They are located outside the digestive tract although the digestive juices they secrete are passed into it. These juices contain a great variety of digestive enzymes (type of proteins that accelerate the breakdown of complex food into nutrients)

● The salivary glands: 3 pair of glands that secrete saliva into the mouth.

● The liver: Largest gland. It secretes bile, which is stored in the gallbladder. Bile helps us to digest lipids by acting as a detergent. The liver also performs other functions such as storing glucose, iron and vitamins and eliminating toxic substances (alcohol) from the blood.

● The pancreas: Arrowhead-shaped gland found under the stomach. 2 functions digestive function endocrine function

The digestive process consists of various different stages: mechanical digestion, chemical digestion, absorption and egestion or defecation. MECHANICAL DIGESTION: Processes designed to reduce the size of food particles and make them travel through the digestive system. 3 stages: Mastication: tearing, cutting, chewing and grinding the food. It is carried out by the teeth and the movement of the lower jaw.

Insalivation: mixing the ground-up food with saliva by moving the tongue. A bolus is formed as a result.

Deglutition: using peristaltic movements to make the bolus travel through the pharynx and oesophagus to the stomach.

ABSORPTION: Process through which nutrients pass through the intestinal walls into the circulatory system to reach all the cells in the body.

➢ Absorption in the small intestine: relatively quick process because of its large absorption surface (200m2 ): – very long (7-8 m) – inside walls covered by intestinal folds with thousands of intestinal villi which have many blood capillaries in its inside and are made up of cells with a plasma membrane that has many tiny folds known as microvilli.

➢ Absorption in the large intestine: water and minerals are absorbed here. It has greater diameter, measures 1 m length and has no villi.

EGESTION or DEFECATION: In this process undigested products (waste) are eliminated. In the large intestine, gut flora (a collection of good bacteria that live in the intestine) transforms undigested products into faeces, which are expelled from the body through the anus. Food contains substances that we cannot digest or, therefore, absorb. Fibre is one of these substances. None of the digestive enzymes in our bodies can digest it and turn it into glucose. However fibre plays an essential role in the activity of the digestive system as it helps to move substances through the intestine and prevents constipation. 

The respiratory system exchanges gases with the external environment. It takes oxygen (O2 ) from the air and transfers it to the blood stream, while taking carbon dioxide (CO2 ) from the blood and expelling it from the body. ➢ The respiratory tract: group of tubes that carry air from outside the body into the lungs and vice versa: nasal passages, pharynx, larynx, trachea, bronchi, bronchioles. ➢ The lungs: spongy organs located in the rib cage and separated from the abdomen by a muscle called the diaphragm. They are surrounded by a double membrane, called pleura, which is full of pleural fluid.

Caused by unhealthy diet viral or bacterial infections Attending to the part of the digestive system affected:

Illnesses of the mouth: dental cavities (= tooth decay): tooth enamel is destroyed. gingivitis: inflammation of the gums that can lead to tooth loss. Stomach illnesses: gastritis: inflammation of the mucous lining the stomach. ulcers: wounds usually found in the stomach or the duodenum.

Liver illnesses: hepatitis: inflammation of the liver caused by viruses, excessive alcohol consumption or certain medications.

Intestinal illnesses: gastroenteritis: caused by bacteria found in contaminated water or food. constipation: condition associated with hardened faeces. salmonellosis: caused by eating food contaminated with Salmonella bacteria. appendicitis:the appendix becomes inflamed and painful.

Some digestive illnesses can be caused by different pathogens (bacteria, fungi, parasites, viruses) present in contaminated food or water.

➢ Salmonellosis: food contaminated with Salmonella bacteria found in contaminated water, in poorly preserved foods made with egg like mayonnaise and cream sauces, and in meat. Symptoms include headache, vomiting and diarrhoea.

➢ Botulism: food contaminated with Clostridium botulinum bacteria that produces botulinum toxin, a potentially lethal toxin that causes neurological disorders. Contamination occurs when consuming inadequately preserved foods.

➢ Trichinosis: associated with eating raw meat (pork) which is infested with the larvae of a nematode called Trichinella. It causes abdominal pain, vomiting, diarrhoea and fever.

➢ Anisakiasis:caused by eating raw or undercooked fish containing the larvae of the Anisakis worm. Symptoms include abdominal pain, vomiting, diarrhoea.

Food-borne illnesses result from eating spoiled food or food that has been contaminated. Raw foods such as fruit and vegetables and undercooked meat or fish may be contaminated by some of this pathogens.

RESPIRATORY ILLNESSES Caused by smoking or long-term exposure to air pollution. viral or bacterial infections allergies

Chronic bronchitis: irritation of the bronchi caused by smoking or exposure of pollutants in the air.

Asthma: inflammation of the bronchi caused by smoking or exposure to pollution, but also by allergies.

Influenza (or flu): caused by the influenza virus, leads to death only in elderly people and high-risk groups.

Lung and throat cancer: most commonly affect smokers.

BLOOD: is a thick, red liquid composed of plasma (formed by water, minerals, nutrients from digestion, waste substances…) and blood cells:

➢ Red blood cells are small cells without a nucleus. They contain haemoglobin (red protein containing iron) that helps transport O2 and CO2 . (4-5 million/mm3 )

➢ White blood cells are larger and less numerous (8000/mm3 ). They defend our body against pathogens and tumour cells.

