3.4 Physiology of the GI Tract Flashcards
Main roles of digestive system
- Ingestion
- Digestion
- Absorption
- Defecation
Ingestion
When food enters the mouth
Digestion
food breakdown occurs when food is moved, mixed, and exposed to enzymes along the gastrointestinal tract. - mechanical digestion
- chemical digestion
Mechanical digestion
- food is physically broken down into smaller pieces
- teeth chew food
- when the stomach churns and mixes food
- food is moved and squeezed along the gastrointestinal tract
Chemical digestion
the chemical breakdown of food by enzymes into smaller nutrients
Absorption
the process of moving digested food into the bloodstream
Defecation
the excretion of indigestible food from the anus
Gastrin
- hormone that stimulates the stomach to secrete gastric juices
- pepsinogens
- mucus
- hydrochloric acid
Parietal cells
- located in the wall of the stomach body secrete hydrochloric acid
- generating a pH of 1.3-3.5
Pepsinogen
- pro-enzyme is secreted by the chief cells in the stomach
- hydrochloric acid converts the inactive pepsinogen into the active enzyme pepsin
- begins the breakdown of proteins
Peptides
- result in first step of protein digestion
- digested by peptidases to amino acids
Maltose
- result of first step in starch digestion
- digested by maltase to glucose
Chyme stimulates the small intestines to secrete two hormones:
cholecystokinin and secretin
Cholecystokinin
Causes the gallbladder to secrete bile
Secretin
Causes the liver to secrete bile
Satiety
The sensation of being full
Hunger
- internal drive to find and eat food
- often experienced as a negative sensation
- churning
- growling
- painful sensation in the stomach
Hypothalamus
- a region of the brain that plays a role in hunger, satiety, and the feeling of “being full”
- If a portion of the hypothalamus is damaged or destroyed, from certain chemicals, trauma, surgery, or cancers, the regulation of hunger and satiety can be lost
Hormones that increase hunger
- Ghrelin
- Endorphins
- Neuropeptide-Y
Hormones that cause satiety
- Leptin
- Serotonin
- Cholecystokinin
Leptin
- produced by adipose tissue (fat cells)
- alert the brain to turn off the hunger center
- activate the satiety center when consuming a meal
Ghrelin
- produced by the stomach
- stimulates the hunger center as it deactivates the satiety center
Types of Lipids
- saturated fat
- unsaturated fat
- cholesterol
Complete proteins
- contain nine essential amino acids
- are meat, poultry, eggs, milk, dairy products, and soybeans
Incomplete protein
- contain less than nine amino acids
- are food such as grains, legumes, seeds, and nuts
Essential amino acids
- nine amino acids required for adult human diet (10 for infant’s diet)
- human body is unable to produce these amino acids
- phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine,, leucine, lysine
- PVT TIM HiLL
Vitamins
- organic compounds that are not consumed in metabolic reaction
- help enzymes carry out the metabolic reactions
- convert nutrients to materials needed by the body
Water soluble vitamins
- excreted in urine
- not able to be stored in the body
Fat soluble vitamins
- are stored in body fat
- vitamins A, K, E, D
- nAKED person
Minerals
- inorganic compounds
- are not used as fuel in metabolic reactions
- combined with other nutrients to form necessary body substances
- calcium
- chloride
- magnesium
- phosphorus
- potassium
- sodium
- sulfur
Peristalsis
- rhythmic muscular contractions
- moves the food along the esophagus to the stomach
Pancreatic juice
includes three enzymes & bicarbonate:
- amylase: digest starch
- trypsin: digest proteins
- lipase: digest fats
- HCO3-: neutralizes the acidic chyme
Large Intestine
- what remains of the food enters the large intestine by the ileocecal valve
- undigested food is compacted in order to be prepared for defecation
- water is absorbed to form feces
- vitamins and ions are absorbed as well
- bacteria metabolize the remaining nutrients, producing vitamins K and B in the process
- feces travel to the rectum where it is defecated via the anus
Saliva
- produced by the salivary glands
- over 99% water
- contains enzymes and proteins that lubricate the oral cavity
- initiates chemical digestion of food
Gastric juice
- produced by gastric glands in the stomach lining
- contains hydrochloric acid and enzymes
- digest food into chyme
Intestinal juice
- secreted by glands in the intestinal wall
- contains enzymes that break down chyme and mucus that protects the intestinal lining
Bile
- contains bile salts that emulsify fats
- produced in the liver
- stored in the gallbladder
- enters the duodenum through the common bile duct
