GI tract Flashcards
Outer surface of the lips
epidermis – stratified squamous with thin layer of stratum corneum
Inner surface of the lips
typical epidermis without stratum corneum but thicker and supported by connective tissue similar to the dermis of the skin.
accessory salivary glands
lie beneath the surface of the lips and continuously secrete small amounts of saliva to moisten the epithelial surface
vermillion region
- transition region between the inner and outer regions of the lips
- thin epithelium with underlying blood vessels
- lacks accessory glands and therefore tends to be dry.
describe the hard palate
- bears ridges
- is covered in stratified squamous epithelium with a thin stratum corneum, it is lightly keratinize
- numerous small salivary gland lie within the connective tissue
- lamina propria becomes more dense connective tissue deeper within the palate
lamina propria
support connective tissue beneath the epithelium
mucosa
epithelium + lamina propria
submucosa
connective tissue just beneath the mucosa
root
- attached tightly to bone within the sockets of the jaw by the periodontal membrane
periodontal membrane
very dense connective tissue with collagen fibers that extend into the bone of the jaw on one side and the cementum connecting to the dentine of the roots on the other
crown
- top part of the tooth above the root line
- used for mastication
incisor
crown is sharp to cut off food
molar
crown is broad and ridged to grind food
pulp
- living tissue of teeth
- fills in the central region of the crown and extends into the roots
- contains blood vessels and nerves which enter the pulp through root canals
root canal
- hollow area in the root which houses pulp extending down into it
dentine
- skeletal tissue that forms the root and most of the crown of teeth
- has fine cellular processes continuous with the pulp
compare dentine to bone
similar matrix but more mineralized and harder
enamel
- skeletal tissue that covers the outer surface of the crown
- contains calcium crystals of hydroxyapatite with denser crystalline structure than bone
what type of skeletal tissue has no cell component?
enamel
what is the hardest of the skeletal tissue?
enamel
inner layer of teeth is derived from…
mesoderm
outer layer of teeth is derived from…
ectoderm
What causes embroyonic development of teeth to begin?
ectodermal epithelium begins to grow into the underlying mesenchyme forming a cap-shaped structure called the enamel organ
dermal papilla
- an aggregation of mesenchyme formed within the enamel gland
- will form dentine and pulp
How does dermal papilla form dentine?
- odontoblasts on the outer surface differentiate
enamel gland
- cap shaped structure formed by ingrowth of oral epithelium
- lined by ameloblasts
- secretes enamel to cover the crown
odontoblasts
- produce dentine
- allow calcium to be added/removed from teeth to contribute to the regulation of blood Ca, though to a lesser extent than bone
What do odontoblasts derive from?
mesodermal precursor cells
they develop from mesenchym
ameloblasts
- line the enamel gland
- secrete enamel
What do ameloblasts derive from?
ectoderm
Cause of gingovitis
- bacteria and food collect in the crevice between the gingiva and tooth
- bacteria can easily breach the thin epithelium here and enter the gingival tissue
symptoms of gingavitis
- inflammation
- receding gums
- exposure of more of the tooth to decay
Compare the matrix of bone, dentine, and enamel
- dentine thin extensions of odontoblasts which remain in mature teeth as tiny, parallel tubes tubes. Highly mineralized and harder then bone
- enamel has no cellular component and is even more highly mineralized than hard. it is the hardest skeletal tissue.
Describe tooth development
i. Tooth formation begins when oral epithelium begins to grow into the underlying mesenchyme forming a cap-shaped structure called the enamel organ. The inner surface is lined with ameloblasts. The underlying mesenchyme forms an aggregate within the cup called the dental papilla. Odontoblasts on the outer surface of the dental papilla secrete dentine. This dentine signals ameloblasts to begin enamel production beneath. The enamel organ will be shed during tooth eruption leaving just the enamel with no cellular covering.
type of muscle in mammalian tongue
skeletal muscle with fibers running in different directions
glands in mammalian tongue
- accessory salivary gland derive from epithelium and open to the surface by ducts
- include serous and mucous glands which continuously secrete a small amount of saliva
epithelium of mammalian tongue
stratified, squamous epithelium
types of papillae on tongue
- fungiform
- filiform
- circumvallate
Where on the tongue will you note find papillae?
