GIT Flashcards
What is long reflex?
Occurs when there is an outside presence of food. I.e. food is seen or smelt which begins the digestive process through salivation
What is the short reflex?
Occurs when there is food or substance present IN the GIT tract
What are the four functions of the oral cavity?
- ingestion and sensory analysis
- mastication
- lubrication
- limited digestion
What are the functions of saliva?
- chemical ad mechanical digestion beginning in the mouth
- exocrine secretion
- under autonomic control
Describe what salivary secretion does?
- softens and lubricates food
- chemical digestion: salivary amylase and some lipase
- saliva has a protective function
What is the protective function of saliva?
It is the first defense we have against bacteria
What is another name for swallowing?
deglutition
What is deglutition?
the swallowing reflex
- Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex
- Breathing is inhibited as the bolus passes the closed airway
- Food moves down into the eosophagus, propelled by peristaltic waves and aided by gravity
What are the three functions of the stomach?
- storage
- digestion: lipids and proteins
- defense against swallowed pathogens
How does digestive activity begin in the stomach?
the long vagal reflex of the cephalic phase
What are the three exocrine cells in the stomach?
- mucus cells
- parietal cells
- chief cells
What are the endocrine/paracrine cells of the stomach?
- enterochramaffin-like (ECL) cells
- D cells
- G cells
What are the two most imprtant cells for stomach digestion?
parietal and chiief cells
Explain the steps of HCL secretions
Parietal cells pump H+ (from carbonic acid breakdown) into stomach lumen via H+/K+/ATPase (proton pumps)
- H+ requires active transport
- K+ can diffuse across the membrane
What are the two roles of HCl in the stomach?
- activates pepsinogen (zymogen) - converts it into active pepsin
- contributes to nonspecific disease resistance by destroying most ingested pathogens
What can be some negative side effects of HCl in the stomach?
Damage to the mucosa lining, breaking down protective measures resulting in erosion of the stomach wall, inflammation and peptic ulcer
What are the two types of control of gastric secretion?
neural and hormonal control
Explain neural control of the regulation of gastric secretion
- Acetylcholine (ACh) - released by intrinsic nerve plexuses within the stomach, under the control of short local reflexes and vagal stimulation
Explain hormonal control of the regulation of gastic secretiion
- Enterochromaffin-like (ECL) cells: secrete histamine among the perietal and chief cells (oxyntic mucosa)
- G cells - secrete gastrin into the bloodstream
- D cells - secrete somatostatin in response to acid
What is segmentation?
Back and forth muscle movement of the SI which helps to mix and move food
What are the three main functions of the liver?
- Metabolic functions
- Bile production
- Blood circulation and filtration
What are the 6 metabolic functions of the liver?
- carbohydrate metabolism
- lipid metabolism
- synthesis of proteins/enzymes and hormones
- drug metabolism/Xenobiotic detoxification
- RBC recycling and waste product removal
- storage of vitamin (A, D, K) and mineral (iron, copper)
What are the functions of bile?
- lipid digestion and absorption, absorption of cholesterol and fat soluble vitamins: A, D, E and K
- Major route for cholesterol synthesis and degradation
What is the function of Bile Salts
emulsify large fat particles into tiny particles that can be attached by lipases
What are the endocrine functions of the pancreas?
secretes insulin and glucagon
What are the exocrine functions of the pancreas?
secretes digestive enzymes and bicarbonate.
- digestive enzymes are secreted as zymogens activated in the the small intestine
hat does the pancreatic dict do?
delivers digestive enzymes and buffers to duodenum.
- common bile duct and pancreatic duct penetrate duodenal wall
What are the exocrine cells of the pancreas?
Acini: clusters of secretory cells called acinar cells - contain zymogen granules with digestive enzymes Ductal cells (epithelial cells): produce alkaline secretion and transport all secretions
What are the endocrine cells of the pancreas?
Endocrine cells of pancreatic (langerhans) islets: secrete insulin and glucagon into bloodstrream
Explain the integration of gastric and intestinal phases for the pancreas
- Chyme activates ENS
- Secretin blocks acid secretion and motility. Also, increase release of bicarbonate
- CCK blocks acid secretion and motility. Also, increase secretion from pancreas.
- Endocrine cells - blocks acid secretion and motility
Explain digestion of molecules in the SI
- carbohydrates absorbed as monosaccharides
- proteins absorbed as short peptides
- lipid digestion depends on bile salts and lipases absorbed by lacteal ducts
- nucleic acids are digested into nitrogenous bases and monosaccharides
How does the small intestine absorb vitamins and minerals?
- fat-soluble vitamins absorbed by fats
- water-soluble vitamins are absorbed by mediated transport: vitamin B12 is absorbed when complexed to intrinsic factor and absorbed in the ileum
- mineral absorption usually occurs by active transport: iron and calcium absorption is actively regulated; sodium is absorbed by enterocytes and colocytes
Explain the breakdown of carbohydrates
Starch, glycogen -> disaccharides -> monosaccharides
What are the two eznymes which move glucose from the lumen on the SI into the body?
GLUT5 and GLUT2
What kind of transport is required for digestion and absorption of carbohydrates?
ACTIVE
Therefore, requires ATP
Where does digestion and absorption of proteins take place?
The stomach
- ACTIVE TRANSPORT
Where does digestion and absorption of fat take place?
Small intestine
- PASSIVE TRANSPORT
Where do we absorb most of our vitamins and minerals?
the large intestine
What are the functions of minerals in the body?
- cell growth and repair
- metabolism
- nerve and muscle function
What are the two most common mineral deficiencies in Australia?
- calcium: leading to osteoporosis
- Iron: leading to anaemia
How does fibre get absorbed through the GIT tract?
resistant to digestion and absorption in the SI and undergo complete or partial fermentation in the LI.
Acidic environment in stomach can break down fibre in stomach
What are factors that stimulate hunger?
- thoughts, sights, smells and sounds of food
- appealing tastes
- contraction of empty stomach
- release of ghrelin
- low levels of nutrients in intestines
- low levels of circulating nutrients
What are factors that cause satiety?
- food in stomach causing stretching and pressure
- intestinal distension and presence of food in the intestines signals brain directly and triggers release of satiety hormones
- high blood levels of nutrients
What is MR?
metabolic rate
- the rate at which energy is spent in the body in a given period of time
What is BMR
Basal Metabolic Rate
- measured under ideal conditions:
- physical and mental rest, no food within 12h
- comfortable room temperature
Immune functions: M cells
M cells sample the gut contents of the gut
- immune cells secrete cytokines: attract additional immune cells, cytokines trigger inflammatory response, increase in Cl-, fluid, and mucus secretion
Why do we vomit?
It’s a protective reflex
