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A-level Biology > Module 3 - Exchange and Transport > Flashcards

Module 3 - Exchange and Transport Flashcards

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1
Q

Features of the gas exchange surface

A
  • Increased SA
  • Thin layers
  • Good blood supply
  • Ventilation to maintain diffusion gradient
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2
Q

Features of the human gaseous exchange system (13)

A

Nasal cavity, nostril, mouth, larynx, intercostal muscles, pleural membrane, trachea, bronchus, bronchioles, alveoli, ribs, diaphragm, abdominal cavity

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3
Q

Nasal cavity - role in gas exchange system

A
  • Blood warms the air
  • Mucus traps particulates
  • Humidifies air to protect more delicate structures in the lungs
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4
Q

Nasal cavity - adaptions for exchange

A
  • Large surface area and good blood supply
  • Goblet cells secrete mucus
  • Moist surfaces (due to mucus)
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5
Q

Trachea - role in the gas exchange system

A

-Funnels inhaled air to the lungs and exhaled air out of the body

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6
Q

Trachea - adaptations for exchange

A
  • Collagen (hyaline cartilage) - strong and flexible
  • Smooth muscle - contracts, decreases trachea’s diameter
  • Goblet cells produce mucus to propel foreign particles towards the pharynx
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7
Q

Bronchi - role in the gas exchange system

A

-Main passageway into the lungs (split into left bronchus and right bronchus)

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8
Q

Bronchi - adaptations for exchange

A
  • Made of cartilage and smooth muscle - strong, flexible, contractible
  • Innervated by nerves of the parasympathetic nervous systems - controls muscle contraction and relaxation
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9
Q

Bronchioles - role in the gas exchange system

A
  • Air passages in the lungs that branch off of bronchi

- Deliver gases to the alveoli

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10
Q

Bronchioles - adaptations for exchange

A
  • Made of elastic fibres and smooth muscle - can stretch
  • Lined with cilia and goblet cells
  • Lined with flattened epithelium - one cell thick, allows gas exchange
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11
Q

Alveoli - role in the gas exchange system

A

-Where gas exchange takes place

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12
Q

Alveoli - adaptations for exchange

A
  • Large surface area
  • Good blood supply
  • One cell thick (squamous epithelium)- reduces diffusion distance
  • Composed of collagen and elastic fibres - for recoil
  • Covered in a layer of fluid to dissolve gases for exchange
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13
Q

What is surface tension?

A

The elastic force created by a fluid surface that minimises the surface area (via cohesion of liquid molecules)

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14
Q

Type II pneumocytes secrete a liquid known as pulmonary surfactant. Does this reduce or increase the surface tension of alveoli?

A

It reduces the surface tension of the alveoli, allowing them to inflate:

  • As an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining
  • This increases surface tension and slows down the rate of expansion, ensuring all alveoli inflate at roughly the same rate
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15
Q

How many alveoli does each alveolar sac contain?

A

20-30

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16
Q

What is the pleura?

A

Each of the lungs is enclosed in a double membrane known as the pleural membrane. The space between the 2 membranes is called the pleural cavity, and is filled with a small amount of pleural fluid

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17
Q

Role of smooth muscle in asthma

A

Relievers are chemicals (similar to adrenaline) that attach to active sites of the surface membranes of small muscle cells in the bronchioles. This makes them relax, dilating the airways. Smooth muscle can affect asthma, as it surrounds airways in a circumferential pattern, which reduces the airway’s luminal diameter as it contracts, causing acute airflow, obstruction, shortness of breath, and wheezing

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18
Q

Role of smooth muscle in exercise

A

Smooth muscle in the lungs helps airways expand and contract, During exercise, smooth muscle in the bronchi relax and dilate. The bronchi and bronchioles use smooth muscle to bring air from the trachea into the lungs

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19
Q

What substances or building blocks do cells need to survive?

A
  • Water - used for many things
  • Minerals - used for many things
  • Oxygen - used in respiration
  • Glucose - used for energy
  • Fats - used for membranes
  • Proteins - used for growth and repair
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20
Q

What substances do many cells need to excrete?

A
  • Carbon dioxide
  • Ammonia (urea)
  • Specialised cells in multicellular organisms may also need to excrete special molecules
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21
Q

How does an amoeba get the substances it needs?

A

They have a large SA:V, so they don’t require exchange systems as they can exchange sufficient materials, needed for life, through their large surface area

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22
Q

Why do multicellular organisms need exchange systems?

A

They require adapted exchange and transport systems to achieve a large SA:V ratio

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23
Q

The rate of metabolism of a cell is related to what?

A

Its mass/volume (larger cells need more energy to sustain essential functions)

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24
Q

The rate of material exchange (in a cell) is related to what?

A

The cell’s surface area (large membrane surface equates to more material movement)

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25
Q

Why do larger cells/organisms have a smaller SA:V ratio?

