Blood Cells and the Lymphatic System

Blood Composition

* red and white blood cells, platelets within plasma

Blood Cells

• rbc carry oxygen to tissues

• wbc have a number of functions, mainly defensive

Plasma

* mainly water and contains various wastes, nutrients, hormones, etc.

Red Blood Cells

• also called erythrocytes

• optimized for gas transport with biconcave disk shape to maximize surface area

• nucleus free cytoplasm packed with hemoglobin

• each hemoglobin molecule can carry 4 molecules of oxygen

• can also carry CO2 but less than 2%

Production of Erythrocytes

• erythrocytes remain in the bloodstream for about 120 days

• new erythrocytes are produced at 2.3million/second

• erythropoietin is released from the kidney and liver when there is a low O2 level which triggers production in bone marrow

• iron, folic acid and vitamin B12 are needed for this process

Destruction of Erythrocytes

• the spleen stores blood cells and removes old blood cells from circulation, the blood cells are destroyed by macrophages and iron is removed from the hemoglobin

• hemoglobin is converted to bilirubin which has a yellow tinge and is released in blood and travels to the liver where it is broken down further to be excreted in feces and urine

Hematocrit

• blood plasma can be separated from formed elements by centrifugation

• reveals the proportion of RBC in the total sample, normally between 35-55%, average is 45%

• simple routine test where abnormal results need to be further studied

White Blood Cells

• also called leucocytes and further divide into granulocytes and agranulocytes

• have nuclei and mitochondria

• can move in ameboid fashion and squeeze through capillary walls to the site of infection

• found in and out of the cardiovascular system and play an important role in the immune system

Granulocytes

1. Neutrophils, 7500 cells/mm3

2. Eosinophils 100-400 cells/mm3

3. Basophils 20-50 cells/mm3

Agranulocytes

1. Lymphocytes 1000-4000 cells/mm3

2. Monocytes 100-700 cells/mm3

Neutrophils

• make up 50-80% of all wbc

• capable of phagocytosis

• engulfs and digests microorganisms, abnormal cells and foreign particles

• circulate in blood for 7-10 hours than migrate into tissues where they live for a few days

• levels increase during bacterial and viral infections and in response to inflammation after surgery

Eosinophils

• make up 1-4% of all wbc, capable of phagocytosis

• mainly attack parasitic invaders too large to be engulfed by neutrophils

• attach to body of parasites and discharge toxic molecules from cytoplasmic granules

• elevated levels often due to parasitic infections, or a results of various diseases such as asthma or eczema

Basophils

• make up <1% of all wbc, are nonphagocytic cells

• thought to defend against larger parasites

• release histamine and other chemicals that contribute to allergic reactions

• during acute reactions, level decreases in blood as they move to the site of the reaction

Monocytes

• make up 2-8% of all wbc, are important phagocytes

• tend to do most of their work outside blood vessels, stay in blood for a few hours then migrate into tissues

• they become 5-10x larger and develop into active phagocytic cells called macrophages and can undergo further differentiation in specific tissues

Lymphocytes

• make up 20-40% of all wbc, also approximately 99% of all cells found in interstitial fluid

• three main types: b-cells, t-cells and null cells (killer cells)

• complete complex functions in the immune system

Platelets

• also called thrombocytes, cell fragments responsible for coagulation (blood clotting)

• fragments of large cells called megakaryocytes (found in bone marrow)

• fragments that enter circulation lack nuclei but are capable of ameboid movement

• live for 5-9 days

Antigens

* certain molecules on surfaces of all cells, recognized as foreign by the immune system of another individual

Blood Typing

• lymphocytes secrete antibodies that bind with antigens of foreign bodies which set off a cascade of reactions that ultimately destroy the cell

• red blood cell antigens are of extreme importance and types must be matched between donors and recipients

• two antigens (A&B) making 4 blood types, distinguished by what kind of antigen is present

Tranfusion Reactions

* if blood types do not match between donor and recipient, the recipient’s antibodies can attach to the donor’s red blood cells, causing the cells to lump together and may block small arteries

Universal Donor

• Type O blood

• any recipient antibodies have nothing to attach to

Universal Recipient

• type AB blood

• recipient lacks antibodies for A and B antigens

Rh factor

• another group of antigens found on red blood cells that is sometimes present

• of particular importance when Rh- mothers give birth to Rh+ babies

• blood systems usually stay separate during pregnancy but at birth, mixing can occur and the mother starts producing antibodies, may effect subsequent pregnancies

Blood Clotting

* also called hemostasis is when a blood vessel is injured, a number of physiological mechanisms work to stop the bleeding


