Digestive System Flashcards
lots of pictures
look at notes to practice with pictures
functions
ingestion
mechanical processing
digestion
secretion
absorption
excretion
gastrointestinal tract
oral cavity (teeth + tongue) > pharynx > oesophagus > stomach > small intestine > large intestine
accessory organs of digestive system - salivary glands, liver, gallbladder + pancreas
peritoneum + mesenteries
peritoneum:
serous membrane- visceral layer covers organs, parietal layer lines cavities
peritoneal fluid- 7l/ day, provides lubrication to allow sliding
mesenteries suspend portions of digestive tract
allow passage of blood vessels, nerves and lymphatic vessels
digestive tract
protects against:
digestive acids and enzymes
mechanical stresses
bacteria
histological organisation - four major layers
1. mucosa
2. submucosa
3. muscularis externa
4. serosa
digestive tract mucosa
superficial layer of digestive tract
mucosal epithelium has stratified squamous epithelium (oral cavity, pharynx, oesophagus) and simple columnar with mucous cells elsewhere
has lamina propia underneath with areolar tissue with blood and lymphatic vessels + nerve endings
underneath- muscularis muscosae- smooth muscle- inner circular layer, outer longitudinal layer
surface covered in villi + also folds, which increases SA
digestive tract submucosa
tougher, dense irregular connective tissue
allows passage of blood and lymphatic vessels
may contain exocrine glands- secretion of buffers + enzymes
submucosal plexus- neural network that innervates the mucosa and submucosa
digestive tract muscularis externa
smooth muscle cells- inner circular layer + outer longitudinal layer propel contents through digestive tract
movements coordinated by enteric nervous system- sensory neurons, interneurons, and motor neurones- innervated by para NS
digestive tract serosa
seroas membrance covering muscularis externa is most of digestive tract
replaced by adventitia (dense sheath of collagen fibers to attach adjacent structures) in oral cavity, pharynx, oesophagus + rectum
movement of digestive materials
rhythmic cycles of smooth muscle activity controlled by pacesetter cells (in muscularis mucis + muscularis externa)
cells undergo spontaneous depol - waves of contraction through entire muscular sheet
peristalisis- waves of muscular contraction
segmentation- cycles of contraction, does not follow a set pattern
- contraction of circular muscles behind bolus
- contrctio of longitudinal muscles ahead of bolus
- contraction in circular muscle layer forces bolus forward
oral cavity
functions- sensory analysis, mechanical processing, lubrication, limited digestion (carbs + lipids), passageway for liquids, food and air - opens to oropharynx
salivary glands
saliva- 1-1.5L a day produced
contains water (99%), electorlytes, buffers, mucins + antibodies
functions- lubricating mouth + contents, dissolving chemicals, initiating digestion of complex carbs by salivary amylase
salivary glands- parotid, sublingual and submandibular
produce saliva controlled by parasymp and symp stimulation
swallowing
- buccal phase
- pharyngeal phase
- oesophogal phase
- bosul enters stomach
oesophagus
conveys solid food and liquids to the stomach
resting muscle tone (contracting when not swallowing) in the superior 3cm of prevents air from from entering
adventitia anchors to surrounding structures
has stratified squamous epithelium, lamina propria and muscularis mucosae
stomach
major functions:
storage of ingested food, mechanical + chemical breakdown
chemical by enzymes- pepsin starts protein breakdown, continued activity of salivary amylase and lingual lipase , by acid (HCl) reduces pH to 2, helps to digest food and destroy pathogens
production of intrinsic factor- needed for b12 absorption
stomach lining
simple columnar epithelium- lines stomach and produces mucus
gastric pits connect gastric glands in mucosa onto gastric surface- cells at base divide, replacing superficial cells
smooth muscle (muscularis mucosa and muscularis externa)- oblique layer in additioon to circular and longitudinal layers
stomach glands
gastric glands- in fundus and body of stomach
parietal cells- secrete intrinsic factor and HCl
chief cells- secrete pepsinogen (precursoR) convterted to pepsin by HCl
G cells- secrete gastrin which helps to increase activity in stomach
plyoric glands- in plyorus, produce mucous
G cells secrete gastrin + D cells release somatostatin (inhibits gastrin release)
HCl secretion
by parietal cells
blood will be alkaline after eating due to large number of bicarbonate ions
1. carbonic anhydrase converts co2 and h2o to carbonic acid which dissociates to form H+ ions
2. contertransport mechanism ejects the bicarbonate ions and import chloride ions
3. chloride ions diffuse across the cell and exit through open chloride channels into the lumen of the gastric gland
4. hydrogen ions are actively transported into the lumen of the gastric gland
stomach protection
mechanisms helping to protect the stomach from acid/ protease:
mucous lining, rapid cell division, seperate secretion of H+ and Cl- in parietal cells, secretion of inactive precursor eg pepsinogen, stimulation of secretion only when needed (sympathetic stimulation, local reflexes, gastrin) , inhibition of secretion - CCk, GIP, secretin
regions of the small intestine
narrower than large intestine but very long
duodenum- 25cm long, netralises chyme, receives secretions from pancreas and liver, few plica circulares, small villi
receives secretions from stomach
jejunum- 2.5m long, location of most chemical digestion and nutrient absorption, prominent plica circulares and villi
ileum- 3.5m long, lymphoid nodules (peyers patches)
intestinal wall
mucosa, muscularis mucosae, submucosa, muscularis externa, serosa
large villi, openings called intestinal crypts, lacteal
functions in small inestine
intestinal glands- epithelial cells divide at base + are displaced towards tips of villi then disintegrate adding enzymes to lumen
brush border enzymes- integral membrane proteins on intestinal microvilli, break down materials in contact with brush border, enteropeptidase - activates pancreatic proenzyme trypsinogen
enteroendocrine cells- produce hormones in response to pH change/ nutrients, CCK and secretin (increase enzyme/ bile secretion), gastric inhibitory peptide- inhibits gastrin activity
duodenal glands- produces mucus + raises pH
intestinal juice- moistens chyme and keeps intestinal contents in solution + buffers acids
pancreas
has ducts leading to small intestine
secretes pancreatic juice- contains pancreatic enzymes including pancreatic alpha amylase, pancreatic lipase, nucleases, proteases + peptidases (secreted as inactive proenzymes, activated after reaching small intestine)
liver
located under diaphragm
2 veins- heaptic and vena cava
2/3 blood from hepatic portal vein- originates from oesophagus, stomach, small intestine, much of large intestine
1/3 blood from hepatic artery proper
