11 & 12: Digestive System: Alimentary Canal (1 & 2)

Front 1

Esophageal Tissue Layers

Back 1

MUCOSA: **esophageal folds of mucosa run parallel to long axis of organ - not encirciling lumen.
- EPITHELIUM: THICK layer: nonkeratinized stratified squamos epithelium continuous with pharynx -> renews itself through mitosis of stem cells in basal layer
- Langerhan cells: antigen presenting functions - for defense of surrounding tissues
LAMINA PROPRIA: papillae undulates into epithlium to increase surface area between the two tissues to bind them together
- Well Vascularized!!: rich in capillaries in nerves (if epithelium is broken, get bleeding from this rich bed of blood vessels)
- not very cellular
- accumulations of diffuse lymphatic tissue
MUSCULARIS MUCOSA: only Longitudinal smooth muscle!!
- thin and discontinuous in upper esophagus -> thicker and more continuous in lower esophagus

SUBMUCOSA: loose CT - esophageal MUCOUS glands
- rich elastic fiber network: impt for reclosure of lumen follow peristalsis of food
- Submucosal Plexus (Meissner's)
-lymphatic tissues, adipose cells, nerves, and BV's
MUSCULARIS EXTERNA: 2 layers
- Upper esophagus: only skeletal muscle! - voluntary control
- Middle: both smooth and skeletal; smooth appears first in inner circular and then eventually outer long. until all smooth!
- Lower: all smooth - involuntary control
- Auerbach's plexus - between 2 layers
SEROSA/ADVENTITIA:
- Cervical/Thoracic (above diaphragm): Adventitia
- After Diaphragm: Serosa (peritoneum)

Front 2

Esophagus-Stomach Junction

Back 2

Esophagus -> LES -> Stomach

Esophagus: nonkeratinized stratified squamos epith.

LES: NO thickening of muscularis externa b/c physiological sphincter under ANS control (& some function by diaphgram constriction)

Stomach: simple columnar epithelium, 2 layers of muscularis mucosae, 3 layers of muscularis externa: middle circular, outer longit., inner oblique: facilitates churning and persitalsis

Front 3

Stomach Layers

Back 3

MUCOSA: thick layer, smooth when relaxed but has Rugae when contracted (incorporates into submucosa that flatten when distended)
**Epithelium: simple columnar Surface Mucous Cells (NOT goblet cells)
- Gastric pits: invaginations of surface mucous columnar epith.
*where cells that are for replacement of damaged luminal cells are found
-base of pits RECEIVE INFO FROM LONG TUBULAR GLANDS that differ in stomach regions
**Lamina Propria: infiltrated with GLANDS!
**Muscularis Mucosae: 2 layers - forms MUCOSAL RIDGE

SUBMUCOSA:
- NO GLANDS (unlike esophagus and duodenum)
- Meissner's plexus present
- Rugae

MUSCULARIS EXTERNA:
3 layers to maximize churning and peristalsis: inner oblique, middle circular, outer longitudinal
- Auerbach's plexus

Front 4

Glands beneath Gastric Pits

Back 4

glands empty into the gastric pits -> lumen of stomach
- glands found in MUCOSA LAYER: takes up most of lamina propria - beneath Gastric pits

Front 5

Cardiac Glands

Back 5

-Cardiac: where esophagus enters stomach (small part)
- simple or branched tubular glands that are the same length as the gastric pits
- Predominate in MUCUS SECRETING cells (differ from surface mucous cells & neck cells)
- Parietal Cells: secrete HCl and IF into lumen and HCO3- into lamina propria

