lecture 3- pancreas and liver Flashcards
Pancreas location
elongated gland lying below and behind stomach,
Pancreas info
mixed gland (contains both exocrine and endocrine tissue), acinar and duct cells predominant, isolated islands of endocrine cells
Pancreas secretions
endocrine and exocrine tissues. endocrine cells release glucagon and insulin to control blood sugar
exocrine secretions
releases 1-2L of pancreatic juices per day
Duct cells
sodium bicarbonate rich
Pancreatic enzymes (acinar cells)
Proteolytic enzymes, Pancreatic Amylase, Pancreatic Lipase
Proteolytic enzymes
Protein digestion
Pancreatic Amylase
Carb digestion
Pancreatic Lipase
Fat digestion
3 major pancreatic proteases
trypsinogen, chymotrypsinogen, procarboxypeptidase
protective mechanisms of pancreas
enzymes stored and released in inactive form, trypsinogen is activated to trypsin by enterokinase in duodenum, pancreas produces trypsin inhibitor, duodenum secretes mucus from epithelium wall
Pancreatic amylase
hydrolyses polysaccharides into disaccharide (maltose). Ir can be secreted in active form as secretory cells do not contain polysaccharides
Pancreatic lipase
hydrolyses TAG into monoglycerides and free fatty acids. Secreted in active form as TAG not structural component of pancreatic cells.
Steatorrhoea
excess fat in faeces
Alkaline Solution
is the largest component of pancreatic juice, neutralises chyme, duct cells
Pancreatic exocrine secretion is regulated by
hormones
Acidic chyme in duodenal lumen activates releases what from the duodenal mucosa?
Secretin which is carried by blood and ends in pancreatic duct cells and neutralises
fats and protein products in duodenal lumen releases what from the duodenal mucosa?
CCK which is carried by blood to pancreatic acinar cells and digests
Liver function
secretion of bile salts (digestive role)
Hepatocytes receive blood from 2 sources
arterial blood from aorta and venous blood from digestive tract
Bile consits of:
bile salts, cholesterol, lecithin (phospholipid), bilirubin (waste product from old red blood cells), aqueous alkaline fluid
Gallbladder
storage of bile between meals
what are gallstones (choleliths)?
crystalline bodies that have precipitated from components of bile
How do bile salts facilitate fat digestion and absorption?
Emulsification (digestion- detergent action) and Micelles (absorption of fat)
Micelles
cholesterol is dissolved in michelles core, amount that is carried depends on amount of bile salts and lecithin. If cholesterol secretion is out of proportion microcrystals form.
Treatment of cholesterol gallstones involves-
ingestion of bile salts> increase bile salt pool> dissolve cholesterol
regulation of bile secretion- chemical
bile salts stimulate their own secretion when returned to the liver during meal digestion
regulation of bile secretion- hormonal
secretin stimulates an aqueous NaHCO3 bile secretion to neutralise chyme
regulation of bile secretion- vagal
stimulation of liver to increase bile flow during cephalic phase plays a minor role
During digestion
fats and proteins products in the duodenum stimulate the release of CCK. CCK stimulates contraction of the gallbladder and relaxation of the sphincter of Oddi, releasing bile into the duodenum, fat digestion/absorption
Bilirubin
2nd major component of bile- a waste product excreted in bile. derived from degradation of the heme (iron-containing) part of the haemoglobin in red blood cells
Bilirubin facts
is a yellow pigment, makes bile yellow, in the intestines it is modified by bacterial enzymes to make feaces brown, makes urine yellow. patients with jaundice have a yellow colour (eyes)
Hepatitis
inflammatory disease of the liver, multiples causes- viral, obesity, toxic agents, prolonged inflammation associated with alcoholism leads to cirrhosis and eventually leads to liver failure
The pancreatic duct cells secrete aqueous alkaline solution in response to what main stimulus in the duodenum?
acid
Autocatalysis is a process whereby the active digestive enzyme in the lumen converts the inactive proenzyme to the active form. Which enzymes undergo this process?
trysinogen and pepsinogen
The liver is an accessory digestive organ and the largest metabolic organ in the body. What is its primary digestive role?
secretion of bile salts
Between meals, bile secreted by the liver hits the closed Sphincter of Oddi and gets diverted back up the common bile duct to the gallbladder. What happens when it gets there?
stored until the next meal and concentrated by actively removing salt
Micelles are vital for absorption of the end products of fat digestion, monoglycerides and FFA. In the hydrophobic core of the micelles you will also find:
cholesterol, lipid soluble portion of bile salts, lecithin and vitamins
Exocrine cells
mucous, chief cells, parietal cells
Endocrine cells
ECI cells, G cells, D cells
Mucous (product, stimuli, function)
Alkaline mucous. Mechanical stimulation by contents. Protects against mechanical pepsin and acid injury
Chief cells (product, stimuli, function)
Pepsinogen gastric lipase. Acetylcholine (Ach), gastrin. Protein digestion (when activated) Fat digestion (small amount)
Parietal cells (product, stimuli, function)
Hydrochloric acid (HCI) and intrinsic factor. Ach and gastrin histamine. Activates pepsinogen, breaks down CT, denatures proteins, kills microorganisms, facilitates absorption of Vit B12
ECI (product, stimuli, function)
Histamine. Ach, gastrin. Stimulates parietal cells
G cells (product, stimuli, function)
Gastrin. Protein products Ach. stimulates chief and ECI cells
D cells (product, stimuli, function)
Somatostatin. Acid. Inhibits parietal, G and ECI cells
