Chapter 24 - Digestive System Flashcards
(262 cards)
1
Q
What are the two groups of organs that make up the digestive system?
A
- Gastrointestinal (GI) tract
2. Accessory digestive organs
2
Q
What are the organs of the gastrointestinal tract?
A
Mouth, most of the pharynx, esophagus, stomach, small intestine, large intestine
3
Q
What are the organs of the accessory digestive organs?
A
Teeth, tongue, salivary glands, liver, gallbladder, pancreas
4
Q
What are the six basic processes of digestion?
A
- Ingestion - eating
- Secretion - release of water, acid, buffers and enzymes into lumen of GI tract
- Mixing and propulsion - churning and propulsion of food through GI tract
- Digestion - mechanical and chemical breakdown
- Absorption - passage of digested products from GI tract into blood and lymph
- Defecation - elimination of feces
5
Q
What is motility?
A
The capability of the GI tract to mix and move material along its length
6
Q
What is mechanical digestion?
A
- teeth cut and grind food
- smooth muscles of stomach and small intestine churn food
7
Q
What is chemical digestion?
A
Food is split into smaller molecules by hydrolysis
8
Q
What are feces or stool?
A
Eliminated material
- wastes, indigestible substances, bacteria
9
Q
What are the four layers of the GI tract?
from deep to superficial
A
- Mucosa
- Submucosa
- Muscularis
- Serosa/adventitia
10
Q
What is the mucosa?
A
Inner lining of the GI tract
- mucous membrane
11
Q
What is the mucosa composed of?
A
- Epithelium layer (direct contact with food)
- Connective tissue layer (lamina propria)
- Smooth muscle layer (muscularis mucosae)
12
Q
Describe the structure and function of the epithelium layer of the mucosa?
A
Stratified squamous epithelium - serves a protective function (mouth, pharynx, esophagus, anal canal)
Columnar epithelium - functions in secretion and absorption (stomach and intestines)
- Tight junctions prevent leaks
13
Q
What are enteroendocrine cells?
A
Secrete hormones into the GI tract
- regulate glucose levels, food intake, and stomach emptying
14
Q
What is the lamina propria?
A
Connective tissue layer of GI tract (middle layer)
15
Q
What does the lamina propria contain?
A
Blood and lymphatic vessels
- routes by which nutrients are absorbed to reach other tissues
16
Q
What are mucosa-associated lymphatic tissues (MALT)?
What do they contain?
A
Lymphatic nodules
- contain immune system cells that protect against diseases
17
Q
What is the muscularis mucosae?
A
Smooth muscle fibre layer of GI tract (superficial layer)
- creates folds in stomach and small intestine to increase surface area
18
Q
What is contained in the submucosa layer?
A
- blood and lymphatic vessels (absorbed food molecules)
- extensive network of neurons (submuscosal plexus)
- glands and lymphatic tissue
19
Q
Where is the muscularis skeletal muscle?
A
Mouth, pharynx, superior and middle parts of esophagus
- produces voluntary swallwoing
External anal sphincter
- voluntary control of defecation
20
Q
Where is the muscularis smooth muscle?
A
The rest of the GI tract
- stomach, small intestine, large intestine
21
Q
What is another name for the serosa?
A
Visceral peritoneum
- forms a portion of the peritoneum
22
Q
What forms the superficial layer of the esophagus, since it lacks a serosa?
A
Adventitia
- single layer of areolar connective tissue
23
Q
What is the enteric nervous syste, (ENS)?
A
“Brain of the gut”
- neurons that extend from esophagus to the anus
24
Q
What two plexuses make up the ENS?
A
- Myenteric plexus
2. Submuscosal plexus
25
What does the myenteric plexus control?
Controls GI tract motility (movement)
| - frequency and strength of contraction of the muscularis
26
What is the submuscosal plexus control?
Controls the secretions of the organs of the GI tract
27
What other nervous SYSTEM is the ENS subject to?
Autonomic nervous system
| - sympathetic and parasympathetic fibres
28
What does the stimulation of parasympathetic nerves in the GI tract cause?
Increase in GI secretion and motility
| - increases the activity of ENS neurons
29
What does the stimulation of sympathetic nerves in the GI tract cause?
