The respiratory system is responsible for gas exchange in the body. Oxygen is used by our cells during respiration. Without oxygen, your body cannot produce enough energy to survive. Carbon dioxide, a product of respiration, is toxic to cells and must be removed from the body. This exchange of carbon dioxide and oxygen takes place in the respiratory system, in small sacs called alveoli.
When you breathe in, air from the nose passes through a muscular tube in the upper throat called the pharynx. The air continues through the larynx, or voice box. Next it passes into the trachea, or windpipe, which divides into two smaller tubes, bronchi that lead to the lungs. Within the lung, the bronchi divide into even smaller tubes called bronchioles, that end in clusters of little air sacs called alveoli. This is where the gas exchange actually takes place. Each alveolus is surrounded by a jacket of capillaries, allowing blood to drop off the carbon dioxide and pick up oxygen.
No matter what you are doing- playing basketball, playing video games, reading or sleeping- your body is constantly transporting nutrients, hormones, and gases and getting rid of wastes. Two systems play a major role in these functions. The circulatory system, which includes the cardiovascular and lymphatic systems, transports materials to different parts of the body.
The cardiovascular system functions like a network of highways, connecting the muscles and organs through an extensive network of vessels. Blood, specialized cells, and fluids are pumped through these vessels by the heart.
What is transported? Nutrients from digested food, oxygen from the lungs, metabolic wastes, hormones, and even heat to help maintain a constant body temperature!
Blood circulates through a network of vessels. Arteries carry blood away from the heart into smaller arteries called arterioles. Eventually blood is pushed into capillaries where the exchange of gases, nutrients, hormones and other molecules take place. From the capillaries, blood flows into venules. From the venules, it empties into larger vessels called veins before returning to the heart.
The lymphatic system collects and recycles fluids leaked from the cardiovascular system and also fights infections. Lymphatic vessels carry the leaked fluid called lymph back to the vessels in the neck. The lymphatic system is also the key element of the immune system. We will discuss it again at the immune system station.
The digestive system is responsible for breaking down the food we eat into molecules that can be absorbed and delivered to where they are needed in the body. The digestion of food begins as soon as we put it in our mouth. We physically break down the food by chewing and chemically start to dissolve the carbohydrates using amylase in our saliva. Once we chew and swallow the food, it travels down the esophagus to the stomach. The esophagus transports the food using peristalsis, a series of wave-like smooth muscle contractions.
In the stomach, the digestive enzyme pepsin and hydrochloric acid are secreted to break the peptide bonds in proteins. The stomach mixes its contents by using peristaltic waves.
Food passes from the stomach to the small intestine where the digestion of lipids takes place. A digestive pancreatic enzyme called lipase breaks down the lipids after they have been treated with bile. Bile is produced in the liver and it breaks up fat globules into tiny droplets during a process called emulsification. Bile is stored in the gallbladder.
Absorption of molecules and liquids also takes place in the small intestine. Nutrients are absorbed into the lining of the small intesting which is covered with tiny finger-like projections called villi. Villi increase the surface area of the small intestine.
Anything that hasn’t been digested and absorbed is passed on to the large intestine, or colon. Any component of food that was not necessary for energy production (such as fiber) is now considered waste. A thriving colony of bacteria live in the colon. These bacteria make many compounds your body needs but cannot get through food you eat. They also help transform and compact undigested material into feces, the final waste product.
Nephron
Excretion describes processes in the body that remove metabolic wastes. The primary organs of excretion are the kidneys. Nephrons, kidney tubules, remove nitrogenous wastes (mainly urea), ions such as sodium and potassium, and water by filtering the blood. Then the filtrate is excreted as urine. The kidneys also play important roles in the maintenance of blood volume, blood pH, and red blood cell production. The skin (water and salt), the lungs (carbon dioxide and water), the liver (bile pigments), and the intestines (mainly salts) play secondary roles in excretion.
The key structures of the urinary system are the kidneys, the ureters, the bladder, and the urethra. Once the urine is produced from the kidney’s filtrate, it passes through the ureters to the bladder. Finally, it is expelled from the urethra.
The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. There are nonspecific defenses that protect the body against any foreign invasion and specific defenses that target invaders based on their antigens. (An antigen is a substance that triggers an immune response.)
Nonspecific Defenses. The first line of nonspecific defense is the body’s skin and mucous membranes. If a pathogen gets past this physical barrier, the body begins its next round of battle. Most bacteria can only live within a certain temperature range. Your body raises its temperature, giving you a fever, to try to keep the bacteria from reproducing. You may also notice the area around a wound getting red, swollen, and hot. This is inflammation. Blood flow to the wounded area is increased to try to deliver more white blood cells to the site of the foreign invaders. The first white blood cells to show up are neutrophils, macrophages, and natural killer cells. These cells patrol the bloodstream and attack any pathogen they come across.
