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Fleur Sam. Ch 14Chapter 14 Cardiovascular physiology
In the most efficient circulatory systems, the heart pumps blood through a closed system of vessels.
This one-way circuit steers the blood along a specific route and ensures systematic distribution of
gases, nutrients, signal molecules, and wastes.
A circulatory system comprised of a heart, blood vessels and blood is known as a cardiovascular
system.
Capillaries, the microscopic blood vessels where blood exchanges material with the interstitial fluid.
14.1 overview of the cardiovascular system
In the simplest terms, a cardiovascular system is a series of tubes (the blood vessels) filled with fluid
(blood) and connected to a pump (the heart). Pressure generated in the heart propels blood through
the system continuously. The blood picks up oxygen at the lungs and nutrients in the intestine and
then delivers these substances to the body’s cells while simultaneously removing cellular wastes and
heat for excretion. In addition, the cardiovascular system plays an important role in cell-to-cell
communication and in defending the body against foreign invaders
The primary function of the cardiovascular system is the transport of materials through the body.
These substances can be divided into (1) nutrients, water and gases from the external environment
and (2) materials that move from cell to cell in the body and (3) waste that the cells eliminate.
O2 enters the body at the exchange surface of the lungs. Nutrients and water are absorbed across
the intestinal epithelium. Once all the materials are in the blood, the cardiovascular system
distributes them.
Steady supply of O2 to cells is important bc many cells deprived of O2 become irreplaceable
damaged within short period of time.
About 5-10 sec. after blood flow to brain is stopped, person loses consciousness. If O2 delivery stops
for 5-10 min. permanent brain damage results. Neurons of brain have high rate of O2 consumption
and cannot meet metabolic need for ATP by using anaerobic pathways, which have low yields of
ATP/glucose. Bc of brain sensitivity to hypoxia, homeostatic controls do everything to maintain
cerebral blood flow, even if it means depriving other cells of O2.
Cell-to-cell communication is key function of cardiovascular system. Bv. Hormones secreted by
endocrine glands travel in blood to targets. Blood also carries nutrients, like glucose from liver and
fatty acids from adipose tissue, to metabolically active cells. Defense team of WBCs and antibodies
patrols circulation to intercept foreign invaders.
Cardiovascular system also picks up CO2 and metabolic wastes released by cells and transports them
to lungs and kidneys for excretion. Some waste products are transported to liver for processing
before they are excreted in the urine/feces. Heat also circulates through blood, moving from body
core to body surface where it dissipates (=verdwijnt).
The cardiovascular system is composed of the heart, blood vessels (vasculature), cells & plasma of
blood.
The heart generates a hydrostatic pressure gradient that causes blood to flow.
,Blood vessels that carry blood away from the heart are arteries, the ones that return blood to the
heart are called veins.
As blood moves through the cardiovascular system, a
system of valves in the heart & veins ensures that the
blood flows in 1 direction only.
The heart is divided by a central wall, or septum, into
right and left valves. Each half functions as an
independent pump that consist of an atrium and
ventricle. The atrium receives the blood returning to
the heart from the blood vessel, the ventricle pumps
blood out into the blood vessels.
The right side of the heart receives blood from the
tissues and sends it to the lungs for oxygenation. The
left side of the heart receives newly oxygenated
blood from the lungs and pumps it to tissues
throughout the body.
Blood in right side of heart=blue, used to show blood
from which the tissues have extracted O2. Although
this blood is often called deoxygenated, it’s not
completely devoid of O2. It just has less O2 than
blood going from lungs to tissue.
In living people, well-oxygenated blood is bright-red, and low-oxygen blood is darker red.
Cyanosis: Low-oxygen blood can impart a bluish color to certain areas of the skin, like around mouth
and fingernails.
From the right atrium, blood is pumped into the right ventricle of the heart. From there it is pumped
through pulmonary arteries to the lungs, where it is oxygenated. From the lungs, blood travels to the
left side of the heart through pulmonary veins. The blood vessels that go from the right ventricle to
the lungs and back to the left atrium are known collectively as pulmonary circulation.
