digestion Flashcards
1
Q
what are the steps to digestion?
A
1) Ingestion: eating
2) Propulsion: movement of food through the alimentary canal
3) Mechanical breakdown
4) Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks
5) Absorption: passage of digested fragments from lumen of GI tract into blood or lymph
6) Defecation: elimination of indigestible substances via anus in form of feces
2
Q
what happens during ingestion?
A
Food is “packaged” in bulk form and contains very complex arrays of molecules, including large polymers and various substances that may be difficult to process or may even be toxic.
3
Q
why cant humans use macromolecules like proteins, fats, and carbohydrates in the form of starch or other polysaccharides?
A
Such polymers are too large to pass through membranes and enter the cells of the animal
4
Q
true or false, the macromolecules that make up an animal are the same that it ingests
A
false. Macromolecules that make up an animal are not identical to those of its food
5
Q
true or false, all animals use the same monomers
A
true
6
Q
what does propulsion include?
A
a) Swallowing
b) Peristalsis
7
Q
what is peristalsis
A
major means of propulsion of food that involves alternating waves of contraction and relaxation by smooth muscles in the walls of the canal, push food along.
8
Q
what do sphincters do?
A
muscular ringlike valves, regulate the passage of material between specialized chambers of the canal
9
Q
what is mechanical breakdown?
A
includes chewing, mixing food with saliva, churning food in stomach, and segmentation
10
Q
what is segmentation?
A
local constriction of intestine that mixes food with digestive juices
11
Q
what is digestion?
A
-Digestion is the process of breaking food down into molecules small enough for the body to absorb.
-Cleaves macromolecules into their component monomers
-The animal uses these to make its own molecules or as fuel for ATP production.
12
Q
what are polysaccharides and disaccharide?
A
they are split into simple sugars
13
Q
how does digestion cleave molecules?
A
Digestion breaks bonds with the addition of water via enzymatic hydrolysis.
14
Q
what are fats cleaved into?
A
digested to glycerol and fatty acids
15
Q
what are proteins cleaved into?
A
are broken down into amino acids
16
Q
what are nucleic acid cleaved into?
A
are cleaved into nucleotides
17
Q
how do chemical digestion and mechanical segmentation go together?
A
Chemical digestion is usually preceded by mechanical fragmentation of the food (chewing) which increases the surface area exposed to digestive juices containing hydrolytic enzymes
18
Q
what do hydrolytic enzymes do?
A
Hydrolytic enzymes catalyze the digestion of each of the classes of macromolecules found in food.
19
Q
what are the two types of digestions that car occur?
A
inside simple columnar cell: intracellular digestion
in lumen/mouth: extracellular digestion
20
Q
what happens during absorption?
A
The animal’s cells take up small molecules such as amino acids and simple sugars from the digestive compartment, a process called absorption.
21
Q
what happens during defecation?
A
undigested material passes out of the digestive compartment
22
Q
what does the digestive system consists of?
A
-alimentary canal
-accessory glands that secrete digestive juices into the canal through ducts.
-
23
Q
what is the alimentary canal?
A
the alimentary canal (also called the digestive tract). This long tube of organs makes a pathway for food to travel through the body.
24
Q
where does the esophagus lead to?
A
stomach
25
what happens in the intestines?
In the intestine, digestive enzymes hydrolyze the food molecules, and nutrients are absorbed across the lining of the tube into the blood.
26
where are undigested waste eliminated from?
anus
27
can we ingest more food before the previous meal is digested?
yes
28
what happens after chewing and swallowing?
After chewing and swallowing it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.
Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours
In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.
29
does digestion happen in the large intestine?
the large intestine produces no digestive enzymes
30
is there a sphincter in the stomach?
yes two. one at the entry and one at the exit
31
what is the caecum?
The caecum is a pouch in the lower abdominal cavity that receives undigested food material from the small intestine and is considered the first region of the large intestine.
32
where is the appendix?
attached to caecum
33
what are the accessory glands?
The accessory glands include the salivary glands, the pancreas, the liver, and the gallbladde
34
what initiates food processing?
The oral cavity, pharynx, and esophagus initiate food processing
35
where does physical and chemical digestion begin?
in the mouth
36
what does chewing allow for?
