1
Q
THE ALIMENTARY TRACT: GI segments
A
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small Intestine
- Large Intestine
- Sphincters between segments
2
Q
THE ALIMENTARY TRACT: Accessory organs
A
- Liver
- Gall bladder
- Pancreas
3
Q
Functions of the Alimentary Tract
A
Provides the body with a continual supply of water, electrolytes, vitamins, and nutrients, by:
- Movement of food
- Secretion of digestive juices and digestion of the food
- Absorption of water, nutrients and digestive products
- Circulation of blood to carry away the absorbed substances
- Local, nervous, and hormonal control
4
Q
Each part of the Alimentary Tract is adapted to its specific functions:
A
- Simple passage of food (esophagus)
- Temporary storage of food (stomach)
- digestion and absorption (small intestine)
5
Q
LAYERS
A
- Serosa
- Longitudinal Muscle Layer
- Circular Muscle Layer
- Submucosa
- Mucosa
The motor functions of the gut are performed by the different
layers of smooth muscle.
6
Q
Gastrointestinal smooth muscle function as a syncytium
A
• Within each bundle, muscle fibers are electrically connected with one another through gap junctions → low-resistance movement of ions
• Electrical signals that initiate contractions → travel readily
from one fiber to the next within each bundle but more
rapidly along the length of the bundle than sideways.
• Each bundle is partly separated from the next by loose connective tissue, but the muscle bundles fuse with one another at many points
7
Q
Gastrointestinal smooth muscle function as a syncytium 2
A
• Each muscle layer represents a branching latticework of
smooth muscle bundles.
• Each muscle layer functions as a syncytium → when an action potential is elicited anywhere within the muscle mass, it generally travels in all directions in the muscle.
8
Q
Electrical Activity of GI Smooth Muscle
A
Electrical Activity of GI Smooth Muscle • Excited by almost continual slow, intrinsic electrical activity along the membranes of the muscle fibers • SLOW WAVES • SPIKE POTENTIALS • TONIC CONTRACTIONS - Exhibited by some GI Smooth Muscles - No slow waves - Last minutes to hours
9
Q
- NOT true action potentials; slow, undulating changes in the RMP
- Slowest: Stomach- Fastest: Small intestines
- Sodium entry
- Pacemaker: Interstial cells of Cajal
A
SLOW WAVES
10
Q
- True action potentials
- Threshold: -40mV
- Sodium and calcium entry
A
SPIKE POTENTIALS
11
Q
- Exhibited by some GI Smooth Muscles
- Not associated with the basic electrical rhythm of slow waves but often lasts several minutes to hours
- often increases or decreases in intensity but continues
A
TONIC CONTRACTIONS
12
Q
Factors that depolarized the membrane (less negative; more excitable)
A
- stretching of muscle
- stimulation of acetylcholine released from the parasympathetic nerves
- stimulation by several specific GI hormones
13
Q
Factors that make the membrane hyperpolarized (more negative; less excitable)
A
- stimulation of norepinephrine/epinephrine
2. stimulation of the sympathetic nerve (secrete norepinephrine at their endings)
14
Q
MECHANISMS FOR TONIC CONTRACTIONS:
A
• Continuous Repetitive Spike Potentials → the greater the
frequency, the greater the degree of contraction
• Hormones → continuous partial depolarization of the smooth
muscle membrane without causing action potentials
• Continuous entry of Calcium (unclear mechanism)
15
Q
- Local, independent neural control of the GI tract → especially important in controlling gastrointestinal movements and secretion.
- Can function independently of these extrinsic nerves
- But stimulation by the parasympathetic and sympathetic systems can greatly enhance or inhibit gastrointestinal functions
A
ENTERIC NERVOUS SYSTEM
16
Q
NEURAL CONTROL OF GI TRACT
A
• Intrinsic Control - Enteric nervous system
- Myenteric (Auerbach’s) plexus
- Submucosal (Meissner’s) plexus
• Extrinsic Control - Autonomic nervous system
- Parasympathetic – mainly stimulates ACh
- Sympathetic – mainly inhibits NE
17
Q
- an outer plexus lying between Inner Circular and Outer
Longitudinal layers - GI Movements
- Mainly excitatory except for Pyloric Sphincter and Ileocecal Valve, where relaxation occurs
A
MYENTERIC (AUERBACH’S) PLEXUS
18
Q
- Submucosa
- GI secretions, absorption, contraction of submucosal
muscle
A
SUBMUCOSAL (MEISSNER’S) PLEXUS
19
Q
• Consists mostly of a linear chain of many interconnecting
neurons that extends the entire length of the GI tract.
• Concerned mainly with controlling muscle activity along the length of the gut, because:
- It extends all the way along the intestinal wall
- It lies between the longitudinal and circular layers of intestinal smooth muscle.
A
MYENTERIC PLEXUS
20
Q
• Not entirely excitatory, some of its neurons are inhibitory
• Fiber endings secrete an inhibitory transmitter, possibly
VASOACTIVE INTESTINAL POLYPEPTIDE or some other inhibitory peptide.
• Inhibitory signals affect intestinal sphincters impeding
movement of food along the GI tract:
- Pyloric sphincter – emptying of the stomach into the duodenum
- Sphincter of the ileocecal valve – emptying from the SI
into the cecum
A
MYENTERIC PLEXUS
21
Q
Principal effects of Myenteric Plexus when stimulated:
A
- ↑ tonic contraction, or “tone,” of the gut wall
- ↑ intensity of the rhythmical contractions
- ↑ rate of the rhythm of contraction
- ↑ velocity of conduction of excitatory waves along the gut wall → more rapid movement of peristaltic waves
22
Q
- Mainly concerned with controlling function within the inner wall of each minute segment of the intestine.
- Control local intestinal secretion, local absorption, and local contraction of the submucosal muscle that causes various degrees of infolding of the gastrointestinal mucosa.
A
SUBMUCOSAL PLEXUS
23
Q
ENTERIC NEUROTRANSMITTERS
A
- Acetylcholine – most often excitatory
* Norepinephrine/Epinephrine – most often inhibitory
24
Q
- Parasympathetic stimulation increases activity of the ENS
* Sympathetic stimulation usually inhibits GIT activity
A
AUTONOMIC CONTROL OF GIT
25
• Cranial parasympathetic nerve fibers are almost entirely in the VAGUS NERVE
- Esophagus, stomach, and pancreas; somewhat less to
the intestines down through the first half of the large
intestine
• Sacral parasympathetics (S2, S3, S4) pass through the PELVIC NERVES to the distal half of the large intestine and all the way to the anus.
