Gastrointestinal tract Flashcards
What organs are involved in the gastrointestinal tract?
- mouth
- oesophagus
- stomach
- small intestine
- large intestine
What is the GI tract?
a tube, differentiated along its length for sequential processing of food
What anchors the suspended intestines within the abdominal cavity?
mesenteries (membranes)
What are immunologic omentum?
immunological organ that is a source if inflammatory cells & stem cells that play a role in the control of infection through wound-healing & regeneration
What separates the different hollow organs?
sphincters & secretory accessory glands/organs
What are sphincters?
muscular rings - control the progression of the food from 1 section to the next. They also prevent the backflow of material from one section to the previous one.
What is the function of GI tract?
- motility propels ingested food
- secretions from associated glands
- digestion/hydrolysis into absorbable molecules
- absorption into the bloodstream of nutrients, electrolytes, water
What are the 2 layers of the GI tract?
- mucosal layer
- submucosal layer
What is in the mucosal layer?
in touch with contents of the lumen - contains epithelial cells.
- either absorbable or secretory cells
- lamina propria (connective tissues with blood & lymph vessels)
- thin muscularis mucosae
What is in the submucosal layer?
connective tissue (collagen, elastin), glands larger blood vessels (that transport molecules, as well as removing & metabolites
What shape are the 2 smooth muscle layers (enteric neurones between)?
circular + longitudinal
What is serosa?
squamous epithelia
What is the function of the mouth?
- mechanical disruption of food
- (mastication) aims to increase the surface area to attack by enzymes & chemicals later in the GI tract.
- also lubricate the food with the secretions of these 3 glands.
What can be found in the multi-parted exocrine glands?
ligual lipase + amylase initiates lipid + starch
What are the 3 sections of the salivary glands?
- parotid gland
- submandibular gland
- sublingual gland
What are the roles of saliva?
- lubricate food (bolus)
- antimicrobial - resists bacterial infection
- buffering - neutralises acid
- dissolves food - detection by taste buds
What controls the level of mastication & swallowing?
the brainstem (CNS) will control the level of mastication & swallowing
What receptors relay sensory information to the CNS?
mechanoreceptors (found in mouth & teeth) & chemoreceptors relay sensory information to brainstem
How do later parts of the GI tract prepare for the arrival of food?
they start to secrete, in preparation for the arrival of the bolus
What does stimulation of the central nervous system enable?
enables later sections of the GI tract to get ready for the arrival of food?
What does swallowing do?
move the bolus into the oesophagus
What is the oesophagus lined with?
lumen lined with stratified squamous epithelia
What is the benefit of having stratified squamous epithelia on the lumen of the oesophagus?
loose cells at the surface allow cells to be lost without causing damage to the underlying tissue, as they are in contact with the bolus
How does the swallowing reflex work?
- closes upper oesophageal sphincter.
- initiates primary peristaltic wave, coordinates sequential contractions
- continued distension (food in the oesophagus) initiates secondary peristaltic wave (by ENS - enteric nervous system - the nervous system within the GI tract)
What initiates the second peristaltic wave?
continued distension - food in the oesophagus - with activates the ENS (enteric nervous system)
What is the ENS (enteric nervous system)?
nervous system within the GI tract
What does the vasovagal reflex control?
lower oesophageal sphincter (LOS) tone
How does the PNS (parasympathetic nervous system) vagus nerve control the LOS (lower oesophageal sphincter) opening?
by releasing VIP neurotransmitter
What is the autonomic nervous system made up of?
- sympathetic nervous system
- parasympathetic nervous system
- enteric nervous system