Histology - Blood and Tissue

Question 1

What is tissue?

Answer 1

A group of cells that have a similar structure and act together to perform a specific function

Blood = the most ‘simple’ structural tissue made in the bone marrow

Question 2

What are the functions of blood?

Answer 2

Gas exchange
Carry nutrients from gut to storage sites to tissues
Carry waste from tissues to kidneys / liver
Carry signals through body (hormones, cytokines)
Carry drugs
Carry defensive chemicals and cells to sites of injury
Carry heat
Maintaing osmotic pressure relative to tissues and cells
Mechanism for stopping leaks on injury (blood clotting)

Question 3

What is the composition of blood?

Answer 3

55% plasma and 45% cells
No nucleus
Red blood cells can be revealed through “Weigert” blood films

Question 4

What are the differences between red blood cells and white blood cells?

Answer 4

Red blood cells = erthrocytes
Biconcave shape optimal for oxygen diffusion into and out of the cell
Few are nucleated cells

White blood cells = leukocytes
Involved in defence and destroy pathogens which invade the body cells
Different types of leukocytes exist

Question 5

What are the different types of white blood cells?

Answer 5

Polymorphonuclear leukocytes (PMNs)
Monocytes
Lymphocytes

Question 6

What are the different subtypes of polymorphonuclear cells (PMNs)?

Answer 6

Neutrophils
Basophilic PMNs
Eosinophilic PMNs

Question 7

What do neutrophils do?

Answer 7

Large percentage of leukocytes
Possess a multi-lobed nucleus
Many granules for phagocytosis and the killing of bacteria via production of oxygen radicals
Degradation of lyosomal enzymes

Question 8

What do basophilic PMNs do?

Answer 8

Become mast cells
Early response to injury (innate immune system)
Contribute to allergy

Question 9

What do eosinophilic PMNs do?

Answer 9

Pink granules present on H&E stain
Possess a bi-lobed nucleus
Relatively low numbers
Deal with parasitic infections and some forms of gut immunity

Question 10

What do monocytes do?

Answer 10

Moderately prevelant in blood
Emigrate into tissues to become macrophages (big bacteria eaters)
Play many roles in inflammation, wound healing, and immunity
Control many aspects of host repsonse through many macrophage forms

Question 11

What are the different types of lymphocytes and what do they do?

Answer 11

T cells, B cells, and NK cells
Specific and viral immunity
Offer tumour protection
Second most prevalent leukocyte

Question 12

What are platelets?

Answer 12

Very tiny with no nuclei

Particles of cells important for blood clotting

Question 13

What do platelets do?

Answer 13

Platelets are micro-aggregates in a blood vessel
Platelets get activated when vessels are damaged
Activation induces shape change, degranulation, and aggregation to form

Question 14

What is plasma?

Answer 14

Equivalent to the extracellular matrix
Fluid = non-cellular component
Proteins, salts, glucose, hormones, oxygen/CO2, buffer, and water

Question 15

What are the differences between plasma and serum in terms of blood constituency?

Answer 15

Plasma prevents clotting in collection by separating WBC/platelets from RBC

• Plasma needs anticoagulants for purification, serum does not
• Plasma can be prepared as soon as it is mixed throroughly, but serum poses a 30 minute delay for clot formation (delay can cause fibrin formation)
• Fibrinogen is present in plasma and not in serum
• Platelets and cells (WBCs) can contaminate the liquid fraction in plasma, whereas serum presents a cleaner sample, depleted of cells and cell remnants
• Serum ion composition reflects circulating blood, serum levels possess elevated potassium due to clot retraction
• Plasma is considered less stable (especially during longer storage), whereas serum is more stable

Question 16

What are protease (proteinase) cascades?

Answer 16

Involved in proteolysis - the breakdown of proteins into smaller polypeptides
Inactive proteinase substrates are activated by proteinase activity
Sequential products become enzymes and the initally small signal is amplified
Explosive production of products until final product is produced in vast amounts

Question 17

What are the stages of achieving normal haemostasis?

Answer 17

1. Transient arteriolar vasoconstriction
2. Priamry haemostasis
3. Secondary haemostasis
4. Counter-regulatory mechanisms established

Question 18

What is vasoconstriction?

Answer 18

Narrowing / constriction of blood vessels by small muscles in their walls to slow or block blood flow

Question 19

What is primary haemostasis?

Answer 19

Inital response of the body to vascular injury

1. Platelet adhesion and activation by extracellular matrix
2. Platelet flattening and release of secretory granules
3. Recruitment of additional platelets (aggregation)
4. Forms a temporary primary haemostatic plug

Question 20

What is secondary haemostasis?

Answer 20

Activatin of coagulation cascade results in activation of thrombin
Thrombin converts soluble fibrinogen in the blood into insoluble fibrin in the thrombus
Thrombin recruits further platelets, yielding the permanent secondary haemostatic plug

Question 21

What counter-regulatory mechanisms are established as the final stage of haemostasis?

Answer 21

Restricts inappropriate extension of the haemostatic plug beyond the site of injury by release from the enothelium of:
1. Tissue plasminogen activator
2. Thrombomodulin
This interferes with and ends the coagulation cascade

Question 22

What are the four steps to formin a clot?

Answer 22

1. Reflex vasoconstriction
2. Inital platelet plug
3. Coagulation cascade
4. Final clot