Lecture on Hemoglobin and Blood Cells

Maturation of Red Blood Cells

Mature red blood cells (erythrocytes) lose nucleus and organelles.
- Results in inability to produce proteins, carbohydrates, lipids.
- No mitochondria present, hence cannot produce ATP via aerobic respiration.
- Energy production limited to anaerobic processes.

Red blood cells rely on anaerobic respiration due to lack of mitochondria and need to preserve oxygen for distribution to body tissues.
Trillions of cells in the body require oxygen to survive, so red blood cells must efficiently transport oxygen without consuming it.

Red blood cells primarily carry oxygen due to hemoglobin content.
Hemoglobin consists of:
- Four polypeptide chains (two alpha and two beta).
- Each chain contains a heme group bonded to an iron atom, crucial for oxygen binding.
Definitions:
- Polypeptide: Chain of amino acids, non-functional alone.
- Protein: Functional structure formed when polypeptides fold and interact.

Hemoglobin undergoes conformational changes between "taut" (tight) and "relaxed" states.
Binding and release of oxygen correlates with these states:
- Taut state: oxygen release to tissues.
- Relaxed state: oxygen binding occurring in lungs.
Conditions like sickle cell anemia impede this ability, causing hemoglobin to remain in the tight state, thus failing to release oxygen effectively.

Carbon monoxide binds tightly to hemoglobin, preventing oxygen from attaching, which can be lethal.
Red blood cells transport:
- 280 million hemoglobin molecules per cell.
- Approximately 25 trillion red blood cells in circulation at any time.
- 2 million red blood cells produced and cleared every second, a minute fraction relative to the total count.
Fetal versus adult hemoglobin differences:
- Fetal hemoglobin has a higher affinity for oxygen compared to adult hemoglobin due to structural differences.

Carbon dioxide is produced during ATP synthesis (cellular respiration) and influences blood pH.
Carbonic Acid Equation: CO2 + H2O \rightleftharpoons H2CO3 \rightleftharpoons H^+ + HCO_3^-
- Enzyme: Carbonic Anhydrase; catalyzes the interconversion of carbon dioxide and carbonic acid.
Low CO2 levels can lead to metabolic alkalosis, while high CO2 levels lead to respiratory acidosis.

pH levels assist in oxygen delivery via hemoglobin:
- Increased hydrogen ions (low pH) enhance oxygen release.
- Thus, metabolically active tissues with high CO2 (and H+) levels receive more oxygen.

Cooperative Binding: As one oxygen binds to hemoglobin, it enhances the binding of subsequent oxygen molecules.
Hemoglobin functions efficiently due to shifting affinities regulated by:
- Concentration of hydrogen ions (pH levels).
- Body temperature.
Conditions dictating shifts in hemoglobin affinity:
- Right shift: High temperature, high CO2, low pH (enhanced oxygen unloading).
- Left shift: Low temperature, low CO2, high pH (enhanced oxygen loading).

Hormone Erythropoietin (EPO) controls red blood cell production in response to hypoxia:
- Stimulates stem cells in bone marrow to produce erythrocytes.
Reticulocytes: Immature red blood cells that enter circulation before fully maturing.

Upon aging, red blood cells undergo hemolysis.
Breakdown results in:
- Globin portion converted into amino acids for recycling.
- Heme group converted into bilirubin, which is metabolized and excreted via bile or urine:
- Heme → Biliverdin (green) → Bilirubin (yellow/orange).

Two categories of leukocytes:
- Granulocytes: Contain granules for inflammatory response (e.g., neutrophils, eosinophils).
- Neutrophils: First responders for infections.
- Eosinophils: Target parasites.
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