Human Physiology Study Guide for McGraw-Hill's ASVAB (page 2)
Physiology is the branch of biology that deals with the parts of the body, their functions, and the various bodily processes. Human physiology deals with the human body.
Cells, Tissues, Organs, and Organ Systems
In the human body, there are many different kinds of cells. Each kind is specialized for the primary function it performs. Examples are fat cells, skin cells, muscle cells, bone cells, and nerve cells. Groups of cells arrange themselves into tissues, and various tissues work together to form organs, such as the skin, liver, heart, gallbladder, and intestines. Organs work together to form organ systems. Organ systems include the muscular system, skeletal system, skin or integumentary system, respiratory system, digestive system, circulatory system, lymphatic system, immune system, excretory system, nervous system, endocrine system, and reproductive system.
The muscular system allows movement and locomotion. The muscular system helps you make body movements and supports the body in its activities. Muscles are involved in breathing, your heart beating, and the working of your digestive system.
Some actions are controlled by voluntary muscles, such as making a face, showing your biceps, or walking. Other muscle systems are involuntary, such as those that control breathing, your heart beating, and your digestive process.
Skeletal muscles help move the bones. They are attached to the bone by bands of tissue called tendons. Skeletal muscles work in pairs; when one muscle of the pair contracts, the other muscle relaxes. Cardiac muscle is found in the heart. Smooth muscles are found in some of your internal organs, such as your intestines and bladder.
The skeletal system is a living system that provides shape and support to your body. It is built to protect your inner organs and to provide attachment points for muscles. The skeletal system provides a rigid framework for movement. It supports and protects the body and body parts, produces blood cells, and stores minerals. In lower animals, such as a grasshopper, the skeleton might be on the outside. This is called an exoskeleton.
Vertebrates have developed an internal mineralized endoskeleton. The endoskeleton is made up of bone and cartilage. Muscles are on the outside of the endoskeleton. Although our endoskeleton is mostly bone, some parts of our body are made of cartilage, such as the trachea, nose, and ears. The skeleton and muscles function together as the musculoskeletal system. Calcium and phosphorus are important components of bone; these elements make bone hard. Osteoblasts are bone-forming cells.
Places where your bones come together are called joints. Joints are held together by bands of tissue called ligaments. Bones move at the joints. There are three major types of joints: ball and socket joints, like the shoulder and hip; pivot joints, like the elbow; and hinge joints, like the knee. These joints, working with the muscles and tendons, allow the body to move in certain ways.
Skin or integument is your outermost protective layer. The skin is the largest organ in your body. It protects you from losing water and from the invasion of foreign organisms and viruses. Special nerve cells in the skin help send information to the brain, helping you to feel hot and cold, texture, softness, and pain. Your skin has hair, oil glands, and sweat glands.
Skin helps to regulate your body temperature by expanding or constricting blood vessels and through the operation of the sweat glands. The sweat glands move perspiration or sweat onto the skin, where evaporation takes place and cools the skin.
The skin has three layers. The epidermis is the outer, thinner layer of skin. Underneath the epidermis, skin cells are continually being produced. The next layer is the dermis, containing blood vessels, nerves, muscles, and oil and sweat glands. Underneath the dermis is a layer of fat. This is where a lot of fat is stored as you gain weight.
Skin gets its color from melanin. People with different color skin have different amounts of melanin. The darker the skin, the more melanin the skin has. Skin also helps produce vitamin D when it is exposed to ultraviolet light.
Skin bruises when tiny blood vessels beneath the skin burst.
The respiratory system takes in oxygen and moves out waste material of carbon dioxide. Our lungs perform this job by breathing in and out (gills do this in fish). This system includes the lungs, pathways connecting them to the outside environment, and structures in the chest involved with moving air in and out of the lungs.
When we breathe in, air enters the body through the nose, where it is warmed, filtered, and passed through the nasal cavity. Air passes the pharynx (which has the epiglottis that prevents food from entering the trachea). The upper part of the trachea contains the larynx. After passing the larynx, the air moves into the bronchi, which carry air in and out of the lungs.
The bronchi are lined with epithelium and mucus-producing cells. The bronchi branch into smaller and smaller tubes known as bronchioles. The bronchioles terminate in little sacks known as alveoli. Alveoli are surrounded by a network of thin-walled capillaries. The exchange of oxygen takes place there, between the alveoli and the capillaries. The capillaries take in the oxygen. The hemoglobin in the blood picks up the oxygen and carries it off to various parts of the body. At the same time, waste material is transferred to the alveoli and eventually out of our bodies during exhalation.
It is important to note that breathing is different from respiration. Breathing is the physical action of moving the diaphragm up and down, which allows air to enter our lungs. Respiration is how our bodies use the oxygen from the air we inhale and eliminate the carbon dioxide when we exhale.
