Lecture 15- circulation, gas exchange, thermoregulation

Introduction

• all organisms must exchange materials between cells and environments

• many of them use circulatory system to distribute those materials throughout the body

• to obtain and transport 02 and C02

• diffusion is used to facilitate this exchange

Diffusion review

movement of molecules from a high concentration to a low concentration and consists of a movement between both solute and solvent molecules

Circulation via diffusion

• diffusion works well for short distance circulation

• body plan diffusion: thins, holes, small is in platyhelminthes, porifera, and cnidaria

• complex: Mollusca, annelida, arthropoda, echinodermata, chordata

• no specialized circulatory system: porifera, cnidaria, platyhelminthes, nematoda

• Porifera has a high SA/V ratio (porous)

Thin in one dimension

• cnidaria: GVC involved

• platyhelminthes: GVC involved

• nematoda

Nematoda

• no circulatory system

• yet they are too complex/large so rely on diffusion alone

• Circulating materials: body movements because they’re pseudocoelomate

Specialized circulatory system

circulation: brings fluid from site of exchange to all other cells of body

Basic components of circulatory system

1. circulatory fluid: blood in closed circulatory system (can include fluid within or hemolymph)

hemolymph: in open system, no distinction between blood and interstitial fluid (body fluid between cells)

2. interconnecting tubes (vessels)

3. muscular pump

Open circulatory

• circulatory fluid bathes the organ directly, allowing exchange between hemolymph and body cells

• mollsuca (bivalve and gastropods), arthropoda, echinodermata

• when heart contracts: it pumps hemolymph through arteries out (arteries= away) into body sinuses

• when heart releases: it draws hemolymph into circulatory system through pores (Ostia)

• body movements that squeeze the sinuses help circulate the hemolymph

Closed circulatory

• circulatory fluid circulates to and from heart through a series of vessels

• Mollusca (cephlapods), annelida, chordata

• one or more “hearts” pump blood into large vessels that branch into smaller ones that penetrate the organs

• materials are exchanged by diffusion between blood and interstitial fluid bathing the cells

Evolutionary advantages of open circulatory

• more efficient for animals with rigid body covering where it deflects circulating fluid back toward the heart

• more suited for animals with a slower metabolism and smaller body

• low hydrostatic pressure in system: less energetically cavity

Evolutionary advantages of closed circulatory

• more efficient using less food for higher and faster levels of distribution

• oxygenated blood reaches body extremities faster allowing animals to move, digest, and eliminate wastes more rapidly

• suited for larger and/or more active animals

Vertebrate circulatory system

• atria: chambers that receive blood entering the heart

• ventricle: chambers that pump blood out of the heart

• arteries: carry blood away from the heart to organs

• veins: carry blood into/toward the heart

• capillaries: small vessels that penetrate tissues where diffusion of gases and chemicals take place

Single circulation

• sharks, rays, bony fishes

• blood passes through body and returns to the heart in a singe loop

• 2 chambered heart: 1 atrium and 1 ventricle

• blood is pumped: body→atrium→ventricle→capillaries in gills (gas exchange)-?body

Double circulation

• amphibians, reptiles, birds, mammals

• pumps for 2 circuits, serve different tissues, but are combined in a single organ (heart)

• first circuit (right side): pumps 02 poor blood to capillary beds in lungs for gas exchange

• second circuit (left side): pumps 02 rich blood throughout the body

Heart evolution in chordata

The more heart chambers the greater the ability to thermoregulate and sustain muscle movement

Respiratory pigments

• proteins that circulate within circulatory fluids (hemolymph/blood)

• transport most of 02 too body tissues and organs

• increase the amount of 02 to body tissues and organs

• increase the amount of 02 that can be carried by circulatory fluid

Gas exchange

• absorption of 02 and release of C02 is essential for cellular respiration

• gas exchange across respiratory surfaces takes place by diffusion (surfaces have high SA/V, thin, and moist)

• obtaining 02 from H20 requires a greater efficient than air breathing, the lower 02 concentrations in water than in air

• respiratory surfaces vary by animal and can include skin, gills, trachea, and wings or a combination of these

Without specialized respiratory surfaces

• porifera, cnidaria, platyhelminthes, nematoda

• shaped in a way to facilitate diffusion

• used no specialized structures

• each cell diffuses gases with the environment

Respiratory surfaces: skin

• in annelida and chordata (amphibian and some reptiles)

• dense network of capillaries just below the skin

• skin must remain moist so live in moist terrestrial or aquatic areas

Respiratory sufraces: gills

• in annelida, arthropoda, echinodermata, aquatic chordata

• outfoldings (evagination) of the body surface

• creates a large surface area for gas exchange

• dense network of capillaries in gills

• aquatic animals move through water or move water over their gills for ventilation

• ventilation moves the respiratory medium over the respiratory surfaces

Gills in fish

• fish gills use a counter current exchange system so blood flows in opposite direction to water passing over the gills

• blood is always less saturated with 02 than water it meets

• removing more than 80% of the waters dissolved 02

Respiratory surfaces: tracheal system

• terrestrial arthropoda

• network of air tubes branched throughout the body supplying 02 directly to body cells

• largest tubes open to the environment

• invaginated system

• does not require circulatory system participation for gas exchange

• efficient gas exchange for flying insects

Respiratory surface: lungs in chordata

• infolding (invagination) of body surface

• circulatory system transports gases between lungs and the rest of the body

• size and complexity of lungs correlate with animals metabolic rate

• breathing ventilates the wings by the alternate inhalation and exhalation of air

Breathing in lungs

• positive pressure breathing: creates high pressure in mouth, forcing air down into trachea and found in amphibians such as frog

• negative pressure breathing: diaphragm creates low pressure within lungs, pulling air into lungs and in mammals

• whatever the mechanism, the results is the same

• a pressure gradient is created and air flows into the lungs

• birds have air sack that function as bellows that keep air flowing through the lungs

• air passes through the lungs in one direction only

• requires cycles of inhale and exhale

• ventilation in birds is highly efficient

Thermoregulation

• regulator: use internal mechanisms to control internal conditions despite external changes

• maintain homeostasis (constant internal environment)

• conformer: internal condition changes with external changes

• endothermic: animals generate heat by metabolism (physiologically), birds and mammals, energetically more expensive

• exothermic: more efficient, animals gain heat from external sources only (behaviorally), most invertebrates, fishes, amphibians, and nonavan reptiles

Thermoregulation adaptations

• insulation: at body surface and beneath, is adjustable

• circulatory: regulate blood flow near body surface, countercurrent heat exchange (bird and mammals)

• cool body using evaporation

• behavioral responses: seeking warm environments (sunlight), social behavior (invading), shivering

• ability to acclimate: endotherms: acclimate in physical level, ectotherms: acclimate on cellular level