Lecture 12: Digestion Flashcards
The digestive system consists of what two things?
1) Digestive tract
2) Accessory digestive organs
1) What are the accessory digestive organs?
2) What type of glands are they? Where are they?
3) Where do they secrete?
1) Salivary glands, exocrine pancreas, liver, gallbladder
2) Exocrine glands outside of the tract
3) Into the digestive lumen
The GI tract is 15 feet long and consists of what 12 parts?
Mouth, pharynx, esophagus, stomach, duodenum, jejunum, ileum, cecum, appendix, colon, rectum, anus
Is the GI tract continuous or separate? Why?
Continuous but separate; due to regional modifications
1) Where in the GI tract and digestive system is there striated muscle? (5 places)
2) What is everywhere else?
1) Mouth, pharynx, upper esophagus, external anal sphincter, pelvic floor
2) Smooth muscle
1) What is the lumen a part of?
2) What does this allow?
1) The external environment
2) The tract to tolerate conditions the rest of the body cannot tolerate
What are the 4 reasons why lumen exists?
1) pH of 2 in stomach
2) Digestive enzymes that would break down body tissues
3) Quadrillions of microorganisms that would be harmful or even lethal elsewhere
4) Food that would cause immune responses (and sometimes does in pathological cases)
What are the 4 layers of the GI tract?
1) Mucosa (3 layers)
2) Submucosa
3) Muscularis externa
4) Serosa
1) The mucosa has 3 layers, but what is the primary layer? What does it do?
2) What does mucosa have the ability to do?
1) Mucous membrane; serves as protective surface
2) Can can secret and/or absorb in certain areas
1) What is the submucosa?
2) What property does it provide?
3) What does it contain?
1) Thick layer of connective tissue
2) Elasticity
3) Larger vessels and nerves
1) What is the muscularis externa?
2) What does it consist of?
3) What constricts the tube?
4) What shortens the tube?
5) What does the muscularis externa facilitate?
1) Smooth muscle coat
2) Circular and longitudinal layers
3) Circular muscles
4) Longitudinal layers
5) Propulsion and mixing
1) What is the serosa?
2) What does it secrete? What does this prevent?
3) What is it continuous with? What does this do?
1) Outer connective tissue
2) A slippery watery serous fluid; friction
3) Mesentery; suspends organs from cavity wall
What prevent reflux between specialized compartments?
Sphincters
List 6 sphincters of the digestive system
1) Upper Esophageal Sphincter
2) Lower Esophageal Sphincter
3) Pyloric Sphincter
4) Ileocecal Sphincter
5) Anal Sphincter
6) Sphincter of Oddi
1) What is motility?
2) What is responsible for most of the movement in the digestive tract? Where is it not responsible for movement?
1) Muscular contractions that mix and move contents
2) Smooth muscle, except the beginning and the end
1) Is the digestive tract’s smooth muscle phasic or tonic? Explain.
2) What is this important for?
1) Digestive tract smooth muscle is phasic (bursts of contractions) but also maintains low level tone
2) Important for steady pressure on contents and returning from distension
List and describe the 2 types of motility
1) Propulsive
-Pushes contents forward
2) Mixing:
-Mixes food with digestive juices
-Facilitates absorption by exposing different parts of food to absorbing surfaces
1) What do exocrine glands do in the digestive system?
2) What do the secretory cells of these glands extract?
3) Why?
1) Secrete digestive juices into the lumen
2) Large volumes of water and raw material from plasma
3) Used to form secretions such as bile salts, mucus, enzymes
1) What happens to exocrine gland fluid?
2) What cells do endocrine tissue of GI tract involve?
1) Fluid is only borrowed; returned to blood unless lost through vomiting or diarrhea
2) Cells throughout the length of the tract
1) Are endocrine tissues of the digestive tract well organized?
2) What do they produce?
1) Not in discrete organization like peripheral endocrine tissues
2) Range of signal proteins called GI hormones or GI peptides
1) Define digestion
2) What 3 things are too large to be absorbed from the lumen?
1) Chemically reducing complex materials into smaller absorbable units
2) Carbohydrates, proteins, and fats
List and describe the 2 types of carbohydrates. What type makes up most carbs?