A

Volume increases faster than surface area in larger cells

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26
Q

Reasons for exchange systems (2)

A
  1. Cells in the centre of the organism would not receive any materials if multicellular organs survived on diffusion across an organism’s surface alone
  2. The high metabolic rate means there is a need to exchange lots of materials quickly
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27
Q

Specialised tissues that increase SA, to optimise material transfer, in exchange systems (2)

A
  1. Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface area of the inner lining
  2. Alveoli within the lungs which function to increase the total membrane space
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28
Q

How to calculate SA

A
  • For a cube - 6 x (length x width)
  • e.g. a cube has 6 sides, each with a measurement of 10μm
  • 6 x (10 x 10) = 600μm²
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29
Q

How to calculate volume (of a cube)

A
  • Length x width x height
  • e.g. a cube has 6 sides, each with a measurement of 10μm
  • 10 x 10 x 10 = 1000μm³
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30
Q

How to calculate SA:V ratio

A
  • SA/V

- e.g. 600/1000 = 0.6

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31
Q

Cuboids - SA and volume equations

A
  • Volume = length x width x height

- SA = (4 x length x height) + (2 x height x width)

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32
Q

Cylinders - Area of a circle, circumference, SA and volume equations

A
  • Area of a circle = πr²
  • Circumference = 2πr
  • Volume = πr² x height
  • Surface area = (2πr x height) + 2πr²
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33
Q

Sphere - SA and volume equations

A
  • Volume = 4/3 πr³

- SA = 4πr²

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34
Q

What is asthma?

A
  • A common, chronic inflammation of the airways to the lungs (i.e. bronchi and bronchioles)
  • Inflammation leads to swelling and mucus production, resulting in reduced airflow and bronchospasm, meaning it is much harder to ventilate
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35
Q

What may trigger asthma?

A

A number of variable and recurring environmental conditions, such as: allergens, smoke, cold air, certain medications, and arthropods (dust mites)

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36
Q

What is ventilation?

A

A term used to describe breathing, where air is constantly moving in and out of the lungs

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37
Q

What is the purpose of ventilation?

A
  • A ventilation system is needed to maintain a concentration gradient in alveoli, continually cycling fresh air into the alveoli from the atmosphere
  • This means O₂ levels stay high in alveoli (and diffuse into the blood) and CO₂ levels stay low (and diffuse from the blood)
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38
Q

What is breathing?

A
  • The active movement of respiratory muscles that enables the passage of air into and out of the lungs
  • The contraction of respiratory muscles changes the volume of the thoracic cavity (i.e. the chest)
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39
Q

The mechanism of breathing occurs according to what law? State what it means

A
  • Boyle’s Law
  • Pressure (P) ∝ 1/Volume (V)
  • As volume increases, pressure decreases, and vice versa
  • Assuming constant temperature and closed environment
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40
Q

When the volume of the thoracic cavity increases, what happens to the pressure in the thorax according to Boyle’s Law?

A

It decreases, according to Boyle’s Law

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41
Q

What is inspiration?

A
  • Also known as “inhalation”, occurs when air pressure in the atmosphere is greater than that of the lungs; forcing air into the alveoli
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42
Q

What is expiration?

A
  • Also known as “exhalation”, occurs when air pressure in the lungs is greater than that in the atmosphere; forcing air out of the alveoli
  • Can be considered passive
  • Elastic recoil of tissues aids expiration
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43
Q

Muscles only work via what?

A

Contraction

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44
Q

Muscles of inspiration and functions (2)

A

Core muscles:

  1. External intercostals (contracts to elevate ribs)
  2. Diaphragm (contracts to expand thoracic cavity)
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45
Q

Muscles of expiration and functions (2)

A

Core muscles:

  1. Internal intercostals (contracts to pull ribs down)
  2. Diaphragm (relaxes to reduce thoracic cavity)
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46
Q

Name of additional muscle groups that help pull ribs up and out (inspiration)

A
  • Sternocleidomastoid

- Pectoralis minor

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47
Q

Name of additional muscle group that help pull the ribs downwards (expiration)

A
  • Quadratas lumborum
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48
Q

What is gas exchange?

A

The exchange of oxygen and carbon dioxide between the alveoli and bloodstream (via passive diffusion)

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49
Q

What is cell respiration?

A

The release of energy (ATP) from organic molecules - it is enhanced by the presence of oxygen (aerobic)

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50
Q

Which methods might you use to measure the capacity of the lungs (volume of air drawn in and out)?

A
  1. Using a peak flow meter
  2. Using vitalographs
  3. Using a spirometer
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51
Q

What is tidal volume?

A

The volume of air that moves into and out of the lungs with each resting breath. It is around 500cm³ in most adults at rest, which uses about 15% of the vital capacity of the lungs

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52
Q

What is vital capacity?

