Lecture 2-Exam 4 (GI) Flashcards
1
Q
- What are the three major salivary glands?
- What is part of the small intestine?
- What is part of the large intestine?
- What are the accessory digestive organs?
A
- Parotid, sublingual and submandibular gland
- Small: Duodenum, Jejunum, Ileum
- Large: Transverse, descending, ascending, sigmoid colon, cecum, rectum, vermiform appendix, anal canal
- Accessory: spleen, pancreas, liver
2
Q
Most of digestive tract follows a basic structural
plan with the digestive tract wall consisting of layers:
* What are the first two layers closest to the lumen+ what is contained in them?
A
Mucosa:
* Epithelum
* Lamina propria (connective tissue)
* Muscularis mucosae (smooth m. to give ridges for increase SA)
Submucosa: Have nerves and plexes here to regulate secretations
3
Q
Most of digestive tract follows a basic structural
plan with the digestive tract wall consisting of layers:
* What is the third and forth layer closest to the lumen+ what is contained in them?
A
Muscularis externa (smooth muscle layers- 3RD ONE IN STOMACH WITH oblique muscle):
* Inner circular layer
* Outer longitudinal layer (propels and breaks down food)
Serosa:
* Areolar tissue: have reticular fiber + others fibers
* Mesothelium: slippery layer to decrease frictrion
4
Q
What is the 2nd brain for GI?
A
- Enteric nervous system: Myenteric plexus, submucosal plexus and parasympathetic ganglion of myenteric plexus
5
Q
What is the definition of digestive system?
A
organ system that processes food, extracts nutrients, and eliminates residue
6
Q
What are the five stages of digestion?
A
- Ingestion: selective intake of food
- Digestion: mechanical (physical turning) and chemical (acid) breakdown of food into a form usable by the body -> polymers to monomers
- Absorption (MAIN GOAL): uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood & lymph
- Compaction: absorbing water and consolidating the indigestible residue into feces
- Defecation: elimination of feces
7
Q
What is mechanical digestion? What are the actions (3)
A
physical breakdown of food into smaller particles
* Cutting and grinding action of the teeth
* Churning action of stomach (via peristalsis, propulsion) and small intestines (via segmentation)
* Exposes more food surface area to digestive enzymes
8
Q
What is chemical digestion? How is it carried out?
A
series of hydrolysis reactions that breaks dietary macromolecules (polymers) into their monomers (residues)
* Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine
9
Q
- Polysaccharides-> _
- Proteins-> _
- Fats-> _
- Nucleic acids-> _
A
- Polysaccharides-> monosacharides (simple sugars)
- Proteins-> amino acids
- Fats-> monoglycerides and fatty acids then we transport them
- Nucleic acids-> nucelotides
10
Q
Some nutrients are present in a usable form in ingested food and can be directly absorbed. What are the examples? (5)
A
Vitamins, amino acids, minerals, cholesterol, and water
11
Q
A
12
Q
What does parasympathetic and sympathetic stimulation cause to salivaty glands?
A
- Parasympathetic stimulation produces a secretion rich in electrolytes and salivary amylase (breakdown carbs, FIRST ONE TO BE BROKEN DOWN) .
- In contrast, sympathetic stimulation produces a secretion rich in mucus, making the saliva much more viscous (dry mouth, decrease watery but still mucus so it is thick)
13
Q
What is the basic functional unit of the salivary gland?
A
Salivon: It consist of clusters of acini cells that drain into a ductal system
14
Q
Low Yield
What is the salivon organization+ what comes in and out of the gland?
A
- Acinus = secretes initial saliva product
- Intercalated duct = secrete HCO3 and K+ & absorb Cl- and Na+
- Striated duct = keep water secreted out (no absorption)
- Excretory duct = secretes final saliva product directly into the mouth
15
Q
What is saliva ph?
A
7-7.4
16
Q
What are the all the parts/cells of the stomach lumen?
A
Mucous neck cells, parietal cells (make HCl+IF), Chief cells (make Pepsinogen+lipase), enteroendocrine (make gastrin, glucagon, serotonin, somatostatin)
CEMP
17
Q
A
- Surface mucous cell: protects the gastric lining dt to pepsin and HCl
- Muscous neck cells: muscin in an acidic fluid
- Parital cells: HCl+ intrinsic factor (needed for B12 absorption)
- Chief cells: Pepsinogen (activated by HCl) and gastric lipase
- G cells/enteroendocrine cells: gastrin
18
Q
What is the difference between lingual lipase and salivary amylase?
