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Biology > 8. Transport in mammals > Flashcards

8. Transport in mammals Flashcards

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1
Q

What type of circulatory system do mammals have?

A
  • A closed, double circulatory system
  • Closed because blood is contained within blood vessels and the heart
  • Double because blood passes through the heart twice in each complete circuit of the body
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2
Q

What are the five types of blood vessels?

A
  • Arteries (carry blood away from heart)
  • Veins (carry blood to heart)
  • Venules (collect blood from capillaries and pass to veins)
  • Capillaries (smallest vessels, serve body cells, link arterioles to venules [thereby linking arteries to veins])
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3
Q

Why is a DOUBLE circulatory system necessary?

A

There are two circuits in mammalian circulatory system – pulmonary (to the lungs) and systemic (to the body).
During the pulmonary circuit to the lungs, the blood loses pressure and is therefore returned to the heart via the pulmonary vein to boost pressure so that it can circulate rapidly to all the tissues and organs of the body. Therefore, the pulmonary circuit returning to heart facilitates pressure for systemic circuit.

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4
Q

How should artery an arteriole and vein and venule size be compared?

A

An arteriole will have a smaller diameter than the artery from which it is branching off. A venule will have a smaller diameter than the vein from which it is branching off.
Generally, arterioles and venules smaller than arteries and veins but can’t always say for certain because e.g., diameter of smallest artery is smaller than diameter of largest arteriole.

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5
Q

What is the capillaries’ function?

A

To facilitate the exchange of substances such as oxygen, carbon dioxide and glucose between the blood and the body cells. The capillaries are bathed in tissue fluid as tissue fluid can seep not tiny intracellular spaces that capillaries can’t reach.

Note: blood has 4 components: blood plasma, red blood cells, white blood cells and platelets. Tissue fluid is a component of blood plasma.

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6
Q

How is cell signalling facilitated through tissue fluid?

A

Body cells produce cell signalling molecules. Secreted into tissue fluid. Enter capillaries. Pass out of capillaries elsewhere to enter tissue fluid in other areas of the body. Cell signalling molecules bind to cells that are target cells.

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7
Q

How is structure of capillaries related to their function?

A
  • Endothelium wall is one cell thick. Thin wall = short diffusion distance = rapid diffusion/exchange of substances.
  • Numerous and branched = large surface area = rapid diffusion/exchange of substances.
  • Narrow diameter so can reach all body tissues, no cell is far from a capillary.
  • Lumen is narrow = red blood cells squeezed flat against side of capillary = red blood cells even closer for gaseous exchange.
  • Endothelial pores/fenestrations = allow white blood cells to escape to combat infections AND allows tissue fluid/blood components to bypass crossing through endothelium layer = rapid diffusion/exchange of substances. Note: basement membrane (specialised extracellular matrix) must still be passed.

Note: brain has no endothelial pores – all substances must pass through endothelial cells.

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8
Q

How to identify common characteristics of capillaries in images?

A
  • Red blood cell can be seen (in transverse sections only one because diameter is that of capillary).
  • Blood vessel wall that is a single layer of cells (endothelium). Remember basement membrane.
  • Nucleus will be wider than endothelial cell and will be bulging.
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9
Q

What is the structure of a normal artery and vein? Starting from the inside going out…

A
  1. Tunica intima
    - Single layer endothelial cells
    - Protective barrier between blood and rest of blood vessel wall
    - Provides smooth surface for blood flow
    - Attached to basement membrane
  2. Tunica media
    - Elastic fibre (made from protein elastin) and smooth muscle
    - Note: the proportion of elastic fibre to smooth muscle depends on the type of blood vessel, varied according to function
  3. Tunica adventitia/externa
    - Collagen fibre and some elastic fibres
    - Thickness varies depending on type of blood vessel
    - Thinner than tunica media
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10
Q

What is the structure of a large artery? Starting from inside going out…

A
  1. Tunica intima
  2. Internal elastic lamina (made from elastic fibres and collagen)
  3. Tunica media
  4. External elastic lamina
  5. Tunica adventitia
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11
Q

What is the structure of arterioles? Starting from inside going out…

A
  1. Tunica intima
  2. Internal elastic lamina
  3. Tunica media (only a few layers of smooth muscle cells though)
  4. Tunica adventitia
    Note: Basically, structure of large artery just missing the external elastic lamina
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12
Q

How many types of arteries are there?

