L5) Small Intestine Motility & Secretion 2.pdf

L5 Small Intestine Motility & Secretion GNT Physiology This lecture was presented by: Prof. Mohammed Alzoghaibi & Dr. Hayam Gad Color Index: • Main text • Important • Female Slides • Male Slides • Notes • Extra Editing File Objectives Motility in the small intestine. Resources Control of intestinal motility. Only GI chapters included Secretions of the small intestine. Digestion in the small intestine (carbohydrates, proteins, fats). Basic principles of intestinal absorption : ● Absorption of carbohydrates. ● Absorption proteins. ● Absorption fats. ● Absorption vitamins ● Absorption and secretion of electrolytes and water. This is prof sultan meo! Click here for a helpful channel by the best physiology team! ❝ ‫َات‬ ِ ‫َ ْ ِ ا ّ َو‬ ِ َ‫ُ ُ ِ ِ ْ و َ َ َ َ ّ ُون‬ (191) ِ‫ُ ْ َ َ َ َ ِ َ َ َابَ ا ّ ر‬ ٰ َ َ َ ‫ا ّ ِ َ َ ْ ُ ُونَ ا ّ َ ِ َ ً و َ ُ ُ د ًا و‬ ً ِ َ ‫َ ٰ َا‬ َ َْ َ َ َ ّ َ‫ض ر‬ ِ ‫و َا ْ ْر‬ Motility in the Small Intestine The movements of the small intestine can be divided into : Propulsive contractions (Peristalsis). 1 Migrating motor complex. Propulsive Movement (Peristalsis) -A contraction ring appears around gut, then moves forward. -Usual stimulus is distention. -Myenteric Plexus is important for these movements. -They can be blocked by atropine. -It organizes propulsion of material over variable distances within the intestinal lumen. -Propulsive movements can occur in any part of small intestine at a velocity of 0.5 to 2 cm/sec. -They normally are very weak and die after traveling only 3 to 5 centimeters, and the net movement along the small intestine normally averages only 1 cm/min. This means that 3 to 5 hours are required for passage of chyme from the pylorus to the ileocecal valve. -They are faster in the proximal intestine and slower in the terminal intestine. Consist of : Male slides Contraction (circular M) Propulsive segment Receiving segment Antiperistalsis Peristaltic rush Relaxation (longitudinal M) Relaxation (circular M) Contraction (longitudinal M) 2 Segmenting (Mixing) contractions. Mixing (Segmentation) Contractions -Usual stimulus is distention. -It is activated by enteric nervous system (ENS). ( Myenteric plexus ) -They can be blocked by atropine. -When a portion of small intestine becomes distended, the segmentation contraction (localized contractions of circular smooth muscle) is activated by ENS to divide the intestine into spaced segments which last for fraction of minute, and have the appearance of a chain of sausages. -As one set of segmentation contractions relaxes, a new set often begins at points between the previous ones. The segmentation contractions become weak when the excitatory activity of ENS is blocked by the drug atropine. Important -The signiﬁcance/functions of segmentation contractions: 1. 2. Blend diﬀerent juices with the chyme. Bring products of digestion in contact with absorptive surfaces. 3 Migrating motor complex (MMC) It is bursts of depolarization accompanied by peristaltic contraction that begins in empty stomach during inter-digestive period (after absorption occurs), Travels along whole length of small intestine to reach ileocaecal valve after 1.5-2 h, where it disappears. Then a new wave of MMC starts. The function of MMC is to sweep material (undigested food residues, dead mucosal cells and bacteria) /(to propel any remnants in stomach & small intestine) into colon keeping the small intestine clean, during the interdigestive period. 