Accessory Respiratory Organs

💫 Common in many fish species, these organs supplement traditional respiratory structures.

Cutaneous Respiration:

💫Significant in both air and water environments, facilitated through thin, moist, and permeable skin layers.

Mudskipper and Fish Larvae:

💫Exhibit cutaneous respiration, especially notable in environments with varying oxygen levels.

Madivas Renfold:

💫 Found in numerous fish species, these structures are supplied by extensive blood vessels, aiding in cutaneous respiration.

Epithelial Lining of Buccal Cavity:

💫Highly vascularized and permeable in certain fish species, facilitating gas exchange directly from the environment.

Specialized Alimentary Canal:

💫 In some fish, the epithelium lining the alimentary canal becomes vascularized and modified to function as a respiratory organ.

South American and Symbranchus Species:

💫Some species can extract oxygen directly from the air using modified structures in their pharyngeal cavities.

Cell Modification in Gut:

💫In select fish species, cells in the gut wall are modified to perform respiratory functions, with thinning of the gut wall layers.

Buccopharyngeal Epithelium:-

🪶In most fishes, the epithelial lining of the buccal cavity is highly vascular and permeable to gases.

🪶This adaptation allows for efficient gas exchange where gases diffuse in and out.

🪶Certain fishes from South America, like Symbranchus, have developed a unique adaptation in their gill and pharyngeal cavities.

🪶They can extract oxygen directly from the atmosphere.

Gut Epithelium:-

🪶In several fish species, the epithelial lining of the alimentary canal becomes vascularized and modified for respiratory functions.

🪶These modifications typically occur behind the stomach, intestine, or rectum.

🪶Air is drawn through the mouth or other openings to facilitate respiratory exchange.

🪶Cells within the gut wall are specialized and modified to perform respiratory functions.

🪶The thinning of the gut wall in these areas supports efficient gas exchange through layers of specialized cells.

Pharyngeal Diverticules :-

💫These are parts of simple sac-like outgrowths of the pharynx, lined by thickened vascular epithelium and extending near the gills.

💫They are very small in size. These structures include the periophthalmus, which are small and smooth, and amphipnous, which are folded in channe fishes that have poorly developed gill filaments. Thus, the stressory respiratory sacs serve to borolte atmospheric and cable for some time coming out of the water.

Dendriticles of Amphipnous Ocular:-

💫The directicale of Amphipnous opens antestody through the mid ventral gills slits.

Branchial Verticula:-

💫The outgrowths from gill chambers form more complicated serial accessory respiratory engers than simple pharyngeal outgrowths in other fishes.

Three well-known examples are :

1.Sacadosanchuy:-

💫The Indian cot fish has a pair of long, tubular, and dorsally situated sacs from gill posteriorly from art pointing chambers and extended.

💫They are highly vascular, are down in and expelled through through.

2.Anabas:

💫Upea Branchial Cartilage and Labyrinthine Organ.

💫Anabas has 2 large space above the gills.

💫These spaces contain a labyrinthine organ made of fold bony plates from epi-bronchial bone covered with a thin blood-rich membrane.

Aerobic Pathway in Fish Respiration:-

Air, entered through the mouth, passes into the supra-branchial cavities and exits through the opercular opening.

Dependence on Atmospheric Oxygen:

Fish need to breathe air from the surface and will drown if unable to access atmospheric oxygen.

Swim Bladder :

🦈The swim bladder is a gas-filled organ found in many fish species. Its main function is to regulate buoyancy. It helps fish control their position in the water column by adjusting the amount of gas (usually oxygen and nitrogen) inside. This allows fish to ascend or descend without much effort, conserving energy during swimming.

💫Structure and Function:-

🦈The swim bladder is typically a two-chambered, sac-like structure located above the fish’s digestive organs. It is lined with a vascularized membrane that helps in gas exchange.

🦈Gas enters or leaves the bladder through a duct called the pneumatic duct or ductus pneumaticus, which connects the bladder to the esophagus or gut in different fish groups.

💫Adaptations:-

🦈The swim bladder’s size and shape can vary among species, depending on their habitat and behavior. Some fish have lost their swim bladders through evolution, while others have modified them for additional functions, such as sound production or hearing.

💫Importance:-

🦈The swim bladder is crucial for the survival of many fish species, as it enables them to maintain neutral buoyancy and control their movements in the water.

🦈This adaptation has contributed significantly to their ecological success and ability to inhabit various aquatic environments.

🦈 The swim bladder is an essential adaptation in fish that allows for efficient movement and positioning in the water column. Its structural diversity reflects the diverse habitats and behaviors of fish species worldwide.