A

The volume of air that can be exhaled when the deepest possible intake of breath is followed by the strongest possible exhalation

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53
Q

What is inspiratory reserve volume?

A

The maximum volume of air you can breathe in over and above a normal inhalation

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54
Q

What is expiration reserve volume?

A

The extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe out

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55
Q

What is residual volume?

A

The volume of air that is left in your lungs when you have exhaled as hard as possible. This cannot be measured directly

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56
Q

What is total lung capacity?

A

The sum of the vital capacity and the residual volume

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57
Q

What is breathing rate?

A

The number of breaths taken per minute

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58
Q

What is ventilation rate?

A

The total volume of air inhaled in one minute

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59
Q

How do you calculate ventilation rate?

A

Tidal volume x breathing rate (per minute)

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60
Q

The normal tidal volume of a male is 500cm³. His ventilation rate is 6dm³ per minute. What is his resting breathing rate?

A
  • ventilation rate = tidal volume x breathing rate
  • 6dm³ = 6000cm³
  • 6000 = 500 x breathing rate
  • breathing rate = 6000/500 = 12 breaths/min
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61
Q

What prevents insects from having a normal gas exchange system?

A

A tough exoskeleton, which allows little to no gas exchange to take place

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62
Q

How does gas exchange in insects take place?

A
  • Air enters (and leaves) through spiracles - small openings along the insect’s abdomen, these can be closed (by sphincters) to minimise water loss
  • Then air moves by diffusion through the trachea - these are tubes that can be up to 1mm in diameter and their job is to carry air into the body. They’re lined with chitin, meaning they’re impermeable (and also strong), so little gas exchange happens here
  • The trachea branch to form narrower tubes of 0.6-0.8μm in diameter called tracheoles. These have no chitin lining, and so are permeable to gases. Due to their small size, they can run in between individual cells, allowing for efficient gas exchange
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63
Q

In insects, what limits the penetration of of air for diffusion?

A

Tracheal fluid, which is found towards the end of tracheoles

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64
Q

Example of a high oxygen demanding activity for insects?

A

Flying

65
Q

Name examples of insects which have high oxygen demands

A

Larger beetles, locusts, grasshoppers, bees, wasps, flies

66
Q

How do insects with higher oxygen demands increase the level of their gaseous exchange?

A
  1. Mechanical ventilation of the tracheal system - air is actively pumped into the system by muscular pumping movements of the thorax and/or abdomen. This changes the volume of the body, which changes the pressure in the trachea and tracheoles; allowing more air to be drawn in to the trachea and tracheoles, or forced out, as pressure changes
  2. Collapsible enlarged trachea or air sacs, which act as air reservoirs - used to increase the amount of air moved through the gas exchange system
67
Q

What are gills?

A
  • Bony fish have an evolved ventilatory system adapted to take oxygen from water
  • Bony fish maintain a flow of water in one direction over the gills - these are organs of gaseous exchange which have large SA, good blood supply, and thin layers. They are contained in a gill cavity and covered by a protective operculum
  • The gills have two main components: the gill lamellae (rich blood supply, large SA, main site of gas exchange) and gill filaments (occur in large stacks called gill plates. A constant flow of water keeps them apart, increasing SA for gas exchange)
68
Q

Process for gas exchange in bony fish?

A
  1. The mouth is opened and the floor of the buccal cavity is lowered. This increases the volume of the buccal cavity
  2. The pressure in the cavity drops and water moves into the buccal cavity. The opercular valve is shut and the opercular cavity containing the gills expands. This lowers the pressure in the opercular cavity.
  3. The floor of the buccal cavity starts to move up, increasing pressure there so water moves from the buccal cavity over the gills
  4. The mouth closes, the operculum opens and the sides of the opercular cavity move inwards. All these actions increase the pressure in the opercular cavity and force water over the gills and out of the operculum
  5. The flow of the buccal cavity is steadily moved up, maintaining a flow of water over the gills
69
Q

Adaptations of gills

A
  1. The tips of adjacent gill filaments overlap - this increases the resistance to the flow of water over the gill surface and slows down the movement of the water, leading for more time for gas exchange to happen
  2. The water moving over the gills and the blood in the gill filaments flow in different directions. This ensures a steep concentration gradient is maintained.
70
Q

Why do animals need specialised transport systems?

A
  • High metabolic demand
  • SA:V ratio gets smaller as multicellular organisms get larger
  • Molecules (hormones, enzymes..) may be made in one place but be needed in another
  • Food will be digested in one organ system, but needs to be transported to every other cell for use in respiration/other aspects of cell metabolism
  • Waste products of metabolism need to be removed from the cells and transported to excretory organs
71
Q

What substances are carried around in multicellular animals specialised circulatory systems?

A
  • oxygen
  • carbon dioxide
  • nutrients
  • waste products
  • hormones
72
Q

What common features to most circulatory systems have?

