Digestive Flashcards
1
Q
Functions of Digestive system
A
- motility
- secretion
- digestion
- absorption
- storage and elimination
- immune barrier
2
Q
Motility
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physical breakdown, preogresses through the 30 feet from mouth to rectum, movement of food trhoguh digestive tract
3
Q
Movement of food through digestive tract
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- ingestion (eating)
- mastication (chewing)
- deglutition (swallowing)
- peristalsis and segmentation
4
Q
Secretion
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both exocrine/endocrine secretions
exocrine: water, HCl, bicarbonate, and digestive enzymes are secreted into lumen of GI tract
endocrine: stomach and small intestine secrete hormones that help regulate the digestive system
5
Q
Digestion
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breakdown of food molecules into smaller subunits: allowing them to be absorbed
6
Q
Absorption
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passage of digested end products into lymph/blood
7
Q
Storage and elimination
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temporary storage and subsequent elimination of indigestible food molecules
8
Q
Immune barrier
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columnar epithelium provides physical barrier to penetration of pathological organisms/ their toxins- cells of immune system reside in connective tissue located under epithelium to promote immune response
9
Q
Anatomy of digestive system
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tube system of 4 layers
10
Q
4 layers of digestive system
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- mucosa
- submucosal layer
- muscular tissue
- serosal layer
11
Q
mucosa
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inner layer next to lumen, primary absorptive epithelium, major absorptive layer and secretary layer
12
Q
submucosal layer
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involves immune, nervous tissues, lymph tissues and other connective tissues (these give it strength/ flexibility)
13
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Muscular tissue
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Made up of circular muscle and longitudinal muscle
i. circular muscle contracts
ii. longitudinal muscle helps move things (motility)
14
Q
Serosal layer
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provides blood supply, connective tissue that holds the 30 ft of GI tract together.
15
Q
First stage: chewing through swallowing to stomach
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chewing (mastication)–> mixes food wiht saliva secreted by salivary glands
16
Q
saliva
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contains mucus and various antimicrobial agents as well as salivary amylase
17
Q
salivary amylase
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enzyme that can catalyze partial digestion of starch
18
Q
Swallowing
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deglutition, divided into 3 phases: oral, pharyngeal, esophageal (oral is voluntary, pharynx/esophageal are automatic)
19
Q
Middle and lower esophagus are
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smooth and innervated by autonomic neurons
20
Q
Swallowing phases
A
oral
pharyngeal
esophageal
21
Q
Oral phase
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First phase of swallowing:
muscles of mouth/tongue mix food with saliva and create a bolus of food, size to be swallowed. Tongue muscle moves it toward oropharynx–> receptors in posterior portion of oral cavity stimulate next phase
22
Q
Pharyngeal
A
Second phase of swallowing:
soft palate lifts to close off the nasopharynx from oropharynx, prevents food from going out the nose, vocal chords close off to larynx, epiglottis covers vocal cords, llarynx moved away from bolus toward esophagus (prevents choking), upeper esophageal sphincter relaxes, this all takes <1 second
23
Q
Esophageal
A
third phase of swallowing
lasts 5-6 seconds, bolus fo food moved by peristaltic contractions toward stomach
24
Q
Stomach functions- role of acid
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- Store food (Stomach very distensible and can accept bolus after colus)
- initiate digestion of proteins (pepsin activation)
- kill bacteria with strong acidity of gastric juice (pH = 2 so very acidic)
- move food into the small intestine as chyme.
25
Role of acid
HCl sterilizes the food we eat, preventing harmful bacteria into GI tract. Triggers the release of enzymes (pepsin) which are essential for protein digestion
26
Acid serves three functions
1. ingested proteins denatured at low pH, so they become more digestible.
2. In acidic conditions weak pepsinogen enzymes partially digest each other
3. pepsin is more active under acidic conditions
4. pepsin/HCl permits partial digestion of food in stomach
27
Mechanisms of stomach secretions
Inner surface of smooth contains rugae folds- gastric mucosa is also folded (Gastric pits) cells that line the folds secrete productsinto stomach (gastric glands)
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Gastric glands
mucous neck cells, parietal cells, chief cells, ECL cells, G cells, D cells
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Mucous neck cells
secrete mucus
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Parietal cells
secrete HCl
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Chief cells
secrete pepsinogen (inactive form of pepsin)
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ECL cells
in stomach/intestine secrete histamine and serotonin as paracrine regulators of GI tract
33
G cells
secrete the hormone gastrin into the blood
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D cells
secrete hormone somatostatin
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Gastric mucosa (parietal cells) secrete
a polypeptide intrinsic factor which is required for intestinal absorption of vitamin B12 (necessary for RBC production)
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Stomach increases its secretion in anticipation of meal
entry of chyme into the duodenum stimulates secretion of hormones which make gallbladder contract, secretion of pancreatic juice, inhibition of gastric activity
37
Roles of Gastrin
hormone secreted by the stomach that stimulates the gastric secretion of HCl and pepsin
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gastrin is secreted by
G cells
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Gastrin does what?
