Where Does Gas Exchange Occur In Animals With A Closed Circulatory System

seven.2 Circulatory systems in animals (ESG8X)

Send systems are crucial to survival. Unicellular organisms rely on simple improvidence for ship of nutrients and removal of waste. Multicellular organisms have developed more than complex circulatory systems.

Open and closed circulation systems (ESG8Y)

There are two types of circulatory systems found in animals: open and closed circulatory systems.

Open up circulatory systems

In an open up circulatory system, blood vessels transport all fluids into a crenel. When the animal moves, the blood within the cavity moves freely around the body in all directions. The blood bathes the organs directly, thus supplying oxygen and removing waste material from the organs. Blood flows at a very dull speed due to the absenteeism of smooth muscles, which, every bit you learnt previously, are responsible for wrinkle of blood vessels. Most invertebrates (crabs, insects, snails etc.) have an open circulatory system. Effigy 7.1 shows a schematic of an open circulatory system delivering blood directly to tissues.

Figure 7.1: Open circulatory system.

Closed circulatory systems

Closed circulatory systems are different to open up circulatory systems because blood never leaves the blood vessels. Instead, it is transferred from one claret vessel to another continuously without entering a cavity. Blood is transported in a single direction, delivering oxygen and nutrients to cells and removing waste products. Closed circulatory systems tin can exist further divided into single circulatory systems and double circulatory systems.

Single and double circulation systems (ESG8Z)

The circulatory organization is a broad term that encompasses the cardiovascular and lymphatic systems. The lymphatic organization will be discussed later in this affiliate. The cardiovascular system consists of the centre (cardio) and the vessels required for transport of blood (vascular). The vascular system consists of arteries, veins and capillaries. Vertebrates (animals with backbones like fish, birds, reptiles, etc.), including nigh mammals, accept closed cardiovascular systems. The two master circulation pathways in invertebrates are the single and double circulation pathways.

Single circulatory pathways

Single circulatory pathways as shown in the diagram below consist of a double chambered heart with an atrium and ventricle (the middle structure will exist described in item later in this affiliate). Fish possess single circulation pathways. The heart pumps deoxygenated blood to the gills where it gets oxygenated. Oxygenated blood is then supplied to the entire fish body, with deoxygenated blood returned to the centre.

Effigy 7.2: Single circulation organisation every bit found in a typical fish species. The red represents oxygen-rich or oxygenated blood, the blueish represents oxygen-deficient or deoxygenated claret.

Double circulatory systems

Double circulation pathways are institute in birds and mammals. Animals with this blazon of circulatory organisation take a four-chambered heart.

The right atrium receives deoxygenated from the torso and the right ventricle sends it to the lungs to be oxygenated. The left atrium receives oxygenated blood from the lungs and the left ventricle sends it to the rest of the trunk. Near mammals, including humans, have this blazon of circulatory system. These circulatory systems are called 'double' circulatory systems considering they are made up of 2 circuits, referred to as the pulmonary and systemic circulatory systems.

Humans, birds, and mammals have a iv-chambered heart. Fish take a two-chambered center, one atrium and one ventricle. Amphibians have a three-chambered eye with two atria and ane ventricle. The reward of a four chambered heart is that at that place is no mixture of the oxygenated and deoxygenated blood.

Human circulatory systems (ESG92)

The homo circulatory system involves the pulmonary and systemic circulatory systems. The pulmonary circulatory arrangement consists of blood vessels that transport deoxygenated blood from the centre to the lungs and render oxygenated blood from the lungs to the heart. In the systemic circulatory system, blood vessels transport oxygenated blood from the center to various organs in the body and return deoxygenated blood to the heart.

Pulmonary circulation system

In the pulmonary circulation organization, deoxygenated blood leaves the heart through the right ventricle and is transported to the lungs via the pulmonary artery. The pulmonary avenue is the but avenue that carries deoxygenated blood. Information technology carries blood to the capillaries where carbon dioxide diffuses out of the blood into the alveoli (lung cells) and then into the lungs, where it is exhaled. At the aforementioned fourth dimension, oxygen diffuses into the alveoli, and then enters the claret and is returned to the left atrium of the heart via the pulmonary vein.

