BIO271 Lecture 7 - Respiratory system II

what are gas exchange sites called?

-they are called respiration

-the entire process of respiration

how do cells of the respiratory surface exchange gases?

-they exchange gases with the external (air or water) and internal environment (interstitial fluid)

how do other body cells exchange gases?

-they exchange gases with the internal environment (interstitial fluid) only

how are O2 and CO2 exchanged and transported? (overall process)

1. oxygen exchange at alveolar-capillary interface

2. oxygen transport down through artery

3. then oxygen exchange at cells

4. CO2 exchange at cells

5. CO2 transport up through the veins

6. CO2 exchange at alveolar-capillary interface

what are the 4 factors that affect diffusion if membrane permeability remains the same?

1. surface area

2. concentration gradient

3. membrane thickness

4. diffusion distance

surface area

-diffusion rate is proportional to available surface area

(we want a large SA for diffusion rate to increase)

-constant

constant (surface area)

-remains the same over a long period of time (SA doesn’t change at this point)

concentration gradient

-diffusion rate is proportional to concentration gradient

what are the most important factors of the concentration gradient?

-O2 and CO2 gradients will be present at lung and tissue capillaries

membrane thickness

-diffusion rate is inversely proportional which is why respiratory surfaces are so thin

-constant

constant (membrane thickness)

-number of cells in walls should not change

diffusion distance

-diffusion rate is inversely proportional, another reason why respiratory surfaces are thin

-constant

what are the 3 factors that influence the movement of gases from air into a liquid?

1. pressure gradient

2. solubility

3. temperature

**important for terrestrial species → they have to ventilate their respiratory surface

pressure gradient

-drives gas flow

solubility

-the gas must be able to dissolve in the liquid, diffusion will continue until it reaches equilibrium, increased pressure may dissolve some gas if solubility is low

temperature

-temperature is constant so it doesn’t play a role in the body unless there is pathology

-constant in general (but exercise can change this)

where is the mammalian respiratory system located?

-it is located within the chest cavity (thorax)

what are the 2 tracts the mammalian respiratory system is divided into?

1. upper respiratory tract

2. lower respiratory tract

upper respiratory tract

-consists of the mouth, nasal cavity, pharynx, and larynx

lower respiratory tract

-consists of the trachea, bronchi, bronchioles, lung and alveoli (gas exchange)

what is the conducting zone?

-conduits to gas exchange sites

-includes all respiratory structures from nose to terminal bronchioles

-cleanses, warms, and humidifies air

what is the respiratory zone?

-site of gas exchange

-microscopic structures-respiratory bronchioles, alveolar ducts, and alveoli

what happens as branching of the airways becomes more numerous?

-as this occurs, the wall thins out

what does the alveoli design allow for?

-it allows for increased surface area, that is why they are hexagonal shaped

tidal volume

-total volume of air moved in one ventilatory cycle

dead space

-areas where gas exchange does not occur

-filled with air that does not participate in gas exchange

-air remaining in passageways; ~150 ml (our lungs are never empty or else they would collapse in mammalians)

what are the 2 components of dead space?

1. anatomical dead space

2. alveolar dead space

anatomical dead space

-volume of the trachea and bronchi not involved in gas exchange

-part of the conducting zone

alveolar dead space

-volume of any alveoli that is not being perfused with blood

-since it is not close enough to the circulatory system

what do some birds have?

-some have an extremely long trachea, which greatly increases the dead space

-changes the amount of air that needs to be breathed in and out

what are the components that make up the structure of mammalian lungs?

1. type I cell

2. type II cell

3. alveolar pores

4. alveoli

5. respiratory bronchiole

6. terminal bronchiole

7. diaphragm

what are the 2 types of cells the alveolar epithelium is composed of?

1. type I alveolar cells

2. type II alveolar cells

type I alveolar cells

-most of the alveoli (95%)

-squamous epithelial cells (aka thin cells)

-form the structure of an alveolar wall, gas exchange

type II alveolar cells

-cuboidal cells (thicker)

-maintain the fluid balance across the lungs

-secrete pulmonary surfactant (lipoproteins) to lower the surface tension of water (important for this since water wants to stick together (cohesive) which can collapse the lung)

-surfactant is continuously released by exocytosis

surfactant

-amphiphilic molecules that lower the surface tension between substances (ex. oil and water) allowing them to mix, foam, or disperse

-lipids produced by alveolar type II cells to reduce surface tension by disrupting the cohesive forces between water molecules

alveolar walls

-single layer type I alveolar cells

basement membranes

-~0.5-μm-thick (2 cell walls thick); gas exchange across membrane by simple diffusion

-alveolar and capillary walls are fused at this

what does the respiratory membrane consist of?

• alveolar epithelium

• fused basement membranes of alveolar epithelium and capillary endothelium

• capillary endothelium

what are the 2 things that work required for ventilation depend on?

