Pancreas & Small Bowel Flashcards
What is the anatomical relationship of the pancreas and stomach?
Stomach: Separated from the pancreas by the lesser sac, the stomach and pylorus lie anterior and to the pancreas.
What is the anatomical relationship of the pancreas and duodenum?
The “C” shaped duodenum curves around and outlines the head of the pancreas. First part of the duodenum resides anteriorly; whereas the second part of the duodenum including the ampulla, resides laterally to the right of the pancreatic head.
What is the transverse mesocolon?
Transverse mesocolon: Attaches to the anterior surface of the pancreas.
What is the relationship of the common bile duct and the pancreas?
Common bile duct: Descends posteriorly to the head of the pancreas.
What is the anatomical relationship between the pancreas and spleen?
Spleen: Located posteriorly and laterally. Lienorenal ligament formed from the peritoneum, connecting the spleen to the tail of the pancreas.
What artery supplies the pancreas?
Superior mesenteric artery
Where is the superior mesenteric artery located in relation to the pancreas?
Lies behind the neck of the Pancras, and anterior to the uncinate process
The splenic and superior mesenteric arteries unite to form which vessel?
Unites to form the hepatic portal vein
Which plexus innervates the pancreas?
Coeliac plexus
What is the head of the pancreas?
Widest part of the pancreas lies within the C-shaped curve created by the duodenum and is connected via connective tissue
What is the uncinate process of the pancreas?
Projection arising from the lower part of the head, extending medially to lie beauty the body of the pancreas
What is the neck of the pancreas?
Located between the head & the body of the pancreas. Overlies the superior mesenteric vessels
What is the body of the pancreas?
Centrally located; crosses midline of the human body to lie behind the stomach, and to the left of the superior mesenteric vessels
What are the main exocrine pancreatic cells?
Acinar cells
What do the acinar cells secrete?
Acinar cells secrete enzyme-rich pancreatic juice into merging ducts.
What does the main pancreatic duct fuse with to form the hepatopancreatic duct?
Common bile duct
What is the accessory duct?
The duct of Santorini, traverses from pancreas directly into duodenum
What are the exocrine acini?
Clusters of secretory units associated to the ducts. They produce pancreatic digestive enzymes on the RER, moving to the Golgi complex forming condensing vacuoles -> Zymogens
What type of enzyme granule are released from pancreatic acinar cells?
Zymogen granules
What are pancreatic secretions secreted into?
Main pancreatic duct
How do pancreatic secretions enter the duodenum?
Main pancreatic duct fuses with the common bile duct, entering through the duodenum through the Ampulla of Vater
What molecule is released into the pancreatic secretions to control pH?
Bicarbonate ions, provide the optimum basic pH for digestive enzymes within the small intestine (lacks thick protective mucous barrier), neutralisation of acidic chyme
What are the endocrine cells of the pancreas?
Islets of Langerhans
alpha cells
beta cells
delta cells
What pancreatic polypeptides and hormone are released by pancreatic alpha cells?
Glucagon
What % of islet tissue is represented by alpha cells?
15-20%
What pancreatic hormone is released by beta cells?
Insulin
What % of islet tissue is represented by beta cells?
60-70%
What pancreatic hormone is secreted by delta cells?
Somatostatin
What % of islet cells are represented by delta cells?
5-10%
Which part of the pancreas has a greater distribution of islet cells?
Within the pancreatic tail.
What cells surround the islet cells?
The acini
Why are the islet cells highly vascular?
Ensures endocrine cells have proximal access for secretion
What granules secrete pancreatic secretions from acinI?
Apical secretion granules
What are the type of secretions released from acinar cells?
Low volume vicious enzyme rich
What are the type of secretions released from ductal cells?
High volume
Watery
Bicarbonate rich
What stimulates bicarbonate secretion from ductal cells?
Acidic chyme entry into the duodenum stimulates the release of secretion
What hormone stimulates acini secretion of pancreatic juice, and enhances secretin activity?
CCK
Which stages of gastric secretion does parasympathetic regulation play a role in?
Cephalic and gastric phases
Why is bicarbonate released by ductal cells?
