Digestive System Flashcards
What is the digestive system responsible for?
the
processing, digestion and absorption of food and the elimination of the residue
What occurs in the oral cavity?
Takes in and fragments food (mastication)
Saliva moistens and begins digestion (alpha amylase)
What is the general function of the esophagus?
conveys food to stomach by peristalsis
What is the general function of the stomach?
gastric juice begins digestion
What is the general function of the samll intestine?
absorption of nutrients begins
What is the general function of the large intestines?
i) absorption continues (especially H20)
II) feces are compacted and expelled
What is the general function of the accessory glands?
1) small glands located in the wall throughout the digestive system
2) large glands (liver, pancreas, salivary) are connected to the tube via ducts
What kind of epithelium is present in Masticatory Mucosa?
Parakeratinized stratified squamous epithelium
What is stratified squamous?
multilayered epithelium with flattened superficial cells
What is parakeratinized?
A moist keratin layer that is still living
What is the epithelial/CT interface like in the masticatory mucosa?
Tall rete pegs and Connective Tissue Papillae
Unerlying CT is fairly immovable and not extensively vascularized
Where is it located and why?
Located in areas subject to wear and tear
(gums and hard palate)
Superficial cells are tightly compacted to facilitate abrasion resistance
What kind of epithelium is present in the lining mucosa?
Nonkeratinized stratified squamous epithelium
What is the epithelial/CT interface like in the lining mucosa?
1) shallow rete pegs and CT papillae
2) underlying CT is fairly movable and more extensively vasularized
Where is it located and why?
lips, cheeks, soft palate
floor of mouth and inferior surface of the tongue
What epithelium is the outer surface of the lips and cheeks covered by?
Orthokeratinized stratified squamous epithelium
What epithelium is the inner surface of the lips and cheeks covered by?
lining mucosa (nonkeratinized stratified squamous epithelium
What is the vermilion of the lips and cheeks?
pink transition zone between the external and internal surfaces
What muscle is located in the lips?
Orbicularis oris muscle - skeletal muscle in the lip
What muscle is located in the cheeks?
Buccinator muscle - skeletal muscle in the cheek
What is the general composition of the tongue?
largely a mass of interlacing bundles of skeletal muscle fibers and CT
What is the general composition of the extrinsic muscles of the tongue?
extrinsic muscles have an attachment point outside of the tongue that function to move the tongue in different directions
What is the general composition of the intrinsic muscles of the tongue?
intrinsic muscles are contained entirely within the tongue that function to change the shape of the tongue
What functional activities does the tongue participate in?
1) manipulate food during mastication
2) essential for production of many sounds during speech
3) move fragmented food toward pharynx to initiate swallowing
What does the presence of intrinsic and extrinsic muscles permit the tongue to do?
Permits the tongue to have complex movements that move in many different planes
What is the sulcus terminalis of the tongue and where is it??
1) superior shallow groove delineating the anterior and posterior regions on tongue
What is the foramen cecum and where is it?
thyroid gland origin that is at the midline of the sulcus terminalis
Where is the Pharyngeal Region of the Tongue located?
posterior third of tongue (root oriented vertically in the pharynx)
How is the Pharyngeal Region of the Tongue oriented?
root oriented vertically in the pharynx
What structures are located in the Pharyngeal Region of the Tongue?
covered by lingual tonsils
What are tonsils?
aggregates of lymphoid nodules
Where is the Palatine Region of the Tongue located?
anterior two thirds of tongue
How is the Palatine Region of the Tongue oriented?
body oriented horizontally in oral cavity
What structures are located in the Palatine Region of the Tongue ?
covered by specialized mucosa containing lingual papillae
What are lingual papillae?
small, bumpy, hair like structures on the dorsum of the tongue, giving it a rough texture
What are the different types of lingual papillae?
Filiform papillae
Fungiform papillae
Vallate (Circumvallate) papillae
Foliate papillae
How common are Filiform Papillae?
Most prevalent
What do Filiform Papillae look like?
conical shaped and covered with a keratinized stratified squamous epithelium
Where are Filiform Papillae found?
evenly distributed over the anterior portion of the tongue
What are Filiform Papillae used for?
contain afferent nerve endings sensitive to touch
Any taste buds located on Filiform Papillae?
no
How common are Fungiform Papillae?
Relatively common
Where can Fungiform Papillae be found?
scattered randomly among the filiform papillae
What do Fungiform Papillae look like?
mushroom shaped and about as tall as filiform papillae
Any taste buds located on Fungiform Papillae?
contain taste buds on the superior surface
How common are Vallate Papillae?
largest in size; fewest in number
Where are Vallate Papillae found?
8-12 located just anterior to sulcus terminalis
What do Vallate Papillae look like?
1) large mushroom shaped papillae recessed into tongue mucosa
2) surrounded by a deep circular groove (moat)
Any taste buds located on Vallate Papillae ?
taste buds present on the lateral sides of these papillae (facing the moat)
How common are Foliate Papillae?
sometimes difficult to see in adult humans
Where are foliate papillae found and what do they look like?
parallel ridges on the lateral edges of the tongue
Any taste buds located on foliate papillae?
contain many taste buds on the sides of these ridges
What are von Ebner’s Glands and where are they located?
small salivary glands intrinsic in the tongue
What do von Ebner’s Glands do and why is it necessary?
flush out taste buds on circumvallate and foliate papillae for sequential tasting, cleaning mechanism
Where are Taste Buds located?
present on fungiform, vallate and foliate papillae
What is the general structure of taste buds?
barrel shaped with a taste pore
What cell types are present in a taste bud?
