Biology - B5

Skeleton - supports the body and allows it to move and protects vital organs.

Fish, amphibians, reptiles, birds and mammals all have vertebrates - internal skeleton and backbones. Insects have an external skeleton, made of chitin. Sharks have skeletons made of ONLY cartilage, whereas parts of the human body are made of BONE AND CARTILAGE.

An internal skeleton is advantageous compared with an external skeleton:

• provides a framework for body
• can easily grow with body
• easy to attach muscles
• more flexible

Cartilage and bone are living tissues and can repair themselves. Long bones are hollow - making them lighter than solid bones and therefore stronger, making it more efficient for movement. The hollow in the middle is filled with bone marrow (makes new blood cells) meaning bones are blood factories. 

Structure of a long bone:

• head with covering of cartilage
• shaft containing bone marrow with blood vessels

Bones start off as cartilage in the womb. Cartilage is living tissue and feels rubbery and can grow and repair itself too.

Eventually, cartilage is replaced by bone. Blood vessels deposit calcium and phosphorus in the cartilage, turning it into bone - ossification.

Whether a person is still growing can be determined by the amount of cartilage present. But some bone still have cartilage present to stop bones from rubbing together at joints.

Despite being very strong, bones can easily be fractured by a sharp knock or get infected.

Elderly people are more prone to fractures because they have weaker bones. This is a condition called osteoporosis where the bones are brittle and more likely to break.

If someone is thought to have a bone fracture it can be dangerous to move them. Movement might make the fracture more serious - for example, it might turn a simple fracture into a compound fracture, or injure nearby tissue. Moving someone with a broken back may damage their spinal cord, leading to paralysis.

Synovial Joints are the most common in the body.

The bones are held together by ligaments (join to other bones), which have high tensile strength but are elastic.

End of bones are covered by cartilage(prevents friction between bones) and because it can be slightly compressed, acting as a shock absorber.

Synovial membrane secretes synovial fluid, which lubricates and cushions bones during movement 

Fixed joint (e.g. skull)

 A ball and socket allows rotation in all directions (e.g. hip or shoulder)

A hinge joint bends only in one direction, backwards and forwards (e.g. knee or elbow)

Bones are attached to muscles by tendons.

Muscles move by contracting as they can only pull on bones to move a joint.

In the arm, the biceps and triceps are the main muscles.

They are antagonistic muscles, when one contracts the other relaxes.

1. To bend the arm, the biceps contract, pulling the lower arm upwards and the tricep relaxes.

2. To straighten the arm, the tricep contracts and the lower arm is pulled back downwards.

The arm acts as a lever when it bends or straightens: the elbow joint is the fulcrum or pivot  

Living things need to be supplied with materials such as oxygen and glucose ad get rid of waste like CO2.

Single celled organisms diffuse material in and out of cells whereas multicellular organisms are larger and so need a blood circulatory system because diffusion alone is not enough for the efficient transfer of materials, as its too slow.

In the circulatory system, the heart acts as a pump and contracts pushing blood. Blodd flows away from the heart through arteries and capillaries and travel back through the veins.

As blood travels AWAY loses pressure, arteries have the highest pressure, and veins the lowest.

A single circulatory system is one circuit from the heart. It has a heart with two chambers. This is the case with fish where the deoxygenated blood is pumped to the gills and oxygenated blood pumped to the body.

A double circulatory system is two circuits from the heart. It has a heart with four chambers, allowing blood to be pumped separately to the lungs and body and maintaining a high pressure. Heart to lungs and back to the heart. Heart to body and back to the heart.

Unborn babies don't need  a double circulatory system as they get their oxygen from the mother via the placenta. Therefore, unborn babies have a hole in their heart, allowing blood to bypass the lungs. It closes after birth.

The blood is under a higher pressure in a double circulatory system compared with a single circulatory system. This allows materials to be transported more quickly around the body.

During each heart beat:

1. Blood flows into the two atria with the atrio-ventricular valves open and the semi lunar valves closed.

2. The atria contract to push blood through the ventricles, with the atrio-ventricular valves still open and semi lunar valves still closed.

