The Digestive System Flashcards
Structures of the GI tract
- Teeth, tongue, oral cavity
- Pharynx
- Esophagus
- Stomach
- Small Intestine
- Large Intestine
- Anus
Basic function of each structure in GI tract
- Oral: mechanical processing, secretion
- propulsion
- transport
- mechanical processing, chemical breakdown
- enzyme breakdown, digestion and absorption
- enzyme digestion and absorption
- excretion
Accessory organs
Gallbladder, liver, pancreas, salivary glands
Functions within GI/digestive tract
ingestion, mech processing, absorption, secretion, digestion, excretion
Peritoneum of the abdo-pelvic cavity structure
visceral serous membrane covering surface of organs and parietal layers of cavity.
Layer of mesothelium supported by thin CT layer
How much peritoneal fluid produced per day
around 7 litres
function of peritoneum
lubrication to allow sliding of organs
Peritoneal mesenteries function
suspend digestive tract and provide pathway for bv, nerves and lymphatics
Falsiform mesentary
ligament attaching liver to superior peritoneal cavity
Lesser Omentum mesentary
attaches liver to stomach
Mesentary Proper
suspends SI
Greater Omentum/ Transverse Mesocolon
suspends LI
Structure of digestive tract
- Mucosa
- Submucosa
- Muscularis Externa
Mucosa of DT
- stratified squamous epithelium in oral cavity, simple columnar epithelium elsewhere.
- Lamina Propria cont areolar tissue, lymphatics, bv and nerves
- Muscularis mucosa inner circular smooth muscle, outer longitudinal muscle
- mucosal epithelium cont villi and plica circulares
plica circulares
large folds of epithelium increasing surface area
submucosa of DT
dense irregular CT, large bv and lymph vessels
Exocrine glands secreting buffers and enzymes
submucosa plexus- neural network
Muscularis Externa of DT
smooth muscle cells
movement coordinated by enteric NS
Innervated by Psymp
contains sensory, motor and interneurons
movement of materials in DT
smooth muscle contraction of muscularis externa and muscularis mucosa.
rhythmic cycles of contraction controlled by pacesetter cells in mucosa
peristalsis
non rhythmic, random waves of muscular contraction to push food from esophagus into stomach and churn food in stomach
- Oral Cavity functions
pathway for food, air and liquids chewing/ mech processing ingestion of food sensory analysis secretion and lubrication limited digestion swallowing
Components of OC
teeth- chewing and mechanical processing
tongue- smash food, sensory tastebuds, lingual lipases
glands
Salivary glands
lubrication, dissolve chemicals- taste/breakdown, initiate digestion of complex carbs- salivary amylase
other glands of OC
parotid, sublingual, submandibular.
controlled by parasymp/ symp stimulation
- Esophagus function
transport food to stomach
structure of esophagus
thick muscular wall, sphincter at inferior end, thick epithelial lining, adventitia anchors esophagus to adjacent structures
esophagus muscular wall
resting muscle tone in superior 3cm, always slight contraction to prevent food coming back up/ air getting in
esophagus thick epithelial lining
protects against sharp food and bacteria
3 phases of swallowing
- Buccal
- Pharyngeal
- Esophageal
Buccal phase
tongue lifts to push food to back of mouth
Pharyngeal Phase
food down pharynx, pushes down epiglottal cartilage to close off airways
Esophageal phase
food transported to stomach
- Stomach function
store food, mechanical breakdown, chemical breakdown via enzymes or acid, produce intrinsic factor
stomach pH
2
function of intrinsic factor
required for B12 absorption
enzymes in stomach
pepsin/ amylase
acid in stomach
HCI
HCI secreted by
parietal cells
Process of HCi secretion
- carbonic anhydrase converts CO2 and H2o into carbonic acid
dissociates into H ions and bicarb ions - bicarb ions exchanged for chloride ions via countertransport mech
- chloride ions diffuse across cell into lumen of gastric gland
Where is HCI mainly formed and how does this protect functional cells?
chloride ions diffuse across lumen into gland so formed in gland lumen not in the cells.
protects functional cells against low pH
what happens in the blood after a big meal?
bicarb ions exchanged into bloodstream to produce HCI. after big meal more bicarb into bstream so more alkaline blood.
structural landmarks of stomach
- fundus
- corpus
- plyorus
- plyoric sphincter
- lesser curvature (medial)
- greater curvature (lateral)
- Rugae
- longitudinal, circular, oblique muscle layers
Fundus
Top portion of stomach
Corpus
Body of stomach
Plyorus
Lower portion of stomach
Greater Curvature
lateral side of stomach. Greater Omentum att
Lesser Curvature
medial side of stomach
plyoric sphincter
inferior end of stomach, allows food into SI
Rugae
ridged lining inside stomach
Lining of stomach
mucosa- gastric pits connected to gastric glands
smooth muscle- oblique layers
simple columnar epithelium producing mucus
Glands of stomach
located in fundus and corpus
includes- Parietal cells, G cells, Plyoric glands, Chief cells, D cells
Parietal Cells
secrete intrinsic factor and HCI
G Cells
secrete Gastrin hormone which increases stomach activity (muscular contraction and glandular secretion)
Chief Cells
secrete pepsinogen (inactive pepsin) converted to pepsin by HCI prevents breakdown of body proteins
Plyoric Glands
produce mucus in plyorus, G cells and D cells
D Cells
secrete somatostatin which inhibits gastrin release => slows down stomach activity
- Small intestine regions
- Duodenum
- Ileum
- Jejunum
Ileum
3.5m long
contains lymphoid nodules and has immune functions
continues breakdown
Duodenum
25cm long
receives digestive enzyme secretions from liver and pancreas
starts breakdown
neutralises chyme
contains plica circulares and small villi
Jejunum
2.5m long
location of most chemical digestion and nutrient absorption
prominent plica circulares and villi
Intestinal Wall contains
large villi, lacteals, intestinal crypts
mucosa, submuc, muscularis externa, serosa
Lacteals structure and function
Lymphatic vessel to transport fats. contains capillary network in villi. Usually milky white
Process of lacteal fat absorption
fats absorbed through wall into lacteal, transported through IVC
Intestinal crypt function
rapid stem cell division at base of epithelium to replace lining and secretions of enzymes into lumen
contain intestinal glands
Brush border enzymes
Intestinal glands function
contained within crypts
produce mucus to increase pH
produce intestinal juice
ex. duodenal glands
Intestinal juice function
moisten chyme, keeps contents in solution, buffers acids
Brush Border enzymes function
integral membrane proteins on intestinal microvilli. Breakdown materials in contact with brush border
Proteins on brush border
enteropeptidase and enteroendocrine cells
Enteropeptidase function
activates pancreatic proenzyme trypsinogen into trypsin in duodenum
Enteroendocrine cells function
produce hormones in response to changes in pH/ nutrients
Cholecystokinin and secretin
Gastric Inhibitory Peptide
Cholecystokinin and Secretin
increase enzyme/ bile secretion
Gastric Inhibitory Peptide
inhibits gastrin activity
Gallbladder function
bile storage and concentration
Liver- avg L of bile per day
around 1L
How is bile transported
via bile ducts
