Unit I: MetabolismDigestive System

Part II

Chapter 21

Tissue Table

Digestive Organ Epithelial Tissue Muscle Type pH

Oral Cavity

Pharynx

Esophagus

Stomach

Small Intestine

Large Intestine

Anal Canal

Small Intestine

• Nearly all chemical digestion and nutrient absorption occurs in small intestine

SegmentsDuodenum

Jejunum

Ileum

Transversecolon (cut)

Ascendingcolon

Descendingcolon

Sigmoidcolon

Cecum Rectum

Ileum

Duodenum

JejunumSerosaMuscularisexternaSubmucosa

Mucosa

Muscularismucosae

Circular folds

Villi

Peyer Patches

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

Lacteal

Columnar epithelial cell

Mucous cell

Nerve

Capillary network

ArterioleLymphatic vesselVenule

Muscularis mucosae

Lamina propria

• 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

Circular folds

Villi

Small Intestine - Surface Area

Intestinal Crypts• absorptive cells, goblet cells and at

base, rapidly dividing cells

• Brunner’s glands

• Secrete 1-2 L of intestinal juice/day

• pH 7.4-7.8Brunner’s Glands

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

Aggregatedlymphoid

nodule

Simple columnarepithelium

Intestinal gland

Mucous cells

Muscularis mucosae

Submucosa

Muscularis Externa

Circular layer

Longitudinallayer

Microscopic Anatomy of Large Intestine

• Mucosa - simple columnar epithelium – anal canal: non-keratinized stratified squamous

• Muscularis Externa – smooth muscle− anal canal: skeletal

• No circular folds or villi

Anatomy of Anal Canal

• 3 cm total length• Anal columns • Anal sinuses• Internal & External anal sphincters

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

Accessory Organs:Liver, Gallbladder and Pancreas

• All release important secretions into small intestine to continue digestion

Gross Anatomy of Liver

• 3 lb. organ located inferior to the diaphragm• Simple cuboidal epithelium• 4 lobes -

– falciform ligament– round ligament

Hepatocytes

Hepatic sinusoids

Bileduct

Hepatic Portal vein

HepaticArtery

Hepatic Triad

Microscopic Anatomy of Liver

• Hepatic lobules (2mm by 1mm)

• Sinusoids lined with fenestrated endothelium

Bileduct

Branch of hepaticportal vein

Branch ofhepatic 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 canaliculiBile ductules hepatic bile ducts in the nearest Triad

Start

Liver Function: Overview

Right and left hepatic ducts

Round ligament Commonhepatic duct

Hepatic portal vein and hepatic artery

Common bile duct

Gallbladder

Cystic duct

Liver Duodenum

Stomach

Pancreas

Pancreas

Common bile ductPancreatic duct

HepatopancreaticsphincterDuodenal

papilla

Intestinallumen

Ducts of Liver, Gallbladder, and Pancreas

Duodenum

CCK

Lipiddroplet

Bile salt

The liversecretes bilecontinuously—roughly 1 literper day.

Between meals, bile becomes moreconcentrated.

CCK triggers dilation ofthe hepatopancreatic sphincterand contraction of the gallbladder.

Liver

Start

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

Head ofpancreas

Body ofpancreas

Pancreatic lobules

Pancreatic duct

Common bile duct

Accessory pancreatic duct(present in 3–10 percent

of individuals)

Duodenal papilla

Duodenum

Tail ofpancreas

Gross Anatomy of Pancreas

• Endocrine and exocrine gland

– secretes insulin and glucagon

– secretes 1500 mL pancreatic juice/day

• Pancreatic juice:

– Water, zymogens, enzymes, and sodium bicarbonate

Pancreatic Acinar Cells

• Zymogens proteases

– Trypsinogen trypsin

– Chymotrypsinogen chymotrypsin

– Procarboxypeptidase carboxypeptidase

• Other enzymes

– Amylase (starch)

– Lipase (fat)

– Ribonuclease (RNA) and deoxyribonuclease (DNA)

Pancreaticduct

Endocrine cells inpancreatic islet

Cells of pancreatic acinus

The exocrine pancreatic acini