Lecture 2-Exam 4 (GI) Flashcards
- What are the three major salivary glands?
- What is part of the small intestine?
- What is part of the large intestine?
- What are the accessory digestive organs?
- Parotid, sublingual and submandibular gland
- Small: Duodenum, Jejunum, Ileum
- Large: Transverse, descending, ascending, sigmoid colon, cecum, rectum, vermiform appendix, anal canal
- Accessory: spleen, pancreas, liver
Most of digestive tract follows a basic structural
plan with the digestive tract wall consisting of layers:
* What are the first two layers closest to the lumen+ what is contained in them?
Mucosa:
* Epithelum
* Lamina propria (connective tissue)
* Muscularis mucosae (smooth m. to give ridges for increase SA)
Submucosa: Have nerves and plexes here to regulate secretations
Most of digestive tract follows a basic structural
plan with the digestive tract wall consisting of layers:
* What is the third and forth layer closest to the lumen+ what is contained in them?
Muscularis externa (smooth muscle layers- 3RD ONE IN STOMACH WITH oblique muscle):
* Inner circular layer
* Outer longitudinal layer (propels and breaks down food)
Serosa:
* Areolar tissue: have reticular fiber + others fibers
* Mesothelium: slippery layer to decrease frictrion
What is the 2nd brain for GI?
- Enteric nervous system: Myenteric plexus, submucosal plexus and parasympathetic ganglion of myenteric plexus
What is the definition of digestive system?
organ system that processes food, extracts nutrients, and eliminates residue
What are the five stages of digestion?
- Ingestion: selective intake of food
- Digestion: mechanical (physical turning) and chemical (acid) breakdown of food into a form usable by the body -> polymers to monomers
- Absorption (MAIN GOAL): uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood & lymph
- Compaction: absorbing water and consolidating the indigestible residue into feces
- Defecation: elimination of feces
What is mechanical digestion? What are the actions (3)
physical breakdown of food into smaller particles
* Cutting and grinding action of the teeth
* Churning action of stomach (via peristalsis, propulsion) and small intestines (via segmentation)
* Exposes more food surface area to digestive enzymes
What is chemical digestion? How is it carried out?
series of hydrolysis reactions that breaks dietary macromolecules (polymers) into their monomers (residues)
* Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine
- Polysaccharides-> _
- Proteins-> _
- Fats-> _
- Nucleic acids-> _
- Polysaccharides-> monosacharides (simple sugars)
- Proteins-> amino acids
- Fats-> monoglycerides and fatty acids then we transport them
- Nucleic acids-> nucelotides
Some nutrients are present in a usable form in ingested food and can be directly absorbed. What are the examples? (5)
Vitamins, amino acids, minerals, cholesterol, and water
What does parasympathetic and sympathetic stimulation cause to salivaty glands?
- Parasympathetic stimulation produces a secretion rich in electrolytes and salivary amylase (breakdown carbs, FIRST ONE TO BE BROKEN DOWN) .
- In contrast, sympathetic stimulation produces a secretion rich in mucus, making the saliva much more viscous (dry mouth, decrease watery but still mucus so it is thick)
What is the basic functional unit of the salivary gland?
Salivon: It consist of clusters of acini cells that drain into a ductal system
Low Yield
What is the salivon organization+ what comes in and out of the gland?
- Acinus = secretes initial saliva product
- Intercalated duct = secrete HCO3 and K+ & absorb Cl- and Na+
- Striated duct = keep water secreted out (no absorption)
- Excretory duct = secretes final saliva product directly into the mouth
What is saliva ph?
7-7.4
What are the all the parts/cells of the stomach lumen?
Mucous neck cells, parietal cells (make HCl+IF), Chief cells (make Pepsinogen+lipase), enteroendocrine (make gastrin, glucagon, serotonin, somatostatin)
CEMP
- Surface mucous cell: protects the gastric lining dt to pepsin and HCl
- Muscous neck cells: muscin in an acidic fluid
- Parital cells: HCl+ intrinsic factor (needed for B12 absorption)
- Chief cells: Pepsinogen (activated by HCl) and gastric lipase
- G cells/enteroendocrine cells: gastrin
What is the difference between lingual lipase and salivary amylase?
- Lingual lipase: Part of saliva but is not activated until the stomach (break down fats)
- Salivary amylase: Part of saliva, already active to break down carbs (REASON WHY CARBS ARE BROKEN DOWN FIRST)
What does the parietal cell secrete? How does it secrete that?
ATPase in the apical cell membrane pumps H+ out of the cell and into the lumen in exchange for K+.
What are gastric enzymes? (4)
pepsin, gastric amylase, gastric lipase, and intrinsic factor
Explain the two ways that we can get the secretion about HCl from parietal cells (directly and indirect)
Acid production in the stomach parallels what ?