Decrease in GI secretion and motility
- inhibits the neurons of the ENS
- fear, anxiety, anger - slow digestion
30
What do receptors in the gastrointestinal reflex pathways send information about?
Nature of the contents in GI tract and degree of distension (stretching) of the GI tract
31
What is the largest serous membrane in the body?
Peritoneum
32
How is the peritoneum divided?
1. Parietal peritoneum - lines the wall of the abdominopelvic cavity
2. Visceral peritoneum - covers organs
33
What is the peritoneal cavity?
Space between the parietal peritoneum and visceral peritoneum
- contains lubrication serous fluid
34
Where is the retroperitoneal located?
Situated or occurring behind the peritoneum
35
What organs are part of the retroperitoneal?
Kidneys, ascending and descending colons, duodenum of small intestine, pancreas
36
Describe the anatomy of the peritoneal.
- large folds that weave between the viscera
- binds the organs to one another
- contain blood vessels, lymphatic vessels, nerves
37
What are the five major peritoneal folds?
1. Greater omentum
2. Falciform ligament
3. Lesser omentum
4. Mesentery
5. Mesocolon
38
Describe the greater omentum.
- largest peritoneal fold
- drapes over the transverse colon and coils of the small intestine like a "fatty apron"
- can cause "beer belly" with excessive weight gain
- contains many lymph nodes to combat GI infections
39
Describe the falciform ligament.
- attaches the liver to the anterior abdominal wall and diaphragm
- liver is the only digestive organ that is attached to the anterior abdomianl wall
- second peritoneal fold
40
Describe the lesser omentum.
- suspends the stomach and duodenum from the liver
- contains hepatic portal vein, common hepatic artery and common bile duct
- third peritoneal fold
41
Describe the mesentery.
- fan-shaped fold of the peritoneum
| - binds the jejunum and ileum of the small intestine to the posterior abdominal wall
42
Describe the mesocolon.
- bind the transverse colon and sigmoid colon to the posterior abdominal wall
- hold intestines loosely in place
43
What is the mouth also referred to as?
Oral or buccal cavity
44
What are the cheeks?
Form the lateral walls of the oral cavity
| - covered externally with skin
45
What are the lips or labia?
Fleshy folds surrounding the opening of the mouth
46
What is the oral vestibule?
The space bounded externally by the cheeks and lips and internally by the gums and teeth
47
What is the oral cavity proper?
Space that extends from the gums and teeth to the fauces
48
What are the fauces?
Opening between the oral cavity and the oropharynx (throat)
49
What is the function of the palate in the mouth?
Makes us able to chew and breathe at the same time
50
What is the hard palate?
Anterior portion of the roof of the mouth
| - bony partition between the oral and nasal cavities
51
What is the soft palate?
Posterior portion of the roof of the mouth
| - muscular partition betwwen oropharynx and nasopharynx
52
What is the uvula?
A fleshy extension at the back of the soft palate that hangs above the throat
53
What is the function of the salivary glands?
Releases saliva
- cleanses mouth and teeth
- lubricates, dissolves, and begins chemical breakdown of food
54
What are the three pairs of major salivary glands?
1. Parotid glands
2. Submandibular glands
3. Sublingual glands
55
Where are the parotid glands located and what do they secrete?
Inferior and anterior to the ears
| - watery (serous) liquid containing salivary amylase
56
How does saliva from the parotid glands reach the oral cavity?
Through the parotid duct
| - pierces the buccinator muscle
57
Where are the submandibular glands located and what do they secrete?
Found in the floor of the mouth
| - fluid that contains amylase but is thickened with mucous
58
Where are the sublingual glands located and what do they secrete?
Beneath the tongue and superior to the submandibular glands
| - secrete a much thicker fluid, contributes a small amount of salivary amylase
59
Where do the sublingual glands open into?
Floor of the mouth in the oral cavity proper
60
Where do the submandibular glands open into?
Submandibular ducts
| - "gleeking"
61
What is the chemical composition of saliva?
- 99.5% water
- .05% solutes
(sodium, potassium, chloride, bicarbonate, phosphate)
- slightly acidic pH 6.35-6.85
62
What is salivary amylase?
An enzyme that starts the breakdown of starch in the mouth into maltose, maltotriose and a-dextrin
63
What are the functions of saliva?