4 Antiperistalsis A wave of contraction in the alimentary canal that passes in an oral (i.e. upward, backwards) direction and force propel the contents (chyme) in the opposite direction Occurs between: 1. Stomach and duodenum to allow more time for neutralization of chyme.(A) 2. Ileum and caecum to allow time for absorption (B) AA *this movement delay emptying The activity of MMC terminates as soon as food is ingested. End When the food is ingested, because it’s in between meal. Regulated by autonomic nerves and by release of hormone “motilin”. ..‫ﺗذﻛرون اﻟﻣﺣﺎﺿرة اﻷوﻟﻰ؟ أﺑد ھو ﻧﻔﺳﮫ وﻗﻠﻧﺎ اﻧﮫ ﻣﮭم ﺑﻌد‬ B 5 Peristaltic rush -Powerful rapid peristalsis due to intense irritation of intestinal mucosa as in infectious diarrhea. -Initiated mainly by extrinsic nervous reﬂexes through the vagus nerve to brain stem and back to gut. What’s the function? Sweeps the contents of intestine into the colon (without much absorption leading to diarrhea) and thereby relieving the small intestine of irritative chyme or excessive distension. Movement of the villi - Villous contraction is Initiated by local nervous reﬂexes in response to chyme in small intestine. The villous movement Consists of fast shortening and slow lengthening as well as side to side movements. Stimulated by villikinin hormone released by intestinal mucosa when it comes in contact with digestive products. Function of villi movement? Facilitate absorption and lymph ﬂow from central lacteals into lymphatic system. Control of intestinal motility Control of intestinal motility Hormonal control Neural control -Vagal excitation increases intestinal and villous movements. -Sympathetic excitation decreases intestinal and villous movements -Gastroileal reﬂex : Initiated by gastric distension, Impulses are conducted through myenteric plexus to initiate a fast peristaltic wave passing to the ileum, The ileocaecal valve relaxes allowing chyme to pass into cecum. This reﬂex is mediated by vagus nerve Gastrin, CCK, insulin and serotonin: stimulate intestinal motility. Gastrin and CCK relax ileocecal sphincter. Motilin secreted from duodenum stimulates intestinal motility and regulate MMC. Secretin and glucagon : inhibits intestinal motility and contract ileocecal sphincter. -Villikinin stimulates movement of the villi. Digestive enzymes in small intestinal secretions Male slides “The enterocytes of the mucosa contain digestive enzymes”, they are: Peptides Splitting small Peptides to amino acids by : 1-Aminopeptidases 2-Oligopeptidases 3- Intracellular Di and Tri peptidases Disaccharides Splitting disaccharides to monosaccharides by : 1-Sucrase 2-Maltase 3-Isomaltase 4-Lactase Neutral fats Splitting neutral fats to glycerol and fatty acids by : Small amounts of intestinal lipase Nucleotide Nucleotides Nucleotidases purine base pyrimidine base phosphoric acid pentose sugar Secretions of small intestine Secretion of Intestinal Juices (succus entericus) by the Crypts of Lieberkühn Secretion of Mucus by Brunner’s Glands in the Duodenum: - - ● Brunner’s glands are located in the wall of the ﬁrst few centimeters of the duodenum. They secrete large amounts of alkaline mucus, which contains a large amount of bicarbonate ions, in response to/stimulated by: 1-Irritating stimuli on the duodenal mucosa 2-Vagal stimulation 3-Secretin !