Download Ch. 49 Notes - The Circulatory System

BIO 102
Dr. Ely
Chapter 49 Notes – The Circulatory System Part 1
I.
Function and Composition of Blood
a. Functions of blood
i. Transportation and Exchange of substances
1. Oxygen, monomers, and ions are delivered to cells
2. Carbon dioxide and organic wastes are removed from cells
ii. Regulation of homeostasis
1. Hormones are circulated throughout the body to deliver signals to
tissues and organs
2. Heat can be conserved or dissipated by the constriction and
dilation, respectively, of capillaries just below the epidermis
iii. Protection
1. The clotting mechanism of blood prevents blood loss due to injury
2. White blood cells detect and disable foreign invaders such as
bacteria and viruses
b. Composition of blood
i. Blood is a connective tissue with two major components
1. Plasma (55%)
a. The fluid matrix in which dissolved chemicals, large
proteins, and cells (see Formed elements) are suspended
b. Plasma is 92% water, 7% plasma proteins, and 1%
dissolved ions, gases, nutrients, wastes, and hormones
2. Formed elements (45%)
a. Erythrocytes – red blood cells; biconcave discs that carry
hemoglobin – the respiratory pigment that delivers oxygen
to cells
b. Leukocytes – white blood cells; larger, round cells that
may leave the capillaries to mount an immune response
c. Thrombocytes – platelets; fragments of blood cells that
are part of the clotting mechanism
i. Blood clotting is the result of an enzyme cascade
where the circulating peptide fibrinogen (inactive
form) is converted into strong protein threads of
fibrin by the enzyme thrombin
ii. Fibrin threads trap platelets and even erythrocytes
to form the blood clot – a plug that prevents blood
loss
BIO 102
Dr. Ely
II.
Animal Circulatory Systems
a. Invertebrates may have open or closed circulatory systems
i. An open circulatory system consists of a circulating fluid called
hemolymph that travels through vessels, but at some point leaves these
vessels to mix directly with extracellular fluid outside of tissues.
ii. A closed circulatory system consists of blood that is always enclosed
within blood vessels; all vertebrates have a closed circulatory system.
b. Vertebrate circulatory systems
i. The selective advantage of each circulatory system to evolve from
lancelet  fish  amphibian  reptile  mammals + birds is increased
efficiency in circulation and oxygen delivery
ii. The lancelet heart is only a more muscular portion of the artery
iii. Fish evolved a true chambered heart
1. The capillary beds that developed inside gills reduce blood
pressure significantly, this was a selective pressure for the coevolving heart
2. A chambered heart is a stronger pump that could more efficiently
circulate blood around the fish body; the fish heart consists of two
chambers: an atrium and a ventricle.
3. Blood travels in a single-loop circulation pattern: from the heart,
blood travels through the gills to be oxygenated and then
continues through the body to deliver oxygen before returning to
the heart for another pump
iv. Amphibians and reptiles evolved more chambers and double circulation
1. The co-evolution of lungs (tremendous capillary network) and
larger body sizes put a premium on more efficient means of
oxygen delivery
2. Double circulation evolved to restore the blood pressure lost over
the lungs before continuing through the body
a. The pulmonary circuit pumps oxygen-poor blood from the
heart to the lungs to pick up oxygen, and then returns the
blood to the heart.
b. The systemic circuit pumps oxygen-rich blood from the
heart throughout the body to deliver oxygen, and then
returns the blood to the heart.
3. Amphibians and most reptiles have a three-chambered heart
a. The right atrium receives oxygen-poor blood from the
body
b. The left atrium receives oxygen-rich blood from the lungs
c. A single, muscular ventricle contracts to push blood out of
the heart
BIO 102
Dr. Ely
i. Both O2-rich and O2-poor blood mix in the single
ventricle; recesses in the ventricular wall reduces
the extent of this mixing.
ii. In some reptiles, mixing is further reduced by an
incomplete septum, a dividing wall that extends
into the ventricle.
4. Mammals and birds have a completely-divided, four-chambered
heart
a. Convergent evolution: the four-chambered heart arose
independently in both birds and mammals because it
provided a selective advantage associated with
endothermy (be able to explain why)
b. Two atria and two ventricles are completely divided
between the left and right halves of the heart (left atrium
and ventricle, right atrium and ventricle)
i. The right side of the heart receives oxygen-poor
blood from the body and pumps it to the lungs
ii. The left side of the heart receives oxygen-rich
blood from the lungs and pumps it to the body