Rate of gastric secretion
* The electrolyte composition of gastric juice changes with secretion rate.
What are the relationships of K, Na, H, and Cl with each other?
- Cl, K, H are all proportional to each other
- Na+ is inversely proportional to H+
LOOK AT THE PUMPS + CA reation ON LEFT/MIDDLE SIDE OF PICTURE
HCL is formed in stomach lumen to then active pepsinogen from chief cells
Gastric secretion is under what control?
Under neural and hormonal control
Parietal cells:
* What do they possess? What does that stimulate?
* What is commonly used for the treatment of peptic ulcer disease or GERD?
* What are the three stimulants of parietal cells? What can happen?
* Potentiation occurs when?
- Parietal cells possess special histamine receptors, H2 receptors, whose stimulation increases HCl secretion.
- H2 blockers are commonly used for the treatment of peptic ulcer disease or GERD.
- The effects of each of these three stimulants (ACh, gastrin, and histamine) augment those of the others, a phenomenon known as potentiation.
- Potentiation occurs when the effect of two stimulants is greater than the effect of either stimulant alone.
- When HCl secretion the most important?
- What happens when we have excess HCl damage?
- HCl secretion is important only during the digestion of food.
- Excess HCl can damage the gastric and the duodenal mucosal surfaces, causing ulcerative conditions
The body has an elaborate system for regulating HCl secretion by the stomach. Explain
If the buffering capacity of protein is exceeded or if the stomach is empty, the pH of the gastric lumen will fall below pH3.
* When this happens, the endocrine cells (D cells) in the antrum secrete somatostatin, which inhibits the release of gastrin and, thus, HCl secretion.
* Another mechanism for inhibiting HCl secretion is acidification of the duodenal lumen. Acidification stimulates the release of secretin, which inhibits the release of gastrin and several peptides from intestinal endocrine cells
SOMATOSTATIN + SECRETIN = INHIBIT GASTRIN SO NO HCL
Explain the three phases of stimulation of acid secretion?
- Cephalic: Vagus nerve stimulates gastric secretion even before food is swallowed
- Gastric: Food stretches the stomach and activates myenteric and vagovagal reflexes. These reflexes stimulate gastric secretion. Histamine and gastrin also stimulate acid and enzyme secretion
- Intestinal: intestinal gastrin briefly stimulates the stomach but then secretin, CCK and enterogastric reflex inhibit gastric secretion and motility while the duodenum processes the chyme already in it. Sym nerve fibers suppress gastric activity while vagal (para) stimulation of the stomach is now inhibited
Fill in
Pancreatic enzymes are produced where?
Pancreatic enzymes are produced in the acinar cells of the exocrine pancreas
What is secreted by the duct cells of pancreatic acinus? What happens?
HCO3- (changes the ph by neutralizes the environment) and Na+
What are the various stimuli that stimulates pancreatic enzyme secretion? What happens when it is stimulated?
Calcium release from intracellular stores stimulates pancreatic enzyme secretion.
pancreatic secretion by hormones and NTs:
* ACh, acetylcholine
* ATP
* cAMP
* CCK (cholecystokinin)
* GRP (gastrin-releasing peptide)
* VIP (vasoactive intestinal peptide)
Circulating GI hormones, particularly secretin and CCK, greatly influence on what?
Circulating GI hormones, particularly secretin and CCK, greatly influence pancreatic secretion of electrolytes and enzymes. Both hormones are produced by the small intestine and bind receptors in the pancreas.
Pnacreatic secretions are rich in what?
* What is this unlike?
* A reciprocal relationship between what exists?
Pancreatic secretions are rich in bicarbonate ions
* Unlike salivary fluid, the osmolality of pancreatic fluid equals that of plasma at all secretion rates.
* A reciprocal relationship exists between the Cl− and HCO3− (inverse) concentrations in pancreatic juice.
Pancreatic fluid _ and _ are altered with flow
Pancreatic fluid pH and electrolytes are altered with flow
The HCO3− concentration and, hence, the pH _ the increased rates of secretion
PARALLEL
Explain how pancreatic duct cells secrete electroyltes and water into pancreatic fluid
The luminal membrane Cl− channel is CFTR (cystic fibrosis transmembrane conductance regulator)
Bile secretion is under what?
Neural and hormonal control
Bile:
* What is it?
* What is it produced by?
* Drains through what?
* Bile facilitates what?
- Bile, a dark green to yellowish brown fluid
- produced by the hepatocytes in the liver
- drains through the bile ducts penetrating the liver
- Bile facilitates the digestion of lipids in the small intestine by emulsifying fat and forming aggregates around fat droplets called micelles
- The dispersion of fat droplets into micelles greatly does what?
