m9 + 10 lecture - digestive system Flashcards
what are the accessory organs of the digestive system?
- tongue
- salivary glands
- pancreas
- liver
- gall bladder
what are the functions are the alimentary tract?
- digest food
- absorb nutrients
- metabolism
- digest fat (gall bladder)
what is the pathway of stimulatory nervous control?
1) parasympathetic system (main controller)
2) vagus nerve plexus
3) enteric nervous plexus
4) esophagus
5) anus
what are the parts of the enteric nervous plexus?
- primarily reflexes
- contains multiple ganglion
1) submucosal plexus
- regulates all gland secretions
2) myenteric plexus
- controls all movements of the tract
what are the events occurring in stimulation?
1) these occur in the brain - sight, sound, smell and hunger thoughts
2) take place to stim. hypothalamus/prefrontal cortex - after food is in the tract, chemical and mechanical receptors in the walls of the organs will augment the process
3) control of digestive activity is accomplished by reflexes that stim. motility, secretions and hormones
what is the pathway of inhibitory nervous control?
1) sympathetic system
2) splanchnic nervous system - inhibits GI activity and releases somatostatin to shut off the secretions and motility of the GI tract
what is digestion?
- can be mechanical or chemical digestion
what is mechanical digestion?
- physically breaking food into smaller pieces —> helps to increase surface area and allow enzymes to work
examples: mastication, churning, segmentation
what is chemical digestion?
- further breakdown of nutrients to chemical compounds
- by water, acid, enzymes (hydrolysis - makes into tiny chemical compounds)
- starts in the mouth by saliva
what are the parts of the oral cavity?
- saliva
- tongue
- teeth
what does saliva do?
- softens food and compacts it into a bolus
- digests starch and carbs w/ amylase
- digests fats w/ lipase
- helps w/ taste
- cleanses the palate
- prod. 1.5L/day –> containing IgA and lysozyme to slow bacterial growth
what does the tongue do?
- is a muscle that helps you swallow, chew (CN 7 + 9) and mix food w/ saliva
- taste is accomplished by taste buds —> circumvallate papillae and fungiform papillae
what do the teeth do?
- units used for mastication
- 20 deciduous that become 32 adult teeth
- protected by enamel and gingiva (the gums)
what is swallowing?
- movement of food into the stomach
- CN 9, 10, 12
- two portions: voluntary (buccal phase) and involuntary (pharyngeal-esophageal phase)
what happens during the voluntary portion of swallowing (buccal phase)?
- upper oropharynx is made from skeletal muscle
—> needs tongue to push the food into the pharynx
what happens during the involuntary portion of swallowing (pharyngeal-esophageal phase)?
- lower laryngopharynx is where smooth muscle begins
—> smooth muscle of the esophagus receives the bolus and peristaltic waves carry it into the stomach
what happens in the esophagus?
a muscular tube about 25cm
- two layers of smooth muscle –> makes contractions called peristalsis
- carries bolus to the stomach
- connects to the stomach by the cardio-esophageal sphincter (aka gastro-esophageal sphincter)
conditions: hiatal hernia, acid reflux –> GERD –> Barret’s or cancer
what happens in the stomach?
- contains 3 layers of smooth muscle to churn food
—> churning helps with mechanical digestion
—> avg. size .5 gal - chemical digestion occurs with HCL and pepsin (breaks down proteins - starts at stomach)
- mucus is alkaline to protect stomach from damage (otherwise leads to ulcerations - stomach starts digesting itself)
—> other causes of ulcerations: H. Pylori, stress, alcohol
what is the structure of the stomach lining?
called gastric pits - contain glandular cells (acini)
1) mucus neck cells
2) parietal cells
3) chief cells
4) enteroendocrine cells
what do mucus neck cells do?
- secrete bicarbonate rich mucus to protect the stomach lining
what do parietal cells do?
- secrete HCL and intrinsic factor (for B12 absorption - hemoglobin prod.)
what do chief cells do?
- secrete pepsinogen (zymogen)
—> is activated by HCL to become pepsin (used in protein breakdown) - rennin in infants
—> to breakdown milk proteins (< 1yr.)
what do enteroendocrine cells do?
- secrete gastrin
—> stimulate churning/secretions
what are the three digestive phases?
1) cephalic phase
2) gastric phase
3) intestinal phase
what occurs during the cephalic digestive phase?
in stomach
- prepares us for digestion in the stomach
—> external stimuli which cause the activation of hunger activity - sight, smell, thought, taste
- receptive relaxation (reflex process)
—> as stomach fills, it stretches due to the food and fluids entering - this will inhibit the smooth muscle from contracting while chewing and swallowing
what is the gastric phase?
(30-45 min)
gastrin
- is stimulated by proteins and distention
- stimulates the secretion of gastric juices and churning
- up to 2 liters of juices
- the stomach is mainly responsible for the breakdown of proteins and mixing food w/HCL
—> turns the bolus into a liquid paste called chyme
—> some absorption of water and alcohol
what occurs in the intestinal phase?
triggered by chyme entering the duodenum
- excites the small intestine
as chyme enter the duodenum, the stretch and chemical receptors will be stimulated by the changes
- inhibits the stomach
enterogastric reflex
- duodenum will then release hormones to inhibit the stomach from secreting and prolong digestion
–> initiates the gastrocolic reflex - mass movement
what is the duodenum called?
