Chapter 26: Digestive System Flashcards
six main functions of the digestive system
1- ingestion
2- motility
3- secretion
4- digestion
5- absorption
6- elimination
ingestion
solid and liquid nutrients into oral cavity
motility
- voluntary and involuntary muscular contractions
- mixing and moving materials through the GI tract
secretion
producing and releasing fluid products to aid in digestion
digestion
breakdown of ingested food into smaller structures
2 kinds of digestion
1- mechanical digestion
2- chemical digestion
mechanical digestion
material physically broken down by chewing and mixing
chemical digestion
large complex molecules to smaller molecules - enzymes break chemical bonds
absorption
digested molecules, electrolytes, vitamins, water from GI tract INTO BLOOD AND LYMPH
elimination
expulsion of indigestible components that are not absorbed
enzymes are
catalysts
catalysts are
- proteins that speed up a chemical reaction
- not changed or used up in the reaction
4 layers/tunics of the GI tract
1- mucosa
2- submucosa
3- muscularis
4- serosa
serosa
is the outermost layer of the GI tract; superficial serous membrane
mucosa
the innermost layer; deep mucous membrane
muscularis
consists of smooth muscle
submucosa
consists of blood vessels, lymph, and nerves
functions of the muscularis to mix and propel contents within GI tract
- peristalsis
- mixing
- mass movements
peristalsis
propels ingested materials through tract
mixing
blends ingested materials with secretions
mass movements
forces fecal matter from the transverse colon through the rest of the large intestine
submucosal nerve plexus
innervates smooth muscle and glands
MALT
mucosa-associated lymphatic tissue
Peyer patches
larger aggregates of lymphatic nodules in distal small intestine
muscularis (externa) inner circular layer
smooth muscle; contraction constricts tube lumen
muscularis outer longitudinal layer
contraction shortens tube
muscularis myenteric nerve plexus
between layers, control contractions
sphincter
closes off the lumen, controls movements
propulsion
forward movement down the tract
2 nervous systems that communicate with the digestion system
1- enteric nervous system (ENS)
2- autonomic nervous system (ANS)
enteric nervous system (ENS)
- includes submucosal plexus and myenteric plexus
- innervates smooth muscle and glands of GI tract
- coordinates mixing and propulsion reflexes
autonomic nervous system (ANS)
- parasympathetic innervation promotes GI tract activity
- sympathetic innervation opposes GI tract activity
nerve receptors in the digestive system
- baroreceptors
- chemoreceptors
short reflex
LOCAL reflex only involves ENS; coordinates small segments of the GI tract
long reflex
involves sensory input to CNS and ANS motor output; coordinate GI tract motility, secretions, and accessory digestive organs
hormonal control
three primary hormones in the regulation of digestion:
1- gastrin, from stomach
2- secretin, from SI
3- cholecystokinin (CCK), from SI
upper GI tract organs and accessory structues
- oral cavity and salivary glands
- pharynx
- esophagus
- stomach
- duodenum
oral cavity and salivary glands
- mechanical digestion
- saliva secreted in response to food
- mixed with ingested materials form bolus
saliva enzymes secreted in response to food
- salivary amylase
- lingual lipase
pharynx
bolus moved to the pharynx during swallowing
bolus
a ball of food that you are ready to swallow
esophagus
- bolus transported from pharynx into stomach
- lubricated by mucus secretions
stomach
- bolus mixed with gastric secretions by smooth muscle contractions
- secretions produced by epithelial cells of stomach
- chyme formed from mixing
chyme
the contents in the stomach;
food and stomach secretions
tongue within the oral cavity
on interior surface of cavity
- manipulates and mixes materials during chewing
- important functions in swallowing and speech
2 kinds of salivary glands
- intrinsic
- extrinsic
intrinsic salivary glands
- located within the oral cavity
- unicellular
- continuously release secretions independent of food
extrinsic salivary glands
- located outside the oral cavity
- larger
- stimulated to release by food
3 pairs of salivary glands
1- parotid salivary glands
2- submandibular salivary glands
3- sublingual salivary gland
parotid salivary glands
