GI Anatomy Flashcards
Where in the GI tract is stratified squamous epithelium found?
mouth/oral cavity, esophagus, anus
What is the function of stratified squamous epithelium?
protection from abrasion
Where in the GI tract is simple columnar epithelium found?
stomach, small intestine, large intestine
What is the function of simple columnar epithelium?
secretion and absorption
What is a simple gland?
Gland where epithelium invaginates to form gland with a single duct
What is a compound gland?
Gland where epithelium invaginates to form gland with 2+ ducts
Why do we have glands?
increased SA for secretion
What are the 4 layers of the gut tube? (from lumen inwards)
- Mucosa
- Submucosa
- Muscularis (externa/proper)
- Adventitia
What makes up the mucosa?
- Epithelium
- Lamina propria (FCT)
- Muscularis Mucosae
*and sometimes small glands
What are found within the lamina propria?
lymphatics and blood vessels
What is the muscularis mucosae?
thin band of smooth muscle specifically associated with the mucosa, creates localised movement to maximise movement of food, secretion etc.
What is contained within the submucosa?
- Larger glands
- Blood vessels
What is the submucosal nerve plexus, and what does it regulate?
nerves within the submucosa which regulate secretion
What is the enteric nervous system (ENS)?
Local nervous system in the gut, regulates most of what happens here
Collagen and elastin fibres primarily make up what layer of the gut tube?
Submucosa
What 2 layers make up the muscularis?
- inner circular
- outer longitudinal
What plexus regulates the muscularis?
myenteric plexus
The myenteric plexus regulates what part of the gut tube?
the muscularis
What is the function of the myenteric plexus?
regulates motility
What is the function of the adventitia?
Maintain structures, also helps with adhesion
What can be found on top of the adventitia, and why is this not considered a layer of the gut tube?
The serosa - only covers organs if in the peritoneal cavity
What is the adventitia made out of?
FCT
What is the function of the peritoneum?
frictionless movement for organs that need to move to function
What is the mesentary?
Double layer of visceral peritoneum that connects organ to body wall
What is the omenta?
Double layer of visceral peritoneum that connects Organ to Organ (remember Os)
What are the 3 pairs of salivary glands called?
• Sublingual
• Submandibular
• Parotid
SSP = spitting noise
What do the salivary glands secrete?
In general: Mucus + serous fluid containing amylase
Specifically:
• Parotid - Serous fluid with amylase
• Sublingual – Mucous only
• Submandibular – Mixed
Are the salivary glands simple or compound?
Compound - multiple ducts
What are the 2 types of cells found in the salivary glands?
- duct cells
- acinar cells (in a clusters call an acinus)
What do acinar cells secrete?
amylase
What do duct cells secrete?
bicarbonate
How is the basic tube modified in the esophagus to pass food?
Highly folded submucosa and mucosa so has capacity to expand
What type of cells are found in the mucosa of the esophagus?
stratified squamous epithelium
How does the muscularis change within the esophagus?
Changes as you go down:
• First 1/3: skeletal muscle
• Middle 1/3: a mixture
• Last 1/3: smooth muscle
= Once swallowed, can continue involuntarily
Why does the esophagus have glands instead of goblet cells for lubrication/protection?
Because don’t fit, and would get knocked off
How is the esophagus protected/lubricated?
by mucus from mucus secreting glands
What is the place where the esophagus passes through the diaphragm called?
esophageal hiatus
What structure prevents reflux?
the lower esophageal sphincter
what is the role of the lower esophageal sphincter?
prevents reflux
What are the parts of the stomach called?
• Cardia
• Fundus
• Body
• Pylorus (pyloric antrum)
What are the 2 bits of omentum connected to the stomach, and where to they attach?
Lesser omentum: Stomach to liver
Greater omentum: Stomach to transverse colon
What other types of cells are found in the greater omentum, and why?
Some fat cells for cushioning
Immune cells, for any infections that break out in the abdomen
How is the muscularis modified for function in the stomach?
Modified for motility which helps promote physical digestion, also mixing.
3 Layers:
• Oblique (inner)
• Circular (middle)
• Longitudinal (outer)
What are rugae?
Rugae are temporary folds that allow for the expansion of the stomach (1.5L)
What volume of secretions do the salivary glands produce daily?
~1L
Describe the structure of the rugae
folded core of submucosa with overlying mucosa
What is function of the submucosa core of the rugae?
