B5 - The Living Body

Job of a skeleton:

• support the body, allow it to move and protect vital organs
• internal skeleton e.g. fish, amphibians, reptiles, birds, and mammals (also vertebrates)
  • can easily grow with the body and give body support
  • easily to attach muscles to it and is more flexible
• external skeleton e.g. insects

Bones are made up of living cells so they can grow and repair themselves:

• long bones e.g. in your thigh are hollow which makes them lighter and stronger, allowing efficient movement
• long bones are filled with bone marrow, a substance that makes new blood cells
• bones start off as cartilage in the womb that gets replaced by bone as you grow
  • blood vessels deposit calcium and phosphorus in cartilage which turns into bone - ossification
• osteporosis - conditon in lderly people where calcium is lost from bones, makeing bones more brittle, soft and more likely to break

Different joints:

• Synovial joints: 
  • bones held together by ligaments - have high tensile strength and are elastic
  • end of bones covered with cartilage to stop bones rubbing together - shock absorber
  • synovial membrane releases synvoial fluid to lubricate joints allowing more easy movement
    
• Ball and socket joint: hip or shoulder, rotate in all directions
• Hinge joint: knee elbow, backwards and forwards

Muscles:

• bones are attached to muscles by tendons
• muscles usually come in antagonistic pairs e.g. biceps and triceos:
  • bicep contracts, tricep relaxes, pulls lower arm upwards, arm bends
  • tricep contracts, bicep relaxes, lower pulled back down, arm straightens

In animals:

• the heart contracts, blood flows away from the heart, along arteries, through capillaries at organs and back to the heart through veins

Single circulatory system:

• two chambered heart - one chamber receives blood and one chamber pumps out blood 

Double circulatory system:

• four chambered heart - blood pumped seperately to lungs and body, which is important for maintaining high blood pressure
• blood loses presuure at lungs, returns to the heart before pumped to the body which increases pressure 
• high pressure allows materials to be transported around the body quickly
• unborn babies have a hole in their heart (gap between atria) because they get oygen via the placenta

Cardiac cycle: - sequence of events in one complete heartbeat

• blood flows into vena cava and pulmonary artery
• vena cava and pulmonary artery contract, pushing blood into ventricles
• ventricles contract forcing blood into aorta and pulmonary artery
• blood flows along arteries, atria fill again, and cycle starts again

Claudius Galen:

• cut up animals to study them - found out about chambers of the heart
• thought blood from arteries was made by heart, blood in veins made by liver and sucked by heart to be consumed by organs

William Harvey:

• heart valves stopped backflow of blood, heart is a pump
• pulse is caused by heart pumping blood into arteries and same blood circulates around body

Pacemakers in the heart: - cells that produce electrical currents that spreads to surrounding cells making them contract

• two clusters of these cells:
  • sino-atrial node (SAN) - stimulate atria to contract
  • atrio-ventricular node (AVN) - stimulates ventricles to contract
• First, SAN produces an electric current first, which spreads to atria and make them contract
• Current stimulates AVN to produce an electric current causing ventricles to contract
• This ensures that the atria always contract before ventricles

ECGs (electrocardiogram) - show electrical activity of the heart

• show heart attacks, irregular heartbeats and general health of heart

Echocardiogram - an ultrasound scan of heart

• show an enlarged heart, decreased pumping ability and valve function

Hole in the heart:

• = a gap in the wall seperating either the two ventricles or the two atria
• allows blood to move directly from one side to another - causes oxygenated and deoxygenated bloo to mix which reduces amount of oxygen in blood
• can be corrected by surgery

Valve damage:

• valves can be damaged by heart attacks, infection or old age
• can cause valve not to open properly and it can allow blood to flow in both directions 
• can be treated by replacing valve with artifical one

Coronary Heart disease (CHD):

• coronary arteries get blocked by fatty deposits which reduce blood flow to heart muscles causing heart attacks
• can be treated by a coronary bypass operation where a piece of blood vessel taken from another part of the body and inserted to bypass blockage

Advantages of using artifical parts instead of heart transplants:

• using artifical parts means rejection isn't a problem
• less drastic procedure

Disadvantage:

• don't last very long so often need replacing 

Blood clots:

• = mesh of proein fibres
• formed when platelets are exposed to damaged blood vessels

Blood types and transfusions:

• anti-A antibody + A antigen = agglutination (same with anti-b and B)
• Blood group donations:
  • A - contains A antigen, anti-B antibody, donates to A and AB, recieves from A and O
  • B - contains B antigen, anti-A antibody, donates to B and AB, recieves from B and O
  • AB - contains A and B antigens, no antibodies, donates to AB, recieves from anyone
  • O - contains no antigens, anti-A + anti-B antibodies, donates to anyone, receives from O

Organ donors must meet criteria:

• must be relatively young and have a similar body weight
• close tissue match - usually being a close family member
• living donors = 18+

Rejection:

• patient's immune system often recognises new organ as foreign so attacks it
• donors should have a similar tissue type to avoid rejection
• doctors could use immuno-suppressive drug which stops donor organ being rejected

Ethical issues:

• religious reasons - body should remain intact
• life and death is up to God
• people might get pressured into becoming living donor (in families) 

Problems with supply of donor organs:

• there is a shortage of organs available for donation
• this means that a person needing a transplant needs to wait but this takes long as the organ donor must meet so many different criteria

Mechanical replacements for organs:

• outside of the body:
  • heart lung machines to keep patient's blood oxygenated
  • kidney dialysis machines filter patient's blood
  • mechanical ventilators that push air in and out of patient's lungs if they stop breathing
• problems with using mechanical replacements:
  • need a constant power supply
  • large and difficult to move around
  • must be made from materials that won't harm the body and won't degrade
  • occasionally cause inflammation and allergic reactions

What happens during inspiration / breathing in:

• intercostal muscles and diaphragm muscle contract and increase volume of thorax
• lungs expand and decrease pressure inside them which draws air in

What happens during expiration / breathing out:

• intercostal muscles and diaphragm relax and decrease volume of thorax
• pressure in lungs increases and air is forced out

Lung capacity:

• total volume of air you can fit in lungs = total lung capacity
• volume of air breathed in in one one breath = tidal air
• volume of air left in lungs to keep lungs open = residual air
• amount of usable air (total lung capacity - residual air) = vital capacity

Gaseous exchange:

• oxygen diffuses out of alveolus and into blood, carbon dioxide diffuses out blood, into alveolus
• when blood reaches body cells, oxygen is released from red blood cells and into body cells
• carbon dioxide diffuses out of body cells and into blood to be carried back to lungs

Adaptation of alveoli for efficient gas exchange:

• very large surface area to increase rate of diffusion
• thin lining so gases don't have to diffuse very far and good blood supply

• In amphibians, oxygen moves in and carbon dioxide moves out through permeable skin, so their skin can't be waterproof
• In fish, gas exchange occurs at gills where a constant supply of oxygen rich water flows in through mouth and forced out through gills
  • water helps keep gill filaments seperate from each other

Cilia and mucus protect the lungs:

• respiratory tract (trachea and bronchi) lined with mucus and cilia that catch dust and microbes before they reach lungs
• cilia beat and push microbe filled mucus out of lungs as phlegm
• lungs are prone to infection by these microbes because they can't easily be flushed out

Causes of lung disease:

• industrial materials e.g. asbestos 
• genetic causes e.g. cystic fibrosis
• lifestyle causes e.g. smoking
• asthma:
  • muscles around bronchioles contract and constrict airways
  • lining of airways becomes inflamed and fluid builds up in airways making it difficult to breathe
  • muscle relaxant drug is taken to open up airways

Digestion:

• process that breaks down large insoluble molecules in food into small soluble molecules so you can absorb them into the blood plasma
• big lumps of food are physically digested (chewing in mouth and churning them in stomach)
• chemical digestion occurs when digestive enzymes break down molecules that are too big to pass through membrane

Three types of digestive enzymes:

• carbohydrase - break down big carbohydrates into simple sugars:
  • first starch broken down into maltose, then maltose broken down into glucose
  • active in mouth and small intestine
• protease - break down proteins into amino acids
  • active in stomach and small intestine
• lipase - break down fats into fatty acids and glycerol
  • active in small intestine

Bile improves fat digestion:

• made in the liver and stored in the gall bladder
• breaks fat into tiny droplets (emulsification) to give a much bigger surface area for lipase enzymes to work on which helps fat digestion
• bile is alkaline, neutralises acid to make condition right for enzymes in small intestine to work