“gut brain”
- releases chemicals and hormones, regulates stomach actions
what happens during gastric mobility?
when the stomach is filled or when you stop swallowing the stomach begins to churn
- top to bottom
- as stomach churns, the chyme is pushed down towards the pylorus and the pyloric sphincter
- greatly affected by contents and by hormones (gastrin)
- eventually emptying into the SI
what is emptying (into SI)?
when food is pressed against the pylorus from contractions of the muscle, around 3mL of chyme is secreted at a time into the duodenum
- if high fat content in chyme, it will slow the contractions and emptying of the stomach
normally the stomach will empty in 2-3 hours
- high fat = 6hrs
- high carbs = shortened time
what is the duodenum (the gut brain)?
first 10 inches of small intestine
- monitors and receives contents of the chyme
- releases hormones to stimulate chemical digestion and prolong digestion in the stomach
hepatopancreatic ampulla
—> the connection of the common bile duct and the pancreatic duct
- sphincter of oddi
—> releases bile and pancreatic juices
what hormones does the duodenum release?
releases hormones to regulate digestion
1) secretin - neutralizes stomach acid
secretion: acid + undigested food in chyme
action: stim. pancreas to release bicarbonate rich juice and inhibits the stomach’s motility
2) CCK - cholecystokinin
secretion: fat + protein in chyme
action: stim. pancreas to release enzymes and gall bladder to release bile
3) GIP - gastric inhibitory polypeptide + gastrin
secretion: fat + glucose in chyme
action: stim. pancreas to secrete insulin and inhibit the stomach’s motility
what do the villi and microvilli in the jejunum and ileum do?
area is characterized by dense microvilli
- villi and microvilli help to increase surface area for nutrient absorption
what characterizes the jejunum and ileum?
area has:
- has intestinal crypts
- has brunner’s glands
- villi and dense microvilli
what do the intestinal crypts do?
provide cell replacements
what do the brunner’s glands do?
produce intestinal juices
- 2 liters/day
- helps to maintain mobility of the chyme
- prevent sedimentation
what are peyer’s patches?
lymph nodes in the SI
what is a lacteal?
-lymphatic capillary
- fat is absorbed here - fat-soluble vit. A, D, E, + K
what is the large intestine (colon)?
connects to the ileum by the ileocecal valve
- chyme enters the large intestine (most of this will be excreted in the feces)
—> the colon is responsible for compacting the feces by absorbing water and vit. B12 + K thru veggies and fruits
—> to get vitamins B12 + K, bacteria in the colon help to break down any fiber in the diet (E-coli – normal flora)
- as these break down fiber, K and B vitamins are produced and absorbed —> by-product of this is gas (flatulence)
what is the gastrocolic reflex?
triggers mass movements
- movement through the colon is prod. by contractions (peristalsis) of the tenaie coli
- triggered by food entering the duodenum
- happens 3-4 times/day
what is the defecation reflex?
- happens when feces are forced into the rectum
- even after absorption, fecal matter is still 60% water
what does the liver do in the digestive system?
- accessory organ, which produces bile
- receives blood from the hepatic portal vein —> carries the blood from the intestines to the liver for processing
- packages and metabolizes all incoming nutrients for the body
what is the liver responsible for?
- fat metabolism
- cholesterol transport
- bile production
- detoxification
- storage of iron + B12, vit. D
- plasma proteins
what does bile do?
bile salts
- emulsifier (breaks down fat)
- made from cholesterol
bilirubin
- waste (turns feces brown)
- black (bleed) , pale (liver Dz, blocked duct)
possible pathologies of the liver and gall bladder?
1) cirrhosis
2) hepatitis
3) gallstones
what is cirrhosis?
- hardening of the liver
- caused by chronic inflammation of the liver
causes: alcoholism, hepatitis
what is hepatitis?
- type A is transmitted from feces - m/c at daycares and restaurants
- type B and C are transmitted through blood, or sexual contact - m/c in heroin users
—> type B is dangerous - causes recurrent infections (vaccine available)
what are gallstones?
- hardened deposits of bile that form in the gallbladder – biliary calculi
what is the pancreas responsible for?
digestive enzyme and hormone production
what types of enzymes are produced by the pancreas?
- amylase –> starch
- lipase –> fat
- nucleases –> DNA, RNA
- trypsin/chymotrypsin –> protein
what hormones are produced by the pancreas?
to regulate blood sugar
- insulin –> lowers
- glucagon –> raises
normal level: 70-110 mg/dL
what do the epithelial cells in the ducts of the pancreas secrete?
bicarbonate (alkaline) –> neutralizes stomach acid in the duodenum
- about 1,500 mL secreted into the duodenum per day
what is metabolism?
- the sum of all chemical reactions in the body
- requires major and minor nutrients to perform all the chemical reactions
- measured by taking the BMR (basal metabolic rate) –> generates heat as by-product
- two types of chemical reactions: anabolic + catabolic reactions
what is a anabolic reaction?
- building up large molecules from small ones
what is a catabolic reaction?
- breaking down large molecules into small ones
what is basal metabolic rate (BMR)?
- measured through heat loss –> most occurs by radiation through our heads
- heat is generated by movement of the skeletal muscle
what is body temperature regulated by?
- the hypothalamus and the thyroid gland
what are the minimum daily dietary requirements?
carbs 270 - 290 g
proteins 80 - 100 g
fats 50 - 65 g
- sat fat 10 - 17 g
not meeting these = results in malnutrition
what disorders can be caused by deficiencies in nutrients/vitamins?
- anemia –> iron, B12
- bleeding disorders –> vit. K
- brain disorders –> vit. D, essential fatty acids (EFAs) - omega-3
- night blindness –> vit. A
- osteoporosis –> Ca++
- osteomalicia –> vit. D
- scurvy –> vit. C
