BIOLOGY > The Digestive System > Flashcards

The Digestive System Flashcards

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1
Q

catabolic reactions

A

reactions the break down molecules to supply energy

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2
Q

anabolic reactions

A

synthesis of macromolecules

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3
Q

purpose of digestion

A

the breakdown of polymers into their building blocks (and also some protection from disease/immune functions)

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4
Q

how is the breakdown of polymers in digestion accomplished?

A

by enzymatic hydrolysis, also involves vitamins which serve a catalytic role as enzyme cofactors or prosthetic groups

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5
Q

gastrointestinal (GI) tract/digestive tract/alimentary canal/gut

A

where digestion is accomplished, a long, muscular tube extending from the mouth to the anus, derived from the cavity produced by gastrulation during embryogenesis

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6
Q

the anus is derived from the:

A

blastopore

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7
Q

GI lumen

A

the inside of the gut, continuous with the space outside the body, compartment where the usable components of foodstuffs are extracted while wastes are left to be excreted as feces

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8
Q

what are the layers from the GI tract? from lumen outwards?

A

lumen, mucosa (with villi/epithelial tissue), submucosa (connective tissue), circular muscularis (smooth muscle), longitudinal muscularis (smooth muscle), serosa (connective tissue)

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9
Q

innermost lining of the lumen is composed of:

A

epithelial cells, the same type of cells that line the outer surface of the body and the inner surface of the respiratory tract

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10
Q

basement membrane

A

attached to epithelial cells

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11
Q

apical surface

A

the surface of the epithelial cells which faces into the lumen, separated from the remainder of the cell surface by tight junctions

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12
Q

tight junctions

A

bands running all the way around the sides of epithelial sides, creating a barrier that separates body fluids from the extracellular environment

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13
Q

basolateral surface

A

the sides and bottom of an epithelial cell form the surface opposite the lumen

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14
Q

microvilli

A

outwards folds of plasma membrane on the apical surfaces of epithelial cells in the small intestine that increase surface area

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15
Q

what is responsible for most of the secretory activity of the GI tract?

A

specialized epithelial cells

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16
Q

GI muscle

A

a type of smooth muscle, two layers of muscle (longitudinal and circular)

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17
Q

GI motility

A

the rhythmic contraction of GI smooth muscle

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18
Q

GI smooth muscle is similar to cardiac muscle in that it displays:

A

automaticity; contracts periodically without external stimulation due to spontaneous depolarization

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19
Q

like cardiac muscle, GI smooth muscle is a _____ _____

A

functional syncytium, meaning that when one cell has an action potential and contracts, the impulse spreads to neighboring cells

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20
Q

enteric nervous system

A

the GI tract’s own nervous system that plays a major role in controlling GI motility, a branch of the autonomic nervous system that helps to control digestion via innervation of the GI tract, pancreas, and gall bladder

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21
Q

GI motility may be increased or decreased by:

A

hormonal input

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22
Q

what is the purpose of GI motility

A

mixing of food (disordered contractions of GI smooth muscle) and movement of food down the gut (orderly contractions=peristalsis)

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23
Q

peristalsis

A

an orderly form of contraction, where contraction of circular smooth muscle prevents food from moving backward while longitudinal muscle contraction causes shortening of the gut and pushes food forward, cycle repeats

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24
Q

bolus

A

a ball of food moving through the GI tract

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25
Q

what are the two networks of neurons that make up the enteric nervous system?

A

the myenteric plexus (between circular and longitudinal muscle layers and help to regulate gut motility) and submucosal plexus (found in the submucosa and regulate enzyme secretion, gut blood flow, and ion/water balance in the lumen)

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26
Q

exocrine glands

A

composed of specialized epithelial cells organized into sacs called acini, acinar cells secrete products which pass into ducts

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27
Q

what are the main digestive organs primarily involved in exocrine secretion?

A

liver, gallbladder, and pancreas, some specialized epithelial cells (miniature exocrine glands that release secretions directly into the gut lumen)

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28
Q

what are some exocrine epithelial cells in the wall of the gut?

