Gastrointestinal Physiology- Monogastrics Flashcards
(318 cards)
1
Q
What are the 6 parts of the digestive tract?
A
- Mouth
- Esophagus
- Stomach
- Large Intestine
- Small Intestine
- Supportive organs (liver, pancreas, gall bladder)
2
Q
GI physio covers organs that take part in ________, ________, and _______.
A
- extraction (of nutrients during digestion)
- absorption
- utilization
3
Q
What are the 6 chemical components of food?
A
- carbohydrates
- proteins
- fats
- vitamins
- minerals / salts
- water
4
Q
What is the first organ of digestion/ first organ food meets?
A
mouth
5
Q
What 2 parameters measure GI physio functionality?
A
- motility (contraction of smooth mm. in GIT walls)
- secretion (secretion of enzymes- very important in lubrication)
6
Q
What are the 5 procedures to diagnoses GI issues?
A
- fecal sample
- endoscopy
- biopsy
- ultrasound
- surgery
7
Q
What organs play accessory roles in digestion and how?
A
- pancreas - secretes enzymes and buffers
- liver - secretes bile to break down fats and cholesterol (first organ to receive absorbed nurtients except for lipids)
- gall bladder - storage sac of bile found in the liver (also an accessory organ of the liver)
8
Q
What are neuroendocrine cells?
A
Special cells in the GIT walls that secrete hormones that are important in regulating digestive functions. (disruption of the hormones can lead to pathologies)
9
Q
What is the major contributor to the breakdown of chemicals in monogastric GIT?
A
enzymes produced by the host
10
Q
What are monogastrics?
A
Vertebrate animals with a simple stomach considered as one organ. They cannot digest plant materials (roughages) because of a lack of microbes that produce enzymes that can digest roughages.
11
Q
What are the general components of the ruminant GIT?
A
- They have a large stomach.
- Forecomponents of each stomach (reticulum, rumen, and omasum)
- the forestomachs are in front of the abomasum (major/true stomach)
They are able to digest plant materials. The forestomachs, especially the rumen, are filled with high density microbes.
12
Q
What is the major contributor to the breakdown of chemicals in ruminants GIT?
A
Enzymes produced by microbes are in the forestomachs (fermentation) and the host in the intestines.
13
Q
What happens if ruminants cannot eructate?
A
The stomach will become bloated and the animal may die from asphyxiation.
14
Q
What is methanogenic bacteria?
A
A bacteria in ruminants that produces CH4-methane- a greenhouse gas
15
Q
What percentage of methane in the environment is produced by ruminants?
A
45% - 65%
16
Q
How can you control methane greenhouse production from ruminants?
A
Make things that reduce methanogens without harming the host or other helpful bacteria.
17
Q
Animal’s dentition is adapted for:
A
Different eating habits to grab food effectively (prehension)
18
Q
What are the 6 different methods of prehension in animals?
A
- Dogs and cats use teeth.
- Horses use lips to channel food in their mouth to be gripped by their teeth
- Ruminants use their tongue because they have less mobile lips.
- Sheep and goats use the tongue, incisor, and lips to a limited extent.
- Pigs are similar to sheep and goats but they exhibit a propulsive movement of the head.
- Poultry have no teeth but have a powerful beak and swallow their food whole.
19
Q
What is mastication?
A
chewing (grinding and shearing actions of teeth)
20
Q
What 5 animals have hypsodont teeth?
A
- horses
- cattle
- sheep
- goats
- other ruminants.
21
Q
Describe hypsodont teeth?
A
the teeth emerge from the gums at a continuous rate as the animal ages (though in very old animals this process can reach an end point)
22
Q
Which 3 animals have brachydont teeth?
A
- dogs
- cats
- humans
23
Q
What are brachydont teeth?
A
Once the teeth emerge, they begin to wear and are not replaced.
24
Q
What is the anatomy of the tooth?
A
** May not ask on the exam**
25
What are the 3 functions of the oral cavity?
1. shred food
2. organize it into small pieces
3. use the tongue to help roll it down to the pharynx
26
Describe the tongue:
1. Made of muscle bundles.
2. Highly flexible.
3. Retracts, protrudes, depresses, or elevates (moves in every direction)
4. Various types of papillae (taste buds)
27
Which nerve controls motor function of the tongue?
hypoglossal (cranial nerve 12)
28
What nerve controls sensory functions of the tongue- specifically temperature, touch, and pain?
The rostral 2/3rds of the trigeminal nerve (cranial nerve 5)
29
Which 2 nerves assist with the sensation of taste?
1. rostral 2/3rds of facial nerve (cranial nerve 7)
2. caudal 1/3 of the glossopharyngeal nerve (cranial nerve 9)
both control through their lingual branches
## Footnote
CN 7 = tastes like heaven, CN9 = tastes fine
30
What 5 tastes are registered by the receptor cells on taste buds?
- salty
- sour
- sweet
- bitter
- umami (amnio acids)
31
What are the 3 stages of deglutition (swallowing)?
1. oral/voluntary stage.
2. pharyngeal stage.
3. esophageal stage.
32
What occurs during the first stage of deglutition (oral/voluntary)
1. closure of the mouth
2. backwards movement of the tongue
3. slight inhibition of inspiration
4. Larynx and nasopharynx is closed.
5. Food is moved to the back of the tongue.
33
What occurs during the second stage of deglutition (pharyngeal)
1. pharyngeal pressure is increased
2. oropharynx, nasopharynx, and larynx are closed.
3. dramatic increase in intrapharyngeal pressure, which opens cranial esophageal sphincter.
34
What occurs during the third stage of deglutition (esophageal stage)?
primary and secondary peristalsis
35
What happens during primary peristalsis?