A
  • A liquid transport medium that circulates around the system
  • Vessels that carry the transport medium
  • A pumping mechanism to move the fluid around the system
73
Q

What is an open circulatory system?

A

A circulatory system with very few vessels to contain the transport medium, and so it is pumped straight from the heart into the body cavity (haemocoel) of the animal, then back to the heart through an open ended vessel (a continuous loop). In the haemocoel, the transport medium is under low pressure, and comes in direct contact with the cells and tissues

74
Q

What organisms have open circulatory systems?

A

They’re mainly found in invertebrates (insects and some molluscs)

75
Q

What is insect blood called? What makes it different to our blood?

A

It’s called haemolymph and it doesn’t carry oxygen or carbon dioxide, as insects have a separate gaseous exchange system for that

76
Q

What is transported in insects blood?

A
  • Food
  • Nitrogenous waste products
  • Cells involved in immunity/defence against diseases
77
Q

What is an closed circulatory system?

A

In this type of circulatory system, blood is enclosed in blood vessels (veins, arteries and capillaries), and therefore does not come into direct contact with the cells of the body

78
Q

What process do substances enter and leave the blood by?

A

Diffusion (through the walls of the blood vessels)

79
Q

What is the name of the blood pigment commonly found in closed circulatory systems?

A

Haemoglobin

80
Q

What organisms have closed circulatory systems?

A

Found in many different animal phyla, including echinoderms (sea urchins, starfish..), cephalopod molluscs (octopuses, squid), annelid worms (e.g. common earthworm), and all the vertebrate groups, including mammals

81
Q

What organisms have single closed circulatory systems?

A

Fish, annelid worms, etc…

82
Q

What is a single closed circulatory system?

A
  • In these circulatory systems, blood flows through the heart and is pumped out to travel all around the body before returning to the heart
  • Simplified, this means that the blood travels only once through the heart for each complete circulation of the body
83
Q

What organisms have a double closed circulatory system?

A

Most land mammals, including birds (because they maintain their own body temperature)

84
Q

What is a double closed circulatory system?

A

An efficient transport system that includes two separate circulations:

  • Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, and 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
85
Q

What blood pressures do a single and double circulatory system maintain?

A
  • Single = low blood pressure, so blood returns to the heart slowly. This is due to the blood passing through two sets of capillaries before it returns to the heart
  • Double = high blood pressure, so blood returns to the heart quickly. This is due to the blood passing through only one set of capillaries
86
Q

What are some examples of different components utilised in blood vessels?

A
  1. Elastic fibres - composed of elastin, can stretch and recoil, allows blood vessels to be flexible
  2. Smooth muscle - contracts or relaxes (this changes size of the lumen)
  3. Collagen - provides structural support to maintain the shape and volume of the vessel
87
Q

What are arteries?

A

These are blood vessels which carry blood away from the heart to the tissues of the body; and they all carry oxygenated blood except from the pulmonary artery, which carries deoxygenated blood away from the heart and to the lungs (as well as the umbilical artery, carrying deoxygenated blood from the fetus to the placenta)

88
Q

Structure of arteries

A
  • Artery walls contain elastic fibres to help them withstand the force of the blood being pumped from the heart, and they stretch to take in a larger volume of blood
  • The lining of arteries (endothelium) is smooth so the blood flows easily over it
  • Artery walls also contain smooth muscle and collagen
  • Small lumen
  • Structures called arterioles link the arteries and capillaries together - these have more smooth muscle and less elastin in their walls than arteries, due to them having little pulse surge, but still can constrict and dilate to control the flow of blood into individual organs
89
Q

What is vasoconstriction?

A

When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into a capillary bed

90
Q

What is vasodilation?

A

When the smooth muscle in the wall of an arteriole relaxes, blood flows into the capillary bed

91
Q

What is an aneurysm?

A
  • A huge bulge or weakness in a blood vessel, most commonly found in the aorta and arteries of the brain
  • One factor that increases risk of aneurysms is high blood pressure
  • Scientists might have discovered a link between aneurysms and the changes in proportion of collagen to elastin in aortic walls
92
Q

What are capillaries?

A

Microscopic blood vessels that link arterioles with venules. They form an extensive network through all the tissues of the body

93
Q

Structure of capillaries

A
  • They have small lumens (7.5-8μm in diameter)

- Substances are exchanged through the capillary walls between the tissue cells and the blood

94
Q

What are the ways in which capillaries are adapted for their role?

A
  • They provide a very large SA for the diffusion of substances into and out of the blood
  • The total cross-sectional area of the capillaries is always greater than the arteriole supplying them so the rate of blood flow falls. The relatively slow movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and the cells
  • The walls are a single endothelial cell thick, giving a very thin layer for diffusion
95
Q

What are veins?

A

These are blood vessels which carry blood away from the cells of the body and towards the heart. They mostly carry deoxygenated blood, however in the pulmonary vein, oxygenated blood is carried instead (also in the umbilical vein, oxygenated blood is carried from the placenta to the fetus)

96
Q

What are venules?

