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Digestive System
Digestion
• -changes foods into form body can
assimilate
– Carbohydrates hydrolyzed into simple sugars
– Fats hydrolyzed into fatty acids and glycerol
– Proteins hydrolyzed into amino acids
• 3 nutrients that are not digested: minerals,
vitamins, water
Physical
Chemical
Types of Digestion
• Large pieces of food are
broken down into smaller
pieces by 2 processes:
mastication
Peristalsis
• Chemical change occurs
as food changes form
using the action of
Enzymes in presence of
water
– Hydrolysis
• Major groups of Enzymes
– lipases
– proteases
– carbohydrases
Structures of the Digestive System
• Mouth, 3 sets of salivary glands, esophagus,
stomach, gall bladder, liver, pancreas,
small intestine, large intestine, rectum.
• Structures containing food are:
– Mouth
– Esophagus
– Stomach, SI, LI, rectum
Digestion in mouth
• Chemical Digestion
– Mastication using teeth and of carbs (using
amylase)
tongue to mix food
• and Lipids (using
• Teeth (Permanent set,
lingual lipase)begins
deciduous set )
• Physical
– Types:
Salivary glands
• Parotid- 70% of saliva production
– Drained by ______duct
• Sublingual- smallest, deep to tongue; 5% of saliva
production
– Drained by Rivinus’duct
• Submandibular- deep to mandibula, 25% of saliva
production
– Drained by Wharton’s duct
• Salivary gland involved in mumps: Parotid
Alimentary Canal
• Foods are digested in the:
– Mouth
– Stomach
– Small intestine
• Foods are absorbed in the: 90% in SI, 10% in LI
Esophagus
• Extends from laryngopharynx to Cardiac
sphincter
• Posterior to Trachea and heart
• No digestive or absorptive function
• Lined with stratified squamous (upper)and
simple columnar epithelium (lower)
• Food chute
Stomach
• proteases (enzymes)= for protein digestion into amino
acids
• Mechanically- mixes and churns food
• 4 regions:Cardia, fundus, body, pylorus
• 3 layers of gastric muscle:circular, longitudinal, oblique
• Rugae
– Are folds on empty inner stomach lining
– Disappear as stomach becomes full
• HCl- pH of 1.5-2/ kills pathogens, inactivates salivary
enzymes, pepsinogen to pepsin, unfolds
proteins(denatures)
• Mucous- (mucous made by goblet cells)
– Protects wall of stomach from its own acids
Cells of Gastric lining
– Parietal cells
• HCl
• Intrinsic factor
– Chief or Zymogenic cells
• Pepsinogen – more gastric contrac. + closes cardiac sph, opens
pyloric
• Rennin
• Gastric lipase
– G cells- gastrin
• Stimulates Parietal cells and chief cells, stimulates stomach activity
– D cells- somatostatin
• Opp of gastrin’s effect
– Mucous cells- protect inner wall of stomach
HCl production
• Why is this acid not produced intact? Would kill
cells that are making it Need Chloride shift
described below to happen.
• H+ ions are made as a result of:
– Carbon dioxide + water => an acid called carbonic acid
• Then, acid called carbonic acid is broken down
into=> bicarbonate ion + H+.
– H+ actively transported into lumen
– Bicarbonate ion moved into interstitial fluid, exchanged
for Cl- ion ( move thru Cl channels into lumen, links to
H + to form HCl.
Layers of the GI tract
• _________,__________,_______,_________,__________
_
• Mucosa has 2 layers= _________,________
• Submucosa = contains ENS or___
• Muscularis externa= 4 places where part of this layer is
skeletal muscle:
________,________,_______,__________
– Modification in stomach_____________________
– Circular layer is____ and longitudinal layer is _____
• Serosa + peritoneum= 4 places in Dig System that do not
have visceral peritoneum
_______________________________________
– Linked to adjacent parts by___________
Mesenteries + Peritoneal folds
• Falciform ligament
• Greater omentum
– ‘Beer belly’
• Lesser omentum
• Mesentery
Other Glands of the Digestive
System
• Gall Bladder- stores bile
– Drained by cystic duct
• Job of bile= emulsification= breaks big fat globs into smaller
fat globs
• Liver- produces bile , largest internal body organ
– When fat digestion not happening, bile and
concentrated in GB
– Liver drained by R + L hepatic duct, join to cystic duct
and form common bile duct.