If a pathogen survives the nonspecific defense system, the body begins an immune response.
Specific Defenses. When a pathogen is recognized by its antigen, Helper T Cells activate B cells and Cytotoxic T Cells.The B cells rapidly divide to form plasma cells and memory B cells. The plasma cells kill the pathogen by releasing antibodies. The memory B cells remain capable of producing specific antibodies to the pathogen, greatly reducing your chances of getting the same infection twice. Cytotoxic T Cells track down and destroy bacteria, fungi, protozoan, or foreign tissue that contains the antigen, including your own infected cells.
Vaccinations. A vaccination is an injection of a weakened or mild form of a pathogen. This allows the B cells to form memory B cells from exposure to the antigen.
Although we rarely think about them, the glands of the endocrine system and the hormones they release influence almost every cell, organ, and function of our bodies. The endocrine system helps regulate mood, growth and development, tissue function, and metabolism, as well as reproductive processes.
The major glands that make up the human endocrine system are the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive glands, which include the ovaries and testes. The pancreas is also part of this hormone-secreting system, even though it is also associated with the digestive system because it also produces and secretes digestive enzymes.
A gland is a group of cells that produces and secretes, or gives off, chemicals called hormones. As the body's chemical messengers, hormones transfer information and instructions from one set of cells to another. Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.
Some types of glands release their secretions in specific areas. For instance, exocrine glands, such as the sweat and salivary glands, release secretions in the skin or inside of the mouth. Endocrine glands, on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body.
Once a hormone is secreted, it travels from the endocrine gland through the bloodstream to target cells designed to receive its message. When hormone levels reach a certain normal or necessary amount, further secretion is controlled by important body mechanisms to maintain that level of hormone in the blood. This regulation of hormone secretion may involve the hormone itself or another substance in the blood related to the hormone.
The human body contains more than 650 individual muscles which are attached to the skeleton.They provide the pulling power for us to move around. The main job of the muscular system is to provide movement for the body. The muscular system consists of three different types of muscle tissues: skeletal, cardiac, and smooth. Each of these different tissues has the ability to contract, which then allows the body to move and the organs to function. The muscles can be categorized as either voluntary or involuntary and either smooth or striated. Muscles we consciously decide to move are voluntary muscles. Muscles that contract and relax on their own are involuntary muscles. Can you imagine if you had to tell your heart to beat and tell your lungs to inhale and exhale?
SKELETAL MUSCLE: Skeletal muscle makes up about 40 % of an adults body weight. It has stripe-like markings, or striations. The skeletal muscle is composed of long muscle fibers. Each of these muscles fiber is a cell. The nervous system controls the contraction of the muscle. We can control the action of the skeletal muscle. For this reason, the skeletal muscle is also called voluntary muscle. Skeletal muscles contract using the sliding filament method. Filaments of actin and myosin slide past each other to contract and relax the muscle.
CARDIAC MUSCLE: The heart is made of cardiac muscle. The tissue that makes up the wall of the heart called the myocardium. Also like the skeletal muscles, the cardiac muscle is striated and contracts through the sliding filament method. However it is different from other types of muscles because it forms branching fibers. Unlike the skeletal muscles, the cardiac muscle is attached together instead of been attach to a bone.
SMOOTH MUSCLE: Many of our internal organsare made of smooth muscle. They are found in the urinary bladder, gallbladder, arteries, and veins. Also the digestive tract is made up of smooth muscle as well. The smooth muscles are controlled by the nervous system and hormones. We cannot consciously control the smooth muscle so that is why they are often called involuntary muscles.
Your skeleton shapes and supports your body, provides protection for internal organs, and along with your muscles, provides movement with a versatile system of levers and joints. The human skeleton contains 206 bones. Eighty of these are found in the axial skeleton, which includes your skull, spine, ribs, and sternum. The other 126 bones, the bones of your arms, legs, pelvis, and shoulder, make up the appendicular skeleton.
Bones are made of a hard outer covering of compact bone surrounded by a porous inner core of spongy bone. Compact bone is dense and provides support. Spongy bone is loosely structured and is filled with a soft tissue called bone marrow. Red bone marrow begins the production of all blood cells and platelets. Yellow bone marrow consists of mostly fat which stores energy. Bones are surrounded by a tough exterior membrane called the periosteum which contains many blood vessels that supply nutrients to bones.
