gas exchange surfaces

Respiratory SystemsChapter 37

2Respiratory Systems

Gas Exchange Surfaces

Respiration:The events associated with gas exchange between the cells and the external environment

Consists of these steps:Ventilation = inspiration (air in) & expiration (air out)External Respiration = gas exchange between external environment & the blood within respiration surfaces. Blood then transports oxygen to the tissues. Internal Respiration = gas exchange between blood & tissue fluid. Cells exchange gases with tissue fluid. Blood transports carbon dioxide back to respiratory surfaces.


Gas Exchange SurfacesFor diffusion to be effective, gas-exchange

tissues must be:Moist because gases must be in solutionThin to allow for rapid diffusionRelatively large in relation to size of body to ensure that cells get oxygen in a timely fashion

Relatively small, and flat, animals don’t need a specialized respiration system:

Planaria - flat, 2-dimensional body allows surface of animal to be gas-exchange surface

Larger, more 3-dimensional animals need specialized gas-exchange surfaces such as gills or lungs.


Gas Exchange Surfaces

Effectiveness of diffusion is enhanced by vascularization:

• Gas-exchange surfaces are usually associated with capillary beds so that oxygen and carbon dioxide can be exchanged efficiently.

Delivery of oxygen to cells is promoted by respiratory pigments such as hemoglobin that can pick up the oxygen and carry it.


Gas Exchange in Water Environments

I. Difficulties obtaining oxygen in water compared to air:

A. Water contains only a fraction of the oxygen that would be present in the same volume of air 1. Oxygen has low solubility in water

0.004% in seawater; 21% in air. B. Diffusion of oxygen in water is thousands of

times slower than in airC. Water is more dense than air

1. Use more energy to respire than do land animals.

•Fish use up to 25% of energy output torespire while terrestrial animals

only use 1-2% of their energy output.


Gas Exchange in Water Environments

II. Small, simple multicellular animals: A. Planaria, hydra

1. Gastrovascular cavity helps put cells in contact with oxygenated water

B. Aquatic worms 1. Use skin that is supplied with blood

vessels

7Animal Shapes and Gas Exchange


Gas Exchange in Aquatic Environments

III. Larger aquatic animals like bony fishes •Often have gills:

Outward extensions of pharynx; said to be evaginated

Have finely subdivided surfaces with a huge total surface area

Contain a rich supply of blood vessels (vascularized)

Ventilation is brought about by combined action of the mouth drawing water in and gill covers (operculum) forcing water out of head area

9Anatomy of Gills in Bony Fishes


Countercurrent Exchange System

Countercurrent Exchange System in Fish Gills: •In lamella of gills:

Blood flows in the direction opposite to the movement of water across the gills.

This maximizes the amount of oxygen picked up by the blood:

- As the blood gains oxygen, it always encounters water having an even higher oxygen content.

- No equilibrium is ever reached. 80-90% of dissolved oxygen is extracted.

If flow of blood was concurrent to water (same direction) an equilibrium point would occur and less oxygen would be transferred into blood.

11Anatomy of Gills in Bony Fishes

12Respiratory SystemsRespiration in

Terrestrial Environments:

Air has much more available oxygen than water but it is a drying environment. Thus, terrestrial animals tend to have invaginated respiratory systems to protect them from too much water loss.

- Exception is earthworms which breathe through their skin but must keep body surface moist by secreting mucus, etc. - Earthworms also do their best to remain in

damp soil during the daytime.

13Respiratory SystemsLand Environments:

Tracheae

Insects and other terrestrial arthropodsRespiratory system consists of branched air tubes called tracheae

Oxygen enters tracheae at spiracles, valvelike openings on each side of the body.

Tracheae branch & branch until they end in tiny channels, the tracheoles, that are in direct contact with body cells.

Very efficient system for delivering oxygen to cells that does NOT involve any respiratory pigments or circulatory system.

14Tracheae of Insects

15Respiratory SystemsLand Environments:

Lungs of VertebratesTerrestrial vertebrates have evolved lungs

Vascular outgrowths from lower pharyngeal region Lungs of amphibians Possess a short tracheae which divides into two bronchi that

open into lungs Many also breathe to some extent through skin

Reptiles Inner lining of lungs is more finely divided in reptiles than in

amphibians Lungs of birds and mammals are elaborately subdivided

All terrestrial vertebrates, except birds, use a tidal ventilation system Air moves in and out by the same route. Thus, fresh incoming air is mixed with some left-over stale air.

