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DigestionDigestionMaster Traithana

ChaowanapreechaMaster Alfredo V. Garcia III

DefinitionDefinition

Digestion – the process of breaking down food particles (macromolecules) into smaller, simple molecules that can be absorbed into cells or the bloodstream.

Examples: Starch Glucose

Protein Amino acids

Enzymes

Enzymes

The digestion of different organisms



1.Intracellular digestion – food is taken into cells by phagocytosis forming a food vacuole, then lysosome fuses the vacuole and releases enzymes to digest food. Food molecules are absorbed to cytoplasm. Waste is expelled by exocytosis.

Examples: Amoeba, paramecium, other protists,

sponges and phagocyte (white blood cell) etc.

Intracellular digestionIntracellular digestion

2. Extracellular digestion – organisms secrete enzymes out of their cells. Food is digested and absorbed into cells.

Examples: Bacteria, fungi, most animals including humans



2 methods to digest:1.Mechanical digestion – Food is

broken into smaller pieces by chewing, contracting muscles (peristalsis of intestines and a stomach). Food can bind to enzymes better.

2.Chemical digestion – Macromolecules are broken down into smaller moleculesby enzymes.



Digestive systems of different

organisms

Digestive systems of different

organisms

A sponge has choanocytes engulfing food into cells and digest inside.

Digestive systems of different organisms


Coelenterates have a gastrovascular cavity, the digestion zone.





A nematode has a complete digestive system including mouth, esophagus, intestine, and anus.

An earth worm also has a complete digestive system including mouth, esophagus, crop, gizzard, intestine, and anus.





An insect has a crop storing food and a gizzard digesting food.

A bird’s digestive system has beak and mouth suitable for different kinds of food, esophagus, crop, stomach, gizzard, intestine, rectum and cloaca.





Herbivorous mammals likes cows and buffaloes have 4-chambered stomach suitable for cellulose digestion.

Four-Chambered StomachRuminant animals, including sheep, domestic cattle, goats, deer, and giraffes, have four-chambered stomachs.

Herbivorous animal digestive system



Carnivorous animal digestive system

Digestive system of a humanDigestive system of a human

Human digestive systemHuman digestive systemAlimentary canalMouth pharynx

esophagus stomach large intestine

small intestine

rectum anus

-Duodenum-Jejunum-Ileum

-Ascending colon-Transverse colon-Descending colon

-Teeth-Tongue

Digestive glands- Salivary glands- Gastric glands- Intestinal glands- Pancreas- Liver

Human digestive systemHuman digestive system

Digestion in the oral cavityOral cavity includes upper jaws,

lower jaws, teeth, gum, cheek lining, hard and soft palates.

Mechanical digestionTeeth cut, tear, and grind food into

small pieces, then a tongue mixes food with saliva secreted from 3 pairs of salivary glands (sublingual, submandibular, and parotid).

Human digestive systemHuman digestive system

There are 2 sets of human teeth formed by ectoderm.

- Deciduous teeth, D.T., are firstly formed at age 6 months and start to fall out at 6 years old. There are totally 20 D.T.

- Permanent teeth, P.T., are completely formed at age 13.

There are totally 32 P.T.

32 Human permanent teeth include:

1.4 upper incisors – cut food (well-developed in rodents)

4 lower incisors2. 2 upper canines – cut, tear, and

separate food2 lower canines (well-developed in carnivores)

3.4 upper premolars – cut and tear food4 lower premolars (well-developed in carnivores)

4.6 upper molars – chew and grind food6 lower molars (well-developed in herbivores)

Salivation is controlled by parasympathetic nervous system (cranial nerve pairs no.7 and 9)

Stimuli: seeing food, smelling, tasting, toughts

Chemical digestionStarch + water dextrinDextrin + water maltose

amylase

amylase

How is food transferred from a mouth to a stomach?

Food travels along esophagus to a stomach by peristalsis (muscle contractions: the waves of involuntary muscle contractions that transport food, waste matter, or other contents through a tube-shaped organ.)

Digestion in a stomach- Capacity when it’s empty = 50 –

100 mL- Capacity when it’s full = 1-2 LEpithelial cells line inner surface of

the stomach and secrete about 2 liters of gastric juices per day. Gastric juice contains hydrochloric acid, pepsinogen, rennin, lipase, potassium chloride, and mucus; ingredients important in digestion.