1) Polysaccharides: most ingested carbs, long chains of sugars
2) Monosaccharides: simplest sugars. Rarely found in diet in this form; glucose, fructose, galactose
Glucose, fructose, galactose are examples of what?
Monosaccharides
Where does most absorption take place?
Small intestine
What are proteins? What are they degraded in digestion into?
Combinations of amino acids held by peptide bonds, into AAs or small polypeptides
1) What are most dietary fats?
2) What does digestion split? What does this leave?
3) What is absorbed?
1) Triglycerides (glycerol with three fatty acid molecules)
2) Two of these; a monoglyceride
3) Fatty acids
1) Where does most absorption occur?
2) What 4 things are transferred into the blood or lymph during this?
1) In the small intestine
2) Nutrients, water, vitamins, and electrolytes
There are four factors involved in regulating digestive system function; what are they? [hint: muscle, nerve, plexus, hormones]
1) Autonomous smooth muscle function
2) Intrinsic nerve plexuses
3) Extrinsic nerves
4) GI hormones
1) What is the function of autonomous smooth muscle?
2) What is this called?
1) Rhythmic cycles of depolarization and repolarization
2) Basic electrical rhythm (BER)
1) What layer of the smooth muscle has pacemaker cells?
2) Are slow-waves action potentials? Explain
1) Muscularis externa
2) No, but their peaks may trigger volley of action potentials
1) The muscularis externa of smooth muscle has pacemaker cells; what are they called and what do they generate?
2) Define what is generated.
1) Cells of Cajal; generate slow-wave potentials
2) Self-excitable activity in which membrane potential undergoes alternating depolarization and repolarization
1) How do slow-waves propagate?
2) What happens at threshold?
3) What does autonomous smooth muscle do when not at threshold?
1) Via gap junctions
2) The entire muscle sheet behaves as one
3) Oscillates between depolarization and hyperpolarization
There are two major nerve fiber networks that run along length of GI tract; what are they? What does each provide?
1) Submucosal plexus: secret motor innervation to mucosa)
2) Myenteric plexus: provides motor innervation to muscular layer
1) What nerve plexus functions as GI system’s own nervous system?
2) How many neurons does it contain?
3) Does it self-regulate? What is this called?
1) Intrinsic (myenteric) nerve plexus
2) As many as the spinal cord
3) Considerable degree of self-regulation; enteric nervous system
What are the two parts of the enteric nervous system?
What does each do? What makes up each?
1) Intrinsic afferent neurons: sensory neurons responding to local stimuli
2) Intrinsic efferent neurons: affect motility, secretion, etc.
1) What are extrinsic nerves? What do they do?
2) How do they do this?
1) Nerve fibers from autonomic nervous system that regulate GI tract function
2) Can modify motility or secretion directly or by acting on intrinsic plexuses
What are the two types of stimulation from extrinsic nerves? What does each do?
1) Sympathetic stimulation: Inhibits tract contraction and secretion
2) Parasympathetic stimulation: Enhances digestion
1) What produces GI hormones?
2) What do GI hormones do?
1) Endocrine cells from different regions of the tract
2) Cause excitatory and inhibitory influences on smooth muscle and gland cells
There are 3 types of sensory receptors in the tract wall; what are they? What is each sensitive to?
What does stimulation of any of these receptors do?
1) Chemoreceptors sensitive to lumen contents
2) Mechanoreceptors sensitive to stretch or tension in the wall
3) Osmoreceptors sensitive to osmolarity of luminal contents
-Receptor stimulation results in effector actions and/or neural reflexes
What are the 3 types of effector cells of the GI system? What does each regulate?
1) Smooth muscle cells: motility
2) Exocrine cells: secretions
3) Endocrine cells: hormones
What are the two types of GI reflexes? What is the difference between the two?
1) Short reflex: located within GI tract
2) Long reflex: involves CNS
1) Where does digestion start? Does a lot of it occur here? 2) Does food absorption occur here?
3) What absorption does occur here?
1) Mouth; is minimal (amylase)
2) No, no food absorption in mouth
3) Some medications
1) What does the mouth do to food?
