1. Unit I: Metabolism Digestive System
Part II
Chapter 21

2. Tissue Table Digestive Organ Epithelial Tissue Muscle Type pH
Oral Cavity
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Anal Canal

3. Small Intestine
Segments
Duodenum
Jejunum
Ileum
Transverse
colon (cut)
Ascending
colon
Descending
Sigmoid
Cecum
Rectum
Longest part of the digestive tract and highly folded  lots of surface area to expose to chyme for absorption
6.6ft long in a living person (due to muscle tone); 19-23ft in cadaver
3 regions: duodenum, jejunum, and ileum
Nearly all chemical digestion and nutrient absorption occurs in small intestine

4. Small Intestine Duodenum -10 in.
neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH increase, pancreatic enzymes
Jejunum - next 8 ft.
Simple columnar
Smooth muscle
Ileum - last 12 ft.
lymphatic nodules
ileocecal junction
Ileum
Duodenum
Jejunum
Serosa
Muscularis
externa
Submucosa
Mucosa
mucosae
Circular
folds
Villi
Peyer Patches
curves around head of pancreas – name refers to length: 12 fingers
receives stomach contents, pancreatic juice and bile
emulsify – physically broken up – by bile acids; pancreatic enzymes take over chemical digestion
2.a. has large tall circular folds, walls are thick and muscular
most digestion and nutrient absorption occur here  rich blood supply
3. Wall is thinner and less muscular and less vascular
a. Peyer patches - remove pathogens
b. ends at … with the large intestine (cecum)

5. Small Intestine - Surface Area
Circular folds
Villi
Small Intestine - Surface Area
Circular folds - up to 10 mm tall
chyme flows in spiral path
Villi - 1 mm tall
contain blood vessels and lymphatics (lacteal)
nutrient absorption
Microvilli 1 micron tall
brush border enzymes
Dextrinase
Glucoamylase
Maltase
Sucrase, lactase
Lacteal
Columnar epithelial cell
Mucous cell
Nerve
Capillary network
Arteriole
Lymphatic vessel
Venule
Muscularis mucosae
Lamina propria
Surface area is increased by (1) Long length (2) Surface elaborations: if it was flat – surface area=0.3m2; with surface elaborations=200m2
1.a. involve only mucosa and submucosa (transverse/spiral ridges)
b. … slows progress  more contact, mixing, and absorption
c. not in distal half of ileum  nutrient absorption done by then
2. Mucosa appears fuzzy due to villi. Fingerlike projections – largest in duodenum getting progressively smaller
blood vessels absorb most nutrients
lacteal (lymphatic capillaries) absorbs fat giving contents a milky appearance
3. Villi appear fuzzy due to microvilli –
a. brush border of cells increase surface area; enzymes not released into lumen
integral proteins of the plasma membrane
b. some need contact for digestion which makes mixing in intestine so important.
CONTACT DIGESTION

6. Intestinal Crypts
absorptive cells, goblet cells and at base, rapidly dividing cells
Brunner’s glands
Secrete 1-2 L of intestinal juice/day pH
Brunner’s Glands
1. Pores opening between villi lead to intestinal crypts - in mucosa:
upper half  like villi (absorptive and goblet cells)
bottom half  dividing stem cells (3-6 days: cells move up to tip of villus)
a. Paneth cells - protect against bacterial infection - antibacterial secretions
2. in submucosa - secrete bicarbonate mucus - neutralize stomach acid
3. water and mucus, pH
little enzymes  most enzymes on brush border or in pancreatic juice

7. Gross Anatomy of Large Intestine
500 ml of indigestible food residue/day
5 ft long and 2.5 inches in diameter in cadaver
Appendix – columnar epithelium, goblet cells, WBC, and lymphocytes
… reduces it to 150 ml of feces by absorbing water and salts  eliminates feces by defecation
3. Begins with cecum 
appendix – columnar epithelium lines it, goblet cells, white blood cells similar to Peyer’s patches
*no digestive function, no nutrient absorption - lymphocytes - significant source of immune cells
4. Colon – between ileocecal junction and rectum
Ascending (right), transverse (horizontal), descending (left), ( form a 3- sided frame around small intestine)
and sigmoid regions (S-shaped portion)
5. In pelvic cavity – large intestine straightens to form rectum.
rectal valves – 3 internal folds enable to retain feces while passing gas

