Digestive System Flashcards
What makes up the digestive system?
Gastrointestinal tract
Accessory digestive organs
What is the gastrointestinal tract?
continuous tube from mouth to anus
what are the accessory digestive organs?
teeth
tongue
salivary glands
liver
gallbladder
pancreas
how does the digestive system contribute to maintaining homeostasis?
Digestive system breaks down food into forms that can be used by cells
Absorbs water, minerals and vitamins
Eliminates waste from the body
What are the processes of the digestive system?
Ingestion
Secretion
Mixing and propulsion
Digestion
Absorption
Defecation
What is ingestion?
Taking foods and liquids into the mouth
Secretion
release of water acids, buffers and enzymes (7L/day)
Mixing and propulsion
determines the motility of the GI tract
mixing (segmentation) - increase contact of food with digestive chemicals
propulsion (peristalsis) - movement of muscles within the GI tract that facilitates movement of food
When doing xrays of markers through bowels what must you include?
time stamp on the image
what feature of the digestive tract ony has peristalsis?
the esophagus
What part of the digestive system has the most segmentation?
the duodenum (in the small intestine)
digestion
catabolic process
Mechanical
- teeth cut and grind food
- mixing and churning food (segmentation)
Chemical
- breaking down large carbohydrate, lipid, protein and nucleic molecules into smaller molecules
- required for these specific molecules to be absorbed
- vitamins, water, ions and cholesterol can be absorbed without chemical digestion
Absorption
entrance of digested molecules into the blood and lymph
defecation
elimination of wastes, undigested material, bacteria, cells sloughed off from the lining of the GI tract
Layers of the GI tract
- mucosa
- submucosa
- muscularis
- serosa
mucosa
epithelium
- direct contact with contents of the GI tract
- every 5-7 days these are sloughed off and replaced
lamina propria
- contain many blood and lymphatic vessels
- MALT (mucosa-associated lymphatic tissue) protects the body against disease
muscularis mucosae
throws the mucosa of the stomach and small intestine into small folds (increases surface area od allows for expansion)
Submucosa
blood and lymphatic vessels (different from the kind in the mucosa)
submucosal plexus
- extensive network of neurons
Muscularis
Inner layer of smooth muscle orientated in circular fibers
Outer layer of smooth muscle orientated in longitudinal fibers
- involuntary contractions help break down food, mix it and propel it
Skeletal muscle is found in the mouth, pharynx, upper esophagus and external anal sphincter and produces voluntary control for swallowing and defecation
contains myenteric plexus
Serosa
Forms the visceral peritoneum
Esophagus lacks this layer
Peritoneum
largest serous membrane of the body
parietal peritoneum
visceral peritoneum
peritoneal cavity
retroperitoneal cavity
parietal peritoneum
lines the wall of the abdominal cavity
visceral peritoneum
lines SOME of the organs and is their serosa layer
peritoneal cavity
peritoneal fluid
what is the peritoneum?
unlike the pericardium and pleura, the peritoneum contains large folds that wave between the viscera
these folds bind the organs to one another and to the abdominal wall
these folds also contain blood and lymphatic vessels and nerves that supply the organs
what are the peritoneal folds?