A
- Lingual lipase: Part of saliva but is not activated until the stomach (break down fats)
- Salivary amylase: Part of saliva, already active to break down carbs (REASON WHY CARBS ARE BROKEN DOWN FIRST)
19
Q
What does the parietal cell secrete? How does it secrete that?
A
ATPase in the apical cell membrane pumps H+ out of the cell and into the lumen in exchange for K+.
20
Q
What are gastric enzymes? (4)
A
pepsin, gastric amylase, gastric lipase, and intrinsic factor
21
Q
Explain the two ways that we can get the secretion about HCl from parietal cells (directly and indirect)
A
22
Q
Acid production in the stomach parallels what ?
A
Rate of gastric secretion
* The electrolyte composition of gastric juice changes with secretion rate.
23
Q
What are the relationships of K, Na, H, and Cl with each other?
A
- Cl, K, H are all proportional to each other
- Na+ is inversely proportional to H+
LOOK AT THE PUMPS + CA reation ON LEFT/MIDDLE SIDE OF PICTURE
HCL is formed in stomach lumen to then active pepsinogen from chief cells
24
Q
Gastric secretion is under what control?
A
Under neural and hormonal control
25
Parietal cells:
* What do they possess? What does that stimulate?
* What is commonly used for the treatment of peptic ulcer disease or GERD?
* What are the three stimulants of parietal cells? What can happen?
* Potentiation occurs when?
* Parietal cells possess special histamine receptors, **H2 receptors,** whose stimulation increases HCl secretion.
* **H2 blockers** are commonly used for the treatment of peptic ulcer disease or GERD.
* The effects of each of these three stimulants (ACh, gastrin, and histamine) augment those of the others, a phenomenon known as **potentiation**.
* Potentiation occurs when the effect of two stimulants is greater than the effect of either stimulant alone.
26
* When HCl secretion the most important?
* What happens when we have excess HCl damage?
* HCl secretion is important only **during the digestion of food.**
* Excess HCl can damage the gastric and the duodenal mucosal surfaces, causing ulcerative conditions
27
The body has an elaborate system for regulating HCl secretion by the stomach. Explain
**If the buffering capacity of protein is exceeded or if the stomach is empty, the pH of the gastric lumen will fall below pH3**.
* When this happens, the endocrine cells (**D cells**) in the antrum secrete **somatostatin**, which inhibits the release of gastrin and, thus, HCl secretion.
* Another mechanism for inhibiting HCl secretion is acidification of the duodenal lumen. **Acidification stimulates the release of secretin**, which inhibits the release of gastrin and several peptides from intestinal endocrine cells
| SOMATOSTATIN + SECRETIN = INHIBIT GASTRIN SO NO HCL
28
Explain the three phases of stimulation of acid secretion?
1. Cephalic: Vagus nerve stimulates gastric secretion even before food is swallowed
2. Gastric: Food stretches the stomach and activates **myenteric and vagovagal reflexes**. These reflexes stimulate gastric secretion. Histamine and gastrin also stimulate acid and enzyme secretion
3. Intestinal: intestinal gastrin briefly stimulates the stomach but then **secretin, CCK and enterogastric reflex inhibit gastric secretion and motility while the duodenum processes the chyme already in it**. Sym nerve fibers suppress gastric activity while vagal (para) stimulation of the stomach is now inhibited
29
Fill in
30
31
Pancreatic enzymes are produced where?
Pancreatic enzymes are produced in the acinar cells of the exocrine pancreas
32
What is secreted by the duct cells of pancreatic acinus? What happens?
HCO3- (changes the ph by neutralizes the environment) and Na+
33
34
What are the various stimuli that stimulates pancreatic enzyme secretion? What happens when it is stimulated?
Calcium release from intracellular stores stimulates pancreatic enzyme secretion.
pancreatic secretion by hormones and NTs:
* ACh, acetylcholine
* ATP
* cAMP
* CCK (cholecystokinin)
* GRP (gastrin-releasing peptide)
* VIP (vasoactive intestinal peptide)
35
Circulating GI hormones, particularly secretin and CCK, greatly influence on what?
Circulating GI hormones, particularly **secretin and CCK**, greatly influence pancreatic secretion of electrolytes and enzymes. Both hormones are produced by the small intestine and bind receptors in the pancreas.
