06 - Respiratory Systems and Breathing

partial pressure of a gas

the pressure that a particular gas exerts when it is in a gas mixture

Composition of Air

79.04 % Nitrogen

20.93 % Oxygen

0.03 % Carbon Dioxide

The air pressure (atmospheric pressure)

is the sum of the partial pressures of all of the gases within the air plus the partial pressure of water vapour (in the case that relative humidity is anything other than 0%).

Pair = PN2 + PO2 + PCO2 + PH2

At sea level, the atmospheric pressur

760 mmHg

how to calculate the partial pressure of any given gas

you multiply the atmospheric pressure by the fractional concentration of a particular gas.

Hypoxia:

Decreased inspired O2 (PIO2)

Hyperoxia:

Increased inspired O2

Normoxia:

Normal inspired O2

Hypercapnia:

Increased inspired CO2 (PICO2)

Hypocapnia:

Decreased inspired CO2

Normocapnia:

Normal inspired CO

torr

• Torr is a unit of pressure.

• 1 Torr = 1 mmHg (millimeter of mercury).

Air versus Water - oxygen

Air has 30X more oxygen than water.

Air versus Water - oxygen diffusion

Oxygen diffuses 10 000X faster in air than in water.

Air versus Water - Respiratory Effort

Water breathers need to move more water over their gills than air breathers need to move air over their lungs in order to extract the same amount of oxygen.

Air versus Water - density

Water is 1000X denser than air.

Air versus Water - viscous

Water is 50X more viscous than air.

Air versus Water - energy required

More energy is required to move water than air over a respiratory surface

Air versus Water - main takeaway

Water breathers face greater energetic challenges in respiration due to the lower oxygen content, higher density, and higher viscosity of water.

Types of Gas Exchange Organs

• Lungs (always internal)

• Gills (can be internal or external)

• Skin (cutaneous respiration in some animals)

• Specialized structures (e.g., some air-breathing fish use modified gills or buccal cavities)

Ventilation Mechanisms

Active ventilation

Passive ventilation

Active ventilation

involves using muscular contraction to move either air or water across the respiratory exchange surface.

Passive ventilation

involves diffusion of gases across a respiratory surface with no active movement of water or air.

eg of active ventillation

Lungs and internal gills are actively ventilated

eg of passive ventillation

external gills are passively ventilated (i.e.,

they just “flap around” in the water

Types of Ventilation Patterns

Tidal ventilation

Unidirectional ventilation

Non-directional ventilation

Tidal ventilation

Tidal ventilation involves moving the respiratory medium in and out of a respiratory organ.

Tidal ventilation example

in the mammalian lung, air goes in and comes out along the same pathway.

Unidirectional ventilation

Unidirectional ventilation involves moving the respiratory medium in one direction only.

Unidirectional ventilation example

For example, water moves

across the fish gill in a unidirectional manner. It moves in through the mouth and out across theoperculum (see gill structure below).

Air flow through the bird lung is also unidirectional; it “loops around” in a circuit (although it does exit through the same point as it entered).

Non-directionalventilation

“free-floating” in the respiratory media (i.e., water).

Non-directional ventilation example

Non-directional ventilation occurs with external gills that are “free-floating”

External Gills

Protrude from the sides of the animal

external gills are found in which animal

tadpoles and axolotols

external gills - gas exchange

Ventilation is generally passive and non-directional. Oxygen diffuses from the water, across the gills into the haemolymph or blood. CO2 diffuses from the haemolymph or blood, across the gills and into the water

Internal Gills: Aquatic Invertebrates

Squid gills

Gills in decapod crustaceans

Squid gills

sit within the mantle cavity.

Water is moved across these gills in a tidal manner when the animal is moving. Water is sucked into the mantle cavity through an opening at the bottom of the cavity.

muscular contraction of the mantle cavity closes off this intake opening and causes the water to be forcefully ejected through a funnel. This serves to both ventilate the gills and propel the animal forward.

Gills in decapod crustaceans

lobsters

arise from the base of the legs and protrude upward under the shell (carapace).

A muscular structure called scaphognathite pumps water forward through the carapace. Water is drawn in from the back and expelled out of the front. This flow of water serves to ventilate the gills.

Internal Gills: Fish location

They sit under a bony (or cartilaginous) flap of tissue called the operculum.

