Gastrointestinal - week 24 Flashcards
(96 cards)
1
Q
what is the goal of the GI system
A
to absorb as much of digested nutrients as possible
2
Q
what is another thing the GI system does
A
- plays role in defensive role against pathogens, toxins and foreign substances entering through food
(vomiting reflex and inc. intestinal motility which leads to diarrhea)
3
Q
what are the primary organs of the GI system
A
- oral cavity
- esophagus
- stomach
- small intestine
- large intestine
4
Q
what are the accessory organs of GI tract
A
- liver (produces bile)
- pancreas
- gallbladder (stores bile)
- salivary glands (near oral cavity but do not directly touch food)
5
Q
what is a lumen
A
tube of cells - center of body
6
Q
A
7
Q
what are the layers of the lumen
A
- mucosa
- submucosa
- muscularis
- serosa
8
Q
mucosa
A
faces the inside of the lumen of GI tract
(comes directly into contact with lumen contents)
- mucous membrane – single layer of epithelial cells that are a component of the mucosa layer
- variable between different organs
9
Q
submucosa
A
connecting tissue adhere mucosa to muscularis externa layer
- within plexus of enteric nervous system called submucosal plexus
10
Q
muscularis externae
A
mad of 2 layers of smooth muscle that are circumferential (circular) or longitudinal (orientation
- within a second plexus of enteric neuros - called myenteric plexus
11
Q
serosa
A
the final layer
- outer protective tissue layer
- continuous with mesentery (connective tissue layer)
- lines abdominal cavity
12
Q
what is the Enteric Nervous system
A
the neuron bodies of ENS found in 2 layers of GI tract
1. in the submucosal plexus
2. and myenteric plexus
- PSNS and SNS both innervate and regulate it but it can also function independently
- a unique organization of ENS is essential for ability to coordinate multiple organs
13
Q
what is the oral cavity secretions
A
saliva - a converging duct system
14
Q
saliva function
A
- lubricates food
- helps with the ability to taste our food
- protects mouth and teeth
- aids with speech
15
Q
glands that secrete saliva
A
- parotid gland
- submandibular gland
- sublingual gland
16
Q
parotid gland composition and location
A
higher volume of watery saliva with enzymes (amylase and lingual lipase)
- located under/infront ear area
17
Q
submandibular gland composition and location
A
mixture of watery saliva and mucus and some enzyme secretion
- located under mandible
18
Q
sublingual gland composition and location
A
more mucus like secretion
- used when talking
located under tongue
19
Q
saliva composition
A
mostly water, ions such as Na+, Cl-, HCO3- (bicarbonate) (neutralizes any acids), mucus (lubricates mouth), proteins (protect teeth) and digestive enzymes (salivary amylase and lingual lipase)
20
Q
what form of digestion is done in oral cavity
A
mechanical (chewing) and chemical (saliva)
21
Q
mastication definition
A
- chewing
- mechanical manipulation of food
- result: breakdown of whole food particles into smaller pieces
- with salivary secretions turns food into bolus
22
Q
what is bolus
A
softened mass that is swallowed
- called bolus as soon as it reaches back of mouth into throat ready to be swallowed
23
Q
how does chemical digestion occur in oral cavity
A
with lingual lipase and amylase
24
Q
what does salivary amylase do
A
chemically digests complex carbohydrates (amylose)
25
what does lingual lipase do
chemically digests lipids (activated in the stomach)
26
what are the 3 motility patterns
1. mastication
2. swallowing - 3 stages
3. peristalsis - occurs in esophagus
27
stages of swallowing
voluntary phase
