Human Processes 1 Exam Revision

Blood, Skeletal, Muscular, Nervous, Endocrine

When and how are erythrocytes produced?

When low oxygen levels are detected, the kidneys release erythropoietin which is responsible for synthesising erythrocytes. Iron (from stored ferritin or dietary intake) is transported in the blood by transferrin and released to cells in the bone marrow. In addition to iron, folic acid and vitamin B12 are required for erythropoiesis. Approximately 200 billion erythrocytes are produced daily.

What happens as erythrocytes age? How are they broken down?

They last around 120 days. As they age, they lose structural integrity. Old cells undergo phagocytosis by macrophages in the spleen and liver. As they are broken down, haemoglobin is released and metabolised to bilirubin. The bilirubin enters the blood stream and travels to the liver where it’s further metabolised and the by-products are secreted in bile and the small intestine to be eliminated in the faeces.

What is haemostasis and its 3 phases?

The process of blood clotting in response to damaged blood vessels. Vascular (spasm), platelet (plug) and coagulation phases.

what is meant by a “committed cell” ?

path of specialisation is determined and cannot regress to its precursor (stem cell)

why might those with kidney disease suffer from anaemia?

when the kidney cells fail, they do not produce enough erythropoietin to sustain erythropoiesis in bone marrow

Explain the process of haemostasis (3 phases)

Vascular phase: trauma to the blood vessel stimulates nociceptors which trigger the smooth muscle to contract, causing vasoconstriction of the injured blood vessel. Endothelial cells become sticky. This allows time for clotting to occur, lasting 30 seconds.

Platelet phase: due to injury, collagen fibres are exposed. Platelets arrive at the site and attach to the sticky basal lamina and collagen fibres. Platelets release chemicals that make them sticky to other platelets (platelet aggregation), forming a plug.

Coagulation phase: blood becomes a gel. prothrombin is converted to thrombin which converts soluble fibrinogen to insoluble fibrin to form a mesh that traps erythrocytes and platelets to form a clot. Takes 30 seconds. Clot retraction is when platelets contract within fibrin mesh, reducing size of clot (30-60 min).

List the functions of blood

distribution (O2, waste, hormones)

regulation (pH, temperature, fluid/water)

protection (clotting, immunity)

Describe the composition and physical characteristics of whole blood

plasma (55%) and formed elements (1% Buffy coat of leukocytes and platelets; 45% erythrocytes)

Discuss the composition and functions of plasma

- Plasma proteins; Albumin, Globulins - α, β transport proteins; γ antibodies; Clotting proteins - Fibrinogen; Prothrombin

• Non-proteins - Urea, Lactic Acid, Creatinine

• Nutrients - Carbs, amino acids, fatty acids, Glycerol, Vitamins

• Electrolytes - Na+, K+, Ca2+, Mg2+, Cl-, HCO3-

• Gases - Respiratory O2 and CO2

• Other - Enzymes; Antigens; Antibodies; Hormones

Describe the structure and function of erythrocytes. What’s the benefit of its shape?

biconcave, anucleate, flattened, rich in haemoglobin. To transport gases (O2 and CO2).

→ Increased surface to volume ratio

→ All areas of cytoplasm close to membrane

→ Ability to squeeze through small vessels

Describe the composition of haemoglobin

Made up of 4 polypeptide chains (2 alpha 2 beta) and 4 heme groups containing iron. Can carry up to 4 oxygen molecules

List the classes, structural characteristics, and functions of leukocytes

(3) granulocyte (-phil), (2) agranulocyte (-cyte).

Defence against disease

Granulocytes (Bound granules)

• Neutrophils - Phagocytise bacteria, multilobed nucleus

• Eosinophils - Kill parasitic worms, bilobed nucleus, red granules

• Basophils - Mediators of inflammation (heparin, histamine), bilobed nucleus

Agranulocytes (Lack granules)

• Lymphocytes - Immune response via attack or antibodies

• Monocytes - Migratory phagocyte, kidney shaped nucleus

How are leukocytes are produced

Occurring in the bone marrow, they begin as haemocytoblast stem cells which divide and turn into myeloid or lymphoid stem cells. Then they divide and turn into one of 3 committed cells: myeloblast, monoblast or lymphoblast then follow their developmental pathway and mature in the bone marrow, with the exception of T cells that mature in the thymus (lymphocytes)

Describe the structure and function of platelets (thrombocytes)

2-4 um in animated, rough discs.

mature platelets are:

• bound by plasma membrane

• anucleate

• age rapidly (degenerate after 10 days)

• rich in serotonin granules to aid clotting process

Describe how platelets are produced

Haemeocytoblast → megakaryoblast → promegakaryoblast → megakarycyte → platelets

What is the body’s natural anticoagulant?

heparin (produced in the granules of mast cells and basophils)

Discuss the difference between monocytes and lymphocytes in their differentiation

They both start from a haemocytoblasts but the haemocytoblast differentiates into either a myeloid stem cell or lymphoid stem cell.

myeloid = monocyte (much larger)

lymphoid = lymphocyte (travel between blood and lymphatic organs)

Oxygen and carbon dioxide are poorly soluble in plasma so they require erythrocytes for their transport in blood. Describe how erythrocytes transport these gases.

Erythrocytes contain two proteins necessary for the transport of oxygen and carbon dioxide: hemoglobin and carbonic anhydrase.

Hemoglobin is a protein that contains four subunits, each of which has a heme group that can bind oxygen reversibly. Thus, hemoglobin can transport up to four oxygen molecules. Hemoglobin can also transport carbon dioxide, but the carbon dioxide binds reversibly to amino acids within the polypeptide chains, not to the heme group.

Carbonic anhydrase is an enzyme that catalyzes the reversible reaction converting carbon dioxide and water to carbonic acid. The carbonic acid can then dissociate into a hydrogen ion and bicarbonate ion. Most of the carbon dioxide transported in blood is transported as bicarbonate ion.

Describe the general format/prefix/suffix for cell differentiation

-blast (initial stem cell) → -blast (committed cell; first half of stem cell + -blast) → pro-(previous cell name)-cyte (drop -blast) → drop pro- → full cell name

e.g. haemocytoblast → myeloid stem cell → myeloblast → promyelocyte → myelocyte → neutrophil/eosinophil/basophil

e.g. hemocytoblast → myeloid stem cells → monoblast → promonocyte → monocyte

List the functions of haemoglobin

→ Hb loads O2 in the lungs and transports it to

the tissues where it is offloaded for cellular use

→ Hb loads CO2 (waste) and transports it

to the lungs where it is offloaded and exhaled to the

atmosphere (maintains acid-base homeostasis)

→ Hb has a role in vasodilation through its release

of small amounts of nitric oxide

Explain how blood clots are removed from thebody

Plasminogen is converted to plasmin, which is fibrinolytic (dissolves clots)