A

These are smaller veins which connect the capillaries and the larger veins together

97
Q

Structure of veins

A
  • Thin layers of smooth muscle and elastin, with a much larger lumen than arteries
  • The walls have lots of collagen, which provides structural support
  • The endothelium is smooth (and thin), allowing blood to flow easily
  • Are able to hold a large reservoir of blood - up to 60% of your blood volume is in your veins at any one time
98
Q

Is the blood pressure in veins low or high?

A

Low, especially when compared to arteries

99
Q

What adaptations do medium-sized veins have?

A

Valves to prevent the backflow of blood

100
Q

Structure of venules

A
  • Very thin walls, with little smooth muscle and elastic fibres
  • Contain collagen
  • Several link to form a vein
101
Q

What main adaptations does the body have in order to help move blood against gravity when it is under low pressure?

A
  1. A majority of the body’s veins have one-way valves at intervals - these are flaps or infoldings of the inner lining of the vein, and they prevent the backflow of blood
  2. Many of the larger veins run between the big, active muscles in the body (e.g. arms and legs) - this means that when the muscles contract they squeeze the veins, which forces blood towards the heart. Valves prevent backflow when these muscles relax
  3. The breathing movements of the chest act as a pump - the pressure changes and the squeezing actions move blood in the veins of the chest and abdomen towards the heart
    * In combination, these adaptations assist in the return of deoxygenated blood to the heart
102
Q

What is blood composed of?

A
  • Plasma = a yellow liquid which carries a wide variety of other components (e.g. dissolved glucose, amino acids, mineral ions, hormones, and the large plasma proteins including albumin, fibrinogen and globulins). Plasma also transports red blood cells, many types of white blood cells, and platelets - these are fragments of large cells (megakaryocytes) found in red bone marrow and are involved in the clotting mechanism of the blood
  • Plasma only makes up 55% of the blood by volume - and most of that volume is water
103
Q

Functions of the blood (transport)

A
  1. Oxygen to, and carbon dioxide from, the respiring cells
  2. Digested food from the small intestine
  3. Nitrogenous waste products from the cells to the excretory organs
  4. Chemical messages via hormones
  5. Food molecules from storage compounds to the cells that need them
  6. Platelets to damaged areas
  7. Cells and antibodies involved in the immune response
104
Q

Functions of the blood (other)

A
  1. Contributes to maintenance of a steady body temperature (thermoregulation)
  2. Acts as a buffer, minimising pH changes
  3. Defence
105
Q

What is tissue fluid?

A

Extracellular fluid which bathes the cells of most tissues, arriving via blood capillaries and being removed via the lymphatic vessels

106
Q

Composition of the blood in percentages

A
  • ~55% plasma
  • <1% buffy coat (platelets, wbc)
  • ~45 red blood cells
107
Q

By what process could you fraction blood?

A

Centrifugation

108
Q

Function of red blood cells

A

They’re responsible for transporting oxygen as it is bound to haemoglobin at the lungs and released from the RBCs at respiring tissues

109
Q

Function of white blood cells

A

Involved in the body’s immune response, detects and eliminates infections

110
Q

The importance of plasma proteins

A
  • About 8% of blood plasma consists of plasma proteins, of which about half may be albumins
  • These are a group of small proteins involved in the transport of other substances (e.g. fatty acids, hormones) and which help regulate the osmotic pressure of blood
  • The balance between the hydrostatic pressure of blood (‘blood pressure’) and the osmotic pressure of blood is important in the formation of tissue fluid
  • Plasma proteins e.g. albumin cannot pass through capillaries. These give blood a high solute potential (lowering the water potential) compared to surrounding fluid
111
Q

Describe the tissue fluid diagram (you know the one, with all the horrid numbers! Arterial end, tissue fluid, venous end)

A
  • As blood arrives at the arteriole end of the capillary it is under pressure from the surge of blood from the heart.
  • Hydrostatic pressure forces fluid out of the capillaries
    (Pressure: approx.. 4.3-4.6kPa)
  • This is higher than oncotic pressure causing water top move in.
  • Net flow out - the fluid flowing out fills the space between the cells (tissue fluid - same composition as plasma except cells and plasma proteins, diffusion occurs here)
  • As the blood reaches the venous of the capillary,
    hydrostatic pressure falls to 2.3kPa and pulse lost.
  • The oncotic pressure is -3.3kPa and is greater than hydrostatic pressure. Water moves back into the capillaries by osmosis.
  • As the blood enters the veins, 90% of the tissue fluid is back in blood vessels.
  • Net flow in
112
Q

What is lymph?

