Erythropoiesis: Topic 1

Question 1

what is erythropoiesis?

Answer 1

the body’s process of making red blood cells

since mature RBCs are unable to divide, erythropoiesis (which involves erythroid stem cells) is a very important process

**Red blood cells are made in different places in fetal and adult life

Question 2

how fast are old RBCs removed?

Answer 2

Old RBCs are removed from circulation at an astonishing rate of about 2 x10ˆ11 cells per day

Question 3

where does erythropoiesis happen?

Answer 3

RBC are made in different places in fetal and adult life

Fetal erythropoiesis begins in the yolk sac at approximately week three of gestation

The process then moves into the liver, spleen, and finally to the bone marrow, where it remains throughout adult life

Question 4

what’s the pneumonic for where RBCs are made?

Answer 4

Young Liver Synthesizes Blood

Yolk Sac
Liver
Spleen
Bone Marrow

Question 5

where does erythropoiesis occur during adulthood?

Answer 5

bone marrow

Question 6

where does erythropoiesis begin?

Answer 6

in an erythroid stem cell

these cells (like other stem cells) are self-renewable; they are able to divide into two cells: one remains a stem cell and the other begins the process of erythroid maturation.

Question 7

what are the 6 stages of erythroid differentiation?

Answer 7

STEM CELL THEN:
1. proerythroblast

2. basophilic erythroblast
3. polychromatophilic erythroblast
4. orthochromatophilic erythroblast
5. reticulocyte
6. erythrocyte

Question 8

what is the first stage of RBC differentiation?

Answer 8

proerythroblast

The first recognizeable stage of erythroid differentiation

a very large cell with super-fine chromatin, prominent nucleoli, and abundant, basophilic cytoplasm.

looks like a random blob

Question 9

what is the 2nd stage of RBC differentiation?

Answer 9

the basophilic erythroblast

cytoplasm is a deeper blue color due to the presence of free ribosomes = ribosomes appear in this stage!

looks like a formed blob with a nucleus that’s most of the cell

Question 10

what’s the 3rd stage of RBC differentiation?

Answer 10

polychromatophilic erythroblast

the ribosomes produce
hemoglobin, and we begin to see a hint of pink in the cytoplasm

looks like an olive with a very dark purple nucleus

Question 11

what is the 4th stage of RBC differentiation?

Answer 11

orthochromatophilic erythroblast

chromatin begins to be more coarse

the nucleus is
very dense, dark, and small

looks like a cell with a small dark nucleus

Question 12

what is the 5th stage of RBC differentiation?

Answer 12

reticulocyte

the nucleus is extruded, leaving behind the rest of the cytoplasmic
contents, including a bit of RNA, which gives the cytoplasm a slight lilac tinge

looks like a plain purple cell with no nucleus

Question 13

how long do reticulocytes stay in the bone marrow? what happens to them after?

Answer 13

Reticulocytes stay in the bone marrow for approximately three days

then they enter the circulation

Question 14

what is the 6th stage of RBC differentiation?

Answer 14

erythrocyte

Reticulocytes stay in the bone marrow for three days then they enter the circulation

Over a period of one to two days, the reticulocyte loses its RNA (and therefore becomes more pink in color), and changes into the biconcave disk shape of the mature erythrocyte

Question 15

how long does the RBC differentiation take?

Answer 15

1 week

Question 16

what’s the lifespan of a RBC?

Answer 16

120 days

then the spleen removes them from circulation

Question 17

what removes RBC from circulation?

Answer 17

spleen

Question 18

what general things happen as the RBC matures from proerythroblast to erythrocyte?

Answer 18

• cell gets smaller
• cytoplasm turns from deep blue to red
• nucleus shrinks and becomes darker in color
• chromatin pattern evolves from very find to very condensed

Question 19

what regulates erythropoiesis?

Answer 19

erythropoietin (EPO)

When there is increased consumption of oxygen, or if the body senses that it has low oxygen levels, the body will stimulate RBC production to help keep up with oxygen demand

Instead of stimulating erythropoiesis by directly acting on the bone marrow, low oxygen levels stimulate the kidneys via a substance called hypoxia-inducible factor

When the kidneys sense low oxygen levels in the blood, they secrete the hormone erythropoietin (EPO), which stimulates the bone marrow to produce erythrocytes

Question 20

when are RBCs made in the yolk sac?

Answer 20

3-8 weeks gestation

Question 21

when are RBCs made in the liver?

Answer 21

6 weeks to birth

Question 22

when are RBCs made in the spleen?

Answer 22

10-28 weeks

Question 23

when are RBCs made in the bone marrow?

Answer 23

18 weeks through adulthood

Question 24

what organ secretes EPO?

Answer 24

kidney