Outline-2, BIO 3220, Respiratory System


A. Introduction

1. External respiration – Gas exchange between environment & body by diffusion

2. Internal respiration – Gas exchange between blood & cells by diffusion

3. Ventilation – Mechanism of bringing gas in contact with respiratory exchange surface; moving water through gills in fish, breathing to move gas to lungs in most tetrapods

4. Cutaneous respiration – Class Amphibia

B. Pharynx

1. External gills – Found in some urodeles, dipnoans

a. Development – skin ectoderm

b. Function – Begin functioning early in life

2. Internal gills

a. Development

1. Pharyngeal pouches (internal)

2. Visceral grooves (external)

3. Visceral arches

4. Aortic arches

5. Gill opening

b. Structure

1. Gill bar

a. Visceral skeleton

b. Blood vessels & Nerves

c. Branchial muscles

d. Respiratory epithelium = Gill filaments with lamellae

2. Gill septae = Interbranchial septum – Gill bar to body surface

3. Gill rakers

c. Holobranch -Gill filaments on both sides of gill bar, Hemibranch -Gill filaments on one side of gill bar, Pseudobranch – False gill, associated with first gill bar and monitors metabolic (oxygen) requirements to eye

d. Blood flow

1. Afferent branchial Artery

2. Capillary beds for diffusion

3. Efferent branchial Artery

4. Countercurrent flow

e. Absorption and Excretion – Sodium absorption and excretion, Nitrogen waste excretion

f. Gill Classification and Ventilation

1. Pouched gills

a. Agnatha (Ostracoderms & Cyclostomes)

b. External & internal branchial pores

c. Ventilation – In cyclostomes, pulsations of branchial muscles move water in and out of same openings, as the mouth is attached to prey

2. Septal gills

a. Elasmobranchs – Plate gills

b. Gill slits, gill septae

c. Spiracle – First gill pouch modified for water intake

d. Ventilation

3. Opercular gills

a. Operculum – Bony covering of gills

b. Spiracle – In some, such as Chondrosteans

c. Ventilation

C. Development of lungs / swim bladder – Develops from endoderm, but lungs tend to be ventral & swim bladder dorsal; about half of bony fish have swim bladder and more than 20 genera are air breathers. Seen as early as Devonian period. Homology of swim bladder and lungs are clear.

D. Swim bladder of FISH

1. Pneumatic duct – Present during swim bladder development, remains open in some; connects pharynx & swim bladder

2. Physostomous, Physoclistous– Open, closed pneumatic duct

3. Gas pathway-hydrostatic bladder

a. Gas gland – Anterior area of bladder where gas is secreted from bloodstream into bladder

b. Rete mirabile – Miraculous network; red due to blood vessels

c. Countercurrent

4. Ventilation-lung-like bladder – Air gulped into mouth >>>pneumatic duct>>>swim bladder

5. Sound production

6. Sound/pressure reception

-Weberian Ossicles – In some catfish, carp, minnows, ossicles transmits sound waves to inner ear in skull

E. Tetrapod Respiratory Tree

1. General Traits

a. Paired lungs

b. Increased Surface area; compartmentalization

c. Trachea – Tube connecting throat region to bronchial tree

d. Blood flow – Tremendous for gas exchange

2. AMPHIBIANS – Anamniotes ventilate by using a pulse pump to force movement of water or air.

a. Anurans

1. Larynx – Cartilaginous entryway to trachea

a. Glottis – Actual opening in larynx

b. Arytenoid – Flank glottis; support vocal cords

c. Cricoids – Ring-like

2. Trachea, bronchi – Cartilaginous rings

3. Lungs – Location of gas exchange

4. Ventilation (internal nares functional for first time in evolutionary history)

b. Urodeles – Lungs often of minor importance; Respiration through external gills & skin


a. Ventilation

1. Inspiration – Suction used in ventilation in amniotes. Negative pressure in chest cavity due to strong intercostal & abdominal muscles

2. Expiration – Passive due to recoil


a. Larynx

1. Vocal cords

2. Arytenoids – Support vocal cords

3. Cricoid

4. Thyroid – New; “Adam’s Apple”

5. Epiglottis – New, cartilaginous flap to prevent food going into larynx

b. Trachea

1. Cartilage (incomplete rings)

2. Cilia – Function as a upward escalator moving dust & debris out of trachea

c. Bronchi (primary, secondary, tertiary)

d. Bronchioles – Tiniest of airways, lacking cartilage in wall

e. Lungs – Alveoli – Typically several lung lobe containing millions of tiny air sacs called ALVEOLI where gas exchange occurs with blood capillaries

f. Ventilation – Diaphragm – As diaphragm contracts, it moves caudally, which creates negative pressure in thoracic cavity causing air to move into airways during inspiration. As diaphragm relaxes, it moves cranially resulting in air passively moving out of airways.


a. Trachea

b. Bronchi – Primary bronchi divide into:

1. Ventrobronchi – Several

2. Dorsobronchi- Several

3. Parabronchi – Thousands

c. Air capillaries – Open ended in the walls of parabronchi forming a honeycomb appearance

1. Ventilation – Extremely efficient, one way air flow, Air sacs act as bellows to allow continuous ventilation.

2. Diffusion – Air capillaries & blood capillaries

d. Air sacs

1. Abdominal – 2

2. Posterior thoracic – 2

3. Anterior thoracic – 2

4. Cervical – 2

5. Interclavicular – 1

6. Function

a. Ventilation – Allows continuous ventilation of lungs

b. Thermoregulatory

c. Buoyancy – In water fowl

e. Syrinx – In interclavicular air sac region are the birds vocal apparatus; no vocal cords in larynx region