36
Pnacreatic secretions are rich in what?
* What is this unlike?
* A reciprocal relationship between what exists?
Pancreatic secretions are rich in **bicarbonate ions**
* Unlike salivary fluid, the osmolality of pancreatic fluid equals that of plasma at all secretion rates.
* A reciprocal relationship exists between the **Cl− and HCO3−** (inverse) concentrations in pancreatic juice.
37
Pancreatic fluid _ and _ are altered with flow
Pancreatic fluid **pH** and **electrolytes** are altered with flow
38
The HCO3− concentration and, hence, the pH _ the increased rates of secretion
PARALLEL
39
Explain how pancreatic duct cells secrete electroyltes and water into pancreatic fluid
The luminal membrane Cl− channel is CFTR (cystic fibrosis transmembrane conductance regulator)
40
Bile secretion is under what?
Neural and hormonal control
41
Bile:
* What is it?
* What is it produced by?
* Drains through what?
* Bile facilitates what?
* Bile, a dark green to yellowish brown fluid
* produced by the **hepatocytes in the liver**
* drains through the **bile ducts** penetrating the liver
* Bile facilitates the **digestion of lipids in the small intestine** by emulsifying fat and forming aggregates around fat droplets called micelles
42
* The dispersion of fat droplets into micelles greatly does what?
* Bile is stored where?
* The dispersion of fat droplets into micelles greatly increases the surface area, enhancing the action of pancreatic lipase.
* Bile is stored in the gallbladder and, under nervous and hormonal control, is discharged into the duodenum
43
Explain the 4 step progess of regulation of bile secretion
44
Are bile acids good or bad? Explain?
Bile acids are potentially toxic to cells, and their concentrations are tightly regulated
45
The bile ducts are lined by cells called what? What do they do?
The bile ducts are lined by cells called cholangiocytes, which secrete bicarbonate-rich fluid into the biliary tree.
46
In addition to lipid digestion and absorption, bile acids also help with what?
Bilirubin excretion
47
Explain the whole long ass process of bilrubin excretion
## Footnote
Bilirubin is the end product of hemoglobin degradation. The liver removes the bile pigment, bilirubin, from the circulation and conjugates it with glucuronic acid.
48
When bile contains too much cholesterol and not enough bile salts, what happens?
bile crystallize and forms **gallstones**.
49
* Gallstones can occur where?
* Obstruction of the biliary tree can cause what?
* Gallstones can occur anywhere within the biliary tree, including the gallbladder and the common bile duct.
* Obstruction of the biliary tree can cause jaundice, and obstruction of the outlet of the pancreatic exocrine system can cause pancreatitis (dt back up of enzymes and the proteases will break down the pancreas)
50
51
Nutrient absorption does not occur without what? Explain with the different marcomolcules
* Does not occur without contacting the microvilli of brush border
52
Intestinal secretions provide what?
Intestinal secretions provide lubrication and protective functions.
53
Small intestine:
* What mainly happens here?
* The epithelial lining of the Small intestine is replaced how often?
* The intestinal crypts do not and do secrete what?
* The small intestine is where the vast majority of **digestion and absorption** of food takes place
* The **epithelial lining** of the small intestine is replaced approximately **every 3 days**
* The intestinal crypts **do not secrete digestive enzymes, but do secrete mucus, electrolytes, and H2O**.
*
54
Small intestine:
* What cells are in the crypt? What do they function like?
* What do goblet cells do?
* The small intestine and colon usually absorb the fluid and electrolytes from intestinal secretions, what happens if this does not happen?
* Intestinal fluid hypersecretion is stimulated by what?
* **Paneth cells** in crypt function like neutrophils and *produce antimicrobial* substances that provide a protective barrier.
* Goblet cells secrete **various mucins**
* The small intestine and colon usually **absorb the fluid and electrolytes** from intestinal secretions, but if secretion surpasses absorption (e.g., in cholera), **watery diarrhea** may result.
* Intestinal fluid hypersecretion is **stimulated by toxins and other luminal stimuli.**
55
What is the lympathic supply for the GI?
Lacteal
56
FILL IN
57
How do we digest nucleic acid?
* **Small intestine (lumen):** Nucleases (deoxyribonuclease and ribonuclease) of pancreatic juice hydrolyze DNA and RNA to nucleotides
* **Small intestine (epithelium):** Nucleosidases and phosphatases of brush border split them into phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases
* **Ciculation:** Membrane carriers allow absorption
58
How do we get the activation of pancreatic enzymes in the small intestine?
