contains specialized cardiomyocytes that function as impulse-generating and
conducting cells regulated by the ANS. The heartalso functions as an
endocrine organ,releasing atrial natriuretic factor[peptides (ANP or
ANF)] in response to increased plasma volume.ANPs reduce plasma vol-
ume by (1) increasing urinary sodium (natriuretic) and water excretion
(diuretic), (2) inhibiting aldosteronesynthesis and angiotensin IIproduc-
tion, and (3) inhibiting vasopressinrelease from the neurohypophysis.
Blood cells include erythrocytes,which are specialized for oxygen
transport;lymphocytesthat function in cellular and humoral immune
responses; neutrophils,which are early responders to acute inflammation;
monocytesthat are the precursors of tissue macrophages; eosinophils,
which respond to parasitic infection and release histaminases to counteract
basophils and mast cells; and basophils,which contain histamine and
heparin and assist mast cell function.
Bone marrow is the site of blood cell development in adults. The ery-
throcyte lineage includes the following stages: proerythroblasts → basophilic
erythroblasts →polychromatophilic erythroblasts → orthochromatophilic
erythrocytes. The white cell series includes myeloblasts →promyelocytes →
myelocytes→metamyelocytes→mature granular leukocytes.
LYMPHOID SYSTEM AND CELLULAR IMMUNOLOGYFunctional cells include B lymphocytes (humoral immunity), T lym-
phocytes (cellular immunity), macrophages (phagocytic and one of
several types of antigen-presenting cells),andmast cells.
Immunity and T and B cells
There are two types of immunity:
- Innate immunity is the first-line of defense and comprises basic mecha-
nisms of host defense includingbarriers(e.g., skin,zonula occludens/
tight junctions) andphagocytic cells such asmacrophagesandneu-
trophils. Innate immunity isnotspecific for particular pathogens or indi-
viduals of the species. - Adaptive immunity is a responseto antigenic challenge and possesses
four essential characteristics which are notpart of innate immunity:- Specificity of response to antigen
- Memory
- Diversity
- Recognition of self versus nonself
High-Yield Facts 25