During chewing, teeth of various shapes cut, smash, and grind food, making it easier to swallow and increasing its surface area
37
when are salivary glands triggered?
Food in the oral cavity triggers the salivary glands to deliver saliva through ducts to the oral cavity.
38
what does saliva contain?
mucin (slippery glycoproteins)
39
what does saliva allow for?
a) protects the soft lining of the mouth from abrasion (1500 ml/day can be produced)
b) lubricates the food for easier swallowing
c) contains buffers that help prevent tooth decay by neutralizing acid in the mouth
d) antibacterial agents in saliva kill many bacteria that enter the mouth with food
e) contains salivary amylase, an enzyme that hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose.
40
what does salivary amylase do?
enzyme that hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose.
41
what does the tongue do?
a) tastes food (papillae)
b) manipulates it during chewing
c) helps shape the food into a ball called a bolus
d) during swallowing, the tongue pushes a bolus back into the oral cavity and into the pharynx.
42
what is the pharynx?
The pharynx, also called the throat, is a junction that opens to both the esophagus and the trachea
43
do we want a bolus to move into the trachea or the esophagus after entering the pharynx?
esophagus
44
how do we avoid food getting into the trachea?
When we swallow, the top of the trachea moves up such that its opening, the glottis, is blocked by a cartilaginous flap, the epiglottis.
This mechanism normally ensures that a bolus will be guided into the entrance of the esophagus and not directed down the trachea.
45
what is the opening fo the trachea called?
glottis
46
what is the covering of the glottis called?
epiglottis
47
true or false, the esophagus has a sphincter
true!
48
what is the uvula?
secretes saliva, plays a role in speech, prevents food from entering nasopharynx
49
what is the function of the larynx?
The primary function of the larynx in humans and other vertebrates is to protect the lower respiratory tract from aspirating food into the trachea while breathing
50
what happens when we are not swallowing?
When not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing airflow through trachea to the lungs.
51
what happens when we are swallowing (food bolus reaches pharynx)?
When a food bolus reaches the pharynx, the larynx moves upward and the epiglottis tips over the glottis, closing off the trachea.
The esophageal sphincter relaxes and the bolus enters the esophagus. After the food has entered the esophagus, the larynx moves downward and the trachea is opened. Waves of peristalsis move the bolus to the stomach.
52
how does esophagus conduct food from pharynx to stomach?
peristalsis
53
are the muscles at the top of the esophagus voluntary or involuntary?
they are striated, therefore they are voluntary
Involuntary waves of contraction by smooth muscles in the rest of the esophagus then takes over
54
what does the stomach do?
The stomach stores food and performs preliminary digestion
55
what are the folds in the stomach called?
rugae
56
where is the stomach located?
Stomach is located in the upper abdominal cavity, just below the diaphragm
57
what does the stomach secrete? what does it do with this
secretes a digestive fluid called gastric juice and mixes this secretion with the food by the churning action of the smooth muscles in the stomach wall.
58
what type of cells is the esophagus?
stratified squamous
59
how come the gastric juices dont digest our own stomach lining?
mucus lining
60
what type of cells are in stomach?
-chief cells
-goblet cells
-parietal cells
61
what is present in gastric juice?
HCL
pepsin
62
what is pepsin?
63
what do chief cells do?
makes pepsinogen, then HCL cleaves pepsinogen into pepsin
64
what do goblet cells do?
produce mucus
65
what do parietal cells do
make HCL
66
what does stomach acid allow for?
- acid disrupts the extracellular matrix that binds cells together.
- kills most of the bacteria that are swallowed with food.
- acid denatures protein, activates pepsin, breaks down plant cell walls
67
what does pepsin do?
it is an enzyme that begins the hydrolysis of proteins by breaking peptide bonds adjacent to specific amino acids, producing smaller polypeptides.
68
what are the characteristics of pepsin?
- works well at low pH
- secreted in its inactive form, called pepsinogen, by specialized chief cells in gastric pits
69
how do pepsinogen molecules have positive feedback inhibition
activated pepsin can activate more pepsinogen molecules
70
how do we limit self digestion in the stomach?
