Kin 132 Digestive system Flashcards
What are the goals of the digestive system?
- Breakdown food to absorbable size
- Elimination of remaining material that wasn’t absorbed
Explain what the macromolecules ingested are turned into
Carbohydrates:
- Macromolecule: Carbohydrates
- Intermediate: Disacharides
- Final: monosaccharides
Proteins:
- Macromolecole: Polly peptide
- Intermediate: Peptide
- Final: Amino acids
Tryglyerides:
- Macromolecule: Triglycerides
- Final: Monoglyceride
Explain the phases of the digestive system
- Ingestion - Enter to GI tract
- Motility - Movement of food for mixing or propulsion
- Secretion - Addition of water, enzymes, and environmental factors to the GI tract. Mixed in during mixing
- Digestion - Breaking down food either physically or chemically
- Absorption - Substances enter body
6 Excretion - Un absorbed substances are secreted at anus
What is a environmental factor?
They create the optimal conditions for enzymes to operate in. usually causing acidity or alkylinity
What process of digestion only happens at a specific spot?
Excretion only happens at the anus
Explain the anatomical components of the digestive system
- Gastrointestinal tract: Muscular tube from mouth to anus
- Accessory structures: Contributes to GI tract, eg. Teeth, pancreas
Explain the receptors in the GI tract that detect the injestion of food, and what effect they have
Receptors:
1. Mechanoreceptors - stretch of GI tract
2. Osmoreceptors - Osmotic pressure
3. Chemoreceptors - acidity and specific nutrient concentrations
These send a signal to…
Smooth muscle:
1. Circular muscle layers: wrap around GI tract
2. Longitudinal muscle layers: run along GI tract
Epithelial cells:
- Enteroendorcrine cells - hormone secretion
- Exocrine cells - Enzyme and environmental factors secretion
- Muscous cells - mucous secretion
Explain the neural regulation of the GI tract
The ENS is made of two main nerve plexuses, that Arte used for communication between: plexuses, receptors to plexuses and CNS to plexuses:
- Myenteric plexus
- most connections with the circular and longitudinal muscles - Submucosal plexus
- Most connections to the epithelial cells
What is the ENS
- Enteric Nervous system
- Works as a second brain for the enteric system
- Functions separately from the CNS
What are the different pathways the ENS can use
Short reflexes:
- Stays inside of the GI tract
- Stimulus causes receptor to send a signal to the nerve plexuses which sends a efferent signal to cause a effect
Long reflexes:
- Travels outside of the GI tract
- Stimulus causes receptor to send a afferent signal to both the nerve plexus and the CNS
- CNS sends a signal back to the nerve plexus
- Nerve plexus send efferent signal to cause a effect
Explain the hormonal regulation of the GI tract
- Enteroendocrine cells have one side facing the lumen of GI tract and one side facing bloodstream
- When stimulus arrives, enteroendocrine cell releases hormone into the bloodstream which circulate to their target cells
- Response from these hormones can be excitatory of inhibitory
- Key hormones released:
1. Gastrin
2. Secretin
3. Cholecystokinin (CCK)
4. Somatostatin
Explain the salivation regulation of the GI tract
- Salivary center is in the medulla oblongata
- Salivary center sends parasympathetic signal to the submucosal plexus = increased salivary gland activation = increase3d salivation
- Always a base level of stimulus being sent to the salivary center, but stimulus such as food, smell, thought of food can increase this stimulation
Explain the cephalic regulation of the GI tract
- Cephalic stimuli sends signal to the salivary center
- Increase cephalic stimulus = increased parasympathetic signal to submucosal plexus = increased salivation = increased water and enzymes
- Cephalic stimuli doesn’t need to involve actually eating, eg, sight smell
- Also sends a parasympathetic signal to the stomach to increase acid secretion and stomach motility to prepare for food
- Cephalic stimuli such as stress or dehydration will cause the salivary center to send a sympathetic signal to the submucosal plexus = decreased salivary gland activity = decreased saliva volume
Explain the composition of saliva
- Saliva enters at the mouth which contains:
- water: moistened food, helps with taste, and cleans mouth
