Gastrointestinal Physiology Flashcards
What are the 4 processes of the digestive system? Describe each one.
- Secretion
- Exocrine = into lumen of digestive tract
- Endocrine = into bloodstream - Digestion
- mechanical
- chemical (enzymes) - Motility
= coordinated movements/contracts through GI tract
- propels food through each tract segment
- can participate in mechanical digestion (can’t control it though) - Absorption
= movement of macronutrients –> cells of digestive tract –> bloodstream
Function of the STOMACH
= holding centre until the bolus can enter the intestines where enzymes can come digest
- liquifies the bolus to enhance enzymatic digestion
- mechanically breaks down contents with coordinated muscular contractions
Function of the SALIVARY GLAND
= makes saliva that have enzymes for digestion
- a converging duct system (single gland cell secretes into its own duct, and multiple ducts flow into large ducts before all meeting at one main duct)
Function of the GALLBLADDER
= stores bile made by the liver
Function of the COMMON BILE DUCT
= where contents of the liver + pancreas + gallbladder gather together and enter the SMALL INTESTINE where it interacts with the stuff
Define ACCESSORY ORGAN (List them.)
= doesn’t directly come in contact with food stuff
Salivary Gland
Gallbladder
Liver
Pancreas
What path does the food take?
Mouth –> Esophagus –> Stomach –> Small Intestine –> Large Intestine –> Rectum
Functions of SALIVA
- helps us talk (so tongue won’t get stuck on roof)
- keep teeth clean and prevent cavities
- digest food (chemical digestion in mouth)
List and describe the 3 stages of swallowing
- VOLUNTARY STAGE
- the bolus is moved from mouth –> pharynx (back of motuh) by You - PHARYNGEAL STAGE
- Involuntary –> takes over once bolus is far enough back
- nasal cavity + trachae closed off (via nervous reflex) and pushed towards Esophagus - ESOPHAGEAL STAGE
- Involuntary
- bolus moving from esophagus –> stomach
Define MASTICTATION
= chewing; mechanical manipulation of food into a bolus
–> a form of mechanical digestion and motility
- mastication + chemical digestion (salivary amylase and lingual lipase) is what starts digestion at the mouth
- *Lingual lipase secreted in the mouth but not activated until stomach
Define PERISTALSIS
= coordinated contractions and relaxations of both circular and longitudinal muscle in ONE Direction that moves the bolus down the esophagus
- under the control of medulla oblongate (involuntary)
- muscular movement (don’t need gravity)
- movement = relaxation of muscle in front of bolus, contraction of muscles behind bolus
What is Secondary Peristalsis?
= a much more vigorous peristalsis
= initiated if food still lodged in the esophagus
What are the 3 parts to the stomach? And what/where are the sphincters located?
- Fundus
- - lower esophageal sphincter (prevents going back up) – - Body
- Antrum
- - pyloric sphincter –
** the 3 layers secrete different things at different ratios
Layers of the Stomach
what are they, what is in each layer, functions of each layer
MUCOSA –> eggs
- single layers of cells that are either endocrine (secrete hormones) or exocrine (secrete acid, enyzmes)
- rugae (large folds that increase V and SA)
- pits (deep invaginations)
SUBMUCOSA –> cheese (sticks it together)
- Submucosal plexus; neurons important for controlling cells/receiving info from them
- connective tissue, which adheres mucosa to smooth muscle
SMOOTH MUSCLE (MUSCULARIS EXTERNA) –> meat
- circular muscle + longitudinal muscles to change shape of the stomach
- Myenteric plexus
SEROSA –> bun (keeps it together, foundation)
- external layer
- dense connective tissue
What are the 3 types of exocrine cells in the gastric glands? What do they secrete? What’s the functions of each secretion?
- MUCUS NECK CELLS
- secretes mucus (to protect stomach from acid) - CHIEF CELLS
- secretes pepsinogen (activated but doesn’t do anything yet) and gastric lipase (digests lipids) - PARIETAL CELLS (oxyntic cells)
- secretes intrinsic factor, HCl (all are extrinsic factors therefore go into stomach)
What is a G cell?
