Circulation: Hearts and Circulatory Plans

Vertebrate hearts

Acts as reservoir and pump

1-way valves to prevent backflow

What is the order of complexity of vertebrate circulatory systems?

Fish → Amphibian → Reptiles (non-crocodilian) → Mammals/Birds

Single-circuit circulatory system

Double-circuit circulatory system

Teleost circulatory plan

Teleost heart

2 contractile elements

Ventricle: larger pump, sends blood to gills

Atrium: collects blood and pumps, rapidly forces blood into ventricle

Teleost vs. Elasmobranch

Difference in arteriosus shape bulbus and conus

Air breathing fish

EX. Bowfin, lungfish, electric eel

Aire breathing organs include mouthparts, gut, and swim bladder

Oxygenated venous blood flows into systemic venous circulation, not arterial circulation

Circulatory plan of the air breathing Snakehead

Air breathing African lungfish

Atrium and ventricle partly divided

Conus arteriosus in partly divided

Shares similarities with both fish and amphibians

Internal carotid artery goes to the brain

Inner wall of lungfish lung

Flow of oxygenated blood in lungfish lung?

Oxygenated blood from lungs flows to left part of atrium and then into left part of ventricle, and then through ventral part of conus arteriosus into gill arches 3 and 4 (w/ no gills)

Flow of deoxygenated blood in lungfish lung?

Deoxygenated blood from tissues to right portions of heart chambers and then into gill arches 5 and 6 (w/ residual gills) and then to the lungs where it can oxygenate.

What does the ductus do?

Ductus provides a shunt to bypass lungs when the fish is not air breathing

Lungfish Heart X-ray

Opaque fluid injected into pulmonary vein

White areas show location of opaque fluid

Only arches 3 and 4 leading to dorsal aorta, carry oxygenated blood

Amphibian Heart

Amphibian heart anatomy

2 atria and 1 ventricle

Left atrium collects oxygenated blood from pulmonary circuit

Right atrium: collects deoxygenated blood from systemic circuit

Undivided ventricle: receives blood from both atria, little mixing due to spiral fold (valve)

Pulmonary Artery: sends blood to lungs and skin

Reptile Heart

Non-crocodilian heart

Ventricle partially divided

Blood flow similar to amphibians, except less to skin

During apnea (intermittent breathing), reduce blood flow to lungs

Crocodilian heart

4 chambers

Structurally different from birds and mammals

Two systemic aortas

Crocodilian ventricles

Delivers oxygenated blood to tissues and deoxygenated to lungs

Reduces pulmonary blood flow to lungs when lung air is oxygen depleted

Bird and Mammal Heart

Hearts of mammals and birds

Multichambered

Muscle tissue is formed from cardiac muscle, called myocardium

Left side has two chambers that receive and pump freshly oxygenated blood from the lungs to the rest of the body

Right side has two chambers that receive deoxygenated blood from the body and pump it to the lungs

What are the two distinct pumps of the avian/mammal heart?

Pulmonary pump = right

Systemic pump = left

Circulatory plan of mammals and birds

What are the advantages of a divided heart?

Can maintain 2 circuits at different pressures

Why have a divided heart?

Often harder to pump blood to the periphery than to the lungs

Endotherms need lots of blood delivery to support the high metabolism of tissues

Disadvantages of a divided heart

Need for a lymphatic system

Must coordinate

Capillaries

Pressure and fluid exchange

Capillary walls are semipermeable

Colloid osmotic pressure

Caused by protiens in blood

What is the net effect of ultrafiltration at capillaries? Where is excess fluid captured?

Loss of fluid

Excess fluid is captured by the lymphatic system

The conducting system and sinoatrial node

Depolarization of the 4-chamber heart

Contraction originates in SA node

Spreads through muscle of atria to AV node

Delay occurs

Atrioventricular bundle conducts contraction to ventricles

Cardiac output

Volume pumped per unit time

CO = HR * SV

What influences cardiac output?

Nervous system

Endocrine system

Autoregulation

Heart size vs. body size

Neither heart size nor stroke volume accommodate high metabolic demands of small endotherms

Elephant weights 3000kg, its heart weights 18kg and beats at a rate of 25bpm

Shrew weights 3g, its heart weights 0.18g and beats at a rate of 600bpm

Distribution of blood flow

Not equivalent throughout body: kidneys, liver, heart and brain make up 5% of body mass but get over 50% of cardiac output

Changes due to physiological condition: e.g., arousal (penis erection)

Changes due to environmental circumstances: e.g., temperature (vasodilation vs. vasoconstriction)

Changes during exercise

Effects of exercise on circulation

Changes distribution of blood flow

Increase oxygen extraction efficiency

Increase cardiac output

Increase ventilation (water loss)

Example: exercise in humans

At rest: muscles receive 1L blood/min, oxygen extraction 25%, cardiac output 5L/minute (avg: 70bpm, SV=70ml)

During exercise: muscles receive 20L blood/min, oxygen extraction 80-90%, cardiac output 25L/min (avg:200bpm, SV=100ml)

Example: pronghorn antelope

Top speed 100km/h

Can travel 11km in 10min w an avg speed of 65km/h

Fastest sustained runners on earth

Sustain running aerobically

Capable of using 3-5x as much oxygen as similarly sized mammals

How does a Pronghorn do it?

Oversized trachea, lungs, and heart

High cardiac output

Blood completely saturated with O2

High hematocrit (concentration of RBCs)