Name ______
The human body is truly amazing! Have you ever thought about how your body works? What happened to the food you ate for dinner last night? How does your body use the oxygen that you inhale? There are pathogens everywhere! Why don’t you get sick more often? How does your body know how and when to grow?
Each body system does a specific job and many of those systems work closely together as a team to keep the human body healthy and functioning. The human body is a system because many separate systems work together to keep the body alive, similar to the way the parts of a bicycle work together to make a bike work.
What’s so amazing is that each of these separate systems is made of parts called organs. Each organ is made of its own special material called tissue, and tissues are made of the smallest players on the team – cells. All organisms are made of cells. A cell is the smallest living part of an organism. Some kinds of organisms, such as bacteria, are made of only one cell. That single cell is the organism’s entire body! Many other kinds of organisms, including elephants, trees, and people, are made of trillions of cells.
The human body is a complex organism. All the body systems must constantly work together so you can survive, grow, and stay healthy!
All Systems Go!
Marvels of Design
Cells
A living thing is an organism. Many kinds of organisms have a body with different parts called structures, and each structure has a “job” or function. All organisms are made of cells. A cell is the smallest living part or structure of an organism. An average cell is about 1/1,000 of inch across. Can you imagine anything as small as that?
Human bodies are marvels of design; they are made of different kinds of cells. Some of these cells are: bone cells, nerve cells, muscle cells, skin cells, sex cells, fat cells, and blood cells. Each kind of cell in an organism performs a different function. For example, nerve cells carry messages to and from your brain. Muscle cells make part of your body move. Red blood cells carry oxygen and nutrients to all your other cells. And each kind of cell has a different shape. No cell works alone; cells work together tirelessly day and night to keep your body working!
The human body is made of trillions of cells. Every second, millions of old cells die and millions of new cells replace them. Cells are grouped together to form tissues. Tissues form organs. And organs form organ systems. Systems work together to keep you alive and healthy.
Blood Cell Nerve Cell Muscle Cells Sperm Cells
Write True or False for each statement below.
1. ______The smallest structure in the human body is the cell.
2. ______Some cells are nerve cells.
3. ______There is only one kind of cell in the human body.
4. ______Each kind of cell has a different function (job).
5. ______Every second, millions of old cells die and new cells replace them.
6. ______All cells have the same shape.
All About Cells and Body Systems (video)
1. The body’s smallest living structures are called ______.
2. Cells work together to form ______.
3. Tissue forms ______, and organs form ______.
4. ______of different kinds of cells make up the human body.
5. Standing, dancing, throwing a ball is possible because of ______
and ______working together.
6. The human adult skeleton has ______bones.
7. The function of the skeleton is to ______vital organs.
8. The skull protects the ______. The ribs protect the ______.
9. The function of muscles is to help animals ______.
10. The ______system breaks down food into nutrients, which are then delivered by red blood cells to all the cells in your body.
11. ______pass through the wall of the small intestine into the bloodstream. This is where the red blood cells pick up the nutrients that all your cells need.
12. Every cell in the human body needs ______& ______.
13. The three main organs of the nervous system are: ______,
______, and ______
14. What type of cells do skeletal bones make? They are the cells that carry oxygen and nutrients to all the other cells in your body, and they pick up waste like carbon dioxide to be removed from the body. These cells are called ______.
15. This system moves the blood around the body: ______system.
16. This organ pumps the blood around the body: ______
17. The endocrine system produces chemical messengers called ______, which tell your body when it’s thirsty or your bladder is full, when to grow or when to sweat.
18. What system removes wastes (carbon dioxide, liquid and solid wastes, salts) from the body?
______
Your heart, your brain, and your stomach are all organs in your body. An organ is a part of the body that does a specific job. Can you name the largest organ in the body? That’s right. It’s the skin.
Super Skin
What would you be like without skin? The answer is, quite simply, a big squishy mess! Your skin is like a very large container. It performs five important jobs:
- Skin is a strong, waterproof, and self-repairing protective wrapping. It protects you from germs, dust, water, and the sun’s ultraviolet rays.
- It helps you maintain a constant body temperature of 98.6F by keeping your body cool and comfortable through sweating. The evaporation of perspiration (water and salt) helps keep your body from overheating.