- Bile is stored where?
- The dispersion of fat droplets into micelles greatly increases the surface area, enhancing the action of pancreatic lipase.
- Bile is stored in the gallbladder and, under nervous and hormonal control, is discharged into the duodenum
Explain the 4 step progess of regulation of bile secretion
Are bile acids good or bad? Explain?
Bile acids are potentially toxic to cells, and their concentrations are tightly regulated
The bile ducts are lined by cells called what? What do they do?
The bile ducts are lined by cells called cholangiocytes, which secrete bicarbonate-rich fluid into the biliary tree.
In addition to lipid digestion and absorption, bile acids also help with what?
Bilirubin excretion
Explain the whole long ass process of bilrubin excretion
Bilirubin is the end product of hemoglobin degradation. The liver removes the bile pigment, bilirubin, from the circulation and conjugates it with glucuronic acid.
When bile contains too much cholesterol and not enough bile salts, what happens?
bile crystallize and forms gallstones.
- Gallstones can occur where?
- Obstruction of the biliary tree can cause what?
- Gallstones can occur anywhere within the biliary tree, including the gallbladder and the common bile duct.
- Obstruction of the biliary tree can cause jaundice, and obstruction of the outlet of the pancreatic exocrine system can cause pancreatitis (dt back up of enzymes and the proteases will break down the pancreas)
Nutrient absorption does not occur without what? Explain with the different marcomolcules
- Does not occur without contacting the microvilli of brush border
Intestinal secretions provide what?
Intestinal secretions provide lubrication and protective functions.
Small intestine:
* What mainly happens here?
* The epithelial lining of the Small intestine is replaced how often?
* The intestinal crypts do not and do secrete what?
- The small intestine is where the vast majority of digestion and absorption of food takes place
- The epithelial lining of the small intestine is replaced approximately every 3 days
- The intestinal crypts do not secrete digestive enzymes, but do secrete mucus, electrolytes, and H2O.
*
Small intestine:
* What cells are in the crypt? What do they function like?
* What do goblet cells do?
* The small intestine and colon usually absorb the fluid and electrolytes from intestinal secretions, what happens if this does not happen?
* Intestinal fluid hypersecretion is stimulated by what?
- Paneth cells in crypt function like neutrophils and produce antimicrobial substances that provide a protective barrier.
- Goblet cells secrete various mucins
- The small intestine and colon usually absorb the fluid and electrolytes from intestinal secretions, but if secretion surpasses absorption (e.g., in cholera), watery diarrhea may result.
- Intestinal fluid hypersecretion is stimulated by toxins and other luminal stimuli.
What is the lympathic supply for the GI?
Lacteal
FILL IN
How do we digest nucleic acid?
- Small intestine (lumen): Nucleases (deoxyribonuclease and ribonuclease) of pancreatic juice hydrolyze DNA and RNA to nucleotides
- Small intestine (epithelium): Nucleosidases and phosphatases of brush border split them into phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases
- Ciculation: Membrane carriers allow absorption
How do we get the activation of pancreatic enzymes in the small intestine?
Explain how the vitamin b12 absorption gets into the blood
Na+ absorption in the gut depends on what?
Gut depends on an Na+/K+-ATPase pump
* Approximately 98% of the electrolytes in the gut are reabsorbed.
* An Na+/K+-ATPase actively pumps Na+ across the basal lateral surface to be absorbed into the blood.
* (A) Na+ absorption by the jejunum. (B) Na+ absorption by the ileum.
What is required for calcium to be absorped by enterocytes?
Parathyroid hormone and
vitamin D
What do we need to transport iorn in plasma?
Transferrin
- Water is absorbed how?
- GI tract is extremely efficient in what?
- Water is absorbed in the gut by osmosis.
- GI tract is extremely efficient in absorbing H2O
Liver:
* Hepatocytes are involved in the metabolism of what?
* Many drugs and metabolites are hydrophobic and are converted into what?
* What affects drug metabolism and transport?
- Hepatocytes are involved in the metabolism of xenobiotics (chemical substances that are foreign)
- Many drugs and metabolites are hydrophobic and are converted into hydrophilic compounds by the liver, contributing to their elimination by the kidneys.
- Age, nutrition, genetics, sex, and hormones significantly affect drug metabolism and transport in the liver.
WOULD KNOW: P450 MAJOR ENZYME AND PHASE 1+2
Explain how the liver plays an important role in blood glucose buffering?
KINDA HOT MESS
What does each one do/promote:
* Kinase:
* Phosphatase:
* Insulin:
* Glucogon:
* Epinephrine:
Explain how the liver plays a vital role in lipid metabolism (PICTURE)
What are chylomirons, VLDLs, LDLs and HDLs?