‫ رﻗم واﺣد‬small intestine ‫ھرﻣون‬ ● ● ● ● Mucus protects the mucosa Brunner’s glands are inhibited by sympathetic stimulation ● ● Brunner’s glands only found in duodenum secretin “ Stimulus is highly acidic chyme “ Low pH -> Stimulate pancreatic secretions “rich in bicarb” and stimulate the Brunner’s glands secretions “which rich in mucous and bicarb”. Also stimulate bile secretion from liver which is alkaline. Crypts of Lieberkühn are small pits which lie between intestinal villi. Volume: 1800 ml/day. pH: 7.5-8. It participates in the neutralization of acid chyme delivered from stomach. Composition: 0.6 % organic, 1 % inorganic substance. Most of the enzymes are found either in the brush border or in the cytoplasm of the enterocytes. The enzymes that are actually secreted into the lumen are enteropeptidase and amylase The surfaces of both the crypts and the villi are covered by an epithelium composed of 2 types of cells: ○ 1- Goblet cells : ○ Secrete mucus+HCO3 ○ 2- Enterocytes : ‫ﻧص ﺣﯾﺎﺗك‬ ○ Secrete large quantities of H2O and electrolytes and over the surfaces of adjacent villi Reabsorb H2O, electrolytes & end products of digestion Control of intestinal secretions Intestinal juice Secretion is stimulated by : 1. Distension, tactile , irritating stimuli and vagal stimulation. 2. Hormones : Gastrin , Secretin, CCK, glucagons, enterocrinin. Sympathetic system inhibits the intestinal secretion. Brunner's glands Secretion is stimulated by : - Secretin (Hormonal) Tactile (Mechanical) Vagal stimulation(Neural) Digestion of carbohydrates Site Male slides 1-In the mouth & stomach. Enzyme Function Notes -The starch digestion sometimes continues in the fundus and body of the stomach for as long as 1 hour before the food becomes mixed with the stomach secretions. -Digestion by : The ptyalin (an α-amylase) enzyme in saliva. **No need for activation they are active.** -Stomach doesn’t have enzymes To digest polysaccharides. - Hydrolyzes starch into the disaccharide (maltose) and other small polymers of glucose. Male slides 2-In the small intestine Polysaccharides ->Disaccharides -Digestion by : -pancreatic secretion has (α-amylase) that is almost identical in its function with the α-amylase of saliva but is several times as powerful. -Therefore, within 15 to 30 minutes after the chyme empties from the stomach into duodenum and mixes with pancreatic juice, virtually all the Carbohydrates will have become digested. Pancreatic Amylase (by pancreas) -The carbohydrates are almost totally converted into maltose and/ or other very small glucose polymers before passing beyond the duodenum or upper jejunum. 3- Hydrolysis of Disaccharides in intestine, by intestinal enzymes (In enterocytes) -Digestion by : Disaccharidases, such as: 1-Lactase. 2-Sucrase. 3-maltase . 4-α-dextrinase. Present in enterocytes lining the villi of the small intestine. -Are capable of splitting the disaccharides lactose, sucrose and maltose, plus other small glucose polymers, into their constituent - These enzymes are located in the enterocytes covering the intestinal microvilli brush border, so that the disaccharides are digested as they come in contact with these enterocytes. Disaccharide ->Monosaccharide Becomes monosaccharide only if they touch the vili. monosaccharides. Digestion of carbohydrates Male slides Starch Trehalose Lactose Sucrose α- Amylase Surcease → Maltotriose Maltase α- Dextrinase Sucrase Lactase → Maltose Trehalase → α- Dextrins Glucose Glucose Glucose Galactose Glucose Fructose Digestion of carbohydrates (summary) We highly recommend it for you. Polysaccharides Starch, Glycogen Salivary and pancreatic Disaccharides Maltose Enterocytes Monosaccharides Amylase Maltase Glucose Sucrose “sugar” Sucrase Glucose + Fructose Lactose “milk” Lactase Glucose + Galactose Digestion of Proteins