- Muscus: lubricates food, pharynx to help with swallowing
- Bicarbonate: Helps neutralize food acids
- Lysomes: kills bacteria
- Enzymes: start of chemical digestion. contains salivary amylase and lingual lipase
Explain the function of Salivary amylase and lingual lipase contained in saliva
Salivary amylase:
- Breaks polysaccharides down into disaccharides
- Opperates best in slight acidity (from the mouth down to fungus of stomach)
Lingual lipade:
- Breaks triglycerides down into monoglycerides
- Opperates best in highly acidic environments (In body and antrum of stomach)
- While this enzyme is added in the mouth it isn’t most effective until the bottom of the stomach
- Both work in all acidity levels but work better in their optimal conditions
Explain chewing (Mastication)
Goals:
- Physical digestion - increases surface area
- Motility - mixing food with enzymes added
- Forming a bolus (semi solid mass for swallowing)
- Absorption in mouth is limited, except for some vitamins and minerals and drugs and alcohol
Explain swallowing (Deglutition)
- The more liquid the bolus is the faster its swallowed
Stage 1: Voluntary stage
- Voluntary
- Tongue pushes bolus up and back moving it from oral cavity to pharynx
Stage 2: Pharyngeal stage
- Involuntary
- Oral pharynx receptors send signal to swallowing centre that bolus is present
- Swallowing center sends signal to:
1. uvula: blocks nasal pharynx
2. Epiglottis: blocks laryngeal pharynx
3. Tounge: blocks oral pharynx - Inhibits respiratory muscles, stopping breathing temporarily
- Relaxes upper esophageal sphincter, helping bolus enter esophagus
- Once bolus enters esophohus = no stimulus to swallowing center, structures move back to normal position and breathing resumes and upper esophageal sphincter contracts blocking back flow into pharynx
3rd stage: esophageal stage
- In esophagus
- Involuntary
- Peristalsis occurs: circular muscles contract above bolus and longitudinal muscles contract to push bolus along
- Lower esophageal sphincter relaxes to let bolus into stomach
Explain regurgitation
- Once bolus is in stomach, lower esophageal sphincter contracts blocking back flow into esophagus
- If lower esophageal sphincter isn’t contracted enough, when stomach motility occurs acid from stomach may regurgitate back into the esophagus
- Not enough contraction can be caused bye alcohol and smoking
Explain the process that occurs in the stomach
- Stomach expands in order to store food before entering the intestines as injection is faster than digestion and absorption
- Mixing waves from propulsion and retropulsion mix the food in the stomach turning it into chyme. Pace determined by pacemaker cell in stomach
- Stronger motility in the antrum and body, weaker in the fundis
- Every time the propulsion causes a wave to go to the duodenum, a small bit of chyme will move into the duodenum. More mixing waves = more chyme into duodenum
Explain the gastric phase
- Food arrives in the stomach, detected by increased distention, lowered acidity, and increase in amino acids and peptides
Neural response:
- Increase HCl secretion
- Increased gastric motility = increased gastric emptying
Hormonal response:
- Increased secretion of gastrin causing:
1. increased HCl secretion
2. increased gastric motility, pyloric sphincter relaxes = increased gastric emptying
3. increased contraction of lower esophageal sphincter = prevent regurgitation
Explain the gastric gland
The gastric gland is a canal in the stomach containing key cells
- Parietal cells - secrete HCl
- Chief cells - secretes pepsinogen into stomach which gets added to chyme
- Entrochromaffin - like - secretes histamine
- Muscous cells - Secrete mucous and bicarbonate into stomach lumen protecting it from HCl
- Enteroendocrine cells
- G cells: secrete gastrin into bloodstream
- D cells - secrete somatostatin into bloodstream
Explain what pepsinogen does
- Enzyme Released by chief cells
- In its inactive form, converted by HCL into pepsin once out in lumen
- Pepsin breaks polypeptides into peptide fragments
- Most active in highly acidic environments
Explain the function of adding HCl
- Affects the enzymes added in the mouth: decrease in activity of salivary amylase, increase for lingual lipase
- Partially open up polypeptides folded structure so its easier to break its bonds