on the root
filiform papillae
- Keratinized and covering the tongue surface
- Most numerous
- Smallest
fungiform papillae
- mushroom shaped
- Medium sized
- Bear taste buds along their sides within the epithelial layer
- No keratin
circumvallate papillae
- Largest
- Least common
- Contain taste buds
- No keratin
What are the largest papillae
circumvallate
what are the smallest papillae
filiform
what papillae are keratinzed
filiform
what are the most numerous papillae
filiform
what are the most rare papillae
circumvallate
what papillae have taste buds
fungiform
circumvallete
Describe the structure of taste buds
- Contain pores which allow fluid in to come in contact with neuro epithelial cells which will generate chemical-specific sensation which is conducted out of the base by nerve fibers that travel to the brain
- Glands secrete fluid into the spaces between papillae as taste buds can only function in a liquid environment
accessory salivary glands
- under local control
- smaller
- short excretory ducts
- secrete saliva continuously
major salivary glands
- large and compound
- outside of the oral cavity
- under autonomic control
- secrete large amounts under the presence of food
- large excretory ducts
list the major salivary glands
- Parotid
- Sublingual
- Submandibular
product of parotid salivary glands
serous
product of sublingual salivary glands
mucous
product of submandibular salivary glands
serous and mucous
describe the structure of salivary glands
contains complex, intercalated duct system which collects saliva and conducts it out of the gland
septa of the major salivary gland
- Made of connective tissue
- Divide major salivary glands into lobules
- Support blood vessels and large ducts
acini of major salivary glands
- May produce mucus, serous, or both
* Store their product in secretory granules which are secreted into a central intercaled duct
myoepithelial cells of major salivary glands
• surround acinia and demilunes contracting to push saliva through the duct system
intercalated ducts of major salivary glands
• fuse with larger striated ducts
striated ducts of major salivary glands
• composed of columnar epithelium and secrete lysozyme
excretory ducts of major salivary glands
• conduct saliva through the tissue
circular muscle
the inner muscle layer of the upper GI tract
fibers run circumferentially
longitudinal muscle
the outer muscle layer of the upper GI tract
adventitia
connective tissue sheath covering the outer surface of the GI tract where the tract is bound to
muscularis mucosae
thin layer of muscle just below the mucosa of the GI tract that separates the mucosa from underlying submucosa
submucosa
under the mucosa
composed of loose and dense connective tissue, blood vessles, nerve, lymphoid tissue, and glands
serosa
connective tissue sheath when the GI is free within the abdominal cavity
submucosal plexus
atunomic ganglia between the submucosa of the GI tract
myenteric plexus
autonomic ganglia between muscle of the GI tract
epithelial type of esophagus
- Stratified squamous
- Not keratinized
mucosa of esophagus
- Thinner mucosa
- Thin lamina propia
glands of esophagus
- Within the submucosa
- Similar to seromucous salivary glands
- Secrete lubricating liquid
muscle of esophagus
- smooth muscle
- Skeletal muscle at anterior end
epithelial type of stomach
Single layer of secretory epithelium
mucosa of stomach
Thicker mucosa due to deep tubular glands
glands of stomach
- Parallel rows of tubular glands
muscle of stomach
- Three muscle layers:
- Longitudinal and circular with the addition of oblique interior bands
How can the stomach expand?
i. Stomach wall contain rugae which are folds with submucosa extended into them, but no muscle extended in them. Can unfold and stretch when food enters, expanding volume
stomach cardia
- Small area at the junction of the esophagus
* Contains mucus secreting glands to lubricate food as it enters
stomach fundus
• Secrete acid-pepsin gastric juices and some protective mucus
stomach body
- Below the fundus
* Secrete acid-pepsin gastric juices and some protective mucus
stomach pylorus
- Below the fundus
- Secrete acid-pepsin gastric juices and some protective mucus
- Almost all glands in this region are mucus secreting
pyloric sphincter
• Almost all glands in this region are mucus secreting
gastric pit
- occupy 1/3 thickness of the mucosa
- in the mucosa
- glands open to the surface via these
mucus cell of gastric gland
- most numerous in epithelium of gastric pits and surface
- small numbers through the gland
- mucus – protective coat
- bicarbonate ions – neutralize acid
parietal cell
- from the isthmus to the base of the stomach gland gland
* secrete acid into the stomach lumen
peptic cell
v. peptic cell
• base of gastric glands
• pepsinogen by exocytosis
neuroendocrine cells
• base of the gastric gland • also in other areas of gi tract • hormones a. mainly gastrin which is stimulated by acid • endocrine so secrete into bloodstream
Stomach ulcers
the epithelial barrier is destroyed by acid and the acid erodes the mucosa
Perforated ulcer
- The stomach wall is eroded and the erosion extends into the abdominal cavity
- Serosa become inflamed due to acid leaking out
- Bacteria leak into body cavity and can cause massive infection which can be life threatening
structure responsible for increasing the absorptive surface of small intestin
i. Pilcae circularis
ii. Villi
iii. microvilli
structure of villi
- Finger shaped mucosal fold over the entire luminal surface including the plicae circularis.