- Sigmoidal, rectal, and anal
- Fibers function especially to execute the defecation
• Postganglionic neurons located mainly in the myenteric and submucosal plexuses
PARASYMPATHETIC CONTROL
26
• Sympathetic fibers to the GIT are from T5-L2
• Most of the preganglionic fibers that innervate the gut enter the sympathetic chains that lie lateral to the spinal column, and many of these fibers then pass on through the
chains to outlying ganglia such as to the celiac ganglion and various mesenteric ganglia
• Most of the postganglionic sympathetic neuron bodies are in these ganglia, and postganglionic fibers then spread through postganglionic sympathetic nerves to all parts of the gut.
• Nerve endings secrete mainly norepinephrine but also small amounts of epinephrine.
SYMPATHETIC CONTROL
27
Inhibits GIT activity causing many effects opposite to those of the parasympathetic system. it exert its effects in two ways:
1. To a slight extent by direct effect of secreted norepinephrine to inhibit intestinal tract smooth muscle (except the mucosal muscle, which it excites)
2. To a major extent by an inhibitory effect of norepinephrine on the neurons of the entire enteric nervous system.
28
• Many afferent sensory nerve fibers innervate the gut.
• Some of them have cell bodies in the ENS itself and in the
DRG of the spinal cord.
• Sensory stimuli:
- Irritation of the gut mucosa
- Excessive distention of the gut
- Presence of specific chemical substances
• Signals transmitted can cause excitation or, under other
conditions, inhibition of intestinal movements or intestinal
secretion
AFFERENT SENSORY INFORMATION FROM THE GUT
29
TYPES OF GASTROINTESTINAL REFLEXES
1. Reflexes that are integrated entirely within the gut wall ENS
2. Reflexes from the gut to the pre vertebral sympathetic ganglia and then back to the GIT
e. g. Gastrocolic, Enterogastric, Colonoileal Reflexes
3. Reflexes from the gut to the spinal cord or brain stem and then back to the GIT
- E.g. defecation reflexes
30
Reflex from stomach to cause colon evacuation
gastrocolic reflex
31
Reflex from colon and small intestine to inhibit gastric motility and secretion
enterogastric reflex
32
Reflex rom the colon to inhibit emptying of ileal contents into the colon
colonoileal reflex
33
TYPES OF GI TRACT MOVEMENTS
* Propulsive movements: cause food to move forward along the tract at an appropriate rate to accommodate digestion and absorption
* Mixing movements: keep the intestinal contents thoroughly mixed at all times
34
• Peristalsis: the basic propulsive movement of the gastrointestinal tract
• A contractile ring appears around the gut and then moves
forward; Any material in front of the contractile ring is moved forward
• Inherent property of many syncytial smooth muscle tubes
• Stimulation at any point in the gut can cause a contractile
ring to appear in the circular muscle, and this ring then
spreads along the gut tube.
• Other stimuli: chemical or physical irritation; parasympathetic signals
PROPULSIVE MOVEMENTS
35
- usual stimulus for intestinal peristalsis
- If a large amount of food collects at any point in the gut, stretching of the gut wall stimulates the ENS to contract the gut wall 2 to 3 cm behind this point, and a contractile ring appears that initiates a peristaltic movement.
Gut distention
36
Effectual peristalsis requires an active myenteric plexus
• Peristalsis occurs only weakly or not at all in any portion of
the GIT that has congenital absence of the myenteric plexus
• Depressed or completely blocked in the entire gut when
treated with atropine → paralysis of cholinergic nerve endings of the myenteric plexus.
37
• Myenteric reflex or peristaltic reflex
- Distention → GI segment excitation → peristalsis: starting
from orad going to anal direction → pushing the intestinal
contents in the anal direction
- Gut sometimes relaxes several cm downstream toward
the anus (receptive relaxation) ➔ allowing food to be
propelled more easily toward the anus than toward the
mouth.
- Complex pattern does not occur in the absence of the
myenteric plexus
• Peristaltic reflex + anal direction of movement of the peristalsis
THE LAW OF THE GUT
38
• Differ in different parts of the GIT
• In some areas, the peristaltic contractions themselves cause most of the this
• At other times, local intermittent constrictive contractions occur every few centimeters in the gut wall.
- These constrictions usually last only 5 to 30 seconds; then new constrictions occur at other points in the gut, thus "chopping" and "shearing" the contents first here and then there.
MIXING MOVEMENTS
39
- Requires active myenteric plexus
- Stimulus: Distention, irritation, parasympathetics
- Myenteric Reflex/Peristaltic Reflex: Muscles upstream
will exhibit contraction while muscles downstream will
exhibit “receptive relaxation”
- LAW OF THE GUT: Myenteric Reflex + Anal Direction of
Peristalsis
Propulsive Movements/Peristalsis
40
- Local intermittent constrictive contractions every few centimeters
- Chopping and shearing of food
Mixing Movements
41
SPLANCHNIC CIRCULATION
* Blood from the gut, spleen and pancreas will go immediately to the liver via the PORTAL VEIN and leave via the HEPATIC VEIN into the SVC
* WATER-SOLUBLE NUTRIENTS - goes to the portal vein and liver
* FATS -not carried in the portal blood; goes to the lacteals and thoracic duct
42
• The time that food remains in each part of the GIT is critical for optimal processing and absorption of nutrients.
• Appropriate mixing must be provided.
• Nervous and hormonal mechanisms control the timing → optimal timing
- Because the requirements for mixing and propulsion are
quite different at each stage of processing
PROPULSION OF FOOD IN THE GI TRACT
43
HUNGER VS APPETITE
* Hunger - Intrinsic desire for food; Principal determinant of the amount of food that a person ingests
* Appetite - Principal determinant of the type of food that a person preferentially seeks
44
```
- Teeth designed for chewing
Anterior teeth (incisors) → cutting
Posterior teeth (molars) → grinding
```
- Mostly due to the CHEWING REFLEX
>>Bolus of food in the mouth → inhibition of CN V → relaxation of jaw muscles → rebound contraction
>>Automatically raises the jaw to cause closure of the
teeth, also compresses the bolus
>>Chewing increases surface area of food
MASTICATION
45
Purpose of Chewing
o Breaks cells - breaks apart indigestible cellulose
o Increases surface area - decreases particle size
o Mixes food with saliva
o Begins digestion of starches (α-amylase, lingual lipase)
o Lubricates food for swallowing
46
- Complicated mechanism
- Pharynx subserves respiration and swallowing
- Pharynx is converted for only a few seconds at a time
into a tract for propulsion of food.
