Respiratory System

By Dr.C.V.N.MURTHY

Respiration

• is the process of obtaining oxygen from the external environment & eliminating CO2.

​

= External respiration - oxygen and carbon dioxide exchanged between the external environment & the body cells

​

= Internal respiration - cells use oxygen for ATP production (& produce carbon dioxide in the process)

Adaptations for external respiration

1. - Primary organs in adult vertebrates are external & internal gills, swim bladders or lungs, skin, & the buccopharyngeal mucosa

​

• - Less common respiratory devices include filamentous outgrowths of the posterior trunk

& thigh (African hairy frog), lining of the cloaca, & lining of esophagus

Gas..Exchange Organs

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Gills (see Respiration in Fishes)

●

Adult fish have a pair of gills. Each gill is covered by a boney lid (removed from the picture). A fish draws in water by closing the lid over its gills and opening its mouth. When the fish closes its mouth and opens the gill lid the water is forced out and over the respiratory surfaces of the gill filaments.

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3 Gill arches - support the

• gills

GILL

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GILL STRUC.TURE

GILL FILAMENTS

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• Due to the low concentration of oxygen in water, the gills must be as efficient as possible in order to extract oxygen.

​

• The gills consist of bony or cartilaginous arches which hold pairs of gill filaments.

​

• Each gill filament consists of an upper and lower surface covered with minute ridges known as lamellae.

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Bony fishes (teleosts):

(See '

Ventilation in Teleost Fishes')

●

usually have 5 gill slits

​

operculum projects backward over gill chambers

​

interbranchial septa are very short or absent

●

●

●

These lamellae are made of extremely thin

membranes (1 cell thick) and are the primary sites of gas exchange. Water flows across the gill filaments and oxygen is removed and passes into the blood by diffusion. To increase the efficiency of oxygen uptake a countercurrent method is used (the same principle as used in force air furnaces); blood flows through the lamellae in a direction opposite to the water flow through the gill filaments. Countercurrent flow insures a steady oxygen

Cartilaginous fishes:

• 5 ‘naked’ gill slits

●

Anterior & posterior walls of the 1st 4 gill chambers have a gill surface (demibranch). Posterior wall of last (5th) chamber has no demibranch.

​

Interbranchial septum lies between 2 demibranchs of a gill arch

​

Gill rakers protrude from gill cartilage & ‘guard’ entrance into gill chamber

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2 demibranchs + septum & associated cartilage, blood vessels, muscles, & nerves = holobranch

●

●

●

●

Agnathans:

●

​

●

6 - 15 pairs of gill pouches

​

pouches connected to pharynx by afferent branchial (or gill) ducts & to exterior by efferent branchial (or gill) ducts

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• The respiratory system of sharks is markedly different from that of bony fishes. Where bony fishes usually have five gilled arches and only one external gill opening, sharks may have as many as seven openings, but the most common number is five. Also, where the gill arches of bony fishes are protected by

an opercle, or plate, the gills of

sharks are not.

●

Sharks generally inhale most of the necessary water through their mouths, but they are also able to inhale water by way of spiracles, which

are opening located close to the gills. When resting, sharks propel water over their gills using the muscles of their jaws and pharynx. Oxygen from the incoming water is absorbed into the blood system by way of the gill filaments. Water exits through the gill slits

.(Davies, 1964).

Respiratory organs:

Cutaneous respiration

●

respiration through the skin can take place in air, water, or both

​

most important among amphibians (especially the family Plethodontidae)

●

Female P. shermani (Red-legged Salamander) from North Carolina

• Utilize countercurrent exchange(except for

cartilaginous fishes)

​

• 🡪 blood flows oppposite to the direction of water movementg against gills

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• SWIM BLADDERS

Gas or swim bladders of fishes may be located high in the cavity to remain upright

1. Physostomous

​

• Function for respiration

2. Physoclitous

​

• Do not function for respiration

Larval gills:

●

●

External gills

●

outgrowths from the external surface of 1 gill arches

found in lungfish & amphibians

or more

●

●

Filamentous extensions of internal gills

●

​

●

project through gill slits

​

occur in early stages of development of elasmobranchs

●

Internal gills - hidden behind larval operculum of late anuran tadpoles

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- most vertebrates develop an outpocketing of pharynx or esophagus that becomes one or a pair of sacs (swim bladders or lungs) filled with gases derived directly or indirectly from the atmosphere. Similarities between swim bladders & lungs indicate they are the same organs.