A
  1. Elastic arteries (ones closest to the heart, so aorta and pulmonary artery)
  2. Muscular arteries (systemic system)
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13
Q

What functions do elastic fibres and smooth muscle serve?

A
  • Elastic fibres allow stretch and recoil
  • Smooth muscle contracts and relaxes
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14
Q

What is the structure of venules?

A

Note: Structure of venules, especially SMALL venules, basically the same as capillary structure
* No tunica media
* No tunica adventitia
But larger venules may have one or two layers of smooth muscle cells.
* Lumen 4-5 times larger than capillary lumen; can fit several blood cells
* Surrounding lumen is a single layer of endothelial cells (but not necessarily just 1 cell thick)

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15
Q

How is vasoconstriction and vasodilation caused?

A
  • Vasoconstriction – contraction of smooth muscle that results in the narrowing of lumen diameters of blood vessels
  • Vasodilation – relaxation of smooth muscle that results in maximum flow of blood because lumen diameter is widest
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16
Q

What are main artery functions that structure must facilitate?

A
  1. Transporting blood rapidly (speed)
  2. Transporting blood under high hydrostatic pressure (speed, prevent backflow)
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17
Q

How is artery structure adapted to suit its function of speedy transport under high hydrostatic pressure?

A
  • Tunica media is thick – artery can withstand high pressure of blood flow.
  • ELASTIC ARTERIES: Tunica media may have a higher proportion of elastic arteries and less smooth muscle – able to withstand the pulse of pressure created as blood is forced into arteries following contraction of ventricles. Elastic allows wall to expand and contract rather than rupture. Recoil action (like an elastic springing back) creates another surge of pressure that carries blood forward in a series of pulses, thereby maintaining blood pressure and forwards blood flow.
  • MUSCULAR ARTERIES: Tunica media may have more smooth muscles and less elastic fibres – smooth muscle contraction is controlled and helps keep blood moving, allows different quantities of blood to be distributed to different locations, when smooth muscle contracts blood vessels constrict = lumen diameter narrowed = regulation of blood flow to tissues
  • Tunica adventitia is tough outer layer (collagen fibres) – also contains elastic fibres to allow for stretching blood flow
  • Wall is much thicker than lumen – withstand pressure
  • No valves – pressure is enough to prevent backflow
  • Larger arteries have own blood supply called vasa vasorum – vasa vasorum is part of tunica adventitia and is needed to support metabolic needs of larger arteries
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18
Q

Describe the blood flow and pressure of arteries, veins and capillaries?

A
  1. Arteries
    * High pressure (10-16 kPa)
    * Blood moves in pulses
    * Blood flows rapidly
  2. Veins
    * Low pressure (1 kPa)
    * No pulses
    * Blood flows slowly
  3. Capillary
    * Reducing pressure (4-1 kPa)
    * No pulses
    * Blood flows slowly
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19
Q

What are the main vein functions that structure must facilitate?

A
  1. Transporting blood under low pressure (slow speed)
  2. Transporting blood from tissues to heart (preventing backflow)
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20
Q

How is vein structure related to function to suit slow speed and prevent backflow?

A
  • Tunica media thin – low pressure does not cause bursting, so no need for thick tunica media.
  • Tunica media has very few elastic fibres and less smooth muscle – elastic fibres not needed because little stretch and recoil, less smooth muscle because veins carry blood AWAY from tissues so flow does not need to be directed and controlled through constriction and dilation.
  • Tunica adventitia provides tough outer layer (collagen fibres) – prevents veins from bursting (more from external forces though because they are nearer to skin surface than arteries.
  • Overall thickness of wall is small – no risk of bursting because of low pressure. Thin wall allows them to be easily flattened, aiding blood flow. Lumen relatively large compared to wall thickness.
  • Semi lunar valves throughout – prevent backflow of blood which might occur due to low pressure. When muscles contract during body movements veins are compressed and blood is pressurised. Valves ensure one-way flow of blood (toward heart only).
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21
Q

What are the constituents of blood?

A
  • 55% plasma
  • 45% red blood cells, white blood cells, platelets
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22
Q

What is blood?

A

The medium in which material are transported around the body

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23
Q

What do I need to know about red blood cells?

A
  • Lifespan 120 days
  • Made in bone marrow
  • Smaller than white blood cells
  • May be found in a stack or pile known as a rouleau
  • 7-8 um in size
  • Biconcave disk shape
  • Mature RBCs missing nucleus and other organelles
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24
Q

How much blood does the human body contain?