59
Which B vitamins are water and fat Soluble?
Water: B+C
Fat: ADK E
60
Explain how the vitamin b12 absorption gets into the blood
61
Na+ absorption in the gut depends on what?
Gut depends on an Na+/K+-ATPase pump
* Approximately 98% of the electrolytes in the gut are reabsorbed.
* An Na+/K+-ATPase actively pumps Na+ across the **basal lateral surface** to be absorbed into the blood.
* (A) Na+ absorption by the jejunum. (B) Na+ absorption by the ileum.
62
What is required for calcium to be absorped by enterocytes?
Parathyroid hormone and
vitamin D
63
What do we need to transport iorn in plasma?
Transferrin
64
* Enterocytes absorb iron where?
* Iron must be in what form?
* Enterocytes absorb iron in the duodenum.
* Iron must be in ferrous form (Fe2+) to be absorbed.
65
* Water is absorbed how?
* GI tract is extremely efficient in what?
* Water is absorbed in the gut by osmosis.
* GI tract is extremely efficient in absorbing H2O
66
Splanchnic circulation:
* What type of system?
* The splanchnic circulation is the largest what?
* Liver blood supply what?
* High-flow, high-compliance, and low-resistance system.
* The splanchnic circulation is the largest regional circulation at rest and receives about **30% of the cardiac output.**
* Liver blood supply - 25% hepatic artery, **75% portal vein**
67
What is postprandial hyperemia?
The period of increased splanchnic blood flow after a meal
68
Splanchnic vasodilation results from several factors, including what?
including the hormonal environment (e.g., high levels of **cholecystokinin**) and the action of **enteric nerves** (e.g., VIPergic neurons).
69
The increase in parasympathetic nerve activity after a meal stimulates what?
after a meal stimulates GI secretion and motility, which also indirectly increases splanchnic blood flow as a result of increased local metabolism
70
71
Architectural arrangement of hepatocytes in the liver lobule enhances what?
the rapid exchange of material.
72
* Bile originating where? Where does that drain into?
* The sphincter of Oddi, located where? What does it do?
* **Bile** originating in the **bile canaliculus** drains into a series of ducts that eventually join the **pancreatic duct** near where it enters the duodenum.
* The **sphincter of Oddi**, located at the duodenal connection between the bile duct and the pancreatic duct, regulates drainage of bile and pancreatic juice into the **duodenum**.
73
What is an unique feature of the liver?
Tissue regeneration in the adult liver is a unique feature to maintain optimal metabolic function
74
Liver:
* What is cool about blood supply?
* Only internal human organ capable of what?
* Regeneration possible because why?
* Liver is a unique organ - **has a dual blood supply**
* Only internal human organ capable of **regenerating lost tissue** - with as little as 25% of the liver remaining, it can regenerate into an entire liver.
* Regeneration possible because hepatocytes are capable of reentering the cell cycle and undergoing **mitosis**.
75
Liver permeability results in what?
Liver permeability results in large quantities of lymph formation with high-flow rates
76
* What are hepatic sinusoids?
* Given their high permeability, sinusoidal epithelia form what?
* Hepatic sinusoids are very porous and allow a large flux of fluid and protein to move into the perisinusoidal space.
* Given their high permeability, sinusoidal epithelia form large quantities of lymph, which under resting conditions makes up half of the body’s formed lymph.
77
What are the five functions of the liver?
(1) **detoxification** of hormones, drugs, and waste products
(2) **metabolism** of carbohydrates, proteins, and fats;
(3) **storage** of iron and vitamins;
(4) **hormone** production;
(5) **innate** and adaptive immunity.
| DIMS H
78
Liver:
* Hepatocytes are involved in the metabolism of what?
* Many drugs and metabolites are hydrophobic and are converted into what?
* What affects drug metabolism and transport?
* Hepatocytes are involved in the metabolism of **xenobiotics** (chemical substances that are foreign)
* Many drugs and metabolites are hydrophobic and are converted into **hydrophilic** compounds by the liver, contributing to their elimination by the kidneys.
* Age, nutrition, genetics, sex, and hormones significantly affect drug metabolism and transport in the liver.
