The Intestines Flashcards
the small intestine is
2 to 3 meters in length, averages 2.5 centimeters in diameter, and extends from the pyloric sphincter to the large intestine
duodenum is
the shortest segment
jejunum is
middle segment
ileum is
longest segment, joins large intestine at ileocecal sphincter
circular folds are
ridges in intestinal mucosa from the duodenum to the ileum
circular folds purpose
increase surface area of small intestine and cause chyme to move in a spiral path along small intestine to enhance absorption of nutrients
the intestinal mucosa also forms
a series of finger like projections called villi
villi are covered with
mucus-secreting goblet cells and columnar absorptive cells ; increase surface area for digestion and absorption of nutrients
each villus has
a core of lamina propria that contains an arteriole, a capillary network, a venule, and a lymphatic lacteal that absorbs fat
each absorptive cell is covered with
microvilli to form a brush border near the lumen of small intestine
one of the enzymes released by the brush border
activates pancreatic enzymes
other enzymes released by the brush border are involved in
contact digestion which requires thorough mixing of chyme
the intestinal mucosa also contains deep crevices lined with
grandular epithelium
intestinal crypts (of Lieberkuhn)
similar to gastric glands
secrete intestinal juice
watery mixutre containing lots of mucous
paneth cells
secrete bactercital enzyme lysozyme
enterendocrine cells
secrete hormones secretin and cholecystokinan
lamina propria contains
lymphatic Peyer’s patches which are abundant in the ileum because they prevent bacteria from entering the blood along with absorbed nutrients
the submucosa of the duodenum contains
duodenal (Brunners) glands which secrete alkaline mucus to neutralize stomach acid in the chyme
contractions mix
chyme, bile and juice
contractions churn chyme to
facilitate contact digestion
contractions move intestinal residue
towards large intestine
segmentations are
localized contractions that mix chyme with digestive secretions in order to enhance contact digestive and nutrient absorption
the migrating motor complex
a type of perstalsis that begins in the duodenum in order to push chyme forward through small intestine
where does the most absorption occur
small intestine
digestion of 200 to 600 of carbs daily begins
in mouth and completed in small intestine
salivary amylase gets
denatured by acidity of gastric juices so any starch not digested gets broken down by pancreatic amylase
contact digestion finishes digestion of
starch
maltase
a brush border enzyme that splits maltose into glucose
sucrase
a brush border enzyme that splits sucrose into glucose and fructose
lactase
a brush border enzyme that splits lactose into glucose and galactose
carbohydrates are absorbed as
monosaccharides
glucose and galactose are
actively transported into intestinal epithelium by a sodium glucose transport protein
fructose is absorbed into
intestinal epithelium by facilitated diffusion and gets converted into glucose
monosacchardies enter into the blood capillaries of a villus by
faciliated diffusion
trypsin and chymotyrpsin
breaks proteins into smaller peptides
carboxypeptidase, aminopeptidase, and dipeptidase
take small peptides apart one amino acid at a time
amino acid absorption
absorped by sodium dependent active transport molecules and transported to liver by hepatic portal system
pancreatic lipase
works on fat globules that have been emulcified by bile salts and splits triglycerides into fatty acids and monoglycerides
fatty acids and monoglycerides are coated with
bile acids to form micelles which then release these components so they can diffuse into absorptive cells
absorptive cells
resynthesize triglycerides and combine them with cholesterol and protein to form chylomicrons which enter lacteal and get transported to blood by lymphatic system
Dna and rna split into
deoxynucleotides and ribonucleotides which are then broken down and transported across intestinal epithelium by carrier proteins to enter blood
vitamins are absorbed
without change
fat soluble vitamins
are absorbed along with other lipids using micelles
vitamin supplements containing D E K A must
be ingested with food containing fat
water soluble vitamins are absorbed by
simple diffusion
vitamin b12 must combine with
intrinsic factor to be absorbed
electrolytes are absorbed
along the entire length of small intestine
sodium ions
actively transported with monsaccharides and amino acids
chloride ions
exchange for bicarbonate ions and actively transported in ileum
potassium ions
absorbed by simple diffusion
iron ions and calcium ions
absorbed in accordance with bodys needs
large intestine is
1.5 meters in length. 6.5 cm in diameter and extends from ileum to anus
ileocecal sphincter allows
materials to pass from ileum into large intestine
cecum
a blind pouch that hangs below the ileocecal sphincter
appendix
twisted and coiled appendix attached to cecum filled with lymphocytes
colon
divided into ascending, transverse, descending and sigmoid regions
rectum
a vertical extension of sigmoid colon and it contains three rectal valves that allow a person to pass gas without releasing feces
terminal end of the rectum
is the anal canal which lies in the periotneum completely outside of the abdominopelvic cavity
mucous membrane of the anal canal
arranged in longitudinal folds called anal columns that contain arteries and veins
fecal matter
travels through the anal canal causes extra mucus to be released to lubricate anal canal
anus
controlled by internal anal sphincter (smooth involuntary muscle) and external anal sphincter (skeletal voluntary muscle)
the intestinal mucosa consists of
simple columnar epithelium without villi or circular folds
absorptive cells
absorb water and goblet cells secrete mucus to lubricate colon
chyme passage
chyme is passed from the ileum thru the ileocecal sphincter into the cecum by the gastroileal reflex which is triggered by the presence of food in the stomach
the gastroileal reflex enhances
segmentation movements in ilium and reflexes ileocecal sphincter
chemical digestion occurs mainly thru
bacterial action not enzyme action
bacteria ferment
any remaining carbs and produce flatus
flatus
mostly swallowed air but also contains other gases which are nitrogen and co2 hydrogen methane hydrgen sulfide unpleasant odor
bacteria cleave
any remaining proteins into amino acids and break them down
bacteria decompose
bilirubin into pigments that give feces color
bacteria aid
in extracting some b vitamins and vitamins k which is needed for synthesizing some clotting factors
the large intestine absorbs
water, minerals, vitamins, and leaves behind solid or semi solid mass of feces
feces consists of
75 water, 25% solid matter of which one third is bacteria, one third is undigested fiber, and one third is inorganic salts and dead cells
distension of the rectum
initiates a defecation reflex to empty rectum
stretch receptors in wall of rectum
send signals to sacral spinal cord
motor signals travel
along parasympathetic fibers to descending colon, sigmoid colon, rectum, anus to increase peristalsis and relax internal anal sphincter
voluntary relaxation of the external anal sphincter
is coupled with voluntary contractions of diaphragm and abdominal muscles allows feces to be expelled from body
diarrhea
frequent defecation of mostly liquid feces because chyme thru small intestine too quickly for sufficient absorption of water to occur
chronic diarrhea
can be caused by stress or microbial irritation of gi mucosa and it can produce dehydration and or electrolyte imbalances
constipation
infrequent or difficult defecation because feces remain in the colon for too long and too much water gets absorbed
causes of constipation
improper bowel habits, insufficient bulk in ones diet, lack of exercise and stress