= enteroendocrine cell in the gastric glands of the stomach
- secrete GASTRIN (hormone) –> gastric motilitycontraction, acid release, & and function
- gastrin travels around the body but comes back and acts on the stomach itself
Describe Mechanical Digestion in the mouth
- gentle mixing waves (every 30sec) = mix food with secretions of gastric glands
- vigorous mixing = as digestion proceeds, begins at the Body and intensifies towards pyloric pump
- Gastric Emptying = pyloric sphincter is slightly open so a small amount of chyme enters into duodenum
- but most of the chyme pushed back into Body so that more mixing can occur
Describe Chemical Digestion in the Mouth
Acidic gastric juices…
What are the different functions of acid in the stomach?
- Activate Lingual Lipase
- lipid digestion
- secreted in mouth, activated with acidic environment
- Activate pepsin
- protein digestion
- converts pepsinogen into pepsin
- Inactivate salivary amylase
- no carb digestion in stomach
- Kill microbes
-Denature proteins - Stimulate secretion of hormones
^ HCl = ^ gastrin = ^ motility = ^ HCl
Describe the 3 regions of the small intestine
DUODENUM
- where enzymes mix with chyme
- most chemical digestion occurs here
- can increase/decrease motility to optimize chem. digestion
- where liver/pancreas secretions enter via bile duct and interact with chyme
JEJUNUM
- many villi to increase SA for optimal absorption
- most absorption occurs here
ILEUM
- less villi, but can still absorb any nutrients that weren’t absorbed before
- backup if jejunum was removed
Describe the Layers in the Small Intestine
MUCOSA
- epithelial cells (endocrine or exocrine)
- capillary system (lyphatic vessels + capillary vessels)
SUBMUCOSA - Submucosal plexus - connective tissue, adheres mucosa to muscularis MUSCULARIS - smooth muscle layer - circular muscle + longitudinal muscles - Myenteric plexus
SEROSA
- dense connective tissue
- external layer that holds small intestine together
Describe SEGMENTATION
= localized mixing contractions that increase interactions of chyme with the absorptive cells in mucosa
- sporadic, shove back and forth
Types of cells in the intestinal wall and their functions
ABSORPTIVE CELLS
- epithelial cells with microvilli
- absorb things across PM into blood vessels/lymphatics
Exocrine:
GOBLET CELLS
- secretes mucus (protect tissue from food and acid)
INTESTINAL GLAND CELLS
- secretes intestinal juice (water, alkaline mucus that neutralizes stomach acid)
PANETH CELLS
- secretes lysozyme (kills microbes)
Endocrine:
S CELLS
- secretes secretin
CCK CELLS
- secretes CCK
K CELLS
- secretes GIP
Define MICROVILLI
“brush border”
- increase the SA of the plasma membrane so that more nutrients can be absorbed
- have Brush Border Enzymes physically attached to the membrane of absorptive cells within the microvilli
Define BRUSH BORDER ENZYMES
= digestive enzymes that break down macromolecules into their smallest, absorbabal level
List the Brush border enzymes and what they digest
–> only monosaccharides and individual AAs can be absorbed, so these enzymes break them down into that
LACTASE
- breaks down lactose –> glucose + galactose
SUCRASE
- breaks down sucrose –> glucose + fructose
MALTASE
- breaks down maltose –> 2 glucose
AMINOPEPTIDASE
- breaks one AA off the end of the peptide
DIPEPTIDASE
- hydrolyzes a pair of AAs into 2 separate AAs
What are the Functions and parts of the LARGE INTESTINE?
- finish absorption (absorbed other contents of the lumen instead of monosaccharides/AAs/fatty acids)
- produce certain vitamins
- formation of feces to be expelled
Parts include: Appendix Ileocecal valve Ascending Colon Descending Colon Rectum
*Haustra = the folds/bumps of the large intestine
What are the 3 parts of motility in the large intestine?
Gastroileal Reflex
- presence food in stomach stimulates opening of ileocecal valve
Haustral Churning
- mixing of contents from one haustra to the next, allowing for optimal absorption
Peristalsis & Mass peristalsis
- unidirectional movement of contents out
What are the cellular structures of the pancreas?