- greater omentum
- lesser omentum
- falciform ligament
- mesentery
- mesocolon
Greater Omentum
Largest
hangs from the greater curvature of the stomach
drops anterior to the small intestine
turns back upward and attaches to the transverse colon (double layered)
May contain a considerable amount of adipose tissue
Contains many lymph nodes that help contain and fight infections
Lesser omentum
extends between the inferior edge of the liver of the lesser curvature of the stomach
contains the proper hepatic artery, hepatic portal vein and common bile duct (portal triad)
also contains lymph nodes
falciform ligament
attaches the liver to the anterior abdominal wall and diaphragm
seperates the right lobe of the liver from the left lobe
Liver is the only digestive organ attached to the anterior abdominal wall
liver and stomach moves with the diaphragm
Mesentery
Fan-shaped
binds the jejunum and ileum to the posterior abdominal wall
mesocolon
binds the transverse colon to the posterior abdominal wall
mesentery and mesocolon
together hold the intestines lossely in place
allows movement from muscular contractions…..mixes and propels contents (motility)
peritoneal cavity
space between visceral and parietal peritoneum
contains lubricating serous fluid
ascite is an abnormal accumulation of fluid
- caused by cirrhosis of the liver, cancer, heart and kidney failure
- would have to drain it
Retroperitoneal structures
S - suprarenal (adrenal) gland
A - aorta/IVC
D - Duodenum (2nd and 3rd - descending and horizontal)
P - pancreas (head and body)
U - ureters
C - colon (ascending and descending)
K - kidneys
E - esophagus (once it has passed below diaphragm - inferior portion)
R - rectum
oral cavity
mouth or oral/buccal cavity
oral vestibule - space between the cheeks, lips, gums and teeth
oral cavity proper - everything inside teeth
fauces - between oral cavity and oropharynx
Pharynx
- nasopharynx
- oropharynx
- laryngopharynx
deglutition (swallowing) phases
- voluntary phase
- pharyngeal phase
- esophageal phase
Esophagus
25 cm long
collapsible tube posterior to trachea
starts at junction with laryngopharynx, passes through esophageal hiatus (opening in diaphragm) at T10 and ends at cardiac antrum (meets the stomach)
2 esophageal sphincters
- upper - C6 (cricoid)
- lower - gastroesophageal junction (T11) - meets the stomach
Cardiac sphincter controls the opening into the stomach
no digestive enxymes
stomach
position and size varies from person to person, but generally “J” shaped
mostly left of the MSP
moves with respirations
Stomach made up of 4 parts
Cardia
Fundus
Body
Pyloric part
Cardia
surrounds the opening of the esophagus
Fundus
fundus is more posterior than the pyloric part
most superior portion under the diaphragm
help determine how it was imaged
pyloric part
- pyloric antrum
- pyloric canal
- pylorus
Mechanical digestion of the stomach
mixes saliva, food and gastric juices to form chyme
Propulsion - peristalsis from the body of the stomach to the pylorus
Retropulsion - food particles are initially too large to fit through pylorus, food forced back to the body of the stomach
Process keeps repeating until particles small enough to pass through
Keeps mixing the food with gastric juices (CHYME)
serves as a resevoir (1-1.5L)
Chemical Digestion of the stomach
Secretes gastric juice into the stomach and gastrin into the blood
what is contained in gastric juice?
HCL - kills bacteria and activates pepsinogen (inactive) and pepsin (active)
Pepsin/pepsinogen - begins the digestion of proteins
Intrinsic factor - aids absorption of Vitamin B12
Gastric Lipase - aids in digestion of fats
gastrin going into the blood
stimulates parietal cells to release HCL
stimulates chief cells to release pepsinogen
contracts lower esophageal sphincter
increases motility of stomach
relaxes pyloric sphincter
gastric emptying
passage of chyme through the pyloric sphincter
slow process - about 3 mL of chyme at a time
In Situ (Stomach)
anterior surface
posterolteral surface
posterior
anterior surface of in situ (stomach)
diaphragm, anterior abdominal wall, left and quadrate lobes of the liver
posterolateral surface in situ (stomach)
spleen
posterior in situ (stomach)
left kidney; pancreas
surface mucous cells and mucous neck cells
secrete mucous
- forms protective barrier that prevents digestion of stomach wall
absorption
- small quantity of water, ions, short-chain fatty acids and some drugs enter the blood stream
parietal cells
some intrinsic factor
- needed for absorption of vitamin B12 (used in red blood cell formation and erythropoiesis)
secrete hydrochloric acid
- kills microbes in food; denatures proteins; converts pepsinogen into pepsin
chief cells
secrete pepsinogen
- pepsin (activated form) breaks down proteins into peptides
secrete gastric lipase
- splits triglycerides into fatty acids and monoglycerides
G cells
secrete gastrin
- stimulates parietal cells to secrete HCL and chief cells to secrete pepsinogen. contracts lower esophageal sphincter, increases motility of stomach, and relaxes pyloric sphincter
Muscularis
mixing waves (gentle peristaltic movements)
- churns and physically breaks down food and mixes it with gastric juice forming chyme. Forces chyme through pyloric sphincter.