Taste receptor cell
Sustentacular cell
Basal cell
What do sustentacular cells do?
Provide structure to the taste bud
What do basal cells do?
renew sustentacular and taste receptor cells
How are tastes perceived?
flavor is perceived as various combinations of four basic tastes:
* sweet, sour, bitter, salt
What and where are the minor salivary glands?
lingual, labial, buccal and palatine
located in many areas of the oral cavity
What are the minor salivary glands’ functional responsibility?
secrete saliva more or less continuously to moisten the oral cavity
What is a compound exocrine gland?
An exocrine gland with many branches and a duct
What are the three major salivary glands?
parotid, submandibular and sublingual
When do the major salivary glands secrete saliva?
secrete saliva intermittently in response to food related stimuli
What is the general composition of saliva?
mixed secretion of mucous and serous secretions (i.e., enzymes)
About how much saliva is produced each day?
about a liter/day of saliva is produced; 90% of it is water
What are the functions of saliva?
moisten the oral mucosa
moisten ingested food (facilitating tasting and swallowing)
begin digesting carbohydrates ( amylase)
buffers the contents of the oral cavity
contains antibodies and lysozyme for antibacterial protection
Where is the parotid gland located?
subcutaneously anteroinferior to each ear (often contains large amounts of adipose)
Where does the parotid duct enter oral cavity?
Upper second molar
What kind of secretions are produced in the parotid gland?
Entirely serous secretion
- watery secretion often containing enzymes
What is the histological appearance when the parotid gland is stained with H&E?
typically stains purple
Where is the submandibular gland located?
bilaterally along the medial surface of the body of the mandible
Where does the Wharton’s duct enter oral cavity?
duct opens onto floor of oral cavity posterior to the lower incisor teeth
What kind of secretions are produced in the submandibular gland?
mixed secretion which is mostly serous
What is mucous?
mucous is a thick viscous secretion containing glycoprotein
What is the histological appearance of mucous when stained with H&E?
typically pale staining
What are serous demilunes?
Mucous cells covered with serous demilunes around the edge
Where are sublingual glands located?
bilaterally under tongue, beneath the mucosal lining of the floor of the oral cavity
Where does the sublingual duct enter oral cavity?
multiple ducts open near the submandibular ducts
What kind of secretions are produced?
mixed secretion which is mostly mucous
What is the histological appearance when stained with H&E?
Light and pale staining
What is the hard palate?
1) Anterior 2/3 of oral cavity roof
bony and covered by masticatory mucosa
2) able to withstand the abrasive activities associated with mastication
What kind of mucosa is in the hard palate?
masticatory mucosa
What is the soft palate?
Posterior 1/3 of oral cavity caivty
What kind of mucosa is on the soft palate?
Lining mucosa
What is the uvula?
1) raises and pushes against posterior pharyngeal wall during swallowing
located posteroinferiorly
What happens when swallowing?
raises and pushes against posterior pharyngeal wall during swallowing
Where are palatine tonsils?
situated bilaterally in the tonsillar fossae
What are palatine tonsils?
paired masses of lymphoid tissue
- most suseptible to chronic inflammation and subject to tonsillectomy
What is the pharynx?
1) located at the back of the mouth
2) serves both as a digestive passageway and as a respiratory airway
Where is the oropharynx?
between the soft palate and larynx
What is type of mucosal lining is found in the oropharynx and laryngopharynx?
Lining mucosa (nonkeratinized stratified squamous epithelium)
Where is the nasopharynx?
above the soft palate
What is respiratory epithelium?
pseudostratified columnar epithelium with cilia and goblet cells
What is pseudostratified?
Falsely layered as it is only one layer but appears to be multilayered but each cell touches basement membrane
What are goblet cells?
Cells that produce mucous
What are cilia?
Cilia are hairlike structures
Where is the pharyngeal tonsil?
1) single midline structure on posterior wall of pharynx
What is the pharyngeal tonsil also known as?
adenoids
What problems arise with swollen adenoids?
when enlarged it may obstruct the nasopharynx
What are tonsils?
aggregates of unencapsulated lymphoid nodules
What are lymphoid nodules?
rounded, dense accumulations of lymphocytes (primarily B lymphocytes)
Where are the tonsils located?
the tonsils (lingual, palatine and pharyngeal) form an incomplete ring around the entrance to the digestive and respiratory tracts
What advantage is there in having tonsils?
1) in this position, immune system cells constantly come in contact with antigens entering from the outside world
2) primes these cells to make antibodies and defend the organism
What 4 layers make up the lumen of the digestive tract?
Mucosa
Submucosa
Muscularis externa
Serosa/Adventitia
What do you need to remember about the lumen of the digestive tract?
It is functionally external to the body
What is the epithelial lining of the mucosa of the digestive tract?
type of membranous epithelium and the presence and nature of any
associated glands is dependent on location along the digestive tract
Function of the epithelial lining of the digestive tract?
