IB Bio Unit 3 B

Gas exchange

Is the exchange of carbon dioxide and oxygen gases at cells and tissues through diffusion.

Large animals require a specialized gas exchange system…

To provide cells with sufficient oxygen for respiration

• More efficient

• Diffusion alone can supply enough oxygen to all cells

Properties of gas-exchange surfaces

• Large surface area: increases the quantity of gas particles exchanged

• Very thin tissue layers: reduces the distance gases must travel

• Permeable membrane: allow the gases to diffuse through them

• Concentration gradient for diffusing gases: allowing gases to diffuse from a high concentration to a low concentration.

• Exchange surfaces are covered in a layer of moisture, allowing the gases to dissolve and diffuse rapidly.

Gas exchange

Exchange of O2 and CO2 at cells and tissue by diffusion

Ventilation

• Movement of air in and out of the lungs, facilitating gas exchange in the alveoli

• Maintains concentration gradients of O2 and CO2

Respiration

Release of ATP energy from organic compounds which occurs in the mitochondria cells.

Adaptations of mammalian lungs for gas exchange

• In a mammal, gas exchange occurs in the Alveoli

label parts of the lungs **look at NOTES

Adaptations around Alveoli

• Branching Bronchioles, which connect to many Alveoli

• All of the alveoli in the lungs provide a very large surface area for gas exchange

• Alveoli secrete a surfactant, which prevents the walls of the alveoli from adhering to each other and provides a moist surface for gas exchange

• Alveoli are surrounded by an extensive capillary bed, which maintains high concentration gradients for O2 and CO2 between the blood and alveoli.

Adaptations of Type I and type II Pneumocytes in alveoli

Type I

• Extremely thin cells

• carry out gas exchange

• cover approximately 95% of the alveolar surface area

Type II

• Rounded cells

• Secrete pulmonary surfactant → reduces surface tension → provides a liquid for rapid diffusion of gases

• Cover 5% of the alveolar surface area

Maintenance of concentration gradients at exchange surfaces in animals

• gases are exchanged by the process of diffusion (passive transport) (high concentration to low concentration)

• Animals need to maintain a high concentration gradient for rapid diffusion of gases

High Concentration gradient

• There is a big difference in the concentration of a substance (like O2 and CO2) between two areas.

• Faster diffusion and more efficient gas exchange

Adaptations to maintain concentration gradients of gases

• A dense network of capillaries: surrounding tissues involved in gas exchange

• Continuous blood flow through the capillaries surrounding the tissues involved in gas exchange

• Structural component:

  • Lungs: ventilation brings oxygen-rich air and removes carbon dioxide

  • Gills: water flow supplies oxygen and carries away carbon dioxide

Ventilation has two stages

• inspiration (breathing in)

• expiration (breathing out)

Inspiration

Diaphragm: Contracts and moves downward

Abdominal muscles: Relax

Internal intercostal muscles: Relex

External intercostal muscles: Contract

Volume: Increases

Pressure: Decreases

Ribcage: Moves up and out

Action: Air - passively moves from the air into the lungs where there is low pressure

Expiration

Diaphragm: relaxes, push the diaphragm upwards

Abdominal muscles: Contract

Internal intercostal muscles: Contract

External intercostal muscles: Relax

Volume: Decreases

Pressure: Increases

Ribcage: moves down and inward

Action: The high pressure in the lungs moves air out of the lungs to the surrounding air, where pressure is lower

Measurement of lung volumes

Tidal volume

The amount of air inhaled or exhaled during normal quiet breathing without effort

AKA

the volume of air that moves in and out of the lungs in a normal breath

Inspiratory Reserve

The amount of air that can be exhaled with maximum effort after a quiet inhalation

Expiratory Reserve

The amount of air that can be exhaled with maximum effort after a quiet exhalation

Vital capacity

The greatest amount of air that can be exhaled with maximum effort after a maximum inhalation (after deepest possible breath)

Vital capacity= tidal volume + inspiratory reserve + expiratory reserve

Methods to measure lung volume

• Spirometers are instruments used to measure the air capacity of the lungs

• Can measure using ballons or water displacement

Adaptations of foetal and adult haemoglobin for the transport of oxygen

• Primary structure: The order of amino acids in the protein chain

• Secondary structure: The chain coils or folds into shapes like alpha helices or beta pleated sheets (depends on the R group)

• Tertiary structure (most enzymes): The chain folds into a 3D shape with a heme group (which holds Iron)
  *The heme group is what the oxygen

• Quaternary structure(further folding of the 3D shape): The four chains joined together to make one hemoglobin molecule that can carry four oxygen molecules

What is a haem molecule made of?

