Digestion 2 Flashcards
What accessory digestive organs does the digestive system consists of?
Accessory digestive organs
-Salivary glands
-Exocrine pancreas
-Biliary system
What are the 3 Classes of Energy-Rich Nutrients
-Dietary carbohydrates
-Dietary proteins
-Dietary fats
Hydrolysis plays an important role in the chemical digestion of polymeric nutrients
Secretion – the mouth/buccal cavity
Name the salivary glands
What is saliva used for?
What is in saliva
Salivary glands
- parotid
- submandibular / submaxillary
- sublingual
Extrinsic glands, ducts open into oral cavity. Neural stim. saliva
Saliva
- speech
- dental health
- lubricate food
- dissolve food
- initiate chemical breakdown
-Mucus
-Lysozyme (breaks down walls of bacteria) protective
-Salivary amylase- digestion of carbohydrates (Starch converted to maltose)
The Stomach
What are the regions of the stomach?
Different parts of the stomach have different cells
cardia, fundus and pylorus
Cardiac Glands Contain mainly mucus-producing cells
Pyloric Glands Mucosubstances, electrolytes (Cl-, HCO3-,
PO42-), pyloric protease, Gastrin, Gastrone.
Principal (corpus-fundic) Glands
Glandular tubule consists of a deep body, intermediary neck and an upper isthmus
4 secretory cell types:
chief cells
Parietal cells
Mucous neck cells
Endocrine cells
Describe gastric glands
top to bottom of pit
mucous surface cells
mucous neck cells
parietal cells (secretes HCL and intrinsic factor)
chief cells (secrete pepsinogens (inactive form of pepsin))
hormone-producing G-cells (secretes gastrin)
Name and describe the secretions of the Stomach
*Chief cells (Zymogenic or peptic cells) = produce pepsinogen, a precursor of proteolytic NZM, pepsin (it is activated at pH optimum 2.0) We need it to release pepsinogen and not pepsin because we don’t want to autodigest)
*Parietal cells (Oxyntic cells) secrete HCl of gastric juice; activating pepsinogen & sterilising stomach contents.
secrete intrinsic factor for Vit B12 resorption
*Mucous neck cells (produce acid mucopolysaccharides sugar modified mucus containing carbohydrates)
Found in neck of gland between parietal cells
*Endocrine cells (Gastroenteropancreatic endocrine system)
- G cells – gastrin-producing cells stimulate acid & pepsinogen secretion
- D cells – somatostatin-producing cells inhibit G cells hence acid production (negative regulatory component)
- D1 cells – VIP(vasointestinal peptide)-producing cells Enterochomaffin cells – Histamine/serotonin -containing Cells - Contraction of lower oesophageal sphincter, increases GI motility, relaxes pyloric sphincter
Describe the process of producing hydrochloric acid
HCl is produced by the parietal cells of the stomach. To begin with, water (H2O) and carbon dioxide (CO2) combine within the parietal cell cytoplasm to produce carbonic acid (H2CO3), which is catalysed by carbonic anhydrase. Carbonic acid then spontaneously dissociates into a hydrogen ion (H+) and a bicarbonate ion (HCO3–).
The hydrogen ion that is formed is transported into the stomach lumen via the H+– K+ ATPase ion pump. This pump uses ATP as an energy source to exchange potassium ions into the parietal cells of the stomach with H+ ions.
The bicarbonate ion is transported out of the cell into the blood via a transporter protein called anion exchanger which transports the bicarbonate ion out the cell in exchange for a chloride ion (Cl–). This chloride ion is then transported into the stomach lumen via a chloride channel.
This results in both hydrogen and chloride ions being present within the stomach lumen. Their opposing charges leads to them associating with each other to form hydrochloric acid (HCl).
