1 Flashcards
How is calcium absorbed in the small intestine? How does calcium cross the basolateral membrane? And, which hormones regulate the absorption of calcium
How is iron absorbed in the small intestines? How is iron stored or transported? And what is the plasma protein carrier called that it binds to?
- Iron is actively absorbed by the small intestine
- Can be stored in a granular form called ferritin or transported into the blood
- When transported in the blood, where it binds to transferrin (plasma protein carrier)
How is the absroption of iron and calcium different from the absorption of vitamins & nutrients in the small intestines?
- The absorption of calcium and iron are regulated, unlike the absorption of nutrients and vitamins
How is vitamin B12 absorbed?
- Absorbed only when bound to an intrinsic factor, which is a protein secreted by the gastric parietal cells.
In the small intestine, what do water-soluble vitamins require to be absorbed?
- Requiring transport proteins on the apical & basolateral surfaces to be absorbed
How are fat-soluble vitamins transported?And,
what mechanism of action do they use to be absorbed?
- Transported in micelles
- Absorbed passively by simple diffusion
In the small intestines, how are fats absorbed as? What are the steps involved to create chylomicrons? And, how do chylomicrons cross the basolateral membrane and where do they enter after?
- Absorbed as monoglycerides and fatty acids
- Intracellularly, monoglycerides and fatty acids enter the SER and reform triglycerides, which are then sent to the Golgi apparatus for packaging into chylomicrons
- Chylomicrons are exocytosed across the basolateral membrane, entering the lympathic system
In the small intestines, how are proteins absorbed as? What are the transport processes involved in the apical and basolateral surface in order to facilitate the absorption of carbohydrates?
- Are absorbed as either amino acids, dipeptides or tripeptides
- Across the apical surface, by either Na+ dependent secondary active transport proteins or by facilitated diffusion carrier proteins
- Across the basolateral surface, by facilitated diffusion carrier proteins
In the small intestines, how are carbs absorbed as? What are the transport processes involved in the apical and basolateral surface in order to facilitate the absorption of carbohydrates?
- Carbs are absorbed as monosacchardies
- Across the apical surface, sodium-dependent secondary active transport proteins
- Across the basolateral surface, diffusion carrier proteins
What has transport proteins that are specific for the absorption of key nutrients & minerals in the small intestines?
- the epithelial cells of the small intestines
Which strucutres allow for the large surface areas of the small intestines, to promote maximal absorption capabilities?
- The presence of circular folds, villi, and microvilli
Why is absorption in the small intestines not regulated?
- For maximal absorption allowance
Where does most of the absorption of water, nutrients, and electrolytes in the small intestines occur? And what are the exceptions to that statement?
- In the duodenum & ileum
- Expect calcium and iron
What is a brush-border enzymes called that is involved in the digestion of peptides?
- Aminopeptidases
What is a brush-border enzymes called that is involved in the digestion of disaccharides?
- Disaccharidases
What is the brush-border enzyme called that activates the pancreatic trypsinogen?
- Enterokinase
What is the function of brush-border enzymes?
- Function in digestion in the small intestines, along side pancreatic and hepatic enzymes
What are the plasma membrane enzymes called that are found on the apical surface of small-intestine epithelial cells?
- Brush-border enzymes
In the small intestine, what is the aqueous salt & mucous secretion called? What is the function of said secretion? And, where is this solution secreted & absorbed?
- Succus entericus
- To lubricate and protect the small intestines
- It is secreted proximally in the duodenum and is absorbed distally in the ileum
What is the secretion produced by the small intestines called?
- Succus entericus
How is the relaxation of the ileocecal sphincter regulated?
- By gastrin and by the distension of the ileum, which triggers a short reflex pathway
What serves to regulate the emptying of the small intestine contents into the large intestine and to prevent bacterial contamination of the small intestine from the large intestine ?
- The ileocecal sphincter and valve
How is the migrating motility complex process of the small intestines regulated? What is the structure called that secretes said hormone? And, why it is secreted?
- By the hormone motilin, which is secreted by the endocrine cells of the small intestine in the absence of chyme.
How is the segmentation process of the small intestines regulated?
- Regulated by distension of the duodenum, by the hormone gastrin, and by ANS innervation
How does the migrating motility complex process occur to provide motility for the small intestines? And, what is its function?
