Chapter 16: The Digestive System Flashcards
What is the purpose of the digestive system
- transfer nutrients, electrolytes. ect. from food to the internal environment (ECF)
ingested food yields ATP that can be used by body cells for (4)
- transportation
- contraction
- synthesis
- secretion
what percentage of ingested food is available for the bodys use
95%
what are the 4 processes used in digestion
- motility
- secretion
- digestion
- absorption
what are the 2 types of motility
- propulsive motility
- mixing movements
what are the three types of digestion
- CHO
- proteins
- lipids/fats
propulsive motility
- muscular contrations propel the food contents forward in the digestive tract
- allows appropriate velocity
mixing movements functions
- mixes the food with the digestive juices
- exposes all portions of the food to the absorbing surface of the digestive tract
secretion control
under neural or hormonal control
secretion
digestive juices from the exocrine glands into the digestive lumen
CHO is broken down into
monosaccarides
proteins are broken down into
amino acids
lipis/fats are broken down into
fatty acids
carbohydrates (CHO)
- form of polysaccaride that consists of chains of interconnected glucose molecules
types of CHO
- starch
- cellulose
- glycogen
- dietary CHO (Sucrose, lactose, ect)
starch
plants
cellulose
plant cell wall
glycogen
body muscles (meat)
what are the 3 disaccarides
- maltose
- sucrose
- lactose
what breaks down maltose
maltase
what breaks down sucrose
sucrase
what breaks down lactose
lactase
maltose breaks down maltase into
glucose
sucrase breaks down sucrose into
glucose and fructose
lactase breaks down lactose into
glucose and galactose
absorption
- takes place in the small intestine
- transfers nutrients from the digestive tract luman to the body / lymph fluid
where does absorption occur
small intestine
what are the accessory digestive organs
- salivary glands
- exocrine pancreas
- bilary system
what are the digestive organs
- mouth
- pharynx
- esophagus
- stomach
- small intestine (duodenum, jejunum, ileum)
- large intestine (cecum, appendix, colon, rectum)
- anus
moth and salivary glands motility
chewing
pharynx and esophagus motility
swallowing
stomach motility
- receptive relaxation; peristalsis
small intestine motility
segmentation; migrating motility complex
large intestine motility
haustral contraction; mass movements
what are the 4 tissues layers of the digestive tract
- mucosa (innermost layer)
- submucosa
- muscularis externa
- serosa (outer layer)
mucous membrane
- protective surface
- modified secretion and absorption
mucous membrane contains
- exocrine gland cells
- endocrine gland cells
- epithelial cells
function of mucosa exocrine cells
digestive enzymes
mucosa endocrine glands function
- blood born gastrointestinal hormones (gastrointestinal peptide, GIP, secretion, gastrin)
mucosa epithelial cells function
absorbing digestive nutrients
what are the 2 divisions of the mucosa
- Lamina propria
- muscularis mucosa
lamina propria
- house gut associated lymphoid tissue (GALT)
- important in defence againt disease causing intestinal bacteria
Muscularis mucosa
- a thin layer of smooth muscle
submucosa
- provides the distensibility and elasticity to the GI tract
- contain blood and lymph vessels
- contains submucosal plexus
Muscularis externa
- forms smooth muscle coat of the GI tract
- contains the myenteric plexus
what are the 2 layers of the muscularis externa
- circular layer (innermost layer)
- longitudinal layer (outermost layer)
circular layer
- decreases the diameter of the lumen
- innermost layer
Longitudinal layer
- contraction shortens the GI
- outermost layer
myenteric plexus
- located in the muscularis externa
- lies between the two muscle layers
mesentery
- part of the serosa
Serosa
secretes fluid that lubricates and prevents friction between digestive organs and the surrounding viscera
mesentery 3 functions
- the attachment provides relative fixation
- secure the digestive organs in proper place
- allow the freedom for mixing and propulsive movements
lips
- help procure, guide, and contain food in the mouth
- important in speech
- provide tactile sensation
palate
- forms roof of the oral cavity
- contains uvula (seals off nasal passages during swallowing)
tongue
- composed of skeletal muscle
- aid in chewing and swallowing
- important role in speech
- houses taste buds
pharynx
