Lactation and especially milk, which is the product of that unique mammalian process, are routinely encountered within our daily lives. Nevertheless, they often are poorly understood by many, even including many who are engaged in the business of producing milk. The overall course goal is to introduce fundamental concepts that form the basis for understanding the biology of lactation, the biology of the mammary gland, and the products of that important physiological process. As a learner in this course, you will be provided with a series of easily understood presentations that collectively will help you build a foundation for greater understanding of lactation. You will be able to engage with other learners so that you can extend your learning beyond the video presentations. Ultimately, you will be able to construct your own mental model for understanding the wide range of topics that relate to the biology of lactation. Upon completion of the course, you will be prepared to expand your knowledge and understanding of lactation from other sources and experiences as you pursue your individual interests. Before you start the course, I suggest that you identify a question or several questions about lactation that you already have on your mind. This could be from your own experiences, something you read about or saw, or something you have wondered about. Write down your question(s) and use that to help you decide how to engage with the content of this course. You might engage with the modules in the order they are presented, or start with a module that is of particular interest to you, or pick and choose modules in any order. I encourage you to engage in all of the types of learning activities that this course has to offer, including but not limited to, the discussion forums, quizzes, peer-review assignments, and concept maps and other learning aids.
Mammals
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来自 University of Illinois at Urbana-Champaign 的课程
Lactation Biology
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从本节课中
Module 1: Introduction to Lactation Biology
In this module, we will introduce some basic definitions of terms related to the biology of lactation, provide an overview of milk, and briefly introduce the phylogenetic organization and evolution of mammals. Learning the definitions will be important for establishing a baseline vocabulary that will help reduce confusion about topics presented in subsequent videos. Milk, a primary product of the lactation process, will be introduced in an effort to provide a foundation for later modules in which milk and milk composition are explored in greater depth. The series of videos about mammals collectively offer a brief overview of the wide spectrum of these animal species, as well as some thoughts on how lactation came to be an integral part of the reproductive strategy of those species.
与讲师见面
Dr. Walter Hurley, PhDProfessor Emeritus
Department of Animal Sciences
[SOUND]
Welcome back.
We want to continue thinking about this field called lactation biology.
In earlier videos we did a little bit of introduction,
just kind of lay some of the ground work on what is lactation biology all about,
we did some definitions.
We also spent some time kind of thinking about milk and what is milk and
what kind of perspectives do we need to bring as we think about milk.
So now I want to shift gears a little bit and
talk a little bit about the animals that lactate, and that is mammals.
So let's take a look at our first slide.
And we're just going to do a real superficial look at mammals here.
Phylogenetic classes is Mammalia.
All mammals are part of this phylogenetic class.
It's derived from the word mamma, Latin word mamma meaning breast or teat.
There are 5,400 species of mammals, quite a large group of mammals.
What's interesting, though, from a lactation biology perspective, and
especially as we just talked a little bit in some earlier videos about milk.
We only know about milk composition in detail, or even in a general sense,
in less than probably 3% of the species of this 5,400 species.
So lots of opportunity to examine other kinds of species and
learn about their milk composition.
Let's go to the next slide.
Distinguishing mammals from other animals, reptiles and birds.
Some adaptations of the neocortex, a skin glad adaptation.
Hair, so mammals have hair.
Some changes in jaw bone and how that relates to the ear and inner bones,
middle ear bones in this particular case.
And then certainly the one that we're particularly interested in this
course are the mammary glands.
Again, skin adaptation, adaptation of the skin.
A gland that's secreting something to the outside of the animal.
And then finally on this set of slides here,
ranging tremendously in size from very,
very small bumblebee bat about an inch and a half long, something like that,
to a blue whale which is the biggest mammal, over a hundred feet long.
So tremendous diversity in terms of size.
And as we'll see later on as we think about these things we have animals
that fly, we have animals that are aquatic animals, that live in the water and.
Obviously many, many terrestrial animals as well.
Let's start to break down this set of 5,400 species of mammals
into some type of mammals that we can easily think about and identify.
So first one I want to talk about is again,
class mammalia, sub-class yinotheria.
A lot of times people refer to these as a prototheria and
the word you may be more familiar with are monotremes.
These are egg laying mammals and so again, the order of the monotremata, again,
they lay eggs.
They have a pouch and usually the pouch,
kind of this big folds of skin that come here.
The mammary structures are right under this area.
They lay an egg.
That egg is placed inside the pouch, and then incubates in the pouch.
The young are kind of hatch out a that.
Very, very, very immature.
Very immature young in that particular case, but
they're able to kind of, there's milk
oozes out on the surface inside the pouch there and they can consume that milk.
There's little hairs that come out next to the different pores and as the young
kind of move around they stimulate those hairs that causes milk ejection.
And again the milk oozes out on the surface of inside the pouch there and
the young ingest that milk.
Five species that we know of that are in existence today,
the duck billed platypus is one and then four species of echidna.
