The GI Tract Flashcards
The general musculature of the GI tract is mostly what?
-smooth muscle except at the ends, by anus and upper esophagu
The intrinsic rhythmicity is what type of nervous system?s
-it contains its own nerve impulse with stimulation from the sympathetic and parasympathetic
What are 3 neurotransmitters in the GI tract?
- bombesin
- motilin
- vasoactive intestinal peptide
Unicellular endocrine cells of the GI tract are what?
-derived from endoderm and secrete neuropeptides
What lymphoid tissue is contained in the GI tract?
- MALT
- GALT specifically in the gut tube
What protective mechanisms are in place in the GI tract?
- large amount of mucous production
- very high activity increases the chances of cancer
- very high turnover due to the harsh environements from pH changes of stomach and other decretory enzymes
The oral cavity consists of what components?
- lip
- cheek
- teeth
- tongue
The oral cavity is line with a mucous membrane on top of vascular FECT. What does the mucosa consist of?
- stratified squamous epithelium
- basement membrane
- lamina propria
What part of the lip is hihg in capillaries and prominent at the free margin of the lip?
Dermis, and high vascularity gives rise to the coloring
The lip is composed of what core skeletal muscle?
-orbicularis oris embedded in the FECT, covered by skin
The cheek si similar to what structure with what difference?
- similar to the lip
- different with higher amount of elastic fibers, allowing increased distensibility
What three tissues help to form the teeth during development?
- ectoderm: forms the enamel
- Neural crest: form dental papilla
- mesoderm: form dental papilla
The neural crest and mesoderm cells form the dental papilla which is composed of what?
-dentin, cementum, pulp, and connective tissue
What does the epithelial bud of the tooth become?
- enamel organ: dead tissue
- dental papilla: living tissue gives rise to pulp and dentin
- dental sac: CT sac around the enamel and dental papilla
What do odontoblasts form?
-dentin matrix, living tissue for the life of tooth.
What are the odontoblasts histologically?
- single layer of cells along pulp cavity
- the processes are called the Tome’s dentinal fibers and actually lay down the dentin
What is the dentin similar to and what is its composition?
-harder than bone, and high amount of collagen I
The ameloblasts of the teeth help form what?
- form the enamel by laying it down in prisms on the crown of the tooth
- 1prism= 1 ameloblast
Where are the ameloblasts located in order to secrete the enamel?
- in ameloblasts on the apical domain for secretion.
- grows in a rhythmic type of pattern
What components of the enamel are removed after calcification?
- amelogenins
- enamelins
Where does the pulp of the tooth originate from?
-dental papilla containing mesenchyme
What does the tooth pulp contain?
-fibroblasts, macrophages, peripheral odontoblasts, reticular fibers, nerve fibers, bloods vessels all pass through the apical foramen
What are the cementum of the tooth?
- is secreted by cementoblasts on the root form the neck to the apex.
- contains coarse collagen fibers in a calcified matrix.
What is the periodontal membrane?
- high metabolic tissue that binds cementum into the socket
- has limited movement but helps absorb pressure.
What components are contained in the periodontal membrane?
-fibroblasts, osteoblasts, cementoblasts, collagen fibers, blood vessels, nerve fibers
What function does the periodontal membrane help to do?
- Anchor the cementum into the bony socket
- allows absorption from pressure to prevent damage to the bone
What are the stages of tooth development?
- bud stage
- early cap stage
- late cap stage
- bell stage
- tooth eruption
What separates the anterior 2/3 from the posterior 1/3?
-sulcus terminalis
Where are the lingual papillae?
- oral surface projections
- formed by CT lamin propria covered with stratified squamous epithelium
THe lingual papillae are formed by what structures?
- filiform papillae
- fungiform papilla
- foliate papillae
- circumvallate papillae
The Filiform papilla are where?
-conical appearance, lack taste buds and cover entire portion
The fungiform papilla are where and do what on the tongue?
- interspersed between filiform
- few in number
- contain taste buds on the the oral surface of the epithelium
Foliate papillae
- contain the lingual tonsils, and therefore lymph nodules
- free of taste buds
Circumvallate papilla?
- located along the sulcus terminalis with taste buds on lateral walls.
- Contain ducts of Von Ebner’s glands to increase ability to taste
Taste buds contain what two cell types?
- sustentacular cells
- taste cells
Sustentacular cells provide what structure?
-spindle-shaped support cell around inner taste pore
Taste cells
- apical microvilli
- neurotransmitters released from basolateral surface
The taste buds are formed from sustentacular cells and taste cells derived from__________
a single stem cell
Sour and salt sensation is signaled how?
-use of ionic transport as a signal transduction mechanism
Sour taste involves what mechanistic step signal?
-a H ion blocks the K ion channels and causes depolarization
Bitter taste uses what intermediate molecule?
- gustucin which is a homologue to retinal transducin
- closes the Na channels to induce hypopolarization of taste cells
What are the general epithelium in the GI tract?
- stratified squamous at either end.
- middle length is simple columnar
- glands scattered throughout
What are the layers of the digestive tube?
- mucosa
- submucosa
- muscularis externa
- outermost layer
The mucosa of the digestive tube consists of what layers?
- epithelium: stratified squamous to simple columnar
- lamina propria: loose areolar CT contain GALT
- muscularis mucosa: 1 layer of smooth muscle
The submucosa of the digestive tube contain what nerve and tissue?
- dense irregular CT
- vascularized
- contain Meissner’s plexus
Muscularis externa layer of the digestive tube is the 3rd layer from deep tissue, of what components?