1. Movement of the bolus down the esophagus as a result of increased pharyngeal pressure gradient between the pharynx and esophagus. (the pressure is higher in the pharynx than the esophagus)
2. no contracture of esophageal muscles.
3. further supported by the size of the bolus and increased esophageal secretions and salivary secretions.
4. Significant reduction in friction but still no contraction of the muscles in the esophagus.
36
What happens during secondary peristalsis?
1. peristalsis generated within the esophageal musculature by the presence and **distention** of the esophagus by the retained food (bolus)
2. if the food is too big or coarse, the food cannot be pushed down.
37
What is released by efferent motor nerves supplying the esophagus during deglutition?
| the nerves respond to the contraction of esophageal mm.
ACh (acetylcholine), a neurotransmitter.
38
What 2 things cause heartburn (acid reflux disease)?
1. chalasia
2. achalasia
39
What is chalasia?
lower esophageal sphincter incompetence or ineffective esophageal sphincter syndrome.
It becomes too weak, food goes back up after stomach contraction.
If it is too powerful, food will not enter the stomach and the esophagus will swell.
40
What is achalasia?
focal or diffused swelling of the esophagus leading to food lodgment following failure of relaxation of esophageal smooth mm. fibers
This could be due to persistent or increased tension of the lower esophageal sphincter tension, incomplete relaxation of the sphincter upon swallowing, and weak esophageal peristalsis.
41
What are the 4 layers of the esophagus?
1. outer layer of connective tissue
2. muscle layer
3. submucosa of neuroendocrine cells
4. mucosa.
42
What are the 4 main anatomical divisions of the stomach?
1. Cardia
2. Fundus
3. Corpus/body
4. Pylorus
43
What are the 4 layers that make up the stomach mass?
1. Inner lining mucosa
2. Submucosa
3. Muscularis
4. Adventitia
44
The mucosa of the stomach is made of:
- epithelial cells
- lamina propria (clusters of neurons- some produce hormones- embedded in the wall, ICC cells)
- ______
45
The submucosa of the stomach is made of:
clusters of neurons
plexus
46
The muscularis of the stomach is made of:
47
The secretions of the stomach (gastric juices) flow through:
gastric pits/ foveolae- invaginations/ ducts on the surface of the mucosa
48
Where are the glands proper of the stomach located?
within the submucosa
there are 3 glandular regions of the stomach in non=ruminants
49
Which part of the stomach are most glands found?
int the body or fundus
50
intrinsic muscularis innervation
51
Hydrochloric acid controls ____.
pH + microbe population
52
Pepsinogen is inactive, but is activated by ___ which converts it to ____.
HCl; pepsinogen -> pepsin
53
When pepsin concentration is increased, HCl concentration is ____.
decreased (autocatalysis)
54
55
What are the 6 main parts of the digestive tract?
Mouth, esophagus, stomach, small intestine, large intestine, supportive organs.
56
What are the supportive organs of the GIT?
Liver, pancreas, and gallbladder.
57
What is contained within the mouth?
Tongue, teeth, salivary glands, and hard/soft palate.
58
Where does the mouth communicate with the trachea and esophagus?
At the pharyngeal region.
59
What is the function of the mouth?
Accepts and holds food, chews/softens food, and pushes it back to the esophagus via swallowing.
60
What is prehension?
Holding food in the mouth.
61
What is mastication?
Chewing (grinding and shearing actions of teeth).
62
What is deglutition?
Swallowing.
63
What are the differences in the extent to which the mouth performs its functions in various species?
Great.
64
What is the role of the esophagus?
Connects pharynx to stomach and delivers food from the oral cavity to the stomach.
65
What is the role of the stomach?
Holds food for mixing with secretions of acids, enzymes, and mucous; food is further crushed by contractions.
66
What is the role of the duodenum?
Most proximal part of the SI where the most digestive enzymes are secreted and digestion progresses.
67
What is the role of the jejunum?
Middle portion of the SI where digestion is completed and absorption begins.
68
What is the role of the ileum?
Distal portion of the SI where absorption is completed.
69
What is the role of the cecum?
Proximal part of the LI where water absorption takes place and waste becomes firmer.
70
What is the role of the colon?
Distal portion of the LI where electrolytes are absorbed if still present.
71
What is the defecation reflex?
Contraction of the colon under neural influence and waste is excreted as feces.
72
What is the role of the liver as a supportive organ for the digestive tract?
Produces bile.
73
What is the role of the pancreas as a supportive organ for the digestive tract?
Secretes enzymes that travel to the duodenum to aid in digestion.
74
What is the role of the gallbladder as a supportive organ for the digestive tract?
Stores and releases bile into the SI to facilitate digestion of lipids and fats.
75
What is the digestive system overall?
Continuous open tube from mouth to rectum that communicates with the external environment and supplies energy at the cellular level.
76
What are the 3 main groupings of food?
Carbs, proteins, fats.
77
What are vitamins/minerals?
Compound elements that facilitate taste and act as regulators for cell life.
78
What kind of energy value does water have?
None.
79
Describe the physical factor of the digestive system.
Anatomical structures that make it up and the events that take place such as chewing, swallowing, prehension, motility, contraction, etc.
80
What is the importance of the nervous influence of the GIT?
Nervous influence supports the movement and contraction of the GIT.
81
What are the different chemical factors of the GIT?
Enzymatic: amylases, proteases, lipases, and gastric secretions; Non-enzymatic: mucus, bile, saliva, and rumen functions; Hormonal.
82
What are the cellular events that take place as part of the GIT?
Absorption processes, metabolism.
83
Functionality of the GIT is based on what?
Secretions and motility.
84
What are the chemical substances of food?
Carbs, proteins, fats, vitamins, minerals/salts, water.
85
What species have prominently developed teeth?