What are the Phases of Gastric Secretion
Cephalic phase= short phase (prepare stomach to receive food) sight, smell, taste or thought of food to get digestion ready. Nervous control, vagus nerve allows for a positive stimulation, stimulating mucous cells to produce mucus, parietal cells to produce HCL and Chief cells to produce pepsinogen and G cell to produce gastrin (switching on stomach and secretion)
Gastric phase= digestion, long phase lasting 3-4 hours, helps perpetuate secretion but also motile forces to mix food with secretions. There is a hormonal influence and secretion cells switch on. These have a positive feedback influence and gastrin specifically helps facilitate excitation of mucosa creating mass peristalsis waves to mix digesta and secretions and break down food
intestinal phase=Switching off the stomach and preparing it to release food into duodenum, it is long lasting (hours), it has neuronal and hormonal influences for secretion. These secretions some obtained from pancreas such as, CCK, GIP and secretin are negative regulatory switch off secretion of chief cells, parietal cells and G-cells ultimately they also switch off contractibility of mucosa, switching off peristalsis. They switch off positive neuronal influence and secretive influences.
Quick summary of digestion in stomach (secretions)
Protein digestion
pepsinogen (zymogen proenzyme) +HCL–>pepsin (active enzyme)
carboxyl protease (endopeptidase) starts to make
protein–>peptides
The Gallbladder and The Pancreas
gallbladder
Hollow, pear-shaped organ
Stores, modifies and concentrates bile. It emulsifies fats
pancreas
Endocrine functions
Insulin and glucagons
Exocrine functions
Majority of pancreatic secretions (alkaline to help buffer stomach acid)
Pancreatic juice secreted into small intestine
Carbohydrases (carbohydrate digestion)
Lipases (fat digestion)
Nucleases
Proteolytic enzymes (protein digestion): Trypsinogen these further digest proteins into peptides
Secretions
Pancreatic and Biliary systems
Name the proteolytic NZMs?
What degrades starch and complex carbohydrates, disaccharides and triglycerides?
What neutralises acid from the stomach?
Pancreas
Digestive NZMs (acinar cells)
Proteolytic NZMs: Trypsinogen, Chymotrypsinogen
Procarboxypeptidase, proaminopeptidase and
proelastase. All zymogens have to be converted to active enzyme first.
Pancreatic amylase (degrades starch and complex carbohydrates to simpler carbohydrates)
Carbohydrases (sucrase, lactase, maltase these digest disaccharides to monosaccharides)
Pancreatic lipase (hydrolyses TriG to fa’s+glycerol)
aqueous NaHCO3 (produced by duct cells, neutralises acid from stomach)
liver/ gall bladder
Whatdoes bile do?
Why is the liver important?
Liver / gall-bladder: an alkaline secretion!
Bile (containing bile salts (for emulsification) and phospholipids)
Emulsify fats (large droplets to small particles)
Liver: important in metabolism of protein, lipid, CHO’s, Vits, minerals, pigments and haem products
The Small Intestine
Name secretions
What helps buffer acids?
Moisten chyme
Help buffer acids
Maintain digestive material in solution to facilitate absorption
Juice secreted does not contain digestive NZMs.
Intracellular activity of NZMs in Brush-border of epithelial cells: (these stay there, they aren’t secreted)
a-dextrinase, maltase, sucrase, lactase, enterokinase
aminopeptidase, dipeptidase nucleosidases, phosphatases.
Intestinal secretion (succus entericus)
What does it do?
Name extracellular enzymes
Name intracellular enzymes
Succus entericus is an acid secretion produced by glands in the duodenum wall that consists of water, biological attributes, and hydrogen carbonate ions. It protects the duodenum by offsetting the acidic environment and proteolytic mucus that tries to enter the small intestine from the stomach.
Consists of: Enzymes
Intestinal mucus
Electrolytes (Cl-, HCO3-, PO42-)
Extracellular enzymes
intestinal alpha amylase
enterokinase (Trypsinogen activator)
Intracellular enzymes
Located within epithelial cells on surface of villi
Peptidases lipases disaccharidases, nucleotidase
Nucleosidase prolinase
Digestion – pancreas/small intestine
How is Trypsin formed?
What cascade does this lead to?
trypsinogen +enterokinase–> Trypsin (endoprotease protein-peptide)
This then cause a cascade of all other zymogens to activated forms as trypsin converts
1) chymotrypsinogen–>chymotrypsin
2)procarboxypeptidase–>carboxypeptidase
3) proelastase–>elastase
OTHERS (fats)
1)triglycerides+lipase (lipolytic NZM)–>fatty acids+glycerol
2)starch glycogen dextrins+amyase–> maltose (disaccharide)