Front 6

Gastric Glands

Back 6

MAIN STOMACH GLANDS!! - glands of Fundus and Body that secrete Digestive Agents

- Branched Tubular glands - 3-7 glands empty into 1 gastric pit base

5 CELL TYPES in gland walls:
1) PARIETAL(oxynitic cell):
- secrete HCl and IF
- large, oval, and eospinophilic plasma (pumps ions from the cell into lumen of gland)
- bulge laterally into surrounding CT
- mainly in UPPER part of glands, up into the base of pits
2) CHIEF (peptic or zymogenic) cell: produce pepsiongen and weak lipase for pancreas
- round nucleus, BASOPHILIC cytoplasm due to ribosomes
- typically artifactually light staining
- usually at BASE of gland
3) MUCOUS "neck" cells:
- concentrated in neck (superficial area) of glands
*DIFFER FROM SURFACE mucous cells:
- secrete soluble mucus vs. surface mucous cells that are INsoluble)
-shorter than surface mucus cells
- less mucinogen in apical cytoplasm
(mucinogen + h20 = mucin) but mucinogen is what stains!
4) STEM cells: small columnar cells in UPPER region of glands and base of pits
- few in quantity but give rise to:
1) all cells of gland
2) surface mucous cells (those residing in pits)
5) ENTEROENDOCRINE (EEC): aka enterochromaffin/argentaffin cells:
- single endocrine cells dispersed near BASE OF GLAND - endocrine secretion!
- cytosplasmic SPHERICAL BASAL granules that contain hormone
- secretions important for motility and glandular secretions
ie) glucagon, somatostatin, gastrin

**1 cell secretes 1 hormone!

Front 7

Pyloric Glands

Back 7

3 Cell Types: no parietal or chief cells!
1) MAINLY mucous cells - mucinogen-PALE-takes up most of cell cytoplasm volume, NUCLEUS PUSHED FAR TO BASE!
2) EEC's: G cells and D cells: light eospinophilic (looks like parietal cell but nucleus more in center)
**ENTER LOCAL CIRCULATION OF GI
3) some stem cells

Short length glands compared to long Gastric glands

Front 8

Pyloric Stomach-Duodenum Junction (Pyloric Sphincter)

Back 8

Fundus of Stomach -> Duodenum of Small Intestine

STOMACH FUNDUS:
- uniform surface mucus cells
- undulating muscularis mucosae that follows mucosa
SUBMUCOSA:
- rugae - folds of submucosa that flatten with distension
- rich in caps/BV in CT

PYLORIC SPHINCTER: anatomical!
thickening of stomach's muscularis externa's Inner circular and oblique layers! (hypertrophy)
-closes down with each peristalic contraction to allow only fluids and small material to pass through to small intestine
- RETROGRADE movement: allows churning of food and homogenization of chyme in stomach!

DUODENUM:
- Submucosa - BRUNNER's GLANDS: pure mucous submucosal glands

Front 9

Rugae

Back 9

Infolding of submucosa

1) In stomach
2) Esophagus
3) Large Intestine
**serves to increase surface area and allow for storage of food
- flattens out when food enters (distension) VS PLICAE CIRCULARIS in small intestine - circular folds that are always there!

Front 10

GI TRACT COMPONENTS

Back 10

22-25 feet long hollow tube
- 4 separate organs that connect oral cavity with anus
1) Esophagus: 1 foot
2) Stomach: 1 foot
3) Small Intestine: 15 feet
4) Large Intestine: 5 feet

- ENTERIC NS

Front 11

FUNCTION of GI

Back 11

1) Mechanical Propulsion: peristalsis
2) Digestion: physical and chemical breakdown
3) Absorption: uptake into system of needed substances
4) Protection: defenses that prevent or limit invasion by ingested viruses and bacteria, also protection against self digestion

Front 12

ENTERIC NS

Back 12

- GI has efferent neurons, afferent, and inerneurons
- can carry out reflexes in absence of CNS input
- motor neurons control intestinal muscles and peristaliss and churning of intestinal contents
- 2 TYPES OF GANGLIA:
1) Auerbach's myenteric plexus
2) Meissner's submucosal plexus

Front 13

Lower Esophageal Sphincter

Back 13

- Physiological sphincter: no pronounced thickening of inner circular layer at junction but a specialized szone of somewhat thickened circular muscle surround esophagus as it traverses the diaphgram and continues into abdomical regiion
- this thickened circular muscle is maintained under TONIC contraction except w/ swallowing
- controlled by Eneteric NS and protects against reflux of acid from stomach
- diaphgram also contributes to esophageal sphincter function
**becomes in lower part under diaphgram, part of abdominal pressure!! harder to reflux!

Front 14

Hiatus Hernia

Back 14

Bulging of the stomach through the diaphragm into thoracic cavity:
- can cause ACID REFLUX BECAUSE MORE FAVORABLE GRADIENT!!