Dogs and cats.
86
What species have well developed but less pointed teeth?
Horses.
87
What species use the lips to channel food into the mouth?
Horses.
88
What species utilize the tongue, incisor, and lips in grasping food?
Sheep and goats.
89
What is the difference between the prehensile attitude of pigs, sheep, and goats?
Pigs exhibit a propulsive movement of the head to aid prehension.
90
What species have no teeth and swallow their food whole?
Poultry.
91
What are hypsodont teeth and what species have them?
Teeth that emerge from the gums at a continuous rate as the animal ages. Species: Horse, cattle, sheep, and goat/other ruminants.
92
What are brachydont teeth and what species have them?
Teeth that wear and are not replaced. Species: Dog, cat, human.
93
What are the characteristics of the tongue?
Made of muscle bundles, highly flexible, can be retracted, protruded, depressed or elevated.
94
Describe the sensory role of the tongue.
Temperature, touch, and pain by the trigeminal nerve; taste by the facial nerve; caudal 1/3 controlled by the glossopharyngeal nerve.
95
The tongue has various types of papillae on the surface that have what?
Taste buds.
96
What are taste buds?
Surface projections of the tongue that have receptors to detect salty, sour, sweet, bitter, or umami tastes.
97
What is umami?
A taste.
98
What are the 3 stages of deglutition?
Oral/voluntary stage, pharyngeal stage, esophageal stage.
99
Describe the oral/voluntary stage of deglutition.
Tongue moves food and forms a moistened bolus and moves it to the pharyngeal region.
100
Describe the pharyngeal stage of deglutition.
CN IX activated to close nasopharynx and epiglottis; increase in pharyngeal pressure opens the cranial esophageal sphincter.
101
Describe the esophageal stage of deglutition.
Food is pushed through the esophagus to the stomach via primary or secondary peristalsis.
102
What is primary peristalsis?
Normal propulsion of food through the esophagus due to pharyngeal pressure.
103
What is secondary peristalsis?
Occurs when the bolus is too large or not well-lubricated, exciting stretch receptors in the esophagus.
104
What is heartburn?
Sensation caused by anti-peristaltic movement of stomach contents into the esophagus.
105
What is the reason for gastroesophageal reflux?
Lower esophageal sphincter incompetence or chalasia or ineffective esophageal sphincter syndrome.
106
What is achalasia?
Focal or diffuse swelling of the esophagus leading to food lodgment following failure of esophageal smooth muscle fibers to relax; usually manifests as dysphagia.
107
What are the 4 layers of the esophagus?
- Outer layer of CT
- Layer of muscle (circular or longitudinal)
- Submucosa (neuroendocrine cells)
- Mucosa (with LP, epithelium, lymphatics, glands, and muscularis mucosae)
108
What is the myenteric plexus?
Network of neurons radiating within the muscularis layer of the esophagus.
109
What is the Meissner's plexus?
Network of neurons within the submucosa of the esophagus.
110
What do the myenteric and Meissner's plexus together make up?
The intrinsic nervous system within the wall of the GIT; can exert their own contraction via electrochemical stimulation from the ANS.
111
What are the 4 main anatomical divisions of the stomach?
- Cardia
- Fundus
- Corpus/body
- Pylorus
112
What are the 4 layers that make up the lining of the stomach?
- Inner lining mucosa
- Submucosa
- Muscularis
- Adventitia
113
How is the stomach described?
Glandular hollow organ.
114
What are gastric pits/foveolae?
Invaginations or ducts located on the surface of the gastric mucosa through which the secretions of the stomach flow.
115
Where are the glands proper of the stomach located?
Within the submucosa.
116
Where are most of the glands of the stomach located?
Fundic region; pylorus and cardia have very few glands.
117
What are the 3 glandular regions of the stomach?
- Cardiac area which bears the cardiac glands
- Fundus which bears the fundic (oxyntic) glands known as gastric gland proper or major gastric juice secreting cells
- Pyloric area which bears the pyloric glands
118
Order the cells of the gastric pit from superficial to deep and what they secrete.
- Surface cell (mucous)
- Neck cell (mucous)
- Parietal cell (HCl and intrinsic factor)
- Chief cell (pepsinogen and gastric lipase)
- G cell (gastrin)
119
What is intrinsic factor responsible for?
Absorption of B12 for maturation of RBCs.
120
What are parietal cells stimulated by in order to secrete?
- ACh via the vagus nerve
- Histamine via H2 receptors
- Gastrin from G cells
121
What is pepsinogen?
Inactive form of pepsin, which it is converted to in the presence of HCl.
122
What is the role of pepsin?
Initiates protein digestion.
123
What is the role of gastrin?
Initiates contraction of the stomach for gastric emptying.
124
What is the intrinsic nervous system of the gut?
Extramural plexus nerve network found in the wall of the stomach that is controlled by the ANS.
125
What is the enteric nervous system of the gut wall?
Lines the gut wall and is capable of conducting impulses on their own independent of the ANS; gives the GIT its own control.
126
What are the 2 levels of the enteric nervous system?
Myenteric plexus: between longitudinal and circular muscles.
Meissner's plexus: located in the submucosa.
127
What do the myenteric plexus and Meissner's plexus lead to within the gut?
Mini contractions that allow for very short movements that are amplified and regulated by superimposition of the ANS.
128
Where do sympathetic nerves that supply the stomach and intestine synapse?
Do not synapse in the paravertebral ganglia, but rather in the prevertebral inferior and superior mesenteric ganglia and/or celiac ganglion.
129
Describe the activity of the vagus nerve on the gut.
- Sensory and motor
- Sensory fibers inform the brain about the condition of the GIT and its contents
- Motor fibers enhance digestive activities by stimulating neurons of the intrinsic nervous system.