2) What makes up saliva?
3) Does saliva have glucose? What enhances sweet and salty tastes?
1) Moistens food, causing it to be lubricated and also making it stick to itself
2) 99.5% H2O, 0.5% electrolytes and protein
3) No glucose; 1/7th NaCl compared to plasma, enhancing sweet and salty tastes
List 2 important proteins found in the saliva
Amylase and lysozyme
1) What does salivary amylase do?
2) What is lysozyme?
3) What does antibodies does lysozyme contain? What else do they contain and what do these do?
1) Salivary amylase begins digestion of dietary starches
2) Lysozyme, salivary antimicrobial that breaks down bacterial cell walls
3) IgA antibodies and lactoferrin; bind to iron that bacteria need
1) What does saliva do for oral hygiene?
2) What is saliva rich in? What does this do?
3) What does saliva help prevent?
1) Flushes food residue and foreign particles
2) Bicarb; neutralizes acid from foods and bacteria
3) Dental caries
1) How much saliva is secreted a day?
2) At what rate?
3) What is the max salivary rate in response to potent stimuli like sucking a lemon?
1) 1-2L
2) Continuous basal rate of 0.5mL/min
3) Maximum 5mL/min
Saliva production is increased by two types of salivary reflexes; what are they?
Simple salivary reflex and conditioned salivary reflex
1) What is the conditioned salivary reflex also called?
2) When does it occur?
1) Acquired.
2) Occurs without oral stimulation. “Mouth-watering” anticipation.
1) What triggers the simple salivary reflex?
2) What impulse is sent by this trigger? Where to and for what effect?
1) Oral stimulation (chemo- and pressure receptors)
2) Afferent impulse to salivary center in brain stem; increases salivation
1) What promote salivation?
2) What does parasympathetic stimulation do to salivation?
3) What does sympathetic stimulation do to salivation?
1) Both sympathetic and parasympathetic stimulation promotes salivation
2) Watery saliva rich with enzymes
3) Thick saliva rich in mucus
1) What is the pharynx?
2) What is it the common passageway for?
3) What does it contain?
4) What does its motility lead to?
1) Cavity at the rear of the throat
2) Common passageway for digestive and respiratory systems
3) Tonsils
4) Swallowing
1) What receptors are responsible for motility of the pharynx (swallowing)?
2) What impulses do they send? To where?
3) Is swallowing all or none?
1) Pharyngeal pressure receptors
2) Afferent to the swallowing center of the brain stem
3) Yes
1) What does the esophagus begin and end with?
2) What are these?
1) Begins and ends with a sphincter muscle
2) Pharyngoesophageal sphincter and gastroesophageal sphincter
1) Where is the pharyngoesophageal sphincter?
2) What does it do?
1) Upper end of esophagus
2) Prevents air from entering digestive tract
1) Where is the gastroesophageal sphincter?
2) When is it contracted? When does this increase?
3) What does it prevent?
1) Lower end of esophagus
2) Stays tonically contracted, increases with inspiration
3) Gastric contents from regurgitating
1) What pushes the bolus between the two esophageal sphincters?
2) What is esophageal secretion protective against?
1) Peristalsis (ringlike contractions of circular muscle)
2) Acid, enzymes, and sharp edges of bolus
What are the 3 sections of the stomach? Describe where each is
1) Fundus lies above esophageal opening
2) Body is the middle part
3) Antrum is the lower part, heavy musculature
What is the pyloric sphincter the barrier between?
Stomach and duodenum
What are the 3 main functions of the stomach? (what does it store, secrete, and mix?)
1) Stores ingested food until it is emptied into the small intestine
2) Secretes HCl acid (and others)
3) Mixes food with acid and pulverizes it to produce a thick liquid mixture called chyme which empties into duodenum
What are the 4 aspects of gastric motility?
1) Filling
2) Storage
3) Mixing
4) Emptying
1) What happens during gastric filling?
2) What happens during stomach storage?
1) Bolus enters via esophagus
2) Stomach volume can increase from 50mL to 1000mL; deep folds flatten
1) What is being generated as the stomach is mixing?
2) What can changes in stomach excitability bring about?
