Special surfaces for exchange
All living cells need certain subtances to keep them alive -
- oxygen for aerobic respiration
- glucose as a source of energy
- proteins for growth and repair
- fats to make membranes and to be store of energy
- minerals to maintain their water potentional and to help enzyme action and other aspect of metabolism.
- organisms may absorb these subtances through the enviroment - or make them inside their cytoplasm as a part of their metabolism - living cells must be able to take up simple substances from the enviroment
- All living cells need to remove waste products from metabolic activities in cytoplasm.
- carbon dioxide ( in animals microorganisms plant cells) that are not actively carrying out photosynthesis
- oxygen from photosynthesis
- other waste such as ammonia urea which contains excess nitrogen.
Single cells and small organisms can exchange gases nutrients and wastes across the outer surface - because they have a large surface to area to volume ratio.
- once the multicellular oganism becomes larger to surface area to volume ratio becomes smaller and its cells need more supplies.outer surface is not large enough for gases and nutrients to enter body fast enough keep all cells alive. they need to travel greater distance to the centre of organism.
What exchange surfaces look like?
- large surface area provides more space - molecules to pass through - often achieved by folding the walls and membranes
- the thin barrier to reduce diffusion distance
- fresh supply of molecules on one side to keep the concentration high.
- removal of required molecules on the other side to keep concentration low.
maintain steep gradiant diffusion
Example if specialised exchange surfaces
- found in all organs where subtances are removed from transport system - waste returned to the transport system eg walls in the alvelio of the lungs
There are more exchange surfaces in living organisms -
- small intestines where nutrients are absorbed
- liver - levels of sugars are adjusted
- roots hair of plants where water and minerals are absorbed
- hyphae of fungi nutrients absorbed.
The lung as an organ of exchange
Lungs are large pair of inflateable structure lying in the chest cavaity.
Air can pass into the lungs through the nose and along the trachea (windpipe), bronchi and bronchiholes. Each one adapted to the function of a;;owing passage of air.
The air reaches a tiny air filled sacs called alvelio - the walls of this is where the surface where exchange of gases take place.
The lungs protected by the ribs - movement of ribs together with action of diaphragm help to produce breathing movements (ventillation)
Gases pass both ways through thin walls of alvelio - oxygen passes from the air to the alveiloi to the blood to the capilliries - carbon dioxide passes from the blood to the air in the alvelio.
Large surface area : - provides more space for the molecules to pass through - indivdual alvelio is small. Total surface area of the lung is larger that that of our skin.
A barrier permeable to oxygen and carbon dioxide- plasma membranes that surrond the thin cytoplasm of cells from barrier to exchange - readily allow diffusion of carbon dioxide and oxgen.
Thin barrier to reduce diffusion distance
Reduce the distance the gases have to diffuse
- alveolus wall in one cell thick
- the capillary wall is one cell thick
- both cell contain squamous cells - flattened or very thin vrlld.
- capilliries are in close contact with the alvelous walls
- the cappiliries are narrow that the red blood cells are squeezed against the cappilary wall making them closer to the air in the alveloi and reducing the rate of flow past in the blood.
- total barrier to diffusion is only two flattened cells.
a thin layer of moisture lines the alveoli - the moisture passes through the cell membranes from the cytoplasm of the alveolus - as we breathe out it evaporates and is lost. - the lungs must produce a substance called a surfactant to reduce the cohesive forces between the water molecules. Without it the alveloio would collapse due to the cohesive forces between water molecules lining in air sac.
Maintaining diffusion gradient
for diffusion to be rapid - steep diffusion gradient is needed.
meaning high concentration of molecules on supply side of exchange surface and low concentration on demand side.
to maintain steep diffusion gradient - fresh supply of molecules on one side is needed to keep conc high - a way of removing molecules from other side conc needs to be low. Achieved by the blood transport system and ventillation movements.
- blood brings carbon dioxide from the tissues to the lungs
- Ensures that the conc of carbon dioxide in blood is higher than the air in the alveloi.
- Carries oxygen away from lungs
- Ensures the concentration of oxygen in blood kept lower than conc air inside the alveloi.
- the heart pumps the blood along the pulmonary artery to lungs - the artery divides up t form finer and finer vessels - eventually carry blood into tiny cappiliries that are wide enough for red blood cells to squeeze through - the capilliries lie over the surface of the alvelio.
Breathing movements of lungs ventialte the lungs - replace the air with fresh air. Brings more oxygen into lungs and ensures the conc of oxygen in the air of alvelous remains higher than the conc in the blood.
- ventiallation also removes air containing carbon dioxide from the alveloli - ensures that the conc of carbon dioxde in alveoli remains lower than that in blood.
This constant supply of gas to one side of exchange surface - and its removal from other ensures diffusion exchange can continue.