SWALLOWING (DEGLUTITION)
47
Swallowing can be divided into:
1. Voluntary Stage - initiates the swallowing process
2. Pharyngeal Stage - involuntary and constitutes passage of food through the pharynx into the esophagus
- Trachea Closed
- UES Relaxes
- Peristalsis Occurs
3. Esophageal Stage - involuntary; transport food from pharynx to stomach
48
Esophageal Stage (2 Types of Peristalsis)
o Primary Peristalsis continuation of the peristaltic
wave: pharynx → esophagus
o Secondary Peristalsis: due to distention of the
esophagus itself by the retained food
49
(NERVOUS CONTROL OF SWALLOWING)
- Sensory input from pharnyx and esophagus
- Coordinates activity from vagal nuclei with other centers
(e. g., inhibits respiratory center)
Swallowing Center - medulla
50
(NERVOUS CONTROL OF SWALLOWING)
- Food in pharynx → afferent sensory input via vagus/glossopharyngeal N. → swallowing center → brain stem nuclei → efferent input to pharynx
Pharyngeal Phase
51
(NERVOUS CONTROL OF SWALLOWING)
1. Primary peristalsis
- Continuation of pharyngeal peristalsis
- Coordinated by swallowing center
- Cannot occur after vagotomy (striated muscle)
2. Secondary peristalsis
- Stretch related afferent sensory input to ENS and
swallowing center are both involved
- Can occur after vagotomy (SM)
Esophageal Phase
52
INGESTION OF FOOD
RECEPTIVE RELAXATION OF THE STOMACH
- Precedes peristaltic wave in the esophagus
- Accommodates incoming food
LOWER ESOPHAGEAL SPHINCTER
- Tonically Contracted (30mmHg)
- Prevents Reflux (along with valve-like mechanism of the esophagus)
- Exhibits receptive relaxation to food also
53
MOTOR FUNCTIONS OF THE STOMACH
1. STORAGE OF FOOD - Up to 1.5 L
2. MIXING OF FOOD WITH GASTRIC SECRETIONS
- Formation of Chyme
- Retropulsion also seen
- Hunger contractions cause Hunger Pangs, especially in young healthy people
3. SLOW EMPTYING OF CHYME
- Intense antral peristaltic contractions against the pylorus
promote gastric emptying
54
- Allows water easily
- does NOT allow food until chyme becomes almost
fluid-like
PYLORIC SPHINCTER
55
GASTRIC EMPTYING (Promoters and Inhibitors)
Promoters: Gastrin, stomach wall stretch(minor only)
Inhibitors: CCK, Enterogastric nervous feedback reflexes,
secretin and GIP
56
Small intestinal motility contributes to digestion and absorption by:
1. Mixing chyme - with digestive enzymes and other secretions
2. Circulation of chyme - to achieve optimal exposure to
mucosa
3. Propulsion of chyme - in an aboral direction
57
Two types of movements in small intestine following a meal
1. Peristalsis - a propulsive movement; recall “Law of
Gut.” → 3-5 hours for food to go from pylorus to ileocecal
valve
2. Segmentation: a mixing movement
58
• Purpose: housekeeping function
- Sweeps undigested residue toward colon to maintain low
bacterial counts in upper intestine.
• Most coordinated, rapid peristalsis
• Occurs between meals
• Characteristics
- Periods of intense peristaltic contractions
- Takes ~90 min to go from stomach to colon
- Mediated by motilin and ENS
MIGRATING MOTILITY COMPLEXES (MMC)
59
• Functions as a valve and a sphincter
• Valvular function
- prevents backflow into small intestine mechanically
• Sphincter function
- regulates movement of ileal contents into large intestine
- ENS and extrinsic nerves
ILEOCECAL JUNCTION
60
• Functions of large intestine smooth muscle:
- Mixes chyme: enhances fluid / electrolyte absorption
(haustral contractions)
- Propels fecal material (mass movements)
• Very sluggish movement - 8-15 hours from ileocecal valve to the colon
• Chyme becomes Feces
• Proximal Half: Absorption of water
• Distal Half: Storage of feces
MOTILITY OF THE LARGE INTESTINES
61
* Purpose - Mixing movements facilitate fluid and electrolyte absorption (minimal propulsion)
* Structural and functional basis
- They appear and disappear every 30-60s
- Require contraction of longitudinal and circular SM
- Circular SM is concentrated in some areas
HAUSTRAL CONTRACTIONS
62
• Propulsive movements that occur from cecum to sigmoid
colon
• Initiated by Gastrocolic Reflex, Duodenocolic Reflex and irritation in the colon
• Stimulates desire for defecation - Prevented by Internal Anal Sphincter and External Anal Sphincter
MASS MOVEMENTS
63
(CONTROL OF DEFECATION)
- Mediated entirely by ENS is initiated when feces enters
rectum via mass movements
- Rectal distention initiates afferent signals that spread through myenteric plexus to descending and sigmoid colon, and rectum.
- Causes contractions that force feces toward anus.
Intrinsic reflex
64
Internal anal sphincter relaxes and if external anal sphincter is voluntarily relaxed, __ occurs.
defecation
65
(CONTROL OF DEFECATION)
- Parasympathetic cord reflex greatly intensifies intrinsic reflex (but is not different qualitatively)
- Rectal distention also initiates cord reflex. Afferent signals go to sacral cord and then back to descending and
sigmoid colon, and rectum by way of parasympathetic fibers in pelvic nerves.
- Sensory and motor fibers for defecation reflex.: S2, S3, S4
- Intact when spinal cord is injured at higher levels.
Spinal cord reflex
66
(CONTROL OF DEFECATION)
- Afferent signals entering spinal cord initiate other effects
that require intact spinal cord.
o Deep breath, closure of glottis, and increased abdominal
pressure (valsalva maneuver)
o All work to move fecal contents downward
- Spinal transection or injury can make defecation a difficult
process
o Cord defecation reflex can be excited (either digitally
or with enema)
Involvement of higher centers
67
Reflex where there is stretch bowel, proximal contraction, distal relaxation.
Peristaltic Reflex
68
Reflex from duodenum to regulate gastric emptying
Enterogastric Reflex
69
(Reflex)
gastric distention relaxesileocecal sphincter
Gastroileal Reflex (gastroenteric)
70
overdistention or injury of bowel segment causes entire bowel to relax.
Intestino-intestinal Reflex
71
distention of stomach/duodenum initiates mass movements.
Gastro- and Duodenocolic Reflexes
72
rectal distention initiates defecation
Defecation Reflex (rectosphincteric)
73
Stimuli for: Protein, Distention, Nerve (Acid inhibit release)
Site of Secretion: G cells of the antrum, duodenum, and jejunum
Actions: Stimulates GASTRIC ACID SECRETION AND MUCOSAL GROWTH.