130
If a patient has diarrhea, how would parasympathetic stimulation affect the situation?
Enhancing parasympathetic would worsen the condition as it encourages gut motility.
131
Contractile tissue of GIT is almost exclusively what type of muscle?
Unitary smooth muscle electrically coupled by gap junctions.
132
What do the gap junctions that unite the smooth muscle cells of the GIT allow for?
Permit rapid cell-to-cell spread of action potentials and allows for coordinated smooth muscle contraction.
133
What are the exceptions to the smooth muscle of the GIT and what type of muscle do they have?
Pharynx, upper ⅓ of esophagus, and external anal sphincter all have striated muscle rather than smooth muscle.
134
What are interstitial cells of Cajal?
Self-excitatory cells found in the wall of the GIT capable of generating spontaneous electric current.
135
What is the myometric myoelectric complex?
Term used to describe the interactions of the ICCs along with the intrinsic neuronal pathway that allow for a migratory current that is always detected in the wall of the GIT to 'clean it up.'
136
Describe the result of depolarization of the longitudinal and circular muscle layers of the GIT.
Longitudinal: decreases the length of GIT segment.
Circular: decreases diameter of GI segment.
137
Describe phasic contractions vs tonic contractions.
Phasic: periodic contraction and relaxation that occurs in the esophagus, antrum of stomach, and SI.
Tonic: maintains a constant level of contraction without regular periods of relaxation as seen in sphincters and orad region of stomach.
138
What are slow waves?
Transient and silent mini contractions of the GIT that are not enough to move material long distances but is the reason why impaction should not occur.
139
Describe how normal action potentials interact with the slow wave rhythm of the GIT.
AP's occur on top of oscillating depolarization and repolarization of slow waves if the membrane potential is enough to reach threshold.
140
The origin of slow waves of the GIT occurs where?
Interstitial cells of Cajal; called the 'pacemaker' for GIT smooth muscle.
141
What is the characteristic frequency of slow waves in the stomach?
3 per minute; slowest of the GIT.
142
What is the characteristic frequency of slow waves in the ileum?
8-9 per minute.
143
What is the characteristic frequency of slow waves in the duodenum?
12 per minute; fastest of the GIT.
144
Describe the mechanism of slow waves.
- Depolarization phase in which there is cyclic opening of Ca channels and inward Ca current depolarizes the cell membrane.
- ICC cells have low excitation energy for Ca, so the ion channels open easily.
- Repolarization phase in which cyclic opening of K channels and outward K current repolarizes the cell membrane.
145
What are the 3 ways that the stomach contracts in non-ruminants?
- Adaptive relaxation
- Peristaltic contraction
- Terminal antral contraction
146
Describe the adaptive relaxation phase of stomach contraction.
- Begins once the first drop of food hits the stomach and continues until stretch receptors are fully activated and thus the satiety center of the brain is activated.
- Stimulates neuroendocrine cells in the LP to secrete vasoactive intestinal peptide.
- Adaptation of the stomach to accommodate food; also occurs in the colon to accommodate fecal material.
147
What is the role of vasoactive intestinal peptide?
Secreted by neuroendocrine cells of the LP of the stomach during the adaptive relaxation phase that causes relaxation of the stomach wall so that it can stretch and accommodate food.
148
Describe peristaltic contractions of the GIT.
- For peristalsis to occur, the segment of the intestine proximal to the bolus needs to reduce in diameter and the segment of the intestine distal to the bolus needs to expand in diameter.
- At the segment proximal to the bolus: contraction of circular muscle and relaxation of longitudinal muscle.
- At the segment distal to the bolus: contraction of longitudinal muscle and relaxation of circular muscle.
149
Describe the terminal antral contraction of the stomach.
- Contraction that facilitates the mixing of food in the stomach to produce chyme.
- Circular muscles around the pyloric sphincter contract so that the sphincter closes, giving the food time to mix in the stomach before escaping into the small intestine.
- Fundic and cardiac regions contract while the body relaxes in syncytium to allow for the food to rebound.
- Antral region stretch receptors are activated and the antral region contracts to continue the mixing process.
- After several rounds, the pyloric sphincter opens to allow chyme into the duodenum.
150
What is the role of G cells in gastric emptying?
Release gastrin just before the pyloric sphincter opens which stimulates the contraction of the entire stomach uniformly so that chyme can be pushed out into the SI.
151
How is gastric emptying controlled?
- Duodenum becomes stimulated by the entrance of chyme and I cells secrete CCK in response to the change in osmotic pressure by lipids and proteins; CCK inhibits gastrin production so that the stomach stops contracting and stimulates contraction of the gallbladder and release of pancreatic juices.
- Through the effect of higher brain centers.
152
What do S cells of the small intestine secrete?
Secretin.
153
What do D cells of the small intestine secrete?
Somatostatin.
154
What is the role of secretin and somatostatin?
Assist CCK in the control of gastric emptying and release of pancreatic juices.
155
What are the vago-vagal reflexes?
They allow for the accommodation of large amounts of food in the GIT and ensure that different parts of the GIT contract in a coordinated fashion.
## Footnote
The ileum can communicate with the stomach to let it know about the status of chyme in its segment to alert the stomach to either contract again (if the ileum is empty) or remain relaxed (if the ileum has just received food).
156
What are the more minor reflexes included in the vago-vagal reflexes?
Local enterogastric reflexes such as vomiting and humoral mechanisms involving GIT hormones.
157
What are the inhibitory factors of gastric emptying?
Duodenal acidic pH, duodenal distension, duodenal hypertonicity, sympathetic stimulation, intense pain, and increased osmolarity of gastric chyme.
158
What are the parts of the small intestine?
Proximal: duodenum; Middle: jejunum; Distal: ileum.