## Footnote
WOULD KNOW: P450 MAJOR ENZYME AND PHASE 1+2
79
Explain how the liver plays an important role in blood glucose buffering?
| KINDA HOT MESS
80
What does each one do/promote:
* Kinase:
* Phosphatase:
* Insulin:
* Glucogon:
* Epinephrine:
81
* RBCs and renal medulla totally depend on what?
* What is the preferred substrate for brain?
* RBCs and renal medulla totally depend on blood glucose for energy
* Glucose is the preferred substrate for the brain.
82
What is the basic unit of the liver? How is it arranged and what does it contain?
* The basic unit of the liver is the **lobule**.
* The lobule is arranged in a hexagonal fashion and is delineated by vascular and bile channels.
* The lobule contains specialized cells, such as hepatocytes, sinusoidal cells, and Kupffer cells.
83
* What is the main carbohydrate stored by the liver? What is a precursor to glycogen?
* Glycogen is the main carbohydrate stored by the liver.
* Uridine diphosphate glucose (UDP-glucose) is a precursor to glycogen.
84
Explain how the liver plays a vital role in lipid metabolism (PICTURE)
85
* Normally, what are the ketone bodies levels?
* What happens when we starve+ in DM? What is the condition called?
* In patients with diabetes, large amounts of β-hydroxybutyric acid can do what?
* The level of ketone bodies circulating in the blood is usually low, but during prolonged starvation and in diabetes mellitus, it is highly elevated, a condition known as ketosis.
* In patients with diabetes, large amounts of β-hydroxybutyric acid can make the blood pH acidic, a state called ketoacidosis
*
86
The liver is involved in what for fats (3)
* the oxidation of fatty acids
* the synthesis of very-low-density lipoproteins (VLDLs)
* the regulation of blood triglycerides, low-density lipoproteins (LDLs), and circulating high-density lipoproteins (HDLs
87
What are chylomirons, VLDLs, LDLs and HDLs?
88
The liver synthesizes important plasma proteins. Explain
89
* Albumin helps to preserve what? What does it maintain?
* The importance of plasma proteins is illustrated by the fact that both liver disease and long-term starvation result in what?
* Albumin helps to preserve plasma volume and tissue fluid balance by maintaining the colloid osmotic pressure of plasma.
* The importance of plasma proteins is illustrated by the fact that both liver disease and long-term starvation result in generalized edema and ascites.
90
What is ammonia?
Ammonia, derived from protein and nucleic acid catabolism, plays a pivotal role in nitrogen metabolism and is needed in the biosynthesis of nonessential amino acids and nucleic acids.
| GOES THROUGH UREA CYCLE
91
What can the liver form from the essential amino acids?
nonessential amino acids
* The liver is the body’s only source of nonessential amino acids
92
Liver is the site for uptake, storage, and release of what?
fat-soluble vitamins
93
# LOW YIELD
94
Liver plays a key role in the transport, storage, and metabolism of what metal? Explain
Iron
* **Kupffer cells** rapidly phagocytize damaged red cells.
* The iron released from the heme molecule during phagocytosis becomes part of the free iron pool.
95
Liver activates and degrades many hormones. list them (7)
96
Liver cells have immune functions:
* Ideal site for what?
* Portal vein does what?
* Sinusoidal structure increases what?
* What acts as APCs?
* Stellate cells release what?
* ideal site for the clearance of blood-borne antigens and pathogens.
* portal vein – **antigen exposure**
* sinusoidal structure - increase the time period in for **APCs**
* Hepatocytes, SECs, Kupper cells act as APCs
* Stellate cells release **interferons and cytokines**
97
98
The major regulated processes (effectors) of the GI are: (3)
i. Gut motility.
ii. Epithelial secretion
iii. Blood flow
99
Enteric nervous system (ENS):
* Responsible for what?
* The myenteric plexus is mainly involved with what?
* The submucosal plexus coordinates what?
* Responsible for much of the moment-to-moment control of gut motility and secretion.
* The **myenteric plexus** is mainly involved with control of gut motility and innervates the inner
circular and outer longitudinal smooth muscle layers.
* The **submucosal plexus** coordinates intestinal absorption and secretion through its innervation of the glandular epithelium, intestinal endocrine cells and submucosal blood vessels
100
Cell bodies of the ENS are clustered/ arranged how? What does that result in?
Cell bodies of the ENS are clustered in ganglia that are interconnected by fiber tracts resulting in the formation of two plexuses that play a major role in controlling local blood flow, endocrine cell activity, and gut motility, secretion, and absorption.
