3.8 - Transport in animals Flashcards
What 3 factors affect the need for a circulatory system?
- size
-level of activity - surface area to volume ratio
Why are specialised transport systems needed
- metabolic demands of most multicellular organisms are high
- surface area to volume ratio gets smaller as organisms get bigger
- molecules such as hormones and enzymes may be made in one place and needed in the other
- food will be digested in one organ system, but needs to be transported to every cell to be used in respiration
- waste products of metabolism need to be removed from the cells and transported to excretory organs
Basic features of most circulatory systems
- they have a liquid transport medium that circulates around the system (blood)
- they have vessels to carry the transport medium
- the have a pumping mechanism to move the fluid around the system
Open circulatory systems
- there are very few vessels to contain the transport medium
- the transport medium is pumped straight from the heart into the body cavity of the animal (haemocel)
- the transport medium is under low pressure in the haemocel
- it comes into direct contact with tissues and cells
- it then returns to the heart through an open ended vessel
open circulatory systems in invertebrates
- insect blood is called haemolymph
- does not carry oxygen or carbon dioxide, as gas exchange occurs in the tracheal system
- transports food and nitrogenous waste products and the cells used in defence against disease
- the body cavity is split by a membrane
- the heart extends along the length of the thorax and the abdomen of the insect
- the haemolymph circulates but steep diffusion gradients cannot be maintained
- the amount of haemolymph flowing to a particular tissue can be varied to meed changing demands
Closed circulatory systems
- the blood is enclosed in blood vessels
- the blood does not come directly into contact with the cells of the body
- the heart pumps blood along the body under pressure and relatively quickly
- the blood returns to the heart
- substances enter and leave the blood by diffusion through the walls of the blood vessels
- the amount of blood flowing to a particular tissue can be adjusted by widening or narrowing blood vessels
- most carry a blood pigment that carries the respiratory gases
Single closed circulatory systems
- found in a number of groups including fish
- the blood flows through the heart and is pumped out to travel all around the body before returning to the heart
- the blood travels only once through the heart for each complete circulation of the body
Hoe do single closed circulatory systems work in fish
- the blood passes through two sets of capillaries before it returns to the heart
- in the first, it exchanges oxygen and carbon dioxide in the gills
- in the second set of capillaries in the different organ systems, substances are exchanged between the blood and the cells
Why do organisms with single closed circulatory systems often have low levels of activity
because the blood passes through two sets of very narrow vessels, the blood pressure drops so the blood returns to the heart quite slowly. This limits the efficiency of the exchange system
How do fish have a relatively efficient single closed circulatory system compared to other organisms
- countercurrent gas exchange system in gills allows them to take lots of oxygen from the water
- body weight is supported by water and they do not maintain their own body temperature, lowering the metabolic demands
- increases efficiency of exchange system, allowing fish to be very active
Double closed circulatory systems
- found in birds and most mammals, which are very active and maintain their own body temperature
- most efficient way of transporting substances around the body
- involves two separate circulations
- blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, then returns to the heart
- blood flows through the heart and is pumped out to travel all around the body before returning to the heart again
- each circuit only travels through one capillary network, meaning a relatively high pressure and fast flow of blood can be maintained
Elastic fibres (in vessels)
Composed of elastin fibres and can stretch and recoil, providing vessel walls with flexibility
Smooth muscle (in vessels)
Contracts or relaxes, which changes the size of the lumen
Collagen (in vessels)
Provides structural support to maintain the shape and volume of the vessel
Arteries
- carry oxygenated blood away from the heart to the tissues
(except from the pulmonary artery) - contain elastic fibres, smooth muscle and collagen
- elastic fibres enable them to withstand the force of the blood pumped out of the heart and stretch to take the larger blood volume
- helps to even out the surges of blood pumped out of the heart to give a continuous flow
Arterioles
- link arteries and capillaries
- more smooth muscle and less elastin in their walls, as have little pulse surge,but can constrict and dilate to control the blood flow into individual organs
Vasoconstriction
When the smooth muscle in the arteriole contracts and constricts the vessel, preventing blood flowing into a cvapillary bed
Vasodilation
When the smooth muscle in the wall of an arteriole relaxes, letting blood flow into the capillary bed
Capillaries
- microscopic blood vessels that link arterioles and venules
- form an extensive network through all the tissues of the body
- so small that red blood vessels have to travel through in single file (8μm diameter)