159
What are the crypts of Lieberkuhn?
Secretory glands embedded within the mucosa of the small intestine.
160
What are plicae circulares?
Folds within the crypts of the small intestine that increase the surface area for absorption.
161
What are villi of the small intestine made up of?
Multiple enterocytes and supportive cells which Paneth cells give rise to.
162
What do enterocytes secrete?
Enzymes for digestion.
163
What are microvilli?
Microspikes on the apical surface of the enterocytes of the SI that are very important for absorption.
164
What is located within each villus?
A nerve, a blood vessel for absorption, and lacteals for absorption of lipids into the lymphatic system.
165
Once lipids are absorbed from the lacteals, how do they enter circulation?
At the subclavian vein.
166
What are two villi separated by?
Crypts, where intestinal glands are located.
167
The entire vasculature of the GIT is drained by what?
A common hepatic portal vein.
168
What is the law of the intestine?
For digestion to happen as well as absorption, materials must move from the oral cavity to the anal region through peristaltic contractions of the GIT.
169
Describe the gastro-ileac reflex and the ileo-gastric reflex.
Gastro-ileac reflex: if the stomach is full, it causes the ileum to contract, and vice versa. Ileo-gastric reflex: if the ileum is empty, it will increase gastric contraction, and vice versa.
170
What are the parts of the large intestine?
Cecum -> colon -> rectum.
171
What are the junctional communications of the large intestine?
Ileocecal junction: some animals' ileum meets the cecum directly without also meeting the colon. Ileocecocolic junction: some animals' ileum meets the cecum and colon together. Rectoanal junction: junction between rectum and anus.
172
What are the functions of the large intestine?
H2O and electrolyte absorption, major ion absorptive site, vat for indigestible materials, site for microbial fermentation, fatty acid absorption (pigs/horses), vitamin production and absorption such as vitamin K, B12, thiamine, and riboflavin.
173
Describe microbial fermentation in the large intestine.
Very important for hindgut fermenters for cellulose and hemicellulose; very little occurs in monogastrics.
174
How can secretions of the digestive system be categorized?
Salivary secretions, esophageal secretions, gastric secretions, intestinal secretions.
175
What are salivary glands controlled by?
ANS, mainly parasympathetic.
176
What is the parasympathetic effect on the salivary glands?
Vasodilation; when food is present, the rate of salivary secretion increases.
177
Saliva acts as a ___________ for the acids of the stomach and duodenum.
Buffer.
178
How do salivary secretions indirectly affect blood pressure?
When secreted in large amounts, kallikrein converts kallidinogen to kalidin. Kalidin is a precursor for bradykinin, which acts on the medial portion of the medulla for vasodilation and inhibits the lateral portion for vasoconstriction.
179
What do parietal cells have on their surface to mediate acid secretion?
Proton pumps.
180
What is an ulcer?
A wound on the mucosa of the stomach.
181
What are proton pump inhibitors used for?
To treat excess stomach acid secretions.
182
What is the role of HCl in the stomach?
Controls microbial population of GIT and converts pepsinogen to pepsin.
183
What happens once pepsin is produced by HCl in the stomach?
It is able to take over the process and converts pepsinogen to itself, called autocatalysis.
184
What is the role of gastric lipase?
Breaks lipids into smaller pieces once they are emulsified to be further acted on by pancreatic lipase.
185
What is achlorhydria and what does it result in?
Low HCl that results in poor protein absorption.
186
In what 3 ways is HCl secretion by parietal cells stimulated?
H2 receptors on parietal cells are acted on by histamine, gastrin from G cells stimulates parietal cell secretion, and muscarinic receptors acted on by ACh from vagus nerve to open Cl and H channels.
187
What is gastric juice made up of?
HCl, gastrin, pepsin, intrinsic factor, saliva, and mucus working together to make food more soluble.
188
Describe the osmolarity of gastric juice.
Highly osmotic due to the high concentration of electrolytes; this stimulates the secretions of I, S, and D cells of the duodenum.
189
What are the functions of HCl?
Promotes solubility of foodstuffs not soluble in water, necessary for activation of pepsin, strong disinfectant for ingested food, regulatory for release of bile and pancreatic juice by stimulating the release of CCK in the duodenum.
190
Regulation of gastric secretions is through what modes?
Hormonal: Gastrin, histamine, ACh, and somatostatin; neurologic control; acidification reduces secretions.
191
What are the 3 phases of gastric secretions?
Cephalic, gastric, intestinal.
192
Describe the cephalic phase of gastric secretion.
Cognitive component when you are looking/thinking about food or it is in the oral cavity.
193
Describe the gastric phase of gastric secretions.
When food is actually present in the stomach and acts on the gastric cells itself.
194
Describe the intestinal phase of gastric secretions.
When food is in the duodenum and osmolality excites the vagus nerve to induce secretions.
195
What are the hormones of the GIT generally responsible for?
GI motility.
196
What is the largest endocrine organ of the body?
GIT.
197
Some GI hormones exert true ________ function while some exert ____________ functions.
Endocrine; paracrine.
198
Most GI hormones are what type of hormone?
Peptide hormone.
199
Most paracrine hormones of the GIT are secreted by cells located where?
In the lamina propria of the intestinal wall.
200
Most endocrine cells of the intestine are secreted by specialized cells where?
In the intestinal epithelium.
201
Where is gastrin produced and what does it stimulate?
Produced in the pyloric region of the stomach and upper SI and pancreas; stimulates gastric secretions.
202
Where is secretin produced and what does it stimulate?
Produced at the upper SI; stimulates the secretion of bicarbonate and water from pancreas; inhibits gastric secretion and motility.
203
Where is CCK produced and what does it stimulate?
