Notes Digestive and Respiratory Systems (1) PDF

!C UNIT 4. NUTRITION. DIGESTIVE AND RESPIRATORY In order to carry out the nutrition function, living organisms need an exchange of substances to take place between their surrounding environment and their cells. This exchange occurs in different ways according to whether the organism is unice...

!C UNIT 4. NUTRITION. DIGESTIVE AND RESPIRATORY In order to carry out the nutrition function, living organisms need an exchange of substances to take place between their surrounding environment and their cells. This exchange occurs in different ways according to whether the organism is unicellular or multicellular. 1.1 How substances are exchanged in living organisms Unicellular organisms perform the nutrition function by exchanging substances directly with their surrounding environment. In other words, nutrients and oxygen enter the cell through a plasma membrane, through which waste is also expelled. In multicellular organisms, such as human beings, most cells do not come into contact with the outside world and cannot exchange substances with it directly. The nutrition function is performed through the joint action of different systems that act as intermediaries between the outside world and cells. 1.2 Substance exchange systems The following systems are involved in the exchange of substances between the outside world and the cells in our bodies: - The digestive system 1: This system transforms the food we eat into simpler substances (nutrients), which are absorbed and passed into the blood stream. - The respiratory system 2: This system takes oxygen (O2) from the air and transfers it to the blood. It also takes carbon dioxide (CO2) from the blood and expels it out of the body. - The circulatory system 3: This system uses blood to carry nutrients and oxygen to the cells. It also transports waste from the cells to the excretory organs, where they are expelled. - The lymphatic system 4: This system works with the circulatory system to transport substances. - The excretory system 5: This system extracts waste substances produced by cellular activity from the blood, before expelling them from the body. Other organs and systems (sweat glands, the respiratory system, etc.) are also involved in the excretion process, and we will study them in this unit.  Anatomy of the DIGESTIVE The digestive system is made up of the digestive tract and accessory digestive glands. The digestive tract is a very long tube made up of the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. VIDEO - The mouth. The mouth is a cavity where food is chewed and ground by the teeth. It contains the tongue, a muscular organ with many taste buds on it, which provide our sense of taste. Both parts carry out mechanical digestion, breaking down food into smaller pieces.The mouth also contains salivary glands. These produce saliva, which is secreted into the mouth and mixed with food by the tongue. The salivary glands, together with the tongue,  carry out the chemical digestion of carbohydrates. Following insalivation and mastication, the food is turned into a bolus. - The pharynx. This is a tube belonging to both the digestive and respiratory systems. Food travels from the mouth to the oesophagus, and air travels from the nose to the larynx. It has a ‘lap’, called the epiglottis, which acts as a lid and closes the respiratory tract to prevent food from blocking it. - The oesophagus. Food travels down the oesophagus to the stomach, as a result of contractions in its walls (peristaltic movements). Video https://www.youtube.com/watch?v=fDm93PENbGA - The stomach. The stomach is connected to the oesophagus through an opening called the cardia. The stomach has very strong muscles in its walls (mechanical digestion), in addition to glands, which secrete gastric juices that are then mixed with food, these gastric juices kill all the bacterias in the food. It is connected to the small intestine through an opening called the pylorus. There is chemical digestion in the stomach because of gastric juices. These are secreted by the glands in the stomach wall so in the stomach carry out the digestion of proteins. Following digestion in the stomach the bolus is turned into chyme. - The small intestine. This is a very long tube. It has glands that secrete intestinal juices and folds called intestinal villi. These contain tiny tubes called capillaries, through which blood flows. The nutrients obtained from the digestion process are passed into the bloodstream through these capillaries.There are three parts: - The duodenum is the first part of the small intestine that the stomach feeds into. It’s a short, descending chute (about 10 inches long) that curves around the pancreas in a “C” shape before connecting to the rest of the coiled intestines. In this part in order to break food down, the small intestine receives digestive juices from other organs in your digestive system, the liver (bile: to break lipids down) and pancreas (make pancreatic liquid to reduce