Figure 7.iii: Pulmonary circulation organization. Oxygen rich blood is shown in reddish; oxygen-depleted blood is shown in blue.

A simulation that shows how the human circulatory system is divided into two circuits: the systemic and the pulmonary circulatory systems: http://world wide web.biologyinmotion.com/cardio/index.html

Systemic apportionment

Systemic circulation refers to the part of the apportionment organisation that leaves the center, carrying oxygenated blood to the body's cells, and returning deoxygenated claret to the centre. Blood leaves through the left ventricle into the aorta, the trunk's largest avenue. The aorta leads to smaller arteries that supply all organs of the torso. These arteries finally co-operative into capillaries. In the capillaries, oxygen diffuses from the blood into the cells, and waste and carbon dioxide diffuse out of cells and into blood. Deoxygenated blood in capillaries then moves into venules that merge into veins, and the blood is transported back to the center. These veins merge into two major veins, namely the superior vena cava and the inferior vena cava (figure:doublecirculation). The motion of blood is indicated past arrows on the diagram. The deoxygenated blood enters the right atrium via the the superior vena cava. Major arteries supply blood to the brain, small intestine, liver and kidneys. However, systemic circulation also reaches the other organs, including the muscles and skin. The following diagram (Figure 7.4) shows the circulatory system in humans.

Figure 7.4: The systemic circulatory system supplies claret to the unabridged body.

TEACHERS RESOURCE:

Circulation animation:

The eye and associated blood vessels (ESG93)

External structure of the centre

The heart is a large muscle, about the size of your clenched fist, that pumps blood through repeated rhythmic contractions. The eye is situated in your thorax, just behind your breastbone, in a space called the pericardial crenel. The heart is enclosed by a double protective membrane, called the pericardium. The region between the 2 pericardium layers is filled with pericardial fluid which protects the heart from daze and enables the heart to contract without friction.

The centre is a muscle (myocardium) and consists of four chambers. The upper two chambers of the heart are called atria (singular= atrium). The two atria are separated past the inter-atrial septum. The lower two chambers of the middle are known as ventricles and are separated from each other past the interventricular septum. The ventricles have more than muscular walls than the atria, and the walls of the right ventricle, which supplies blood to the lungs is less muscular than the walls of the left ventricle, which must pump blood to the whole torso.

Clench your fist - the size of your fist is more or less the size of your centre.

In add-on, there are a number of big blood vessels that deport claret towards and abroad from the heart. The terms `avenue' and `vein' are not adamant by what the vessel transports (oxygenated blood or deoxygenated) only past whether the vessel flows to or from the eye. Arteries take claret away from the middle and generally carry oxygenated blood, with the exception of the pulmonary avenue. Veins transport claret towards the center and generally carry deoxygenated blood, except the pulmonary vein. On the correct side of the heart, the superior vena cava transports deoxygenated blood from the head and arms and the inferior vena cava transports deoxygenated blood from the lower office of the torso back to the middle, where it enters the right atrium. The pulmonary artery carries deoxygenated blood away from the right ventricle of the heart towards the lungs to be oxygenated. On the left side of the eye, the pulmonary vein brings oxygenated claret from the lungs towards the left atrium of the centre and the oxygenated blood exits the left ventricle via the aorta and is transported to all parts of the trunk.

Since the heart is a muscle, and therefore requires oxygen and nutrients itself to go on beating, information technology receives claret from the coronary arteries, and returns deoxygenated claret via the coronary veins.

In humans, the left lung is smaller than the right lung to make room in the chest cavity for the heart.

Figure seven.5: The external structure of the centre: the major part of the heart consists of muscles and is known as the myocardium. The region in which the heart is plant is known as the pericardial cavity, which is enclosed by the pericardium.