3) What propels chyme distally during stomach mixing? What does this also facilitate?
1) Cells of Cajal in upper fundus generate 3 slow-waves per minute.
2) Action potentials.
3) Strong antral contractions; emptying
1) What two body parts influence gastric emptying rate?
2) The stomach empties at a rate proportional to what?
3) What increases the emptying rate?
1) Stomach and duodenum
2) The volume of chyme.
3) Gastric distention (triggered via stretch receptors)
1) Which is more influential on gastric emptying, duodenum or stomach?
2) What can the duodenum do to motility?
3) How many factors influence gastric emptying?
1) Duodenum more influential
2) Reduce strength of antral contractions until duodenum is ready
3) Four
What are the 4 factors that influence gastric emptying?
1) Fat
2) Acid
3) Hypertonicity
4) Duodenal distension
1) What does fat strongly stimulate? What is this?
2) What does this inhibit? What does this induce?
1) Cholecystokinin (CCK) ; a hormone
2) Antral contractions, induces pyloric sphincter contraction.
A high fat meal can take longer than _____ hours to gastrically empty vs _______ hours for very low fat meal
6; 3
1) What ionic compound does the duodenum contain? What does this do?
2) What happens if chyme (acidic) volume is too high? What does this do?
1) Sodium bicarbonate (from pancreas); neutralizes HCl
2) Secretin is released, slows gastric emptying
1) How does osmolarity affect gastric emptying?
2) What does osmolarity depend on?
3) What does each amino acid have? What would this cause if left unchecked?
1) Increased osmolarity inhibits gastric emptying
2) Number of molecules (not their size)
3) The same osmotic activity as the original protein molecule; food components in chyme would draw too much water into the lumen.
How does distention affect the gastric emptying rate? Why?
Increased volume of chyme inhibits gastric emptying to prevent further chyme build up
1) Define vomiting (emesis)
2) What controls it?
3) Does this involve reverse peristalsis? Does the stomach participate?
1) Forceful expulsion of gastric contents through the oral cavity
2) Vomiting center of the brain stem
3) No and stomach does not participate
What does the major force of vomiting (emesis) come from?
Respiratory muscle contraction (esp. diaphragm and abdominal muscles)
Vomiting can be initiated by afferent input from various receptors, which can be triggered by what? (list 6 examples)
1) Tactile stimulation of the back of the throat
2) Distention or irritation of the stomach and duodenum
3) Elevated intracranial pressure
4) Dizziness
5) Drugs
6) Psychogenic factors (emotions)
1) What does vomiting involve a large loss of? (2 things)
2) What 2 things can this lead to?
1) Acid and fluid volume
2) Dehydration and metabolic alkalosis
1) How much gastric juices are secreted per day?
2) What do mucous cells secrete?
3) What do chief cells secrete?
4) What 2 things do parietal cells secrete?
1) 2L
2) A thin, watery mucus
3) The enzyme precursor pepsinogen
4) HCl and intrinsic factor
1) What is intrinsic factor necessary for?
2) What does it bind to? What does that trigger?
1) B12 absorption
2) Binds to B12 to trigger receptor mediated endocytosis
1) B12 is essential for what cells?
2) Without it what can result?
1) RBCs
2) Pernicious anemia
1) In gastric juices, what two ions are actively secreted by separate pumps?
2) Which is actively transported against a concentration gradient?
1) H+ and Cl-
2) H+
1) H+ in the lumen can be _________________ times greater than in the blood.
2) Where does this H+ come from?
1) 3 million
2) Breakdown of H2O in the parietal cells
1) Cl- has a much smaller gradient than H+ of only ______ times.
2) Does HCl digest things? Explain
1) 1.5 times
2) Doesn’t technically digest things as it does not break nutrient chemical bonds
1) What does HCL activate?
2) What does it break down?
3) What does it denature?
4) What does it kill?
1) Pepsinogen into pepsin
2) Larger food particles into smaller particles (connective tissue, muscle)
3) Protein (unfolding them)
4) Microorganisms
1) Parietal cells secrete HCl which activates ___________ into _____________
2) What begins protein digestion? What does it do?
