Biology Chapter on Animal Respiration

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Questions and Answers

What is the primary function of respiration in animals?

To obtain oxygen and eliminate carbon dioxide (correct)

To maintain body temperature

To facilitate muscle movement

To circulate nutrients throughout the body

Which statement accurately describes the role of partial pressure in gas exchange?

Gases diffuse from regions of higher to lower partial pressure. (correct)

Gases move toward regions of higher partial pressure.

Gases do not rely on partial pressure differences to diffuse.

Gases diffuse from regions of lower to higher partial pressure.

Which of the following is NOT a step in the gas-transfer system of animals?

Diffusion across capillary walls

Breathing movements

Diffusion across respiratory epithelium

Photorespiration in tissues (correct)

Which characteristic is essential for effective diffusion in gas-exchange regions?

Moist and thin respiratory surfaces Signup and view all the answers

Why is obtaining oxygen from water more challenging than from air?

There is less available oxygen in a given volume of water compared to air. Signup and view all the answers

What is the role of methemoglobin reductase in the body?

It reduces methemoglobin to its functional ferrous form. Signup and view all the answers

What structural feature is shared by the globin molecule?

It is composed of two dimers, each forming a tightly cohering unit. Signup and view all the answers

What occurs to hemoglobin upon oxygenation?

Conformational changes occur that alter salt bridges. Signup and view all the answers

What condition prevents hemoglobin from binding oxygen effectively?

Oxidation of Fe2+ to Fe3+ in methemoglobin. Signup and view all the answers

Which compounds are known to impair oxygen transport by affecting methemoglobin levels?

Nitrites and chlorates. Signup and view all the answers

What is the primary result of carbon monoxide's higher affinity for hemoglobin compared to oxygen?

It leads to the formation of carboxyhemoglobin. Signup and view all the answers

How does the oxygen saturation of hemoglobin change with varying partial pressures of oxygen (Po2)?

It increases until all binding sites are occupied. Signup and view all the answers

Which of the following statements accurately describes hemoglobin's oxygen transport capacity?

Human blood has an oxygen capacity of 20.2 vol%. Signup and view all the answers

Which pigment is characterized by its ability to bind oxygen and can immediately turn blood bright red upon saturation?

Carboxyhemoglobin Signup and view all the answers

What is the significance of the oxygen dissociation curve in relation to hemoglobin function?

It illustrates the relationship between percent saturation and oxygen partial pressure. Signup and view all the answers

What is the role of hemoglobin in the blood?

It carries oxygen and increases oxygen transport capacity. Signup and view all the answers

What is the Bunsen solubility coefficient for oxygen at 37°C?

0.3 ml of oxygen per 100 ml of blood per atmosphere of pressure. Signup and view all the answers

How does the color of hemoglobin change with oxygen content?

It transitions from bright red when oxygenated to dark maroon-red when deoxygenated. Signup and view all the answers

What is the molecular weight of hemoglobin?

68,000 Signup and view all the answers

Which component of hemoglobin is responsible for binding oxygen?

The heme groups containing iron Signup and view all the answers

How much oxygen can blood carry without respiratory pigments?

0.3 vol % O2 Signup and view all the answers

Which of the following best describes the composition of hemoglobin?

A tetrameric protein with four iron-containing porphyrin groups Signup and view all the answers

In what state does hemoglobin primarily exist when it is oxygenated?

Oxyhemoglobin Signup and view all the answers

What occurs during inhalation in terms of diaphragm and rib muscles?

Diaphragm contracts and rib muscles relax Signup and view all the answers

Which structure is responsible for carrying deoxygenated blood to the lungs?

Pulmonary arteries Signup and view all the answers

How do avian lungs differ from mammalian lungs in terms of air movement?

Air flows through air sacs for efficient gas exchange Signup and view all the answers

Which group of the brain is primarily responsible for maintaining the basic rhythm of respiration?

Medullary rhythmicity area Signup and view all the answers

What is the role of the intercostal muscles during respiration?

Lift ribs to expand the chest cavity Signup and view all the answers

Which factor has the least influence on the control of breathing under normal circumstances?