A

4-6 dm^3 blood

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25
Q

Why do mature RBCs not have a nucleus or other organelles and what effect does this have?

A
  • More room for haemoglobin to carry O2 and CO2
  • 120 day lifespan (quite short)
  • More flexible to change shape so can be flattened against capillary wall = decreased diffusion distance
  • Biconcave disk shape increases SA:V ratio
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26
Q

What are the two categories of white blood cells according to function?

A
  • Phagocytes (monocytes, neutrophils, macrophages)
  • Lymphocytes
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27
Q

What are the two categories of white blood cells according to morphology?

A
  • Granulocytes (neutrophils, macrophages)
  • Agranulocytes (monocytes)
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28
Q

What function do phagocytes serve?

A
  • Remove microorganisms, foreign material and dead cells through phagocytosis
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29
Q

What function do lymphocytes serve?

A
  • Act against disease-causing microorganisms (pathogens)
  • B-lymphocytes – secrete antibodies that immobilise pathogens for phagocytosis
  • T-lymphocytes – different types (e.g., T-helper, T-killer, T-suppressor) that perform different functions
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30
Q

What are the features of monocytes?

A
  • Larger than neutrophil
  • Less numerous than neutrophil
  • Irregular shape, but roughly spherical
  • Kidney-shaped/indented nucleus
  • Agranulocyte
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31
Q

What are the features of neutrophils?

A
  • Irregular shape
  • Most common type of white blood cell
  • Smaller than monocytes
  • Lobed nucleus
  • Granulocyte
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32
Q

What are the features of macrophages? (similar to monocytic features because develop from monocytes)

A
  • Granulocytes
  • Large shape
  • Kidney-shaped nucleus
  • Rarely seen in blood slides
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33
Q

How does the transfer of substances occur?

A
  1. Capillaries (carry glucose, oxygen, carbon dioxide, cell signalling molecules and waste substances)
  2. Tissue fluid (bathes all cells and tissues even where the capillaries do not reach; formed from blood plasma)
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34
Q

What is blood plasma?

A

The fluid component of blood (solvent) and the source of tissue fluid

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35
Q

What are the constituents of blood plasma?

A
  • 90 % water
  • 10% chemicals
  • Nutrients (glucose, amino acids, vitamins)
  • Waste products (urea)
  • Mineral ions (calcium, iron)
  • Hormones (insulin, adrenaline)
  • Plasma proteins (fibrinogen, prothrombin, albumen)
  • Respiratory gases (oxygen, carbon dioxide)
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36
Q

What is the function of blood plasma?

A
  • Making tissue fluid
  • Transporting substances from source to sink
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37
Q

What is tissue fluid?

A

The means by which materials are exchanged between blood and cells, bathes all cells of the body, made from blood plasma.
“Filtered blood plasma”

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38
Q

What is tissue fluid made from?

A
  • Blood plasma that has been filtered out of the capillary through a fenestration through the process of ultrafiltration.
  • Contains gases, nutrients and amino acids
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39
Q

What are the functions of tissue fluid?

A
  1. Provides cells with O2 for aerobic respiration
  2. Transfer CO2 and other waste substances to blood plasma
  3. Supplies dissolved C6H12O6, AA, mineral ions, nutrients to body cells for metabolic processes
  4. Provides aqueous environment (of the same w.p.) for body cells
  5. Provides medium for movement of macrophages within body tissues to defend against infection - facilitates immunity
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40
Q

How is tissue fluid formed?

A
  1. Blood plasma coming from arteriole end of capillary is under pressure, causes ultrafiltration to occur.
  2. Dissolved substances (gases, nutrients, amino acids, glucose) filtered OUT as they are forced out of endothelial pores/fenestrations and into the fluid bathing the cells and tissues. That fluid now becomes tissue fluid.
  3. Exchange of substances occurs.
  4. RBC, proteins, platelets stay in capillary and create oncotic pressure. Lower the water potential of capillary and water moves back into capillary via osmosis. Low hydrostatic pressure.
  5. Tissue fluid eventually drains back into lymphatic system.
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41
Q

How is oncotic pressure created?

A

Pressure exerted by proteins in blood plasma. It is a form of osmotic pressure that is due to the presence of large molecules of collids (primary proteins) that cannot pass through capillary fenestrations.

