The Digestive System - Anatomy and Physiology - Biology and Geology 3rd CSE - Spain

06/02/17VÍCTOR GIL GARCÍA * www.clil.science CONTENTS

Biology and Geology 3rd CSE - Spain

THE DIGESTIVE SYSTEMAnatomy and

Physiology

06/02/17VÍCTOR GIL GARCÍA * www.clil.science CONTENTS

Contents● Functions of the digestive

system● Anatomy of the digestive system

– Gastrointestinal tract● Mouth● Pharynx and oesophagus● Stomach● Small intestine● Large intestine

– Accessory digestive organs● Salivary glands● Liver and gall bladder● Pancreas

● Physiology of the digestive system– Ingestion– Secretion

● Saliva● Gastric and pancreatic juices● Bile

– Mixing and propulsion– Digestion

● In mouth and stomach● In small intestine● In large intestine

– Absorption– Defecation

06/02/17VÍCTOR GIL GARCÍA * www.clil.science CONTENTS

Functions of the digestive system● To break down the

food● To absorb the

nutrients from the food

● To eliminate solid wastes

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Anatomy of the digestive system● The organs of the digestive system are

organised in two groups:– Gastrointestinal tract

● Contains the food from the time it is eaten until it is digested and absorbed or eliminated from the body

● From the mouth to the anus● About 5-7 meters long

– Accessory digestive organs● Secrete substances into the gastrointestinal tract

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The gastrointestinal tract● Mouth (oral cavity)

– Cavity where the food is chewed

– Include teeth (incisors for cutting, canines for tearing and premolars and molars for grinding)

– Include tongue, palate and uvula

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The gastrointestinal tract● Pharynx and

oesophagus– Muscular conduits

that carry the swallowed food to the stomach

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The gastrointestinal tract● Stomach

– Muscular mixing cavity and storage container for food

– Secretions of acid and other substances break down food

– Lining of mucous membrane

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The gastrointestinal tract

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The gastrointestinal tract● Small intestine

– Absorbs sugars, lipids, peptides (proteins), water, minerals and vitamins from food

– 3 parts: duodenum, jejunum and ileum

– Special lining called villi for increasing the absorption surface

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The gastrointestinal tract● Large intestine

– Absorbs water, minerals and vitamins

– 3 parts: caecum, colon and rectum

– Faeces are formed which get expelled through the anus

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Accessory digestive organs● Salivary glands

– Secrete saliva into the mouth. Saliva lubricates food and begins the digestion of carbohydrates

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Accessory digestive organs● Liver

– Secretes bile which is stored in the gall bladder. Bile helps digest lipids

– Receives, transforms and stores nutrients absorbed from the small intestine

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Accessory digestive organs● Pancreas

– Secretes substances to break down food● Liver and pancreas pour their secretions into the

duodenum (small intestine)

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Physiology of the digestive system● The physiology of the digestive system can be

summarized in these six functions:– Ingestion: taking food into the mouth– Secretion: releasing several substances into the

gastrointestinal tract– Mixing and propulsion: shaking and pushing the

food through the gastrointestinal tract– Digestion: physically and chemically braking down

food

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Physiology of the digestive system– Absorption: passing digested products from the

gastrointestinal tract into the circulation– Defecation: eliminating faeces from the

gastrointestinal tract

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Ingestion● The mouth receives the food● The jaw muscles and the teeth help you chew● Movements of the tongue shape the chewed

food into a soft, rounded flexible mass called bolus

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Ingestion● Deglutition

(swallowing) comes after the formation of the bolus with a combination of voluntary and involuntary movements of tongue, pharynx and oesophagus

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Secretion● Salivary glands secrete saliva into the mouth.

Saliva mixes with the food, lubricates it and kills bacteria (with lysozyme). It also begins the digestion of starch (a complex carbohydrate)

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Secretion● Gastric glands in the epithelium of the stomach

secrete mucus and gastric juices, with hydrochloric acid and other chemical substances

● Intestinal glands in the epithelium of the small intestine secrete mucus and lysozyme

● Pancreatic cells secrete pancreatic juice, which neutralizes stomach acid and has several digestive substances. Pancreatic juice is released into the duodenum

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Secretion● Liver cells (hepatocytes) make bile. The gall

bladder stores bile and releases it into the duodenum. Bile salts break down large lipid globules

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Mixing and propulsion● The smooth muscular

tissue that forms part of the organs of the gastrointestinal tract contracts without voluntary control to shake and push the food. These movements are called peristaltic movements

● The three muscular layers of the stomach are specially powerful to mix the food with the gastric juices

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Digestion● Begins in the mouth with the physical action of

chewing and the chemical action of the amylase, a substance of saliva, which breaks down starch

● The stomach stores the ingested food growing in size. The movements of the stomach shaking the food help physical digestion. The gastric juices carry out chemical digestion of proteins (thanks to pepsin) and lipids (thanks to lipase). The bolus is this way transformed in a substance called chyme

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Digestion● When chyme goes out of the stomach into the

duodenum it is mixed with the bile and the pancreatic juice. Bile salts help with the chemical digestion of lipids. Pancreatic juice contains:– Amylase to break down starches– Trypsin to break down proteins into amino acids– Lipase to break lipids into fatty acids– Substances to break down nucleic acids

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Digestion● Numerous bacteria live within the large intestine,

which break down remaining proteins, produce essential vitamins and release gases by fermentation of remaining carbohydrates

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Absorption● The stomach can absorb some substances like

water, minerals, certain fatty acids and some drugs such as aspirin, alcohol, ibuprofen…

● Most of the absorption takes place in the small intestine (90% of water and nutrients)– Inner surface highly folded macroscopically (villi)

and microscopically (microvilli). This way the surface area is increased by 300-400%

– Nutrients pass from epithelial cells into circulation

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Absorption (intestinal villi)

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Absorption● Many of the absorbed nutrients are processed in

the hepatocytes of the liver● Water, certain minerals and some vitamins are

absorbed in the large intestine (9% of water and nutrients)

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Defecation● Is the elimination of the waste material. Only

around 1% of the ingested food becomes faeces● Faeces are formed in the large intestine from

the chyme and accumulate in the rectum, the last section of the intestine

● Involves voluntary and involuntary muscle contractions to expel faeces by the anus

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Biology and Geology 3rd CSE - Spain

THE DIGESTIVE SYSTEMAnatomy and

Physiology

06/02/17VÍCTOR GIL GARCÍA * www.clil.science CONTENTS

Bibliography● FREUDENRICH, C. Visualizing Anatomy and

Physiology. Wiley. United States of America, 2011.