1. Vasoconstriction
2. Formation of Platelet Plug
3. Production of a Web of Fibrin Proteins

Function of Platelets

• in the absence of vessel damage, platelets repel from each other and the vessel wall to prevent inappropriate clotting

• damage to a vessel wall exposes collagen, which platelets stick to

Platelet Plug

• damage to a vessel wall exposes collagen which platelets will stick to

• other molecules are released that attract more platelets causing aggregation

• also contains red blood cells and is reinforced by strong fibers from fibrin

Formation of Fibrin

• final product of a number of clotting factors

• can either be an intrinsic pathway, requiring no additional extrinsic chemicals, or an extrinsic pathway from chemicals released from damaged tissue

Bleeding Disorders

• can be from the result of an incomplete plug formation due to deficiencies in one or more of the clotting factors

• majority of disorders are inherited or caused by a low rbc count or certain medications

Lymphoid Tissue

• composed of reticular connective tissue and macrophages attached to fibers

• diffuse lymphoid tissue is found in nearly every organ

• lymphoid nodules are solid, spherical bodies that contain lots of B-lymphocytes

Nodes

• hundreds of small organs located along lymphatic vessels

• groups occur near the surface in the cervical, axillary and inguinal regions

• function to filter blood before returning it to the blood stream and activating the immune system

Swollen Lymph Nodes

• if large numbers of bacteria become trapped in a node they can get inflamed causing swelling and tenderness

• typically occurs in the neck, armpit or groin

Spleen

• similar in shape and structure to a lymph node but much larger

• largest lymphoid organ that filters blood in a similar way that lymph nodes filter lymph

• also stores breakdown products of red blood cells and recirculates them to the liver

Thymus

• located just above the heart, large in newborns and continues to increase in size until puberty when it decreases

• functions for the processing and maturation of T-lymphocytes and development of immune responses

• function declines as we get older

Mucosa-Associated Lymphoid Tissue (MALT)

• patches of lymphoid tissue located on mucosa membranes throughout the body that are strategically placed to protect us from pathogens entering the body

• includes the tonsils, peyer’s patches and appendix

Tonsils

• form a ring of lymphoid tissue around the entrance to the pharynx

• remove many of the pathogens entering through the nose or mouth

Peyer’s Patches

* patches of lymphoid tissue located in the small intestine

Appendix

• tubular offshoot at the beginning of the large intestine

• along with Peyer’s patches, helps destroy bacteria in the intestine

Movement of Lymph

• lymphatic capillaries are blind ending tubes, located with blood capillaries

• extremely permeable

• endothelial cells fit together like flaps that open when fluid between cells increases, acting like a one-way swinging door, same mechanisms that propel blood along veins

• lymphatics near the skin travel along superficial veins while deep lymphatics travel along deep arteries, more variable than blood vessels

Lymph Flow into Larger Vessels from Lymphatic Capillaries

1. Capillaries

2. Collecting Ducts

3. Trunks

4. Ducts

Lymph Flow into Thoracic Region

• lymph is eventually transported into the thoracic duct or right lymphatic duct

• each of these ducts empties into the jugular vein where it meets the subclavian vein

Cardiovascular Interaction with Lymphatic

• returns fluid and proteins that have been filtered out of blood vessels

• any fluid that remains in tissues is picked up by the lymphatic vessels

• one way flow of fluid that enters the circulatory system at the subclavian artery

• blood is filtered along the way

Hydrostatic Pressure

* caused by ventricular contraction and declines when close to capillaries but still high enough to favour fluid flowing out of the capillaries

Osmotic Pressure

• results from unequal concentrations of proteins inside and outside of the arteriole

• favours fluid moving back into the circulatory system

As blood approaches capillaries

• hydrostatic pressure > osmotic pressure

• fluid is forced back into tissues

As blood leaves the capillaries

• osmotic pressure > hydrostatic pressure

• about 90% of all fluid is forced back into the circulatory system and the rest is picked up by lymphatic tissues

Immune Interaction with Lymphatic

• acts as filters to help capture and destroy foreign pathogens

• major part in our immune response for the continual exposure to micro-organisms

• organisms must first get past both physical and toxic barriers to be dealt with by the immune system

• lymph fluid must be continually presented to immune system cells

Digestive Interaction with Lymphatic

• picks up absorbed fat and transfers it into the circulatory system, almost all fats absorbed by the intestines are taken up by the lymphatic system

• the small intestine has specialized vessels of the lymphatic system called lacteals that are found in the absorptive layer of the intestine

• lacteals absorb fats and fat soluble vitamins while blood capillaries take up everything else