The liver synthesizes important plasma proteins. Explain
LOW YIELD
Liver plays a key role in the transport, storage, and metabolism of what metal? Explain
Iron
* Kupffer cells rapidly phagocytize damaged red cells.
* The iron released from the heme molecule during phagocytosis becomes part of the free iron pool.
Liver activates and degrades many hormones. list them (7)
Enteric nervous system (ENS):
* Responsible for what?
* The myenteric plexus is mainly involved with what?
* The submucosal plexus coordinates what?
- Responsible for much of the moment-to-moment control of gut motility and secretion.
- The myenteric plexus is mainly involved with control of gut motility and innervates the inner
circular and outer longitudinal smooth muscle layers. - The submucosal plexus coordinates intestinal absorption and secretion through its innervation of the glandular epithelium, intestinal endocrine cells and submucosal blood vessels
What are the 7 sphincters of the GI tract? What do they separte?
- Explain the myogenic contractile activity?
- What causes the sphincter to transiently relax?
- Active inhibitory neuron: open sphincter
- Inhibit (inactive) inhibitory neuron: closed sphincter
- Specific signals (e.g., distention, pressure, and nervous input) cause the sphincters to transiently relax
Spike potentials:
* Triggered if what?
* What enters? What does that cause?
* What does this explain?
- triggered if the peak of a slow wave depolarizes the membrane to a threshold potential.
- Ca 2+ entry into smooth muscle cells during spike potentials and triggers muscle contraction
- explains why amount of force developed by muscle contraction correlates with the appearance of spike potentials.
Where are there no slow waves? What do they produce instead?
- There are no slow waves in the esophagus, which remains quiescent unless stimulated by swallowing or by the presence of a bolus in the lumen.
- The proximal stomach does not produce slow waves but has a steady tone that pushes the contents toward the pylorus.
What are the following reflexes:
* Gastro-ileal
* Ileo-gastric
* Gastro-colic
* Ortho-colic
* Colono-gastric
What are the three esophageal phases?
- What are the major types of GI motility?
- Peristalsis occurs when?
- Peristalsis and propulsion are the major types of GI motility.
- Peristaltic propulsion involves the formation of a propulsive and a receiving segment, mediated by reflex control of the intestinal musculature.
- Peristalsis occurs during and shortly after a meal.
- The gastric reservoir is specialized for what?
- What does the musculature in the region of the antral pump exhibits?
- What does not exist?
- The gastric reservoir is specialized for receiving and storing a meal.
- The musculature in the region of the antral pump exhibits phasic contractions that function in the mixing and trituration of the gastric contents.
- No distinctly identifiable boundary exists between the reservoir and the antral pump.
The stomach is divided into what?
three/four anatomical and two functional regions
Three types of relaxation responses occur in the gastric reservoir. Explain them
Which ones are faster, slower: Solid, liquid and semisolid meal?
The mixing pattern of small intestinal motility is characteristic of the digestive state. Explain
inhibitory musculomotor activity determines what?
determines the distance and direction a contraction travels
Fecal continence is maintained by the action of several anal sphincters:
* The internal anal sphincter is a thickening of what? What is it controlled by?
* The external anal sphincter is made up of what?
* The pelvic diaphragm is also important in what?
- The internal anal sphincter is a thickening of smooth muscle around the anal canal and is controlled by autonomic nerves
- The external anal sphincter is distal to the internal sphincter and is composed of skeletal muscle around the anal canal.
- The pelvic diaphragm is also important in the maintenance of fecal continence and is a sling of skeletal muscle, originating from the bony pelvis that forms the acute anorectal angle.
Neural control of defecation involves the central and enteric nervous systems. Explain the process
What is the parasympathetic defecation reflex?
Migrating motor complex (MMC):
* The small intestinal ENS “runs” the digestive state motor program when ?
* Conversion to the interdigestive state motor program starts when ?
* The MMC is a pattern of motility that occurs when?
* The MMC involves what?
* The functions of MMCs are to what?
* MMCs are an ENS-controlled motor program. The ENS stimulates secretion of what?
- The small intestinal ENS “runs” the digestive state motor program when nutrients are present and digestive processes are ongoing.
- Conversion to the interdigestive state motor program starts when digestion and absorption of nutrients are complete, 2 to 3 hours after a meal.
- The MMC is a pattern of motility that occurs about every 90 minutes between meals; the start of an interdigestive period is defined by the first MMC that occurs after the last meal.
- The MMC involves intervals of strong propulsive contractions, which pass down the distal stomach and small intestine.
- The functions of MMCs are to sweep the stomach and small intestine of indigestible materials and to prevent bacterial colonization of the upper intestine.
- MMCs are an ENS-controlled motor program. The ENS stimulates secretion of the hormone motilin, which stimulates propulsive contractions of the intestine.
