Transcript The Circulatory System

The Circulatory System
By: Ali James
P.1
3/15/14
Overview

Through the process of diffusion, the circulatory system is able to rapidly
transport bulk fluid throughout the body that connects the aqueous
environment to the organs that exchange gases, absorb nutrients, and dispose
of wastes

Ex. Red blood cells can receive oxygen from the lungs to form oxygen-rich
blood throughout the body to replace oxygen-depleted blood 
Gastrovascular Cavity or a Circulatory
System?

Most invertebrates have a gastrovascular cavity or a circulatory system for a
internal transport

Hydras and cnidarians have a body plan that makes a circulatory system
unnecessary. Instead they use a central gastrovascular cavity that takes care
of digestion and distribution of substances throughout the body

For animals with many cell layers, a gastrovascular cavity is insufficient for
internal transport because the diffusion distances is to great for adequate
exchange of nutrients and wastes. Therefore, a circulatory is used 
Open or Closed Circulatory System

Both a Open and Closed Circulatory System have three basic components: a
circulatory fluid (blood), a set of tubes (blood vessels) through which the
blood moves through the body, and a muscular pump (the heart)

The heart powers circulation through blood pressure which is the motive force
for fluid movement in the circulatory system

Open Circulatory System:

Blood bathes the organs directly in blood and interstitial fluid called
hemolymph

One or more hearts pump the hemolymph into interconnected system of
sinuses (spaces surrounding the organs) where chemical exchange occurs
between the hemolymph and the body cells

Ex. insects, arthropods and mollusks
-> -> ->
Open and Closed Circulatory System
Continued…

Closed Circulatory System:

Blood is confined to vessels and is distinct form the interstitial fluid

One or more hearts pump blood into large vessels that branch in to smaller
ones coursing through the organs

Diffusion then takes place between the blood and the interstitial fluid bathing
the cells

Ex. Earthworms, squids, octopuses and vertebrates 
Vertebrate Phylogeny

Humans and other vertebrates have a closed circulatory system called a
cardiovascular system

The heart, which is apart of the cardiovascular system has one atrium or two
atria that receive blood returning from the heart

The heart also contains one to two ventricles that pump blood out of the
heart

Arteries, veins and capillaries are the three main kinds of blood vessels that
extend a total distance of 100,000 km

Arteries carry blood away from the heart to organs throughout the body

Within organs, the arteries branch into arterioles (small vessels that convey
blood to the capillaries)
-> -> ->
Vertebrate Phylogeny Continued…

Capillaries are microscopic vessels with thin, porous walls

Networks of capillaries are called capillary beds that infiltrate tissue

Diffusion takes place across the thin walls of the capillaries

Capillaries at their “downstream end” converge into venules which become
veins that return blood back to the heart

Note: the arteries and veins are distinguished by the direction in which they
carry blood, not by the characteristics of the blood they carry. Therefore,
arteries carry blood toward the capillaries while veins returns the blood from
the capillaries. 
Complexity of an Organism depends on
the Metabolism they possess

Metabolic rate is an important factor in the evolution of cardiovascular
systems

Animals that have high metabolic rates have more complex circulatory
systems and more powerful hearts than animals with low metabolic rates.

The complexity and number of blood vessels in a particular organ is also
determined by the organ’s metabolic requirements

Differences in cardiovascular adaptations can be determined by the
environments they live in

Ex. Aquatic or terrestrial 
Anatomy of Fishes

A fish heart has two main chambers, one atrium and one ventricle

Blood pumped from the ventricle travels gills (gill circulation) where is picks
up oxygen and disposes of carbon dioxide across capillary walls

The gill capillaries converge in to vessels that carry oxygen-rich blood to
capillary beds in the rest of the body (systemic circulation)

Blood then returns in the veins to the atrium of the heart

A fish’s blood passes through two capillary beds during each circuit

When blood flows through a capillary bed, blood pressure drops substantially
which makes the systemic circulation move slowly

Constraining the delivery of oxygen to body tissues which in return restricts
the maximum aerobic metabolic rate of fishes

This can also be referred to as single circulation 
Anatomy of Amphibians

Amphibians have three-chambered hearts with two atria and one ventricle

The ventricle pumps blood into a forked artery that splits it’s output into the
pulmocutaneous and systemic circulations

Pulmocutaneous circulation leads to the capillaries where the blood picks up
oxygen and releases carbon dioxide before returning to the heart’s left atrium

