A unique electrical system in the heart causes it to beat in its regular rhythm. The sinoatrial or SA node, a small area of tissue in the wall of the right atrium, sends out an electrical signal to start the contracting of the heart muscle. These electrical impulses cause the atria to contract first; they then travel down to the atrioventricular or AV node, which acts as a kind of relay station. From here the electrical signal travels through the right and left ventricles, causing them to contract and force blood out into the major arteries.
In the systemic circulation, blood travels out of the left ventricle, to the aorta, to every organ and tissue in the body, and then back to the right atrium. The arteries, capillaries, and veins of the systemic circulatory system are the channels through which this long journey takes place. Once in the arteries, blood flows to smaller arterioles and then to capillaries.
While in the capillaries, the bloodstream delivers oxygen and nutrients to the body's cells and picks up waste materials. Blood then goes back through the capillaries into venues, and then to larger veins until it reaches the vena cavae. Blood from the head and arms returns to the heart through the superior vena cava, and blood from the lower parts of the body returns through the inferior vena cava. Both vena cavae deliver this oxygen-depleted blood into the right atrium. From here the blood exits to fill the right ventricle, ready to be pumped into the pulmonary circulation for more oxygen.
In the pulmonary circulation, blood low in oxygen but high in carbon dioxide is pumped out the right ventricle into the pulmonary artery, which branches off in two directions. The right branch goes to the right lung, and vice versa. In the lungs, the branches divide further into capillaries. Blood flows more slowly through these tiny vessels, allowing time for gases to be exchanged between the capillary walls and the millions of alveoli (pronounced: al-VEE-oh-lie), the tiny air sacs in the lung.
During the process called oxygenation, oxygen is taken up by the bloodstream. Oxygen locks onto a molecule called haemoglobin in the red blood cells. The newly oxygenated blood leaves the lungs through the pulmonary veins and heads back to the heart. It enters the heart in the left atrium, and then fills the left ventricle so it can be pumped into the systemic circulation.
Lungs & Respiratory System Basics
Each day we breathe about 20,000 times. All of this breathing couldn't happen without help from the respiratory system, which includes the nose, throat, voice box, windpipe, and lungs. With each breath, you take in air through your nostrils and mouth, and your lungs fill up and empty out. As air is inhaled, the mucous membranes of the nose and mouth warm and humidify the air.
Although we can't see it, the air we breathe is made up of several gases. Oxygen is the most important for keeping us alive because body cells need it for energy and growth. Without oxygen, the body's cells would die.
Carbon dioxide is the waste gas that is produced when carbon is combined with oxygen as part of the body's energy-making processes. The lungs and respiratory system allow oxygen in the air to be taken into the body, while also enabling the body to get rid of carbon dioxide in the air breathed out.
Respiration is the term for the exchange of oxygen from the environment for carbon dioxide from the body's cells. The process of taking air into the lungs is called inhalation or inspiration, and the process of breathing it out is called exhalation or expiration.
Even if the air you breathe is dirty or polluted, your respiratory system filters out foreign matter and organisms that enter through the nose and mouth. Pollutants are breathed or coughed out, destroyed by digestive juices, or eaten by macrophages, a type of blood cell that patrols the body looking for germs to destroy.
Tiny hairs called cilia protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles that enter the nose with the breathed air. As air is inhaled, the cilia move back and forth, pushing any foreign matter (like dust) either toward the nostrils, where it is blown out, or toward the pharynx, where it travels through the digestive system and out with the rest of the body's waste.
The two openings of the airway (the nasal cavity and the mouth) meet at the pharynx (pronounced: far-inks), or throat, at the back of the nose and mouth. The pharynx is part of the digestive system as well as the respiratory system because it carries both food and air. At the bottom of the pharynx, the pathway for both food and air divides in two. One passageway is for food (the esophagus,, which leads to the stomach) and the other for air. The epiglottis, a small flap of tissue, covers the air-only passage when we swallow, keeping food and liquid from going into our lungs.
The larynx, or voice box, is the uppermost part of the air-only passage. This short tube contains a pair of vocal cords, which vibrate to make sounds. The trachea, or windpipe, extends downward from the base of the larynx. It lies partly in the neck and partly in the chest cavity. The walls of the trachea are strengthened by stiff rings of cartilage to keep it open so air can flow through on its way to the lungs. The trachea is also lined with cilia, which sweep fluids and foreign particles out of the airway so that they stay out of the lungs.
At its bottom end, the trachea divides into left and right air tubes called bronchi, which connect to the lungs. Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles. Bronchioles, which are as thin as a strand of hair, end in tiny air sacs called alveoli. Each of us has hundreds of millions of alveoli in our lungs — enough to cover a tennis court if they were spread out on the ground. The alveoli are where the exchange of oxygen and carbon dioxide takes place.
