CASE 9 Flashcards
peritoneum
- most extensive membrane
- visceral peritoneum -> covers external surfaces of most digestive organs and is continuous with parietal peritoneum –> lines the body wall
- peritoneal cavity –> between 2 peritoneums, contains serous fluid that lubricate the mobile digestive organs
- mesentery –> double layer of peritoneum, extends to digestive organs from body wall, provides routes for blood vessels, lymphatics and nerves to reach the digestive viscera, holds organs in place and store fat
- there are dorsal and ventral mesenteries
retroperitoneal organs
- pancreas, duodenum and parts of large intestine have no mesentery.
intra peritoneal/ peritoneal organs
- stomach, keep mesentery and remain in the peritoneal cavity
digestive system begins with oral cavity (mouth and pharynx)
- three pairs of salivary glands:
1. sublingual glands
2. submandibular glands
3. parotid glands - swallow
- epiglottis
- pharynx
- larynx
- esophagus
- stomach
epiglottis
prevents food from going to the trachea
esophagus
travels through the thorax to the abdomen
- wall is skeletal muscle initially
- but smooth muscle 2/3 length
- ends in stomach
stomach
3 sections
- upper fundus
- central body
- lower antrum -> facilitates the emptying of the contents into the small intestine
cardia
point where the esophagus connects to stomach
chyme
stomach continuous digestion that started in the mouth by adding acid and enzymes to food creating chyme
pylorus
opening between stomach and small intestine is guarded by pyloric valve –> thickened band of smooth muscle relaxed to allow only small amounts of chyme into the small intestine
small intestine
divided into three sections
- duodenum
- jejunum
- ileum
- more digestion takes place here, nearly all digested nutrients and secreted fluids are absorbed there
accessory glandular organs
- pancreas
- liver
- exocrine secretions secrete intestinal enzymes which carry out digestion
- secretions enter the initial section of duodenum through ducts.
- sphincter of Oddi keeps pancreatic fluid and bile from entering the small intestine
large intestine
five main regions
- ileocecal valve
- cecum
- colon
- rectum
- anal canal
ileocecal valve
- located between ileum and cecum
- controls flow of chyme from small intestine to large intestine
cecum
- absorption of water and salts
- appendix is tube that attaches to the cecum
colon
consists of
- ascending colon
- right colic flexure
- transverse colon
- left colic flexure
- descending colon
- sigmoid colon
- watery chyme is converted into semisolid feces, as water and electrolytes are absorbed out of the chyme into the ECF
rectum
- rectal valves: three lateral bends that create a trio of internal transverse folds –> help separate the feces from gas to prevent simultaneous passage of feces and gas
anal canal
- has two sphincters:
internal and external anal sphincter
internal : smooth muscles
external : skeletal muscle
gut
portion of GI tract from stomach to anus
The basic structures of the gastrointestinal wall is similar in the stomach and intestines. Layers
- an inner mucosa facing the lumen
- submucosa
- layers of smooth muscle known collectively as muscularis mucosae, thin layer of smooth muscle
Mucosa
- inner lining of GI-tract. Created from:
1. single layer of epithelial cells
2. lamina propria
3. muscularis mucosae
increase amount of mucosal surface area to enhance absorption
- rugae in stomach, folds
- plicae, folds in small intesine
- villi, small fingerlike extensions project into the lumen
- gastric glands: tubular invaginations of surface that extend down into supporting connective tissue in stomach
- crypts: tubular invaginations of surface that extend down into supporting connective tissue in intestine.
transporting epithelial cells, enterocytes
- endocrine, secrete in blood
- exocrine, secrete on to an epithelium
- secrete ions and water into lumen and absorb ions, water and nutrients into the ECF
- mucosal surface (apical), secretory cells release enzymes, mucus and paracrine molecules into lumen
- serosal surface (basolateral), secretory cells secrete hormones into blood or paracrine messengers into the interstitial fluid
paracellular pathway
- because intestinal epithelium is leaky, water and solutes can be absorbed between cells instead of through them
Submocosa
- has larger blood and lymph vessels
- contains submucosal plexus, one of two major nerve networks of the enteric nervous system (helps coordinate digestive function)
muscularis externa and serosa
- consists of two layers of smooth muscle, inner circular layer and outer longitudinal layer
myenteric plexus
- second nerve network of enteric nervous system
- lies between longitudinal and circular muscle layers
- controls and coordinates the motor activity of muscularis externa
serosa
- outer covering the entire digestive tract
- connective tissue membrane that is a continuation of peritoneal membrane (peritoneum) lining the abdominal cavity
- the peritoneum also forms sheets of mesentery that hold the intestines in place so that they do not become tangled as they move
motility
two purposes
- moving food from the mouth to anus
- mechanically mixing food to break it into uniformly small particles
- determined by properties of tract’s smooth muscle
- modified by chemical input from nerves, hormones and paracrine signals
migrating motor complex
- sweeps food remnants and bacteria out of the upper GI-tract and into the large intestine
peristalsis
- progressive waves of contraction that move from one section of the GI to the next.