- where substances are exchanged, as the gaps between endothelial cells that make up capillaries are relatively large
- the place where blood enters oxygenated and leaves deoxygenated (apart from lungs and placenta)
Ways capillaries are adapted for their role
- provide a very large surface area for diffusion
- relatively slow movement of blood through capillaries dives more time for exchange of materials
- walls are a single endothelial cell thick, giving a very thin layer for diffusion
Veins
- carry blood away from the cells of the body towards the heart
- carry deoxygenated blood (apart from pulmonary vein)
- do not have a pulse, as the surges are gone after the blood travels through narrow capillaries
- blood pressure is very low compared to arteries, so have valves to prevent backflow of blood
- walls contain lots of collagen and relatively little elastic fibre
- vessels have a wide lumen and a smooth, thin lining so the blood flows easily
Passage of deoxygenated blood
- deoxygenated blood flows from the capillaries into the venules and then into larger veins
- then reaches inferior and superior vena cava, carrying the blood back to the heart
Venules
- link the capillaries and veins
- have very thin walls with just a little smooth muscle
- several venules join to form a vein
Adaptations that allow veins to move blood under low pressure and against gravity
- the majority of veins have one-way valves at intervals. When blood flows in the direction of the heart, the valves open so blood can pass through. If the blood starts flowing backwards, the valves close to prevent it from happening
- many of the bigger veins run between big, active muscles. When the muscles contract, they squeeze the veins, pushing blood towards the heart. The valves prevent backflow when the muscles relax
- The breathing movements of the chest act as a pump. The pressure changes and the squeezing actions move blood in the chest and abdomen towards the heart
Functions of the blood
Transport of:
- oxygen to, and carbon dioxide from respiring cells
- digested food from the small intestine
- nitrogenous waste products from the cells to the excretory organs
- hormones (chemical messages)
- food molecules from storage compounds to the cells that need them
- platelets to damaged areas
- cells and antibodies involved in the immune response
Also contributes to the maintenance of a steady body temperature and acts as a pH buffer
What makes up blood
Plasma (largely composed of water) carries:
- dissolves glucose and amino acids
- mineral ions
- hormones
- large plasma proteins
- erythrocytes
- white blood cells
- platelets
Platelets
Fragments of large cells called megakaryocytes found in the red bone marrow. Involved in the clotting mechanism of the blood as well as plasma proteins such as albumin and fibrinogen
structure of tissue fluid
As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
This results in the formation of tissue fluid. The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins
Proteins are too large to fit through gaps in the capillary walls and so remain in the blood
Function of tissue fluid
Tissue fluid bathes almost all the cells of the body outside of the circulatory system
- exchange of substances between cells and the blood occurs via the tissue fluid
For example, carbon dioxide will leave a cell, dissolve into the tissue fluid surrounding it, and then diffuse into the capillary
Oncotic pressure
The tendency of water to move into the blood in the capillaries from the surrounding tissue fluid. The oncotic pressure of the blood is always -3.3kPa
Hydrostatic pressure
The pressure exerted by a fluid. The blood is still under pressure from the surge of blood that occurs every time the heart contracts
The formation of tissue fluid
- When blood is at the arterial end of a capillary, the hydrostatic pressure is greater than the oncotic pressure, so the net flow of fluid is out of the capillary, forming tissue fluid
- At the venous end of the capillary, the hydrostatic pressure within the capillary is reduced, making the oncotic pressure stronger than the hydrostatic pressure, so water begins to flow back into the capillary from the tissue fluid
- The 10% not reabsorbed remains as tissue fluid
Filtration pressure equation
hydrostatic pressure - oncotic pressure
Lymph
- the tissue fluid eventually drains into a system of blind-ended tubes (closed at one end) called lymph capillaries
- lymph is similar to plasma and tissue fluid , but has less oxygen and fewer nutrients
- contains fatty acids, which have been absorbed from the villi of the small intestine
- transported through lymph vessels by the squeezing of the body vessels
- valves prevent backflow
- eventually returns to the blood
Lymph nodes
- along the lymph vessels
- lymphocytes build up in the lymph nodes when necessary and produce antibodies which are then passed into the blood
- lymph nodes also intercept bacteria and other debris from the lymph, which are then digested by phagocytes in the node
- enlarged lymph nodes are a sign the body is fighting off a pathogen
Adaptations of erythrocytes
- biconcave shape, increasing surface area and helping them pass through capillaries
- no nuclei, maximising the amount of haemoglobin that can fit in the cell, but also limits their life
- contain haemoglobin, which oxygen binds loosely to, forming oxyhaemoglobin
- each haemoglobin molecule can bind to four oxygen molecules (8 atoms)
Oxygen dissociation curve
Shows the affinity of haemoglobin for oxygen.