A
  • 10% of the liquid that leaves the blood vessels (tissue fluid) drains into a system of blind-ended tubes called lymph capillaries, where it is known as lymph
  • It has a similar composition to plasma and tissue fluid but has less oxygen and fewer nutrients
  • It also contains fatty acids, which have been absorbed into the lymph from the villi of the small intestine
  • The lymph capillaries join up to form larger vessels, where the lymph is transported by the squeezing of the body muscles
  • There are one-way valves that prevent the backflow of lymph
  • Eventually lymph will return to the blood, flowing into the right and left subclavian veins (under the clavicle, or collar bone)
113
Q

What build up in the lymph nodes (when necessary)?

A

Lymphocytes - these are WBCs which produce antibodies to fight of disease

114
Q

Roles of lymph nodes?

A
  • They intercept bacteria and other debris from the lymph, which are ingested by phagocytes found in the nodes
  • The lymphatic system plays a major role in the defence mechanisms of the body
115
Q

What are enlarged lymph nodes a sign of?

A
  • They’re a sign that the body is fighting off an invading pathogen
  • This is why doctors often examine the neck, armpits, stomach, or groin of their patients, as they are major sites of lymph nodes (also referred to as lymph glands) in the body
116
Q

How have erythrocytes adapted to their function?

A
  • They have a biconcave shape, meaning it has an increased SA available for diffusion of gases (than a simple disc or sphere structure, for example). The shape also allows it to pass through narrow capillaries
  • Mature erythrocytes have no nuclei, maximising the amount of haemoglobin that fits into them
117
Q

Structure of haemoglobin

A

(Very large) globular conjugated protein made up of four polypeptide chains, each with an iron-containing haem prosthetic group

118
Q

How many oxygen molecules can each haemoglobin molecule bind to?

A

4

119
Q

Equation for oxygen and haemoglobin binding

A
  • Haemoglobin + Oxygen ⇌ Oxyhaemoglobin

- Hb + 4O₂ ⇌ Hb(O₂)₄

120
Q

What is positive cooperativity?

A

When the shape of the haemoglobin molecule changes as soon as one oxygen molecule binds to it, which makes it easier for the next oxygen molecule to bind to it
(- Once the first oxygen molecule is released by the haemoglobin, the molecule again changes shape and it becomes easier to remove the remaining oxygen molecules)

121
Q

Why is there a steep concentration gradient between the inside of the erythrocytes and the air in the alveoli?

A

Because when erythrocytes enter the capillaries in the lungs, the oxygen levels in the cells a relatively low

122
Q

When the blood reaches the body tissues, which has the lower oxygen concentration: the cytoplasm of the body cells or the erythrocytes? What happens next?

A
  • The cytoplasm of the body cells

- As a result, oxygen moves out of the erythrocytes down a concentration gradient

123
Q

X and Y axis labels for an oxygen dissociation curve

A 
X = partial pressure of oxygen/kPa
Y = percentage saturation of haemoglobin with oxygen
124
Q

What do oxygen association curves show?

A

They show the affinity of haemoglobin for oxygen

125
Q

In relation to erythrocytes, what does it mean when haemoglobin has become saturated?

A

When all the haem groups have bound to 4 oxygen molecules, meaning haemoglobin can’t take up anymore oxygen

126
Q

What is the Bohr effect?

A

As the partial pressure of carbon dioxide rises (in other words, at high partial pressures of CO₂), haemoglobin gives up oxygen more easily

127
Q

Why is the Bohr effect important in the body?

A
  1. In active tissues with a high partial pressure of carbon dioxide, haemoglobin gives up its oxygen more readily
  2. In the lungs where the proportion of carbon dioxide in the air is relatively low, oxygen binds to the haemoglobin molecules easily
128
Q

What is fetal haemoglobin?

A

Found in fetal blood, it has a higher affinity for oxygen than adult haemoglobin. This is important as if both haemoglobins (fetal and maternal) had the same oxygen affinity, little to no oxygen would be transferred from the maternal blood to the fetal blood. As fetal has a higher affinity, it removes oxygen from the maternal blood as they move past each other (oxygenated blood of the mother runs close to the deoxygentated blood of the fetus in the placenta)

129
Q

What 3 ways are carbon dioxide molecules transported from the tissues to the lungs?

A
  1. About 5% is carried dissolved in the plasma
  2. 10-20% is combined with the amino groups in the polypeptide chains of the haemoglobin to form a compound called carbaminohaemoglobin
  3. 75-85% is converted into hydrogen carbonate ions (HCO₃⁻) in the cytoplasm of the red blood cells
130
Q

Carbon dioxide reacts slowly with water to form what? What does this dissociate into?

A
  • Carbonic acid (H₂CO₃⁻)

- It dissociates to form hydrogen ions and hydrogen carbonate ions

131
Q

Carbonic acid reversible reaction symbol equation

A

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

132
Q

What does the enzyme carbonic anhydrase catalyse?

A

It catalyses the reversible reaction between carbon dioxide and water to form carbonic anhydrase (which dissociates to form H⁺ and HCO₃⁻ ions)

133
Q

What is chloride shift?