A small percentage of proteins are digested to free AA by the pancreatic enzymes. Most protein digestion occurs in the duodenum and jejunum by aminopeptidases, oligopeptidases. (in the brush border) Most proteins remain as dipeptides and tripeptides digested by intracellular di and tripeptides To free AA. Aminopeptidases And oligopeptidases digest proteins into amino acid and dipeptides and tripeptides, which then enter cells and digested intracellularly by di and tripeptidases. . Male slides Male slides Digestion in the stomach Digestion by pancreatic secretion Pepsin is the important peptic enzyme of the stomach . (active at PH=2.0-3.0 and is inactive at pH above about 5). ● Most protein digestion occurs in the duodenum and jejunum. ● ● Pepsin initiates the process of protein digestion, usually providing 10-20% of the total protein digestion. ● Both trypsin and chymotrypsin split protein molecules into small polypeptides. Carboxypolypeptidase then cleaves individual AA from the carboxyl ends of the polypeptides. ● The pH of the stomach averages around 2.0-3.0. ● ● One of the most important feature of pepsin digestion is its ability to digest protein collagen. Proelastase is converted into elastase, which then digests elastin ﬁbers that partially hold meats together. ● Collagen is a major constituents of the intracellular connective tissue of meats ; therefore, for the digestive enzymes of the digestive tract to penetrate meats and digest the other meat proteins, it is ﬁrst necessary that the collagen ﬁbers be digested. Only a small percentage of the proteins are digested all the way to their constituent AA by the pancreatic juices. ● Most remain as dipeptides and tripeptides to be digested by peptidases in the Enterocytes. (mainly in the duodenum and jejunum) ● ● ● Digests proteins into proteoses , peptones & polypeptides. *Simply, we have got 4 sites to digest proteins : 1-Stomach 2-Duodenum and jejunum 3-brush border 4-intracellular( Only (di-tri peptides) ). Digestion of Proteins Male slides (A) Protein Stomach → pepsin (Lumen) Amino Acids Oligopeptides (B) Small intestine Protein trypsin, chymotrypsin, elastase, carboxypeptidase A, carboxypeptidase B (Lumen) This route is rare in normal diets Dipeptides Amino Acids Oligopeptides Tripeptides Peptidase (brush border) Amino Acids Dipeptides Tripeptides Activation of Gastrointestinal Proteases Same Diagrams but from Drs’ slides Male slides (A) Stomach Pepsinogen → Low PH Pepsin (B) Small intestine -Enterokinase deﬁciency prevents activation of pancreatic enzymes and stops digestion of proteins.(M)important Trypsinogen → enterokinase (brush border) Trypsin Trypsinogen Elastase trypsin Carboxypeptidase A Procarboxypeptidase B → Chymotrypsin trypsin Procarboxypeptidase A → trypsin Proelastase → Trypsin → → trypsin Chymotrypsinogen -Protein can be absorbed in form of di-tri peptide as well as amino acids. Unlike polysaccharides must be absorbed into its smallest constituent (monosaccharides). trypsin Carboxypeptidase B Digestion of fat Male slides ● ● Less than 10% of triglycerides is digested in the stomach by lingual lipase. All fat digestion occurs in the small intestine. (Approximately all) Emulsiﬁcation of fat by bile acids : Break the fat globules into very small sizes under the inﬂuence of bile salts, so that the water-soluble digestive enzymes can act on the globule surfaces (emulsiﬁcation of the fat). Deﬁnition Male slides Information ● What is the signiﬁcance of Emulsiﬁcation of fat ? -to increase the surface area of fat globule surfaces, so that water-soluble digestive enzymes can act on it.