Tejido conectivo

Introduction to Histology and Embryology

Welcome and Overview

• Fernando Pérez introduces himself as a lecturer in Histology and Embryology at the National University of Rosario's Faculty of Medicine.

• He discusses the recommended bibliography for the course, emphasizing the importance of histological images.

Understanding Connective Tissue

Definition and Functions

• Connective tissue is defined as a collection of cells with abundant interstitial substance, blood vessels, and nerves, always associated with other tissues.

• It serves multiple functions including support, structural filling, compartmentalization, physical protection, fat storage, water/electrolyte storage, and microcirculation facilitation.

Microcirculation Dynamics

• The capillary network allows for nutrient exchange (oxygen, carbon dioxide), hormone transport, and metabolic waste removal.

• Lymphatic drainage originates from loose connective tissue through blind capillaries that converge into regional lymph nodes.

Components of Connective Tissue

Cellular Components

• Key cellular components include mesenchymal stem cells, fibroblasts, mast cells, plasma cells, macrophages, adipocytes, and leukocytes.

Fibroblasts

• Fibroblasts are spindle-shaped cells responsible for producing amorphous fundamental substances and three types of fibers essential for tissue structure.

Mast Cells

• Mast cells are pro-inflammatory; they release various substances like histamine that trigger inflammatory responses. Their granules exhibit metachromasia when stained.

Plasma Cells

• Plasma cells arise from B lymphocytes; they produce antibodies (IgG type). They have large nuclei with characteristic chromatin arrangements resembling a "wheel" or clock face.

Macrophages

• Macrophages originate from monocytes that migrate into connective tissue. They play a defensive role due to their high phagocytic capacity.

Adipocytes

Overview of Connective Tissue Components

Key Cellular Elements in Connective Tissue

• The transcript discusses polymorphic nuclear lymphocytes characterized by dense chromatin, round nuclei, and a halo of cytoplasm.

• It introduces the amorphous fundamental substance, which is translucent and extensively hydrated, providing a gelatinous consistency that supports various connective tissue components.

• Glycosaminoglycans (GAGs), secreted by fibroblasts, are highlighted for their role in attracting cations like sodium due to their negatively charged nature, contributing to tissue turgor.

Structural Components of Connective Tissue

• Three types of fibers are identified: collagenous, elastic, and reticular fibers. Collagen fibers resist stretching and are crucial for forming strong bundles found in tendons and ligaments.

• Collagen fibers have significant tensile strength; they are composed mainly of type I collagen and appear in dense regular or irregular arrangements depending on their orientation.

Elastic Fibers Characteristics

• Elastic fibers consist of tropoelastin and can stretch significantly without breaking; they adapt to changes in diameter within organs such as blood vessels.

• These fibers can increase up to 150% of their original length while maintaining structural integrity.

Reticular Fibers Functionality

• Reticular fibers form a mesh-like network providing support to surrounding tissues; they cannot stretch but offer essential structural support.

• They require special staining techniques for visibility under microscopy, appearing black when treated with silver salts.

Types of Connective Tissue

Varieties of Connective Tissue

• The transcript categorizes connective tissue into loose, dense, elastic, and reticular types. Special connective tissues include adipose (brown and white), cartilage, blood (hematopoietic), and lymphatic tissues.

Loose vs. Dense Connective Tissue

• Loose connective tissue features an equilibrium among cellular components, amorphous substances, and fibrous elements; it supports epithelial structures effectively.

• Dense connective tissue shows a predominance of collagen fibers over the matrix; it is classified as either regular or irregular based on fiber arrangement.

Microscopic Observations

• The images illustrate different epithelial types supported by loose connective tissue. For instance, pseudostratified ciliated columnar epithelium rests upon loose connective structures.

Tissue Types and Functions in Connective Tissue

Overview of Dense Connective Tissue

• The balance between matrix cells and fibers is crucial, with dense irregular connective tissue showing a predominance of collagen fibers over other components.

• Collagen fibers are observed in multiple directions within the amorphous matrix, indicating structural complexity.

• Dense regular connective tissue features collagen bundles aligned in a single direction, with fibroblasts having larger nuclei compared to flattened or smaller nuclei of fibrous tissues.

Elastic and Reticular Fibers

• When elastic fibers dominate, they provide flexibility; reticular fibers form a supportive mesh for other tissues.

• Adipose tissue can be categorized into brown and white varieties, with brown adipose tissue being significant during embryonic development for thermoregulation.

Characteristics of Adipose Tissue

• Brown adipocytes are multiocular with centrally located round nuclei, while white adipocytes have a single lipid vesicle and peripheral flattened nuclei.

• Infants gradually lose brown adipose tissue as it is replaced by white adipose tissue after six months, particularly in specific regions like the dorsal interscapular area.

Functions of White Adipose Tissue

• White adipose tissue serves energy storage, protection, cushioning, and plays a role in glucose homeostasis through endocrine functions.

• Hormones produced by adipocytes include leptin (regulating food intake via the hypothalamus) and adiponectin (enhancing insulin sensitivity).

Implications of Obesity

• Excessive fat distribution leads to different obesity types: android (apple-shaped) versus gynoid (pear-shaped).

Functions of Loose Connective Tissue

Role in Inflammation Response

• Loose connective tissue provides support and nutrition through microcirculation and lymphatic drainage essential for inflammatory responses.

Structural Support from Dense Connective Tissue

• Dense connective tissue forms capsules around organs that may contain complete or incomplete septa dividing them into lobes or lobules.

Ligaments and Tendons Composition

• Ligaments connect joint surfaces while tendons attach muscles to bones; both consist primarily of dense regular connective tissue featuring parallel collagen fiber arrangements.

Muscle Attachment Insights

• Images illustrate how skeletal muscle connects to bone via tendons made from dense connective tissues.

Inflammatory Response and Tissue Repair

Normal Processes in Inflammation

• The release of pro-inflammatory substances, such as histamine, leads to increased fluid leakage from blood vessels, resulting in congestion or accumulation of water in the extracellular matrix. This condition is known as lymphedema, which is characteristic of the inflammatory response.

Transition to Chronic Inflammation

• As inflammation progresses, there is a shift from polymorphonuclear leukocytes to predominantly mononuclear cells, primarily lymphocytes and some monocytes that activate into macrophages. This transition marks the characteristics of chronic inflammatory responses.

Tissue Repair Mechanisms