Parietal cells, also in the pits, secrete HCl which converts pepsinogen to active pepsin. basically, stomach makes enzyme in their inactive form
71
what are enteroendoctrine cells?
Other cells in the stomach, called Enteroendocrine cells: secrete chemical messengers
72
what does serotonin do?
causes contraction of stomach muscle
73
what does histamine do?
activates parietal cells to release HCl
74
what does somatostatin do?
various inhibitory functions
75
what does gastrin do?
stimulating functions, including HCl secretion
76
what is the stomach's second line of defence from self-digestion?
The stomach’s second line of defense against self-digestion is a coating of mucus which is secreted by epithelial cells. the mucus protects the stomach's lining
77
true or false, stomach epithelium stays forever.
stomach epithelium is continually eroded and completely replaced by mitosis every three days.
78
what are gastric ulcers?
lesions in the stomach lining caused by the acid-tolerant bacterium Heliobacter pylori
79
what goes from the stomach to the small intestine?
chyme
80
what is the name of the two sphincters of the stomach?
coming into stomach: cardiac orifice/sphincter
leaving stomach: pyloric sphincter
81
what causes heartburn?
backflow of acid chyme from the stomach into the lower esophagus causes heartburn.
82
when does the cardiac orifice dilate?
opening from the esophagus to the stomach, the cardiac orifice, normally dilates only when a bolus driven by peristalsis arrives
83
what is mesentery?
a fold of tissue that attaches organs to the body wall. Blood vessels, nerves, and lymphatics branch through the mesentery to supply the organs
84
what is the major organ of digestion and absorption?
the small intestine
85
what is the longest section of the alimentary canal?
small intestine
86
what is the duodenum?
The first part of the small intestine.
87
what secretes digestive juices?
pancreas, liver, gall bladder, and gland cells of the intestinal wall
88
what happens in duodenum?
In the duodenum, acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gall bladder, and gland cells of the intestinal wall
89
what does the pancreas produce?
a) several hydrolytic enzymes
b) an alkaline solution, rich in bicarbonate, which buffers the acidity of the chyme from the stomach.
90
what does the liver produce?
bile
91
where is bile stored?
gallbladder
92
what does bile salts/acid do? what is this process called?
The bile acids will break fats into small drops so that there is a greater surface area for lipase to work. This process is called emulsification.
93
how is bile amphipathic?
Bile salts/acids are amphipathic. The hydrophobic portion is provided by a cholesterol-like compound, and the hydrophilic portion is provided by an amino acid.
94
what are bile pigments?
pigments that are by-products of red blood cell destruction in the liver.
95
how are bile pigments eliminated?
Bile pigments are eliminated from the body with the feces.
96
the digestion of starch and glycogen is special. what happens during it?
begins by salivary amylase in the oral cavity
and continues in the small intestine.
- pancreatic amylases hydrolyze starch, glycogen, and smaller polysaccharides into disaccharides.
- disaccharidases hydrolyze each disaccharide into monomers.
- maltase splits maltose, sucrase splits sucrose
- disaccharidases are built into the membranes and extracellular matrix of the intestinal epithelium (site of sugar absorption).
97
where does small intestine get enzymes from?
pancreas
98
where are disacharidases found?
disaccharidases are built into the membranes and extracellular matrix of the intestinal epithelium (site of sugar absorption)
99
how does the body store glucose?
as glycogen
100
how are Trypsin, Chymotrypsin, and Carboxypeptidase secreted?
by the pancreas in their inactive form
101
where is dipeptidase found?
in the lining of the intestine
102
how does the digestion of proteins happen?
Digestion of proteins in the small intestine completes the process begun by pepsin.
Enzymes in the duodenum dismantle polypeptides into their amino acids or into small peptides that in turn are attacked by other enzymes.
- Trypsin and chymotrypsin attack peptide bonds adjacent to specific amino acids, breaking larger polypeptides into shorter chains.
- Dipeptidase, attached to the intestinal lining, split smaller chains.
- Carboxypeptidases and aminopeptidase split off one amino acid from the carboxyl or amino end of a peptide, respectively.
103
what do carboxypeptidase and aminopeptidase do?
