GI Part 1 Flashcards
Digestive System
Primary Function
- _____ nutrients, water, and electrolytes from food we eat into the body’s internal environment
- A _______ line
- _____ down huge (1) into (1) that can be ______
- Transfer
- disassembly
- Breaks down, macromolecules into smaller molecules that can be absorbed
GI Tract Structure
From inner to outermost layer
-
(1) : type of mucus ____ that represents our ____ ____ ____*
- (1): an epithelial barrier where there are mucus producing cells in between epithelial cells creates constant lubricated area
- (1) : behind mucous membrane, type of basement membrane, acellular connective tissue layer
- (1) : smooth muscle layer
- (1) : thicker layer of connective tissue just beyond mucosa
-
(1) : thick layer of smooth muscle
- (1) : smooth muscles arranged around the _______ of the tube, reduces the _______ of the tube when contracting (squeezes on the tube)
- (1) : runs ______ down the tube, _____ the tube when contracting
- (1) : outer covering associated with _____ membranes in the body cavity
-
Mucosa: mucus membrane that represents our absorptive surface area
- Mucous membrane
- Lamina propria
- Muscularis mucosa
- Submucosa
-
Muscularis Externa
- Inner circular muscle: circumference, reduces the diameter
- Outer longitudinal muscle: lengthwise, shortens
- Serosa: serous membranes
Mucous Membrane Properties
Epithelial cells are specialized for ______ transport across their membrane
(1) plasma membrane that faces the interior of the tube
(1) faces neighboring epithelial cell
(1) opposite of apical, faces vascular tissue layers
selective
Apical Surface
Lateral Surface
Basal Surface
Mucus Membrane Properties
- Can things move in between epithelial cells?
(1) designed to not allow any substances to move between them, must pass through apical and basal surfaces
- Other cells besides epithelial cells dispersed among the GI tract
(1) mucus producing cells (general term aka mucosa cells)
(1) secrete digestive enzymes and juices into GI tract
(1) produce specific GI hromones released directly into bloodstream designed to regulate and coordinate GI function
- No
Tight Junctions
- Other cells
Goblet Cells
Exocrine Cells
Endocrine Cells
Different Mucosal Anatomy in Different Regions
No matter where along the GI tract you look, the wall will still have all the basic layers, just minimized or elaborated based on the function of the organ you’re in, so describe the
Esophagus =
Small Intestine =
Purpose is to fast transport food, no absorption or breakdown of food = minimal mucosal layer, thick muscularis externa layer
Purpose is absorption = thin muscle layer, elaborate tower like vili of mucosal cells (to increase SA available for absorption)
Peritoneum
=
- Parietal Peritoneum =
- Peritoneal Cavity =
- Visceral Peritoneum =
- Mesentery =
Comprises the serous membranes of abdominal and pelvic cavity
- serous membranes that line the body cavity
- in between both membranes
- serous membranes that lines the organs
- double layer of peritoneum that connects visceral and parietal layers, designed to connect visceral structures to each other and to the body cavity wall
Mesentery
Serves as a _____ for ____ vessels, ____, and ____ vessels
Shiny stained glass is the mesentery
Conduit for blood vessels, nerves, lymphatic vessels
Four Basic Digestive Processes
(4)
Motility
Secretion
Digestion
Absorption
Motility
Two Movements
(1) Propulsive =
- Frequency of peristaltic waves is ____ in the stomach than in the colon
- Pattern of muscle contractions requires contraction of (2) muscles to move bolus of food forward
(1) Mixing =
Peristalsis = wave of muscle contraction that moves down a length of GI tract
- greater
- both circular and longitudinal muscles
Segmentation Contractions = primarily circular muscle contractions around one segment of tube designed to mix together, chop up, and evenly distribute digestive enzymes and juices with food
2 Exceptions to only Mixing or Propulsion
Stomach
vs.