- In the presence of sunlight, the skin produces vitamin D.
- It gives you the sense of touch, including pain, pressure, and temperature sensations.
- It burns and stores fat. Fat insulates you against all kinds of bumps, bangs & wear and tear.
Skin is alive. Every square inch of skin contains layers of fat, dozens of hairs, cells in which you’ll find nerves, sweat glands, sensory receptors, and blood vessels. Skin also teems with life on its surface. No matter how hard you wash, there are millions of bacteria on each square inch of skin. Some cause illness. In fact, skin is our first line of defense against the diseases that some bacteria cause.
Skin can identify heat, cold, pain, and pressure. Just one square inch of skin on the back of your hand contains around 30 hairs and 9,000 nerve endings. They automatically inform your brain of the conditions around you. But the skin on your lips is much more sensitive than the skin on your elbows. That is because lips have more nerves that are packed closely together.
Microscopic cells are the body’s building blocks. It takes about 100 trillion of them to make up one adult. Like all other cells, skin cells are constantly being replaced. Roughly 30,000 to 40,000 dead skin cells flake off invisibly every minute. They pop off like tiles blown from a roof in a strong wind. They have to make way for an equal number of fresh ones the body is producing. In fact, about 28 days from now, you will have a completely new skin! But when these dead layers pile up and don’t shed, they create calluses, warts, and thick white skin flakes of psoriasis.
Factoid:
- As an adult, you may have more than 20 square feet of skin – about the size of a blanket
- You are likely to shed some 40 pounds of skin in a lifetime
- Right now, there are over a million dust mites, microscopic critters invisible to the naked eye, on your mattress and pillow, chomping on the dead skin cells that fell off you last night!
Skin’s Three Main Layers
Epidermis or growth layer – Although this outer layer of skin is about as thick as a piece of paper, it still has four layers. This is where new skin cells are continuously made and dead cells are pushed outward.
Dermisor true skin – The dermis contains blood vessels, nerve endings, sweat glands, oil glands, hair follicles, muscles, and fatty tissue. It is made of tough but bendable fibers called collagen and elastin. They allow the skin to keep its shape even after it’s been pinched. Most of the blood flow and nerves can be found in the dermis.
Subcutaneous Fat – This layer of fat is made mainly of blood vessels and cells that store fat. The fat helps insulate the body and protects it against blows. The body can burn this fat when it is short on food and needs energy.
Fight Fat!
Fat is the body’s best way to store energy. Most of it is part of the subcutaneous fat layer, although fat is found in organs and other tissues as well. Our ancient ancestors often got fat when food was plentiful. During lean times, that fat gave them energy to survive. But most Americans have no shortage of food. Many people eat and eat without burning off the extra fat. They also eat fattening junk food and get little exercise. The result? One out of three Americans is obese (severely overweight). 15% of children and teens are obese, up from 5% in 1980. Many believe that obesity will soon surpass smoking as the Number 1 cause of preventable death. Diseases caused by too much fat occur most often in adults. Exercising and eating a healthy diet today can help prevent diseases later in life.
Skin Gone Wrong
The world’s most common skin ailment is acne vulgaris – clogged pores, pimples, and deeper lumps that occur on the face, neck, chest, and other parts of the body. Many people believe that chocolate or greasy foods cause it. Others say not washing thoroughly enough is the problem. Both are myths, although a nutritious diet and good hygiene are still crucial to being and staying healthy. Rising hormone levels causes teenage acne. Hormones are the body’s internal chemical messengers. They carry information that controls the function of almost all of the body’s cells and tissues. Hormones greatly increase the production of oil and then the hair follicles can become clogged by dead skin cells. This leads to whiteheads, blackheads, and angry red lumps. The good news about acne is that it’s treatable. Stores sell creams and medicines that can get rid of mild-to-moderate acne.
Skin cancer is the most common type of cancer. The tanning craze has also made skin cancer the fastest growing type of cancer in the U.S. Fair-skinned people are especially vulnerable. Many people don’t realize that a sunburn or tan is the body’s way of signaling sun damage or radiation poisoning. When in the sun, always put on a sun block or a sunscreen and reapply it often.
Move Your Body!