Secreted at the upper portion of the SI; stimulates pancreatic secretion just like secretin; also important in promoting emptying of the gallbladder by stimulating gallbladder contraction (cystic contraction).
204
What is the role of enterogastrone?
Decreases gastric emptying; also called anthelone E or entheroanthelone.
205
What is the name of another hormone of the GIT that has very similar function to enterogastrone?
Gastric inhibitory peptide (GIP).
206
What is the function of enterocrinin?
Stimulates intestinal secretions.
207
Where is vasoactive intestinal peptide found and what is it responsible for?
Found in the duodenum; responsible for gastric receptive relaxation.
208
Where is motilin found and what does it stimulate?
Obtained from gastric mucosa; stimulates gastric motor activity and is thought to be involved in gastric emptying.
209
What is the role of villikinin?
Stimulates motility of intestinal villi and aids in the transport of lymphatic fluid into the lymphatic ducts.
210
What is the pancreas?
A very large compound gland, which lies parallel to and beneath the stomach and secretes digestive enzymes and large volumes of Na bicarbonate.
211
What are the cells of the pancreas that secrete digestive enzymes?
Acini cells.
212
What are the cells of the pancreas that secrete bicarbonate?
Ductile cells via carbonic acids and carbonic anhydrase reactions.
213
What are the digestive enzymes secreted by the pancreas?
Proteases, lipase, and amylase.
214
What are the proteases secreted by the pancreas?
Trypsin, chymotrypsin, ribonuclease, elastase, deoxyribonuclease, and carboxypeptidase A and B.
215
What is the role of proteases secreted by the pancreas?
Splits whole and partially digested proteins into small peptides or AAs; breaks them into short chains but not their final absorbable form, called luminal digestion.
216
Where does luminal digestion take place?
In the lumen of the duodenum.
217
What are ribonuclease and deoxyribonuclease specifically responsible for splitting?
The two types of nucleic acids.
218
How are trypsin and chymotrypsin secreted?
As their proenzymes trypsinogen and chymotrypsinogen.
219
How are trypsinogen and chymotrypsinogen converted into their active forms?
Trypsinogen is acted on by enterokinase, then trypsin is able to activate itself as well as chymotrypsinogen.
220
Describe how proteins are broken down for digestion.
Initially into peptide fragments in the stomach by pepsin in acidic pH conditions; in the SI, the peptides are cleaved under alkaline conditions into oligopeptides and AAs by trypsin and chymotrypsin.
221
What is the optimal pH for trypsin and chymotrypsin?
7-8 due to bicarbonate.
222
What are carboxypeptidases?
Zinc-containing pancreatic exopeptides that remove single AAs from the carboxyl end of oligopeptides.
223
What is the role of ribonuclease?
Nuclease that catalyzes the degradation of RNA into smaller components.
224
What is the role of deoxyribonuclease?
Degrades DNA via hydrolysis of its phosphodiester backbone; DNase 1 enzymes cleave single or double-stranded DNA and require divalent metal ions to hydrolyze DNA yielding 3'-hydroxyl and 5'-phosphorylated products.
225
What is the role of elastase?
The primary role is the breakdown of elastin, a protein that imparts elasticity to connective tissue; it also catalyzes the cleavage of carboxyl groups present on small hydrophobic amino acids such as Gly, Ala, and Val.
226
What are the two classes of proteases?
1. Endopeptidase: attacks peptide linkages involving specific amino acids in the interior of a polypeptide.
2. Exopeptidase: those which liberate the amino acid carboxyl groups.
227
What is membranous digestion?
It is the portion of intestinal digestion in which the dipeptides created from luminal digestion are converted to free amino acids by amino-peptidases from the intestinal mucosa; the final absorbable product.
228
What do the liver and biliary system use to produce bile salts?
Cholesterol and amino acids.
229
What do the secretions of the biliary system serve as?
They aid in intestinal digestion and act as an excretory organ for the elimination of by-products of metabolism from the body.
230
What are the names of the cells that synthesize bile?
Hepatocytes of the liver.
231
Describe the flow of bile from the liver to the gallbladder and then from the gallbladder to the duodenum.
Canaliculi -> small ducts -> large ducts -> left/right hepatic duct -> common hepatic duct -> gallbladder -> common bile duct -> sphincter of Oddi -> duodenum.
232
What is the sphincter of Oddi?
It is the conjoined opening for bile and pancreatic juices into the duodenum.
233
Describe the differences in the bile and pancreatic ducts between species.
In the cow and pig, the bile and pancreatic duct open into the duodenum separately. In goat and sheep, the duct systems join prior to arrival at the duodenum. In the horse, cat, dog, and man, there is a common pancreatic bile duct.
234
Bile contains _______ digestive enzymes.
No.
235
What component of bile gives it digestive relevance?
Bile salts.
236
What are the main components of bile salts and what is their role?
Cholic acid and deoxycholic acid; they bring about emulsification of fat by dispersing large fat droplets into smaller ones.
237
How does the emulsification of fat droplets by bile salts prepare it for digestion?
It exposes fat to lipase for maximum contact and digestion.
238
What species have no gallbladder?
Horses and rats.
239
What is the enterohepatic circulation of bile?
It is the process of most bile salts being reabsorbed by the ileum and then resecreted by the liver.
240
What is the pigment contained in bile and what color is it?
Bilirubin; yellow color.
241
What are the other components of bile other than bile salts?
Bile pigments, water, and inorganic salts.
242
How does bile pigment help keep bile salts in solution within the gallbladder?
It is the product of hemoglobin catabolism, and sodium bicarbonate keeps salts in solution.
243
How is bile secreted by the liver?
Continually and stored in the gallbladder until it is needed.
244
What is the difference between conjugated and unconjugated bilirubin?
