3.2.2. Digestion

The digestion

The digestion is the transformation of foods, previously ingested into simpler substances that can be absorbed and utilized by the cells .

Throughout the digestive tract, food is transformed into different substances. Digestion can be of two types:

Mechanical digestion. The food is fragmented, kneaded, mixed, etc.
Chemical digestion. Some substances, such as digestive enzymes, are responsible for breaking down food, aided by other chemicals. These substances are secreted by the walls of the digestive tract and by the adjacent glands.

Digestion begins in the mouth, when the amylase or ptyalin enzyme contained in saliva begins to chemically digest carbohydrates. In addition, the teeth and the tongue facilitate this digestion with their mechanical action.

But the most important digestion processes occur in the stomach and small intestine, where the pancreas and liver also play a role in digestion.

Answer in your notebook

3.6.- What is the difference between chemical and mechanical digestion?

Answer in your notebook

3.7.- What parts of the mouth are involved in mechanical digestion? And in chemical digestion?

Answer in your notebook

3.8.- How can a person's missing teeth affect the digestion of food?

Stomach

In the stomach, it is a widening of the digestive tract that connects with the esophagus through the cardia (unlike the pylorus, it is always open) and with the small intestine through a valve, the pylorus, which prevents the backward movement of food.

Partes del estómago

Modificado de By Stomach_diagram.svg:Indolences at en.wikipediaderivative work: Mcstrother (Stomach_diagram.svg) [CC BY 3.0], from Wikimedia Commons

The stomach produces gastric digestion, in which the glands that line the inner walls produce gastric juice, which when mixed with the food bolus forms a more fluid mass called chyme.

The gastric juice contains:

Hydrochloric acid: with bactericidal action and favoring the action of pepsin.
Pepsin: it is a digestive enzyme that digests proteins.

To prevent gastric juice from damaging the proteins in the stomach lining, the stomach is lined with mucus.

The stomach is made up of layers of muscles that allow (mechanical) movements to be made so that the chyme mixes well. The longer it is in the stomach, the more gastric juice is secreted and the more it is digested, until the pylorus opens and the chyme passes into the small intestine. There are foods, such as fats and proteins, that need to be in the stomach for a long time, while others, such as carbohydrates, need to be in the stomach for less time.

Activity: Actions of the stomach in digestion.

3D model: Anatomy of the stomach.

Answer in your notebook

3.9.- If gastric juice (contains hydrochloric acid and pepsin) digests proteins, why doesn't it also digest the walls of the stomach, which are also proteins?

Small intestine

The small intestine is a tube that is about 7 meters long that connects the stomach (pylorus) with the large intestine (ileocecal valve). The small intestine is divided into three parts: the duodenum, the jejunum, and the ileum.

In the first part, the duodenum, about 25 cm long, the intestinal cells secrete intestinal juice, with a large amount of enzymes that digest food, breaking it down so that it can be absorbed and passed into the blood.

In addition to the intestinal juice, they reach the intestine through the bile duct, the pancreatic juice and bile (from liver) which assist digestion, forming a slurry called chyle.

The intestinal juice and pancreatic juice containing lipases, amylases and proteases that attack lipids, carbohydrates and proteins, respectively.

The bile emulsifies the fats, converting them into small droplets, thus facilitating the action of the lipases in the pancreatic juice.

The action of all these enzymes allows the chemical digestion of all foods.

Peristaltic movements continue to occur throughout the small intestine.

Discovering words

Where does the word intestine come from? And duodenum? And jejunum? And ileum?

Feedback

The word intestine comes from the Latin intestinus , which means interior. It does not refer only to this part of the digestive system, but to everything that is inside. Therefore, if you ever hear the expression internal wars , it refers to a conflict that happens within a country, organization, company, family, etc. without any intervention from outside.

The first part of the small intestine the duodenum, which also comes from the latin duodenum, which means "twelve fingers", although it actually measures about 25 cm.

It is followed by the jejunum, which comes from the Latin ieiunum, which means empty because it always appeared empty in the dissections of the corpses. The same origin has the word fast, empty when we have not eaten anything, and breakfast, when we break that fast.

The word ileum, on the other hand, comes from the Greek eiléōn , which is twisted. Don't confuse it with the ilium, the hip bone.

Pancreas

The pancreas is an organ located in the abdomen, below and behind the stomach that has dual functions:

Endocrine secretion: produces hormones such as insulin and glucagon, as will be seen in the topic of the endocrine system.
Exocrine secretion: produces pancreatic juice, which together with bile mixes with intestinal juice to form chyle.