A

The negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient and negatively charged chloride ions move into the erythrocytes, which maintains the electrical balance of the cell

134
Q

How does haemoglobin (in erythrocytes) act as a buffer?

A

It prevents changes in pH by accepting free hydrogen ions in a reversible reaction to form haemoglobonic acid

135
Q

Which side of the heart does deoxygenated blood flow into?

A

The right

136
Q

What is the heart made out of? Which muscles supply this so that the heart can keep doing its job?

A
  • Cardiac muscle, allowing it to contract and relax in a regular rhythm
  • Coronary arteries supply the cardiac muscle with the oxygenated blood it needs to keep contracting and relaxing all the time
137
Q

What structure in the heart separates the left and right side of the heart, so that oxygenated and deoxygenated blood don’t mix?

A

The septum

138
Q

What type of membrane is the heart surrounded by which helps prevent what?

A

Inelastic pericardial membranes, they help prevent the heart from over-distending with blood

139
Q

Name all the features of the heart (15+1 valves from major artery)

A

Superior/inferior vena cava, right pulmonary artery, right atrium, tricuspid valve (right atrioventricular valve), tendons, right ventricle, aorta (and carotid arteries), left pulmonay artery, pulmonary veins, left atrium, semilunar valves, biscuspid valves (left atrioventricular valves), septum, left ventricle, muscular left ventricular wall

140
Q

Which major blood vessels are found in the right and left sides of the heart?

A
  • Right: Superior/inferior vena cava (vein), pulmonary artery
  • Left: Pulmonary vein, aorta (artery)
141
Q

Flow of blood in the heart

A
  1. Deoxygenated blood enters the right atrium from the upper body and head through the superior/inferior vena cava at relatively low pressure
  2. As blood flows in, slight pressure builds up until the tricuspid valve opens to let blood pass into the right ventricle
  3. When both the atrium and ventricle are filled with blood, the atrium contracts, forcing all the blood into the right ventricle and stretching the ventricle walls. As the right ventricle starts to contract, the tricuspid valve closes to prevent the backflow of blood to the atrium
  4. The right ventricle contracts fully and pumps deoxygenated blood through the semi-lunar valves into the pulmonary artery, which transports it to the capillary beds of the lungs. The semi-lunar valves close to prevent backflow of blood into the heart
  5. At the same time, oxygenated blood enters the left atrium from the lungs through the pulmonary vein
  6. As pressure builds in the left atrium, the bicuspid valve opens between the atrium and the ventricle, filling the ventricle with oxygenated blood
  7. When both atrium and ventricle are filled with blood, the atrium contracts, forcing all blood into the left ventricle and stretching the ventricular walls
  8. The left ventricle contracts fully and pumps oxygenated blood through the semi-lunar valves into the aorta and around the body. During contraction, the tricuspid valve closes, preventing backflow of blood
142
Q

What feature of the heart ensures that valves will not flip inside out by the pressures exerted when the ventricle contracts?

A

Tendons

143
Q

Why is the left ventricular wall much thicker than the right ventricular wall?

A

The left side of the heart has to pump blood around the whole of the body, and also has to overcome the resistance of the aorta and the arterial systems of the whole body, moving blood under pressure to all the body’s extremities. This is compared to the right side, which has to pump the blood a relatively short distance (to the lungs) and only has to overcome the resistance of the pulmonary circulation

144
Q

In a fetus, where is blood oxygenated?

A

In the placenta, not the lungs

145
Q

What is the cardiac cycle?

A

The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, dubbed systole

146
Q

What happens in diastole (cardiac cycle)?

A

The heart relaxes - the atria and then the ventricles fill with blood. The volume and pressure of the blood in the heart build as the heart fills, but the pressure in the arteries is at a minimum

147
Q

What happens in systole (cardiac cycle)?

A

The atria contract (atrial systole), closely followed by the ventricles (ventricular systole). The pressure inside the heart increases dramatically and blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation. The volume and pressure of the blood in the heart are low at the end of systole, and the blood pressure in the arteries is at a maximum

148
Q

Describe aortic pressure (graph)

A

Aortic pressure rises when ventricles contract as blood is forced into the aorta. It then gradually falls, but never below around 12kPa, because of the elasticity of its wall, which creates a recoil action - essential if blood is to be constantly delivered to the tissues. The recoil produces a temporary rise in pressure at the start of the relaxation phase

149
Q

Describe atrial pressure (graph)

A

Atrial pressure is always relatively low because the thin walls of the atrium cannot create much force. It is highest when they are contracting, but drops when the left atrioventricular valve closes and its walls relax. The atria then fill with blood, which leads to a gradual build-up of pressure until a slight drop when the left atrioventricular valve opens and some blood moves into the ventricle

150
Q

Describe ventricular pressure (graph)

A

Ventricular pressure us low at first, but gradually increases as the ventricles fill with blood as the atria contract. The left atrioventricular valves close and pressure rises dramatically as the thick muscular walls of the ventricle contract. As pressure rises above that of the aorta, blood is forced into the aorta past the semi-lunar valves. Pressure falls as the ventricles empty and the walls relax

151
Q

Describe ventricular volume (graph)

A

Ventricular volume rises as the atria contract and the ventricles fill with blood, and then drops suddenly as the blood is forced out into the aorta when the semi-lunar valve opens. Volume increases again as the ventricles fill with blood

152
Q

What are the characteristic ‘lub-dub’ heart sounds made from? What is ‘lub’ and what is ‘dub’?