- largest salivary glands
- 25-30% of saliva
submandibular salivary glands
60-70% of saliva
sublingual salivary gland
3-5% of saliva
saliva
1.0 - 1.5 L secreted daily, most produced during mealtime
functions of saliva
- moistens ingested food to help become bolus
- dissolves chemicals that stimulate taste buds
- cleanses oral cavity
- antibacterial substances inhibit bacterial growth
antibacterial substances that inhibit bacterial growth
- lysozyme
- IgA antibodies
regulation of salivary secretions are regulated by
salivary nuclei within brainstem
another name for swallowing
deglutition
3 phases of swallowing
1- voluntary phase
2- pharyngeal phase
3- esophageal phase
voluntary phase
bolus of food is pushed by tongue against hard palate and then moves toward oropharynx
pharyngeal phase
- soft palate and uvula close off the nasopharynx
- larynx elevates so the epiglottis closes over laryngeal opening
esophageal phase
- bolus passes through esophagus
- propels bolus toward stomach
- esophageal sphincters closed at rest
salivary amylase
enzyme for carbohydrate digestion
mucin
mucus
lysozyme
antibacterial enzyme
gastric glands extend
deep into mucosa from base of each gastric pit
gastric secretions produced by 5 types of secretory cells
1- surface mucous cells
2- mucous neck cells
3- parietal cells
4- chief cells
5- G-cells
parietal cells
produce intrinsic factors and hydrochloric acid
chief cells
- most numerous secretory cells within gastric glands
- secretes pepsinogen and gastric lipase
hydrochloric acid activates
pepsinogen to transform into pepsin
pepsinogen is a
proteolytic enzyme
intrinsic factor
- required for the absorption of vitamin B12 in the ileum
- B12 is necessary for the production of normal erythrocytes
hydrochloric acid functions
- helps break down plant cell walls and animal CT
- denatures proteins, facilitating chemical digestion
- converts inactive enzyme pepsinogen into active pepsin
- kills most microorganisms entering stomach
lipase
cutting fats
G-cell
- enteroendocrine cells that are widely distributed in gastric glands
- secrete gastrin hormone
gastrin
stimulates stomach secretions and motility
stomach
holding bag for partially digested food until the food is moved into the small intestine where digestion is completed
pacemaker cells in stomach
- spontaneously depolarize
- establish a basic rhythm of muscular contraction
- signals spreading through smooth muscle cells in the muscular layer
force of contraction and gastric gland secretion are regulated by what and what are the three phases it’s organized into?
nervous reflexes and hormones
- organized in three phases;
1- cephalic
2- gastric
3- intestinal
vagus nerve=
“rest and digest”; PNS
cephalic phase
- initiated by thought, smell, sight, or taste of food (or even sounds of food preparation)
gastric phase
initiated by presence of food in stomach
intestinal phase
initiated by presence of acidic chyme in duodenum
the small intestine is how long
20 ft
accessory digestive organs
- liver
- gallbladder
- pancreas
the large intestine is how long
5 ft
small intestine
- small bowel, long tube inferior to stomach
- ingested nutrients reside in small intestine at least 12 hours
- absorbs most nutrients and large percentage of water, electrolytes, and vitamins
organic compounds/nutrients
- carbs
- lipids
- proteins
- nucleic acids
carbs break down into
simple sugars
duodenum
receives accessory gland secretions from the liver, gallbladder, and pancreas
intestinal glands
- invaginations of mucosa between intestinal villi
- secrete intestinal juice
SI surface area from largest to smallest
- 20 ft long
- circ. folds
- villi
- microvilli
simple columnar epithelial cells with microvilli in intestinal villi
absorbs nutrients
lacteals
fats (large)
intestinal capillaries
mainly absorb amino acids + carbs
goblet cells
produces mucin
3 secretions made by the intestinal glands
1- enteropeptidase
2- CCK
3- secretin
brush border enzyme
enteropeptidase
brush border
referring to the villi
gastroileal reflex
moves contents from ileum to cecum in response to food arrival in stomach
- ileocecal sphincter and cecum reflexes
liver
accessory digestive organ and the largest internal organ
- production of bile
bile is secreted by
liver
gallbladder _________ and _____________ bile
