Morphology and Anatomy of Frog PDF

Morphology and Anatomy of Frog Created @December 20, 2024 10:29 AM Tags Morphology and Anatomy of a Frog (Rana tigrina) Classification: Kingdom: Animalia Phylum: Chordata C...

Morphology and Anatomy of Frog Created @December 20, 2024 10:29 AM Tags Morphology and Anatomy of a Frog (Rana tigrina) Classification: Kingdom: Animalia Phylum: Chordata Class: Amphibia Order: Anura Family: Ranidae Genus: Rana Species: Tigrina Habit and Habitat: 1. Frogs are amphibious, living both in water and on land. 2. Cold-blooded (poikilothermal/ectothermic): Their body temperature varies with the environment. 3. Enter hibernation (winter sleep) during cold seasons, burrowing into damp earth at the bottom of ponds. 4. Enter aestivation (summer sleep) during extreme heat. 5. Most active during the rainy season, which provides optimal temperature and food availability. Feeding and Predators: Morphology and Anatomy of Frog 1  1. Carnivores, feeding on: Insects Spiders Earthworms Snails Small fish 2. Natural enemies include: Snakes Mongooses Birds of prey 3. Use camouflage (body color change) for protection, blending into green vegetation. This protective coloration is called mimicry. Skin: 1. Moist and slippery due to mucus from cutaneous glands. 2. Coloration: Dorsal side: Olive green with dark, irregular spots. Ventral side: Pale yellow. 3. Loosely attached to the body, with long wrinkles (dermal plicae) on either side of the mid-dorsal line. Body Structure: 1. Divided into: Head Trunk 2. Streamlined shape aids swimming. 3. No neck or tail. Morphology and Anatomy of Frog 2  Head: 1. Triangular with a blunt snout. 2. Nostrils (external nares) at the snout's tip allow breathing. 3. Mouth: Large, stretching across the head with thin, immovable lips. 4. Eyes: Large, bulging, and positioned for a wide field of vision. Upper eyelid is thick; lower eyelid is thin. Upper part of lower eyelid has a transparent fold (nictitating membrane) for eye protection and underwater vision. 5. Tympanic membrane: Circular patch behind each eye covering the ear, used for hearing. 6. Vocal sacs: Bluish, wrinkled patches on the throat (present only in males) amplify croaking sounds. Trunk: 1. Short with a hump at the hind upper part. 2. Two pairs of limbs: Forelimbs: Short, consist of three segments: Upper arm Forearm Hand (raised palm with four digits). Male frogs have a copulatory (amplexus) pad on the undersurface of the first digit of each hand, which becomes more prominent during the breeding season to help hold the female during mating. Hind limbs: Long, powerful, and consist of three segments: Upper thigh Middle shank Lower foot (with ankle, sole, and five digits). Morphology and Anatomy of Frog 3  3. Hind limb digits are joined by webs for efficient swimming. 4. Hind limbs are used for jumping, leaping on land, and swimming. 5. Cloacal aperture (located at the end of the trunk between hind legs): Discharges fecal matter, urine, and reproductive products. Body Cavity (Coelom): 1. Lined by two layers: Parietal peritoneum (outer layer). Visceral peritoneum (inner layer). 2. Divided into two parts: Pericardial coelom: Small, anterior chamber enclosing the heart. Abdominal coelom: Large, posterior chamber housing the digestive, respiratory, vascular, nervous, excretory, and reproductive systems. Digestive System of a Frog: 1. Alimentary Canal: mouth opens into buccopharyngeal cavity a. Buccopharyngeal Cavity: Formed by the union of the buccal cavity and the pharynx. Contains the mouth, teeth, and tongue. Opens into a wide opening called the gullet, which leads into the esophagus. 1. Internal Nares: Located near the vomerine teeth. Help in the exchange of gases. 2. Teeth: Present only on the upper jaw (lower jaw is toothless). Teeth Type: Homodont, acrodont, and polyphyodont. Vomerine Teeth: Morphology and Anatomy of Frog 4  Two backwardly directed vomerine teeth are present on the roof of the buccopharyngeal cavity. Prevent the prey from escaping from the mouth. 3. Tongue: Posteriorly bifid (forked) and free. Attached to the floor of the mouth in front. Bilobed posterior ends help in catching prey. b. Esophagus: Short tube that opens into the stomach. c. Stomach: Sac-like structure divided into: Cardiac region (anterior). Pyloric region (posterior). The cardiac sphincter guards the opening from the esophagus into the cardiac region, preventing backflow of food. The pyloric sphincter guards the opening from the pyloric region into the duodenum. d. Small Intestine: Longest part of the alimentary canal. Divided into duodenum and ileum. Inner layer of duodenum and ileum contains villi (finger-like projections) to increase surface area for digestion, absorption. e. Large Intestine: Ileum leads into the rectum, which opens into the cloaca through the anus. The rectum stores fecal matter and helps absorb