- buffer acidic foods
- starts breakdown of starch
- help remove waste from the body
- lubricates food
64
What is salivation?
The secretion of saliva
| - controlled by ANS
65
What is the tongue and what does it form?
Accessory digestive organ
| - forms the floor of the oral cavity
66
How do the extrinsic muscles move the tongue?
- From side to side
- In and out
- Maneuver food for chewing, shape the food and force the food to the back of the mouth
67
How do the intrinsic muscles move the tongue?
Alter the size and shape
| - for speech and swallowing
68
What is the lingual frenulum?
Fold of mucous membrane in the midline of the undersurface of the tongue
- attached to the floor of the mouth
- limits movement of tongue posteriorly
69
What are papillae?
Projections of the lamina propria that cover the upper and lateral surfaces of the tongue
- some contain taste buds
- some contain touch receptors
70
What is the function of lingual glands?
Secrete mucous and watery serous fluid that contains lingual lipase
71
What does lingual lipase do?
Acts on as much as 30% of dietary triglycerides (fats and oils), converts them to simpler fatty acids and diglycerides
72
What are teeth?
Dentes
- accessory digestive organs
- located in sockets of the alveolar processes of the mandible
73
What are gingivae?
Gums!
| - extend slightly into each socket
74
What is the function of the periodontal ligament?
Anchors the teeth to the socket walls and acts as a shock absorber during chewing
- lines each socket
75
What are the three major external regions of a tooth?
1. Crown
2. Root
3. Neck
76
What is the crown of a tooth?
Visible portion above the level of the gums
77
Where are the roots of a tooth located?
Embedded in the socket
| - contains 1-3 roots
78
What is the neck of the tooth?
Constricted junction of the crown and root near the gum line
79
Internally, what forms the majority of the tooth?
Dentin
80
What is dentin?
Calcified connective tissue
- gives shape and rigidity
- harder than bone
81
Where can you find enamel?
Covering the dentin of the crown of a tooth
| - hardest substance in the body
82
What is the function of enamel?
Protects the tooth from wear and tear of chewing
| - protects against acids
83
What is cementum?
Bone-like substance
| - attaches the root to the periodontal ligament
84
What is the pulp cavity?
Enlarged space that lies within the crown
| - filled with pulp
85
What is pulp?
Connective tissue containing blood vessels, nerves and lymphatic vessels
86
What are root canals?
Extensions of the pulp cavity
| - run through the root of the tooth
87
What are dentitions?
| How many do humans have?
Sets of teeth
| - 2!
88
What are the names of the two dentitions?
1. Deciduous teeth
| 2. Permanet teeth
89
What are deciduous teeth?
```
Baby teeth (primary/milk teeth)
- there are 20 deciduous teeth
```
90
What are incisors?
| central or lateral incisors
Closest to the midline, chisel-shaped teeth
- adapted for cutting into food
- contain 1 root
91
What are cuspids?
Used to tear and shred food
- beside the incisors
- contain 1 root
92
What are the first and second molars?
Crush and grind food to prepare for swallowing
- beside the cuspids
- have 4 cusps
93
How many roots do upper molars have?
| Lower molars?
Upper: 3 roots
Lower: 2 roots
94
What are permanent teeth?
Secondary teeth
- replace baby teeth
- contains 32 teeth
95
What are deciduous molars replaced with?
First and second premolars
- two cusps
- 1 root
- used for crushing and grinding
96
What do the permanent molars replace?
Nothing!
| - erupt as the jaw grows to accomdate them
97
When do the first, second and third molars (permanent) appear?
First: at age 6
Second: at age 12
Third: after age 17 (wisdom teeth) - sometimes do not erupt
98
What is mastication?
Mechanical digestion in the mouth
| - results from chewing
99
What is a bolus?
Soft, flexible, easily swallowed mass
| - results from mastication
100
What two enzymes contribute to chemical digestion in the mouth?
1. Salivary amylase - breakdowns starch
| 2. Lingual lipase - breakdowns lipids
101
How does lingual lipase become activated?
In the acidic environment of the stomach
| - starts to work after food has been swallowed
102
What are the three parts of the pharynx?
1. Nasopharynx - only in respiration
2. Oroparynx - digestive and respiratory functions
3. Laryngopharynx - digestive and respiratory functions
103
What is the pharynx?