The returning oxygen-rich blood is pumped into the systemic circulation
which transports the blood to all the organs and replaces the oxygen-poor
blood which goes to the right atrium

These processes is called double circulation due to the blood being pumped a
second time after it loses pressure in the capillary beds of the lungs and skin

In the ventricle of amphibians, there is also a slight mixing of oxygen-rich and
oxygen-poor blood 
Anatomy of Reptiles, Birds and Mammals
Reptiles:

Most reptiles have a three chambered heart that has a ventricle that is
partially divided

Reptiles also have double circulation with pulmonary (lung) and systemic
circuits, but have less mixing of oxygen-rich and oxygen-poor blood than
amphibians
Birds, Mammals and Crocodilians:

Has four chambered heart

Has double circulation

The ventricle is separated into right and left chambers

The left side of the heart receives and pumps only oxygen-rich blood

The right side handles only the oxygen-poor blood

More oxygen delivered due to the blood never mixing 
Characteristics of a Four Chambered Heart

Essential adaptation for endotherms (birds and mammals)

Endotherms use 10 times as energy as ectoderms

Therefore, their circulatory system needs to deliver 10 times as much fuel
and oxygen to their tissues

However, due to their separate and independent systemic and pulmonary
circulations as well as their large and powerful hearts, the necessary volume
of blood can be pumped efficiently 
Route of Circulation

The right ventricle pumps blood to the lungs by pulmonary veins

Blood flows through the capillary beds in the lungs to exchange carbon dioxide for
oxygen

The oxygen-rich blood returns to the left atrium of the heart via pulmonary veins

The oxygen-rich blood into the left ventricle which opens while the atrium
contracts

The left ventricle pumps the oxygen-rich blood to the body systems through the
systemic circuit

Blood leaves ventricle via the aorta which gives it arteries which gives it the rest
of the body including the capillaries

Once at the capillaries, the blood replaces its oxygen with carbon dioxide

Capillaries rejoin to form venules that convey blood to the veins which collect to
the anterior or posterior vena cava depending on the location the blood came
from

From there, the anterior and posterior vena cava dump the blood back into the
right atrium which gives it back to the right ventricle where the cycle continues
once more 
The Heart

The atria have thin walls that give blood to the thicker ventricles which
contract much more strongly to deliver blood to the rest of the body

The heart beats in a rhythmic cycle: when it contracts, it pumps blood and
when it relaxes, the chambers fill with blood

Cardiac Cycle: one complete sequence of pumping and filling

Systole: contraction phase of cycle

Diastole: relaxation phase of cycle

Cardiac output: the volume of blood per minute that the left ventricle pumps
into the systemic circuit

Cardiac output depends on the rate of contractions (heart rate) and stroke
volume (amount of blood pumped by the left ventricle in each contraction

Average stroke volume for a human is 75mL

Cardiac output can increase about fivefold during heavy exercise -> -> ->
The Heart Continued…

There are four valves in the heart that contain connective tissue that force
blood to go in the right direction and prevent backflow

Atrioventricular Valve (AV): lies between each atrium and ventricle, is
anchored by strong fibers that prevent them from turning inside out and close
when the ventricle contracts to keep the blood from going back into the artia

Semilunar Valves: located at the two exits of the heart (where the aorta
leaves the left ventricle and the pulmonary artery leaves the right ventricle),
forced open by the pressure if the ventricular contraction and closes when
the ventricles relax so the blood wont go back into the ventricles

Pulse: the rhythmic stretches of arteries caused by the pressure of blood
driven by the contractions of the ventricles

Heart sounds we hear are from the closing of valves in the heart

Heart Murmur: a defect in one or more valves that is not normally life
threatening 
Maintaining the Heart’s Rhythmic Beat

Certain cells of vertebrate cardiac muscle are self-excitable (they contract
without any signal from the nervous system) and have their own intrinsic
contraction

Sinoatrial Node (SA): also known as a pacemaker, the SA sets the rate and
timing at which all cardiac muscle cells contract and is located in the right
atrium

The SA node generates electrical impulses to the walls of the atria (that make
them contract in unison) and the atrioventricular node (where the impulses
are delayed for a 0.1 sec to ensure that the atria empties completely before
the ventricle contracts)

Physiological cues like nerves, hormones and temperature can all affect the
way the SA node works for your body 
Structural differences of Arteries, Veins and
Capillaries correlate with their Function