1. the elastic properties of the lung and chest wall (compliance and elasticity) → we can change how fast we can breathe but not our blood flow

2. the resistance to airflow into the pulmonary airways

compliance

-distensibility (stretchability)

-lungs are 100 x more distensible than a balloon.

-is reduced by factors that produce resistance to distension

-surfactants increase this characteristic of the lung

-scar tissue will reduce this characteristic in the lungs

elasticity or elastance

-tendency to return to initial size after distension (lungs are trying to go back to its smallest size as possible)

-high content of elastin proteins

-very elastic and resist distension

-recoil ability

what happens in emphysema?

-the walls of the alveoli break down

-increases lung compliance, but reduces lung elastance (easily stretched)

what is emphysema?

-a chronic, progressive lung disease and a form of COPD characterized by damaged, inelastic air sacs (alveoli) that cannot properly exchange oxygen and carbon dioxide

what are both our lungs surrounded by?

-they are surrounded by the pleural sac

pleural sac

-surrounds our lungs

-a double-layered serous membrane, that encloses each lung, creating a fluid-filled cavity

what are the 2 layers of cells the pleural sac consists of?

1. parietal pleura

2. visceral pleura

parietal pleura

-on thoracic wall, superior face of diaphragm, around heart, between lungs

visceral pleura

-on external lung surface

pleural cavity

-the space in between the two layers of the pleural sac

-filled with pleural fluid

-provides lubrication and assists in expansion and recoil

what is the process of inhalation/inspiration in mammals? (tidal ventilation)

1. somatic motor neuron innervation

2. contraction of the external intercostal muscles and the diaphragm

3. ribs move outwards and upward, the diaphragm moves down

4. volume of thoracic cavity increases

5. air is pulled in

**need to expand the volume of our thoracic cavity in order to breathe in

what is the process of exhalation/expiration in mammals? (tidal ventilation)

1. innervation stops

2. muscles relax

3. ribs and diaphragm return to their original positions

4. volume of the thoracic cavity decreases

5. air is pushed out via elastic recoil of the lungs (decrease volume of thoracic cavity)

what happens during rapid and heavy breathing?

-exhalation is active via contraction of the internal intercostal muscles

atmospheric pressure (Patm)

-pressure exerted by air surrounding body

-760 mmHg at sea level = 1 atm (atmosphere)

negative respiratory pressure

-less than Patm

positive respiratory pressure

-greater than Patm

zero respiratory pressure

-equal to Patm

what are the 2 types of pressures that are exerted in the thoracic cavity and lungs during process of respiration?

1. intra-alveolar pressure or intrapulmonary pressure (Ppul)

2. intrapleural pressure or intrathoracic pressure (Pip)

intra-alveolar pressure or intrapulmonary pressure (Ppul)

-pressure in the alveoli which fluctuates with breathing

-always eventually equalizes with Patm (because we never completely empty our lungs so when we exhale that’s why that occurs)

Inspiration: Ppul (↓) when lung V (↑)

Expiration: Ppul (↑) when lung V (↓)

intrapleural pressure or intrathoracic pressure (Pip)

-pressure within the fluid of the pleural cavity

-fluctuates with breathing

-always a negative pressure (<Patm and <Ppul)

-fluid level must be minimal

Inspiration: Pip (↓) when lung V (↑)

Returns to initial value as lung V (↓)

transpulmonary pressure

-the pressure difference across the wall of the lung

-keeps the lungs open against the chest wall

→ (Ppul - Pip) = this pressure

what happens if Pip = Ppul or Patm?

-if this happens, the lung collapses

how does negative intrapleural pressure occur?

-it is caused by opposing forces

how many forces promote lung collapse?

-2 inward forces promote this

→elastic recoil of lungs decreases lung size

→ surface tension of alveolar fluid reduces alveolar size

(ex. lung + chest wall pushing inward)

how many forces tend to enlarge lungs?

-1 outward force tends to do this

→ elasticity of chest wall pulls thorax outward

(ex. lung or chest wall)

lung volume

-during each breath, the pressure gradients move 0.5 L of air in and out of lungs

in a graph plotting inspiration/expiration, what value draws in air?

-negative values shows that this in occurring

→ this relates to Boyle’s law because there is no gradient

what is normal intrapleural pressure?

-the pressure difference between the intra-alveolar pressure and intrapleural pressures keeps the lungs inflated

-maintain the integrity of the lungs

what happens to the lung at rest?

-the elastic recoil of the chest wall tries to pull the chest wall outward

-the elastic recoil of lung creates an inward pull

• pressure= -3 mmHg (intrapleural pressure is subatmospheric → negative pressure)

pneumothorax

-air in the lungs (→ if the sealed pleural cavity is opened to the atmosphere, air flows in)

-intrapleural pressure becomes positive

-results in collapsed lung that cannot function normally (lung collapses to unstretched size and rib cage expands slightly)

-there can be no gas exchange that can happen (when this occurs)

(ex. getting stab with a knife in the chest, opening the pleural cavity)

what are 2 ways you can fix pneumothorax?