Bicarbonate secretion counterbalances level of HCl secretion from parietal cells of body and fundus of stomach. Hydrogen ions enter the blood upon pancreatic bicarbonate secretion. Therefore, acidic blood draining from the pancreas neutralises the alkaline blood draining from the stomach, maintain the pH of venous blood that flows to the liver.
What does pancreatic juice comprise of?
Water, sodium bicarbonate, digestive enzymes
Which enzyme is inactivated by bicarbonate ions and alkaline environments?
Pepsin
What are the three main pancreatic enzymes?
Trypsin
Chymotrypsin
Carboxpeptidase
Where are pancreatic enzymes activated?
Activated within the duodenum
Which enzyme activates trypsinogen into trypsin?
Enteropeptidase/Enterokinase
How does pancreatitis occur in relation to enzymes?
Due to production of activated enzymes in the pancreas
Which two cells produce bicarbonate?
Ductal & centroacinar cells
Which enzyme catalyses the production of carbonic acid from water and carbon dioxide?
Carbonic anhydrase
Carbonic acid dissociates into which two ions?
Hydrogen ions
Bicarbonate ions
what happens to the hydrogen ions within pancreatic ductal cells?
Hydrogen ions are transported out of the pancreatic ductal cell exchanged for sodium ions by the Na+/H+ anti porter on the basolateral membrane into the blood
How are sodium ions removed out of the pancreatic ductal cell?
Na+/H+ ATPase
What junctions do sodium ions leave into the lumen?
Paracellular tight junctions
How does water move through paracellular tight junctions?
Water succeeds into the intercalated ducts via osmosis, due to the osmotic potential gradient
What is the fate of bicarbonate ions produced from the dissociation of carbonic acid in pancreatic ductal cells?
Bicarbonate ions are transported into intercalated ducts of the pancreas in exchange for chloride ions
How are intracellular chloride concentrations controlled?
Chloride ion channels facilitate the movement of chloride ions into the lumen of intercalated ducts
What is the bicarbonate anion exchanger on ductal cells?
Anion exchanger bicarbonate/chloride ions at the lumen
What ions and molecules move through the intercalated ducts into the pancreatic ducts?
Bicarbonate, sodium ions & water
Why is bicarbonate neutralisation important in the duodenum?
Neutralises acidic chyme from stomach, prevents damage to duodenal mucous, raises optimum pH range for pancreatic enzymes to be functional
Which glands also secrete alkaline fluid?
Brunner’s glands
Describe the extracellular concentrations of sodium ions in comparison to ductal cells?
High extracellular Na+ ions
Describe the extracellular concentrations of chloride ions in the lumen in comparison to the ductal cells
High chloride ions in lumen
What is the acidity of gastric venous blood?
Alkaline
Why its gastric venous blood alkaline?
The subsequent generated hydrogen ions within parietal cells contribute towards hydrochloric acid secretion, achieved through the exchanged of 𝐻𝐶𝑂3− into circulation
Why is pancreatic venous blood acidic?
The subsequent 𝑯𝑪𝑶𝟑− ions secreted into the pancreatic juice, thus results in acidic venous pancreatic blood, though hydrogen ion transfer into circulation
What is pancreatic amylase?
Carbohydrate digestion, brush border enzymes catalyses alpha-dextrin, hydrolysing glycosidic bonds, resulting in glucose removal
What does sucrose break into?
Fructose and glucose
What does maltase catalyse?
Catalyses the hydrolyses of maltose into 2 glucose molecule s
What does lactase catalyse?
Catalyses lactose into glucose & galactose
What granules are enzymes stored within the pancreatic acinar cells?
Zymogen granules
What is the role performed by gastric pepsin?
Proteins consist of polypeptides composed of amino acids by peptide linkages, digestion reduces polypeptide into their constituent amino acids.
HCl secretion from gastric parietal cells subsequently denatures proteins, enabling pepsin to hydrolyse protein into smaller polypeptides
What are the roles performed by amino peptidases and dipeptidases?
Hydrolyses peptide chains into sufficient amino acids diffusible into circulation
Where are amino peptidases and dipeptidases located?