- Kills pathogens
Explain how parietal cells create HCl
- Parietal cells form H+ and bicarbonate from water and carbon dioxide
- H+ crosser apical membrane into stomach lumen by primary active transport
- Bicarbonate crosses basolateral membrane, pushing Cl- into the cell
- Cl- crosser apical membrane into stomach lumen via facilitated diffusion and brings with H+ to form HCl
Explain acid regulation in the stomach
- If gastrin, histamine, or acetylcholine is released, they bind to receptors on the basolateral membrane of the parietal cell
- If this happens it increases the release of second messenger inside the parietal cell, which bind to receptors on the apical membrane
- This causes more pumps to be inserted on the apical membrane, allowing more H+ to cross into the stomach lumen, resulting in a higher stomach acidity
- If somatostatin is released it binds to receptors on the basolateral membrane causing a decrease in second messenger = lower insertion of pumps = decreased movement of H+ = decreased stomach acidity
Explain the intestinal phase that regulates gastric emptying
- When food arrives in the duodenum
- Tells the stomach to decrease gastric emptying by decreasing gastric motility and increases contraction of pyloric sphincter in order to match gastric emptying to small intestine digestion and absorbtion
- Food arrives = receptors detect a increase in amino acids, acid level and distention
Can either go the neural pathway or hormonal pathway
Neural pathway:
1. Short reflex: tell the stomach to decrease gastric emptying via enteric neurons
- Long reflex: signals to CNS to increase sympathetic firing and lower parasympathetic firing to stomach = decreased gastric emptying
Hormonal pathway:
1. Cause a secretion of CCK and secretin into bloodstream which bind to target cells on stomach = decreased gastric emptying
What are some other factors that can affect gastric emptying
emotions:
- Sadness pain: inhibit
- Anger, aggression: stimulate
Exersize:
light activity: stimulate
High intensity: inhibit
Explain the accessory structures, the liver and gallbladder
- Bile is produced in the liver
- When bile not needed immediately it flows into the gallbladder for storage
- When needed for digestion, fatty acids in the duodenum trigger release of CCK into bloodstream = binds to gallbladder and sphincter of Oddi
- This contracts the gallbladder = increased bile flow into common bile duct = flows into duodenum
- This also relaxes the sphincter of Oddi = increased bile flow into duodenum
What is bile composed of?
- Bicarbonate
- Phospholipids
- Bile salts
-etc
Explain the accessory structure: The pancreas
- When chyme enters duodenum from stomach its very acidic
- Acid must be neutralized for pancreatic enzymes to be optimal
- Bicarbonate from bile helps neutralize, but most bicarbonate comes from the pancreas
- High acidity in duodenum = secretion of secretin from the small intestine = higher plasma secretin level = signals for pancreatic duct cells to make bicarbonate
- Pancreatic duct cells create bicarbonate from water and CO2
- Bicarbonate is released into the pancreatic duct
- Pancreatic duct flows into the duodenum
- Small intestine acidity is neutralized
Explain the digestive enzymes that get released into the duodenum by the pancreas
- Trypsin, chymotrypsin: Split polypeptides into peptide fragments
- Carboxypeptidase: splits a amino acid off the end of a polypeptide
- Pancreatic lipase: Splits triglycerides into fatty acids and monoglycerides
- Pancreatic amylase: Splits polysaccharides into disaccharide maltose
Proteins are secreted inactively and are activated inside the duodenum
- Tripsinogen activated to: tripsin by: enterokinase (a brush border enzyme)
- Chymotripsinogen activated to: chymotrypsin by: trypsin
- Procarboxypeptidase activated to carboy peptidase by: trypsin
What is a brush border enzyme
Enzyme attached to the apical membrane of the stomach
Explain pancreatic digestive enzyme regulation
- High fatty acids and amino acids in intestines results in a I crease in CCK secretion = high CCK plasma level
- Increased CCK plasma level = stimulates the pancreatic Acinar cells to increase enzyme secretion into the small intestine
- Increased enzymes = increased digestion and absorption of fat and proteins
Where does most of the absorption occur?