And sometimes these are referred to as spiny anteaters.
Typically these monotremes, well not typically,
these monotremes are found in Australia and New Guinea.
So in that part of the world.
Really not anywhere else in the world.
So again, egg laying mammals, we think of these as very primitive on the other hand
they had in fact existed for many millions of years.
And so, as our reproductive strategy for
these animals it seems to be pretty successful for them.
Now let's talk a look at another group of mammals and these are subclass theria.
And this particular group or clade is called metatheria.
And here we're talking about the marsupials.
So Marsupialia are the animals that we're talking about.
These are animals that are born, the young are born live.
Remember the monotremes, they hatched out of an egg.
These are born live but they are extremely immature.
They have fairly developed fore limbs and that's about it.
So once they're born, they can literally crawl up and they go down into a pouch.
So they nurse in that pouch.
They will actually essentially swallow a teat.
It goes down about that far into their throat there.
And they will essentially continually nurse on that teat,
growing in the pouch and eventually they'll start leaving the pouch,
sticking their head back in and so on and so forth.
So very, very complex system.
If you think about this, really changes the way we think about intrauterine
development versus lactation and extrauterine development compared
to most of the animals that we're used to say cows or pigs and so on and so forth.
334 species have been identified, kangaroos, wallabies, koalas, possums,
wombats, Tasmanian devils, bandicoots and a number of other ones.
About two-thirds of those are in Australia and New Guinea.
In the Americas there are about 100 species that are identified in
the Americas.
only one of those is in North America and that is the Virginia opossum.
And so we have one in North America a bunch of them here and
then the bulk of them are in Australia and New Guinea.
So marsupials, again, this idea that the young are very, very immature.
Develop in a pouch, are nursing in that pouch and that has again,
a lot to do with their reproductive strategy in how that works.
Now let's talk about the mammals that most of us are familiar with,
including our own species.
And that is again, subclass Theria.
Eutherian mammals, think of this as a true placenta.
So these are Placentalia, they have a true placenta.
Part of what that means is that the young are able to develop in the womb
of the mother for a much longer time.
So they're born much more mature than those monotremes hatch out or
the marsupials are born.
Still tremendous diversity in terms of how mature they are.
A newborn calf, for example, can get up after fairly short period of time,
an hour perhaps and walk around and suckled from the mother.
Newborn babies obviously are not going to be able to get up and walk right away.
Newborn rat pups, for example, are born with their eyes closed and
it takes several days for those eyes to open.
So tremendous diversity.
Nevertheless, all of them are much more mature than some of the animals
we just talked about a moment ago, again for example, types of marsupials.
Able to nurse on a dependent mother.
And here what I'm talking about is, again, the monotremes and the marsupials have
a pouch, either a pouch kind of like a pocket in the marsupials or
the folds of skin and in the case of the monotremes.
And they're in there so the younger in there and they're kind of trapped in
there but they're really dependent upon that environment whereas these other
animals are out they can nurses the mother somewhat independently in that sense.
The vast majority of extant mammals in existence today
are these Eutherian mammals, Placentalia mammals.
Largest orders, in the terms of the largest numbers of animals, diversity
there, Rodentia, of course, mice, rats, beavers, and those kinds of things.
Chiroptera bats, many, many species of bats.
So a lot of flying mammals in terms of different kinds of species.
As this Soricomorpha, moles, shrews, and this solenodons,
these are thought of a bit more primitive types of placental mammals.
Some of those are actually considered to be venomous.
So there's a group of those, not very many of them but
they're into this order of soricomorpha.
Where we find mammals?
Again, we find them in the oceans, we find them in the air.
So flying animals, such as bats.
Terrestrial, we find them in all sorts of different environments.
That's again part of what makes these animals very, very interesting.
Lactation again is a key part of the reproductive strategy of animals.
So again intrauterine development.
But then there's still an absolute requirement for lactation to help that
animal continue developing extra-uterine, or past the point after which it's born.
So let's quickly review what we've talked about in this video.
So the extant mammals, that is, those that exist today, again, over 5,400 species.
So we have the monotremes, prototheria or the metatherian or the marsupials.
And then most of the animals that we're familiar with the placental mammals or
the eutherian mammals.
Mammary glands, they all have mammary glands again depends where,
which species it is where those glands are.
Clearly in the monotremes, the mammary glands inside the pouch there,
and the marsupials, that's again inside the pouch.
Lactation for all of these species is a key part of their reproductive strategy.
So as evolution has occurred,
how they reproduce, lactation's really a key part of that overall strategy.
Occupy a wide range of environments.
So again, we have porpoises and whales and
dolphins, etc., etc., in sea, in water.
In air we have bats flying around.
In fact, you look around, you see pictures of the baby bat actually
as mom is flying is still sitting there nursing on the mother.
And then certainly land mammals.
So most of the animals that we're going to be talking about in this course,
cows, the pigs, our own species, and so on are obviously going to be terrestrial, or
land mammals.
