platelets Flashcards
(6 cards)
platelets
Not true cells:
Platelets are cell fragments, not full cells.
Where they come from:
They come from megakaryocytes — huge, bizarre-looking cells with multiple nuclei found in bone marrow.
These cells break apart, releasing thousands of tiny fragments into the bloodstream.
What platelets look like:
Under a microscope, they appear as dark-staining, irregularly shaped little pieces scattered among red and white blood cells.
Do platelets have a nucleus?
❌ No — they are anucleate, meaning they do not have a nucleus.
Platelet count:
A normal count is about 300,000 per cubic millimeter (mm³) of blood.
Function:
Platelets are essential for blood clotting.
When a blood vessel breaks, platelets gather at the site and form a temporary plug to help stop bleeding.
🩸 Quick Recap:
Platelets = broken-off bits of megakaryocytes
No nucleus
Help stop bleeding
Normal count ~300,000/mm³
hemotopoasis
What is it?
Hematopoiesis is the process of making new blood cells.
Where does it happen?
It occurs in red bone marrow, also called myeloid tissue.
Location of red bone marrow in adults:
Axial skeleton (skull, vertebrae, ribs, sternum)
Pectoral girdle (shoulder bones)
Pelvic girdle (hip bones)
Proximal epiphyses (ends) of the humerus and femur (upper arm and thigh bones)
How it works:
The body adjusts the production of different blood cells depending on what it needs (like more RBCs if oxygen is low, or more WBCs during infection).
Once the blood cells are fully matured, they are released into nearby blood vessels.
Fun Fact:
Red bone marrow makes about 1 ounce of new blood per day, which contains around 100 billion new blood cells daily!
breakdown of rbc
Red Blood Cell Breakdown (RBC Demolition)
🔚 Why RBCs break down:
RBCs have no nucleus or organelles, so they can’t repair or divide.
They live about 100–120 days before wearing out and becoming stiff.
🧹 Where they are destroyed:
Cleared out by macrophages (special immune cells)
Mainly in the spleen, liver, and bone marrow (“RBC graveyards”)
♻️ What happens to RBC components:
1. Hemoglobin is split into:
Heme (iron-containing pigment)
Globin (protein part)
🔬 HEME breakdown:
Iron (Fe²⁺) is:
Removed and stored as ferritin in the liver or spleen
Later reused to make new RBCs
Heme without iron is:
Converted to biliverdin (green pigment)
Then to bilirubin (yellow pigment)
Bilirubin goes to the liver, enters bile, and is sent to the intestines
In the intestines, it becomes stercobilin (brown pigment in poop)
🍗 GLOBIN breakdown:
Broken down into amino acids
These amino acids are released into the blood to be reused for protein synthesis elsewhere in the body
🧠 Easy Way to Remember:
RBC dies → Macrophage eats it → Hemoglobin splits → Iron stored, Heme → Bilirubin → Poop brown, and Globin → amino acids reused
Let me know if you’d like
formation of rbc
Old RBCs die after about 120 days and are removed by phagocytes in the spleen and liver (this is called the RBC “graveyard”).
To replace them, hemocytoblasts (blood stem cells) in the red bone marrow begin making new RBCs.
These developing cells:
Multiply
Start producing hemoglobin, especially the globin protein part (with help from the rough ER)
As the cell matures, it:
Ejects the nucleus and most organelles (including mitochondria)
Becomes a reticulocyte (a nearly mature RBC that still has a little rough ER left)
Reticulocytes enter the bloodstream and start transporting oxygen, even though they’re not fully mature yet.
Within about 2 days, the reticulocyte ejects the last bits of rough ER, becoming a fully mature erythrocyte.
🕒 Total time for this process: 3 to 5 days
✅ So yes — the rough ER helps build the globin part of hemoglobin early on, but is gone by the time the cell is mature.
erythopoten
Erythropoietin and RBC Production (Erythropoiesis)
Erythropoietin (EPO) is a hormone that regulates red blood cell (RBC) production.
It’s usually present at low levels in the blood to keep RBC production steady.
When blood oxygen levels drop (due to blood loss, high altitude, or lung problems), the body needs more RBCs to carry oxygen.
The kidneys detect this drop in oxygen.
Although the liver can make some EPO, the kidneys are the main producers.
The kidneys release more erythropoietin, which travels through the blood to the red bone marrow.
In the bone marrow, EPO stimulates hemocytoblasts (stem cells) to divide and produce more RBCs.
Once oxygen levels return to normal, EPO production slows back down.
✅ Summary:
Low oxygen → Kidney makes more EPO → EPO goes to bone marrow → Hemocytoblasts make more RBCs
You’re explaining this like a pro! Let me know if you want to turn this into a flowchart or memory trick.
when does epo get triggered to make more rbc
As you might expect, an overabundance of erythrocytes, or an excessive amount of oxygen in the bloodstream, depresses erythropoietin release and red blood cell production. However, RBC production is controlled not by the relative number of RBCs in the blood, but by the ability of the available RBCs to transport enough oxygen to meet the body’s demands.