8. Microscopic Anatomy of Large Intestine
Aggregated
lymphoid
nodule
Simple columnar
epithelium
Intestinal gland
Mucous cells
Muscularis mucosae
Submucosa
Muscularis Externa
Circular layer
Longitudinal
layer
Mucosa - simple columnar epithelium
anal canal: non-keratinized stratified squamous
Muscularis Externa – smooth muscle
anal canal: skeletal
No circular folds or villi
Comparing large to small intestine
1. A. used for absorption and secretion.
b. provides more resistance to abrasion from feces – protection
3. Intestinal crypts – deeper, more goblet cells for producing mucus only

9. Anatomy of Anal Canal 3 cm total length Anal columns Anal sinuses
Last 3 cm of large intestine terminates at the anus.
Mucosa forms longitudinal ridges called anal columns
separated by mucus secreting anal sinuses (depressions) between columns  lubricate canal during defecation
Anus regulated by:
Internal anal sphincter – smooth muscle; involuntary
external anal sphincter – skeletal muscle; voluntary
Hemorrhoids are permanently distended veins
3 cm total length
Anal columns
Anal sinuses
Internal & External anal sphincters

10. Bacterial Flora and Intestinal Gas
Bacterial flora populate large intestine
ferment cellulose and other undigested carbohydrates;
synthesize vitamins B and K
Flatus (gas)
average person produces 500 mL per day
most is swallowed air
hydrogen sulfide, indole and skatole produce odor
800 species of bacteria in large intestine
they digest cellulose, polysaccharides and we absorb the resulting sugars.
some also: … vitamin K needed for blood clotting.
everyone’s bacterial flora is different.
2. Intestinal gas
a. reabsorbs the rest (7-10L of gas total)
b. … but bacteria adds to it: flatus is composed of N, CO2, H, methane (CH4), hydrogen sulfide (H2S) and 2 amines: indole and skatole
produce the odor of feces and gas; H gas is known to be combustible

11. Liver, Gallbladder and Pancreas
Accessory Organs:
Liver, Gallbladder and Pancreas
All release important secretions into small intestine to continue digestion

12. Gross Anatomy of Liver 3 lb. organ located inferior to the diaphragm
Simple cuboidal epithelium
4 lobes -
falciform ligament
round ligament
1. Body’s largest gland. GLANDS SECRETE fluids! And have simple cubiodal cells
main function associated with digestion: secretion of bile
no muscle!
2. right, left, quadrate (square) and caudate (tail like)
a. … separates left and right – suspends it from the diaphragm.
b. remnant of umbilical vein – carries blood from umbilical cord bypasses liver in fetus.
3. Gallbladder adheres to ventral surface between right and quadrate lobes

13. Microscopic Anatomy of Liver
Hepatocytes
Hepatic sinusoids
Bile
duct
Hepatic
Portal vein
Artery
Hepatic Triad
Tiny innumerable cylinders (functional units) called …
Lobule consists of a central vein passing down its core, surrounded by sheets of cuboidal cells called hepatocytes. Sheets 1-2 cell layers thick
2. Spaces between sheets of hepatocytes are blood-filled channels called hepatic sinusoids. … fenestrated endothelium (thin layer of epithelial cells) – perforated with holes or slits.
3. Hepatic triad – two blood vessels and a bile ductule.
a. Blood vessels are branches of hepatic artery and hepatic portal vein bring blood to liver.
Hepatic lobules (2mm by 1mm)
Sinusoids lined with fenestrated endothelium

14. Liver Function: Overview
Bile
duct
Branch of hepatic
portal vein
Branch of
hepatic artery
Blood enters the hepatic sinusoids from
hepatic portal vein and hepatic artery.
Hepatocytes regulate solute and nutrient
levels and absorb or secrete molecules.
Kupffer, phagocytic cells, engulf pathogens,
cell debris, and damaged blood cells. Also
responsible for storing iron, some lipids, and
heavy metals (such as tin or mercury).
Central vein  hepatic veins  inferior
vena cava.
Hepatocytes secrete bile into bile canaliculi
Bile ductules  hepatic bile ducts in the
nearest Triad
Start
…Roughly one-third of the blood supply to the liver is arterial blood from the hepatic artery. The rest is venous blood from the hepatic portal vein, which begins in the capillaries of the esophagus, stomach, small intestine, and most of the large intestine.
Hepatocytes perform most functions. … After a meal, hepatocytes remove glucose, amino acids, vitamins, and nutrients for metabolism or storage. Removes and degrades hormones, toxins, bile pigments, drugs. Secretes albumin, lipoproteins, clotting factors, and angiotensin. Inbetween meals, release glucose back into bloodstream.
Sinusoids  thru hepatocytes and Kupffer cells  central vein collects blood from the sinusoids of the lobule. The central veins of all the lobules ultimately merge to form the …
… extend outward, away from the central vein.
Bile canaliculi merge to form …

