Circulatory Systemsin Animals

Basic Components of All Circulatory Systems

• A fluid, blood, that serves as a medium of transport

• A system of channels, or vessels, that conduct the blood throughout the body

• A pump, the heart, that keeps the blood circulating

Types of Circulatory Systems

1) Open Circulatory System

example: arthropods and mollusks

2) Closed Circulatory System

example: earthworms, vertebrates

Open Circulatory System

• Have an open space, the hemocoel

• Vessels empty blood into and pick blood up from the hemocoel

• Tissues within the hemocoel are bathed directly in the blood

BloodBlood Vessel

Hemocoel

Closed Circulatory System

• Blood is confined to the heart and a continuous system of blood vessels

• Each body cell has a direct blood vessel connection

Functions of the Vertebrate Circulatory System

1. Transport of oxygen from lungs to tissues

2. Transport of carbon dioxide from tissues to lungs

3. Transport of nutrients from digestive system to all body cells

4. Transport of waste products from all body cells to the liver, then kidney

Functions of the Vertebrate Circulatory System

5. Distribution of hormones from gland to target organ

6. Regulation of body temperature by adjustments in blood flow

7. Prevention of blood loss by means of clotting

8. Protection of body from microbes by circulating white blood cells and antibodies

Evolution of Vertebrate Heart

• Two distinctly different chambers:

1) atrium (pl. atria)

thin walls and very elastic

designed to collect blood from the body

2) ventricle

thick walls and very muscular

designed to pump blood to the body

Ventricle

Atrium

Evolution of Vertebrate Heart

1. Fish have a 2 chambered heart = one atrium and one ventricle

2. Amphibians and reptiles have a 3 chambered heart = two atria and one ventricle

3. Birds and mammals have a 4 chambered heart = two atria and two ventricles

Fish Amphibian, Reptile Bird, Mammal

Fish Circulatory System

• Single loop circulatory system

1. Atrium collects blood from body

2. Atrium transfers blood to ventricle

3. Ventricle pumps blood to gills

4. Gills pick up oxygen and give off carbon dioxide

5. Blood travels to body cells and gives off oxygen and picks up carbon dioxide

Amphibian and Reptile Circulatory System

• Two loop circulatory system1. Right atrium collects low

oxygen/ high carbon dioxide blood from body

2. Left atrium collects high oxygen/ low carbon dioxide blood from lungs

3. Both atria empty into the common ventricle

4. Deoxygenated and oxygenated blood mix in ventricle and is pumped to body and lungs

Bird and Mammal Circulatory System

• Two distinct loops circulatory system

1. Right loop= pulmonary circulation

2. Left loop = systemic circulation

Deoxygenated blood is always kept separate from oxygenated blood Low O2

Low O2High O2

High O2

The Blood Vessels

• There are 3 types of blood vessels:

1. Arteries (and smaller arterioles)

2. Capillaries

3. Veins (and smaller venules)

Artery Capillary Vein

The Blood Vessels: ACV

Heart

Arteries Arterioles

Capillaries

VenulesVeins

Arteries and Arterioles

• Carry blood under pressure away from the heart towards the capillaries

• Middle tissue layer of arteries is thick smooth muscle

Lumen

Thick layer of smooth muscle

Arteries and Arterioles

• Smooth muscle contractions regulate blood flow and blood pressure in arteries

• Contraction of arteries and arterioles increases blood pressure

• Relaxation of arteries and arterioles decreases blood pressure

Capillaries

• Capillaries have cell walls one cell thick easy diffusion of molecules between blood in capillaries and cells in body

RBC

O2CO2

Capillary wallLumen

BodyCell

Capillary Bed

• While individual capillaries are small, capillaries form large capillary beds in tissues very large total area which slows down blood flow increases the rate of diffusion

Capillary Bed

Capillary Bed and Total Area

Blood Shunting in Capillary Bed

• Body regulates the flow of blood through capillary beds

• When precapillary sphincters are closed, blood is moved in bulk through a thoroughfare channel called the arteriovenous shunt

• This prevents diffusion between blood in capillaries and cells in tissue

Blood Shunting in Capillary Bed

• Example: after eating, precapillary sphincters in digestive system capillary beds are open while precapillary sphincters in muscle capillary beds are closed priority is for the blood to pick up the nutrient molecules from digestive system

Veins and Venules

• Veins (and smaller venules) drain blood from the capillaries and return it to the heart under low blood pressure

• Veins have the same tissue layers as arteries, but have less smooth muscle in the middle layer walls of a vein are thin in comparison to arteries

Veins and Venules

Smooth Muscle

Connective Tissue

Veins and Valves

• Theoretically, because veins are thin walled and blood pressure is low in veins, blood should tend to move slowly through the veins