Blood O2 levels Signup and view all the answers

During forced expiration, what mainly happens in relation to the diaphragm?

Diaphragm relaxes, increasing abdominal pressure Signup and view all the answers

What happens to the thoracic cavity volume during expiration?

It decreases, forcing air out Signup and view all the answers

What is the significance of the 'root' of the lung?

It contains all vessels, nerves, and lymph vessels entering the lung Signup and view all the answers

What type of breathing is primarily used by mammals to ventilate their lungs?

Negative pressure breathing Signup and view all the answers

What shape do the oxygen dissociation curves of myoglobin and lamprey hemoglobin have?

Hyperbolic Signup and view all the answers

What causes hemoglobin to undergo a conformational change in the lungs?

Oxygenation of the molecule Signup and view all the answers

In tissue capillaries, what is favored due to the partial pressure gradients?

O2 diffusion into the interstitial fluids Signup and view all the answers

Which type of oxygen dissociation curve is typically seen in other vertebrates' hemoglobin?

Sigmoid Signup and view all the answers

What is the state of blood arriving in the lungs in terms of CO2 concentration?

Low partial pressure of O2, high CO2 Signup and view all the answers

What role do the alveolar epithelial cells play in gas exchange?

Facilitate diffusion of O2 and CO2 Signup and view all the answers

What type of heme structure does myoglobin possess?

Single heme group Signup and view all the answers

What is the primary factor enabling O2 diffusion from the alveoli into the blood?

Pressure gradient Signup and view all the answers

Study Notes

Respiration

Respiration is the process of obtaining oxygen from the environment and eliminating carbon dioxide.
Cellular respiration refers to the oxidative processes within cells.
External respiration involves gas exchange between the organism and its environment.

Physical Properties of Gases

Partial pressure (Px) is the individual pressure of a gas in a mixture.
Gases diffuse from areas of higher Px to areas of lower Px.
The rate of gas diffusion is determined by the formula: Rate = KA (P1-P2)/d.

Partial Pressure Gradients in Gas Exchange

Gases diffuse down pressure gradients. Differences in partial pressure cause this diffusion.
Partial pressure is the pressure of a specific gas in a mixture.
Gases diffuse from a region of higher partial pressure to a region of lower partial pressure.
In the lungs and tissues, oxygen (O2) and carbon dioxide (CO2) diffuse from higher partial pressures to lower partial pressures.

Components of the Gas-Transfer System

Breathing movements ensure a continuous supply of air or water to the respiratory surface (e.g. lungs or gills).
Diffusion of O2 and CO2 occurs across the respiratory epithelium.
Bulk transport of gases happens through the blood.
Diffusion of O2 and CO2 happens between blood and mitochondria in tissue cells.

Gas Exchange Surfaces

For effective diffusion, gas exchange regions must be: moist, thin, relatively large, and in contact with the environment.
The effectiveness of diffusion is enhanced by vascularization.

Respiratory Media

Animals use air or water as a respiratory medium.
There is less oxygen available in water than in air.
Obtaining oxygen from water requires greater efficiency compared to air breathing.

Ventilation (Breathing)

Ventilation is a convection process that moves respiratory medium (water or air) over exchange membranes.
Ventilation can be passive or active (nondirectional, unidirectional, or bidirectional).

Types of Ventilation

Unidirectional ventilation is common in fish gills; water flows continuously through the mouth, across the gill curtain, and out.
Bidirectional or tidal ventilation occurs in lung ventilation, with air entering and exiting through the same channel.

Patterns of Gas Exchange

Countercurrent flow is seen in fish gills, with water and blood flowing in opposite directions to maximize gas exchange.
Crosscurrent flow is observed in avian lungs, where airflow and blood flow cross each other obliquely.
Uniform pool is a type of ventilation found in mammalian lungs, where the partial pressure of gases is kept uniform throughout the alveoli.

Respiratory Organs

Gills or branchiae are both external and internal structures that facilitate gas exchange in some animals.
Lungs are localized organs that perform gas exchange in many animals.