1) selective barrier between luminal contents and body tissues
2) secretory for HCl, digestive enzymes and mucous
3) absorptive for metabolic substrates and H2O
What is the lamina propria of the digestive tract?
usually loose CT often rich in immune system cells (diffuse lymphatic tissue)
Function of the mucosa of the digestive tract?
1) supports membranous epithelium and accommodates small intrinsic glands
2) contains the vasculature for receiving the absorbed metabolites
3) contains the GALT (gut associated lymphatic tissue) as first line of defense
Where is diffuse lymphatic tissue located?
located deep to epithelial linings of digestive, respiratory, urinary and reproductive tracts
What role does diffuse lymphatic tissue play in the immune system?
ready to respond to entry of infectious organisms and toxins crossing these barriers
What do lymphoid nodules look like?
1) rounded, dense accumulations of lymphocytes appearing within diffuse lymphatic tissue
2) lack a connective tissue capsule so their borders are diffuse
Where are lymphoid nodules unencapsulated nodules found?
Tonsils, Peyer’s patches, Appendix
What does it mean to say lymphoid nodules are transient?
Most are temporary
What are tonsils and where are they located?
aggregates of unencapsulated lymphoid nodules in walls near the soft palate, in the nasopharynx and on the tongue
What are Peyer’s patches and where are they located?
1) large aggregates of confluent lymphoid nodules
2) situated mostly in the walls of the ileum (part of small intestine)
What is the function of lymphoid nodules?
provide immunological protection against pathogenic invasion via vulnerable exposed absorptive surfaces
Where is the appendix located?
In the lower right abdomen
Where are plasma cells typically found?
typically located just deep to the epithelial lining of the GI and respiratory tracts
Plasma cells are the tissue form of what circulating cell?
a B lymphocyte that migrated into connective tissue
What cells are found in the dense lymphatic tissue of lamina propria?
Various leukocytes including neutrophils, eosinophils and lymphocytes
Plasma cells are often associated with what kind of CT?
often associated with loose connective tissue
What is the shape of plasma cells?
typically a rounded cell with an eccentric round nucleus
What is the heterochromatin like in plasma cells?
often the nuclear heterochromatin is positioned like spokes on a wheel
What is a negative golgi image?
Does not stain purple
What does plasma cells do?
produce tissue based antibodies
Why is immunity safety from reinfection as opposed to infection?
Immunity refers to being exposed to an antigen to allow for proper protection from the same antigen therefore it is safety to reinfection
What is an antigen?
is any macromolecule (possibly on a bacterium) that is determined to be
“foreign” to the body
How does a plasma cell react to antigens?
1) plasma cell is part of a system (Immune system) which can respond to the
antigen and facilitate destruction/remova
2) plasma cell responds by synthesizing antibodies
What is an antibody?
protein produced with specificity for only one antigen
How does an antibody facilitate antigen removal?
antibody binds specifically to antigen and antigen is removed
Why are antibodies continually available?
following initial immune response antibodies are circulating and continually
available to respond to antigenic presence
How common are macrophages?
almost as common as fibroblasts in ordinary connective tissue
Macrophages are the tissue form of what circulating cell?
Monocytes
What is the morphology of macrophages?
1) large round/oval cell with eccentric bean-shaped nucleus
2) many lysosomes (primary and secondary) and probably residual bodies
What is the function of the macrophage?
1) major function is phagocytosis of infectious microorganisms, cell debris, particulate matter, old erythrocytes
2) antigen presentation in the immune system
3) many together may form foreign body giant cells
What is the muscularis mucosa’s typical composition?
two thin layers of smooth muscle (inner circular; outer longitudinal)
In what way does contraction in muscularis mucosa facilitate digestion and/or absorption?
facilitates digestion/absorption by maximizing contact between luminal contents and surrounding mucosal surfaces
What is the typical tissue composition of submucosa?
mostly dense irregular CT (with some areas of nondense CT)
What other kinds of structures are seen in the submucosa?
contains larger neurovascular elements, autonomic plexuses and lymphatic vessels
Does submucosa ever contain glands and/or GALT?
sometimes contains glands which are distinctive to certain regions of the tract
Mast cells are closely related to what circulating cell?
Basophils
Mast Cells are usually located near what structures?
typically found near blood vessels throughout body
What is the mast cell’s morphology?
highly granulated cell with cytoplasmic granules that contain heparin, histamine, chemotactic factors
What is heparin?
weak anticoagulant
What is histamine
an inflamitory agent (causes BV dilation, endothelial contraction)
What do chemotactic factors do?
chemotactic factors attract neutrophils and eosinophils
What is the combined effect of mast cell degranulation?
degranulation leads to the formation of “leaky” endothelium
How does degranulation facilitate immune responses?
promotes the infiltration of serum components into the tissue space
What is the typical tissue composition of muscularis externa?
usually two relatively thick layers of spiraling smooth muscle
What is the orientation of this tissue?
- inner sublayer (closer to lumen) generally circular
- outer sublayer is generally longitudinal
- sometimes modified to form sphincters
What is the function of the muscularis externa layer?
create peristaltic contractions to mix and propel luminal contents distally
How is the muscularis externa activity coordinated?
coordinated by myenteric plexuses between the two layers
What is the composition of serosa?
loose CT, rich in adipose, blood and lymph vessels
What is mesothelium?
simple squamous epithelium
Where is mesothelium found in serosa?