With each inhalation, air fills a large portion of the millions of alveoli. In a process called diffusion, oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels,) that line the alveolar walls. Once in the bloodstream, oxygen gets picked up by a molecule called haemoglobin in the red blood cells. This oxygen-rich blood then flows back to the heart, which pumps it through the arteries to oxygen-hungry tissues throughout the body.
In the tiny capillaries of the body tissues, oxygen is freed from the haemoglobin and moves into the cells. Carbon dioxide, which is produced during the process of diffusion, moves out of these cells into the capillaries, where most of it is dissolved in the plasma of the blood. Blood rich in carbon dioxide then returns to the heart via the veins. From the heart, this blood is pumped to the lungs, where carbon dioxide passes into the alveoli to be exhaled.
The lungs also contain elastic tissues that allow them to inflate and deflate without losing shape and are encased by a thin lining called the pleura This network of alveoli, bronchioles, and bronchi is known as the bronchial tree.
The chest cavity, or thorax, is the airtight box that houses the bronchial tree, lungs, heart, and other structures. The top and sides of the thorax are formed by the ribs and attached muscles, and the bottom by a large muscle called the diaphragm. The chest walls form a protective cage around the lungs and other contents of the chest cavity.
The diaphragm, which separates the chest from the abdomen, plays a lead role in breathing. When we breathe out, the diaphragm moves upward, forcing the chest cavity to get smaller and pushing the gases in the lungs up and out of the nose and mouth.
When we breathe in, the diaphragm moves downward toward the abdomen, and the rib muscles pull the ribs upward and outward, enlarging the chest cavity and pulling air in through the nose or mouth. Air pressure in the chest cavity and lungs is reduced, and because gas flows from high pressure to low, air from the environment flows through the nose or mouth into the lungs.
As we exhale, the diaphragm moves upward and the chest wall muscles relax, causing the chest cavity to contract. Air pressure in the lungs rises, so air flows from the lungs and up and out of respiratory system through the nose or mouth.
Food Is the Body's Fuel Source
What's the first step in digesting food? Believe it or not, the digestive process starts even before you put food in your mouth. It begins when you smell something irresistible or when you see a favourite food you know will taste good. Just by smelling that homemade apple pie or thinking about how delicious that ice cream is going to taste, you begin to salivate — and the digestive process kicks in, preparing for that first scrumptious bite.
If it's been a while since your last meal or if you even think about something tasty, you feel hungry. You eat until you're satisfied and then go about your business. But for the next 20 hours or so, your digestive system is doing its job as the food you ate travels through your body.
Food is the body's fuel source. The nutrients in food give the body's cells the energy and other substances they need to operate. But before food can do any of these things, it has to be digested into small pieces the body can absorb and use.
Body Basics: Digestive System
Almost all animals have a tube-type digestive system in which food enters the mouth, passes through a long tube, and exits as faces (poop) through the anus. The smooth muscle in the walls of the tube-shaped digestive organs rhythmically and efficiently moves the food through the system, where it is broken down into tiny absorbable nutrients.
During the process of absorption, nutrients that come from the food (including carbohydrates, proteins, fats, vitamins, and minerals) pass through channels in the intestinal wall and into the bloodstream. The blood works to distribute these nutrients to the rest of the body. The waste parts of food that the body can't use are passed out of the body as faces.
About the Digestive System
Every morsel of food we eat has to be broken down into nutrients that can be absorbed by the body, which is why it takes hours to fully digest food. In humans, protein must be broken down into amino acids, starches into simple sugars, and fats into fatty acids and glycerol. The water in our food and drink is also absorbed into the bloodstream to provide the body with the fluid it needs.
The digestive system is made up of the alimentary canal and the other abdominal organs that play a part in digestion, such as the liver and pancreas. The alimentary canal (also called the digestive tract) is the long tube of organs — including the esophagus, the stomach, and the intestines — that runs from the mouth to the anus. An adult's digestive tract is about 30 feet long.
How Digestion Works
Digestion Begins in the Mouth
The process of digestion starts well before food reaches the stomach. When we see, smell, taste, or even imagine a tasty snack, our salivary glands, which are located under the tongue and near the lower jaw, begin producing saliva. This flow of saliva is set in motion by a brain reflex that's triggered when we sense food or even think about eating. In response to this sensory stimulation, the brain sends impulses through the nerves that control the salivary glands, telling them to prepare for a meal.
As the teeth tear and chop the food, saliva moistens it for easy swallowing. A digestive enzyme called amylase which is found in saliva, starts to break down some of the carbohydrates (starches and sugars) in the food even before it leaves the mouth.
Swallowing, which is accomplished by muscle movements in the tongue and mouth, moves the food into the throat, or pharynx. The pharynx, a passageway for food and air, is about 5 inches long. A flexible flap of tissue called the epiglottis reflexively closes over the windpipe when we swallow to prevent choking.
