Lecture 25 - Blood Contents and Blood Production

Question 1

3 functions of blood

Answer 1

1. Transport - nutrients, dissolved gases, hormones, wastes
2. Defence - against fluid loss, pathogens, toxins
3. Regulation (homeostasis) - pH, ions, water, temperature

Question 2

What is blood and what does it consist of?

Answer 2

It is a specialized connective tissue that contains:

• Cells: RBCs, WBCs, and platelets
• Extracellular matrix: plasma
• Extracellular proteins: plasma proteins

Question 3

What does plasma consist of?

Answer 3

Consists of water, dissolved substances, and proteins (ex. protein clotting factors). It is more than half of the volume of blood and it is an extracellular fluid

Question 4

What are “formed elements”

Answer 4

They refer to cells or cell fragments found in blood that help carry out its various function

Question 5

What are the main components of a complete blood count (CBC)?

Answer 5

1. Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Volume (MCV) measures of RBC maturity and size
2. Cell counts measures which formed elements are present
3. Hematocrit - packed red blood cell volume (% of RBCs in whole blood)

Question 6

What are 2 notable features of RBCs and how are they useful?

Answer 6

1. Biconcave shape
2. Lack of nucleus, mitochondria, and other organelles

Their shape allows them to be flexible and stackable for flow. Their lack of organelles allows more space for storage

Question 7

What does a hemoglobin molecule consist of?

Answer 7

4 globin chains, 4 heme units, and 4 Fe2+ ions

Question 8

Function of hemoglobin (Hb)

Answer 8

Mature RBCs contain Hb, which is responsible for O2 transport

Each Heme+Fe can carry a molecule of O2

Question 9

What is hemostasis and give one example

Answer 9

It is all the physiological processes that limit or halt blood loss through damages blood vessels

Ex. Clotting/coagulation

Question 10

How do WBCs help stop blood loss?

Answer 10

They contain specialized cell fragments (platelets) and proteins that give it the ability to form clots

Question 11

What is a serum?

Answer 11

It is the fluid that is left after blood clotting. It contains water, solutes, and blood proteins that are not related to clot formation (ex. antibodies)

Question 12

What are the 3 phases of hemostasis?

Answer 12

1. Vascular phase
2. Platelet phase
3. Coagulation phase

Question 13

Describe the vascular phase of hemostasis (primary hemostasis)

Answer 13

Fastest phase; rapid changes to cells in the blood vessel wall. Contraction occurs (vascular spasm), then increased endothelial stickiness

Question 14

Describe the platelet phase of hemostasis (primary hemostasis)

Answer 14

Platelets attach to the sticky endothelial cells and basement membrane and become activated. The activated platelets change shape and release chemicals that attract other platelets to stick to each other, plugging the broken vessel

This is a POSITIVE FEEDBACK LOOP - activated platelets and chemicals attract MORE platelets

Question 15

Describe the coagulation phase of hemostasis (secondary hemostasis)

Answer 15

A fibrin mesh network forms around platelets, producing a clot by binding aggregated platelets and blood cells from strands of insoluble fibrin. It involves a cascade of enzymes that catalyze the formation of fibrin from soluble fibrinogen

Question 16

Describe the enzymes involved in the coagulation phase

Answer 16

Factor X -> Prothrombin activator -> Prothrombin -> Thrombin -> Fibrinogen -> Fibrin

Question 17

Where are blood cells and platelets produced?

Answer 17

Produced by red bone marrow found in the space around spongy bone. Red marrow contains blood-forming stem cells

Question 18

What are the 2 main multipotent lineages that come from hematopoietic stem cells?

Answer 18

Lymphoid and myeloid

Question 19

What do megakaryocytes do?

Answer 19

They produce platelets. Megakaryocytes survive for 9-12 days in the bloodstream

Question 20

Describe the structure of platelets

Answer 20

They lack organelles and are constantly recycled by phagocytic cells (primarily in the spleen) and replaced

Question 21

What do Myeloid cells do?

Answer 21

They produce RBCs via a series of distinct stages. Their production is stimulated by erythropoietin (EPO)

Question 22

Where is the hormone, erythropoietin (EPO), secreted and what is its function?

Answer 22

Secreted by the kidneys in response to hypoxia. It stimulates RBC progenitors to divide and differentiate, enhancing RBC production

Question 23

What are the stages of the production of RBC?

Answer 23

Myeloid stem cells -> erythroblasts at day 2 -> reticulocyte after day 4 -> red blood cell (erythrocyte)

RBC maturation is completed after reticulocytes enter the bloodstream

Question 24

Typical lifespan of an RBC

Answer 24

~4 months. RBC contents are recycled into new RBCs, and/or excreted