Circulatory System – Blood (Part 1 of 4)

The Circulatory System is made up of 4 parts:
1. Blood
2. Blood Vessels
3. Heart
4. Lymphatic System

Blood is the only liquid connective tissue in the body.

Human adults have 4.7 liters of blood in their bodies.

Blood has roles in transport, regulation and protection.
– It transports oxygen, carbon dioxide, nutrients, hormones, heat and waste.
– It is involved in the regulation of body temperature, PH and the water content of cells.
– The body is protected from blood loss through clotting and against disease by PHAGOCYTIC WHITE BLOOD CELLS and ANTIBODIES.

– Plasma makes up 55% of the blood.
– It is a clear; straw-colored liquid, which is mostly water.
– It is the bloods SOLVENT (able to dissolve substances).
– It transports nutrients, waste products of metabolism, respiratory gases and hormones.
– There are 3 main PLASMA PROTEINS:
– Is the smallest and most numerous protein.
– It helps recover water that has been lost.
– It transports some of the steroid hormones.
2. IMMUNOGOBULIN (antibodies)
– Aids the immune system by attacking bacteria and viruses.
– Other globulins help in the transport of iron, lipids and fat-soluble vitamins.
– It plays an essential role in the clotting of blood, by providing the necessary protein network.
– Various ions act as solutes in plasma; they play key roles in osmotic balance, PH buffering and the regulation of membrane permeability.

Blood cells make up about 45% of the blood.

There are 3 main types of blood cells:
– They transport oxygen to all cells.
– The oxygen-carrying protein HEMOGLOBIN is the pigment that gives blood its red color.
– They are the simplest cells in the body; mature red blood cells lack a nucleus, ribosomes and mitochondria.
– They are also the most numerous cells in the body; 5 million/ml of blood.
– About 2.5 million are made every second in the red bond marrow.
– Mature cells are flattened and disc-shaped with a central depression.
– They are non-reproducing sacks of oxygen binding hemoglobin.
– The hormone, ERYTHROPOIETIN, triggers transformation of skin cells in the marrow to produce red blood cells.
– After circulating for 3 to 4 months in the blood, red blood cells are engulfed by liver and spleen SCAVENGER CELLS.

– They contain a nucleus.
– Most live only a few days, although some, particularly LYMPHOCYTES can live for several months or longer.
– During infections white blood cells may only live for a few hours.
– The shape of their nuclei and the staining properties of their granules distinguish white blood cells from each other.
– The number and type of white blood cells can indicate a person’s health. Most infections stimulate an increase in circulating white blood cells.
– There are 5 classes of white blood cells:
– Are active in PHAGOCYTOSIS (the engulfing of particles by phagocytes); ingesting bacteria and cellular debris.
– Certain chemicals released by bacteria and inflamed tissue attract the white blood cells to the site.
– After engulfing the bacteria, neutrophils lysozymes are released that destroy the bacteria.
– Strong oxidants are then released, like peroxide and proteins called DEFENSINS that have antibiotic activity.
– Monocytes arrive after the neutrophils and enlarge to become macrophages, which clean up cellular debris and bacteria after an infection.
– They enter tissue fluid from the capillaries and release enzymes to combat allergic reactions.
– Intensify the inflammatory response when they enter the tissue from the capillaries.
– They are the major combatants in the immune response.
– They are the B-CELLS, T-CELLS and the natural killer cells.
– These cells are active in fighting infections caused by viruses, bacteria and fungi.
– They are also responsible for transfusion reactions, allergies and the rejection of transplanted organs.

– They are the small cell-like fragments that come from special white blood cells, called MEGAKARYOCYTES.
– They have no nucleus and live for about 5 to 9 days.
– Aged and dead platelets are removed by macrophages in the liver and spleen.
– Platelets release chemicals in blood clotting.

Humans have highly individualized blood that is credited to proteins and other genetically determined factors located on the surface of red blood cells and the plasma bathing the red blood cells.

The main types of blood are A, B, AB, and O.

Transfusions of blood are possible only when the blood types of the donor and recipient are compatible.

If the blood types are not compatible, proteins in the plasma will recognize foreign antigens and respond by causing the cells to AGGLUTINATE (clump) which will block the small vessels.

Type AB is considered the UNIVERSAL RECIEPENT (this person can receive blood from any type in the ABO blood group).

Type O is considered the UNIVERSAL DONOR (this type of blood can be given to any blood type in the ABO blood group).


Types of Tissue

Tissues are groups of cells with a common structure and function.

They work together to perform a particular task.

– Organs are a collection of 2 or more of the basic body tissue types.
– Multiple tissues adapt as a group to perform specific functions and form structures called ORGANS.

– A collection of 2 or more of the organs that together perform some complex body function.
– The human body is a cooperative of organ systems that are interdependent upon one another, either chemically or physically.

There are 4 main CATEGORIES OF TISSUE:
1.  EPITHELIAL TISSUE (covers and lines the body)
2.  CONNECTIVE TISSUE (binds and supports other tissue)
3.  MUSCLE TISSUE (is involved with movement)
4.  NERVOUS TISSUE (forms a communication network)


Epithelial tissue is covering and lining tissue, it covers body surfaces in general and lines cavities within the body.