Gastrin
74
Stimuli for secretion: Protien, Fat, Acids
Site of Secretion: I cells of the duodenum, jejunum, and ileum
Actions:
- Stimulates pancreatic enzyme secretion, pancreatic bicarbonate secretion, gallbladder contraction, growth of exocrine pancreas
- Inhibits gastric emptying and appetite to prevent overeating
Cholecystokinin
75
Stimuli for secretion: Acid, Fat
Site of Secretion:S cells of the duodenum, jejunum, and ileum
Actions:
- Stimulates Pepsin secretion, Pancreatic bicarbonate secretion, Biliary bicarbonate secretion and Growth of exocrine pancreas
- Inhibits Gastric Acid secretion
Secretin
76
Stimuli for secretion: Protein, Fat, Carbohydrate
Site of Secretion: K cells of the duodenum and jejunum
Actions:
- Stimulate Insulin release
- Inhibits Gastric acid secretion
*slows the emptying of gastric contents into the duodenum when user intestine is overloaded with food products
Gastric inhibitory peptide (GIP) or Glucose-dependent insulinotropic peptide
77
Stimuli for secretion: Fat, Acid, Neve
Site of Secretion: M cells of the duodenum and jejunum
Actions: Stimulates Gastric motility and Intestinal motility
Motilin
78
Motilin is released cyclically and stimulates waves of gastrointestinal motility called __ that move through the stomach and small intestine every 90 minutes in a fasted person.
interdigestive myoelectric complexes
79
Throughout the gastrointestinal tract, secretory glands subserve two primary functions:
1. digestive enzymes are secreted in most areas of the alimentary tract, from the mouth to the distal end of the
ileum
2. mucous glands, from the mouth to the anus, provide mucus for lubrication and protection of all parts of the alimentary tract.
80
Anatomical Types of Glands
Single secretory cells - goblet cells
Pits – Crypts of Lieberkuhn
Tubular glands – oxyntic gland
Complex glands – salivary gland and pancreas
81
(stimulation of GIT)
Trophic stimulation – contact with food increases mucus secretion and juices
Local stimulation
82
Stimulation of enteric nervous system:
(1) tactile stimulation
(2) chemical irritation
(3) distention of gut wall
83
Autonomic stimulation of GIT: Parasympathetic
stimulates secretion via CN IX (glossopharyngeal) and CN X (vagus) (salivary, esophageal, gastric, pancreas, Brunner’s glands in the duodenum
pelvic parasympathetic nerves (distal portion of the large intestines)
84
Autonomic stimulation of GIT: Sympathetic
dual effect; sympa alone slightly increases secretion, superimposed on parasympathetic stimulation, decreases secretion (primarily via reduction of blood supply of glands)
85
Stimulation of GIT: Hormonal
GI hormones – polypeptides or polypeptide derivatives
Significant in the release of gastric and pancreatic secretion
86
Source: Gastric antrum (G cells)
Stimulus for secretion: Oligopeptides
Pathway of action: Endocrine
Targets: ECL cells and parietal cells of the gastric corpus
Effects: Stimulation of parietal cells to secrete H+ and ECL cells to secrete histamine
Gastrin
87
Source: Duodenum (I cells)
Stimulus for secretion: Fatty acids, hydrolyzed protein
Pathway of action: Paracrine, endocrine
Targets: Vagal afferent terminals, pancreatic acinar cells
Effects: Inhibition of gastric emptying and H+ secretion; stimulation of pancreatic enzyme secretion, gallbladder contraction, inhibition of food intake
Cholecystokinin
88
Source: Duodenum (S cells)
Stimulus for secretion: Protons
Pathway of action: Paracrine, endocrine
Targets: Vagal afferent terminals, pancreatic duct cell
Effect: Stimulation of pancreatic ductile secretion (H2O and HCO3-)
Secretin
89
```
Source: Intestine (K cells)
Stimulus for secretion: Fatty acids, glucose
Pathway of action: Endocrine
Targets: Beta cells of the pancreas
Effect: Stimulation of insulin secretion
```
Glucoinsulinotropic peptide (GIP)
90
Source: Intestine (L cells)
Stimulus for secretion: Fatty acids, glucose, hydrolyzed protein
Pathway of action: Endocrine, paracrine
Targets: Neurons, smooth muscle
Effects: Inhibition of gastric emptying, pancreatic secretion, gastric acid secretion, intestinal motility, food intake
Peptide YY (PYY)
91
Source: Intestine (L cells)
Stimulus for secretion: Fatty acids, glucose, hydrolyzed protein
Pathway of action: Endocrine, paracrine
Targets: Neurons, epithelial cells
Effects: Glucose homeostasis, epithelial cell proliferation
Proglucagon-derived peptides 1/2 (GLP-1/2)
92
Basic Mechanism of Secretion
- Secretion of Organic Substances
- Water and Electrolyte Secretion
>>Some electrolytes are actively secreted, some are passively secreted along an electrochemical gradient
>>Water follows by osmosis
>>Needed to “wash away” the organic substances through the secretory border of the cells
93
- Lubricant and protectant
- Composed of water, electrolytes, glycoproteins
- Secreted along the entire GIT
Mucus
94
Functions of Mucus
(1) Adhere tightly to food or other particles and to spread as a thin film over the surfaces
(2) Sufficient body that it coats the wall of the gut and prevents actual contact of most food particles with the mucosa
(3) Low resistance for slippage, so the particles can slide along the epithelium with great ease
(4) Causes fecal particles to adhere to one another
(5) Strongly resistant to digestion by the gastrointestinal enzymes
(6) Buffering and neutralizing capacity: glycoproteins, bicarbonate ions
95
Salivary Glands
Major: Parotid, submandibular and sublingual glands
Minor: Buccal glands
96
Location: Anterior to ear
Type of gland: Compound tubuloalveolar gland
Type of secretion: Serous
Parotid
97
Location: Infero-lateral area of oral cavity
Type of gland: Compound tubuloalveolar gland
Type of secretion: Mixed
Submandibular
98
Location: Floor of oral cavity
Type of gland: Compound tubuloalveolar gland
Type of secretion: Mucous
Sublingual
99
Saliva Composition and pH
```
Composition:
Water
Electrolytes: Na, Cl, K, HCO3, Ca, Mg
Protein: Enzymes: Ptyalin (salivary amylase);Lingual Lipase; Lysozymes;
Mucin; Growth factors
```
pH: 6-7
100
Functions of Saliva
- Oral hygiene and protection of oral mucosa
- Lubrication of food
- Initial digestion of protein and fat
- Facilitation of taste
- Mucosal growth
101
- Flow of saliva washes away bacteria and food particles
- Anti-bacterial factors
Thiocyanate ions
Lysozymes – directly kill bacteria, helps thiocyanate ions enter bacteria, digest food particles
- Immunoglobulins (IgA)
Functions of Saliva as Oral Hygiene
102
Saliva contains two major types of protein secretion:
(1) a serous secretion that contains ptyalin (an α-
amylase) , which is an enzyme for digesting starches
(2) mucus secretion that contains mucin for
lubricating and for surface protective purposes
103
Nervous Regulation of Salivary Secretions: PARASYMPATHETIC STIMULATION
- Salivatory nuclei (Superior and Inferior) in the junction of the medulla and pons
- Taste and tactile stimuli (sour, smooth)
- Appetite center (increases salivation in response to smell, taste or thought of food)
- Reflexes from the stomach or small intestine (irritating food, nausea - to dilute or neutralize irritating substance)
104
Nervous Regulation of Salivary Secretions: SYMPATHETIC STIMULATION
- Can slightly increase salivation
- The sympathetic nerves originate from the superior cervical ganglia and travel along the surfaces of the blood vessel walls to the salivary glands.
