digestive system Flashcards
Oral cavity: teeth, tongue palate
tongue- intrinsic and extrinsic muscles in the tongue - allowing so much movement
frenulum=under tongue
palate- seperates oral cavity and nasal cavities
transverse mucosal ridges - for swallowing
hard and soft plate
salivary glands
salivary gland - 3 major pairs (secretion on demand)
parotid: serous(runny watery secretion) - very long duct, serous secretion enters mouth by 2nd upper molar
submandibular: seromucous secretion (watery/thick)-long thinduct
sublingual: mucous secretion(thick)-lots of short ducts under neath tongue
also have hundreds of salivary glands-secreting continuously to keep mouth moist
Pharynx
channels food down into oesophagus- area covers back of mouth down to bottom of pharynx
made of superior/middle/inferior constrictor muscles
larynx - seperates what u swallow from breathing
Oesophagus
muscular tube connecting pharynx to stomach, passes through the diaphragm.
no part in digestion
passes food on as quick as possible
Stomach: structure & functions
parts of stomach:
cardiac and pyloric sphincter- control entry/exit of the stomach
fundus-small top bit-air swallowed goes here
body-middle
pylorus-bottom connecting to duodenum
lesser and greater curvature
rugae: folds in the stomach- allows for expansion and contraction of the stomach
(folds dissapear as stomach gets full-reappear when stomach empties)
Functions:
* Some protein digestion(pepsin)
* Reduction of solid food to
loose, semisolid chyme
* Delivery of chyme to duodenum
Acts as a hopper
*Receives materials irregularly,
stores and delivers them regularly
to duodenum until empty
Makes Intrinsic Factor
*needed for absorption of vitamin
B12 in intestine
Small intestine – regions: duodenum, jejenum, ileum
DUODENUM
DUODENUM(25cm)-C-shaped, bent around head of pancreas, on back wall of abdomen
*Receives acid material from stomach; protected by mucus glands
*Receives products of pancreas and bile from liver - common duct
Digestive secretion to duodenum: Bile from liver + pancreatic juice from pancrease with digestive enzymes
JEJUNUM(1m)+ILEUM(2m)
*Tightly folded within abdomen
*Completes digestion, absorbs its products into blood and lymph streams
*All have similar structure, some subtle differences
(liver & pancreas)
peritoneum & mesenteries
Visceral peritoneum
Parietal peritoneum
Folds of peritoneum = mesentaries
Hold gut in position
Contain many big blood vessels
small intestine movements
Peristaltic movements propel food along
Intermittent churning movements for mixing: segmentation
Movements controlled by myenteric plexus of nerves within muscle layers of gut wall
bile + secretion of bile
Continuous secretion of bile,
intermittent secretion from pancreas
- both to common duct, sphincter to duodenum
- bile stored in gall bladder until
pancreatic secretions released
Both secretions released when chyme enters duodenum; sphincter relaxes, gall bladder contracts, bile and pancreatic juice mixes with chyme.
Bile: allows mixing of pancreatic
enzymes and fatty food material: lowers surface tension and emulsifies fat
Large intestine – ileo-caecal junction and parts of large intestine
ileo caecal junction- end of small intestine, guarded by ileo caecal valve
food arrives 3-4hrs after swallowing
((appendix-nearby, variable in
position and length (2-20 cm)
Blind ending tube
Prone to abscess formation))
caecum-first part
colon – ascending, transverse, descending, sigmoid(AKA pelvic colon)
- ascending and descending colon have no mesentaries-attached to rear abdominal wall
rectum - Rectum is normally empty: distension of its walls triggers
defecation:
Contraction of colon, relaxation of involuntary
sphincter. Voluntary sphincter gives conscious control
anal canal
(microscopic)
Oral cavity/mucosal lining:
*Masticatory mucosa
*Ordinary lining mucosa
*Specialised mucosa, tongue
Tongue and lingual papillae: taste buds
filiform, fungiform and circumvallate
masticatory mucosa:
Gingiva & hard palate-Stratified squamous keratinised epithelium
Firmly anchored to underlying bone by collagen fibres in submucosa
ordinary lining mucosa:
Anywhere other than top surface of tongue, gingiva & hard palate - Inside of lips, Underside of tongue, Soft palate, Gums away from gingiva
Stratified, squamous, non-keratinised epithelium
Lots of minor salivary glands in submucosa
common plan of hollow tube parts of gut:
Mucosa, submucosa, muscularis externa, adventitia
Layers:
1. Mucosa - the lining,
This has 3 layers: epithelium, lamina propria (connective tissue layer), and the muscularis mucosae (thin layer of muscle)
- Submucosa - connective tissue outside mucosa, contains many blood vessels, lymphatics TF gives position for things to get in/out
- Muscularis mucosa- muscle layer, 2 layers-most of gut it is smooth muscles, inner most layer runs circularly, outer most runs longitudinally
==>Contracting circular layer-makes gut narrow
Contract longitudinal- scrunches gut up
THESE MUSCLES Drive peristaltic movements in hollow tube parts of gut - adventitia
nerves networks/plexus:
Muscle layers act semi independently from nervous system - (interic nervous system) in walls of gut.
