NEW! Larynx diagram

RESPIRATORY SYSTEM = responsible for bringing oxygen to blood in lungs or
gills and expelling CO2 from blood.
- Contains large surface area by folding and refolding upon itself; also exhibits:
- Diffusion of gases occurs 2 layers of thin squamous epithelium w/ basal lamina; gases
must be dissolved in fluid in respiratory tract to diffuse (causes water loss
problems in Tetrapods)

Respiratory Structures:
1) Lungs - Terrestrial
2) Gills - Aquatic, in some fish buccal cavity and anterior stomach serve as
accessory respiratory structures
3) Cutaneous - amphibians (esp. lungless salamanders)

- Terrestrial Situation = bidirectional flow (expired and inspired air over same
surfaces), except in birds (unidirectional crosscurrent system)
- Aquatic Situation = water flow over gills is unidirectional, countercurrent
exchange = blood and water pass in opposite directions

Terrestrial Respiratory System consists of paired lungs and branching system of
bringing air to respiratory surface for gas exchange.
- Sequence (anterior to posterior, for mammal):

1) Nasal Cavity
2) Pharynx
3) Larynx
4) Trachea
5) Bronchi
6) Bronchial Tree:
a) Secondary Bronchus
b) Tertiary Bronchus
c) Bronchiole
d) Terminal Bronchiole
e) Respiratory Bronchiole
f) Alveolar Duct
g) Alveolar Sac
h) Alveolus

- Paired, divided by nasal septum
- Open to outside via external (anterior) nares, open interiorly to nasopharynx via
internal nares (choanae)
- Walls of nasal cavities of hyaline cartilage and bone to keep them open
- Consist of 3 regions, anterior to posterior:

Olfactory Epithelium = PSC containing:
Respiratory Epithelium = ciliated PSC with goblet cells; nuclear-free border
about 1/3 of epithelial height; located ventrally in nasal cavity and lines larger
respiratory tubes
- In nasal cavity L. propria composed of cavernous (erectile) tissue - swelling gives
plugged nose; L. propria also contains mucoserous glands

Nasal Conchae (Turbinates) = shelves of bone projecting medially from lateral
walls of nasal cavity
- Covered by a mucous membrane
- Act to increase surface area of nasal cavity; function as countercurrent heat exchanger
(exhaled air temperature is less than body temperature) and therefore
decrease respiratory water loss (since cold air holds less water than warm air)

Larynx = connects pharynx to trachea, tube supported by cartilage interconnected
by dense CT and skeletal muscle; functions to guard respiratory
tract from possible food entry and produces voice
- Vestibular Folds of mucous membrane extend from lateral walls (false vocal
cords). They lie above and protect the Vocal Folds (vocal cords) beneath.
- Vocal Ligaments = elastic fibers in vocal cords with skeletal muscle at core.
Contraction of muscle changes tension and length of cords and opening between them,
thereby creating changes in voice.
- Epiglottis = extension of anterior wall of larynx, supported by elastic cartilage
plate; covers opening to larynx to keep food out

Trachea = shares a large number of characteristics with lesser ducts; contains
mucosa, submucosa, fibrocartilaginous coat (tunic) of adventitia and cartilage; mucosa
and submucosa separated by an elastic membrane


Alveolus = terminal division of respiratory system where gas exchange occurs;
open into alveolar sac, atrium, alveolar duct or respiratory bronchiole.
- Alveoli are tightly packed, partitions (interalveolar septa) separate individual
alveoli. These septa are composed of basement membrane + delicate elastic and
reticular fibers and numerous capillaries
- Alveoli lined primarily by extremely flat simple squamous epithelial cells (Type 1 Pneumocytes)
- Alveolar - Capillary Barrier = simple squamous pneumocyte + fused basement
membrane + simple squamous endothelial cell lining capillary. Varies
from 0.2 - 2.5 Ám in thickness.
- Type 2 Pneumocytes are scattered along alveolar walls. These are rounded cells
incorporated into simple squamous epithelium. Secrete surfactant = phospholipid film that counteracts surface tension forces on alveoli preventing their
collapse on expiration.
- Fibroblasts and Macrophages may be present in interalveolar septa (Septa Cell).

To Lecture 18b