The walls of arteries and veins have three similar layers:
1.Outside: connective tissue with elastic fibers allows the vessels to stretch and
recoil
2.Middle:smooth muscle and more elastic fibers
3.Endothelium: a single layer of flattened cells that provides and smooth surface
that minimizes resistance to blood flow and lines the lumen of all blood vessels
(including capillaries)
Capillaries:

Lack two outer layers and have thin walls that consist only of endothelium
and basement membrane

Perfect for facilitating exchange of substances between blood and interstitial
fluid
-> -> ->
Structural differences of Arteries, Veins and
Capillaries correlate with their Function
Continued…
Arteries:

Have a thicker middle and outer layers than veins

Due to the blood flowing at uneven speeds and pressures, the thick walls the
arteries have provide strength to accommodate these varying situations and
maintain blood pressure
Veins:

Thin walled due to the low velocity and pressure that is needed to bring the
blood back to the heart 
Physical Laws affect Blood Flow and Pressure
Blood Flow Velocity:

Law of Continuity: describes fluid movement through pipes like the aorta and
capillaries

If a pipe’s diameter changes over length, a fluid will flow through narrower
segments of the pipe faster than it flows in wider segment
Blood Pressure:

Fluids exert a force called hydrostatic pressure against surfaces they contact,
and it is that pressure that drives fluids through pipes

Fluids flow from areas of high pressure to low pressure

Blood pressure is greater in arteries than in veins due to narrow openings that
impede the exit of blood

Blood pressure is determined by cardiac output and peripheral resistance

Contractions of smooth muscles in the walls of arterioles constricts tiny
vessels, increases peripheral resistance, and therefore increases blood
pressure upstream

When smooth muscles relax, the arterioles dilate, blood flow through the
arterioles increases, and the pressure in the arteries falls -> -> ->
Physical Laws affect Blood Pressure
Continued…

Cardiac output is adjusted with changes in peripheral resistance which
maintains blood flow as the circulatory demands
Gravity:

Gravity can also affect blood pressure due to the gravity needed to push
blood above the heart

Due to extraneous actions to raise blood above the heart, by the time the
blood reaches the veins, the pressure of the blood is not affected by the
heart

Instead the rhythmic contractions, exercise and inhalation can cause the
smooth muscles in the walls of venules and veins to account for the delivering
blood back to the heart 
Transfer of Substances between the Blood
and Interstitial Fluid occurs across the
Capillaries
 At any given time, 5-10% of the body’s capillaries have blood flowing through
them

Depending on what the body is doing at any given time, blood is asserted to
different areas of the body more than others

Two mechanisms, dependent on smooth muscles controlled by nerve signals
and hormones, regulate the distribution of blood in the capillary beds

Mechanism #1: contraction of smooth muscle layer in the wall of an arteriole
constricts the vessel, decreasing blood flow in the capillary bed. When the
muscle layer relaxes, the arteriole dilates, allowing blood to enter the
capillaries

Mechanism #2: rings of smooth muscle, called precapillary sphincters, control
the flow of blood between arterioles and venules
Capillary Exchange:

Takes places in the thin, endothelial walls of the capillaries -> -> ->
Transfer of Substances between the
Blood and Interstitial Fluid occurs across the
Capillaries Continued…

Some substances are carried across the endothelial cell in vesicles that form
by endocytosis on one side of the cell and then release their contents by
exocytosis on the opposite side

Others can just diffuse between the blood and the interstitial fluid

Small molecules diffuse down concentration gradients across the endothelial
cells

Others can diffuse through clefts between adjoining cells

About 85% of the fluid that leaves the blood at the arterial end of the
capillary bed reenters from the interstitial fluid at the venous end, and the
remaining 15% is returned to the blood by the vessels of the lymphatic system

The Lymphatic System

So much blood passes through the capillaries that the cumulative loss of fluid
adds up to 4 L a day

The lymphatic System returns fluid to the blood and aids in body defense

Fluid enters this system by diffusing into tiny lymph capillaries intermingled
among capillaries of the cardiovascular system

Once inside the lymphatic system, the fluid is called a lymph

The lymphatic system drains into the circulatory system near the junction of
the venae cavae with the right atrium

Like vein, lymph vessels have valves that prevent backflow of fluid toward
the capillaries and depend mainly on the movement of skeletal muscles to
squeeze fluid toward the heart