- Common Bile Duct
- Pancreatic Duct
- Ductal cells
- Acher cells (exocrine)
- Islet of Langerhans (exocrine)
Define PANCREAS
= accessory organ that’s connected to the small intestine via two ducts
–> pancreatic secretions come into contact with the chyme in the duodenum, which is vital for digestion
Functions of Exocrine Secretions of the Pancreas
BICARBONATE
- by Ductal cells
- neutralizes acid from stomach
PANCREATIC AMYLASE
- digestion of carbs
PANCREATIC LIPASE
- digestion of fats
TRYPSINOGEN –> Trypsin
- Once cleaved into trypsin (active form), it activates other secretions once in the intestine lumen
CHYMOTRYPSINOGEN –> Chymotrypsin
PROCARBOXYPEPTIDASE –> Carboxypeptidase
PROPHOSPHOLIPASE –> Phospholipase
- digestion of phospholipids
PROCOLIPASE –> Colipase
- lipid digestion
Functions of the Endocrine Secretions (and origin)
INSULIN
- made and secreted by beta cells
- moves glucose into skeletal muscles and adipose cells
GLUCAGON
- secreted from alpha cells
- releases glucose from storage into the blood
SOMATOSTATIN
- secreted by delta cells
- decreases digestive activity (decreases acid secretion in the stomach)
- inhibits insulin and glucagon secretion
Path of Blood Flow TO THE LIVER
- Hepatic Artery (from the heart = oxygenated blood)
- Hepatic Portal Vein (from the GI organs = nutrient rich, deoxygenated blood)
- Hepatic artery and portal vein combine into the Sinusoids (=permeable blood capillaries)
- Sinusoids join together to deliver blood in a central vein
- then, this becomes the Hepatic vein (takes deoxygenated blood to heart)
- comes back again via Hepatic artery (goes towards GI organs and liver)
Define HEPATOCYTE
= cell of the liver
The Functions of THE LIVER
SYNTHESIS OF BILE SALTS
= hepatocyte cells in the liver secrete bile, which aids in the digestion/absorption of lips
- bile is secreted into the bile calculus, which then ultimately merges and goes into the common bile duct (via a converging duct system) and is stored in the bile
- biles salts contained in the bile
EXCRETION OF BILIRUBIN
- waste product excreted via bile and urine
METABOLISM OF CARBS, LIPIDS, PROTEINS
- modification/interconversion of molecules
PROCESSING DRUGS/HORMONES
- metabolic and convert drugs
Path of Bile
Hepatocytes (secreted) –> bile canaliculus –> left and right bile ducts –> Common bile duct
Components of Bile
- BILE SALTS
- help in lipid digestion via helping expose lipids to the lipases that digest them (thru Emulsification)
- CHOLESTEROL
- key base of steroid synthesis, made by liver
- BILE PIGMENTS (Bilirubin)
- give its yellow/green colour
- WATER AND IONS
- to get correct consistency
Function of the Gallbladder (and release of bile)
= stores the bile made by the liver
- as bile remains in the gallbladder, it becomes more concentrated (some of the water is reabsorbed back into the body)
- greater concentration = better at aiding digestion
- Bile is stimulated for release via hormones (i.e CCK)
- secretes bile into duodenum via muscular contraction of tissue surrounding gallbladder
Cephalic Phase Regulation
stimulus, method of control, result
Stimulus: sight, smell, taste of food
Neural Control
- Medulla oblongata
- activation of the enteric (intestine) nervous system
Results in: Increased secretion from - salivary glands - stomach - intestine Increased motility of - stomach - small intestine
Gastric Phase Regulation
stimulus, method of control, result
Stimulus: presence of food/beverage in the stomach, causing Distention
Neural Control
- sensory info to Submucosal Plexus (causes inc. secretions) and Myenteric Plexus (motility)
Hormonal Control
- gastrin
Results in: Increased secretions from - stomach (Hal) - intestine (mucus) Increased motility of - stomach (more gastric emptying)
Intestinal Phase Regulation
stimulus, method of control, result
Stimulus: presence of chyme in the intestine
Neural Control: - sensory info to submucosal plexus (secretions) and myenteric plexus (motility) Hormonal Control: - secretin (S cells) - CCK (CCK cells) - GIP (K cells)
RESULTS IN
Increased secretions from:
- intestine
- pancreas
–> bicarbonate from ductal cells (secretin)
–> digestive enzymes from acinar cells (CCK)
–> insulin from Beta cells (*GIP)
Increased motility of:
- intestine
- gallbladder (contracts and releases bile due to CCK stimulation)
Decreased secretions from:
- stomach (HCl)
Decreased motility of:
- stomach (less gastric emptying)
Sources of Carbohydrates
Simple
- Monosaccharides (glucose, galactose, fructose)
- Disaccharides (sucrose, maltose, lactose)
Complex
- starch
- glycogen
Sources of Proteins
- animal and plant sources
- amino acids (20 different kinds)
- dipeptides
- tripeptides
- polypeptides
Sources of Fat
Triglycerol = glycerol + 3 fatty acids
- fatty acids are variable in length (4-24C, 18C is most common)
- can be saturated or unsaturated
Two Classifications of Vitamins? What are the vitamins within them?
