chapter 18 cardiovascular system blood notes

When you donate a unit of blood during a blood drive (approximately 475 mL, or about 1 pint), your body typically replaces the donated plasma within 24 hours, but it takes about 4 to 6 weeks to replace the blood cells. This restricts the frequency with which donors can contribute their blood. The process by which this replacement occurs is called

hemopoiesis

Throughout adulthood, the liver and spleen maintain their ability to generate the formed elements. This process is referred to as

(meaning hemopoiesis outside the medullary cavity of adult bones).

extramedullary hemopoiesis

is the zygote, or fertilized egg. The totipotent (toti- = “all”) stem cell gives rise to all cells of the human body.

The totipotent stem cell

which gives rise to multiple types of cells of the body and some of the supporting fetal membranes.

pluripotent stem cell

is a stem cell that develops only into types of connective tissue, including fibrous connective tissue, bone, cartilage, and blood, but not epithelium, muscle, and nervous tissue.

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the mesenchymal cell

All of the formed elements of blood originate from this specific type of cell.

hematopoietic stem cell, or hemocytoblast

is exposed to appropriate chemical stimuli collectively called hemopoietic growth factors, which prompt it to divide and differentiate.

Hemopoiesis begins when the hematopoietic stem cell

give rise to a class of leukocytes known as lymphocytes, which include the various T cells, B cells, and natural killer (NK) cells, all of which function in immunity.

Lymphoid stem cells

quickly migrate from the bone marrow to lymphatic tissues, including the lymph nodes, spleen, and thymus, where their production and differentiation continues.

lymphoid stem cells

give rise to all the other formed elements, including the erythrocytes; megakaryocytes that produce platelets; and a myeloblast lineage that gives rise to monocytes and three forms of granular leukocytes: neutrophils, eosinophils, and basophils.

Myeloid stem cells

is a connective tissue.

it is made up of cellular elements and an extracellular matrix.

that blood

makes blood unique among connective tissues because it is fluid. This fluid, which is mostly water, perpetually suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system.

extracellular matrix, called plasma,

The cellular elements—referred to as the formed elements—include red blood cells (RBCs), white blood cells (WBCs), and cell fragments called

platelets

is to deliver oxygen and nutrients to and remove wastes from body cells, but the specific functions of include defense, distribution of heat, and maintenance of homeostasis.

blood

exercising on a warm day, your rising core body temperature would trigger several homeostatic mechanisms, including_____ which is typically cooler.

blood passes through the vessels of the skin, heat would be dissipated to the environment, and the blood returning to your body core would be cooler.

increased transport of blood from your core to your body periphery

In contrast, on a cold day,

blood is diverted away from the skin to maintain a warmer body core

act as buffers, which thereby help to regulate the pH of body tissues. Blood also helps to regulate the water content of body cells.

Proteins and other compounds in blood

measures the percentage of RBCs, clinically known as erythrocytes, in a blood sample.

hematocrit

above the erythrocytes is a pale, thin layer composed of the remaining formed elements of blood. These are the WBCs, clinically known as leukocytes, and the platelets, cell fragments also called

thrombocytes

its color; it normally constitutes less than 1 percent of a blood sample.

buffy coat

normally a pale, straw-colored fluid, which constitutes the remainder of the sample.

blood plasma

volume of erythrocytes after centrifugation is also commonly referred to as

packed cell volume (PCV)

is a measure of a fluid’s thickness or resistance to flow, and is influenced by the presence of the plasma proteins and formed elements within the blood.

Viscosity

of blood has a dramatic impact on blood pressure and flow.

viscosity

averages about 7.4; however, it can range from 7.35 to 7.45 in a healthy person.

The pH of blood

is therefore somewhat more basic (alkaline) on a chemical scale than pure water, which has a pH of 7.0.

blood

is composed primarily of water: In fact, it is about 92 percent water. Dissolved or suspended within this water is a mixture of substances, most of which are proteins.

plasma

is the most abundant of the plasma proteins. Manufactured by the liver, albumin molecules serve as binding proteins—transport vehicles for fatty acids and steroid hormones.

Albumin

also the most significant contributor to the osmotic pressure of blood; that is, its presence holds water inside the blood vessels and draws water from the tissues, across blood vessel walls, and into the bloodstream. This in turn helps to maintain both blood volume and blood pressure.

Albumin

normally accounts for approximately 54 percent of the total plasma protein content, in clinical levels of 3.5–5.0 g/dL blood.

Albumin

A heterogeneous group, there are three main subgroups known as alpha, beta, and gamma

globulins

transport iron, lipids, and the fat-soluble vitamins A, D, E, and K to the cells; like albumin, they also contribute to osmotic pressure.

