Gastrointestinal Physiology (GI) Flashcards
1
Q
Functions of the Gastrointestinal Tract (GIT)
A
-Transfers digested organic nutrients, minerals and water from the external environment to the internal environment.
-Digestion
-Absorption
-Excretion
-Host defense
2
Q
Digestion
A
Form absorbable molecules from food through GIT motility, pH changes, and biologic detergents and enzymes (enzymes are predominantly produced by the pancreas)
3
Q
Absorption
A
Movement of digestive food from the intestine into the blood or the lymphatic system.
4
Q
Excretion
A
Non-absorbable components of food (such as fiber), bacteria, intestinal cells, and hydrophobic molecules (drugs), cholesterol and steroids are excreted.
5
Q
How does the GIT function as a host defense?
A
- Lumen of the GIT is considered to be outside the body. It is continuous with the exterior of the body.
- The GIT forms a barrier with the outside environment and contains a highly developed immune system. The GIT can can inactivate harmful bacteria or other microorganisms.
6
Q
What are the components of the GIT
A
Mouth, pharynx, esophagus, the stomach, the small intestine (duodenum, jejunum, ileum), large intestine
7
Q
3 Accessory organs of the GIT
A
pancreas, liver, gallbladder
8
Q
Describe the structure of the GIT
A
- GIT is a long muscular tube stretching from the mouth to the anus. Composition is similar from mid-esophagus to anus. The top third of the human esophagus is made of skeletal muscle, while the rest of the GIT is composed of smooth muscle.
- Tube of the intestine
- Lumen- inside of the tube; contains many folds and processes to increase the surface area; circular folds in on itself
The circular fold contains villi which projects into the lumen of the tube, and below the surface is a crypt or an invagination.
9
Q
Layers of the GIT
A
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
10
Q
Mucosa
A
This is the predominant layer of the GIT
Contains three different subsections:
- Epithelium- very thin layer of cells
- Lamina propria
- Muscularis mucosa- very thin, smooth muscle layer
11
Q
Muscularis externa
A
outer muscular layer
12
Q
Serosal layer
A
connective tissue layer
13
Q
Epithelium
A
- layer of mucosa
- layer of cells that lines all body cavities and surfaces
- epithelial cells are polarized cells: they have basolateral surface and an apical surface.
14
Q
Apical surface
A
inserts the inside of the tube or the lumen of the tube
15
Q
Basolateral surface
A
closest to the blood surface, facing away from the tube; basal surface and lateral surface.
16
Q
The polarized epithelial layer has different transport proteins at the _______ surface compared to the _______ surface allowing broken down nutrients to be transported first into the cell and then across the surface to the blood.
A
apical, basolateral
17
Q
Transport proteins are confined to the different cell surfaces due to presence of ___________.
A
tight junctions.
18
Q
Functions of the epithelial layer (single layers) of Mucosa
A
- selective uptake of nutrients, electrolytes, and water.
- prevent the passage of harmful substances.
19
Q
Surface area of epithelial layer is amplified by the presence of ______ and ______.
A
villi and crypts
20
Q
Villus (Villi)
A
contains a single layer of epithelial cells containing microvilli
21
Q
Crypt
A
a region which invaginates into the lamina propria
22
Q
Stem cells
A
- Stem cells within the crypts divide and produce daughter cells which differentiate into a variety of cells.
- Stem cells divide and migrate up the villus. At the top of the villus, they reach the end of their life and slough off.
23
Q
In the small intestine, the epithelial cell layer is replaced every ___ days.
As these cells are dividing rapidly, they are affected by anticancer drugs and are killed by the drugs before they can be replaced.
A
5
24
Q
Epithelial layer is selective, allowing specific nutrients across the intestinal epithelium and into the body.
2 Pathways that chemicals or molecules can use to get across an epithelial layer:
A
- Paracellular pathway
- Transcellular pathway
25
Paracellular pathway
chemicals move between cells across the cell junctions; limited by tight junctions between cells, so only water and small ions can actually diffuse through the tight junctions; not many substances can get through this way in a healthy intestine.
26
Transcellular pathway
cross the cell and therefore require transport proteins
27
Lamina propria
layer of the mucosa
- includes everything above the muscle layer
- connective tissue, blood vessels, nerve fibers, and lymphatic vessels, immune and inflammatory cells for immune protection.
Lacteal or lymphatic vessel
28
Muscularis mucosa
layer of the mucosa
- thin layer of smooth muscle.
- not involved in contraction of the GIT and may function in moving the villi.
29
Submucosa
- located beneath the mucosa layer.
- contains blood vessels, lymphatic vessels, submucosal nerve plexus (network of nerves), connective tissue
30
Submucosal nerve plexus
network of nerves
relays information to and away from the mucosa.
31
Muscularis externa
- Composed of circular muscle, myenteric nerve plexus, longitudinal muscle
32
Circular muscle
- part of the muscularis externa
- fibers are oriented in a circular pattern and contract and relax to close and open the tube.
33
Myenteric nerve plexus
myo= muscle
-located below the circular muscle
- regulate the muscle function of the GIT
34
Longitudinal muscle
lengthens and shortens to control the length of the tube (does not change the diameter)
located below the myenteric plexus
35
Serosa layer (serosa)
a connective tissue layer that encases the intestine and forms connections with the intestine and the abdominal wall.
36
Blood supply to the GIT
- GIT blood supply carries away many nutrients as well as other components absorbed from the diet.
- Blood supply transports water-soluble nutrients and other molecules.
37
Lacteals (lymphatic system; lamina propria in the mucosa layer)
are important for fat absorption
38
How does food move through the GIT
Food -> digested in the stomach -> absorption and secretion in the small intestine -> processing in the colon -> elimination of feces containing ingested material that cannot be digested and absorbed.
39
What type of blood enters the GIT
highly oxygenated blood.
This blood then loses oxygen as it perfuses the intestine
40
Blood doe snot flow directly from GIT back to the heart. Blood is taken to the _____ before returning to the heart.
liver
41
Blood that perfuses the intestine goes to the liver via the _______ ______.
portal vein
42
Portal circulation
- circulation that carries the blood from the intestinal tract to the liver.
- blood in the portal circulation is nutrient rich.
important for:
- liver removes harmful substances (liver acts as a filter and has many enzymes)
- processing of nutrients
43
Other organs in the body are perfused by arterial blood (fully oxygenated) but ______ is an exception.
liver
44
When you have not been eating, ~____% of the blood in the liver is from an arterial source (ie. fully oxygenated). After eating, this is reduced to ____%
30%, 10%
45
Hepatic artery
- part of the portal circulation
- contains fully oxygenated blood that perfuses the liver
46
Hepatic portal vein
- part of the portal circulation
- carries blood to the liver that has already perfused the stomach, pancreas, SI and LI.
These two blood supplies mix, so that the liver is perfused with nutrient-rich blood coming from the GIT organs with a poor oxygen content.