- circular muscles contract just behing the bolus –> pushes bolus forward into receiving segment, circular muscles relax
segmental contractions
- short segments of intestine alternately contract and relax
- circular muscles contract while longitudinal muscles relax
tonic contractions
sustained for minutes or hours and occur in some smooth muscle sphincters and in the anterior portion of the stomach
phasis contractions
contractions-relaxation cycles lasting only a few seconds, occur in posterior region of stomach and small intestine
large intestines have less segmental contraction
haustral contraction
- presense of food residues in the colon
- primarily in the transverse and descending colon
mass movement
- starts mid transverse colon, forces contents towards the rectum
- occurs while you eat or immediately after
Acid secretion
parietal cells in gastric glands secrete hydrochloric acid into the lumen of stomach.
- bicarbonate made from CO2 and the OH- from water is absorbed into the blood.
other stomach cells
- chief cells: produce pepsinogen
- G-cells (goblet cells): produce mucous
- ECL-cells: produce histamine
Bicarbonate secretion
- neutralizes acid entering from the stomach
- comes from pancreas
pancreatic cells produce
- trypsin
- deoxyribonuclease
- ribonuclease
- bicarbonate
crypt cells
- secrete isotonic NaCl solution that misces with mucus secreted by goblet cells to help lubricate the contents of the gut
digestive enzymes
- secreted by either exocrine glands or epithelial cells in mucosa of stomach and small intestine
- some enzymes are secreted in an inactive proenzyme form –> they must be activated in the GI lumen before they can carry out digestion
salivary glands
- produce alfa-amylase which breaks down glycogen and starch into dextrin and maltose
stomach glands
- secrete pepsin which breaks down proteins into polypeptides
liver
- produced bile, stored in gallbladder, emulsifies lipids
pancreas
- secretes trypsin and chymotrypsin. break down proteins in the small intestine. - break amino acids down to polypeptides –> pancreas secretes peptidase breaks proteins down into amino acids.
- secretes lipase –> breaks down emulsified fats into monoglycerides and fatty acids
- secreted alfa-amylase, breaks down starch and glycogen
- all enzymes from pancreas work in the small intestine and enter via the duodenum
enzyme producing cells in intestine
- produce peptidase –> breaks down proteins into amino acid
- produce isomaltase –> breaks down dextrin into glucose and maltase into maltose into glucose
- produce sacharase, breaks down lactose into glucose and galactose
- enzymes nuclease, nucleotidase and nucleosidase break down DNA and RNA
mucus produced in exocrine cells
- mucous cells in stomach
- serous cells in salivary glands
- goblet cells in intestines
Bile
- non enzymatic solution secreted from hepatocytes (liver cells)
1. bile salts, facilitate enzymatic fat digestion
2. bile pigments: bilirubin, waste products of hemoglobin degradation
3. cholesterol, excreted in feces - secreted into hepatic ducts that lead to the gallbladder
- during meal, contraction of gallbladder sends bile into the duodenum through the common bile duct
crypt cells in large intestine
secrete NaCl
absorption saccharides
- amylase breakd long glucose polymers into smaller glucose chains and into the disaccharide maltose
- maltose enzo are broken down by intestinal brush-border enzymes known as disaccharides
absorption proteins
two types of enzymes for digestion
- endopeptidase: attack peptide bonds in the inferior of the amino acid chain and breaks a peptide into smaller fragments. Secreted as inactive cells in stomach, intestine and pancreas, pepsin, trypsin and chymotrypsin
- exopeptidase: release single amino acids from peptides by chopping them of at the end
absorption fats
- liver secretes bile salts into small intestine to increase surface available for enzymatic fat digestion
- carried out by lipases, enzymes that remove two fatty acids from each triglyceride and form two free fatty acids and one monoglyceride.
- co-lipase, protein cofactor secreted by pancreas because lipase is unable to penetrate bile salts
absorption nucleic acids
- digested by pancreatic and intestinal enzymes
absorption vitamins and minerals
- fat soluble vitamins are absorbed in small intestine along with fats
absorption water
- most water is absorbed in small intestine, and 0,5 L a day in colon.
- water follows an osmotic gradient