Fat-soluble vitamins (KADE)
- A
- D
- E
- K
Water-soluble vitamins
- B vitamins (except B12)
Process of fat vs. water-soluble vitamin absorption
Fat soluble:
- found in lipid droplets in the GI tract (**need fat in diet to absorb these fat vitamins)
- formation of micelles by bile and then collapse help absorption
- no safety mechanism, therefore can overdose on these
Water soluble:
- requires transporters
- Vitamin B12 also requires intrinsic factor (from parietal cells in stomach)
- if too much, transporters become saturated and excess is excreted
Described the 4 sets of reactions in Cellular Respiration
- Glycolysis
- glucose –> Pyruvate
- cytoplasm of mitochondria
- ATP made - Oxidation of Pyruvate
- pyruvate –> Acetyl CoA
- in matrix - Krebs Cycle
- Acetyl CoA metabolized to form ATP and energy carriers (NADH & FADH2)
- in matrix - Electron Transport Chain
- energy carriers –> ATP
- in inner membrane
The Fates of Glucose
- ATP Production
- oxidized to make ATP - Amino acid synthesis
- converted to AAs if needed - Glycogen Synthesis
- storage of glucose (but limited space) - Triglyceride Synthesis
- when glucose in excess
Describe glucose uptake in the cells of the body
- cells take up glucose from the blood –> ATP production
- via glucose uriporters in membranes
- requires insulin
Describe GLYCOGENESIS
Glucose –> G6P –> Glycogen
- some cells have large capacity to store glucose as glycogen (skeletal muscles, liver)
- some don’t (brain)
Describe GLYCOGENOLYSIS
Glycogen –> G6P –> Glycolysis (or –> glucose if liver)
- glycogen converted to G6P to be used for ATP production
- Liver = unique –> can form glucose straight from glycogen which can then be released into circulation
Describe GLUCONEOGENESIS
- liver creating new glucose molecules from non-carb sources (AAs, lactic acid, and glycerol)
Lactic Acid/AAs –> Pyruvic Acid –> G3P –> G6P
Glycerol –> G3P –> G6P
The fates of Lipids
- stored in adipose tissue as fat deposits
- oxidized to produce ATP
- formation of structural molecules (phospholipids, myelin sheaths)
Triglyceride Storage
Triglycerides store in adipose tissue = major energy source
- 50% in subcutaneous layer of skin
- rest is around kidneys, genitals, between muscles etc.
Describe LIPOLYSIS
= Triglycerides –> Glycerol and fatty acids
Glycerol –> G3P (–> glucose)
Fatty acids –> Acetyl CoA
- longer the chain = more Acetyl-CoA produced
Describe LIPOGENESIS
- liver and adipose cells can make triglycerides from non-lipid sources (glucose and AAs)
Was (can’t form glycerol) –> Acetyl CoA –> Fatty acids –> Triglycerides
Glucose –> G3P –> Glycerol –> Triglycerides
or, technically, glucose can go all the way down to Acetyl CoA and then be turned into fatty acids
Describe KETOGENESIS/Ketone Bodies
Ketone Body = two acetyl CoA condensed
- able to diffuse out of the cell (acetyl-CoA can’t) into blood
- used by other cells for energy
- then, ketone bodies converted back into 2 Acetyl CoA and enter Krebs cycle
** heart and kidneys prefer ketone bodies instead of glucose
Define Protein Anabolism
= formation of proteins from AAs
- as soon as AAs transporter into cells after digestion, they’re reassembled into proteins
List some types of proteins
- enzymes
- hormones
- structural components
- transporters
Define Protein Catabolism
Proteins –> AAs
- released AAs can be converted to other amino acids
- hepatocytes can turn AA –> …..
- fatty acids
- ketone bodies
- glucose
- generate ATP via Krebs (first have to be deaminated to enter Krebs though)