- Covered by simple, columnar epithelium
- Lamina propria extending through the center
- Muscularis mucosae marks boundary between mucosa and submucosa
- Not visible without microscope
in what part of the lower GI tract will you not find villi?
colon
duodenal villi
a. Leaf-shaped, broad in one plane
b. tallest
jejunal villi
a. Cylindrical or finger-shaped
b. Shorter
ileum villi
a. Cylindrical or finger-shaped
b. Shortest
Cell types of the intestinal epithelium
enterocytes
goblet cells
endocrine cells
Paneth cells
enterocytes
digest and absorb nutrients
goblet cells
secrete mucus
endocrine cells
secrete hormones that influence the local motility of the intestine and regulate the secretion of other cell types
Paneth cells
secrete antimicrobial chemicals when exposed to bacteria to ensure they do not colonize crypts
microvilli
i. Surface structure of enterocytes
ii. Form the brush border
iii. Contain digestive enzymes to complete membrane digestion
crypts
i. Epithelium tunnels into the lamina propria at villus base
ii. Located at the base of mucosa and open to the epithelial surface through tiny opening at the base of the villi
iii. Lined with stem cells which will differentiate
The role of crypts in epithelial turnover of the villi
– immature cells emerge from crypts and join cells at the villus base.
- They then migrate toward the villus tip and mature into functional enterocytes and goblet cells.
- They also differentiate into endocrine and Paneth cells which will remain in the crypts.
lymph tissue within the small intestine
i. Lacteals within villi merge to form increasingly larger lymph vessels.
ii. in submucosa
luminal digestion
- Within the lumen of the small intestine
- Bile emulsifies fat
- Lipase digests fat
- Trypsin continus protein digestion
- Amylase digests starch
- Ends with fatty acids and glycerol, small peptides, and disaccharide
membrane digestion
- At the surface of the intestinal membrane by digestive enzyme located in the membrane of microvilli
- Completes digestion of proteins and carbohydrate
- Fatty acids are absorbed
capillary beds in villus
i. Dense capillary beds located just below the basement membrane in each villus. Digested peptides and monosaccharides are absorbed into these
lacteals in villus
ii. Lacteals are large lymph vessels within the center of the villus. Chylomicrons enters these to enter the lymphatic system.
How is fat absorbed
i. Fatty acids are passively absorbed through the microvillus membranes into the enterocytes. Once inside, they are reconstituted as chylomicrons which will diffuse into the center of the villi and enter the lacteals. They are then transported through the lymphatic system.
chylomicron
lipid surrounded by a protein coat
Brunner’s glands
i. Found in duodenal submucosa
ii. Produce thin mucus with bicarbonate which helps to neutralize the acid contents of chyme as it emerges from the stomach
function of muscularis mucosae in small intestine
i. Muscularis mucosea underlies the crypts and also has strands that run into the villi allowing them to wave and stir up luminal contents to expose it to each enterocyte
function of longitudinal and circular muscle in small intestine
- under the submucosa
- allow peristalsis
Celiac disease pathology
- The villi short and may disappear entirely
- The region of crypts thicken and the epithelium is reduced to a thin layer covering the crypt region
- Reduces surface area for digestion and absorption increasing risk of malnutrition
- Causing severe diarrhea and cramping
parts of the large intestine
- colon
- cecum
- rectum
colon
makes up the majority of the large intestine
- the site of water absorption
- contains bacteria.
cecum
at the beginning of the large intestine
rectum
at the end of the large intestine
functions of the large intestine
i. Water absorption
ii. Packaging feces for expulsion
iii. Some vitamin production – vitamin K mainly
symbiotic bacteria
- produce vitamins and lipid products
- digest nutrients the body cannot
- prevent colonization by pathogenic bacteria
tubular glands in the colon
i. The mucosa of the colon contains many tubular glands. They are similar to the crypts in the small intestine and contain dividing cells. Most of the cells are goblet cells but there are also a few endocrine cells.