- a common passageway for the digestive and respitory
tomsils
- within the walls of the pharynx
- lymphoid tissue
teeth
- responsible for mastication
mastication
chewing
3 functions of chewing
- grind and break food into smaller pieces to make swallowing easier and increase surface area for the salvairy enzyme to act
- mix food with saliva
- simulate taste buds
saliva is produced by
the salivary glands
compositionof saliva
99.5% H2O
0.5% electrolytes and protein (amalyze, mucus, lysozymes)
8 functions of saliva
- contains salivary amylase (carbohydrate digesting enzyme)
- facilitates swallowing by moistening food
- mucus provide lubrication
- antibacterial actions (lysozyme destroys bacteria)
- solvent for molecule that stimulates taste buds
- aids speech by movement of the tongue and lips
- helps keep the mouth clean
- rich in bicarbonate buffers
what transport is responsible for glucose and galactose reabsorption
- secondary active transport mechanisms
what transport mechanism is responsible for fructose reabsorption
facilitated diffusion
simple salivary reflex is activated by
- presence of food in the mouth
- pressure receptors and chemoreceptors in the mouth
conditioned salivary reflex is activated by
- prior experience of food
- cerebral cortex: thinking/smelling/seeing food
neural regulation of saliva is controlled by
- salivary centre in the medulla
- automatic nerves
effect of parasympathetic and sympathetic nervous system on salivary secretion
work SYNERGISTICALLY to increase salivary secretion
parasympathetic NS effect on salivary secretion
- stimulates a prompt and abundant saliva is rich in enzymes
Sympathetic NS effect of salivary secretion
- elicits smaller saliva volume; feeling mouth drier than usual 9during stress such as speech)
salivary secretion is einterly under ______ control
neural control
Swallowing is associated with
pharynx and esophargus
stages of swallowing
- oropharyngeal stage (voluntary)
- Esopharengeal stage (involuntary)
what are the two spinchters in the esophagus
- pharyngoesphageal
- gastroesophagea;
pharyngoesophageal sphincter
- prevent large volumes of air from entering into the esophagus and stomach during breathing
gastroensphageal sphincter
- prevents reflux of gastric contents
what pushes food through the esophagus
peristaltic waves
what protects the esophagus
mucus / secretions
stomach
j shaped sac-like chamber lying between the esophagus and the small intestine
what are the three sections of the stomach
- fundas
- budy
- antrum
what are the three functions of the stomach
- food storage
- secretions of HCl and enzymes for protein digestion
- pulverizes semi-solid food into chyme
Pyloris sphincter
- severs as a barrier between the stomach and the upper part of the small intestine
what are the four aspects of the stomachs gastric motility
- gastric filling
- gastric storage
- gastric mixing
- gastric emptying
gastric filling
- involves receptive relaxation
- enhances the stomachs ability to accommodate the extra volume of food
- triggered by the act of eating
- mediated by the vagus nerve
gastric storage
the body of the stomach
gastric mixing
the antrum of the stomach
gastric emptying
- controlled by factors in the duodenum
what are the factors in the stomach that regulate gastric emptying
- the amount of chyme in the stomach (influences the strenght of contractions)
what are the 4 factors in the duodenum that regulate gastric emptying
- fat(presents of fat in the duodenum prevents gastric emptying)
- acid (unneutralized acid inhibits gastric emptying)
- hypertonicity
- distension
fat digestion and reabsorption only takes place in the
small intestine
what are the 2 factors that trigger gastric motility
- neural response
- hormonal response
neural response
- mediated through the intrinsic nerve plexuses and automatic nerve reflexes
- collectively called enterogastric reflex
hormonal response
- involves relase of hormones from the duodenal mucosa, collectively known as enterogastrones
what are the enterogastrones
- secretin
- cholecytokinin (CCK)
vomiting is controlled by
the vomiting center in the medulla
vomiting is caused by
- deep inspiration
- closure of the glottis
vomiting is follwoed by
- salivation
- sweating
- rapid heart rate
- snesation of nausea
what are 7 causes of vomiting
- tactile stimulation of the throat
- irritation or distention of the stomach and duodenum