1) pepsinogen into pepsin
2) Pepsin; splits amino acid links to yield peptide fragments (small amino acid chains)
True or false: Multiple cells of the stomach are involved in regulation
True
1) Multiple cells of the stomach are involved in regulation; what do G cells secrete? Where?
2) Describe the substance they secrete and what it stimulates.
1) A type of endocrine cell that secretes gastrin into the blood
2) Major GI hormone. Stimulates HCL and stimulates ECL cells to release histamine.
Name a major GI hormone that stimulates HCl and stimulates ECL cells to release histamine.
Gastrin
1) What do ECL (enterochromaffin-like) cells release? When?
2) What does this increase?
1) Release histamine in response to ACh and gastrin
2) HCl secretion
1) What do D cells do?
2) What does this inhibit?
3) What kind of feedback loop is this?
1) Secrete somatostatin in response to increased acidity
2) Inhibits parietal cells, G cells, and ECL cells
3) Negative
1) What 3 cells (along with ACh) primarily regulate gastric juices?
2) What do all of them do? What is the exception?
3) What two things also increase pepsinogen?
1) G cells, ECL cells, D cells
2) All of them stimulate secretion, except somatostatin which inhibits HCl
3) ACh and gastrin
Gastric secretion is divided into 3 phases; what are they?
Cephalic, gastric, and intestinal
1) What is the cephalic phase of gastric secretion? What two things are increased?
2) Give examples of when this phase is triggered
1) Feedforward mechanism increasing HCl and pepsinogen secretion in response to stimuli (even before reaching stomach)
2) Thinking about, seeing, or smelling food
1) What happens during the gastric phase of gastric secretions?
2) Give examples of what triggers this phase
1) Food reaches the stomach and increase secretion by various means.
2) Distention, caffeine, and alcohol.
1) Describe the intestinal phase of gastric secretion
2) What type of feedback is this?
1) Duodenal factors inhibit secretion.
2) Negative feedback
1) What is mucus?
2) Besides mucus, what do mucous cells secrete?
3) What are gastric mucosal cells impermeable to?
4) What join the lateral edges of mucosal cells?
5) How often is the stomach lining replaced?
1) A protective coating
2) HCO3-
3) H+
4) Tight junctions
5) Every 3 days
1) Carbohydrate digestion continues in stomach due to what?
2) What two things are not absorbed in the stomach?
3) 2 non-nutrients are directly absorbed by the stomach; what are they?
1) Salivary amylase
2) Food or water
3) Ethyl alcohol (alcohol), and aspirin
1) Gastric contents in the duodenum are mixed with what?
2) What is the elongated gland behind the stomach that consists of exocrine and endocrine tissue?
3) What two things does this gland secrete?
1) Secretions from the small-intestine, exocrine pancreas, and liver
2) Pancreas
3) Pancreatic enzymes and alkaline secretion rich in sodium bicarbonate
1) What make up pancreatic enzymes? (3 things)
2) What can pancreatic enzymes do?
3) What does the pancreas’s alkaline secretion (rich in sodium bicarbonate) do?
1) Proteolytic enzymes (protein), pancreatic amylase (carbs), and pancreatic lipase (fat)
2) Almost completely digest food without other secretions
3) Neutralizes HCl
What is unique about pancreatic lipase?
The only secretion in the GI system that can meaningfully digest fat
1) Predominant stimulation of pancreatic secretion occurs during what digestive phase?
2) What are the two major factors controlling pancreatic exocrine secretion?
1) Intestinal phase
2) Secretin and CCK
1) What stimulates secretin? (4 things)
2) What stimulates CCK release?
3) What does CCK stimulate?
1) Fat, hypertonicity, distention, and especially acid
2) Fat
3) Digestive enzymes of pancreas to be released
1) What stimulates CCK release?
2) What does CCK stimulate? (reiterating)
3) What are enzymes packed into and how are they released? What does this mean for their proportion?
1) Fat
2) Digestive enzymes of pancreas to be released
3) The same granules; released by exocytosis; their proportion remains the same regardless of food composition
1) Besides pancreatic secretions, the other secretory product is ________________
2) What 3 things make up the biliary system?
