Happy Thursday! 2/24/11 Explain the need for, and the mechanism of, ventilation of the lungs in humans. (Total 8 marks)

8 max (Plus up to [2] for quality) Need: draws fresh air / oxygen into the lungs; removal / excretion of CO2; maintains concentration gradient of O2 / CO2 / respiratory gases; Mechanism: diaphragm contracts; (external) intercostal muscles contract; increased volume (of thorax / thoracic cavity); decreasing air pressure in lungs; air rushes in down air pressure gradient; converse of the above causes exhalation; abdominal muscles contract during active exhalation; elastic recoil of lungs helps exhalation;

Chapter 22 Gas Exchange

Surviving in Thin Air Himalayas Have claimed many lives Air at height of world’s highest peak, Mt. Everest Is so low in O2 : most people would pass out instantly if exposed to it!

Twice a year, flocks of geese migrate over Himalayas able to fly at such high altitude b/c lung efficiency have hemoglobin w/very high affinity for oxygen (Adaptation) carry lg amts oxygen to tissues, to exchange with carbon dioxide

The process of gas exchange, often called respiration interchange of O2 and CO2 between an organism and its environment

MECHANISMS OF GAS EXCHANGE 22.1 Overview: Gas exchange involves breathing, transport of gases, and exchange of gases with tissue cells 1 Breathing O2 CO2 Lung Circulatory system 2 Transport of gases by the circulatory system Mitochondria 3 Exchange of gases with body cells O2 CO2 Capillary Figure 22.1 Cell

Gas exchange Provides O2 for cellular respiration and removes its waste product, CO2

22.5 Terrestrial vertebrates have lungs 22.5 Terrestrial vertebrates have lungs In mammals, air inhaled through the nostrils Passes through the pharynx and larynx into the trachea, bronchi, and bronchioles Air tube? Smaller? & Smaller? (Heart) Diaphragm Bronchiole Bronchus Right lung Trachea Larynx (Esophagus) Pharynx Nasal cavity Left lung Figure 22.5A

bronchioles end in clusters of tiny sacs called alveoli Online Review Activity: Labeling Parts bronchioles end in clusters of tiny sacs called alveoli Where gas exchange occurs Process? Colorized SEM 6,200 Oxygen-rich blood Bronchiole Oxygen-poor Alveoli Blood capillaries Figure 22.5B, C

22.6 Smoking is a deadly assault on our respiratory system CONNECTION 22.6 Smoking is a deadly assault on our respiratory system Mucus and cilia in the respiratory passages Protect the lungs Can be destroyed by smoking Structures, features?

Causes lung cancer, heart disease, and emphysema Smoking Causes lung cancer, heart disease, and emphysema Lung Heart Figure 22.6

22.7 Breathing ventilates the lungs 22.7 Breathing ventilates the lungs alternation of inhalation and exhalation

The contraction of rib muscles and the diaphragm Expands chest cavity, reduces air pressure in alveoli (negative pressure breathing) Names of muscles? Air inhaled Air exhaled Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Lung Diaphragm Diaphragm relaxes (moves up) Diaphragm contracts (moves down) Inhalation Figure 22.7A Exhalation

Vital capacity is the maximum volume of air we can inhale and exhale Vital capacity is the maximum volume of air we can inhale and exhale But our lungs still hold a residual volume Who read last night?

Air sacs empty; lungs fill Air flows in one direction Through the more efficient lungs of birds! Air Anterior air sacs Posterior Trachea Lungs tubes in lung 1 mm Exhalation: Air sacs empty; lungs fill Inhalation: Air sacs fill Figure 22.7B

22.9 Breathing is automatically controlled 22.9 Breathing is automatically controlled Breathing control centers in the brain Keep breathing in tune with body needs, sensing and responding to the CO2 level in the blood What gas? Where? Brain Cerebrospinal fluid Pons Medulla Nerve signals trigger contraction of muscles Breathing control centers stimulated by: CO2 increase / pH decrease in blood indicating CO2 and O2 levels CO2 and O2 sensors in aorta Diaphragm Rib muscles Figure 22.8

A drop in blood pH Triggers an increase in rate & depth of breathing

TRANSPORT OF GASES IN THE BODY 22.9 Blood transports respiratory gases heart pumps O2 - poor blood to lungs picks up O2 , drops off CO2 heart pumps O2 - rich blood to body cells drops off O2 , picks up CO2 Where? Where?

Gas transport and exchange in the body Exhaled air Inhaled air Air spaces Alveolar epithelial cells CO2 O2 CO2-rich, O2-poor blood O2-rich, CO2-poor Heart Tissue capillaries Interstitial fluid Tissue cells throughout body capillaries of lung Figure 22.9

Gases diffuse down partial-pressure gradients In the lungs and the tissues Online Animation of Gas Exchange

22.10 Hemoglobin carries O2 and helps transport CO2 and buffer the blood Hemoglobin in red blood cells Transports oxygen, helps buffer the blood and carries some CO2 Molecule? Molecule? Iron atom Heme group O2 loaded in lungs O2 unloaded in tissues Polypeptide chain Figure 22.10

transported as bicarbonate ions in plasma Most CO2 in blood transported as bicarbonate ions in plasma CO2 + H2O H2CO3 H+ HCO3– Carbon dioxide Water Carbonic acid Hydrogen ions Bicarbonate

CONNECTION 22.11 The human fetus exchanges gases with the mother’s bloodstream In the placenta Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Uterus Figure 22.11

Fetal hemoglobin Enhances oxygen transfer from maternal blood At birth, increased CO2 in fetal blood Stimulates breathing control centers to initiate breathing

To be continued...(Reproduction Unit!)

22.2 Animals exchange O2 and CO2 across moist body surfaces 22.2 Animals exchange O2 and CO2 across moist body surfaces Respiratory surfaces Must be thin and moist for diffusion of O2 and CO2 to occur

Some animals, like the earthworm Some animals, like the earthworm Use their entire skin as a gas-exchange organ Cut Cross section of respiratory surface (the skin covering the body) CO2 Capillaries O2 Figure 22.2A

In most animals Specialized body parts provide large respiratory surfaces for gas exchange Body surface Respiratory surface (air tubes) Body cells (no capillaries) O2 CO2 Body surface Respiratory surface (gill) Capillary CO2 O2 Figure 22.2C Body surface Respiratory surface (within lung) Capillary CO2 O2 Figure 22.2B Figure 22.2D

22.3 Gills are adapted for gas exchange in aquatic environments 22.3 Gills are adapted for gas exchange in aquatic environments Gills are extensions of the body That absorb O2 dissolved in water

In a fish, gas exchange Is enhanced by ventilation and the countercurrent flow of water and blood Gill arch Direction of water flow Blood vessels Gill filaments Oxygen-rich blood Oxygen-poor Lamella 15% 40% 70% 100% 60% 80% 30% 5% % O2 in water flowing over lamellae % O2 in blood flowing through capillaries in lamellae Countercurrent exchange Figure 22.3

22.4 The tracheal system of insects provides direct exchange between the air and body cells Land animals Exchange gases by breathing air

Tracheal systems in insects Tracheal systems in insects Transport O2 directly to body cells through a network of finely branched tubes Air sacs Tracheae Opening for air LM 250 Body cell Tracheole Air sac Trachea Body wall CO2 O2 Figure 22.4A, B