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MCAT
Course: MCAT > Unit 7
Lesson 11: Immune system- Immune system questions
- Innate immunity
- Adaptive immunity
- Role of phagocytes in innate or nonspecific immunity
- Types of immune responses: Innate and adaptive, humoral vs. cell-mediated
- B lymphocytes (B cells)
- Professional antigen presenting cells (APC) and MHC II complexes
- Helper T cells
- Cytotoxic T cells
- Review of B cells, CD4+ T cells and CD8+ T cells
- Clonal selection
- Self vs. non-self immunity
- How white blood cells move around
- Blood cell lineages
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Types of immune responses: Innate and adaptive, humoral vs. cell-mediated
Innate vs. adaptive immunity. Humoral adaptive immunity vs. cell-mediated adaptive immunity. Created by Sal Khan.
Want to join the conversation?
- basically where does the immune system takes place??(16 votes)
- It's practically everyhwere. Our whole bodies are full of different kinds of immune cells, they're in our bone marrow, skin, mucous membranes (respiratory tract, digestive tract etc.), connective tissue (including blood), and even the central nervous system has its immune cells, despite the fact that immune cells of the blood normally cannot enter the CNS.
So, why is it "everywhere"? You may think of it as water in earth or sand: it is everywhere, but you can't just take all the water out and say, "this is the whole quantity of water".(14 votes)
- Then why doesn't the immune system attack medicinesand drugs if it is supposed to attack ALL foreign particles entering the body?(14 votes)
- Innate immunity is based upon a generalized response to known pathogen motifs. Upon recognition of these motifs, the generation of an avid immune response is generated. Most medicines lack these motifs. Note however that if something keeps a more permenant presence in the body, the adaptive arm of immunity can take over. This is because adaptive immunity is not constrained by these motifs and can freely express anything not reactive to "self" tissue. This response cannot be achieved in the timeframe of a typical, non-recurring medical regimen(10 votes)
- So basically, nonspecific system is police, B-lymphocytes are FBI and T-lymphocytes are SWAT?(21 votes)
- What are macrophages? What do they do?(6 votes)
- Macrophages are phagocytes. They essentially "eat" the shady looking stuff that makes its way into our bodies. They are non-specific so they are part of the Innate immune system.(15 votes)
- Is it safe to say that the humoral response is initiated before the cell mediated response or is that wrong?(9 votes)
- If I remember correctly, both pathways are initiated by an immune reaction to some foreign substance, so both would be initiated.(6 votes)
- AtSal said "the specific immune that's particular to humans". What kind of differences do other animals have that have specific immune systems? 2:33(6 votes)
- Usually, the rate with which their immunity is aquired agianst antigens of a specific pathogen is different than that of humans. For example, a wound can take many days for humans to heal completely but crocodilians on the other hand have an immune system that can quickly cure those of wounds. Also what the others said, it depends on the environment you leave in. If you live in an environment where you get injured and affected by pathogens frequently then your immune system will work faster for survival in that environment. On the other hand if you live in a healthier environment your immune system will work much slower because you are not exposed frequently to diseases.(8 votes)
- At, Sal says "only viruses have double stranded DNA..." does he mean single stranded DNA? All eukaryotes have double stranded DNA. 2:07(7 votes)
- There's a correction on the video to say that it should be double stranded RNA (often written as dsRNA). dsRNA is only ever found in viruses, so it makes a good target for innate immunity. There are ssDNA viruses, but they tend to make complementary strands pretty quickly after they get into a cell.(5 votes)
- what is the difference between an antigen and an antibody?
also, why is it called the humoral response?(2 votes)- The word humoral come from the latin word for liquid (and also juice :D). So the humoral response refers to an immunological response happening in a liquid of our body, but not to an immunological response to an antigen inside of one of our cells. Hope this helped.(11 votes)
- If the immune cells that eat bad thing recognize that they are bad, then how do allergies work? How is it that an immune cell in one person doesn't recognize somethings (peanuts for example) but someone else's immune cells do?(4 votes)
- Allergies are examples pf hyperactivity of our immune systems. Altered activities of the immune system.
It is really hard to adjust immune systems - from one side we have to be strong enough to recognize and destroy pathogens, but from the other side we must thrive and not react when there are not pathogens but harmless substances.
Allergies are a really common thing and caused by two factors: host and environment.
If we eliminate heredity as a factor than we come to those environments, such as exposure to diseases during early childhood or environmental pollution.
