The Respiratory System
THE RESPIRATORY SYSTEM
Respiration – (also known as respiratory exchange)
- exchange of gases which takes place when an organism breathes.
• External Respiration - actual exchange of gases (02 & CO2), between the organism and the environment.
• Cellular respiration - responsible to produce energy, in the form of ATP, with the use of sugars.
The Gas Exchange in Animals = Oxygen (Aerobic) and Carbon dioxide Carbon dioxide must be released to prevent physiological pH in tissues from being very acidic.
In plant, the carbon dioxide that is released as a by-product of cellular respiration may again be taken up for the process of photosynthesis.
Some basic principles influencing gas
Exchange
Respiratory organs must be moist (like nasal cavities with mucus), large enough, and protected from desiccation (with hair and cilia for filtration).
Respiratory systems rely on the diffusion of gases down pressure gradients.
•Partial pressures for each gas in the atmosphere can be computed; For example, the partial pressure of oxygen is 160 mm Hg.
•Fick’s Law states that the amount of diffusion of a gas across a membrane is proportional to the surface area and the difference in partial pressure between the two sides and inversely proportional to the thickness of the membrane.
Surface-to-volume ratio
•As an animal grows, the surface area increases at a lesser rate than its volume, making diffusion of gases into the interior more difficult
•Animals must have a body design that keeps internal cells close to the surface (e.g. flatworms) or must have a system to move the gases inward.
Ventilation
• movement of the respiratory medium (air or water) over the respiratory surface.
• Bony fish moves the gill covers (operculum) for water-carrying oxygen to flow across the gill.
• Humans move the muscles of the thorax to expand and
contract the chest cavity and move air in and out of the lungs.
Respiratory Pigments or Proteins
• Adaptations of animals for gas exchange include respiratory pigments that bind and transport gases.
• The respiratory pigment of vertebrates is hemoglobin while that of invertebrates (e.g., arthropods and mollusks) is hemocyanin.
• Blood cannot carry sufficient oxygen and carbon dioxide in dissolved form to meet the body’s requirements; hemoglobin helps enhance its capacity.
• Coordination of air flow with blood flow:
• Gas exchange in the alveoli is most efficient when air flow equals the rate of blood flow.
• Local controls within the lung's correct imbalances in air and blood flow by constricting or dilating both bronchioles and arterioles.
• Control of respiration in vertebrates:
• The nervous system controls oxygen and carbon dioxide levels for the entire body by regulating the rate and depth of breathing.
• The brain monitors the pH of the cerebrospinal fluid through sensors (reflecting carbon dioxide concentration in the blood).
• Secondary control is exerted by sensors in the aorta and carotid arteries that monitor blood levels of oxygen as well as carbon dioxide (via blood pH).
OXYGEN IN TERMS OF LAND AND WATER
Oxygen present in the air is about 20 times greater than the oxygen in water.
With these conditions, aquatic organisms were able to develop an efficient way of extracting the oxygen from the water.
The downside from this process is that these organisms need to utilize about 20% of their energy to accomplish the task as compared to terrestrial animals which need to utilize only 1-2% of their energy to obtain oxygen.
The Respiratory Organs of Animals:
Single-celled organisms
• Single-celled organisms as well as lower forms of animals are able to obtain oxygen from the environment through direct diffusion in cell surface/membrane.
The Respiratory Organs of Animals:
The Cutaneous Respiration
Cutaneous respiration – a kind of integumentary respiration with the usage of skin.
Flatworms increase their body surface in relation to their body mass to supply oxygen to their body by direct diffusion.
For vertebrates, it serves as a supplement for
their actual mode of oxygen assimilation.
The Respiratory Organs of Animals:
The Tracheal System
• Tracheae - systems of tubes.
• Tracheoles - fluid-filled small channels within the end of tracheae.
• Spiracles - valves that open and close -allowing entry of air and can aid in preventing the loss of fluids in the system.
• Some insects are also able to ventilate freely using the tracheal system while it exhibits motions.
• Since the cells have direct contact with the
tracheal systems, any incoming oxygen from the
said apparatus can freely be obtained by the
surrounding cells.
• Carbon dioxide is also able to diffuse freely because of this direct contact. This is the reason why insect blood plays minimal roles in the transport of gases.
The Respiratory Organs of Animals:
The Gills
Gills are the primary respiratory mechanism which is used by higher forms of aquatic organisms.
• External gills - usually found as extensions of the
body; obtain oxygen from the water through simple diffusion
• Internal gills - are found inside the body of the
organisms. It has filamentous structures which areheavily supplied by blood vessels. It has countercurrent flow that greatly enhances the
oxygen intake of the organism.
