This document summarizes pulmonary ventilation and the respiratory system. It describes the types of respiration including aerobic and anaerobic. It details the structure of the lungs and respiratory pathway in humans. The process of inspiration and expiration are explained as active and passive respectively. Pulmonary values like tidal volume and vital capacity are defined. The countercurrent mechanism that increases gas exchange efficiency in fish gills is described, including how it maintains steep concentration gradients along capillaries. A table compares the surface area, diffusion distance, and respiratory organs used for gas exchange across different organisms.

1. Pulmonary Ventilation
K.Kamatchi
Assistant Professor
Department of Zoology
Vivekananda College
Tiruvedakam West

2. •Types of respiration
• Aerobic respiration
• complete breakdown of glucose
• C6H12O6+6O2⟶6CO2+6H2O+Energy
• Anaerobic respiration
• absence of oxygen
• intramolecular Respiration
• Glucose⟶Alcohol+CO2+Energy
• Anaerobic Respiration in Muscles
• take place in our muscles for a short time
• heavy physical exercise

3. Structure of Lungs:
Man – two lungs
Spongy
Thoracic cavity
Cone shaped
Right 3 lobes
Left 2 lobes

4. Respiratory Pathway
External nostrils
Nasal cavity
Internal nostrils
Pharynx
Larynx
Trachea
Bronchus
Primary bronchi
Secondary bronchi
Teritary bronchi
Terminal bronchi
Bronchioles

5. Alveolar ducts
Wide space – vestibule
Infundibula
Alveolus – air sacs
Pulmonary artery
Pulmonary vein

6. Inspiration
Active process
Contraction of diaphragm
Increase thoracic volume
Contraction of parasternal
Increase lung volume
Intrapleural pressure
Alveolar pressure
Air move into lungs

7. Expiration
Passive process
Decrease lung volume
increase intra plural pressure
Increase alveolar pressure

10. Pulmonary values
Siprometer
Tidal volume (TV) – amount of air exhaled normal inspiration
Expiratory resource volume: (ERV) – forced exhaled air
Inspiratory resource volume: (IRV) – forced inhaled air
Residue volume: can’t forcible exhaled.
Vital capacity: largest volume (IRV + ERV + TV)
Dead space: not gas exchange takes place.

11. Fig: A total volume of activity in rates that ventilation of Lungs through the Inspiration and Expiration

13. Counter Current Mechanism:
Definition:
 Gills efficient oxygen is present in the water.
 efficiency stems from an adaptation known
as countercurrent exchange.
 blood in the capillaries flowing in the opposite
direction to the flow of water.
 Gases diffuse faster from one area to another when
the concentration difference between the two areas is
at its greatest

14. Features of the Counter Current Flow:
1. circulatory systems associated with their specialized gas-exchange surfaces
2. opposite direction to the flow of blood in the gas exchanger. gills of fish and many other
aquatic creatures.
3. The gas-containing environmental water is drawn unidirectional across the gas-exchange
surface, with the blood-flow in the gill capillaries beneath flowing in the opposite direction.
4. almost complete transfer of a respiratory gas 80% of the oxygen in the water flowing over
the gills is generally transferred to the blood.
5. Alternative arrangements are cross current systems found in birds and dead-end air-filled
sac systems found in the lungs of mammals. In a counter current flow system, the blood and
gas moves in the same direction through the gas exchanger. Counter current flow gas
exchange systems are not known to be used in nature.

15. Mechanism of Counter Current Flow:
i. The dissolved oxygen content in fresh water is approximately 8–10 milliliters per liter compared to that of air
which is 210 milliliters per liter.
ii. Water is 800 times more dense than air and 100 times more viscous. Therefore, oxygen has a diffusion rate in
air 10,000 times greater than in water. The use of sac-like lungs to remove oxygen from water would therefore
not be efficient enough to sustain life.
iii. Rather than using lungs, gaseous exchange takes place across the surface of highly vascularized gills. Gills are
specialized organs containing filaments, which further divide into lamellae.
iv. The lamellae contain capillaries that provide a large surface area and short diffusion distances, as their walls
are extremely thin.Gill rakers are found within the exchange system in order to filter out food, and keep the
gills clean.
v. It increases the efficiency of oxygen-uptake (and waste gas loss). Oxygenated water is drawn in through the
mouth and passes over the gills in one direction while blood flows through the lamellae in the opposite
direction.
vi. This countercurrent maintains steep concentration gradients along the entire length of each
capillary "Interaction with circulatory systems“. Oxygen is able to continually diffuse down its gradient into the
blood, and the carbon dioxide down its gradient into the water. The deoxygenated water will eventually pass
out through the operculum (gill cover).
vii. Although countercurrent exchange systems theoretically allow an almost complete transfer of a respiratory gas
from one side of the exchanger to the other, in fish less than 80% of the oxygen in the water flowing over the
gills is generally transferred to the blood.

17. Surface area Diffusion distance
Maintaining
concentration gradient
Respiratory organs
Human
Total alveoli = 70–
100 m2
Alveolus and capillary
(two cells)
Constant blood flow in
capillaries; breathing
Lungs
Fish
Many lamellae and
filaments per gill
Usually one cell Countercurrent flow Gills
Insects
Specialised tracheole
cell
One cell Buccal pumping Spiracles
Sponges Ostia pores One cell Water movement None
Flatworms Flat body shape Usually one cell Countercurrent flow None
Cnidarians Oral arms Usually one cell Water movement None
Reptiles
Many lamellae and
filaments per gill
Alveolus and capillary
(two cells)
Countercurrent flow Lungs
Amphibians
Many lamellae and
filaments per gill
Alveolus and capillary
(two cells) or one cell
Countercurrent flow Lungs, skin and gills
Plants
High density of
stomata; air spaces
within leaf
One cell Constant air flow Stomata
Respiratory system – A biological system of specific organs and structures for gas
exchange in animals and plants.