At high partial pressure of oxygen in the lungs, the haemoglobin is rapidly loaded with oxygen as it has high affinity to oxygen. At low partial pressure of oxygen in respiring tissues, haemoglobin has a low affinity for oxygen, so oxygen is dissociated from haemoglobin rapidly to diffuse into cells.
A very small change in in the partial pressure of oxygen in the surrounding tissues makes a significant difference in the saturation
Oedema
If blood pressure is high (hypertension) then the pressure at the arterial end is even greater
This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues.
Why is the oxygen dissociation curve curved?
- Due to the shape of the haemoglobin molecule it is difficult for the first oxygen molecule to bind to haemoglobin
- this means that binding of the first oxygen occurs slowly, explaining the relatively shallow curve at the bottom left corner of the graph
- After the first oxygen molecule binds to haemoglobin, the haemoglobin protein changes shape
- makes it easier for the next haemoglobin molecules to bind
- this speeds up binding of the remaining oxygen molecules and explains the steeper part of the curve in the middle of the graph
- known as cooperative binding
- As the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites, explaining the levelling off of the curve in the top right corner of the graph
The effect of carbon dioxide on the oxygen dissociation curve
As the partial pressure of carbon dioxide increases, haemoglobin gives up oxygen more easily (less affinity)
- Known as the Bohr effect (curve shifts to the right)
- in active tissues with a high partial pressure of carbon dioxide, haemoglobin gives up its oxygen more readily
- in the lungs where the partial pressure of carbon dioxide is relatively low, oxygen binds to haemoglobin easily
Foetal haemoglobin
- The haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
- This is vital as it allows a foetus to obtain oxygen from its mother’s blood at the placenta, which has low levels of oxygen
- Fetal haemoglobin can bind to oxygen at low partial pressure of oxygen
At this low partial pressure the mother’s haemoglobin is dissociating with oxygen - On a dissociation curve graph, the curve for foetal haemoglobin shifts to the left of that for adult haemoglobin
- This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin
- After birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin
- This is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual
-The foetal haemoglobin has a higher affinity for oxygen; its oxygen dissociation curve therefore lies further to the left
Ways of transporting carbon dioxide from the tissues to the lungs
- 5% dissolved in plasma
- 10-20% combined with amino groups in polypeptide chains of haemoglobin (carbaminohaemoglobin)
- 75-85% converted into hydrogen carbonate ions (HCO3-) in the cytoplasm of the red blood cells
How carbon dioxide is converted into hydrogen carbonate ions
- carbon dioxide reacts slowly with water to form carbonic acid
- the cytoplasm of erythrocytes contain carbonic anhydrase, catalysing this reaction
- the carbonic acid dissociates to form hydrogen ions and hydrogen carbonate ions
- the negatively charged hydrogen carbonate ions move out of the erythrocytes into the blood plasma by diffusion
- negatively charged chloride ions move into the erythrocyte, maintaining the electrical balance of the cell
- converting carbon dioxide into hydrogen carbonate ions maintains the concentration gradient for carbon dioxide to diffuse from the respiring tissues to the erythrocytes
How hydrogen carbonate ions are converted back into carbon dioxide in the lungs
When blood reaches the lung tissues, there is a low concentration of carbon dioxide
- hydrogen carbonate ions move back into the erythrocytes to combine with hydrogen ions to form carbonic anhydrase
- carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into water and carbon dioxide
- carbon dioxide diffuses into the lungs and chloride ions diffuse out if the erythrocytes back into the plasma down an electrochemical gradient
How does haemoglobin act as a pH buffer
- it accepts free hydrogen ions in a reversible reaction to form haemoglobinic acid
What is the heart made of
Cardiac muscle
- myogenic; has its own rhythm at about 60bpm
- does not get fatigued and need to rest like skeletal muscles