Small intestine
Explain what segmentation is in the small intestine
- alternating areas of contraction vs relaxation of the circular muscle cells creating a back and forward motion
- This helps: mechanical digestion, motility to mix chyme with enzymes for chemical digestion
- Helps bring the chyme into contact with absorbing surfaces
What increased and decreases the rate of segmentation?
increases: Parasympathetic stimulus and gastrin
Decrease: sympathetic stimulus
Explain absorption in the small intestine
- Substances get absorbed through the apical membrane into the absorptive cell
- Moves from absorptive cell through the basolatteral membrane into interstitial fluid
- Interstitial fluid into usually blood capillaries, or into lacteal
- Small amount can travel paracellularly
Explain the process of absorption of carbohydrates in the small intestine
- Carbs arrive in the lumen as disaccharides
- Disaccharides get broken into monosaccharides:
- Sucrose into sucrose by brush border enzyme: sucrase
- Lactose into galactose by brush border enzyme: Lactase
- Maltose into glucose by brush border enzyme: maltase
- Glucose and galactose get moved into cell by second active transport (cotransport) with sodium with (SGLT) transporter
- Fructose moved into cell via facilitated diffusion using (GLUT) transporters
- Fructose, glucose, and galactose move across the basolateral membrane by facilitated diffusion with GLUT transporters (different types)
- They move from interstitial fluid into blood capillaries via simple diffusion
Explain the absorption of proteins in the small intestine
- 2 pathways for absorption across the apical membrane
- Pathway one
- Small peptides are broken down into amino acids by brush border peptidase (brush border enzymes for proteins)
- Amino acids cross apical membrane via co transport with sodium - Pathway two
- Some small peptides cross the apical membrane into the cell via cotransport with hydrogen
- Small peptides are broken down into amino acids via peptidase inside of the cell
- Amino acids cross the basolateral membrane into interstitial fluid via facilitated diffusion (10 different types of AA transport proteins)\
- AA enter blood capileries via simple diffusion
Explain the absorption of fats in the small intestine
- Fats not soluble in the intestine juices so they form together into fat globules
- Small pieces of the fat globule break off and are covered in bile salts and phospholipids which move polar side outwards to form emulsification droplets
- This prevents emulsification droplets from rejoining the fat globule as well as increasing surface area to be exposed to pancreatic lipase which turns triglycerides into monoglycerides and fatty acids
- Free fatty acids and monoglycerides cross into cell via simple diffusion. Creates problem if too much than can cross
- As a temporary storage, MG and FFA are surrounded by bile salts and phospholipids (polar side facing out) forming a micelle
- Micelle tend to move closer to the apical membrane before releasing the MG and FFA
- Once inside epithelial cell, monoglycerides and FFA reform triglycerides which then combine with phospholipids and cholesterol to form a chylomicron (lipoprotein for transport) which are carried in a vesicle and released into the interstitial fluid
- Chylomicrons enter the lacteal (lymphatic capillarie) as too big for blood capillaries
Explain the problem that occurs if too much monoglycerides and free fatty acids try and cross the apical membrane at once
In order to cross the basolateral membrane, the monoglycerides and FFA bust be released from the emulsion droplet. Only a certain amount of monoglycerides and FFA can cross at once so if theirs a buildup, it causes the reformation of triglycerides since their no longer in the emulsion droplets
What is the difference between a emission droplet and a micelle
Emulsion droplette: contains triglycerides
Micelle: contains monoglycerides and free fatty acids
Explain the absorption of electrolytes in the small intestine
- Sodium absorbed actively brining with it proteins and amino acids
- Negative ions follow sodium via electrical gradient
- Other ions move due to concentration gradient caused by movement of water
- Most ions get re absorbed no matter what not because body needs them
- 2 ions that get reabsorbed based on necessity:
- Calcium
- Responds to blood calcium level
- eg low blood calcium level = increased absorption
- 2 ways its absorbed: Trancellular where parathyroid hormone increases absorption and paracellular which is absorption due to concentration gradient - Iron
- Based on stored levels in epithelial cells
- Transcellular absorption via active transport
Explain absorption of vitamins in the small intestine
Fat soluble:
- Fat soluble vitamins go into micelles and get absorbed with fats
Water soluble:
- Water soluble vitamins get absorbed by simple, facilitated and active transport
- Some get absorbed in large intestine
- Eg. B12 needs to bind to a intrinsic factor produced by parietal cells in stomach to be absorbed in the ileum via endocytosis
Explain the absorption of water in the small intestine
- water follows changes solutes
- Most moves transcellular via aquaporins, but some move paracellular
After absorbed into capillaries where do the materials go?