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42
Q

What are the two forces opposing the high hydrostatic pressure at the arteriole end of the capillary bed (coming out of endothelial pore) ? (4.8 kPa)

A
  1. Hydrostatic pressure of tissue fluid outside capillary, resisting movement of ultrafiltration.
  2. Lower w.p. of blood due to oncotic pressure in capillary that causes osmosis of tissue fluid back into capillary
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43
Q

What is the role of water in transport?

A
  1. Solvent Action
    * Due to dipolar property
    * Allows ions and molecules to dissolve and be transported
    * Facilitates bulk transport
    * Main component of blood and plasma
  2. High specific heat capacity
    * Homeostasis
    * Functioning of enzymes
    * Ensures thermal stability of blood and tissue fluid
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44
Q

How are lipids transported in blood since they are hydrophobic?

A

Lipid molecules transported in spherical complex known as a lipoprotein. Lipoprotein has a hydrophilic exterior that dissolves in plasma.

45
Q
A
46
Q

What is haemoglobin?

A
  • Large globular protein
    • Hb is common way of abbreviating
    • Hb4O8 (an Hb molecule with all 4 haem groups carrying an O2 molecule – so fully saturated Hb molecule)
47
Q

What is haemoglobin?

A
  • Large globular protein
    • Hb is common way of abbreviating
    • Hb4O8 (an Hb molecule with all 4 haem groups carrying an O2 molecule – so fully saturated Hb molecule)
48
Q

What is the function of haemoglobin?

A

• To readily associate with O2 at a gas exchange surface (loading)
• To readily dissociate with CO2 at a respiring tissue (unloading

49
Q

What is the structure of haemoglobin?

A

• 4 polypeptide subunits that form one cohesive quaternary structure
• Each polypeptide subunit has a haem prothestic group – an O2 molecule binds to an Fe 2+
• 2 alpha globin chains
• 2 beta globin chains

50
Q

How is oxyhemoglobin formed?

A

• Formed when one molecule of oxygen combines with one of the 4 haem groups in the quaternary structure.

51
Q

What does allosteric mean?

A

Relating to the alteration of the activity of an enzyme by means of a conformational change induced by a different molecule.

52
Q

What is positive cooperativity?

A

Conformational changes caused by the binding of O2 to haemoglobin that increase the ability of haemoglobin to bind more O2.

53
Q

What is the function of an oxygen dissociation curve?

A

Shows the relationship between partial pressure of O2 and % saturation of Hb WITH O2.

Note: Hb does not load and unload O2 evenly.

54
Q

What is partial pressure?

A

• Quantity of a gas that is present in a mixture of gases that is measured by the pressure it contributes to the total pressure of the gas mixture.
• pO2 is partial pressure of oxygen
• measured in kPa
• also known as oxygen tension

55
Q

How to explain the shape of the oxygen dissociation curve with regards to oxygen loading?

A
  1. The shape of the Hb makes it difficult for the 1st O2 molecule to bind to one of the haem groups. Therefore, at low O2 concentrations little O2 binds to haemoglobin. At low O2 concentrations haemoglobin has a low affinity for oxygen. Gradient of curve not steep initially.
  2. Binding of this 1st O2 molecule changes quaternary structure of Hb molecule. Causes conformational change which makes it easier for another Hb group to bind to O2 molecule. Known as the allosteric effect.
  3. As a consequence of the allosteric effect, it takes a smaller increase in the pO2 to bind to the 2nd O2 molecule than it did to bind the 1st one. This known as positive cooperativity. Binding of 2nd makes binding of 3rd easier, binding of 3rd makes 4th easier… gradient steepens.
  4. High O2 concentrations most – at all – haemoglobin molecules saturated. Gradient reduces and begins to plateau. Reason for plateau is because majority of the binding sites are saturated/occupied so it’s difficult for an O2 molecule to find an empty site to bind to. Never completely 100% saturated. Note: Oxygen dissociation curve will never fully reach 0% either because Hb affinity too high. It’s hard for the 1st O2 molecule to associate and last O2 molecule to dissociate.
56
Q

Why are there many different types of oxygen dissociation curves?

A
  1. There are a number of different respiratory pigments, haemoglobin isn’t the only one.
  2. Haemoglobin exists in a number of different forms.
  3. The behavior of each pigment changes under different conditions, e.g., change in pH, temp, altitude
57
Q

Why is adult haemoglobin often specified?