Stimulates parietal cells to secrete HCl, stimulates chief cells to secrete pepsinogen, maintains structure of gastric mucosa
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Gastrin can stimulate ECL cells
ECL cells secrete histamine serotonin, which can enhance stimulation of B12, activates chief cells, activates stomach muscles/motility, stimulate relaxing pyloric sphincter, activates pancreas secretions, activates gallbladder contraction, activates D cells--> somatostatin (acts as feedback loop to inhibit the production of G cells)
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Importance of food bolus/stomach distention
Formed while chewing--> food mixed with saliva
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When bolus is present
the esophageal pyloric sphincter opens allowing bolus to enter
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Bolus in stomach
presence of bolus stimulates secretion of acid and gastric juices and which begins process of further mixing the bolus--> presence of bolus sparks acid secretion
Mix of gastric juice/acid with food creates chyme. Stomach mixes/churns bolus until its chyme.
Stomach is place of storage--> its ability to distend and accept bolus after bolus of food allows for distention
44
Distention activates
production of G cells which produce gastrin which Stimulates parietal cells to secrete HCl, stimulates chief cells to secrete pepsinogen, maintains structure of gastric mucosa
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Cells involved in stomach function
mucous cells, parietal cells, chief cells, g cells, d cells
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Mucous cells
secrete copious amounts of mucus that has bicarbonate that stick to tissue in contact with food
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Parietal cells
secrete H+ and Cl- as well as an intrinsic factor which plays an important role in absorption of vitamin B12
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Chief cells
secrete enzyme pepsinogen which is the inactive form of pepsing (protein-digesting enzyme)
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G cells
produce/secrete the hormone gastrin (hormone in blood supply--> receptors for gastrin are in stomach)
50
D cells
secrete hormone somatostatin which acts as a negative feedback loop to inactivate production of G cells
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Somatostatin
acts as a negative feedback loop to inactivate production of G cells
52
Pyloric sphincter
One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the pylorus (opening into the small intestine) that holds food in the stomach until it is thoroughly mixed with gastric juices.
53
Small intestine general anatomy
longest part of the GI system (12-14 feet) made up of three sections: 1. duodenum 2. jejunum 3. ileum
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Duodoenum
chemical digestion/absorption
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Jejunum
where most absorption occurs
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Ileum
colon. Absorption of H2O, electrolytes, bile, salts, vitamin B12
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Absorption occurs most rapidly because of
extensive foldings
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Microvilli
microscopic folds in mucosa, allows absorption to occur rapidly in small intestine
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Enterokinase
embedded in microvilli wall allows trypsinogen to get hydrolyzed to active form trypsin
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Sucrase
digests sucrose to glucose/fructose
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Maltase
digests maltose to glucose
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Lactase
digests lactose into glucose/galactose (lactose intolerance if unable)
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Aminopeptidase
produce free amino acids
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phosphatase
necessary for Calcium reabsorption, requires vitamin D
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Activation of small intestine
motility of small intestine activated by chyme, creates a slow peristalsis. Contractility is enhanced by chyme but it is also intrinsic, so it is happening the absence of food via pacemaker cells connected by gap junctions
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What does chyme in the small intestine activate?
Activates CCK, activates secreton hormong which inhibits: gastrin, HCl, and stomach motility--> activates insulin from pancreas (increases pancreatic secretion
67
Functions of secretin and CCK
both are secreted by duodenum response to different stimuli and have different primary effects
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CCK function
secretion stimulated by protein and fat content of chyme. CCK then stimulates secretion of pancreatic juice enzymes that help digest these molecules. Partially digested proteins/fats stimulate CCK secretion which lowers as the chyme passes out of the duodenum into the jejunum
69
Secretin function
After a meal when acidic chyme reaches duodenum secretin stimulates bicarbonate and water secretion from pancreatic ductules. Uses cAMP as a second messender--> potentiated by ACh using calcium as a second messenger to stimulate bicarbonate and water secretion. Bicarbonate entering chyme helps prtoect the duodenum mucosa and provides optimal pH environment for pancreatic juice digestive enzymes. HCl passes from stomach into the duodenum releasing secretin into bloodstream and stimulating pancreas to secrete water and bicarbonate into pancreatic ducts which drain into the duodenum. Inhibits secretion of gastrin which triggers initial release of HCl into the stomach--> delays gastric emptying
70
Esophageal pyloric sphincter
sometimes called gastroesophageal sphincter, or pyloric sphincter. a ring of muscular tissue that when the bolus of food contacts the sphincter it allows the presentation f the bolus into the stomach.
71
What functions are served by churning bolus into chyme?
Storage-distensible, antimicrobial function (Acidic) pH=2. Acid enables denature of proteins. Acid enables activation of pepsin from pepsinogen to degrade proteins.
72
mucosal layer
Folds have these deep crevices, and coating all of this is a thick layer of mucus, and so you can see up near the top of the folds are mucus cells, that are secreting a thick layer of mucus pretty much all the time. Stimulated by the bolus entering the stomach, when the bolus comes in, that stimulates bolus cells to secrete more. So then we see a little farther down in these crevices are cells called parietal cells which secrete HCl
Light pink cells are the schematic parietal cells to show how HCl gets secreted into the lumen of the stomach
On the apical surface (inside surface) are K/H ATPases, primary active transport using energy of ATP hydrolysis to secrete hydrogen ions. Which come from carbonic anhydrase.