• Actually, the flow of blood in the veins increases due to the presence of one-way valves in veins and skeletal muscle contraction around veins

Veins, Blood Pressure and Velocity

Cross-section of Vein

Summary of Blood Vessels

Artery Capillary Vein

Flow of Blood From heart to capillaries

Diffusion between capillary and body tissue

From capillaries to heart

Blood Pressure High Low Lowest

Smooth Muscle Layer

Thick None Thin

Valves None None Yes

Summary of Blood Vessels

Artery Capillary Vein

Total Cross-sectional area

Low High Low

Blood Velocity High Low High

The Human Heart

• The human heart weighs between 200 to 425 grams and is a little larger than the size of your fist

• The heart is located between your lungs in the middle of your chest, behind and slightly to the left of your sternum

• The apex of the heart is oriented to the left side of the body

LeftSide

RightSide

Left Side

Right Side

Lungs

Lungs

Heart

Diaphragm

Liver

Rat Dissection

Pericardium• A double-layered

membrane sac called the pericardium surrounds the heart

• The outer parietal pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spine, diaphragm, and other parts of your body

• The inner visceral pericardium is attached to the heart muscle

(myocardium)

Pericardium

• A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body

• This space between the visceral and parietal pericardium is the pericardial cavity

Myocardium• The major portion of the heart is composed of cardiac

muscle cells, collectively called the myocardium• Myocardium has a "stringy" look compared to skeletal

muscle• Striated skeletal muscle cells are large and lie next to

each other in more or less parallel bundles

Myocardium

• Cardiac muscle cells are small, butted together at their ends, irregularly shaped, and have numerous blood vessels (BV) between them

• Intercalated disks are specialized cell-to-cell adhesion/communications sites and are found only in cardiac muscle.

Heart Chambers

• Your heart has 4 chambers

• The upper chambers are called the left and right atria ( atrium, singular) and have protruding appendages called auricles

• The lower chambers are called the left and right ventricles

Heart Septum

• A wall of muscle called the septum separates the left and right atria and the left and right ventricles the right side of the heart is a pump for pulmonary circulation and the left side of the heart is a pump for systemic circulation

Left Ventricle

RightVentricle

Heart Valves

• The heart has two types of valves: atrioventricular valves and semilunar valves

• The tricuspid and mitral (or bicuspid) valves are atrioventricular valves

• They have fibrous strands called chordae tendineae on their leaflets that attach to papillary muscles located on the respective ventricular walls

• The papillary muscles contract during ventricular contraction and generate tension on the valve leaflets via the chordae tendineae to prevent the AV valves from bulging back into the atria no back flow

• The pulmonary and aortic valves are called semilunar valves and do not have chordae tendineae

Blood Flow Through the Heart• The right atrium receives

deoxygenated blood from the body via the superior and inferior vena cava

• Deoxygenated blood flows from the right atrium, across the atrioventricular tricuspid valve, and into the right ventricle

• The right ventricle contracts and pumps deoxygenated blood to the lungs via the pulmonary artery

• The semilunar pulmonary valve prevents back flow of the blood into the right ventricle

Blood Flow Through the Heart• Oxygenated blood returns to the

heart from the lungs via four pulmonary veins that enter the left atrium

• Oxygenated blood flows from the left atrium, across the atrioventricular mitral (or bicuspid) valve, and into the left ventricle

• The left ventricle has a very thick muscular wall so that it can generate high pressures during contraction

• Oxygenated blood from the left ventricle is pushed across the semilunar aortic valve and into the aorta for transport to the body

Human Circulatory System

Two distinct loops circulatory system

1. Right loop= pulmonary circulation

2. Left loop = systemic circulation

Deoxygenated blood is always kept separate from oxygenated blood Low O2

Low O2High O2

High O2

Heartbeat and Cardiac Cycle

• When surgically removed from the body, the heart will continue to beat for several hours provided it is supplied with the appropriate nutrients and salts

• This is possible because the heart possesses its own specialized conduction system and can beat independently even after being separated from its nerve supply

• The extrinsic (arising external to the heart) nerve supply coming from the nervous system serves to modify and control the intrinsic (inherent to the heart itself) beating established by the heart

Heart Conduction System

SA node

AV node Purkinjefibers

Inter-nodalFiber Bundle

AtrioventricularBundle

Heartbeat and Cardiac Cycle

• There are five basic components to the heart's intrinsic conduction system

• (1) sinoatrial node (SA node)

• (2) inter-nodal fiber bundle

• (3) atrioventricular node (AV node)

• (4) atrioventricular bundle

• (5) Purkinje fibers

SA Node

• The sinoatrial (SA) node is a small mass of specialized cardiac muscle situated in the upper dorsal surface of the right atrium