- circular and longitudinal smooth muscle
- Myenteric nerve plexus
- regulates size of lumen, and peristalsis
Outer most layer of the digestive tube consists of what layers?
- serosa: dense irregular CT, visceral peritoneum, and mesothelial lining
- adventitia: dense irregular CT with adipose tissue, covers retroperitoneal portion
What sympathetic fibers are located in the gut wall?
- sympathetic postganglionic fibers that pass through the gut wall to glands and smooth muscles
- from celiac ganglion, inferior mesenteric ganglion, superior mesenteric ganglion
The parasympathetic innervation of the gut wall?
-preganglionic fibers synapse with postganglionic ganglia in the gut itself
Meissner’s Plexus does what?
-regulate local secretion, blood flow, and absorption
The auerbach’s plexus?
- located in the gut wall
- coordinate the muscle activity of the gut wall
- constitute peristalsis and mechanical degradation of food
Isolated lymph follicles in the lamina propria are formed by what two components in the GALT?
- antigen stimulated B cells in the follicle secrete IgA.
- specialized squamous epithelial cells which transport food antigens to the lymph follicles
What are two aggregated lymph follicles of this system?
- form tonsils of the oropharynx (Waldeyer’s rings)
- Peyer’s patches of submucosa of ileum
What are the two structures associated with the esophagus?
- mucosa: stratified squamous nonkeratinized epithelium
- muscularis externa: transitions in thirds from skeletal muscle to complete smooth muscle.
Linings of the stomach consist of what?
- epithelial lining
- gastric glands
- muscularis externa
What gland, cells and surface features are located on the epithelial lining of the stomach?
- simple columnar with mucous columnar cells
- mucous cells secrete insoluble mucous to protect against low pH
- Rugae
What is unique of the third musclaris externa layer of the stomach?
- inner oblique layer
- this helps give rise to mechanistic churning of chyme
What are the regions of the stomach?
- cardia
- fundus
- body
- pylorus
The fundus of the stomach contain what cells?
- gastric glands
- parietal, chief, stem, enteroendocrine cells
What type of glands are localized to the pylorus?
-mucous glands and enteroendocrine cell that secrete hormone.
Describe the structure and cells of the gastric glands.
- simple branched tubular gland
- mucous cells: soluble mucous
- stem cell: replace gastric pit cells
- chief cell: secret pepsinogen
- parietal cell: form HCl, intrinsic factor
- enteroendocrine cell:secrete hormone and uptake amines
What forms the protective gel of the stomach lining?
- mucous surface cells and apical granules with glycoproteins
- able to secret HCO3 when needed
What helps to activate the chief cells to secrete pepsinogen?
- acetycholine stimulates secretion.
- pH
What is the primary function of the parietal cells, and other functions?
- secretion of HCl and intrinsic factor
- H ion is formed from carbonic acid
- tubulovesicle pools form exo-/endocytosis function
What are the three levels of folding that increase surface area and aid in the absorption of nutrients in the GI tract?
- Plicae:
- Crypt-villus system
- microvilli
Plicae are best described as what?
-mucosa folds that each contain a submucosal core
The crypt-villus system contain help to make up what portion of the small intestine?
-contain: glands of SI, simple columnar with goblet cells, a capillary plexus, lacteals, and lamina propria
What intestinal glands open between villi and extend deep into the mucosa down to the muscularis mucosa?
-Glands of Lieberkuhn
What type of enzymes are located in glycocalyx that covers the microvilli brush border?
-maltase, sucrase, isomaltase, lactase, lipase, peptidases
What structures help support the microvilli?
- villin, fibrin
- myosin I, calmodulin
Villin and Fibrin in the small intestine.
- support the microvilli.
- cross-linking proteins that bind actin filaments together
Myosin I and calmodulin have what role in the small intestine microvilli?
- microvilli support structures
- anchor actin filaments to the plasma membrane covering the villus
The serosa of the digestive tube forms what layer?
-visceral peritoneum
The adventitia of the digestive tract out layer helps to form what covering?
-retroperitoneal portion of the digestive track
What is the dominant immunoglobulin in the gut tract?
-IgA, found coating the luminal surface
What is an M cell?
- specialized squamous epithelium in the gut that transport food antigen to lymph follicles
- associate with food allergies
What are the two functions the esophaagus serves?
- digestion (by amylase degrading starch)
- adds mucous to food bolus
What is significant about the transition zone between the stratified squamous epithelium and the simple columnar epithelium?
Is this significant of other areas that have an analogous type of transition occurring?
- cancer is common in these areas.
- second area is the transition from intestines to colon, or later structure for feces excretion
The mucous neck cells secrete what special substance?
-water soluble mucous
What cells are able to produce HCl and intrinsic factors?
-parietal cells
Zymogenic cells in general secrete zymogenic granules which means what exactly?
- cells that secrete inactive hormones/components
- pepsinogen from chief cells
Where does pepsinogen come from, and what activates it to become pepsin?
- secreted from the chief cells
- activated by acidic environent
Where do peptide hormones and serotonin come from?
-enteroendocrine cells
What is necessary for the intestine to absorb Vit B12?
-gastric intrinsic factor
How do enteroendocrine cells release their peptide hormones and serotonin?
-these small cells use secretory vesicles that are in close proximity to blood vessels to release their secretions.
What are the three ways the intestine increase surface area?
- microvilli
- crypt villus system
- plicae
What is considered the first degree of folding?
- evagination of the mucosa and part of submucosa
- form the plica
What is the second degree of folding?
- Evagination of the mucosa
- forms the crypt of villus
What is the third degree of folding?
- evagination of apical domain of enterocyte
- folding of the microvilli