Carbs and proteins:
- enter blood capillaries which merge into the portal vein going to the liver
Fats (chylomicrons)
- Enters lacteal which eventually enters the bloodstream near the subclavian vein going to the liver
When does segmentation in the small intestine stop?
When food leaves the small intestine
When segmentation stops what takes over?
Migration miolectric complex
- Begins in stomach antrum and travels down small intestine
- Peristalsis like movement that travels for a short distance then stops, then restarts
- If some material is still in the small intestine when MMC gets to allium it runs it again to collect everything
What relaxes the ileocecal valve for movement from small intestine into large?
- Gastroileal reflex (neural): Food arrives in stomach and sends signal via plexuses to ileocecal valve
- Gastrin (hormonal): Released by G cells and binds to ileocecal valve as target cell
Explain digestion and absorption in the large intestine
- Minimal chemical digestion, more bacterial digestion
- Absorbes: water, electrolytes and bacterial products
- Formes feces from unabsorbed material
- Stores faces until excretion
What is bacterial digestion in the large intestine
- Bacteria in large intestine that…
- Ferment carbohydrates that weren’t absorbed producing gas
- Synthesize vitamins
- Undigested fiber converted to short chain fatty acid
Explain what Haustral churning is
- Large intestine made of compartments called haustra
- When a hautsra is filled enough it contracts moving the contents to adjacent haustra
- This mixes material and brings it into contact with absorbative surfaces
Is their peristalsis in the large intestine?
- Most of the time its very weak
- During mass movements its strong
mass movement:
- 3-4 times a day
- Intense peristalsis
- triggered by…
1. gastrocolic flex: signal from food arising in stomach to large intestine via plexus
2. Gastrin: released by G cells and binds to large intestine
Explain the defication reflex
- Rectal muscles are relaxed and sphincters contracted
- When mass moves into rectum it causes distention initiating dedication reflex (urge to dedicate signal sent to spinal chord)
Reflex:
Involuntary:
- Contraction of rectal muscles and relaxation of internal anal sphincter
Voluntary:
- If involuntary phase followed by a signal from the higher brain center for external anal sphincter to relax then excretion happens
Explain the parts of the rectum
- Rectal muscles
- Internal anal sphincter
- External anal sphincter
Explain what happens if voluntary signal isn’t sent to the external anal sphincter
- Rectal; muscles are still contracting, but since external sphincter is closed, it pushes material back out of the rectum into the sigmoid colon
- This removes the distention from rectum and stops signal to spinal chord
- urge to deficate goes away
What is anabolism and catabolism
Anabolisme: building reactions
Catabolisme: breakdown reactions
Explain the two different types of metabolic rates
basal metabolic rate:
- Energy needed to stay alive with basic functioning
Total metabolic rate
- total daily energy use
- 60% of this is basal metabolic rate
