T. S. Passing Through Stomach



  • Stomach is a broad tube, highly muscularised, having masticatory and digestive function. Histologically stomach is composed of serosa, muscle layer, sub-mucosa, muscularis mucosa and mucosa.
  • Serosa forms the outermost thin layer. It is derived from visceral peritoneum and is composed of flat squamous cells, called as mesothelium.
  • Muscle layer consists of outer longitudinal and inner circular muscle fibres.
  • Outer longitudinal muscles run longitudinally and are made up of unstriped fibers. By the contraction of longitudinal muscles, stomach becomes shortened and the volume of lumen is widened.
  • Inner circular muscles consist of circular fibers. By the contraction of these muscles, stomach increases in the size but the volume of the lumen is reduced.
  • By alternate contractions and relaxations of longitudinal and circular fibers, the food is pushed backward and is also masticated.
  • Sub-mucosa is made up of the loose areolar connective tissue. It serves to bind loosely muscularis mucosa with the muscular coat. It also contains blood vessels.
  • Muscularis mucosa is a thin layer consisting of longitudinal and circular layers.
  • Mucosa is the innermost layer thrown into folds. Mucosa consists of endodermal columnar epithelial cells, and connective tissue. Mucosa contains, oxyntic cells (HCL secreting), zymogen cells (pepsin secreting) and mucous cells (mucus secreting). The villi are of different sizes.

Special features (functions) : As soon as food reaches into the stomach, its muscular walls masticate the food; its gastric glands secrete digestive enzymes which hydrolyse the food. Pepsin breaks peptide bonds and converts proteins into derived proteins i.e., peptones and proteoses. HCL kills the bacteria or living food. The secretion of the gastric glands is under neurohormonal control.
Identification : Since the section has thick musculature and mucosal folds and above features, hence it is T.S. of stomach of frog.




  • Vertical section passing through the skin reveals two layers, outer epidermis and inner dermis, distinctly seen under high magnification.
  • Epidermis is thin and made up of startified squamous epithelium. Multilayered epidermis is differentiated into two layers : (a) outermost layer is stratum corneum and (b) inner layer called as stratum germinativum or stratum malpighi consisting of single layered closely placed nuclei.
  • Beneath the epidermis is thin basement membrane and then dermis.
  • Dermis constitutes major part of the skin and is largely made up of connective tissues. It is distinctly differentiated into two layers. Outer layer is made up of areolar spongy connective tissue and hence
    called as stratum spongiosum. It contains mucous glands, poison glands and chromatophores. Inner layer is made up of compact zigzag parallel fibres and hence called as stratum compactum. Dermis also contains few vertical fibers, blood vessels nerves and lymph space.
  • A cellular layer separates stratum spongiosum and stratum compactum.
  • Just beneath the stratum compactum is lymph layer and then body musculature.
  • Connective tissue consists of horizontal connective tissue and vertical connective tissue.

Special features: Skin of frog performs various functions. It is protective, water observant, respiratory, mucous secreting, sensory, excretory and swimming. Skin is an organ consisting of an ectodermal epithelium, the epidermis, and its supporting mesodermal connective tissue, the dermis. When the cells of stratum corneum die, they are shed off and this is called as moulting.
Identification: Since the section has thin epidermis and thick dermis and above features, hence it is V.S. of skin of frog.

FROG SLIDES – T.S. Passing Through Duodenum


  • HIstologically duodenum resembles with ileum but its mucosa is peculiar. Section shows serosa, muscle layer, sub-mucosa, muscularis mucosa and mucosa.
  • Serosa forms outer covering of duodenum. It is derived from the visceral peritoneum and is composed of flat squamous epithelial cells, called as mesothelium.
  • Muscle layer is composed of an outer thinner longitudinal and inner thicker circular fibres.
  • Longitudinal muscles are composed of unstriped fibres. By their contraction, the duodenal tube is shortened but the volume of its lumen is widened.
  • Circular muscles consist of circular fibres. By their contraction, the duodenal tube increases in size but the volume of its lumen decreases.
  • Circular and longitudinal muscle layers contain nerves and lymphocytes.
  • Sub-mucosa is well developed and is composed of loose connective tissue. In it the blood vessels and lacteals ramify before entering or after leaving the mucous membrane. It also contains nerves and blood vessels.
  • Mucosa is thrown into irregular and branched villi.