the acidity). Moreover, the walls of duodenum make intestinal juices in order to break food down into nutrients. Consequently, the macromolecules are broken down into their basic components, this process turns the chyme into a milky fluid called chyle. - Jejunum:The remaining small intestine lays in many coils inside the lower abdominal cavity. Its middle section, called the jejunum, makes up a little less  than half of this remaining length. The jejunum is characterized by villi, special cells that amplify their surface of absorption. https://www.youtube.com/watch?v=5BeCEO96LFg - Ileum:The ileum is the last section of the small intestine. Here the walls of the small intestine begin to thin and narrow, and blood supply is reduced. Food spends the most time in the ileum, where the most water and nutrients are absorbed. - The large intestine. This is wider than the small intestine and has three parts: the caecum, the colon and the rectum, which leads outside the body through the anus, where faeces are expelled. The accessory glands The accessory glands are located outside the digestive tract; however, the digestive juices they secrete are passed into it. These juices contain a great variety of substances, the most important of which are digestive enzymes. The accessory glands are constituted by the salivary glands, the liver and the pancreas. - The salivary glands. There are three pairs of glands that secrete saliva into the mouth through their ducts, they contain amylase in order to break down carbohydrates. - The liver. This is the largest gland in the body. It performs important functions, for instance, secreting bile, stored in the gallbladder, as part of the digestive function. Although bile does not contain digestive enzymes, it helps us to digest lipids (fats) by acting as a detergent. The liver also performs other functions, such as storing glucose, iron and some vitamins, in addition to eliminating toxic substances, such as alcohol, from the blood. - The pancreas. This is an arrowhead-shaped gland found underneath the stomach. It serves two functions: a digestive function (it secretes pancreatic juices into the intestine in order to reduce the acidity) and an endocrine function, where it releases substances into the blood stream. KIND OF DIGESTIONS Mechanical digestion Mechanical digestion is a series of processes designed to reduce the size of food particles and make them travel through the digestive system. It consists of several stages: - Mastication. This consists of tearing, cutting, chewing and grinding the food we put in our mouths. It is carried out by the teeth and the movement of the lower jaw. - Insalivation. This consists of mixing the ground-up food with saliva by moving the tongue. A bolus is formed as a result. - Deglutition. This consists of using peristaltic movements to make the bolus travel through the pharynx and oesophagus to the stomach. Chemical digestion Chemical digestion is a series of processes that transform food into nutrients via the action of substances in the digestive juices. It takes place in different parts of the digestive system: - In the mouth. During the formation of the bolus, substances in the saliva act on carbohydrates, breaking them down into simpler substances. - In the stomach. When the bolus reaches the stomach, the stomach walls secrete gastric juices (with pepsin) that specifically act on proteins. The resulting half-liquid mush is called chyme. - In the small intestine. The intestinal juices (secreted by the intestinal walls), the bile (secreted by the liver) and the pancreatic juices (secreted by the pancreas) all act in the small intestine. Their action brings the chemical transformation of the chyme to an end, turning it into chyle. Chyle contains water, the nutrients resulting from digestion and other undigested products. Nutrients must reach all the cells in the body. They do this through the blood. Absorption in the small intestine The absorption of nutrients in the small intestine is a relatively quick process. This is because the intestinal wall has a large surface for absorption, which measures approximately 200 metres squared. This is because: - It is very long, measuring between 7 and 8 metres. - Its inside walls (known as intestinal mucus) are covered by a series of structures which increase the absorption surface area by about 600 times. Among these structures, the following are particularly important: - All along the small intestine, there are intestinal folds. In turn, these folds have thousands of intestinal villi, which cover the inside wall of the intestine. Inside them, there are many blood vessels and capillaries. - These villi are made up of cells with a plasma membrane that has many tiny folds known as microvilli. Absorption in the large intestine Most of the water and minerals present are absorbed into the large intestine. The large intestine has a greater diameter than the small intestine, measuring approximately 1 metre in length, and does not have villi. In