The alpha and beta globulins

are proteins involved in immunity and are better known as an antibodies or immunoglobulins

The gamma globulins

immunoglobulins are produced by

specialized leukocytes known as plasma cells

make up approximately 38 percent of the total plasma protein volume, in clinical levels of 1.0–1.5 g/dL blood.

globulins

is the third of the three major groups of plasma proteins. Like albumin and the alpha and beta globulins, fibrinogen is produced by the liver. It is essential for blood clotting, a

Fibrinogen

accounts for about 7 percent of the total plasma protein volume, in clinical levels of 0.2–0.45 g/dL blood.

Fibrinogen

various electrolytes, such as sodium, potassium, and calcium ions; dissolved gases, such as oxygen, carbon dioxide, and nitrogen; various organic nutrients, such as vitamins, lipids, glucose, and amino acids; and metabolic wastes.

nonprotein solutes combined contribute approximately 1 percent to the total volume of plasma

from stem cells to precursor cells to mature cells is again initiated by hemopoietic growth factors.

Erythropoietin (EPO), Thrombopoietin, and Cytokines

two major subtypes of cytokines known as

colony-stimulating factors and interleukins

is a glycoprotein hormone secreted by the interstitial fibroblast cells of the kidneys in response to low oxygen levels. It prompts the production of erythrocytes.

Erythropoietin (EPO)

another glycoprotein hormone, is produced by the liver and kidneys. It triggers the development of megakaryocytes into platelets.

Thrombopoietin

are glycoproteins secreted by a wide variety of cells, including red bone marrow, leukocytes, macrophages, fibroblasts, and endothelial cells. They act locally as autocrine or paracrine factors, stimulating the proliferation of progenitor cells and helping to stimulate both nonspecific and specific resistance to disease.

Cytokines

are glycoproteins that act locally, as autocrine or paracrine factors. Some trigger the differentiation of myeloblasts into granular leukocytes, namely, neutrophils, eosinophils, and basophils.

Colony-stimulating factors (CSFs)

are stimulated by GM-CSF; granulocytes, monocytes, platelets, and erythrocytes are stimulated by multi-CSF. Synthetic forms of these hormones are often administered to patients with various forms of cancer who are receiving chemotherapy to revive their WBC counts.

Both granulocytes and monocytes

are another class of cytokine signaling molecules important in hemopoiesis.

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Interleukins

may play other roles in body functioning, including differentiation and maturation of cells, producing immunity and inflammation. To date, more than a dozen interleukins have been identified, with others likely to follow. They are generally numbered IL-1, IL-2, IL-3, etc.

Interleukins

are now known to be produced by a variety of cells including bone marrow and endothelium.

Interleukins

run the risk of infection, significantly increasing the viscosity of the blood and the potential for transmission of blood-borne pathogens if the blood was collected from another individual.

blood doping the use of supplemental RBC

is injected under the skin and can increase hematocrit for many weeks. It may also induce polycythemia and raise hematocrit to 70 or greater. This increased viscosity raises the resistance of the blood and forces the heart to pump more powerfully;

Synthetic EPO

a diagnostic test of a sample of red bone marrow

bone marrow biopsy

a treatment in which a donor’s healthy bone marrow—and its stem cells—replaces the faulty bone marrow of a patient.

bone marrow transplant

individual requiring a transplant, a matching donor is essential to prevent the immune system from destroying the donor cells—a phenomenon known as

tissue rejection

commonly known as a red blood cell (or RBC), is by far the most common formed element:

remain within the vascular network.

erythrocyte

are estimated to make up about 25 percent of the total cells in the body.

small cells, with a mean diameter of only about 7–8 micrometers (µm)

erythrocyte

are to pick up inhaled oxygen from the lungs and transport it to the body’s tissues, and to pick up some (about 24 percent) carbon dioxide waste at the tissues and transport it to the lungs for exhalation.

primary functions of erythrocyte

typically leave the blood vessels to perform their defensive functions,

leukocytes

erythrocyte matures in the red bone marrow, it extrudes its nucleus and most of its other organelles.

erythrocyte

During the first day or two that it is in the circulation, an immature erythrocyte, known as a ______, will still typically contain remnants of organelles.

reticulocyte

should comprise approximately 1–2 percent of the erythrocyte count and provide a rough estimate of the rate of RBC production, with abnormally low or high rates indicating deviations in the production of these cells. These remnants, primarily of networks (reticulum) of ribosomes, are quickly shed, however, and mature, circulating erythrocytes have few internal cellular structural components. Lacking

reticulocyte

do not utilize any of the oxygen they are transporting,

they rely on anaerobic respiration.

lack endoplasmic reticula and do not synthesize proteins.

erythrocyte

contain some structural proteins that help the blood cells maintain their unique structure and enable them to change their shape to squeeze through capillaries. This includes the protein spectrin, a cytoskeletal protein element.

erythrocyte

are biconcave disks; that is, they are plump at their periphery and very thin in the center

erythrocyte

also provides a greater surface area across which gas exchange can occur, relative to its volume; a sphere of a similar diameter would have a lower surface area-to-volume ratio.