Internal Gills: Fish water flow

Water enters through the mouth into the buccal cavity. Water then flows across the gills into the opercular cavity and exits via the gill slit (or opercular opening).

how many gills do fish have

In most fish there are four sets of gills on each side of the fish.

gill arch

The main structure of the gills is the gill arch.

gill filaments

Coming off each gill arch are two sets of gill filaments.

secondary lamellae

On all gill filaments there are structures called secondary lamellae with are oriented perpendicular to the gill filament.

blood vessels in Internal Gills: Fish

There are blood vessels that carry deoxygenated blood to the gills and into the gill arches. Blood then enters the gill filaments, flows across the secondary lamellae and collects on the opposite side of the filament before returning to a vessel within the arch.

mechanism of gas exchange in fish gills

countercurrent gas exchange

countercurrent gas exchange

Water flows between the secondary lamellae.

The direction of water flow between the secondary lamellae is opposite to the direction of blood flow within the secondary lamellae.

The lamellae are the site of gas exchange and this mode of gas exchange is referred to as countercurrent gas exchange because the water and blood move in opposite directions. This is an extremely efficient arrangement for gas exchange to occur

process of oxygen diffusion fish gills

As deoxygenated blood enters the secondary lamellae, it encounters oxygenated water flowing across the outside of the lamellae.

Oxygen diffuses across the lamellae into the blood and carbon dioxide diffuses from the blood, across the lamellae and into the water.

Oxygenated blood leaves the secondary lamellae and enters a blood vessel in the filament before moving into the vessel in the gill arch.

do all fishes breathe water

no

obligate air-breathers

breath air all of the time and do not breathe water.

facultative air-breathers

Some fish breathe water when there is enough oxygen in the water but switch to breathing air when the oxygen levels in the water are low (i.e., they are hypoxic).

Air-Breathing Organs

Specialized structures allow fish to extract oxygen from air.

swimbladder

(also called an air bladder or buoyancy bladder)

a air-breathing organ.

Air enters the swimbladder and oxygen diffuses across the swimbladder into the blood

Arapaima gigas

(Piaruchu) is an obligate water-breather as a new-born, a facultative air-breather as juvenile and an obligate air-breather as an adult.

gut for air breathing

Some fish such as catfish and mudskippers exchange gases across their gut. They will swallow air and then oxygen diffuses across the gut into the blood.

Facultative Air-Breathing in Mudskippers

These animals can actually walk on land at which time they are breathing atmospheric air.

• Tide in (burrow entrance covered with water) → Stays in burrow.

  • Initially breathes water

  • As oxygen levels drop in the burrow water switches to breathing air stored in air pockets

• Tide out (burrow entrance open to air) → Moves onto mudflats.

  • Breathes atmospheric air

Lungfish Lungs

From an evolutionary perspective, lungfish are the first animals to have “true lungs”.

Their lungs are sub-divided into numerous compartments which increase the surface area available for gas exchange between the air in the lung compartments and the blood that flows through capillaries within the lungs.

Lungfish Lungs - complexity compared to other lungs

Lungfish lungs are much more complex (in terms of being subdivided into compartments) than are amphibian lungs but they are much less complex than mammalian lungs. They resemble reptilian lungs

Amphibian Lungs

Amphibians have very simple lungs; they are basically “bags-of-air” with no subdivisions into smaller compartments.

There are a few ridges or partitions on the inner wall but these are very small and really don’t do anything to increase the surface area of the lung.

amphibian Lungs - complexity compared to other lungs

• Unlike mammalian lungs, which are highly subdivided into alveoli.

• Amphibians have no trachea (see below for the human lung). nut a glottis

glottis

The amplibian lungs are directly connected to the mouth via a muscular opening called the .

The Mechanics of Breathing in Amphibians

Amphibian breathing involves A) The nostrils (or nares); B) the buccal cavity (or mouth); C) the glottis (the opening to the lungs); and D) the lungs.

The process of Breathing in Amphibians

1. In the first phase of a breathing cycle, the nares are open and the glottis is closed. The floor of the buccal cavity is lowered and this causes air to flow from the external environment, through the open nares and into the lower region of the mouth.

2. In the second phase, the glottis opens and air that was previously being held in the lungs exits the lungs via the glottis, flows across the upper regions of the mouth and leaves the animal via the open nares.