A

gastric glands (secrete acid and pepsinogen) and goblet cells (mucus)

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29
Q

mucus membrane

A

any body surface covered with mucus (protects and lubricates the gut)

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30
Q

endocrine secretion is accomplished by:

A

specialized organs (the pancreas) and cells in the wall of the gut

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31
Q

what are the two types of cells in the pancreas?

A

1) exocrine cells: pancreatic acinar cells

2) endocrine cells: islets of Langerhans

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32
Q

mouth

A

1) fragmentation by mastication
2) lubrication
3) some enzymatic digestion

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33
Q

incisors

A

front teeth (cutting)

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34
Q

cuspids

A

canine teeth (tearing)

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35
Q

molars

A

grinding

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36
Q

saliva

A

a viscous fluid secreted by salivary glands in the mouth which perform lubrication and some digestion, contains salivary amylase , lingual lipase, lysozyme

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37
Q

salivary amylase (ptyalin)

A

hydrolyzes starch, breaking it into fragments, disaccharide

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38
Q

lingual lipase

A

fat digestion

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39
Q

lysozyme

A

attacks bacterial cell walls, performs innate immunity

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40
Q

pharynx

A

contains the opening of two tubes: trachea (cartilage-lined tube which conveys air to and from the lungs) and the esophagus (muscular tube behind the trachea which conveys food and drink to the stomach)

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41
Q

epiglottis

A

cartilaginous flap that excludes solids and liquids from the trachia during swallowing

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42
Q

upper esophageal sphincter

A

near the top of the esophagus

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43
Q

lower esophageal sphincter

A

aka cardiac sphincter, lower end of the esophagus, at the entrance to the stomach, prevents reflux from stomach into esophagus

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44
Q

stomach

A

a large, hollow, muscular organ that serves 3 purposes:

1) partial digestion of food
2) regulated release of food into the small intestine
3) destruction of microorganisms

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45
Q

gastric pH

A

approximately 2, due to secretion of HCl by parietal cells in the gastric mucosa, allows for:
destruction of microorganisms
acid-catalyzed hydrolysis of many dietary proteins
conversion of pepsinogen and pepsin

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46
Q

chief cells

A

found in the stomach wall that secretes pepsinogen (inactive precursor) that is converted to active pepsin by gastric acidity

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47
Q

pepsin

A

catalyzes proteolysis (converted by gastric acidity from inactive pepsinogen form)

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48
Q

zymogen

A

inactive form of an enzyme, most are activated by proteolysis (except for pepsinogen which is activated by gastric acidity)

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49
Q

chyme

A

food mixed with gastric secretions

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50
Q

lower esophageal sphincter prevents:

A

reflux of chyme into the esophagus

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51
Q

pyloric sphincter

A

prevents the passage of food from the stomach into the duodenum, opening is inhibited when the small intestine already has a large load of chyme

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52
Q

what inhibits stomach emptying past pyloric sphincter into the duodenum?

A

stretching or excess acidity in the duodenum, this is mediated by nerves connecting the duodenum and stomach, and by hormones

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53
Q

cholecystokinin

A

hormone secreted by epithelial cells in the wall of the duodenum into the bloodstream that mediates pyloric sphincter opening

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54
Q

gastrin

A

hormone secreted by G cells in the stomach wall, stimulates acid and pepsin secretion and gastric motility, secretion is stimulated by food in the stomach and by parasympathetic stimulation

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55
Q

histamine

A

small molecule which is secreted in response both to stomach stretching and to gastrin, binds to parietal cells which stimulate acid release

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56
Q

what are the segments of the small intestine

A

duodenum, jejunum, ileum, where digestion is completed by absorption

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57
Q

what allows for the large surface area of the small intestine?

