TONGUE: Morphological feature, anatomical features, circumvallate papillae (slide view), fungiform papillae, filiform papillae, foliate papillae.

Tongue of vertebrate shows much diversity and are not homologous. Tongue is gustatory organ. It is a soft muscular organ situated on the floor of the buccal cavity. The mucous membrane below the tongue forms a median fold called frenulum which joins tongue to the floor of the mouth.

MORPHOLOGY OF TONGUE

Tongue is divided into two regions:

1.     Papillar area: anterior 2/3 of the tongue where lingual papillae are present.

2.     Lymphoid area: posterior 1/3 of the tongue which lacks lingual papillae but is lymphoidal.

The dorsal surface of the papillar area shows a median groove called median succus or lingual septum.

Tongue in section reveals following details:

SLIDE VIEW OF TONGUE

Tongue is composed of intercalary bundles of striped muscle fibers which are embedded in a bedding substance called lamina propria, made up of areolar tissue. Also present in areolar tissue are blood vessels, nerves and glands of von ebner.

The muscle fibers are disposed in three directions: oblique, transverse and longitudinal.

The entire tongue is covered by mucous membrane lined by squamous epithelium.

Along the ventral surface of the mucous membrane is smooth but along the dorsal surface it is thrown into a number of projections called lingual papillae.

There are four types of lingual papillae:

        i.            Circumvallate papillae: lie on the base of the tongue they have taste buds at its base. They are large but few in numbers, each are surrounded by a groove.

CIRCUMVALLATE PAPILLAE

SLIDE VIEW OF CIRCUMVALLATE PAPILLAE

      ii.           Fungiform papillae: are second largest but more in number than circumvallate papillae. They are distributed all over the surface of the tongue. Each Fungiform papillae show a narrow basal end and a club shaped free end that projects above the surface prominently. The papillae appear red in colour as they have rich blood supply. Secondary papillae are also present.

FUNGIFORM PAPILLAE

    iii.            Filiform papillae: are smallest but numerous of all types of papillae. They are distributed all over the tongue. Each papilla has a conical elevation directed posteriorly. It is covered by cornified epithelium that is produced into thread like strands.

FILIFORM PAPILLAE

   iv.            Foliate papilla: are broad and leaf like lying hear the base of the tongue in parallel rows and are sharp in nature. They bear taste buds on their sides. Usually these are found at the tip of the tongue. In cows it is more common. In human it is absent.

OBTURATOR OF PLANT: Meaning, occurance, features, anatomy & function.

In several families of angiosperms a characteristic placental outgrowth is present near the ovule and is referred to as obturator. This obturator grows into the space between the nucellus and the integuments and also between the ovary and ovary wall.

An obturator is said to be helping in directing the growth of pollen tube towards micropyle. Obturator exhibits a great amount of diversity in its origin, morphology, anatomy and mode of development.

Obturator originated from placenta of funiculus or from both. In Combretum, Sterculia the obturator arises at a swelling of the funiculus. In Rivina humilis the obturator arises from the wall of the ovary. In Ceratocephalus, the cells of the funicular epidermis a little above the micropyle radially elongate and develop into the obturator. In some species obturator arises from placenta. Obturator may arise from stylar canal.

OBTURATOR FROM FUNICLE

In Chrozophora the obturator is composed of small thin walled compactly arranged cells, while in Euphorbia the cells of the obturator are loose elongated and hair like. In some species obturator constitutes of short hair developed from the inner surface of the funicle.

Structurally the cells of the obturator may be generally said to be thin walled loosely or compactly arranged may be isodiametric or long and hair like. Sometimes the cells may be secretory in function.

Ultra structurally, the cells of the obturator are rich in ER, dictyosomes, vesicles and many other organelles. The cells of the obturator may secrete an exudates which may chemotropically guide the pollen tube.

HYPOSTASE: Meaning, occurance, feature, structural details & function.

Hypostase is one of the unusual features present at the chalazal region of the embryo sac and situated immediately below it. It represents an irregularly outlined group of nucellar cells which are poor in cytoplasmic contents but have their walls partially lignified or suberized.