Small Intestine
Peristalsis in Stomach accomplishes both propulsion and mixing
Segmentation Contrations in Small Intestine accomplishes both propulsion and mixing
Secretion
- _____ secreted throughout gut (ubiquitous)
- Also (3)
- The product secreted is dependent on _____ within the digestive tract
- Timing of secretion is controlled via (2)
- Mucus
- Acid, Digestive enzymes (pancreas), Bile salts (liver)
- location
- nervous and endocrine system
Digestion
Food = ______ composed of individual subunits that are covalently bonded together -> ______ is breaking those covalent bonds
The big (3) Macronutrients are?
macromolecules, digestion breaks covalent bonds
Carbohydrates
Proteins
Fat
Carbohydrates
What are the absorbable units of carbs? (3)
- Usually consumed as
(1) long chains of monosaccharides
(1) enzyme used to break down polysaccharides
(1) two monosaccharides covalently bonded together
(1) breaks down sucrose like in table sugar
(1) breaks down lactose like in milk
(1) breaks down maltose (2 sugar molecules)
- (1) plant source of polysaccharides
- (1) animal sources of polysaccharides from _____ cells
Individual subunits are monosaccharides which are simple sugars (glucose, galactose, fructose)
Polysaccharides
Amylase
Disaccharides
Sucrase
Lactase
Maltase
- Starch
- Glycogen
Proteins
What are the absorbable units?
- Digestion involves breaking them down first into (1) then into individual (1)
- Long list of protein-____ enzymes that our digestive tract employs
- Protein _____ once it comes in contact with HCL -> helps break it into fragments
Amino acids
- polypeptide fragments then into individual amino acids
- protein-lytic
- denatures
Fats
We primarily consume fats in the form of (1) - made up of?
(1) Enzyme used to digest triglycerides
What are the absorbable units?
Triglycerides - 3 fatty acids attached to a glycerol backbone
Lipase
Breaks it down into two free fatty acids and one monoglyceride which is still connected to the glyceride backbone which are all the absorbable units
Absorption
Most ______ process in the digestive tract
(1) has a specific mechanism for transporting water, monosaccharides, fatty acids, and amino acids across mucosal wall and into blood vessels (vast majority of absorption happens here)
Important
Small Intestine
Digestive Processes in the Mouth
Motility - ______
Secretion - ______ (3)
Digestion - ______ digestion begins
Absorption - No _____ is absorbed
Chewing
Saliva - Amylase, Mucus, Lysozyme
Carbohydrate
No food is absorbed
Digestive Processes of the Liver
Motility?
Secretion?
Digestion?
Absorption?
No Motility
Bile
No digestion in Liver
No absorption
Non-Digestive Functions of the GI Tract
- (1)
- (1) Small intestine ______ up to __-__ L/day
-
(1)
- _ _ _ _
- _____ and ____ cells located in between epithelial cells in the lamina propria
- The ______ _____ System
- _____ system of phagocytic cells called (1)
- Excretion - gut is responsible for excretingw waste
- Fluid/Electrolyte Balance reabsorbs up to 9-11 L/day
-
Immunity
- Gut Associated Lymph (GALT)
- Lymphocytes and Mast cells
- Hepatic Phagocytic
- Liver phagocytic cells - Kupffer cells
If a pathogen happens to get into the bloodstream by breaking a gut associated mucosal barrier next place it goes is the liver - Kupferr cells can phagocytize pathogens and initiate immune response
Control and Regulation of the Digestive System
Local Short Loop =
Extrinsic Long Loop =
- Both loops contain a sensor, controller, and effector
- In short loop =
- In long loop =
Local control of the gut when completely separated from signals coming from brain or body, is fully autonomous
Where the brain can influence or directly control, override digestive function
- sensors, mini control centers where sensation can be interpreted, and effecters all throughout GI tract
- sensors throughout the GI tract, but the control center is the brain
Enteric Nervous System
=
- Postganglionic fibers of the _______ nervous system that innervate the gut
- Extremely complex, same number of nerves as _____ cord
- Considered the 3rd branch of the (1)
- Autonomous closed loops: sensory - efferent - _____ feedback
- Controls (4)
An autonmous (short loop) nervous system that regulates gut function and is actually a branch of the parasympathetic nervous system
- parasympathetic
- spinal
- autonomic nervous system
- negative
- motility, secretion, digestion, absorption
While the brain can have some influence over it, can completely regulate gut function without any input (even in spinal cord injuries) “is the brain of the gut” and much more basic than the actual brain
Extrinsic Control of Gut
=
From ______ Nervous System
______ stimulation _____digestion (inhibits secretion and motility)
________ (____) stimulation ______ digestion (stimulates secretion and motility)
Autonomic Action also _______
Ex) ____ food, increases salivary, stomach, pancreatic and liver ______
Extrinsic Long Loop
Autonomic
Sympathetic - SLOWS
Parasympathetic (Vagal) - PROMOTES
discreet
Chewing, secretions
Sympathetic nerves interface the GI tract and
Parasympathetic through the Vagus nerve (which is outside of the enteric nervous system) - PNS can control the enteric nervous system but it doesn’t need that control
Enteric Nervous System (ENS)
ENS is considered the _______ neural system
(2) major neural networks (controllers) of the ENS
Intrinsic
The Myenteric Plexus
The Submucosal Plexus
The Myenteric Plexus
Located where?