- elevated intracranial pressure caused by cerebral haemorrhage
- rotation or acceleration of head producing dizziness
- chemical agents (drugs)
- chemotherapy agents
- emotional factos
3 effects of vomiting
- loss of fluids and acid (results in metabolic alkalosis)
- reduction in plasma volume
- dehydration and circulatory problems
2 advantages of vomiting
- removal of noxious material
- removal of accidental ingestion of emetics and posion from the body
emetics
vomiting agents
what are the 2 distinct areas of gastric mucosa (gastric secretions)
- oxyntic mucosa
- pyloric gland area (PGA)
oxyntic mucosa location
- lines body and fundus
pyloric gland area location
lines the antrum
what are the three types of gastric exocrine seretory cells
- mucosal cells
- chief cells
- parietal (oxyntic) cells
mucosal cells
- line the gastric pits and the entrance of glands
- secrete thin, watery mucus
cheif cells
- secrete enzyme precursor pepsinogen
parietal cells
- secrete HCl and intrinsic factor
what are the functions of alkaline mucous
- protects mucosa against mechanical, pepsin, and acid injury
what is the function of pepsinogen
- when activated, begins protein digestion
what is the function of HCl
- activates pepsinogen, breaks down connective tissue, denatures proteins, kills microorganisms
what is the function of intrinsic factor
- facilitates absorption of vitamin B12
what are the 3 endocrine / paracrine cells
- Enterochromaffin - like cells (ECL)
- G cells
- D cells
what does the ECL cells secrete and function
- histamine
- stimulate parietal cells
what does G cells secrete and function
- gastrin
- stimulates parietal, cheif and ECL cells
what does the D cells secrete and function
- somatostain
- INHIBITS parietal, G and ECL cells
hormonal control of gastric activities is controlled by
the presence of acid in the duodenal luman
Negative feedback of gastric activities process
- acid in the duodenal lumen
- increases Secretin release from the duodenal mucosa
- stimulates pancreatic duct cells
- increases secretion of aq NaHCO3 (bicarbonate) into the duodenal lumen
- nutralizes
the presences of acid in the duodenum stimulates the relase of
secretin in the blood
secretin functions
- inhibits emptying to prevent acid from entering the duodenum
- inhibits gastric secretions to reduce the normal acid production s
- stimualtes the pancreatic duct cells to produce bicarbonate to neutralize the acid
secretin and CCK are ______
trophic hormones to pancreas
presence of protein rich food in the stomach causes
gastrin release
functions of gastrin
- increases HCl (parietal cells) and pepsinogen (cheif cells) secretion –> promotes protein digestion
- enhances gastric mitility, stimulates ideal motility
-relaxes the ileocecal sphincter and induces mass movements of the colon
gastrin has trophic effects on the
stomach and small intestine
- to keep digestive tract viable
what are the major proteolytic enzymes on protein digestion
- trysinogen
- chymotrysinogen
- procarboxypeptidase
Dietary and endogenous proteins are hydrolyzed to their constitutes amino acids and a few small peptide fragments by
gastric pepsin and pancreatic proteolytic enzymes
amino acids enter the blood through
Na and energy dependent secondary active transport
pancreas is a ______ gland
mixed
pancreas endocrine functions
Islets of langerhans
- secrete insulin and glucagon
pancreas exocrine functions
secrete pancreatic jucies
pancreatic juice consits of
- pancreatic enzymes (secreted by acinar cells
- NaHCO3 (alkaline solution)–> secreted by duct cells
exocrine secretion of the pancreas is regulated by
- secretin
- CCK
proteolytic enzymes fucntion
digest protein
trysinogen
converted to active form trypsin
Chymotrysinogen
converted to active form chymotrysin
procarboxypeptidase
- converted to active form carboxypepidase
pancreatic amalyse
- converts polysaccarides into disaccarides
pancreatic lipase
- a fat digesting enzyme secreted throughout the entire digestive system
after participating in fat digestion, bile salts are reabsorbed back into the blood via
active transport mechanism
recycling of bile salts between the liver and the small intestine is refered to as
enterohepatic circulation
bile is secreted by
the liver
bile is stored and concentrated in the
gallbladder
bile consits of
- bile slats
- cholesterol
- lecithin
- bilirubin
bile salts are responsible for
emulfification
bile salts
- derivatives of cholestrol