3. The ventricles contract, pushing blood into the arteries (aorta and pulmonary artery). The semi-lunar valves open to allow this whilst the atrio-ventricular valves close.

4. Then blood flows along the arteries and the process starts again.

Galen -2nd Century - discovered the chambers in the heart and thought atrial blood was made by heart, while blood in veins was made by liver.

William Harvey - 17th century - discovered heart valves stopped backflow, heart is a pump, pulse is caused by heart pumping blood and the same blood was circulated around the body. 

The heart rate is linked to activity. During exercise, muscles demand more energy so the heart rate speeds up to supply oxygen and glucose to respiring muscles more efficiently. Hormones can also affect your heart rate by increasing them to supply your muscles with plenty of oxygen. E.g. adrenaline is released in a 'fight or flight' response.

The heart contractions are controlled by groups of cells called pacemakers which produce a small electrical current that stimulates muscle contraction.

1. Pacemakers make up the sino atrial node (SAN) which generate nervous impulses which spread across the atria through a contraction and also stimulate the AVN.  

2. The atrio ventricular node (AVN) then causes the ventricles to contract by generating another impulse.

3. Purkinji fibres then carry the impulses up the sides of the ventricles, causing them to contract.

4. The complete heartbeat ensures the atria ALWAYS contract before the ventricles.

Artificial pacemakers are now commonly used to control heart beat.

Techniques such as ECG and echocardiograms are used to investigate heart action.

Electrocardiogram (ECG) shows the electrical activity of the heart. The show:

Heart attacks

Irregular heartbeats and general health of heart

Echocardiograms show an ultrasound of the heart, which shows:

• An enlarged heart
• Decreased pumping ability
• Valve function

Hole in the heart

A gap in the wall separating the two ventricles or two atria.

Allows blood to directly move from one side to another (mixing oxygenated and deoxygenated reducing amount of oxygen in blood)

Corrected by surgery

Valve damage

Valves damages or weakened by heart attacks, infections or old age.

Valves may not open properly, causing high blood pressure, or causes blood to flow in both directions, meaning blood doesn't circulate as effectively.

Replace valve with artificial one

Coronary heart disease

Coronary arteries get blocked by fatty deposits.

Reduces blood flow to heart causing heart attacks

Treated by coronary bypass operation, where a blood vessel from another part of your body is take and replaced in the heart.

Surgery for heart problems:

Heart transplants

New fitted parts - valves and pacemakers

Heart assist device- takes over pumping of a failing heart

Advantages of heart pacemaker or artificial heart valves:

• less risk of rejection
• involve much less traumatic operation
• human donor not needed
• shorter waiting time

Disadvantages:

• they may need replacing
• don’t last very long

Blood clots to prevent excess bleeding. A clot is a mesh of protein fibres (fibrin fibres). They are formed through chemical reactions that take place when platelets are exposed to damaged blood vessels.

Too little clotting - bleed to death

Too much clotting - cause strokes and deep vein thrombosis

Drugs such as, warfarin, heparin and aspirin all prevent blood from clotting.

Haemophilia - when the blood doesn't clot easily because a clotting factor cannot be made by the body. 

If you have lost a lot of blood, transfusions will need to be carried out.

There are different blood types or groups - A, B, O, AB

• The letters refer to the ANTIGENS on the surface of the person's RED BLOOD CELLS
• (Antigen - a substance that can trigger a response from a person's immune system)
• BLOOD PLASMA contains antibodies.

Agglutination - the blood clumps together.

Blood group      Antigens           Antibodies          Can give blood to          Can get blood from

A                      A                     anti-B                 A and AB                    A and O

B                      B                     anti-A                 B and AB                    B and O

AB                   AB                    none                  only AB                       anyone

O                     none                 anti-A, anti-B       anyone                       only O

Living donors can donate organs, but the organs of those who have recently died can also be used.

All donors must be:

Realtively young o organ is fit and healthy

Similar body weight to the patient that needs a tansplant

A close tissue match to prevent problems of rejection (for living donors they have to be a close family member)

Living donors must be over 18

Donors that have dies must have done so recently (only usable for few hours) and close relatives must give their permission.