Modificado en la obra de CNX OpenStax [CC BY 4.0], via Wikimedia Commons

Liver

The liver forms bile that is stored in the gallbladder.

The bile contains no enzymes but some bile salts to emulsify fat, leaving as small droplets that can be attacked by digestive juices.

In addition, bile contains other pigments, such as bilirubin, which is red in color, and biliverdin, which is green, from the breakdown of hemoglobin, which give the characteristic color of stool.

The liver is responsible for removing different substances from the blood that may be harmful to the body, such as alcohol, making them harmless.

Activity: Digestion in each part of the digestive system.

3D model: Anatomy of the liver.

Answer in your notebook

3.10.- How does the liver intervene in digestion? What about the pancreas?

Answer in your notebook

3.11.- What are the differences between chyme and chyle?

Answer in your notebook

3.12.- Make a table in which the names of the digestive juices and their function appear in order.

Curiosity: Termites digest wood thanks to microorganisms

Would you like to watch a video that explains how termites can digest wood thanks to microbes?

Licensed under the Creative Commons Attribution Share Alike License 4.0

BIOLOGÍA - GEOLOGÍA . COM
1st ESO	3rd ESO	4th ESO	Biology 2nd Baccalaureate
Index by courses	Forums	Geología 2º Bach.

Skip navigation Biology and Geology 3rd compulsory secondary education Biology and Geology 3rd ESO 01. General organization of the human body 1.1. Levels of organization of the human body 1.2. The cell 1.2.1. The prokaryotic cell 1.2.2. The eukaryotic cell 1.2.2.1. The eukaryotic animal cell 1.2.2.2. The eukaryotic plant cell 1.3. Tissues 1.4. Organs, systems and apparatus 1.5. Bibliography and student work 02. Food and health 2.1. Feeding and nutrition 2.2. Nutrients 2.2.1. Types of nutrients 2.2.2. The energy of nutrients 2.3. The food 2.4. Diets 2.5. Food consumption 2.5.1. Labelled 2.5.2. How to shop and cook 2.6. Food preservation and hygiene 2.7. Food production 2.7.1. Intensive agriculture 2.7.2. Intensive livestock 2.7.3. Aquaculture 2.7.4. Transgenic foods 2.7.5. Organic food 2.8. Eating-related illnesses 2.9. Bibliography and student work 03. The digestive system and digestion 3.1. Nutrition function 3.2. Digestive system 3.2.1. Ingestion 3.2.1.1. Chewing 3.2.1.2. Insalivation 3.2.1.3. Swallowing 3.2.2. Digestion 3.2.3. Absorption 3.2.4. Expulsion or egestion 3.3. Diseases of the digestive system 3.3.1. Diseases in the mouth 3.3.2. Diseases in the stomach 3.3.3. Diseases in the intestine 3.3.4. Liver disease 3.4. Healthy habits related to the digestive system 3.5. Bibliography and student work 04. The respiratory system and respiration 4.1. Respiratory tract and lungs 4.1.1. Airways 4.1.2. Lungs 4.1.3. The gaseous exchange 4.2. Respiratory activity 4.3. Diseases of the respiratory system 4.4. Healthy habits related to the respiratory system 4.5. Bibliography and student work 05. The circulatory system and circulation 5.1. General organization of the circulatory system 5.2. The blood 5.3. The heart 5.4. Heart movements 5.5. Blood vesels 5.6. Blood pressure 5.7. The blood circulation 5.8. Lymph and lymphatic system 5.9. Diseases of the circulatory system 5.9.1. Diseases of the blood vessels 5.9.2. Heart disease 5.9.3. Blood diseases 5.10. Healthy habits for the circulatory system 5.11. Bibliography and student work 06. The excretory system and excretion 6.1. Excretion 6.2. Urinary system 6.2.1. Kidneys 6.2.2. Urine formation 6.2.3. Urinary tract 6.3. Kidney disease 6.4. Healthy habits for the excretory system 6.5. Bibliography and student work 07. The nervous system 7.1. Relationship function and the nervous system 7.2. Cells of the nervous system 7.2.1. Neuron 7.2.2. Glia 7.3. Nerve impulse 7.4. Organization of the nervous system 7.4.1. The Central Nervous System 7.4.1.1. Encephalon 7.4.1.2. Spinal cord 7.4.2. The Peripheral Nervous System 7.4.2.1. Somatic Nervous System 7.4.2.2. Autonomic nervous system 7.5. Nervous acts 7.6. Nervous system diseases 7.6.1. Brain injuries 7.6.2. Spinal cord injuries 7.6.3. Neuropsychological diseases 7.6.4. Pathologies related to lifestyle 7.7. Healthy habits and mental health 7.8. Drug addiction 7.8.1. Common characteristics of drugs 7.8.2. Classification of drugs 7.9. Bibliography and student work 08. The endocrine system 8.1. The types of responses 8.2. The endocrine system 8.2.1. Endocrine glands 8.2.2. Hormonal control 8.3. Endocrine system diseases 8.4. Bibliography and student work 09. Sensory receptors. The sense organs 9.1. Perception: sensory receptors 9.1.1. The touch and the pain 9.1.2. The sense of smell 9.1.3. Taste 9.1.4. The eye and vision 