Respiratory System

Exchange of Gases:-

The respiratory system facilitates the exchange of gases;oxygen (O₂) and carbon dioxide (CO₂), essential for cellular respiration.

💫Respiratory Organs:-

Respiratory organs are specialized structures necessary for gas exchange between the body and the environment.

💫External Respiration:-

The process of exchanging oxygen and CO₂ between the body cells and the environment is termed external respiration.

💫Internal Respiration:-

Oxygen is utilized in metabolic activities within the body cells, known as internal respiration, producing ATP.

💫Types of Respiration:-

a. Cutaneous Respiration:

Occurs through the skin.

Found in some animals like amphibians.

b. Pulmonary Respiration:

Occurs in lungs.Found in mammals, birds, and reptiles.

Respiration Through Skin

Examples :

💫Fish: Utilize gills for respiration, with efficiency varying based on species and environmental conditions.

💫Amphibians: Perform cutaneous respiration in addition to respiratory functions through lungs or gills, depending on habitat.

💫Pledantidas selamanders:

Adult amphibians directly rely on cutaneous respiration to meet the needs of metabolic activities.

💫Humans:

Not as reliant on cutaneous respiration, but our skin is permeable to some chemicals, typically many medicinal ointments are absorbed.

🌿Both they and the skin’s cutaneous respiration through their highly volatile works, they eliminate as much as 12% of CO2 work ‘ D.

🌿They only take up to 1% – 0.2% of their total O2 requirement through this route.

💫Reptiles:In reptiles, the area between the scales and the area of reduced scales is heavily vascularized allowing some cutaneous respiration.

💫Monopterus Albus larvae: The newly hatched, some off teleost fish use their skin as the primary respiratory oxygen during sad stocks of book, it helps to perform all the metabolic activity during this stage

RESPIRATION THROUGH GILLS

💫Pharyngeal Development:

🪶During pharyngeal development, the pharynx wall forms pouches composed of endodermal.

🪶The tissue between these pouches consists of lateral plate mesoderm called neural crest.

🪶The ectoderm covers the outer pharynx and joins the pouches to create grooves induced by endoderm.

💫Gills Formation:

🪶Gills develop from these pharyngeal structures. In vertebrates, there are typically 7 pharyngeal arches. Each arch is supported by a cartilage rod. The aortic arches connect the ventral aorta to the dorsal aorta via branchial vessels. The number of arches decreases in higher vertebrates.

💫Specific Developments:

1.First Visceral Arch:

– In most vertebrates, this forms the jaw.

– In tetrapods (four-legged vertebrates), the first pharyngeal pouch becomes the tympanic cavity or middle ear.

2.Second Visceral Arch:

-Forms part of the jaw or moves into the middle ear.

3.Other Visceral Arches:

– Support gills in fish.

– Support the tongue and form the teeth in higher tetrapods.

Anatomy of Fish Gills

General Structure:

🪶Fish gills are covered externally by ectoderm and internally by endoderm.

🪶They develop bone/cartilage and muscles to support their function.

Gill Function:

🪶Gills consist of filaments that are covered in lamellae.

🪶Water with high oxygen content contacts blood with low oxygen content, allowing for oxygen diffusion from higher to lower concentration.

Types of Gill Covers in Fish:

I.Pouched Gill in Agnathans (Jawless Fishes):-

🕸Have 6-13 pairs of gill pouches.

🕸Each pouch is connected to the pharynx and has branched ducts.

🕸Water enters through the mouth and exits through the gill pouches during feeding.

II.Septal Gill in Cartilaginous Fishes:

🕸Consists of five or more gill slits.

🕸Each slit is supported by cartilage and associated with blood vessels, muscles, and nerves.

🕸Gill filaments are richly supplied with capillaries for efficient gas exchange.

III.Opercular Gill in Bony Fishes:

🕸Covered by an operculum, which protects the gills.

🕸Operculum helps in creating a unidirectional flow of water over the gills for efficient oxygen uptake.

Characteristics of Gill Structures in Bony Fishes :

1.Operculum:

A bony flap covering the gill chamber.

Typically five pairs of gill pouches.

2.Spiracles:

– Closed or lost in adults.

LARVAL GILLLS

1.External Gill Outgrowths:

– Found on larval lamprey, lungfish, and amphibians.

– Arise from the external surface of the gill arch and ectodermal tissues.

– In amphibians, larval gills are absent during metamorphosis.

Types of Gills:

– Both external gills and gill slits exist in different forms:

– Pectinate

– Bipectinate

– Dendritic

– Leaf-like

2 . Internal Gills

a) pouched gills

b) septal gills

c) aseptal gills

– Found in tadpoles and some fish species.

– Initially hidden behind larval operculum.