Tissues in the lungs
The trachea, bronchi, bronchiholes airways that allow passage of air into lungs in and out. - Airways must meet a certain requirement
- the larger airways must be large enough to allow sufficient air to flow without obstrucion.
- must also divide into smaller airways to deliver air to all alvelio
- airways must be strong enough to prevent them collapsing when the air pressure inside is low (inhalation)
- must be flexible
- allow movement
- strectch and recoil
Trachea and Bronchi
Similar structure differ in size - bronchi narrower than trachea relatively thick walls severeal layers of tissue.
- much of walls consist cartalidge
- cart in the form of incomplete ring C rings in trachea - but less regular in bronchi
- inside surface of catilidge is layer of glandular tissue - connective tissue, elastic fibres smooth muscle and blood vessels. 'loose tissue'
- inner lining is an epithuluem layer two types of cells. Most cells have cilia and this is called ciliated epithuliem - among them goblet cells.
Bronchiholes - much narrowerer than bronchi - larger bronchiholes have some cartilidge smaller ones NO. Wall made of mainly smooth muscle and elastic fibres - smallest bronchiholes have clusters of alvelio (air sacs) at their ends.
Role of each tissue
Cartiligde - structural role. Supports trachea and bronchi holding them open - prevents collapse when air pressure inside running low during inhaltion - does not form complete ring - flexiability allows you to move your neck without constricting airways - allows tube to expand during swallowing.
Smooth muscle - Contract, when contract constricts the airway - this makes lumen of airway narrower - effect on smooth muscle is most obvious in bronchiholes - constricting lumen restrict flow of air to and from alvelio.
flow of air in alvelio important controlling because of harmful substances in air - contraction smooth muscle and control of airflow not voluntary act - allergic reaction bronchi holes constricts making difficult to breathe causing astma.
smooth muscles contract reduces diameter of lumen of airway - smooth muscle cannot reverse effect - when airways constricts it deforms the eleastic fibres in the loose tissue - smooth muscles relaxes elastic fibres recoil to their orginal size and shape - helps to dilate (widen) airways.
Goblet and glandular tissues - they are under the epithelium and secret mucus - role of it is to trap any tiny particles from the air - may include pollem and bacteria - remove it without a risk of infection.
Ciliated epithelium - constist of ciliated cells - hair like structures projecting from the membrane - these are cilia, move in a pattern to waft the mucus up the airway to the back of throat mucus is swallowed and acidicty in the stomach kill bacteria.
Measuring lung capacity
air moves in and out of lungs about 12 times per min - diaphraghm and intercostal muscles contract and relax - each breath refreshes some air if your lungs carries away some of the carbon dioxide generated by your body. Breathe deeply quickly - this gets more oxygen rich air into your lings and removes more carbon dioixde rich air out of your lungs.
Inspiration - and expiration are terms used to describe breathing in and breathing out.
Different elements of lung volume
- tidal volume - volume of air moved in and out of lungs with each breathe when you are at rest - provides the rest enough oxygen for its resting needs while removing enough carbon dioxide to maintain at safe level.
- vital capacity - largest volume of air that can be moved into and out of lungs in any one breath - varies between men and women , persons size and age. Regular exercise increase capacity.
- Residual volume - volume of air that always remains in the lungs even after possible exhaltion.
- Dead space - air in the bronchiholes. bronchi, trachea - no gas exchange between this air and blood.
- Inspiratory reserve volume how much more air can be breathed in over and below the normal tidal volume when you take a big breath - reserve when exercising.
- Expirtory reserve volume how much more air can be breathed out over and above the amount that is breathed in a tidal volume breath.
Spirometer and lung volume
A spirometer consists of a chamber filled with oxygen that floats on a tank of water. Person breathes from disposable mouthpiece attatched to tube connected to the chamber of oxygen.
Breathing in takes in oxygen from the chamber which sinks down - breathin gout pushes air into chamber and floats up.
Measuring oxygen uptake
If someone breathes in and out of spirometer for a period of time - level of carbon dioxide will increase dangerously.
- avoid this soda lime is used to absorb the carbon dioxide that is exhaled. Total volume of gas will go down - because volume of co2 breathed out is the same as the volume of oxygen breathed in
as carbon is removed this total reduction is equal to the vol of oxygen used up by the person breathing in out out.
Transport in Animals
Large animal transport systems -
living animal cells need suppy of oxygen and nutrients - also need to remove waste products so that it does not build up and become toxic.
Diffusion will supply enough oxygen and nutrients to keep the cell alive.
Three main factors that affect the need for transport system -
- surface area to volume ratio
- level of activity.
if animal has severeal layers of cells - any oxygen or nutrients diffusing in from the outside will be used up by outer layers of cells - oxygen and nutrients will not reach cells deeper within body.
