Tejido sanguíneo y linfático

Introduction to Histology and Embryology

Celebrating 100 Years of Histology Education

• The lecture marks the centenary of the histology and embryology department, initiated by Professor Tomás Ser Root on June 1st.

• Emphasis on the importance of medical professionals who understand their role in medicine, encouraging students to strive for excellence.

Key Literature in Histology

• Recommended texts include "El Sol," "Gardner," "Junqueira," "Stevens," and "La Rosa" as essential resources for current knowledge in histology.

Understanding Blood as Connective Tissue

Classification and Definition of Blood

• Blood is classified as a type of connective tissue, consisting of cells suspended in plasma (45% cells, 55% plasma).

• The intercellular substance in blood is liquid, circulating through a closed cardiovascular system.

Functions of Blood

• Main functions include transporting gases, nutrients, metabolic products, waste products, hormones, and immune cells throughout the body.

• Additional roles involve thermoregulation and hemostasis to prevent blood loss from damaged vessels.

Components of Blood

Cellular Composition

• Blood consists of four main components: plasma (protein solution), erythrocytes (oxygen transport), leukocytes (defense against pathogens), and platelets (prevent bleeding).

Erythrocytes vs. Leukocytes

• Erythrocytes function within the circulatory system while leukocytes travel through it passively until they exit into tissues for immune response.

Blood Cell Counts and Variations

Normal Ranges for Hematological Parameters

• Typical values: erythrocytes at approximately 600,000/mm³; leukocytes range from 3,000 to 8,000/mm³; platelets between 160,000 to 360,000/mm³.

Changes During Development

• Newborn leukocyte counts can reach up to 18,000/mm³ with a high percentage of neutrophils that shift towards lymphocytes as children grow older.

Hematopoiesis: Formation of Blood Cells

Role of Bone Marrow

• Bone marrow is responsible for hematopoiesis; its functionality relies on various cytokines and hormones that stimulate cell production.

Stem Cells and Differentiation

• Red bone marrow contains undifferentiated stem cells that undergo mitotic division leading to differentiated lineages such as granulocytes or erythrocytes.

Colony Forming Units in Hematopoiesis

Types of Colony Forming Units

• Different colony-forming units produce specific blood cell types including eosinophils, basophils, neutrophils, monocites along with megakaryocytes which form platelets.

Lymphoid Lineage

• The lymphoid lineage produces T-cells and B-cells crucial for adaptive immunity.

Hematopoiesis and Blood Cell Development

Overview of Bone Marrow Function

• The functioning red bone marrow comprises 75% white nests and 25% red nests, indicating that three out of four nests are white.

• Erythropoiesis is regulated by erythropoietin hormone produced in the kidneys, leading to the formation of reticulocytes which are released into circulation still nucleated.

Development of Blood Cells

• Immature leukocytes develop into polymorphonuclear cells: neutrophils, eosinophils, and basophils, each characterized by distinct granules.

• Monocytes serve as precursors to macrophages; they enter circulation before maturing into their final form.

Changes in Bone Marrow with Age

• Red bone marrow is present at birth but reduces after puberty, transforming into yellow marrow primarily in the diaphysis of long bones.

• Yellow marrow contains stem cells that can revert to red marrow under certain conditions such as hemorrhage or altitude changes.

Characteristics of Blood Components

• In images showing blood flow, erythrocytes dominate while some leukocytes are also visible; erythrocytes adapt for gas transport due to high hemoglobin concentration.

• Mature erythrocytes have a biconcave shape allowing them to deform and pass through narrow capillaries effectively.

Erythrocyte Lifespan and Functionality

• Erythrocytes lack nuclei and organelles but remain metabolically active through anaerobic glycolysis; their shape enhances gas exchange efficiency.

• Aged erythrocytes lose elasticity over time, making them less able to navigate the spleen's circulation where they are eventually phagocytized by macrophages.

Leukocyte Characteristics

• Leukocytes vary in size (8 to 20 microns), contain nuclei and organelles, with normal counts ranging from 3,000 to 8,000 per cubic millimeter.

Classification and Function of Leukocytes

Overview of Leukocyte Activation and Migration

• Leukocytes circulate in an inactive state, adhering to the capillary endothelium through adhesion molecules. They become activated by stimuli, allowing them to migrate through the endothelium into connective tissue.

Classification of Leukocytes

• Leukocytes can be classified based on their nuclei:

• Polymorphonuclear: Multiple lobes in the nucleus.

