Fifth diseas e is viral illness that most kids

Fifth diseas e is viral illness that most kids recover from quickly and without complications. Also called
erythema infectiosum, it's caused by parvovirus B19. It's especially common in kids ages 5 to 15. Fifth
disease causes a distinctive red rash on the face that makes a child appear to have a "slapped cheek."

Erythema multiforme is a syndrome characterized by inflammation of the skin and mucous membranes,
often associated with a T-cell–mediated immunologic reaction to a drug or microorganisms (e.g., herpes
simplex virus) that targets small blood vessels in the skin or mucosa
Chapter 20: Structure and Function of the Hematologic System
Components of the Hematologic System
The cellular elements of blood are the red blood cells (erythrocytes), white blood cells (leukocytes), and
platelets. Erythrocytes are the most abundant cells of the blood, occupying approximately 48% of the
blood volume in men and approximately 42% in women. Erythrocytes are responsible for tissue
oxygenation.
Platelets are a nuclear disk-shaped cytoplasmic fragments. Platelets are essential for blood
coagulation and control of bleeding.
The lymphoid organs are sites of residence, proliferation, differentiation, or function of
lymphocytes and mononuclear phagocytes.
The spleen is the largest lymphoid organ and functions as the site of fetal hematopoiesis,
filters and cleanses the blood, and acts as a reservoir for lymphocytes and other blood cells.
The lymph nodes are the site of development or activity of large numbers of lymphocytes,
monocytes, and macrophages.
Development of Blood Cells
Hematopoiesis , or blood cell production, occurs in the liver and spleen of the fetus and in
the bone marrow after birth. two stages: proliferation and differentiation, or maturation. Each
type of blood cell has parent cells called stem cells. Continues throughout life to replace blood cells that
grow old and die, are killed by disease, or are lost through bleeding.
Bone marrow consists of red (hematopoietic) marrow (blood vessels, mononuclear
phagocytes, stem cells, blood cells in various stages of differentiation, stromal cells) and
yellow marrow (fatty tissue). BM contains multiple populations of stem cells; mesenchymal stem cells
develop into fibroblasts, osteoclasts, and adipocytes; and hematopoietic stem cells develope
into blood cells.
Regulation of hematopoiesis occurs in bone marrow niches in which hematopoietic stem
cells differentiate and are controlled by multiple cytokines and chemokines and through
direct contact with osteoblasts (osteoblastic niche) or vascular endothelial cells (vascular
niche), as well as several other specialized cells, including CAR cells and nestin-expressing
cells.
Hemoglobin, the oxygen-carrying protein of the erythrocyte, enables the blood to transport
100 times more oxygen than could be transported dissolved in plasma alone.

Erythropoiesis depends on the presence of vitamins (especially vitamin B12, folate vitamin,
vitamin B6, riboflavin, pantothenic acid, niacin, ascorbic acid, and vitamin E). Regulation of