How does the colon compare to the small intestine
ii. Like the small intestine, it has two layers of smooth muscle. It has an inner layer of thick circular muscle. Its outer longitudinal muscle has varying thickness. However, it becomes thicker at four bands called the teniae coli. Its longitudinal muscle takes the form of 4 bands called the teniae coli
iii. It does not contain villi
iv. It has a particularly thick muscularis mucosae
teniae coli
4 bands along the longitudinal smooth muscle layer of the colon
how does the colon contract
By the mucosa and submucosa folding. When they flatten, the colon flattens outs.
Histology of anal canal
i. The anal canal is exposed to more friction and therefore is lined by stratified epithelium – thicker layer
ii. It has no tubular glands
iii. In addition to the skeletal muscle, it also contains skeletal muscle within the sphincter to allow there to be some voluntary control to this sphincter
diverticulitis
- Occurs when intestinal muscle weakens and deep pockets form within the wall
- Ingrowth of mucosa to form deep, thin pckets withtin the wall
- Feces and bacteria may become trapped leading to infection and inflammation
benign polyps
- form in the intestinal wall
- increase with age
- may become malignant
- especially common in the rectum and colon
adenocarcinoma
colon cancer
• occurs when a polyp becomes malignant
• Disrupt the normal structure of the mucosa and circular muscle
• Malignant cells can easily enter the numerous capillaries and lymph vessels found in intestinal tissue, spreading cancer throughout the body
embryonic origin of liver, gall bladder, and pancreas
i. Develop as outgrowth from the embryonic gut tube
ii. Endodermal
embryonic development of liver, gall bladder, and pancreas
- Liver appears first and grows rapidly
- Pancreas originates from the dorsal and ventral outgrowth
- The gall bladder from the expanded tip of the original liver outgrowth which becomes the bile duct
- As development continues, the liver grows large and the dorsal and ventral pancreas fuse forming a single organ
liver functions (broad)
- synthetic
- excretory
- detoxification
- digestion
liver synthetic functions
a. Production of plasma protein
b. Glycogen for glucose storage
c. Storage of iron from old erythrocytes
liver excretory functions
a. Hemoglobin through the bile duct
b. Excess cholesterol
c. Detoxification products
d. Wastes products enter the intestine to be excreted
liver detoxification functions
a. Metabolism of metabolic wastes
b. Detox of poisons – ie alcohol
liver digestion functions
a. Production/secretion of bile
gallbladder functions
• Stores and concentrates bile
pancreas functions
- Secretes pancreatic enzymes trypsinogen, amylase, and lipase
- Secretes bicarb
- Secretes insulin
- Secrete glucagon
liver lobules
- the functional unit of the liver
- hexagonal units of liver tissue divided by very thin lines of collagenous tissue
- contain portal tract in corner and central vein in center
- contains hepatocytes
- blood enters from the vessels at the corners and flows through the sinusoids to the center, leaving through the portal vein
what is the functional unit of the liver
liver lobule
liver sinusoids
- blood filled channels which lie between rows of hepatocytes
- single with single layer of squamous epithelial cells
- similar to capillaries but larger diameters
how does the epithelium of sinusoids contribute to their role in gas exchange?
• the epithelial cells that line the sinusoids are thin and provide little barrier between hepatocyte and blood. Additionally, gaps within the lining allow blood to directly contact the hepatocyte plasma membrane
hepatocytes
- liver cells surrounded by blood and in contact with a sinusoid on at least two sides
- perform most of the livers functions of detox
- produce bile
endothelial cells of liver
- line the sinusoids
* thin to provide little barrier between the hepatocyte and blood
Kupffer cells
• Macrophages of the liver and remove particulate matter from the sinusoid and degrade old erythrocytes
lipocytes
- large white cells in liver with lipid droplets storing vitamin A
- also synthesize collagen which forms scar tissue after certain types of liver damage
reticulin fibers of the liver
- form a scaffold to support the hepatocytes and delicate sinusoids
- merge with the collagen fibers of the connective tissue around the blood vessels
portal tracts
- located in the corners of liver lobules
- is surrounded by connective tissue containing lymph vessels
- blood enters the liver lobules through them
what is in a portal tract
a. small hepatic artery
b. branch of the hepatic portal vein
c. small bile duct
bile canaliculi
- tiny channels between adjacent cells which collect bile
- have no structure of their own but instead consist of the channels bounded by the plasma membranes of hepatocytes
- form a branching network that runs between the rows of cells throughout the liver tissue
Describe the blood flow through a liver lobule
i. Blood enters from vessels in the portal tract – the hepatic arteries and portal veins- and flows through the sinusoids to the center when it is collected by the central vein.
