Comprehensive Study Notes: Blood (Anatomy & Physiology)

Blood: Internal Transport System

Overview

Blood is the life-sustaining transport vehicle of the cardiovascular system, responsible for delivering nutrients, removing wastes, and supporting homeostasis.

Functions of Blood

Transport

• Delivering O2 and nutrients to body cells

• Transporting metabolic wastes to lungs and kidneys for elimination

• Transporting hormones from endocrine organs to target organs

Regulation

• Maintaining body temperature by absorbing and distributing heat

• Maintaining normal pH using buffers, alkaline reserve of bicarbonate ions

• Maintaining adequate fluid volume in circulatory system

Protection

• Preventing blood loss (platelets and plasma proteins initiate clot formation)

• Preventing infection (antibodies, complement proteins, and WBCs)

Composition of Blood

Main Components

• Plasma: Non-living fluid matrix

• Formed elements: Living blood cells (erythrocytes, leukocytes, platelets)

Component	Description
Plasma	Fluid portion, contains water, proteins, nutrients, hormones
Erythrocytes (RBCs)	Red blood cells, transport oxygen and carbon dioxide
Leukocytes (WBCs)	White blood cells, immune defense
Platelets	Cell fragments, involved in clotting

Blood Separation

• Spun tube of blood yields three layers:

  • Erythrocytes on bottom (~45% of whole blood)

  • Buffy coat (WBCs and platelets, <1%)

  • Plasma on top (~55%)

Physical Characteristics and Volume

• Blood is sticky, opaque fluid with metallic taste

• Color varies with O2 content (scarlet red = high O2, dark red = low O2)

• pH: 7.35–7.45

• Volume: 5–6 L (males), 4–5 L (females)

Blood Plasma

Composition

• Straw-colored, sticky fluid

• ~90% water

• Contains over 100 dissolved solutes:

  • Proteins (albumin, globulins, fibrinogen)

  • Nutrients, gases, hormones, wastes, electrolytes

Plasma Protein	Function
Albumin	Osmotic pressure, carrier protein
Globulins	Immune response, transport
Fibrinogen	Blood clotting

Formed Elements

• Only WBCs are complete cells; RBCs have no nuclei or organelles

• Platelets are cell fragments

• Most formed elements survive in bloodstream for only a few days

Erythrocytes (Red Blood Cells)

Structural Characteristics

• Biconcave discs, anucleate, essentially no organelles

• Filled with hemoglobin (Hb) for gas transport

• RBC diameter larger than some capillaries

• Contain plasma membrane proteins (spectrin, others)

Function

• Dedicated to respiratory gas transport

• Hemoglobin binds reversibly with oxygen

Hemoglobin Structure: Each molecule consists of four polypeptide chains (globin) and four heme groups. Each heme group contains an iron atom that binds one O2 molecule.

• Each RBC contains ~250 million hemoglobin molecules

• O2 loading in lungs produces oxyhemoglobin (ruby red)

• O2 unloading in tissues produces deoxyhemoglobin (dark red)

• CO2 loading in tissues produces carbaminohemoglobin

Production of Erythrocytes (Erythropoiesis)

• Occurs in red bone marrow

• Stages:

  • Hematopoietic stem cell → proerythroblast → erythroblast → reticulocyte → erythrocyte

Equation: $\text{Hematopoietic stem cell} \rightarrow \text{Proerythroblast} \rightarrow \text{Erythroblast} \rightarrow \text{Reticulocyte} \rightarrow \text{Erythrocyte}$

Regulation of Erythropoiesis

• Too few RBCs → tissue hypoxia

• Too many RBCs → increased blood viscosity

• Balance depends on hormonal controls and dietary requirements

Hormonal Control: Erythropoietin (EPO) stimulates formation of RBCs, released by kidneys in response to hypoxia.

Fate and Destruction of Erythrocytes

• Life span: ~120 days

• Old RBCs become fragile, Hb degenerates

• Macrophages engulf dying RBCs in spleen

• Iron salvaged, heme degraded to bilirubin

Leukocytes (White Blood Cells)

General Structure and Function

• Complete cells with nuclei and organelles

• Make up <1% of total blood volume

• Function in defense against disease

• Can leave capillaries via diapedesis

Classification

Type	Subtypes	Main Function
Granulocytes	Neutrophils, Eosinophils, Basophils	Phagocytosis, inflammation, allergy
Agranulocytes	Lymphocytes, Monocytes	Immune response, phagocytosis

Granulocytes

• Neutrophils: Most numerous, phagocytic, "bacteria slayers"

• Eosinophils: Digest parasitic worms, modulate immune response

• Basophils: Release histamine, attract WBCs to inflamed sites

Agranulocytes

• Lymphocytes: T cells (attack virus-infected cells, tumor cells), B cells (produce antibodies)

• Monocytes: Differentiate into macrophages, phagocytize pathogens

Platelets

Structure and Function

• Fragments of megakaryocytes

• Essential for blood clotting (hemostasis)

• Form temporary platelet plug that helps seal breaks in blood vessels

Hemostasis

Steps in Hemostasis

1. Vascular Spasm: Vasoconstriction reduces blood flow

2. Platelet Plug Formation: Platelets stick to exposed collagen fibers

3. Coagulation (Blood Clotting): Reinforces platelet plug with fibrin threads

Equation: $\text{Prothrombin} \xrightarrow{\text{Prothrombin activator}} \text{Thrombin} \xrightarrow{\text{Thrombin}} \text{Fibrinogen} \rightarrow \text{Fibrin}$

Blood Transfusions and Blood Typing

Blood Groups

• RBC membranes contain antigens (agglutinogens)

• ABO and Rh blood groups are clinically important

Blood Type	Antigens Present	Antibodies Present	Can Receive From
A	A	Anti-B	A, O
B	B	Anti-A	B, O
AB	A and B	None	A, B, AB, O
O	None	Anti-A, Anti-B	O

• Type O: Universal donor

• Type AB: Universal recipient

Transfusion Reactions

• Occur if mismatched blood is transfused

• Recipient's antibodies attack donor RBCs

• Can cause renal failure, shock, death

Blood Typing

• Blood is mixed with antibodies against common antigens

• Clumping indicates presence of antigen

• Cross-matching: Mix recipient's serum with donor RBCs and vice versa

Additional info: These notes expand on the original bullet points with definitions, examples, and tables for clarity and completeness, suitable for college-level Anatomy & Physiology study.