water. Digestive Glands: Morphology and Anatomy of Frog 5  1. Liver: Composed of two unequal lobes: Left lobe (larger). Right lobe (smaller). Gallbladder: Situated between the two lobes. Functions of the liver: Secretes bile. Bile ducts transport bile to the gallbladder through several narrow hepatic ducts. Gallbladder functions: Stores and concentrates bile. Bile Duct: The cystic duct arises from the gallbladder and extends towards the duodenum as the bile duct. The bile duct joins the pancreatic duct from the pancreas and opens into the duodenum as the common hepato-pancreatic duct. 2. Pancreas: Elongated, leaf-like gland located in the loop between the stomach and duodenum. Exocrine function: Secretes digestive enzymes via the lobules. Endocrine function: The islets of Langerhans secrete hormones: Insulin. Glucagon. Respiratory Organs and Modes of Respiration: Morphology and Anatomy of Frog 6  1. Cutaneous Respiration: Skin characteristics: Thin, moist, and highly vascular. Acts as an efficient organ for gaseous exchange. Function: Constantly occurs in the frog. During hibernation (winter sleep) and aestivation (summer sleep), cutaneous respiration is the only mode of respiration. 2. Buccopharyngeal Respiration: Process: Occurs primarily when the frog is on land. External nares: Located at the tip of the snout, leading to the nasal chamber. Each nasal chamber connects to the buccopharyngeal cavity via an internal nostril. Muscles involved: Sternohyal muscles (between sternum and hyoid apparatus). Petrohyal muscles (between hyoid apparatus and auditory capsule). Inspiration: Sternohyal muscles lower the floor of the buccal cavity. The mouth and internal nostrils remain closed, causing a decrease in pressure, drawing air in. Expiration: Petrohyal muscles contract, raising the floor of the buccal cavity. Increased pressure opens the internal nostrils, releasing air. 3. Pulmonary Respiration: Lungs: Morphology and Anatomy of Frog 7  Thin-walled, elastic, sac-like structures. The lungs have septa (partitions) that create several small cavities called alveoli. Alveoli: The walls are highly vascular, allowing for rapid exchange of respiratory gases. Lungs and Pulmonary Respiration: 1. Structure of the Lungs: The lungs are elastic structures. The walls of the lungs have several septa (partitions). These septa divide the lung into small cavities known as alveoli. The walls of the alveoli are highly vascular, allowing for the rapid exchange of respiratory gases. 2. Inspiration Process: The floor of the buccal cavity is raised by petrohyal muscles. The nostrils remain closed during this phase. This action forces air into the lungs through the glottis (the opening of the larynx). 3. Expiration Process: After inspiration, the elastic lungs contract. Simultaneously, the sternohyal muscles lower the floor of the buccal cavity. This causes the air to rush out of the lungs and into the buccal cavity, making the lungs appear collapsed. The air is then driven out from the buccal cavity through the nostrils. RESPIRATORY PATHWAY Morphology and Anatomy of Frog 8  External nares ——> nasal chambers ——> internal nares ——> buccopharyngeal cavity ——> glottis ——> laryngotracheal chamber ——> lungs Heart of a Frog: 1. Chambers: The frog's heart has three chambers: Two auricles (left and right) One ventricle 2. Auricles: The left and right auricles are separated by an interauricular septum. The right auricle receives blood from the body through the sinus venosus, which opens into the auricle via the sinu-auricular aperture. This aperture is guarded by sinu-auricular valves. The left auricle receives oxygenated blood from the lungs through the pulmonary veins, which open into the auricle via a common opening (without a valve). 3. Ventricle: Both auricles open into the ventricle via a common aperture that is guarded by the atrioventricular valve. This valve is supported by collagen fibers known as chordae tendineae. The ventricle is thick and muscular, with its inner walls folded into columnar muscles called columnar carnae. 4. Arteries and Valves: From the right side of the ventricle, a truncus arteriosus arises, with the opening to the truncus guarded by three semilunar valves. The truncus arteriosus is divided into: Conus arteriosus (muscular part, also called pylangium) Synangium (distal part) Morphology and Anatomy of Frog 9  Conus arteriosus and synangium are separated by three semilunar valves. The pylangium is incompletely divided by a longitudinal spiral valve, which arises from its dorsal wall, dividing the cavity into two: Dorsal cavum aorticum Ventral cavum palmocutaneum 5. Aortic Trunks: The synangium bifurcates into two aortic trunks. Each aortic trunk gives rise to three arches: Palmocutaneous arch Systemic arch Carotid arch Nervous System of a Frog: 1. Divisions: The nervous system is divided into three parts: Central Nervous System (CNS): Brain and spinal cord Peripheral Nervous System (PNS): Cranial and spinal nerves Autonomic Nervous System (ANS): A chain of ganglia running parallel to the spinal cord 2. Central Nervous System (CNS): The brain is located in the cranium and is protected by two layers of membranes: Dura mater: Outer, thick fibrous membrane Pia-arachnoid: Inner, thin, and vascular membrane The space between the meninges and the brain is filled with cerebrospinal fluid (CSF), which protects the brain from mechanical shocks and injuries. 