Iron (Fe)

Haem groups can bind to how many oxygens?

1 Oxygen

Each hemoglobin can carry how many oxygens?

4

cooperative binding in oxygen

• Means that when one oxygen attaches to hemoglobin, it makes it easier for the next ones to bind

• When hemoglobin has no oxygen, it doesn’t grab oxygen easily (it needs a high O2 level of start binding)

• But once O2 attaches, hemoglobin changes shapes which makes it easier for more oxygens to stick

Three ways CO2 is transported in the blood?

1. A small amount of CO2 is dissolved in the blood

2. Some CO2 is bound to hemoglobin

3. Most CO2 is reversibly converted to hydrogen carbonate ions and hydrogen ions in red blood cells

Adult Hemoglobin

Has two alpha and two beta chains of polypeptides

Fetal Hemoglobin

Has two alpha and two gamma chains of polypeptides

How is oxygen transferred from the mother’s blood to the fetal blood

• Oxygen is transferred from the mother’s blood to the fetal blood at a faster rate because the maternal blood has a higher partial pressure of oxygen and the fetal blood has a lower partial pressure.

• Fetal hemoglobin has a high affinity for oxygen (oxygen moves from the mother’s to the baby’s)

• Foetal: ability to grab oxygen faster

Bohr shift

Is the shift of the oxygen dissociation curve (to the right) due to carbon dioxide partial pressures

Why does the Bohr shift happen?

High partial pressures of CO2 reduce the affinity of hemoglobin for oxygen, which shift the oxygen dissociation curve to the right
(when there’s a lot of CO2, hemoglobin holds oxugen less tightly, so it releases O2 more easily)

In the lungs ***

• The PCO2 is high because fresh air fills the alveoli

• As a result, O2 diffuses from the alveoli into the blood and binds to haemoglobin, forming oxyhaemoglobin

• The PCO2 is low since CO2 is being exhaled

• Haemoglobin affinity for O2is high, meaning it readily binds to O2

Carbon dioxide and red Blood cells

• Most of the CO2 in the blood diffuses into blood cells and reacts with water to form carbonic acid

• Carbon dioxide reacts with water to form carbonic acid (CO2 +H2O → H2CO3)

• Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions. This reaction is catalysed by carbonic anhydrase (enzyme)
  H2CO3 → HCO3- + H+

• The hydrogen carbonate ion leaves the cell, the chloride ions(cl-) enter the cell. This is known as the chloride shift

• The hydrogen ion binds to haemoglobin, causing a conformational change, which increases the affinity of haemoglobin for oxygen (AKA pick up more oxygen)

• The reactions are reversible, releasing CO2 when the partial pressure of carbon dioxide is low in the blood plasma

What is partial pressure of gas?

Is the pressure extended by a single gas when it is found in a mixture of gases

Partial pressure depends of two things:

• The total pressure exerted by all of the gases in a mixture

• The concentration of the gas in the mixture of gases

*Partial pressure of gases is correlated with the concentration of a gas in solution

An oxygen dissociation curve shows that hemoglobin has a very low affinity for oxygen

AKA

An oxygen dissociation curve shows that at low partial pressures of oxygen, the haemoglobin has a low affinity for oxygen.

As the partial pressure of oxygen increases…

hemoglobin affinity for oxygen increases

At high partial pressure…

The curve flattens as most haemoglobin molecules have four oxygen molecules attached.

(Each haem group can only hold 1 oxygen)

Shape of oxygen dissociation curve

• S-shaped (sigmoid)

• Low oxygen pressure: hemoglobin binds oxygen slowly

• once one oxygen binds, hemoglobin changes shape and grabs oxygen more easily
  

*Example of cooperative binding (one oxygen binds = allows more oxygens to bind)

Oxygen dissociation curve in relation to oxygen in capillaries surrounding the alveoli of the lungs

• This results in a rapid increase in the oxygen saturation of haemoglobin as the partial pressure of oxygen increases, which allows two additional oxygen molecules to bind to haemoglobin
  

• Example of cooperative binding (as attachment of one oxygen enhances affinity of haemoglobin → allowing more oxygen)

• At high partial pressures the curve flattens (as most haemoglobin are saturated with oxygen)

Oxygen dissociation curve in relation to oxygen in capillaires near respiring tissue

• In the lungs, there is a high oxygen pressure, so oxygen moves into the blood

• Haemoglobin binds oxygen easily and becomes fully loaded with oxygen

• Respiring tissues have low oxygen pressure because they use up oxygen.