stores and concentrates
bile contains
- water
- bicarbonate ions
- bile salts and pigments
- cholesterol, lecithin, and mucin
main pancreatic duct carries
pancreatic secretions
bile salts and lecithin help
mechanically digest lipids
RBC recycling of “Heme” turns into
bile
pancreas endocrine function
produces and secretes insulin and glucagon
pancreas exocrine function
produces pancreatic juice to assist with digestive activities
pancreatic juice
formed by acinar cells
- composed of alkaline fluid and digestive enzymes
pancreatic juice contains
- pancreatic amylase
- pancreatic lipase
- inactive proteases
- nucleases
pancreatic amylase
to digest starch (amylose- carbohydrate)
pancreatic lipase
digest triglycerides (lipids)
inactive proteases
digest proteins when activated (ex: trypsinogen- proteins)
nucleases
digestion of nucleic acids
trypsinogen is activated by
enteropeptidase
cholecystokinin (CCK)
hormone released from enteroendocrine cells of SI in response to fatty chyme
secretin
released from SI in response to increased chyme acidity
large intestine functions
- absorbs water, electrolytes and vitamins from remaining digested material
- stores feces until eliminated through defecation
4 big nutrient groups
1- carbs -> sugars and starches
2- lipid -> oils, butter, nuts, dairy, and animal fat
3- proteins -> meat, nuts, veggies, and dairy
4- nucleic acids
normal bacteria flora in large intestine
indigenous microbiota
haustral churning in the colon
mixing; increases churning and moves material to distal haustra
mass movement in the colon
propels the fecal material toward the rectum
peristalsis
weak and sluggish
gastrocolic reflex
- initiated by stomach distension
- causes a mass movement
defecation reflex
- increases parasympathetic output to the sigmoid colon and rectum
- relaxes (involuntary) internal anal sphincter
voluntary defecation
- learned about age 3
- called Valsalva maneuver
- relaxes external (voluntary) anal sphincter
carbohydrates
- monosaccharides
- disaccharides
- polysaccharides
________ and _______________ broken down into individual monosaccharides (glucose)
starch and disaccharides
main digestion sites
oral cavity- salivary amylase and small intestine- pancreatic amylase
monosaccharide ex
glucose and fructose
disaccharide ex
sucrose- table sugar
polysaccharide ex
starch and cellulose- leafy plants
proteins
- polymers composed of amino acid linked by peptide bonds
- broken down by enzymes (pepsinogen, trypsinogen)
pepsinogen is made by the
stomach
trypsinogen is made by the
pancreas
what activates pepsinogen
hydrochloric acid (HCL)
what activates trypsinogen
enteropeptidase
proteins in the body
- albumin
- fibrinogen
- hemoglobin
- immunoglobin
- myoglobin
- collagen fibers
- elastic fibers
- reticular fibers
- myosin
- actin
- troponin
- tropomyosin
- hormones
- enzymes
amino acids are called the monomers of
proteins
saccharides are
carbs
lipids
- not water-soluble, highly variable structures
- triglycerides
- cholesterol
triglycerides
- made of glycerol and three fatty acids
- several enzymes required to break bonds
cholesterol
does not need to be broken down for reabsorption
lipid breakdown in the stomach
these start triglyceride digestion
- lingual lipase
- gastric lipase
- pancreatic lipase
lingual lipase
- component of saliva in the mouth
- activated when reaches the stomach
gastric lipase
produced by chief cells
pancreatic lipase
- requires separation of large lipid droplets into smaller droplets called EMULSIFICATION
- digests triglycerides into monoglycerides and two fatty acids
lipid absorption
lipids transported to the simple columnar epithelial lining by micelles
triglycerides and cholesterols are wrapped with protein to form
chylomicrons
water absorption
- small intestine absorbs almost all ingested water
- large intestine absorbs some
- rest passed in feces
vitamin absorption
- fat-soluble vitamins absorbed in small intestine along with lipids within micelles
- water-soluble vitamins absorbed through diffusion and active transport
fat-soluble vitamins
A, D, E, and K
water-soluble vitamins
B and C
B12 absorption requires
intrinsic factor (formed by parietal cells in stomach)
micelles
tiny, spherical structures formed by bile salts that encapsulate digested fat molecules (like fatty acids and monoglycerides)