1) mesothelium covering underlying CT
2) seen on organs that are suspended in the peritoneal cavity
What is the difference between serosa and adventitia?
Serosa contains mesothelium whereas adventia does not
Where is adventitia located?
seen on organs that are fixed in place and not freely seen in a cavity
What does the esophagus look like?
1) relatively muscular tube that conveys chewed food and liquids from pharynx to
stomach by rapid peristaltic activity (about 25cm long)
What does the esophagus look like when it is not conveying chewed food to the stomach?
Lumen is normally collapsed except when food is passing through
What does the mucosa look like throughout the esophagus?
stratified squamous nonkeratinized epithelium
What does the submucosa look like throughout the esophagus?
1) dense irregular CT exhibiting longitudinal folds when relaxed
2) mucous secreting esophageal glands present
How does the muscularis externa vary in the esophagus?
Superior third - skeletal muscle
Middle third - skeletal and smooth muscle
Inferior third - smooth muscle
Is it covered by serosa or adventitia?
Superior third - adventitia (binds to other structures in the neck and thoracic cavity)
Inferior third - serosa (seen only after esophagus passes through diaphragm)
What is the primary activity occurring in the stomach?
digestion and absorption begin in this expandable muscular-walled reservoir
How is digestion accomplished in the stomach?
acidic fluid is added to the ingested food here and the muscular activity
transforms this mixture into a viscous semifluid mass called chyme
What is chyme?
viscous semifluid mass
What makes up gastric juice?
- hydrochloric acid
- pepsin (secreted initially as pepsinogen)
- mucous
- water and electrolytes
What is the anatomy of the stomach?
Cardia
Fundus
Body
Pylorus
What are rugae?
1) longitudinal folds present in the undistended stomach
2) flatten as stomach expands
3) mucosal covering and submucosal core
What are gastric pits?
tubular invaginations
What are gastric pits lined by?
lined by simple columnar mucous
secreting cells
What are gastric glands?
compound tubular glands
What does compound tubular mean?
Multiple branches of ducts
What are gastric glands lined by?
lined by enzyme and acid secreting cells
What are gastric glands surrounded by?
these epithelial structures are surrounded by lamina propria
How is the stomach muscularis externa unique in the stomach?
has 3 layers:
1) inner/oblique
2) middle/circular
3) outer/longitudinal
Why is the 3 layers of muscularis externa advantageous in the stomach?
1) necessary for the churning action required in the stomach
2) thickened on either end of the stomach to form sphincters
What is the cardiac sphincter?
prevents reflux back into esophagus
What is the pyloric sphincter?
regulates exit to duodenum
Is this layer covered by serosa or adventitia?
serosa - covers all regions of the stomach
Where is the cardiac region of the stomach?
narrow circular region (1.5-3cm in width) at junction between esophagus and stomach
What kind of cells line the gastric pits and gastric glands?
simple columnar mucous secreting cells
Are there any goblet cells in the stomach?
these cardiac glands are entirely mucous, no goblet cells though
What is acid reflux or heart burn?
irritation to esophageal mucosa due to acid reflux from stomach
What is the length relationship between the gastric pits and gastric glands in the fundus and body of the stomach?
gastric pits in these regions are relatively short
and gastric glands in these regions are relatively long
What are Gastric pits and gastric glands are lined with?
Surface mucous cells Mucous neck cells Parietal cells Chief cells Enteroendocrine cells Stem cells
Where are surface mucous cells?
line the luminal surface and the upper portion of the gastric pits
What do surface mucous cells look like?
pale staining simple columar cells
What kind of mucous do surface mucous cells secrete?
secretes a very thick, viscous protective mucous coating for stomach lumen
Where are mucous neck cells?
located deep in the gastric pit or superficially in the gastric gland (i.e., neck)
What do mucous neck cells look like?
pale staining simple cuboidal to columar cell
What kind of mucous do mucous neck cells secrete?
secretes mucous (of a thinner nature than surface mucous cell mucous)
Where are Parietal (Oxyntic) Cells located?
predominate cell type in the upper two-thirds of the gastric glands
What do Parietal (Oxyntic) Cells look like?
large pyramidal to round cells
eosinophilic cytoplasm and sometimes binucleated
What do Parietal (Oxyntic) Cells secrete?
secrete HCl
Where are Chief (Zymogenic) Cells located?
usually limited in location to the lower third of the gastric glands
What do Chief (Zymogenic) Cells look like?
have all the characteristics of a typical protein secreting cell
* basophilia, granular cytoplasm, nucleolus
What do Chief (Zymogenic) Cells secrete?
secrete pepsinogen
Where are Enteroendocrine Cells located?
located in the lower parts of the gastric gland
What do Enteroendocrine Cells look like?
pale staining cell
What is unique about the position of Enteroendocrine Cells’ secretory vesicles?
secretory granules are adjacent to the basement membrane
What and where do Enteroendocrine Cells secrete?
secrete gastrointestinal hormones in response to luminal conditions
- gastrin
- motilin
What effect does gastrin have?
stimulates acid production by parietal cells
What effect does motilin have?
stimulates smooth muscle activity
What do Gastric Stem Cells look like?
