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 MammalsReptiles:Most reptiles have a three chambered heart that has a ventricle that is partially dividedReptiles 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 heartHas double circulationThe ventricle is separated into right and left chambersThe left side of the heart receives and pumps only oxygen-rich bloodThe right side handles only the oxygen-poor bloodMore 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 PressureBlood Flow Velocity:Law of Continuity: describes fluid movement through pipes like the aorta and capillariesIf 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 pipesFluids flow from areas of high pressure to low pressureBlood pressure is greater in arteries than in veins due to narrow openings that impede the exit of bloodBlood pressure is determined by cardiac output and peripheral resistanceContractions of smooth muscles in the walls of arterioles constricts tiny vessels, increases peripheral resistance, and therefore increases blood pressure upstreamWhen 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 oxygen-rich 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