Regulates what?
What are the effectors?
Located between the longitudinal and circular muscle layers of Muscularis Externa
MOTILITY
Muscle layers are the effectors
Submucosal Plexus
Located where?
Senses what?
Directly Regulates what? (2)
Indirectly Regulates what? (2)
- ______ release of enzymes _____ motility -> ____ absorption
- ______ release of enzymes _____ motility -> _____ absorption
Blue stars in the submucosa
Sensation it receives portrays composition of what’s inside the tube: fat content, osmolarity, pH, presence of bacterial toxins
DIRECTLY regulates
- water and ion transport across epithelial cells
- intestinal SECRETION
INDIRECTLY influences
- gut motility by communicating with myenteric plexus
- absorption depending on secretion and motility
- Stimulation of enzymes -> Slows motility -> Enhances absorption
- Limit enzymes -> Speeds up motility -> Decreased absorption
-
Submucosal Plexus
Sensory neurons are capable of detecting (5)
Toxin causes
- ______ Absorption
- ______ Water secretion
- ______ Gut Motility
- Net effect =
Distension, pH, Osmolarity, nutrients, toxins
- Decreased
- Increased
- Increased
- Removal of toxin
Ex) Food poisoning in Cabo - submucosal plexus detects toxins and starts to increase mucus secretion, stimulates myenteric plexus to speed up motility, therefore not absorbing much and going to bathroom like crazy -> the whole point is to get rid of the toxin
The Enteric Endocrine System
Where the redundancy of GI regulation comes in
- Endocrine cells can regulate function by?
- Can be instructed to release hormones by the (3)
- Out of the three, how many represent the long loop?
- Secreting GI hormones
- Submucosal plexus of the ENS, Brain through the vagus nerve, or by other GI hormones can stimulate release of second GI hormone
- Only 1 which is the input from the brain through the vagus nerve
The Esophagus
We chew food and push it to the back of the throat which causes distension and the ____ ______ -> triggers opening of the _______ sphincter -> wave of peristalsis down -> food passes ______ sphincter into stomach
Waves of peristalsis will continue if there is _____ food that causes distention that triggers swallow reflex (ie peanut butter that is sticky)
swallow reflex -> Pharyngoesophageal Sphincter -> Gastroesophageal Sphincter
lingering
Anatomy of the Stomach
- (1) small area above level of sphincter
- (1) larger area in center of stomach
- (1) lower portion before entering small intestine where gastric _____ occurs
(1) connects stomach and small intestine
(1) First portion of small intestine
- Fundus
- Body
- Antrum - where gastric MIXING occurs
Pyloric Sphincter
Duodenum
Gastric Filling
Volume of stomach when empty - ___ mL
Up to ___ fold change in volume
2 types of Motility in the Stomach
(1) mixes and propels the food
(1) refers to the deeply folded interior of the stomach called _____
- When folds are at maximal _____, shrinks capacity of stomach to about 50ml of volume
- When we consume food, the _____ and expansion of those rugae to expand volume of stomach to 20x bigger
50
20x
Peristalsis
Receptive Relaxation - Rugae
- depth
- relaxing
Motility in the Stomach
Governed by the _____ plexus of the enteric nervous system
(1) group of cells found in myenteric plexus of the stomach that have spontaneous waves of depolarization and set frequency
- At rest, waves of depolarization are not large enough to reach _____
- During food consumption, ______ of pacesetter cells increases and sudden waves depolarization reach threshold and triger waves of action potentials that originate at _____ and move down wall of stomach
- With each wave of action potential comes a wave of _______
myenteric
Pacesetter Cells
- threshold
- excitability
- fundus
How the Stomach Mixes Food
Food enters stomac and mixes with (1)
(1) thick liquid that forms by the time food reaches the antrum, represents food that has been very well mixed with digestive enzymes and gastric juices
Waves of peristalsis move a few ______ of chyme through the pyloric sphincter
digestive enzymes
Chyme
millimeters
How the Stomach Mixes Food
(1) Once wave of food gets down to the pyloric sphincter, what happens?
