It is an amphibian organism. It has five toes and four fingers. Frog has neither neck nor tail. It has slippery skin due to the secretions of the glands. It comprises two bulging eyes, two tympanic membranes and two nostrils. Frogs are bundantly found during rainy season. During winter they are buried into the mud and at the return of favourable condition they again resume their normal life; this process is termed as hibernation.
1. Digestive System
The break down of complex food into simpler food is called digestion. The organs taking part in digestion constitute a system called as digestive system. It comprises of buccal cavity, pharynx, esophagus, stomach and intestine.
a) Buccal Cavity
Upper and lower jaws collectively form a cavity (space) known as buccal cavity. It has teeth which are only used to hold the prey from splipping out of the mouth. Frog has sticky and unique type of tongue. The front part of the tongue is attached to the floor of the buccal cavity and free from behind.
It is short and narrow tube. It leads to oesophagus.
It is a wide tube which transports food into stomach.
It is thick walled, muscular and glandular sac. Anterior part of stomach is called cardiac end where as posterior end is called pyloric end. In stomach food is grounded with pepsin enzyme and is changed in to a paste like substance known as chyme.
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Intestine is a long narrow tube. It is divided into small and large intestine. In small food is converted in the form of blood while in large intestine (rectum) undigested food is entered that undigested food is an opening called cloaccal aperture.
It is large reddish brown gland located adjacent to the stomach. Its secretions are known as bile. In between two lobes of liver there is a pouch like structure known as gall bladder.
It is a long narrow and flattened gland near the stomach. Its secretions are called pancreatic juice. Bile duct and pancreatic duct collectively from hepato-pancreatic duct.
2. Respiratory System
It is a process with requires oxygen for oxidation and co2 for reduction. It complete into two phases.
i. Extra cellular respiration
ii. Cellular respiration
In frog there are three types of respiration as under.
a) Pulmonary Respiration
This type of gaseous exchange takes place in lungs. During this type of respiration O2 is taken and CO2 is given out by the following route.
External nostrills ==== Internal nostrils === glottis == Larynx == Bronchi == Lungs
b) Cutaneous Respiration
This type of gaseous exchange is carried through skin. It takes place during swimming or hibernation with the help of network of blood capillaries.
c) Buccal Respiration
This kind of gaseous exchange takes place through the blood capillaries of buccal cavity.
The transportation or movement of the material within the body is called circulation whereas the whole transportation system is called circulatory system. This system is also called cardiovascular system. In from closed type of circulatory system occurs. It contains:
i. Blood Vessels
a) Arteries : Carrying blood away from heart
b) Veins : Carrying blood into the heart
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c) Capillaries : Exchange materials between tissues and blood
Heart is a strong, conical, muscular and pumping organ. It is enclosed in a layer or membrane called pericardium. The contraction and the expansion of heart is called heart beat. The heart of frog consists of three chambers.
a) Right auricle
b) Left auricle
Inspite of three chambers there are also accessory chambers known as truncus arteriosus and sinus venosus. Truncus arteriosus exists at ventral side of the heart having arteries and sinus venosus exists at the dorsal side having veins.
Process of blood circulation: Blood circulation occurs into two path ways.
i. The oxygenated blood from the lungs enters the left auricle through pulmonary veins.
ii. The deoxygenated blood from all parts of the body enters into sinus venosus from there into right auricle. Then after blood is pushed into the ventricle then it is pumped into truncus arteriosus. Finally blood enters into lungs through pulmonary arteries or it is supplied to whole body parts through systematic arteries or it is supplied to brain through carotid arteries. There are valves between various chambers which prevent the back flow of blood.
4. Arterial System
This is a type of system which carries blood away form heart to various parts. It comprises three components as given below.
a) Pumo- Cutaneous arteries: It is supplies blood to lungs and exchanges c02 and O2.
b) Carotid arteries: These arteries develop from truncus arteriosus and supply the oxygenated blood to head region.
c) Systematic arteries: These types of arteriosus combine together to from a major vessel called aorta, which gives rise to various branches. These arteries supply blood to various parts except head and lungs.
5. Venous System
This system comprises of the veins which carry blood from the different parts towards heart. The major components of venous system are.
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a) Pulmonary veins
It regulates the oxygenated blood from lungs towards the left auricle of the heart.
b) Precaval veins
These veins transport blood from head and fore limbs towards heart. They only carry deoxygenated blood.
c) Post caval veins
These veins collect blood from lower or trunk part towards sinus venosus from where the blood is pumped into the right auricle of heart.