• Because the SA node is able to initiate each beat of the heart, it is often referred to as the pacemaker of the heart

• The excitation impulse occurs every 0.85 seconds approximately 72 times per minute

SA Node

• Excitation of the SA node sends a nerve impulse to: (1) the muscles of the atria causing them to contract (atrial systole) while the ventricles relax (ventricular diastole), and (2) the AV node along the inter-nodal fiber bundle

• Atrial systole takes 0.15 seconds of the 0.85 second cardiac cycle

AV Node

• From the SA node, inter-nodal fiber bundles conduct the nerve impulse to the atrioventricular (AV) node

• The AV node is located in the right atrium near the lower part of the interatrial septum

• There is a short delay in transmission of the impulse to the ventricles

• This is important because it permits the atria to complete their contraction and empty their blood into the ventricles before the ventricles contract

Purkinje Fibers• Once the nerve impulse leaves

the AV node, it enters specialized muscle fibers called Purkinje fibers

• Purkinje fibers permit a very rapid and simultaneous distribution of the nerve impulse throughout the muscular walls of both ventricles

• This results in a contraction of the ventricles that proceeds upward from the apex of the heart toward its base

• Ventricle contraction (systole) and atria relaxation (diastole) takes 0.30 seconds of the cardiac cycle

Purkinje Fibers

• Once the ventricles have contacted, there is a period of atrial and ventricular relaxation

• This recovery period occupies the final 0.40 seconds of the cardiac cycle

Cardiac CycleAtrialSystole

VentricularSystole

Atrial & VentricularDiastole

0.15 sec 0.30 sec 0.40 sec

Review of Cardiac Cycle1. The spontaneous generation of a nerve impulse within the SA node

represents the start of the cardiac cycle. This electrical impulse spreads throughout the atrial muscle and leads to contraction of the two atria.

2. As the atria contract, the AV valves remain open and blood is forced into the ventricles. The aortic and pulmonary semilunar valves remain closed, keeping blood in the ventricles.

3. After the atria have contracted and the ventricles have filled, the AV valves close.

4. The nerve impulse reaches the AV node, travels through the Purkinje fibers and the ventricles begin their contraction.

5. Ventricular contraction forces blood through the semilunar valves into the aorta and pulmonary arteries.

6. As the ventricles begin to relax, the aortic and pulmonary valves close, the AV valves open, and blood flows into the ventricles to begin another cycle.

Vascular Pathways

• The human heart has two pumps:

1) right atrium and ventricle pump deoxygenated blood from the body cells to the heart pulmonary circulation

2) left atrium and ventricle pump oxygenated blood from the lungs to the body cells systemic circulation

Major Blood Vessels

Arteries1. Aortabody2. Subclavianarms3. Carotidbrain4. Pulmonarylungs5. Mesentericintestines6. Renalkidneys7. Iliaclower body8. Femorallegs9. Cardiacheart

Veins1. Bodyvena cavae2. Armssubclavian3. Brainjugular4. Lungspulmonary5. Intestineshepatic

portal6. Liverhepatic7. Kidneysrenal8. Lower bodyiliac9. Legsfemoral10.Heartcardiac

Blood Flow

• Blood pressure, the pressure of blood against the wall of a blood vessel, keeps the blood moving through the circulatory system

• Blood pressure is measured with a sphygmomanometer, usually around the brachial artery in the arm

Blood Pressure

• Systolic pressure = the highest blood pressure in the arteries is reached when the ventricles contract

• Diastolic pressure = the lowest blood pressure in the arteries is reached when the ventricles are relaxed

Blood Pressure

• The ratio of systolic pressure to diastolic pressure is commonly referred to as “blood pressure”

• For the average human, “blood pressure” is 120 mm mercury systolic pressure to 80 mm mercury diastolic pressure 120/80

Blood Pressure and Velocity

Fetal Circulation

Fetal Circulation

• The developing human fetus has several features that are not present in adult human circulation

• These differences exist because the fetus is not using its lung for gas exchange

• Gas exchange for the fetus is accomplished by the mother via the umbilical blood vessels

Fetal Circulation Features

1. Foramen ovale = oval opening

Shunts blood from right to left atrium in order to bypass inoperable lungs

2. Ductus arteriosus = arterial duct

Shunts blood from right ventricle and pulmonary artery to aorta in order to bypass inoperable lungs

Fetal Circulation Features

3. Umbilical arteries carry low oxygen blood and waste from fetus to placenta

4. Placenta allows gas, waste and nutrient exchange between the mother and fetus

5. Umbilical veins bring high oxygen blood and nutrients from placenta to fetus

Fetal Circulation Features

6. Ductus venosus = venous duct

Shunts blood from umbilical vein and fetal liver to the inferior vena cava of fetus