Unconjugated: transported in blood as a compound bound to albumin. Conjugated: separated from albumin in the liver and incorporated into bile.
245
What are the factors that control the rate of bile secretion?
1. Neural mechanism
2. Hormonal mechanism
3. Rate of blood flow
4. Concentration of circulating bile salt.
246
How is bile secreted when food reaches the duodenum?
CCK is secreted which relaxes the sphincter of Oddi and contracts the gallbladder.
247
Where do bile salts work?
They digest fats in the jejunum and then are reabsorbed in the ileum.
248
What is obstructive jaundice caused by and what does it cause?
Caused by a disorder associated with blockage of free flow of bile from the gallbladder, either by gallstones or parasites. Causes yellow coloration of tissues.
249
What is biliary reflux/duodenogastric reflux?
Frequent and very painful heartburn, nausea, and vomiting as well as inexplicable weight loss; different from GERD.
250
What are the causes of biliary reflux?
1. Gastric ulcers (H. pylori)
2. Gastritis
3. Peptic ulcers
4. Complications of cholecystectomy.
251
Endoscopic examination of the GIT could be helpful in revealing the occurrence of what?
Pyloric valve stenosis.
252
What is the papilla of Vater?
Swelling around the opening of the pancreatic duct that is stimulated by chemoreceptors to regulate the flow of bile and prevent reflux.
253
What is the role of Brunner's glands and goblet cells?
They secrete watery mucus into the small intestine for lubrication.
254
Where are goblet cells found in the small intestine?
In the crypts of Lieberkühn along with immune cells.
255
What are the digestive enzymes of the small intestine?
1. Peptidases
2. Sucrase, maltase, isomaltase, and lactase
3. Lipase
## Footnote
Secretin and CCK enhance the secretory potential of these enzymes.
256
What is the predominant cell type of the mucosal epithelium of the large intestine?
Goblet cells.
257
How many digestive secreting glands are there in the large intestine?
None.
258
What is the main thing that takes place in the large intestine and how can it be harmful?
Microbial fermentation of cellulose; large intestine bacteria can deprive the host of ascorbic acid, B12, and choline.
259
What kinds of secretions take place in the large intestine?
1. Mucous
2. Alkaline secretions
3. Water and electrolytes can be secreted in the situation of damage or intense irritation on the large intestine epithelium.
260
What are the functions of the large intestine?
1. Volatile fatty acid production
2. Urea converted to ammonia
3. Vitamin K, B12, thiamine, riboflavin, biotin, and folic acid are formed and absorbed.
261
What are the 4 main types of intestinal motility?
1. Villous: muscularis mucosae
2. Segmentation: circular muscle
3. Peristaltic
4. Anti-peristaltic.
262
What are the 2 types of antidromic peristaltic waves of the large intestine?
1. Haustration: movement of small pouches in the large intestine called haustra, which allows for maximal absorption of contents.
2. Pendular: periodic contractions and relaxations of the longitudinal smooth muscle of the intestinal wall.
263
What gives the colon its segmented appearance?
Haustra.
264
What are the 2 types of diarrhea?
Osmotic and endotoxic.
265
Describe osmotic diarrhea.
The tight junction may not be destroyed, but a high osmotic gradient is created whereby the intestinal content becomes hyperosmotic compared to interstitium. Diffusion of fluids from the interstitium into the lumen occurs, increasing bulk and further increasing motility of the intestines.
266
What can cause osmotic diarrhea?
Excessive solutes, electrolytes, excessive intake of milk, etc. can cause this.
267
Describe endotoxic diarrhea.
Driven by infection; toxins destroy the claudins in the tight junctions between epithelial cells, and a significant amount of Na, K, and Cl are lost into the lumen of the intestinal tract.
268
What is the result of endotoxic diarrhea?
The body is more acidic; predisposed to metabolic acidosis and erosion that can cause bleeding, known as hemorrhagic diarrhea.
269
What is the protective reflex mechanism that helps to remove unwanted substances?
Vomiting.
270
What is the vomiting center of the brain?
Medulla.
271
What are the steps of the vomiting reflex?
1. Nausea: the uncomfortable feeling prior to vomiting.
2. Retching: contraction of abdominal muscles and antiperistaltic movement.
3. Vomiting proper: forceful expulsion of substances from the oral cavity.
272
Where does efferent output go to for the vomiting reflex?
1. Lower esophageal sphincter and upper esophageal sphincter.
2. Powerful contraction of the abdominal muscles in an antiperistaltic manner.
3. Epiglottis closes off the larynx to prevent aspiration pneumonia.
273
What are the causes of the vomiting reflex?
1. Psychological
2. Motion sickness
3. Presence of toxins in blood, GIT, or body fluids.
274
What is the chemoreceptor trigger zone?
Area of the medulla that receives signals from chemicals or hormones in the blood through weak blood-brain barrier at H1 receptors and induces vomiting reflex.
275
How is vomiting treated?
Antiemetic drugs: dopamine antagonists, serotonin blockers, and antihistamines.
276
What is constipation?
Delayed peristalsis and mass movement with infrequent defecation which can be painful due to increased water reabsorption. When motility of the colon decreases, there is more time for the colon to absorb excess water, leading to hardening of the fecal material.
277
What are the causes of constipation?
1. Delayed motility of the colon
2. Dysfunction of the pelvic floor muscles: dyssynergic defecation
3. Obstruction of the colon due to rectal prolapse, strictures, or tumors
4. Dietary or lifestyle factors.
278
How is constipation treated?
Increased fiber content (raw vegetables and fruits) in the diet improves fecal bulk, which in turn stimulates colon motility and defecation, relieving the constipation.
279
Chemical digestion by enzymes is by what kind of reaction?
Hydrolysis.