Success rates depends on lots of things, e.g. type of organ, age of patient, skill of surgeon

Main problem is that patient's immune system recognises the organ as foreign and attacks it, known as rejection.

To reduce this, organs must have a 'close tissue match'

Doctors also use immuno suppressive drugs that suppress the patient immune system to stop rejection - but the patient is left vulnerable to infections.

Religious reasons say that life is God's and the body should remain intact.

Others worry doctors won't save them as their organs are needed for transplant. But there are safeguards in place for this.

There are also concerns of pressurising living donors to sign up.

The UK has a shortage of organ donors

The NHS organ donor register shows you are willing to donate organs if you sign up. However families consent is still need before they can use the organ.

Another system of on opt out system has been suggested, saying unless the person has said so, they have registered to be a donor.

Shortage of donors means patients have to wait for organs to become available and the wait could last a long time.

Mechanical replacements can be used when someone is waiting for a donor. They can be used inside or outside the body.

Heart lung machines - keep the patients oxygenated blood pumping during heart or lung surgery.

Kidney dialysis machine - filters a patient's blood while they wait for a kidney transplant

Mechanical ventilator - used to push air in and out of a patients lung if they stop breathing. 

Problems:

• Need a constant power supply
• Large and difficult to move around
• Must be made from materials that don't harm the body and won't degrade (break down/rust)
• Can occasionally cause inflammation or allergic reactions

When we breath, we take in oxygen and release CO2. CO2 is a waste product of respiration and at high levels its toxic. When the brain detects a rise in CO2 levels in the blood, it increases rate of breathing.

Inspiration (Breathing in)

Intercostal muscles and diaphragm contract and increase the volume of the thorax. This expand the lungs and decreases the pressure inside, which draws air in.

Expiration (Breathing out)

Intercoastal muscles and diaphragm relax and decrease volume of the thorax. This increases pressure of lungs and air is forced out.

Doctors measure lung capactiy using a spirometer.

Total lung capacity - total volume of air you can fit in your lungs

Tidal air - the volume of air breathed in or out in a normal breath.

Residual air - the volume of air that stays in the lungs when we breath out.

Vital Capacity air - the maximum volume of air that can be used for gas exchange in the lungs - a maximum breath in followed by a maximum breath out.

Lungs contain mullions of alveoli which Is where gas exchange takes place. The blood passing next to the alveoli contains lots of CO2 and little oxygen meaning:

Oxygen diffuses out of the alveolus into the blood

Carbon dioxide diffuses out of the blood into the alveolus to breathed out

When the blood reaches the body cells that need oxygen, its released from the red blood cells and diffuses into body cells. At the same time, CO2 diffuses out of body cells and into the blood, where its carried back to lungs.

Alveoli adaptations:

• Large surface area
• Moist surface - help O2 and CO2 dissolve
• Permeable surface - quick gas exchange
• Thin lining
• Good blood supply

Amphibians - simple lungs and permeable, moist skin, where O2 and CO2 moves out à but this means skin can't be waterproof, meaning they lose a lot of water if they live in a dry environment, hence live in a moist habitat.

Fish - gas exchanges at gills, where a constant supply of oxygen rich water flows through the mouth and is forced over the gill filaments àThe water supports the gills as it keeps them separated. If water wasn't there, the gills would stick together and fish would suffocate.  

The human respiratory tract consists of: trachea (windpipe) and bronchi (tube to lungs). It's lined with mucus and cilia which catch dust and microbes before they reach the lungs. The cilia push the microbe filled mucus out of the lungs as phlegm.

Sometimes the microbes get past the defence system and cause an infection. The lungs are particularly prone to infections because they are dead end and microbes can't be easily flushed out.  

Industrial materials - Asbestos can cause asbestosis. This is where inflammation and scarring limits gas exchange in the lungs. Asbestos is used as an insulator in roofs, floors but the use of it is tightly controlled.

Genetic - Cystic fibrosis is a genetic condition where s ingle defective gene causes the lungs to produce thick, stick mucus, clogging up bronchioles, making breathing difficult.

