UNIT 3

NUTRITION AND DIGESTION

3.1WHAT IS

NUTRITION?

The process of nutrition allows living beings to obtain the matter and the energy they need for making their own matter and for carrying out their vital functions.

3.2 KINDS OF

ORGANISMS ACCORDING

TO NUTRITION

Living beings can be placed into two groups according to what they need from the environment:Producer organisms: they take inorganic substances from the environment. They also need a source of energy that they can use. Example: photosynthesis→sunlight.Consumer organisms: they need to take food from the environment, this is always organic matter already formed by other living beings.

3.3 HOW SUBSTANCES

ARE TAKEN IN AND

EXPELLED

The process of nutrition means that various substances enter the organism and other different substances are expelled either because they aren´t useful or because they are toxic.

SUBSTANCES WHICH ENTER THE ORGANISM

Substance Entrance Use

Air

Into the lungs by means of respiratory movements

The lungs take the oxygen

contained in the air

Water

Through ingestion into the digestive

system

We use the water we drink and the water contained in

foods

Foods

Through ingestion into the digestive

system

We make use of proteins, sugars

and fats

PRODUCTS EXPELLED BY THE ORGANISM

Product Exit Use

Air

From the lungs by means of respiratory movements

The expelled air is rich in carbon

dioxide

Urine and sweat

Through the urinary tract and sweat

glands

Water and toxic substances for the organism such as urea

Faeces Expulsion of solid waste

from digestion

Undigested remains of food

substances

3.4 THE SYSTEMS

INVOLVED IN HUMAN

NUTRITION

The processes related to nutrition are carried out by four organ systems in our body: the digestive system, the respiratory system, the circulatory system and the excretory system. All these systems and processes are controlled by the nervous system.

THE SYSTEMS RELATED TO NUTRITION

Digestive system

Excretory system

Respiratory system

Circulatory system

System Processes carried outDigestive(the digestive tract and associated glands)

Digestion: this occurs in the mouth, the stomach and the small intestine. It consists of the separation of the substances that can be used from the foods.Absorption: this occurs in the small intestine. The substances which can be used pass into the bloodstream. Expulsion of wastes: this occurs in the large intestine. Undigested remains and unusable substances are expelled.

Respiratory(the respiratory paths and the lungs)

The exchange of gases in the alveoli, where the blood takes oxygen and releases carbon dioxide. The respiratory movements are produced constantly and allow air to enter and leave the lungs.

Circulatory(the heart and the blood vessels)

This circulates the blood throughout the body. Food substances, water and oxygen are transported from the digestive system to cells. Carbon dioxide and waste substances produced by the cells are collected.

Excretory(the kidneys, the urinary tracts and sweat glands )

The elimination of waste substances transported in the blood and which may be toxic. The kidneys filter the blood and separate all these substances which are expelled in the urine. The sweat glands also participate in the excretion process by producing sweat.

System Processes carried out

Digestive

(the digestive tract and associated glands)

Digestion: this occurs in the mouth, the stomach and the small intestine. It consists of the separation of the substances that can be used from the foods.Absorption: this occurs in the small intestine. The substances which can be used pass into the bloodstream. Expulsion of wastes: this occurs in the large intestine. Undigested remains and unusable substances are expelled.

Respiratory

(the respiratory paths and the lungs)

The exchange of gases in the alveoli, where the blood takes oxygen and releases carbon dioxide. The respiratory movements are produced constantly and allow air to enter and leave the lungs.

Circulatory

(the heart and the blood

vessels)

This circulates the blood throughout the body. Food substances, water and oxygen are transported from the digestive system to cells. Carbon dioxide and waste substances produced by the cells are collected.

Excretory(the

kidneys, the urinary tracts and

sweat glands )

The elimination of waste substances transported in the blood and which may be toxic. The kidneys filter the blood and separate all these substances which are expelled in the urine. The sweat glands also participate in the excretion process by producing sweat.

3.5 THE DIGESTIVE

PROCESS

Animals obtain proteins, lipids and sugars from food. This is a very difficult task and it is done by the digestive system. There are three phases in food processing: digestion, absorption and the expulsion of waste.

The movement of food through the digestive tract is done thanks to peristaltic movements. These consist of the narrowing of the tube through the contraction of the muscles of the walls. The muscles contract successively in such a way that the progressive narrowing pushes the food regardless of the position of the body. On ocassion, such as vomiting, reverse peristaltic movements occur.

PERISTALTIC MOVEMENTS

3.6 DIGESTION

According to the changes in food, digestion can be:Mechanical: It consists of cutting, crushing, removing and diluting foods, bringing about physical changes.Chemical: It is done through the action of various substances which attack the food and bring about chemical changes in it, breaking it down into substances which are smaller.