(easily) ● The polar parts (the points where ionization occurs in water) of the bile salts and lecithin molecules are highly soluble in water. So, they are amphipathic molecules. ● Bile Salts and lecithin in the bile help fat digestion by making the fat globules readlity fragmentable with water in the small intestine (emulsiﬁcation of fat) . ● The major function of the bile salts and lecithin, especially lecithin, in the bile is to make fat globules readily fragmentable by agitation with water in the small bowel. ● CCK contracts the walls of gallbladder to help in digestion of fat. Digestion of Triglycerides by Pancreatic Lipase Male slides The most important enzyme for digestion of the triglycerides is pancreatic lipase. Reduction in pancreatic secretion leads to Steatorrhea. -End Products of Fat Digestion: Triglycerides Cholesterol ester Fatty acid Fatty acid Phospholipase A2 Cholesterol ester hydrolase Lingual and pancreatic lipases Monoglyceride Phospholipid Cholesterol Fatty acid Lysolecithin Fatty acid Basic Principles Of Gastrointestinal Absorption 1 The absorptive surface area of the small intestine is about 250㎡ (almost 2,700 square feet)- (provides the surface area equivalent to a tennis court). a.Mucosal folds (valvula connivents)(kercking), well developed in the duodenum and jejunum (3 times/fold) 2 The following increase the intestinal surface about 600 times: 3*10*20=600 b. The villi on the mucosal surface enhances (10 times/fold) c.The microvilli on the epithelial cells, the brush borders (20 times/fold) The epithelial cell on each villus is characterized by a brush border, consisting of as many as 1000 microvilli protruding into the intestinal chyme Longitudinal section of the small intestine, showing the valvulae conniventes covered by villi. Brush border of a gastrointestinal epithelial cell Anatomy of small intestine Microvasculature of the villus Inside each villus there is a lymph vessel and blood vessel ( arterioles and venules ). Most of the diﬀerent type of the end products of digestion of carbohydrates, protein and fat are absorbed into the bloodstream ( into the capillary blood, then to the portal circulation to the liver, EXCEPT the fatty acids specially long chain fatty acids goes to the central lacteal then lymphatic vessels. Female slides Absorption in the Small Intestine The small intestine It is about 5-7 meters, extends from the pyloric sphincter to the ileocecal valve, consists of:● Duodenum (0.5 meters) ● Jejunum (2-3 meters) ● Ileum (3-4 meters) ● ● Approximately 90% of protein & CHO digestion (and essentially all lipid digestion) takes place in the ﬁrst two sections of the small intestine. The small intestine has the key role in absorption. End products of digestions: Carbohydrates Monosaccharides Proteins Amino acids Fat Fatty acids + monoglycerides Vitamin, minerals & water No digestion Overview of the Absorption Mechanisms Absorption in the Small Intestine Vitamins Proteins Carbohydrates Electrolytes, water 2 1 Absorption of Carbohydrates All the carbohydrates in the food are absorbed in the form of monosaccharides; only a small fraction are absorbed as disaccharides. • Glucose and galactose absorption occurs in a co-transport mode with active transport of Na+ (2ry active transport) Na+ dependence. • Fructose is independent on Na+ but it transports in luminal membrane via facilitated diﬀusion. • Pentose (comes from DNA and RNA digestion) is transported by passive diﬀusion 3 Absorption of proteins • Proteins are absorbed in the form of dipeptides, tripeptides, and a few free amino acids • L-AA are transported by secondary active transport. •D- AA are transported by passive diﬀusion. • Di and tripeptides cross the brush border by active transport protein carrier. Di and tripeptides are hydrolyzed by brush border and cytoplasmic oligopeptidase. • AA leaves the cell at the basolateral membrane by facilitated transport. 