Brush border of the duodenum.
What is the purpose of anitrypsin?
Inhibits trypsin activation.
Zymogen undergo activations within the duodenum
How is trypsinogen converted into trypsin?
Enteropeptidase
What is the role of trypsin on pancreatic zymogens?
Converts precursor proteolytic & lipolytic enzymes into activated forms
What is orlistat?
Pancreatic lipase inhibitor, reduces fat absorption causing steatorrhea
What is the cephalic phase?
Conditioned reflex response to sight, smell and taste of food. Enzyme-rich component only; low volume -> Mobilisation of pancreatic zymogens into the duodenum
What is the gastric phase?
Stimulation of pancreatic secretion originating from food arrival into the stomach; enhancing proenzyme secretion into main pancreatic duct -> Duodenum
What is the intestine phase?
Hormonally mediated when gastric chyme enters duodenum through the pyloric sphincter, proenzymes and bicarbonate secretion into the duodenum (70-80% of pancreatic secretion).
Which nerve innervates pancreatic juice secretion from acini?
Vagus nerve
Which bicarbonate consoling hormone is secreted upon acidic chyme entry into the duodenum?
Secretin
Which cells release CCK?
Enteroendocrine I cells
Which cells secrete gastrin?
Enteroendocrine G cells within the pyloric antrum
What effect does Gastrin have on parietal cells?
Increases HCl secretion
Which peptide stimulates the secretion of gastrin?
Gastrin-releasing peptide
Which substrates exert a stimulatory effect on CCK release?
Fatty acids and amino acids
Which peptide controls the release of CCK?
CCK-releasing peptide
What effect does trypsin exert no CCK release?
Negative feedback upon CCK release, inhibition of CCK-RP biding action to duodenal I enteroendocrine receptor sites, therefore an increase in protein substrate result
What is the relationship between acinar fluid an plasma?
isotonic
What simulates the secretion of acini fluid?
CCK
Which hormones stimulates the secretion of bicarbonate?
Secretin
Which cells secrete water and bicarbonate?
Ductal cells lining the extra lobular ducts of the pancreas
Which cells secrete secretin?
Enteroendocrine S cells
What effect does independent CCK have on bicarbonate secretion?
No effect
What effect does secretin and CCK have on bicarbonate secretion?
Markedly increase in bicarbonate through combined stimulation exerted by secretin
Which nerve stimulates CCK secretion?
vagal stimulation
What effect does secretin have on enzyme secretion?
No effect
What are the three main sections of the small intestine?
Duodenum, jejunum, and ileum
Which part of the small intestine absorbs the most water?
Jejunum
Where does the duodenum begin?
begins in the pyloric sphincter
The presence of which glands distinguishes the duodenum?
Brunner’s glands, submucosal tubular glands secreting alkaline fluid
The duodenum connects to which section?
Jejunum
Which is the longest region of the small intestine?
Ileum
3.75m
Compare the walls of the ileum with the jejunum?
Thicker and more vascular walls with increased developed mucosal folds than the jejunum
presence of more place circulare (increase density)
Where does the ileum connect with the caecum?
Connects with the caecum at the ileocecal sphincter
How is the jejunum and ileum attached to the posterior abdominal wall?
By the mesentery
Which parasympathetic fibres stimulate the ileum?
Vagus nerve
Which nerve fibres provides sympathetic innervation to the extrinsic small intestine?
Splanchnic nerve
Which artery supplies the majority of the small intestine?
The superior mesenteric artery
Where does the superior mesenteric artery drain into?
Superior mesenteric vein ->Hepatic portal vein
What is the mesentery?
Suspends small and large bowel from the posterior abdominal wall; anchoring them in place whilst facilitating movement
Provides conduit for blood vessels, nerves and lymphatics
What structures does the superior mesenteric artery supply?
Supplies the transverse colon, large and small bowel, splenic and hepatic flexure
Why is embolism of the superior mesentery artery deadly?
Results in necrosis through subsequently ischaemia to the small and large bowel
What are the four layers of the gut wall (Deep to superficial)?
Mucosa
Submucosa
Muscularis
Serosa
How is the surface area of the mucosa increased?