STAGES OF DIGESTION

Digestion in the mouth is a result of mastication and salivation. Mastication cuts and crushes the food. Saliva is a liquid which is produced by the salivary glands in the mouth, there are three pairs of glands called the sublingual, the submaxilary and the parotoid glands. Saliva contains substances which act chemically on food.

After swallowing, food reaches the stomach where gastric digestion begins. Physical and chemical digestion also occur simultaneously in the stomach. The food moves and is softened thanks to the movement of the walls of the stomach and it is mixed with gastric juices. As a result of gastric digestion, a pulp known as chyme is produced and this gradually leaves the stomach via the pylorus.

The first section of the small intestine, the duodenum, continues the chemical digestion of the food. There, the chyme is mixed with intestinal juices (made by the walls of the duodenum), bile (produced by the liver) and pancreatic juice (from the pancreas). The result is a milky fluid known as chyle in which the substances that the body can assimilate have been separated.

3.7 ABSORPTION AND

THE ELIMINATION OF

WASTE

The chyle passes from the duodenum to the following parts of the small intestine, the jejunum and the ileum. The intestinal walls are very rough and filled with intestinal hairs, deep folds in the wall and many blood vessels.

The absorption consists of the useful substances in the food crossing through the intestinal wall and into the blood vessels. The blood then takes them to all the cells in the body.

The remains of the chyle which can not be used pass into the large intestine. In the first part, the ascending colon, begins to recover water and some ions. This process continues in the transverse colon. The final tract of the large intestine is the descending colon which stores the faeces. When a certain amount has been formed, the faeces pass to the rectum ready to be expelled via the anus.

DIGESTIVE SYSTEM

Mouth Liver Gall bladder Vermiform appendix Anus Large intestine: ascending colon (), transverse

colon () and descending colon() Small intestine: duodenum (), jejunum () and

ileum () Spleen Stomach Pancreas Pharynx Oesophagus Salivary glands Rectum

TEETHThe tooth formula is 4I+2C+4PM+6M per jaw. Adults have a total of 32 teeth. The third molar, also called the wisdom tooth, appears in adult-hood.

Molar 3rd (Wisdom tooth)Molar 2nd

Molar 1st

Pre-molar 2nd

Pre-molar 1st

Canine Incisors

THE STOMACH

OesophagusLower oesophageal sphincterCardiaStomach fundusGastric foldsStomach, greater curvatureStomach, lesser curvatureLayers of the wall of the stomach ():

mucus tunic (), muscular tunic () and serous tunic ()

Pylorus Initial stage of the duodenum

ASSOCIATED GLANDS AND THE DUODENUM

The liver and the pancreas share the final stage of the bile duct which releases the products of both glands (bile and gastric juices) into the duodenum. This duct opens into the duodenum through what is known as the ampulla of Vater

StomachPancreasLiverDuodenumGall bladderCystic conductBile ductPancreatic ductAmpulla of Vater

VOCABULARY

NutritionMechanical digestionChemical digestionMasticationSalivaChymeChyle

Nutrition: It is the process that allows living beings to obtain the matter and the energy they need for making their own matter and for carrying out their vital functions.Mechanical digestion: It consists of cutting, crushing, removing and diluting foods, bringing about physical changes.Chemical digestion: It is done through the action of various substances which attack the food and bring about chemical changes in it, breaking it down into substances which are smaller.

Mastication: It is a process in which the food is cut and crushed.Saliva: It is a liquid which is produced by the salivary glands in the mouth and contains substances which act chemically on food.Chyme: It is a pulp formed by food and gastric juices which is the result of gastric digestion.Chyle: It is a milky fluid formed by the chyme mixed with intestinal juices, bile and pancreatic juice, in which the substances that the body can assimilate have been separated.

UNIT MAP

TMUOHILVREGLAL BEADLDRVOMERIFRM NAXPEPDIUASNOAGESPHOUSALSVAIRY NGADLSURCTEM SOACTMHENPARASCYPNARXH

ELRAG NTNETISEI EDSCDINGEN OLCONSMALL IENESTITNDEOUDNMU AICNSDNGE OCONL UJUNJME ILMEU NTVASERSRE LCONO LSEPEN

MouthLiverGall bladderVermiform appendixAnusOesophagusSalivary glandsRectum StomachPancreasPharynx

Large intestine Descending colonSmall intestine Duodenum Ascending colon Jejunum Ileum Transverse colon Spleen

Mouth Liver Gall bladder Vermiform appendix Anus Large intestine: ascending colon, transverse

colon and descending colon Small intestine: duodenum, jejunum and ileum Spleen Stomach Pancreas Pharynx Oesophagus Salivary glands Rectum