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Digestive tract (Stomach (Histology (Simple columnar epithelium: secrete…
Digestive tract
Stomach
J shaped; widest part of alimentary canal
Temporary storage and mixing - 4 hours
into
chyme
Starts sfood breakdown
Pepsin (protein digesting enzyme needing acid environment)
HCL: kills bacteria
Most nutreitns wait until get to SI to be absorbed except
Water, electrolytes, some drugs and alcohol (absorbed through stomach)
Mostly in left upper quadrant
just inferior to diaphragm
Anterior of spleen and pancreas
Tucked under left lower margin of liver
Fundus
Body
Greater and less curvature
Pyloric antrum
Pyloric canal
Pylorus (sphincter)
Rugae
: longitudinal folds: internal surface (helps -distensibility)
Muscularis
: additional innermost oblique layer (along with circular and longitudinal layers)
Histology
Simple columnar epithelium: secrete bicarbonate - buffered mucus
Gastric pits opening into gastric glands
Mucus neck cells
Parietal cells
HCL
Intrinsic factor (B12 absorption)
Chief cells
Pepsinogen (activated to pepsin with HCL)
Stimulated by gastrin
Large Intestine
absorb water and electrolytes
Cecum
Appendix
Colon
Rectum
Anal canal
No villi (fewer nutrients absorbed)
Columnar cells (absorptive cells): taken in water and electrolytes
Lot of goblet cells mucus ( lubricates stool)
More lymphoid tissue ( lot of bacteria in stool)
Teniae coli
(3 longitudinal muscle strips)
Haustra
(puckering into sacs)
Epiploic appendages
(omental or fat poyches)
vermiform appendix
: blind tube
cecum
: 1st part
Ileocecal valve
: between ileum and cecum
Right and left colic flexure
: RUQ and LUQ (hepatic and splenic)
S shaped sigmoid colon
Rectum
In pelvis
No teniae
Strong longitudinal muscle layer
valves
Anal canal
Pectinae line
inferior to it: sensitive to pain
Sphincters:
internal
smooth muscle
involuntary
External
skeletal muscle
voluntary
Defecation
Triggered by stretching of wall, mediated by spinal cord parasympathetic reflex
Stimulates contraction smooth muscle in wall and relaxation of internal anal sphincter
Voluntary motor neurons stimulate relaxation of external anal sphincter ( aided by diaphragm + and wall muscles ( valsalva maneuver)
Liver
Inferior to diaphragm (RUQ and epigastric area protected by ribs)
R and L lobes: Plus 2 smaller lobes
Falciform ligament: mesentery binding liver to anterior abdominal wall
2 surfaces: diaphragmatic and visceral
Covered by peritoneum: except bare area fused to diaphragm
Fissure
: visceral surface
Porta hepatis
: major vessels and nerves enter and leave
Ligamentum teres
: remnant umbilical vein fetus, attaches navel
Hepatic veins
IVC
Bare area
Right hepatic artery
Right hepatic duct
Cystic duct
Gallbladder
Right lobe
Quadrate lobe
Ligamentum teres
Falciform ligament
Fissure
Common hepatic duct
Left hepatic duct
Left heaptc artery
Prta hepatis
Ligamentum venosum in fissure
Left lobe
Caudate lobe
Hepatic portal vein
Function
Produce bile
Picks up glucose from blood
Stores glucose as glycogen
Processes fats and amino acids
Stores some vitamins
Detoxifies poisons and drugs
Makes blood proteins e.g. albumin
Histology
Liver lobules
Hexagonal solid made of sheets of
hepatocytes
(liver cells) around a central vein
Corners of lobules have
portal triads
Cells
Liver sinusoids
Large capillaries between plates of hepatocytes
Contribute to central veins and ultimately to hepatic veins and IVC
Kupffer cells
Liver macrophages
Old blood cells and microorganisms removed
Portal triad
Portal arteriole
Portal venule
Branches of hepatic portal vein
Delivers substances from intestines for processing by hepatocytes
Bile duct
Carries bile away
Hepatocytes
Many organelles
Rough ER: manufactures blood proteins
Smooth ER - help produce bile salts and detoxifies blood-borne poisons
Peroxisomes: detoxifies other poisons e.g. alochol
Golgi apparatus
Mitochondria: lot of energy needed
Glycosomes: role in storing sugar and regulation of blood glucsoe levels
Produced 500-1000ml bile each day
Secrete into bile canaliculi (little channels) then ducts
Regeneration capacity through liver stem cells
Small intestine
Most enzymatic digestion occurs here
Almost all absorption
3-6 hours
Duodenum (5%)
Jejunum (40%)
Ileum (60%)
Bile
: form liver and gallbladder via bile duct
Enzymes
: from pancreas via main pancreatic duct
Blood supply
: superior mesenteric artery
Veins
: drains into hepatic portal vein
Structural modifications
Circular folds (plicae circulares)
Villi: single columnar epithelium: velvety
Microvilli
Lacteal: netwrok of blood and lymph capillaries
Carbs and proteins into blood to liver via hepatic portal vein
fat into lymph
Intestinal crypts
: inbetween villi
Cells here divide every 3-6 days to renew epithelium
Secrete watery intestinal juice which mixes with chyme
Intestinal flora
: permanent normal bacteria
Manufacture some vitamins e.g. K, which gets absorbed
Duodenal glands
Mucus to counteract acidity
Hormones
CCK: Stimulate GB to release stored bile, also pancreas
Secretin: stimulates pancreatic ducts: relase acid neutraliser
Histology
Plica (mucosal folds)
Mucosa: mucosal epithelium and lamina propria
Billi
Mucosal glands
Submucosal gland
Muscularis mucosae
Lymphatic vessel
Artery and vein
Submucosal plexus
Circular muscle layer
Myenteric plexus
Longitudinal muscle layer
Pancreas
Endocrine and Exocrine
Lies LUQ behind stomach + retroperitoneal
Head, body and tail
Head : in C shaped curve of duodenum
Tail extends touch spleen
Main pancreatic duct runs length of pancreas, joins bile duct
Endocrine
Islet of langerhans, Insulin and glucagon
Exocrine
Compound
acinar
(sac-like) glands opening into large ducts (exocrine)
Acinar
make 22 types enzymes
Stored in zymogen
Grape like arrangement
Enzymes to duodenum where activated
Pharynx
Three muscles constrictors
Sequneitally squeex bolus of food into oesophagus
Are skeletal muscles
Voluntary action
Vagus nerve (X)
Oropharynx and laryngopharynx
Stratified squamous epithelium
Oesophagus
Continous of pharynx in mid neck
Muscular tube collapsed when lumen empty
Descends through thorax
On anterior surface of vertebral column
Posterior to trachea
microscopic anatomy
Epithelium: nonkeratinized stratified squamous epithelium
At GO junction - thin simple columnar epithelium
Muscle glands in wall
Muscle (muscularis externa) changes as it goes down
Superior 1/3 oesophagus: skeltal muscle (like pahrynx)
Middle 1/3:mixture of skeletal and smooth muscle
Inferior 1/3 smooth muscle (as in stomach and intestines)
When empty, mucosa and submucosa lie in longitdunal folds
Gall bladder
Bile produced in liver
Bile stored in gallbladder
Bile excreted into duodenum
Bile helps dissolve fat and cholesterol
Bile salts crystallize: gall stones