Introduction to Organismal Biology (BIOL221) - Dr. S.G. Saupe; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe/

Animals Transport (Circulatory) Systems

I.  Functions

• transport nutrients, gases (carbon dioxide, oxygen), hormones (essentially a system to interconnect body cells and systems)
• maintain fluid balance
• removes wastes
• defense (blood; immune)
• distribute heat
• maintain pH
• homeostasis

II.  Types

A. No specialized system  

• hydra, flatworm, sponges
• unnecessary due to body plan (i.e., have a large S/V ratio)  
• central cavity � functions in digestion/transport (=gastrovascular cavity)
• e.g., sponges have multiple pores that "enable a sponge to bring seawater directly to all its cells, making it, in a sense, a multicellular animal trying to live a unicellular life." (Zimmer, 2000)

B.  Open System

• insects, arthropods, mollusks  
• no distinction between blood and interstitial fluids
• hemolymph = body fluid  
• heart(s) pump hemolymph around organs (hemocoel)
• disadvantages:  (1) can't selectively direct blood to sites of greatest need; (2) can't develop large enough pressure to pump through large organisms

C.  Closed System

• worms, squids, vertebrates
• heart pumps blood thru vessels
• pulmonary circuit - heart → lungs → heart (connects heart & lungs)
• systemic circuit - heart → body → heart (connects heart & body)
• advantages:  more rapid movement,  can selectively direct blood to needed tissues, support higher levels of metabolic activity; allowed/required for animals to get 'big'

III.  Cardiovascular systems

A.  General Vertebrate

1.  Heart

• atrium � receive blood from veins  
• ventricles � pump blood into arteries
• valves - separate chambers

2.  Vessels  

• arteries branch to arterioles  
• arterioles → capillaries  
• capillaries → site of chemical exchange between interstitial fluid and blood  
• capillaries → venules
• venules → veins
• veins → heart

B.  Fish

• single circuit
• two chambers - one atrium & one ventricle
• ventricle → gill capillaries → aorta → systemic capillaries → veins → atrium
• see diagram

C.  Amphibians (& most reptiles)

• 3 chambered heart (2 atria, 1 ventricle)
• amphibians also have absorption thru skin
• in frogs � some mixing of blood but a ridge in ventricles diverts most; in reptiles less mixing
• see diagram

D.  Birds & Mammals

• 4 chambered heart (2 atria, 2 ventricles)
• pulmonary circuit - right side; connects heart to lungs
• systemic circuit - left side; connects heart to body (systemic capillaries)
• see diagram

E.  Evolutionary Trend Summary

1.  increase in # chambers
2.  single →  double circuits
2.  full separation of atria and ventricles

• reduces mixing of oxygenated and deoxygenated blood
• increased exchange of blood gases
• venous and arterial system can operate at different pressures

IV.  Mammalian heart

A.  General

• fist sized  
• beneath breast bone  
• in sac (2 layer wall � pericardium)  
• lubricating fluid  
• cardiac muscle  
• atria � thinner, ventricles � thicker

B.  Cardiac Cycle � one complete heart beat

• sequence of filling and pumping  
• systole � contraction  
• diastole � relaxation  
• valves between atria and ventricles - atrioventricular (AV)  
• valves at exit of ventricles - semi-lunar  
• Heart sounds � closing valves;  lub dup  lub  dup  
• lub = blood against closed AV valves = ventricular contraction = systole
• dup = blood against semilunar valves = ventricular relaxation = diastole
• typical pressure 120/80 = systolic / diastolic  
• murmur - leakage thru valves

 V.  Control

A.  Heart cells

• "self excitable"  
• pulsate on own without external stimulus
• cardiac muscles - intercalary disks, electrical (gap) synapses

B.  Sinoatrial node (SA) or Pacemaker

1. maintains rhythms  
2. located wall of atrium (junction of rt atrium & superior vena cava)  
3. electrical impulse (like nerve)  
4. spreads quickly � cardiac cells connected � intercalary disks  
5. sets tempo � slowed by parasympathetic NS (noradrenaline);  sympathetic NS -speeds up  

C.  Atrioventricular Node (AV)

• between right atrium and right ventricle  
• delay signal approximately 0.1 sec ; allow atria contract & empty

D.  EKG � electrical activity pattern

• P � atria depolarize & contract  
• QRS � ventricle depolarize & contract  
• T � ventricle repolarize & relax

VI.  Vessels & Flow

A.  Parts

• endothelium � squamous inner  
• smooth muscle � middle  
• connective tissue � outer

B.  Flow & Size  

• rate of flow inversely related to diameter  
• smaller diameter = faster flow since volume of flow remains constant (think hose)  
• Paradox:  aorta 30 cm/s   capillaries 0.026 cm/s  
• Explanation � flow related to cross sectional area or total pipes delivering fluids � although individual capillaries narrow, collectively large area.

C.  Pressure  

• force on walls = blood flow (volume cardiac cycle) x resistance (blood viscosity, resistance)  
• artery > veins  
• systole > diastole  
• heat contracts → blood enters arteries faster than exits → vessels stretch (systole) → arteries elastic, snap back → heart contracts before completely empties (diastole) →  therefore, always pressure  

VII.  Blood Flow

A.  Veins

• little pressure  
• veins sandwiched between muscles which pinch and squeeze blood  
• values - insure one way flow
• varicose veins - back flow on valves  

B.  Capillary Beds

• smooth muscle in wall of arterioles  
• contracts → constricts → blocks flow  
• sphincters � rings of smooth muscle at entrance of capillary bed

C.  Capillary Exchange

• exo/endocytosis  
• diffusion (i.e., carbon dioxide, oxygen)  
• bulk flow (pressure gradient)