47
"In Series" versus "In Parallel" Circulation
- Most organs are perfused in parallel within the systemic circulation, but the liver is perfused in series as the liver is perfused predominantly by blood that has already perfused another organ; blood flows from the digestive organs to the liver.
The venous supply is referred to as "in series"
48
The liver receives _____(more/less) oxygen than most organs but ______(more/less) nutrient-rich blood.
less, more
49
GI processes include ______ and _______, or the movement of the GI tract.
secretion and motility
50
GI process are governed by
the volume and composition of what is inside the intestinal tract
51
Reflexes regulating GI processes are initiated by:
1. Distension of the GIT wall by the volume of luminal contents.
2. Osmolarity of the contents
3. pH of the contents
4. The concentrations of the specific digestion contents, such as monosaccharides, fatty acids, peptides and amino acids.
The digestion contents initiate different regulatory pathways
52
Distention of the wall, osmolarity, pH of the contents and the concentration of specific digestion contents initiates reflexes by acting through various receptors located in the wall of the tract.
What are these receptors?
1. Mechanoreceptors- activated by mechanical stimuli (pressure and stretch)
2. Osmoreceptors- activated by a change in osmolarity
3. Chemoreceptors- activated by specific chemicals
53
Function of intrinsic neural regulation of GI Processes
To control motility and secretion
54
What does intrinsic mean?
contained wholly within the organ
55
Intrinsic neural regulation occurs through
- occurs through nerve plexi located in the GIT wall itself.
56
Branching networks of intersecting nerves
Nerve plexi
57
Enteric nervous system
- Intrinsic nerve regulation
- controls the activity of the secretomotor neurons which play a role in secretion and motility
- contained completely within the walls of the GIT
- has large number of neurons: "Brain of the gut"
- Can function independently of the CNS
- critical for involuntary functions (allows us to digest our food without having to think about it)
58
Two main nerve networks of the enteric nervous system
1. Myenteric plexus
2. Submucosal plexus
59
Myenteric plexus
- nerve network of the enteric nervous system
- found between the two muscle layers, the circular muscle and the longitudinal muscle, of the muscularis externa
- responsible for influencing and regulating the smooth muscle
60
Submucosal plexus
- nerve network of the enteric nervous system
- found in the submucosa
- predominantly influences secretion
61
Nerves extend from the _______ _______ to the _______ to control secretion.
submucosal plexus, mucosa
62
Why is communication important between myenteric plexus and submucosal plexus?
Communication occurs between the two layers so that motility and secretion of digestive enzymes work together.
The neural activity in one plexus influences the activity in the other.
63
Extrinsic Neuronal Regulation of GI Processes
- Extrinsic regulation occurs through the autonomic nervous system (ANS) - parasympathetic and sympathetic
- Nerve fibers from the parasympathetic and sympathetic pathways enter the intestinal tract and synapse with neurons in both plexuses.
- Through the ANS, the CNS can influence motility and secretion.
64
Examples on how through the ANS, CNS can influence motility and secretion
- smell of food sends signals through your brain to the GIT through the ANS
- different emotional states in the brain (CNS) will influence appetite.
65
Parasympathetic pathway
- "Rest and digest" response
- stimulates the flow of a large volume of watery saliva
- stimulates peristalsis (muscle contraction)
- stimulates secretion
- stimulates bile release from the liver - important for fat digestion.
66
Sympathetic pathway
- "Fright, flight, fight" response
- stimulates the small volume of a thick saliva
- inhibits peristalsis
- inhibits secretion within the GI tract
67
Long reflex
extrinsic pathway
68
Short reflex
intrinsic pathway
69
Why does the long and short reflex pathway coordinate?
To modify the motility and secretion of the GIT
70
what happens after eating a meal?
1. Eating a meal activates receptors in GIT wall (mechanoreceptors, osmoreceptors, chemoreceptors).
2. Stimulus from the receptors feeds into the nerve plexus and stimulates the smooth muscle to contract or a gland to secrete.
3. This causes a response in the GIT (ie. contraction of the muscle which breaks down the food)
71
What happens next after smell of food when hungry/emotional state?
1. Smell of food when hungry/emotional state
2. Stimulates the CNS
3. Efferent autonomic neurons fire and interact with the same nerve plexus
4. Stimulates the smooth muscle to contract or a gland to secrete
5. Causes a response in the GIT (ie. contraction of the muscle which breaks down the food)
- Stimulation of CNS causes the same response but response is due to a CNS stimulation
72
TRUE or FALSE
Responses in the GIT can occur without any input from the CNS
TRUE
73
Receptors are activated in response to different stimuli causing the release of ________ _________.
chemical messengers
74
What are the 4 categories of chemical messenger regulation?
1. Endocrine
2. Neurocrine
3. Paracrine
4. Autocrine
75
Endocrine regulation
a hormone secreting gland cell releases a hormone across its basolateral surface into the blood; the hormone enters the blood and travels to its target cells in one or more distant places in the body.
76
Neurocrine regulation
a nerve cell produces an electrical signal resulting in the release of a neurotransmitter which travels across a synapse and acts on a post-synaptic target cell (either a neuron or an effector cell)
77
Paracrine regulation
a local cell releases a paracrine substance which diffuses through the interstitial fluid to act on target cells in close proximity to the site of release of the paracrine substance; this would occur across the apical surface of the cell into the lumen of the gland.
78
Autocrine regulation
a local cell releases a substance which acts on the cell that released it.
79
Endocrine cells
- produce hormones
- found in the epithelium of the stomach and the small intestine
80
These cells release hormones which control GI functions.
Hormones released across the opposite surface of the cell into blood vessels in the lamina propria.
Enteroendocrine cells
81
what are the 3 GI hormones
- Secretin
- Cholecystokinin (CCK)
- Gastrin
82
Facts about the 3 GI hormones
- they are all peptide hormones
- each hormone participates in a feedback control system
- most of these hormones affect more than one type of target cell
83
Cholecystokinin (CCK)
- release is stimulated by the presence of fatty acids and amino acids in the small intestine
- released into blood
- stimulates the pancreas to increase digestive enzyme secretion and causes contraction of the gallbladder
84
What happens due to contraction of gallbladder?
Releases bile acids for fat breakdown
85
What stops the release of CCK?
Absorption of fats and amino acids
(Negative feedback control system)
86
Stimulated by the contraction and relaxation of the two muscle layers in the outer portion of the GIT ; causes contents to move along tract.
Intestinal motility
87
Peristalsis
- the main driving force for food moving through the intestinal tract; propulsion
- circular muscle contracts on the oral side of a bolus of food (longitudinal layer relaxes)
- circular muscle contracted moved toward the anus, propelling the contents of the lumen in that direction, as the ring moves, the circular muscle on the other side of the distended area reflexes (longitudinal muscle contracts), facilitating smooth passage of the bolus.
