Digestion And Metabolism Flashcards
Name layers of digestive tract
1) mucosa
2) sub-mucosa
3) muscularis externa
4) serosa
What is the secrete and absorb layer of GI tract?
Mucosa
3 layers of muscoa
1) epithelial
2) lamina propria
3) muscularis mucosa
What are the mucus producing cells between epithelial cells of mucosa?
Goblet cells
True/false: epithelial cells are specialized for selective transport across membrane
True
Are junctions between epithelial cells tight or leaky?
Very tight
Surface of epithelial that faces inward in mucosa
Apical or lumenal
How many membranes must a substance pass through in the epithelium of muscoa?
2 (apical and basal)
2 specialized cells in epithelium
1) exocrine
2) endocrine
Where do exocrine cells release substances?
Interior of GI tract
Where do endocrine cells release substances?
Into blood stream
What do GI endocrine cells produce?
GI specific hormones
What do GI specific hormones do?
Regulate and coordinate GI function
What do GI exocrine cells make?
Digestive enzymes and juices
What is sub-mucosa made of?
Thick layer of connective tissue
What are 2 layers of muscularis externa?
1) Inner circular muscle
2) Outer longitudinal muscle
What does inner circular muscle layer do when it contracts?
Decreases diameter of tube
What does outer longitudinal muscular layer do when it contracts?
Shortens the tube
True/false: all layers can be found throughout GI tract but vary in thickness based on function
True
What is purpose of esophagus?
Rapid transport from mouth to stomach
Does the esophagus absorb?
No
What layer is thickest in esophagus?
Muscular
What layer is thin in esophagus?
Mucosa
What is purpose of small intestine?
Digest and absorb food
Does food move fast or slow through small intestine?
Slow
What is thickest layer in small intestine?
Mucosa
What is thinnest layer in small intestine?
Muscular
What part of GI tract has villi/microvilli?
Small intestine
What purpose do villi of small intestine serve?
Increase surface area for absorption
What are serous membranes surrounding GI tract called?
Peritoneum
Serous membrane that lines abdominal and pelvic cavities?
Parietal peritoneum
Serous membrane that lines organs in abdominal cavity?
Visceral peritoneum
“Double layer” that connects parietal and visceral to each other and to body cavity?
Mesentery
Serous membrane that also acts as a conduit for blood vessels, nerves and lymphatic vessels to GI?
Mesentery
What are the 4 basic digestive processes?
1) motility
2) secrete
3) digest
4) absorb
What are 2 movements in motility?
1) mixing
2) propulsion
What is the wave-like movement in GI tract?
Peristalsis
Where is peristalsis more common vs less common?
Stomach vs large intestine
What type of muscles are involved in peristalsis?
Both circular and longitudinal
What type of muscle motion is mostly used to mix?
Circular “segmenting”
What 2 areas of GI only use one type of motility to mix AND move?
1) Stomach
2) Small intestine
What one movement does stomach use to mix and propulse ?
Peristalsis
What does small intensities use to mix and propulse?
Segmentation
What is secreted throughout the gut?
Mucus
What else is secreted into GI tract?
Acids
Bile
Enzymes
What produces digestive enzymes?
Pancreas
What produces bile?
Liver
Are the liver and pancreas part of the digestive tract?
No. Accessory organs.
What 2 things controls timing of secretions?
1) Nervous
2) endocrine
Do secretions start before and after a substance enters GI tract?
Yes
What is the chemical breakdown of food to smallest sub-unit?
Digestion
What are 3 categories of food?
Carbs
Protein
Fats
What are two types of carbs?
Polysaccharides
Disaccharides
What is a polysaccharide made of?
Long chain of monosaccharides connected by glycogen
What is the smallest form of a carb?
Monosaccharides
What are 3 monosaccharides?
Glucose
Galactose
Fructose
What are disaccharides?
2 monosaccharides covalently bonded
What are 3 disaccharides?
Maltose
Sucrose
Lactose
Which monosaccharide can be immediately used by the body?
Glucose
What are monosaccharides, galactose and fructose, converted to before the body can use them?
Glucose
What taste sweet on the tongue?
Disaccharides
What enzyme breaks down polysaccharides?
Amylase
What breaks down lactose?
Lactase
What breaks down maltose?
Maltase
What breaks down sucrose?
Sucrase
What are long chains of amino acids called?
Protein
What enzymes break down protein?
Proteolytic
What enzymes break down fats?
Lypase
What are fats made of?
3 fatty acids connected by a glycerol backbone
What are fats broken down into?
2 free fatty acids + 1 monoglyceride
What is the most important part of digestion?
Absorption
Where does absorption mostly happen?
Small intestine (some in large)
3 non-digestive functions of GI tract
1) excretion (waste)
2) fluid/electrolyte balance
3) immunity
How much fluid does small intestine reabsorb per day?
