Name: 人體生理學 - 先天免疫系統 (Human Physiology - Innate Immune System)
Uploaded: 2021-01-14T05:42:54.000Z
Duration: 14 min 26 s
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>>Dr. Ketchum: So we are going to go ahead and continue our discussion of the immune

system, and we’ll be discussing innate immunity. Now before we discuss innate immunity, you

need to understand that there’s actually two different types of immunity—one of those

being innate immunity, which is also called nonspecific immunity, and the other is called

acquired or adaptive immunity, which is also known as specific immunity. But just to give

you a quick overview of both of these, when you first think about the nonspecific or the

innate immunity, it’s a very rapid response. This is your first line of defense. And what

this does is it gives your body time for the specific immunity to kick in. So innate immunity

is always there. It’s present; it’s going to happen as soon as your body is invaded

by a foreign object, and then the specific immunity will take over after that. It’s

rapid, and it’s also not selective. So it’s not targeting specific species of invaders,

for example. It’s not specific. It just wants to kill foreign invaders, and that’s

the end of it. The innate immunity involves physical and chemical barriers, and it also

includes cellular defenses. Now once the innate immunity has occurred, then the next type

of immunity that will occur or kick in is the acquired immunity. It’s a slow response.

And so because it’s a slow response, it’s very selective in what it’s killing. It

may kill a specific bacterial cell or a specific virus, and specific immunity includes two

different types of responses—humoral responses, which are also called antibody-mediated responses,

and cell-mediated responses, which are also called cytotoxic lymphocytes. Here’s our

analogy. When you think about an innate response, the castle is the body. And the first thing

that this innate response wants to do is it wants to prevent that invader from entering

the body. And once that invader invades the body, then the innate response will have some

other methods for killing the invaders as well. These things are all taking place as

the acquired response is just getting started—but remember it’s slow, so it takes a while

So neutrophils, the eosinophils, basophils and monocytes are all cells that are important

in an innate response. The lymphocytes, on the other hand, are the type of white blood

cell that are important in the acquired response. You don’t have to memorize the amount of

each of these cells in a microliter or their diameters or any of that. You need to understand

their anatomical features and their functions. So these are important columns here, but you

do also have to know their abundance—their relative abundance. So again, if you remember

“Never Let Monkeys Eat Bananas,” that tells you the most abundant leukocyte all

the way to the least abundant leukocyte, which are your “bananas” or your basophils,

so that way you don’t have to memorize the amount per microliter. The reason this is

important is because if you’re looking at a slide—let’s say you take a blood smear

on a microscope slide—and, and this is a healthy person, and you’re going through

and you’re identifying all the various white blood cells. Well if you’re finding more

basophils than you are neutrophils, then you’re probably not correctly identifying those cells.

Okay, so here’s a flow chart that I put together to help organize the innate versus

the adaptive response. So you’re definitely going to want to use this as your road map.

We’re discussing the innate responses in this part, in part two.

First let’s start with the physical and the chemical barriers; you think about these

as being the wall of the castle. So the first thing I’d like to discuss are the lysozymes.

So you have lysozymes that are in your tears and other secretions. These are not lysosomes;

lysosomes are different. Lysozymes are antibacterial. So when you cry, it’s actually a good thing

because you’re killing any kind of bacteria that’s on your skin. You also have the skin,

then, and the skin is a physical barrier. The skin also has fatty acids and normal flora

as well that’ll affect the pH and some foreign invaders cannot survive on the skin just because

of the normal flora on our skin. Then you have the mucus and the cilia that line the

trachea. The mucus traps any formed particles, and then the cilia works that debris up the

respiratory tract and into your mouth so that you can either swallow it or spit it out.

If you swallow it, it goes down into your stomach. And remember, the stomach has a pH

of two; it’s very acidic. So it’s likely to kill most invaders, but not all. Now taking

a closer look at the skin, we’re not going to spend time on the skin. This isn’t anatomy,

but you should realize in this course that you do have two major skin layers: the epidermis

and the dermis. So pay attention to those two layers and know where those two layers

are located—which one’s on the outermost which ones on the innermost.

The dermis, then, the only thing that you need to know about the dermis are the sebaceous

glands, and I want you to use your textbook to figure out what’s the function of those

sebaceous glands? Why are they important in the immune response? Then we have inflammation.

So inflammation is part of the innate immunity as well. When you think about inflammation,

it’s your body’s response to tissue damage or microbial invasion. So you’ve sprained

your ankle and your ankle is now inflamed. You stepped on a nail, and—so now you have

tissue damage and microbial invasion by stepping on a nail. So the goals of inflammation are

listed here for you. You want to bring phagocytes to the injured area, because if you can control

those invaders at the area that they’ve invaded, then they can’t spread throughout

the body. You want to stop them there. So if you can bring those phagocytes to the

injured area, you can destroy, inactivate invaders, you can remove any kind of cellular

debris, and you can start preparing for healing. So let’s take a look at this flow chart.

The leukocyte that automatically will start phagocytizing as soon as invaders enter into

that wound are your macrophages. So those macrophages are there, and they immediately

start attacking foreign invaders that enter the wound. The bacterial invasion itself and

the tissue damage as well can cause the mast cells to release histamine. Histamine then,

we know, causes vasodialation. So when an arterial vasodialates that means you have

less resistance, right, and therefore more blood flow to the injured area. So because

there’s more blood flow to the injured area—that’s why it becomes red and that’s why it gets

hot. So because there’s more blood there, that means that you have an increase in certain

plasma proteins that may be important in the healing process. So these may be clotting

factors, for example, that would prevent you from bleeding out.

The release of histamine by the mast cells also increases the capillary permeability.

So what I want you to do is think about a capillary here, and I’m just going to draw

three endothelial cells that are forming the walls of this capillary. And when you have

histamine release, the pore size has increased significantly. So if you increase the pore

size, that means more fluid can flow through those pores. So that means you’re going

to get a local accumulation of fluid, some of that fluid being in the interstitial fluid.

Remember that we’ve talked about swelling or what we call edema, an excess of interstitial

fluid. It can also cause pain, because you have excess fluid in an area and the skin

can only stretch so much—that causes pain. Pain is a good thing, because pain actually

forces you to rest whatever part of your body is injured, and that way it can repair itself

if it’s resting. Because you have this increased capillary permeability, then that’s going

to increase the number of phagocytes that can make it to the tissue, like your macrophages.

If you have more phagocytes, that’s going to increase their secretions. And their secretions

can cause systematic responses like fever, for example. All in all, then, this is an

inflammatory response and all of the information in red here—these are all cardinal signs

of inflammation. And all of these cardinal signs of inflammation are because you had

changes in blood vessel function—the blood vessel vasodialated.

When we talk about phagocytosis—this is a form of endocytosis, but specifically, how

is it achieved? So it’s going to be your job to fill in the steps. Don’t go into

more—any more detail than what these four steps are asking for here. Opsonins, I do

want you to look at opsonins and, and, why do we need opsonins? Why are opsonins important

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人體生理學 - 先天免疫系統 (Human Physiology - Innate Immune System)

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