1. Lesson 4: ”Animal Systems” What are the skeletal and muscular systems”
The skeletal system is made of bones, tendons, and ligaments.
The bones in the skeletal system have two main functions which are to provide protection for some soft body organs and to provide a solid framework for the body.
While bones do move freely, they do not have the power to move on their own without the help of the muscular system.
Skeletal muscles are attached to bone by tough, rubbery tendons.
Muscles that cause movement work in pairs or opposing groups.

2. Lesson 4: ”Animal Systems” What are the digestive and excretory systems?
The digestive system is a set of organs that break down food so it can be absorbed into the bloodstream.
Step 1 – Human digestion begins in the mouth where your teeth grind food into smaller pieces which is then mixed with saliva thus beginning the chemical breakdown of food.
Step 2 – The chewed food travels through the esophagus to the stomach where acid helps break it down even further.
Step 3 – The stomach empties its partially digested contents into small intestine. It is there where digestive juices produced by the liver and pancreas combine with the food to break down sugar, proteins, and fats into nutrients.

3. Lesson 4: ”Animal Systems” What are the digestive and excretory systems? (Continued)
Step 4 – As food moves through the small intestine, nutrients are absorbed. The villi deliver nutrients to tiny blood vessels which transport these nutrients throughout the body.
Step 5 – Any undigested food moves to the large intestine where any remaining water is absorbed. Any remaining materials leave the body as waste. (POOP!)
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4. Lesson 4: ”Animal Systems” What are the digestive and excretory systems? (Continued)
The excretory system removes wastes from the body.
Some animals remove excess water, salt, and other waste through their skin in the form of perspiration. (sweat)
The liver filters nitrogen wastes from the blood and converts them into urea.
Urea is carried by the blood to the kidneys where it is filtered even more by tiny filters called nephrons.
The kidneys produce urine (PEE) from excess water and the collected wastes from the nephrons.
Urine flows from the kidneys to the bladder and exits the body through the urethra.

5. Lesson 4: “Animal Systems” What are the respiratory and circulatory systems?
The cells of all animals are living things that require oxygen and food.
The respiratory system and the circulatory system work together to provide oxygen and food to cells.
The respiratory system is made of the lungs and the passageways that lead to them.
The circulatory system consists of the heart and blood vessels.

6. Lesson 4: “Animal Systems” What are the respiratory and circulatory systems? (Continued)
Oxygen-poor blood flows into the heart.
The oxygen-poor blood is then pumped to the lungs.
In the lungs, the blood drops off carbon dioxide and picks up oxygen.
Oxygen-rich blood flows into the heart and is then pumped to the body.
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7. Lesson 4: “Animal Systems” What is the nervous system?
The nervous system works with other body systems to help organisms respond to stimuli…changes in the environment that bring about responses from the body.
The nervous system includes the brain, the spinal cord, nerves, and sense organs.
The nervous system is divided into two parts called the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves and sense organs).
The central nervous system receives and interprets messages from the peripheral nerves.
The brain also controls heartbeat, breathing, and the digestive system.

8. Lesson 4: “Animal Systems” What is the nervous system? (Continued)
Nerve cells are called neurons.
Neurons are divided into three types with each type doing a different job to help your body respond to stimuli.
Sensory neurons receive messages from the body and the environment.
Motor neurons carry messages fro the brain and spinal cord to the body’s organs and glands.
Associative neurons connect the sensory neurons to the motor neurons.