Front 15

Protective Mechanisms of the Esophagus

Back 15

1) thick stratified nonkeratinized squamos epithelium of mucosa
**renewed every 5-7 days from basal stem cells
2) dispersed lymphatic tissue in lamina propria and submucosa
**B lymphocytes from plasma cells that produce antibodies
**more lymphatic tissue near esophageal glands because have simple cuboidal spithelium at ducts

Front 16

Swallowing/Problems with Esophagus

Back 16

Problems with Esophagus will present as Dysphagia:
1) Physical Blockage: lumen growth causes impingement -> malignant!
2) Aclasia: no innervation from myenteric plexus, so no sympathetic innervation and no relaxation of LES
- tonically active so food gets stuck in esophagus (dilated esophagus)

Front 17

Esophagus: MAIN FUNCTION

Back 17

1) Propulsion
2) Protection

Front 18

Stomach: Main Function

Back 18

1) Digestion - physical and chemical
2) Propulsion
3) Protection (also from self!)

Front 19

Mucosal Ridges

Back 19

Formed from smooth muscle fibers in muscularis mucosa of Stomach extending into interglandular lamina propria

Front 20

Protection mechanisms of Stomach

Back 20

1) Surface Mucous Cells - protect from normal "wear and tear"
2) Secreting Mucous cells in Cardiac region and Pyloric area
3) HCO3- from Parietal Cells: neutralize any H+ that may leak through
4) replacing surface cells via stem cells every 3-5 days
5) if above mech's DONT WORK --> Rapid Re-Epithilization

Front 21

Rapid Re-Epithelization:

Back 21

- occurs when surface mucus cells are lost or HCO3- doesn't protect cells
- Migration of Surface mucous cells located WITHIN gastric pits (protected b/c exposed to less toxin) -> surface to replace damage surface mcuous cells
- Simple Columnar Epithelium Surface Mucus Cells -> Squamos Epithelial Lining (20 min) --> back to columnar cells (if not constantly damged)

** if constant damge: no repopulation of by stem cells and surface epithelial cells lost --> ULCERS due to lack of ability of cells in pits to re-epithelialize surface

Front 22

Mucosal Geometry of Large Intestine

Back 22

Epithelium:
-Intestinal Glands = CRYPTS OF LIEBERHUKHN
- Enterocytes have Microvill (but less developed as those in small intestine)

Submucosa:
1) Meisner's plexus
2) Rugae

Muscularis Externa:
1) Auerbach's

Front 23

Mucosal Geometry of SMALL intestine

Back 23

Epithelial Layer:
- Microvilli - folds in enterocyte plasmolemma with actin filaments (cell membrane)
- Enterocytes
- Terminal Bar/Web
- Intestinal Glands = Crypts of LIberkhukhn

Lamina Propria:
- Intestinal villi: highly vascularized folds of lamina propria that extend up into lumen --> increases SA of small intestine to increase absorption
Muscularis Mucosae:
discontinous throughout small intestine because of structures such as
1) Brunners glands - submucosal glands in duodenum
2) Peyer's patches - GALT in ileum (SUBMUCOSA!!)

Submucosa:
1) Plicae Circulares (Valves of Kerkring): similar to rugae but don't disappear with distension of lumen.
- Function: slow the passage of intestinal contents and increase absoprtive surface area.
- Large in upper small intestine and diminishes in frequency towards distal ileum.
2) Brunner's glands - mucosal glands!!
3) Meisnesser's plexus (also Auerbach's)

Front 24

Cells of Luminal Epithelium: COLON

Back 24

1) Enterocytes - absorptive cells (less frequent than in Small intestine
- responsible for ionic exchange and other transepithelial transport activities (ie. ionic regulation and h20 resoprtion)
- Enteroctyes have apical microvill

2) Goblet cells: secrete mucus --> more found in distal small intestine than in duodenum
**for fecal lubrications - very abundant in lower colon and rectum!

3) M (microfold) cells: flattened cells with basal folds that overlies GALT
- transport stuff from lumen to lymphocytes in gut

4) Stem cells: lie in middle of Intestinal glands
- migrate up and down to replace mature cells

5) EEC: solitary hormone produce cells located throughout epithelium but mainly in base of gland
- triangular shaped, basal zymogen granules (secrete hormones to blood
- each cell -> different hormone!

Front 25

Small Intestine Luminal Epithelium Cells

Back 25

Intestinal Villi have terminal bars/webs so material needs to pass THROUGH ENTEROCYTES & not between them.

