6 4 Gas Exchange Understanding Ventilation maintains concentration

6. 4 Gas Exchange

Understanding Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles Muscle contractions cause the pressure changes inside thorax that force air in and out of the lungs to ventilate them Different muscles are required for inspiration and expiration because muscles only do work when they contract

Applications External and internal intercostal muscles and diaphragm and abdominal muscles as examples of antagonistic muscle action Causes and consequences of lung cancer Causes and consequences of emphysema Skills monitoring of ventilation in humans at rest and after mild and vigorous exercise

Purpose of the Respiratory System There are three major purposes of the respiratory system: 1. 2. 3. To delivery oxygen to the body To remove Carbon dioxide (a waste product) from the body To clean and filter the air before it enters the body so pathogens cannot enter.

Parts of the Respiratory System The respiratory system is made up of: The mouth and nose The larynx The trachea Bronchi (left and right) Lungs (left and right) The diaphragm

The Lungs Most people think that lungs are like balloons but that is not the case Lungs have lots of space for air but they have a spongy feel to them and are definitely not hollow

Lungs A tube called the trachea that starts at the larynx and branches to form two bronchi These tubes deliver air to the lungs but they are not the only tubes Bronchi divide, and divide until a huge network of tubes permeates the lungs

Lungs Here is a picture of what the tubes look like when the rest of the lung tissue has been cut away

Alveoli The tubes end at tiny hollow sacs that resemble a bunch of grapes These are called alveoli This is where the gas exchange between the lungs and the blood takes place

Alveoli Continued Alveoli are extremely thin and have tiny blood vessels called capillaries surrounding then This is where oxygen, coming from the atmosphere passes into the blood Conversely, carbon dioxide gas that accumulated in the blood passes into the alveoli and is exhaled

Pneumocytes – Cells in Alveoli Type 1 Also called squamous cells Makes up most of the cells in the alveoli Very thin cells where gas exchange takes place Oxygen and CO 2 cross over the wall according to the pressure gradient Type 2 Secrete a substance called surfactant that decreases the surface tension in the alveoli and allows them to stretch and expand

Pneumocytes https: //www. youtube. com/watch? v=v. Cvkwtsh 2 z 0

Alveoli Blood without oxygen is a purplish blue colour and comes to the alveoli to get oxygenated

The Mechanics of Breathing physics: is based on a very basic principle of Increasing volume will decrease pressure Hmmm… What does that mean?

Mechanics of Breathing Air is a gas and it is made up of a mixture of different molecules. Gas pressure is the force that is pushing on the container that the gas is trapped in. If we increase the volume of the container, then the molecules will spread out and won’t be pushing as hard

Mechanics When we contract our diaphragm, we decrease the pressure in the area under our lungs. This causes them to expand. When they expand, air rushes into them from the outside. When we relax our diaphragm, it pushes the air back out into the atmosphere

Antagonistic Muscles make different parts of your body move by contracting. This pulls on your bones and makes them move Most muscles in your body are organized in pairs called antagonistic pairs When one of these muscles contracts, the other one relaxes and lengthens. Each muscle causes an opposite movement when you contract it Example – Bicep and tricep muscles of the arm. The bicep flexes (bends) your elbow while the tricep extends (straightens) it

Muscles of Breathing Muscles Involved With Breathing Include: 1. Diaphragm 2. Intercostals 3. Abdominals

Breathing Muscles that cause Inspiration (breathing in): Diaphragm External intercostals These cause the chest cavity to expand down and out Muscles that cause Expiration (breathing out): Abdominal muscles Internal intercostals Cause chest cavity to restrict up and in See chart on pages 315 -6 of your text book*** Note: Normal expiration doesn’t require any muscle contraction but if you have to force air out quickly, abdominals and intercostals are needed.

Mechanics of Breathing Summary

Mechanics Here’s a simple video: https: //www. youtube. com/watch? v=SWJHSTAWTCk Here’s a more detailed one: https: //www. youtube. com/watch? v=GD-HPx_ZG 8 I