Swim bladder & origin of lungs

• Vertebrates without swim bladders or lungs include cyclostomes, cartilaginous fish, and a few teleosts (e.g., flounders and other bottom-dwellers).

Swim bladders:

may be paired or unpaired (seen previous slide)

●

have, during development, a pneumatic duct that usually connects to the esophagus. The duct remains open (physostomous) in bowfins and lungfish, but closes off (physoclistous) in most teleosts.

​

serve primarily as a hydrostatic organ (regulating a fish's specific gravity)

​

gain gas by way of a 'red body' (or red gland); gas is reabsorbed via the oval body on posterior part of bladder

●

●

May also play important roles :

●

hearing - some freshwater teleosts (e.g., catfish,

goldfish, & carp) 'hear' by way of pressure waves transmitted via the swim bladder and small bones called Weberian ossicles (see diagram below)

●

sound production - muscles attached to the swim bladder contract to move air between 'sub-chambers' of the bladder. The resulting vibration creates sound in fish such as croakers, grunters, & midshipman fish.

​

respiration - the swim bladder of lungfish has number subdivisions or septa (to increase surface area) & oxygen and carbon dioxide is exchanged between the bladder & the blood

●

Lungs & associated structures

• Larynx

●

Tetrapods besides mammals - 2 pair of cartilages: artytenoid & cricoid

​

Mammals - paired arytenoids + cricoid + thyroid + several other small cartilages including the epiglottis (closes glottis when swallowing)

​

Amphibians, some lizards, & most mammals - also have vocal cords stretched across the laryngeal chamber

●

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Super-i hor o

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Crycoid Car tilage

C niculate Ca "Iage

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Vocal ugamen

Tile Larynx :v lewed from above

Trachea & syrinx

• Trachea

●

usually about as long as a vertebrates neck (except in a few birds such as cranes)

​

reinforced by cartilaginous rings (or c-rings)

​

splits into 2 primary bronchi &, in birds only, forms the syrinx at that point

●

●

Found in songbirds

Lungs

• Amphibian lungs

●

​

●

2 simple sacs internal lining may

be smooth or have simple sacculations or pockets

air exchanged via p

●

Reptilian lungs

●

●

simple sacs in Sphenodon & snakes

​

Lizards, crocodilians, & turtles - lining is septate, with lots of chambers & subchambers

​

air exchanged via positive-pressure ventilation

●

●

●

Avian lungs - modified from those of reptiles:

●

air sacs (diverticula of lungs) extensively distributed throughout most of the body

​

arrangement of air ducts in lungs ----> no passageway is a dead-end

​

air flow through lungs (parabronchi) is unidirectional

●

●

Mammalian lungs:

●

●

multichambered & usually divided into lobes

air flow is bidirectional:

●

air exchanged via negative pressure ventilation, with pressures changing due to contraction & relaxation of di intercostal muscles

Frog

Uzard

​

​

Parabronc hI I

Nostrils opsn Buccal cavi expards

Nostrils close Glolls o ns

Bucca cavily contracts

Buccal cavity expands

Lungs contracts

Noslrils open

Gloijs clooes

Buccal ca·Aiy con:racts

salamander

tree frog

newt common toad

Glottis (open)

Nares

(closed) Glottis

(o en)

Glottis

(closed)

·Air enters pocket

of buccal cavity

2 • Glottis opens

• Elastic recoil of lungs and compression of chest wall reduces lung volume

·Air forced out of the lungs and out the nares

3 • Nares close

• Floor of buccal

cavity rises

• Air Is pushed

into lungs

4 • Glottis closes

• Gas exchange

occurs in lungs

Inhalation: ribs move forward and outward, thorax expands

I Exhalation: ribs move backward and inward, thorax compresses

Lung

Intercostal muscles

(a) Lung ventilation in lizards

/

/

Expansion//

Compression//

of chest

-"'""'-'<4o

of chest

-=...n•-

Posterior

air sacs

Air

/

Expansion//

ofchest .. ._-

Copyrighl 02009 PeatSon EducaiJOn. Inc..publishing as Pearson Benjamon Cumm>ngs.

Posterior

air sacs

Nares & Mouth

i

Trachea

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r

Trachea

Syrinx

Primary Bronch i

(2)

Posterior

Air Sacs

Anterior Air

Sacs

t

.,..._ Parabronchi

"air capillaries"

.,..._ Dorsobronchi

-... -\---Dorsobronchus

-;---Primary bronchus

Bird lung in

eros section

ntrobronchus