Biology B5



Advantages of an internal skeleton:

- provides internal framework for the body.

- it grows with the body.

- it has many joints therefore it is flexible.

- it allows easy attachment of muscles.


When humans are in the early stages of life, their whole skeleton is made of cartilage. By the process of ossification the cartilage is slowly replaced by bone. If there is still some cartilage left between the head and the shaft then this means the bone is still growing.

- Even though bones are very strong they can still be broken easily by a sharp knock.

- The bones of elderly people can lack calcium and phosphorus, which can result in osteoporosis, making the prone to fractures.

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- Synovial joints, such as ball and socket joints and hinge joints, contain synovial fluid, a synovial membrane, ligaments and cartilage. 

- A hinge joint only allows up-and-down movement of the joint whereas a ball and socket allows a wider range of movement in all directions.

Each part of a synovial joint has a special function:

- Synovial fluid acts as a cushion and lubricates the joint to prevent the bones rubbing.

- The synovial membrane holds in the synovial fluid.

- Cartilage protects the bone head.

- Ligaments hold the bones in place.

An antagonistic pair is two muscle which work together to move a joint. One will relax as the other contracts. An example of this is the bicep and tricep. To raise the forearm, the bicep contacts and the tricep relaxes. To lower the arm, the opposite happens. 

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Circulatory System

Single circulatory system = has only one blood circuit which goes to the whole body and the heart. This is used in fish.

Double circulatory system = this is found in mammals and it consists of two circuits. The first in a circuit between just the heart and the lungs to obtain oxygen, the other is from the heart to the rest of the body.

A double circulatory system requires a four-chambered heart: two atria to recieve blood and two ventricles to distribute blood. This ensure the blood pressure stays high and the circulation of food and oxygen is faster. 

A single circulatory system on has two chambers, one to distribute and one to receive blood.

In the second century, Galen knew that the heart acted as a pump of blood and the importance the the hearts pulse. However, he believed the blood was made in the liver and it flowed from there. Later on, William Harvey knew blood circulated around the body through tiny vessels and that the heart contained four chambers.

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Cardiac Cycle & Heart Rate

Cardiac cycle:

The cardiac cycle is a sequence of events as blood enters and leaves the heart.

  • the two atria contract as the ventricles relax to recieve blood through the atrio-ventricular valves.
  • the two ventricles the contract to force blood out to the lungs and around th body.

Semi-lunar valves prevent backflow into the ventricles.

Heart rate:

When muscles are being used, they have more of a demand for oxygen, meaning the heart must pump blood faster to reach this demand.

Groups of cells called pacemakers control the rate the heart contracts by producing a small electric current to stimulate muscle contraction. If these cels do not work then an artificial replacement can be placed near the heart.

Two groups of pacemaker cells coordinate the contractions of the heart muscles:

  • impulses from the SAN (sino-atrial node) cause the atria to contract, and stimulate the AVN
  • impulses from the AVN (atrio-ventricular node) cause the ventricles to contract
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Running Repairs

Hole in the heart - This results in deoxygenated blood mixing with oxygenated which means the body does not receive as much or enough oxygen to run effectively. This can be fixed by surgery.

Weak/leaking valves - This is when the hearts valves are damages or allow backward flow of blood back into the heart. This lowers a persons blood pressure so could lead to dangerous illness. Valves can be repaired by surgery ao you can receive artificial replacements.

Coronary heart disease - This is when the coronary artery get blocked and reduces blood flow to the heart muscles. This can be by-passed by transplanting a blood vessel from another part of the body and replacing it to do the same job.

Faulty pacemaker cells - When pacemaker cells are not working it means the heart rate becomes irregular and and this can be fixed by and artificial pacemaker which carries on sending electrical impulses to the heart so it contracts effectively.

Major heart problems can also be resolved by full heart transplants.

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Gaseous Exchange

When humans breathe in, we contract out intercostal mucles and muscles in the diaphragm. This results in the chest moving upwards and the chest volume increases. The high pressure air outside then enters the lungs.

When we breathe out, the muscles the relax, causing the ribs to move back down and the diaphragm to curve upwards. The chest volume therefore decreases, which increases the pressure in the lungs resulting in the air getting pushed back out again.

Tidal volume = the amount of air breathed in and out while at rest.

Vital capacity = the maximum amount of air which can be breathed in at once.

Residual air = the amount of air which does not leave the lungs and cannot be forced out.