The throat
104
What is the esophagus?
Food tube
- collapsible, muscular tube
- 25 cm long
- lies POSTERIOR to the trachea
105
What is the esophageal hiatus?
Opening that pierces the diaphragm
| - opens into the stomach (superior portion)
106
What are the layers of the esophagus?
Mucosa, submucosa, and muscularis
107
What is the function of the mucosa layer of the esophagus?
- contains mucous glands
| - protects against abrasion, wear and tear
108
What does the submucosa layer of the esophagus contain?
Blood vessels and mucous glands
109
What does the muscularis layer of the esophagus contain?
First third: skeletal muscle
Second third: skeletal and smooth muscle
Last third: smooth muscle
110
What does the upper esophageal sphincter (UES) consist of? What is it's function?
Skeletal muscle
| - regulates movement of food from pharynx into esophagus
111
What does the lower esophageal sphincter (LES) consist of? What is it's function?
Smooth muscle
| - regulates movement of food from esophagus into stomach
112
What is the superficial layer of the esophagus called?
Adventitia
- **not called the serosa
- attaches to esophagus and surrounding structures
113
What is the physiology of the esophagus?
Secretes mucus and transports food into the stomach
- does NOT produce digestive enzymes
- does NOT carry on absorption
114
What is deglutition?
Swallowing
| - movement of food from the mouth into the stomach
115
What are the three stages of swallowing?
1. Voluntary stage
2. Pharyngeal stage
3. Esophageal stage
116
What happens during the voluntary stage of deglutition?
Bolus is passed into the orophyarynx
117
What happens during the pharyngeal stage of deglutition?
Involuntary passage of bolus through the pharynx into the esophagus
118
What happens during the esophageal stage of deglutition?
Involuntary passage of the bolus through the esophagus into the stomach
- peristalsis
119
Where is the deglutition center located in the brain?
In the medulla oblongata and lower pons of the brain stem
120
What happens after the bolus has stimulated receptors that send impulses to the deglutition center?
Returning impulses cause the soft palate and uvula to move upward (close off nasopharynx)
- prevents swallowed foods and liquids from entering the nasal cavity
Epiglottis closes off the opening to the larynx
- prevents bolus from entering the respiratory tract
121
What is peristalsis?
A progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis
- pushes bolus onward
122
Where is the stomach located and what does it connect
Located directly inferior to the diaphragm in the abdomen
| - connects the esophagus to the duodenum
123
What is the function of the stomach?
Serves as a mixing chamber and holding reservoir
- most distensible part of the GI tract (expand to accommodate large quantities of food)
Secretes gastric juice
Secretes gastrin into blood
124
What are the four main regions of the stomach?
1. Cardia
2. Fundus
3. Body
4. Pyloric part
125
What is the cardia of the stomach?
The superior opening
126
What is the fundus of the stomach?
Rounded portion superior to and to the left of the cardia
127
What is the body of the stomach?
Inferior to the fundus, large central portion
128
What are the three regions of the pyloric part?
1. Pyloric antrum - connects to the body of the stomach
2. Pyloric canal - leads to the third region
3. Pylorus - connects to the duodenun
129
How does the stomach lie when it is empty?
Muscosa lies in large folds, called rugae
130
What is the sphincter in the stomach called?
Pyloric sphincter
131
What is the concave medial border of the stomach called?
| Convex lateral border?
Medial border: lesser curvature
| Lateral border: greater curvature
132
What is the surface layer of the stomach called?
Mucosa
| - layer of simple columnar epithelial cells called SURFACE MUCOUS CELLS
133
What does the mucosa layer of the stomach contain?
Lamina propria: areolar connective tissue
| Muscularis mucosae: smooth muscle
134
The gastric gland contains what three kinds of EXOCRINE gland cells that secrete their products into the stomach lumen?
1. Mucous neck cells
2. Chief cells
3. Parietal cells
135
What do surface mucous cells and mucous neck cells secrete?
Mucus
136
What do parietal cells secrete into the stomach?
Produce intrinsic factor (needed for vitamin B12 absorption) and hydrochloric acid
137
What do chief cells secrete?
Pepsinogen and gastric lipase
138
What forms gastric juice?