In the case of mollusks, water is being pulled with the
help of cilia.
The dual pump system of fishes
The buccal cavity of fishes are separated to the
opercular cavity by gill curtains (differentiates the
pressures between the two cavities).
• Buccal pump – in suction phase, water enters the
mouth of the fish, where it slightly increases the
pressure present in the buccal cavity. Due to the difference in pressures, the water will move from high concentration, to low concentration.
• Opercular pump. The water will then flow through the gill curtain then enters the opercular cavity. Upon the entrance of water in the opercular cavity, the mouth closes while the operculum opens. The difference in pressure will then again allow the water to move freely across the operculum to exit the system.
This type of respiration results in a unidirectional flow.
Countercurrent flow
• Countercurrent flow - Water flows over the gills and blood circulates through them in OPPOSITE DIRECTIONS. This mechanism is highly efficient in extracting oxygen from water, whose oxygen content is lower than air.
• Many diving animals have unusually high hematocrits (ratio of the volume of packed red blood cells to the volume of whole blood) and also muscles with high amounts of myoglobin (an oxygenbinding protein found in muscle cells)
The Respiratory Organs of Animals: The Lungs
(Lungfish)
Why fishes can not breath in terrestrial despite the high Oxygen concentration compared to bodies of water?
• A certain type of fish, the lungfish, possess a structure which is like the lungs known as the gas bladders.
(1) Anatomical positioning: Gas bladders are positioned dorsal to the digestive tract while lungs are positioned ventrally.
(2) gas bladders are usually a single structure whereas
lungs are paired.
(3) The blood from swim bladders goes to the systemic circulation before entering the heart. For the case of the lungs, blood enters the heart separately from the systemic circulation.
The Respiratory Organs of Animals:
The Lungs (Amphibians)
Amphibian lungs are varied depending on species. The salamander species have a simple, smooth-walled lungs while the anurans have subdivided lungs. Amphibians undergo buccal pumping during their respiration. The nostrils
will then be closed off and the glottis will then be opened. The collected air will then be forced through the glottis to enter the lungs. The excess air will thenbe released from the body.
The respiratory system of a frog includes the nares, glottis, trachea, and lungs.
• Bronchioles, bronchi, and trachea - tubes leading into and out of the lungs.
• Alveoli - tiny air sacs for transfer of air.
The Respiratory Organs of Animals:
The Lungs (Birds and Mammals)
Avian lungs are improved as compared to other terrestrial vertebrates by the addition of an extensive system of air sacs.
During the intake of air, about 25% passes through lung parabronchi while 75% bypasses the lungs and goes to the air sacs ,
Mammalian lungs contain millions of tiny air sacs known as the alveoli that is located at the end of the bronchioles.
• Bidirectional respiration - air enters and exits in the same opening, preventing the mixing of incoming and outgoing air.
• Animals that inhabit high altitudes have larger hearts and lungs, and hemoglobin with a high affinity for binding oxygen.
• Visceral pleura – Thin but tough covering epithelium of mammalian lungs.
• Parietal pleura-lines the indeed surface of the chest.
• Pleural cavity - maintains a negative intrapleural pressure which allows the lungs to be expanded The two pleura are closely in contact and are lubricated by the surrounding tissue. Every time the lungs expand and contract, the two pleura slide over onE another.
The Ventilation of the Lungs
Ventilation - movement of air in or out of a system.
• Inspiration or intake of gases - ribs will be pulled upward with the help of the intercostal muscles while the diaphragm contracts and flattens. The volume of the lungs will increase thereby decreasing the pressure in the lungs. Since the atmospheric pressure has a higher concentration, it will rush into the system in order to equalize the pressures.
• Expiration or the release of gases - the ribs will return to their normal position. The diaphragm relaxes which in turn decreases the volume of the lungs and increases its pressure. The increase of pressure in the lungs eventually forces the air to exit the system.
• Mammals ventilate their lungs by negative pressure
breathing which pulls air into the lungs when the volume of the lungs expands as the rib muscles and diaphragm contract. However, the incoming and outgoing air mix, decreasing the efficiency of ventilation
The Transportation of Gases
For invertebrates, gases are freely transported
throughout the body together with their body fluids
since they usually have an open type of circulation.
For some cases, the oxygen is being transported by
proteins which are known as the respiratory pigments.
• Hemoglobin - The heme group (high affinity)
constitutes to 5% of the molecule which contains
the iron group and the color red while the remaining 95% is the globin group which is a colorless protein.
Once the blood cell reaches the tissues, the oxygen
concentration becomes significantly lower which
allows the release of the oxygen molecule.