B5

The job of a skeleton is to support the body and allow it to make- as well as protect vital organs. 

Fish, amphibians, reptiles, birds and mammals are all vertebrates- all have a backbone and an internal skeleton.

Insects have their skeleton outside their bodies. Advantages of an internal skeleton:

• It can easily grow with the body
• It's easy to attach muscles to it
• It's more flexible than an external skeleton

Bones are made up of living cells so can grow and repair themselves if damaged. Long bones are hollow-this makes them lighter than solid bones of te same size and makes movement far more efficient. 

The hole in some long bones is filled with bone marrow. This is a spongy substance that makes new blood cells.

Bones start of as cartilage in the womb. As you grow, cartilage is replaced by bone. Blood vessels deposit calcium and phosphorus in the cartilage which eventually turns into bone. This process is called ossification. You can tell if someone is still growing by looking at how much cartilage is present. If there's a lot, they're still growing. 

Bones and Cartilage are both made up of living tissue and so can get infected. Even though bones are strong, they can be fractured by a sharp knock.

Elderly people are more prone to breaking bones as they often suffer for osteoporosis- a condition where calcium is lost from the bones. 

A broken bone can easily injure nearby tissue so you cant move anyone who might have a fracture. 

The bones at a joint are held together by ligaments. Ligaments have tensile strength but are elastic.

The ends of bones are covered with cartilage to stop the bones rubbing together, it can also act as a shock absorber.

Membranes at joints release oily synovial fluid to lubricate the joints, allowing them to move more easily. 

BALL AND SOCKET: the joint can move in all directions/rotate (like hip or shoulder)

HINGE: the joint can go backwards and forwards but not side to side (like the knee or elbow)

Muscles pull on bones to move them. Bones are attached to muscles by tendons. They move bones by contracting. Muscles usually come in pairs-antagonistic pairs. When one muscle in the pair contracts, the joint moves in one direction. When the other contracts, it moves in the opposite direction. 

The biceps and triceps are an antagonistic pair of muscles. When the biceps contracts it pulls the lower arm upwards and when the triceps contracts the lower arm is bulled back down. 

Joints can be replaced with artificial joints. However, there are disadvantages:

• The surrounding tissue may become inflamed and painful.
• Hip dislocation (ball comes out of its socket)
• Risk of infection
• Length of legs may be different
• They have to be replaced

In any circulatory system, the heart acts as a pump. The heart contracts, pushing blood round the body. Blood flows away from the heart along arteries, through capillaries at the organs, and then back to the heart through veins. 

As blood travels round the body through blood vessels, it loses pressure. So arteries have the highest pressure, veins have the lowest and capillaries are in between.

Humans have a double circulatory system. One circuit goes to the body and the other to the lungs. 

Different organs need different volumes of blood depending on what they're doing. 

In one heartbeat:

The blood flows into the two atria

The atria contract, pushing blood into the ventricles

The ventricles contract, forcing the blood into the aorta and the pulmonary artery

Blood flows along the arteries, the atria fill again and the cycle starts over.

Claudius Galen: 

thought arterial blood was made by the heart while the blood in veins was made by the liver.

William Harvey:

showed that the heart s a pump and that the same blood circulated round the body 

The heart is told how fast to beat by pacemaker cells. These cells produce a small electric current which spreads to the surrounding muscle cells, causing them to contract.

There are two clusters of these cells in the heart:

SAN stimulates the atria to contract.

The AVN stimulates the ventricles to contract.

In one heartbeat, the SAN produces an e;ectric current first, which spreads to the atria, making them contract. The current stimulates the AVN to produce an electric current, causing the ventricles to contract. This ensures that the atria always contract before the ventricles.

An artificial pacemaker can be used to control heartbeat if the pacemaker cells don't work properly.

Lifestyle affects the circulatory system

Unhealthy diet-eating too much saturated fat can raise the level of cholesterol in  the blood which can clog up blood vessels. Too much salt can raise blood pressure.

Drinking alcohol -regular drinking raises blood pressure 

Smoking - Can increase your blood pressure 

Stress- excessive stress raises blood pressure.

When youre injured, blood clots to prevent too much bleeding. Platelets clump together to plug the damaged area. They are held together by a mesh of protein called fibrin

Hemophilia- when blood doesn't clot easily.

To make gaseous exchange efficient the alveoli have:

• a very large surface area
• a moist surface to help oxygen and carbon dioxide dissolve
• a thin lining so gases can diffuse
• a good blood supply 

Causes of Lung Disease:

Industrial materials, Genetic causes e.g cystic fibrosis, Lifestyle causes e.g smoking, Asthma.

The kidneys:

• Removal of urea from the blood. Urea is produced in the liver from excess amino acids. 
• Adjustment of ion levels in the blood
• Adjustment of water content of the blood.

Ultra filtration:

• A high pressure is built up which squeezes water, urea, ions and glucose out of the blood and into the capsule. Membranes between the blood vessels and the capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. 

Re absorption:

All the sugar is reabsorbed. Sufficient ions are reabsorbed. Sufficient water is reabsorbed. 

Urea, excess ions and water are not reabsorbed, they continue out the nephron

The amount of water reabsorbed in the kidney nephrons is controlled by a hormone called anti-diuretic hormone (ADH)

The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed. 

If the water content gets too high or too low a mechanism will be triggered that brings it back to normal:

Water Loss..brain detects it...pituitary gland release more ADH..ADH makes kidney reabsorb more water...Hydrated

Water gain..brain detects it...pituitary gland releases less ADH..lack of ADH makes kidney reabsorb less water...hydrated

1: Day one- bleeding starts. The uterus lining breaks down for about four days.

2.: The lining of the uterus builds up again, from day 4 to 14, into a thick layer of blood vessels ready to receive a fertilised egg.

3: An egg is developed and then released from the ovary

4: The wall is then maintained for 14 days untul day 28. If no fertilized egg has landed on the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts again. 

It is controlled by four hormones: FSH-produced in pituitary gland. Causes egg to develop in ovaries, stimulates ovaries to produce oestrogen

• Oestrogen-produced in the ovaries, causes the lining of uterus to thicken and grow, stimulates production of LH
• LH-stimulates release of an egg
• Progesterone-produced in the ovaries, maintains the lining of uterus