pale columnar cell difficult to distinguish from a mucous neck cell
What do Gastric Stem Cells give rise to?
give rise to replacement cells for each of the stomach epithelial cell types
What is the average life span of a mucous cell?
mucous cells have a life span of about 3-5 days
What is the average life span of a parietal, chief or enteroendocrine cell?
parietal, chief and enteroendocrine cells have a life span of about 1 year
Where is the Pyloric Region of Stomach?
evident where the body narrows as it gets close to the duodenum
What is the importance of the pyloric sphincter?
thickening of the muscularis externa
which regulates the outflow from the stomach
What is the length relationship of the gastric pits and the gastric glands in pyloric region of the stomach?
gastric pits are relatively long and gastric glands are relatively short
What kind of cells line the gastric pits and gastric glands in the pyloric region of stomach?
predominately mucous secreting cells
What is the most common cause of ulcers?
most commonly due to a chronic infection by helicobacterium pylori
- causes the protective mucous layer in the stomach to break down
What happens as the stomach mucous breaks down?
acid in the stomach can eat away the epithelium and lamina propria
What may happen in very severe cases of stomach ulcers?
in severe cases a hole can be made in the stomach wall
Why are severe cases of stomach ulcers so dangerous?
Would allow gastric contents to enter the peritoneal cavity. This condition can lead to peritonitis and even death
What are the two main functional activities of the small intestine?
digestion is completed and the products of digestion are absorbed here
To optimize absorption and digestive activities, what must the small intestine prolong contact between?
- chyme and digestive enzymes
- digested products and the absorptive cells of the epithelial lining
What are the three sections of the small intestine?
Duodenum
Jejunum
Ileum
What small interestinal features faciliate absorption?
Plicae circulares
Villi
Microvilli
What is the gross anatomical appearance of plicae circulares?
circular mucosal folds with submucosal cores
Where are plicae circulares most prevalent?
most prevalent in the distal duodenum and the jejunum
How much do plicae circulares increase surface area?
increases intestinal surface area about 3-fold
What is the villi histological structure?
finger-like mucosal projections with cores of lamina propria
Where are they the villi most prevalent?
common throughout the small intestine
How much do villi increase surface area?
increases intestinal surface area about 10-fold
What is the histological structure of microvilli?
apical cytoplasmic extensions covered by cell membrane
Where are microvilli most prevalent?
finger-like projections on luminal surface of the absorptive epithelial cells
What provides support to microvilli?
actin cytoskeletal core linked to cell membrane and the terminal web
What is the terminal web?
layer of actin at the apical side of cell
What is terminal web function?
significantly increase membrane surface area available for absorption/secretion
What is the striated border?
about 2000-3000 microvilli present on each cell that form a layer known as the striated border
How much does does microvilli increase surface area?
increases intestinal surface area about 20-fold
What is the cumulative increase in surface area resulting from plica circulares, villi and microvilli?
increase small intestinal surface area 600-fold to a total of about 200 square meters
How is the small intestinal mucosa protected from carry-over gastric juice digestion?
mucosa is protected by mucous secreted by goblet cells and Brunner’s glands
What enzymes do enterocytes secrete?
enterocytes secrete disaccharidases and dipeptidases
What enzymes come from the pancreas?
1) trypsinogen, chymotrypsinogen and carboxypeptidase - digest protein
2) amylase - digests carbohydrates
3) lipase - digests lipids
4) deoxyribonuclease and ribonuclease - digest nucleic acids
What comes from the liver for digestion in the small intestine?
bile salts - digest lipids
What is the small intestional villi morphology?
cells (enterocytes) and goblet cells
What kind of epithelial covering is present?
covered by simple columnar absorptive
What does simple columnar mean?
Column shaped and one layer
What is the distribution pattern for goblet cells?
goblet cells continually increase in number distally in the intestinal tract
What layer forms the core of a villous?
Lamina propria
What layer Contains neurovascular and lymphatic elements?
Lamina Propria
Where are junctional complexes located?
found at apical end of columnar cells of GI tract
What are the 3 components of junctional complexes ?
zonula occludens (tight junction) zonula adherens macula adherens (desmosome)
Why are zonula occudens known as a tight junction?
no intercellular gap exists (occludes the intercellular space)
What are sealing strands?
IMPs on adjacent cells
How does zonula occudens act as a barrier?
Controls travel through a cell instead of in between cells.
Prevents water soluble components but fat soluble are unaffected
Why is it zonula occudens selectively leaky?
disallows travel between adjacent cells (selectively leaky)
What is the difference between zonula occulens and zonula adherens?
Zonula occludens have no intercellular gap and function to be a selective barrier for entry into the lumen
Zonula adherens have intercellular gaps and function to lateral adhere epithelial cells and incorporate actin
What is the terminal web of zonula adherens?
cytoskeletal elements incorporated internally by zonula adherens
What is the function of a zonula adherens?
lateral adhesion between epithelial cells
How is the strength compared to ZO?
Stronger as every zonula occudens is supported by a zonula adherens
What is a Central Lacteal?
central lymphatic capillary
What does a central lacteal do?
participate in the absorption and transport of lipids
Where is Central Lacteal found?
in the lamina propria core of each villous
How are products of fat digestion transported away from the small intestine?