Core of submucosa = connective tissue = this is what allows it to flatten
How is the mucosa modified in the stomach for function?
- Simple columnar epithelium
• In-folding increases surface area for secretion (1.5L/day)
• Mucosa invaginates down to form simple gastric glands- Permanent = don’t flatten with the rugae
what cells are found within gastric glands?
- parietal cells
- G cells
- chief cells
What do parietal cells secrete?
Secrete acid and intrinsic factor
What do G cells secrete?
Secrete hormones (gastrin)
What do chief cells secrete?
Secrete pepsinogen (an
inactive precursor of pepsin)
What does gastrin do, and what cells is it secreted from?
G cell -> gastrin -> regulates motility, secretion in stomach
Describe the shape/organelle distribution of chief cells
• Abundant rough endoplasmic reticulum (because producing lots of protein)
• Apical zymogen granules (contain enzymes)
• Basal nucleus (because granules in apical aspect forces other organelles down)
Describe the shape/organelle distribution of parietal cells
Parietal cells produce acid, so:
• Pump ions (H+)
• Abundant mitochondria
• Central nucleus
• Folded structure to increase surface area for H+ pumps
What regulates stomach function? (2)
- Endocrine control: gastrin and ghrelin secreted into bloodstream
- Neural control: local reflexes from ENS, and by CNS regulating ENS function
What structure controls the release of chyme from stomach?
pyloric sphincter
What is a histological feature of the pyloric sphincter?
Region of thickened muscle
What needs to happen to the chyme once it has left the stomach?
• Further digestion (enzymes)
• Protection for small intestine from acidic chyme => mucous and neutralisation of acid
What provides mucus from protection from chyme as it leave the stomach?
glands in the submucosa of the duodenum
T or F: the pancreas is a retroperitoneal organ
True!
Where do secretions from the liver and the pancreas meet? What are these structures called?
Bile duct meets pancreatic duct at the entrance to the hepatopancreatic ampulla
How are secretions delivered from pancreas/liver into the duodenum?
Via the duodenal papilla
What controls the release of secretions into the duodenum?
The hepatopancreatic sphincter
How does the pancreas show endo and exocrine functions?
Endocrine = secretions of HORMONES from islet (a and b) cells into the blood
Exocrine = secretion of ENZYMES/BICARBONATE into the lumen (= outside world)
Describe the structure of pancreatic acinar cells
• Apical zymogen granules
• Basal nucleus
• Abundant rough ER
What is the function of pancreatic acinar cells?
Secrete digestive enzymes
What is the function of pancreatic duct cells?
secrete bicarbonate for neutralisation of acidic chyme from stomach
What structures in the stomach allow STORAGE?
- sphincters
- rugae = distension
What gastric structures are needed for mechanical digestion?
- smooth muscle
- sphincters
What gastric structures are needed for chemical digestion?
- secretion of acid and enzymes
- protective epithelium
What are the 3 regions of the small intestine?
- Duodenum
- Jejunum
- Ileum
Describe the small intestine in relation to the peritoneum
- Duodenum is retroperitoneal because it doesn’t really move, just a receiving space
- Rest of small intestine is peritoneal for movement patterns, visceral peritoneum covers surface
- Small intestine held in place by mesentery so it doesn’t get tangled
What can be found sandwiched in the mesentery?
Arteries, veins, nerves and lymphatics
Describe how/where/by what mucus is produced in the SI
Mucus secreting cells are interspersed throughout mucosa cells and present throughout all regions.
Duodenum needs more mucus, has glands
What 4 ways is the SI modified for function?
1: Long
2: Plicae Circulares = permanent folds in the submucosa
3: Villi = folds in the mucosa (not the muscularis mucosa)
4. Microvilli = folds in the apical plasma membrane of the epithelium
What are plicae circulares?
PERMANENT folds in the small intestine. They have a CORE OF SUBMUCOSA with OVERLYING MUCOSA
What is the function plicae circulares?
Stick out into lumen
- Increase SA
- Spiral food, show it down
What is the difference between rugae and plicae circulares?
Plicae = permanent
Rugae = temporary
Permanent folds in the small intestine are known as…
Plicae circulares
What are villi?