- Is a series of short-distance peristaltic waves that move from the duodenum to the ileum in between meals
- To move any remaining chyme left behind during segmentation toward the large intestine.
How does the process of segmentation occur to provide motility in the small intestines? And, what is the frequency of the basic electric rhythm?
- It involves alternating contractions and relaxation of the circular muscle initiated by the pacemaker cells of the small intestine
- Where the frequency of the basic electric rhythm (BER) decreases from the duodenum to the ileum
What processes in the small intestines does motility occur through?
- Segmentation & the migrating motility complex
Which digestive processes is the small intestines involved in? And, what is the primarily site of nutrient digestions and absorption in the digestive system?
- The small intestine is involved in all 4 digestive system processes
- The small intestines
What seals the exit of the small intestines?
- The Ileocecal sphincter and Valve
What seals the enterance to the small intestines?
- The pyloric sphincter
What are the 3 sections of the small intestines called?
- Duodenum, jejunum, and ileum
What are the hormones that regulate bile secretion called? And, how are the hormonal regulations of bile secretion stimulated?
- Secretin, secretion is stimulated by increased acid in the duodenum
- CCK, secretion is stimulated by protein digestion products and fat in the duodenum
List the 3 stimulants of bile secretion
- The return of bile salts through enterohepatic circulation stimulates secretion
- The increased activity of the parasympathetic vagus nerve (X) stimulates secretion
- The hormone secretin and cholecystokinin (CCK) stimulate secretion
What is the bile salt circulating path way called? And how does it flow/operate?
- Called the enterohepatic circulation
- Bile salts are released in the proximal part of the small intestine (duodenum) and are reabsorbed in the distal part of the small intestine (ileum)
- and are returned to the liver through the hepatic portal vein
- Upon returning to the liver, bile salts will be re-secreted in the bile
Why is the formation of micelles (micellar) by bile salts important?
- For the transport of monoglycerides & fatty acids, cholesterol, and fat-soluble vitamins
- Facilitating the process of absorption
Why is the emulsification of fat globules by bile salts important?
- To increase the surface area of the fat globule for digestion by lipases
- Also, increases the solubility of the fat globule in an aqueous environment
What are bile salts? And why are they important for the digestion & absorption of fats?
- Are amphipathic molecules (possessing hydrophobic & hydrophilic elements)
- Aids the digestion of fats through emulsification
- Aids the absorption of fats through micellar formation (micelles)
What is Bile?
- Is an aqueous, alkaline fluid that contains bile salts, cholesterol, lecithin, and bilirubin?
What are the organs that form the biliary system?
- The liver, gallbladder, and bile duct
Where is bile produced and stored? Where does it drain following its storage organ? And where does it release following the drainage phase?
- Bile is produced by the liver and is stored in the gallbladder
- From the gallbladder, it is drained into the bile duct
- From the bile duct it is released into the small intestines (duodenum)
How does the liver digest and absorb fats?
- Through it synthesis of bile
What Delivers the nutrients absorbed by the small and large intestine to the liver for processing; and returns blood and nutrients to the general venous circulation?
- the heptaic portal vein
What delivers oxygen (O2)-rich blood and metabolites to the liver for processing.
- The hepatic artery
What do the hepatic arteries and portal veins form in the liver’s hepatocytes?
- Form sinusoids and bile ducts, which form bile canaliculi
What are the cells of the liver called, and what is contained inside each lobule?
- Called hepatocytes organized into lobules
- Each lobule contains hepatic arteries & portal veins
List the liver functions
- The secretion of bile
- Nutrient processing & storage
- Detoxification
- Plasma protein synthesis
- Vitamin D activation
- Removal of cells & debris from plasma
- Excretion of cholesterol & bilirubin
What is the mechanism of action for pancreatic exocrine secretions, and how they are regulated?
- Acid in the duodenal lumen increases the release of secretin, which regulates the secretion of the aqueous alkaline solution by the pancreatic duct cells
- Fat and protein products in the duodenal lumen increase the release of cholecystokinin (CCK), which regulates the secretion of digestive enzymes by the pancreatic acinar cells
How are the pancreatic exocrine secretions regulated?
- Independently by secretin and Cholecystokinin (CCK)
How is the pancreatic enzyme proteases activated? What are the steps involved?
