Session 1 Flashcards
Describe the broad functions of the mouth, oesophagus and stomach
Mouth
◦ Physical breakdown of food
◦ Initial digestive enzymes released
◦ Infection control (Los of bacteria in mouth so saliva prevents infection)
Oesophagus
◦ Rapid transport of bolus to stomach through thorax (reduces infection)
◦ Upper Oesophageal Sphincter - Prevents air from entering GI tract
◦ Lower oesophageal artery - Helps prevents reflux into oesophagus
Stomach
◦ Storage facility
◦ To produce chyme
◦ Physical breakdown
◦ Chemical breakdown
◦ Digestion started
◦ Storage
◦ Infection control (HCL)
◦ Secrete intrinsic factor(Vit B12)
What is chyme?
A fluid that passes out from the stomach that consists of gastric secretions and partially digested food.
Describe the broad functions of the Duodenum, Jejunum/Ileum, Large Bowel and Rectum/Anus
Duodenum
◦ Start of small intestine
◦ Neutralisation/osmotic stabilisation of chyme
◦ HCO3 rich secretions
◦ Digestion wrapping up
◦ Pancreatic secretions
◦ Bile
Jejunum/ileum
◦ Final digestion
◦ Nutrient absorption (Mainly jejunum)
◦ Water/electrolyte absorption (Mainly ileum)
◦ Bile recirculation (Ileum)
◦ B12 absorption (Terminal ileum)
Large bowel
◦ Final water absorption (harder to absorb this water)
◦ Temporary storage
◦ Final electrolyte absorption
◦ Some bile salt absorption
◦ Production of some SCFAs - Contains lots of gut bacteria
Rectum/anus
◦ defaecation
Label the regions of the stomach
Where and how do the liver and pancreas connect to the digestive tract?
The Liver and Pancreas connect to the (second part of the) duodenum via the biliary tree too deliver bile and pancreatic secretions into the gut tube. From the liver the left and right hepatic ducts join to form the common hepatic duct which joins the cystic duct from the gallbladder to form the common bile duct which joins the pancreatic duct to form the ampulla of vater which drains into the duodenum via the sphincter of odi.
What is the terminal ileum?
Terminal ileum is the end of the ileum just before the start of the large bowel.
Which absorbs more water, the large or small bowel?
Although one of the main functions of the large bowel is water absorption, the small bowel absorbs a greater volume of water overall
Briefly describe of the autonomic nervous system works?
Cell bodies reside in CNS (brain and spinal cord)
Each pathway has two neurons
◦ Preganglionic (Short in sympathetic and long in parasympathetic)
◦ Postganglionic (long in sympathetic and short in parasympathetic)
The preganglionic fibre synapse with an autonomic ganglia outside the CNS
Postganglionic fibre synapse on peripheral effector organs
All preganglionic fibres release Ach
Post ganglionic fibres release Ach, neuropeptides or norepinephrine
Describe the parasympathetic nervous system in relation to gut
On button for gut (rest and digest)
Vagus nerve From upper region origin
Pelvic splanchnic nerves (S2-4) from lower region origin (Craniosacral outflow)
Postganglionic fibres release:
Acetylcholine
Peptides: Gastrin releasing peptide, Vaso-inhibitory peptide
Preganglionic fibres synapse in walls of the viscera so post ganglionic neurone is in the walls of viscera
Innervate smooth muscle/endocrine and secretory cells
Describe the sympathetic nervous system in relation to gut
Turned off (generally) - fight or flight
Mainly innervate blood vessels and generally constricts blood flow to slow function of affected region.
T5-L2 (innervation to gut)
Pass through (paravertebral) sympathetic trunk without synapsing
Form (abdominopelvic) presynaptic splanchnic nerves
◦ Greater (T5-9)
◦ Lesser (T10-11)
◦ Least (T12)
These splanchnic nerves synapse with prevertebral ganglia: Coeliac, renal, superior mesenteric, inferior mesenteric and others
Give a brief summary of the parasympathetic nervous system in the GI tract
Originates in brain and sacral spine (craniosacral)
Vagus- oesophagus-transverse colon
Pelvic nerve- transverse colon-anal canal
Long preganglionic fibres extend to viscera (postganglionic fibres essentially in visceral wall), to myenteric and submucosal plexuses (enteric nervous system)
Releases Ach or a neuropeptide like GRP
Switches on gut functions
Give a brief summary of the sympathetic nervous system in the GI tract
Originates T1-L2 spine
Preganglionic fibres (pathway)
Spine to sympathetic chain, pass through chain without synapsing, join with other preganglionic fibres to form splanchnic nerves (greater, lesser, least), splanchnic nerves synapse on prevertebral ganglia (coeliac, superior mesenteric and inferior mesenteric)
Postganglionic fibres extend from prevertebral ganglia to viscera to myenteric and submucosal plexuses (enteric nervous system)
Generally inhibits function
Describe the Enteric nervous system
One of the divisions of the nervous system
Can operate completely independently (like a second brain)
◦ But has extensive connection with the autonomic nervous system
Exists from oesophagus to anus
Two main plexuses:
◦ Submucosal (Meissner’s) - Submucosa
◦ Myenteric (Auerbach’s) - In between circular and longitudinal muscle
Submucosal (Meissner’s) ◦ Secretions ◦ Blood flow
Myenteric (Auerbach’s) ◦ Motility
Communicates with: ◦ Parasympathetic (vagus and pelvic nerves) ◦ Sympathetic (prevertebral ganglia)
What are the 4 layers of the gut tube wall?