Exchange of gases takes place by diffusion between the alveoli and the air in the air sacs. The exchange surfaces are adapted by having a large surface area and good blood supply to make the gas exchange more efficient. They are also permeable, moist and only one cell thick.

Readings from a spirometer are a measure of different lung capacities and the rate of air flow. They can be used to help diagnose lung diseases.

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Physical digestion is important because:

  • it allows food to pass more easily through the digestive system.
  • it prepares the food for chemical digestion by giving it a larger surface area.

amylase - starch    →    sugars

protease - proteins    →    amino acids

lipase - lipids    →    fatty acids + glycerol

Food molecules are small and soluble because they need to be able to pass through the walls of the small intestine and dissolve in the blood or lymph. The small intestine is adapted for efficient absorption of food by having an extensive system of blood capillaries and an extensive lymphatic system of lacteals. The small intestine also has a large surface area which is created by:

  • many villi  in the walls of the small intestine.
  • many microvilli from the walls of the villi.
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Excess and unwanted amino acids are broken down in the liver, forming urea, which is taken in the blood to the kidneys.

Urine contains urea, as well as water and salt.

Each kidney has millions of microscopic kidney tubules (nephrons) where filtration takes place to form urine. Each nephron has:

  • a network of capillaries surrounded by a capsule.
  • a region where some materials such as glucose are selectively reabsorbed.
  • a region where reabsorption of some salt and water takes place.

Since the kidney is responsible for the removal of waste from the blood, any damage (either from accidents or disease) can lead to a build-up of poisonous waste products in the body.

We can survive without one kidney very well, but total kidney failure would be fatal if not treated. Treatment can take the form of dialysis on a kidney machine or a kidney transplant.

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Regulating Urine Concentration

- After drinking large amounts of water, the quantity of your urine increases but the concentration decreases. 

- When the body sweats and loses water, the quantity of urine decreases but the concentration increases

- The pituitary gland in the brain produces the anti-diuretic hormone (ADH) which controls the concentration of urea by:

  • increasing the permeability of the kidney tubeles to allow more water to be reabsorbed.
  • using a negative feedback mechanism to control ADH production.

Carbon dioxide concentration:

- Carbon dioxide must be removed from the body because high concentrations in the body can be toxic.

- An increase of carbon dioxide in the blood is sensed by receptors in the carotid artery. Nerve impulses then inform the brain which lead to an increase in breathing rate to remove the carbon dioxide from the lungs.

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Sex Hormones & Human Fertility

  • FSH - stimulates an egg to develop in an ovary
  • LH - controls ovulation (egg release)
  • Progesterone - maintains the uterus wall
  • Oestrogen - repairs the uterus wall

- FSH and LH are released by the pituitary gland in the brain.

- Negative feedback controls the levels of the sex hormones in the menstrual cycle. The cycle is triggered by the receptors in the hypothalamus.

- If fertilisation does not occur, the levels of oestrogen and progesterone decrease. When these levels are low, menstruation occurs.

- If an egg is fertilised, the levels of progesterone remain high and no FSH is produced.

Fertility in humans:

Fertility in humans can be controlled by the use of artificial sex hormones by controlling egg release and implantation. The contraceptive pill prevents ovulation and fertility drugs help to ensure ovulation.

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Infertility Treatment

Artificial insemination - where sperm are placed into the vagina by syringe.

IVF - where an egg is fertilised by sperm outside the body.

Egg donation - where an egg is donated from another female, then fertilised and placed back in the uterus.

Surrogacy - where a fertilised egg is placed inside a surrogate mother (another female)

All fertility treatments increase the chances of a successful fertilisation and pregnancy.

Foetal screening:

A developing foetus can be checked to see if there are anyabnormalities. This checking can be done by: 

  • extracting and testing cells in the amniotic fluid (amniocentesis)
  • using a blood test to test cells for any chromosome abnormalities (chromosomal analysis)
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Growth and Repair

Growth rate:

A balanced diet and regular exercise can increase growth. Extremes of height are usually caused by hormone imbalance or by genes.

The human growth hormone is produced by the pituitary gland and it stimulates general growth, especially in long bones.

Organ donation:

Transplants are at risk of being rejected by the recipient's body and so need life-long immuno-suppressive drug treatments, which can lead to the body not being able to protect itself from microorganisms.

People over the age of 18 can be put on a donor register so their organs can be used after they die. Some people believe an 'opt out' this is against their human rights

Trends in transplant and survival rates can be shown by interpreting data.

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