blood cells and structure

Red Blood Cells: Structure

• Highly specialized cell

• Mature cell lacks a nucleus, mitochondria, ribosomes

• Appearance:

  • Non-nucleated

  • Biconcave disks with a thinner central zone

  • Stain red

RBC: Function

• Blood is a living tissue even after it is taken from an animal

  • RBCs utilize plasma glucose for energy

  • Glucose cannot be replenished in a tube after RBCs use it

• Functions:

  • Transport oxygen to tissues (hemoglobin)

  • Transport carbon dioxide to lungs

  • Maintain cell shape and deformability

RBC: Life Span and Destruction

RBC: Process of aging = senescence

• Enzyme activity decreases

• Cell membrane loses deformability

• About 1% of cells removed from circulation daily

• Destruction: extravascular or intravascular

White Blood Cells (Leukocytes / WBCs)

• Mature WBC generally larger than mature RBC

• 5 types normally present in circulating blood:

  • Granulocytes — basophils, neutrophils, and eosinophils

  • Agranulocytes — lymphocytes and monocytes

Function of White Blood Cells

• Provide defense for the body against foreign invaders

  • Phagocytosis

  • Immunity

• Produced in bone marrow

  • Use peripheral blood to travel to site of activity

• Each type has its own role

The Lymphatic System

Overview — 2 separate parts of an animal's immune system:

• System of ducts and fluid lymph

  • Picks up fluid leaked from capillaries

  • Lymph ducts carry lymph to blood vessels near the heart

  • Lymph is put back into the bloodstream

• System of lymphoid organs and tissues

  • Lymph nodes, spleen, thymus, tonsils, and gut-associated lymph tissue (GALT)

Lymphatic System Functions

• Removal of excess tissue fluid (inadequate lymph drainage can result in edema)

• Waste material transport

• Filtration of lymph (lymph passes through lymph nodes)

• Protein transport

Lymph Formation

• Lymph starts out as excessive tissue fluid

• Capillaries in tissue join to form larger vessels to propel lymph toward the heart

• Lymph eventually joins the bloodstream

Lymph Circulation

• Excessive interstitial fluid picked up by small lymph capillaries

• Fluid enters/leaves tissue spaces due to blood pressure and osmotic pressure

• Lymph capillaries join together to form larger and larger lymph vessels

• One-way valves and body movements propel lymph toward the heart

• Lymph passes through at least one lymph node and picks up lymphocytes

• Macrophages in lymph node remove microorganisms

• Lymph is emptied into the vena cava just before the large vein enters the heart

• Lymph has come full circle — originated in plasma, has returned to plasma

Lymph Characteristics

• Transparent or translucent liquid

• Contains varying numbers of cells, primarily lymphocytes

• Different from plasma:

  • More water, sugar, and electrolytes

  • Fewer of the larger proteins found in plasma

• Lymph from the digestive system = chyle (fat)

  • Postprandial lipemia

Lymphoid Organs — 2 Classifications

• Primary:

  • Thymus

  • Bursa of Fabricius (avians)

  • Peyer's patches 

• Secondary:

  • Spleen

  • Lymph nodes

  • Tonsils

Thymus

• Located in cranial thoracic region

• Most prominent in young animals

• Produces mature T-cells from precursors sent from the bone marrow

• Cells leave thymus and travel to secondary lymphoid tissue

  • Important in stimulating cell-mediated immune response

Bursa of Fabricius vs. Peyer's Patches

Bursa of Fabricius	Peyer's Patches
Found only in birds	Located in wall of small intestine (GALT)
Round sac located above the cloaca	Structure and functions vary among species
Similar in structure and function to the thymus	Activate B cells to produce antibodies

Secondary Lymphoid Organs

• Include spleen, lymph nodes, and tonsils

• Enlarge in response to antigenic stimulation

• Main function: trap and process antigens and mature lymphocytes that mediate immune responses

Lymph Nodes

• Small, kidney bean-shaped filters located along lymphatic vessels

• Trap antigens and other foreign materials in lymph

• 2 sections:

  • Cortex — lymph nodules

  • Medulla — tissue macrophages

• Found throughout the body

• Drain organs in their associated locations

• Can give clue to health of an animal

  • Nodes more easily palpated when enlarged in response to antigenic stimulation

  • Fine Needle Aspirate (FNA) and cytology used for evaluation of abnormalities

The Spleen

• Tongue-shaped organ located on the left side of the abdomen

  • Near stomach in simple-stomached animals

  • Near the rumen in ruminants

• Covered with a capsule of fibrous connective tissue and smooth muscle

  • Trabeculae from capsule go into soft tissue of spleen

  • Smooth muscle cells contract and squeeze blood out of spleen and back into circulation

• Interior divided into 2 areas: white pulp and red pulp

• Acts as a reservoir for blood when animal is at rest

  • Spleen gets larger when storage spaces are filled with blood

• When body needs excess blood cells:

  • Trabeculae contract

  • Blood is squeezed back into circulation

  • Spleen gets smaller

• Not essential for life (bone marrow could replace it)

The Tonsils

• Nodules of lymphoid tissue that are not covered with a capsule

• Found in epithelial surfaces all over the body

  • Most familiar in pharyngeal region

  • Others in larynx, intestine, prepuce, vagina

• Function to prevent spread of infection into respiratory and digestive systems

Abnormal Lymphatic System / Edema

• Abnormal increase in interstitial fluid (fluid between cells)

• Filtration exceeds absorption capability by lymphatic vessels

  • Filtration = interstitial fluid colloid osmotic pressure

  • Reabsorption = blood colloid osmotic pressure

Causes of Edema

1. Increase in BP

2. Decrease [concentration] of plasma proteins

3. Increase permeability of capillaries

4. Decreased fluid excretion

5. Blocked lymphatic drainage