ADRENAL GLAND: Location, Structure (histology), function.

T.S OF ADRENAL GLAND 

POSITION OF ADRENAL GLAND

ADRENAL GLAND IN SECTION

Histologically adrenal gland is divided into two regions;

1.     Stroma

2.     Parenchyma

T.S OF ADRENAL GLAND

ü Stroma represents the outer most protective capsule. It is actually made of an outer coat of fibrous connective tissue and an inner zone of areolar tissue containing arterioles. Extending from the protective capsule is a number of delicate trabeculae which pass through adrenal cortex.

ü  Parenchyma consists of two zones which are different in origin, structure and function. They are called – outer adrenal cortex and inner adrenal medulla.

a)     Adrenal cortex – Adrenal cortex is derived from mesoderm. It is sub-divided into three zones.

·        Zona glomerulosa: it represents 15% of the cortex and lies inner to the protective capsule. It consists of columnar pyramidal cells arranged in the form of rounded masses around an inelastic lumen or arched loops. Glomerulosa cells secrete mineralo-corticoid.

·        Zona fasciculate: It is the middle zone of the adrenal cortex and widest of all three zones representing 70-80% of the total adrenal cortex. It consists of columnar or polyhedral or irregular cubical uninucleated or binucleated cells arranged in long straight cords usually 2 cell thick. This zone secretes gluco-corticoids which controls glucose metabolism.

·        Zona reticularis: It is the inner most zone of the cortex. It is very thin zone which represents about 5-10% of total adrenal cortex. It consists of branching cords of small cells showing network like arrangements. The cells secrete sex hormones.

b)    Adrenal medulla– It represents the central core of the gland. It is derived from ectoderm and is light brown in colour. Medulla consists of chromaffin cells containing chromaffin granules that stain brown with chromic acid or potassium dichromate. These cells are seen around large central vein that drains the capillaries of the adrenal cortex. Adrenal cortex stores and secretes the hormones- adrenalin and non-adrenalin secreted by sympathetic nervous system.

MICROSPORANGIUM: Meaning, structure, origin, development, function & signinficance

DEVELOPMENT OF MICROSPORANGIUM

In a huge mass of cells, few cells in the hypodermal region become differentiated, by their large size, radial growth and dense cytoplasm and conspicuous nuclei. They make the archisporium. Generally archisporium consists of 2-3 cell wide plate running along the entire length of the lobe.

The micro sporangial initials (archisporial cells) divide periclinally forming a primary parietal layer and primary sporogenous layer. The cells of the primary parietal layer laying immediately beneath the epidermis divide repeatedly both periclinally and anticlinally giving rise to 3-5 concentric layers forming the wall of the young sporangium.

Cells of the epidermis divide anticlinally only. The cells thus formed become greatly stretched and flattened. Sometimes its cells may be generally lignified or cutinized.

The layer next to the epidermis is the endothecium or fibrous layer. As a rule, by the development of fibrous bands of thickening the endothecium is hygroscopic and is therefore mainly responsible for the dehiscence of the mature anther

.

             NOTE: The cells of the endothecium are thin walled along the line of dehiscence of each anther lobe. The opening through which the pollen grains are discharged from pollen sac is called STROMIUM.

The inner most layer of the wall layer develops into a single layered tapetum. The tapetal layer has dense cytoplasm and conspicuous nuclei. Tapetum makes a nutritive layer for the developing microspores.

FORMATION OF ANTHER LOBES FROM UNDIFFERENTIATED MASS OF CELLS

  In meantime, the primary sporogenous layer cells give rise to microspore mother cell (mmc) or the pollen mother cells. In the beginning mmc remains closely packed but as anther enlarges in size, the pollen sac also increases in size, the mmc also increases in size and becomes spherical in shape and gets loosely arranged. 

MATURED ANTHER

MATURED ANTHER

HAUSTORIUM (haustoria): structure (microscopic view), formation and function.

It is wondering structure in plant kingdom. From primitive fungi to highly evolved angiosperms we can see this structure. It is a projection originated from normal tissue to get better nourishment from neighboring source. 

Haustorium

Haustorium has hypotonic cytoplasm compared to surrounding host tissue. Hence it helps to grab the nourishment by osmosis.

 Amazing fact here is, how can Haustorium maintain its hypotonic nature with its own tissue..??? 

Its size varies, in fungi it is nodule like structure just penetrates into the host tissue and sucks the required nutrition. In fungi, haustoria can be seen at the base of the mycelium where it is in contact with host tissue.

HAUSTORIUM IN HOST TISSUE 

HAUSTORIUM IN HOST TISSUE 

In higher plants (Gymnosperm onwards) haustoria are quite rare. In the embryos of Angiosperms we can see haustoria where the requirement of nutrition is more. Endosperm of the Cucumis shows beautiful Haustorium. It grows to a size that it uses to cross out the integument of ovary to grab the nourishment. In advanced plants, in embryogeny the micropylar end shows slightly bulged haustoria.

MICROSCOPIC VIEW OF HAUSTORIUM

(ITS OBSERVED IN ENDOSPERM OF CUCUMIS)

Formation of haustoria is shown in sequence.

Different views of haustoirum........

 Haustoria play an important role for the survival of the plant and some other organisms.