6. Portal system
It is a type of system which is composed of portal veins that collect blood from one organ and discharge it into the other organ. In this system the veins work into the form of bundles.
i. Hepatic portal system
In this system all veins join to from hepatic portal vein, which further breaks up into the capillaries and allows the transfer of digested food and blood into the liver. Further form liver the blood is firstly entered into post caval vein and then sinus venosus finally into the heart. Hepatic portal vein is also joined with an abdominal vein that also drains blood into liver.
ii. Renal portal system
This is a kind of system in which the blood from hind limbs is carried into kidney by the help of the blood capillaries ultimately blood is returned into heart.
7. Excretory system
The removal of waste matter from the body is called excretion. The set of organs involved in the process of excretion is called excretory system. It is performed by the help of kidney. There are two reddish brown kidneys in frog in which filter the waste matter of blood and convert it in the form of urine. Urine is carried to cloaca through tube like structures called ureters. Here urine either is excreted outside through cloaccal aperture or it is stored in bag like structure called ureters. Here urine either is excreted outside through cloaccal aperture or it is stored in bag like structure called as urinary bladder.
8. Reproductive System
The process in which the new babies are produced by the parents is called reproduction. The organs included in reproduction collectively form a system called reproductive system. In frog male and female frog are separated. The reproductive organs consist of gonads and duck. Male gonad is known as testis while female gonad is known as ovary. Both of the gonads are located near the kidneys. Testes produce sex cells called sperm where as ovary produces ovum (plural ova) or eggs. During breeding season both the gonads release their sex cells through duct into the water. The sex cells move through water current and fuse with each other to form zygote, then embryo and ultimately a new frog is produced.
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9. Nervous system
The set to organs which control and co-ordinate all the activities of the body is called nervous system. It is composed of two parts.
i. Central nervous system (CNS)
ii. Peripheral nervous system (PNS)
i. Central Nervous System (CNS): Includes brain and spinal cord
It controls all the activities taking place in the body. It is protected in skull (or cranium = frame of bones).
Exclusive of nerves it contains following parts:
a) Olfactory lobes
It is anterior and foremost part of the brain. It is connected to nose with the help of olfactory nerves. It transfers smell sensations towards cerebral hemisphere.
b) Cerebral hemisphere
These are tow large outgrowths existing next to olfactory lobes. These are also called as the seats of intelligence.
c) Optic lobes
Behind the cerebral hemisphere two prominent outgrowths are present known as optic lobes. These are connected to eye with the help of optic nerves. It functions to control all the visionary activities.
It is the part that is present between optic lobes and hemisphere. At the dorsal end of it exists pineal (a gland that attached brain to the cartilage) while at its ventral end pituitary gland ( a gland that inter connects brain and pituitary membrane of nose) is attached. Diencephalon functions to receive the impulses from internal and external environment of the body and also controls secretions of hormones of the pituitary glands.
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e) Cerebellum and medulla oblongata
Both of these control the movement and balance of the body.
It starts from the posterior side of medulla oblongata, passing from skull hole it enters into the vertebral column. Spinal cord controls the movement of trunk area.
ii. Peripheral Nervous System (PNS)
It comprises of cranial and spinal nerves. Cranial nerves connect brain with other head regions while at the other end spinal nerves that work automatically in both the head and trunk regions.
The organs which detect changes taking place in their surrounding and respond to theses changes are called sense organs. In frog microscopic receptors are present on the skin for touch, olfactory receptors in nostrils for smell and taste sensory cells in the taste buds of tongue for the purpose of taste.
Pinna is absent in frog so the outer most part of ear is tympanic membrane. On the inner side of it is a cavity known as tympanic cavity. This cavity contains small rod like bones called ossicles. These bones lead the sound to the inner ear. These receptors receive the stimulating sound waves of inner ear take them towards the brain. In spite of hearing, the ear also maintains the balance of the body.
It is the organ of vision. Frog has two bulging eyes. It consists of the following parts:
a) Sclerotic: It is the outer most hard, opaque, fibrous and white part of the eye.
b) Choroid: It is blackish part of the eye that is presented immediately internal to the sclerotic.
c) Cornea: It is anterior, transparent coat of an eye ball. It receives sun rays.
d) Iris: It is the coloured region behind the cornea which admits the sun rays further. It has a window like structure called pupil. Pupil contains eye lenses. Cornea, pupil and lenses focus light on retina.
e) Retina: It is the innermost layer that conveys the light first to the optic nerve then to the brain with the help of photoreceptor cells (the cells sensitive to sun light).
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