- convert large fat globules into liquid emulsion
what percentage of bile salts are recycles
95%
what breads down triglycerides into monoglycerides and fatty acids
pancreatic lipase
monoglycerides and fatty acids are enclosed in a shell called
micelle
process of emulsification
bile salts –> large fat droplets –> small fat droplets –> enclosed in micelle
bile salts and lecithin contain both
a water soluble protion and a lipid soluable portion
the hydrophobic core of the micelle is made up of
- cholesterol
- bile salts (lipid soluble portion)
- lecithin (lipid soluble portion)
the hydrophilic shell of the micelle is made up of
- bile salt (water soluble portion)
- lecithin (water soluble portion)
what type of action do bile salt preform
detergent
water insoluable products are carried within the interior of the
micelle
micelles are extruded through the basal membrane by
exocytosis
iron absorbed into the blood is bound to
transferrin
ferritin
the pool of iron not absorbed by the blood
- converted to fecal matter
negative feedback of pancreatic lipase under control of CCK
fat and protein products in the duodenal lumen –> increases CCK release from the duodenal mucosa –> pancreatic acinar cell –> increases the secretion of pancreatic digestive enzymes the the duodenal luman –> digest fat and proteins
CCK is released in response to
the presences of fat and other nutrients
CCK functions
- inhibits gastric motility and secretion (allows more time for nutrients to be absorbed)
- stimulates pancreatic enzyme secretion of acinar cells
- causes the contration of the gall bladder and relaxation of the sphincter of oddi
- involved in long term adaptive changes
- stimulate food intake (satiety)
hepatitis
an inflammatory disease of the liver caused by a viral infection or exposure of a toxic substance
- can result in acute massive liver damage
Cirrhosis
- prolonged hepatic infection.
- associated with chronic alcholism
- damaged hepatocytes are permanently replaced by connective tissue
- causes gradual reduction in acute liver tissue, leading to chronic liver failure
where does most digestion and absorption take place
the small intestine
what percentage of absorption takes place in the small intestine
99%
what are the three segements of the small intestine
- duodenum
- jejunum
- ileum
segmentation
- the primary method of motility in the small intesitne consists or ring-like contractions
- action mixes chyme throughout the small intestine lumen
Segementation is intitated by
the pacemaker cells in the small intestine
- produce basic electrical rhythm (BER)
functions of segmentation
- mixes chyme with digestive juices screted into the small intestine lumen
- exposes all chyme to absorbative surfaces of the small intestine
where does absorption take place
the duodenum and jejunum
vili
microscopic figure like projections that increase the surface area of the small intestine
microvili
arise from the luminal surface of epithelial cells and increase surface area in the small intestine
functions of the colon
- extracts water and slat from contents
- temporary storage of feces
taeniae coli
- longitudinal bands of muscle
haustra
- pouches or sacs
- actively change location as a result of contration of cicular smooth muscle
haustual contractions
- main motility
- initiated by the autonomous rhythmicity of colonic smooth msucles cells
mass movements
- massive contractions
- moves colonic contents into the distal part of the large intestine
Gastrocoloic reflex
- mediated from the stomach to the colon by gastrin and by autonomic nerves
- most evident after the first meal of the day
- often followed by the urge to deficate
Defication reflex
- caused by the distention of the rectums stretch receptors
- internal and external sphincter relax
- voluntary
Constipation
- delay in deification; may result in constipation
constipation causes
- retention of colonic contents is longer than normal
- more than usual amount if water is reabsorbed from the feces; stool may be hard and dry
- delay is deification frequencies beyond normal
constipation symptoms
abdominal discomfort, dull headache, loss of appetites, followed by nausea, and mental depression
- disappear after defication
appendicitis
deposition of the hardened fecal material in the appendix causes inflammation
- appendix becomes swollen and filled with pus; may die as a result of local circulary interference