A

Because fetal haemoglobin has a different structure and a higher affinity for oxygen.

58
Q

Note: The measure of partial pressure on an oxygen dissociation curve can also be indicative of what environment oxygen loading is taking place in. E.g., lungs will have higher pO2 so Hb affinity for O2 increases.

A

.

59
Q

What is the difference between the allosteric effect and positive cooperativity?

A

The allosteric effect refers to the regulation of a protein’s activity through the binding of a molecule at a site other than the active site, changing the protein’s shape and function.
Positive cooperativity on the other hand occurs when the binding of a substrate to one active site of a multi-subunit enzyme increase the affinity of other active sites for additional substrate molecules.

60
Q

What does the shape of the oxygen dissociation curve explain?

A
  1. Lungs – haemoglobin associates with oxygen (loading) to carry it in form of oxyhaemoglobin
  2. Respiring tissue – reverse occurs, oxygen dissociates (unloading) from oxyhaemoglobin
61
Q

Haemoglobin affinity at a higher partial pressure in the lungs?

A

• As pO2 increases, so does Hb affinity
• There is a high pO2 of about 13.3 kPa
• 12-14 kPa in alveolar capillaries in lungs
• Curve plateaus at about 98% oxygen-haemoglobin saturation
• Very little O2 dissociated from oxyhaemoglobin because of high affinity

62
Q

Haemoglobin affinity for oxygen at low partial pressures in respiring tissues?

A

• For any one tissue pO2 will be lower when tissue is active compared to pO2 when it is resting (because respiration uses O2 and produces CO2)
• Pressures typically 2-6 kPa
• Only a small decrease in pO2 will cause a larger difference in the quantity of oxygen that dissociates from oxyhaemoglobin (this is because affinity of haemoglobin for O2 changes with levels of CO2).

63
Q

What is the Bohr Effect?

A

Effect by which haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.

64
Q

What is the purpose of the Bohr Effect?

A
  • Explains differing behaviour of haemoglobin in
    1. Different regions of the body
    2. In the same regions of the body but under different conditions
  • Allows the body to respond and adjust to changing conditions in respiring tissues (so satisfies respiratory demands of tissues)
65
Q

How does the Bohr Effect occur at a gas exchange surface/the lungs?

A
  • pCO2 is reduced because CO2 is being excreted through exhalation
  • pO2 high because O2 being inhaled into the lungs
    = Hb affinity for O2 is increased and Hb readily associates with O2 to form oxyhaemoglobin
66
Q

How does the Bohr Effect occur in respiring tissues/muscles?

A
  • pCO2 increased because it is a product of respiration
  • PO2 low because being use for respiration
    = Hb affinity for O2 is reduced and Hb readily dissociates from O2
67
Q

Why does the Bohr Effect occur?

A
  • Bohr Effect occurs as a consequence of the acidity of dissolved CO2
  • Dissolved CO2 becomes H+ ios and HCO3- ions. H+ lowers pH and thereby lowers affinity of Hb for O2.
    Note: low pH of other chemicals – e.g., lactate/lactic acid in anaerobic respiration – may further reduce Hb affinity for O2, causing O2 to dissociate
68
Q

What is an exam tip for interpreting and comparing oxygen dissociation curves?

A

At any one pO2:
- The more to the LEFT the curve is, the more readily it will associate with O2 and less easily it dissociates (LEFT = HB affinity INCREASE)
- The more to the RIGHT the curve is, the less readily it associates with O2 and the more easily it dissociates
(RIGHT = Hb affinity DECREASES)

69
Q

How is CO2 transported in the circulatory system?

A

• 5% is transported in BLOOD PLASMA in solution
• 95% is transport involving HAEMOGLOBIN
Of that 95%…
- 85% is transported as hydrogencarbonate ions (HCO3-) *The Chloride Shift
- 10% is combined with haemoglobin to form carbaminohaemoglobin
(haemoglobin + carbon dioxide -> carbaminohaemoglobin + hydrogen ions)
Note: hydrogen ions alter pH

70
Q

What does the chloride shift demonstrate?

A

Hb acts as a buffer, helps keep pH of blood about 7.4

71
Q

What is the chloride shift?

A

The chloride shift is something that occurs when Cl- ions compensate for HCO3- ions that have diffused out of RBCs so that there is no overall change in the charge of the cell. It is the way that 85% of the 95% of CO2 being transported in combination with haemoglobin is transported (in form of hydrogencarbonate ions). Also explains the dissociation of oxygen from oxyhaemoglobin as a result of a changed pH.

