Blood Composition and Function

Blood Composition and Function

Blood is a vital, fluid connective tissue that performs essential roles in transporting substances, defending the body, and maintaining homeostasis. An adult human body typically contains about 5 liters of blood, making up roughly 7%–8% of total body weight ([britannica.com1. How Blood Is Structured

When allowed to stand, whole blood separates into layers due to component density:

Plasma (\~55%): a straw-yellow liquid, primarily water, holding dissolved substances ([ncbi.nlm.nih.gov][2]).

Buffy coat (<1%): sliver-thin layer containing white blood cells (leukocytes) and platelets ([en.wikipedia.org][3]).

Red blood cells (erythrocytes) (\~45%): dense, hemoglobin-rich cells that give blood its color ([ncbi.nlm.nih.gov 2. Plasma: The Liquid Medium (\~55%)

Composition:

Water (90%–92%): Solvent for all plasma solutes ([pharmaacademias.com][4]).

Plasma proteins (6%–8%):

Albumin: Helps maintain osmotic pressure and transports hormones and fatty acids .

Globulins: Include transport proteins and antibodies (immunoglobulins) for immune defense .

Fibrinogen: A clotting protein, converted into fibrin during coagulation .

Electrolytes: Sodium, potassium, calcium, chloride, bicarbonate — crucial for pH balance and nerve function .

Nutrients & metabolic wastes: Glucose, amino acids, fatty acids; plus urea, creatinine, bilirubin — transported to and from tissues ([pharmaacademias.com][4]).

Hormones & gases: Includes O₂, CO₂, and various endocrine messengers .

Functions:

* Transports nourishment, gases, hormones, waste products, and proteins throughout the body .

* Regulates osmotic balance, pH, and body temperature.

* Delivers clotting factors and immune agents to sites of injury or infect 3. Formed Elements: Solid Components (\~45%)

Erythrocytes (Red Blood Cells)

* Biconcave, nucleus-free disks packed with hemoglobin (\~96% of their dry weight) ([en.wikipedia.org][3], [en.wikipedia.org][5]).

* Hemoglobin binds O₂ in the lungs and releases CO₂ at tissues.

* Average lifespan: \~120 days, after which bone marrow replenishes them ([profedu.blood.ca][6]).

* Account for \~40–45% of blood volume, measured as hematocrit .

Leukocytes (White Blood Cells)

* Represent less than 1% of blood volume.

* Types include neutrophils (first-line defenders), lymphocytes (T and B cells), monocytes, eosinophils, and basophils .

* Defend against pathogens and coordinate immune responses.

Platelets (Thrombocytes)

* Cell fragments derived from megakaryocytes.

* 150,000–400,000 per microliter of blood ([kenhub.com][7]).

* Crucial for clotting: they release factors that convert fibrinogen to fibrin, forming a plug at injury sites .4. Key Roles of Blood

* Transport: Carries oxygen, nutrients, hormones, and waste to and from tissues .

* Protection: Immune cells and antibodies in plasma defend against infections; platelets and clotting proteins prevent bleeding ([profedu.blood.ca][6]).

* Regulation: Maintains temperature, pH balance (\~7.35–7.45), and fluid volume .

5. Clinical Insights

* Plasma separation (e.g., through centrifugation or plasmapheresis) is used to collect plasma or specific proteins for transfusions and treatments .

* Donors with type AB blood are universal plasma donors, while type O is ideal for red cell transfusions ([verywellhealth.com][8]).

* Hematocrit, hemoglobin levels, electrolytes, and platelet counts are standard blood tests for diagnosing health conditions.

✅ In summary

Blood is a dynamic tissue of fluid and cellular components:

| Component | % of Blood | Main Roles |

| ----------------------------- | ---------- | ------------------------------------------------- |

| Plasma | \~55% | Transport medium; homeostasis; immunity; clotting |

| Red Blood Cells | \~45% | Oxygen delivery, CO₂ removal |

| White Blood Cells + Platelets | <1% | Immune defense; blood clotting |

It’s essential in transport, protection, and regulation—integral for life and health.

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[1]: https://www.britannica.com/science/blood-biochemistry?utm_source=chatgpt.com "Blood | Definition, Composition, & Functions | Britannica"

[2]: https://www.ncbi.nlm.nih.gov/books/NBK2263/?utm_source=chatgpt.com "Blood and the cells it contains - Blood Groups and Red Cell Antigens - NCBI Bookshelf"

[3]: https://en.wikipedia.org/wiki/Blood?utm_source=chatgpt.com "Blood"

[4]: https://www.pharmaacademias.com/composition-and-function-of-blood/?utm_source=chatgpt.com "Composition and function of blood - Pharmaacademias"

[5]: https://en.wikipedia.org/wiki/Hemoglobin?utm_source=chatgpt.com "Hemoglobin"

[6]: https://profedu.blood.ca/en/transfusion/publications/blood-basics?utm_source=chatgpt.com "Blood: the basics | Professional Education"

[7]: https://www.kenhub.com/en/library/anatomy/the-blood?utm_source=chatgpt.com "Blood: Composition, components and function | Kenhub"

[8]: https://www.verywellhealth.com/what-is-plasma-in-the-body-8690557?utm_source=chatgpt.com "What Is Plasma's Role in the Body?"