The secretions of the mucous, parietal and chief cells
139
What is the G cell?
```
Enteroendocrine cell (gastric gland)
- secretes hormone gastrin into the bloodstream
```
140
Where are gastric glands located?
In a gastric pit
141
What are the three additional layers of the stomach that are deep to the mucosa?
1. Submucosa: areolar connective tissue
2. Muscularis: three layers of smooth muscle
(outer longitudinal, middle circular and inner oblique)
3. Serosa: part of visceral peritoneum
142
What muscularis layer is exclusive to the stomach?
Inner oblique layer
143
What are mixing waves?
| How often do they occur?
Gentle, rippling, peristaltic movements
| - every 15 to 25 seconds; several minutes after food enters the stomach
144
What is the function of mixing waves?
Macerate food, mix it with gastric secretions, and reduce it to a soupy liquid (chyme)
145
What is gastric emptying?
Each mixing wave empties about 3 mL of chyme into duodenum through gyloric sphincter
146
What is the function of the proton pump in the stomach?
Responsible for the acidification of the stomach contents
- H+ and Cl- go into lumen
- K+ goes into parietal cell
147
What is the alkaline tide?
During the production of HCl by parietal cells in the stomach, the parietal cells secrete bicarbonate ions across their basolateral membranes and into the blood, causing a temporary increase in pH
148
What is pepsin?
The only protein digesting enzyme in the stomach
| - secreted by chief cells
149
What prevents pepsin from breaking down the protein in the stomach cells, along with food?
Initially secreted in inactive form (pepsinogen)
- converted to pepsin once it makes contact with hydrochloric acid
- stomach is also coated in alkaline mucus
150
What does gastric lipase do?
Splits the short-chain triglycerides (fats and oils) into fatty acids and monoglycerides
151
What are the three parts of the pancreas?
1. Head - expanded portion of the organ near the curve of the duodenum
2. Body - superior to and left of the head
3. Tail - tapering
152
What are the two pancreatic ducts?
1. Pancreatic duct (Duct of Wirsung)
| 2. Accessory duct (Duct of Santorini)
153
Which pancreatic duct enters the duodenum and is formed by the pancreatic duct, common bile duct and gallbladder?
Hepatopancreatic ampulla (Ampulla of Vater)
154
What regulates the passage of pancreatic juice and bile through the hepatopancreatic ampulla into the small intestine?
Sphincter of the hepatopancreatic ampulla
- mass of smooth muscle
- also known as Sphincter of Oddi
155
Which duct leads from the pancreas and empties into the duodenum about 2.5 cm superior to the hepatopancreatic ampulla?
Accessory Duct (Duct of Santorini)
156
What are acini?
Small clusters of glandular epithelial cells
| - 99% of clusters, constitute the exocrine portion of the organ
157
What do acini secrete?
Mixture of fluid and digestive enzymes
| - pancreatic juice!
158
What is the name of the remaining 1% of clusters, the endocrine portion of the pancreas?
Pancreatic islets (islets of Langerhans)
159
What do pancreatic islets secrete?
Glucagon, insulin, somatostation, and pancreatic polypeptide
160
What is pancreatic juice defined as and what is it's function?
- an alkaline secretion of the pancreas
| - creates the proper pH for the action of digestive enzymes in the small intestine
161
What does pancreatic amylase break down?
Starch
| - digesting enzyme of the pancreas
162
What are the enzymes that digest proteins into peptides?
| produced by the pancreas
Trypsin, chymotrypsin, carboxypeptidase, elastase
163
What is the principle triglyceride (fat and oil) digesting enzyme in adults?
Pancreatic lipase
164
What are the nucleic acid-digesting enzymes of the pancreas?
Ribonuclease and deoxyribonuclease
165
What is the heaviest gland in the body?
The liver
| - weighs 1.4 kg
166
What are the two principal lobes of the liver called?
1. Large right lobe
| 2. Smaller left lobe
167
What is the falciform ligament?
Divides the live into right and left lobes
168
What are the other two lobes of the liver called that are associated with the left lobe?
1. Inferior quadrate lobe
| 2. Posterior caudate lobe
169
What are the histological components of the liver?
1. Hepatocytes
2. Bile canaliculi
3. Hepatic sinusoids
170
What are hepatocytes?