1. remove the air

2. seal the hole

oxygen carrying capacity

-the amount of oxygen that the blood can carry

metalloproteins

-O2 is 98.5% reversibly bound to this

-contain metal ions which reversibly bind to oxygen and increase oxygen carrying capacity by 50-fold and then deliver it to cells

-referred to as respiratory pigments

what percentage of molecular O2 carried in circulatory fluid is dissolved in plasma?

-1.5% is dissolved in plasma

what is the solubility of oxygen in aqueous fluids?

-solubility of oxygen in aqueous fluids is low

what is the amount of oxygen that can be dissolved in plasma limited by?

-amount of oxygen that can dissolve in plasma is limited at physiological PO2 (→ partial pressure) (refer to Henry’s Law)

what happens by binding O2 to carriers?

-PO2 in the blood remains low and results in improved oxygen extraction

→ because oxygen isn’t contributing to it at that time

what is the driving force of oxygen transport?

-PO2 in the blood remaining low (partial pressure of O2)

what do partial pressure gradients promote?

-they promote gas movements in the body

what happens in the lungs for oxygen transport?

-pressure gradients favour CO2 unloading, and pick up of O2

→ since CO2 is more soluble than O2 (requires a higher pressure gradient than CO2 does)

what happens at the tissues for oxygen transport?

-the pressure gradients favor unloading of O2 and pick up of CO2

-promotes offloading of O2 from the haemoglobin

are the partial pressure gradients for CO2 and O2 the same or different?

-they have very different partial pressure gradients at different parts of the body

what is the primary factor determining whether oxygen is loaded or unloaded onto hemoglobin?

-the primary factor determining whether oxygen is loaded or unloaded onto hemoglobin is the surrounding partial pressure of oxygen

what are metalloproteins responsible for?

1. oxygen-binding molecules that increase the amount of O2 in blood

2. contain metal ions

3. gives them a strong colour (often change colour when bound to oxygen)

what are the 3 major types of respiratory pigments?

1. hemoglobins

2. hemocyanins

3. hemerythrins

hemoglobin (Hb)

-most common type and is found in vertebrates, nematodes, some annelids, crustaceans, and insects

-vertebrate types of this are tetramers

-each chain contains a heme group

-heme molecule containing iron

-reversibly binds O2 and CO2

-usually located within red blood cells (RBCs) (→ usually because sometimes ppl with disorders cause it to be in the plasma instead of RBCS)

-appears red when oxygenated

-1 Hb molecule can bind 4 O2 molecules

-exhibit a cooperativity of binding

-aka multimeric respiratory pigments (mammalian

tetramers

-two α chains and two β chains

heme group

-contain iron

-each group can bind 1 molecule of O2

hemocyanins

-arthropods and mollusks

-contain copper

-copper is complexed directly to amino acids in the protein

-multimeric (up to 48 subunits)

-usually dissolved in the hemolymph

-blue when oxygenated

hemerythrins

-sipunculids, priapulids, brachiopods, some annelids (mostly aquatic organisms)

-do NOT contain heme

-iron directly bound to amino acids in the protein

-usually 2 iron molecules per subunit

-molecules are usually trimeric or octomeric

-violet-pink when oxygenated; colorless when deoxygenated

myoglobin (Mb)

-type of hemoglobin found in vertebrate muscle

-a globular protein

-monomer (different from hemoglobin)

-each Mb molecule binds one molecule of oxygen

-acts as a reservoir of oxygen

-stays in the muscle till it is needed

-bind oxygen independently

-aka monomeric respiratory pigments

what do oxygen-hemoglobin equilibrium curves show?

-it shows the relationship between partial pressure of oxygen (PO2) in the plasma and the percentage of oxygenated respiratory pigment in a volume of blood

P50

-oxygen partial pressure at which the respiratory pigment is 50% saturated

oxygen equilibrium curves (OEC)

-can be expressed as percentage of saturation or as oxygen content in blood

-obey the law of mass action

→ Hb + O2 ←→ HbO2

what happens to the OEC if oxygen concentration increases?

-the reaction shifts to the right

what happens to the OEC if oxygen concentration decreases?

-the reaction shifts to the left

what affects O2 binding by Hb?

-allosteric modulators do this

what are some positive modulators?

1. oxygen → promotes binding to hemoglobin (onloading of oxygen)

what are some negative modulators?

1. H+

2. CO2

3. 2,3-DPG

→ all these promote offloading of oxygen

what is the shape of myoglobins (Mb) OEC?

-it is a hyperbolic shaped curve

cooperativity of binding

-hemoglobin has a higher affinity for oxygen when more of its heme groups are bound to oxygen