Blood from the lungs enter the heart at the left atrium and passes into the left ventricle. Blood
pumped out of the left ventricle enters the large artery, the aorta, which branches in a series of
smaller and smaller arteries that finally lead into networks of capillaries. After leaving the capillaries,
blood flows into the venous side of the circulation, moving from small veins into larger and larger
veins. The veins from the upper part of the body join together to form the superior vena cava and
the lower part of the body form the inferior vena cava. These two venae cavae empty into the right
atrium. The blood vessels that carry blood from the left to the right side of the heart are collectively
known as systemic circulation.
The first branch of the aorta division are the coronary arteries (coronary veins, and coronary sinus),
which nourish the heart muscle itself. Blood from these arteries flows into capillaries, then into
coronary veins, which empty directly into the right atrium at the coronary sinus.
Ascending branches from the aorta go to the arms, head and brains. The abdominal aorta supplies
blood to the trunk, legs, the internal organs such as liver (hepatic artery) and kidneys (renal arteries).
2 special arrangements of the circulation:
, 1. blood supply to the distal tract and liver. Both regions receive well-oxygenated blood through
their own arteries, but in addition, blood leaving the digestive tract goes directly to the liver by
means of the hepatic portal vein. Liver is important site for nutrient processing and plays major role
in detoxifying foreign substances. Most nutrients absorbed in intestine are routed directly to the
liver, allowing that organ to process material before its released into the general circulation. The 2
capillary beds of the digestive tract and liver, joined by the hepatic portal vein are an example of a
portal system.
2. second portal system occurs in the kidneys. Where 2 capillary beds are connected in series. A 3 rd
portal system, is the hypothalamic-hypophyseal portal system, which connects hypothalamus and
the anterior pituitary.
14.2 pressure, volume, flow and resistance
Blood flows because gases and liquids flow down pressure gradients (ꙙP) from regions of high
pressure to regions of lower pressure. For this reason, blood can flow in the cardiovascular system
only if 1 region develops higher pressure than other regions.
Heart creates high pressure when it contracts, blood flows out of heart (region of highest pressure)
into the closed loop of blood vessels (region of lower pressure). As blood moves through the system,
pressure is lost bc of friction between fluid & blood vessel walls. Consequently, pressure falls
continuously as blood moves farther from heart.
Highest pressure in vessels of cardiovascular system is found in the aorta and systemic arteries as
they receive blood form the left ventricle. Lowest pressure is in the venae cavae, just before they
empty into the right atrium.
High to low pressure: aorta arteries arterioles capillaries venules veins venae
cavae.
Pressure in a fluid is the force exerted by the fluid on its container, often measured in millimeters of
mercury, mm Hg. ( 1 mm of mercury is equivalent to the hydrostatic pressure exerted by a 1-mm-
high column of mercury on an area of 1 cm^2). Some report pressures in torr (1 torr= 1 mm Hg) or
cm of water: 1 cm H2O= 0.74 mm Hg.
If fluid is not moving, the pressure is exerts is called hydrostatic pressure, and force is exerted
equally in all directions. Bv. Column of fluid in a tube exerts hydrostatic pressure on the flood and
sides of the tube. In a system in which fluid is flowing, pressure falls over distance as energy is lost bc
of friction.
In addition, pressure exerted by moving fluid has 2 components: a dynamic, flowing component that
represents the kinetic energy of the system, and a lateral component that represents the hydrostatic
pressure (potential energy) exerted on the walls of the system.
Pressure within our cardiovascular system is usually called hydrostatic pressure (or hydraulic
pressure) even though it’s a system in which fluid is in motion.
In human heart, contraction of blood-filled ventricles is similar to squeezing a water balloon:
pressure created by contracting muscle is transferred to the blood. This high-pressure blood then
flows out of the ventricle and into the blood vessels, displacing lower-pressure blood already in the
vessels.
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