Digestive System (2) Flashcards
Where is food converted into chyme?
- chyme is a type of juice
- food it converted into creamy chyme in stomach
What is the stomach?
- temporary storage tank where chemical breakdown of proteins begin and food is converted into chyme
Where is stomach located?
- upperleft quadrant of the peritoneal cavity, almost hidden by liver and diaphragm
Types of gland cells in the stomach
- mucous neck cells
- Parietal cells
- chief cells
- enteroendocrine cells
Mucous neck cells
- scattered in “neck” and more basal regions of glands
What do parietal gland cells secrete?
- HCl (hydrochloric acid)
Function of hydrochloric acid in stomach
- makes stomach contents extremely acidic (pH 1.5 - 3.5)
- necessary for activation and optimal activity of protein-digesting enzyme pepsin
- acidity helps digest food by denaturing proteins and breaking down cell walls
- kills bacteria ingested with food
Protein digesting enzyme in stomach
- pepsin
Where are chief cells found in glands?
- basal regions of gastric glands
Function of chief cells in glands
- produce pepsinogen (inactive form of pepsin)
- produce lipases (fat-digesting enzymes)
What is the inactive form of pepsin?
- pepsinogen
What are fat digesting enzymes called?
- lipases
Where are enteroendocrine cells found in glands?
- deep in the gastric glands
Function of enteroendocrine glands
- release a variety of chemical messengers directly into the interstitial fluid of the lamina propria
Examples of chemical messengers released by enteroendocrine glands
- local paracrines like histamine and serotonin
- somatostatin which acts as paracrine locally and hormones that diffuse into the blood capillaries to influence several digestive system target organs
- gastrin, a hormone which regulates stomach secretion and motility
What are paracrines?
- endocrine hormones that impact nearby cells and tissues
- not released into the bloodstream
Histamine hormone
- produced in basophils
- inflammatory responses
- increases permeability of capillaries to WBCs
- in stomach, aid production of gastric acid (enteroendocrine glands)
Serotonin hormone
- 90% found in GI tract, 10% in brain
- paracrine
- inhibits gastric acid production
- causes contraction of stomach muscles
Somatostatin hormone
- works to inhibit release of other hormones
- function in GI tract - reduces gastric secretion
- function in pancreas - inhibits release of pancreatic hormones; insulin, glucagon, gastrin
Where does protein digestion begin in digestive system?
- stomach
- is the main type of enzymatic breakdown there
- protein digesting enzyme is pepsin
- HCl denatures the proteins in preparation
Hormones are produced by which cells in stomach?
- enteroendocrine cells
Which nerves stimulate stomach secretion?
- vagus nerves
Where does majority of digestive activity happen?
- small intestine
Which organs’ secretion help small intestine digestive activity?
- liver (bile) and pancreas (digestive enzymes in pancreatic juice)
longest part of alimentary canal
- small intestine
3 subdivisions of small intestine
- duodenum
- jejunum
- ileum
Duodenum
- shortest subdivision of small intestine
- about 10 inches long
- curves around head of pancreas
- bile duct and pancreatic duct unite with small intestine here
Jejunum
- subdivision of small intestine
- 2.5 m (8 ft) long
- extends from duodenum to ileum
Ileum
- subdivision of small intestine
- 12 ft (3.6 m) in length
Nerve fibres serving the small intestine
- parasympathetics from vagus
- sympathetic from thoracic splanchnic nerves
Amount of daily intestinal juice
- produced by glands in small intestine
- 1 to 2L daily
Stimulus for intestinal juice
- hypertonic or acidic chyme -> causes distension or irritation of the intestinal mucosa
pH of intestinal juice
- 7.4 to 7.8; slightly alkaline
- isotonic with blood plasma
What does the intestinal juice consist of?
- largely water with some mucus
- mucus is secreted by duodenal glands and goblet cells of mucosa
- enzyme-poor (enzymes are limited to bound enzymes of brush border)
What are brush border enzymes?
- enzymes embedded in microvilli of apical plasma membrane
Role of liver in digestive system
- produce bile for export to the duodenum
What is bile?
- fat emulsifier that breaks down fats into tiny particles to make them more digestible
- yellow-gren alkaline solution
Largest gland in the body
- the liver
How many primary lobes does liver have?
- 4 primary lobes
4 primary lobes of the liver
- largest right lobe
- smaller left lobe
- posteriormost caudate lobe
- qyadrate lobe inferior to left lobe
Where is the gall bladder?
- inferior surface of the right liver lobe
Which duct supply bile to the duodenum?
- common hepatic duct leave the liver and fuses with cystic duct draining the gall bladder to form “bile duct”
Liver cells
- hepatocytes
Hepatic artery
- supply oxygen rich blood to liver
Function of hepatocytes
- process blood-borne nutrients in various ways (store glucose as glycogen; use amino acids to make plasma proteins)
- store fat soluble vitamins
- detoxification (ridding the blood of ammonia and converting to urea)
Composition of bile
- bile salts, bile pigments
- cholesterol
-triglycerides
-phospholipids - electrolytes
Actual stuff in bile that aid digestion
- bile salts and phospholipid
Function of bile salts
- separate large fat globules entering smol intestine into millions of smaller fat droplets for large surface area for enzymes
- facilitate fat and cholesterol absorption
Enterohepatic circulation for bile ducts
bile salts are
- reabsorbed into blood by ileum
- returned to liver via hepatic portal blood
- resecreted in newly formed bile
Chief bile pigment
- bilirubin (waste product of heme of hemoglobin formed during breakdown of worn out erythrocytes)
- globin and iron parts are saved and recycled
- bilirubin is absorbed from blood by liver cells, excreted into bile, metabolized in small intestine by bacteria
What gives feces a brown colour?
- stercobilin: breakdown product of bilirubin
- in the absesnce of bile, feces is grey-white
What is the gall bladder?
- thin walled muscular sac about 10 cm long
- inferior surface of liver
- stores bile that is not immediately needed and concentrates it by absorbing water and ions from it
Pancreas in the digestive system
- produces enzymes that break down all categories of food stuff
exocrine product of pancreas
- pancreatic juice
- drains from pancreas into duodenum via main pancreatic duct
- fuses with bile duct as it enters duodenum
Where does bile duct enter duodenum?
- at hepatopancreatic ampulla
mini endocrine glands in pancreas
- pancreatic islets (islets of langerhans)
- release insulin and glucagon; for carbohydrate metabolism
composition of pancreatic juice
- mainly water wiht enzymes and electrolytes (bicarbonate ions)
Acinar cells
- produce enzyme rich component of pancreatic juice
high pH of pancreatic juice
- helps neutralize acid chyme entering duodenum and provides optimal environment for intestinal and pancreatic enzymes
protein-digesting enzymes in pancreas
- proteases
- release in inactive forms in pancreas
- activated in the duodenum
pancreatic enzymes secreted in active form
- amyase, lipase, nucleases
Absorption in small intestine
- accomplished by absorptive cells with their rich crop of apical microvilli
What do amylase, lipase and nuclease require for optimal activity?
- for ions or bile to be there in the small intestine
Accessory pancreatic duct opens at the
minor duodenal papilla
How many premolars in adult?
8
Common bile duct joins the
duodenum