➢ Platelets are not true cells, but pieces of cytoplasm. They help our blood to clot. (300000/mm3 )

The functions of blood nutrients absorbed during digestion

➢ It transports substances: blood carries to the cells. oxygen obtained from the lungs waste products of cellular activity to the excretory organs.

➢ It regulates body temperature: blood helps maintaining body temperature by distributing heat throughout the body.

➢ It defends the body: White blood cells defend our body from pathogens and tumour cells. Platelets also help our blood to clot, ensuring that we do not lose too much blood when we have an accident.


➢ Arteries: thick and elastic walls. They carry the blood from the heart to the organs. They branch off into arterioles (smaller arteries).

➢ Veins: thinner and less elastic walls. They have valves which prevent blood from flowing backwards. They take the blood from the organs to the heart. They are formed by the joining of small veins called venules.

➢ Capillaries are microscopic blood vessels that reach all the cells. They join the arterioles and venules to form a closed circuit.Their walls are very thin and allow nutrients, gases and waste to be exchanged between the blood and the cells.

The heart… – is a muscular, hollow organ in charge of pumping the blood through the blood vessels – is located in the rib cage (thoracic cage) between the lungs – is divided into two halves, right and left, and is separated lengthwise by the septum.

Each half has two cavities: an atrium and a ventricle.

➢ The atria (upper chambers). The pulmonary veins end in the left atrium. The venae cavae, through which the blood from the rest of the body’s veins flows, end in the right atrium.

➢ The ventricles (lower chambers): joined to the atria by valves that prevent the blood from flowing backwards (left: mitral valve/ right: tricuspid valve). The pulmonary artery leaves the right ventricle and carries blood to the pulmonary alveoli so that gas exchange takes place. The aorta artery leaves the left ventricle and distributes blood containing O2 around the body. These arteries have valves at the point of exit called semilunar valves, which prevent the blood from flowing back into it.


➢ The heart has a special muscle tissue, called the cardiac muscle, which allows it to contract and dilate in order to pump the blood. The sequence of these contraction movements (or systole) and dilatation movements (or diastole) is called the cardiac cycle.

➢ During a cardiac cycle, the blood enters the heart through the veins and leaves it through the arteries. However, the blood vessels remain full of blood at all times, as this is a continuous cycle.

The stages of the cardiac cycle

➢ Diastole: the atria are relaxed and dilated. This allows the blood to enter the heart: it flows to the right atrium from the venae cavae and to the left atrium from the pulmonary veins.

➢ Atrial systole: the atria contract and the blood flows into the ventricles: it flows from the right atrium to the right ventricle through the tricuspid valve and from the left atrium to the left ventricle through the mitral valve (preventing the blood from flowing back into the atria).

➢ Ventricular systole: the ventricles contract forcing the blood into the arteries through the semilunar valves: the blood leaves the right ventricle through the pulmonary artery and the left ventricle through the aorta.


➢ Humans have a double and complete circulatory system.

➢ It is double because blood passes through the heart twice in every single complete cycle; in other words, it runs through two circuits: the pulmonary circuit and the systemic circuit. In the pulmonary circuit, the blood releases CO2 into the alveoli and picks up oxygen. In the systemic circuit, the blood delivers O2 and nutrients to all the cells so that they can carry out the vital functions, and picks up CO2 and waste produced by cellular metabolism.

➢ It is complete because oxygen-rich blood and carbon-dioxide-rich blood do not mix because the right side of the heart is completely separated from the left side by the septum.

The pulmonary circuit (or shorter circuit) Path the blood takes between the heart and the lungs. Blood is pumped through this circuit by the right side of the heart.

➢ It begins when oxygen-poor blood picked up from all the body organs reaches the right atrium and flows into the right ventricle, from where it exits to the pulmonary artery.

➢ The pulmonary artery branches off into two arteries divide further, following the branches of the bronchioles.

➢ When the blood passes through the alveoli, it releases carbon dioxide and picks oxygen. Once this gas exchange has taken place, the blood flows into the pulmonary veins, which carry it to the left atrium of the heart.

The systemic circuit (or longer circuit) Path the blood takes between the heart and the different organs of the body. Blood is pumped through this circuit by the left side of the heart. ➢ The oxygen- and nutrient-rich blood in the left atrium flows into the left ventricle from where is pumped into the aorta. The aorta divides into arterioles and capillaries that eventually reach all the organs. ➢ As it passes through the body´s tissues and organs, the blood releases nutrients and O2 and picks up waste substances and CO2 . Then it flows back into the right atrium of the heart through the venae cavae and the pulmonary circuit begins again.

The exchange of substances between the circulatory system and the cells is not carried out directly because capillaries and cells are not in direct contact: there is a liquid between them called interstitial fluid. The capillaries fill the interstitial fluid with nutrients and oxygen that then pass into the cells. The cells discharge waste substances into the interstitial fluid that then pass into the capillaries´ blood.

The lymphatic system maintains the interstitial fluid with a constant composition for the correct functioning of our bodies. Lymph is a clear liquid formed from interstitial fluid that is carried by the lymphatic system. The lymphatic system is in charge of collecting any excess of interstitial fluid that remains between the cells and returning it to the blood. It also transports fats that are absorbed in the intestine, and takes part in the body’s defence system by creating white blood cells.