Digestive System Flashcards
4 factors that regulate digestive function
Autonomous smooth muscle function, Intrinsic nerve plexuses, Extrinsic nerves, GI hormones
What are the four basic processes performed by the digestive system?
Motility, Secretion, Digestion, Absorption
What are the two types of motility movements? Which type of muscle produces them?
Mixing movements - aid digestion of food
Propulsive movements - push contents forward
~ Accomplished by smooth muscle lining digestive tract
What is the difference between exocrine and endocrine secretions?
Exocrine - secretions into the digestive tract (mix of H2O, electrolytes, enzymes)
Endocrine - secretions of GI hormones & peptides that enter blood
Where does absorption mostly occur?
small intestine
What are the three main categories of energy-rich food components?
carbohydrates, proteins, fats
What is hydrolysis?
how digestion is accomplished; adding H2O to bond site to break bond
What are the absorbable units of carbohydrates? …proteins? …fats?
Carbohydrates (monosaccharides), protein (amino acids/small polypeptides), fats (triglycerides)
What do starch and glycogen consist of? What are soluble and insoluble fibers?
Glycogen: storage form of glucose in muscle
Starch: mixture of amylose (unbranched) and amylopectin (branched)
soluble/insoluble fibers: dietary polysaccharides that cannot be digested
Accessory digestive organs
salivary glands, pancreas, liver, gallbladder
What are the four layers of the digestive tract?
Mucosa, Submucosa, Muscularis, Serosa
In what layer(s) are cells that secrete found? Which layer mainly contains smooth muscle?
(Mucosa) Mucous membrane - exocrine gland cells, endocrine gland cells; contains smooth muscle
(Serosa) secretes serous fluid
Where are the two plexuses?
(Submucosa) contains submucosal plexus - nerve network
Myenteric plexus - nerve network between layers of muscularis externa
What is function of serous fluid?
prevents friction between digestive organs and surrounding viscera
What are the four means by which digestive activity can be regulated?
1 - Autonomous smooth muscle function
2 - Intrinsic nerve plexuses
3 - Extrinsic nerves
4 - Gastrointestinal (GI) hormones
What do interstitial cells of Cajal do? (Autonomous smooth muscle function)
pacemaker calls throughout muscularis externa
generate spontaneous, rhythmic, slow-wave membrane potentials
How does electrical activity pass between smooth muscle cells in the digestive tract?
Slow wave potentials propagate to adjacent smooth muscle cells via Gap Junctions (depolarization spreads down tract)
Does the slow-wave potential always lead to contraction?
If depolarization peak crosses threshold, multiple action potentials fire –> contraction of smooth muscle
Enteric nervous system (Intrinsic nerve plexuses) comprised of?
submucosal plexus and myenteric plexus together
How does sympathetic activity change digestive processes?
inhibits digestive motility and secretion
How does parasympathetic activity change digestive processes?
promotes digestive motility and secretion
Where are GI hormones secreted? What do they act on?
Secreted from endocrine cells in digestive tract —> act on smooth muscle and exocrine cells
What are the functions of mastication (chewing)?
break food up smaller pieces, mix with saliva, expose food to taste buds
What are the functions of saliva?
- begins digestion of dietary starch (salivary amylase enzyme)
- facilitates swallowing by lubricating with mucus
- inhibits bacteria
- solvent for tastants
- aids speech (allows tongue, lips, cheeks to glide)
- neutralizes acids in food/bacteria (bicarbonate buffer)
What secretes saliva? (3 glands)
3 glands: Parotid, Submandibular, Sublingual glands
What brain structure controls swallowing?
Medulla (swallowing center)
What receptors sense pressure form food entering mouth?
Pharyngeal mechanoreceptors
What are the three functional sections of the stomach?
fundus, body, antrum
Main functions of the stomach
1) Stores food until it can be emptied into the small intestine at a rate appropriate for digestion and absorption
2) Secretes HCl and enzymes that begin protein digestion
3) Pulverizes ingested food and mixes with gastric secretions to produce thick liquid called chyme
What is receptive relaxation of the stomach?
relaxation of smooth muscle due to the vagus nerve –> allows stomach to unfold, volume expands
Which area of the stomach has thicker smooth muscle? What function does it provide?
antrum – thickest smooth muscle = greater force for propulsion and mixing (retropulsion)
Does chyme simply dump straight into the duodenum from the stomach?
Elongated gland consisting of exocrine tissue
Pancreas
secretes exocrine pancreatic enzymes that break down carbohydrates, proteins, fats..
First digested in…
Carbo - saliva
Protein - stomach (pepsin)
GI hormones enterogastrones secreted
Secretin and CCK
Liver
role in digesting fats
Liver anatomy: Lobules
functional unit; veins and arteries branched/organized here
Sphrincter of Oddi relaxes..
gallbladder contracts — squeezes bile into small intestine (duodenum)
Bile constantly produced— bile ducts — can’t go into small intestine — goes into gallbladder
gallbladder filled with bile in-between meals — when stomach fills with fats — gallbladder contracts
Bile
contains bile salts; derived from cholesterol; lecithin, bilirubin (waste product from RBC breakdown)
How do the products of fat digestion (monoglycerides and free fatty acids) reach the luminal membrane for absorption?
- Lecithin and bile salts aggregate to form tiny micelles
Bilirubin
waste product in the breakdown of heme from hemoglobin in worn-out red blood cells; produced by Kupffer cells (macrophages)
Jaundice
Small intestine - Motions?
alternating ring-like contractions (Segmentation)
Segmentation
1- mixes chyme together
2- expose chyme to absorptive surfaced of intestinal lining
__________ prevent small intestine from being contaminated by bacteria in large intestine
ileocecal valve & sphincter
Small intestine large surface area for absorption..how?
large scale circular folds, villi (lined with epithelial cells), microvilli (extends from top of one epithelial cell)
epithelial cells linked by ____
tight junctions
Where are Crypts of Lieberkühn? What is it?
between villi; contain stem cells that produce new epithelial cells
where do the old epithelial cells go?
sloughed off at the top (digested), old ones move up replacing it
Final stage of digestion of carbohydrates & proteins
Brush border
All products of carb, protein and fat digestion, most h2O, electrolytes and vitamins, are absorbed in small intestine without regulation
if you eat, it is incorporated into body — isnt regulated like the kidneys
Carbohydrate absorption
absorbable until (monosaccharides)
Proteins become digested
ingested proteins, digestive enzymes, proteins within epithelial cells sloughed off, small amounts of plasma proteins leaked into digestive tract lumen
Fat absorption
1- dietary fats (triglycerides) liver secretes Bile salts — breaks up fat
2- pancreatic lipase; micelles; passive diffusion into epithelial cell
3- triglycerides coated with lipoprotein (water soluble) –> chylomicrons (large)
4- Chylo exit thru exocytosis (enter into lymphatic system; too big to enter capillary pores)
Large intestine
drying and storage organ
- additional water absorbed in large intestine (9 out of 9.5 L by small intestine)
- 4 lbs of bacteria in colon
What do bacteria do?
- digest cellulose into fatty acids (lipid soluble can diffuse thru wall into bloodstream; small amount)
- Reabsorbs NaCl and H2O
Feces contains
mostly water, undigested cellulose, bilirubin (color), bacteria, small amount of salt
Tania coli
smooth muscle lining colon
layers gathered into pouches (haustra)
Gastrocolic reflex
stomach releases gastrin –> massive contraction of colon, drive colon contents forward quickly
Defecation reflex
feces distend rectum, activate stretch receptors
- like bladder, relax internal/anal sphincter and contract of rectum