Internal construction of the heart

Every bit previously mentioned, the heart is made up of iv chambers. In that location are two atria at the top of the heart which receive blood and 2 ventricles at the lesser of the heart which pump blood out of the heart. The septum divides the left and correct sides of the heart. In guild to brand sure that claret flows in merely one management (forward), and to foreclose backflow of claret, in that location are valves betwixt the atria and ventricles (atrioventricular valves). These valves only open in one management, to allow claret into the ventricles, and are flapped shut by the pressure of the blood when the ventricles contract.

The tricuspid valve is situated betwixt the right atrium and the right ventricle while the bicuspid/ mitral valve is institute between the left atrium and the left ventricle. Stiff tendinous cords (chordae tendineae) attached to valves prevent them from turning inside out when they close. The semi-lunar valves are located at the bottom of the aorta and pulmonary artery, and prevent blood from re-inbound the ventricles after it has been pumped out of the heart.

Figure seven.6: The internal structure of the mammalian heart.

In the previous sections we have discussed pulmonary and systemic circulation, and nosotros have described the four sleeping room structure of the centre besides as some of the major arteries and veins that ship blood towards and abroad from the heart. In gild to summarise all this data, study the flow diagram below which describes the passage of deoxygenated blood through one full cycle.

Figure 7.seven: Flow diagram depicting movement of blood from the heart through the circulatory organisation. The blue boxes represent deoxygenated blood, the purple boxes stand for capillary networks where gaseous exchange occurs and the reddish boxes correspond stages at which the claret is oxygenated.

Memory pull a fast one on: the tRI cuspid valve is found on the RIght side of the heart.

Major organs and systemic circulation (ESG94)

All the organs of the body are supplied with blood. This is necessary so that the cells can obtain oxygen, which is required for cellular respiration, as well as essential nutrients. Each organ has an artery that supplies it with blood from the heart. Metabolic wastes, including carbon dioxide, need to be removed from cells and returned to the heart. These movement into the capillaries which enter into veins that eventually enters either the superior or inferior vena cava which then enters the right atrium.

Arteries and veins have been named according to the organ to which they supply blood. The liver receives oxygenated blood from the heart via the hepatic artery. This artery runs alongside the hepatic portal vein. The hepatic portal vein contains nutrients that have been absorbed by the digestive system. This nutrient-rich blood must kickoff laissez passer through the liver, and so that the nutrient composition of the claret can be controlled. Blood passes from the liver to the center through the hepatic vein. Metabolic waste is circulated in the blood, and if allowed to accumulate, would somewhen achieve toxic levels. The kidneys are supplied with blood (which comprise waste matter) via the renal arteries. The kidneys filter metabolic waste from the blood, passing it to urine to exist excreted safely. Claret leaves the kidney via the renal vein.

The encephalon is supplied with blood via the carotid arteries and the vertebral arteries. The blood from the brain is drained via the jugular veins. The brain is supplied with \(\text{15}\%\) of the total amount of blood pumped by the middle. The heart is also a muscle (myocardium) that requires claret menses to work. Blood is supplied to the heart via ii coronary arteries, and leaves the heart via four cardiac veins.

Dissecting a mammalian heart

Aim

To dissect a mammalian heart (sheep or ox heart).

Appliance

• your teacher volition requite each group a heart to dissect
• a scalpel handle with a blade or a precipitous not-serrated pocketknife
• a sharp pair of scissors
• a pair of forceps
• gloves
• newspaper towel
• pictures of the external and internal views of the heart

Method

1. Work in groups of 4.

2. Identify the heart on the dissecting board with the atria at the tiptop and the ventricles facing downwards.
3. Carefully examine the external view of the heart. Try identify the vertical and horizontal groves on the heart. This is the position of the internal walls between the chambers of the heart.
4. Examine and note the departure in the walls of the ventricles and atria. Also note the difference in appearance between the walls of the ventricles and atria.
5. With the scalpel or precipitous knife advisedly cut the heart open across the left atrium.
6. Compare the thickness and the size of the correct ventricle and atrium.
7. Identify the valves and examine the tendinous cords which are attached to the valves.
8. Place the semi-lunar valves at the bottom of the pulmonary artery.
9. Now cut through the left side of the centre in the same way as you did the right side of the heart.
10. Carefully cut through the septum of the heart then that you have two halves.

