Chapter 10: The Circulatory System
Become familiar with the basic vertebrate circulatory system.
Understand the basic pattern of blood flow in vertebrates.
Note circulatory changes associated with respiratory changes in a phylogenetic sequence.
Understand the evolution of the craniate heart in a phylogenetic context.
Mammalian Anatomy: The Cat
-Circulatory System chapter
Ch. 10 Circulatory System slide guide
Liquids in the body are carried by two distinct pathways, both considered part of the circulatory
system: the lymphatic system and blood-vascular system. Because it is so difficult to see its vessels
in our dissections, the lymphatic system will not be dealt with in depth here. However, you have
encountered in your cats a number of small, rounded, brownish glands scattered throughout the
viscera, particularly around the small
intestine and colon. These are
. In many disease
states, these organs are where bacteria or cancer cells can accumulate.
The circulatory system, composed of the heart and associated blood vessels, carries an enormous
range of structures and substances including blood cells (erythrocytes, leukocytes, and
thrombocytes), oxygen (using proteins within the erythrocytes as carriers), carbon dioxide (stored as
the bicarbonate ion), food molecules (
, lipids, monosaccharides, and amino acids), and
Structurally, the blood vessels are broken down into three categories:
as any blood vessel carrying blood away from the heart, irrespective of its oxygen content;
defined as a blood vessel carrying blood towards the heart, irrespective of its oxygen content; and
, thin vessels in which the exchange of material between blood and other cells of the
body occurs. Typically, the walls of arteries are very rigid and have low compliance (stretchiness);
the opposite is true of veins. Why is this important? Arteries are not uniform in size, but show a
progressive shift in size from larger to smaller as they approach the capillaries; a reverse pattern is
found in the veins.
You are responsible for knowing the vessels of both
sheep heart, and the plastic heart models found in the laboratory.
Blood leaves the heart anteriorly via a single
, then passes dorsally through
. The primitive condition (presumably intermediate between early craniates and vertebrates)
involves six pairs of aortic arches (six left and six right). The retention of 6 pairs of aortic arches in
the developing embryo serves as the foundation for the adult circulatory system. In typical aquatic
organisms the aortic arches pass through the
region via capillary beds where gas exchange
occurs. In these aquatic forms the vessels
leading to the gills
afferent branchial arteries,
leading away from the gills
efferent branchial arteries
. In adult craniates blood