THE MAMMALIAN RESPIRATORY SYSTEM

Mammalian Respiratory System Mammals (yes that includes humans – Gifty) have a very

complex respiratory system that includes: Breathing = taking air into the lungs (inspiration), and

forcing air out of the lungs (expiration) External respiration = the exchange of O2 and CO2

between air and blood Internal respiration = the exchange of O2 and CO2

between blood and the cells of the surrounding tissue Cellular respiration = the complex series of chemical

reactions in the mitochondria of cells that uses O2 to produce ATP and CO2

The Respiratory Tract

Mammalian lungs must be shielded within the body: To prevent water loss – the respiratory surface must

be moist To guard against damage – lungs are delicate, fragile

structures with many folds and fine membranes Protected deep within the body by the bone and

muscular structure of the thoracic cavity. Therefore, we need a passageway to allow air to

move from the external environment to the respiratory surface deep inside the body

Upper Respiratory Tract

The Upper Respiratory Tract

Air first enters through the nostril cavity Or in humans and many other animals, also through the

mouth Air passes through hollow nasal passages which

contain thin bones, called turbinates, that hang suspended from the nasal chambers Increases the surface area of the nasal chambers and

secrete mucus to moistens the incoming air The cell linings of the nasal chambers and the

turbinate bones are well supplied with capillaries warm the incoming air increase its relative humidity

Serves to protect the delicate lung tissue

Turbinates

Upper Respiratory Tract Air then passes through the pharynx, the

glottis, and the larynx: The pharynx connects the mouth and nasal

cavity to the larynx and esophagus The glottis is the opening of the trachea, the

passageway that conducts air to the lungs. This opening is protected by the epiglottis

The pharynx is the dividing point between the trachea (air) and the esophagus (food)

Upper Respiratory Tract The larynx, or “voice box,” contains the two folded

structures of the vocal cords. When you breathe normally, there is a large gap between

the two cords. When you prepare to speak, muscles around the larynx

contract, bringing the cords closer together. The passage of air through this narrower space causes

the cords to vibrate, producing a sound. The pitch of the sound varies with the length of the

cords: a long cord produces a low sound a shorter cord produces a higher sound.

At puberty, the vocal cords of males grow quickly

Upper Respiratory Tract After the larynx, air goes down the flexible tube of the

trachea. The trachea is supported in part by semicircular

cartilage rings. Prevent the trachea from collapsing

The nasal and other passages of the upper respiratory tract are lined with ciliated cells that secrete mucus. Traps foreign particles such as dust and bacteria The cilia helps to propel this material back into the nose

and throat where it can be expelled by coughing or sneezing.

So why do we cough/sneeze more when we’re sick?

The Lower Respiratory Tract

The trachea branches into two smaller passageways called bronchi (singular bronchus)

One bronchus enters each lung

Each bronchus subdivides many times to produce a network of finer and finer tubes called bronchioles. the bronchi and bronchioles are also lined with a

ciliated mucous membrane.

Lower Respiratory Tract Each bronchiole ends in a grape-like cluster of tiny

sacs called alveoli (singular alveolus). In the moist alveoli is where the actual exchange of

gases takes place The wall of each alveoli is one cell thick and is

adjacent to a network of tiny capillaries These capillaries are the site for the exchange of oxygen

and carbon dioxide in the body. Most of the exchange of gases takes place through

simple diffusion, but facilitated diffusion accounts for some (possibly as much as 30%) This allows the blood to take up oxygen more quickly

than would otherwise be possible.

Lower Respiratory Tract In the spaces between the individual

structures of the respiratory tract is elastic connective tissue Keeps the alveoli and bronchi in a relatively

permanent position

The alveoli are also lined with a lubricating film that helps to keep them from collapsing

Lower Respiratory Tract Each lung is divided into lobes.

The right lung has 3 lobes The left lung has only 2. Why?

To accommodate the heart The lungs themselves are enveloped in layers

of tissue called pleura. A flexible membrane that contains the lungs

while still allowing them to expand and contract during inspiration and expiration

Each pleuron is made up of two layers separated by a thin film of lubricating fluid