Mucosa (contains epithelium, lamina propria, muscularis mucosa) (Innermost)
Submucosa
Muscularis Propria (External muscle layers)
Serosa (outermost)
Describe the mucosa layer of the gut tube wall and its functions
Epithelial layer
◦ Selectively permeable barrier
◦ Facilitate transport and digestion of food
◦ Promote absorption
◦ Produce hormones
◦ Produce mucus
Lamina propria
◦ Lots of lymphoid nodules and macrophages
◦ Produce antibodies (mainly IgA which is resistant to proteases)
◦ Protect against bacterial/viral invasion
Muscularis mucosae
◦ Layers of smooth muscle orientated in different directions
◦ Keeps epithelium in contact with gut contents
◦ Helps keep crypt contents dynamic
Describe the submucosa layer of the gut tube wall
Sub mucosa
◦ Contains dense connective tissue, blood vessels, glands, lymphoid tissue
◦ Contains submucosal plexus (Meissner’s)
Describe the Muscularis Propria
Consists of:
Inner circular muscle which contains: Myenteric (Auerbach’s) plexus - result in peristalsis
Outer longitudinal muscle, can shorten gut to have food in areas for longer/shorter periods of time.
Describe the serosa layer of the gut tube wall
Contains:
◦ Blood and lymph vessels and adipose tissue
Its continuous with mesenteries
Describe the epithelia of the gut
Stratified squamous in oesophagus and distal anus
Everything in between is simple columnar
What is an enterocyte?
A simple columnar epithelial cell that absorbs. Predominant cell of small intestine and colon
◦ One cell thick layer - Need to transport nutrients through
◦ Apical membrane is lumen facing and Basolateral membrane
◦ Blood vessels/lymphatics lie immediately below the enterocyte (in Lamina Propria)
Features: ◦ Microvilli (collectively termed brush border)
What are Goblet cells?
Scattered in between enterocytes
◦ Increasing in number from duodenum to colon as colon has more bacteria. They get their name from a narrow base and larger apical size (helps to identify them). Mucus compresses nucleus to its base Mucus protects epithelia from:
◦ Friction (acts as lubricant)
◦ Chemical damage (acidic environment)
◦ Bacterial inflammation (forms physical barrier)
What are foveolar cells?
Gastric surface mucous cells
Line gastric mucosa/gastric pits Secrete mucus/HCO3 that forms barrier to stomach acid
What is the function of the folds/villi and crypts of the GI system?
The gut tube does not have a flat internal surface
◦ Absorptive areas need as large a surface area as possible so they have:
◦ Permanent folds (plicae circulares)
◦ Villi
◦ Microvilli
What are rugae?
◦ The stomach needs to be easily expandable so it has temporary folds called rugae which allow it to expand.
What are Plicae circulares
Permanent folds in small intestine to allow larger surface area
Where are villi found in the GI system?
Small intestine (but not in colon)
What are the crypts in the GI system?
◦ In small and large intestine
◦ Sometimes known as crypts of Lieberkuhn/intestinal glands
◦ Contain specialised cells:
◦ Stem cells ◦ Paneth cells ◦ Enteroendocrine cells
What is the function of stem cells in the GI tract?
Cells that reside in crypts that constantly divide to replace epithelia
◦ Every 2-4 days
What do Paneth cells do?
Located at base of crypts
Secrete antibacterial proteins
◦ Protect stem cells
◦ Secretory vesicles are bright red
What is the function of Enteroendocrine cells?
Predominantly located deeper in crypts and gastric glands
◦ Secrete hormones that control the function of the gut
◦ For example: ◦ Gastrin ◦ Cholecystokinin ◦ Secretin
Describe the exocrine glandular tissue in the gut
Organised secretory cells
◦ Acini
◦ Tubules
Connected to a duct Examples are:
◦ Salivary glands
◦ Pancreas
◦ Brunners glands in duodenum, help to neutralise acidic chyme
What are the layers of the abdominal wall? (superficial to deep)
Skin Fascia/fat
◦ Superficial
◦ deep
3x anterolateral muscles:
◦ External oblique
◦ Internal oblique
◦ Transverse abdominis
◦ Rectus abdominis
Transversalis fascia
Peritoneum
What is an aponeurosis? Describe the ones present in the abdominal wall
Thin sheet like tendon
These have them:
◦ External oblique
◦ Internal oblique
◦ Transverse abdominis
These lateral muscles have aponeurosis that envelops the midline rectus abdominis muscles
What is the rectus sheath
The aponeurosis of the lateral abdominal muscles surrounding the rectus abdominis
What is the arcuate line? How does it relate to the order in which the aponeuroses relate to the rectus abdominis?
- Lower limit of the posterior layer of rectus sheath
- Roughly half way between umbilicus and pubic crest
Above the arcuate line you find that the rectus muscles are enveloped equally anteriorly and posteriorly by the aponeuroses of the lateral abdominal muscles. Aponeuroses from: Internal oblique splits, external oblique is anterior and transversus abdominis is posterior.
Below the arcuate line, all of these aponeuroses are anterior so that the rectus muscles align on transversalis fascia.
Describe the peritoneal cavity?
Mesothelium lined cavity
Flattened simple squamous epithelium
Has a basement membrane
Dense irregular connective tissue
Produces lubricating fluid
Envelopes Intraperitoneal viscera (projects off cavity wall). This bit of the cavity is called visceral peritoneum
Lines the cavity wall - This bit of the cavity is called parietal peritoneum
Viscera that are not enveloped and lie posterior to peritoneal cavity are called retroperitoneal viscera
What is the mesentery?
A double fold of peritoneum that attaches certain viscera to the posterior abdominal wall
◦ Jejenum ◦ ileum ◦ Appendix ◦ Transverse colon ◦ Sigmoid colon ◦
Rectum
Contains: Blood vessels, Lymph vessels, Nerves, fat
Point to where the linea alba, arcuate line, inguinal ligament and linea semilunaris is on the abdomen