A
  • They’re made by blood pressure closing the heart valves
  • Lub = comes when blood is forced against the atrioventricular valves as the ventricles contract
  • Dub = comes as a backflow of blood closes the semi-lunar valves in the aorta and pulmonary artery as the ventricles relax
153
Q

Cardiac muscle is myogenic. What does this mean?

A

It has is own intrinsic rhythm at around 60 bpm, preventing the body wasting resources maintaining the basic heart rate

154
Q

What is the average resting heart rate of an adult?

A

70 bpm

155
Q

What factors might affect our heart rate?

A

Exercise, excitement, stress, etc…

156
Q

How is the basic rhythm of the heart maintained?

A
  • By a wave of electrical excitation (similar to a nerve impulse)
  • A wave begins in the pacemaker area called the sino-atrial node (SAN), causing the atria to contract and so initiating the heartbeat. A layer of non-conducting tissue prevents the excitation passing directly to the ventricles
  • The electrical activity from the SAN is picked up by the atrio-ventricular node (AVN). The AVN imposes a slight delay before stimulating the ‘bundle of His’, a bundle of conducting tissue made up of fibres (Purkyne fibres), which penetrate through the septum between the ventricles
  • The bundle of His splits into two branches and conducts the wave of excitation to the apex (bottom) of the heart
  • At the apex the Purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitation triggers the contraction of the ventricles, starting at the apex. Contraction starting at the apex allows more efficient emptying of the ventricles
  • The way in which the wave of excitation spreads through the heart from the SAN, with AVN delay, makes sure that the atria have stopped contracting before the ventricles start
157
Q

What is an electrocardiogram?

A

You can measure the spread of electrical excitation through the heart as a way of recording what happens as it contracts. This recording of the electrical activity of the heart is called an electrocardiogram (ECG). An ECG doesn’t directly measure the electrical activity of your heart. It measures tiny electrical differences in your skin, which result from the electrical activity of the heart. They can be used to diagnose heart problems, such as heart attacks, where reconisable changes take place in the electrical activity of the heart, allowing diagnosis and correct treatment

158
Q

What are the heart rhythm abnormalities that commonly show up on ECGs? (4)

A
  1. Tachycardia - When the heartbeat is very rapid, over 100 bpm. This is often normal, for instance when you exercise, if you have a fever, if your are frightened or angry. If it is abnormal it may be caused by problems in the electrical control of the heart and many need to be treated by medication or by surgery
  2. Bradycardia - When the heart rate slows down below 60 bpm. Many people have bradycardia because they are fit - training makes the heart beat more slowly and efficiently. Severe bradycardia can be serious and many need an artificial pacemaker to keep the heart beating steadily
  3. Ectopic heartbeat - Extra heartbeats that are out of the normal rhythm. Most people have at least one a day. They are usually normal but they can be linked to serious conditions when they are very frequent
  4. Atrial fibrillation - This is an example of an arrhythmia, which means an abnormal rhythm of the heart. Rapid electrical impulses are generated in the atria. They contract very fast (fibrillate) up to 400 times a minute. However, they don’t contract properly and only some of the impulses are passed on to the ventricles, which contract much less often, As a result the heart does not pump blood very efficiently
159
Q

How is blood measured traditionally?

A

By using a manual sphygmomanometer - a cuff, which is connected to a mercury manometer (a way of measuring pressure using the height of a column of mercury), is placed around the upper arm. The cuff is then inflated until the blood supply to the low arm is completely cut off. A stethoscope is positioned over the blood vessels at the elbow. Air is slowly let out the cuff. The pressure at which blood sounds first reappear as a slight tapping sound is recorded. The first blood to get through the cuff is that under the highest pressure - in other words, when the left ventricle of the heart is contracting strongly. The height of the mercury at this point gives the systolic blood pressure in mmHg (the height of the mercury column). The blood sounds return to normal at the point when even the lowest pressure during diastole is sufficient to get through the cuff. This gives the diastolic blood pressure. A reading of 120/80 mmHg is regarded as being normal. More recently, a digital sphygmomanometer is often used - but the same principles apply, with the stethoscope being built into the cuff applied around the arm

A-level Biology (32 decks)

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