• Mononuclear: Single nucleus without lobulation.

Granulocyte vs. Agranulocyte Distinction

• Polymorphonuclear leukocytes are granular, while mononuclear leukocytes lack granules, categorizing them as agranulocytes.

Proportions of Different Types of Leukocytes

• Granulocytes make up approximately 70% of leukocytes:

• Neutrophils: ~65%

• Eosinophils: ~4%

• Basophils: ~1%

• Agranulocytes constitute about 30%, with lymphocytes being the majority (25% or more).

Characteristics of Neutrophils

• Neutrophils are the most abundant leukocytes (~65%) and play a crucial role in phagocytosis with high mobility. They respond primarily during acute inflammatory responses.

Mechanisms for Increased Neutrophil Response

• The increase in neutrophils during bacterial infections occurs via two mechanisms:

• Rapid release from loosely adhered reserves in bone marrow capillaries.

• Stimulation from the bone marrow to produce more neutrophils.

Structure and Functionality of Neutrophils

• Neutrophils have a typical nucleus with multiple lobes (2 to 5). They contain three types of granules:

• Primary granules with hydrolytic enzymes.

• Secondary granules containing inflammatory mediators.

Identification and Characteristics of Other Granulocytes

• Eosinophils are slightly larger than neutrophils, characterized by reddish granules and increased activity against parasites and allergic reactions.

• Basophils possess segmented nuclei and numerous violet-stained granules containing histamine, playing a role in inflammatory responses. Upon leaving circulation, they transform into mast cells.

Lymphocyte Characteristics

• Lymphocytes are smaller than other leukocytes (7 to 9 microns), featuring dense chromatin and minimal cytoplasm. They are essential for specific immune responses but cannot be differentiated without special functions.

Monocyte Features

Overview of Macrophages and Platelets

Characteristics of Macrophages

• Macrophages are characterized by their kidney-shaped nuclei and lack of granulation in the cytoplasm, making them distinct among leukocytes.

• They originate from monocytes that migrate to connective tissues, where they differentiate into macrophages, playing a crucial role in the immune response.

• Various types of macrophages exist in different regions: hepatic macrophages (Kupffer cells), splenic macrophages, alveolar macrophages, and those found in synovial fluid.

Functions of Leukocytes

• Leukocytes are the largest blood cells, approximately 20 micrometers in diameter. Their types include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.

• Typically inactive under normal conditions, leukocytes can actively pursue bacteria for phagocytosis when needed.

Role of Platelets

• Platelets are small cell fragments (about 3 micrometers), derived from megakaryocytes. They play a vital role in hemostasis by forming clots at injury sites.

• The production of platelets is regulated by thrombopoietin synthesized continuously by the liver.

Coagulation Process

Mechanism of Hemostasis

• Upon endothelial damage, platelets aggregate to form plugs that help close wounds and prevent hemorrhage through coagulation processes involving fibrin.

• Factors released during endothelial damage initiate coagulation while inhibiting anticoagulants to promote clot formation effectively.

Lymphatic Tissue Overview

Structure and Function

• Lymphatic tissue is a type of connective tissue characterized by an abundance of lymphocytes responsible for immune responses. It can be diffuse or organized into encapsulated lymphoid organs.

Types of Lymphocytes

• There are two main types: B lymphocytes (responsible for humoral immunity) and T lymphocytes (responsible for cellular immunity). Both work together to neutralize antigens.

Activation and Response Mechanisms

Immune Activation

• Activated B lymphocytes transform into plasma cells that secrete antibodies (immunoglobulins), while activated T helper cells assist other immune functions.

Variations in Lymphatic Tissue

Understanding Lymphatic Structures and Immune Response

Overview of Follicular Structures

• The transition from activated to follicular status occurs when the structure elongates, indicating a dense lymphatic tissue with underlying intestinal criteria.

• Dense or diffuse lymphatic images show activated lymphoblasts in the central zone of follicles, while inactive lymphocytes are located peripherally.

Germinal Centers and Immune Development

• The follicle serves as the germinal center for immune response; dense diffuse lymphatic tissue is observed alongside elongated structures in the medulla.

• Central germinal zones contain inactive lymphocytes surrounded by a corona of active cells, highlighting the organization within lymphatic tissues.

Immune Response Mechanisms

• Immune responses develop across various tissues, with cell proliferation occurring primarily in bone marrow, thymus, lymph nodes, and spleen.

• Primary organs (bone marrow and thymus) generate lymphocytes; secondary organs receive these cells for further immune functions.

