BIO156 online / summer – Chapter 14 (part A): the body’s organization – connective & nervous tissues

BIO156 online / summer – Chapter 14 (part A): the body’s organization – connective & nervous tissues


Hi! Welcome to Chapter 14, or Chapter 22. Which one you use depends a little bit on
which edition of the textbook you use. I believe that one of the versions even calls
this as Chapter 13. Regardless of whatever number we use, this
is the chapter titled as ‘Being Organized and Steady.’ On this chapter we are taking a step back,
and looking at a human body on a larger scale. For much of this course we have talked about
very small stuff – such as, atoms, molecules and cells – as well as looked at genetics
– DNA, how genes are passed on from the parents, and genetic disorders. So, now it certainly is time for us to look
at the body as a whole. And, we will start by looking at: How body
is organized? And, you might remember this slide from our
very first lecture together. What this slide shows is, essentially, that
life is organized on various levels. And, we were interested, especially on the
levels of cells, tissues, organs, organ systems, and eventually the whole organism. Let’s look at these a little bit more. And, this next slide, which we will be building
up together, is going to be a very good reminder of these different levels of organization
in a human body. And, we remember that cells were the structural
and functional unit of life. They were the smallest unit of life that could
exists independently, on its own. And, of course, if we have a group of cells
that come together, they form a tissue. And, what we see here, I think, it is going
to be an animal cell, and cuboidal epithelial tissue. But, we will talk about different types of
tissues in a few moment’s time. So, remember that tissues were composed of
specialized cells of same type that perform a common function in a body. And, then we get to the level of organs! In this case, the example that we will use
is a kidney. And, an organ is formed when different tissues
come together, and they share same overall aim in the body. In case of a kidney, they all would function
to make up this structure that filters the blood and excretes urine. Well, when we have a bunch of organs, which
all function together as one system, we talk about an organ system. In this example, it is the urinary system,
which includes also the ureters, urinary bladder, and urethra. And, finally, all of our organ systems together
make up the organism. The example that we have picked, since this
is a human biology introductory course, is a human, of course! So, I think that on this diagram you can see
really nicely how we have had to start with talking about the small stuff, before on your
later courses you can move to understand organs and organ systems, which allow you to have
an appreciation of the entire human body. And, we have got some great courses ahead
for you in the future! So, what we will do next in this chapter is
going to be that we will review the four main types of tissues that you will find in the
human body. And, these will be: epithelial, connective,
muscular and nervous tissues. And, what we will do is that I have a slightly
different plan for us to revise the epithelial and muscular tissue types, so we will look
at in this presentation the connective tissues and nervous tissues. But, do not forget to review these two others
in the upcoming items in this module! So, let’s start by discussing about connective
tissues. The main function of the connective tissues
is to do what it ‘says in the tin,’ they connect parts! So, really, their role is to bind structures
together, and provide support and protection. They can also fill spaces, and store material
(like fat cells), and of course we have a special group of connective tissue known as
our blood. And, I find that this textbook lists connective
tissues in a few different ways, and it can feel a bit overwhelming and confusing. So, fear not, I have something better for
you! All connective tissues (with a very few exceptions)
contain these three components. So, first of all, we have some sort of a ground
substance. This is usually clear, colorless, viscous
fluid, within the intracellular space. And, a good example of this would be the plasma of the blood. So, here you see the red blood cells, these
dark-pinkish ‘blobs’ that are very numerous. And, we also have white blood cells that have
taken the darker, blueish color. And, the tiny platelets, these smallest structures. But, most importantly, there is a lot of this
matrix in-between all these cells. And, that is the ground substance; in this
case the plasma. The other reason why I like to use this as
an example is that it shows all these cells, and in this case they are fairly far spread
out from each other. But, it is not always the case. So, we have here aerolar connective tissue,
and again, we are seeing the matrix. But, one thing that stands out, as something
that we did not see with the blood (which was a bit of an exception in this sense) is
the numerous fibers running across the sample. And, they run in many different directions,
forming this strong structure of this connective tissue. You can even also see some cells here and
there, too. Here we see another example of a connective
tissue. And on this one, there is not that many cells
or that much of matrix to be seen. But, we can see that this time the fibers
are very well aligned. And, this would make horizontally very strong
tissue. Well, here we have another type of connective
tissue. And, this time we see a lot of cells, instead. And, here, this is adipose (fat) tissue. You see these big nice round fat cells that
dominate this connective tissue type. So, really, what I guess that I am trying
to say is that: Rather than worrying about memorizing everything about connective tissues,
you might prefer to approach these through looking at these three components that typically
are found in nearly all connective tissues. It is just the proportions of these that vary. So, a few examples of connective tissues here,
that I want to mention. You have your dense fibrous tissue. So, it is characterized by a lot of similarly
aligned fibers, and this makes a very strong tissue. Adipose tissue we already mentioned. This is our fat cells. And, as they store more and more fat, they
grow in size. Really, to become fatter, or larger in size,
the number of fat cells usually does not grow drastically – they just come bigger! That is why it is soeasy to get fat again
after losing a lot of weight. There is still the same amount of fat cells,
they just are smaller. But, ready to grow big again… Another interesting one here, is bone. Yes, bone is connective tissue, too. You see this beautiful structure of a bone
on a microscopic level, these osteons here. They are really strong, usually. And, then we have a picture of our hyaline
cartilage, which is not aimed to withhold as much of a tensile strength as our dense
fibrous tissue was. But, you see nicely the cells in there. So, overall, this is kind of a nice slide,
showing how different tissues the main group of connective tissues holds. Finally, the last one that we have here a
picture of is the blood. It is a special kind of connective tissue. Okay, and before we wrap up this video, we
are going to talk quickly about nervous tissues. So, the nervous tissues serve the purpose
of receiving and conducting stimuli. And, your textbook actually says that it is
the only type not subdivided into more types, but I think that this is slightly incorrect. Let’s revisit this in a second. But, what you see here is a generalized figure
of a typical nerve cell. Usually, nerve cells would differ, and they
all would not look like this, but this one shows main parts. So, the electrical impulse that the nerve
cell carries would progress in this direction. Study the different parts from your textbook. And, here is another figure of a nerve cell. This time it is a real microscopy image, so
you see that it really looks quite a lot like that diagram that you just saw. But, what I think is really important here
to note is these neuroglial cells. And, for a long time we thought that it was
only neurons, which you saw that drawing of earlier, that were important in nervous tissue. But, what we have started to realize is that
it is actually the glial cells that are just as important. Although they do not conduct nerve impulses,
like neurons do, they are super important in the maintenance of a nervous tissue. They support nervous tissue; both structurally
and physiologically. And, it turns out, that for a long time we
have been ignoring their importance. For example, Alzheimer Disease and many other
diseases are actually largely due to the issues in these cells. So, really, these are important. – And, I feel, often not given enough emphasis
on textbooks. So, now we have discussed the connective tissue
and nervous tissue. And, we will look at epithelial tissues, and
then muscular tissues in the next items of this module. I will see you then!

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