9.1.5. The ear: hearing and balance 9.2. Healthy habits for the sense organs 9.3. Bibliography and student work 10. Effector organs. The locomotor system 10.1. The skeleton 10.1.1. The bones 10.1.1.1. Bones of the human body 10.1.2. Joints 10.2. Musculature 10.2.1. Muscles of the human body 10.3. Healthy habits of the locomotor system 10.4. Musculoskeletal disorders 10.5. Bibliography and student work 11. Human sexuality and reproduction 11.1. Human reproduction 11.1.1. The male reproductive system 11.1.2. Spermatozoon 11.1.3. The female reproductive system 11.1.4. The ovule 11.1.5. The menstrual cycle 11.1.6. Fertilization, pregnancy and childbirth 11.1.6.1. Fertilization 11.1.6.2. Pregnancy 11.1.6.3. Birth 11.2. Natality control 11.2.1. Contraceptive methods 11.2.2. Reproduction techniques 11.2.2.1. Exploratory techniques 11.2.2.2. Assistance techniques in childbirth 11.2.2.3. Assisted reproductive techniques 11.3. Adolescence and sexuality 11.4. Main sexually transmitted diseases and prevention 11.5. Prevention and sexual hygiene 11.6. Bibliography and student work 12. Health and disease 12.1. What is health? 12.1.1. Health indicators 12.1.2. Health determinants 12.2. The disease and types of diseases 12.3. Infectious diseases 12.3.1. Types of infectious diseases 12.3.2. Immunity and immune system 12.3.3. Prevention and cure of infectious diseases 12.4. Non-infectious diseases 12.5. First aid 12.6. Transplants and donation of cells, blood and organs 12.7. Bibliography and student work 13. Ecosystems 13.1. Ecosystem components 13.2. Types of ecosystems 13.3. Factors influencing the ecosystem 13.4. Balance in ecosystems 13.5. The soil as an ecosystem 13.6. Bibliography and student work 14. The external geological activity of the Earth 14.1. Solar energy on Earth 14.2. External geological processes 14.2.1. Weathering 14.2.2. Erosion, transport and sedimentation 14.3. Factors that condition the modeling of the relief 14.4. Forms of relief modeling 14.4.1. Wild or stream waters 14.4.2. Torrential modeling 14.4.3. River modeling 14.4.4. Karst modeling. Groundwater 14.4.5. Littoral modeling 14.4.6. Glacier modeling 14.4.7. Wind or desert modeling 14.5. Geological action of living beings 14.6. Geological action of the human being 14.7. Bibliography and student work 15. The internal geological activity of the Earth 15.1. The internal energy of the Earth 15.2. Volcanoes 15.2.1. Types of volcanoes 15.2.2. Volcanic risk 15.3. Earthquakes 15.3.1. Seismic risk 15.4. Bibliography and student work « Previous \| Next » 3.2.2. Digestion The digestion The digestion is the transformation of foods, previously ingested into simpler substances that can be absorbed and utilized by the cells . Throughout the digestive tract, food is transformed into different substances. Digestion can be of two types: Mechanical digestion. The food is fragmented, kneaded, mixed, etc. Chemical digestion. Some substances, such as digestive enzymes, are responsible for breaking down food, aided by other chemicals. These substances are secreted by the walls of the digestive tract and by the adjacent glands. Digestion begins in the mouth, when the amylase or ptyalin enzyme contained in saliva begins to chemically digest carbohydrates. In addition, the teeth and the tongue facilitate this digestion with their mechanical action. But the most important digestion processes occur in the stomach and small intestine, where the pancreas and liver also play a role in digestion. Answer in your notebook 3.6.- What is the difference between chemical and mechanical digestion? Answer in your notebook 3.7.- What parts of the mouth are involved in mechanical digestion? And in chemical digestion? Answer in your notebook 3.8.- How can a person's missing teeth affect the digestion of food? Stomach In the stomach, it is a widening of the digestive tract that connects with the esophagus through the cardia (unlike the pylorus, it is always open) and with the small intestine through a valve, the pylorus, which prevents the backward movement of food. Modificado de By Stomach_diagram.svg:Indolences at en.wikipediaderivative work: Mcstrother (Stomach_diagram.svg) [CC BY 3.0], from Wikimedia Commons The stomach produces gastric digestion, in which the glands that line the inner walls produce gastric juice, which when mixed with the food bolus forms a more fluid mass called chyme. The gastric juice contains: *Hydrochloric acid: with bactericidal action and favoring the action of pepsin. Pepsin: it is a digestive enzyme that digests proteins. To prevent gastric juice from damaging the proteins in the stomach lining, the stomach is lined with mucus. The stomach is made up of layers of muscles that allow (mechanical) movements to be made so that the chyme mixes well. The longer it is in the stomach, the more gastric juice is secreted and the more it is digested, until the pylorus opens and the chyme* passes into the small intestine. There are foods, such as fats and proteins, that need to be in the stomach for a long time, while others, such as carbohydrates, need to be in the stomach for less time. Activity: Actions of the stomach in digestion. 