Classification of Lymphoid Organs

• Bone marrow produces B-cell precursors and dendritic cells; it is crucial for forming all blood cells within the linfoid lineage.

• The thymus matures T-cell precursors from bone marrow through hormonal stimulation before returning them to circulation.

Thymic Structure and Function

• The thymus consists of cortical and medullary zones where T-cells mature; epithelial reticular cells provide structural support instead of connective tissue.

• Images illustrate how immature T-cells exit circulation through the cortex after activation.

Evolution and Adaptation of Thymic Tissue

• Thymic involution leads to functional cord remnants that continue producing T-cells throughout life while synthesizing hormones for regulation.

• Concentrically arranged Hassall's corpuscles within the thymus serve specific roles in supporting T-cell maturation.

Mucosal Associated Lymphoid Tissue (MALT)

• MALT comprises diffuse lymphatic tissue associated with non-lymphatic organs along mucosal surfaces, playing a vital role in local immunity.

Characteristics of Mucosal Immunity

Digestive, Respiratory, and Lymphatic Systems Overview

Key Structures in the Digestive and Respiratory Systems

• The transcript discusses various structures associated with the digestive, respiratory, urinary, and genital systems. It highlights a large follicle with a germinal center and diffuse lymphatic tissue predominantly composed of lymphocytes.

• The tonsils are identified as key components at the entrance of the respiratory and digestive tracts, including pharyngeal, palatine, and lingual tonsils. These structures are lined with epithelial tissue.

• The epithelium in these areas is primarily stratified squamous except for the pharynx which has respiratory epithelium to increase surface area through invaginations known as crypts.

Lymphatic Circulation

• A discussion on lymphatic circulation emphasizes that lymph originates from extracellular fluid in connective tissue. Antigens can enter this fluid and be transported to nearby regional lymph nodes.

• The infrastructure of connective tissue supports lymphatic circulation throughout the body (excluding CNS and thymus), where lymph vessels converge into nodes before draining into major ducts like the thoracic duct.

Immune Response Mechanisms

• Lymph nodes serve as primary sites for immune response expansion; they proliferate when responding to antigens. Normally non-palpable nodes become visible upon activation due to hypertrophy or hyperplasia.

• Nodes contain B-cell follicles predominantly in their structure while T-cells dominate in the dense diffuse cortex. Lymph enters through convex borders filtering through sinuses that contact antigen-presenting cells.

Antigen Processing within Lymph Nodes

• Antigen-presenting cells such as macrophages and dendritic cells process antigens received via lymph. They present these antigens to T-cells within the cortex of the node.

• Dendritic cells and macrophages play crucial roles by phagocytizing antigens and presenting them to T-cells in both cortical areas (where dendritic cells reside) and medullary regions (where plasma cells produce antibodies).

Summary of Lymph Node Architecture

• An overview of lymph node architecture illustrates how incoming lymph traverses subcapsular sinuses leading into trabecular sinuses before reaching medullary sinuses surrounded by phagocytic cells that process antigens.

Overview of Lymphatic Tissue and Spleen Function

Structure of Lymphatic Tissue

• The lymphatic cortex contains activated T lymphocytes, particularly in the follicular region, indicating an immune response.

• Antigens are transported through cortical sinuses where they are processed by macrophages and dendritic cells for presentation to lymphocytes.

• Medullary cords consist of dense lymphatic tissue interspersed with medullary sinuses that facilitate antigen filtration.

Functions of the Spleen

• The spleen plays a crucial role in filtering aged erythrocytes, which lose elasticity and cannot pass through capillaries, leading to their phagocytosis by macrophages.

• It is responsible for filtering antigens from the bloodstream, highlighting its importance in immune surveillance.

Composition of Spleen Tissue

• The spleen consists of red pulp (containing blood vessels and macrophages) and white pulp (composed of lymphoid tissue), including follicles rich in T lymphocytes.

• Areas surrounding white pulp contain antigen-presenting cells like macrophages and monocytes that assist in immune responses.

Structural Characteristics

• In animals, the spleen has more muscle fibers compared to humans; this affects its structural integrity and function.

• Trabecular structures within the spleen contain smooth muscle fibers that support blood vessel transport within red pulp.

Follicular Structures in the Spleen

• Dense nodular tissue forms around arteries within splenic follicles, characterized by a germinal center surrounded by inactive lymphocytes.

• Central arteries are prominent features within these follicles, facilitating blood flow while supporting immune cell organization.