Folds of the mucosa of the small intestine, found on the surface of the plicae circulares
Describe the muscularis mucosae in reference to the villi
- not folded
- allows villi to wiggle back and forth to aid absorption
What is found within the core of villi?
lymph and capillary networks
core of lamina propria
Describe blood flow away from the small intestine
• Nutrient rich, deoxygenated blood absorbed in the small intestine enters into the MESENTERIC VEINS
• These drain into the HEPATIC PORTAL VEIN -> liver detoxifies
Describe how lymph is drained away from the small intestine
• Lymph lacteals ultimately drain the products of fat digestion into the cisterna chyli, thoracic duct and then left subclavian vein
What type of epithelium is found in the SI? Any special features?
Simple columnar with microvilli on apical surface
What is the glycocalyx?
The layer of epithelial cells in the small intestine, and the layer of glycoproteins which helps to tether brush border enzymes in place
What is contact digestion?
Chemical digestion involving the brush border enzymes
Broadly describe how particles move into epithelial cells in the gut
• Through the selectively permeable plasma membrane through proteins channels/transporters, or by simple diffusion if lipid soluble
• Through tight junctions between cells
- Only small molecules may diffuse through, and require a gradient
What 5 types of specialised epithelial cell may be found in the intestinal crypts? What are their functions?
Enterocytes - Absorptive cells
Goblet cells - Secrete mucous for protection
Stem cells - Make all cell types
Paneth cells - granules, antibacterial enzymes
Endocrine cells - secrete hormones
What are the 3 main sections of the large intestine?
• Cecum
• Colon
• Rectum
What are the parts of the colon?
• Ascending
• Transverse
• Descending
• Sigmoid
Describe the large intestine in relation to the peritoneum
• Ascending and descending colon are
retroperitoneal
• Transverse and sigmoidal colon are intraperitoneal
What is the function of the ileocecal valve?
• Regulates the passage of material into the cecum
• Prevents backflow
Where does the appendix attach?
To the cecum, with a variety of possible locations/directions
What is the role of the appendix?
Lymphoid tissue - immune role
Reserve of large intestine bacteria, repopulates the gut after diarrhea etc.
How can we image the large intestine and check the function of the ileocecal valve?
With a barium enema and xray
What are teniae coli?
- bands of LONGITUDINAL smooth muscle
- Modification to muscularis external
- Not in small intestine
What are haustra?
Series of pouches in colon wall
What is the function of haustra?
For expansion/elongation of large intestine
What does movement across the haustra stimulate?
further contraction of the smooth muscle => defecation
What is the function of the teniae coli?
- Helps pucker into pouches/haustra
- Creates stronger contraction
T or F - villi are found in both the large and small intestine
False! No villi in the LI
Describe the intestinal glands found in the LI
Mucosa invaginates down to form intestinal glands.
Which layers of the mucosa invaginate to form intestinal glands? Which do not?
Mucosa consists of:
• Epithelium
• Lamina propria
• Muscularis mucosae
The muscularis mucosae does not invaginate, but epithelium and lamina propria both do.
What is the function of mucosa in the colon?
WATER AND SALT ABSORPTION
What structure marks boundary where
epithelium changes?
Anal columns
Describe the change in epithelium at the anal canal
Before anal columns = simple columnar
Epithelium of anal canal = stratified squamous to protect from abrasion
Describe the 2 anal sphincters and how they are controlled
• The internal anal sphincter is smooth
muscle (under involuntary control)
• The external anal sphincter is skeletal muscle (under voluntary control)
Describe the defecation relex
• Movement of faeces into rectum stimulates stretch receptors
• Internal anal sphincter relaxes (involuntary)
• Conscious decision to defecate – external anal sphincter relaxes
Describe where the blood to the liver comes from, and in what proportions
1/3 from hepatic artery
2/3 from hepatic portal vein (intestines to liver)
Describe the blood that arrives from the intestines to the liver
- nutrient rich
- deoxygenated
What structure do the blood vessels of the liver travel through?
the lesser omentum
function units of the liver =
lobules
What are hepatocytes, and what do they produce?
liver cells, produce bile
where are liver sinusoids found?
between rows of hepatocytes
Where are bile canaliculi found?
between hepatocytes/cells
What constitutes the portal triad?
• Branch of hepatic artery
• Branch of hepatic portal vein
• A bile duct
Where are the portal triads found?
at the corner of the lobules
After bile is produced, where does it go?
Bile secreted into canaliculi, travels to bile duct, then into central vein -> hepatic vein -> inf vena cava
Where is bile stored and concentrated?
the gall bladder
What id the function of the gall bladder?
Store and concentrates bile
Where does the bile duct join the pancreatic duct?
At the hepatopancreatic sphincter