105
Secondary Regulation of Salivary Secretions
- Dependent blood supply to the glands
- The parasympathetic nerve signals that induce copious salivation also moderately dilate the blood vessels.
- In addition, salivation itself directly dilates the blood vessels, thus providing increased salivatory gland nutrition as needed by the secreting cells.
- Part of this additional vasodilator effect is caused by KALLIKREIN secreted by the activated salivary cells, which in turn acts as an enzyme to split one of the blood proteins, an alpha2-globulin, to form BRADYKININ, a strong vasodilator
106
ESOPHAGUS: Types of glands
1. Simple mucous glands – throughout the body of the esophagus
2. Compound mucous glands- at gastric end and to a lesser extent in the initial portion of the esophagus
107
Functions of Mucus in the Esophagus
1. Provide lubrication for swallowing
| 2. Protection from excoriation by food and from digestion by acid from the stomach during reflux
108
Parts of the Stomach
Gastric glands – body and fundus (80%); secrete HCL, pepsinogen, intrinsic factor and mucus
Pyloric glands – antral portion (20%); secrete mainly MUCUS
109
Cell Types and Substance secreted
1. Mucous neck cells - secrete mainly MUCUS and also BICARBONATE
2. Parietal/Oxyntic Cells - secrete HCL and INTRINSIC FACTOR
3. Peptic/Chief Cells - secrete large quantities of PEPSINOGEN
4. Enterochromaffin-like cell - secrete HISTAMINE (stimulates acid)
5. D cells - secrete SOMATOSTATIN (inhibit acid)
6. G cells - secrete GASTRIN (stimulates acid)
110
Gastric Juice: Composition and pH
```
Composition:
Hydrochloric acid
Pepsinogen
Intrinsic factor
Mucus
Gastrin
```
pH – 0.08 (1-2)
111
Phases of Gastric Secretion
1. Cephalic
2. Gastric
3. Intestinal
112
(Phases of Gastric Secretion)
- Sight, smell, thought, or taste of food
- The greater the appetite, the more intense is the stimulation
- Originates in the cerebral cortex and in the appetite centers of the amygdala and hypothalamus -> dorsal motor nuclei of the vagi -> vagus nerves to the stomach
- 30 % of the gastric secretion
Cephalic Phase
113
(Phases of Gastric Secretion)
- Long vagovagal reflexes from the stomach to the brain and back to the stomach
- Local enteric reflexes
- Gastrin mechanism
* All of these cause secretion of gastric juice during several hours while food remains in the stomach
- 60 % of the total gastric secretion
Gastric Phase
114
(Phases of Gastric Secretion)
- Food in the upper portion of the small intestine, particularly in the duodenum cause stomach secretion of small amounts of gastric juice
- Due to gastrin secreted by duodenal mucosa
- 10 % of the acid response to a meal
Intestinal Phase
115
Regulation of pepsinogen secretion by the peptic cells in the oxyntic glands occurs in response to two main types of signals:
(1) stimulation of the peptic cells by acetylcholine released from the vagus nerves or from the gastric enteric nervous plexus
(2) stimulation of peptic cell secretion in response to acid in the stomach.
116
Inhibition of Gastric Secretion
1. The presence of food in the small intestine initiates a reverse enterogastric reflex
2. The presence of acid, fat, protein breakdown products, hyperosmotic or hypo-osmotic fluids, or any irritating factor in the upper small intestine
117
Production of HCl
1. K+ ions diffuse passively from the parietal cell into the lumen
2. An active transport pump brings K+ ions back into the parietal cell, simultaneously secreting H+ from the cell to the lumen.
3. Cl- ions diffuse passively from the cell to the lumen, and their negative charges balance the positive charges of the secreted H+
4. An exchanger on the opposite face of the parietal cell balances this loss of Cl- by importing Cl- from the blood in exchange for bicarbonate ions (HCO3-)
5. Within the cell, water reacts with CO2 to form carbonate (H2CO3), which dissociates into H+ and HCO3
118
- slightl to moderate effects in inhibiting gastric secretion
GIP, Vasoactive intestinal polypeptide, somatostatin
119
- lies parallel to and beneath the stomach
| - is a large compound gland with most of its internal structure similar to that of the salivary glands
Pancreas
120
__ are secreted by pancreatic acini, and large volumes of sodium bicarbonate solution are secreted by the small ductules and larger ducts leading from the acini.