4 Absorption of Vitamins -Vitamins are absorbed mainly in the jejunum & ileum. A, D, E, and K are fat soluble vitamins, absorbed in the jejunum in combination with fat. The B’s and C vitamins are water soluble vitamins, absorbed in the jejunum and upper ileum. -Fat-soluble vitamins (A, D, E, & K) (KADE=‫)ﻛﺎدي‬ are incorporated into micelles and absorbed along with other lipids. -Most water-soluble vitamins (C, B1, B2, B6, and folic acid) are absorbed by Na+- dependent cotransport mechanisms -Vitamin B12 is absorbed in the terminal part of ileum and requires intrinsic factor. Important Guyton Review 2e -Vitamin B12 is absorbed in the terminal ileum and needs intrinsic factor (secreted from the stomach). Ileal resection can cause vitamin B12 deﬁciency(pernicious anemia) due to? Only site of absorption. Gastrectomy /Atrophy of gastric mucosa results in the loss of parietal cells and loss of intrinsic factor —> pernicious anemia Answer: E Fats Absorption of Fats -Bile salts have the ability to form micelles, (Bile salt are amphipathic molecules, each bile salt molecule is composed of a sterol nucleus that is fat-soluble and a polar group that is water-soluble). -Micelles are small spherical, cylindrical globules 3 to 6 nm in diameter composed of 20 to 40 molecules of bile salt. Long chain FA, MG, cholesterol and fat soluble vitamins are incorporated into the interior of the micelle. -The polar groups are (-) charged, they allow the entire micelle globule to dissolve in the water of the digestive ﬂuids and to remain in stable solution. the micelles perform a “ferrying” function that is highly important for fat absorption -The micelles act as a transport medium to carry the monoglycerides and free fatty acids to the brush borders of the intestinal epithelial cells (The micelles carry FA & MG to the luminal borders of the intestinal epithelial cells). -In the presence of an abundance of bile micelles, about 97% of the fat is absorbed; in the absence of the bile micelles, only 40 to 50 % can be absorbed. Failure to synthesize Apo B results in abetalipoproteinemia. • Abnormality at any one of lipid dig & absorption steps will interfere with lipid absorption and results in Steatorrhea (fat excreted in feces). Absorption in the Small Intestine Vitamins Proteins Carbohydrates Steps of Fat Absorption Fats Electrolytes, water Female slides Fatty acids (FA) & monoglycerides (MG) associated with the micelles in lumen of intestine. 1 FA & MG leave micelles and enter epithelial cell by diﬀusion. 2 FA are used to synthesis triglycerides in agranular endoplasmic reticulum. 3 Fatty globules are combined with proteins to form chylomicrons within Golgi apparatus.Triglycerides ( from RER ) partially covered by protein 4 Vesicles containing chylomicrons leave epithelial cells by exocytosis (Because it is bigger than the pores in cell membrane) and enter a lacteal (lymph capillary). 