The name Hypostase to this group of unusual cells was first given by Van Tieghem. According to him the hypostase forms a barrier or boundary to prevent the further growth of the embryo sac.

Even though hypostase is limited to basal region of the embryo sac occasionally they may cover the embryo sac extending up to the micropylar half.

Hypostase has been reported from a number of families Amaryllidaceae, Villiaceae, Zingiberaceae, Euphorbiaceae, Crossomataceae, Theaceae and Umbelliferae.

At the stage of the organized embryo sac the cluster of hypostase cells appear like a beard at the chalazal region of the embryo sac.

HYPOSTASE OF PLANT (ANATOMICAL VIEW)

FUNCTIONS:

       I.            It prevents excessive growth of the embryo sac of the chalazal region acting as a barrier.

    II.            It plays a role in the water balance of the resting seed.

 III.            It serves as a link between the vasculature of the funicle and the embryo sac facilitating the rapid transport of the nutrients.

 IV.            It may acts as secondary storage tissue.

    V.            It produces certain enzymes or hormones and has a role to play in the protection of the seed.

GASTRIC GLANDS: structural components, structural details, functions of individual structures, significance and microscopic view.

The mucosal layer is divided into gastric area which shows a number of gastric pits,into each pit a number of simple branched or unbranched gastric glands open. There are about 15-20 million gastric glands. They are tubular in character, and are formed of a delicate basement membrane, consisting of flattened transparent endothelial cells lined by epithelium.  There are two types of gastric glands.

                                    

SECTION SHOWING GASTRIC GLAND

A.    Cardiac glands: The cardiac glands are few in number, occur close to the cardiac orifice and they have more mucous secreting cells.

B.     Gastric glands:  also known as fundus glands. They occupy largest area of the stomach that almost reaches up to muscularis mucosa. The fundus glands are found in the body and fundus of the stomach; they are simple tubes, two or more of which open into a single duct. The duct, however, in these glands is shorter, sometimes not amounting to more than one-sixth of the whole length of the gland; it is lined throughout by columnar epithelium. The gland tubes are straight and parallel to each other. At the point where they open into the duct, which is termed the neck, the epithelium alters, and consists of short columnar or polyhedral, granular cells, which almost fill the tube, so that the lumen becomes suddenly constricted and is continued down as a very fine channel. They are known as the chief or central cells of the glands. Between these cells and the basement membrane, larger oval cells, which stain deeply with eosin, are found; these cells are studded throughout the tube at intervals, giving it a beaded or varicose appearance. 
                      These are known as the parietal or oxyntic cells, and they are connected with the lumen by fine channels which run into their substance. Between the glands the mucous membrane consists of a connective-tissue frame-work, with lymphoid tissue. In places, this later tissue, especially in early life, is collected into little masses, which to a certain extent resemble the solitary nodules of the intestine, and are termed the lenticular glands of the stomach.

                          


     They are not, however, so distinctly circumscribed as the solitary nodules. Beneath the mucous membrane, and between it and the submucous coat, is a thin stratum of involuntary muscular fiber (muscularis mucosae), which in some parts consists only of a single longitudinal layer; in others of two layers, an inner circular and an outer longitudinal.

                             

STRUCTURAL ARRANGEMENT WITH FUNCTION

NOTE: 

·        Neck cells are located in the cardiac region and they secretes mucous.

·        Chief cells or peptic cells forms the bulk of the gland and secretes pepsin.

·        Parietal cells or oxyntic cells are large permeable cells which uncharacteristically passes intracellular canalculi which leads to intercellular canalculi. Parietal cell secretes HCl.

SLIDE VIEW OF GASTRIC GLANDS

SLIDE VIEW OF GASTRIC GLANDS

   

SPLEEN: Location, morphological and anatomical features.

Spleen is largest lymphoid organ, oval in outline and protected by thick firm fibroblastic capsule or Stroma containing a thin layer of smooth muscles in its inner portion.