How a Fish Ventilates its Gills

Fish gills are ventilated by the movement of water. The operculum expands and closes to direct the water flow over the gills.

Respiration in Sharks and Teleosts

Sharks and teleosts have different gill structures and ventilation mechanisms.

Countercurrent Flow/Exchange

Countercurrent exchange is an efficient way to exchange substances between two fluids flowing in opposite directions.

Lungs

Lungs act as localized organs for gas exchange. Different animal groups have different lung structures, with examples like salamanders, frogs, lizards, birds, and mammals.

Respiratory system (mammals)

The respiratory system in mammals consists of branching ducts to convey air to the lungs. The system features a pharynx, larynx, esophagus, trachea, bronchus, bronchioles, alveoli, and diaphragm.

Hair-like projections called cilia

Cilia line the primary bronchus to remove microbes and debris from the interior of the lungs to maintain the respiratory system. (mammals)

Breathing - alternating inhalation and exhalation

Breathing, or pulmonary ventilation, is the process of inhalation and exhalation, which ventilates the lungs. In frogs, this is achieved via positive pressure breathing.

Mammals ventilate their lungs by negative pressure breathing

Mammals use negative pressure breathing to ventilate their lungs. Rib cage expansion and diaphragm movement create a lower pressure in the lungs, drawing air in.

Accessory respiratory muscles

Pectoralis, scalene, and external intercostals are inspiratory muscles
Transversus and internal intercostals are expiratory muscles.

Breath volume (L) - Various pressures during breathing (mmHg)

Various pressures (atmospheric, alveolar, transpulmonary, and intrapleural) fluctuate during inspiration and expiration. Diaphragm and intercostal muscle contraction and relaxation lead to changes in these pressures.

Breathing - important activity

Breathing is essential to supply oxygen needed by all body cells. Respiratory muscles are used to control the volume of the thoracic cavity, thus ventilating the alveoli. Breathing consists of inspiration and expiration.

How does air get to alveoli?

The trachea branches into primary bronchi, which further divide into secondary bronchi (one for each lobe). These divide into tertiary bronchi and bronchioles, the smallest respiratory tubes. Alveolar ducts and sacs lead to alveoli, where gas exchange occurs. Vessels accompany the respiratory tree extending all the way to the alveoli.

Located in pleural cavities

Lungs are located in pleural cavities. The apex is posterior to the clavicle, and the base rests on the diaphragm. The root is where vessels, nerves, and lymphatics enter the lung. Pulmonary veins take oxygenated blood from each lung to the heart. Pulmonary arteries carry deoxygenated blood to each lung for oxygenation.

Primary muscle of respiration (involuntary)

The diaphragm is the primary involuntary muscle for respiration.
Diaphragm contraction increases thoracic cavity volume and decreases pressure, pulling air into the lungs.
Diaphragm relaxation decreases thoracic cavity volume and increases pressure, pushing air out of the lungs.

Forced contraction (voluntary)

Forced contractions (voluntary) increase abdominal pressure to help with activities like urination, labor, or defecation.
These contractions also push the abdominal organs to expel their contents.

Intercostal muscles lift ribs to expand the chest cavity for inspiration

External and internal intercostal muscles work together to move ribs for inspiration.

Avian lungs – no blind-ended alveoli

Avian lungs differ from mammalian lungs. They do not have alveoli but instead parabronchi and air sacs. Air flows through parabronchi and air sacs during both inhalation and exhalation, providing continuous gas exchange.

Air sacs

Air sacs connect to the parabronchi. These are voluminous thin-walled diverticula of the lungs extending throughout the body.

Birds – gas transfer

Birds have a unique, extremely efficient respiratory system. Gas transfer occurs in small air capillaries, and air sacs participate in both inhalation and exhalation phases.

Bird respiratory system

Birds have an extremely efficient system. Air sacs fill and empty and participate in both inhalation and exhalation phases, enabling continuous gas exchange.

