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MCAT Biology > Lymphatic, Immune System > Flashcards

Lymphatic, Immune System Flashcards

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1
Q

What are the functions of the lymphatic system?

A

Collect excess interstitial fluid that results from fluid exchange in the capillary beds and return it to the blood
Removes proteins and other particles that are too large to be taken up by the capillaries (glycerides)
Takes excess fluid through lymph nodes (can elicit immune response)
Recycles interstitial fluid while monitoring it for infection, reroutes low-solubility fat digestates around small capillaries of intestine and into large veins of neck

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2
Q

Where does lymph circulate to?

A

Through lymphatic vessels, eventually dumping into the thoracic duct and vena cava

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3
Q

Is lymphatic system an open or closed system?

A

Lymphatic system is an open system
Fluid enters at one end and leaves at the other
contrast to closed circulatory system

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4
Q

How do substances enter the lymphatic system?

A

Insterstitial fluid flows between overlapping endothelial cells
large particles push their way between cells into the lymph
Once inside, large particles cannot push their way out
Lymph capillaries are like tiny fingers protruding into tissues

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5
Q

What factors affect interstitial pressure and what is it normally?

A

Typically interstitial fluid has slightly negative gauge pressure
Lymph flow increases when interstitial pressure rises towards zero
Blood pressure, plasma osmotic pressure, interstitial osmotic pressure, and permeability of capillaries affect interstitial pressure

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6
Q

How is fluid propelled through lymph vessel valves?

A

Have valves to prevent backflow
Smooth muscle in walls of larger lymph vessels contract when stretched
Lymph vessels may also be squeezed by adjacent skeletal muscles, body movements, and arterial pulsations (lymph flow greater in active individual)

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7
Q

Where does the lymph system empty?

A

Empties into large veins at thoracic duct and right lymphatic duct (right arm and head)

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8
Q

Lymph Nodes

A

Part of lymphatic system, filter lymph through
Contain large quantities of lymphocytes
Filter and trap particles and site of stimulation of lymphocytes to respond to pathogens

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9
Q

What is the purpose of the immune system?

A

Protect human body from toxins and from invasion by other organisms, including bacteria, viruses, fungi, and parasites

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10
Q

What are the two strategies immune cells use to accomplish primary goals of immune system?

A
  1. Phagocytose (‘eat’) dangerous material

2. Secrete effector molecules that have downstream functions

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11
Q

What are the two main interconnected branches of the immune system?

A
  1. Innate immunity: non-specific and quick, providing generalized protection from most intruding organisms and toxins
  2. Adaptive / Acquired immunity: develops more slowly and only after the body has experienced the initial attack, provides protection against specific organisms or toxins (B-cell mediated and T-cell mediated)
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12
Q

What are some cellular and non-cellular defenses that innate immunity includes?

A
  1. Skin as barrier to organisms and toxins
  2. Stomach acid and digestive enzymes to destroy digested organisms / toxins
  3. Phagocytotic cells: neutrophils and macrophages
  4. Chemicals in the blood
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13
Q

What happens when tissues are injured?

A

Inflammation
Functions to “wall-off” affected tissue and local lymph vessels from rest of the body, impeding spread of infection
Includes dilation of blood vessels, increased permeability of capillaries, swelling of tissue cells, migration of granulocytes and macrophages to inflamed area

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14
Q

What are some causative agents of inflammation?

A

Histamines, prostaglandins, and lymphokines are released by tissues

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15
Q

What is one way innate immune cells can recognize foreign invaders?

A

Pathogen-Associated Molecular Patterns (PAMPs)
Innate immune cells look for molecules that are expressed by pathogens, but not by humans
E.g. many gram-negative bacteria express a carbohydrate called lipopolysaccharide or LPS. LPS alone could send a person into septic shock

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16
Q

Phagocytes

A

Many of earliest responders to pathogens, ingest (‘eat’) dangerous substances and destroy them
Local Macrophages: phagocytotic giants that can engulf as many as 100 bacteria
Neutrophils
Monocytes: arrive and mature to become macrophages

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17
Q

Neutrophils

A

Arrive to injured or infected site after macrophages, stored in bone marrow until needed. Move towards infected areas drawn by chemical signals. Slip between endothelial cells of capillary walls (diapedesis). Phagocytose 5-20 bacteria
Die after engulfing bacteria and dead tissue

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18
Q

Monocytes

A

Circulate in blood until they move into tissues by diapedesis
In the tissues, monocytes mature to become macrophages

