The Excretory System
Organs in the excretory system
The kidneys are the most important organs in the excretory system. They clean the blood in our body. There are many capilleries in our kidneys which the blood passes through.
Ureters are tubes that connect the kidneys to the bladder. Urine passes from the kidneys to the bladder through the ureters.
Urine is stored in the bladder. The bladder has the shape of a ball and is made of muscular tissue.
The urethra is a tube that carries urine out of the body.
When blood enters the kidneys it is carrying water and harmful substances. The kidneys filter the blood separting the harmful substances and some water which is
We also lose harmful substances when we sweat. Sweat leaves the skin through tiny holes called pores.
The Skeletal System
Our skeletal system has 206 bones. We have bones in our head, trunk and limbs. We have long bones like the ones in our arms and legs and short bones like the ones in our fingers and toes.
Our skeletal system has four main functions:
It gives our body shape.
It holds our body upright.
Bones work with muscles so we can move.
Bones protect our soft organs like our skull protects our brain.
Joints help us move
The place where two or more bones mneet is called a joint. Joints allow our skeleton to bend and turn. The ends of bones are covered by rubbery tissue called
The Muscular System
Our muscular system has more than 600 muscles. Muscles are made of a tissue of muscular cells. Most muscles in our body move our bones but some muscles move other
parts like our lips and eyes.
Functions of the Muscular System
Our muscles give shape to our body.
Muscles make other parts of our body move.
Some musclesw also help protect soft organs of our body.
Muscles are attached to bones by tendons. When muscle cells contact, the muscle they are a part of gets shorter. Muscles can only pull bones so they work in pairs.
One muscle pulls the bone one way and anopther muscle pulls the same bone in the opposite direction.