88
Segmentation
- important for the mixing of food
- involves contraction and relaxation of intestinal segments with very little net movement of the food towards the large intestine
- mostly occurs in the small intestine
89
Functions of segmentation
- allows the mixing of the contents of the GIT with digestive enzymes
- slows the transit time to allow for the absorption of nutrients and water
90
Pacemaker cells
- cells in the GIT that are distributed throughout the smooth muscle cells
- constantly under spontaneous depolarization-repolarization cycles called slow waves
91
Slow waves
- give the GIT the basic electrical rhythm
- propagated through the circular and longitudinal muscle layers through gap junctions
92
What happens every time the pacemaker cells undergo spontaneous depolarization-repolarization cycles?
If there is a stimulus, there is the potential for action potential generation and muscle contraction
93
What happens to the slow waves in the absence of any neural or hormonal input?
the spontaneous slow waves do not result in any contraction
94
What happens to slow waves when there is stimulation such as excitatory hormone or neurotransmitter?
Further depolarization occurs and the membrane potential is increased enough that threshold is reached and an action potential is generated resulting in muscle contraction.
95
What happens to slow waves at rest?
At rest, period fluctuations drift up and down due to regular variations in ion flux across the membrane
96
What happens to slow waves when there is an excitatory input?
the slow waves are depolarized above threshold, and an action potential occurs leading to smooth muscle contraction.
97
In the basic electrical rhythm, the number of an action potential is proportional to what?
To the force of the contraction
98
The frequency of the contraction is dictated by the ____________ and the force of contraction is mediated by _______ and _______ input.
basic electrical rhythm
neuronal and hormonal
99
If you have no action potentials, will you still have depolarization and repolarization?
YEs, you still have this flow of depolarization and repolarization or the slow waves.
100
Neural and hormonal control of the gastrointestinal system is divisible into 3 phases:
and is classified based on where the stimuli initiates the reflex, or where the stimulus is perceived
1. Cephalic (head)
2. Gastric (stomach)
3. Intestinal
101
Cephalic phase: head
- this phase is initiated through stimulation of receptors in the head by the sight, smell, taste and chewing of food and the emotional state
- these reflexes are predominantly regulated by parasympathetic fibers that activate neurons in the GIT nerve plexuses
102
Gastric phase: stomach
- receptor sin the stomach are stimulated by distension, or stretching of the stomach, acidity, amino acids, and peptides
- the responses to these stimuli are mediated by both short and long neural reflexes
Gastrin (hormone) represents the short reflex
Acetylcholine represents the long neural reflex
103
Intestinal phase: intestine
- receptors in the intestine are stimulated by distension, acidity, osmolarity and digestive products
- the intestinal phase is mediated by short and long neural reflexes and by the hormones secretin, CCK, and GIP, which are all secreted by endocrine cells in the small intestine
104
Role of Hypothalamus in control of food intake
- important for maintaining homeostasis, command center for neural and endocrine control coordination and for control of behavior
- contains a feeding center in the lateral region
- contains a satiety center in the ventromedial region
105
Hypothalamus contains a feeding center in the lateral region. What happens when this region is activated?
What happens to animals with lesions in this region?
Activation of this region increases hunger
Animals with lesions in this region become anorectic and lose weight
106
Hypothalamus contains a satiety center in the ventromedial region. What happens when this region is activated?
What happens to animals with lesions in this region?
Activation of this region makes you feel full
Animals with lesions in this area overeat and become obese
107
Factors that influence food intake
- Orexigenic factors
- Anorexigenic factors
108
Orexigenic factors
- increase intake
- Neuropeptide Y and Ghrelin
109
Neuropeptide Y
neuropeptide in the hypothalamus that stimulates hunger or appetite
110
Ghrelin
synthesized and released form the endocrine cells in the stomach during fasting; when you start to starve.
- released into the blood and travels to the hypothalamus stimulating the release of neuropeptide Y in the hypothalamus feeding center to try and increase food intake
111
Anorexigenic factors
- decrease intake or cause a loss of appetite
- Leptin, Insulin, Peptide YY, Melanocortin
112
Leptin
anorexigenic factor produced by adipose or fat tissue
113
Insulin
anorexigenic factor produced by the pancreas; stimulates a reduction in food intake
114
Peptide YY
anorexigenic factor released form the intestine to reduce food intake
115
Melanocortin
anorexigenic factor released directly form the hypothalamus and acts to reduce intake of food
116
How does Leptin affect food intake
(steps)
1. Take in more energy/ eat more than burned during exercise
2. Deposit fat in tissues
3. Increased secretion of leptin from the adipose tissue
4. Plasma leptin concentrations increase
5. Leptin travels to the hypothalamus through the blood altering the activity of the integrating center in the hypothalamus
6. Leptin inhibits neuropeptide Y release (neuropeptide stimulates eating)
7. Results in a decrease in appetite and reduced energy intake and an increase in the metabolic rate
117
what happens in lack of leptin?
Lack of leptin results in no appetite regulation, overeating, and obesity
118
Hypothalamus, which contains a thirst center, is stimulated by:
1. Increased plasma osmolarity (most important factor)
2. Decreased plasma volume
3. A dry mouth and throat stimulates thirst
4. Prevention of over-hydration
119
How does increased plasma osmolarity regulate water intake?
Increased plasma osmolarity stimulates osmoreceptors (sensory receptors in the thirst center of the hypothalamus
Increased osmolarity of the blood stimulates thirst and the release of a hormone called vasopressin or anti-diuretic hormone resulting in conservation of water at the kidney.
120
How does decreased plasma volume regulate water intake?
- Pathophysiological conditions (large blood loss or diarrhea and vomiting) which cause dehydration and reduce plasma volume
- As significant decrease in blood volume will reduce blood pressure and stimulate arterial baroreceptors which will act to alter sympathetic and parasympathetic outflow to increase arterial pressure towards normal levels
- affect intrarenal baroreceptors within the kidneys
121
How does a decreased in plasma volume affect intrarenal baroreceptors within the kidney and eventually increase Angiotensin II
- Juxtaglomerular cells located in the walls of the afferent arterioles act as pressure receptors
- When blood pressure in the kidney decreases, baroreceptors in the kidney afferent arteries are stimulated and activate the renin-angiotensin system
- Activation of the renin-angiotensin system produces angiotensin II, which has a direct effect on the hypothalamus to increase thirst; studied in experimental animals, but its occurrence in humans has not been proven
122
Why does prevention of over-hydration occurs?
Occurs so that a person stops drinking well before water is absorbed by the GIT and has had a chance to affect baroreceptors and osmoreceptors in the body
Mediated by stimulus from the mouth, throat, and the GIT
123
Most important factor which regulates thirst under physiological conditions
Osmolarity
124
What are the three main pairs of salivary glands?
Parotid - watery (serous) secretion
Submandibular - serous/mucous secretion
Sublingual - mucous secretion
125
Saliva is hypotonic, and slightly alkaline. What is it composed of?