A

length, villi, microvilli

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58
Q

villi

A

macroscopic (multicellular) projection in the wall of the small intestine

59
Q

microvilli

A

microscopic foldings of the cell membranes of individual intestinal epithelial cells

60
Q

brush border

A

the lumenal surface of the small intestine, brush-like appearance due to microvilli

61
Q

the structure of the villus has 3 important structures

A

1) capillaries which absorb dietary monosaccharides and amino acids, merge into veins which merge to form the large hepatic portal vein which transports blood containing nutrients from the gut to the liver
2) small lymphatic vessels/lacteals, which absorb dietary fats and transport to thoracic duct which empties into the bloodstream
3) Peyer’s patches, part of the immune system, collections of lymphocytes dotting the villi that monitor GI contents and thus confer immunity to gut pathogens and toxins

62
Q

what are the two ducts that empty into the duodenum?

A

pancreatic duct (delivers the exocrine secretions of the pancreas) and the common bile duct (which delivers bile)

63
Q

bile

A

green fluid containing bile acids, which are made from cholesterol in the liver and are normally absorbed and recycled

64
Q

gallbladder

A

where bile is stored until needed, vehicle for the disposal/excretion of waste products by the liver and is essential for the digestion of fats

65
Q

sphincter of Oddi

A

orifice by which both the bile duct and the pancreatic duct empty into the duodenum

66
Q

enterokinase/enteropeptidase

A

secreted by duodenal epithelial cells and activates the pancreatic zymogen trypsinogen by proteolysis

67
Q

trypsinogen

A

zymogen form of trypsin

68
Q

brush border enzymes

A

duodenal enzymes that are not truly secreted but rather do their work inside or on the surface of the brush border epithelial cell, hydrolyzes the smallest carbohydrates and proteins (disaccharides and dipeptides) into monosaccharides and amino acids

69
Q

what are the 3 main hormones secreted by duodenal epithelial cells?

A

cholecystokinin (CCK), secretin, enterogastrone

70
Q

cholecystokinin (CCK)

A

secreted in response to fats in the duodenum, causes the pancreas to secrete digestive enzymes, stimulates gallbladder contraction (bile release), and decreases gastric motility (preventing further stomach emptying to help with fat digestion)

71
Q

secretin

A

released in response to acid in the duodenum, causes the pancreas to release large amounts of a high-pH aqueous buffer (bicarbonate in water) which neutralizes HCl released by the stomach

72
Q

duodenum pH

A

neutral or even slightly basic (required for pancreatic digestive enzyme function)

73
Q

enterogastrone

A

decreases stomach emptying

74
Q

lower small intestine (jejunum and ileum) function

A

performs special absorptive processes (ex. absorption of vitamins) and absorbs substances not absorbed in the duodenum

75
Q

ileocecal valve

A

separates the ileum from the cecum (the first part of the large intestine)

76
Q

role of colon (large intestine)

A

a muscular tube that absorbs water and minerals, and forms and store feces until the time of defecation

77
Q

appendix

A

finger-like appendage of the cecum, composed primarily of lymphatic tissue

78
Q

rectum

A

last portion of the colon

79
Q

anus

A

through which feces exit from the rectum

80
Q

anal sphincter

A

controls defecation, consists of the internal sphincter (smooth muscle/autonomic control) and external sphincter (skeletal muscle/voluntary control)

81
Q

what kind of bacteria can be found in the colon?

A

facultative or obligate anaerobes, metabolizes undigested materials

82
Q

colonic bacteria are important for two reasons:

A

1) helps prevent dangerous bacteria from proliferating due to competition of space and nutrients
2) supply vitamin K, which is essential for blood clotting

83
Q

what are the GI accessory organs?

A

plays a role in digestion, but are not part of the alimentary canal (pancreas, liver, gallbladder, salivary glands)

84
Q

pancreatic amylase

A

hydrolyzes polysaccharides to disaccharides

85
Q

pancreatic lipase

A

hydrolyzes triglycerides at the surface of a micelle

86
Q

nucleases

A

hydrolyze dietary DNA and RNA

87
Q

pancreatic proteases

A

responsible for hydrolyzing polypeptides to di- and tripeptides, secreted in their inactive zymogen forms which are activated by proteolysis

88
Q

trypsinogen

A

zymogen which is converted to active trypsin by enterokinase, an intestinal enzyme

89
Q

chymotrypsinogen

A

activated by trypsin into chymotrypsin

90
Q

procarboxypeptidase

A

activated by trypsin into carboxypeptidase

91
Q

procallagenase

A

activated by trypsin into collagenase

92
Q

islets of Langerhans

A

regions within the pancreas that contain endocrine cells

93
Q

what are the endocrine hormones secreted by the pancreas?