Food molecules are absorbed into the blood by diffusion:

• products of fat digestion can't get into blood plasma so they diffuse out of gut and into lymph where they are emptied into blood and nutrients travel to where they are needed

Adaptations of small intestines for absorption of food:

• walls of intestine are covered in villi and each cell on surface of villus has a microvilli that increase the surface area
• villio have a single permeable layer of surface cells and a very good blood supply to allow quick absorption

Three main roles of kidneys:

• removal of urea. adjusting of salt levels in blood, adjustment of water content of blood

When blood passes through the kidneys:

• 1) Ultrafiltration:
  • high pressure built up which squeezes water, urea, salts and glucose out of blood and into capsule
• 2) Reabsorption:
  • as liquid flows along nephron:
    • all sugar is reabsorbed using active transport
    • sufficient salt is reabsorbed using active transport
    • sifficient water is absprbed according to levels of ADH
• 3) Release of wastes:
  • urea, excess salt and excess water are not absorbed so continue out of nephron into ureter and down to bladder as urine

Water content:

• important to keep constant concentration of water molecules to prevent too much water moving into or out of tissues by osmosis which keeps blood pressure constant
• amount of water reabsorbed in nephrons is controlled by anti-diuretic hormone which makes nephrons more permeable so tha more water is reabsorbed back into blood
• water content regulation controlled by negative feedback:
  • when water content is too high:
    • brain detects water gain, pituitary gland releases less ADH, ADH makes kidneys reabsorb less water
  • when water content is too low:
    • brain detects water loss, pituitary gland releases more ADH, ADH makes kidneys reabsorb more water

Urine concentration depends on:

• heat - you sweat more when it's hot which causes the release of ADH into blood so kidneys reabsorb more water, producing a small amount of quite concentrated urine
• exercise - makes you sweat so same effect as heat = concentrated, small volume of urine
• water intake - not drinking enough water will produce concentrated urine as there is little excess water to dilute

Dialysis:

• keeps dissolved substances at right concentrations and removes waste
• dialysis fluid has same concentration of sodium and glucose as blood plasma
• barrier is permeable to things like ions and waste but not big molecules like proteins
• waste substances and excess water from blood move across membrane into dialysis fluid

Menstrual cycle:

• stage 1 - uterus lining breaks down for four days
• stage 2 - uterus lining builds up again into a thick sponger layer ready to recieve egg
• stage 3 - ovulation: egg develops and is released
• stage 4 - wall is maintained for 14 days until day 28 where if no fertilised egghas landed on uterus wall, spongy lining starts to break down and cycle starts again

The menstrual cycle is controlled by four hormones:

• FSH (follicle stimulating hormone) - produced in pituitary gland, causes egg to develop on ovaries, stimulates ovaries to produce oestrogen
• Oestrogen - produced in ovaries, causes lining of uterus to thicken and grow, stimulates production of LH and inhibits production of FSH
• LH (luteinising hormone) - produced in pituitary gland, stimulates release of egg at day 14, indirectly stimulates progesterone production
• Progesterone - produced in ovaries, maintains lining of uterus (when levels fall, lining breaks down), inhibits production of LH

• the pill contains oestrogen which keeps levels permanently high, mimicking a pregnancy which inhibits the release of FSH and this stops egg development and production

Infertility is treated in different ways:

• AI - man's sperm is placed into uterus
• FSH injection - increase fertility by stimulating egg production
• IVF - woman is given hormones to stimulate egg prodcution which are mized with sperm and a few fertilised eggs are placed back into uterus
• Ovary transplants - transplanting a healthy ovary donated by someone else

Why some may not agree:

• throwing away fertilised eggs is morally wrong
• increases chances of mulitple preganancies which is dangeros to mother's health 
• Screening - increases risk of miscarriage

Human growth hormone is produced y the pituitary gland and it stimulates grwoth of the whole body but especially the growth of long bones.

A baby's growth:

• a baby's growth is regularly monitored after birth to make sure it's growing normally
• average grwoth charts shows a number of percentiles e.g. 50th percentile = mass that 50% of babies will have reached

Life expectancy has increased because:

• medical advances means fatal conditions can be treated
• places of work and housing are safer and healthier

Problems with increasing life expectancy:

• shortages of housing and more environmental pollution
• older people have more medical problems and need more care = cost to taxpayer increases