72
Q

Describe the chemical process of the chloride shift?

A

H2O + CO2 -> (carbonic anhydrase: enzyme) -> H2CO3 (carbonic acid) -> (dissociates) -> H+ (hydrogen ions, changes pH) + HCO3- (hydrogencarbonate ion)

73
Q

What happens during the chloride shift?

A
  1. Membrane transport protein (called anion exchanger) in RBC facilitates:
    • HCO3- (hydrogencarbonate ion) diffusing OUT and simultaneously…
    • Cl- (chloride ion) diffusing INTO RBC
    = No change in the overall charge of the cell
  2. Hydrogen ions (previously produced as a result of the dissociation of carbonic acid [H2CO3]) combine with Hb/haemoglobin to form haemoglobinic acid (HHb)
  3. HHb causes O2 to dissociate from Hb
  4. The now dissociated O2 diffuses out of the RBC and into the blood plasma, then enters the tissue fluid
  5. From the tissue fluid the O2 then diffuses into respiring cells which need O2, thereby meeting the demand for O2 in respiring tissues
74
Q

Reverse of Chloride Shift?

A
  1. HC03- (hydrogencarbonate ion) in, Cl- (chloride ion) out (through anion exchanger)
  2. H+ (hydrogen ion) released from haemoglobin, it combines with HCO3- ions to form H2CO3 (carbonic acid)
  3. Carbaminohaemoglobin is converted to haemoglobin and releases CO2
  4. Haemoglobin is free to bind to oxygen
75
Q

What is the heart made of?

A

Cardiac muscle (appears striped under a microscope)

76
Q

How does the heart muscle get oxygenated?

A

Gets oxygenated through the coronary arteries and deoxygenated by cardiac veins.
When there is a blockage in the C artery, leads to heart attack.

77
Q

Where is the heart located?

A

The thoracic cavity (thorax)

78
Q

What is left atrioventricular valve called?

A

Mitral/bicuspid valve (2 cup shaped flaps)

79
Q

What is right atrioventricular valve called?

A

Tricuspid valve (3 cup shaped flaps)

80
Q

What does septum do?

A

Separates oxygenated and deoxygenated blood

81
Q

How are valves prevented from turning inside out under pressure?

A
  • Valves are attached to papillary muscles on the heart wall
  • Attached via chordinae tendinae
82
Q

What is the difference in the thickness of atria and ventricular walls?

A
  1. Atria
    * Thinner
    * Short distance (to ventricles)
    * Little resistance to blood flow
  2. Ventricles
    * Thicker
    * Longer distance (to lungs or the rets of the body – pulmonary or systemic circulation)
    * Thick walls present resistance. Therefore, more cardiac muscle needed to generate force to overcome resistance and maintain pressure
83
Q

Why is the LV wall thicker than the RV wall?

A
  • LV wall -> purpose is systemic circulation = far distance (1.5 m) and must pump to the whole body -> need thick muscle to create a powerful contraction which creates high pressure
  • Whereas RV wall -> pulmonary circulation = must pump only to lungs so shorter distance = thinner muscle wall cuz not as much force required
84
Q

How often does the cardiac cycle repeat?

A

70 times per minute

85
Q

What does the cardiac cycle consist of?

A
  1. Diastole
  2. Systole
    * Atrial systole
    * Ventricular systole
86
Q

What is the cardiac output?

A

The volume of blood pumped by the heart in a given time. Measured in dm^3/min

87
Q

What does the cardiac output depend on?

A
  1. Heart rate
  2. Stroke volume (volume of blood pumped out at each beat)
88
Q

How to calculate cardiac output?

A

Heart rate x stroke volume

89
Q

What happens during diastole?

A
  • Cardiac muscle of both atria and ventricles relaxed (so diastole occurs in all chambers of heart at same time)
  • During diastole the atria are relaxed and fill with blood. Ventricles are just relaxed.
    1. Blood enters atria from venae cavae (R) and pulmonary veins (L).
    2. Semi-lunar valves closed.
    3. Left and right atrioventricular valves open.
    4. Relaxation of ventricles draws blood from the atria into the ventricles.
90
Q

What causes the valves to open and close?

A

Relaxation and contraction of muscles lower and higher pressures, which causes valves to open and close and causes blood to flow into and out of chamber.