It has little or no intercellular material between its cells.

The free surface of this tissue is exposed either to air or fluid.

The base of the cell is attached to a BASEMENT MEMBRANE (a dense layer of extra cellular material).

The cells are closely joined and may act as a barrier against injury, microbial invasion or fluid loss.

These cells may be specialized for absorption or secretion of chemical solutions.

Epithelial tissue is categorized by the number of LAYERS and the SHAPES of the free surface of the cells.

LAYERS can be:
1. SIMPLE: one layer of cells.
2. STRATIFIED: multiple tiers of cells.
3. PSEUDOSTRATIFIED: one layer that appears multiple because the layers vary in length.

SHAPES include:
SIMPLE SQUAMOUS epithelial tissue is thin and leaky.
– These cells aid in the exchange of material by diffusion.
– They line blood vessels and air sacs in the lungs.
STRATIFIED SQUAMOUS tissue regenerates rapidly near the basement membrane.
– New cell are pushed to the free surface as replacements for the cells that are continually sloughed off.
– Stratified Squamous tissue is located on surfaces that are subject to abrasion, like the outer skin.

– They are like a cytoplasm filled water balloon.
– They are found where secretion or active absorption of substances is an important function, like the intestines, where they secrete digestive juices or absorb nutrients.
STRATIFIED COLUMNAR epithelial tissue line the inner surface of the urinary bladder.
PSEUDOSTRATIFIED CILIATED COLUMNAR epithelial tissue line the nasal passage.

SIMPLE CUBOIDAL epithelial tissue is specializes for secretion.
– They can be found in the kidney tubules, the thyroid gland and the salivary glands.


Connective tissue binds and supports other tissue.

It has a sparse cell population scattered throughout an extensive extracellular matrix;  it has a lot of intercellular material between its cells.

The matrix contains long, slender rods and connective tissue fiber in a substance similar to soft-set gelatin.

This fiber helps connective tissue to do its job, to directly or indirectly connect body parts together.

3 types of FIBERS make up the various types of connective tissue:
– They are bundles of fibers containing 3 collagen fibers each.
– These fibers are strong and resist stretching.
– The parallel lines on the palm of your hand are collagen bundles.

– They are long threads of the protein, elastin.
– If stretched, this tissue can return to its original shape.

– They are branched and tightly woven.
– They join connective tissue to neighboring tissue.

There are 6 CATEGORIES of connective tissue:
– Contains all 3 fiber types; collagen, elastin and reticular.
– Holds organs in place and attaches the epithelium to underlying tissue.
– Contains 2 types of cells:
1. FIBROBLASTS: secrete proteins of extracellular fibers, like collagen.
2. MACROPHAGES: act as the “attack dogs” of the body’s immune system.

– It is a loose connective tissue that is specialized to store fat.
– The fat is stored in adipose cells distributed throughout its matrix.
– Each adipose cell stores one fat droplet, which can vary in size.
– The stored fat insulates the body and is used for fuel when needed.

– Large numbers of collagenous fibers in parallel bundles makes this tissue very dense.
– This density gives it the great strength needed for tendons (to attach muscle to the bone) and ligaments (to attach bone together at joints).

– It is the strong and flexible connective tissue found in the skeleton of all vertebrate embryos.
– Most vertebrates convert the cartilage to bone, but they retain cartilage in the nose, ears and trachea.
– It is composed of collagenous fibers embedded in chondroitin sulfate (a protein-carbohydrate).

– Bone is hard, but not brittle or completely solid.
– It is mineralized connective tissue.
– OSTEOBLASTS (bone-forming cells) deposit a matrix of collagen and calcium phosphate that hardens into the mineral hydroxyapatite.

– Blood is the only liquid connective tissue in the body.
-It is a liquid extracellular matrix of plasma containing water, salt and proteins.
– Blood contains RED BLOOD CELLS (that transport oxygen), WHITE BLOOD CELLS (for the immune system) and PLATELETS (which are cell fragments that help in the clotting of blood).
– Blood cells are made in the red marrow of long bones.
– Blood vessels and nerve cells occupy slender canals in the bone tissue call HAVERSAIN CANALS.


There is more muscle tissue available in the human body than any other type of tissue.

It consist of long, slender muscle fibers, that contract or shorten to create body movement.

There are 3 types of muscle:
– It is multinucleated and is usually attached to bones by tendons.
– Contractions are voluntary.
– This muscle appears striated under the microscope.

– It is found in the walls of the internal organs and arteries.
– The spindle-shaped, uninucleated cells contract involuntarily.

– It is located only in the wall of the heart.
– The cells are striated, uninucleated, and are joined by intercalated disks.
– Contractions are involuntary.

– It is the major tissue for communication and control within the body’s internal environment.
– It is designed to sense stimuli.
– It communicates by means of NEURONS (nerve cells).
– The neuron conducts impulses or bioelectric signals.
– It transmits signals from one part of the organism to another.