Carboxypeptidases and aminopeptidase split off one amino acid from the carboxyl or amino end of a peptide, respectively
104
what does dipeptidase do?
attached to the intestinal lining, split smaller chains after the pancreatic enzymes act
105
which enzymes are secreted by the pancreas for protein digestion?
carboxypeptidase, trypsin and chymotrypsin
106
how do Trypsin, Chymotrypsin, and Carboxypeptidase get activated?
- An intestinal enzyme, enteropeptidase, converts inactive trypsinogen into active trypsin.
- Active trypsin then activates the other two and also further converts trypsinogen to trypsin
107
what is aminopeptidase secreted by?
intestinal epithelium
108
what happens during the digestion of nucleic acid?
- A team of enzymes called nucleases hydrolyzes DNA and RNA into their component nucleotides.
- Other hydrolytic enzymes then break nucleotides down further into nucleosides, nitrogenous bases, sugars, and phosphates
109
which macromolecule gets slightly s=digested in the stomach?
proteins (thanks to pepsin)
110
where does nucleic acid digestion happen?
all in small intestine
111
which macromolecule only gets digested by pancreatic enzymes, and no epithelium secreted enzymes?
fats (only lipase digests them)
112
how are fats digested?
after bile makes fat molecules into small droplets, Large surface area of these small droplets is exposed to lipase, an enzyme that hydrolyzes fat molecules into glycerol, fatty acids, and monoglycerides.
113
which pancreatic enzyme digests fats?
lipase
114
what's a vili?
Intestinal villi are tiny, finger-like projections made up of cells that line the entire length of your small intestine. Villi absorb nutrients from the food you eat and then shuttle them into your bloodstream so they can travel where they're needed
115
what happens to fats after they are digested?
products are absorbed by epithelial cells and recombined into triglycerides.
-They are then coated with phospholipids, cholesterol and proteins. This forms water-soluble globules called chylomicrons.
-The chylomicrons are transported from the epithelial cell into a lacteal, which is a lymphatic vessel at the core of each villus.
A lacteal is also known as a lymphatic capillary.
- the lacteals converge into the larger vessels of the lymphatic system, eventually draining into large veins that return blood to the heart
116
what are chylomicrons?
formed after fats are digested and reassembled into triglycerides, and aborde into epithelium to be coated with phospholipids, cholesterol and proteins to be water-soluble
117
where does most digestion occur?
duodenum
118
what are the functions of the jejunum and ileum
mainly in the absorption of nutrients and water, because to enter the body, nutrients in the lumen must pass the lining of the digestive tract.
119
what does the enormous size of the small intestine allow for?
Enormous surface of the small intestine is an adaptation that greatly increases the rate of nutrient absorption
120
what is a lacteal?
a single vessel of the lymphatic system called a lacteal
121
what do microvilli allow for?
Microvilli located in the small intestine function to increase the surface area in order to absorb more nutrients.
122
what penetrates each villus?
Penetrating the core of each villus is a net of microscopic blood vessels (capillaries) and a single vessel of the lymphatic system called a lacteal.
123
how do nutrients enter the body after digestion?
they travel through the lacteal to enter the lymphatic system
124
what do we call microscopic blood vessels?
capillaries
125
how are nutrients absorbed?
Nutrients are absorbed across the intestinal epithelium and then across the unicellular epithelium of capillaries or lacteals.
126
what are the two layers of the epithelial that separate nutrients from the bloodstream?
epithelium of intestine
epithelium of capillaries
127
how are lipids absorbed into the body?
through the lacteal system (and need to be dissolved cause lacteal is liquid)
128
what are the different types of transport across the epithelium?
active and passive
129
what is passive transport? give an example of passive transport in digestion
down their concentration gradients from the lumen of the intestine into the epithelial cells, and then into capillaries
ex fructose
130
what is active transport. give an example of active transport in digestion
pumped against concentration gradients by epithelial membranes.
- allows absorption of a much higher proportion of the nutrients in the intestine than would be possible with passive diffusion
ex amino acids, small peptides, vitamins, and glucose
131
where do the nutrients go after absorption?
to the liver, and then to the heart
132
what is the hepatic portal?
all capillaries converge here into one thick tube and then.
carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart
133
what does the liver do?
