1

Digestion, Absorption,

Excretion

Today’s topics:

• Digestive System

Hydrolysis

• Stomach, Liver,Pancreas

Absorption

• Intestine

• Excretion• Kidney (if time) 6 April 2009

Fig. 41-7

Ingestion Digestion Absorption Elimination

Undigestedmaterial

Chemical digestion

(enzymatic hydrolysis)Nutrientmoleculesenter bodycells

Smallmolecules

Mechanicaldigestion

Food

Piecesof food

1 2 3 4

Fig. 41-UN1

Bloodstream

Veins to heart

Lymphaticsystem

Small intestine

Esophagus

StomachLipids

Mouth

Hepatic portal vein

Absorbed food(except lipids)

Absorbedwater

Secretions from

the gastric glands

of the stomach

Secretions from the

pancreas and the liver

Liver

Rectum

Anus

Largeintestine

Fig. 41-8

Gastrovascularcavity

Food

Epidermis

Mouth

Tentacles

Gastrodermis

Cecum

Ascendingportion oflarge intestine

Gall-bladder

Smallintestine

Largeintestine

Smallintestine

Pancreas

Liver

Stomach

Appendix

Digestive System

Fig. 41-12b

Interior surfaceof stomach

Chief cells

Epithelium

Parietal cell

Pepsinogen and HClare secreted.

HCl convertspepsinogen to pepsin.

Pepsin activatesmore pepsinogen.

Chief cell

PepsinPepsinogen

HCl

H+

Cl–

Parietal cells

Mucus cells

Gastric gland2

3

1

1

2

3

2

Fig. 41-13

Oral cavity,pharynx,esophagus

Stomach

Lumen ofsmall intestine

Epithelium

of small

intestine

(brush

border)

Carbohydrate digestion

Polysaccharides

Smaller polysaccharides,maltose

Polysaccharides

Maltose and otherdisaccharides

Disaccharides

Protein digestion Nucleic acid digestion Fat digestion

Proteins

Small polypeptides

Pepsin

Pancreatic amylases

Salivary amylase

Disaccharidases

Monosaccharides

Small peptides

Amino acids

Amino acids

Polypeptides

Smallerpolypeptides

Pancreatic trypsin andchymotrypsin

Pancreatic carboxypeptidase

Dipeptidases, carboxypeptidase,and aminopeptidase

DNA, RNA

Pancreatic nucleases

Fat globules

NucleotidesFat droplets

Nucleosides

Nitrogenous bases,sugars, phosphates

Nucleotidases

Nucleosidasesandphosphatases

Glycerol, fattyacids, monoglycerides

Bile salts

Pancreatic lipase

(starch, glycogen) (sucrose, lactose)

Liver

Gallbladder

Pancreas

Spleen

Kidney

Stomach

Duodenum

Fig. 41-10a

Cecum

Ascendingportion oflarge intestine

Smallintestine

Intestine

Appendix

Intestinal villi and brush border

increase surface area for

absorption

http://www.vanderbilt.edu/exploration/text/index.php?action=view_section&id=1268&story_id=304&images=

Vein carrying bloodto hepatic portal vein

Villi

Intestinal wall

Key

Nutrientabsorption Capillaries

Villi

Lymphvessel

LactealEpithelial cells

Fig. 41-15

Absorption

Brush Border

Brush border

Key

Nutrientabsorption

Bloodcapillaries

Epithelialcells

Villi

Lymphvessel

Lacteal

Epithelial cells

Fig. 41-15b

Absorption

3

Back to the Liver

• Hepatic vein takes absorbed nutrientsto liver

– Adjust nutrient balance

– De-tox poisons

Liver is a majorprotein synthesis site

Maintaining

Glucose

Balance

Homeostasis:90 mg glucose/100 mL blood

Stimulus:Blood glucose

level risesafter eating.

Stimulus:Blood glucose

level dropsbelow set point.

Fig. 41-21

Cecum

Small intestine

HerbivoreCarnivore

Colon(largeintestine)

StomachSmall intestine

Colon

Fig. 41-19

Fig. 41-20

Esophagus

OmasumAbomasum

Intestine

Rumen Reticulum1 2

4 3

Liver

Gallbladder

Pancreas

Spleen

Kidney

Stomach

Duodenum

Kidney is a

blood filterCapillary

Excretion

Secretion

Reabsorption

Excretorytubule

Filtration

Filtra

teU

rine

Fig. 44-10

4

Fig. 44-14d

Loop ofHenle

Collectingduct

Bowman’scapsule

Glomerulus Kidney uses

osmosis to

concentrate

urine

Key

Activetransport

Passivetransport

INNERMEDULLA

OUTERMEDULLA

H2O

CORTEX

Filtrate

Loop ofHenle

H2O K+HCO3–

H+ NH3

Proximal tubule

NaCl Nutrients

Distal tubule

K+ H+

HCO3–

H2O

H2O

NaCl

NaCl

NaCl

NaCl

Urea

Collectingduct

NaCl

Fig. 44-15

Kidney uses

osmosis to

concentrate

urine

Key

Activetransport

Passivetransport

INNER

MEDULLA

OUTERMEDULLA

CORTEXH2O

300300

300

H2O

H2O

H2O

400

600

900

H2O

H2O

1,200

H2O

300

Osmolarity of

interstitialfluid

(mOsm/L)

400

600

900

1,200

100

NaCl

100

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

200

400

700

1,200

300

400

600

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

Urea

Urea

Urea