3. In the third phase, the nares close and the floor of the buccal cavity is raised. This causes air to be pumped from the bottom regions of the buccal cavity, through the open glottis and into the lungs. This type of breathing mechanism is therefore called a buccal force pump.

4. In the fourth phase, the glottis closes trapping air in the lungs and the nares re-open.

Reptilian Lungs

more complex than amphibian lungs. but nowhere near as complex as a mammalian lung, They are similar to lungfish lungs in complexity.

begin to see numerous subdivisions into smaller chambers.

Reptilian breathing

Reptilian lungs are suction lungs. Unlike the amphibian buccal force pump, in which muscular contraction causes the floor of the buccal cavity to move up and “pump air into the lungs, in reptiles, anegative pressure is developed which causes air flow in-and-out of the lungs.

purposing subdividing a lung into smaller compartment s

The purpose of subdividing a lung into smaller and smaller chambers is to increase the surface area available for gas exchange.

Bird Lungs - structure

Bird Lungs - structure

• Very different from amphibian, reptilian, or mammalian lungs.

• More similar to dinosaur lungs than to those of any extant species.

• Rigid lungs → Do not change in volume during breathing.

• Air sacs act as pumps/bellows to move air through lungs.

Bird Lungs - division of air sacks

Anterior air sacs

Posterior air sacs

Thoracic air sacs (further divided into anterior & posterior thoracic sacs).

Bird Lungs - Airflow Process

Requires two full cycles of inspiration & expiration to move air completely through the system.

First Inspiration → Air moves from trachea into posterior air sacs.

First Expiration → Air moves from posterior air sacs into lungs (bronchi).

Second Inspiration → Air moves from lungs into anterior air sacs.

Second Expiration → Air moves from anterior air sacs into trachea and out.

• During any single inspiration:

• Air moves from the trachea to posterior air sacs.

• Air moves from the lungs to anterior air sacs.

• During any single expiration:

• Air moves from posterior air sacs to lungs.

• Air moves from anterior air sacs to the trachea (then out).

where does gas exchange take place in birds

There are a series of air capillaries that branch off from the bronchi (labeled parabronchus in the

diagram below to the right). These air capillaries are the site of gas exchange

birds lungs Gas Exchange

• Occurs in air capillaries, which branch off from bronchi (parabronchi).

• Air moves bottom to top through bronchi & air capillaries.

• Blood capillaries run perpendicular to air flow.

• This arrangement enables crosscurrent gas exchange.

Mammalian Respiratory Tract

• Entry of Air:
  Air enters through the mouth or nose, passing through the nasal cavity.

• Upper Respiratory Tract:
  The air moves from the nasal cavity or mouth into the pharynx, then to the larynx.

• Lower Respiratory Tract:
  The air travels down the trachea and branches into the right and left bronchi.

• Bronchial Tree:
  The bronchi divide into smaller bronchioles, leading to the terminal bronchioles, then to the respiratory bronchioles, and finally the alveolar sacs.

• Gas Exchange:
  Oxygen diffuses from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli.

• Exhalation:
  Air moves from the alveoli, through the bronchioles, bronchi, trachea, larynx, and pharynx, and is exhaled through the mouth or nose.

epiglottis

the flap/valve that covers the glottis during the swallowing reflex. It blocks the opening to the trachea and prevents food from entering the trachea and the lungs.

trachea

relatively rigid; it is supported by rings of cartilage that helps prevent it

from collapsing.

alveoli

• Trachea branches into various levels of bronchi.

• Bronchi branch further into smaller bronchioles.

• Bronchioles divide into terminal bronchioles.

• Terminal bronchioles lead to respiratory bronchioles.

• Respiratory bronchioles terminate in alveolar sacs.

• Alveolar sacs contain aggregates of alveoli.

purpose of alveoli

Alveoli are the site of gas exchange.

• Oxygen moves from alveoli into the blood.

• Carbon dioxide moves from the blood into the alveolar air.

how are lungs protected

chest wall

chest wall

contains the ribs, sternum (breast bone),

thoracic vertebrae as well as the internal and external intercostal muscles that sit between the ribs.

diaphragm

the primary respiratory muscle in mammals. It is a curved-shaped muscle that sits below the lungs. The diaphragm is the “border” between the chest (thoracic cavity) and the abdominal cavity.