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19
Q

Macrophages

A

Phagocytotic giants that are usually present locally and respond first to injury or infection by engulfing pathogens
Can engulf as many as 100 bacteria
Can also be produced by maturing from monocytes
Die after engulfing bacteria and dead tissue

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20
Q

Pus

A

Tissue fluid, dead tissue, and dead leukocytes (neutrophils, macrophages) form this substance

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21
Q

Eosinophils

A

Innate immune cell related to neutrophil
Responds mostly to parasitic infections and control mechanisms associated with allergy and asthma
Granulocytes that develop during hematopoiesis in the bone marrow before migrating into blood

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22
Q

Basophils

A

Least common, but largest granulocytes
Responsible for inflammatory reactions during immune response, formation of acute and chronic allergic diseases
Produce histamine, serotonin that induce inflammation, heparin that prevents blood clotting

23
Q

What are the two types of acquired immunity?

A

B-cell / humoral / antibody-mediated immunity

T-cell / cell-mediated immunity

24
Q

B-cell Immunity

A

Effective against bacteria, fungi, parasitic protozoans, viruses, and blood toxins
Cannot act against invading substances that have already made their way into cells
Promoted by B-lymphocytes (each make specific antibody which can bind to antigen on pathogen)

25
Q

B-lymphocytes

A

Differentiate and mature in adult bone marrow and fetal liver
Each makes a single type of antibody / immunoglobulin, which recognizes and binds to foreign particle / antigen
B-lymphocyte displays antibody on membrane (B cell receptor or BCR)
Recognizes antigen by binding and triggers primary response (20 days)

26
Q

Antigen-antibody recognition

A

When B cell receptor (BCR) binds to specific foreign antigen

Portion of antibody is highly specific to antigen and is known as antigenic determinant

27
Q

What is the primary response of B-cell mediated adaptive immunity?

A

BCR of B-lymphocyte binds to foreign antigen
Assisted by helper T-cell, B-lymphocyte then differentiates into plasma cells and memory B-cells which can produce many antibodies to respond to foreign invaders
Takes 20 days to reach full potential

28
Q

What is the secondary B-cell mediated response?

A

When memory B-cells and Plasma cells have already been made be previous recognition, the B-cells and plasma cells will act to produce many antibodies to bind to foreign invader quickly
Takes ~5 days to reach full potential

29
Q

How do antibodies promote destruction of harmful invading substances?

A
  1. Antibodies may mark antigen for phagocytosis by macrophages and natural killer cells
  2. Antibodies can bind and start cascade of complement protein response to perforate foreign cell
  3. Agglutination or precipitation of antigenic substances, or block chemically active portion
  4. Free antibodies attach bases to mast cells, which release histamines and other chemicals once antibody binds to antigen
30
Q

How do vaccines use the adaptive immune system?

A

Expose body to inactivated portion of pathogen to build memory B-cells and plasma cells, which can then mount a powerful and specific attack against pathogen once exposed
Protects against future infection

31
Q

Antibody Structure

A

Made up of two heavy chains and two lights chains
Has variable region which is the antigen-specific region, constant region which is just below this, and then transmembrane domain which attaches antibody to cell in some cases
Connected via disulfide bonds
Variable region: composed of 110-130 amino acids from both heavy and light chains

32
Q

T-cell Immunity

A

Effective against free-floating substances and involves T-lymphocytes, which have T cell receptors (TCRs) that recognize antigens
TCR recognizes appropriate antigen and differentiates into helper T-cells, memory T-cells, suppressor T-cells, and killer T-cells (cytotoxic T-cells)

33
Q

Helper T-cells

A

Assist in activating B-lymphocytes

Activate other types of T-lymphocytes, including killer and suppressor T-cells

34
Q

Memory T-cells

A

Long-lived memory cells which have similar function to memory B-cells in secondary immune response

35
Q

Suppressor T-cells

A

Play negative feedback and regulatory role in immune system

36
Q

Killer T-cells

A

Bind to antigen-carrying cell and release perforin (protein that punctures the antigen-carrying cell)
Can attack many cells because they do not phagocytize their victims (unlike macrophages, or neutrophils)
Not destroyed when they kill pathogens
Responsible for fighting some forms of cancer and for attacking transplanted tissue

37
Q

Major histocompatibility complex (MHC)

A 
All human cells express these molecules on their cell surface (except cells without nuclei)
Display antigens for recognition
Two classes: MHC class I, MHC class II
38
Q

MHC Class I

A 
Display antigens derived fro intracellular pathogens, such as viruses and some bacteria
All nucleated cells have MHC class I
Endogenous pathway: process by which intracellular antigens are processed and displayed on cell surface
39
Q

MHC Class II

A

Display antigens derived from extracellular pathogens
Antigens must be phagocytosed, so displayed on phagocytotic cells termed professional antigen presenting cells (APCs)
- include macrophages, dendritic cells, some B-cells
Exogenous pathway: Process by which antigens are processed and displayed by MHC class II moelcules

40
Q

What purpose does the requirement of two signals to active B and T cells have?