1) products of fat digestion are monoglycerides and free fatty acids
2) these are absorbed by villous columnar cells and used in lipid synthesis
3) lipid-containing vesicles are produced and released into the intercellular space (deep to the junctional complexes)
What are the produced fat globules known as?
Chylomicrons
How does the delivery of chylomicrons into the blood differ from other metabolites?
chylomicrons reach the blood indirectly by first entering the lacteal and being transported by lymphatics
What is the morphology of intestinal crypts?
simple or compound tubular invaginations between the villi and surrounded by lamina propria
what does the Epithelial lining of intestinal crypts consist of?
simple columnar absorptive cells and goblet cells, paneth cells, enteroendocrine cells and crypt base stem cells
What do paneth cells look like?
large cell with very large distinctive acidophilic cytoplasmic granules
What do paneth cells do?
granules contain lysozyme (antibacterial)
What do enteroendocrine cells look like?
pale staining columnar cell
What do enteroendocrine cells do?
small basophilic secretory granules basally located in the cell
What do the crypt base stem cells do?
may give rise to paneth, enteroendocrine, goblet or simple columnar absorptive cells
How does Intestinal Mucosal facilitate absorption?
via striated border on enterocytes
How does Intestinal Mucosal facilitate digestion?
via enzyme secretion by enterocytes
How does Intestinal Mucosal provide protection?
via mucous secretion and junctional complexes
Why is the small intestine lamina propria very well vascularized with type II capillaries?
involved in absorption of nutrients
What kind of tissue is the lamina propria?
loose CT heavily populated with immune system cells (GALT)
Why is there a lot of GALT in the intestines?
protection from ingested pathogens
What are Peyer’s patches?
Aggregations of lymphoid nodules typically found in the ileum
What does intrinsic innervation mean?
Regulation occurs within the structure
What does extrinsic innervation mean?
Regulation occurs by nervous system
Where is Auerbach’s myenteric plexus located?
Between two layers of the muscularis externa
What activity does Auerbach’s myenteric plexus regulate?
regulates contractile activity of the muscularis externa
Where is Meissner’s submucosal plexus located?
located in the submucosa
What activity does Meissner’s plexus regulate?
regulates gastrointestinal secretion and local blood flow
What effect does parasympathetic and sympathetic innervation have on intestinal activity?
Parasympathetic innervation - stimulates intestinal smooth muscle activity
Sympathetic innervation - depresses intestinal smooth muscle activity
What are some distinctions in the duodenum?
1) Entirely retroperitoneal
2) receives ducts from liver and exocrine portion of pancreas
3) contains villi and crypts with moderate numbers of goblet cells
4) contains Brunner’s glands
Where specifically are brunner’s glands located?
In the duodenum
What do they Brunner’s glands secrete?
secrete alkaline mucoid material and urogastrone
Why is all this mucous required in the duodenum?
1) protects mucosal surface by neutralizing the acidic chyme
2) brings pH up to an optimal level for pancreatic digestive enzymes to work
What effect does urogastrone have?
inhibits acid secretion by the stomach
What are some distinctions of the jejunum?
1) main absorptive unit in the small intestine
2) greatest number of plical folds with most complex arrangement of villi
3) Paneth cells are most easily seen here in the bottom of intestinal crypts
What are some distinctions of the ileum?
1) greatest collection of GALT (Peyer’s patches)
2) goblet cells are most numerous here
3) villi and crypts present with rare Paneth cells
4) Brunners glands absent
What is the primary function of large intestine?
completes absorption and retrieves water from luminal contents leaving
compact indigestible waste residue (feces)
What and where are the regions of the colon grossly?
Cecum
Ascending, transverse, descending and sigmoid colon
Rectum
Anal Canal
Are there any villi in the large intestine?
No, luminal surface is “smooth”
Are there any crypts in the large intestine?
yes, fairly thick with deep crypts compared to the small intestine
By what mechanism does digestion occur in the large intestine?
digestion may continue here as a result of residual enzymatic action as well as decomposition by bacteria
Where does the mucous come from in the large intestine?
epithelial lining produces abundant mucous but no digestive enzymes
What is absorbed in the large intestine?
mainly water
What do the columnar absorptive cells do in the large intestine?
play no active role in digestion
primary function is water and electrolyte absorption
What is the distribution pattern for the goblet cells in the large intestine?
increasing in number proportionately from ascending colon to rectum
Are there stem cells present in the crypts in the large intestine?
located at the base of the crypts
mitotically replaces both the columnar absorptive and goblet cells
What is the turnover rate for differentiated cells in the large intestine?
differentiated cells are shed in the lumen every 6 days or so
How does the lamina propria and submucosa compare from small intestine to large intestine?