101
Submucosal plexus:
* Where is it in the layers and in the GI tract?
* Does not exist where?
* Involved in what?
* What does it alter?
* Submucosal region between the circular muscle and the mucosa.
* In small and large intestine, but better developed in small intestine.
* Does not exist esophagus and is sparse in the submucosal space of the stomach.
* Involved in regulating **secretion, absorption, blood flow, and endocrine cell activity** in addition to regulating the contraction of the submucosal muscle fibers.
* Contraction and relaxation of these fibers alters the amount of mucosal folding
102
Myenteric plexus:
* Where is it located in the layers and in the GI tract?
* Regulates what?
* Controls what?
* What cells are located here?
* Extends the length of the GI tract and runs between the longitudinal and circular muscle layers.
* **Regulating** both the strength and frequency of smooth muscle contraction necessary to move materials along the tract.
* controls **sphincter activity**.
* **Interstitial cells of Cajal (ICC)** (GI pacemaker cells) are located in the myenteric plexus.
103
Although physically separated, the two plexuses are not functionally what?
* Although physically separated, the two plexuses are not functionally isolated from one another.
* Specific neurons link the two networks into a functionally integrated nervous system
104
The ENS utilizes many neurotransmitters:
* Acetylcholine is primary NT involved in what?
* What are the inhibitory NTs?
* What are gut brain peptides?
* **Acetylcholine** is the primary neurotransmitter involved in the stimulation of secretion and motility.
* **ATP and nitric oxide** function as inhibitory neurotransmitters.
* **Peptide neurotransmitters** are found in both the ENS and the CNS and are referred to as gut-brain peptides.
105
The ENS is linked with the CNS via what? What does that give rise to?
The ENS is linked with the CNS via parasympathetic and sympathetic nerves, giving rise to the concept of a gut-brain neural axis
106
107
What is the first pass metabolism for GI hormones?
GI hormones are secreted into the capillary blood in the GI tract and must pass through the portal venous system and the liver before entering the systemic circulation, a process known as first-pass metabolism.
108
109
* Sphincters are characterized as what?
* Distention of the gut segment immediately what? What does this prevent?
* Sphincters are characterized as zones of high resting pressure that **relax in response to an appropriate stimulus.**
* Distention of the gut segment immediately distal to a sphincter causes it to contract, **preventing retrograde flow**
110
What are the 7 sphincters of the GI tract? What do they separte?
111
* Explain the myogenic contractile activity?
* What causes the sphincter to transiently relax?
* Active inhibitory neuron: open sphincter
* Inhibit (inactive) inhibitory neuron: closed sphincter
* Specific signals (e.g., distention, pressure, and nervous input) cause the sphincters to transiently relax
112
A basic electrical rhythm (slow waves) in the GI smooth muscle are what?
are spontaneous oscillations in the membrane potential that underlie many of the phasic contractions of the GI tract
113
Spike potentials:
* Triggered if what?
* What enters? What does that cause?
* What does this explain?
* triggered if the peak of a slow wave depolarizes the membrane to a threshold potential.
* Ca 2+ entry into smooth muscle cells during spike potentials and triggers muscle contraction
* explains why amount of force developed by muscle contraction correlates with the appearance of spike potentials.
114
The observed pattern of gut motility (e.g., segmentation) is programmed by the ENS,
which determines what?
determines when slow waves will produce spike potentials and give rise to a contraction.
115
What are the excitatory and inhibitory transmitters of the spike potentials?
* **Excitatory transmitters** often cause nonselective cation channels in the smooth muscle cells to open; the resting membrane potential is **depolarized** and **more slow waves cross the threshold** for the generation of a spike potential.
* **Inhibitory transmitter**s often act by **opening the K+ channels** in smooth muscle cells, **hyperpolarizing** the membrane potential and preventing the slow waves from reaching threshold.
116
Cells of cajal:
* What are they?
* Present where?
* What do they generate?
* What do Gap junctions allow?
* The slow-wave electrical current then does what?
* Cell of Cajal (ICCS) are the **pacemaker cells** of the GI tract
* ICCs are present along the length of the GI tract
* Generate **the slow waves** observed in the stomach and intestinal tract.
* **Gap junctions** allow electrical current to flow from the ICC network to the circular muscle leading to the generation of an action potential followed by a contraction.
