Question

Describe three ways by which one maximize O2 uptake across the respiratory surface?

How do cardiac muscle and brain tissue override the effect of strong sympathetic stimulation in order to prevent ischemia?

Crocodiles are an endless source of fascination for people because they are one of the few animals which can still get the better of us. Justify this statement.

Describe the challenges and adaptations of aquatic and air breathing vertebrates. What challenges did they have to face? How did they solve the problems?

Answer 1

Ans. The three ways by which one can maximize O2 uptake across their respiratory surfaces

Since large animals unable to maintain an exchange of gases by diffusion process across their outer surface. They developed a variety of respiratory surfaces that increases the surface area for gaseous exchange in larger bodies. A respiratory surface is covered with thin, moist epithelial cells that allow the exchange of oxygen and carbon dioxide. These gases can only cross cell membranes when they are dissolved in water or an aqueous solution so that the respiratory surface can be kept moist.

1. Skin and Gills - Earthworms and amphibians use their skin (integumentary system) for respiration while Pisces kingdom(fish) uses their gills for respiration.

2. Tracheal Systems - Insect uses the tracheal system for their respiration which consists of a network of small tubes that carries oxygen to the entire body. Blood does not play a role in respiration in arthropods(insects).

3. Mammalian Systems - In mammals, pulmonary ventilation occurs via inhalation (breathing) to bring air into the lungs (infoldings of the throat or body surface that enclose respiratory surfaces).

Cardiac muscle and brain tissue override the effect of strong sympathetic stimulation in order to prevent ischemia

The sympathetic nervous system is the component of the ANS that is responsible for controlling the human body’s reaction to situations of stress or emergency (otherwise known as the “fight-or-flight” response),

During a sympathetic stimulation of heart (exercise), the SA node of the heart stimulated, hence the stroke volume is greater than at any end-diastolic volume, similarly SA node is stimulated by parasympathetic output the stroke volume is less than the given end-diastolic volume

Sympathetic neurotransmitters: Neurotransmitters are chemical substances released into the synaptic cleft from nerve terminals in response to action potentials by the transmission of signals from a neuron to a target cell across a synapse, e.g., acetylcholine for neuromuscular junctions.

Sympathetic receptors: There are two types of adrenergic receptors β and α.

the cardiovascular system there are β1, β2, α1, and α2 adrenergic receptors.

β1 adrenergic receptors are expressed in the heart (in the SA node, AV node, and on atrial and ventricular cardiomyocytes). The activation of β1 receptors increases the heart rate.

β2 adrenergic receptors are mainly expressed in vascular smooth muscle, skeletal muscle, and in the coronary circulation. Their activation elicits vasodilatation, which, in turn, increases blood perfusion to target organs (especially the liver, heart, and skeletal muscle.

α1 adrenergic receptors are expressed in vascular smooth muscle proximal to sympathetic nerve terminals.

α2 adrenergic receptors are expressed in vascular smooth muscle distal from sympathetic nerve terminals.

As β2 adrenergic receptors, α1 and α2 adrenergic receptors also elicit vasodilation.

Sympathetic nervous system control and heart function: Stimulation by the sympathetic nervous system results in the following effects on the heart Positive chronotropic effect (increase in heart rate).

The sinoatrial (SA) node known as the pacemaker of the heart within the upper posterior wall of the right atrium, and is responsible for maintaining a sinus rhythm of between 60 and 100 beats per minute.

This rate is constantly being affected by innervations from both the sympathetic and parasympathetic nervous systems. Stimulation by the sympathetic system nerves results in an increase of heart rate, as occurs during the “fight-or-flight” response.

Positive inotropic effect (an increase of contractility) Myocardial contractility represents the ability of the heart to produce force during contraction. Stimulation by the sympathetic nervous system causes an elevation in intracellular (Ca2+) and thus an increase in contraction of both the atria and ventricles.

Positive dromotropic effect (enhancement of conduction) It is stimulated by the sympathetic nervous system which affects the conduction of electric impulses through the heart.

For example- increases in Atrioventricle (AV) conduction velocity.

Crocodiles are an endless source of fascination for people because they are one of the few animals which can still get the better of us

Crocodilians are the world's largest and perhaps most exciting and fascinating reptiles having a variety of features

They have distinctive anatomical and physiological features such as long jaws, protective armor, streamlined body, and long tail. These anatomical and physiological features, make the crocodile suited for an aquatic and predatory lifestyle.

In all amphibians, Crocodiles have 4 Chambered heart are cold-blooded and have a body temperature similar to the surrounding air, land, and water.

Crocodiles have a tendency to retain hard, indigestible objects in their stomach and most crocodiles over two meters long have been found to have stones in their stomach. It is believed that the stones are used as gastroliths (to aid in grinding up food) and that they also may function as ballast (just as in a ship’s hull)

Unlike vertebrates valves, the crocodile valve has "cog teeth" which is made up of nodules of connective tissue. The cog teeth mesh together, takes blood away from the lungs and into their bodies. These "teeth" are controlled by the amount of adrenalin in the bloodstream.

In the right ventricle of crocodiles, valves are located for pumping the blood to the pulmonary arteries feeding the lungs as well as to the left aorta which supplies the body. Crocodilians have the ability to shunt blood away from the lungs, despite having an anatomically divided ventricle.

The challenges and adaptations of aquatic and air-breathing vertebrates :

Amphibians were the first terrestrial vertebrates and before the amphibians, all organisms were aquatic, so there were certain unfavorable conditions as mentioned below :

Unfavorable aquatic temperatures,

Environmental hypoxia (low oxygen levels),

Predation

Increased salinity

When these vertebrates moved from the aquatic environment to land the major problem was with respiration. Aquatic organisms are well accustomed to the branchial mode of respiration i.e respiration through gills. When they came onto land, gills become nonfunctional. This was a major challenge for these organisms. This was overcome by the evolution of lungs that were suitable for respiration on land.

When the vertebrates migrate from aquatic surroundings to land the main complication found with respiration because aquatic organisms were adapted to respiration through gills, gills become nonfunctional for those organisms who survive on land.

This problem was resolved by the evolution of lungs for the respiration process for the organisms of land survival

Sensory perception was also a challenge as visual and auditory perception is different in water and land. This was overcome by having eyes on the forehead instead of on the sides of the skull.

Locomotion is yet another challenge as a movement in water is different from that of land.

Distinct head and neck are present along with modified hind limbs favoring movement on land.