From the throat, food travels down a muscular tube in the chest called the esophagus. Waves of muscle contractions called peristalsis force food down through the esophagus to the stomach. A person normally isn't aware of the movements of the esophagus, stomach, and intestine that take place as food passes through the digestive tract.
The Stomach
At the end of the esophagus, a muscular ring called a sphincter allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the esophagus. The stomach muscles churn and mix the food with acids and enzymes, breaking it into much smaller, more digestible pieces. An acidic environment is needed for the digestion that takes place in the stomach. Glands in the stomach lining produce about 3 quarts of these digestive juices each day.
Most substances in the food we eat need further digestion and must travel into the intestine before being absorbed. When it's empty, an adult's stomach has a volume of one fifth of a cup, but it can expand to hold more than 8 cups of food after a large meal.
By the time food is ready to leave the stomach, it has been processed into a thick liquid called chime. A walnut-sized muscular tube at the outlet of the stomach called the pylorus keeps chime in the stomach until it reaches the right consistency to pass into the small intestine. Chime is then squirted down into the small intestine, where digestion of food continues so the body can absorb the nutrients into the bloodstream.
The Small Intestine
The small intestine is made up of three parts:
1. The duodenum, the C-shaped first part
2. The jejunum, the coiled midsection
3. The ileum, the final section that leads into the large intestine
The inner wall of the small intestine is covered with millions of microscopic, finger-like projections called villi . The villi are the vehicles through which nutrients can be absorbed into the body.
The Liver
The liver (located under the ribcage in the right upper part of the abdomen), the gallbladder (hidden just below the liver), and the pancreas (beneath the stomach) are not part of the alimentary canal, but these organs are still important for healthy digestion.
The pancreas produces enzymes that help digest proteins, fats, and carbohydrates. It also makes a substance that neutralizes stomach acid. The liver produces bile, which helps the body absorb fat. Bile is stored in the gallbladder until it is needed. These enzymes and bile travel through special channels (called ducts) directly into the small intestine, where they help to break down food.
The liver also plays a major role in the handling and processing of nutrients. These nutrients are carried to the liver in the blood from the small intestine.
The Large Intestine
From the small intestine, food that has not been digested (and some water) travels to the large intestine through a valve that prevents food from returning to the small intestine. By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished. The large intestine's main function is to remove water from the undigested matter and form solid waste that can be excreted. The large intestine is made up of three parts:
1. The cecum is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine. This transition area allows food to travel from the small intestine to the large intestine. The appendix, a small, hollow, finger-like pouch, hangs off the cecum. Doctors believe the appendix is left over from a previous time in human evolution. It no longer appears to be useful to the digestive process.
2. The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum. The colon has three parts: the ascending colon and transverse colon, which absorb water and salts, and the descending colon, which holds the resulting waste. Bacteria in the colon help to digest the remaining food products.
3. The rectum is where faces are stored until they leave the digestive system through the anus as a bowel movement.
Amylase
Amylase is a digestive enzyme that acts on starch in food, breaking it down into smaller carbohydrate molecules. The enzyme is made in two places. First, salivary glands in your mouth make salivary amylase, which begins the digestive process by breaking down starch when you chew your food, converting it into maltose, a smaller carbohydrate. When starchy foods like rice or potatoes begin to break down in your mouth, you might detect a slightly sweet taste as maltose is released. Cells in your pancreas make another type of amylase, called pancreatic amylase, which passes through a duct to reach your small intestine. Pancreatic amylase completes digestion of carbohydrate, producing glucose, a small molecule that is absorbed into your blood and carried throughout your body.
Protease
Any enzyme that breaks down protein into its building blocks, amino acids, is called a protease, which is a general term. Your digestive tract produces a number of these enzymes, but the three main proteases are pepsin, trypsin and chymotrypsin. Special cells in your stomach produce an inactive enzyme, pepsinogen, which changes into pepsin when it contacts the acid environment in your stomach. Pepsin breaks certain chemical bonds in proteins, producing smaller molecules called peptides and beginning protein digestion. Your pancreas makes trypsin and chymotrypsin, enzymes that are released into your small intestine through the pancreatic duct. When partially digested food moves from your stomach into your intestine, trypsin and chymotrypsin complete protein digestion, producing simple amino acids that are absorbed into your circulation.
Lipase
Lipase is an enzyme that breaks down dietary fats into smaller molecules called fatty acids and glycerol. A small amount of lipase, called gastric lipase, is made by cells in your stomach. This enzyme specifically digests butter fat in your food. The main source of lipase in your digestive tract is your pancreas, which makes pancreatic lipase that acts in your small intestine. First, bile made in your liver and released into your intestine converts dietary fat into small fatty globules. Pancreatic lipase, also called steapsin, acts on these fat globules, converting them into fatty acids and glycerol, which are small, energy-dense molecules used by all your cells. Fatty acids and glycerol travel in blood and your lymph vessels to reach all parts of your body.