Special features (functions) : Cholecystokinin and secretin, secreted in duodenum stimulate liver to secrete bile and pancreas to secrete pancreatic juice, respectively. In duodenum food is converted into amino acids and polypeptides, maltose and fatty acids and glycerol.

Identification : Since it has thin musculature, long and branched mucosal villi and above, hence it is T.S. of duodenum of frog.

FROG SLIDES – T.S. Passing Through Intestine


  • Intestine is modified for absorption and hence it is less muscularised. T.S. passing through it shows serosa, muscle layer, sub-mucosa, muscular is mucosa and mucosa.
  • Serosa coat is complete except over part of the duodenum. Serosa originates from the visceral peritoneal layer and is composed of flat squamous epithelial cells, called as mesothelium.
  • Outer longitudinal and inner circular muscle layers are distinct.
  • Longitudinal layer consists of unstriped fibers. Size of the intestine is decreased and the volume of the intestinal lumen is increased by the contraction of the longitudinal layer.
  • Circular muscle fibres form comparatively thick layer than longitudinal muscle layer. When they contract, size of the intestine is increased and the volume of the lumen is decreased.
  • Between longitudinal and circular layers, a network of the lymphatic vessels and plexus myentericus, consisting of plexus of amyelinated nerve fibres, is found. However this layer is indistinct even in high magnification.
  • Sub-mucosa is also well developed, made up of connective tissue and having nerves, rich lymph spaces and blood vessels.
  • Blood vessels and lacteals ramify before or after leaving the mucous membrane. Nerve plexus is called as plexus of Meissner.
  • Muscularis mucosa is not well developed.
  • Mucosa is thrown into villi of different sizes. In a complete cut section the villi occupy most of the space of the lumen. Very small lumen is left. The branching of the mucosa increase~ thesurface area of absorption.

Special features (functions) : Goblet cells secrete mucous, while absorptive cells absorb food material. Intestinal enzymes are peptidases, maltase, lipase, invertase and lactase, which hydrolyse the food into amino acids sugar, fatty acids and glycerol, glucose and fructose and glucose and galactose, respectively.
Identification : Since it has goblet cells in mucosal folds, and all above features, hence it is T.S. of intestine of frog.

FROG SLIDES – T.S. Passing Through Liver


  • Amphibian liver is dark chocolate coloured and large in proportion to the size of the body. The liver of frog contains three unequal lobes but connected with each other. T.S. passing through the liver shows the following histological details.
  • It is a solid glandular organ, made up of rounded hepatic lobules or acini in the form of branched columns, separated from one another by the connective tissue. Externally it is covered by serous coat.
  • Each acini or hepatic lobule contains roughly 5 to 10 hepatic cells which are penetrated by fine network of connective tissue and sinusoid vessels called as hepatic capillaries.
  • Portal vein, afferent blood vessel and hepatic artery enter its undersurface, where bile duct passes from the gland. Fine branches from above three form interlobular and intralobular vessels. Vessels are indistinct.
  • Bile ducts and bile canaliculi are also seen.
  • Each hepatic cell is rounded and nucleated.
  • Glycogen formation occurs in the middle of the lobule, while peripheral area secretes bile.
  • Large ducts drain bile capillaries and they unite to form hepatic duct.
  • Bile secreted by liver is stored into large pear-shaped saccular structure, called as gall bladder.

Special features (functions) : Liver has the following functions :

  1. It secretes bile juice, consisting of bile salts, bile pigments, cholesterol and lecithin, which act as fat emulsifier.
  2. It stores glycogen inorganic salts of iron and copper. Glycogenesis and glycogenolysis take place in liver.
  3. Liver produces fibrinogen and prothrombin, which are essential components of clotting of blood. It produces heparin, which prevents blood clotting.
  4. Liver changes ammonia into urea. Urea synthesis takes place by ornithine cycle. This process is also called as deamination.
  5. Liver also controls oxidation of sugar.
  6. It is excretory.
  7. In embryonic condition liver produces blood corpuscles
  8. Various enzymes are synthesized in liver.
  9. Liver also stores and synthesizes vitamins.
  10. Liver is a very important organ for metabolism.