1. water
2. electrolytes- potassium and bicarbonate (gives alkaline nature); poor in sodium and chloride
3. digestive enzymes - amylase (breaks down starches into disaccharides and trisaccharides); lipase (breaks down fat into fatty acids)
4. glycoproteins, such as mucin
5. antimicrobial factors - lysozyme (breaks down the bacterial cell wall) lactoferrin (chelates iron which prevents the multiplication of bacteria as iron is required for bacterial growth)
126
Mucin mixed water is called
mucus
127
Functions of saliva
- Moistens and lubricates the food to make it easier to swallow
- Initiates digestion with digestive enzymes (amylase and lipase)
- Dissolves a small amount of food to allow it to diffuse to the taste buds
- Prevents microbial colonization due to the presence of antibacterial factors
- Aids in speech
- Buffers- contains bicarbonate which helps to neutralize acid from food or acid reflux
128
Structure of a salivary gland or a salivary duct
- salivary glands are made up of many microscopic ducts that branch out from grossly visible ducts
- composed of 3 different cell types: acinar cells, ductal cells, myoepithelial cells
- saliva moves from the acinus to the striated duct; myoepithelial cells contract to constrict the acinus end of the duct and move the components of the saliva towards the striated duct
129
Acinar cells
secrete the initial saliva
130
Ductal cells
create the alkaline and hypotonic nature of saliva
131
Myoepithelial cells
have characteristics of both smooth muscle (can contract) and epithelial cells
132
Acinar cells have tight junctions. What does this do?
Acinar cells have tight junctions between them which are leaky and allow the passage of water and small ions through them
133
Ductal cells have tight junctions. What does this do?
Ductal cells have tight junctions which do not allow the passage of water through
134
All of the components of saliva are pumped into, or passed into, the lumen of the ______
acinus
135
The primary secretion of saliva is from the acinar cells is not yet alkaline or hypotonic; it is _______ (has a similar osmolarity to the blood)
isotonic
136
The primary secretion of saliva will contain:
sodium, potassium, chloride, bicarbonate, and water
137
Enzymes, as well as mucous, are produced within the acinar cells and added to the saliva through _________
exocytosis
138
Acinar cells have very leaky tight junctions; electrolytes in the primary secretion (bicarbonate, chloride and potassium) are actively secreted into the saliva and sodium and water can follow between the cells into the saliva through the ___________
leaky tight junctions
139
Paracellular transport
movement of substances between cells
140
Why is the primary secretion of saliva isotonic?
There is no limitation to the passage of sodium and water through the leaky tight junctions
141
Steps in the formation of saliva
1. Acinar cells secrete the initial saliva 9water, electrolytes, and proteins)
- proteins are released by exocytosis
- chloride, bicarbonate, and potassium are actively secreted
- sodium and water follow paracellularly via leaky tight junctions
2. Initial secretion is isotonic due to the leakiness of acinar cell layer
3. Myoepithelial cells contract and expel formed saliva from acinus into the duct
4. Ductal cells modify the initial saliva to a hypotonic, alkaline state
- Net loss of sodium and chloride (active reabsorption)
- addition of potassium and bicarbonate (active secretion); topo a lesser extent
- duct cells are tightly joined and impermeable to H2O
142
What are the two pathways involved in regulation of salivary gland function?
1. Parasympathetic pathways
2. Sympathetic pathways
143
Parasympathetic pathway in regulation of salivary gland function
- stimulated by the smell and taste of food, by pressure receptors in the mouth and during situations of nausea
- can be inhibited and reduce salivary production by tiredness or fatigue, during sleep, fear, dehydration
- some drugs have a dry mouth side effect (psychiatric drugs have anticholinergic effects and reduce parasympathetic stimulation of the salivary glands)
144
Sympathetic pathway in regulation of salivary gland function
- stimulatory but is minor
- increases saliva flow
- increase protein secretion from the acinar cells and stimulate the myoepithelial cells to contract to increase flow
145
Amylase/ Ptyalin
- found in saliva
- an enzyme that can breakdown starches
- inhibited by the acidic pH in the stomach once swallowed
- greater than 95% of carbohydrates consumed are digested in the small intestine by pancreatic amylase
146
Plant starch is made up of glucose polymers including ______ and ________.
amylose and amylopectin
147
Polymer
a large molecule made up of many repeated subunits
148
Amylose
a straight chain of glucose molecules with alpha-1,4 linkages
149
Amylopectin
chain of glucose molecules with alpha-1,4 linkages as well as alpha-1,6 linkages
150
This enzyme can only cleave the internal alpha-1,4 linkages
Amylase
151
Breakdown of amylose leads to the formation of _________ (disaccharide) and _________ (trisaccharide)
maltose, maltotriose
152
Breakdown of amylopectin leads to the formation of ________, _________, and ________
maltose, maltotriose, and alpha-limit dextrin
153
Amylase can only cleave the ________ linkages; it cannot cleave the _______ linkages so it generates these branched glucose molecules in alpha-limit dextrin
alpha-1,4
alpha-1,6
154
Lingual lipase
- found in saliva
- stable in acid and therefore can remain active in the stomach
155
Amylase and lingual lipase are minor pathways for digestion.
These two are important for:
1. Pathological conditions- where there is reduced pancreatic activity
- pancreatic secretions include digestive enzymes
2. Important for neonates as they tend to have immature digestive enzymes
156
Xerostomia
dry mouth
157
What are the conditions where salivary secretion is impaired? (4)
- Congenital
- Sjögren syndrome- autoimmune disease; the immune system destroys the salivary glands
- Side effects of drugs- antidepressants, psychotropic, antihypertensives, anticancer drugs
- Radiation treatment
158
What are the consequences of impairment to salivary secretion? (3)
1. dry mouth
2. decreased oral pH
- increased susceptibility to tooth decay
- esophageal erosions as there is no saliva to neutralize the stomach acid that is coming up into the esophagus
3. Difficulty in lubricating and swallowing food
159
Treatment for Xerostomia or dry mouth
Frequent sips of water and fluoride treatment to combat the microbial populations which flourish in the absence of saliva
160
Swallowing
- complex reflex initiated by pressure receptors in the walls of the pharynx
- stimulated by food/liquid entering the pharynx
161
Pharynx
the passage at the back of your throat that is common to air and food
162
Receptors are stimulated by food or liquid entering the pharynx and send signals to the swallowing center in the brainstem which signals muscles in the ________, the _______ and the __________.
pharynx
esophagus
respiratory muscles
163
Process of swallowing
1. Chew food
2. Tongue pushes it to the back of throat
3. Soft palette elevates to stop food from entering nose
4. Impulses from the swallowing center inhibit respiration, raise the larynx and close the glottis
5. Epiglottis covers the trachea to prevent fluid or liquid from entering the trachea
6. Food descends into the esophagus
164
Esophagus
- a tube containing skeletal muscle in the top 1/3 and smooth muscle in the lower 2/3
- food passes very rapidly in esophagus- no absorption
- mucus is secreted to lubricate and aid in the passage of the food
165
Stratified squamous epithelium
- found in esophagus
- layers of flattened cells, or stratified cells
- protect the underlying regions of the esophagus from food
Stratified= in layers
Squamous= flattened
166
Upper esophageal sphincter
- located just below the pharynx
- ring of skeletal muscle
167
Lower esophageal sphincter
- located where the esophagus joins the stomach
- ring of smooth muscle
168
Both upper and lower esophageal sphincter are closed except when: (3)
swallowing
vomiting
burping
169
Esophageal phase of swallowing
1. Upper esophageal sphincter relaxes to allow the food to pass through
2. Sphincter closes and glottis opens to breathe again
3. Peristaltic waves move the food bolus down the esophagus towards the stomach (~5-9 seconds)
4. Lower sphincter at he stomach opens and allows food to pass through
5. Sphincter closes
170
What is the main force for the swallowing phase?