ii. It leaves the lobule by the central vein
describe the blood brought in by hepatic arteries
Hepatic arteries bring blood rich in oxygen into the lobule.
describe the blood brought in by portal veins
Portal veins bring blood poor in oxygen but rich in nutrients absorbed from the GI tract as it is connected to the hepatic portal vein which connects the capillary beds of the stomach and intestines to the liver
biliary system
a network of ducts that collect and transport bile
the role of bile canaliculi
• collect bile from individual hepatocytes and transport it to ductules which merge and lead into the bile ducts within the portal tracts of the liver lobules. The bile ducts merge and eventually lead to the two large hepatic ducts which exit the liver
role of bile ducts within portal tracts
collect bile form the canaliculi and transport it to hepatic ducts
hepatic ducts
- two large ducts formed by merging of bile ducts within the portal tracts
- point of exit for bile from the liver
- will join with the cystic duct
cystic ducts
conveys bile to the gallbladder for storage
common bile duct
- Receives bile from the gall bladder through the cystic duct with gall bladder contraction
- Enters the duodenum
- Joins with the pancreatic duct as it enters the duodenum
cirrhosis
i. Excessive alcohol or drug consumption
ii. Hepatocytes deteriorate and are replaced by fibrous tissue
early cirrhosis
fibrous tissue begins to replace hepatocytes in the center but exterior remain healthy
late cirrhosis
fibrous regions extend from portal tracts and surround the lobule. Most hepatocytes are swollen and deteriorating. No normal hepatocytes or sinusoids are present.
muscle and mucosa of the gall bladder
i. Simple columnar epithelium that absorbs water
ii. Highly folded mucosa forming rugae similar to those of the stomch
iii. Lamina propria of loose tissue with many elastin fibers
iv. No muscular mucosae
v. Single layer of smooth muscle
vi. Surrounded by thick connective tissue – adventitia/serosa
function of the epithelium of the gall bladder
absorbs water from bile to concentrate it
exocrine part of the pancreas
- similar to the parotid salivary gland
- large compound gland with fibrous septa in which larger ducts and blood vessels are found
- contain tightly packed acini and intercalated ducts
pancreatic acini
- found in exocrine region
- tightly packed
- each cells contains a large nucleus and is roughly triangular-shaped
- the point of each cell borders the lumen
- apical cytoplasm is packed with zymogen granules and large amounts of rER
zymogen granules
contain trypsinogen, amylase, lipase
pancreatic intercalated ducts
- secrete bicarbonate
- drains the secretion of several acini
- conveys pancreatic enzymes to larger ducts which lead to the main duct
epithelium of pancreatic intercalated ducts
- simple columnar
- secretes bicarb to enter the duodenum and neutralize acid
need for bicarb with pancreatic enzymes
they are only active in a neutral environment
three sources of bicarb in the duodenal lumen
- pancreas
- liver
- brunner’s glands
endocrine region of pancreas
- scattered patch of cells called islets of Langerhans which stain lightly
islet of langerhans
- clumps of hormone secreting cells surrounded by blood vessels
- stain lightly because have less protein than the exocrine regions - no rER
- small round cells
- have extensive capillary network surrounding them as they are endocrine and secrete their products into the bloodstream
beta cells
main endocrine cell type of the pancreas
secretes insulin
insulin
stimulates tissue to take up glucose from the blood stream
alpha cells
secrete glucagon
less prevalent endocrine cell type in the pancreas
glucagon
stimulate liver to release glucose into the blood stream
intercalated ducts
- Secrete bicarbonate
- Found in the exocrine portion
- Drain the secretions of several acini and convey pancreatic enzymes to larger ducts leading to the main duct
- Simple columnar epithelium
excretory ducts
• Supported by septa
• Merge throughout the pancreas and the largest fuses with main pancreatic duct which carries pancreatic secretions out of the organ
- multiple intercalated may drain into one
what are the digestive enzymes secreted by the pancreas
trypsinogen
amylase
lipase
trypsinogen
- Activated in the duodenum by enterokinase into trypsin
- Digests proteins into peptides
- Secreted inactively to protect pancreatic tissue from digestion
amylase
• Breaks down starch into glycogen and maltose
lipase
• Emulsifies fat into fatty acids and glycerol