• At low pressure, haemoglobin holds oxygen weakly and releases it for the cells to use in aerobic respiration

Human transport

Label a heart! Look at notes

Blood flow through the heart

• Deoxygenated blood returns from the body via the superior and inferior vena cava

• Blood enters the right atrium

• It passes through an atrioventricular valve into the right ventricle

• The right ventricle contracts, pushing blood through a semilunar valve into the pulmonary artery

• The pulmonary valve carries blood to thelungs for oxygenation

• Oxygenated blood returns via the pulmonary vein to the left atrium

• Blood passes through an atrioventricular valve into the left ventricle

• The left ventricle, sending blood through a semilunar valve into the aorta

Adaptations to the heart

• Atria

• Ventricle

• Cardiac Muscles

• Pacemaker(sinoatrial node)

• Atrioventricular valve

• Semilunar valve

• septum

• arteries

• veins

Atria

receive blood from the body and lungs

Ventricle

contains lots of cardiac muscle to pump blood to the lungs and the body

Cardiac Muscles

allows the heart to contract to create high pressure

• The cardiac muscle for the left ventricle is much thicker than the right ventricle

• The left ventricle requires high blood pressure to more blood around the body

Pacemaker(sinoatrial node)

Initiates and controls the rate of heart beat

Atrioventicular valve

prevent the back flow of blood from the ventricles to the atria

Semilunar valve

prevent the back flow of blood from the arteries to the ventricles

Septum

prevents oxygenated and deoxygenated blood from mixing

Arteries

Move blood away from the heart at high pressure

Veins

Return blood back to the heart

Capillary

• Are small blood vessels which connect arteries to veins

Function: exchange materials between the blood and cells

Adaptations of capillaries

• Large surface area, as capillaries are highly branched with narrow diameters

• Narrow lumen, which is wide enough for one red blood cell to pass through at a time

• Thin walls allow rapid exchange of materials by diffusion. Capillaries are typically one cell thick

Structure of artery vs vein

Artery: have a relatively thick wall and narrow lumen

Vein: have a relatively thin wall and wide lumen

Adaptations of arteries for the transport of blood away from the heart

• Arteries have a thick wall, allowing them to withstand high blood pressure

• Collagen in the outer wall of the artery strengthens the artery to withstand high blood pressure

• Smooth muscle in the artery can contract to maintain blood pressure between heartbeats

• Elastic fibers in the artery wall allow the arteries to stretch and recoil as pressure increases and decreases due to heartbeats. The recoil helps keep the blood moving in the artery

• A narrow lumen helps maintain high blood pressure

• The lumen is lined with smooth endothelial cells, which reduces friction as blood flows

Adaptations of veins for the return of blood to the heart

• Veins return blood to the heart

• Blood returning to the heart is moving slowly, and is not under high pressure

• Valves in veins prevent the back flow of blood

• Thin wall, which allows the veins to be compressed by skeletal muscles. The compression moves blood back to the heart

• Wide lumen, which allows the veins to carry a large volume of blood

Summary of artery vs veins

Artery:

• Lumen: narrow, maintaining high pressure

• Direction of blood flow: away from the heart

• Valves: none

Veins:

• Lumen: wide

• Direction of blood flow: Back to the heart

• Valves: prevent backflow of blood

Atherosclerosis

is the hardening and narrowing of the arteries due to the build of cholesterol, triglycerides, and other substances on artery walls

Occlusion of Arteriosclerosis

• Coronary arteries branch from the aorta to supply the heart with oxygen and nutrients

• If these arteries become blocked by atherosclerosis it can cause heart tissue to die, leading to a heart attack

Cause of arteriosclerosis

• Macrophages move to damaged areas in arteries

• They release growth factors that cause fibrous tissue to form

• Macrophages absorb cholesterol and create plaque

• Plaque builds up over time, narrowing or blocking the artery

• If plaque breaks loose, it can cause a blood clot

Risk factors for arteriosclerosis

Not under our control:

• Genetics: several genes are associated with increased risk of arteriosclerosis

• Age: as the arteries of older poeple are more likely to be damaged

• Gender: males are more likely to develop arteriosclerosis

Under our control:

• Obesity: which increases blood pressure and damages artery walls

• Physical inactivity: can lead to obesity

• Smoking: which increases blood pressure

• A diet high in fats and cholesterol

Pearson coefficient

Measures the strength of the relationship between variables

• To quantify correlations between variables and allow the strength of the relationship to be assessed.

What does a correlation coefficient close to -1, +1 and 0 mean?