Control of Breathing - Chemical control of breathing

Breathing depends on blood CO₂ levels, which influence pH. CO₂ reacts with water to form carbonic acid, increasing H⁺ concentrations. Chemoreceptors (central and peripheral) monitor H⁺ and CO₂ and send signals to control the rate and depth of breathing. Oxygen levels are less important for regulating breathing unless they are very low.

Control of Breathing - Nervous control

The cerebral cortex controls voluntary breathing, while involuntary breathing is governed by the respiratory center in the medulla oblongata. The pons coordinates transitions between inspiration and expiration. Inspiratory and expiratory neurons are involved in increased ventilation demands.

Control of breathing in Humans

Breathing control centers in the brainstem respond to changes in CO₂ and O₂ levels in the blood. These changes affect the pH, and the control centers adjust the rate and depth of breathing accordingly.

Medullary center

The medullary respiratory center involves inspiratory (DRG) and expiratory (VRG) groups of neurons, controlling the basic rhythm of breathing.

DRG/Medullary center

Dorsal respiratory group (DRG) of neurons is the site of the normal rhythmic respiratory drive and contains proprioceptive afferents from the respiratory muscles and chest wall.

Medullary center - ventral respiratory group

Ventral respiratory group (VRG) innervates respiratory muscles and increases output to meet the need for forceful expiration (e.g., exercise, airway resistance).

Chemoreceptors - Central and Peripheral

Chemoreceptors monitor blood CO₂ levels and pH to regulate breathing. Central chemoreceptors in the CSF detect changes in H⁺ and CO₂ concentration to regulate breathing. Peripheral chemoreceptors in the carotid and aortic bodies monitor the O₂ level and adjust respiration as needed.

Respiratory Pigments

Respiratory pigments increase oxygen-carrying capacity of blood. They are complexes of proteins and metallic ions, having characteristic colours. Hemoglobin is the main respiratory pigment.

Respiratory Pigments - properties and functions

Hemoglobin is the main respiratory pigment in most vertebrates and some invertebrates. It greatly increases the amount of oxygen that blood can carry due to the presence of heme and iron within the complex.

Respiratory Pigments - Bunsen Coefficient

Bunsen solubility coefficient is the volume of oxygen that can be dissolved in 100 mL of blood at 37 ⁰C, with an initial oxygen pressure of 1 atmosphere. It is important for understanding oxygen transport in the absence of hemoglobin.

Respiratory Pigments - total oxygen content

The total oxygen content of arterial blood at a normal arterial Po2 is about 20 vol %. Combining oxygen with hemoglobin has a significant 70-fold increase in oxygen carrying capacity of the blood, making hemoglobin an efficient transport system.

Hemoglobin

Hemoglobin is the main respiratory pigment in vertebrates. It is a complex protein containing iron that binds oxygen reversibly. Its characteristic color changes as it binds and unbinds oxygen, becoming bright red when oxygenated and dark red when deoxygenated.

Hemoglobin properties

Hemoglobin is composed of heme and globin. It contains four iron atoms, each of which can bind to one molecule of oxygen.

Hemoglobin - alterations

Hemoglobin alterations, like those when oxygenated and deoxygenated, or when CO₂ binds, cause conformational changes, influencing oxygen delivery rates. Methemoglobin is a form of hemoglobin that cannot bind oxygen and needs reduction.

Hemoglobin, iron, met

Hemoglobin's iron is in the ferrous state (Fe2+). Methemoglobin contains iron in the ferric state (Fe3+) and cannot bind oxygen. Methemoglobin reductase reduces methemoglobin back to the ferrous form for oxygen transport.

Hemoglobin structure

Hemoglobin consists of four heme groups with iron atoms that bind to oxygen molecules. There are four globin polypeptide chains associated with the heme groups. Different polypeptide chains can have different oxygen affinity and binding properties which affect oxygen transportation.

Coordination of Circulation and Gas Exchange

In the lungs, blood has low oxygen and high carbon dioxide partial pressures compared to alveolar air. O₂ diffuses into the blood, and CO₂ diffuses out into the air. Partial pressure differences promote O₂ diffusion into interstitial fluids and CO₂ diffusion into the blood.

