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BISC1404 Introductory Biology 2 Spring 2024, Exam 3 Predictor Short answer questions
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BISC1404 Introductory Biology 3Spring 2024, Exam 3 Predictor
Short answer questions (24 points Total): Please answer ONLY 2 of the following 4
questions (complete both part a and b for your selections). Diagrams are allowed.
Each Questions has 6 marks/points
Short Answer 1:
Question 1a
In mammals, gas exchange between the atmosphere and the pulmonary blood occurs in the
alveoli. Describe the tissue structure associated with diffusion from the lumen of the
alveolus to the blood.
The tissue structure associated with gas exchange in the alveoli is specialized for efficient
diffusion. Here’s a breakdown of its key components:
1. Alveolar Epithelium: The walls of the alveoli are lined with a thin layer of epithelial
cells called type I alveolar cells (pneumocytes). These cells are flat and cover the
majority of the alveolar surface, facilitating rapid diffusion of gases due to their minimal
thickness.
2. Surfactant Layer: A thin film of pulmonary surfactant lines the alveolar surface,
reducing surface tension and preventing alveolar collapse. This layer also plays a role in
gas exchange by keeping the alveolar surface moist.
3. Interstitial Space: Between the alveolar epithelium and the capillary endothelium is a
very thin interstitial space, which minimizes the distance for diffusion.
4. Pulmonary Capillary Endothelium: Surrounding each alveolus are dense networks of
pulmonary capillaries, lined with endothelial cells that are also thin, facilitating gas
exchange. The walls of these capillaries are very permeable, allowing for the easy
passage of gases.
5. Basement Membrane: The alveolar epithelium and capillary endothelium are separated
by a shared basement membrane, which is also quite thin and further aids in reducing the
diffusion distance.
This combination of thin epithelial and endothelial layers, along with the small interstitial space,
ensures that oxygen and carbon dioxide can efficiently diffuse between the alveolar lumen and
, the bloodstream. The overall structure is highly adapted to maximize surface area and minimize
the barriers to gas exchange.
Question 1b
How does ventilation work in the human respiratory system? What is driving inhalation
and exhalation?
Ventilation in the human respiratory system involves the process of inhalation (breathing in) and
exhalation (breathing out), driven primarily by changes in pressure within the thoracic cavity.
Here’s how it works:
Inhalation
1. Muscle Contraction: Inhalation is mainly driven by the contraction of the diaphragm
and the intercostal muscles (the muscles between the ribs). When the diaphragm
contracts, it moves downward, and the intercostal muscles pull the rib cage upward and
outward.
2. Decrease in Pressure: As the thoracic cavity expands due to these muscle contractions,
the pressure inside the lungs decreases (intrapulmonary pressure falls below atmospheric
pressure).
3. Airflow into the Lungs: This pressure difference causes air to flow into the lungs from
the atmosphere, filling the alveoli.
Exhalation
1. Muscle Relaxation: Exhalation is typically a passive process during quiet breathing,
involving the relaxation of the diaphragm and intercostal muscles. The diaphragm moves
upward, and the rib cage moves downward and inward.
2. Increase in Pressure: As the thoracic cavity decreases in volume, the pressure within the
lungs increases (intrapulmonary pressure rises above atmospheric pressure).
3. Airflow out of the Lungs: This pressure difference causes air to flow out of the lungs
and back into the atmosphere.
Active Exhalation
During vigorous activities (like exercise), exhalation can become an active process, where
abdominal muscles and other accessory muscles (like those in the neck) contract to forcefully
expel air.
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