3D model: Anatomy of the stomach. Answer in your notebook 3.9.- If gastric juice (contains hydrochloric acid and pepsin) digests proteins, why doesn't it also digest the walls of the stomach, which are also proteins? Small intestine The small intestine is a tube that is about 7 meters long that connects the stomach (pylorus) with the large intestine (ileocecal valve). The small intestine is divided into three parts: the duodenum, the jejunum, and the ileum. In the first part, the *duodenum, about 25 cm long, the intestinal cells secrete intestinal juice, with a large amount of enzymes that digest food, breaking it down so that it can be absorbed and passed into the blood. In addition to the intestinal juice, they reach the intestine through the bile duct,* the pancreatic juice and bile (from liver) which assist digestion, forming a slurry called chyle. The intestinal juice and pancreatic juice containing lipases, amylases and proteases that attack lipids, carbohydrates and proteins, respectively. The bile emulsifies the fats, converting them into small droplets, thus facilitating the action of the lipases in the pancreatic juice. The action of all these enzymes allows the chemical digestion of all foods. Peristaltic movements continue to occur throughout the small intestine. Discovering words Where does the word intestine come from? And duodenum? And jejunum? And ileum? Feedback The word intestine comes from the Latin intestinus , which means interior. It does not refer only to this part of the digestive system, but to everything that is inside. Therefore, if you ever hear the expression internal wars , it refers to a conflict that happens within a country, organization, company, family, etc. without any intervention from outside. The first part of the small intestine the duodenum, which also comes from the latin duodenum, which means "twelve fingers", although it actually measures about 25 cm. It is followed by the jejunum, which comes from the Latin ieiunum, which means empty because it always appeared empty in the dissections of the corpses. The same origin has the word fast, empty when we have not eaten anything, and breakfast, when we break that fast. The word ileum, on the other hand, comes from the Greek eiléōn , which is twisted. Don't confuse it with the ilium, the hip bone. Pancreas The pancreas is an organ located in the abdomen, below and behind the stomach that has dual functions: Endocrine secretion: produces hormones such as insulin and glucagon, as will be seen in the topic of the endocrine system. Exocrine secretion: produces pancreatic juice, which together with bile mixes with intestinal juice to form chyle. Modificado en la obra de CNX OpenStax [CC BY 4.0], via Wikimedia Commons Liver The liver forms bile that is stored in the gallbladder. The bile contains no enzymes but some bile salts to emulsify fat, leaving as small droplets that can be attacked by digestive juices. In addition, bile contains other pigments, such as bilirubin, which is red in color, and biliverdin, which is green, from the breakdown of hemoglobin, which give the characteristic color of stool. The liver is responsible for removing different substances from the blood that may be harmful to the body, such as alcohol, making them harmless. Activity: Digestion in each part of the digestive system. 3D model: Anatomy of the liver. Answer in your notebook 3.10.- How does the liver intervene in digestion? What about the pancreas? Answer in your notebook 3.11.- What are the differences between chyme and chyle? Answer in your notebook 3.12.- Make a table in which the names of the digestive juices and their function appear in order. Curiosity: Termites digest wood thanks to microorganisms Would you like to watch a video that explains how termites can digest wood thanks to microbes? Feedback Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » You can ask, comment, contribute, get in touch with other users in the forum of this course. This course is translated from https://biologia-geologia.com/BG3/
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The digestion

Stomach

Small intestine

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Pancreas

Liver

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