Identification: Since it has rounded hepatic lobules, and all above features hence it is T.S. of liver of frog. 

FROG SLIDES – T.S. Passing Through Pancreas


  • Pancreas is noteworthy because in amphibians one or more pancreatic ducts open either directly into duodenum or indirectly through bile duct.
  • Pancreas is a large and yellow-coloured compound tubulo-alveolar gland, situated between duodenum and stomach, and covered with coelomic epithelium.
  • Histologically it is composed of several lobules or acini, connected by loose connective tissue, nerves and blood vessels. Pancreatic acini represent the secretory part of gland. Cut lobules may be rounded or tubular.
  • Large veins and arteris and several blood capillaries lie in the connective tissue.
  • Centre of the acinus communicates with the nearest duct and it secretes digestive enzymes.
  • Lightly coloured islets of Langerhans are scattered groups of cells surrounded by pancreatic acini.
  • Central mass is peculiar and contains special cells, called as islets of Langerhans.
  • Pancreas is very vascular and also innervated by parasympathetc nerves.

Special features (functions) : Pancreas plays a dual role in the body, serving both as exocrine and endocrine glands. Exocrine secretion consists of digestive enzymes, such as amylopsin, trypsin and lipase. Endocrine secretion is that of islets of Langerhans which produce insulin and glucagon, secreted by ~-cells and a-cells, respectively. Insulin plays an important role in carbohydrate metabolism. It regulates blood sugar level. Its deficiency causes a disease, called as diabetes. Glucagon increases the blood sugar level. Its deficiency causes hypoglycemia.

Identification : Since the above section contains pancreatic lobules and islets of Langerhans and all above, hence this is T.S. of frog passing through pancreas. 

FROG SLIDES – T.S. Passing Through Spleen


  •  Spleen is a small, rounded and dark brown structure, found above rectum.
  • Spleen is covered with a fibrous and muscular capsule and externally covered by visceral peritoneum.
  • Capsule sends bands or trabeculae, which ramify into the substance of the gland.
  • Into the network of the trabeculae there is a soft pulpy mass, called as splenic pulp.
  • Spleen T.S. shows presence of centrally located red pulp and white pulp.

Special features (functions) :

  1. B-Iymphocytes produce antibodies,
  2. Spleen stores and synthesizes leucocytes (W.B.C.). Spleen is dilatable and contractile.
  3. It contains macrophages, whichnare responsible for the destruction of old erythrocytes.
  4. In embryonic condition it produces erythrocytes but after birth leucocytes are produced.

Identification : Since the above section contains red pulp, white pulp and trabeculae and all above features, hence it is T.S. of spleen of frog.

FROG SLIDES – T.S. Passing Through Lung


  • There is a pair of sac-like lungs, one on either side of heart. Lung of frog is not much elongated, but it is well developed having more alveolar spaces and rich blood supply.
  • T.S. of lung shows peritoneal layer, lung wall, alveoli and a central cavity.
  • Lung wall is composed of outer peritoneum made-up of squamous epithelial cells, connective tissue and unstriped muscle fibres. Inner wall is composed of ciliated epithelial cells, mucous glands and blood capillaries. Mucous glands are indistinct.
  • Blood capllaries form network.
  • Central cavity is partly divided into numerous chambers or alveoli, partitioned by trabeculae.
  • Trabeculae partly contain flattened squamous epithelium and partly ciliated columnar epithelial cells. They are richly vascularised and contain several nuclei.
  • Alveoli and trabeculae increase the respiratory surface.

Special features (functions) : Lung is an important respiratory organ meant for external respiration, where oxygen from the atmosphere is taken to combine with haemoglobin forming oxyhaemoglobin. From the lungs oxyhaemoglobin is transported to cells for tissue or cellular respiration.
Identification : Since it has alveoli and air spaces and all above features, hence it is section of lung of frog.