Secretions are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals.

The stomach secretes hydrochloric acid and pepsin. Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated. Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. The stomach also mechanically churns the food.

Protein short polypeptides

Chyme, the mix of acid and food in the stomach, leaves the stomach and enters the small intestine.

pepsin

© Microsoft Corporation. All Rights Reserved.Anatomy of the StomachLocated on the left side of the body, under the diaphragm, the stomach is a muscular, saclike organ that connects the esophagus and small intestine. Its main function is to break down food. Cells in the stomach lining secrete enzymes, hydrochloric acid, and other chemicals to continue the digestive process begun in the mouth and produce mucus to keep these substances from digesting the lining itself.Microsoft ® Encarta ® Reference Library 2003. © 1993-2002 Microsoft Corporation. All rights reserved.

Ulcers โรคแผลในกระเพาะอาหารPeptic ulcers result when these

protective mechanisms fail. Bleeding ulcers result when tissue damage is so severe that bleeding occurs into the stomach.

Perforated ulcers are life-threatening situations where a hole has formed in the stomach wall. At least 90% of all peptic ulcers are caused by Helicobacter pylori. Other factors, including stress and aspirin, can also produce ulcers.

Functions of the stomachFunctions of the stomach

- Storing food- Producing intrinsic factor (IF) important in B12

absorption at the small intestine- Digesting protein- Controlling the proper amount of food leaving

the stomach for the small intestine- Producing hormone gastrin helping in pepsin

and HCl production (in the stomach) and bile production (in the liver)

- Buffering the food condition if it’s too alkaline.

Digestion in the small intestine- Final digestion and absorption occur.

- The small intestine is a coiled tube over 3 meters long. Coils and folding plus villi give very large surface area.

- Final digestion of proteins and carbohydrates must occur, and fats have not yet been digested.

- Food has been broken down into particles small enough to pass into the small intestine.

- Sugars and amino acids go into the bloodstream via capillaries in each villus. Glycerol and fatty acids go into the lymphatic system.

- Absorption is an active transport, requiring cellular energy.

Structure of the small intestine

Liver, gall bladder

and pancreas

Digestion in the small intestine


1.CarbohydratesPolysaccharides + water

disaccharides

Disaccharides + water monosaccharides

Pancreatic amylase

Disaccharidases from intestine



2. ProteinsPolypeptides + water

protein fragments

Fragments + water amino acids

Fragments + water amino acids

Trypsin and chymotrypsin

Carboxypeptidase from pancreas

Aminopeptidase from intestine

Carboxypeptidase

Aminopeptidase



3. LipidsTriglycerides + water

fatty acids + monoglycerides

What is the function of bile??????

Pancreatic lipase + bile (liver)

Pancreatic lipase + bile (liver)

4. Nucleic acids

DNA and RNA nucleotides

Nucleotides nucleotide bases + monosaccharides

(ribose or deoxyribose)

Pancreatic nuclease

Intestinal nuclease

AbsorptionAbsorption

- Alcohol and aspirin are absorbed through the stomach lining into the blood.

Most absorption occurs in the duodenum and jejeunum. The circular folds and villi covered with epithelial cells provide a large surface area for absorption. The epithelial cells are lined with microvilli that further increase the surface area; a 6 meter long tube has a surface area of 300 square meters.

Glucose, fructose, and galactose are absorbed by the microvilli by active transport, then leave the cell and enter the capillary. Amino acids cross the epithelial cell membranes by active transport, then enter the capillary. Water, vitamins and minerals are absorbed by diffusion without digestion.Absorbed food molecules will be transported to the liver by hepatic portal vein.

Absorption of lipids by cells in the small intestine.

Any activities happen in large intestine?

Any activities happen in large intestine?

- Water, vitamin, and mineral absorption happens.

- Bacteria E. coli synthesizes vit. K.

- Feces formation

AppendectomyAppendicitis is a painful inflammation of the appendix, a finger-sized tube attached to the large intestine. To remove an inflamed appendix, surgeons perform a surgical procedure known as an appendectomy. The inflammation can be caused by undigested food particles and bacteria.Microsoft ® Encarta ® Reference Library 2003.

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