Questions

1. What is the smoothen outer layer of the heart chosen?
2. Did you notice whatsoever fat around the heart?
3. Did you observe a divergence between the atria and ventricles externally?
4. Name the blood vessels visible on the outside of the heart.
5. Compare the thickness of the walls of the atria and ventricles. Explain why they are different.
6. Explain the divergence between the left and correct ventricular walls.

Questions

1. What is the smoothen outer layer of the middle called?
2. Did you notice any fat around the middle?
3. Did you notice a difference betwixt the atria and ventricles externally?
4. Name the claret vessels visible on the outside of the heart.
5. Compare the thickness of the walls of the atria and ventricles. Explicate why they are dissimilar.
6. Explain the divergence between the left and correct ventricular walls.

Answers

1. Pericardium
2. Yes - fat should be nowadays in some places, peculiarly in the grooves.
3. Yes – the atria are much smaller than the ventricles, they have thinner muscle walls and are at the top of the middle, whereas ventricles are at the lesser.
4. Coronary arteries and veins
5. Atria take thin, flexible walls and ventricles accept much thicker, stronger walls. This is because atria just accept to pump blood downward to the ventricles (short distance), then they practice non have to be as strong as ventricles, that pump claret much further (to the lungs or the entire trunk).
6. The wall of the left ventricle is much thicker than that of the correct ventricle, since it needs to exert greater strength / be stronger. The left ventricle pumps blood to the unabridged body, which requires much more force than just pumping claret from the right ventricle to the lungs, which are besides in the thoracic cavity.

The cardiac cycle (ESG95)

A cardiac cycle refers to the sequence of events that happens in the heart from the start of one heartbeat to the start of the subsequent heartbeat. During a cardiac cycle the atria and the ventricles work separately. The sinoatrial node (pacemaker) is located in the correct atrium and regulates the contraction and relaxing of the atria.

• At rest, each heartbeat takes approximately \(\text{0,8}\) seconds.
• The normal center rate at remainder is approximately \(\text{72}\) beats per minute.
• During systole the center muscle contracts.
• During diastole the heart muscle relaxes.

The phases of the cardiac cycle will be broken down and explained in the following section:

Phase 1: Atrial systole (Atrium contracts)

• Blood from the superior and inferior vena cava flows into the right atrium.
• Blood from the pulmonary veins flows into the left atrium.
• The atria contract at the aforementioned time.
• This contraction lasts for about \(\text{0,one}\) seconds.
• Blood is forced through the tricuspid and bicuspid valves into the ventricles.

Phase ii: Ventricular systole (Ventricle contracts)

• Ventricles relax and fill with blood.
• The ventricles contract for \(\text{0,three}\) seconds.
• Blood is forced upwards, closing the bicuspid and tricuspid valves (lubb sound).
• The blood travels up into the pulmonary artery (on the right) and the aorta (on the left).
• The atria are relaxed during ventricular systole.

Phase 3: General diastole: (General relaxation of the heart)

• The ventricles relax, thus decreasing the flow from the ventricles.
• One time there is no force per unit area the claret flow closes the semi-lunar valves in the aorta and the pulmonary artery (dubb audio).
• Full general diastole lasts for most \(\text{0,iv}\) seconds.

TEACHERS Resources:

View Cardiac Magnetic Resonance imaging of a beating eye. Large magnets are used to create images of the heart within the body, without the need for surgery.

• View from the front (upside down):

• View from the top:

• View from the side:

The sound the heart makes

The centre makes ii chirapsia sounds. 1 is loud and ane is soft. We call this the lubb dubb sound. The lubb sound is caused by the force per unit area of the ventricles contracting, forcing the atrioventricular valves close. The dubb sound is caused past the lack of pressure in the ventricles which causes the blood to menstruation dorsum and close the semi-lunar valves in the pulmonary artery and aorta. A doc uses a stethoscope to listen to the heartbeats. Alternatively, a person'south pulse can be measured by pressing a finger (other than the pollex which already has a pulse) against the brachial avenue in the wrist or the carotid avenue next to the trachea. The pulse of the heart allows u.s.a. to measure the centre rate which is the number of heartbeats per unit time.

