Human Digestive System PDF

 Human Digestion Humans have a complete digestive system. The tube our food is digested through is called the gastrointestinal tract, or GI tract for short It is approximately 7-9 meters long Its purpose is to ingest, digest, absorb and egest our food ...

 Human Digestion Humans have a complete digestive system. The tube our food is digested through is called the gastrointestinal tract, or GI tract for short It is approximately 7-9 meters long Its purpose is to ingest, digest, absorb and egest our food  The Journey Begins Both physical and chemical digestion of your food starts in the mouth Physical breakdown in the mouth is done by: Teeth ○ Incisors and canines tear and cut the food ○ Molars grind and crush food It is broken down chemically with your saliva which contains the enzyme amylase  Saliva Your saliva helps digest your food in many ways Amylase is an enzyme which breaks down complex carbohydrates (polysaccharides) into smaller disaccharides It also contains mucus which is a protective lubricant which helps you swallow When the food is ready to be swallowed as a moist ball of food it is called a bolus  Chemical Digestion RECAP Carbohydrates start getting broken down in mouth  Swallowing Food When you swallow, your tongue pushes the food to the back of your mouth It is then pushed into the pharynx and your soft palate is raised to prevent food entering your nasal passage At the same time the epiglottis covers the entrance to your trachea Ingestion: The process of taking food into the body by swallowing.  Esophagus Once food is swallowed, it is moved to the stomach through the esophagus Esophagus is a long muscular tube As it is stretched by food, peristalsis pushes the food downwards Peristalsis: Wave-like muscles contractions  Stomach The food enters the stomach through a circular piece of muscle called the gastroesophageal sphincter When this muscle relaxes, food can enter the J-shaped muscular organ called the stomach Stomach can accommodate 2L of food Chyme: Food mixed with gastric juices then exits the stomach through the pyloric sphincter  Digestion in the Stomach Both chemical and physical digestion of food occur in the stomach. The stomach muscle churns which physically breaks down food and mixes gastric juice with food Gastric juice is made of hydrochloric acid (HCl), salts, enzymes, water and mucus ○ Produced by glands in the stomach to help digest food HCl converts pepsinogen into an active form called pepsin ○ Pepsin breaks up peptides which breaks down protein  Chemical Digestion RECAP Protein begins to get broken down in stomach  Small Intestines Most of your digestion happens in the small intestine 7 m long tube, 2.5 cm in diameter ○ Digests lipids, carbohydrates and proteins There are 3 sections: ○ Duodenum: where most enzymes are added ○ Jejunum: digestion continues, most nutrients are absorbed ○ Ileum: where more nutrients are absorbed  Absorption in the Small Intestines The inner surface of the small intestine is made of villi and microvilli Villi: Finger-like projections that maximize the surface area and absorption of nutrients. Nutrients enter the bloodstream through capillaries in villi.  REMEMBER: Accessory Organs Liver produces bile which is sent to be stored in the gallbladder. Gallbladder secretes bile into the duodenum. Pancreas secretes pancreatic fluid into the duodenum. (The pancreas contains numerous enzymes)  Chemical Digestion RECAP Fats and nucleic acids begin to breakdown in small intestine Carbohydrates and proteins continue to break down  The Large Intestine The Large intestine is 1.5 m in length, 7.6 cm in diameter It is joined to small intestines through the cecum The colon is the longest part of the large intestine It is made up of: Ascending colon Transverse colon Descending colon Sigmoid colon  Role of the Large Intestine After nutrients have been absorbed, remaining material moves to the large intestine. The large intestine plays a vital role in the absorption of: Water Ions Vitamins Large intestine also houses about 500 species of anaerobic bacteria (they live without oxygen) Important in vitamin production and the proper digestion of food  Egestion The last 20 cm of the digestive tract is called the rectum Holds feces until it can be eliminated or egested through the anus Egestion: removal of waste food materials from the body Respiratory Surfaces 2 requirements for respiratory surfaces 1. They must be large enough for gas exchange to occur - Quick enough to meet body’s needs 2. They must be moist so gases can dissolve Types of Respiratory Surfaces: Lungs Most land animals use lungs since they can provide more gas exchange Lungs contain sacs lined with a moist surface (epithelium) Blood transports gases to cells by diffusion  The Human Respiratory System Respiratory tract allows air to travel into the body to reach the moist lungs  The Lungs Provide the respiratory membrane, large surface area and supply of blood required for diffusion They are contained within your thoracic cavity and are protected by your rib cage  Inhalation Nasal Cavity: warms and moistens air from outside before it enters the lungs prevents damage to the thin, delicate tissue of your lungs Nasal cavity is lined with hairs (cilia) and mucus to filter out and trap any airborne particles  Inhalation Air then travels into… Pharynx: the membrane-lined cavity behind the nose and mouth, connecting them to the esophagus Epiglottis: is a flap that acts as a switch between the larynx and the esophagus. permits air to enter the trachea to the lungs and food to pass into the esophagus.  Larynx The air then moves into the larynx Larynx: voicebox, made of cartilage and used for sound production in mammals  The Trachea Trachea: hollow tube that allows air to pass from the pharynx into the lungs Has c-shaped rings of cartilage around it to keep it semi-rigid and open Lined with mucus producing cells and cilia which protect the lungs from foreign matter  The Trachea The trachea branches into two bronchi (bronchus singular) The bronchi then branch off into smaller tubes called the bronchioles These tubes end in small sacs called the alveoli  Alveoli Alveoli: made of warm, moist and extremely thin membrane Allows for easy diffusion of gases across the membrane and into the blood Each alveolus is tiny, and is surrounded by a bed of even tinier capillaries. Large number of alveoli allow for maximum surface area for gas exchange Green arrows represent CO2 movement, blue arrow represents O2 movement  Transporting Gases Hemoglobin → a protein in red blood cells. Hemoglobin binds with oxygen from the lungs and transports it to the body’s tissues. There, the hemoglobin releases enough oxygen to meet the needs of the cells. When CO2 leaves the cells, it also enters the blood. Some is carried by hemoglobin, most is carried in the blood fluids.