Carbonic anhydrase comes from red blood cells to move co2 like in the kidneys
73
Major cells in stomach
Mucus cells- mucus +HCO3
Parietal cells- h+, cl-, intrinsic factor (b12)
Chief cells- pepsinogen pepsin (active form) which can feed back to form more
G cells- gastrin, secreted in response to protein/peptides (signals in stomach)
74
The vagus nerve
stimulates g cells, chief cells, parietal cells
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Digestive enzymes in microvilli (brush border)
```
enterokinase
lactase, sucrase, maltase
aminopeptidase
phosphatase
lipase
```
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Enterokinase
activates trypsinogen from trypsin
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Phosphatases
calcium absorption requires vitamin D
78
Muscle activity in small intestine
slow peristalsis
| segmentation-intrinsic pacemaker cells
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Colon (large intestine) anatomy
no villi- much smoother. Three patts, ascending( right) colon, transcverse colon, descending (left colon, sigmoid colon, rectum aanus
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Pancreas
endocrine gland secretes insulin and glucagon. Exocrine gland secretes bicarb and 20 enzymes
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Regulation of digestive system
enteric nervous system- presence of chyme, protein. Autonomic nervous system (vagus nerve) gut hormones.
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Intestinal regulation
enteric nervous system and hormones regulate motility. Reflexes: gastroileal, ileogastric; intestino-intestinal. paracrine regulation: ECL cells secrete serotonin and motilin.
83
The presence of lipids and carbohydrates stimulates
CCK and GIP which inhibit chief cells (from producing pepsinogen) and parietal cells (from producing HCl) and peristalsis.
84
Decreased pH stimulates during the intestinal phase
secretin, which contributes to inhibiting chief cells (from producing pepsinogen) and parietal cells (from producing HCl) and peristalsis.
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Stomach to intestine
chyme enters duodenum causing the release of CCK and secretin from duodenal enteroendocrine cells
86
CCK
induces secretion of enzyme rich pancreatic juice
87
secretin
causes the secretion of bicarbonate rich pancreatic juice
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Bile salts and to a lesser extent secretin transported via blood stream stimulate
liver to produce bile more rapidly
89
CCK via blood stream causes
gall bladder to contract and hepatopancreatic sphncter to relax so that bile enters the duodenum
90
What is the bottom-line message of Richards + Gumz’s review?
Circadian regulation of all body systems
Important of down-time
Central/peripheral “clocks”
How are physiological systems regulated and coordinated to optimize overall functions
Heart and lungs would regulate with endocrine system, and nervous system, ex: hypothalamaic adrenal
91
Functions of the colon
absorb water, electrolytes and certain vitamins from the chyme it gets from SI. passes waste products out of the body through rectum
92
Anatomy of the colon
descending, colon, peritoneum, ascending colon, transverse colon, sigmoid colon, rectum, anal canal
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Descending colon
stores food to be emptied into rectum . walls absorb water and remaining nutrients/vitamins from feces
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peritoneum
holds colon together. thin layer of tissue that supports abdominal organs
95
ascending colon
carries feces from cecum superiorly along the right side of the abdominal cavity to the transverse colon
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cecum
first part of the colon between the small intestine and large intenstine
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Liver
monitors all the material coming through intestinal system, place where things like alcohol can be detoxified, where cholesterol metabolism si regulated. Blood is screened and old RBCs degrade and hemoglobin is metabolized. the site of the production of plasma proteins like albumin but also the proteins that are part of the blood clotting cascade
98
Gallbladder
tissue-organ that stores bile and contraction of that duct can be regulated by the digestive process
99
pancreas
has endocrine function through insulin secretion into the bloodstream and exocrine function via bicarbonate
100
Enteric nervous system
neurons/glial cells organized into ganglia that are interconnectedby outer myenteric plexus (found along entire GI tract) and the inner submucosal plexus (located in small/large intestine). Intrinsic afferents= sensory neurosn that have theri cell bodies in the myenteric or submucosal plexuses and synpase with interneurons of ENS. Out number extrinsic afferents (Regulated by autonomic NS) emphasis is on local regulation of intestinal function. Recevies input formautonomic NS but it can and will operate independently of brain and spnal cord
101
Bolus of chyme and GI regulation
stimulates intrinsic afferents-activates enteric interneurons which stimulate motor neurons
102
Extrinsic afferents and different peptide hormones released from intestine alert brain to condition of gi tract
impt for CNS regulation of digestion and in both conscious/unconscious perceptions of food intake.
103
ECL cells of intestinal mucosa and GI regulation
secrete serotonin which stimulates intrinsic afferents which conduct impulses into submucosal myenteric plexus and there activate motor neurons
104
Primary function of GI hormones
maintain strucutre of their target organs by gastrin hormone
