pancreas

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pancreas:

pancreas Dr.Abhijit Gogoi

Functional anatomy:

Functional anatomy An elongated,accessory digestive gland,lies retroperitoneally and transversely across post abd wall. Anatomically:head,neck,body and tail physiologically: a)Exocrine b)endocrine

Structural characteristics:

Structural characteristics Exocrine part:serous,tubulo alveolar gland. 1) Acinar cells:lines the alveoli;numerous secretory granules are present in the apical . Produce thick secretions containing enzymes 2) centroacinar cells 3) ductal cells

Pancreatic ducts:

Pancreatic ducts 1)main pancreatic duct(duct of wirsung ): Begins in the tail and runs the whole length. Joins common bile duct and opens in 2 nd part of duodenum on the major duodenal papilla. Ampulla of vater is guarded by sphincter of oddi

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2)accessory pancreatic duct:(duct of santorini ) Drains the upper part of head Opens into duodenum,2mm above main duct. Frequently communicates with main duct 3)intercalated ducts:receive secretions from acini and pass it to interlobular ducts. Finally the secretion goes to main duct and accessory duct.

Pancreas:

Pancreas Exocrine: Acini: Secrete pancreatic juice. Endocrine: Islets of Langerhans: Secrete insulin and glucagon. Insert fig. 18.26

Vessels and nerves of pancreas:

Vessels and nerves of pancreas Arterial supply Veins Lymphatics Nerve supply:both p/s and sympathetic Preganglionic vagal fibres synapse with ganglionic cells in pancreatic tissue. Postganglionic fibres innervate both acinar cells and smooth muscles of ducts. Vagal stimulation increases p/secretion

Pancreatic juice:

Pancreatic juice Transparent colourless fluid;isotonic 1200-1500ml/day Markedly alkaline(ph=7.8-8.4) due to high conc of HC03

composition:

composition Enzymes:amylase,lipase,protease and trypsin inhibitor Inorganic substances:Na,K,Ca,Mg,HC03,Cl

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1) amylase:secreted in active form Hydrolyses glycogen,starch andother complex carbohydrates except cellulose. 2) lipases:a ) lipase:lipolytic enzyme,hydrolyses neutral fats to glycerol esters and fatty acids.activity is more in presence of bile salts. B)cholesterol ester hydrolase:converts cholesterol esters to alcohol.

c)Phospholipase A2:

c) Phospholipase A2 Acts on lysophospholipids i.e lysolecithin and lysocephalin and converts them to phosphorylcholine . Gets activated in acute pancreatitis

Pancreatic proteases:

Pancreatic proteases 3endopeptidases:trypsin,chymotrypsin and elastase 2 exopeptidases:carboxypeptidaseA and B TRYPSIN:most powerful,activated by enterokinase . Hydrolyses proteins to proteoses and polypeptides Activates trysinogen and other pancreatic enzymes.

Pancreatic Juice:

Pancreatic Juice Contains H 2 0, HC0 3 - and digestive enzymes.

Pancreatic Juice:

Pancreatic Juice Complete digestion of food requires action of both pancreatic and brush border enzymes. Most pancreatic enzymes are produced as zymogens. Trypsin (when activated by enterokinase) triggers the activation of other pancreatic enzymes. Pancreatic trypsin inhibitor attaches to trypsin. Inhibits its activity in the pancreas. Fig. 18.29

Functions of pancreatic juice:

Functions of pancreatic juice 1)digestive functions 2)neutralizing functions:neutralises the gastric HCl in the chyme in duodenum

Secretion of Pancreatic Juice:

Secretion of Pancreatic Juice Secretion of pancreatic juice and bile is stimulated by: Secretin: Occurs in response to duodenal pH < 4.5. Stimulates production of HC0 3 - by pancreas. Stimulates the liver to secrete HC0 3 - into the bile. CCK: Occurs in response to fat and protein content of chyme in duodenum. Stimulates the production of pancreatic enzymes. Enhances secretin. Stimulates contraction of the sphincter of Oddi.

Mechanism of pancreatic secretion:

Mechanism of pancreatic secretion Secretion of pancreatic enzymes:the acinar cells of the exocrine part synthesised in ribosomes of RER. After synth enz pass to golgi complex,then released into cytoplasm as zymogen granules. The granules then move to luminal surface of cells.

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When stimulated,the acinar cells pour the enz in the lumen of acini by exocytosis . Then pass through intercalated ducts,interlobar ducts and ultimately into duodenum.. Within the cells,enz are stored in inactive form.they bcom active only after mixing with duodenal contents.