3. Brain Structure: Morphology and Anatomy of Frog 10  The brain is divided into three parts: 1. Forebrain: Largest part, includes: Olfactory lobes (control sense of smell) Cerebral hemispheres (control voluntary activities) Diencephalon (transfers impulses to cerebral hemisphere and regulates metabolism) Endocrine glands: Pineal body (epiphysis) on the dorsal side Pituitary body (hypophysis) on the ventral side Optic chiasma: Where the optic nerves cross on ventral side of diencephalon 2. Midbrain: Includes: Optic lobes (control vision) Crura cerebri: Brain thickened to form fibrous strands of nervous tissue 3. Hindbrain: Includes: Cerebellum (controls and coordinates muscular movements, but is poorly developed in frogs) Medulla oblongata (regulates involuntary activities like heartbeat and respiration, and continues posteriorly as the spinal cord) 4. Ventricles of the Brain: The brain contains hollow cavities filled with cerebrospinal fluid (CSF), secreted by the choroid plexus. These ventricles include: Rhinocoels: Ventricles of the olfactory lobes Lateral ventricles (paracoels): Ventricles of the cerebral hemispheres Lateral ventricles open into diocoel through Foramen of Monro Morphology and Anatomy of Frog 11  Third ventricle (diocoel): Ventricles of the diencephalon Optocoel: Ventricles of the optic lobes Optocoel open into narrow tubular cavity called Iter. Iter opens into myelocoel Myelocoel: The fourth ventricle of the medulla oblongata Metacoel: Ventricles of the cerebellum The myelocoel communicates with the central canal of the spinal cord 5. Functions of the Brain: Olfactory lobes: Control sense of smell Cerebral hemispheres: Control voluntary activity Diencephalon: Transfers impulses to cerebral hemispheres and regulates metabolism Optic lobes: Control sense of vision Cerebellum: Controls and coordinates muscular movements Medulla oblongata: Regulates involuntary activities such as heartbeat and respiration Male Reproductive System of a Frog Primary Function: Production of sperms and their transport to the outside. 1. Sexual Dimorphism: Male frogs are distinguishable from females by: Vocal sacs in the throat region. Nuptial pad at the base of the first finger on the forelimbs. Females lack these features. 2. Testes: Frogs have two oval, pale yellow testes, located at the anterior outer border of the kidneys. Morphology and Anatomy of Frog 12  Each testis is connected to its corresponding kidney by a mesorchium (a fold of peritoneum). Fat bodies are attached to the anterior border of the testes. 3. Structure of Testes: Composed of numerous seminiferous tubules, which: Have walls made of germinal epithelium that forms sperms through spermatogenesis. Produce sperms that cluster into bundles called spermatophores. Interstitial cells in the connective tissue between seminiferous tubules secrete the hormone testosterone. 4. Sperm Transport: Vasa efferentia: Transverse fine ducts arising from each testis. Transport spermatophores into the Bidder's canal. Bidder's canal: A longitudinal duct that leads spermatophores into uriniferous tubules. Ureter: Uriniferous tubules open into the ureter. The proximal half of the ureter has a swelling called the seminal vesicle, where spermatophores are stored. Spermatophores move from the seminal vesicle to the cloaca, where they are expelled. Female Reproductive System of a Frog Primary Function: Production of ova and their transport for external fertilization. 1. Ovaries: Morphology and Anatomy of Frog 13  A paired structure, attached to the anterior border of the peritoneum via the mesovarium. Not connected to the kidneys internally. During the breeding season, ovaries: Become darker. Develop significantly. Ovaries rupture to release ova into the body cavity. 2. Oviducts: Long, coiled paired tubes lying on either side of the body cavity. Divisible into three parts: Ovarian funnel: Receives ova through ostia. Ovarian tubule: Conducts ova. Ovisac: Stores ova before release. 3. Reproduction: A mature female lays 2,500 to 3,000 ova at a time. Ova are released through the cloacal aperture. Fertilization is external, occurring in water. Development is indirect, involving: A fish-like larval stage called a tadpole. Tadpoles undergo metamorphosis to transform into adult frogs. Morphology and Anatomy of Frog 14