2018 Biology2 Chapter 22. Gas Exchange

MECHANISMS OF GAS EXCHANGE Respiration is the interchange of O2 and CO2 between an organism and its environment

22.1 Overview: Gas exchange involves breathing, the transport of gases, and the servicing of tissue cells Gas exchange is essential because energy metabolism requires O2 and produces CO2 There are three phases of gas exchange The O2/CO2 gas exchange involves the respiratory system and the circulatory system.

22.2 Animals exchange O2 and CO2 through moist body surfaces O2 enters an animal and CO2 leaves by diffusion through a respiratory surface Respiratory surface: the part of an animal where O2 diffuses into the animal and where CO2 diffuses out to the surrounding environment Respiratory surfaces are made up of a single layer of living cells Respiratory surfaces must be moist

Some animals use their entire skin as a gas-exchange organ. e. g Some animals use their entire skin as a gas-exchange organ. e.g., earthworm, flatworm They lack specialized gas-exchange organs

In most animals, specialized body parts carry out gas exchange 1. Gill: extension or outfolding of the body surface specialized for gas exchange. e.g., most aquatic animals

2. Trachea in insects Extensive system of internal tubes specialized for gas exchange Tracheae branch throughout the body, exchanging gases directly with body cells The circulatory system is not needed for the gas exchange

3. Lungs in most terrestrial vertebrates

22.3 Gills are adapted for gas exchange in aquatic environments Gills are extensions of the body that absorb O2 dissolved in water In fish, gill filaments bear numerous platelike lamellae Lamellae are packed with blood vessels They are the respiratory surfaces

The structure of fish gills Four gill arches on each side of the body Two rows of gill filaments project from each gill arch Each filament bears many plate-like structures called lamellae Watermouthgillwater

Blood flows through the lamellae in a direction opposite to water flow This countercurrent maintains a diffusion gradient that maximizes the uptake of O2 Blood flow through lamellae Water flow over lamellae Countercurrent exchange The transfer of something from a fluid moving in one direction to another fluid moving in the opposite direction

22.4 The tracheal system of insects provides direct exchange between the air and body cells Land animals exchange gases by breathing air Air contains more O2 and is easier to move than water But water loss from the respiratory surfaces can be a problem

Tracheal system e.g., insects The tracheal system of insects is made up of air tubes that branch throughout the body Air tube Trachea Tracheole The tiny tips of the tracheoles are closed and contain fluid The circulatory system is not involved in transporting O2 Air sac

Terrestrial vertebrates have lungs e.g., reptiles, birds, mammals, and many amphibians In contrast to the tracheal system, lungs are restricted to one location in the body  the circulatory system is required for transporting O2 The size and complexity of lungs are correlated with an animal’s metabolic rate e.g., the surface area of respiration: endotherm > ectotherm Amphibians have small lungs  respiration through the skin

22.6 In the human respiratory system, branching tubes convey air to lungs located in the chest cavity In humans and other mammals, air enters through the nasal cavity It passes through the pharynx and larynx into the trachea The trachea forks to form two bronchi Each bronchus branches into numerous bronchioles Lungs are located in the chest cavity Diaphragm: contraction of the diaphragm  inhalation

The human respiratory system

The bronchioles end in clusters of tiny sacs called alveoli Alveoli form the respiratory surface of the lungs (the inner surface of alveoli is lined with the simple squamous epithelium) Oxygen diffuses through the thin walls of the alveoli into the blood

22.7 Connection: Smoking is a serious assault on the respiratory system Mucus and cilia in the respiratory passages protect the lungs Pollutants, including tobacco smoke, can destroy these protections Smoking kills about 430,000 Americans each year

Smoking causes lung cancer and contributes to heart disease Smoking also causes emphysema Cigarette smoke makes alveoli brittle, causing them to rupture This reduces the lungs’ capacity for gas exchange

22.8 Negative pressure breathing ventilates our lungs Breathing is the alternation of inhalation and exhalation

Vital capacity is the maximum volume of air we can inhale and exhale But our lungs hold more than this amount The alveoli do not completely collapse A residual volume of “dead” air remains in the lungs after exhalation Figure 22.6C Figure 22.6B Oxygen-rich blood Oxygen-poor blood Alveoli Blood capillaries Bronchiole In-and-out flow of air

22.9 Breathing is automatically controlled Breathing control centers are located in the medulla oblongata (연수, 숨뇌) and pons of the brain These automatic controls keep breathing in tune with body needs Basic breathing rhythm

Cerebrum Forebrain Thalamus Cerebral cortex Hypothalamus Pituitary gland Midbrain Pons Hindbrain Medulla oblongata Spinal cord Cerebellum

During exercise, the CO2 level in the blood rises, lowering the blood pH Sensors in aorta and carotid arteries Monitor O2 and CO2 levels in the blood as well as blood pH Increase in the breathing rate and depth

22.10 Blood transports the respiratory gases TRANSPORT OF GASES IN THE BODY 22.10 Blood transports the respiratory gases The heart pumps oxygen-poor blood to the lungs In the lungs it picks up O2 and drops off CO2 In the tissues, cells pick up CO2 and drop off O2 Gases diffuse down pressure gradients in the lungs and the tissues

Gas exchange in the body Atrium : 혈액이 들어오는 방 Ventricle : 혈액이 나가는 방 The right part of the heart handles oxygen-poor blood The left part of the heart handles oxygen-rich blood The exchange of gases between capillaries and the cells around them occurs by diffusion High partial pressue  low partial pressure

Hemoglobin is a protein in red blood cells It carries most of the oxygen in the blood

Bohr effect Lungs Tissues at rest Tissues during exercise

22.11 Hemoglobin carries O2, helps transport CO2, and buffer the blood Hemoglobin helps buffer the pH of blood and carries some CO2

Most CO2 in the blood combines with water to form carbonic acid TISSUE CELL CO2 produced INTERSTITIAL FLUID CO2 BLOOD PLASMA WITHIN CAPILLARY Capillary wall H2O H2CO3 Carbonic acid RED BLOOD CELL HCO3– + H+ Hemoglobin picks up CO2 and H+ Bicarbonate Most CO2 in the blood combines with water to form carbonic acid The carbonic acid breaks down to form H+ ions and bicarbonate ions These help buffer the blood Carbonic anhydrase in RBC Figure 22.11A

Most CO2 is transported to the lungs in the form of bicarbonate ions ALVEOLAR SPACE IN LUNG CO2 H2O H2CO3 HCO3– + H+ Hemoglobin releases CO2 and H+ Most CO2 is transported to the lungs in the form of bicarbonate ions 7% of CO2 is dissolved in plasma 23% binds to Hb 70% is converted to bicarbonate Figure 22.11B

22.12 Connection: The human fetus exchanges gases with the mother’s bloodstream A human fetus depends on the placenta for gas exchange O2, CO2, nutrients, wastes

A network of capillaries exchanges O2 and CO2 with maternal blood that carries gases to and from the mother’s lungs At birth, increasing CO2 in the fetal blood stimulates the fetus’s breathing control centers to initiate breathing