Pyloric sphincter
opens to permit passage of chyme into duodenum
- regulates passage of chyme from stomach to duodenum; prevents backflow of chyme from duodenum to stomach
what is the hiatus hernia?
when the stomach pushes up though the diaphragm
small intestine function
chyme entering small intestine contains partially digested carbohydrates, proteins and lipids
to complete this process involves a collective effort of pancreatic juices, bile and intestinal juices
structure of small intestine
2.5cm in diameter
most digestion and absorption occurs
disigned accordingly
- 3m in living person
- circular folds (10mm tall) - permanent
- villi (0.5 to 1mm)
- microvilli (1micrometer) - so they form a small “brush border”
Duodenum - 0.25m
Jejunum - 1m
Ileum - 2m
What is the duodenum?
4 parts - L1 to L4
1. Duodenal Bulb (superior)
2. Descending
3. Horizontal
4. Ascending
what do the duodenal or Brunner’s glands of the submucosa secrete?
alkaline mucous
What is the jejunum?
chemical digestion and absorption
- very mobile
What is the ileum?
ileocecal valve
joins the cecum at the medial wall
- very mobile
Histology of the small intestine?
Mucosa - epithelial layer
Absorptive cells
goblet cells
crypts of liberkuhn (intestinal glands)
what are absorptive cells of the small intestine?
contain microvilli (brush border) - absorption
produce brush border enzymes - carbohydrates, protein (enterokinase which activates trypsin) and nucleotides
what are goblet cells?
secrete mucous
What are the crypts of lieberkuhn (intestinal glands)?
secrete intestinal juice
1-2L clear yellow fluid
contains water and mucous and is slightly alkaline (pH 7.6)
What cells are in the crypts of lieberkuhn?
paneth cells - secrete lysozyme - regulate the microbial population
Enteroendocrine cells
- S cells - secretin - stimulates secretion of pancreatic juice and bile by causing liver to increase its output
- CCK cells - Cholecystokinin - acts mostly on gall bladder and stimulates release of pancreatic juices
- K cells - gastric inhibitory peptide - stimulates release of insuin by pancreas and slows gastric emptying
Phases of digestion
- cephalic phase
- gastric phase
- intestinal phase
cephalic phase
purpose - to prepare the mouth and stomach for food we are about to eat
receptors: thought, taste and smell of food
increase saliva, gastric juice and G cells
Gastric phase
begins at the arrival of food
lasts 3-4 hours
stomach stretches and pH increases
stomach release of gastric juices and increases peristalsis
intestinal phase
controls rate of chyme entering small intestine
distension of duodenum
CCK, GIP and secretin
what is the large intestine
large in diameter (6.5cm)
1.5 m long
muscularis - longitudinal muscle forms 3 bands - “taeniae coli” - muscular tone creates “haustra”
cecum, colon, rectum, anal canal
forms an arch around small intestine
screte mucus from goblet cells
no villi
Functions of the large intestine
absorb water
absorb vitamins
formation of feces
elimination of feces
what is the cecum?
large blind pouch
inferior to the level of the ileocecal valve
vermiform appendix - posteromedial
what is the colon?
ascending > hepatic flexure > transverse > splenic > descending > sigmoid colon (“S” shaped)
large intestine placement in body
cecum, transverse colon and proximal part of sigmoid colon are the most anterior
ascending and descending colon are posterior to the transverse colon
rectum and recto-sigmoid colon are most posterior
large intestine ends at?
rectum 6” or 15cm
anal canal
how do you best demonstrate the hepatic flexure?
LPO or RAO
how do you best demonstrate the splenic flexure?
RPO or LAO
Histology of large intestine?
absorptive cells - water absorption (still have microvilli)
goblet cells - mucus
Tongue
skeletal muscle
body - anterior 2/3 in the oral cavity
root - posterior 1/3 in the oropharynx
lingual frenulum - limits posterior movement
attaches inferiorly to the hyoid, mandible and styloid process of the temporal bone
extrinsic muscles - move tongue side to side, in and out, form bolus and force food back for swallowing
intrinsic muscles - change shape of tongue for speech and swallowing
papillae - taste buds, increase friction to make it easier to form bolus
lingual glands - secrete mucus and lipase (fats - triglycerides to simpler fatty acids)
Teeth
occlusion and mastication (first step in mechanical digestion)
Salivary glands
saliva 1-1.5L a day
typically once enough saliva produced to keep mouth moist and to cleanse the mouth and teeth
salivation increases with food (taste, smell and thought - cephalic)
saliva - 99.5% water and 0.5% solutes
pH is slightly acidic (6.35 - 6.85)
What are the solutes of the salivary gland?