pancreatic digestive enzymes
121
Pancreatic Juice
- HCO3
- Enzymes – in the form of zymogens or inactive enzymes
- Water
122
Phases of Pancreatic Secretion
1. Cephalic Phase
2. Gastric Phase
3. Intestinal Phase
123
(Phases of Pancreatic Secretion)
- Acetylcholine release by the vagal nerve endings in the pancreas
- Causes moderate amounts of enzymes to be secreted into the pancreatic acini (20% of the total secretion of pancreatic enzymes after a meal)
Cephalic Phase
124
(Phases of Pancreatic Secretion)
- Nervous stimulation of enzyme secretion continues
- Accounts for another 5 to 10 % of pancreatic enzymes secreted after a meal
Gastric phase
125
(Phases of Pancreatic Secretion)
- After chyme leaves the stomach and enters the small intestine, pancreatic secretion becomes copious, mainly in response to the hormone secretin
Intestinal Phase
126
Control of Pancreatic Secretions
- Acetylcholine, which is released from the parasympathetic vagus nerve endings and from other cholinergic nerves in the enteric nervous system
- Cholecystokinin, which is secreted by the duodenal and upper jejunal mucosa when food enters the small intestine
- Secretin, which is also secreted by the duodenal and jejunal mucosa when highly acidic food enters the small intestine
127
PROTEIN: Pancreatic Enzymes and products
Trypsin - Peptides
Chymotrypsin - Peptides
Carboxypolypeptidase - Free amino acids
128
CARBOHYDRATES: Pancreatic Enzymes and products
Pancreatic amylase -> Mostly disaccharides and a few trisaccharides
129
FATS: Pancreatic Enzymes and products
Pancreatic Lipase - Hydrolyzing neutral fat into fatty acids and monoglycerides
Cholesterol esterase - Hydrolysis of cholesterol esters
Phospholipase - Splits fatty acids from phospholipids
130
- prevents activation of trypsin both inside the secretory
cells and in the acini and ducts of the pancreas
- prevents activation of the others as wel
Trypsin Inhibitor
131
Secretion of bicarbonate ions
- HCO3 actively transported out
- Na leaks out
- Water follows by osmosis
132
Functions of Bile
1. Role in fat digestion and absorption
2. Means for excretion of several important waste products from the blood.
- bilirubin, an end product of hemoglobin destruction
excesses of cholesterol
133
Bile acids in the bile do two things in Fat digestion and absorption
1. Help to emulsify the large fat particles of the food into many minute particles
2. Aid in absorption of the digested fat end products through the intestinal mucosal membrane
134
Bile is secreted in two stages by the liver:
(1) The initial portion is secreted by the principal functional
cells of the liver, the hepatocytes; this initial secretion contains large amounts of BILE ACIDS, CHOLESTEROL,
AND OTHER ORGANIC CONSTITUENTS. It is secreted into minute bile canaliculi that originate between the
hepatic cells.
(2) second portion of liver secretion is added to the initial bile. This additional secretion is a WATERY SOLUTION OF SODIUM AND BICARBONATE IONS secreted by secretory epithelial cells that line the ductules and ducts
135
Regulation of Bile Secretion by Secretin
- Adds a second portion of liver secretion in its course through the bile ducts
- Watery solution of sodium and bicarbonate ions secreted by secretory epithelial cells that line the ductules and ducts
- Can increase the total quantity of bile by as much as an additional 100 percent
136
- most potent stimulus for causing gall bladder contraction
Cholecystokinin
137
Storage and Concentration of Bile
- Maximal volume: 30-60 ml
- Can store up to 12 hours worth of bile (450ml)
- Via active transport of Na
- Followed by secondary absorption of Cl, water and other contents
- Usual concentration is 5-fold
- Maximal concentration is 20-fold
138
Enterohepatic Circulation of Bile Salts
About 94 percent of the bile salts are reabsorbed into the blood from the small intestine
- about one half of this by DIFFUSION THROUGH the mucosa in the early portions of the small intestine
- remainder half by an ACTIVE TRANSPORT process through the intestinal mucosa in the distal ileum.
139
- strong stimulating effect of bile acids to cause bile secretion
- also stimulate pancreatic secretion
Secretin
140
- Compound mucous glands located in the wall of the first few centimeters of the duodenum between pylorus and papilla of vater
- Inhibited by sympathetic stimulation
Brunner’s Glands
141
Brunner's Glands secrete large amounts of alkaline mucus in response to
(1) tactile or irritating stimuli on the duodenal mucosa
(2) vagal stimulation
(3) gastrointestinal hormones, especially secretin.
142
- Located over the entire surface of the small intestine
Epithelium:
Goblet cells – secrete mucus
Enterocytes – in crypts, secrete water and electrolytes ; on the villi, reabsorb water and electrolytes ; absorb nutrients
Crypts of Lieberkuhn
143
Digestive Enzymes in the Small Intestine
(1) several peptidases for splitting small peptides into amino acids
(2) four enzymes-sucrase, maltase, isomaltase, and lactase-for splitting disaccharides into monosaccharides
(3) small amounts of intestinal lipase for splitting neutral fats into glycerol and fatty acids
144
Enterocyte Secretion
- Average 1800mL/day
- pH 7.5-8
- Provides a watery vehicle for the absorption of substances from chyme
- Two active secretory processes:
1. Active secretion of Cl
2. Active secretion of HCO3
145
Components of Enteric Juice
- Mucus
- Water
- Electrolytes
146
Regulation of Enteric Juice Secretion
- Local enteric nervous reflexes, especially reflexes initiated by tactile or irritative stimuli from the chyme in the intestines
147
Colonic Secretions
- Also produced by crypts similar to that of the small intestines
- No digestive enzymes; contains NO VILLI
- Principal secretion is mucus by mucous cells
- The amount of fluid within the large intestines is determined by the balance between secretion and absorption for fecal formation
148
Regulation of Colonic Secretions
- Direct, tactile stimulation of the epithelial cells lining the large intestine
- Local nervous reflexes to the mucous cells in the crypts of Lieberkühn
- Stimulation of the pelvic nerves from the spinal cord, which carry parasympathetic innervation to the distal one half to two thirds of the large intestine, also can cause marked increase in mucus secretion
149
General Principles of Digestion
- Chemical vs. Mechanical Digestion
- Mainly by hydrolysis (reverse of formation of complex molecules)
- Partial chemical digestion – mouth, stomach
- Complete chemical digestion – small intestines (Luminal enzymes; Brush border enzymes)
150
Brush Border Enzymes
Peptidases – oligopeptides to free amino acids
Disaccharidases – di- to monosaccharides (Sucrase; Maltase; Isomaltase; Lactase)
Intestinal Lipase – neutral fats into glycerol and free fatty acids
151
Enzymes for Carbohydrate digestion
Ptyalin or Salivary Amylase – oral cavity
Pancreatic Amylase – small intestine
Brush border enzymes – small intestine
152
Brush Border Carbohydrate Hydrolases (enzyme and products)
Sucrase: Glucose, fructose
Isomaltase: Glucose
Glucoamylase: Glucose
Lactase: Glucose, galactose
153
Hydrolysis of Fats
Fat in the diet: Triglycerides
Enzyme: Pancreatic Lipases
Products: Glycerol and free fatty acids
154
Hydrolysis of Proteins
Enzymes: Trypsin, chymotrypsin, carboxypeptidase
Products: Free amino acids
155
- the important peptic enzyme of the stomach
- is most active at a pH of 2.0 to 3.0 and is inactive at a pH above about 5.0.
- for this enzyme to cause digestion of protein, the stomach
juices must be acidic
Pepsin
156
- is converted into elastase, which then digests elastin fibers that partially hold meats together.