280
What are the bonds that must be broken for digestion of carbs, proteins, fats, and nucleic acids?
1. Glycosidic linkages in carbs
2. Peptide bonds in proteins
3. Ester bonds in fats
4. Phosphodiester bonds in nucleic acids.
281
What component of carb digestion is absent in carnivores?
Salivary amylase.
282
How are lactose, sucrose, and maltose/isomaltose broken down in the GIT?
1. Lactose → galactose and glucose by lactase.
2. Sucrose → fructose and glucose by sucrase.
3. Maltose and isomaltose → 2 glucose molecules.
283
How are proteins broken down in the GIT?
Proteins are acted on by endopeptidases to form large peptides. Large peptides are acted on by exopeptidases to form small peptides and amino acids.
284
What is the role of colipases?
Enzymes that help prevent the inhibitory effects of bile salts on pancreatic lipase so that lipase can easily act on lipids.
285
What initiates lipid digestion?
Pancreatic enzymes.
286
How are the end products of lipid digestion absorbed?
Triglycerides are broken into fatty acids and glycerol that are absorbed into the enterocytes. When they are absorbed, they recombine through an ester bond and cannot be transported in blood. Apoprotein-C unites with the triglyceride to form a chylomicron to be transported in a lacteal through the lymphatic system.
287
Where does absorption take place specifically?
Either through blood capillaries or lymphatics of the villi; can be passive (K) or active (Fe, Ca, and Na)
288
In what portions of the GIT does absorption mainly take place?
Jejunum and ileum
289
In general, ________ electrolytes are easily absorbed while most of the ___________ electrolytes are poorly absorbed.
Monovalent, polyvalent
290
How is water, Na, bicarb, Cl, P, Fe, and Ca absorbed?
- Water: osmosis
- Na, P, Fe: active
- Bicarb and Cl: passive
- Ca: either passive or active
291
Ca absorption is facilitated by what?
Lactose and protein
292
Ca absorption is inhibited by what?
- Phosphates and oxalates as they form insoluble salts with Ca in the intestine
- Large concentrations of fat can also interfere
293
How is Mg absorbed?
Active and involves Mg-stimulated ATPase
294
How are glucose and galactose absorbed?
By active transport which is dependent on the Na carrier system; galactose is transported slower than glucose
295
How are fructose and pentoses absorbed?
Passive
296
How are proteins absorbed?
- Naturally occurring AAs by active transport that is Na-dependent
- Intact proteins by pinocytosis
297
How are purines and pyrimidines absorbed?
Active transport
298
What is intermediary metabolism?
The mechanism through which energy is developed, trapped, and delivered to the active functional machinery in individual cells
299
What is metabolism?
The sum of all anabolic and catabolic reactions in a living organism that pertain to the use of all nutrients, such as glucose, AAs, FAs, purines, pyrimidines, water, and oxygen
300
Most dietary carbs are in what form?
Polysaccharides
301
On entry into the cell, glucose has several metabolic fates depending on what?
The cell type and energy status of the cell
302
Describe glycolysis.
- If aerobic, glucose catabolized to pyruvate in the cytoplasm that then moves into the mitochondria to produce acetyl CoA and CO2
- If anaerobic, glucose catabolized to lactate
303
What happens after carbs are broken down into pyruvate?
Pyruvate forms acetyl-CoA and CO2 and then acetyl CoA enters the citric acid cycle to be completely oxidized to CO2
304
What are the catabolic pathways of carb metabolism?
- Skeletal muscle derive energy from ketones and fatty acids
- RBCs and brain depend only on glucose for energy
305
What are the anabolic pathways of carb metabolism?
- Acetyl-CoA is a precursor for several compounds such as FAs and cholesterol
- Glucose can be polymerized and stored as glycogen mainly in liver and muscle
306
Where does glycolysis occur?
All animal cells
307
Does glycolysis require oxygen?
No
308
What does glycolysis consume in order to initiate the process?
2 molecules of ATP and 2 molecules of NAD per glucose
309
What is produced by glycolysis?
2 molecules pyruvic acid, 4 molecules of ATP, and 2 molecules of NADH, for a net yield of 2 molecules NADH and 2 molecules ATP
310
True or false: glycolysis is the cell's primary source of ATP.
False
311
What is the pentose pathway?
Alternative oxidation method of glucose to form ribose phosphate or triose phosphate, which gives rise to glycerol moiety of acylglycerol
312
What are the 2 stages of cellular respiration?
Krebs cycle and ETC
313
Describe the Krebs cycle.
- Glucose = 2 pyruvate = 2 turns of Krebs cycle
- Occurs in mitochondria
- For each molecule of glucose, Krebs cycle produces 2 ATP, 2 FADH2, and 6 NADH
- Acetyl CoA formed from pyruvic acid also produces 2 molecules of NADH each producing 3 ATP
314
What is the final stage of cellular respiration which produces the majority of ATP for the cell?
Electron transport chain
315
Where does the electron transport chain occur?
In the inner wall of the mitochondria
316
Describe the electron transport chain.
- NAD and FAD -> NADH and FADH2
- These molecules are carried down a chain of electron carrier molecules collectively called cytochromes, where each cytochrome has an iron core that accepts electrons and releases them at a lower energy level
- At each step, free energy is produced that creates a gradient
- When protons flow back into the membrane as a result of the gradient, energy is captured in the formation of ATP via ATP synthase
- At the end of the chain, low energy electrons are accepted by O2 to form water
317
How much ATP is produced in total as a result of the metabolism of glucose?
38 total: 2 from glycolysis, 14 from Krebs, and 22 from ETC
318
What species have an ileocecal junction vs an ileocecocolic junction?
Ileocecal: dog and cat
## Footnote
Ileocecocolic: horse, pig, ruminant
