Gas Exchange

6.4.1 Distinguish between ventilation, gas exchange and cell respiration

Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries

Breathing is NOT respiration! Ventilation Movement of air into and out of the lungs in two stages: inspiration & expiration. Controlled by diaphragm & ribcage. Gas Exchange The exchange (diffusion) of oxygen and carbon dioxide to and from the blood at the alveoli and the respiring tissues Cell Respiration This is production of ATP at the cellular level (mitochondria). Aerobic respiration uses oxygen, whereas anaerobic does not.

Ventilation Movement of gases 1st , in the lungs where oxygen moves from the air into the bloodstream 2nd, in a capillary bed elsewhere in the body where the opposite gas exchange occurs, (O2 & CO2)

6.4.2 Explain the need for a ventilation system

Why do we need a ventilation system? We are large organisms. Oxygen cannot diffuse into all our cells directly from the air, nor can waste products be directly ejected from the body. The ventilation system ensures the blood can be the medium for this.

Why a ventilation system? We are land-borne. Gases need moist surfaces in order to diffuse Lungs are moist membranes Vent. System maintains a large concentration gradients The constant flow of blood past the alveoli brings blood with a high CO2 concentration and low O2 concentration Exhaling keeps the CO2 concentration in the alveoli low, so it diffuses out.

Ventilation System High concentration gradients must be maintained in the alveoli. Breathing in increases the concentration gradient of oxygen between the alveoli & blood (diffuse in) Breathing out removes (CO2) increasing the concentration gradient of CO2 between blood and alveolus – CO2 diffuses out

Gas Exchange If the alveoli were not ventilated, equilibrium would be reached and no gas could be exchanged.

Respiratory Basics

6.4.3 Describe the features of alveoli that adapt them to gas exchange

Alveoli are well adapted to gas exchange Alveoli increase the surface area for gas exchange. Millions in number (300), each with their own network of capillaries Rich blood supply maintains a high concentration gradient of O2 and CO2 Surfaces are wet

Alveoli Membranes are very thin Diffusion path is short Both of the alveoli and the capillaries Diffusion path is short Composed of single layer of cell (2 different types of cells)

2 Types of Pneumocytes Type 1 pneumocytes Type 2 pneumocytes Very thin Large membrane surface area Great for diffusion If damaged – no mitosis Cuboidal in shape Little membrane surface area Produce & secrete a solution that acts as a surfactant Prevents the sides of the alveoli from sticking to each other Damaged – stil mitosis

Which process(es) of membrane transport are being used in gas exchange at the membranes of the alveoli?

How many membranes must an oxygen molecule pass through in order to enter an erythrocyte?

6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli.

6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

Gas Exchange

Gas exchange

Antagonistic Muscles Muscles only work when they contract Opposite state is relaxation Inspiration Expiration diaphragm Moves downward & flattens Moves upward and becomes more domed ribcage Moves upwards and outwards Moves downwards and inwards

Mechanisms of inspiration The diaphragm contracts & at the same time the abdominal muscles and intercostal muscles help to raise the rib cage. All of these help increase the volume of the thoracic cavity. Because of the increase in volume, the pressure inside the cavity decreases. Leads to less pressure “pushing on” the passive lung tissue

Mechanism of inspiration The lung tissue increases its volume because there is less pressure exerted on it. This leads to a decrease in pressure inside of the lungs, also known as a partial vacuum Air comes in through your open mouth or nasal passages to counter the partial vacuum within the lungs

Mechanism of Expiration Previous steps reversed.

Emphysema Alveoli are progressively destroyed Main cause smoking COPD(chronic obstructive pulmonary disease) Turns healthy alveoli into large, irregularly shaped structures with gaping holes

Nature of Science: Epidemiology Epidemiology is the study of the incidence and causes of disease Most studies are observational rather than experimental Survey data is collected

Epidemiology Correlation between a risk factor and a disease does not prove that the factor causes the disease. Example: Association between leanness and increase risk of lung cancer Yet among smokers leanness is not significantly associated with risk So what’s up with this?

Lung Cancer Cancerous growth beginning in lungs Prone to spreading (metastisizing) Lung becomes dysfunctional May cause internal bleeding in the lungs Caused by carcinogens

Lung Cancer Most common cancer in the world Cases and death Smoking causes about 87% of cases Risk increase by number of cigarettes smoked per day & number of years Passive smoking causes about 3% Decreasing with ban of smoking indoors

Lung Cancer Air pollution causes about 5% Diesel exhaust fumes, nitrogen oxides, smoke from burning coal, wood, etc Radon gas causes significant number of cases in some parts of the world Radioactive gas that leaks out of certain rocks (granite)

Lung Cancer Asbestos Silica and some other solids Dust or other particles inhaled Construction sites, quarries, mines, factories