5 Not directly in blood!! Lymph in the lacteal transport chylomicrons away from the intestine. Disorders of Carbohydrate Digestion and Absorption: • Lactose intolerance (lactase deﬁciency) causes osmotic diarrhea Important Male slides Disorders of Proteins Digestion and Absorption: Cystinuria: is a genetic disorder in which the transporter Na-AA is absent in small intestine and kidney. Absorption in the Small Intestine Vitamins Proteins Carbohydrates ❖ ❖ - Fats Electrolytes, water Electrolytes and H2O cross intestinal epithelial cells by either transcellular or paracellular route The permeability of the tight junctions varies with the type of epithelium Leaky epithelia are in the small intestine and gallbladder A tight epithelium is in the colon Absorption of Na+ 1) 2) 3) 4) - passive diﬀusion. Na+-Glucose or Na+-Amino acid Cotransport Na+-Cl exchange Na+-H+ exchange The next step is osmosis of water into the paracellular space, because a large osmotic gradient has been created by the elevated concentration of ions in the paracellular space. Aldosterone Greatly Enhances Na+ Absorption. This eﬀect is especially important in the colon because it allows virtually no loss of NaCl and water. - Cl- absorption accompanies Na+ absorption by the following mechanisms: Absorption of Cl- 1. 2. 3. - Absorption and Secretion of K+ Secretion of Bicarbonate Ions in the Ileum ❖ ❖ Passive diﬀusion Na+-Cl- cotransport Cl¯- HCO₃¯ exchange K+ is absorbed in the small intestine by passive diﬀusion K+ secretion (active)in the colon is stimulated by aldosterone Excessive loss of K+ in diarrheal ﬂuids causes hypokalemia(metabolic acidosis also happen in sever diarrhea-loss of HCO3) The epithelial cells on the surfaces of the villi in the ileum and large intestine have a special capability of secreting bicarbonate HCO₃¯ in exchange for absorption of chloride ions Cl¯. This provides alkaline bicarbonate HCO₃¯ that neutralize acid products formed by bacteria in the large intestine. Plasma Ca⁺⁺ Ca⁺⁺ Absorption by Enterocytes 1,25 dihydroxy-vitamin D3 stimulates synthesis of Ca++-binding protein and Ca++ -ATPase in enterocytes ❖ Parathyroid hormone In the kidney 25-hydroxy-vitamin D3 Electrolytes transport in small intestine • Jejunum: Net absorption of NaHCO. • Ileum: Net absorption of NaCI Male slides 1,25 dihydroxy-vitamin D3 Absorption of nutrients (summary) Site Absorbed Nutrient Duodenum and upper jejunum Most minerals Jejunum and upper ileum Carbohydrates, amino acid, water-soluble vitamins Jejunum Lipids and fat-soluble vitamins Terminal ileum Vitamin B12. (M) Female slides Where will the absorbed nutrients go ? Hormonal control of Absorption and secretion Glucocorticoid = ↑ Absorption of H²O & ions (small & large intestine) Somatostatin = ↑ H²O & ions absorption ( ileum & colon ) Epinephrine = ↑ NaCl absorption (ileum) Aldosterone = ↑ Synthesis of Na+ channels (colon) !‫تَحَـــ ّدِي‬ .‫ﻗﺪﻫﺎ؟ إﺿﻐﻂ ﻫﻨﺎ‬ Doctors’ Notes 1: Propulsive movement, ‫ ھﻲ اﻟﻠﻲ ﺗﻧزل ﻟﻠﻘوﻟون وﯾﺗﻐﯾر اﺳﻣﮭﺎ اﻟﻰ‬->mass movement 2: I can inhibit mixing movement by ATROPINE “cholinergic blocker” because vagus nerve -> cholinergic neurone. ➔ (Parasympathetic is usually excitatory) BUT ‘during swallowing’ it’s inhibitory for (LES) sphincter only during swallowing so between swallows, it increase the tone. ➔ While sympathetic is inhibitory to gut body, while excitatory to sphincters. 