electrolytes - sodium, potassium, chloride, phosphate and bicarbonate
mucus - lubricates food mass
lysozyme - kills bacteria
immunoglobulin A (IgA) - inhibits bacteria growth
Salivary Amylase - starts the breakdown of starch into simpler sugars
Parotid or Stensen’s salivary duct
enters into oral vestibule opposite second upper molar
Submandibular gland - Wharton’s duct
submandibular duct is medial and inferior to angle of the mandible
emptied through whartons duct to lingual frenulum in oral cavity proper
60-70% of all saliva
sublingual - rivinus ducts
under tongue
pancreas anatomy
head and body (retroperitneal) the tail (introperitneal)
99% exocrine (secretes through a duct) and 1% endocrine
Head L2-L3 - sits adjacent to the descending duodenum
Body and Tail are posterior to the stomach
exocrine function of the pancreas
secrete pancreatic juice into the pancreatic duct
acinar cells
- secrete oancreatic juice (1.2 to 1.5L/day)
- alkaline pH (7.1 - 8.2); buffers acidic chyme, stops the action of pepsin and creates the proper pH for the digestive enzymes
pancreatic juice makeup
water
pancreatic amylase - starch
proteolytic enzymes - proteins
pancreatic lipase - fats
nucleases
exocrine function of the pancreas
pancreatic duct - joins with the common bile duct to form the hepatopancreatic duct
endocrine function of pancreas
islets of Langerhans or pancreatic islets
- secrete hormones directly into blood; glucagon, insulin and somatostatin
gall bladder pain exhibits as
upper right quadrant pain
what is in the pancreatic duct?
pancreatic amylase, pancreatic lipase and inactive protein digestive enzymes (trypsinogen)
trypsinogen activated by enterokinase when entering duodenum turning it into trypsin
trypsin activates the other inactive protein-digesting enzymes
liver
right hypochondriac and epigastric region
right lobe - larger
left lobe - smaller
lobes separated by the falciform ligament
caudate lobe - IVC is lateral to the caudate lobe
Quadrate lobe - gallbladder is latera to quadratic lobe
functions of the liver
produce bile - emulsify fats
detoxify - waste or drugs
make plasma proteins
metabolism: store glycogen and convert to glucose
lipid and protein metabolism
vitamin and mineral storage
phagocytosis of old red and white blood cells and some bacteria
Histology of the liver
hepatocyte
bile canaliculi
hepatic sinusoids
hepatocyte
major functional cells
bile canaliculi
small ducts between hepatocytes collect bile
hepatic sinusoids
highly permeable capillaries between rows of hepatocytes
receive oxygenated blood from branches of the hepatic artery proper
receive nutrient-rich, de-oxygenated blood from branches of the hepatic portal vein
portal triad
branch of hepatic artery proper
branch of hepatic portal vein
bile duct
blood supply to liver
hepatic artery proper 30%
hepatic portal vein 70%
- central vein
- hepatic vein
- inferior vena cava
bile
right hepatic duct + left hepatic duct = common hepatic duct
common hepatic duct + cystic duct = common bile duct
gall bladder
pear shaped sac
depression on posterior, inferior surface of liver
stores and concentrates bile
chemical digestion of the mouth
lingual lipase
salivary amylase
chemical digestion of the stomach
gastric lipase (chief cells)
pepsin (pepsinogen from cheif cells converted to pepsin by HCL secreted from parietal cells)
Gastrin (hormone) promotes release of more HCL and pepsinogen and increases gastric motility
chemical digestion of the small bowel
presence of acidic chyme and stretching of duodenum causes secretion of:
- CCK (cholecystokinin) - stimulates pancreas to secrete enzymes and stimulates gallbladder to contract and sphincter of ODdi to relax
- Secretin - stimulates pancreas to secrete enzymes
- GIP (gastric inhibitory peptide) - reduces gastric motility
All 3 hormones reduce gastric motility and emptying
chemical digestion of the pancreas
pancreatic amylase
pancreatic lipase
proteolytic enzymes
- trypsinogen (inactive so it does not digest pancreas) - enterokinase (brush border enzyme) activates trypsinogen to trypsin
- trypsin activates all other protein-digesting enzymes