Lymph nodes: a honeycomb of connective tissue specialized for defense that
filter lymphs and attack viruses and bacteria

When fighting off an infection the lymph nodes become swollen and tender
allowing doctors to know immediately whether or not you are sick 
Blood

Blood is a connective tissue with cells suspended in plasma
Plasma:

90% water

Contain solutes and inorganic salts in the form of dissolved ions (blood
electrolytes)

Combined concentration of these ions is important in maintaining the osmotic
balance of blood, the buffering of blood and the normal functioning of muscle and
nerves
Plasma Proteins:

Act as buffers against pH changes, help maintain the osmotic balance between
blood and interstitial fluid, and contribute to the blood’s thickness

There are many different types of plasma proteins

Immunoglobulins/ Antibodies: combat viruses and other foreign agents that invade
the body

Fibrinogens: clotting factors that help plug leaks when blood vessels are injured

Blood plasma that has had these clotting factors removed are called serum 
Cellular Elements

Three types of elements are suspended in plasma: red and white blood cells
and platelets

Red Blood Cells: also known as erythrocytes, are the most numerous,
transport oxygen (oxygen transport depends on the rapid diffusion of oxygen
across the red cell’s plasma membranes), lack room for a nuclei or
mitochondria but contain hemoglobin (250 mil. iron-containing protein that
transports oxygen) and generate their ATP by anaerobic metabolism

White Blood Cells: also known as leukocytes, there are five types: monocytes,
neutrophils, basophils, eosinophils and lymphocytes, function in defense,
located outside of circulatory system and patrol the interstitial
fluid/lymphatic system

Platelets: pieces of cells that are involved in clotting, have no nuclei,
originate as pinched-off cytoplasmic fragments of large cells in the bone
marrow 
Stem Cells and the Replacements of Cellular
Elements

Erythrocytes, leukocytes and platelets all develop from a common source

A single population of cells is called pluripotent stem cells in the red marrow
of bones

Pluripotent means that they have the potential to differentiate into any type
of blood cell or into cells that produce platelets

A negative feedback mechanism controls erythrocyte production

When the kidney detects that the tissues aren’t receiving enough oxygen, it
secretes a hormone called erythropoietin which starts making erythrocytes

Purified pluripotent stem cells may soon provide an effective treatment for a
number of human diseases in the future 
Blood Clotting

When we are cut, the inactive sealant fibrinogen becomes active, turns into
fibrin and precedes into threads that form a framework for clotting

Hemophilia: an inherited defect in any step of the clotting process that leads
to excessive bleeding from minor cuts and bruises

Sometimes, platelets clump and fibrin coagulates within a blood vessel
blocking the flow of blood (also known as thrombus)

This is more likely to happen in individuals with cardiovascular diseases,
diseases of the heart and blood vessels 
Cardiovascular Diseases

Are the leading cause of death in the U.S. and most other developed nations

Affects the heart and blood vessels

Final blow is a heart attack or stroke

A heart attack is the death of cardiac muscle tissue resulting form prolonged
blockage of one or more coronary arteries and the vessels that supply oxygenrich blood to the heart

A stroke is the death of nervous tissue in the brain, usually a result of form
rupture or blockage of arteries in the head

Both normally happen due to thrombus clogging and artery

Embolus: a transported clot that will eventually get clogged in a artery to
small to let it pass and blocks the transportation of oxygen

Atherosclerosis: plaque forms on the inner walls of the arteries and narrows
their bore -> -> ->
Cardiovascular Diseases Continued…

A plaque forms at a site where the smooth muscle layer of an artery thickens
abnormally and becomes infiltrated with fibrous connective tissue and lipids
such as cholesterol

Plaques can also harden by calcium deposits that resulting in arteriosclerosis

Warnings like the occasional chest pain called angina pectoris can warn an
individual of impending doom

Hypertension: promotes atherosclerosis and increases the risk of heart
attack/ stroke and tends to increase blood pressure by narrowing the bore of
the vessels and reducing their elasticity

Can be controlled by change of diet, exercise and medication and studies
show that this is an inherited disease

Non-gentic ways to get this disease include smoking, lack of exercise and high
levels of cholesterol (low-density lipoproteins)

To hinder the effects on low- density lipoproteins, doctors recommend an
increase in exercise that can result in higher concentration of “good
cholesterol” called high-density lipoproteins 
The End 