CELLS:
1) Enterocytes: highest in frequency (Duodenum > colon)

2) Goblet cells: lowest in frequency (Colon > Duodenum)
EXOCRINE cell

3) EEC (APUD): present at base of crypts and on surface of intestinal villi
- AMINE precursor uptake and decarboxylation

4) M cells

5) Stem Cells

6) PANETH CELLS:
EXOCRINE cells - in BASE of glands/crypts
- eosinophilic granules packing apical cytoplasm
- lysozyme: - stains eosinophilic
- Zinc - binds Pb-Hematoxylin as black
**BREAKDOWN PRODUCTS BROUGHT TO M CELLS -> LYMPHOCYTES = Immune exclusion

Front 26

Central Lacteals & Pathway of lipids

Back 26

present in SMALL INTESTINE - INTESTINAL VILLI
- lymphatic vessels that transport CM from intestines and deliver lipids to circulation

PATHWAY of LIPIDS (CM):GOES THROUGH LYMPHATIC CIRCULATION FIRST -> SYSTEMIC CIRCULATION -> PORTAL CIRCULATION (intestine, heart, liver)
CM made in Small intestine -> central lacteal -> lymphatic ducts -> thoracic ducts -> inferior/superior vena cava-> hepatic artery -> liver

**CENTRAL LACTEAL - WITHIN THE BASAL SIDE OF ENTEROCYTES IN INTESTINAL VILLI

Front 27

Mesentery

Back 27

pathway for blood vessels and nerves that go to and from the Small intestine

*attached jejunum and ileum to abdominal wall

Front 28

Differences in Submucosa of Small Intestine: Duodenum vs. Jejunum vs. Ileum

Back 28

DUODENUM
1) Brunner's glands
2) high frequency of enterocytes
3) high frequency of Plicae Circularis

JEJUNUM:
1) NO Brunner's glands or Peyer's patches

ILEUM:
1) Peyer's patches
- 10 lymph nodules
- patches of follicles and interfollicular lymphoid tissue = GALT (specific to ileum: always present!!)
2) INTRAepithelial lymphocytes: migrated from underlying lymph tissues
ie. M cells: always overlying GALT - important for TRANSPORT (not APC's or macrophages)
3) Unnamed GALT

Front 29

Ileoceccal Valve

Back 29

Ileum -> Cecum

Ileum:
MUCOSA:
- intestinal villi: rapped mucosal lining
- Crypts of Liberkuhn

ILLECOCECCAL VALVE: no sphincter!
- thickening fold of tissue
- extension muscularis externa of colon wall
- in TONIC contraction by SYMPATHETIC innervation
- VALVE PREVENTS REFLUX from cecum to ileum
- may act as a SPHINCTER: prevent ileal contents into cecum

Colon:
MUCOSA:
- smooth mucosal lining
- simple tubular glands (no microvilli)

Front 30

Large Intestine: Colon->Rectum

Back 30

SURFACE EPITHELIUM:
- Intestinal glands - crypts
- high frequency of GLOBLET CELLS (highest in rectum)
- low frequency of enterocytes

Muscularis Externa:
- Taeniae Coli: 3 evenly spaced longitudinal bands of outer longitudinal muscle (but not present in rectum!!)

Front 31

Large Intestine: Rectoanal Junction

Back 31

BASICALLY WHERE PECTINATE LINE IS (right before start of External sphincter which does overlap with internal anal)

AT JUNCTION:
- termination of muscularis mucosae
- dense irregular CT in lamina propria
- Submucosa and lamina propria - highly vascular!! ie) NEAR OR IN AREA OF EXTERNAL SPHINCTER has HEMORRHOIDAL veins --> hemororhoids!)
**RECTUM
-part of large intestine: dilated portion of it
- HIGHEST frequency of GOBLET cells
- NO Taeniae Coli

**ANUS
INTERNAL ANAL SPHINCTER: hypertrophy and extension of circular layer of SMOOTH MUSCLE e of muscularis externa

PECTINATE LINE: site of embryonic anal membrane (Endoderm -> ectoderm); WITHIN ANAL CANAL
- SIMPLE COLUMNAR EPITH. -> Stratified squamos NON keratinized epith (short transition zone) --> STRAT SQUAMOS KERTINZED EPITH. (skin beyond anus!)

EXTERNAL ANAL SPHINCTER:
circumferential RING OF SKELETAL MUSCLE
- not continuous with Internal sphincter

Front 32

Rectum Anal Canal

Back 32

- includes Pectinate Line
- plus or minus 4cm of pectinate line

Front 33

Hemorrhoids

Back 33

2 plexuses veins within Submucosa become distended and varicose
**IN OR NEAR AREA OF EXTERNAL ANAL SPHINCTER!

