Introduction

In unicellular organisms, a single cell performs all tasks such as digesting, respiration and reproduction. A set of identical cells, as well as intracellular molecules, fulfil a specific role in multicellular creatures, and this arrangement is known as tissue.

To form an organ, tissues are arranged in a certain proportion and arrangement. The stomach, lungs, heart, and kidney are only a few examples.

When two or more organs interact physically and/or chemically to execute a shared function, they create an organ system—for instance, the digestive system, the respiratory system, and so on.

For the survival of the entire organism, cells, tissues, organs and organ systems demonstrate division of labour.

Morphology

Classification

• Phylum – Chordata
• Subphylum – Vertebrata 
• Superclass – Tetrapoda 
• Class – Amphibia

The Rana tigrina is one of the most frequently occurring frog species. 

Body of Frog is Divided into Two Parts:

(i) Head 

(ii) Trunk 

Head

The snout is the anterior conical section of the triangular head.

Structures found on the head are:

• Mouth
• 1 pair of nostrils
• 1 pair of eyes
• 1 pair of tympanic membranes
• 1 pair of vocal sacs

Trunk

• A frog is a Tetrapoda
• Swimming, walking, leaping, and digging are all assisted by the forelimbs and hindlimbs. Four digits are present on the forelimbs. The hind limbs feature five digits

Internal Morphology of Frog

Respiratory System

• Frogs breathe on land and in water using a variety of mechanisms 
• Frogs have three different forms of respiration. The respiratory organs are the buccal cavity, skin and lungs

Digestive System

• Food ingestion, digestion and egestion of undigested food are functions of the digestive system
• There are two sections: the alimentary canal and digestive glands

(a) Digestive tract

The food is passed through: 

Mouth-oral cavity-pharynx-oesophagus-stomach-intestine-rectum-cloaca-aperture of cloaca.

(b) Stomach

It’s a strong muscular bag with HCl as well as a proteolytic enzyme. HCl causes food to have an acidic pH and is bacteriolytic.

• The intestine is where digestion is completed. Food is broken down by the action of HCl and gastric secretions released from the stomach’s walls
• The duodenum receives bile from the gallbladder and pancreatic secretions from the pancreas through a shared bile duct 
• Pancreatic fluids digest carbs and proteins, while bile emulsifies fat
• The intestine is where the final digestion takes place. The many finger-like folds in the intestine’s inner wall called villi and microvilli absorb digested food. The solid waste that has not been digested enters the rectum and exits through the cloaca

(c) Digestive Glands

(i) Liver: Bile is produced by the liver and stored in the gallbladder. It is secreted into the intestine. Bile juice is a highly alkaline liquid. This emulsifies fat.

(ii) Pancreas: Pancreatic juice is secreted into the intestine by the pancreas. It is known as a digestive juice.

Circulatory System

The frog has both closed and partial double circulation.

The job of the circulatory system is to move food, gases, and hormones throughout the body.

• Heart

It has a three-chambered, muscular myogenic heart with two auricles and one ventricle. The blood is delivered to the auricles. The ventricle pumps blood to all regions of the body at a pace of 64 beats/minute.

• Portal systems

Frogs have a venous connection between the liver and gut, as well as the kidney and the lower body. The former is referred to as the hepatic portal system, whereas the latter is referred to as the renal portal system.

• Lymph

Lymph, lymph channels and lymph nodes make up the lymphatic system. Lymph is deficient in RBCs and a few proteins.

Nervous System 

The function of the nervous system is to control and coordinate the many sections of the body.

(a) Central Nervous System

The central nervous system is engaged in sensory analysis and comprises the brain and spinal cord. The brain is protected by a bony structure known as the cranium. The brain is divided into three sections: the forebrain, the midbrain, and the hindbrain.

• The olfactory lobes, a diencephalon and paired cerebral hemispheres are located in the forebrain

• A pair of optic lobes can be seen in the midbrain

• The hindbrain consists of the cerebellum and medulla oblongata. The foramen magnum is where the medulla oblongata exists

• The spinal cord that continues from the hindbrain is present inside the vertebral column

(b) Peripheral Nervous System

This system consists of cranial and spinal nerves. The frog has ten pairs of cranial nerves and ten pairs of spinal nerves.

(c) Autonomous Nervous System

The autonomic parts of the body, such as the heart, lungs, and intestine, are controlled by this system. 

Conclusion

A frog is a member of the Anura order, a diverse and primarily carnivorous group of short-bodied, tailless amphibians. Frogs account for more than 88 per cent of all amphibian species. Toads are a common name for warty frog species, but the distinction between them is based on habit rather than taxonomy or evolutionary history. Frogs typically lay their eggs in water. Tadpoles are aquatic larvae that hatch from eggs and have tails and internal gills. Their rasping mouthparts are highly tailored to herbivorous, omnivorous, or planktivorous diets. The frog skin microbiota is critical to their health. Frogs are especially efficient in converting their food into body mass.