Proelastase
157
Sites of absorption
Stomach – alcohol and drugs (aspirin); very minimal
Small intestines – nutrients
Large intestines – water and electrolytes
158
The __ is a poor absorptive area of the gastrointestinal tract because it lacks the typical villus type of absorptive membrane, and also because the junctions between the epithelial cells are tight junctions.
stomach
159
- increase the surface area of the absorptive mucosa about threefold; well developed in the duodenum and jejunum
valvulae conniventes (folds of Kerckring)
160
- lie so close to one another in the upper small intestine that they touch in most areas
- presence of it on the mucosal surface enhances the total absorptive area another 10-fold
villi
161
Absorption of Water
- Transported entirely by diffusion or osmosis
- Lumen to enterocyte (villus) to plasma
- Opposite direction in diarrhea when hyperosmotic solutions are discharged from the stomach into the duodenum
162
Absorption of Sodium
Primary: Active transport via NA+/K+ PUMPS at the basolateral membrane of the epithelial cells; powers and provides the electrochemical gradient needed for the secondary active absorption of glucose and amino acids
Secondary: Sodium channels and co-transport proteins (glucose, amino acids and Na+/H+ exchanger); drag of Cl ions
163
Absorption of Chloride
- Mainly by diffusion; follows electrochemical gradient produced by Na transport
- Via chloride-bicarbonate exchangers in the brush border (ileum)
- Exits through Chloride channels on the basolateral membrane
164
Absorption of Bicarbonate
- Via Active Absorption of Bicarbonate Ions
- In the lumen of the small intestines
- HCO3- + H+ → H2CO3 → CO2 + H2O
- CO2 eventually absorbed in the blood and eliminated via the lungs
165
Absorption of Calcium, Iron, Potassium, Magnesium , Phosphate
- Actively absorbed depending on the needs of the body
| - Monovalent ions more readily absorbed than bivalent ions
166
Absorption of Carbohydrates
- Absorbed mainly as glucose (80%)
| - Galactose and fructose (20%)
167
Absorption of Other Monosaccharides
GLUCOSE: via secondary active transport with sodium (SGLT1) from the lumen going inside the epithelial cell; via facilitated diffusion through the basolateral membrane and into the paracellular space (GLUT2)
GALACTOSE: Exactly the same as glucose
FRUCTOSE: Via facilitated diffusion only (GLUT5); phosphorylated and transported as glucose across the basolateral membrane (GLUT2); rate of transport is half that of glucose and galactose
168
Absorption of Proteins
- Absorbed as free amino acids, dipeptides and tripeptides
- Mostly via SECONDARY ACTIVE TRANSPORT WITH SODIUM
- Some via FACILITATED DIFFUSION through specific transport proteins
- PepT1 is a transporter of oligopeptides; symporter with H+
169
Absorption of Fats
- Absorbed mainly as monoglycerides and free fatty acids
- Transported mainly by diffusion via micelles
- Enter the cell’s smooth ER and synthesized as triglycerides (TGs)
- The new TGs enter the lacteal as chylomicrons
- Some short- and medium- chain fatty acids are absorbed directly into the portal blood.
170
Functions of Bile Salts
Primary: Help in the absorption of fatty acids, monoglycerides, cholesterol and other lipids from the intestinal tract
Secondary: Detergent/emulsifying action on the fat particles in the food -> decreases the surface tension of the particles and allows agitation in the intestinal tract to break the fat globules into minute sizes
171
Absorption in the colon:
Absorbing colon = proximal half
| Storage colon = distal half
172
Absorption in the colon: Formation of Feces
Volume of chyme entering the large intestines: 1500mL
Volume of water excreted in feces: 100mL
Concentration of ions excreted in feces: 1-5mEqs/L ( Na, Cl)
Maximum absorptive capacity of large intestines: 5-8L/day
173
Absorption of Ions in the Colon
In the colon, Na+ and Cl- ions are actively absorbed.
174
Three driving forces for osmotic movement of water (fluid absorption) in the large intestines:
1. Electroneutral NaCl absorption stimulated by various growth factors
2. Absorption of short-chain fatty acids (acetate, butyrate, propionate) via sodium-monocarboxylate transporters (SMCTs)
3. Absorption of Na+ via Na channel ENaC
175
- Capable of digesting small amounts of cellulose
| - Produce vitamin K, vitamin B12, thiamine, riboflavin, and various gases
Colonic Microflora
176
Where is the swallowing center found?
Medulla
177
What happens to the soft palate and uvula during swallowing?
Rises up to close posterior nares
178
What happens to the glottis during swallowing?
Closes to prevent aspiration
179
Paralysis of Swallowing: CAUSES
- Damaged CN V, IX, X
- Damaged swallowing center (Encephalitis, Poliomyelitis)
- Paralyzed swallowing muscles (Muscle Dystrophy, MG, Botulism)
- Deep anesthesia ->may lead to aspiration
180
4 Basic Layers of the GI Tract?
Mucosa
Submucosa
Muscularis
Serosa
181
Differentiate between Myenteric vs Submucosal Plexus
Myenteric: Auerbach’s Plexus, for motility, between inner circular and outer longitudinal muscle layers
Submucosal: Meissner’s Plexus, for secretion, at the Submucosal layer
182
- Damage to the Myenteric plexus of the lower 2/3 of the esophagus
- Lost of receptive relaxation
- May lead to Megaesophagus -> infection -> ulceration -> rupture -> death
- Dx: Bird’s Beak Appearance
- Tx: Heller’s Myotomy with fundoplication
Achalasia
183
- Inflammation of the stomach lining
- Range from superficial to severe excoriation (ulcers)
- Certain Substances may damage gastric barrier (mucosa + tight junctions between cells), e.g. Aspirin, NSAIDs, Alcohol, Smoking
Gastritis
184
Types of Gastritis
Type A Gastritis: Autoimmune
Achlorhydia
Pernicious Anemia
Type B Gastritis: Bacteria-associated (H. pylori)
185
Differentiate Brunner’s Gland from Peyer’s Patches
Brunner’s Gland: submucosa of the duodenum, secretes bicarbonate (alkaline)
Peyer’s Patches: lamina propia of the mucosa of the ileum, secretes IgA
186
Source: S Cells, Duodenum
Stimulus: Acid entering duodenum
Stomach motility and secretion: Inhibits
Pancreas: stimulates Fluid Secretion (HCO3-)
Secretin
187
Source: I Cells, Duodenum
Stimulus: Fat and amino acids entering duodenum
Stomach Motility and Secretion: Inhibits Emptying
Pancreas: Stimulates enzyme secretion
Gallbladder: GB contraction and Sphincter of Oddi relaxation
CholeCystoKinin (CCK)
188
Source: G Cells, Stomach Antrum,
Stimulus: Stomach distention, GRP; stomach acid inhibits
Stomach Motility and Secretion: Stimulates
Gastrin
189
Source: K Cells, Duodenum
Stimulus: Fat, CHO, amino acids
Stomach Motility and Secretion: Inhibits (only above normal physiologic levels)
Glucose-dependent Insulinotropic Peptide
190
Source: Upper duodenum
Stimulus: Fasting
Stomach Motility and Secretion: Stimulates
Motilin
191
- Excoriated mucosa of the stomach and intestines
| - Imbalance between gastric acid-pepsin secretion and protective mechanisms of stomach and intestines
Peptic Ulcer Disease (PUD)
192
Protective Mechanisms in GIT to prevent Peptic Ulcer Disease
- Gastric barrier
- Alkaline secretions in the duodenum by pancreatic juice and Brunner’s Glands
- Feedback mechanism for gastric acid secretion
- Secretin secretion
193
- is a common accompaniment of gastric atrophy and achlorhydria. Normal gastric secretions contain a glycoprotein called intrinsic factor, secreted by the same parietal cells that secrete hydrochloric acid.