3) Is there a lot of specialization within the liver cells (hepatocytes)?
1) bile
2) Liver, gallbladder, and associated ducts
3) No; little
What is the most important metabolic organ, aka the “body’s biochemical factory”?
Liver
List 9 liver functions
1) Secretes bile salts
2) Processes nutrients
3) Detoxifies blood
4) Synthesizes plasma proteins
5) Stores glycogen, fat, and many micronutrients
6) Activates Vit D
7) Secretes hormones: thrombopoietin, hepcidin, IGF-1
8) Excretes cholesterol and bilirubin
9) Resident macrophages remove bacteria and worn RBCs
1) Each hepatocyte is in direct contact with what two things?
2) How does venous blood enter the liver?
3) What is the hepatic portal system?
1) Arterial blood coming from the heart and venous blood from the digestive tract
2) Via hepatic portal system
3) Unique and complex vascular structure connecting the digestive tract and the liver
1) Veins from stomach and intestine enter what vein?
2) What does this vein carry?
1) Hepatic portal vein
2) Absorbed products to the liver for processing, storage, or detoxification, before they return to general venous circulation
1) Liver is organized into ___________.
2) What eventually form common bile duct?
3) What transports bile to the duodenum?
1) lobules
2) Bile ducts from lobules converge
3) Common bile duct
1) Bile is continuously secreted by the _______ and stored in the _____________.
2) Bile contains what 4 things?
3) What part of bile emulsifies fat?
1) liver; gallbladder
2) Bile salts, cholesterol, lecithin, and bilirubin
3) Bile salts
Describe the 4 steps of bile formation
1) Passive diffusion along the small intestine
2) Carrier-mediated active absorption in the terminal ileum
3) Deconjugation to primary bile acids before being absorbed either passively or actively
4) Conversion of primary bile acids to secondary bile acids with absorption of deoxycholic acid
1) What 3 things facilitate fat absorption by forming micelles?
2) What do micelles allow for?
1) Bile salts, lecithin, and cholesterol
2) Water-insoluble (fat) substances to be transported through luminal contents (which are watery)
How is bile discharged into the duodenum? When?
Fat stimulates CCK which stimulates contraction of gallbladder, discharging bile into duodenum to emulsify and transport the fat
A waste product excreted in bile that’s derived from worn-out RBCs which are removed by liver macrophages is called what?
Bilirubin
1) What is the pigmented end-product from hemoglobin degradation called?
2) What color is it? What modifies this?
3) When would feces be grayish white?
1) Bilirubin
2) Yellowish; modified by bacteria to give brown color of stool
3) Bile duct obstruction
slide 61
1) What gives urine its yellow color?
2) What does the accumulation of this substance cause?
3) Define this condition
1) Small amount of bilirubin is reabsorbed and excreted in urine
2) Accumulation in the body causes jaundice
3) Yellowish appearance, especially in eyes
1) What is the small intestine the site of most of?
2) What is it arbitrarily divided into?
3) What two things are included in small intestine motility?
1) Digestion and absorption
2) Duodenum, jejunum, and ileum
3) Segmentation and migrating motility complex
1) When does segmentation in the small intestine occur? What does it do?
2) What kind of contractions is this?
3) What type of contractions are NOT involved?
4) Describe what segmentation looks like
1) It’s the primary motility during digestion; mixes and propels chyme.
2) Oscillating contractions of circular smooth muscle
3) Wave like contractions like peristalsis
4) Imagine squeezing a pastry tube with your hands
Next wave of contractions occurs in previously relaxed segments
1) What is the migrating motor complex? What does it do?
2) When do segmentation contractions end and are replaced by MMC activity? How long does this last?
1) Unique motor activity of the SI; sweeps the intestine to keep it clean between meals
2) During periods of fasting they’re replaced by MMC activity, which cycles every 90 minutes as long as the person is fasting
1) What do MMC contractions do?
2) What are they responsible for?
1) Sweeps away remnants of preceding meal along with debris and bacteria
2) “Stomach” growling
1) What occurs at the end of the small intestine (SI)?
2) This region acts as a barrier between what two things?
3) What does this area prevent?
