Mammalian Respiratory System • Mammals (yes that includes humans – Gifty) have a very complex respiratory system that includes: • Breathing= taking air into the lungs (inspiration), andforcing air out of the lungs (expiration) • External respiration=the exchange ofO2 and CO2between air and blood • Internal respiration=the exchange ofO2andCO2between blood and the cells of the surrounding tissue • Cellular respiration=the complex series of chemical reactions in the mitochondria of cells that uses O2to 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 structureswith many folds and fine membranes • Protecteddeep within the bodyby the bone and muscularstructure of the thoracic cavity. • Therefore, we needa passageway to allow air to move from the external environment to the respiratory surface deep insidethe body
The Upper Respiratory Tract • Air first entersthrough the nostril cavity • Or in humans and many other animals, also throughthe mouth • Air passes through hollow nasal passageswhich contain thin bones, called turbinates,that hang suspended from the nasal chambers • Increases the surface area of the nasal chambers and secrete mucus tomoistens theincoming air • The celllinings 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
Upper Respiratory Tract • Air then passesthrough the pharynx, the glottis, and the larynx: • The pharynxconnects the mouth and nasal cavity to the larynx and esophagus • The glottis is the opening of the trachea, the passageway that conducts air to thelungs. • This opening is protected by the epiglottis • The pharynx is thedividing 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 • ashorter 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 arealso 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 theactual exchange of gases takes place • The wall of eachalveoliis 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 bronchiin a relatively permanent position • The alveoli arealso lined with a lubricating film that helps to keep them from collapsing
Lower Respiratory Tract • Each lung is divided into lobes. • The right lung has3 lobes • The left lung has only2. Why? • To accommodate the heart • The lungs themselves are enveloped in layers of tissue called pleura. • Aflexible membranethat contains the lungs while still allowing them to expand and contract duringinspiration and expiration • Each pleuron is made up of two layers separated by a thin film of lubricating fluid