Peristalsis
171
Is gravity needed to swallow?
No, gravity is not necessary. You can swallow in zero gravity and when hanging upside down
172
This prevents gastric contents from reaching the esophagus and is aided by the equal pressure of the lower esophagus and stomach
Lower esophageal sphincter
173
What happens when small amounts of acid get into the esophagus?
- stimulation of peristalsis to push the acid back into the stomach
- increased salivary secretion
- aids with neutralization of the acid with saliva and clearance of the acid out of the esophagus
174
Heartburn can occur: (3)
- lower esophageal sphincter does not close properly
- after a big meal
- during pregnancy
175
the Stomach
- muscular saclike organ located between the esophagus and the small intestine
176
Functions of the Stomach
- storage of food
- mechanical breakdown of food (breaking food into smaller pieces)
- chemical breakdown of food
- controls the rate at which food enters the small intestine
- secretes intrinsic factor
177
The stomach chemically breakdown food by secreting ________ which is a protein digesting enzyme and it is cleaved to form an enzyme called _________
pepsinogen, pepsin
178
Pepsin
enzyme that is important for initiating protein digestion
179
The stomach secretes _________ that dissolves food and partially digests macromolecules in food. Also results in the "partial" sterilization of food
Hydrochloric acid (HCl)
180
All the steps (mechanical and chemical breakdown of food in the stomach) reduces food to fragments of proteins and polysaccharides, droplets of fat, salt and water. This is referred to as __________
Chyme
181
What is an intrinsic factor?
A glycoprotein important for the absorption of Vitamin B12 in the ileum
182
Vitamin B12 is required for
required for normal red blood cell formation
183
What happens after failure to absorb vitamin B12?
It can result in pernicious anemia and red blood cell deficiency
184
Is the stomach an absorption phase?
No, stomach is not an absorption phase. Very little absorption occurs across the stomach
185
What can be absorbed across the stomach?
Alcohol and a small amount of water
186
Anatomy of the stomach
1. Fundus and body
2. Antrum
187
Fundus and body
- upper part of stomach
- both have thin layer of smooth muscle
- secretes mucus, pepsinogen, and hydrochloric acid
188
Antrum
- lower region of the stomach
- thicker smooth muscle layer
- important for physically breaking down, mixing and grinding food
- secretes mucus, pepsinogen, and gastrin
189
Pyloric sphincter
controls emptying of the stomach
190
Excocrine
- a chemical messenger secreted into ducts and then onto an epithelial surface without passing into the blood
Endocrine- requires passage into the blood
191
What are the major exocrine secretions of the stomach?
Mucus, HCl, Pepsinogen
192
Mucus
protects the stomach epithelium from acid and digestive enzymes, predominantly pepsin
- helps to avoid self-digestion
193
HCl
important for the hydrolysis (breakdown) of proteins into their component amino acids, dissolving food, digesting macromolecules and sterilization of food
194
Pepsinogen
precursor to the enzyme pepsin which is important for the digestion of proteins
195
What are the minor excretions of the stomach?
- Intrinsic factor for Vitamin B12 absorption
- Gastrin (endocrine)
- Histamine (paracrine)
- Somatostatin (paracrine)
196
Gastrin
a hormone important for stimulating HCl production and increasing stomach motility
197
Histamine
stimulates HCl production
198
Somatostatin
inhibits HCl production
199
Generalized gastric gland
It is called generalized because some of these cell types are not found in all regions of the stomach
200
Cells found in the generalized gastric gland
1. Mucous cell
2. Parietal cell
3. Chief cell
4. Enteroendocrine cell
5. Enterochromaffin-like cell (ECL cell)
6. D cell
201
Mucous cell
- at luminal end of generalized gastric gland
- produce mucus to protect the stomach lining from cell digestion
202
Parietal cell
- secretes intrinsic factor and hydrochloric acid (HCl)
- found mostly in the body and the fundus of the stomach (not found in the antrum)
203
Chief cell
- found in gastric glands in all regions of the stomach
- secretes pepsinogen
204
Zymogen
a precursor for a protein that is not active and some type of chemical reaction needs to occur to make it active
205
Pepsinogen is cleaved by __________ to pepsin
stomach acid
206
________ accelerates protein digestion
Pepsin
207
Enteroendocrine cell
- found in gastric glands in the antrum
- also known as G cells
- secretes gastrin (hormone), which stimulates HCl production by the parietal cell and stimulates GI motility
208
Enterochromaffin-like cell (ECL cell)
- found in gastric glands in all regions of the stomach (more in antrum)
- secretes histamine, which stimulates HCl production
209
D-cell
- found in gastric glands in all regions, but more are found in the antrum
- secretes somatostatin, which inhibits HCl production
210
Parietal cell
- found in gastric glands in the fundus and body regions of the stomach
- also called oxyntic cell
- secretes HCL and intrinsic factor
- modified surface with canaliculi
- contain many mitochondria to produce ATP required for active acid secretion
211
Canaliculi
- increase the surface area of the cells to maximize the secretion of the acid and intrinsic factor into the lumen of the stomach
- an inactive parietal cell has much less defined, or smaller, canaliculi
- as the parietal cell is activated, the canaliculi become more defined; movement of membrane to the canaliculi, distending them and greatly enlarging them, and insertion of proton pumps
212
Transporters and channels acidify the stomach lumen while maintaining a _______ pH in the cell
neutral
213
The apical surface of parietal cell faces the ________.
stomach lumen
214
What can you find in a parietal cell?
1. Na+/K+ ATPase
2. H+/K+ ATPase
3. Carbonic anhydrase
4. Cl-/HCO3- exchanger
5. K+ channels
6. Cl- channels
215
Na+/K+ ATPase
- pumps 3 Na+ out of the cell and pumps 2 K+ into the cell for every molecule of ATP hydrolyzed
- establishes electrochemical gradients with a high concentration of K+ inside the cell and a low concentration of Na+ inside the cell
216
H+/K+ ATPase
- located in the apical/luminal membrane of parietal cell
- pumps out a proton (acid) form the parietal cell into the stomach lumen
- primary active transport pathway (ATP is hydrolyzed)
- as acid is leaving the parietal cell, the cell will become more basic. Mechanisms prevent the cytosolic pH of the parietal cell from becoming too basic
217
Carbonic anhydrase
- parietal cell gets rid of base by removing bicarbonate (HCO3), which is a base
- catalyzes the formation of H2CO3 (carbonic acid) from H2O and CO2 (CO2 is produced during metabolism)
- H2CO3 dissociates into H+ (for secretion into lumen) and HCO3-
218
Cl-/HCO3- exchanger
- HCO3- is pumped out in exchange for a chloride ion (Cl-) (secondary active transport)
219
K+ channels
- as protons are pumped out through the apical primary active transporter, K+ levels increase in the cytosol; K+ channels in the apical surface open and allow K+ to leave the cell down its concentration gradient.
