HEPATOBILIARY APPARATUS: HISTOLOGY OF LIVER AND GALL BLADDER

Structure of the liver

The histological features of the liver are summarized below.

•         Structural component of liver include

–        Connective tissue stroma

–        Parenchyma

–        Portal triad

–        Sinusoids

–        Bile canaliculi

HISTOLOGICAL FEATURES OF SPLEEN

General Structure of spleen

The spleen is the largest accumulation of lymphoid tissue in the body. The spleen is surrounded by a capsule of dense connective tissue from which emerge trabeculae, which divide the parenchyma, or splenic pulp, into incomplete compartments. Large trabeculae originate at the hilum, on the medial surface of the spleen; these trabeculae carry nerves, arteries and veins.

In humans, the connective tissue of the capsule and trabeculae contains only a few smooth muscle cells, contrary to what occurs in several animals (eg, horses, dogs, and cats). 

HISTOLOGICAL FEATURES OF TONSIL

Tonsils

Tonsils belong to the mucosa associated lymphoid tissue (MALT), but because they are incompletely encapsulated, they are considered organs and will be studied apart from the MALT. The tonsils constitute a lymphoid tissue that lies beneath, and in contact with, the epithelium of the initial portion of the digestive tract. Depending on their location, tonsils in the mouth and pharynx are called palatine, pharyngeal, or lingual.

HISTOLOGICAL FEATURES OF LYMPH NODE

Lymph Nodes

Lymph nodes are distributed throughout the body along the course of the lymphatic vessels. The nodes are found in the axilla and the groin, along the great vessels of the neck, and in large numbers in the thorax and abdomen, especially in mesenteries. Lymph nodes constitute a series of in-line filters that are important in the body's defense against microorganisms and the spread of tumor cells. All this lymph, derived from tissue fluid, is filtered by at least one node before returning to the circulation.

Gross Features of Lymph Nodes

Lymph nodes are elongated or kidney-shaped organs that have a convex surface that is the entrance site of lymphatic vessels and a concave depression, the hilum, through which arteries and nerves enter and veins and lymphatic vessels leave the organ (Figure- 1). A connective tissue capsule surrounds the lymph node, sending trabeculae into its interior.

GROSS ANATOMY AND HISTOLOGICAL FEATURES OF THYROID GLAND

The thyroid is a highly vascular ductless gland found deep in the neck region and overlapped by the anterior neck muscles.

Location of the thyroid gland:

It situated in front and at the sides of trachea opposite 5th, 6th, 7th cervical and 1st thoracic vertebrae in the neck region.

Structure and Function of Skin

Structure of Skin

Layers of the skin (from superficial to deep) are:

Epidermis – it is made up of stratified squamous epithelium keratinized

Dermis – it is made up of connective tissue.

Histology of Bone Tissue

Microscopic examination of bone shows two varieties:

1.  Primary, immature or woven bone

In addition to irregular array of collagen fibres, other characteristics of primary bone tissue are a lower mineral content and a higher proportion of osteocytes than that in secondary bone tissue. The newly formed bone during development or during healing process are woven bone.

  

Connective Tissue: General Considerations

Connective tissue provides a matrix that connects and binds the cells and organs and ultimately gives support to the body. (Hence called support tissue also.)

The main constituent of connective tissue is the extracellular matrix. Due to this abundance of extracellular matrix, the cells in connective tissues are widely placed. Other tissues (like epithelium, muscular and nervous) are formed mainly by cells.

Gross anatomy and histological features of Pituitary Gland

What is pituitary gland?

Also known as hypophysis cerebri, pituitary is an ovoid neuroglandular organ.

It is suspended from the floor of the third ventricle by a stalk known as infundibulum.

It is located in a depression called hypophyseal fossa of sella turcica of body of sphenoid. The fossa is roofed by the diaphragm sellae which is a fold derived from the meningeal layer of dura mater. The diaphragm sellae is pierced by the pituitary stalk or infuldibulum.