Blood: Structure, Function, and Composition – Study Notes for Anatomy & Physiology II

Blood

Overview

Blood is a specialized fluid connective tissue es

sential for the maintenance of homeostasis in the human body. It serves as the primary transport medium for nutrients, gases, hormones, and waste products, and plays a critical role in defense, regulation, and repair mechanisms.

Introduction to the Cardiovascular System

Components of the Cardiovascular and Circulatory Systems

• Cardiovascular System: Composed of blood, the heart, and blood vessels. Responsible for the circulation of blood throughout the body.

• Circulatory System: Includes both the cardiovascular system and the lymphatic system, which together facilitate the movement of fluids and immune cells.

• Blood: A fluid connective tissue with a liquid matrix called plasma and suspended formed elements (cells).

Functions of Blood

Major Roles of Blood in the Body

• Transport: Carries dissolved substances such as gases (O2, CO2), nutrients, hormones, and metabolic wastes.

• Regulation: Maintains pH and ion composition of interstitial fluids, and helps regulate body temperature.

• Fluid Volume Maintenance: Ensures adequate fluid volume in the circulatory system.

• Restriction of Fluid Loss: Initiates clotting mechanisms to prevent blood loss at injury sites.

• Defense: Leukocytes (white blood cells) defend against toxins and pathogens.

• Stabilization of Body Temperature: Distributes heat throughout the body and to the skin for dissipation.

Blood Composition

Main Components

• Plasma: The non-living fluid matrix of blood, making up about 55% of total blood volume. Contains water, proteins, nutrients, hormones, gases, and waste products.

• Formed Elements: The living blood "cells" suspended in plasma, including erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (cell fragments).

Blood Separation and Hematocrit

When a blood sample is centrifuged, it separates into three distinct layers:

Layer	Composition	Percentage of Whole Blood	Density
Plasma	Water, proteins, solutes	~55%	Least dense
Buffy coat	Leukocytes and platelets	<1%	Intermediate density
Erythrocytes	Red blood cells	~45%	Most dense

Hematocrit is the percentage of blood volume occupied by erythrocytes (RBCs). Normal values are:

• Males: 47% ± 5%

• Females: 42% ± 5%

Plasma

Composition and Major Proteins

• Water: Makes up about 90% of plasma volume.

• Dissolved Solutes: Includes nutrients, gases, hormones, waste products, and inorganic ions.

• Plasma Proteins: Most abundant solutes, primarily produced by the liver. Major types include:

  • Albumin (60%): Functions as a substance carrier, blood buffer, and major contributor to plasma osmotic pressure.

  • Globulins (36%): Involved in transport and immune functions.

  • Fibrinogen (4%): Essential for blood clotting.

Plasma

Composition and Major Proteins

• Water: Makes up about 90% of plasma volume.

• Dissolved Solutes: Includes nutrients, gases, hormones, waste products, and inorganic ions.

• Plasma Proteins: Most abundant solutes, primarily produced by the liver. Major types include:

  • Albumin (60%): Functions as a substance carrier, blood buffer, and major contributor to plasma osmotic pressure.

  • Globulins (36%): Involved in transport and immune functions.

  • Fibrinogen (4%): Essential for blood clotting.

Most formed elements have a short lifespan and are produced in the bone marrow.

Additional info:

• Blood is a vital tissue for maintaining homeostasis and supporting cellular metabolism.

• Plasma proteins play key roles in maintaining osmotic balance, immune responses, and clotting mechanisms.