Major functional cells of the liver
- perform metabolic, secretory and endocrine functions
- secrete bile
171
What are bile canaliculi?
Small ducts between hepatocytes that collect bile produced by the hepatocytes
172
What is the function of bile ducts?
From bile canaliculi, bile passes into bile ductules and then bile ducts
- merge to form right and left hepatic ducts
173
What is the name of the duct that exits the liver?
Common hepatic duct
| - joins with the cystic duct (from the gallbladder) to form the common bile duct
174
What are hepatic sinusoids?
Highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and nutrient-rich de-oxygenated blood from branches of the hepatic portal vein
175
What do hepatic sinusoids converge and deliver blood into?
Central vein
176
What are the bile duct, branch of the hepatic artery and branch of the hepatic vein referred to as?
Portal triad
177
What is the hepatic lobule described as?
Functional unit of the liver
| - shaped like a hexagon, with a central vein (at the center)
178
What is the portal lubule describe as?
Emphasized the exocrine function of the liver
| - bile secretion
179
What is the pathway of blood as it passes through the liver to the heart?
1. Hepatic artery and hepatic vein
2. Liver Sinusoids
3. Central vein
4. Hepatic vein
5. Inferior vena cava
6. Right atrium of the heart
180
The liver receives blood from two sources, what are they?
1. Hepatic artery
| 2. Hepatic vein (from gastrointestinal tract)
181
What is the principal bile pigment?
Bilirubin
- phagocytosis of aged red blood cells liberates iron, globin and bilirubin (derived from heme)
- bilirubin is secrete into bile, broken down in the intestine
182
What role does bile serve in digestion?
Role in emulsification
- break-down of large lipid globules into a suspension of small lipid globules
- small lipid globules can then be broken down by pancreatic lipase
183
What are the vital functions of the liver, other than bile secretion?
1. Carbohydrate metabolism (normal blood glucose level)
2. Lipid metabolism (stores fats)
3. Protein metabolism
4. Processing of drugs and hormones
5. Excretion of bilirubin
6. Synthesis of bile sales
7. Storage of vitamins and minerals
8. Phagocytosis
9. Activation of vitamin D
184
What are the three regions of the small intestine?
1. Duodenum
2. Jejunum
3. Ileum
185
What is the duodenum?
Shortest region of small intestine
- starts at the pyloric sphincter (of the stomach)
- "C" shaped tube that extends approx. 25 cm
186
What is the jejunum?
Middle region of the small intestine
- 1m or 3ft long
- means "empty" b/c that is how it is found during death
187
What is the ileum?
Final and longest region of the small intestine
- 2m or 6ft long
- joins with large intestine
188
What is the function of the ileocecal sphincter (valve)?
Joins the ileum (small intestine) to the large intestine
189
What are the 4 layers of the small intestine?
1. Mucosa
2. Submucosa
3. Muscularis
4. Serosa
190
What is the function of absorptive cells in the mucosa layer of the small intestine?
Digest and absorb nutrients in small intestinal chyme
| - found in the epithelium layer of the mucosa
191
What is the function of goblet cells in the mucosa layer of the small intestine?
Secrete mucus
| - found in epithelium layer of the mucosa
192
What do intestinal glands (crypts of Lieberkuhn) secrete?
Intestinal juices
193
Besides absorptive cells and goblet cells, what other two kinds of cells do the intestinal glands also contain?
1. Paneth cells - secrete lysozyme, capable of phagocytosis
| 2. Enteroendocrine cells
194
What are the three kinds of enteroendocrine cells in the small intestine and what do they secrete?
1. S cells - secrete secretin
2. CCK cells - cholecystokinin (CCK)
3. K cells - glucose-dependent insulinotropic peptide (GIP)
195
What does the submucosa layer of the duodenum contain?
| What does it secrete?
```
Duodenal glands (Brunner's glands)
- secrete alkaline mucus that helps neutralize gastric acid in the chyme
```
196
How many layers of smooth muscle does the musclaris of the small intestine contain?
2 layers
197
The serosa completely surrounds the small intestine, expect for which part?
A major portion of the duodenum
198
What are the special structural features of the small intestine that facilitate the process of digestion and absorption?