- diffusion through channels
- loss of positive charge with every K+ ion lost; must lose a negative charge to compensate through the loss of Cl-
220
Cl- channels
- apical membrane
- Cl- lost into lumen of stomach as it diffuses through Cl- channel
- compensates for loss of positive charge through K+ channels
221
HCl is secreted into the lumen of the stomach as a proton leaves the cell through the ___________ and Cl- through the _________
H+/K+ ATPase
Cl- channel
222
What are the 4 chemical messengers that regulate the insertion of the H+/K+ ATPase into the plasma membrane of the parietal cell?
1. Gastrin
- gastric hormone released by G cells
- stimulates insertion of the H+/K+ ATPase into the membrane, stimulating HCl secretion
2. Acetylcholine
- neurotransmitter
- increased parasympathetic activity causes the release of acetylcholine
- increases insertion of the H+/K+ ATPase into the membrane, stimulating acid secretion
3. Histamine
- paracrine released form the ECL-cells
- stimulates insertion of the H+/K+ ATPase into the membrane, stimulating acid secretion
4. Somatostatin
- paracrine released from D-cells
- inhibits the release of HCl, gastrin and histamine
223
Histamine potentiates the effects of ________ and ______ to stimulate acid production
gastrin and acetylcholine
224
Pepsinogen secretion and activation
- secreted by chief cells as an inactive precursor
- release is stimulated by the enteric nervous system
- parallels the release of HCl
- cleaved and activated to pepsin by acidic pH in the lumen
~ release of an inactive precursor is a mechanism to prevent autodigestion
~ pepsin is irreversibly inactivated in the small intestine
225
What are the phases of gastric secretion?
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
226
Cephalic phase
- stimulation occurring in the brain
- sight, smell or tase of food provides excitatory stimulation mainly via the vagus nerve to the stomach
- vagal nuclei in the brain cause the parasympathetic nerve to release acetylcholine at the parietal cell; results in the stimulation of acid production
227
Gastric phase
- occurs when food reaches the stomach
- major phase for regulating acid production
- stimulatory phase mediated mainly via the release of gastrin
- food in the stomach causes G cells to release gastrin into the blood
- Gastrin interacts with the parietal cell to increase acid production
228
Intestinal phase
- occurs when food that has been partially broken down by the stomach enters the small intestine (duodenum)
- inhibitory phase
- mainly inhibitory due to the presence of acid, fat, digestion products and hypertonic solutions in the duodenum
- mediated by gastrointestinal hormones including secretin and CCK
229
Secretin
- secreted by small intestinal epithelial cells
- enter the blood and have a negative influence on gastrin production
230
what are the four chemical messengers that regulate the insertion of the H+/K+ ATPase into the plasma membrane of the parietal cell?
- gastrin
- ACh
- histamine
- somatostatin
231
What chemical messengers directly stimulate acid secretion in parietal cell?
ACh, histamine and gastrin
232
Which chemical messenger negatively regulates acid secretion of parietal cell?
Somatostatin
233
What are the indirect effects of ACh on acid secretion from parietal cell?
- stimulates ECL cells to release histamine which stimulates the parietal cell
- inhibits somatostatin production from the D cells to stimulate acid secretion
- stimulate G cells to produce gastrin which stimulates acid secretion
234
What is the indirect effects of Gastrin on acid secretion from parietal cell?
- stimulates ECL cells to release histamine which stimulates the parietal cell
235
What happens to ACh once acid secretion is occurring at a high rate?
- ACh is released form the parasympathetic nerves
- as eating and acid production are occurring, the stimulation will be reduced -you will not be hungry anymore
236
What happens to gastrin once acid secretion is occurring at a high rate?
- acid production itself has a negative effect on gastrin release
- H+ released from the parietal cell inhibit gastrin release from G cells
237
What happens to somatostatin once acid secretion is occurring at a high rate?
- somatostatin inhibition by ACh is reduced as ACh levels decrease
- has a direct negative effect on the parietal cell and inhibits acid secretion from the parietal cell
- can inhibit histamine release from the ECL cells
- can inhibit gastrin release from the G cell
238
Gastric motility
- important component for breaking down food
- huge capacity to stretch
- after you consume a meal, smooth muscle in the stomach relaxes, allowing the stomach to increase without increasing pressure
- this relaxation is mediated by the parasympathetic nerves to the enteric nervous system
239
Arriving food causes peristaltic wave. What happens?
- weak contractions in the body of the stomach
- antrum powerfully contracts to allow the mixing of the luminal contents and closes the pyloric sphincter.
- closure of the sphincter results in a small amount of stomach contents reaching the duodenum, but most is retained and forced backwards towards the body of the stomach to allow more mixing to occur.
240
Pyloric sphincter
sphincter between the antrum and the duodenum
241
What happens after a peristaltic wave in the body of a stomach and a stronger force of contraction in the antrum?
- peristaltic wave in the body of a stomach and a stronger force of contraction in the antrum will result in the pyloric sphincter closing
- a small amount of chyme will enter the duodenum; the backwards flow of contents towards the body of the stomach allows mixing due to this muscle contraction
242
Stomach has pacemaker cells in the smooth muscle layer. What happens?
- spontaneous slow waves of depolarization and repolarization
- in the absence of neural or hormonal input, the basic electrical rhythm does not cause any contractions as depolarizations are too small
- the basic electrical rhythm allows the timing of contractions
- the presence of excitatory hormones and neurotransmitters will act upon the smooth muscle to further depolarize the membrane, resulting in contraction
- amount of stimulus determines strength of contraction
- the frequency of contraction is determined by the basic electrical rhythm
243
Causes of vomiting
- Psychogenic (has a psychological origin, ex: smelling something really bad)
- Gastrointestinal disturbances
- Inner ear infections
- Chemoreceptors in the brain and the gastrointestinal tract that can detect toxins
- Pressure in the CNS
244
Where is the vomiting center?
Medulla oblongata
245
What are the different stimuli that feed into the vomiting center?