While we cannot completely avoid environmental pollution, one thing we can control in our children is exposure to 'pathogens' during early childhood. What does it mean? It means that the highly 'sterile' environment does not work in favor of our immune system.(4 votes)
- What exactly is the difference between antigens and antibodies?(3 votes)
- Antigens are the foreign molecules that elicit a response from your immune system. Antibodies are released to bind to the antigen receptors to deactivate the antigen.(5 votes)
Video transcript
In the last video, we
talked a little bit about the immune system. In that video, we focused on the
nonspecific or the innate immune system. So let me write that. And even in the nonspecific
immune system, we subdivided that into kind of the
first line barriers. And those were things like the
skin, or the stomach acid, or the acidity of the oils on
the outside of your skin. These are just natural barriers
to not allowing things inside of your body, but
then once they get in-- so you can almost imagine
these were the first line of defense. And then you had your second
line of defense, but these are still nonspecific-- and when we
say nonspecific, it means that they don't necessarily know
what type of virus, what type of protein, what
type of bacteria. They just know that this
thing looks shady. Let me eat it up. Let me kill it. Let me have an inflammatory
response. So in there, we said, well,
there's an inflammatory response, which I'm actually
going to talk about after we do videos on the specific
immune system. You have your inflammatory
response, which really just gets things to where the action
is at and then you also have your phagocytes, which
are these cells that are engulfing things. And just so you know, all the
phagocytes that we talked about in the last video, these
are all instances of white blood cells or leukocytes. These phagocytes right here,
these are all-- I talk about dendritic cells and macrophages
and neutrophils. These were all white
blood cells. These weren't all the kinds
of white blood cells. We're about to talk about more--
and the other word for white blood cell is
also leukocyte. So that is nonspecific. Well, one, it just doesn't let
you in, but then when you're in, it says, hey, you're
just shady. I'm going to eat you up. I have receptors. You have some double stranded
DNA floating around. Only viruses have double
strand DNA. I'm going to eat you up. I don't know what type
of virus you are. I don't know if I've seen
you before or not. That's why it's nonspecific. Now the really interesting
thing about our immune system-- and this nonspecific,
this exists across many, many, many species and types of
organisms. But the specific is kind of a-- it's thought to
be a newer adaptation. What I'm going to talk about is
the specific immune system that's particular to humans. That's our other
classification. Let me do it like that. So then you have your specific--
or you can imagine it's an adaptive
immune system. You've probably heard
of things like that. I have resistance to that
bacteria or that virus. So this is adaptive. And it's really all based on
having exposure to things. And within the specific immune
system, we talked a little-- when we talked about the antigen
presenting molecules that phagocytes do-- that
plays a role in this. We're going to go into more
detail, but I don't want to confuse you. But the main actors here are
called lymphocytes, not to be confused with leukocytes--
because they still are leukocytes. So let me write this down. These are specific. Phagocytes, for the most part,
are nonspecific, but both of these are white blood cells. Lymphocytes are another
type of white blood cell or leukocyte. Don't want to confuse you with
this convoluted diagram, but I just want to make the
terminology clear. When someone talks about a
white blood cell, they're really just talking about a set
of cells that when people first tried to separate the
components of blood-- you'd have your red blood cells that
would kind of settle in the bottom, then you'd have this
layer of white frothy stuff in the middle that was really made
of white blood cells, and then on the top, you had the
fluid, the plasma from your blood, kind of the
watery part. So that's where the name came
from, but they have different roles, but they interact
with each other. Now lymphocytes can be divided
into B lymphocytes, usually referred to as B cells--
and T lymphocytes. And the B and T just come from
where they're developed. B lymphocytes were first
recognized in the bursa of Fabricius. That's why it's called B. That's actually a part of birds
that participate in the immune system. And so the B came from bursa,
but B also applies to the human immune system because it's
produced in bone marrow. So that might be an easier
way to remember. It's produced in bone marrow. It's developed in bone marrow,
but historically, the B came from the bursa of Fabricius,
just in case you want to know. But it's easy to remember. The B could also stand for bone
marrow because that's where it's produced. T lymphocytes actually do start
off in the bone marrow, but they mature and become what
they are in the thymus. So that's where the
T comes from. Now in this video, I'm going
to focus just on the B lymphocytes-- because frankly,
if I focused on everything, it would be an hour-long video. But the B lymphocytes frankly on
some level-- well, I don't want to pick and choose
favorites, but something in my brain-- I just really like
the B lymphocytes. So the B lymphocytes participate
in what's called the humoral response. And I'll tell you what humoral
means in a second. You'll see that T lymphocytes
participate in what's called the cell mediated response and
we're going to do that in a future video. They actually do certain classes
of T lymphocytes. We'll see that there are helper
T cells and there are cytotoxic T cells. I know it's all very confusing
the first time you see it, but that's why I just want
to focus on just this part right here. We're going to see in the future
that the helper T cells play a role in amplifying
and really activating this humoral response. But a simple way to think about
the difference between the humoral response and the
cell mediated response is, when I get infected--
let's say I get infected by a virus, right? At first, when a virus comes
into my system, it's just floating around in the
fluids in my system. The fluids of our system--
that's really what humoral responds to, into the humoral
fluids of your body. So you have your viruses. These are little viruses
floating around. So while they're floating around
and they're not sitting inside of cells, that's where
the humoral response can come into play. Same thing if we have little
bacteria floating around and they haven't infiltrated
cells yet. They're just floating around in
the fluid, then the humoral response can be useful
for that. Now if all of a sudden, these
guys have infiltrated cells-- so if the cells are now infected
with the virus and they're producing the viruses
using the mechanisms of the cell to produce more, then all
of a sudden we have to be a little bit more sophisticated
in how we deal with these cells and how we deal with the
viruses because they're not just going to be floating
around anymore. We probably want to just kill
this cell even though it was one of our own, but now it's
helping to make viruses. Or maybe it's been colonized
by bacteria. So in either case, you
want to kill this. And we'll talk more about that
in the cell mediating.