RBC Membrane

Question 1

RBCs are biconcave,_____ in diameter, with a volume range of ______ and a mean volume of_____

Answer 1

7 to 8 MM

80 to 100 fL

90 fL

Question 2

RBC

Their average surface area is______’, which is a_____ excess of surface area compared with a sphere of______ in diameter.’ This excess surface area-to-volume ratio enables RBCs to stretch undamaged up to 2.5 times their resting diameter as they pass through narrow capillaries and through splenic pores 2 um in diameter. This property is called RBC______.

Answer 2

140 um

40%

7 to 8 um

deformability

Question 3

The RBC______ is 100 times more elastic than a comparable latex membrane, yet it has tensile (lateral) strength greater than that of steel.’

The deformable RBC membrane provides the broad surface area and close tissue contact necessary to support the delivery of O2 from the lungs to body tissues and to transport CO2 from body tissues to the lungs.

Answer 3

plasma membrane

Question 4

RBC deformability depends not only on RBC geometry but also on relative cytoplasmic (hemoglobin)______.

The normal mean cell hemoglobin concentration (MCHC) ranges from________, and as MCHC rises, internal viscosity rises.

Answer 4

viscosity

32% to 36%

Question 5

MCHCs greater than_____% compromise deformability and shorten the RBC life span because viscous cells become damaged as they stretch to pass through narrow capillaries or splenic pores.

As RBCs age, they lose membrane surface area, while retaining hemoglobin.

As the MCHC rises, the RBC, unable to pass through the splenic pores, is phagocytized and destroyed by______

Answer 5

36

splenic macrophages

Question 6

Besides geometry and viscosity, membrane ________also contributes to deformability.

The RBC membrane consists of approximately____% carbohydrates, _____% proteins, and____% lipids.

The lipid portion, equal parts of cholesterol and phospholipids, forms a bilayer universal to all animal cells

Answer 6

elasticity (pliancy)

8

52

40

Question 7

________form an impenetrable fluid barrier as their______ polar head groups are arrayed on the membrane’s surfaces, oriented toward both the aqueous plasma and the cytoplasm, respectively, as depicted in the fluid mosaic membrane model (FMMM).

Their______ nonpolar acyl tails arrange themselves to form a central layer sequestered (hidden) from the aqueous plasma and cytoplasm.

Answer 7

Phospholipids

hydrophilic

hydrophobic

Question 8

The_______ provide a dynamic fluidity to the membrane; if a portion of the lipid bilayer is lost, the membrane can_____ to retain the cytoplasmic contents.

The membrane also maintains extreme differences in osmotic pressure, cation concentrations, and gas concentrations between external plasma and the cytoplasm through the dynamic interaction of the lipids and proteins.

Answer 8

phospholipids

self-seal

Question 9

_________, esterified and largely hydrophobic, resides parallel to the acyl tails of the phospholipids.

It is equally distributed between the outer and inner layers of the phospholipid bilayer, and evenly dispersed within each layer, approximately____ cholesterol molecule per phospholipid molecule.

Answer 9

Cholesterol

one

Question 10

The ______ group of cholesterol, the only hydrophilic domain of the mol-ecule, anchors within the phospholipid polar heads, while the rest of the molecule becomes intercalated among and parallel to the acyl tails.

Cholesterol confers tensile strength to the lipid bilayer.

As______ concentration rises, the membrane gains strength but loses elasticity.

Answer 10

B-hydroxyl

cholesterol

Question 11

The ratio of_____ to _____ remains relatively constant to maintain the balance of deformability or elasticity and strength.

Membrane enzymes maintain the cholesterol concentration by regularly exchanging membrane and plasma cholesterol.

Deficiencies in these enzymes are associated with RBC membrane abnormalities such as_____ and _____

Answer 11

cholesterol to phospholipids

acanthocytes and target cells (codocytes)

Question 12

The phospholipids are asymmetrically distributed. ________ and ________ predominate in the outer layer;

________ and _______ form most of the inner layer.

Distribution of these four phospholipids is energy dependent, relying on a number of membrane-associated enzymes, termed ______, _______, and ________for their functions.

Answer 12

Phosphatidylcholine and sphingomyelin

phosphatidylserine (PS) and phosphatidylethanolamine

flippases, floppases, and scramblases

Question 13

When phospholipid distribution is disrupted, as in________ and _______ or in aging RBCs, PS, the only negatively charged phospholipid, redistributes to the outer layer.

________possess receptors that bind to the PS displayed on senescent and damaged RBCs and remove them from circulation.

________ and inflammatory conditions increase the PS distribution in the outer layer of the RBC membrane leading to increased RBC death (also called eryptosis)

Answer 13

sickle cell anemia and thalassemia

Splenic macrophages

C-reactive protein

Question 14

Membrane phospholipids and cholesterol may also redistribute laterally so that the RBC membrane may respond to stresses and deform within______ of being challenged by the presence of a narrow passage, such as a capillary.

Answer 14

100 milliseconds

Question 15

As the proportion of_______ increases, however, the RBC becomes more rigid and is unable to deform as readily.

Answer 15

cholesterol

Question 16

In liver disease, membrane cholesterol concentration becomes increased because of an increased plasma bile salt concentration.

As a result, the cell membrane surface area-to-volume ratio increases giving the RBC a ______appearance

Answer 16

target cell

Question 17

______ (sugar-bearing lipids) make up 5% of the external half of the RBC membrane.

They associate in clumps or rafts and support carbohydrate side chains that extend into the aqueous plasma to anchor the______.

Answer 17

Glycolipids

glycocalyx

Question 18

The_______ is a layer of carbohydrates whose net negative charge prevents microbial attack and mechanical damage caused by adhesion to neighboring RBCs or to the endothe-lium.

________may bear copies of carbohydrate-based blood group antigens, such as antigens of the ABH and the Lewis blood group systems.

Answer 18

glycocalyx

Glycolipids

Question 19

RBC Membrane Proteins

Although cholesterol and phospholipids constitute the principal RBC membrane structure,______ and ______ (skeletal, peripheral) proteins make up 52% of the membrane structure by mass.

Answer 19

transmembrane (integral) and cytoskeletal

Question 20

A proteomic study revealed there are at least______ RBC membrane proteins, including______ transmembrane proteins.

Some proteins have a few hundred copies per cell, and others have more than a million copies per cell.

Of the purported 300 membrane proteins, about 50 have been characterized and named.

Answer 20

300

105

Question 21

serve many functions including: transport sites, adhesion sites, and signaling receptors.

Any disruption in transport protein function changes the osmotic tension of the cytoplasm, which leads to a rise in viscosity and loss of deformability.

Any change affecting adhesion proteins permits RBCs to adhere to one another and to the vessel walls, promoting fragmentation (vesiculation), reducing membrane flexibility, and shortening the RBC life span.

Answer 21

Transmembrane Proteins

Question 22

Signaling receptors bind plasma ligands and trigger activation of intracellular signaling proteins, which then initiate various energy-dependent cellular activities, a process called_______

Through glycosylation, the transmembrane proteins also support surface carbohydrates, which join with glycolipids to make up the protective glycocalyx.

Answer 22

signal transduction