- nausea, salivation, breath held in mid-inspiration
- glottis closes off trachea
- lower esophageal sphincter and esophagus relax
- diaphragm and abdominal muscles contract
- reverse peristalsis moves upper intestinal contents into stomach
- stomach contents move up through esophagus and out through mouth (soft palate is raised) to prevent vomit from going through your nose
246
Benefits of vomiting
- remove harmful substances before they are taken into your body
- nausea and feeling bad associated with vomiting are a negative conditioning, so that if you experience these, they may prevent you from consuming the noxious substance again
247
Negative consequences of vomiting
- dehydration
- electrolyte imbalance
- metabolic alkalosis
- acid erosion of tooth enamel
248
metabolic alkalosis
a condition in which the pH of a tissue is elevated beyond the normal range, due to the loss of acid from your stomach
249
What is a peptic ulcer?
- damage to or erosion of the GIT mucosa
- occurs in regions which are acidic such as the esophagus, the stomach or the duodenum
250
What causes an ulcer?
- imbalance of aggressive factors (acid and pepsin) and protective factors (mucus and bicarbonate)
- most common cause of ulcers: infection from the bacterium Helicobacter pylori, which results in inflammation of the lining and irritation and eventually chronic inflammation and erosion
- non bacterial factors: non-steroidal anti-inflammatory drugs which reduce prostaglandin production, smoking, excessive alcohol, gastrinomas
251
Treatment for ulcers
- antibiotics to get rid of the H. pylori infection
- H+/K+ pump inhibitors
- histamine receptor antagonists
- prostaglandin-type drugs
252
Where can ulcers occur?
esophagus, stomach, duodenum
253
Is the stomach essential for life?
No, it is not essential, but problems can occur without it.
254
Gastric bypass surgery
used in the treatment of morbid obesity
- they tie up the stomach so that it is a smaller pouch
255
Importance of stomach
- stomach is important for producing intrinsic factor. Intrinsic factor is secreted by the stomach lining and aids in vitamin B12 absorption. People that have lost a lot of their stomach must have Vitamin B12 injections so they do not become anemic
- stomach is useful for reducing the amount of bacteria that enter your system-. HCl in the stomach secretes sterilizes food
- stomach regulates how much food enters the SI
256
Pancreas
- an exocrine and endocrine gland
257
Exocrine pancreas
- important for digestion
- produces secretions that go into the GIT
- source of the majority of enzymes required for digestion of carbohydrates, proteins, fats and nucleic acids
- problems with digestion and absorption will not be noticed until the organ function falls below 10%
- secretes bicarbonate into the duodenum for neutralization of stomach acid.
Digestive enzymes produced by the pancreas are completely inactive under acidic pH. The stomach acid must be neutralized by bicarbonate for these enzymes to be functional
258
Endocrine pancreas
- not involved in digestion but it is important for producing hormones that regulate the entire body (eg. insulin)
259
Main pancreatic duct
- drains the exocrine secretions into the SI
- joins common bile duct form the liver just before entering duodenum
260
Sphincter of Oddi (hepatopancreatic sphincter)
sphincter common to the bile duct and to the main pancreatic duct
regulates the release of both liver and pancreatic contents into the SI
261
secrete substances into ducts that drain onto the epithelial surface, or the apical surface, and converge into the pancreatic duct. Secretions ultimately enter the SI
Exocrine pancreas
262
_______ is a ductless gland.
secretion occurs across the epithelial basolateral surface for diffusion into blood
eg. insulin
endocrine pancreas
263
These cells surround capillaries
endocrine cells
264
Pancreatic islets (Islets of Langerhans)
produce the hormone insulin
265
What are the two pancreatic duct cells? And define
1. Acinar cells
- pancreatic ducts have acinar cells at the end portion of the duct
- produce and secrete digestive enzymes
Exocytosis of vesicles within the acinar cells
2. Ductal cells
- secrete bicarbonate for neutralization of acid
- water is also secreted
266
Pancreatic juices
- isotonic and alkaline
-Alkaline because of bicarbonate (HCO3-)
- contains electrolytes:
-high in HCO3- and low in Cl-
-Na+ and K+ concentrations are the same as in plasma (this is why pancreatic juice is isotonic; iso=same)
-HCO3- and water are secreted by duct cells
-HCO3- neutralizes gastric acid in duodenum
- contains digestive enzymes:
-essential for the digestion of proteins, carbohydrates, fats and nucleic acids
-secreted by acinar cells
-proteolytic enzymes (break down proteins into amino acids) are stored and secreted in inactive forms
Activated in the duodenum
267
Ductular Cell Secretion of HCO3-
1. Chloride channel (CFTR) opens
- allows diffusion of Cl- into duct lumen.
2. Cl- in lumen is exchanged for HCO3- in cell
3. H2O and Na+ follow paracellularly in response to electrochemical gradient across epithelium
4. Neutral pH of cytosol is maintained by exchange of H+ (exported from cell) for Na+ (imported)
- secondary active transport dependent upon the electrochemical gradient generated by the Na+/K+-ATPase.
- resulting watery alkaline secretion neutralizes gastric acid and washes digestive enzymes through
268
Where is the Cl- channel located in the ductal epithelium?
apical (luminal) surface
269
CFTR
Cystic fibrosis transmembrane conductance regulator
- allows Cl- to diffuse out of the duct cell into the lumen
270
Alkaline Tide
After a big meal:
- acid is produced by the parietal cell and enters the lumen of the stomach
- base leaves the cell into the bloodstream as bicarbonate (HCO3-)
- whatever is moving into the blood is referred to as the tide
- in the stomach, a large amount of bicarbonate (alkaline) is pumped across the basolateral surface into the blood
= Alkaline tide
271
Acid Tide
After a big meal:
- in the pancreas, the duct cells are producing base as bicarbonate, which is moving into the lumen of the pancreatic ducts
- large amounts of acid are being pumped across the basolateral surface into the blood stream
= acid tide
272
How the alkaline and acid tide occur simultaneously?
- in the stomach, acid is produced by the parietal cells and secreted into the stomach lumen, resulting in base moving into the blood.
- in the pancreas base moves into the lumen while acid moves into blood.
- while the process is first initiated in the stomach, the two processes occur simultaneously
- eventually, HCO3- which is released into the blood form the stomach and the acid that is released into the blood form the pancreas meet up in the portal vein
- these two separate processes will compensate for each other and maintain the acid-base balance in the blood stream.
273
Digestive function of the pancreas
source of the major enzymes required for digesting carbohydrates, proteins, fats and nucleic acids
274
What would happen without pancreas?
Starvation would occur because you can't digest food and absorb nutrients across the intestinal tract
275
What are the enzymes produced by the pancreas and what do they do?
1. Proteases- digest proteins into peptides and amino acids
2. Amylolytic enzymes- digest starch into sugars
3. Lipases- digest triglycerides into free fatty acids and monoglycerides
4. Nucleases- digest nucleic acids into free nucleotides
276
Enzymes are synthesized ad packaged into vesicles by _____________________
pancreatic acinar cells
Enzymes are packaged as proenzymes into zymogen granules that are stored at the apical pole of the acinar cell until appropriate stimuli causes exocytosis
277
Zymogens
proenzymes or inactive precursor enzymes
278
Most pancreatic enzymes are secreted as inactive forms. They are inactivated in the ____________
duodenum
279
Enterokinase
- enzyme attached to the apical, or luminal, surface of the epithelial cells in the duodenum
- cleaves pro-protease called trypsinogen into the protease trypsin
Trypsinogen- is an inactive precursor molecule
Trypsin- activates other enzymes
280
Pancreas produces and stores proenzymes. Proenzymes are not activated until they reach the ______________
small intestine
281
Why does pancreas secretes a variety of trypsin inhibitors?
to prevent any premature activation of trypsin
282
What are some prevention of autodigestion of the pancreas under normal conditions?