1) Internal Hemorrhoidal Plexus: above Pectinate line (between rectum and anus; and where intouernal and external sphincter overlap!)

2) External Hemorrhoidal Plexus: occurs at junction of anal canal and anus

Front 34

Crypts of Lieberkuhn

Back 34

= Intestinal Glands (both small and large intestine)

- have stem cells near the base of the pits that renew surface epithelium every 3-5 days and Paneth Cells & EEC cells that turn over every 3-5 weeks

- cells in these crypts secrete salts and H20

Front 35

Digestive Mechanisms of Small Intestine:

Back 35

1) Enzymes from Pancreas - complete digestion of chyme from stomach
a) Amylase
b) Lipase
c) Peptidases
d) Trypsinogen -> trypisin via Enterokinase from Enterocyte glycocalyx

Front 36

Bile Absorption (why important?)

Back 36

- water and bile absorbed in samll intestine

1) liver only produces 3g bile a day but need 10 g for digestion so need to recycle bile for re-processing in liver and gall bladder!
--> complete digestion of fat
2) bile absorption facilitates h20 absorption --> if problem then diarrhea!

Front 37

Protective Mechanisms of Small Intestine

Back 37

1) protect from SELF DIGESTION from acidic chyme!!
- Glycocalyx: glycoproteins surrounding microvilli of enterocytes
- Goblet cells: alkaline secretions coating epithelial surface
- Brunner's glands: alkaline secretions from duodenal glands
- Bile: secreted from liver - alkaline and buffers acidic chyme
- pancreatic fluid: secreted with pancreatic enzymes into lumen of duodenum; alkaline
**NET: secrete alkaline fluid!

2) protection from INVASION OF EXOGENOUS ORGANISMS:
- Lymphoid tissue:
1. Intraepithelial lymphoid tissue in mucosa
2. diffuse lympoid tissue in lamina propria
3. isolated lympoid nodules in lamina propria/submucosa
4. circular aggregations of lymph nodules in ileum (Peyer's Patches - GALT)
5. Paneth cells - secrete lysozyme: lyses walls of bacteria that have survived through the base of the crypts --> IgA
**principal function is "IMMUNE EXCLUSION" - TO DELIVER ANTIGENIC MATERIAL TO M CELLS -> lymphocytes -> immune response triggered > plasma cells (within in Peyer's patches) SECRETE IgA-type antibodies sepcific
(gi tract -> lymph -> gi)

Front 38

Appendicitis

Back 38

acute inflammation of appendix

1) ULCERATION of mucosa - abdominal pain
2) PERITONITIS: inflammation spreads -> bursting of appendix

Front 39

Appendix

Back 39

- filled with diffuse lymphatic tissue and with nodules (looksl ike GALT but NOT peyer's patches)
- lymph nodules contain antibody producing plasma cells and immunocompotent B and T lymphocytes
- no INTESTINAL VOLUME like in small intestine

Front 40

Anal (Rectal Columns) = columns of Morgagni

Back 40

- 1st part of anal canal formed into longitudinal folds --> allow gas to pass out while feces retained
- where columns end = pectinate line (simple columnar epith -> stratified squamos non keratinized epith.

- stratified squamos non keratinized epith -> keratinized at anus to skin

Front 41

External Sphincter

Back 41

addition of skeletal muscle layer (not continuous with circular layer of muscularis externa that thickens in Internal anal sphincter)

- overlaps with some of internal anal sphincter!

- voluntary control!!

Front 42

Immune Exclusion

Back 42

-of SMALL INTESTINE

MECHANISM:
M-cells in the epithelium trans-
port antigens from the lumen to underlying lymphocytes capable of initiating an immune response. Lymphocytes from the stimulated clone of effector and mem-
ory cells then return to the GI tract. In the GI tract plasma cells secrete IgA-type antibodies specific for the antigen previously presented to their lymphocyte precursors. This immunoglobulin is taken up actively by the columnar absorp- tive cells that bind it to the glycocalyx where it protects by “immune exclusion”.

Front 43

HEV

Back 43

specialized post capillary venule in GALT and lymph nodes that is the location of where lymphocytes REENTER FROM BLOOD TO LYMPH!!