FROG SLIDES – T.S. Passing Through Spinal Cord


  • Medula oblongata after emerging from foramen magnum, and continues posteriorly as spinal cord.
  • T.S. of spinal cord shows that it is coated by outer durameter and inner piameter.
  • Bioplasm of the nerve cord is divided by dorsal and ventral fissures and is differentiated into outer white matter and inner grey matter.
  • White matter is devoid of nerve cells and represents lighter area.
  • Grey matter contains nerve cells and a central canal, which is continued with the ventricles of brain. It is lined by a single epithelial layer; called as ependyma.
  • Grey matter forms squarish area, but dorsal and ventral horns are not very much distinct.
  • In mid-dorsal axis, dorsal and ventral
  • fissures are seen.

Special features (function) : Spinal cord has the following functions :

  1. It receives stimulus from dorsal and ventral roots.
  2. It transmits impulses to the brain.
  3. It causes reflex action.

Identification: Since it has white matter and grey matter and all above features, hence it is T.S. of spinal cord of frog.

FROG SLIDES – T.S. Passing Through Kidney


  • Kidney of adult frog is opisthonephros.
  • There are two kidneys, each representing a compound tubular gland. T.S. passing through a kidney shows nephrostomes, uriniferous tubules and Bowman’s capsules.
  • Each kidney is bean-shaped structure covered by visceral peritoneal layer.
  • Interior of the kidney is filled with large number of uriniferous tubules cut in various planes.
  • Nephrostomes are funnel-like structures communicating with the coelom and to the vein of kidney.
  • Bowman’s capsules are cup-shaped structures, containing tuft of blood vessels called as glomerulus.
  • Bowman’s capsule and glomerulus are collectively called as Malpighian body. These capsules are concentrated towards ventral region.
  • Renal arteries and renal veins are cut at several places in section.
  • Nephrostome or coelomic funnel is in the form of wide opening and it leads into collecting chamber and then into tubule. Other structures are Bowman’s capsule, glomerulus, uriniferous tubules, renal
    arteries and peritoneal covering.

Function of kidney: It functions to stabilize blood stream by filtration extracting water, urea, uric acid, phosphates and sulphates, etc. Various diseases associated with kidney are glycosuria, albuminuria
and nephritis, etc.

Identification : Since the section has glomerulus and Bowman’s capsule, hence it is T.S. of kidney of frog.

FROG SLIDES – T.S. Passing Through Testis


  • T.S. passing through testis shows that it is made up of peritoneal epithelium, tunica, albuginea, blood vessels, intertubular connective tissue and mesorchium.
  • Testis are attached with kidney with mesorchium.
  • T.S. of a seminiferous tubule shows that it is composed of a germinal epithelium which gives rise to spermatogonia or sperm mother cells.
  • Other stages are spermatocytes, spermatids and sperms representing various stages of spermatogenesis are seen in the section.
  • Section shows cut blood vessels and inter-tubular connective tissue.
  • In section interstitial cells primary spermatocytes, secondary spermatocytes, spermatids and sperms are seen.
  • Interstitial cells present in the section secrete male hormone testosterone, which is responsible for developing secondary sexual characters.

Function : It produces sperms.

Identification: Since sections contains sperms and above features, hence it is T.S. of testis of frog.

FROG SLIDES – T.S. Passing Through Ovary


  • There are two ovaries attached to kidneys by mesovarium.
  • Each ovary is composed of several hollow lobules containing developing ova in various stages of development, cunnective tissues, young follicles, blood vessel, primary oocytes germinal epithelium and
  • Each lobule is surrounded by theca extema, theca intema, germinal, epithelium, follicular cells and ova in various stages of development.
  • An ovum under high magnification shows theca extema, theca intema, yolk granules, cytoplasm and nucleus.

Identification : Since A, B and C contains ova and above features, hence it is T.S. of ovary of frog.

FROG SLIDES – T.S. of Bone


  • T. S. bone shows outer periosteum, then outer zone of bone layer, inner zone of bone layer, bone marrow and central narrow cavity or canal.
  • Outer most layer periosteum.
  • Below periosteum is outer osteoblast layer.
  • Beneath outer blast layer are lamellae osteocyte cells and inner osteoblast layer.
  • Innermost in endosteum enclosing bone marrow.

Identification Since the above section has osteocyte cells and above features hence it in T. S. of bone of frog

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