Digestion is accomplished by mechanical and chemical means, breaking food into particles small enough to pass into the bloodstream. The digestive process begins as soon as you put food into your mouth. Mechanical breakdown begins in the mouth by chewing (teeth) and moving the food around with your tongue. The food interacts with your saliva to begin a chemical breakdown. This mixture of food and saliva is then pushed into the pharynx and esophagus when you swallow. The esophagus is a long tube with muscles that contract and move the food to the stomach. The stomach is a sack or bag. It breaks down the food by both mechanical and chemical means. The stomach mixes the food by a process called peristalsis. Peristalsis is merely waves of muscle contractions. The stomach releases enzymes and hydrochloric acid to break down the food even further. Eventually the food moves to your small intestine.
The small intestine is narrow in diameter but very long in length. The upper part of the small intestine is the duodenum. This is where most digestion takes place. Bile is introduced from your liver. Bile breaks up the fat particles. Next comes the pancreas, which introduces pancreatic fluid. This fluid promotes the chemical digestion of carbohydrates, proteins, and fats. The fluid also neutralizes the stomach acid and makes insulin. Absorption of the food takes place in the small intestine.
Food that is not digested continues to move through your system into the large intestine by means of peristalsis. The large intestine absorbs water, making the contents more solid. Eventually the rectum and anus control the release of the semisolid waste called feces.
The circulatory system is one of the transportation systems in your body. The main job of the circulatory system is to move oxygen, carbon dioxide, nutrients, waste products, immune components, and hormones through your body. The circulatory system is composed of vessels and muscles that control the flow of blood around the body. This process of blood flowing around the body is called circulation. The main components of the circulatory system are the heart, arteries, capillaries, and veins.
There are three types of circulation, coronary circulation, pulmonary circulation, and systemic circulation. Coronary circulation is the circulation of blood within the heart itself by the coronary veins and arteries. If this circulation is blocked, it could result in a heart attack. Pulmonary circulation is the flow of blood from the heart to the lungs and back. Systemic circulation is the blood (with oxygen) moving through your body to your important organs.
The heart is a strong muscle that operates as the engine of the circulatory system. It has four compartments that are called chambers. The two upper chambers are called atriums and the two lower chambers are called ventricles. When your heart beats, the two ventricles contract at the same time, followed by the two atria. Blood flows from an atrium to a ventricle and then from the ventricle to a blood vessel. The pulmonary valves keep the blood from flowing backward. There is a wall between the two atria and the two ventricles, keeping blood that has a lot of oxygen apart from blood that does not have as much oxygen.
Blood returns from the body to the right atrium of the heart. At this point, the blood is low on oxygen. When the right atrium contracts, it moves the blood to the right ventricle. The blood then moves via the pulmonary artery to the lungs, where it picks up oxygen and eliminates waste (carbon dioxide). The oxygenated blood leaves the lungs and comes into the heart through the left atrium. Blood leaves the heart from the left ventricle and goes into the biggest artery, called the aorta. Fresh blood from the aorta goes to various parts of your body, including the brain, which needs a constant supply of oxygen. Blood returns to the heart through the veins, starting the cycle over. Arteries are blood vessels that carry blood away from the heart. Veins carry blood to the heart. Arteries and veins are connected by thousands of miles of tiny vessels called capillaries.
Blood About five liters of blood flows through your body, delivering essential elements and removing harmful wastes. Blood transports oxygen from the lungs to body tissues and carbon dioxide from body tissues to the lungs. It also transports disease-fighting substances to the tissue and waste to the kidneys.
Blood contains red blood cells and white blood cells. These cells are responsible for nourishing and cleansing the body. Red blood cells are shaped like disks and contain hemoglobin, which carries oxygen and carbon dioxide. Unlike other cells, they do not have a nucleus. White blood cells fight bacteria, viruses, and other intruders in your body. The white blood cells are carried to the place where an intruder has invaded and go into that tissue. Their job is to destroy the bacteria or viruses.
Cell fragments called platelets are carried along with the red and white blood cells. Platelets plug holes in small blood vessels to stop bleeding. They help to clot blood.
Red and white blood cells and platelets are carried by a fluid called plasma. About 55 percent of the blood's volume comes from plasma. Nutrients, minerals, and oxygen are carried by the plasma to various parts of the body. Waste products are also carried by the plasma.
There are four different blood types: A, B, AB, and O. Types A, B, and AB have certain chemical tags called antigens. Type O has no antigens. Blood also has antibodies that destroy or neutralize substances that do not belong there. This prevents certain blood types from being mixed. The following chart indicates who can receive and give certain blood types.
People with type O blood are called universal donors; those with type AB are called universal receivers.
Your blood also has Rh factors, making it even more unique. The Rh factor is an additional chemical tag. If the blood has the Rh factor, it is labeled Rh-positive. If the factor is not present, the blood is called Rh-negative. If the wrong blood is given to a person, the blood will try to destroy the other person's blood. That's why it is important to know your blood type.