1) Ileum empties into the cecum
2) Small intestine and large intestine
3) Bacteria of large intestine from colonizing the small intestine
What are the two features of the region that acts as a barrier between SI and LI? Describe each
1) Ileocecal valve: Folds of tissue form a valvelike arrangement.
-Easily pushed open but forced closed if contents move backward
2) Ileocecal sphincter remains mildly constricted, pressure in cecal side makes this more forceful
1) What are responsible for most of the digestion as contents move through the small intestine (SI)?
2) What enhances SI fat digestion?
1) Pancreatic enzymes
2) Bile
1) Does the small intestine (SI) absorb selectively? Explain
2) About 50% of the SI can be removed without decreasing absorption except for what part? Why?
1) No, absorbs indiscriminately, except calcium and iron (which are absorbed according to need)
2) Terminal ileum, which is where B12 and bile salts (for recycling) are absorbed
1) How is water absorbed?
2) What 4 substances are linked to sodium reabsorption?
1) Sodium is actively and passively absorbed from the intestinal lumen and water osmotically follows
2) Cl-, H2O, glucose, and amino acids
Na+ transport causes Cl-, H2O, glucose, and amino acids to each do what?
1) Cl-: diffuses down electrical gradient
2) H2O: diffuses due to osmotic pressure
3) Glucose: absorbed by symport carriers (like sodium and glucose cotransporter; SGLT) powered by Na+ concentration gradient
4) Amino acids: also absorbed by transport mechanisms involving Na+
What 4 substances get a “free ride” on the energy spent to transport the Na+?
Cl-, H2O, glucose, and amino acids
How is fat absorbed? (2 steps)
1) Micelles reach membranes of the epithelial cells
2) Fatty acids passively diffuse across lipid component of membranes
1) How are water soluble vitamins absorbed?
2) What abt fat soluble vitamins?
3) What is unique about B12 absorption?
1) Passively with water
2) They’re carried in micelles and absorbed with fatty acids
3) B12 must be combined with gastric intrinsic factor for receptor mediated endocytosis in the terminal ileum
1) Most absorbed nutrients immediately pass through the __________ for processing
2) What 4 sections make up the large intestine?
1) liver
2) Colon, cecum, appendix, and rectum
1) What makes up most of the large intestine (LI)?
2) What forms a pouch at the ileocecal valve?
3) What does the appendix house?
1) Colon
2) Cecum
3) Lymphocytes
1) LI (large intestine) is primarily a __________ and ____________ organ
2) Why?
3) What 2 things does the LI extract more of? What does this form?
1) drying and storage
2) Most digestion and absorption has already occurred
3) H2O and salt, forming feces which is stores until defecation
Are large intestine secretions proactive or reactive?
What are these secretions and what do they do?
Proactively secretes sodium bicarbonate mucus, protects against mechanical and chemical injury
1) What is the LI layered into?
2) What does slow-wave activity initiate?
3) Describe this movement that slow-wave activity initiates.
1) Pouches called haustra
2) Haustral contractions
3) Slow and non-propulsive, move contents back and forth
1) What happens in the large intestine several times per day?
2) What can trigger this? What is this called?
1) A marked increase in motility in large segments of the LI, driving contents into distal portion
2) Stretch receptors in the stomach; gastrocolic reflex
Feces is eliminated via what reflex?
Defecation reflex
What are the 4 steps of the defecation reflex?
1) Internal anal sphincter (smooth muscle) relaxes
2) Rectum and sigmoid colon contract vigorously
3) External anal sphincter (skeletal muscle) relaxes
4) Contents emptied
1) What causes the large intestine to form a microbiome?
2) There are ______ times more bacteria in large intestine than cells in the human body
3) How many species of LI bacteria have been identified?
1) Slow movement allows bacteria time to grow
2) 10 times
3) 2,000
1) How much do gut microbes weigh?
2) What are they an important area of?
1) 4 pounds in total
2) Current medical research
What do gut microbes do? (6 things)
1) Promote motility
2) Maintain mucosal integrity
3) Aid immune function
4) Compete with pathogens for nutrients and space
5) Digest food
6) Perhaps influence brain activity/behavior/mood