Pretty similar, except there are no submucosal Brunner’s glands
Why are the lamina propria and submucosa of the large intestine usually rich in GALT?
presumably as a response to the abundant luminal bacterial population
What are teniae coli?
longitudinal layer of smooth muscle arranged in three
longitudinal bands along the cecum and colon (lacking in the appendix)
Are there any advantages of teniae coli in the large intestine?
maintain tonus and allow the remainder of the wall to sacculate
What comprises the internal anal sphincter?
thickening of the circular layer of smooth muscle at the anal-rectal junction
What controls internal anal sphincter activity ?
under autonomic control and responds to distension
What comprises the external anal sphincter?
consists of skeletal muscle
What controls external anal sphincter activity ?
voluntary control of defecation
Is the large intestine covered by serosa or adventitia?
retroperitoneal segments of colon and rectum covered by adventitia and remainder is covered by serosa
What is the epithelial transition at the anus?
simple columnar epithelium -> stratified squamous nonkeratinized -> stratified squamous orthokeratinized
Where is the appendix?
blindly ending tubular diverticulum of the cecum
What does appendix look like grossly?
about 5-10cm long; 0.8cm in diameter
What does appendix look like histologically?
resembles other parts of the large intestine
What is appendicitis?
results largely from blockage of its lumen or twisting
Why does appendicitis occur?
1) prone to bacterial infection
What is the risk associated with perforation of the appendix?
may become inflamed and risk perforation which would spread bacteria into peritoneal cavity (bacterial peritonitis)
What is an appendectomy?
common surgical procedure to remove inflamed appendix
What are the accessory glands of digestion?
1) Salivary Glands (Parotid, Submandibular, Sublingual)
2) Pancreas
3) Liver
Where is the pancreas located?
mixed exocrine and endocrine gland located in the “C” shaped duodenal loop
What is an exocrine gland?
Contains a duct
What is an endocrine gland?
Does not contain a duct
How can the pancreas be both?
Secretes enzymes through a duct and hormones directly into the blood
What does compound acinar mean?
branched ducts with cluster of cells
What percentage of pancreatic tissue is exocrine?
occupies the bulk of the pancreatic tissue (98 -99 %)
What do the serous secreting cells look like?
1) very basophilic triangular shaped cells
2) basal spherical nucleus with apical zymogen granules
What enzymes are produced in the pancreas?
1) trypsinogen, chymotrypsinogen and carboxypeptidase digest proteins
2) amylase digests carbohydrates
3) lipase digests lipids
4) ribonuclease and deoxyribonuclease digest nucleic acids
Where are digestive enzymes delivered to?
Duodenum
What percentage of pancreatic tissue is endocrine?
1-2%
What do the pancreatic islets look like?
pale staining islets (of Langerhans) scattered throughout the exocrine pancreas
Where are the hormones delivered to?
Blood
What percentage of islet cells produce insulin? (beta cells)
70%
What action does insulin have?
Lowers blood sugar
What percentage of islet cells produce glucagon? (alpha cells)
15-20%
What action does glucagon have?
Increase blood sugar
What percentage of islet cells produce somatostatin? (gamma cells)
5-10%
What action does somatostatin have?
Inhibits insulin and glucagon secretion
Why is the liver described as the principal metabolic organ in the body?
organ where nutrients absorbed in digestive tract are processed for use by other
parts of the body
What is the body’s largest compound gland?
Liver
What are the functions of the liver?
carbohydrate metabolism and storage plasma protein and lipoprotein synthesis and secretion drug and alcohol detoxification bile formation and secretion fetal hematopoiesis
How many lobes make up the liver?
2, left and right lobes
Is the liver covered by serosa or adventitia?
Serosa
What and where is the porta hepatis?
deep transverse fissure on inferior surface of liver (essentially a hilum)
What enters the porta hepatis?
major blood vessels, ducts and lymphatics
What percentage of blood enters the liver via the proper hepatic artery?
25% comes via proper hepatic artery
Where is the blood from the proper hepatic artery coming from and what is its composition?
highly oxygenated arterial blood coming indirectly from aorta (via celiac trunk)
What percentage of blood comes via the hepatic portal vein?
75% comes via hepatic portal vein
Where is blood from the hepatic portal vein coming from and what is its composition?
1) poorly oxygenated but nutrient rich venous blood from the intestinal tract
2) Broken down products due to blood cell degradation in the spleen
Does the blood from the hepatic portal vein and the proper hepatic artery mix
at the porta hepatis?
no, blood from these two vessels will mix in the liver sinusoids
What are liver sinusoids?
sinusoids are type III capillaries located between the rows of hepatocytes
What happens with the blood in the liver sinusoids?
Blood from the hepatic portal vein and the proper hepatic artery mix together
Where does the venous drainage from the liver go?
drain from the liver via the hepatic venous system
What is the path the efferent lymphatics use to exit the liver?
efferent lymphatics travel with the BVs and bile ducts and exit at the porta hepatis
Why are there no afferent lymphatics?
???
What are Bile canaliculi?
small bile ducts (canaliculi) that form in the liver parenchyma
Where do the bile canaliculi drain into?
bile ducts
What structures do bile ducts travel with?
Blood vessels and lymphatics
What do bile ducts combine to become?
Right and left hepatic ducts
What do the right and left hepatic ducts combine to form?
Common hepatic duct
What do the common hepatic duct and cystic duct combine to form?
Common bile duct
What are hepatocytes?
parenchymal cell of the liver
What do hepatocytes do?
carries out all of the biochemical functions of the liver
What do are some properties of hepatocytes?
