Blood Cycle

Question 1

How is iron absorbed in the intestinal lumen and in what form?

Answer 1

DMT-1 transporters. Ferrous (Fe2+). Ferric iron can be reduced in the gut lumen by ferric reductase.

Question 2

How is iron stored in enterocytes?

Answer 2

Ferritin molecules. Found in the cytoplasm of most tissues. Release iron in a controlled way. Some secreted into serum- indirect marker for iron deficiency anaemia.

Question 3

How is iron transported out of enterocytes?

Answer 3

Ferroportin in basolateral membrane.

Question 4

How is iron transported to other cells?

Answer 4

Plasma glycoproteins called transferrins. Bind to receptors on cells and endocytosed. Low pH= iron release. Taken up by the cell and stored.

Question 5

Where does erythropoiesis occur?

Answer 5

Myeloid tissue- red marrow. Up to 5 years in all bones. 5-25 in long bones. 25+ in membranous bones- vertebrae, ribs, sternum, cranial bones.

Question 6

When and where are erythrocytes formed in the foetus?

Answer 6

3rd week= mesoblastic stage- nucleated RBCs form in yolk sac and mesothelial cells of placenta.
6th week= hepatic stage- liver and spleen.
3rd month onwards= myeloid stage

Question 7

Summarise erythropoiesis.

Answer 7

Haematopoietic stem cell commits to myeloid line-> proerythroblast fills with Hb-> erythroblast-> normoblast-> nucleus ejected-> reticulocyte-> erythrocyte

Question 8

What could be indicated by high levels of reticulocytes?

Answer 8

Haemorrhage or erythrocyte destruction

Question 9

Why might EPO be produced by the kidney?

Answer 9

Oxygen conc not affected by exercise and blood pressure. Good measure of hypoxia.

Question 10

What does EPO do?

Answer 10

Increases speed of maturation of erythropoietic stem cells

Question 11

How do erythrocytes make ATP?

Answer 11

Anaerobic glycolysis. Lactate is exported and taken up by liver and cardiac muscle to be converted into glucose.

Question 12

What does ESR show?

Answer 12

Erythrocyte sedimentation rate. Erythrocytes are negatively charged so sink at roughly age (plus 10 for females) over 2. Fibrinogen is produced in inflammation. Neutralises negative charge and increases ESR.

Question 13

How and when are old red blood cells removed from circulation?

Answer 13

After ~120 days. High methaemoglobin makes erythrocytes less deformable so they are trapped in splenic capillaries. Engulfed by macrophages.

Question 14

How is haem broken open?

Answer 14

Haemoxygenase

Question 15

Where does the iron from haem go?

Answer 15

It is collected by transferrin and taken to the liver and then the bone marrow- recycled.

Question 16

How is urobilinogen excreted?

Answer 16

Mostly faeces. 10% returns to liver via portal vein and is recycled into the venous blood and excreted through urine.

Question 17

What is the first step in the metabolism of the porphyrin ring?

Answer 17

It is reduced (from biliverdin) to bilirubin by biliverdin reductase.

Question 17

How is bilirubin transported in the blood?

Answer 17

Binds to albumin in the spleen. Called unconjugated bilirubin

Question 18

How is bilirubin conjugated?

Answer 18

Attached to glucuronic acid in the liver.

Question 19

How is urobilinogen formed?

Answer 19

Conjugated bilirubin passed to small intestine in bile and bacteria convert it to urobilinogen.