* The slow-wave electrical current then spreads from muscle cell to muscle cell
117
Electrical slow-wave frequencies differ in the stomach, small intestine, and colon:
* Slow waves with similar waveforms occur at a frequency ranging from what in the antrum/pylorus, duodenum and colon?
* Since each slow wave does not result in the generation of an action potential and muscle contraction, what may happen?
* What does the ENS determine?
* from about 3 waves/min in the antrum/pylorus, 11 to 12 waves/min in the duodenum, and 2 to 13 waves/min in the colon.
* the contractile frequency of the muscle may be less than but never greater than the frequency of the slow waves
* The ENS determines the nature of the contractile response during each slow wave.
118
Where are there no slow waves? What do they produce instead?
* There are no slow waves in the esophagus, which remains quiescent unless stimulated by swallowing or by the presence of a bolus in the lumen.
* The proximal stomach does not produce slow waves but has a steady tone that pushes the contents toward the pylorus.
119
What are the following reflexes:
* Gastro-ileal
* Ileo-gastric
* Gastro-colic
* Ortho-colic
* Colono-gastric
120
What are the muscle types in the esophagus
Skeletal muscle in upper one- third, mix of muscle types in middle one-third, and only smooth muscle in bottom one- third
121
What are the three esophageal phases?
122
What is primary and secondary peristalsis?
* Primary peristalsis is initiated by the act of swallowing.
* Secondary peristalsis is a subconscious process that is triggered by distention associated with failed downward transport (i.e., food lodging in the esophagus) or by the presence of acid due to gastric reflux.
* Secondary peristalsis accompanied by the stimulation of salivary secretion is the normal mechanism for “dislodging” the bolus as well as removing acid irritation.
123
* What are the major types of GI motility?
* Peristalsis occurs when?
* Peristalsis and propulsion are the major types of GI motility.
* Peristaltic propulsion involves the formation of a propulsive and a receiving segment, mediated by reflex control of the intestinal musculature.
* Peristalsis occurs during and shortly after a meal.
124
* The gastric reservoir is specialized for what?
* What does the musculature in the region of the antral pump exhibits?
* What does not exist?
* The gastric reservoir is specialized for receiving and storing a meal.
* The musculature in the region of the antral pump exhibits phasic contractions that function in the mixing and trituration of the gastric contents.
* No distinctly identifiable boundary exists between the reservoir and the antral pump.
125
The stomach is divided into what?
three/four anatomical and two functional regions
126
What is the receptive relaxtion?
As food enters the esophagus, the stomach muscles are stimulated to relax, receptive relaxation, allowing the stomach to accommodate a change in volume
127
Three types of relaxation responses occur in the gastric reservoir. Explain them
128
Tonic contraction of the musculature of the gastric reservoir does what?
decreases the volume and exerts compressive force on the contents
129
* One function of the vagovagal reflex is to control what?
* This reflex also allows for the what?
* One function of the vagovagal reflex is to control GI tract smooth muscle contraction in response to distention of the tract by food; the reflex is activated to relax the stomach muscles in response to swallowing food.
* This reflex also allows for the accommodation of large amounts of food in the GI tract.
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* Do not want to deliver gastric chyme to the duodenum how?
* Neural control mechanisms adjust what?
* Do not want to deliver gastric chyme to the duodenum at a rate that overloads the digestive and absorptive functions of the small intestine
* Neural control mechanisms adjust the rate of gastric emptying to compensate for variations in the volume, composition, and physical state of the gastric contents
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132
Which ones are faster, slower: Solid, liquid and semisolid meal?
133
The mixing pattern of small intestinal motility is characteristic of the digestive state. Explain
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inhibitory musculomotor activity determines what?
determines the distance and direction a contraction travels
135
LARGE INTESTINAL MOTILITY:
* What is unique here?
* Primary stimulus is what? What is another strong stimulus?
* Power propulsion is unique to the large intestine.
* Primary stimulus is the presence of fat from the small intestine
* Distention of the colon can also act as a strong stimulus.
*
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What is the gastrocolic reflex?
* Ascending colon receives intestinal content from the terminal ileum.
* Chemoreceptors and mechanoreceptors in the cecum and ascending colon provide feedback for controlled delivery of the ileum contents into the ascending colon, analogous to gastric emptying into the small intestine.
