Digestion and Metabolism Flashcards
what is the gastrointestinal tract (GI tract)?
long tube that is open at both ends for the transit of food during processing
- named portion of the tube include the oesophagus, stomach, small intestine, large intestine, and rectum
what are accessory structures?
are not part of the GI tract, but they do contribute to food processing
include the teeth, tongue, salivary glands, liver, gall bladder, and pancreas
outline the 6 basic processes involved in digestion
- ingestion: taking food into mouth
- secretion: release of water, acid, buffers, and enzymes into lumen of GI tract
- mixing and propulsion: churning and movement of food through the GI tract
- digestion: mechanical and chemical breakdown of food
- absorption: passage of digested products from GI tract into blood and lymph
- defecation: elimination of faeces from GI tract
outline the phases of digestion.
cephalic (head) phase
- stimulates gastric secretion and motility
gastric phase
- neural and hormone mechanisms
intestinal phase
- neural and hormonal mechanisms
name the 4 tunics of the GI tract and state the major functions of each tunic
tunica serosa: protection/covering
tunica muscular: longitudinal and circular (inner layer) work together to propel food/chyme through the digestive tract
tunica submucosa: loose tissue containing blood and lymphatic vessels. provides nervous control to the mucosa
tunica mucosa: innermost layer with variable structure (secretion, absorption and hormone production)
what is mechanical and chemical digestion?
mechanical: chewing mixes food with saliva and forms a bolus which can be easily swallowed
chemical: salivary amylase enzyme coverts polysaccharides to disaccharides
what is deglutition? explain the process.
the action or process of swallowing
- tongue shapes the chewed, lubricated food and moves it to the back of the mouth cavity
- tongue rises against the palate ad closes the nasopharynx
- the uvula and palate seal off the nasal cavity
- the epiglottis covers the larynx
breathing temporarily interrupted
outline the functions of the stomach.
- mixes saliva, food and gastric juice to form chyme
- serves as reservoir for food before release into small intestine
- secretes gastric juice, which contains HCI (kills bacteria and denatures proteins), pepsin (begins the digestion of proteins) etc.
- secretes gastrin into blood
what impact would the removal of stomach or small intestine have on digestion?
if stomach is removed, digestive tract can still absorb food but as the stomach acts as a reservoir for food patients may experience gastric dumping in undigested food through the digestive tract causing pain, diarrhoea and drop in BGL levels
what is the pancreas?
gland that lies posterior to the stomach
- produces enzymes that digest carbs, proteins, fats and nucleic acids
- produces sodium bicarbonate which buffers stomach acid
- empties its contents into duodenum
how does pancreatic juice affect digestion of nutrients?
pancreatic juice helps protect and prevent erosion of the intestinal mucosa
it contains bicarbonate (alkaline that can neutralise acidic liquid coming from the stomach)
what is the importance of the livers production of bile?
important in the emulsification of fats - carbs, lipid and protein metabolism - cholesterol synthesis - metabolism of drugs and hormones - bilirubin excretion - storage of glycogen and blood - phagocytosis of bacteria from GI tract (kuppfer cells) - vitamin D activation - secretes clotting factors gallbladder stores bile until it is needed
what is the function of the bile?
bile contains water, electrolytes and organic molecules such as bile acids, cholesterol, phospholipids and bilirubin that flows through the biliary tract into the small intestine
has two important functions:
- contains bile acids, which are critical for digestion and absorption of fats and fat-soluble vitamins in small intestine
- contains waste products which are eliminated from the body via secretion into bile and elimination in faeces
describe the relationship between liver, metabolism and detoxification
the liver is responsible for metabolising certain hormones and many drugs, which is why substances pass directly to the liver in the blood stream via the hepatic portal system
receives substances in the blood from all parts of the gastrointestinal system to process/metabolise before they travel in the bloodstream to the heart and the rest of the body
hepatitis is a condition where the liver is inflamed. describe what would happen if liver function was impaired?
- detoxification decreases or ceases
- build-up of toxins e.g. alcohol or drugs - changes the properties of drugs and can lead to overdose
- increase in ammonia - may lead to brain injury
name the function and the three subdivisions of the small division.
the majority of digestion and absorption occurs in the small intestine.
duodenum, jejenum, ileum
the duodenum receives substances from different regions of the gastrointestinal system to facilitate digestion of nutrients. name these regions.
- common bile duct (bile)
- pancreatic duct (pancreatic enzymes)
- stomach (processed food)
duodenum is the first and shortest segment of the small intestine
what are the major functions of the large intestine?
- reabsorption of water and mineral ions such as sodium and chloride
- formation and temporary storage of faeces
- maintaining a resident population of over 500 species of bacteria
- bacterial fermentation of indigestible materials
- defection (emptying they rectum)
describe mechanical digestion in the colon.
haustral churning
- distension reaches a certain point and the walls of the hausfrau contract to squeeze contents onward
peristalsis
- propulsive contractions
mass peristalsis
- a strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum
describe chemical digestion in the colon.
the last stages of digestion occur through bacterial action
- substances are further broken down by bacteria
- some vitamins are synthesised by bacterial action
define metabolism.
metabolism refers to all chemical processes occurring within a cell or organism that are necessary for the maintenance of life
nutrients are broken down in the GI tract, absorbed into the blood and then transported to cells.
in the cells these molecules are either catabolised or anabolised
define catabolism.
the process by which metabolic pathways break down molecules into smaller units and release energy
large molecules are broken down into digestible units:
- polysaccharides are broken down into monosaccharides
- lipids are broken down into fatty acids
- proteins are broken down into amino acids
define anabolism.
the set of metabolic pathways that construct molecules from smaller units - e.g. the production of a protein from amino acids
identify reasons for vomiting
- food poisoning
- pregnancy
- CNS disorders e.g. meningitis, tumours
- drugs (narcotics), excess alcohol, spicy foods
- stress, fear
what are the physiological effects of excessive vomiting?
sudden, forceful oral explosion of stomach contents
- usually preceded by nausea
- protective mechanism, often to rid the body of potential noxious agents
what happens to a person who has no food source?
starvation causes many physiological and psychological changes in the human body.
- the body is designed to fend for itself when it does not receive adequate nutrition
- metabolism slows down to conserve energy and muscle mass is broken down for energy to conserve fat stores and keep vital organs functioning
- people who are starving are more likely to become ill, and in some cases, die.
state some physical effects of starvation.
- emaciation
- dehydration
- poor growth
- bone loss
- fragile bones
- poor immune function
- fatigue
- muscle weakness
- dizziness