Peristaltic contraction -The sphincter tightly shuts and food rebounds in the antrum to achieve the mixing of stomach contents
Structure of the Stomach Mucosa
(1) deep invaginations where cells that are responsible for secreting _____ and juices are found at the _____ of these pits
Type of cells found at the bottom of these pits are different in the body and fundus vs. the antrum so we call the mucosa by different names
(1) mucosa in the body and fundus
(1) mucosa in the antrum
Gastric pits - enzymes, bottom
Oxyntic mucosa
Pyloric gland area
Cells of the Oxyntic Mucosa
Mucosa Cells = aka _____ cells that produce very ____, _____ mucus, most common cells found in the pits - purpose is to create a thick protective coating for epithelial cells and ______ from ____ gastric juices - is why we don’t digest our own stomach
Chief Cells = produces ______ in its inactive form ______ -> activated by (1) to convert it to pepsin, functions to break down ______ (is a proteolytic enzyme)
Parietal cells = exocrine cells that secrete ____ and _____ factor (substance that binds to _____ necessary for its ______ in the terminal portions of the small intestine)
ECL cells = releases hormone _______ into vasculature but has paracrine effects (meaning that it acts on the same organ, so it’s actions are local) - histamine acts on _____ cells and ____ cells to stimulate production of ____ and ______
AKA Goblet cells, thick, alkaline mucus, protects from acidic gastric juices
Pepsin, pepsinogen, activated by acidic gastric juices (HCL), breaks down protein
HCL and intrinsic factor (binds to VB12, necessary for its absorption)
histamine, chief and parietal cells to stimulate production of HCL and pepsin
Cells of the Pyloric Gland Area
_____ cells + 2 ______ cells
G cells =
D cells =
Mucosal cells + 2 Endocrine cells
produces hormone Gastrin - stimulates gastric motility and secretion (aka gastrin refers to stomach)
- Secretes mucus, pepsinogen, HCL, intrinsic factor from all above cells and enhances peristaltic waves
- Since it’s a hormone, gets into bloodstream and enhances motility throughout GI tract
produces hormone Somatostatin which is inhibitory - decreases gastric motility and secretion
- Secreted in the intestinal phase
Phases of Gastric Secretion
(4)
Interdigestive Phase
Cephalic Phase
Gastric Phase
Intestinal Phase
Interdigestive Phase
=
Gastric Secretion lowest in the _____, highest in the ______
When we are not eating, thinking, or smelling food (sleeping)
Lowest in the morning, highest in the evening
Cephalic Phase
=
Cephalic refers to head - cues that come outside of the stomach in anticipation of food entering stomach -> long loop of brain
ie) thinking, looking, smelling food makes your stomach grumble and you get hungry which then stimulates secretion and motility
Cephalic Phase Mechanism #1
_____ stimulation of the ______ nervous system through t______, s_______, ch______, and s______ food
- Submucosal pleuxus to stimulate secretion of (2)
- Myenteric plexus to stimate (1)
Vagal, enteric, tasting, smelling, chewing, swallowing
- Chief cells to secrete pepsinogen and parietal cells to secrete HCL
- motility
Cephalic Phase Mechanism #2
Also _____ stimulation of (1) cells to stimulate ______ ->to also act on (2) cells
Vagal, G cells -> Gastrin -> parietal cells (HCL) and ECL cells (histamine)
This is all before food hits the stomach, involves vagal input controlled by the brain
Gastric Phase
=
- D_____ and presence of p______, c_____, a______ are sensed by the submucosal plexus to stimulate (3) cells
- _____ _____ (sensory arm of vagus nerve) also senses food in stomach and further stimulates submucosal plexus -> further stimulates (4)
- So what started in the cephalic phase is just getting _____ in the gastric phase
When food enters stomach and stimulates secretion and motility - both short and long loop
- Distension, protein, caffeine, alcohol -> chief, parietal, and G cells (to again stimulate parietal and ECL cells)
- Vagal afferents -> chief, parietal, ECL, G cells
- bigger
Intestinal Phase
=
- _____ in stomach is withdrawn
- _______ release
- Same signal as gastric ______
D cells =
Helps shut off the flow of gastric juices
- Protein
- Somatostatin
- Emptying
mainly sense the withdrawal of protein from stomach and drop in pH -> release of somatostatin to inhibit parietal, G, and ECL cells
2 sets of triggers for this phase = Food leaving stomach and food entering duodenum (both short and long loop) -> shuts off gastric secretion and slow down motility
Gastric Emptying
Depends on the strength of?