Mechanisms for controlling cardiac cycle and heart rate (pulse)

The cardiac cycle is controlled past nerve fibres extending from nodes of nerve bundles through the heart muscle. At that place are two nodes, namely the sinoatrial node (SA node) and the atrioventricular node (AV node). The SA node is located within the wall of the right atrium while the AV node is located between the atria and the ventricles. Electrical impulses generated in the SA node cause the right and left atria to contract first, initiating the cardiac wheel. The electric indicate reaches the AV node, where the signal pauses, before spreading through conductive tissues called the bundles of His and Purkinje fibres. These fibres co-operative into pathways which supply the correct and left ventricles, causing the ventricles to contract. The SA node is the pacemaker of the eye since electrical signals are normally generated there - without any stimulation from the nervous arrangement (automaticity). However, although the center rate is automated, it changes during do or when experiencing intense emotions like fear, anger and excitement. This is as a consequence of added stimulation from the nervous system and hormones, such as adrenaline.

Uncomplicated simulation of how electric activity spreads over the eye. http://en.wikipedia.org/wiki/File:ECG_Principle_fast.gif

TEACHERS Resource:

Elementary simulation of how electric activity spreads over the heart.

Simulation: 2CTX

Electric activeness

The electrical activity in the heart is and so strong that it can be measured from the surface of the body as an electrocardiogram (ECG). A normal heart has a very regular rhythm. Arrhythmia is a status where the middle has an aberrant rhythm, as shown in the figures. Tachycardia is when the resting heart rate is too fast (more \(\text{100}\) beats per minute), and bradycardia is when the heart rate is also tedious (less than \(\text{lx}\) beats per infinitesimal).

Figure 7.8: Electrocardiogram depicting dissimilar heart rhythms.

TEACHERS Resources:

Before conducting the following activity, it may be useful to read the following resource on measuring pulse rate:

Investigating heart rates earlier, during and after strenuous exercise

Aim

To investigate your heart charge per unit before, during and afterward strenuous exercise

Apparatus

• stopwatch

• pen and paper for recording

Method

1. Work in pairs on the field and ensure you lot have a end watch.
2. I partner performs the experiment and the other records the results. Partners and then swap roles.
3. Take the resting pulse charge per unit before exercising.
4. Ane partner runs quickly around the field twice.
5. Immediately later the run take his/her pulse.
6. Proceed to take his pulse every infinitesimal for 5 minutes.
7. Tape the results and plot a graph using the data pertaining to you.

Results

Tape your results hither:

Time	Center rate (beats/infinitesimal)
Before practice (resting)
\(\text{0}\) \(\text{min}\)(immediately later on do)
\(\text{1}\) \(\text{min}\) (subsequently exercise)
\(\text{two}\) \(\text{min}\)
\(\text{three}\) \(\text{min}\)
\(\text{four}\) \(\text{min}\)
\(\text{5}\) \(\text{min}\)

Draw a line graph to illustrate your results. Prove the resting pulse rate as a carve up dotted line on the axis.

Conclusions

Write your conclusion.

Questions

1. Write a hypothesis for this investigation.
2. Write down the independent variable.
3. Write down the dependent variable.
4. Proper noun One factor that must be kept constant during this investigation.
5. Write down TWO means in which the accuracy of this investigation can be improved.
6. What conclusions can be made about your cardiovascular fitness?
7. Explain why the heart rate increases during practice.

Results:

Learners should have a resting pulse that is significantly lower than the pulse charge per unit after running effectually. Check that if they accept taken their pulse for 30 seconds x 2, all readings should be Fifty-fifty numbers. In the minutes after running, pulse should gradually render to resting pulse charge per unit. Most teenagers should take a resting pulse around 60 – 84 beats per minute.