External to capsule is serous coat which is derived from peritoneum; it is thin smooth and adherent to fibroblastic coat. Blood vessels enter and leave the spleen at a point called hilus, represented by capsular tissue projected inside. From the inner surface of the fibroblastic coat numerous small fibrous bands arise and are distributed in all the directions, they are called as trabeculae. Uniting of these trabeculae forms the frame work of the spleen. Therefore the spleen consists of a number of small spaces or areolae. Areolae are also called as spleen lobules. These areolae contain the spleenic pulp.

Fibroblastic coat and trabeculae are composed of white and yellow fibrous tissue. Large amount of WBC’S are found in blood of spleenic pulp. Spleenic pulp shows the presence of spleenic cells which show amoeboid movement. These cells often contain pigments and RBC in their interior. Nucleated red-blood corpuscles have also been found in the spleen of young animals.

Spleenic pulp contains a unique structure called germinal center which is surrounded by a typical white pulp, which is slightly differs from spleenic pulp.

SECTIONAL VIEW

SLIDE VIEW

THYROID GLAND: Location, anatomy and function.

Thyroid gland arises in embryo as a diverticulum of the floor of the pharynx which proliferates to form follicles and loses its connection with pharynx. In lower vertebrates it arises mid ventrally from between the second and fourth visceral clefts but in higher forms it develops between the first and second clefts. The thyroid has small follicles of cuboidal cells, the lumen of follicles is filled with an iodine rich colloid and the follicles are enclosed in a capsule of connective tissue.

This colloid secretion is a globular protein known as thyroglobulin which is also known as iodothyronins or thyroid hormones of which thyroxin is one.

Thyroxin regulates metabolism that is heat production and energy liberation in all the organ systems. The under secretion of this hormone lowers the rate of metabolism and causes the animal to become fatty, sluggish and feeble minded and even growth is retarded. The heart rate is also lowered and sexual development is retarded. This condition is known as cretinism. The deficiency of thyroxin may stimulate the formation of new gland tissue resulting in an enlargement of the thyroid called goiter. The goiter is actually caused by the deficiency of iodine in the diet. The over-secretion of this hormone increases the rare of oxidation and is responsible for the quick consumption of the food. Therefore fat is not stored. Over secretion also results in the bulging of eye balls and irregular heart rate, etc.

SLIDE VIEW

Parathyroid gland: these are small oval glands situated on the lobes of thyroid. These glands are either found embedded in the thyroid or located close to them. Parathyroid secretes two hormones which are responsible for regulating the amount of calcium and phosphorous in blood. The two hormones are parathormone and calcitonin. Over secretion of these hormones results in tumers on the gland and causes calcium to be withdrawn from bones, thus producing a high calcium level in the blood. In such conditions bone may become soft, porous and weak. Its deficiency lowers the calcium level in the blood due to which normal functioning of muscles bone growth and teeth formation are retarded. It has been seen experimentally that the removal of parathyroid result in the death of the individual.

MORPHOLOGICAL VIEW

SLIDE VIEW

Ribulose bisulphate carboxylase: occurance, function and significance.

Ribulose bisulphate carboxylase 

Ribulose bisulphate carboxylase is world’s most abundant enzyme. The enzyme is found in plant containing eight copies of two types of subunits. The larger subunit, which has a molecular weight of 56000 and contains the catalytic site, is synthesized within the chloroplast under the direction of chloroplast DNA and ribosomes. The smaller subunit, with a molecular weight of 14000 is synthesized on cytoplasmic ribosome under the direction of nuclear DNA.

CO2 acts as a substrate as well as activates ribulose bisulphate caboxylase by binding to the amino group of a lysyl residue in the large subunit to form a carbamate (lysine-NH-CO2⁻). This process is catalyzed by another enzyme and requires Mg⁺⁺, which binds to the carboxyl group of the carbamate. The Mg⁺⁺ in turn forms part of the binding site for a second molecule of CO2, which acts as the substrate in the carboxylase reaction. The reactive molecule of CO2 adds to the enolate of ribulose-1, 5-bisulphate to form 2-carboxy-3-ketoarabinitol-1, 5-bisulphate as an intermediate.

Studies showed that Ribulose bisulphate carboxylase has the same active site that catalyses a competing reaction in which O2 replaces CO2 as a substrate. It means enzyme acts as oxygenase.

REACTION MECHANISM

REACTION MECHANISM