A

glucagon, insulin and somatostatin

94
Q

glucagon

A

secreted by alpha cells in Islets of Langerhans in response to low blood sugar, functions to mobilize stored fules by stimulating the liver to hydrolyze glycogen and release glucose into the bloodstream, and by stimulating adipocytes to release fats into the bloodstream

95
Q

insulin

A

secreted by beta cells in Islets of Langerhans in response to elevated blood sugar, stimulates the removal of glucose from the blood for storage as glycogen and fat

96
Q

somatostatin

A

secreted by delta cells in the islets of Langerhans, inhibits many digestive processes

97
Q

what are the 3 hormones responsible for raising blood glucose?

A

glucagon (polypeptide hormone from the pancreas), epinephrine (amino acid derivative from the adrenal medulla), and cortisol (steroid or glucocorticoid from the adrenal cortex)

98
Q

what is the exocrine secretory activity of the liver?

A

it secretes bile

99
Q

what are the principal ingredients of bile?

A

bile acids/bile salts, cholesterol, bilirubin

100
Q

role of bile

A

emulsifies large fat particles in the duodenum, creating smaller cluster of fat particles called micelles

101
Q

gallstone

A

large crystal formed from bile made with ingredients made in incorrect proportions

102
Q

bile release from the gallbladder is determined by:

A

both the endocrine system and the nervous system

103
Q

the liver receives blood from two places:

A

oxygenated blood from the hepatic arteries, venous blood draining the stomach and intestines through the hepatic portal vein (the nutrients in this blood is extracted by hepatocytes-liver cells)

104
Q

hepatocytes

A

liver cells that monitor the blood and make changes to the body’s physiology based on what is and is not present

105
Q

how is glycogen breakdown in skeletal muscle and liver different?

A

liver can release glucose into the bloodstream (dephosphorylated)

106
Q

liver converts ammonia to:

A

urea, which is absorbed in the bloodstream and excreted by the kidney in urine

107
Q

how does the liver assist with lipid metabolism?

A

chylomicrons are degraded by lipases into triglycerides, glycerol, and cholesterol-rich chylomicron remnants which are taken up by hepatocytes and combined with proteins to make lipoproteins that can then re-enter the blood and provide a source of cholesterol and triglycerides for other body tissues

108
Q

chylomicrons

A

how lipids enter the lymphatic system from lipids that exited the intestine

109
Q

the smooth ER in hepatocytes contains enzyme pathways that:

A

break down drugs and toxins into forms that are less toxic: liver is a major centre for drug and toxin detoxification

110
Q

ghrelin

A

hormone secreted by gastric cells when the stomach is empty to stimulate appetite

111
Q

peptide YY

A

secreted by the jejunum when the colon is full to reduce appetite

112
Q

leptin

A

hormone produced by white adipose tissue that acts as an appetite suppressant to maintain stable lipid content in adipose tissue, secreted in response to increased triglyceride levels and works to suppress appetite until appropriate levels are restored

113
Q

the apical surface of intestinal epithelial cells transport glucose into the cell by:

A

symport transports which allows sodium into the cell as well (concentration of sodium maintained by constant activity of Na/K ATPases), glucose reaches high concentration and driven out of cell by facilitated diffusion on basolateral surface where it is picked up by capillaries that flows toward the hepatic portal vein towards the liver

114
Q

amino acid absorption

A

a secondary active transporter (symport) specific to each amino acid couples the uptake of an amino acid to the entrance of sodium into the cell, and a uniporter facilitates movement out of the intestinal epithelial cells into the interstitium (hepatic portal vein)

