Blood, Immunity and the lymphatic system

BMA1012

Functions of red blood cells

• Distribution → move nutrients, remove waste. hormones

• Protection → infection, blood loss

• Regulation → body temp, pH, fluid volume

Composition of blood

• 55% plasma

• <1% of Buffy coat (contains WBC and platelets)

• 45% red blood cells

Plasma

• liquid component of blood

• 90% water

• contains many dissolved components:

  • electrolytes

  • plasma proteins

  • metabolic by-products

  • nutrients

  • respiratory gases

  • hormones

Red blood cells structure

• flexible to move through vessels

• large surface area

• allows for varying hydration levels:

  • dehydrated → shriveled

  • over-hydrated → swollen

Red blood cell oxygen transport

• has hemoglobin

• 4 heme groups → 4 oxygens can bind

• Oxygen can bind loosely and reversibly to iron molecules

• Allowing oxygen to be picked up at lungs and released into active tissue around the body

  • High affinity at lungs helps to bind oxygen

  • Low affinity at working muscle tissues help release oxygen into cells

= 98% of oxygen is transported, 2% goes into the plasma

Red blood cell carbon dioxide transport

• 7% of carbon dioxide stays in blood as it is

• 23% interacts with red blood cells

  • binding to hemoglobin at a different area from oxygen

• 70% of carbon dioxide undergoes reaction by carbonic anhydrase to convert to hydrogen and bicarbonate to transport

Platelets

• involved in blood clotting, working with plasma protein fibrinogens

• usually kept inactive and mobile by intact endothelial cells

• Attracted to any damage to endothelial cells

3 main steps when there is an opening

1. Vascular spasm → puts pressure on either size to squeeze to reduce blood flow, nearby blood vessels contract

2. Platelet plug → platelet gets stuck on rough edges and change shape for more platelets to get stuck
   - Broken endothelial cells trigger present plug cascade

3. Coagulation → weave them all together, fibrinogen turns into fibrin, thicken blood clots and trap red blood cells

4. Fibrinolysis → uses an enzyme called Plasmin: breaks up the fibrin fibres breaking down the clot

The lymphatic system functions

• Lymphatic drainage

• Fat/lipid absorption

• Immunity

What is lymphatic drainage

process where lymphatic system collects excess fluid from interstitial spaces that leaks from capillaries and to put it back into cardiovascular circulation

Fat/lipid absorption

due to large size of fat molecules they cannot be absorbed directly, fat within small intestine is absorbed into Lacteals

Functions of immunity

• Production of immune cells

• Maturation of immune cells

• Sites of surveillance → immune cells monitor local situation for pathogens

  • provides site of proliferation to allow for fast, strong, reactions to infections

What is in the lymphatic system

• Primary lymphatic organ: produces WBC

• Secondary lymphatic organ: sites of surveillance and proliferation

Primary organs

• red bone marrow: makes b cells → producing immune cells

• thymus: above the heart → makes t cells

Secondary organs

• Lymphatic nodes

• Spleen

• MALT (mucus associated)

  • Tonsils

  • Appendix

  • Payer’s patches (dispersed into small intestine)

Why does lymphatic drainage happen?

• Cardiovascular system loses up to 3L of blood volume daily

• The fluid accumulates in the interstitial space

• Responsible for returning this fluid back into the circulatory system

How does lymphatic drainage work?

• One way system → vessels flap like mini valves to prevent back flow

• Contraction of muscles allow fluid movement

• Joined to surrounding connective tissue

• Fluid fills up to interstitial space, valves pull open to allow fluid to drain

• Negative gradient: generated by cardiovascular system and venous system and draws fluid towards the heart

The branching of white blood cells

• Starts from stem cells to differentiate into → myeloid progenitor (blood) and lymphoid genitor (lymphoid)

• Myeloid progenitor → mast cell, myeloblast

• Lymphoid genitor →natural killer cells, small lymphocytes

• Myeloblast → basophil, neutrophil, eosinophil, monocyte

• Small lymphocytes → T and B lymphocyte

5 types of white blood cells

• Basophils

• Eosinophils

• Neutrophils

• Lymphocytes

• Monocytes

Basophils

are responsible for allergic response, releasing histamine

Eosinophils

are the predominant inflammatory cell in allergic reactions

Neutrophil

first responder and will phagocytose pathogens

Lymphocytes

involved in destruction of pathogens: B cells, T cells, Natural Killer

Monocytes

longer lived phagocytosing cells, acting as vacuum cleaners of the immune system

Pathogen

bacteria, fungi, virus or other micro-organism that causes disease

Antigen

molecule that induces an immune response within the body

3 main levels of defence

1. Barriers

2. Innate defences

3. Adaptive defences

Barriers

• Works by stopping pathogen or disease from getting into the body (physical or chemical)

Innate defences

• Non-specific response

• Works quickly towards a wide variety of antigens

• Born with this defence

Adaptive defences

• Specific immune response

• Happens since some antigens don’t trigger innate defence

• Slower response due to producing and replicating immune cells to destroy pathogens

• produces a long form of immunity that will evolve

Barrier types

• Physical: doesn’t interact just blocks

  • skin

  • hairs

  • mucociliary escalator

  • normal flora

• Chemical: interacts with pathogens, dissolving or deactivating

  • sweat, saliva and tears

  • sebum

  • mucus

Scientific name of white blood cell

Leukocytes

Macrophages and Neutrophils in innate response

• Phagocytosis

  • ingest via endocytosis

  • digest using lysosomes

  • release residual material

Natural killer cells

• finds target then binds

  • uses perforins to make a pore

  • releases granzymes enter through the pores and initiate apoptosis

Interferons

• Host cell 1:

  • gets infected

  • makes interferons

  • killed by virus

• Host cell 2:

  • binds interferons

  • interferon induces synthesis of antiviral proteins

  • viral replication inhibited

Complement system

• Complement protein:

  • stimulates inflammation

  • Opsonisation

  • Membrane attack complex: creating pores in the membrane causing osmolysis

Fever

• initiated by pyrogens

• mild or moderate fevers can be beneficial

• inhibits growth of bacteria and viruses

• increasing cellular metabolism

• accelerating immune defences

Inflammation

• helps repair tissue

• release of histamine and prostaglandins (dilates arterioles to increas