* Neuromuscular mechanisms, analogous to adaptive relaxation in the gastric reservoir, permit filling of the ascending colon to occur without large increases in intraluminal pressure
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Large intestinal motility:
* Most contractions are what?
* Occasional giant migrating contractions (mass movements) does what?
* Mass movements are what increase how and by what?
* Most contractions of the large intestine are segmenting contractions that continually mix the fecal contents.
* Occasional giant migrating contractions (mass movements) propel fecal material into the rectum.
* Mass movements are increased in frequency and intensity by the gastrocolic reflex, which is triggered by the entry of food into the stomach and duodenum. The neuronal pathway includes both the ENS and the autonomic nerves.
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Large intestinal motility:
* What is haustra?
* What is haustration?
* Haustral formation differs from what and how?
* Ringlike contractions of the circular muscle divide the colon into pockets called haustra
* Haustration is reminiscent of the mixing (segmentation) movements in the small intestine
* Haustral formation differs from small intestinal segmentation in that the contracting and receiving segments on either side remain in their respective states for extended periods of time.
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Fecal continence is maintained by the action of several anal sphincters:
* The internal anal sphincter is a thickening of what? What is it controlled by?
* The external anal sphincter is made up of what?
* The pelvic diaphragm is also important in what?
* The internal anal sphincter is a thickening of smooth muscle around the anal canal and is controlled by autonomic nerves
* The external anal sphincter is distal to the internal sphincter and is composed of skeletal muscle around the anal canal.
* The pelvic diaphragm is also important in the maintenance of fecal continence and is a sling of skeletal muscle, originating from the bony pelvis that forms the acute anorectal angle.
140
Neural control of defecation involves the central and enteric nervous systems. Explain the process
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What is the parasympathetic defecation reflex?
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Migrating motor complex (MMC):
* The small intestinal ENS “runs” the digestive state motor program when ?
* Conversion to the interdigestive state motor program starts when ?
* The MMC is a pattern of motility that occurs when?
* The MMC involves what?
* The functions of MMCs are to what?
* MMCs are an ENS-controlled motor program. The ENS stimulates secretion of what?
* The small intestinal ENS “runs” the digestive state motor program when nutrients are present and digestive processes are ongoing.
* Conversion to the interdigestive state motor program starts when digestion and absorption of nutrients are complete, 2 to 3 hours after a meal.
* The MMC is a pattern of motility that occurs about every 90 minutes between meals; the start of an interdigestive period is defined by the first MMC that occurs after the last meal.
* The MMC involves intervals of strong propulsive contractions, which pass down the distal stomach and small intestine.
* The functions of MMCs are to **sweep the stomach and small intestine** of indigestible materials and to prevent bacterial colonization of the upper intestine.
* MMCs are an ENS-controlled motor program. The ENS stimulates secretion of the hormone **motilin**, which stimulates propulsive contractions of the intestine.
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* Parasympathetic neurons innervate the gut from what?
* PNS stimulation activates the entire what?
* Parasympathetic neurons innervate the gut from the medulla oblongata and sacral spinal cord.
* PNS stimulation activates the entire ENS and also increases overall blood flow to the gut and general gut activity including increased secretion.
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* What controls the upper GI tract?
* The center is more directly involved in controlling what?
* The neural networks in the dorsal vagal complex and their interactions with higher centers are responsible for what?
* **Dorsal vagal complex** in the medulla controls the upper GI tract.
* The center is more directly involved in controlling the **specialized functions of the esophagus, stomach, duodenum, gallbladder, and pancreas** than those of the distal small intestine and large intestine.
* The neural networks in the dorsal vagal complex and their interactions with higher centers are **responsible for the rapid and precise control necessary for adjustments to rapidly changing conditions in the upper GI tract** during anticipation, ingestion, and digestion of meals of varied composition.
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Sympathetic nerves innervate what? What does it do?
Sympathetic nerves innervate gut blood vessels, mucosa, and muscularis and suppress gut activity when stimulated.
146
Sympathetic suppression of digestive functions?
What is the main mediator of SNS?
* Sympathetic suppression of digestive functions, including motility and secretion, occurs as a coincident adaptation for reduced blood flow.
* Norepinephrine (NE) released from sympathetic postganglionic neurons is the main mediator of these effects and acts directly on the LES and IAS to increase tension and keep the sphincter closed.
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What are the prevertebral sympathetic ganglia?
* Celiac
* Superior mesenteric
* Inferior mesenteric