-1: strong negative correlation

+1: strong positive correlation

0: no correlation between variables

Correlation does not indicate causation!

Relationship between saturated fat intake and deaths from coronary heart disease

A strong positive correlation!

• Evidence suggests saturated fat increases heart disease risk

The R value is 0.92 (closer to +1)

Tissue fluid

• Surrounds cells, enabling the exchange of materials between the blood and cells

• Is formed by the liquid part of the blood plasma, leaking out of capillaries

Release of fluid tissue

• Blood leaves an artery at high pressure and enters a capillary

• The high hydrostatic pressure of the blood filters the blood plasma through the gaps in the capillaries, forming tissue fluid

Reuptake of fluid tissue

• Blood pressure decreases as the blood moves along the capillary

• Plasma proteins decrease the osmotic potential of the blood

• Most of the tissue fluid returns to the blood by osmosis due to oncotic pressure, which is higher than the hydrostatic pressure

*Oncotic pressure: pressure with proteins

How is fluid tissue formed?

When high blood pressure forces small molecules and solutes out through tiny gaps in the walls, while large proteins and blood cells remain in the blood

Compare and contrast the composition of blood plasma and tissue fluid

Both tissue fluid and blood have(COMPARE):

• Dissolved nutrients

• Dissolved oxygen

• Metabolic waste, including CO2

• White blood cells

Only blood has(CONTRAST):

• Red blood cells and platelets

• Large plasma proteins

Role of tissue fluid

Surrounds cells and its function is the exchange of materials

• Has high oxygen and nutrient levels and low waste levels

• cells use O2 and nutrients for metabolism, producing CO2 and wastes.

• O2 and nutrients diffuse from tissue fluid into cells (passive)

• Metabolic wastes like CO2 diffuse from cells into the tissue fluid (facilities)

How does tissue fluid move from blood → lymph nodes → back to the blood

• Tissue fluid that doesn’t re-enter the blood becomes lymph

• Lymph moves through the lymphatic system

• It passes through lymph nodes and is eventuay returned to the bloodstream

Adaptations of lymph vessels

• Gaps: in the walls of the lymph ducts, which allow tissue fluid to enter

• Thin walls: which are compressed by skeletal muscles to move the lymph fluid

• Valves: prevents backflow of lymph fluid

Differences between the single circulation of bony fish and the double circulation of mammals

Single circulatory system

• Fish have a single circulatory system

  • The ventricle pumps blood from the heart to the gills

  • gas exchange occurs in gill capillaries - oxygen enters, CO2 leaves

  • oxygenated blood travels from the gills to the body tissues

  • gas exchange occurs again in tissues, oxygen is used, and CO2 is produced

  • Deoxygenated blood returns to the heart

Double circulatory system

• Mammals have a double circulatory system

  • The right side of the heart pumps blood into the lungs

  • Gas exchange in the lungs: oxygen enters and CO2 leaves

  • Oxygenated blood returns to the left side of the heart and is pumped to the body

  • Gas exchange in body tissues: oxygen is used, CO2 is produced

  • Deoxygenated blood returns to right side of the heart

What controls the rate at which heart beats

• cardiac muscle is myogenic as it contracts without stimulation

(Cardiac muscles don’t need a nerve to initiate contractions)

• The sinoatrial node (pacemaker) controls the rate of heart beat

Stages in the cardiac cycle

1. SA node: sinoatrial node/pacemaker

2. AV node: Atrioventricular node

3. AV Bundle: Bundle of HIS

4. Right and left ventricles bundle branches

5. Purkinje fibers

SA node

The pacemaker of the heart: it initiates the electrical signal that causes the atria to contract

AV node

Delays the signal briefly to ensure the atria finish contracting before the ventricles contract

Bundle of HIS

The electrical impulse travels from the AV node through the Bundle of HIS, which carries the signal down the septum between the ventricles

Left and right bundle branches

The signal spreads down both sides of the septum toward the apex (tip) of the heart

Purkinje Fibers

The impulse moves upward through the ventricles, causing ventricular contraction from the apex toward the top of the heart, efficiently pumping blood out

*Right ventricle: sends blood to the lungs through pulmonary arteries
Left ventricle: sends blood to the rest of the body through the aorta

Systole

Is the contraction of hear muscles

Dystole

Is the relaxation of heart muscles

Blood pressure measures….

• Systolic pressure: caused by ventricular systole (higher number)

• Diastolic pressure: between ventricular contractions (lower number)

A healthy blood pressure is

120/80

A high blood pressure is

140/90