Graph to show changes in pulse rate earlier, during and after exercise

• Graph should take Fourth dimension (minutes) on horizontal axis and Pulse rate (beats per min) on the vertical axis.
• Both axes must become up in equal intervals along the unabridged length.
• Resting pulse is shown as a dotted line parallel to the horizontal centrality.
• Graph should beginning ON resting pulse and go upward, and so gradually back down to resting pulse rate.

Decision:

Pulse charge per unit increases when practise is washed, then gradually returns to resting pulse after the practice. (Learners may notice that individuals who are fit return to resting pulse FASTER than unfit individuals.)

Questions

1. Write a hypothesis for this investigation.
2. Write downwardly the contained variable.
3. Write down the dependent variable.
4. Proper name Ane factor that must exist kept constant during this investigation.
5. Write downwards Two ways in which the accuracy of this investigation tin can be improved.
6. What conclusions can be made about your cardiovascular fitness?
7. Explain why the center rate increases during practice.

Answers

1. Pulse rate during practice will be higher than resting pulse rate.

   Accept ANY hypothesis, as long as it is:

   • geared towards the aim of the investigation
   • written as a argument, not a question
   • written in the Hereafter tense
   • a clear expectation of what will be institute – it does not have to be correct
2. There are Ii independent variables. The master one is Resting, Doing Practice and Recovering (or Type of Activity), but time can also be seen as a secondary contained variable.
3. The dependent variable is Pulse Rate.
4. In that location are several variables that need to be controlled:
   • The same learner needs to be used when taking the pulse before and after do.
   • Both learners in a group must do the same exercise (run effectually field twice).
   • Pulse must be taken before and immediately after do.
   • Pulse must exist taken exactly at ane minute intervals during recovery.
   • Always accept pulse equally 30 seconds x 2 or over a full minute.
5. Several things may be done:
   • Repeat the investigation over again 2 or more times with one learner and obtain an boilerplate. Use big groups of individuals in a certain age group and boilerplate their results.
   • Go on measuring pulse rate until it returns to resting rate – this may have longer than 5 min in some learners.
   • Use a heart charge per unit monitor for greater accurateness with pulse rates.
   • Control more variables in order to get similar groups of people – yet age, same gender, same fitness level, same mass approximately etc.
6. The conclusions MUST exist based on the results obtained and will probably also point relative fitness levels – fit individuals tend to recover faster after do. It must also be linked to the original hypothesis and state whether this hypothesis is accepted or rejected. Learners must be encouraged to evaluate the hypothesis and should be told that it is perfectly acceptable for the hypothesis to have been wrong – they must Non become back to information technology and change it.
7. Centre rate increases due to the higher charge per unit of prison cell respiration that is required to provide the necessary energy during running. The cells demand MORE oxygen and release More than carbon dioxide than normal, so animate and heart rate both speed up to evangelize the greater amount of \(\text{O}_{2}\) and remove the greater corporeality of \(\text{CO}_{ii}\) formed.

Stroke Book

The stroke volume is the amount of blood pumped through the heart during each cardiac bicycle. The stroke book can modify depending on the needs of the body. During do, muscles need more oxygen and glucose in order to produce free energy in the form of ATP. Therefore the eye increases its stroke volume and stroke charge per unit to meet this demand. This is a temporary change to maintain homeostasis, and after do the heart rate and stroke volume return to normal.

When a person exercises regularly, and is fit, the heart undergoes sure long-term adaptations. The eye muscle gets stronger, and expels more blood with each wrinkle. At that place is therefore a greater stroke volume with each heartbeat. Since the heart expels more claret with each stroke, the center has to vanquish less ofttimes in order to maintain the same volume of blood flow. Therefore, fit people frequently accept lower resting centre rates.

Cardiac output is the volume of claret that is pumped past the heart in i-minute. Cardiac output is equal to the stroke book (SV) multiplied by the eye rate (HR).

Blood Pressure

Blood pressure level refers to the forcefulness that the blood exerts on the blood vessel walls. Blood pressure is determined by the size of the blood vessels and ensures that blood flows to all the parts of the body. Normal blood force per unit area is 120/80 (120 over 80) measured in units of mercury (mm Hg). The 120 represents the systolic pressure, which is when the ventricles contract. The lxxx represents the diastolic force per unit area, which is when full general diastole occurs.