15. Ducts of Liver, Gallbladder, and Pancreas
Right and left hepatic ducts
Round ligament
Common
hepatic duct
Hepatic portal vein
and hepatic artery
Common bile duct
Gallbladder
Cystic duct
Liver
Duodenum
Stomach
Pancreas
Pancreatic duct
Hepatopancreatic
sphincter
Duodenal
papilla
Intestinal
lumen
1. Bile passes from bile canaliculi between cells to bile ductules to right and left hepatic ducts
2. Right and left ducts join outside liver to form common hepatic duct
3. Cystic duct from gallbladder joins common hepatic duct to form bile duct ( through lesser omentum to near duodenum)
4. Pancreatic duct and bile duct combine (to form hepatopancreatic ampulla) emptying into duodenum at major duodenal papilla
sphincter of Oddi (hepatopancreatic sphincter) regulates release of bile and pancreatic juice
(closed between meals to prevent release of bile into intestine)

16. Gallbladder and Bile Gallbladder: 10 cm long
Bile: minerals, bile acids, cholesterol, bile pigments, fats and phospholipids
bilirubin
intestinal bacteria convert to urobilinogen = brown color
bile acid (salts)
enterohepatic circulation – hepatocytes liver small intestine
Duodenum
CCK
Lipid
droplet
Bile salt
The liver
secretes bile
continuously
—roughly 1 liter
per day.
Between meals, bile
becomes more
concentrated.
CCK triggers dilation of
the hepatopancreatic sphincter
and contraction of the gallbladder.
Liver
Start
Sac on underside of liver made of folded mucosa and simple columnar epithelium – store bile
smooth muscle to push bile out
Picture: 1. Liver produces bile. Bile backs up into gallbladder from a filled bile duct.
2. between meals, water and electrolytes are absorbed from bile and concentrated.
3. Duodenum releases CCK … This ejects bile into duodenum through duodenal ampulla.
3. Yellow-green fluid containing …
a. pigment from hemoglobin breakdown (bile pigments) gives bile its color
i. … brown color of feces
b. bile acids are steroids from cholesterol. Used for - Fat digestion and absorption; all other components of bile are destined for excretion. Increases surface area of fat globules for more efficient digestion by enzymes in small intestine
ii. Circulation: 80% recycling of bile acids from ileum - bile acids are reabsorbed by small intestine ileum  returned to liver  resecreted by hepatocytes (2 or more times during digestion)
The body’s only way of eliminating excess cholesterol. If built up they (cholesterol) form gallstones.
Remove gallbladder  bile duct stores bile; functions as gallbladder

17. Gross Anatomy of Pancreas
Head of
pancreas
Body of
Pancreatic lobules
Pancreatic duct
Common bile duct
Accessory pancreatic duct
(present in 3–10 percent
of individuals)
Duodenal papilla
Duodenum
Tail of
Endocrine and exocrine gland
secretes insulin and glucagon
secretes 1500 mL pancreatic juice/day
Pancreatic juice:
Water, zymogens, enzymes, and sodium bicarbonate
(Ventral side covered by peritoneum.) spongy, simple cuboidal epithelium (gland) no muscle!
head (surrounded by duodenum), body and tail
2.a. Endocrine part is the pancreatic islets that secrete insulin … into the blood which affect carbohydrate metabolism (discussed w/ endocrine system)
b. most (99%) is exocrine tissue. … into duodenum
3. Alkaline – to neutralize stomach HCl (pH = 8)
b. Pancreatic juice consists of water, zymogens (enzyme precursor molecules), and enzymes secreted by acinar cells and sodium bicarbonate secreted by ducts.

18. Pancreatic Acinar Cells
duct
Endocrine cells in
pancreatic islet
Cells of pancreatic acinus
The exocrine pancreatic acini
Zymogens  proteases
Trypsinogen  trypsin
Chymotrypsinogen  chymotrypsin
Procarboxypeptidase  carboxypeptidase
Other enzymes
Amylase (starch)
Lipase (fat)
Ribonuclease (RNA) and deoxyribonuclease (DNA)
Functional exocrine unit – acinus (pl. acini)
Acinar cells – high density of rough ER  lots of ribosomes  enzymes
Secrete: Proteases – splits proteins to smaller peptides
large amount of protein production
1. Have a precursor (zymogens) so they don’t digest intracellular proteins.
a. trypsinogen converted to trypsin in intestine by enterokinase  digests dietary protein and converts the other two.
all “finished” enzymes are involved in protein digestion
2. A. carbohydrate digestion
b. lipid digestion