pharyngeal phase
esophageal phase
28
voluntary phase
- mastication is done by choice - creates bolus
- moving bolus to back of mouth done voluntary - through manipulation of tongue
29
pharyngeal phase
involuntary phase
- sensation of bolus at the pharynx triggers this stage of swallowing
- sensory neurons activate the neural reflexes required to close off the nasopharynx
- done by lifting uvula of soft palate to close over nasopharynx
- epiglottis bent back over the glottis to prevent food/fluid going into trachea
- upper esophageal sphincter relaxes, allows bolus down esophagus
30
esophageal stage
- bolus pushed down esophagus through coordinated muscular contractions and relaxations
- called peristalsis
- lower esophageal sphincter coordinated relaxing to allow for bolus to enter top part of stomach`
31
motility pattern of esophagus
peristalsis
- system of coordinated contractions and relaxations of esophageal circular and longitudinal muscles
secondary peristalsis
- initiated if bolus does not successfully make it to the stomach
- this is a more forceful set of muscular contractions of esophagus to push bolus unidirectionally down into stomach
peristalsis is not relied on gravity
32
oral cavity absorption
- minimal absorption occurs at oral cavity
- most macronutrients ingested are not adequately chemically digested in the mouth
- some sublingual absorption occurs for small non-polar molecules
- glucose can be absorbed in oral cavity because some expression if glucose carriers in epithelial cells of mouth
33
what is xerotomia
"dry mouth"
- inability or reduction in salivary production
- patients often suffer from infections in oral cavity due to lack of protection from saliva
- saliva provides defense against microbe growth in mouth
- patients have challenge eating food
- reduced taste flavours
34
types of xerostomia
1. Sjogren's disease
2. radiation therapy
3. nerve damage
35
Sjogren's disease
where body's own immune system attacks the salivary glands which damages them
36
radiation therapy
treatment of neck and oral cancer, common treatment
- medications include antidepressants and BP medications
37
nerve damage
neurons that innervate the salivary glands can be damaged
- when nerves damaged (could be from neck injury/surgery or head injury), can cause reduction in saliva production
38
stomach anatomy
- lower esophageal sphincter: how bolus enters stomach
- fundus: first receives bolus, needs to stretch out in response to the bolus since stomach is not an opened sac at rest
- stretching known as: receptive relaxation
- body: where bolus sits
- antrum: causes muscle contractions for bolus to become liquified
- rugae: help expand stomach by stretching out when meal is larger
*stomach is partially collapsed on itself when no bolus is inside
39
how many smooth muscle layers does the stomach have
1. longitudinal
2. circular
3. oblique
40
layers of the stomach
mucosa
submucosa
muscularis externae
serosa
41
difference between stomach and small and large intestine
mucosa layer:
- types of secretions made by epithelial cells in mucosa dictate function of that segment of digestive tube
muscularis externae layer
- also has an oblique smooth muscle
42
what are epithelial cells:
a tissue that covers the surfaces of organs and cavities in the body.
They are tightly packed together, serving as a barrier between the interior and exterior of the body, and can be found lining various systems such as the skin, respiratory tract, digestive tract, and blood vessels.
Epithelial cells play crucial roles in protection, absorption, secretion, and sensation.