Lifestyle - Smoking causes lung cancer where it forms a tumour around the lung, reducing the surface area of the lungs.

Asthma - Asthmatics are over sensitive to things like dust, pollen, smoke.

When they encounter them, the muscles around the bronchioles contract, constricting the airways. The lining of the airways becomes inflamed and fluid builds up making it hard to breathe (asthma attack).

Symptoms: difficulty breathing, wheezing and a tight chest

Inhalers help open up airways and sometimes drugs are used, but no cure is in place.  

Breaks down large insoluble molecules in food into smaller soluble molecules so you can absorb them into your blood plasma or lymph (fluid that carries products of fat digestion).

The food is first physically digested - chewing in the mouth, churning in stomach. Physical digestion allows food to easily pass through the digestive system and provides a large surface area for chemical digestion.

Chemical digestion involves enzymes which break down molecules that are too big to pass through cell membranes.

CARBOHYDRASE

Starch à Maltose à Glucose

Active places: Mouth, Small intestine

PROTEASES

Proteins à Amino acids

Active places: Stomach, Small intestine

LIPASES

Fat à Fatty acids and glycerol

Active: Small intestine

The pH in the stomach is very acidic (1-2) and its maintained at this level to be the optimum pH for protease enzymes to work.

The pH in the mouth and small intestine is alkaline or neutral.

Bile

Bile is made in the liver and stored in the gall bladder. It helps fat digestion by breaking it down into tiny droplets (emulsification) and gives it a larger surface area for lipase to work on. Bile is alkaline so it neutralises acid from the stomach to make the conditions for enzymes in the small intestine right.

Glucose and amino acids are small enough to diffuse into blood plasma.

The products of fat digestion can't get into blood plasma, so they diffuse out of the gut and into lymph In the lymphatic system. From here its emptied into the system. The nutrients the travel to where they're needed and diffuse out again.      

Small intestine:

Very long - time to break down food

Big surface area for absorption - walls are covered in villi

Villi also have microvilli

Single permeable layer (thin lining)

Good blood supply (quick absorption)

Roles of the kidneys:

• Removal of urea from blood - produced from excess amino acids
• Adjustment of salt levels
• Adjustment of water content
• Blood gets filtered in the nephrons

Ultrafiltration - A high pressure squeezes water, urea, salts and glucose out of the blood and into the capsule.

Membranes between blood vessels in the glomerulus and capsule act like filters so big molecules, such as proteins and blood cells are not squeezed out and stay in the blood.

Reabsorption - As the liquid flows along the nephron, substances are selectively reabsorbed.

All the sugar and sufficient salt is reabsorbed (active transport)
Sufficient water is reabsorbed according to the level of ADH

Excretion - Urea, excess salt and excess water are not reabsorbed but continue out of the nephron, down the ureter and down the bladder as urine. 

It important to keep a constant concentration of water molecules in the blood plasma. This prevents too much water entering tissue through osmosis, keeping blood pressure constant.

Amount of water reabsorbed is controlled by ADH (anti-diuretic hormone). ADH makes the nephron more permeable so more water is reabsorbed back into the blood.

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

Water content regulation goes through negative feedback, meaning the mechanism will always bring it back to normal. 

Amount and concentration of urine is controlled by ADH and this depends on:

HEAT - When its hot, you sweat, losing water from the body. This causes the release of ADH so more water can be reabsorbed. This urine is concentrated and only a small amount is produces as there is only a small amount in excess.

EXERCISE - Makes you hot , so you sweat more to cool down and lose water. This has the same effect as heat, so small amount of concentrated urine is produced.

WATER INTAKE - Not drinking enough water means you're dehydrated and that will produce concentrated urine. Drinking lots of water will produce lots of dilute urine. 

Patients with kidney failure use a dialysis machine.

Dialysis has to be done regularly so dissolved substances are kept at the right concentrations to remove waste.

Dialysis fluid has the same concentration of sodium and glucose as blood plasma (meaning these aren't removed from the blood)

The barrier is permeable to things like ions and waste substances, but not big molecules like proteins (like in the kidney). Therefore, waste substances and excess water can move across into the dialysis fluid. 