Liver = 3.3____
1. In R/L hypochondriac, epigastric and umbilical regions.
Color =Reddish brown
2. Falciform ligament divides the R/L lobes
3. Thickening in # 1s posterior surface =ligamentum teres
4. On posterior surface of liver IVC divides=R and caudate
5. Between GB and L lobe is quadrate lobe
6. 1/3 of blood supply from hepatic artery, 2/3 from hepatic
portal veins
7. Liver lobules1.
2.
hexagon shapes- each corner a triad or portal area
caontaining= hepatic poratl vein, hepatic artery, bile duct
Each lobule looks like a wheel with spokes, spokes are
irregular rows of liver cells. Each lobule separated by septa.
Liver
• 3.3 lbs.
– Produces blood cells=hematopoiesis + filters poisons=
detoxification
– L, R, caudate + quadrate lobes; can regenerate
– L + R divided by falciform ligament (liver to
diaphragm)
– Common bile duct joins Pancreatic duct or duct of
Wirsung to enter SI thru ampulla of Vader
– Spincter of Oddi( inside the ampulla of Vader)can close
off flow of bile into SI, then it refluxes into liver and
blood .
Microscopic Anatomy of Liver
• Hepatocytes- liver cells
• sinusoids- ‘capillary like’ blind sacs in liver,
exchange or filtering happens here
• triad- hepatic artery, central vein, bile duct
• The route of blood to liver from GI:
– Hepatic portal vein
Sinusoids
• Exchange vessels within a lobule, very similar to
capillaries
• Empty blood into a central vein, to hepatic vein to IVC
– Sinusoids have larger crossection than the capillary
– Gaps between cells in sinusoid wall allow blood solutes and large
proteins to exit the blood stream
• Lining of sinusoids- contains Kuppfer cells
– Aka stellate reticuloendothelial cells
– Phagocytic
• Engulf pathogens, cell debris, damaged RBC’S
• Store iron, lipids and heavy metals like tin and mercury
More Liver functions
• Synthesizes proteins from amino acids
– Prothrombin, thrombin, albumin
• Ammonia to Urea= deamination (removal of amino
groups)
• Glycogenesis -glucose --- glycogen
• Lipogenesis- synthesis of lipids from nonipid precursors
• Glycogenolysis- glycogen----glucose
• Glyconeogenesis – synthesis of glucose from proteins or
lipids
• Cholesterol synthesis from fatty acids
More liver functions
• Bilirubin made
– From old RBCs , gotten rid of with wastes in feces
• Stores FATsoluble vitamins(A,D,E,K) and Vit
B12
• Detox= removal of drugs and alcohol
• Stores these minerals = iron+ iron-protein
complexes
• Synthesizes plasma proteins=albumins(maintain
water content of blood)
• Absorbs cholecalciferol (Vit D) , made into 25
hydroxy-D3. 25 H-D3 is absorbed by kidneys and
used to make calcitriol.
Pancreas
• Retroperitoneal, exocrine = >90% of organ, 12 in long
• Name means ‘all flesh’
– Drained by pancreatic duct or duct of Wirsung(if blocked, pancreas
will……digest itself
– Accessory pancreatic duct or Duct of Santorini
– Empties into ampulla of Vater into SI
– produces pancreatic juice as its exocrine function
– Pancreatic juice has pH>7 and [high] of bicarbonate ion HCO3– Glucagon +insulin are produced as its endocrine function
– Insulin hyposecretion Drops blood sugar levels.