91
Q

What happens during systole?

A

Systole = contraction
1. Atrial systole (ventricular diastole)
* RA and LA contract simultaneously
* Atrial contract to push remaining blood into ventricles
* Semi-lunar valves closed
* Left + right atrioventricular valves open
* Blood pumped from atria to ventricles
2. Ventricular systole (atrial diastole)
* Ventricles contract, which pushes blood away from the heart through the pulmonary arteries and the aorta
* Semi-lunar valves open
* Left and right atrioventricular valves closed
* Ventricles contract
* Blood pressure rises = forces shut atrioventricular valves
* Blood pressure in ventricles rises = forces semi-lunar valves open

92
Q

What is the purpose of valves?

A

To control blood flow by preventing backflow of blood. In doing so controls direction of blood flow.

93
Q

How do valves control blood flow?

A
  • Valves open when the direction of flow is desired
  • Valves close when the direction of flow is not desired
  • This is done through pressure differences which are created by muscular contraction and relaxation
94
Q

What are the three types of valves and their functions?

A
  1. Atrioventricular valves
    * Biscuspid valve (L)
    * Tricuspid valve (R)
    * Prevent backflow when ventricular pressure is higher than atrial pressure = stops backflow of blood into atria and therefore ensures that blood moves into aorta and pulmonary artery
  2. Semi-lunar valves
    * Prevent the backflow of blood into ventricles during ventricular diastole (from aorta and pulmonary artery)
  3. Pocket semi-lunar valves
    * Found throughout venuous system
    * Ensure that when veins are squeezed when muscles contract that blood flows back to heart
95
Q

What are valves made from?

A

Design of valves are all basically the same.
* Flaps of tough, flexible and fibrous tissue which is cusp-shaped

96
Q

Chordinae tendinae

A

string-like tendons

97
Q

Papillary muscles

A

pillars of muscles on ventricle walls

98
Q

Myogenic

A

Contraction is initiated from within the muscle

99
Q

Neurogenic

A

Contraction initiated by nerve impulses from outside

100
Q

What is the AVN and where is it?

A
  • Atrioventricular node
  • Group of cells which lies in the septum between the atria
101
Q

What does the AVN do?

A
  1. Relays impulses generated by SAN down the septum to the Purkyne tissue (via Bundle of Hess)
  2. Delays SAN impulse by 0.1-0.2 seconds in order to:
    * Give atria time to empty and ventricles time to fill with blood
    * Prevent simultaneous atrial and ventricular systole
102
Q

What is the SAN and where is it?

A
  • Sinoatrial node
    1. Pacemaker
    SAN has basic rhythm of stimulation that determines the heartbeat
    2. Initiates heartbeat
    It is where the initial stimulus for contraction of myogenic cardiac muscle originates
  • Located as a distinct group of cells within wall of RA
103
Q

How does the SAN initiate the heartbeat?

A
  • Sends out impulses/waves of excitation across the walls of both atria = causes atrial systole
  • Sends out these impulses at regular intervals, produces rhythmic contractions of heart
104
Q

What is Purkyne tissue and where is it?

A
  • Specialised muscle fibres between the ventricles
105
Q

What do purkyne tissues do?

A
  1. Conducts wave of AVN impulses through septum to the base of the ventricles (stimulates contraction of cardiac muscle by releasing wave of excitation)
  2. Ensures that ventricle contract from the apex upwards
  3. Ensures simultaneous ventricular systole
106
Q

What is the complete sequence of events in the control of the cardiac cycle?

A
  1. SAN releases impulses/waves of excitation – causes simultaneous atrial systole
  2. Septum prevents the impulse from crossing to the ventricles – prevents simultaneous atrial and ventricular systole
  3. Impulse passes through the AVN
  4. AVN delays impulse for 0.1-0.2 seconds, passes an impulse down septum to Purkyne tissue (through bundle of His)
  5. Purkyne tissue releases impulse which passes along cardiac muscle – causes ventricular systole (from apex upwards)
107
Q

What is maximum blood pressure?

A

Systolic blood pressure during ventricular systole.

108
Q

What is minimum blood pressure?

A

Diastolic blood pressure

109
Q

What is an ECG?

A
  • Electrocardiogram
  • Record of wave of electrical activity caused by:
  • Atrial systole
  • Ventricular systole
  • Start of ventricular diastole

Biology (12 decks)

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