Regulated by signals from the _____ and _____
Gastric Factors (2)
Antral peristalsis
stomach and duodenum
Volume of Chyme
Fluidity of Chyme
Gastric Emptying Notes
When food enters intestines, it needs to slow down a lot for many reasons
1) Lining of duodenum does not have thick ______ mucus covering its lining -> so vulnerable to?
2) Duodenum immediately senses a low pH and things like protein and fat -> all of these things are triggers of intestinal phase and inhibits secretion and motility to slow down gastric emptying bc in order for duodenum to deal with all of these things (acid, fat, protein) needs to stimulate?
- Liver = (1)
- Pancreas = (2)
1) Lining of duodenum does not have thick alkaline mucus, so vulnerable to acidic damage from acidic chyme
2) Pancrease and liver to deliver it’s secretions
Secretes Bile to help with fat digestion
Secretes Digestive enzymes (big package of enzymes capable of breaking down every category of food), enzymes are are dissolved in Sodium bicarbonate solution which neutralizes the acid
Gastric Emptying
Duodenal Factors
What slows down gastric emptying the most?
- F
- A
- H
- D
(1) Neural Response
(1) Hormonal Response
FAT bc fat digestion begins and ends in the duodenum, so 2 most important are fat and acid
- Fat
- Acid
- Hypertonicity (refers to the fact that the macromolecules are converted into multiple particles that elevates the osmolarity of the fluid dramatically (digestion elevates osmolarity of fluid)
- Distension
Enterogastric reflex neuronal reflex of the myenteric plexus to slow down gastric emptying
Enterogastrones 2 hormones released to coordinate liver and pancreatic secretion
Enterogastrones
(1)
(3) functions
(1)
(3) functions
Cholecystokinin (CCK) hormone released when we eat fat
Inhibits gastric emptying
Increases pancreatic secretion*
Increases bile secretion*
Secretin
Inhibits gastric emptying
Decreases gastric acid secretion
Increases pancreatic secretion of HCO-3*
Pancreas
We are focusing on the exocrine portion of the pancreas made up of pancreatic ducts composed 2 cell types
(1) cells secrete (1) - target cells of ____
(1) cells secrete (1) - target cells of ____
Acinar cells -> Digestive enzymes, CCK
Duct cells -> Sodium bicarbonate, Secretin
Three Types of Pancreatic Enzymes
- _____ enzymes (3)
- Pancreatic ______
- Pancreatic ______
-
Proteolytic enzymes
- Trypsinogen — Trypsin
- Chymotrypsinogen — Chymotrypsin
- Procarboxypeptidase — Carboxypeptidase
- Amylase
- Lipase
Pancreatic Enzymes (Notes)
Proteolytic enzymes: breakdown _____
- Active form names (3)
- First to be activated is _____ by an enzyme called _______ found attached to plasma ____ of _____ cells in small intestine
- Aminopeptidase converts trypsinogen to trypsin and then trypsin activates ______ and ______
Amylase: breaks down _______
Lipase: breaks down ______
protein
- Trypsin, Chymotrypsin, Carboxypeptidase
- Trypsin, aminopeptidase, membrane of mucosa cells
- chymotrypsin, carboxypeptidase
carbohydrates
fat
Enzymes going down the GI tract
- In the mouth we have (1)
- In the stomach we have (1) - breaks down proteins
- First time we encounter lipase is in the _____ - pancreatic lipase is our ____ source of lipase
- Again, fat digestion ____ and ____ in the duodenum bc we need ____ from liver and ____ from pancreas to digest fat, overall slows down our digestion
- Benefit =
- Chronic pancreatitis, Cystic fibrosis (deficient pancreatic lipase) = pts look very ____, difficulty maintaining ____ bc can’t digest fat
- Salivary amylase
- Pepsin
-
Lipase in the duodenum, only source
- fat digestion starts and ends in the duodenum, bile, lipase
- fat is the most calorically dense category of food, so in terms of maintaining adequate caloric intake, we are very reliant on fat
- skinny, weight