43
what do epithelial cells secrete in stomach
the ones in the the glands of fundus and body secrete HCL and various enzymes
epithelial cells at top of glans and on rugae folds are mucus neck cells and secrete mucus and bicarbonate
44
what do parietal cells secrete
secrete acid and intrinsic factor (important protein that aids in vitamin B12 absorption in intestine
45
what do chief cells secrete
secrete gastric lipase, zymogen (inactive precursor protein which when activated, function as enzymes), and pepsinogen (this is a zymogen when activated, functions as the pepsin enzyme
46
what do G cells secrete
secrete gastrin which is involved in controlling gastric motility and stimulating acid secretion from parietal cells
47
what do D cells secrete
secrete somatostatin which inhibit gastrin release from G cells
they are contained within antrum of stomach mucosa layer
48
what is the role of acid in stomach
acidic gastric juices inactivated salivary amylase and activate lingual lipase
1. inactivate enzyme salivary amylase
2. activate lingual lipase
3. produces pepsin from zymogen pepsinogen
4. denatures protein
5. destroys ingested microbes
49
motility patterns of stomach
propulsion: gentle mixing waves are generated every 15-25 seconds to mix food with secretions of gastric gland within few minutes of food entering stomach
grinding: intensified mixing towards the pylorus
retropulsion: movement of chyme back into body of stomach where more mixing can occur
50
gastric emptying
contents moving from stomach into small intestine through pyloric sphincter
51
absorption in stomach
minimal to no nutrient absorption - thick mucus layer covering epithelia cell layer
there is an exception of some absorption of small, lipophilic drugs and alcohol
52
what is pyloric stenosis
- when pyloric sphincter becomes abnormally thickened
- called hypertrophy
can block or narrow opening into small intestine
- cause vomiting
- develop in adults
- most common in infants 2-6 weeks after birth
53
what is the treatment to pyloric stenosis
pyloromyotomy which is a surgery to fix it
54
exocrine cells
found in fundus and body region
- mucus neck cells: secrete mucus
- chief cells: secrete pepsinogen and gastric lipase
- parietal cells: secrete intrinsic factor (H+ and Cl-)
55
endocrine cells
found in antral regions
- G cells: secrete gastrin
- D cells: secrete somatostatin
56
what are the 3 functional segments of the small intestine
duodenum
jejunum
ileum
57
duodenum
- shortest segment but where most chemical digestion happens
- where secretions of pancreas and liver first interact with chyme
- mucosa wall has villi - increase surface area, improves chemical digestion and aid in some nutrient absorption
58
jejunum
- many villi - aid in maximal nutrient absorption
- has many absorptive epithelial cells found to help with absorption as apical membrane of these cells have necessary transporters to move contents of lumen across absorptive epithelia
59
ileum
- longest segment
- has villi for increased surface area
- extra length of lumen with enterocytes to assist in nutrient absorption
- B12 and bile salts predominantly absorbed in ileum
60
mucosa layer of the small intestine
similar to stomach
mucosa layer different from stomach
- instead of rugae (folds) it has finger like projections villi
- villi increase surface area - aid in chemical digestion and nutrient absorption
61
enterocytes
absorptive epithelial cells in mucosa layer
62
goblet cells
secrete mucus
- have a role in stimulating bicarbonate secretions from pancreas and liver
63
I cells
release cholecystokinin (CCK)
- important regulator of digestive tract
- stimulate enzyme secretions from pancreas
- causes gall bladder to contract, releasing bile solution into small intestine
64
endocrine cells of small intestine
located within mucosa epithelial cells
65
S cells
secrete secretin - role in stimulating bicarbonate secretions from pancreas and liver
66
intestinal gland cells
secrete watery mucus
- contains bicarbonate which aids in neutralization of the acidic chyme coming from stomach
- mucus helps protect mucosa layer of small intestine
- not as think as the one in stomach
67
k cells
secrete glucose dependent insulinotropic peptide (GIP)
- important for stimulating release of insulin
68
enterocytes of small intestines
absorptive cells
- mucosa layer of small intestine participate in macronutrient absorption
- brushed border: due to it looking blurry/brushed surface under the microscope due to the microvilli
69
function of microvilli
increase surface area off apical plasma membrane of enterocytes more nutrients can be absorbed
70
what are brush border enzymes
digestive enzymes
- by the presence of these enzymes on plasma membrane, many macromolecules are digested
- these enzymes are not secreted, they are a part of enterocyte membrane