115
Q

once fats are emptied into the duodenum:

A

CCK is released which stimulates gallbladder contraction and sends bile into duodenum, bile acids emulsify the lipids to form micelles, pancreatic lipases hydrolyzes triglycerides to monoglycerides and free fatty acids which then move into intestinal epithelial cells bysimple diffusion, once inside, they are packaged into chylomicrons which then enter lacteals by exocytosis and are later emptied into the thoracic duct and bloodstream (causing lipemia), circulate throughout the body and are gradually whittled away by removal of fat

116
Q

lipoprotein lipase

A

found in adipose and liver tissues, hydrolyzes chylomicron triglycerides into monoglycerides and free fatty acids, diffuses into adipocytes and liver cells, are remade into triglycerides and then stored

117
Q

vitamins

A

nutrients which must be included in the diet because they cannot be synthesized in the body, can be fat-soluble or water-soluble

118
Q

fat-soluble vitamin require:

A

bile acids for solubilization and absorption, excess fat-soluble vitamins are stored in adipose tissue

119
Q

excess water-solube vitamins are:

A

excreted in urine by the kidneys

120
Q

vitamin A (retinol)

A

fat-soluble; a visual pigment that changes conformation in response to light

121
Q

vitamin D

A

fat-soluble; stimulates calcium absorption from the gut; helps control calcium deposition in bones

122
Q

vitamin E

A

fat-soluble; prevents oxidation of unsaturated fats

123
Q

vitamin K

A

fat-soluble; necessary for blood coagulation factors

124
Q

vitamin B1 (thiamine)

A

water-soluble; necessary for enzymatic decarboxylations

125
Q

vitamin B2 (riboflavin)

A

water-soluble; made into FAD; an electron transporter

126
Q

vitamin B3 (niacin)

A

water-soluble; made into NAD+, an electron transporter

127
Q

vitamin B6 (pyridoxine)

A

water-soluble; a coenzyme involved in protein and amino acid metabolism

128
Q

vitamin B12 (cobalamin)

A

water-soluble; a coenzyme involved in the reduction of nucleotides to deoxynucleotides

129
Q

vitamin C (ascorbic acid)

A

water-soluble; necessary for collagen formation; deficiency results in scurvy

130
Q

biotin

A

water-soluble vitamin; prosthetic group essential for transport of carbon dioxide groups

131
Q

folate

A

water-soluble vitamin; enzyme cofactor used in the transport of methylene groups; synthesis of purines and thymine; required for normal fetal nervous system development

132
Q

what are the fat-soluble vitamins?

A

A, D, E, K (require bile acids for solubilization and absorption, excess is stored in adipose tissue)

133
Q

vitamin A (retinol)

A

a visual pigment that changes conformation in response to light, fat-soluble

134
Q

vitamin D

A

stimulates calcium absorption from the gut, helps control calcium deposition in bones, fat-soluble

135
Q

vitamin E

A

prevents oxidation of unsaturated fats, fat-soluble

136
Q

vitamin K

A

necessary for formation of blood coagulation factors, fat-soluble

137
Q

vitamin B1 (thiamine)

A

needed for enzymatic decarboxylations, water-soluble

138
Q

vitamin B2 (riboflavin)

A

made into FAD, an electron transporter, water-soluble

139
Q

vitamin B3 (niacin)

A

made into NAD+, an electron transporter, water-soluble

140
Q

vitamin B6 (pyridoxine)

A

a coenzyme involved in protein and amino acid metabolism, water-soluble

141
Q

vitamin B12 (cobalamin)

A

a coenzyme involved in the reduction of nucleotides to deoxynucleotides, water-soluble

142
Q

vitamin C (ascorbic acid)

A

necessary for collagen formation; deficiency results in scurvy, water-soluble

143
Q

biotin

A

prosthetic group essential for transport of CO2 groups, water-soluble

144
Q

folate

A

enzyme cofactor used in the transport of methylene groups; synthesis of purines and thymine, required for normal fetal nervous system development, water-soluble

MCAT-BIOLOGY (17 decks)

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