A

First signal: BCR or TCR recognizes appropriate antigen
Second signal: ‘danger’ signal received with active infection
Protects against autoimmune response

41
Q

What are the four general steps of the exogenous and endogenous pathway for MHC molecules?

A
  1. Antigen uptake: antigen either already present or phagocytosed into cell
  2. Antigen processing: pathogen or molecule processed into smaller peptides (antigens). Cytosol in endogenous pathway, vesicles in exogenous
  3. Peptide-MHC association: antigens associate with MHC molecules, which are folded in ER. Endogenous, fuses with ER, exogenous vesicle with MHC molecules fuses with vesicle with antigens
  4. Cell surface expression: antigen-MHC complex expressed on cell surface to interact with immune cells
42
Q

Where do T-cells receive signals 1 and 2 for activation?

A

Signal 1 is from professional APCs through binding to MHC complex II with antigen
Signal 2 provided via different cell surface receptors- components of innate immune system in response to infectious insults (cytokines or other membrane surface proteins)
Causes proliferation and differentiation

43
Q

Where do B cells receive signals 1 and 2 for activation?

A

Signal 1: free floating antigen cross-links multiple BCRs on same cell
Signal 2: usually by helper T cells
Both required for proliferation and differentiation

44
Q

Where does lymphocyte activation usually occur?

A

Infection often occurs in connective tissues
B-cell and T-cell activation often take place in nearest lymph node
Spleen, gut, and other locations with lymphatic tissues in body

45
Q

Why do lymph nodes swell during infection?

A

B and or T-lymphocytes are rapidly proliferating in response to pathogen

46
Q

Why is proper regulation important for immune system function?

A

Too much regulation renders the immune system deficient and unable to properly protect against foreign invaders
Too little regulation can result in autoimmune diseases, where a hyperactive immune system attacks the body’s own tissues

47
Q

Clonal selection

A

A process in which after the random generation of BCRs or TCRs, only certain types are permitted to mature and proliferate

  1. Cells must show that they are capable of recognizing antigens in context of host MHC molecules. If cannot recognize MHC molecule, undergoes apoptosis (positive selection)
  2. Cells must show that they are not inappropriately activated by host cells in absence of infection. B and T cells that respond too strongly to MHC molecules with self-antigens undergo apoptosis (negative selection)
48
Q

Where do B and T cells undergo clonal selection?

A

T cells undergo clonal selection in thymus
B cells undergo clonal selection in bone marrow
Cells that survive selection process are released to lodge in lymphoid tissue or to circulate between blood and lymph fluid

49
Q

What are some causes of autoimmune diseases?

A

One major cause could be a failure of clonal selection
For example, a failure in negative selection can result in the production of B or T cells that respond to self-antigens
There are many other immunoregulatory mechanisms can result in autoimmunity as well

50
Q

What types of cells will react to an antigen bound to an MHC class I molecule?

A

Cytotoxic T cells which then are stimulated by helper T cells as well to differentiate into memory cytotoxic T-cells and active cytotoxic T cells
Active cytotoxic T cells will cause lysis of infected cells
Memory cytotoxic T-cells will respond quicker in secondary infection

51
Q

In secondary infection, what does an antigen stimulate?

A

Stimulates memory B-cells, Memory helper T-cells, and Memory cytotoxic T-cells

52
Q

How are blood types identified?

A

A and B surface antigens
In type A blood, RBCs have A antigens and not B antigens
Immune system will make B antibodies and not A antibodies
In type O blood, immune system makes both A and B antibodies

53
Q

Rh factors

A

Surface proteins on RBCs, first identified in Rhesus monkeys
Individuals that encode for nonfunctional products of Rh gene are Rh-negative, while others are Rh positive
In second Rh positive pregnancy, mother has produced Rh positive antibodies which could pass through placental barrier and attack the fetus

MCAT Biology (14 decks)

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