Plicae circulare
Villi
Microvilli
What is the function of plciare circulare?
Ridges within mucosa initiating at the proximal region of the duodenum and terminating at the mid line of the ileum folds facilitate absorption
Circular shape enables chyme to undergo spiral movements through the small intestine -> Impedes flow of chyme , providing time fo nutrient absorption
What is the function of villi?
Residing within the plicae circulares are vascularised projections, villi. Increases surface area of presented mucosal epithelium (composed predominantly of (enterocytes) columnar absorptive cells).
What does one villus cpaillarybed compose of?
One arteriole, one venue and one lacteal
Which surface are microvilli projected from?
Apical surface
How are lipids absorbed by enterocytes?
Lacteals into lymphatic system
Which plexus innervates the secretions of the small intestine?
Submucosal plexus
Where are Paneth cells and stem cells located?
Crypts of Lieberkuhn
What type of cells are enterocytes?
Columnar cells with microvilli on apical surface & basal nucleus, specialised for absorption and transport for substances
What is the typical lifespan for enterocytes?
1-6 days
What is the cylindrical internal surface area of the small bowel?
0.4m^2
What is glycocalyx?
Carbohydrates layer on apical membrane , provides protective layer from digestive enzymes. Unstirred layer, layer of water & mucous entrapped within the glycocalyx, regulates the rate of absorption rom intestinal lumen.
What are goblet cells?
Mucous containing granules accumulate at apical polarity of the cell, conforming the goblet shape, mucin secretin into the intestinal lumen -> Mucous secretion providing superficial layer on mucosal epithelium, glycoprotein that facilitates passage of chyme through the bowel
What is the pattern of distribution of goblet cells through the bowel?
Increases in prevalence through the duodenum to the colon
Where do the enterendocrine cells reside within the intestine?
Within the intestinal brush border
Predominantly located within the Crypts of Lieberkuhn
What do G cells secrete?
Gastrin
What do I cells secrete?
CCK, which stimulates the release of pancreatic juices and bile
What do K cells secrete?
Secretion of the hormone glucose-dependent insulinotrophic peptide; stimulates the release of insulin
What do M cells secrete?
Motilin, accelerates gastric emptying stimulates intestinal peristalsis and stimulates production of pepsin
What is the function of Paneth cells?
Paneth cells have the ability to undergo phagocytosis to engulf bacteria & protozoa, in addition to regulate intestinal flora
What do S cells secrete?
Secretin
Where do Paneth cells reside?
The crypts of lieberkuhn
Which granules are located within Paneth cells?
Acidophilic granules
What are located with acidophilic granules?
Antibacterial enzymes, lysozymes (protects stem cells), and glycoproteins and zin c
Which metal is secreted by Paneth granules?
Zinc
What is function of zinc metal for enzymes?
Trace metal for enzymes
What are stem cells (gut)?
Undifferentiated cells with pluripotent capability of cell division to replace degenerated cells. Epithelial stem cells are essential in the GI tract to continually replace the surface epithelium.
Where are intestinal stem cells located?
Crypts of Lierberkuhn
What is the role performed by intestinal stem cells in terms of migrational cells?
Upwards migration from the Crypts of Lieberkühn to the superior tip of villus, replacing apoptosed enterocyte, enteroendocrine, Paneth or Goblet cells Digested and reabsorbed.
Describe the turnover for enterocytes?
Rapid turnover
Why do enterocytes have rapid turnover?
Enterocytes are the initial line of defence against GI pathogens, and are suspectable to direct impact of toxic substances presented in the diet. Subsequently, these intracellular and extracellular damage is associated with a likelihood to develop dysfunctional cell abilities in addition with a diminished metabolic rate.
Therefore, these sustained lesions which impair cellular function are short-lived Minimises risk of malignancy
Compare the arterial arcade structure between the jejunum and ileum?
Arterial arcades from the superior mesenteric artery, jejunum infrequency and longer arcades compared to the ileum
Why are there multiple arcades into the ileum?
Peyer’s patches (Lymphoid tissue)
What are the three main functions of intestinal motility?