- Proteases is secreted in zymogen form, and is activated
- in order for it to be activated, trypsinogen must be converted to its active form by the brush border enzyme enterokinase
- Which converts trypsinogen into its active form trypsin
- Trypsin then converts other zymogens to their active forms, such as proteases
What are the pancreatic enzymes, such as amylase, lipase, and proteases important for?
- Amylase, is important for the digestion of carbs
- Lipase, is important for the digestion of fats (lipids)
- Proteases, is important for the digestion of proteins
What do the acinar & duct cells of the exocrine cells of the pancreas secrete?
- Acinar cells, secrete the pancreatic enzymes
- Duct cells, secrete an aqueous alkaline solution into the pancreatic duct
How is the pancreas both an endocrine and an exocrine gland?
- Endocrine cells, of the pancreas form the islets of Langerhans, which are important to fuel metabolism, through the secretion of the hormones insulin and glucagon
- Exocrine cells, of the pancreas form acini and ducts (Acinar & duct cells)
Where are the secretions produced that chyme is mixed with upon entering the small intestines?
- the pancreas
How are the intestinal phase factors of gastric secretion regulated? And, what do they secrete as a result?
- Is An inhibitory mechanism, where increased osmolarity, increased concentrations of fats & acids, and increased distension in the small intestines
- Stimulate short-&-long- reflexes pathways
- That results in the secretion of cholecystokinin (CCK), secretin, and the gastric inhibitory polypeptide (GIP)
How is the gastric-phase control of gastric secretion regulated? And, what is its mechanism of action pathway?
- Is stimulated by proteins & protein digestion in the stomach, causing distention of the stomach
- Activating chemo-&-mechano-receptors & initiating short-&-long- reflexes
- Which alert parietal & chief cells to increase gastric acid and pepsinogen secretion
How is the cephalic-phase control of gastric secretion regulated?And, what is the pathway they take?
- Through the initial inputs of senses of sight, smell, and taste of food (chewing and swallowing)
- Which increases PNS activity
- Can either go through G cells or parietal & chief cells to increase the secretion of gastric acid and pepsinogen
What are gastric secretions reguated by?
- By cephalic, gastric, and intestinal phase factors
What is the function of the mucus secreted in the esophagus?
- functions to lubrication for the movement of the bolus through to the stomach
List the 5 steps involved in the esophageal stage of the swallowing reflex
- stretching of the esophagus triggers a primary peristaltic wave
- Peristalsis moves the bolus through the esophagus
- The lower esophageal sphincter relaxes as its met by the bolus
- Bolus moves into the stomach
- If necessary, a secondary peristaltic wave is initiated, and the events above are repeated
What seals the exit of the esophagus?
- The lower esophageal (gastroesophageal) sphincter
What seals the enterance of the esophagus?
- The upper esophageal (pharyngoesophageal) sphincter
What is the function of the esophagus?
- It is a passagage way for the bolus, and is involved in motility through its participation in the esophageal stage of the swallowing reflex
What is function of mucus secretion in the pharynx?
- To provide lubrication for the movement of the bolus through to the esophagus
List the 6 steps involved in the swallowing reflex in the pharynx
- Tongue moves bolus into the pharynx
- Bolus descends on the epiglottis and covers it
- Uvula elevates to close the nasal passages
- Swallowing centre of the medulla inhibits the respiratory centre
- Upper esophageal (pharyngoesophageal) sphincter relaxes
- Bolus finally moves into the esophagus
What does the pharynx contain? Where does the food lead to next after the pharynx? What is the primarily function of the pharyn?
- Contains tonsils
- Food leads into the esophagus from the pharynx
- Functions in motility, through the oropharyngeal stage of the swallowing reflex
Where does the digestion of carbohydrates begin? Which enzyme is responsible for this digestion in this first location?Where is the majority of carbohydrates digested in? And what enzyme used in this circumstance?
- Begins in the mouth, utilizing salivary amalyse in the saliva
- Majority of carbs are digested in the small intestines, by pancreatic amaylse
What occurs in an increased innervation to the salivary glands by the SNS?
- They produce mucus-rich viscous saliva
What occurs in an increased innervation to the salivary glands by the PNS?
- They produce enzyme-rich, watery saliva