15 - respiration

7/27/2019 15 - Respiration

1/16

Lecture 15

Respiratory Systems and Gas Bladders

Kardong Chapter 11, Hildebrand Chapter 13


2/16

Respiratory Systems

Large surface area.

Thin barrier between blood and air or water.

Flow or exchange of air or water. Favorable diffusion gradient between blood

and air or water.

Organs for external respiration (i.e., gas exchange

with the environment) are required by large, active

animals like vertebrates. Gases include O2 and CO2.

Requirements of external respiratory surfaces:


3/16

The Early Development of GillsGill openings develop in

the pharynx from insideout and from front to

back. Each branchial arch

between these openings

contains an element of the

splanchnocranium (notshown) and a branch of the

ventral aorta.KK 10.22, H&G 13.1


4/16

Gills KK 11.4, H&G. 13.2

Lamprey gills are called

pouched gills and the 7

openings are almost tubular.

Sharks have 5 gill openings

covered by septa. There is a

half-gill or hemibranch onthe hyoid arch, plus 4

holobranchs. The opening

ahead of the hyoid arch is the

spiracle.

Teleosts have 4 branchial

arches without septa, covered

by the operculum.


5/16

External GillsKK 11.4, H&G 13.5External gills are larval

structures found in someOsteichthyes, including

Sarcopterygii, and Amphibia

(rememberNecturus?).

In fish, external gills develop before

pharyngeal gills and are an adaptation

to low O2 environments. (Larval fish

are small enough that under most

conditions they do not need gills.)

Tetrapods, including Amphibia, never

have functional pharyngeal gills.


6/16

Holobranch of a shark.KK 11.17, H&G 13.2

Shark gills are protected

by the gill septa separating

the two halves of the

holobranch.


7/16

Teleost GillsKK 11.19, H&G 13.3Teleost gills are free, in the sense that they do not have a gill septum.

They are protected by the operculum instead. Note the direction of blood

flow in the secondary lamellae, which are like fins on a radiator.


8/16

The direction of water flow

across the gills is opposite to the

direction of the blood flow

within the gill lamellae.

That the water and blood flow in

opposite directions is important;it maintains a constant +ve

gradient for gain of O2 or loss of

CO2. This is called

countercurrent gas

exchange.


9/16

Lungs are evaginations of the

anterior gut behind the gills.

Their surfaces are highlyfolded and vascularized to

maximize gas exchange. This

is not true of fishes that have

lungs that they do not use

(e.g., sturgeon) or fishes that

have gas bladders (teleosts).

Most fish lungs or gas

bladders are dorsal in

position, while tetrapod

lungfish lungs and tetrapod

lungs are more ventral.

Why lungs?

Lungs

KK 11.5, H&G


10/16

Gas Bladders KK 11.22, H&G 13.7

Although some teleostsmaintain a connection

from the gas bladder to

the gut (e.g., trout) most

lose this connection in

development. Eitherway, the gas content of

the bladder is maintained

by adding or removing

gas from the circulatory

system via the red body

and the oval body,

respectively. Some fish

use gas bladders for

sound reception and/or

production.


11/16


12/16

The importance of cutaneous

respiration varies from

100% to near 0.

KK 11.6


13/16

Mammalian lungs,

as illustrated bythe hippopotamus,

have a large

surface area for

respiration because

of their complex

internal structure

of alveoli. In

humans this area is

about 70 m2.

KK 11.36


14/16

Avian Lungs

Avian lungs are small and constant involume, but are associated with

hollow air sacs that take up space in

the body and lighten it. Extensions of

the air sacs penetrate even into the

bones, so they are hollow.

Air flow through the lungs is achieved

not by expanding the lungs

(aspiration) but by action of the

sternum and muscles on the air sacs.

This efficiently capitalizes on theaction of muscles during flight.


15/16

Air passes through bird lungs in

one direction, not tidally, through

air capillaries called parabronchi.

The blood flows through the lungin the opposite direction.

This greatly increases the gas

exchange efficiency of bird lungs

relative to those of other tetrapods.

Diagram of left

lung of a bird.

KK 11.37, H&G 13.12


16/16

The tidal flow of air in the lungs of

mammals and other tetrapods isrelatively inefficient compared to the

cross-current flow of air through the

lungs of birds. Birds can undergo

strenuous exercise (flying) at altitudes

where we would pass out standing still.

KK 11.36, H&G 13.10, 13.13

15 - respiration

Documents