- coronary arteries supply the heart with oxygenated blood
How the heart pumps blood to the lungs
- Deoxygenated blood enters the right atrium from the superior vena cava (upper body and head) and the inferior vena cava (lower body) at relatively low pressure
- as the blood flows in, slight pressure builds up until the atrioventricular valve opens to let blood pass into the right ventricle
- the right ventricle starts to contract and the atrioventricular valve closes
- the right ventricle contracts fully and pumps deoxygenated blood through the semilunar valves into the pulmonary artery
- pulmonary artery transports blood into the lungs
- the semilunar valves prevent backflow of blood back into the heart
How the heart pumps blood to the body
- oxygenated blood from the lungs enter the left atrium from the pulmonary vein
- as pressure in the atrium builds, the atrioventricular valve opens and the left ventricle fills with oxygenated blood
- when both the atrium and ventricle are full, the atrium contracts, forcing all of the blood into the left ventricle
- the ventricle contracts, pushing all the blood through the semilunar valve into the aorta and around the body
- the semilunar valve closes preventing any backflow of blood
Septum
The inner dividing wall of the heart that prevents the mixing of oxygenated and deoxygenated blood
Superior vena cava
Brings deoxygenated blood into the heart from the head and upper body
Inferior vena cave
Brings deoxygenated blood into the heart from the lower body
Left pulmonary artery
Carries deoxygenated blood from the heart to the left lung
Right pulmonary artery
Carries deoxygenated blood from the heart to the right lung
Aorta
Carries oxygenated blood away from the heart to the rest of the body
Pulmonary veins
Carry oxygenated blood from the lungs to the heart
Why is the muscular wall on the left side of the heart thicker than the right side?
The left side has to produce enough force to pump the blood all around the whole body, whereas the right side only pumps blood to the lungs
What is the cardiac cycle
describes the events in a single heartbeat
-the right and left side of the heart empty and fill together
Diastole
- the heart relaxes
- the atria and then the ventricles fill with blood
- the volume and pressure in the heart build
- the pressure in the arteries is at a minimum
Systole
- the atria contracts (atrial systole), closely followed by the ventricles (ventricular systole)
- the pressure inside the heart increases dramatically and blood is forced out the right side into the lungs and the left side into the body
- the volume and pressure in the heart are low at the end of systole, and the blood pressure in the arteries are at a maximum
Where does the sound of a heartbeat come from
- first sound is blood forced against atrioventricular valves as the ventricles contract
- second sound is the semilunar valves in the aorta and pulmonary artery closing from the backflow of blood as the ventricles relax
How is the basic rhythm of the heart maintained?
- wave of electrical excitation begins at pacemaker area called sino-atrial node (SAN), causing the atria to contract
- a layer of non-conducting tissue prevents the excitation directly passing to the ventricles before they are full
- the electrical activity from the SAN is picked up by the atrio-ventricular node (AVN)
- AVN imposes a slight delay before stimulating bundle of His, a bundle of conducting tissue made up of Purkyne fibres
- bundle of His splits into two branches and penetrates through the septum between the ventricles
- fibres conducts the wave of excitement to the apex of the heart, through the walls of the ventricles
- triggers the contraction of the ventricles starting with the apex of the heart, allowing efficient emptying of the ventricles
Tachycardia
rapid heartbeat over 100bpm
- either from fear , exercise etc or from problems in electrical control of the heart
Bradycardia
heart rate slows down under 60bpm
- either from being fit or severe bradycardia needing a pacemaker
Ectopic heartbeat
Extra heartbeats out of the normal rhythm
- usually normal but linked to serious conditions if frequent
Atrial fibrillation
Example of arrhythmia (abnormal rhythm)
- atria contracts very fast from rapid electrical impulses
- only some impulses are passed on to the ventricles, heart does not pump blood effectively