A joint is where two bones meet. Pads of cartilage cushion the ends of the bone in a joint. The bones of a joint are held together by strong bands of tissue called ligaments. There are three main types of joints: immovable joints, slightly movable, and freely movable. The bones in the cranium of the skull are joined together so tightly that little or no movement can occur. Yet the bones in the vertebrae of the spine allow for flexibility but cannot move like our arms and legs.
Freely movable joints are the most familiar to us.
Movable JointsJoint / Type of Movement / Examples
Ball-and-socket / All types / Shoulders and hips
Pivot / Rotation / Top of spine (turning of head)
Hinge / Bending and straightening / Elbows, knuckles of fingers, and toes
Gliding / Sliding motion / Wrists and ankles
Saddle / Rotation, bending, and straightening / Base of thumbs
Neurons are the most important cells of the nervous system. The functions of the nervous system depend on the complex interaction between billions of neurons. Networks of neurons constantly gather, integrate, interpret, and respond to information about the body’s internal state and environmental conditions.
There are two main divisions in the nervous system- the central nervous system, consisting of the brain and spinal cord, and the peripheral nervous system, containing sensory and motor neurons. Sensory neurons send information from sense organs, such as the skin, to the CNS. Motor neurons send commands from the CNS to muscles and other organs.
The brain is the body’s main processing center. Thoughts, feelings, emotions, behavior, perception, and memories are controlled by your brain. Your brain also enables you to learn and process information. The brain is connected to the body by the brain stem and spinal cord. These structures relay information throughout the body. In addition to relaying messages, the spinal cord functions in reflexes, sudden, involuntary contractions of muscles in response to a stimulus.
The peripheral nervous system connects the brain and spinal cord to the rest of the body. The motor division of the PNS consists of the somatic nervous system and the autonomic nervous system. The somatic nervous system stimulates skeletal muscles under our conscious control. The autonomic nervous system regulates smooth muscles that do not require our conscious control. It regulates heart rate, blood flow, digestion, and respiration. The autonomic nervous system is also divided into two parts- the parasympathetic, which is most active under normal conditions, and the sympathetic, which dominates in times of physical or emotional stress. You may have heard of the “fight or flight” response that it controls. During stress, the sympathetic division increases heart rate, blood pressure, and breathing rates. It also directs blood flow to your heart and skeletal muscles.
Neurons are specialized cells in the nervous system. The unique structure enables it to conduct electrical signals called nerve impulses. Dendrites receive information from other cells and relay it to the other parts of the neuron. A junction at which a neuron meets another cell is called a synapse, a tiny gap between each cell. A nerve impulse triggers the release of neurotransmitters into the synapse which either excite or inhibit the activity of the next cell.
Male Reproductive System
The role of the male in sexual reproduction is to produce sperm cells. Sperm cells are produced in the testes, or testicles, which are located in the scrotum. Sperm production begins during puberty in the lining of the seminiferous tubules. Luteinizing hormones stimulate the secretion of testosterone and follicle stimulating hormone, along with testosterone, stimulates the sperm production. After production in the seminiferous tubules, the sperm enter the epididymis where they mature as they are stored. From the epididymis, the sperm pass through the vas deferens and out the urethra.
A sperm cell contains enzymes at the tip to penetrate the egg cell during fertilization. The mid piece contains mitochondria to provide energy for the sperm to swim. ATP from the mitochondria provides the energy for the whip-like flagellum to move the sperm.
Female Reproductive System
Each month the female reproductive system prepares a mature egg cell. The egg cells are produced in the ovaries. At birth, the ovaries contain about 2 million immature egg cells. When a female reaches puberty, the release of hormones causes the egg to mature. The ovum, mature egg, is release from the ovary every 28 days. Cilia sweep the egg into the fallopian tubes which transport it to the uterus. This takes 3-4 days to complete. If pregnancy occurs, the ovum attaches to the wall of the uterus where develops. The ovarian cycle is a complicated series of events regulated by the release of hormones from the endocrine system. There are four hormones involved. Luteinizing hormone and follicle stimulating hormone cause the follicle to produce estrogen to aid the growth of the follicle which holds the developing ovum. These hormones are regulated by negative feedback mechanisms. After the ovum is released, the follicle develops into the corpus luteum which functions like an endocrine gland secreting estrogen and progesterone. Estrogen and progesterone inhibit the release of FSH and LH preventing the development of new follicles. If pregnancy does not occur, the production of progesterone slows and the uterus sheds its lining. This is called menstruation.