Blood pressure tin can exist increased past smoking, stress, adrenalin surges, water retentivity, high cholesterol, obesity and lack of exercise. High blood force per unit area (hypertension) is dangerous and increases the adventure of an aneurysm, stroke or eye assail. Low blood pressure (hypotension) tin pb to low-cal-headedness and fainting because of insufficient blood supply to the brain.

Blood vessels (ESG96)

We will at present examine the construction and function of arteries, capillaries, veins and valves.

Arteries

Arteries deport blood Away from the heart. The pressure created by the pumping eye forces claret through the arteries. Arteries accept three layers. They have an outside layer fabricated upwards of connective tissue; a middle layer fabricated up of polish muscle, to allow contraction of the arteries in order to regulate the pressure of blood catamenia, and an inside layer of tightly continued simple squamous endothelial cells. The big arteries close to the heart branch into smaller arterioles (smaller arteries) and eventually branch into capillaries.

Laughing is practiced exercise for your heart. Whenever you laugh, the claret vessels amplify (open up), causing the claret menses to increase, thus keeping your heart healthy.

Figure seven.ix: Micrograph of artery.

Capillaries

Capillaries are little more than than a single layer of endothelial cells. Capillaries form intricate networks throughout the tissues. They permit water, nutrients and gases to diffuse out of the blood and waste material materials to diffuse into the blood. This commutation occurs between the claret and the tissue fluid. The tissue fluid is the fluid surrounding the cells. The claret cells never come into contact with the cells. The blood and tissue fluid exchange material, and the tissue fluid then exchanges material with the cells.

Veins

The intricate networks formed by the capillaries somewhen converge to form venules, (small veins). The venules and so converge to form veins which return the blood to the center. Vein walls but consist of ii layers. The outer layer is fabricated up of connective tissue whereas the inner layer is made up of endothelial cells.

Effigy 7.x: Schematic diagram of a vein.

Figure 7.11: Diagram representing the branching of an artery into arterioles. These subsequently course the capillary bed which empties into several venules, leading to the vein.

Valves

Once the blood has passed through the capillaries very little blood pressure remains to return blood to the heart.Instead of pressure from the middle veins use a series of valves to strength blood to return to the eye. Wrinkle of the muscles squeezes the veins, pushing the claret through them. The valves crusade the blood to flow in but one management, dorsum to the heart.

Figure 7.12: Valves ensure that claret flows one merely style though veins.

TEACHERS RESOURCE:

Interactive diagram illustrating arterial and venous structure:

Comparing between arteries, veins and capillaries (ESG97)

The figure and table beneath summarise the differences betwixt arteries, capillaries and veins.

Figure seven.13: Cross-department showing the differences between a) arteries, b) veins and c) capillaries.

Arteries	Capillaries	Veins
blood moves away from the heart	blood supply at tissue level	blood returned to the heart
thick heart layer of involuntary muscle to increase or decrease bore	one layer of endothelium with very modest diameter	sparse middle layer every bit pressure is reduced
inner layer of endothelium which reduces friction	only endothelium layer present	larger diameter of inner cavity, lined with endothelium to reduce friction
situated deeper in the tissue to maintain body temperature	situated at tissue level only	situated nearly the surface of the skin to release heat
no valves except in the base of the aorta and the pulmonary arteries	no valves present	semi-lunar valves are nowadays at intervals, to prevent dorsum flow of blood
blood always under high pressure	blood is under high pressure where red blood cells are forced to flow through in unmarried file	blood is under low pressure
a pulse tin can be felt as blood flows	no pulse	no pulse tin be detected

Tabular array 7.1: Table comparing arteries, capillaries, and veins

The average developed heart beats:

• \(\text{72}\) times a minute
• \(\text{100 000}\) times a day
• \(\text{3 600 000}\) times a year
• A billion times during a lifetime.

Source: https://www.siyavula.com/read/science/grade-10-lifesciences/transport-systems-in-animals/07-transport-systems-in-animals-02

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