Circular folds, villi and microvilli
199
What is the function of circular folds in the small intestine?
Enhance absorption by increasing surface area
| Cause chyme to spiral (rather than move in a straight line)
200
What is the function of villi in the small intestine?
Enhance absorption and digestion by increasing surface area
201
What is a lacteal and where is it found?
A lymphatic capillary
| - found in each villus of the small intestine
202
What are microvilli of the small intestine?
Projections of the apical (free) membrane of the absorptive cells
- too small to be seen individually
- forms the brush border
203
What does intestinal juice contain?
| What does it do?
Water, mucus, and is slightly alkaline (pH 7.6)
| Aids the absorption of substances from chyme
204
What are the four brush-border enzymes that digest carbohydrates? (in the small intestine)
1. Dextrinase
2. Maltase
3. Sucrase
4. Lactase
205
What are the two brush-border enzymes that digest proteins? (in the small intestine)
Peptidases
1. Aminopeptidase - cleaves off amino acid at the amino end of a peptide
2. Dipeptidase - splits dipeptides into single amino acids
206
What are the two brush-border enzymes that digest nucleotides? (in the small intestine)
1. Nucleosidases
| 2. Phosphatases
207
What are the two types of movement in the small intestine?
1. Segmentations
| 2. Migrating motility complexes
208
What are segmentations?
Localized, mixing contractions that occur in portions of intestine distended by a large volume of chyme
209
What is the purpose of segmentation?
Mix chyme with the digestive juices and bring the particles of food into contact with the mucosa for absorption
- do NOT push contents along the tract!
210
What is migrating motility complex? (MMC)
Pushes chyme forward along a short stretch of small intesting before dying out
- slowly migrates down the small intestine
211
What is the digestive enzyme that acts on carbohydrates?
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Salivary amylase
- primarily in the mouth
- pH of stomach inactivates it
Pancreatic amylase
- acts in the small intestine (from pancreas)
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212
How are sucrose, lactose and maltose broken down, and where?
In the small intestine by brush-border enzymes
213
What are the enzymes that act on proteins?
Pepsin (in the stomach)
| Trypsin, chymotrypsin, carboxypeptidase and elastase (pancreatic juice)
214
What are the three lipases that participate in lipid digestion?
1. Lingual lipase
2. Gastric lipase
3. Pancreatic lipase
- lipases mostly act in the small intestine
215
What are the enzymes that digest nuclei acids?
Ribonuclease - digests RNA
| Deoxyribonuclease - digests DNS
216
What are the substances that the small intestine is able to absorb?
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Monosaccharides (from carbohydrates)
Single amino acids (from proteins)
Fatty acids (from triglycerides)
```
217
What is enterohepatic circulation?
The circulation of biliary acids, bilirubin, drugs, or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver
218
What is the overall function of the large intestine?
1. Churning, peristalsis, and mass peristalsis
2. Convert proteins to amino acids, break down amino acids, produce some B vitamins and vitamin K (bacteria do this)
3. Absorbing water, ions and vitamins
4. Forming feces
5. Defecating
219
What are the four regions of the large intestine?
1. Cecum
2. Colon
3. Rectum
4. Anal canal
220
What is the mesocolon?
Double layer of peritoneum
| - how it attaches to the posterior abdominal wall
221
What is the function of the ileocecal sphincter?
Fold of mucous membrane
| - allows materials to pass from the small intestine to the large intestine
222
What is the cecum?
A pouch connected to the junction of the small and large intestines
223
What is the appendix?
Twisted, coiled-tube attached to the cecum
224
What is the colon?
Long tube that the cecum merges with
| - divided into ascending, transverse, descending and sigmoid portions
225
What are the four parts of the colon?
1. Ascending (right side)
2. Transverse
3. Descending colon
4. Sigmoid colon
226
What is the rectum?
Last 20 cm of the GI tract
227
What is the anal canal?
The last 2-3 cm of the rectum
228
What is the anus?
The opening of the anal canal to the exterior
229
What is the anus guarded by?
Internal anal sphincter (smooth muscle, involuntary)
| External anal sphincter (skeletal muscle, voluntary)
230
What are the four layers of the large intestine?
1. Mucosa
2. Submucosa
3. Muscularis
4. Serosa
231
Where does the most absorption occur? In the small or large intestine?