External and internal respiration

External and internal respiration each occur in specific locations and utilize tissue and capillary exchanges.

Oxygen Transport in Blood

Heme groups within hemoglobin proteins combine with oxygen molecules, allowing for efficient oxygen transport. Affinity of hemoglobin to carry oxygen adjusts depending on the partial pressure of oxygen and other factors.

Oxygen Transport in Blood - various pressures

The extent of oxygen binding to hemoglobin is dependent on the partial pressure of the gas (PO₂). At higher partial pressures, more oxygen binds to hemoglobin. At lower partial pressures, oxygen is released from hemoglobin.

Oxygen capacity of blood

The oxygen capacity of the blood increases as hemoglobin concentrations increase. The oxygen content is the percentage of the oxygen capacity at a given oxygen saturation.

Oxygen dissociation curves

Oxygen dissociation curves illustrate the relationship between the partial oxygen pressure (P₀₂) and the percentage saturation of hemoglobin with oxygen. These curves can show the change in oxygen affinity depending on other factors, e.g. temperature or CO₂ levels.

Myoglobin and other hemoglobin

Myoglobin and certain other hemoglobins have different oxygen dissociation curves (hyperbolic versus sigmoid curves). Myoglobin's single heme group has a higher oxygen affinity compared to other hemoglobins' four heme groups, making better oxygen storage than transport.

Coordination of Circulation and Gas Exchange - lungs

Lung gas exchange has low partial pressure for O2 and high for CO2 in the blood, compared to alveolar air. The partial pressure differences promote gas exchange.

Carbon Dioxide Transport in Blood

CO₂ diffuses into the blood from tissues, is transported in the blood, and diffuses across the respiratory surface into the environment. CO2 and water can react to form carbonic acid, resulting in the bicarbonate system. Carbon dioxide is transported in the blood as dissolved gas, carbamino compounds or plasma bicarbonate.

Carbon dioxide transport - conditions

Blood CO₂ content varies with PCO₂. Lower pH at a constant PCO₂ is linked to a lower bicarbonate concentration. Most blood bicarbonate is found in the plasma.

External and internal respiration - oxygen and carbon dioxide

Oxygen and carbon dioxide move across the respiratory membrane in the lungs during external respiration depending on their partial pressure differences. During internal respiration, oxygen moves from the capillaries into the tissues and carbon dioxide moves from the tissues to the capillaries.

Lung ventilation

Eupnea is considered the normal quiet breathing. Hyperventilation is the increased rate and depth of breathing, caused by hypercapnia and hypoxia. Hypoventilation is a decreased rate and depth of breathing. Apnea is the absence of breathing. Dyspnea is labored breathing. Polypnea is an increase in breathing rate without an increase in breathing depth.

Normal Breathing

Normal breathing rate and depth depend on several factors, such as age, activity, emotions, and health. For an adult, 14-20 breaths/minute is considered normal.

Effect of hyperventilation

Hyperventilation leads to a decrease in blood carbon dioxide which results in a decrease in pH and a reduced stimulation of respiratory centers.

Effects of voluntary hyperventilation

Voluntary hyperventilation can lead to a sustained elevated oxygen concentration which can cause a false decrease in CO2 and the brain to stop triggering respiratory muscle activity

Some effects of hyperventilation

Repetitive episodes of apnea (cessation of breathing)
Simultaneous hypoxia
Increased cerebral blood flow
Decrease in bicarbonate values
Increased sway

Bohr shift/Bohr effect

A decrease in pH (increased H⁺ concentration) causes a reduction in the oxygen-binding affinity of hemoglobin, which allows for greater oxygen release in tissues. A decrease in pH (and increase in CO₂ concentration) reduces the affinity that hemoglobin has for CO2.

Reverse Bohr shift

Hemocyanin from gastropods and horseshoe crabs exhibit a reverse Bohr shift, with the affinity for oxygen increasing as pH decreases.

Temperature

An increase in temperature reduces not only oxygen solubility, but also the oxygen affinity of hemoglobin, impacting oxygen transport.