The liver regulates nutrient distribution, interconverts many organic molecules, and detoxifies many organic molecules
134
what has first access to amino acids and sugars absorbed?
liver
The liver modifies and regulates this varied mix before releasing materials back into the blood stream
135
what is the glucose concentration in the blood?
0.1 percent
136
what is most of the undigestible material?
cellulose from plant cells
137
what happens when we smell, taste or see food?
When we see, smell, or taste food, impulses from the brain initiate the secretion of gastric juice (the fluid released by the stomach wall, includes enzymes, hydrochloric acid and mucus).
138
what does gastrin do?
As it recirculates, gastrin stimulates further secretion of gastric juice.
If the pH of the stomach contents becomes too low, the acid will inhibit the release of gastrin.
139
what are enterogastrones secreted by?
are secreted by the walls of the duodenum.
140
what neutralizes the acidic chyme?
bicarbonate, and its secreted by the pancreas
141
how is secretin released and what does it do?
The acidic pH of the chyme entering the duodenum stimulates epidermal cells to release the hormone secretin which signals the pancreas to release bicarbonate to neutralize the acidic chyme.
142
what is CCK?
Cholecystokinin (CCK), secreted in response to the presence of amino acids or fatty acids, causes the gallbladder to contract and release bile into the small intestine and triggers the release of pancreatic enzymes.
143
what is CCK released from?
secreted in response to the presence of amino acids or fatty acids,
144
what happens if the chyme is too rich in fats?
causes the duodenum to release other enterogastrones that inhibit peristalsis by the stomach, slowing entry of food. In addition, when the chyme is rich in fats, the high levels of secretin and CCK will act on the stomach to inhibit peristalsis and secretion of gastric juices, thereby slowing digestion.
145
what does CCK tell the stomach?
dont send more chyme, cause we're not done digesting the chyme from before, so if there's some present
146
what is another word for the large intestine?
the colon
147
how is the small intestine connected to the large intestine?
The large intestine, or colon is connected to the small intestine at a T-shaped junction where a sphincter controls the movement of materials.
148
what are the differences between the small and large intestine?
- colon does not contain villi
- colon contains more mucous secreting Goblet cells than the small intestine
149
what is the cecum?
Cecum of humans has a fingerlike extension, the appendix, that makes a minor contribution to body defense
150
what is the appendix?
Cecum of humans has a fingerlike extension, the appendix, that makes a minor contribution to body defense.
151
what is the function of the colon?
A major function of the colon is to recover water (entered the alimentary canal as the solvent to various digestive juices)
152
why does the colon need to recover water?
cause lots of it is used as a solvent for various digestive juices
153
where is most of the water reabsorbed?
small intestine
154
true or false, feces become more solid as they move along colon
true!
155
how does diarrhea happen?
Diarrhea results if insufficient water is re- absorbed into the body from the colon.
156
how does constipation happen?
Constipation results if too much water is re-absorbed into the body from the colon
157
what is the most common inhabitant of the colon?
Escherichia coli
158
what do colon bacteria release as a result of their metabolism?
As a byproduct of their metabolism, many colon bacteria generate gases, including methane and hydrogen sulfide
159
why are bacteria in our colon good for our health?
Some bacteria produce vitamins, including biotin, folic acid, vitamin K, and several B vitamins, which supplement our dietary intake of vitamins.
160
what vitamins do bacteria in our colon make?
biotin, folic acid, vitamin K, and several B vitamins
161
what do feces contain?
Feces contain masses of bacteria and undigested materials including cellulose
162
what do humans do with cellulose?
Cellulose fibers have no caloric value to humans.
Cellulose in the diet helps move food along the digestive tract.
163
do cellulose fibers contain salt?
may also contain excess salts that are excreted into the lumen of the colon
164
what is the terminal position of the colon?
rectum
165
are the two sphincters between the anus and the rectum involuntary or voluntary?
Between the rectum and the anus are two sphincters, one involuntary and one voluntary
166
what creates the urge to defecate?
Once or more each day, strong contractions of the colon create an urge to defecate.
167
where are nutrients absorbed?
he walls of the small intestine absorb the digested nutrients into the bloodstream. The blood delivers the nutrients to the rest of the body.
