Respiratory System

By : Geonyzl L. Alviola

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

    2 - Less common respiratory devices include filamentous outgrowths of the posterior trunk & thigh (African hairy frog), lining of the cloaca, & lining of esophagus

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.    

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.

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

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

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

Cartilaginous fishes:

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

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 

 Larval gills: External gills

outgrowths from the external surface of 1 or more gill arches

found in lungfish & amphibians 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

- 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

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 positive-pressure ventilation

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 diaphragm & intercostal muscles

The End