2: Migratory Motor Complex: interdigestive periods‫ ﺑﺎﻟﺣﻘﯾﻘﮫ وﻟﻛن ﻣﺎ ﻧﺷوﻓﮭﺎ اﻻ ﺑﺎﻟـ‬propulsive movement ‫ھﻲ‬ (ً‫)وﻗت اﻟﺻوم ﻣﺛﻼ‬ ➔ MMC only seen during fasting, when motilin hormone goes up Hunger sensation‫وھو أﯾﺿﺎ ً ﻣﺳؤول ﻋن ﺟزء ﻣن اﻟـ‬ ➔ Also Responsible for pushing remnants in stomach/small intestines down into colon, Starts at middle of the stomach it steps at terminal ileum. When this movement stops? .MMC ‫ ﺑﺣد ذاﺗﮫ ﻣش ﺣﯾوﻗف‬smelling of food ‫ ﺑﻣﻌﻧﻰ أن‬،‫ ھو اﻟﻠﻲ ﯾﻌطﻲ أواﻣر اﻧﮭﺎ ﺗوﻗف‬stomache‫وﺟود اﻷﻛل ﺑﺎﻟـ‬ Immediately stops when is ingest, even if it didn’t reach ilem. 3: Peristaltic rush ➔ diarrhoea‫داﯾﻣﺎ ً ﻧﺷوﻓﮭﺎ ﺑﺎﻟـ‬ Toxic Substances or any kind of infection that activates the wall of the small intestine to maximum power to push materials down to large intestines. 4:movement of villi : ➔ fast shortening, slow lengthing <- ‫ﯾﺳﻣوھﺎ‬ Villikinin hormone is not considered main GI hormone, but it activates aslo muscularis mucosa. 5: control of intestinal motility: In neural, small intestine‫اﻟﻠﻲ ﻧﺷوﻓﮭﺎ ﺑﺎﻟـ‬ **it’ vagovagal reflex (‫)اﻟدﻛﺗور ﯾﻘول ﻛذا ﻣﺎﻟﻲ دﺧل‬ ‫ ﻟﮫ دور ﻛﺑﯾر ﻓﻲ اﻟﺣرﻛﺔ اﻟﻣﺗﻣﻌﺟﺔ‬Gastroilieal reflex also called(Gastrocolic) In Hormonal, (secretin, GIP, Glucagon) these are inhibitory. ➔ Gastrin, CCK they work together in increasing motility in small intestine but they work against each other in terms of gastric motility. Brunner's glands: acid ‫ اذا ﻓﯾﮫ‬،‫ ﺑﻣﻌﻧﻰ‬neutralization ‫ ﺑﺷﻛل ﻛﺑﯾر ﻣﻣﺎ ﯾﺳﺎھم ﻓﻲ ﻋﻣﻠﯾﺔ‬HCO3 ‫ﻻن ﻋﻧدھﺎ اﻟﻘدرة ﻋﻠﻰ اﻧﺗﺎج‬،‫اﻟﻘﻼﻧد ھﺎذي ﺻدﯾﻘﺗﻧﺎ اﻟروح ﺑﺎﻟروح‬ !‫ ﻟن ﯾﺗم ھﺿﻣﮫ وﻻ اﻣﺗﺻﺎﺻﮫ‬solution in duodenum How brunner's gland/crypts of lieberkuhn is controlled? By hormones(secretin), vagal stimulation destention/tactle ‫ ھو‬secretin or vagus ‫واﻟﻣﺣﻔز ﻟﮭم ﺳواءا‬ Carbohydrates digestion starts in mouth (a amylase), stopped in stomach (because of high acidity), and completed by pancreatic Amylase 15 to 30 m ⬇ .‫ اﻟﻠﻲ ﻧﺎﺧذھﺎ‬majority ‫ وھﺎذي‬disaccharide ‫ﻣﺎﺗﺎﺧذ وﻗت طوﯾل ﺧﺻوﺻﺎ ً ﻟو ﻛﺎﻧت‬ Digestion of proteins start in stomach, but real digestion is in the small intestine If pepsin doesn’t get released in stoma, what do you think will happen? disorder in protein digestion and absorption ‫وﷲ ﻣﺎ ﺣﯾﺻﯾر اي‬”.. trypsin/chymotrypsin ‫ وﺗﺣت ﺗﺻرف اﻟﺑﻧﻛرﯾﺎس ﻷن ﻋﻧده "اﻟﺷﻠﺔ ﺣﻘت‬dudenum ‫ ﯾﺗم ھﺿﻣﮫ ﻓﻲ‬bulk of protein ‫اﻟﺳﺑب أن‬ TEST YOURSELF ! MCQ: Q1) Mixing Contraction can be blocked by? B) Atropine A) Heparin C) NSAIDs D) Warfarin Q2) What’s the most important enzyme that digest Triglycerides A) pancreatic lipase B) Pancreatic amylase C) Aminopeptidase D) Phospholipase A2 Q3) Amino acids leave the cell at the basolateral border via: A) Primary active transport B) Facilitated diﬀusion C) Secondary active transport D) passive diﬀusion Q4) it’s Powerful rapid peristalsis due to intense irritation A) Antiperistalsis B) Propulsive contractions C) Peristaltic rush D) segmenting contractions Answers: Q1:B | Q2:A | Q3:B | Q4:C SAQ: Q1) Mention the site of absorption for each of the following: Absorbed Nutrient Site Most minerals Duodenum and upper jejunum Carbohydrates, amino acid, water-soluble vitamins Jejunum and upper ileum Lipids and fat-soluble vitamins Jejunum Vitamin B12. (M) Terminal ileum Q2) What are the mechanisms of Na+ absorption? 1) 2) 3) 4) passive diffusion. Na+-Glucose or Na+-Amino acid Cotransport Na+-Cl Cotransport Na+-H+ exchange Well done! You’ve just ﬁnished the last midterm physiology lecture! Here’s a gift for you ! The BEST Team Leaders EVER.. Rafan Alhazzani Fahad Almughaiseeb Ghaida Aldossary Faisal Alzuhairy Team Members Sarah Alshahrani Hamad Alziyadi mansour Alotaibi Melaf Alotaibi Nazmi A Alqutub Layan aldosary Raghad Almuslih Nazmi M Alqutub Norah alhazzani Layla Alfrhan khalid Alanezi Jouri Almaymoni Lama Almutairi Abdulaziz abahussain Salma Alkhlassi Remas mohammed Yousof Badoghaish Shoug Alkhalifa

L5) Small Intestine Motility & Secretion 2.pdf

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