Physiology of Hematopoiesis (Nursing)

00:01 Now, we typically think of hematopoiesis or blood cell production has been in the bone marrow.

00:08 And for the most part for most of life, that is true, but it actually changes over time.

00:15 So initially, in the very, very earliest stages, it's in a very transient structure called the yolk sac.

00:22 But then by mid gestation, the majority is actually coming from the liver and the spleen.

00:29 And it's really not until birth that the bone marrow is ramped up to really be the dominant source of hematopoiesis.

00:37 And even though hematopoietic production of the liver and spleen tells off by the time of birth, the liver and spleen always retain the ability to make blood cells.

00:48 So in some extreme cases, the liver and spleen can re start blood cell production to help out the body.

00:57 And there'll be something called extramedullary hematopoiesis, basically hematopoiesis outside of a bone.

01:06 And again, by birth, bone marrow has really picked up.

01:10 But even then, it's not in every bone equally.

01:14 In childhood, it is kind of diffuse, it's in both what we would say the axial or centrally located skeleton, as well as the appendicular skeleton or the skeleton of the limbs.

01:25 But by adulthood, it's really confined to the more centrally located bones, something we call the axial skeleton, there's not a whole lot of hematopoiesis going on in the bones of the upper and lower limbs.

01:40 So if we were to look at a cross section of a typical bone, we would see that the outer part of the bone is very compact.

01:50 And there's really not room for any sort of hematopoiesis.

01:53 In fact, it's called compact or cortical bone.

01:57 And that's really the bone that is giving bone its structure and strength.

02:01 It's the inner part of the bone called the cancellous bone or the spongy bone that has room for bone marrow elements, or hematopoietic elements to make blood cells.

02:15 Now again, and especially by the time we reach adulthood, a lot of the long bones don't have any hematopoiesis.

02:22 And they really just have fat in the inner part of the bone.

02:26 And so that's typically called the yellow marrow, because just fat, and then the red marrow is where you actually have hematopoiesis.

02:37 Now, again, by adulthood, you're pretty much confined to the axial or more centrally located skeleton in terms of active hematopoiesis.

02:47 And that's going to guide you where you aim to get bone marrow biopsies.

02:53 So if you want to collect bone marrow to look at hematopoiesis, especially for things like various hematologic cancers, you have to think where are we going to find our best chances of getting hematopoietic elements.

03:07 Well somewhere along the axial skeleton, and it's actually down in the pelvis where we have a lot of bone marrow activity, where it's actually still relatively close to the skin surface, certain parts of the pelvis are right below the skin.

03:24 And therefore you don't have to go quite as far with the needle to procure all of that bone marrow for examination.

03:32 And so you use this part of the pelvis or hip bone here with your biopsy needle to gain access through the cortical bone and into the marrow.

03:42 And you can actually aspirate out a sample of bone marrow without having to cause too much damage or any incisions in order to reach it.

03:53 Now, when you were to look at this bone marrow under the microscope, you'd see there's a lot going on.

03:59 So a lot of it hopefully is made up of hematopoietic cells or the cells that are making blood cells.

04:06 But these little white dots you see here, these are fat cells.

04:11 And so those fat cells are going to change over time.

04:15 And essentially, over time we lose hematopoietic cells and gain fat cells.

04:21 And as a rough rule of thumb, you can basically go 100 minus a person's age to see what percentage of hematopoietic elements you would expect to find.

04:32 So at birth, it should be pretty much all hematopoietic elements and little fat.

04:37 And by middle age by 50, for example, it should be about 50/50 hematopoietic elements and fat.