Mix ingested food with digestive secretions and enzymes
Facilitate contact between contents of intestine and intestinal mucosa
To propel intestinal contents along alimentary tract
What are the two main movements of intestinal motility?
Segmentation and peristalsis
What is the purpose of segmentation in terms of motility contractions?
Combines chyme with digestive juices and pushes food particles against the mucosa to be absorbed.
Mixed contents of lumen occurs by stationary contraction so internal circular muscles at intervals, frequency. Enables pancreatic enzymes and bile to mix with chyme, both directions
Where is the frequency of segmental contractions highest within the small intestine?
Duodenum
Which muscles are mainly involved in segmentation?
Circular muscles
Which hormone responds to reduced distention and localised segmentation , to stimulate intestinal peristalsis?
Motilin
Which cells secrete motilin?
Enteroendocrine M cells
What is the function of peristalsis?
Involves sequential contraction of adjacent rings of smooth muscles ; propels chyme towards the colon
What is a migrating motor complex?
Cycles of smooth muscle contractions through gut; initiates in stomach towards colon
Prevents migration of colonic bacteria into ileum
Which enzymes digest carbohydrates within the oral cavity?
Salivary amylase
How is salivary amylase inactivated?
Inactivated by stomach acid pH
How is glucose and galactose absorbed into the enterocytes?
SGLT-1 carrier protein on apical membrane
How is fructose transported into the enterocyte?
GLUT-5
How does glucose leave the enterocytes into the circulation?
GLUT-2 facilitates the exit of glucose at the basolateral membrane into circulation
How are dipeptides and tripeptides absorbed into enterocytes?
Catalytically degraded into amino acids whiten the enterocyte before entering circulation through facilitated diffusion
Which amino acids form from protein degradation upon brush border proteases activity?
Single Amin oacids
Oligopeptides
How are luminal peptides broken down at the brush border to enter into the enterocyte?
Luminal peptidases at the enterocyte brush border progressively hydrolyses to single amino acids
What cotransporter directly absorbs AAn into enterocytes?
H+/Oligopeptide cotranspoRTER PEPt1
How are oligopeptides degraded inside the enterocytes?
Cytoplasmic peptidases
How are lipids digested?
Secretion of bile salts and pancreatic lipase assist with the emulsification of lipids
What is the role of lipase?
Degrades lipids into fatty acids and monoacylglycerols, through the hydrolysis of ester linkages
What co-enzyme complex assist with lipase activity?
Co-lipase
What is the function of collipase?
Colipase complexes with lipase prevents bile salts displacing lipase from fat droplet. Solubilisation of lipolytic products in bile salt micelles.
How are lipids absorbed?
Large hydrophobic long-chain fatty acids and monoacylglycerides not easily suspended in aqueous intestinal chyme. However, bile salts, and lecithin encloses the fatty acids within a micelle, tiny spheres with hydrophilic heads exposed to the aqueous environment, and hydrophobic tails presented internally. The core enables cholesterol, in addition to fat-soluble vitamins to be stored.
Micelles enables lipids to become into contact with the luminal surfaces of enterocytes, pass through microvilli to luminal cell surface membrane. Lipids exit micelle Absorbed through simple diffusion.
Free fatty acids and monoacylglycerides that enter the enterocyte are reincorporated into triglycerides, manufactured with phospholipids and cholesterol, surrounded with donated apoproteins to form chylomicrons (Synthesised in the Golgi apparatus) Enter through large pores of lacteals Lymphatic vessels Thoracic duct into the subclavian vein.
Lipoprotein lipase hydrolyses the triglycerides of the chylomicrons into FFA + Glycerol
what is the purpose of the ileacecal valve?
Sphincter in constricted state, however as motility in the ileum increased the sphincter relaxes facilitating the passage of residue into the caecum
What is the purpose of the gastroileal reflex?
Increases the fore of ill segmentation, gastrin enhances ill motility, thus relaxing the iloceceal sphincter
How does chyme not go back into the ileum?
Chyme traverses through the sphincter, the generated backwards pressure subsequently closes the sphincter preventing backflow into the ileum (In addition to bacteria impedance).