- conveniently located because these enzymes cause production of absorbable nutrient units
71
what are some brush border enzymes
- lactase
- sucrase
- maltase
- alpha-limit dextrinase
- dipeptidase
- aminopeptidase
- enterokinase
72
lactase
aka disaccharidase because it chemically digests the disaccharide lactose, into 2 monosaccharide (glucose and galactose)
73
sucrase
disaccharidase that chemically digests sucrose into 2 monosaccharides (glucose and fructose)
74
maltase
disaccharidase that chemically digests maltose into 2 units of glucose
75
alpha-limit dextrinase
enzyme, chemically digests branched polymers of glucose (complex carbohydrates like amylopectin)into linear glucose polymers
76
dipeptidase
protein digesting enzyme aka protease
- chemically digests a peptide into 2 single amino acid
77
aminopeptidase
a protease that chemically digests a peptide or protein
- done by removing a single amino acid from the amino-terminus of the protein strand
78
enterokinase
aka enteropeptidase, protease
- chemically digests proteins/peptides, including an important zymogen called trypsinogen into the enzyme trypsin
79
small intestine motility in fed state
- when chyme solution enters into small intestine
- specialized mixing contractions stimulated to occur to function to mix chyme with digestive juices secreted into small intestine
80
what are segmentations
vigorous smooth muscle contractions and relaxation patterns
- results inefficient chemical digestion of macronutrient and optimized interactions of nutrients with enterocytes for absorption
localized mixing contractions that also function to increase the interactions of food particles in the chyme with absorptive cells in intestinal mucosa
they are more rapid at the start of the small intestine (duodenum and die down as they move towards the ends of the small intestine (ileum)
81
what is peristalsis in the small intestine
coordinated contractions of smooth muscle behind chyme
- chyme pushed unidirectionally to the next small intestine segment
- movement by peristalsis pushes chyme from duodenum to jejunum and then ileum
82
what is the small intestine motility in the fasted state
fasted state is when there is no chyme
the motility pattern is called migrating motility complex
83
what is the migrating motility complex
pushes out any particles of food that remain in stomach or in small intestine
- it is initiated first in the stomach and waves through the small intestine
- chyme usually moves out of stomach efficiently during regular digestion but the pyloric sphincter only allows food particles 1-2mm in size
- therefore the larger fragments are moved through MMC because the pyloric sphincter is fully relaxed in this state
- MMC is automatic (involuntary)
- waves continue from stomach to large intestine until it is disrupted by food. MMC (migrating mobility complex) will stop and fed state mobility will begin.
84
what are the three phases of MMC
gentle
moderate
vigorous
85
Absorption and small intestine
Most nutrient absorption happens here. Approx 100% ingested carbohydrates and 95-98% of proteins and lipids are absorbed.
86
What is peptic ulcer disease
When there is open sores in the digestive tract. They can occur in the stomach (gastric ulcers), in the small intestines (duodenal)
87
Reason of peptic ulcer disease
Due to imbalance in the protection of the mucosa layer, by mucus or due to more than usual acid secretion.
Can also occur due to infection with bacteria (heliobactor H. pylori)
- Reduces protective layer of mucus
-Best treatment is anti-biotics or NSAIDS if too many ulcers
88
main function of large intestine
finish process of absorption and responsible of production of certain vitamins and formation of feces
89
what to enter large intestine
chyme enters through ileocecal valve
- moved up ascending colon
- across transverse colon
- down descending colon
through sigmoid colon
towards rectum
90
what is haustra
interesting feature of mucosa layer
- pocket like structure force lumen contents to churn as they propel forward
- flip contents over to expose chyme contents to surface of mucosa
91
large intestine secretions
mucus from goblet cells (main secretion) - part of epithelial cells in the mucosa
potassium and chloride also secreted
92
large intestine motility
peristalsis
haustral
gastroileal reflex
93
peristalsis in large intestine
unidirectional movement of lumen contents from ileocecal valve towards rectum
94
haustral
mixing of large intestine contents from one haustra to the next
95
gastrileal reflex
presence of new bolus in stomach will stimulate ileocecal valve to open
- encourages the emptying of small intestine contents into large intestine
96
bacteria of large intestine and absorption
entire digestive tract has bacteria
- majority in large intestine
produces significant amounts of absorbable vitamins (vitamin K)
