Blood

BLOOD

• Essence of life
• Uncontrolled loss can  lead to death
• Has  magical qualities
• Thought to define our character and emotions
• Blue blood ⎯  people with noble bloodline
• “bad” blood ⎯ criminals
• Anger causes blood to  “boil”
• Fear makes it “curdle”
• Performs many functions essential  to  life and reveal much about our health
• Blood  maintains homeostasis in several ways
• 8% of total body weight

FUNCTIONS

1. Transport of gases, nutrients and waste products

• Oxygen enters the blood in the lungs and is carried to cells

(Oxygen → blood in lungs → cells)

• CO2 , produced by cells is carried in the blood to lungs, from which it is expelled  

(CO2 in cells→blood→lungs)

• Transports ingested nutrients, ions, and water from the digestive tract to cells
• Transports waste products of cells to the kidneys for elimination

1. Transport of processed molecules

• Many substances are produced in one part of the body and transported in the blood to another part,  where they are modified
• Vitamin D

• Produced in the skin
• Transported by blood → liver→  kidneys (processing into active vit. D)
• Blood transports active vit. D to small intestine (promotes uptake of calcium)

• Lactate

• Produced by skeletal muscles (anaerobic respiration)
• Blood carries lactate to the liver (lactate→glucose)

1. Transport of regulatory molecules

• Blood carries many of the hormones and enzymes
• hormones and enzymes

• regulate body processes from one part of the body to another

1. Regulation of pH and osmosis

• Buffers  ⎯ help maintain blood’s pH within its normal limits of 7.35-7.45
• Osmotic composition ⎯ critical for maintaining normal fluid and ion balance

1. Maintenance of body temperature

• Warm blood

• Transported from the interior of the body to the surface (heat is released from the blood)

• One of the mechanisms that help regulate body temperature

1. Protection against foreign substances

• Certain cells and chemicals in the blood constitute an important part of the immune system

• Protects against foreign substances such as microorganisms and toxins

1.  Clot formation

• When blood vessels are damaged, blood clotting protects against excessive blood loss
• When tissues are damaged, the blood clot that forms is also the first step in tissue repair and restoration of normal function

COMPOSITION OF BLOOD

• PLASMA

• Liquid matrix containing cells and cell fragments
• Slightly more than half  of total blood volume

• FORMED ELEMENTS

• Cell  and cell fragments
• Slightly less  than half of total  blood volume

• Total blood volume: 5-6 L (M);                       4-5 L (F)

PLASMA

• Pale yellow fluid that consists of about 91% water, 7% proteins and 2% other components (ions, nutrients, gases, waste products and regulatory substances)
• Contains dissolved proteins
• Include albumin, globulins, and fibrinogen

Albumin

• 58% of plasma proteins
• Makes an important contribution in the osmotic pressure of blood

Globulins

• 38% of plasma proteins
• E.g.  antibodies and complement are part of the immune system
• Other globulins and albumin function as  transport molecules because they bind to hormones and carry them in the blood throughout the body
• Some are Clotting factors  ⎯ necessary for formation of  blood clots

Fibrinogen

• Clotting factor (4% of plasma proteins)
• Activation of clotting factors ⎯ convert fibrinogen to fibrils (threadlike proteins that form blood clots

       Serum

• Plasma without clotting factors

FORMED ELEMENTS

• 95% erythrocytes/red blood cells
• 5%  leukocytes/white blood cells and platelets/thromobocytes(cell fragments)
• RBC 700x more numerous than WBC
• RBC 17x more numerous than platelets

PRODUCTION OF FORMED ELEMENTS

• Hematopoiesis

⎯ Blood cell production

⎯ In the fetus, occurs in several tissues:

• Liver
• Thymus
• Spleen
• Lymph nodes
• Red bone marrow

        ⎯ After birth hematopoiesis is confined primarily to red bone marrow with some WBC produced in lymphatic tissues

• Stem cells/hemocytoblasts

• Single population of cells where all  formed elements are derived
• Differentiate to give rise to different cell lines, each of which ends with the formation of a particular type of formed element

• Growth factors

• determine the types of formed elements derived from stem cells
• determine number of formed elements produced