The products of digestion include amino acids, fatty acids, glycerol and maltose. A digestive system does consistently handle protein, carbohydrate and fat. It breaks down of foods into small constituents to be absorbed for use in the body. These products are very essential to one's growth in terms of health.
The proteins are digested by proteases ( enzymes) into amino acids and the fats are digested by lipids( enzymes) into fatty acids and glycerol and also the carbohydrates are digested by starch is broken down to maltose by salivary amylase( enzyme) and then . Maltose is broken down by maltase into Glucose. The end products are amino acids glycerol and fatty acids and glucose (all these are absorbed by the blood vessels and to all the body parts) after that the undigested food passes through the anus to be expelled ) Undigested food includes Vitamins ,Minerals , Water and some others.
If we have too many peptides and amino acids, sugars, glycerol and fatty acids they will store has fat and that how people get over weight.
M1 discuss the role of energy in the body.
Our body gets energy chemical from digesting food and using it in the respiration process. Carbohydrates are the first thing the body uses for energy, then fat, then protein. Sugars are quick energy.
Energy can be within cells, the respiratory system, cardio-v and digestive systems make up the energy in the body. Energy can be defined easily as the capacity to do work but energy doesn’t easily appear, it comes in different forms.
The body breaks down most carbohydrates from the foods we eat and converts them to a type of sugar called glucose. Glucose is the main source of fuel for our cells. When the body doesn't need to use the glucose for energy, it stores it in the liver and muscles. This stored form of glucose is made up of many connected glucose molecules and is called glycogen. When the body needs a quick boost of energy or when the body isn't getting glucose from food, glycogen is broken down to release glucose into the bloodstream to be used as fuel for the cells.
Every time you swallow a bite of sandwich, your body works hard to process the nutrients you've eaten. Long after the food is digested, the nutrients you've taken in become fuel needed by your body. Your body gets the energy it needs from food through a process called metabolism.
What Is Metabolism?
Metabolism is a collection of chemical reactions that takes place in the body's cells. Metabolism converts the fuel in the food we eat into the energy needed to power everything we do, from moving to thinking to growing. Specific proteins in the body control the chemical reactions of metabolism, and each chemical reaction is coordinated with other body functions. In fact, thousands of metabolic reactions happen at the same time - all regulated by the body - to keep our cells healthy and working.
After food is eaten, molecules in the digestive system called enzymes break proteins down into amino acids, fats into fatty acids, and carbohydrates into simple sugars (e.g., glucose). In addition to sugar, both amino acids and fatty acids can be used as energy sources by the body when needed. These compounds are absorbed into the blood, which transports them to the cells. After they enter the cells, other enzymes act to speed up or regulate the chemical reactions involved with "metabolizing" these compounds. During these processes, the energy from these compounds can be released for use by the body or stored in body tissues, especially the liver, muscles, and body fat.
•Anabolism, or constructive metabolism, is all about building and storing: It supports the growth of new cells, the maintenance of body tissues, and the storage of energy for use in the future. During anabolism, small molecules are changed into larger, more complex molecules of carbohydrate, protein, and fat.
•Catabolism, or destructive metabolism, is the process that produces the energy required for all activity in the cells. In this process, cells break down large molecules (mostly carbohydrates and fats) to release energy. This energy release provides fuel for anabolism, heats the body, and enables the muscles to contract and the body to move. As complex chemical units are broken down into more simple substances, the waste products released in the process of catabolism are removed from the body through the skin, kidneys, lungs, and intestines.
Several of the hormones of the endocrine system are involved in controlling the rate and direction of metabolism. Thyroxin, a hormone produced and released by the thyroid gland, plays a key role in determining how fast or slow the chemical reactions of metabolism proceed in a person's body.
Another gland, the pancreas secretes (gives off) hormones that help determine whether the body's main metabolic activity at a particular time will be anabolic or catabolic. For example, after eating a meal, usually more anabolic activity occurs because eating increases the level of glucose - the body's most important fuel - in the blood. The pancreas senses this increased level of glucose and releases the hormone insulin, which signals cells to increase their anabolic activities.
Metabolism is a complicated chemical process, so it's not surprising that many people think of it in its simplest sense: as something that influences how easily our bodies gain or lose weight. That's where calories come in. A calorie is a unit that measures how much energy a particular food provides to the body. A chocolate bar has more calories than an apple, so it provides the body with more energy - and sometimes that can be too much of a good thing. Just as a car stores gas in the gas tank until it is needed to fuel the engine, the body stores calories - primarily as fat. If you overfill a car's gas tank, it spills over onto the pavement. Likewise, if a person eats too many calories, they "spill over" in the form of excess fat on the body.