The menstrual cycle has 4 stages:

Day 1 - Menstruation starts - Uterus lining breaks down for about four days

Day 4 - 14 - Uterus lining builds up again - A thick pongy layer full of blood vessels develops, ready to receive a fertilised egg

Day 14 - 28 - Egg develops and is released - Egg released from the ovary (ovulation)

Day28 - Wall is maintained and when no fertilised egg lands on the uterus wall, lining breaks down and cycle starts again 

FSH (Follicle stimulating hormone)

Produced in the pituitary gland

Causes an egg to develop in one of the ovaries

Stimulated the ovaries to produce oestrogen

Oestrogen

Produced in the ovaries

Causes the lining of the uterus to repair (thicken and grow)

Stimulates production of LH (causing release of egg) and inhibits production of FSH

LH (Luteinising hormone)

Produced by pituitary gland

Stimulated release of an egg (day 14 - ovulation)

Indirectly stimulates progesterone production

Progesterone

Produced in the ovaries

Maintains lining of uterus. When levels of progesterone fall, lining breaks down

Inhibits production of LH

The production of hormones is controlled by negative feedback

The production of hormones is controlled by negative feedback

Example 1:

FSH stimulates the ovary to release oestrogen, which inhibits the release of FSH.

So when there's lots of FSH, oestrogen is releases and FSH production is inhibited, causing FSH levels to fall.

Example 2:

LH indirectly stimulated production of progesterone, which inhibits the release of LH.

When here's lots of LH, progesterone is released and then LH production is inhibited, meaning LH levels fall.

Contraceptives contain oestrogen - preventing the release of an egg. If oestrogen is taken every day, the levels are kept permanently high meaning it mimics pregnancy and inhibits the release of FSH. This means egg development will stop and stay stopped.

• Artificial insemination - sperm placed directly into uterus
• Use of FSH injections - stimulates egg production and be released making fertilisation more likely
• "In viro" fertilisation (IVF) - woman's eggs are fertilised outside the body. And then a few fertilised eggs are implanted back in the uterus. But for IVF you need sperm, eggs and a healthy uterus.
• Some women get donated eggs
• Some women can produce eggs but always miscarry, meaning they can use a surrogate.
• Egg donation - if doesn't produce eggs, donated by another women and then IVF is used. (can happen with sperm)
• Surrogacy - embryo produced by IVF then transplanted into a surrogate mother.
• Ovary Transplants - gives women supply of eggs if her own ovaries do not function

Not all the eggs are implanted back into the woman meaning its denying a life by throwing it away.

IVF increases the chances of multiple pregnancies which could danger a mother's life or cause financial problems.

Foetal Screening can be used to check foetal development and to identify conditions such as Down's syndrome using amniocensis and chromosomal analysis.

This raises ethical issues because some people think that foetal screening offers the unacceptable option of ending an unborn babies life, and that termination is unethical.

Diet and exercise can influence growth:

• Diet - a healthy diet contains protein needed for muscle growth, and calcium and vitamin D for bone growth.
• Exercise - needed to encourage muscle growth and to make bones dense and hard (strong). It also stimulates release of growth hormone.
• Human growth hormone is produced by the pituitary gland which stimulated the growth of the whole body, but especially the growth of the long bones.

Growth is also affected by hormonal or genetic factors. Gigantism is the result of a tumour of the pituitary in childhood, causing too much growth hormone to be produced. Dwarfism is genetic factors and results in stunted bone growth.

Different parts of a foetus and a baby grow at different rates - The brain and head develop quickly to coordinate the complex human structure and chemical activity

A baby's length, mass and head size are regularly monitored during their first months to provide early warning of any growth problems.

Charts show different percentiles. Babies vary in size and may follow on percentile, but crossing over of percentiles shows inconsistent growth. 

Life expectancy increased:

Medical advancements

Places of housing and work and safer and healthier

Better lifestyles and diets

Less industrial diseases

Problems:

Population grows leading to shortages of housing and more environmental pollution

Number of elderly increased meaning state wouldn't be able to give everyone pensions

Older people have more medical problems and need more care, increasing taxpayer costs