• Symptoms: polyuria(
lots of urine), polydipsia (thirsty),
and polyphagia (hungry)
Pancreatic Juice
• 1000 to 1500 pancreatic juice made a day
• Drains from duct of Wirsung and duct of
Santorini into Ampulla of Vater
• Made of H2O, NaCl and NaHCO3
• Basic pH= 7.1-8.2 because of bicarbonate
ion
• Basic nature stops action of HCl, prepares
chyme for SI digestion
Pancreatic secretions
proenzymes converted to enzymes
Proenzymes- end in suffix ogen or begin with prefix pro• Proteases /Proteolytic enzymes
–
–
–
–
Trypsinogen - enterokinase needed to make trypsin
Chymotrypsinogen- needs trypsin to make chymotrypsin
Procarboxypeptidase needs trypsin to make carboxypeptidase
Proelastase needs trypsin to make elastase
• Pancreatic lipase- breaks down lipids
• When Duodenum senses chyme
– CCK makes GB squeeze out bile, increases production of all
intestinal enzymes
– Secretin- makes bile in iver, increases production of all intestinal
buffers by liver and pancreas/ reduces stomach activity
• Pancreatic Amylase- breaks down starches, almost
identical to salivary amylase
Gall Bladder
• Pear shaped muscular sac located in the recess of the R
lobe of the liver
• 3 parts: fundus, body, neck
• Produces one liter of bile each day
• Chyme entering duodenum stimulates CCK secretion
• CCk causes strong contraction of the gall bladder
– More CCK secreted the more lipids are present
• Holds 40-70 ml of bile and as it is left there, water leaves
the bile and it is gradually Concentrated,
• Gall stones are crystals of insoluble minerals and salts
• Cholecystitis= inflammation of the GB
Terms of importance in digestion
• Deglutition = swallowing
• Peristalsis
Rhythmic contractions of the smooth muscle in walls of digestive
organs pushing food along.
• Defecation-release of solid waste from anus
• Sphincter- circular muscles that close circular openings
–
–
–
–
Cardiac- between esophagus and stomach
Oral beginning of alimentary canal
Anal- end of alimentary canal
Pyloric between duodenum and stomach
Small Intestine
• Most important digestive organ/ pH is >7
• 23feet long/ 1 in diameter
• Duodenum= bile+ pancreatic juice enter thru the bile duct
+ pancreatic duct( common papilla)
• Villi- fingerlike, has capillaries + lacteals, increase
Mucosal surface area from 3.2 sq. feet to 2200sq. Ft.
• Plicae circularis- permanent duodenal, jejunal and midileal muscular folds
• Ileum= means" twisted”
• Peyer’s Patches- lymph tissue at end of ileum, protects SI
from bacteris in LI
• All food types are chemically changed in SI
• All food absorption occurs in SI
More SI jobs
1. GIP- k
cells
2. Secretins cells
3. CCKCCK cells
4. mucous
pH <7
1. GIP=stops stomach emptying,
starts insulin release
2. SECRETIN= Incr. bicarbonate
in pancreatic juice, stops gastric
juice secre.
3. Incre. Bile secretions from liver
+ GB, closes pylorus, gives
feeling of fullness= satiety
4. Mucous made by Brunner’s
glands
Villi
• “tuft –like
srtructures”
• Cells have brush
border or cells
lining the villi with
microvilli covering
their surfaces.
• lacteals =Lymph
capillaries, collect
absorbed
chylomicrons
• Paneth cells– are found in the intestinal
tract. They contain zinc and
lysozyme (an enzyme that
lyses certain kinds of
bacteria) as well as large
eosinophilic refractile
granules within their apical
cytoplasm. Their exact
function is unknown but due
to the presence of lysozyme
it is likely that Paneth cells
contribute to host defense.
Colon
• 5 to 6 feet long/ 3 in wide
• Several sections:
– Cecum, ascending, transverse, descending, sigmoid
• Reabsorbs water from undigested food
• Stores waste until defecation
• Bacterial residents of colon make 3 vitamins available for use:
– Vitamin K- necessary for liver to make clotting factors like
prothrombin
– Biotin- needed for glucose metabolism
– Vitamin B5- needed for the manufacture of steroid hormones and
certain neurotransmitters