Surface area to volume ratio -
small animals have large surface area compared to volume - ratio affected by animals shape flat body large surface volume ratio.
To allow animals to grow in size they need range of tissues and structural support to give body strength - volume increases as body grows thicker.
Level of activity -
animals need energy from food - so move around - releasing energy from food by repiration requires oxygen, if animal is very active cells need good supplies of nutrients and oxygen. keep themselves warm.
Features of good transport system
Effective transport system include -
- fluid or medium to carry nutrients and oxygen around the body - blood.
- a pump to create pressure that will push the fluid around teh body - heart
- exchange surfaces that enable oxygen and nutrients to enter the blood and to leave it where its needed.
it will also include
- tubes or vessels to carry the blood
- two circuits - one to pick up oxygen and another to deliver oxygen tissues
Singe and double circulatory systems
Fish have single circulatory system - blood flows from the heart to the gills and then onto the body before returning to the heart
heart > gills > body > heart
Mammals have 2 seperate circuits - double circulatory system
- one circuit carries the blood to the lungs to pick up oxygen ( pulmonary circulation)
- the other circuit carries oxygen and nutrients around the body to the tissues - ( systemic circulation.
Two pumps one for each circulation - blood flows through the heart twice for each circulation of body.
Advantages of double circulation
efficient circulatory system will deliver oxygen and nutrients quickly to the parts of the body where they are needed - increasing the blood pressure.
In fish single circulatory systems
- blood pressure is reduced as blood passes through capiliries of the gills
- means it will not flow quickly to the rest of body
- limits the rate of oxygen and nutrients are delivered to repiring tissues.
fish are not active as mammals and do not need to maintain body temp. less energy. Single system delivers oxygen and nutients quickly enough for their needs.
- the heat can increase the pressure of blood after it has passed through the lungs so blood flows more quickly to body tissues.
- systematic circulation can carry blood at higher pressure than pulmonary circulation
- the blood pressure must not be to high in pulmonary or it migh damage delicate capiliries in lungs.
Mammals are active - need to maintain body temp, energy released from food in the process of repiration - release a lot of energy the cells need good supplies of both nutrients and oxygen.
mammalian heart muscular double pump. divided into 2 sides.
the right side pumps deoxygenated blood to the lungs to be oxygenated. the left side pumps oxygenated blood to the rest of the body. Both side the heart squeees the blood putting it under pressure. Forces the blood along arteries.
External features of the heart
heart sits slighly off centre to the left of chest cavity - lies with the atria in middle of cavaity.
main part of the heart consists dark red muscle feels very firm - this is the muscle surronding two main pumping chambers - the ventricles - above ventricles are two thin walled chambers - atria - smaller than ventricles.
Cornory artiers lie over the surface of the heart. carry oxygenated blood to heart. heart is a hard working organ arteries very important.
if they become constricted it has sevre consequences for the health of the heart or the animal.
restricted blood flow to heart muscle reduces delivery of oxygen and nutrients such as fatty acids - may cause angina or heart attack.
internal features of heart
heart divided into 4 chambers - two upper chambers are atria - recieve blood from major veins - deoxygenated blood from body flows from the vena cava into the right atrium. Oxygenated blood from lungs flows from pulmonary vein into left atrium.
from the atria the blood flows down through the atrioventricular valnves into the ventricles. these valves are thin flaps of tissues arranged in cup shape - when ventricles contract the valves fill with blood and remain closed. this ensures that blood flows upwards in major arteries and not back to atria (back flow) - tendinous cords - attached to valves to the walls of ventricles prevent flimsy valves turning inside out - allow blood to flow up atria.
wall of muscle called septum seperates ventricles from eachother ensures oxygenated blood in the left side of heart and deoxygenated on right - seperate.
deoxygenated blood leaving right ventricle flows to pulmonary artery leading to lungs. oxygenated blood leaving left flows to aorta. carries blood to a no. arteries supply all body parts. at base of major arteries where they exit the heart are valves - semilunar valves prevent blood returning to heart as venticles relax
muscle of each chamber contracts to create increased pressure of blood - higher pressure created in heart further it push the lood.
Atria - muscle of the atria very thin - chambers do not need to create more pressure function to push blood into the ventricles.
right ventricle - walls of right ventricle thicker than wall of atria - enable right ventricle to pump blood out of heart.
right thinner than left - right pumps dexogentated blood to lungs - lungs are in chest activity beside heart so blood does not need to travel far - lungs contain a lot of fine capiliries close in contact with walls of alveoli - alveoli walls are thin and there is little or no tissue fluid - so capiliries are not supported can easily burst pressure of blood must be kept down to prevent capaliries in lungs from bursting.
left ventricle - two 3 times thicker - blood from left pumped out through aorta and needs sufficient pressure to overcome resistance of systematic circulation.