The biconcave shape

can diffuse into the plasma and then through the capillary walls to reach the cells, whereas some of the carbon dioxide produced by the cells as a waste product diffuses into the capillaries to be picked up by the

In the capillaries, the oxygen carried by the erythrocytes

Capillary beds are extremely narrow, slowing the passage of the erythrocytes and providing an

extended opportunity for gas exchange to occur.

allowing them to bend over themselves to a surprising degree, then spring back again when they enter a wider vessel.

structural proteins like spectrin are flexible,

wider vessels, erythrocytes may stack up much like a roll of coins, forming a

rouleaux

is a large molecule made up of proteins and iron. It consists of four folded chains of a protein called globin, designated alpha 1 and 2, and beta 1 and 2

Hemoglobin

Each of these globin molecules is bound to a red pigment molecule called ___, which contains an ion of iron (Fe2+)

heme

lungs, hemoglobin picks up oxygen, which binds to the iron ions, forming

oxyhemoglobin

darker red _____, sometimes referred to as reduced hemoglobin.

deoxyhemoglobin

About 76 percent dissolves in the plasma, some of it remaining as dissolved CO2, and the remainder forming bicarbonate ion. About 23–24 percent of it binds to the amino acids in hemoglobin, forming a molecule known as

carbaminohemoglobin

results in insufficient numbers of RBCs and results in one of several forms of anemia.

Ineffective hematopoiesis

An overproduction of RBCs produces a condition called

polycythemia

is not a failure to directly deliver enough oxygen to the tissues, but rather the increased viscosity of the blood, which makes it more difficult for the heart to circulate the blood.

primary drawback with polycythemia

determining oxygenation of tissues, the value of greatest interest in healthcare is the percent saturation; that is, the percentage of hemoglobin sites occupied by oxygen in a patient’s blood. Clinically this value is commonly referred to simply as

“percent sat.”

Normal pulse oximeter readings range from 95–100 percent. Lower percentages reflect _____, or low blood oxygen.

is more generic and simply refers to low oxygen levels.

hypoxemia

less oxygen will exit the vessels supplying the kidney, resulting in hypoxia (low oxygen concentration) in the tissue fluid of the kidney where oxygen concentration is actually monitored. Interstitial fibroblasts within the kidney secrete EPO, thereby increasing erythrocyte production and restoring oxygen levels. In a classic negative-feedback loop, as oxygen saturation rises, EPO secretion falls, and vice versa, thereby maintaining homeostasis.

In response to hypoxemia,

Consequently, people traveling to high elevations may experience symptoms of

Hypoxemia

In response to the hypoxemia, the kidneys

secrete EPO to step up the production of erythrocytes until homeostasis is achieved once again.

erythrocyte production also requires several trace elements:

Iron,copper,zinc, and Iron.

Erythrocytes live up to 120 days in the circulation, after which the worn-out cells are removed by a type of myeloid phagocytic cell called a

macrophage

the protein portion of hemoglobin, is broken down into amino acids, which can be sent back to the bone marrow to be used in the production of new erythrocytes.

Globin

is broken down in the circulation, releasing alpha and beta chains that are removed from circulation by the kidneys.

Hemoglobin that is not phagocytized

The non-iron portion of _____ is degraded into the waste product biliverdin, a green pigment, and then into another waste product, bilirubin, a yellow pigment.

heme

_____ to albumin and travels in the blood to the liver, which uses it in the manufacture of bile, a compound released into the intestines to help emulsify dietary fats.

Bilirubin binds

injury, biliverdin from damaged RBCs produces some of the dramatic colors associated with a

bruise

failing liver, bilirubin cannot be removed effectively from circulation and causes the body to assume a yellowish tinge associated with

jaundice

within the feces produce the typical brown color associated with this waste.

Stercobilins

And the yellow of urine is associated with the

urobilins

When the number of RBCs or hemoglobin is deficient, the general condition is called anemia.

anemia

those caused by blood loss, those caused by faulty or decreased RBC production, and those caused by excessive destruction of RBCs.

Anemia can be broken down into three major groups:

Normal-sized cells are referred to as

normocytic

smaller-than-normal cells are referred to as

microcytic

larger-than-normal cells are referred to as

macrocytic

sickle cell anemia, iron deficiency anemia, vitamin deficiency anemia, and diseases of the bone marrow and stem cells.

Anemias caused by faulty or decreased RBC production include

A characteristic change in the shape of erythrocytes is seen in

sickle cell disease

A genetic disorder, it is caused by production of an abnormal type of hemoglobin, called ____, which delivers less oxygen to tissues and causes erythrocytes to assume a sickle (or crescent) shape, especially at low oxygen concentrations (

hemoglobin S