9-11 liters
What are lymphocytes and mast cells between epithelial and lamina propria called?
GALT (Gut associated lymphatic tissue)
What is GALT a subset of?
MALT (mucus associated lymphatic tissue)
If a pathogen gets through MALT, what are phagocytes in liver that will eat it and trigger an immune response?
Kupffer Cells
True/False: digestion is a very redundant, old system with multiple layers of control
True
Can a quadriplegic still digest food?
Yes
The gut regulating digestion on its own is called local control or?
Short loop
When brain overrides short loop, it’s called the?
Long loop
What is considered the “3rd branch” of the autonomic nervous system?
Enteric Nervous System (ENS)
What does ENS regulate?
Gut function
What part of autonomic nervous system is the ENS a division of?
Parasympathetic
Extremely complex system of post-ganglionic fibers that controls gut and has same number of nerves as spinal cord
ENS
Who is the controller in the extrinsic long loop?
Brain
True/false: ENS is the intrinsic neural system of the gut?
True
ENS operates in what type of feedback loop?
Negative (afferent and efferent)
2 networks of ENS
1) Myenteric
2) Submucosal plexus
What network of the ENS regulates motility?
Myenteric plexus
Where is Myenteric plexus found?
Between circular and longitudinal muscles
What network in ENS regulates H2O, senses composition, directly controls secretions and indirectly controls motility and absorption?
Submucosal plexus
Where is Submucosal plexus located?
In Submucosa
What 2 things influence Extrinsic Control (long loop) of gut?
1) Sympathetic nervous system
2) Vagus input (parasympathetic)
What part of Extrinsic control inhibits digestion?
Sympathetic
What part of Extrinsic control promotes digestion?
Vagus input (parasympathetic)
System of endocrine cells throughout GI tract that release GI hormones?
Enteric Endocrine System
1st way enteric endocrine system will release hormones
Senses change in gut
2nd way Enteric Endocrine System releases hormone
Instructed by ENS submucosal plexus
3rd way Enteric Endocrine System releases hormones
Gets instructions from Vagus nerve (only long loop)
4th way Enteric Endocrine System can release hormones
If instructed by other GI hormones
Anticipatory control
Extrinsic nervous system
How many different amino acids make up proteins
20
Does food absorption take place in the mouth?
No
What triggers a wave of peristalsis through the esophagus?
Food passing through pharyngoesophageal sphincter
What sphincter leads from esophagus to stomach?
Gastroesophageal
Three regions of stomach
Fundus (top)
Body (middle)
Antrum (bottom)
Where are pacesetter cells that start peristalsis in stomach?
Fundus
What is middle stomach used for?
Storage of food
What part of stomach uses its thick muscle to mix food with digestive juices?
Antrum
What leads from stomach to duodenum?
Pyloric sphincter
What is volume of stomach when empty?
50 ml
How much can stomach expand to when full?
20 fold
Folds of stomach are called?
Rugae
When rugae relax to allow for expansion, it’s called?
Receptive relaxation
What part of ENS controls motility in stomach?
Myenteric plexus
In Fundus, what happens to pacemaker cells when food is eaten?
Depolarization
When depolarization of pacemaker cells reach a threshold, what happens?
Action potential
What does action potential waves from pacemaker cells do?
Cause peristalsis
Food mixed with digestive enzymes is called?
Chyme
A small amount of chyme enters duodenum via?
Pyloric sphincter
Stomach mucosa gastric pits have glands with endocrine and exocrine cells that do what
Excrete digestive enzymes and gastric juicers
Mucosa of fundus is called?
Oxyntic mucosa
Mucosa of antrum is called?
Pyloric gland area
How is mucus produced in Oxyntic gastric glands different from anywhere else?
It’s very thick and highly alkaline
Why is mucus in Oxyntic mucosa thick and alkaline?
To protect epithelial cells from acidic gastric juices
What cells in oxcyntic gastric gland make HCl acid and intrinsic factor?
Parietal cells
What cells in oxyntic gastric gland make pepsinogen (inactive form of pepsin)?
Chief cells
What does intrinsic factor do?
Binds to B-12 to help it absorb in end of small intestine
How is pepsinogen activated to make pepsin?
When it hits stomach acids
What is endocrine cell of gastric gland?
ECL cell
What do ECL cells release?
Histamine
Why is histamine that is released by ECL cells considered a hormone?
Because it’s released directly in bloodstream
What does histamine from ECL do?
Locally acts on parietal and chief cells to help them release HCl and pepsinogen
What is a hormone that acts locally on the gland that secretes it?
Paracrine
What are endocrine cells of pyloric gland area in antrum?
G-cells
D-cells
What do G-cells produce?
Gastrin
What stimulates stomach secretion and motility by acting on chief and parietal cells?
Gastrin
What do D-cells produce?