Small intestine
| - large intestine does not have as many structural adaptations that increase surface area
232
What are teniae coli?
Three bands of thickened longitudinal muscle in the large intestine
233
What are haustra?
Series of pouches of gathered colon
| - give colon a puckered appearance
234
What is the gastroileal reflex?
Peristalsis intensifies after a meal in the ileum
| - forces any chyme into the cecum
235
What happens during haustral churning?
- haustra remain relaxed and become distended as they fill up
- when distension reaches a certain point, the walls contract and squeeze the contends into the next haustrum
236
At what rate does peristalsis occur in the large intestine?
3-12 contractions per minute
| - slower than in more proximal portions of GI tract
237
What does mass peristalsis do?
Drives the contents of the transverse colon into the rectum
- strong peristaltic wave
- occurs 3-4 times per day
238
How does chemical digestion occur in the large intestine?
Activity of bacteria
- mucus is secreted by large intestine, but no enzymes
- bacteria break down proteins, amino acids, bilirubin
239
What are feces?
Solid or semi-solid chyme
| - results from remaining in the large intestine for 3-10 hours
240
Where is water absorbed in the GI tract?
- 90% in the small intestine
| - .5-1 litres in the large intestine
241
What happens during the defecation reflex?
Rectum empties
- distension of rectal wall, receptors send sensory nerve impulses to the sacral spinal cord
- motor impulses from cord travel along parasympathetic nerves back to the descending colon/sigmoid colon/rectum/anus
- contraction of longitudinal rectal muscles shortens the rectum, increases pressure
242
What is diarrhea?
Increase in the frequency, volume and fluid content of the feces
- caused by increased motility and decreased absorption
243
What is constipation?
Infrequent or difficult defecation
| - caused by decreased motility and excessive absorption
244
What are the three phases of digestion?
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
245
What happens during the cephalic phase of digestion?
Smell, sight, thought or initial taste of food activates neural centers in the cerebral cortex, hypothalamus and brain stem
- salivary glands are stimulated
- Gastric glands are stimulated
- PREPARES the mouth and stomach for food that is about to be eaten
246
What happens during the gastric phase of digestion?
```
Neural regulation
- stretch receptors
- chemoreceptors
Hormonal regulation
- gastrin release
```
247
What hormone regulates gastric secretion during the gastric phase of digestion?
Gastrin
| - released from G cells
248
When does the intestinal phase of digestion occur?
Once food enters the small intestine
249
What are the two hormones secreted in the small intestine that mediate the intestinal phase of digestion?
1. Cholecystokinin - stimulates secretion of pancreatic juice, ejects bile from gallbladder, induces satiety
2. Secretin - stimulate secretion of pancreatic juice and bile
250
What is dental caries?
Tooth decay
| - demineralization of the enamel and dentin
251
What is periodontal disease?
Enlargement and inflammation of the soft tissue and bleeding of the gums
252
What is peptic ulcer disease?
Ulcers that develop in areas of the GI tract exposed to acidic gastric juice
253
What is diverticular disease?
Saclike outpouchings of the wall of the colon
| - develop inflammation
254
What is colorectal cancer?
Cancer of the colon
| - very deadly
255
What is hepatitis?
Inflammation of the liver
| - caused by viruses, drugs and chemcials
256
What is bulimia?
an emotional disorder involving distortion of body image and an obsessive desire to lose weight, in which bouts of extreme overeating are followed by depression and self-induced vomiting, purging, or fasting
257
What is cirrhosis?
Distorted or scarred liver
| - result from chronic inflammation due to hepatisis, chemicals, parasites, or alcoholism
258
What is colitis?
Inflammation of the mucosa of the colon and rectum
- watery bloody feces
- absorption is reduced
259
What is a colostomy?
a surgical operation in which a piece of the colon is diverted to an artificial opening in the abdominal wall so as to bypass a damaged part of the colon
260
What is flatus?
Air (gas) in the stomach or intestine
261
What is inflammatory bowel disease?
1. Crohn's disease - inflammation of GI tract (from mucosa through serosa)
2. Ulcerative colitis - inflammation of mucosa of the colon
262
What is irritable bowel syndrome?
Disease of the entire GI tract
| - person reacts to stress by developing symptoms