Euchromatic nucleus Prominent nucleoli Abundant mitochondria Extensive RER and SER Several Golgi apparati Abundant glycogen particles
How does the hepatocyte nucleus appear?
large spherical and central with prominent nucleoli
Why is there extensive rough endoplasmic reticulum in hepatocytes?
extensive for synthesizing plasma proteins and lipoproteins
What is there extensive smooth endoplasmic reticulum in hepatocytes?
extensive for lipid and cholesterol synthesis and drug/alcohol detoxification
Why are there several golgi apparatus in hepatocytes?
several typically present for packaging products for secretion
Why are glycogen particles present in hepataocytes?
abundant for storing glucose
Why does approximately 70% of the hepatocyte cell surface border sinusoids?
maximizes the surface area available for exchanging materials with the blood
Why does approximately 15% of the cell surface border bile canaliculi?
facilitates secretion into the bile duct system
What’s happening along the remaining 15% of the cell surface?
both adhering and communicating junctions are present
What happens to most of the water, cholesterol and ions in the body?
largely reabsorbed and recycled in the gut
Why are the bile salts important?
1) facilitate digestion and absorption of fats in the intestines
2) largely reabsorbed in the gut and recycled to the liver
Where does the bilirubin come from?
waste product of hemoglobin degradation in the spleen
What happens to conjugated bilirubin?
excreted in the feces and gives them color
How does bile get from the liver to the duodenum?
bile is transported in bile ducts from liver to gall bladder where it is stored and concentrated prior to excretion into duodenum
What is the gall bladder used for?
bile is transported in bile ducts from liver to gall bladder where it is stored and concentrated
What does a jaundiced person look like?
creates a distinctive yellow color (easily seen in skin and sclerae
Why does the jaundice yellow color occur?
1) excess bilirubin pigment accumulates in blood and tissues
2) results from inadequate removal of bilirubin from blood by hepatocytes
Why would excessive erythrocyte degradation lead to jaundice?
causes extra bilirubin from destroyed RBC’s resulting on inadequate removal of excess bilirubin
How could hepatocyte problems cause jaundice?
The removal of the bilirubin via the conjugated form is impaired and thus bilirubin builds up in the blood and tissues without being properly removed
What about gall stones?
Gall stones are due to the calcification of bile typically in the bile ducts therefore obstructing the bile duct and causing pain
What is the typical diameter of a liver sinusoid?
sinusoids are vascular channels 10-30m in diameter
What kind of endothelium is present in liver sinusoids?
lined by a discontinuous, highly fenestrated endothelium
Is there a basement membrane in liver sinusoids?
the basement membrane is discontinuous or missing from large areas
What is the perisinusoidal space or space of Disse?
space located between the rows of hepatocytes and the sinusoidal endothelium
What structures extend from the hepatocytes into the perisinusoidal space?
the microvilli extending from the hepatocytes
Why do hepatocytes have microvilli in the perisinusoidal space?
increase the surface area about 6x
What is significant about the space of Disse?
this is the space in which bidirectional transfer occurs between the hepatocytes and the blood plasma
What are Kupffer cells?
permanent population of sinusoid-associated macrophages that are derived from monocytes
Where are Kupffer cells located?
line the sinusoid and sometimes span across the sinusoidal lumen
What do Kupffer cells do?
keep the sinusoid clear of particulate
What happens to Kupffer cell activity following splenectomy?
subsequent to splenectomy, play an active role in erythrocytic turnover
What is the classic liver lobule?
Basically hexagonal with rows of hepatocytes and sinusoids radiating away from the center
What and where is the central vein?
this is the initial hepatic venule at the center of the classic lobule
What drains into the central vein?
the liver sinusoids drain to the central vein
Where does the central vein ultimately drain to?
heptic venous system?
Where are the portal triads located in the classic liver lobule?
found in Connective Tissue portal tracts at the corners of the hexagonal lobule
What kind of blood is in the hepatic portal vein?
1) nutrient rich venous blood from the intestines
2) venous blood from the spleen containing bilirubin
What kind of blood is in the hepatic artery?
oxygen rich blood (indirectly from the aorta)
How does bile flow in the classic liver lobule?
bile duct carries bile away from the hepatocytes
How does blood flow in the classic liver lobule?
from hepatic portal vein and/or hepatic artery into liver sinusoids and out via the hepatic vein
Where does the lymphatic vessel go from the liver lobule?
???
A liver acinus is a functional model of liver tissue in relationship to what?
relation to its blood supply
How does the liver acinus shape and location relate to the classic liver lobule?
corresponds to roughly ovoid mass of liver parenchyma extending over contiguous regions of two adjacent classic lobules
Where is zone 1 in the acinus located?
located at the contiguous borders of 2 classic liver lobules
Why is zone 1 in the acinus described as being a relatively privileged location?
1) nearest the portal triads and furthest from the central vein
Why are cells in zone 1 in the acinus least susceptible to hypoxia?
hepatocytes in this zone receive nutrient rich and oxygen rich blood primarily
Why are in zone 1 in the acinus most susceptible to blood borne toxins?
hepatocytes in this zone receive first contact with the toxins
Where is zone 3 in the acinus located?
these liver cells are furthest from the portal triads and closest to the central vein
Why is zone 3 in the acinus described as being a less desirable location than zones 1 and 2?
blood delivered here is low in oxygen and nutrients
Why are cells here most susceptible to ischemic necrosis?
these hepatocytes are most susceptible to ischemic necrosis (due to hypoxia)
Why are these cells the last to respond to blood borne toxins?
last to respond as they are furthest away from contact to the toxins