Somatostatin
Decreases gastric secretion and motility when food moves out of stomach; antagonist to Gastrin
somatostatin
4 phases of gastric secretion and motility (ICGI)
1) inter-digestive
2) cephalic
3) gastric
4) intestinal
Phase without thought, smell, etc of food
Inter-digestive
Inter-digestive phase gastric secretion is highest when?
Evening
Inter-digestive phase gastric secretion is lowest when?
Morning
What phase of gastric secretion are all cues anticipatory?
Cephalic
Is there food in GI tract in cephalic phase?
No
What stimulates secretion/motility in cephalic phase?
Smell, taste, chew—anything before food hits stomach
Phase when food enters stomach
Gastric
Gastric phase is short or long loop?
Both
Final phase of gastric where secretion/motility slow?
Intestinal
2 triggers of intestinal phase?
Food leaves stomach
Food enters duodenum
Is intestinal phase short or long loop?
Both
What does brain trigger in cephalic phase upon smell, thought, taste, etc of food?
Vagal stimulation of ENS
What secretions are stimulated in cephalic phase?
Pepsin, HCl,
When food is in stomach in gastric phase, what senses stomach expansion?
Submucosal plexus
What sensory arm senses food in stomach in gastric phase
Vagal afferent
What cells sense movement of food from stomach to duodenum?
D-cells
What factors do D-cells sense?
Drop in ph and protein
What does gastric emptying depend on?
Strength of antral peristalsis
What do signals from stomach and duodenum regulate?
Gastric emptying
What key things does the duodenum sense during gastric emptying?
Low pH
Protein
Fats
When duodenum senses acid, fat, (hypertonicity, protein, distension) what does it signal to stomach?
Slow down
What does slowing down motility of stomach signal the release of
Bile (liver)
Digestive enzymes and NaHCO3 (pancreas)
The presence of what slows gastric emptying the most?
Fat (creates bottle neck at duodenum)
Where does fat digestion begin and end?
Duodenum
When mucosal cells of duodenum are triggered, what are the 2 types of responses?
Neural
Hormonal
What is the neural response of the duodenum?
Enterogastric reflex (slow down)
What hormones are released by duodenum?
CCK
Secretin
What does CCK do?
Increases enzymes and bile
Slows emptying
Secretin triggers release of what?
NaHCO3
In pancreatic ducts, what cells release digestive enzymes?
Acinar cells
What hormone targets acinar cells?
CCK
In pancreatic ducts, what cells release sodium bicarbonate?
Duct cells
What hormone targets duct cells?
Secretin
3 pancreatic proteolytic enzymes are
1) trypsin
2) chymotrypsin
3) carboxypeptidase
Which is first of pancreatic protein enzymes to be activated?
Trypsin
What activates trypsin?
Aminopeptidase
Where is aminopeptidase found?
Mucosa of small intestine
True/false: trypsin activates chymotrypsin and carboxypeptidase
True
What does salivary amylase in mouth break down?
Carbohydrates
What is antibacterial enzyme in saliva?
Lysozyme
Where is our only source of lipase made?
Pancreas
What is bile made of?
Alkaline fluid
Organic compounds (salts, lipids..)
What does bile do to fat?
Emulsifies it
What is purpose of making smaller droplets of fat thru emulsification?
Increase surface area for lipase action
Bile goes from liver through what structure?
Bile duct
What is sphincter between bile duct and duodenum?
Sphincter of Oddi
If not digesting fat, what happens to sphincter of oddi?
Tightly closes
Where is backed up bile in duct stored?
Gallbladder
If we eat fat and protein, what hormone opens sphincter of oddi, contracts gallbladder and stimulates bile production?
CCK
How much of bile salts get reabsorbed in terminal section of small intestine?
50%
When small intestine reabsorbs bile salts, where do they go and what do they do?
Back to liver and trigger liver to make more bile
What kind of feedback loop is bile going back to liver from small intestine and stimulating more bile production?
Positive feedback
When does positive feedback loop of bile reabsorption/production get shut off?
Fat digestion complete
CCK not released
Sphincter shuts
Bile stored in gallbladder
3 sections of small intestine
Duodenum
Jejunum
Ilium
What motility mixes and moves small intestine?
Segmentation
Propulsion in small intestine is fast or slow?
Slow
Rate of contractions from high to lower small intestine
12/min to 9/min
Brush border villi and microvilli increases surface area how much?
600 times
Structure of villi is specialized for what?
Absorption
Smallest form of absorbable fat
Micelle
What is reabsorbed in large intestine
Water, salts, etc
Two types of movements in large intestine
Haustral contractions
Mass movement
What type of movement are haustral contractions?
Mixing (Slow, segmentation)
What type of movement is Mass movement?
Strong Propulsive
What strongly triggers mass movement?
Gastrin
If feces enters rectum and distends it, what is triggered?
Defication reflex
Stretch receptors in rectal wall cause relaxation of what?
Internal anal sphincter
