Cisternal vs Alveolar Milk Pools

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Lactation Biology

7 classificações

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University of Illinois at Urbana-Champaign

Lactation Biology

7 classificações

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.

Na lição

Module 6: Lactation

In this module, we explore the many facets of lactation as a complex physiological process. We will find that removal of the milk in the gland is critical to continued production of that fluid. The interactions between milk removal, the systemic factors stimulating the gland to produce milk, such as several hormones, and the local factors that inhibit further milk secretion are examined. Some of the effects of milk removal, as well as the absence of milk removal, are discussed in this series of videos. The responses of the mammary gland to milk removal provide a means of understanding the impact of management practices on lactation.

Feedback Inhibition of Milk Secretion10:21

Frequency of Milk Removal5:25

Cisternal vs Alveolar Milk Pools7:01

Frequency of Milk Removal - Cows6:35

Determinants of Milk Yield6:08

Intensity of Milk Removal9:57

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Dr. Walter Hurley, PhD
Professor Emeritus
Department of Animal Sciences

I want to introduce you to another concept that relates to milk removal and

relates to frequency of milk removal.

And this is particularly true for the dairy cow as well as the number of other

species including a number of dairy species, sheep's, goats and so on.

So let's take a look at the next slide so something to remind you about the anatomy

of the mammary gland and that is in a cow, this is a cross section of a dairy cow.

I've kind of outlined the cisternal ducts, the teat cistern and

the gland cistern here.

And then these cisternal ducts are the major ducts coming down.

Those are not secreting milk.

The alveolar part, on the other hand, up here, is secreting milk.

So we might say, well,

what that means is that any milk that's down here where the yellow is indicated

feedback inhibitor of lactation is in that milk just like it is on all the milk.

But there's nothing to feed back on because there's nothing there

secreting milk.

On the other hand, feedback inhibitor lactation up here is going to feedback and

then impact that secretion rate like we just we saw in

the graphs a few moments ago.

So the proportion of cisternal volume,

what they call cisternal volume versus alveolar volume, can impact

the ultimate milk production of a cow, again a goat, sheep and so on.

So animals that have this cisternal volume in them.

Compare that say, to a pig, and remember in the case of the pig,

they don't have cisterns, they might have a lactiferous sinus.

Again there would be two of those coming out of the nipple here.

But there's really no milk collecting area, so essentially all the feedback due

to lactation is up here in the alveolar tissue.

So if you don't get all the milk out, that's going to feedback and

impact secretion rates.

So again, this animal we're milking two, three, four times a day.

This animal's being nursed roughly once an hour or once every 50 minutes,

something like that, and getting that feedback of lactation very quickly.

[COUGH] So I want to examine that a little bit better here, and

in a little more detail of what the impact of that is.

So let's go to the next slide.

[COUGH] So what I've done is to set this up in kind of like pools of milk.

So the white area up here, in each case, cow A, B and C here,

represents the alveolar area.

So again, alveolar volume's in white.

Yellow represents cisternal volume.

So if we compare Cow A and Cow B,

both of them have the same total volume In that sense.

So the pull of milk in both of these is the same because

the total box size is the same.

However, this one has a smaller Alveolar Volume but

a larger Cisternal Volume compared to Cow B.

We might actually expect, even though this has a smaller alveolar volume,

we might expect that these cows to give roughly the same amount of milk.

Because, remember, milk is being secreted here.

So again, remember, this pink arrow indicates

milk that's in the alveolar volume, that has the feedback inhibitor lactation,

is feeding back and impacting further milk secretion.

Whereas, the stuff in the yellow It's nothing to feedback on, so

it's kind of out of the way.

So again we might expect cow a and cow b to end up

producing the same amount of milk or pretty close the same amount of milk.

Again, even though this one has a smaller alveolar volume compared to cow b.

If we then go to cow c,

we see that she has basically the same alveolar volume as cow B.

Excuse me, cow C has the same alveolar volume as cow B but

has a bigger cisternal volume.

Again, we might expect this cow to give even more milk because again,

lot more alveolar volume as well as somewhere for

that to go in terms of the cisternal volume.

What else do we know about cisternal volume, alveolar volume?

So a couple things that people have found for example,

cisternal volume is a proportionate total.

So again, this would be total, and

the cisternal volume would be the part in yellow here, down in those cisterns.

It tends to increase as the animal gets through more and more lactations,

tends to increase with parity.

In terms of a proportion.

Cisternal volume as proportion of total volume tends to decrease the stage of

lactation.

And ultimately this is going to influence the impact of changing milking frequency.

So, how the milk is distributed can impact how that animal is going to

respond going say from two times a day, to three times a day milking.

Or vice versa, three times a day back to two times a day milking and so on.

So this is part of the whole story as we think about milking frequency,

this idea that there are multiple pools of milk in there.

This alveolar milk which again, feedback inhibitor of lactation's impacting

further milk secretion whereas the cisternal volume feedback inhibitor

of lactation's there, but there's nothing to feedback on.

Before we go on, I want to tell you a little story, personal story.

For many, many, many years, I looked at this idea of cisternal milk as being,

yeah, okay, it's there, it doesn't do much.

In the milk ejection module,

we will see that actually as milk is ejected and pushed down,

this volume expands for a moment, temporarily till the milk comes out.

So it is fairly dynamic.

And now we've now seen that physiologically there's an impact of

having the cisterns again compared to species like the pig.

A number of years ago, I was privileged enough to spend sometime at

the Hammond Research Institute in Scotland.

It's now been dissolved.

It's gone.

And went in to one of my colleagues there, Colin Wild, and

was asking about another colleague, Chris Knight, who was at that a time there.

He's currently at the University of Copenhagen.

[LAUGH] And, I kind of asked Dr. Wild, what's Chris up to.

And he was talking about, well he's looking at the relationship,

the anatomy of the mammary gland, with regard to milking frequency and

those kinds of things.

And I thought to myself, what were you talking about?

It's anatomy, it doesn't change.

There's nothing, it just there.

So I went up to Chris and

he started explaining this idea of alveolar versus cisternal milk to me.

And yeah, that makes complete sense.

because again, they're some of the people who have come up with this feedback in

a lactation concept.

And so it started to make a great deal of sense.

So that's my personal introduction to this alveolar versus cisternal.

And the recognition that again, for many many years, the cisternal

part of the mammary gland was very very boring, because it didn't change.

And now we know that in fact it's extremely important

to thinking about the total physiology of that mammary gland.

Both with regard to again the milk ejection process but

also with regard to this how the feedback lactation impacts the mammary gland.

How we think about milking frequency, milk removal, and those kinds of things.

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