The GI tract (Dr Campbell) Flashcards
What are the 5 main functions of the GI tract ?
- Ingestion
- Mechanical digestion
- Chemical digestion (secretion)
- Absorption
- Excretion
How long is the GI tract ?
8 meters long (muscular tube).
What is the GI tract lined w/ ?
What can this lining be specialized for ?
An epithelium –> specialized for protection, absorption and/or secretion
What are the four general layers (and their sub-layers) found almost consistently throughout the GI tract ?
From inside to outside:
- mucosa (M) : epithelium, lamina propria, muscularis mucosae
- sub-mucosa (SM)
- muscularis externa (ME): circular muscle (thickest part of musc externa) + longitudinal muscle
- serosa (S): adventitia + epithelium
What are the main components of the GI tract and their respective general fcts ?
- Oesophagus –> carry food to stomach
- Stomach –> acid & enzymes, breakdown proteins
- Small intestine –> digestion, absorption of nutrients
- Large intestine –> absorption of water
What are the 4 layers of the oesophagus ?
From inside to outside:
- M (E, LP + MM)
- SM
- ME
- A
What are the main fcts of the stomach ?
- Storage
- Mechanical breakdown
- Acid & enzyme breakdown
- Intrinsic factor - Vitamin B12
- Hold ~ 4 litres
What are the 3 layers of muscle in the stomach ?
From inside to outside:
- oblique
- circular
- longitudinal
What are the ruggae w/in the stomach ?
Folds that can flatten –> allows stomach expansion –> increase in available volume
What is the stomach lined w/ ?
Simple columnar epithelial cells + gastric pits.
What are the four layers of the stomach ?
What do these contain ?
M: - columnar/(cuboidal) mucus epithlium - LP --> capillaries + projctions from lympatic vessels - MM SM --> arteries, veins + lymphatic vessels ME: - oblique - circular - longitudinal Plexus in CT between circular and longitudinal layer S: - adventitia - epithelium
What is a plexus ?
Plexus = a network of nerves or vessels in the body
How many liters of gastric juice are produced by the gastric glands of the stomach each day ?
2-3L/day
What are the different cells making up the stomach epithelium ?
What are their respective fcts ?
From “top” to “bottom” of the gastric pit:
- surface mucus cell –> secretes mucus
- mucus neck cell –> secretes mucus
- parietal cell –> secretes HCl + intrinsic factor
- chief cell –> secretes pepsinogen
- hormone-producing G cell –> secretes gastrin
Mucus neck, parietal, chief + G cell –> in the gastric gland
In which layer of the stomach are:
- the gastric pits ?
- the gastric glands ?
Gastric pits –> E
Gastric glands –> LP
What are the fcts of the small intestine ?
• Digestion –> enzymes from liver & pancreas & microvilli/
brush border
• Absorption –> 90% of nutrients
What are plicae in the small intestine ?
Plicae = folds or ridge of inner small intestine
What are villi ?
Why are they useful ?
Villi = minute elongated projections set closely together on the inner small intestinal surface –> increasing its surface area for the absorption of substances
What are the different layers of the small intestinal wall ?
What do these contain ?
- M –> simple columnar E + LP: villi, intestinal glands (Crypts of Liberkuhn), lympoid nodules
- MM
- SM: submucosal arteries + veins, lymphatic vessels, submucosal plexus
- ME –> circular + smooth layer, myenteric plexus between the 2
- S –> A + E
What are lacteal ?
What is their fct ?
Lacteal = the lymphatic vessels of the small intestine that absorb digested fats
What epithelial cells make up the villus ?
What are their fcts ?
From “top” to “bottom”:
- enterocytes –> have microvilli to digest + absorb nutrients
- goblet cells –> secrete mucus
- endocrine cells –> secretes secretin, cholecystokinin (CCK) + gastric inhibitory polypeptide (GIP)
- paneth cells –> secrete lysozyme + capable of phagocytosis
Where do the venules leaving the villi of the small intestine carry ?
Where do they lead to ?
They carry deoxygenated blood from the villi of the small intestine (containing short chain FAs, monosaccharides and AAs) to the hepatic portal vein (into the liver and subsequently go to the heart).
Where do the lymphatic vessels leaving the lacteals of the villi in the small intestine carry ?
Where do they lead to ?
They carry chylomicrons (= droplets of fat present in the lymph after absorption) from the villus to the thoracic duct.
What can also be found on the surface of the many villi in the small intestine ?
Microvilli.
What are the main fcts of the large intestine ?
- Absorption of water & vitamins
- Digestion –> 10% of nutrients
- Lubrication of contents
What are the different layers of the large intestine ?
What do these contain ?
M –> clumnar epthelium + LP: intestinal glands, goblet cells + mucosa associated lympoid tissue, lympoid nodules
SM: veins + arteries
ME –> circular + longitudinal layer
S –> A + E
What cells can be found in (large) intestinal glands ?
What are their roles ?
Enterocytes –> absorptive cells (absorb water)
Goblet cells –> secrete mucus
What is a lympoid nodule ?
Lympoid nodule = small, localized collection of lymphoid tissue, usually located in the loose CT beneath wet epithelial membranes
What is the structure that allows defecation made of ?
- the rectum
- the anal canal
- the anal columns
- the internal and external sphincters
- the anus