16Ventilation in Frogs

Amphibians use both negative & positive pressure to ventilate their lungs:

1. Negative pressure: With mouth closed but nostrils open, the floor of the mouth is lowered. The lower air pressure will cause air to rush into their mouth cavity.

2. Positive pressure: With mouth & nostrils shut, floor of mouth rises & pushes air into the lungs.

17Respiratory SystemsVentilation in

Terrestrial Vertebrates Inspiration in mammals (Inhalation)Create negative pressure in lungs

The rib cage is elevated by intercostal muscles. The diaphragm contracts and pushes down towards belly Thoracic pressure decreases to less than atmospheric pressure

Atmospheric pressure forces air into the lungsExpiration in mammals (Exhalation)Create positive pressure in lungs

The rib cage is lowered as intercostal muscles relax The diaphragm relaxes and rises back up towards chest Thoracic pressure increases to more than atmospheric pressure

Forces air out the lungs

18Inspiration Versus Expiration


Ventilation in Birds

Birds use a one-way ventilation mechanism in lungsHow does this work? - Incoming air does not directly enter the lungs,

instead it is carried by trachea to a set of posterior air sacs.

- Air is then pushed through tiny tubes called parabronchi which are surrounded by capillaries

- Air ends up in anterior air sacs which expel it from body.

Thus, fresh & used air never mix in the lungs of birds. Results in a higher partial pressure of oxygen in the lungs

Oxygen uptake with each breath is greater than in other vertebrates

20Respiratory System in Birds


Human Respiratory System

As air moves through upper respiratory system (nostrils, nasal cavities, pharynx, larynx, trachea): It is filtered to free it of debris (cilia help thisWarmed, andHumidified

When air reaches lungs It is at body temperature, and Its humidity is 100%

22The Human Respiratory Tract


Human Respiratory SystemAir passes from pharynx through glottis, an opening in

larynxLarynx (voice box) contains vocal cords which allow us

to produce soundsTrachea

Permanently held open by cartilage rings Facilitates movement of air

When food is swallowed: The larynx rises, and The glottis is closed by a flap of tissue called the epiglottis

Backward movement of soft palate covers the entrance of nasal passages into the pharynx


Human Respiratory System

Trachea divides and forms two primary bronchiBronchi enter the right and left lungs

Bronchi branch until there are a great number of tiny bronchioles. The walls of bronchioles get thinner & rings of cartilage are no longer present. Each bronchiole terminates in an elongated space enclosed by a great number of air pockets, or sacs, called alveoli. Gas exchange occurs between air in sacs and blood in surrounding capillaries.


Control of Breathing Rate in Humans

Average person takes a breath about 14 times per minute when at restRespiratory control center, located in pons & medulla oblongata of the brain, can change the normal rate according to circumstances.

- When a drop in pH is noted (due to increase in CO2) the control center increases rate & depth of breathing.

- Normally, O2 concentration in blood has little effect on breathing rate. However, if O2 level is very low detectors in aorta & carotid arteries send an alarm to resp. control centers in brain.


Gas Exchange and Transport

External Respiration 1. Blood flowing into pulmonary capillaries has

higher CO2 concentration than air in the alveolar air sacs.

CO2 diffuses out of pulmonary capillaries & into air sacs.

2. Blood coming into pulmonary capillaries has lower concentration of O2 than alveolar air.

O2 diffuses from alveoli into capillaries.

29External and Internal respiration


Transport of OxygenMost oxygen that enters the pulmonary capillaries combines with hemoglobin in red blood cells to form oxyhemoglobin.

- Each of the 4 polypeptide chains of hemoglobin is folded around a heme (iron) group. Iron forms a loose bond with oxygen.

•At normal partial pressure of O2 in lungs, hemoglobin is almost saturated with oxygen.

•At partial pressure of O2 in tissues, oxyhemoglobin gives up much of its oxygen during internal respiration.- Acidity & warm temperatures promote this response in the tissues.