the large intestine, gut lora (a collection of good bacteria that live in the intestine) transforms undigested products into faeces, which are expelled from the body through the anus. (Egestion or defecation) 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. Videos: - https://www.youtube.com/watch?v=HXrl37BC3QU - https://www.youtube.com/watch?v=1UvuBYUbFk0 - https://www.youtube.com/watch?v=6eQrZpnsUK0 RESPIRATORY SYSTEM  Our body needs oxygen to perform cellular respiration (mitochondria) in order to obtain energy. The goal of the respiratory system is to obtain oxygen and release the carbon dioxide from our body. The respiratory system is divided into two parts: the respiratory tract and the lungs. - The respiratory tract (Airways): The respiratory tract is a group of tubes that carry air from outside the body into the lungs and vice versa. It consists of the nostrils, pharynx (epiglottis), larynx, trachea, bronchi (bronchus) and bronchioles. The bronchioles end in sacs (called alveoli) with very thin walls that are surrounded by a network of capillaries. - The lungs: The lungs are two 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 the pleura, which is full of pleural fluid. This liquid protects the lungs from rubbing against the rib cage and facilitates the movements involved in breathing. Respiratory System Anatomy. - Nostrils: There are many capillaries, which warm air as it passes through. Also there is mucus in the nostrils in order to humidify the air and acts as a defence against some microorganisms too. In these passages there are also tiny hairs that avoid the entrance of some substances. - Pharynx: This is a tube belonging to both the digestive and respiratory systems. It has a ‘lap’, called the epiglottis, which acts as a lid and closes the respiratory tract to prevent food from blocking it. - Larynx: The epiglottis regulates the entrance to the larynx. This fibrous structure closes to stop food from entering the airways. The walls of the larynx are made of cartilage that makes sure it's always open. Here we can find the vocal cords. They are two ring-shaped folds that when air passes through them, they vibrate and make sounds. These sounds vary depending on the position of the tongue, lips and teeth. - Trachea: This is a tube that has c-shaped cartilage rings that are open at the back. It contains mucus, which traps foreign particles in the air, and cells with vibrating filaments known as cilia. Cilia move the mucus filled with foreign particles towards the larynx where it’s redirected to the oesophagus and the stomach (or outside as a spittle). - Bronchi: The trachea is divided into two bronchi. Each bronchi is connected to one of the lungs. - Bronchioles: Each bronchus branches out generating smaller and smaller ducts, bronchioles. The last branches of the bronchioles end in tiny sacs known as pulmonary alveoli. Each of them is cover by one blood capillary in order to exchange the gases. - Lungs: The lungs are formed by the bronchi, bronchioles, pulmonary alveoli and a wide network of blood capillaries all of them cover by the pleura, a layer composed of two membranes. In between membranes, there is a liquid that keeps them together and allows them to move gently against each other. Gas exchange: Gas exchange takes place in the bronchioles. Gases move from where there is a higher concentration to where there is a lower concentration without energy consumption. This process is known as diffusion. Air from outside the body has more oxygen than the air circulating in the capillaries. When air enters the body, this causes diffusion and the oxygen passes from the alveoli to the capillaries. Blood has more CO2 than the outside air so diffusion moves CO2 from the blood to the alveoli. When the CO2 is in the alveoli it can then be released from the body. Video Pulmonary ventilation: There are three stages to breathing in the respiratory system: inhalation, gas exchange and exhalation. Inhalation During inhalation, air from the atmosphere enters into the lungs. In order for this to happen, the diaphragm contracts and the lungs expand. Air enters the respiratory system through the mouth or through nasal passages, where it is heated before travelling through the respiratory tract to the alveoli. Gas exchange Gases difuse naturally. In other words, they pass through cell membranes, moving from where they are most concentrated, to where there is least concentration. For this reason, O2 (which is highly concentrated in the alveoli) passes through the walls of these alveoli into the incoming blood (which is low on O2 surround them. For the same reason, the abundant CO2) and is then expelled.), difusing through the thin walls of the capillaries that in this blood coming from the cells difuses into the inside of the alveoli (where there is little CO2 Exhalation During exhalation, the diaphragm relaxes and the lungs reduce in volume. This ensures the air they contain, which is loaded with CO2 expelled through the respiratory tract.