Formation of aqueous component:

Formation of aqueous component Aq comp is produced by columnar epithelial cells. Secretion by acinar cells:isotonic ,secretion of acinar fluid and proteins is stimulated by CCK and Ach. Secretion by intralobular ductal cells:higher conc of K and HCO3 Secretion by extralobular cells:stimulated by hormone secretin .

Secretion of HCO3:

Secretion of HCO3 HCO3 in the blood perfusing panc duct is the major source rather than produced by ductal epithelial cells. Blood perfusing the ducts is acidified by Na-H exchangers and H-K- ATPases in the basolat membrane resulting in formation of co2. Co2 diffuses into ductal cells and forms H2CO3

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H2CO3 dissociates into H and HCO3. HCO3 flows down its electrochemical gradient across the luminal membrane via Cl,HCO3 exchanger

Bicarbonate Ion Production in Pancreas:

Bicarbonate Ion Production in Pancreas 1-CO 2 diffuses to the interior of the ductule cells from blood and combines with H 2 O by carbonic anhydrase to form H 2 CO 3 which will dissociate into HCO 3 - and H + . The HCO 3 - is actively transported into the lumen. 2- The H + formed from the dissociated H 2 CO 3 is exchanged for Na + ions by active transport through blood , which will diffuse or actively be transported to the lumen to neutralize the – ve charges of HCO 3 - . 3- The movement of HCO 3 - and Na + ions to the lumen causes an osmotic gradient causes water to move from blood to ductule cells of the pancreas producing eventually the HCO 3 - solution.

Bicarbonate Ion Production in Pancreas:

Bicarbonate Ion Production in Pancreas

Effect of flow rates:

Effect of flow rates Pancreatic secretions are isotonic. At low flow rates ,composed mainly of Na and Cl and at high rates composed mainly of Na and HCO3

Regulation of pancreatic solution:

Regulation of pancreatic solution Both neural and hormonal mechanism are involved. Neural regulation is through vagal efferents Hormonal regulation is through secretin,CCK,gastrin and somatostatin .

CONTROL OF PANCREATIC SECRETIONS:

27 CONTROL OF PANCREATIC SECRETIONS

Cephalic phase:

Cephalic phase Little secretion Regulation is mainly thru reflex vagal stimulation which occurs by conditioned and unconditioned reflexes

Gastric phase:

Gastric phase Regulated by neural control through vagus and hormonal control through Gastrin . Intestinal phase:characterised by marked increase in secretion of both enzymes and aq component of panc juice. Regulated by hormones secretin and CCK

Regulation of Pancreatic Secretion:

Regulation of Pancreatic Secretion Figure 23.28

Disorders of pancreas:

Disorders of pancreas Acute pancreatitis Chronic pancreatitis Cystic fibrosis pancreatectomy

Pancreatic function test:

Pancreatic function test 1)analysis of pancreatic juice 2)Analysis of products of digestion 3)estimate of serum amylase levels

Analysis of pancreatic juice:

Analysis of pancreatic juice 1) secretin test:IV fusion of secretin given(12.5units/ kgbodywt ) and uodenal aspirate is collected Normal values:vol output:>2.0 ml/kg in 80min HCO3 conc >80meq/L HCO3 output>10meq/L in 30 min Secretory activity of ductal cells is decreased in chronic pancreatitis

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2)combined secretin and CCK test:to evaluate the secretory capacity of both ductal cells and acinar cells. This test helps to differentiate patients with steatorrhoea due to intestinal malabsorption or due to chronic pancreatitis

3)Lundh test:

3) Lundh test Pancreas is stimulated indirectly by ingestion of a test meal(containing fats,proteins and carbohydrates) Assessment of trypsin activity is done Mean trypsin activity <6 IU /L indicates presence of pancreatic exocrine insufficiency

Analysis of products of digestion:

Analysis of products of digestion 1) faecal fat excretion test:diet with 100gm of fat/day given. Stools are collected and tested for fat content Van De Krammer method is applied results:normally 5-6gm/day In exocrine pancreatic insufficiency= upto 40-50gm/day is excreted

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2) faecal nitrogen excretion test:normally 7gm of nitrogen is excreted/day Increased in exotic pancreatic insufficiency due to deficiency of proteolytic enzymes 3) tripeptide hydrolysis test:B2-T4-PABA is given. PABA is measured in urine 4)dual label schilling test

Estimation of serum amylase:

Estimation of serum amylase To rule out acute pancreatitis Normal value of serum amylase=50-120units/l Increased in acute pancreatitis

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