● Gill Chambers:

– Multi-chambered structure.

– External gill slits are small and shaped like an ‘A’.

● Branchial Chambers:

– Presence of buccal branchial chamber between branchial chambers anteriorly.

– Branchial septum acts as valve-like structures.

RESPIRATION THROUGH LUNGS

Lungs of Fish:-

🕸Swim bladder acts as a hydrostatic organ for buoyancy in vertebrates, especially bony fishes.

🕸But in some bony fishes, air bladders function in addition to or instead of lungs for respiration.

🕸The swim bladder is vascularized and associated with blood vessels.

Example:

🕸In Amia, the bladder is elongated and closed dorsally but opens ventrally into the pharynx.

🕸In Polypterus, the bladder is lobed and opens ventrally to the pharynx.

🕸The swim bladder aids in gas exchange. The gills of these fishes are poorly developed if they remain above the water surface for extended periods, potentially leading to suffocation.

🕸This passage discusses the respiratory adaptations in fish, focusing on the gills and swim bladder.

Gills are essential for aquatic respiration, while the swim bladder assists in buoyancy and gas exchange.

🕸Some fish species have evolved specialized respiratory structures like air bladders alongside or instead of gills.

🕸Maintaining proper gas exchange is crucial for their survival, as prolonged exposure above water can compromise their respiratory function and lead to asphyxiation.

Amphibian Lungs:-

🕸Amphibians have lungs that are relatively simple in structure:

🕸They are sac-like, operculum-shaped, and highly elastic.

🕸The outer surface is covered by a visceral peritoneum, while the inner surface has folds that form alveoli, which increase the respiratory surface area.

Respiration Process:

Amphibians use positive pressure ventilation:-

🕸When they breathe, they close their mouth and nostrils. The floor of the mouth is lowered, expanding the buccal cavity and reducing internal pressure.

🕸The throat opens, allowing air to enter. Contraction of the floor of the mouth forces air into the lungs.

Reptilian Lungs:

Reptiles have more complex lungs:–

🕸They often have large lungs divided into multiple chambers.

The lung lining may feature numerous small pockets called alveoli, which significantly increase the internal respiratory surface area.

Respiration Adaptations:-

Reptiles have adapted to their environments

🕸Snakes have elongated bodies, with the left lung reduced or absent, and the right lung elongated to accommodate the body shape.

🕸Some turtles use a mucous membrane in their mouths to extract oxygen from water while submerged.

🕸Crocodiles and other aquatic reptiles utilize their skin for respiration when submerged, similar to soft-shelled turtles like Trionyx.

Avian Lungs Structure:-

Avian respiratory systems are adapted for efficient gas exchange during flight, characterized by unique features:

1.Air sacs:

Extensively distributed throughout the body, divided into anterior and posterior groups. They are thin-walled and vascularized, facilitating efficient gas exchange and ventilation.

2.Lungs:

Located in the thoracic cavity, connected by a system of tubes (parabronchi) that ensure unidirectional airflow.

Respiration Process;-

First inspiration:

Air enters the posterior air sacs initially, with a smaller portion passing into the lungs.

First expiration:

Air moves from the posterior air sacs into the lungs for gas exchange.

Second inspiration:

Fresh air enters the posterior air sacs while the previously inhaled air remains in the lungs.

Second expiration:

Air from the lungs is expelled as fresh air from the posterior air sacs moves into the trachea and out of the body through the nostrils.

Avian lungs are unique due to their efficient air sac system and unidirectional airflow through parabronchi, facilitating continuous gas exchange essential for high metabolic demands, particularly during flight.

Mammalian Lungs:-

💫Structure:-

🕸Mammalian lungs are multi-chambered and usually divided into lobes (1-6 lobes).

🕸The respiratory system starts from the nose, passes through the pharynx, larynx, and trachea, and into the lungs.

🕸The trachea contains C-shaped cartilage rings to prevent collapsing and branches into bronchi, bronchioles, and alveoli.

💫Respiration:

Ventilation Mechanism:–

– Air flow in mammals is bidirectional, from nose to alveoli and back.

– Ventilation occurs via negative pressure: the diaphragm and intercostal muscles contract to expand the thoracic cavity, creating a vacuum that draws air in. Relaxation of these muscles decreases thoracic volume, expelling air due to increased pressure.

– Extensive blood supply to the lungs supports efficient oxygenation of blood.

🕸Mammalian lungs are specialized for efficient gas exchange. The structure, from the conducting airways (nose to bronchioles) to the alveoli, ensures that oxygen is absorbed into the bloodstream and carbon dioxide is released during exhalation.

🕸The bidirectional airflow and negative pressure ventilation mechanism optimize respiratory efficiency in mammals.

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