Your body has two organ systems that work together to help you move. They are the skeletal system and the muscular system. The skeletal system is made of bones and cartilage. Cartilage is a strong tissue that is more flexible than bone. Bones and cartilage make up the framework of your body.
Skeletal System
Without your system of bones, you’d be floppy like a beanbag. Could you stand up? Forget it. Could you walk? No way! Without bones, you’d be just a puddle of skin and guts on the floor.
The skeletal system…
- Creates a frame of 206 bones, which supports your body
- Makes red blood cells that carry oxygen and white blood cells to fight disease
- Provides places for muscles to hold on to so that you can move
- Protects important body organs from injury (ribs protect heart & lungs, skull protects brain)
- Stores an important mineral – calcium – to keep bones hard and strong
Together with the skeletal system, the muscular system and its 650 muscles help us to walk, run, play and even show facial expressions. Many muscles are attached to bones and when muscles tighten up, or contract, they move the bones, which in turn move the body!
Bones are alive! Bones are made of living cells, which help them grow and repair themselves. Like other cells in your body, the bone cells rely on blood to keep them alive. Blood brings nutrients and oxygen to all of your cells and takes away waste. If bones weren’t made of living cells, things like broken toes or arms would never mend, but don’t worry, they do!
Bones store an important nutrient called calcium, which gives bones their hardness and strength. We get calcium from drinking milk and eating foods like cheese. Without enough calcium, bones become softer and can break more easily. But bones do not start out being hard and strong.
Babies are born with about 350 bones, many of which are soft and bendable and made of cartilage. Over time, softer cartilage is replaced by hard bone and some of the bones join together to form one bone. By the time you become an adult, you will only have about 206 bones in your body.
1. List 3 functions of the skeletal system.
______
______
______
2. Bones are alive! What are they made of? ______
3. What nutrient keeps bones strong and hard? ______
4. Blood brings ______and ______to keep all your cells healthy.
Inside a Bone
Bones are made of hard, strong tissue. Bone tissue is made of cells, microscopic living structures. All living things are made of cells. Bones make up the skeletal system. An important job or function of the skeletal system is to make red blood cells that carry oxygen and white blood cells that fight germs.
Bone marrow is found in the center of many bones.
Bone marrow makes new red and white blood cells.
Red blood cells deliver oxygen and nutrients to all
parts of your body.
Moving Your Bones
Our bones don’t simply work by themselves. Two or more bones join together at a joint. Different kinds of joints allow different kinds of movement. For example, your shoulder joint lets you move your arm in a large circle. Your elbow joint lets you move your lower arm toward and away from your upper arm. The bones of some joints are not moveable. For example, the bones that make up your skull are joined tightly together and do not move.
A tough, smooth shiny tissue called cartilage covers the end of each bone, this keeps your bones from scratching and bumping against each other when you move. Strong stretchy bands called ligaments hold our bones together. Ligaments are tough, flexible cables that attach bones to other bones to help keep them in place.
How do your bones move? You need muscles to pull on bones so that you can move. Your muscles are attached to bones with tendons. Tendons are strong cords that attach skeletal muscles to bones. When muscles contract, the bones to which they are attached act as levers and cause various body parts to move.
Muscular System
Muscular System
Your muscular system is made of muscles that cause parts of your body to move. Muscles move your bones. They make your heart beat. They make you breathe. They even make the pupils of your eyes become larger or smaller. There are about 650 muscles in your body.
So, what do muscles do? Muscles move cows, snakes, worms and humans. Muscles move you! Without muscles you couldn’t open your mouth, speak, shake hands, walk, talk, or move food through your digestive system. There would be no smiling, blinking, or breathing.
There are three kinds of muscles in your body and each kind has a special function.
Skeletal muscles move bones. For example, when you hold a pencil, skeletal muscles pull on your finger bones. When skeletal muscles contract, or shorten, they pull the bones to which they are attached. That’s how the body moves and bends. Many skeletal muscles work in pairs; when one muscle in the pair contracts, the other muscle relaxes. When your biceps muscles contract, your triceps muscles relax. Your lower arm is pulled toward your upper arm. You can control your skeletal muscles; skeletal muscles are voluntary muscles.
Cardiac musclesmake your heart beat and pump blood through your body.You cannot control your heart muscles. Your heart beats automatically without thinking about it…it is an involuntary muscle movement.