Muscularis mucosae(in mucosae layer) has network of nerves sitting on outside-controls contraction of cells in that muscle layer. =meissners plexus
Muscularis externa- similar network sitting between inner + outer layer = auerbachs plexus
Oesophagus: epithelium and muscle; folds
lining is: stratified squamous non-keratinised epithelium
(Because there is no absorption in oesophagus - just transporting into stomach)
mucus secreting glands - At top-lubricates what’s swallowed
At bottom-protects wall from stomach acids that may get to the oesophagus
muscle type in muscularis externa: voluntary skeletal at top, smooth at bottom and mixed in middle
Reason: swallowing is voluntary - then automatic systems take over to digest
Stomach: epithelial lining, gastric glands and muscle layers
epithelial: simple columnar(all mucous sells)
–> with gastric pits followed by gastric glands
surface mucous cells - keeps acid away from cells(protective mechanism)
gastric glands- makes hydrochloric acid + pepsinogen
2 types of cells:
parietal cells(oxyntic)-makes HCl
chief cells(zymogen)-makes pepsin
Small intestine;
plicae circulares, villi and microvilli; epithelium
crypts of leiberkuhn
Plicae circulares-submucosal layer(just folds in the duodenum wall) - this is to increase SA for the villi
Villi - mucosal layer (increases SA for microvilli)
Microvilli - Apical plasma membrane layer (form brush border) (most microscopic)
crypts of leiberkuhn (between villi)
Epithelium on villus: can only be simple epithelium to allow absorption-although very hostile environment TF cells only live a few days - cells must be continually replaced(by cells deep in the crypts)
Large intestine: epithelium, goblet cells, deep crypts, muscle
Purpose of lg. intestine: Prepare materials you can’t digest for expulsions
TF compress down/concentrating by removing water/ions/solutes(no villi)
Krypton of lieberkuhm - to produce replacement cells- ALSO produce goblet cells(mucous secreting glands)
muscle:
Longitudinal muscle layer - 3 ribbons of muscle(called taeniae coli)
Eg. Ascending colon, transverse colon, descending colon
* contraction causes bulge = haustrae
Anal canal – epithelium, sphincters
muscle sphincters:
smooth muscle- relaxes when rectum needs to empty
skeltal muscle on outside-voluntary control when ready to empty
simple columnar epithelium->SSNK epithelium
regulation of gastric secretion and motility - phases
Regulated by combination of nervous and hormonal factors
3 phases of secretion:
*cephalic
*gastric
*intestinal
gastric phase
control of HCl secreting parietal cells
–Neural negative feedback
*stretch receptors and chemoreceptors routed via the submucosal plexus - peristalsis stimulated
–Hormonal negative feedback mechanisms → emptying
*distension, partly digested proteins, caffeine, stimulate the G (enteroendocrine) cells
*gastrin secretion is:
–inhibited at pH < 2
–stimulated when pH rises
*gastrin is transported in the blood to the gastric glands
–stimulates gastric secretions
–contraction of lower esophageal (cardiac) sphincter
–. motility
–relaxes pyloric sphincter
*stimulation by three signal chemicals
–gastrin
–acetylcholine
–histamine
All three needed for strong H+ secretion
cephalic phase
-Cause
-sensations & thoughts
-Effect
-Cerebral cortex hypothalamus
-Parasympathetic - vagus (x cranial nerve)
intestinal phase
Excitatory
*stretch receptors respond
*chemoreceptors detect fatty acids, & glucose in the chyme in the duodenum
*enteroendocrine cells in the stomach release gastrin
*increases gastric peristalsis and gastric emptying
Inhibitory
*Enterogastric reflex
*Enterogastrone secretion
enteroendocrine cells in the small intestine release:
»Cholecystokinin (CCK)
»Gastric inhibitory peptide (GIP)
»Secretin
–they inhibit gastric secretion
pancreas
- Parasympathetic impulses along vagus (X) nerves
- Stimulates secretion of pancreatic enzymes
- Acidic chyme containing partially digested fats (fatty acids) and proteins (amino acids) in the small intestine
- CCK and secretin are secreted from small intestine travel through blood to stimulate pancreas
- Stimulates secretion of pancreatic juice rich in bicarbonate ions
- Stimulates secretion of pancreatic juice rich in digestive enzymes
liver
- Parasympathetic impulses along vagus (X) nerves stimulate bile production by liver
- Fatty acids and amino acids in chyme entering the duodenum stimulate secretion of cholecystokinin (CCK) into blood.
Acidic chyme entering duodenum stimulates secretion of secretin into blood. - CCK causes contraction of gallbladder
- Secretin enhances flow of bile rich in HCO^- 3, from liver
hormones gastrin and CCK feedbacks/routes
each step causes/promotes next step -however 2 inhibitors of previous steps
1.Food in stomach
=>2. Release of gastrin from stomach mucosal cells
=>3. Gastrin circulates in blood and returns to stomach
=>4. Gastrin stimulates secretion of HCI and pepsin, and increases motility of stomach
=>lowers pH inhibiting 2. + => 5. Increases delivery of acid chyme to small intestine
(acid in chyme)
=>6i. Release of secretin by intestinal mucosa
Release of bile from gallbladder.
(Undigested fats and + proteins in chyme)
=>6ii. Release of cholecystokinin by intestinal mucosa
6ii. causes 3 different things:
->slows movement of stomach TF inhibiting 2.
=>7. release of bile from gallbladder. Bile salts emulsify fats
=>8. Release of digestive enzymes from pancreas
6i. => 9. Release of bicarbonate solution from pancreas neutralizes acid
7., 8. and 9. => Digestion of food