- In the absence of intrinsic factor, only about 1/50 of the vitamin B12 is absorbed. And, without intrinsic factor, an adequate amount of vitamin B12 is not made available from the foods to cause young, newly forming red blood cells to mature in the bone marrow. The result is __.
Pernicious anemia
194
What are the two divisions of the pancreas?
Exocrine Pancreas: Proteases, Amylases, Lipases, Bicarbonate
| Endocrine Pancreas: Insulin, Glucagon, Somatostatin
195
Pancreatic juice will eventually drain into which structure?
Ampulla of Vater
196
- Inflammation of the pancreas
- Maybe acute or chronic
- Other causes: trauma, scorpion bites, etc.
- Amount of trypsinogen overwhelms trypsin levels, activating other proteases in a vicious cycle (autodigestion)
- Serum amylase, lipase levels increase
- SSx: epigatric pain radiating to the back, Cullen’s Sign, Grey-Turner’s Sign
- Tx: Meperidine, Supportive
Pancreatitis
197
The most common cause of pancreatitis is __, and the second most common cause is __
drinking excess alcohol; blockage of the papilla of Vater by a gallstone
198
In what forms are carbohydrates, proteins and fat absorbed?
Monosaccharides, amino acids/di or tri-peptides, micelles
199
Several diseases can cause decreased absorption by the mucosa; they are often classified together under the general term __
sprue
200
- Due to deficient Lactase especially in adult Asians (Due to non-milk drinking habits of adult Asians)
- Decreased Lactase ->bdecreased breakdown of Lactose by small intestines -> Lactose metabolized by intestinal bacteria -> Acids released as metabolic waste products by bacteria -> osmotic diarrhea
Lactose Intolerance
201
- Susceptibility to Gluten (found in wheat and rye)
- Causes blunting of microvilli of villi -> malabsorption of nutrients
- Tx: remove gluten from diet
Non-Tropical (Gluten Enteropathy/Celiac Sprue)
202
- Due to unknown infectious agent
- Found in the Tropics
- Also with blunted microvilli
- Tx: antibiotics (e.g. Doxycycline)
Tropical Sprue
203
Signs and Symptoms of Sprue
Steatorrhea (non-absorption of fats)
Wasting (decreased carbohydrates, proteins)
Inadequate blood coagulation (decreased Vit K)
Megaloblastic anemia (decreased Vit B12 and folic Acid)
204
Differentiate Bolus, Chyme and Feces
Bolus: from mouth to stomach
Chyme: in the small intestines
Feces: in the large intestines
205
Main site for the absorption of carbohydrates, proteins and fats?
Jejunum
206
Main site for absorption of water?
Jejunum
207
- Slow movement of feces in the large intestines
- it is often associated with large quantities of dry, hard feces in the descending colon that accumulate because of overabsorption of fluid.
- Infants rarely affected (but must learn to control defecation)
Constipation
208
- One of the many causes of constipation
- Basically Achalasia of the Large Intestines
- Can lead to Megacolon
Hirschprung Disease
209
- Rapid movement of feces in large intestines
- Many types (e.g. infectious, osmotic, psychogenic)
- Infectious diarrhea: helps clear GI tract of offending agent
- Cholera: can lead to severe dehydration and death
Diarrhea
210
- means inflammation usually caused either by a virus or by bacteria in the intestinal tract. In usual infectious diarrhea, the infection is most extensive in the large intestine and the distal end of the ileum.
- Everywhere the infection is present, the mucosa becomes irritated and its rate of secretion becomes greatly enhanced. In addition, motility of the intestinal wall usually increases manifold.
Enteritis
211
- diarrhea that accompanies periods of nervous tension, such as during examination time or when a soldier is about to go into battle
- is caused by excessive stimulation of the parasympathetic nervous system, which greatly excites both (1) motility and (2) excess secretion of mucus in the distal colon.
psychogenic emotional diarrhea
212
- is a disease in which extensive areas of the walls of the large intestine become inflamed and ulcerated
- The motility of the ulcerated colon is often so great that mass movements occur much of the day rather than for the usual 10 to 30 minutes
- Also, the colon's secretions are greatly enhanced
- > repeated diarrheal bowel movements.
Ulcerative colitis
213
- upper gastrointestinal tract rids itself of its contents when almost any part of the upper tract becomes excessively irritated, overdistended, or even overexcitable.
- Excessive distention or irritation of the duodenum provides an especially strong stimulus for __
- Preceded by nausea and anti-peristalsis
- Can also happen when Chemoreceptor Trigger Zone (floor of 4th ventricle) is stimulated
- Stimulated by morphine, digitalis, motion sickness
Vomiting
214
GI Obstruction: SSx depends on site of obstruction
Pylorus: vomiting of gastric contents, metabolic alkalosis
Small intestines: severe dehydration, possibly no acid-base abnormality (equal acids and antiacids vomited)
Large intestines: feces accumulation, no vomiting at the start, may lead to rupture
215
- GI Gases
- Derived from
Swallowed air (nitrogen, oxygen)
Gut bacteria (methane, carbon dioxide, hydrogen)
Diffusion of gases from blood to GI tract
- Certain food increase __ from anus
beans, cabbage, onion, cauliflower, corn, and certain irritant foods such as vinegar
Reason: may serve as suitable medium for bacteria
Flatus
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