Human digestion

Human digestive system (General plan)

Accessory digestive organs

Organ/s Mechanical digestion

Carbohydrate digestion Protein digestion

Nucleic Acid digestion

Lipid digestion

Oral cavityEsophagusPharynx

ChewingPeristalsis

Stomach ChurningMixingPeristalsis

Small intestineLumen

PeristalsisMixing

Small intestineEpithelium

Polysaccharides(starch,

glycogen)

Disaccharides(sucrose, lactose)

Salivary amylaseSmaller polysaccharides,

maltose

Polysaccharides

Pancreatic amylase

Maltose and other disaccharides

Disaccharidases

Disaccharidases

Monosaccharides

Proteins

Pepsin

Small polypeptides

Pancreatic trypsin and chymotrypsin Smaller polypeptides

Small peptidesDipeptidases,

carboxypeptidase,

aminopeptidase

Amino acids

DNA, RNA

Pancreaticnucleases

Nucleotides

NucleotidasesNucleosides

Nucleosidases, phosphatasesNitrogenous

bases,sugars,

phosphates

Fat globules

Bile saltsFat droplets

Pancreatic lipase

Glycerol, fattyacids, glycerides

Sites of digestion

Composition of the adult human body

• Salivary glands– Produce saliva• Mostly water• Some enzymes

– Salivary amylase– Lysozyme

• Mucus or mucin

• Teeth

Digestion in the Mouth

Swallowing: from mouth to stomach

Muscular sac◦ Churns & mixes food

Gastric glands◦ Parietal cells HCl,

intrinsic factor◦ Goblet cells mucus◦ Chief cells

pepsinogen, weak gastric lipase

◦ Gastrin Hormone Controls gastric juices

Comes out as chyme (2-6 hours)

Digestion in the Stomach

LiverSecretes bile (stored in gall bladder)Emulsifies fats

GallbladderStores, concentrates,

and releases bile into duodenum

Stimulated by the hormone cholecystokinin (CCK)

• Exocrine function• Acinar cells secrete

pancreatic juice– Amylase– Lipase– Trypsin– Chymotrypsin– Carboxypeptidase– Nuclease– NaHCO3

-

• Secretin and cholecystokinin (CCK) fr intestinal wall stimulates PJ production

Pancreas

Chemical digestion in the duodenum (con’t.)

Absorption in the small intestine

Reabsorption and elimination in the large intestine

• Areas of the colon• Cecum • Rectum • Anus

• Absorption of water and electrolytes

• Concentration & elimination of solids

• Home for bacteria that produce biotin, folic acid, vitamin K, several B-vitamins, gases

Hormones coordinate secretion of digestive juices

Name Source Stimulant Target Organ Function

Stomach GastrinPyloric mucosa

Partially-digested food

Gastric glandsSecretion of gastric juice

Intestinal Gastrin

Intestinal mucosa

Stomach

SecretinAcidity of

chymePancreas and

liverSecretion of PJ rich in

HCO3- and bile production

Cholecystokinin (CCK)

Fats or combination of acids and

fats

Pancreas and gallbladder

(Sphincter of Oddi in CBD)

Secretion of PJ, bile from gallbladder, opening of

SO

EnterocrininAcidity of

chymeDuodenum

Secretion of intestinal juice

Enterogastrone or Gastric Inhibitory

Peptide (GIP)

Fats StomachInhibits secretion of

gastric juice and decreases gastric motility

Liver

Gall-bladder

CCK

Entero-gastrone

Gastrin

Stomach

Pancreas

Secretin

CCK

Duodenum

Key

Stimulation

Inhibition