- pancreas store proenzymes
- pancreas secretes a variety of trypsin inhibitors to antagonize any prematurely activated trypsin
- trypsin degrade itself if activated prior to reaching the intestine
283
Major proteases secreted by the pancreas
Endopeptidases:
- Trypsinogen
- Chymotrypsinogen
- Pro-elastase
Exopeptidases:
- Pro-carboxypeptidase A and B
284
Trypsinogen
- activated by enterokinase in the duodenum to trypsin
Trypsin is important as it activated other enzymes
285
Chymotrypsinogen
activated by trypsin to the active enzyme chymotrypsin
286
Pro-elastase
activated by trypsin to the active enzyme elastase
287
Pro-carboxypeptidase A and B
activated by trypsin to the active enzyme carboxypeptidase A and B
288
Example of an amylolytic enzyme and what does it do?
Pancreatic amylase- cleaves starches to sugars
-end product of this digestion is disaccharides and trisaccharides, maltose, maltotriose and alpha-limit dextrins
289
Examples of lipolytic enzymes and what do they do?
1. Lipase- hydrolyzes triglycerides into free fatty acids and monoglycerides
2. Phospholipase A2- hydrolyzes phospholipids into free fatty acids and lysophospholipids
3. Cholesterolesterase- hydrolyzes cholesterol-esters into free fatty acids and cholesterol
290
Pancreatic juice secretion is primarily mediated by food and acid entering the ________________
small intestine
291
what are the 2 cells in the epithelial layer of the duodenum?
- S cells
- I cells
292
Acid entering the duodenum from the stomach stimulates _________ to produce the hormone secretin
S cells
293
This is a hormone released into the blood and finds its way to the pancreatic duct cells where it stimulates the release of HCO3-
Secretin
294
digested fats and protein are entering into the upper SI from the stomach stimulate ________ to release the hormone cholecystokinin (CCK)
I cells
295
This hormone is released into the blood and acts on the acinar cells in the pancreatic duct to stimulate the zymogen granules to release the digestive enzymes
CCK
296
Activity in _______________ nerves will also cause the release of digestive enzymes (minor regulatory pathway)
parasympathetic
297
Circulating CCK stimulates the __________ to increase the secretion of digestive enzymes. It also stimulates the _____________ to contract
pancreas
gallbladder
298
What happens after CCK stimulates the gallbladder to contract?
- release of bile acids for fat breakdown
- Sphincter of Oddi relaxes
299
As the _______ and ____________ are absorbed, the stimuli for CCK release is removed, as it is the these two themselves in the SI that trigger CCK secretion (negative feedback control system)
fats and amino acids
300
Circulating secretin stimulates: (2)
- pancreas (duct cells) to increase HCO3- secretion
- liver (duct cells) to increase HCO3- secretion
301
When the stomach ________ is neutralized, the stimulation of secretin release is stopped. (negative feedback control system (negative feedback control system)
acid
302
This phase of pancreatic secretion involves stimulation that is occurring in the brain
Sight, smell, and taste of food stimulate pancreatic secretion via the parasympathetic nerves
Cephalic phase
303
Secretin and CCK both inhibit gastrin secretion. This results in
reduced stomach motility (slows stomach emptying) and reduced acid secretion
304
This phase of pancreatic secretion involves distension of the stomach and this will stimulate the pancreatic secretion via the parasympathetic nerves
Gastric phase
305
This phase is a major regulatory phase of pancreatic secretion.
Acid from the stomach in the duodenum stimulates secretin release and digested fat and protein i the duodenum stimulate CCK release
Intestinal phase
306
The Cl- channel involved in HCO3- secretion in the pancreas is the channel that is mutated in the disease ___________________
cystic fibrosis
307
A defective __________ channel is produced in cystic fibrosis
chloride
308
In cystic fibrosis, patients suffer from ______________ insufficiency
pancreatic
309
In cystic fibrosis, patients must receive supplements of _____________________ and ____________ to allow for adequate nutrition
digestive enzymes and antacids
310
Biliary system components
- Gall bladder
- Bile ducts (Main pancreatic duct, common bile duct)
- Sphincter of Oddi
311
This organ is a small sac located underneath a lobule of the liver
Gall bladder
312
These run from the liver and join to form the common hepatic duct, which then joins with the common bile duct
Bile ducts
313
____________ controls the release of contents into the SI
Sphincter of Oddi
314
Liver receives blood by 2 distinct circulatory routes:
- systemic circulation= arterial blood
- hepatic portal circulation= venous blood
315
The blood in the ________ circulation is oxygen rich but nutrient poor
systemic
316
The blood in the __________ circulation is nutrient rich, oxygen poor
hepatic portal
317
This is the functional unit of the liver
Hexagonal structure with a central vein running through the center and a portal triad in each corner
Hepatic lobule
318
The ______________ consists of a hepatic artery, a hepatic portal vein, and a bile duct
Portal triad
319
Epithelial cells of the liver that form the canalicular networks
Hepatocytes
320
Liver (exocrine gland) major functions
- important for the formation and secretion of bile
- metabolizing and strong nutrients
- deactivation and detoxification
- producing circulating proteins
321
Bile is important for the breakdown of ______
fat
322
6 major components of Bile
- Bile acids
- Cholesterol
- Salts (sodium, potassium and bicarbonate) and water
- Phospholipids
- Bile pigments (bilirubin)
- Trace metals
323
This is important for the breakdown of heme. It gives color to urine and feces
Bilirubin
324
_____________ are made within the hepatocyte from cholesterol
Important for the emulsification of fats
Bile acids
325
________________ is a water-soluble enzyme and can only work on the surface of the lipid droplets
Bile works with this enzyme
Pancreatic lipase
325
Large lipid droplets need to be made smaller so that pancreatic lipase can access them. This process is called ________________
emulsification
326
Emulsification requires: (2 things)
- mechanical disruption to make the lipid droplets smaller
- emulsifying agent to prevent droplet from re-aggregating
327
Micelle has ________ head groups facing the outside in contact with the aqueous solution and ___________ groups facing the inside
polar, nonpolar
328
During formation of Bile, _____________ produce and secrete bile acids. It also secrete phospholipids, cholesterol and bile pigments into the bile canaliculi
hepatocytes
329
During formation of Bile, ________________ add bicarbonate and other salts and water to the bile
Bile duct cells
330
______________ is important for storing and concentrating bile between meals and releasing it when chyme enters the duodenum
Gallbladder
