GIT tract 1 Flashcards
GI tract includes
mouth oesophagus stomach intestines anus
structural organisisation throughout GI tracts
mucosa
submucosa
sub plexus
connective tissue
purpose of the accessory organs and name them
- organs which contribute to the breakdown of food
- control secretions for breakdown of food
- liver, pancreas, gull bladder, and parotid, salivary glands
function of GI tract
Breaks down ingested food into small molecules which can be taken into body tissue
how does the GI tract perform its fuction
digestion
- chemical and mechanica
Absorption (movement across gut mucosa into circulation)
food and water once ingestied
Food and water forms a bolus
- broken down into stomach,
- smaller particles broken down further via enzymes in small intestine
- then absorbed
- smaller particles put together to then be excreted from the body
swallowing
process in which food passes from mouth to stomach
phases of swallowing
oral phase
pharyngeal phase
oesophageal phase
oral phase
- voluntary phase
- tongue compresses bolus by moving upwards against hard palate
- respiration inhibited
- retraction of tongue forces bolus into pharynx
pharyngeal phase
- involuntary
- pushes bolus from pharynx into oesophagus
- soft palate reflected backward closing nasal pharynx
- epiglottis closes to stop food going into respiratory system
oesophageal phase
- upper oesophageal sphincter relaxes an bolus moves into oesophagus
- start primary peristaltic wave (vagal nerve)
- secondary peristaltic wave (enteric, intrinsic nerve wave)
- lower oesophageal sphincter relaxes
oesophagus
muscular tube
2cm diabeter
from pharynx to stomcah
contract/relax moves stomach down
lower oesophageal spincter
prevents reflux of material back into oesphagus
acts as barrier from stomach
regions of the stomach
1) fundus
2) cardia
3) body
4) pylorus
openings of the stomach
oesphagus
duodenum
roles of stomach
motility
digestion
protection
absroption
motility of stomach
- Gastric accommodation (temporary storage reservoir)
- trituration (dissolve, mix and grind food particles)
- gastric emptying (control delivery to small intestine)
digestion of stomach
- initiate digestive process (proteins) via gastric juice
protection of stomach
- foreign invasion (Acid/proteases)
- mechanical abrasion (mucus)
- prevents autodigestion (mucus)
what does the stoomahc have
rugae
gastric pits
HCL in stomach purpose
- provides low pH
- prevents bacterial growth
- catalyses cleavage of pepsinogens to pepsin
pepsinogens
- proenzyme of pepsin
- pepsin breaks down proteins into peptides
glycoproteins purpose in stomach
- binds to vitamin B12, allowing digestion in the ilium
what does mucus do
protects gastric mucorsa
gastrin
from G cells
regulated acids secretion
gastric glands and secretions
Cardiac glands - mucus - HCl Oxyntic glands (acid secreting) - mucous - HCl - pepsinogen - intrinsic factor Pyloric glands - mucous - pepsinogen
gastric secretly response to a meal
1) Cephalic phase
- site
- smell
- thoughts of food triggers gastric secretion
- instigated by vagal fibres (central NS)
- i.e. prepares the stomach for food
2) Gastric phase
- food entering stomach stretching it
- triggers secretion via long (vagal) and short (myenteric) reflexes
3) Intestinal phase
- intestinal gastrin release in response to distension of duodenum and/or products of protein digestion
regions of small intestine
duodenum
jejunum
ilium
what are the 3 orders of folding creating the area for absorption
1) plicae
- naked eye
2) villi
- light microscope
3) microvilli
- Electron microscope
function of large intestine
remove water
salt
sugar
vitamins
regions of large intestine
1) cecum
2) acending colon
3) transverse colon
4) decending colon
5) sigmoid colon
what is found in the intestine
Tightly packed mucosa - goblet cells for mucosa secretion - help with movement of reforming material through intestine Areas of lymphoid tissue - Peyers patches for local immune protection Lots of bacteria - for fermentation of fibre - helps us make short chain fatty acids
control mechanisms and what do they regulate
Control mechaisms
1) Autonomic NS
2) enteric NS
- local NS
3) gut peptides
- paracrine
- endocrine
Regulate:
- Reflexes - long and short
- peristalsis and motility
- secretion and absorption
autonomic nervous system
extrinsic nerves i.e. outside the gut
speed up or slow down the sysem
enteric NS
guts own NS 2 nerve plexi in the gut wall - sense luminal contents controls muscles and glamds can respond to signals from central NS
what does the ENS contain
ENS contains all elements of an independent nervous system - sensory - motor - interneuron - muscle - glands Complex system of motility and secretion controlled by reflexes - autonomic reflexes
ENS vs CNS reflexes
Long reflexes
- external stimuli i.e. sight and smell of food
- involves CNS
- alters activity of ENS
- causes changes in motility and secretion
Short reflexes
- internal stimuli i.e. when molecules in lumen
- ENS
- local neural circuits
- causes changes in motility and secretion
Hirschprungs disease
Innervation of large intensive either non existent or reduced
- surgical removal of the colon
- congenital disorder
- all or part of colon has no innervation
what are the hormones secrete by
enteroendocrine cells in mucosa
hormonal control
stimulis chemcial osmotic and pH
- negative feedback mechanisms to bring back luminal contacts back to normal
enteroendocrine cells and fucntion
present throughout gut between epithelial cells
single cells throughout GI tracts
- link between luminal contents and capillaries
- intestinal ‘ taste cells’
- densely packed with vesicles
- sense luminal contents and respond via release of hormones
