Hearts in Different Vertebrate Groups Obj 12

The challenge of multicellularity• Being >2 cells thick creates problems for those on

the inside• How to breath? Eat? Get rid of waste?• Exchange calls for lots of surface area

• many tiny vessels• need a major mover

Functions of the circulatory system

• Supply metabolically active cells with food• Glucose, fats, amino acids• O2

• Remove wastes• Nitrogenous wastes• Metabolic H2O• CO2

• Others (homeostasis, immune response)

Planaria

• Aquatic, small, and high surface area• Receives O2 and releases CO2 by diffusion• No true circulatory system

Terrestriality and larger body size selected for adaptations for nutrient and gas transport

http://designmatrix.wordpress.com/2010/02/25/circulatory-systems/

Universal solutions

• Move stuff from where it is to where it isn’t• Circulatory system is transit• Respiratory system provides gas exchange

Fish: Simple Heart

This and following heart figures (unless otherwise noted) from http://bio1151.nicerweb.com/doc/class/bio1151/

Under Pressure?

Lungfish

A ‘sometimes’ circuit useful when no water

Lungfish photo credit: http://animals.howstuffworks.com/fish/lungfish-info.htm from Sadava, Life, pp. 1048-9

A commitment to lungs comes with a dedicated circuit

Amphibian:Increased Separation

Two aortas for a stop-and-go metabolism

Periods of low metabolism (no need to maintain constant body temp!!); option to skip the lungs

Reptiles: Bypass

Crocodilians:Better bypass

The underwater option: 4 chambers, lung-skipping

Croc vales ‘actively controlled’: not just resistive to backflow, can be ‘set’ open or closed. Why send blood to the lungs when there’s no air there?

http://www.iucncsg.org/pages/The-Crocodilian-Body.html

http://media.web.britannica.com/eb-media/62/117362-004-C401D1FD.gif

Why might hearts get fancier?“Four-fifths of a mammal’s food consumption is invested in keeping it warm. A reptile has much lower running costs – about one-tenth of the food needed by an endotherm of the same size”

The Book of Life, Stephen Jay Gould, ed. p. 129

Mammals, birds:Closed circuit

Full-blown compartmentalization

• Flight and body temp maintenance place huge metabolic demands on the system.

• Blocking all possibility of leakage (assuming development went well) means max delivery of deoxy blood to lungs; oxy blood to tissues.

Do the 4-chambered hearts of birds and mammals most likely represent common ancestry or convergent evolution?

Hearts…• Fish – 2-chambered. Why is this ‘okay’?

• Amphibians – 3-chambered. Why is this okay?

• Reptiles – 3-4-chambered; pretty well developed septum keeps blood separate.

• “Warm Bloods” – 4-chambered hearts

Questions on 13-15?• rbc – “no” organelles: nucleus, mitochondria,

ribosomes!, etc.

• Can’t divide and “make new cells”

• Yet, you produce over 2 million NEW rbc’s per second!!!

• “Short” life span ~ 100 days

• Takes about 30 seconds to circulate

Questions on 13-15?

HEMOGLOBIN!!

Hemoglobin• 250-300 MILLION per rbc• Made of four subunits (2 and 2)

Hemoglobin• 250-300 MILLION per rbc• Made of four subunits (2 and 2)• Hb in blood, MYOglobin in muscles• VERY similar molecules• Myoglobin binds

oxygen ‘better’

Hemoglobin vs Myoglobin• Myoglobin binds oxygen ‘better’

Obj 17 CO2 and O2• Why hemoglobin?• Let’s see what you remember…• Gaseous oxygen is O=O; chemically what does

this mean?• What is MOST of your blood?• Hb binds O2 so it can be carried• Carbon dioxide is O=C=O; same thing

Obj 17 CO2 and O2

• Hb doesn’t bind CO2 as well• But it combines with water (with enzymes

from rbc) to form carbonic acid• This WILL dissolve in blood• Lower pH DECREASES Hb’s ability to

bind O2!

Blood and your Brain

• Your ‘brain’ monitors blood pH• When it drops, respiration increases• Hyperventilation?

Back to Fetal Circulation…• If Hb binds oxygen, why would the mother’s

Hb give it up AT THE SAME POINT the fetus binds it?

• Different Hb!• Fetal Hb has a higher affinity for oxygen!

Back to Fetal Circulation…

Your turn• Obj 20

Homework• Obj 23 due tomorrow• Find diseases that are interesting to YOU!!!• Turn it in