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
airways
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


NASAL CAVITIES
- 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)


RESPIRATORY TUBES
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


SEE HANDOUT FOR CROSS-SECTIONAL STRUCTURE OF RESPIRATORY TUBES

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