31Hemoglobin

32Hemoglobin Saturationin Relation to Temperature and Acidity


Transport of Carbon DioxideInternal RespirationCarbon dioxide enters blood from the tissues 1. Some carbon dioxide combines with hemoglobin to

form carbaminohemoglobin 2. Most carbon dioxide is transported in the form of

bicarbonate ions (HCO3-)

- CO2 combines with water, forming carbonic acid (H2CO3) & then dissociates into H+ & HCO3

-.- Carbonic anhydrase, an enzyme, speeds up

this reaction. - H+ combines with globin part of hemoglobin

(HHb) & HCO3- diffuses into plasma. This plays

vital role in maintaining proper pH of blood.


Transport of Carbon DioxideExternal Respiration 1. As blood enters the pulmonary capillaries,

most of the CO2 is present in plasma as HCO3

-

2. HHb gives up the H+ it has been carrying & carbonic anhydrase speeds up this

reaction:

H+ + HCO3- H2CO3 H2O + CO2

3. Now free CO2 diffuses out of blood into the

alveoli of lungs.


Respiration and Health

Upper Respiratory Tract Infections

Consists of nose, pharynx & larynx. Infections can spread from nasal cavities to sinuses, to middle ears & to larynxStrep ThroatUsually starts as viral infection that becomes a secondary bacterial infection.Caused by Streptococcus pyogenes. Can become generalized upper respiratory infection.Symptoms: severe sore throat, high fever, white patches on dark red throat



Sinusitis Infection of sinuses, facial cavities that drain into nasal cavitiesDevelops when nasal congestion blocks openings into the sinuses

Tonsillitis Infection of tonsils, masses of lymphatic tissue.Tonsils help to remove pathogens from pharynx

Laryngitis Infection of larynx accompanied by hoarseness & possibly an inability to talk.



Lower Respiratory Tract Infections Infections of trachea, bronchi, bronchioles &

lungsAcute bronchitis Infection of primary and secondary bronchiUsually preceded by a viral upper respiratory infection that led to secondary bacterial infection



PneumoniaViral, bacterial or fungal infection of the lungs in which bronchi and alveoli fill with pus & fluidMost often preceded by influenza, the “flu”.Can be localized in specific lobules of lungs; more lobules the more serious the infectionAIDS patients often get a rare pneumonia caused by a fungus called Pneumocystis carinii.



Pulmonary tuberculosis (TB)Caused by tubercle bacillus, a type of bacterium.Can test people with a simple skin test to see if they have been exposed to tuberculosisReaction to bacterium: 1. When the bacteria invade the lung, the cells

build a protective capsule around the bacteria. This capsule is called a tubercle.

2. With a good immune system the body might kill the encapsulated bacteria

3. With a weakened immune system, like in AIDS, the bacteria can be released & hurt the

body

42CommonBronchial and Pulmonary Diseases


Disorders

Pulmonary fibrosisFibrous connective tissue builds up in the lungsDue to inhalation of particles such as silica, coal dust, asbestos & fiberglass.

Lungs can’t inflate properlyAsbestos also associated with cancer

Chronic bronchitisAirways inflamed and filled with mucusCoughing causes bronchi to undergo changes, including loss of cilia & normal cleansing action

Most frequent cause is smoking.


Disorders

EmphysemaAlveoli are distended (stretched) and walls are damaged reducing surface area available for gas exchange

Often preceded by chronic bronchitisElastic recoil of lungs is reduced; thus expiration is very difficult

Heart works harder to force more blood to lungsSymptoms: breathlessness & cough, depression & irritability


Disorders

AsthmaAirways are unusually sensitive to specific irritantsWhen exposed to the irritants, the smooth muscles in the bronchioles undergo spasms Irritants can be pollen, animal dander, dust, cigarette smoke, fumes & even cold airNot curable but is treatable with inhalers that can control inflammation of bronchioles & prevent attack or stop muscle spasms during an attack


Disorders

Lung CancerBegins with thickening and callusing of the cells lining the airways

Loss of cilia follows; thus it is impossible to prevent dust & dirt from settling into lungs

Atypical nuclei appear in callused liningCreates a tumor of such cellsFinal step is when some cells break loose & penetrate other tissues (metastasis)

gas exchange surfaces

Documents

gasexchange tissues

gasexchange surfacelarger

blood gains oxygen

diffusion of oxygen

cells exchange gases

delivery of oxygen

dissolved oxygen

water environmentsii