Circulatory Systems

Natural Selection - 2 solutions for slow diffusion and exchange of materials

• body shape and size that keeps cells in direct contact with the environment

• circulatory system to move fluid between the cells immediate surroundings and the tissues where gas exchange occurs

Distribution without a circulatory system

• flat body enhances diffusion by increasing the surface area and minimizing diffusion distance

• use cilia, flagella, gastrovascular cavities… to circulate substances

Circulatory System Components

• circulatory fluid

• set of interconnecting vessels

• muscular pump (the heart)

Circulatory System Purpose

• exchange gases

• absorb nutrients

• transport hormones, immune cells…

• dispose of wastes

Open Circulatory Systems

• contains vessels that are not entirely enclosed

• no clear division between plasma and interstitial fluid

• generally hemolymph that circulates through blood vessels

• bathe organs directly

Organisms with Open Systems

• anthropods

• most molluscs

• some annelids

• some invertebrate chordates

Closed Circulatory Systems

• blood transported through closed vessel

• more pressure

Capillaries

so small that red blood cells have to go through single file

• blood vessels squeeze the cells as they go through

• lots of exchange occurs here

Advantages of Closed Circulatory Systems

• more efficient at transporting circulatory fluids to tissues and cells (high pressure)

• distribution of blood flow can be regulated

  • can send different amounts of blood to specific places

Disadvantages of Closed Circulatory Systems

• energetically expensive

Closed Circulatory System Components

Heart

• two or more muscular chambers

Blood Vessels

• Arteries, Capillaries, Veins

Atria

receive blood

Ventricles

pump blood out of the heart

Arteries

carry blood away from the heart

Veins

carry blood towards the heart

Closed Circulatory System - Single Loop

blood passes through the heart once in each complete circuit

Closed Circulatory System - Double Loop

blood passes through the heart twice

• blood moving from the heart to the rest of the body (systemic route)

• blood moving from the heart to respiratory organs (pulmonary circuit)

Evolution from Single to Double Circulation

fish → amphibians → reptiles → mammals or birds

Circulation in fish

• single circulation

  • blood passes through the heart once in a circuit (no division between pulmonary and systemic circuits)

• Blood passes through capillary beds before returning to the heart

Benefits of Single Circulation in Fish

• doesn’t take much energy

Limitations of Single Circulation in Fish

• heart needs to pump with enough force to pump blood through two capillary beds

• heart receives oxygen-poor blood

Fish Circulatory System Parts

• Sinus Venosus

  • pacemaker, weakly contractile

• Atrium

  • weakly contractile, used to fill ventricle

• Ventricle

  • main propulsive force

• Bulbus Arteriosus (conus arteriosus in cartilaginous fish)

  • extension of ventricle

Amphibians Circulatory System

• incomplete separation of pulmonary/systemic circuits (beginning of double circulation)

  • blood passes through the heart twice

Benefits of Incomplete Separation in Amphibians

• allows for shunting of blood depending on of they’re on water or land

  • don’t waste energy on blood for the lungs when they’re underwater not using the lungs

Limitations of Incomplete Separation in Amphibians

• Still some mixing of blood in ventricle

Two Circuits

• Pulmonary Circuit

  • heart → respiratory organs → heart

• Systemic Circuit

  • heart → rest of body → heart

Amphibian Circulatory System Parts

• three-chambered heart

• two separate atria

  • left receives blood from respiratory organs

  • right receives blood from rest of the body

• one ventricle

  • partial separation of oxygen-rich and oxygen-poor blood

Reptiles Circulatory System

• Almost complete separation of pulmonary and systemic circuits

  • blood passes through the heart twice and there is more division of the ventricle

Benefits of Almost Complete Separation in Reptiles

• more separation of oxygen-rich and oxygen-poor blood

• still opportunities for shunting

Shunting

Blood enters the bloodstream without passing through functioning lung tissue

Limitations of Almost Complete Separation in Reptiles

• still some mixing of blood

Reptiles Circulatory System Parts

• left and right atria

• one ventricle divided into 3 chambers

• left atrium → cavum arteriosum → body

• right atrium → cavum venosum → cavum pulmonale → lungs

Crocodiles Circulatory System

• completely separated ventricles

  • don’t have complete double circulation because of a link between the right and left systemic aortae (foramen of panizzae)

Birds and Mammals Circulatory System

• Double circulatory system

  • blood passes through the heart twice with complete double circulation

Benefits of Double Circulation in Birds and Mammals

• allows for more oxygenation of tissue

  • important in endotherms that use a lot of oxygen to generate heat

Limitations of Double Circulation in Birds and Mammals

• takes a lot of energy

Mammals and Birds Circulatory System Parts

• four-chambered heart with 2 atria and 2 ventricles

  • left atria and ventricle receive oxygen-rich blood

  • right atria and ventricle receive oxygen-poor blood

What Would Happen if Systemic and Pulmonary Circuits were not Divided

pressure would also rise in the pulmonary circuit

• pulmonary edema = fluid in the lungs = drowning

Blood Flow Through Mammalian Circulatory System

lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → systemic aorta → body

body → superior and inferior venae cavae → right atrium → tricuspid valve → right ventricle → pulmonary arteries → lungs

Systemic Pressure

blood pressure

Valves

prevent backflow of blood

Atrioventricular Valve Names

Right - tricuspid
Left - bicuspid

Chordae Tendineae

prevent atrioventricular valves from being pushed into atria

• attached to papillary muscle

Cardiac Cycle

from the beginning of one heartbeat to the beginning of the next heartbeat

• one contraction and one relaxation of cardiac muscle

• atria contract first, then ventricles

Systole

contraction of the heart

• systolic pressure (blood pressure during contraction)

Diastole

relaxion of the heart

• diastolic pressure (blood pressure during relaxation)

Cardiac Cycle - Contractile Events

1. Late Diastole: both sets of chambers are relaxed and ventricles fill passively

2. Atrial Systole: atrial contraction forces a small amount of additional blood into ventricles

3. Isovolumetric Ventricle Contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves

4. Ventricular Ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected

5. Isovolumetric Ventricular Relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cusps of semilunar valves and snaps them closed

Cardiac Output

the volume of blood pumped by the heart in one minute

• heart rate X stroke volume

Stroke Volume

volume of blood pumped by the left ventricle per heart beat