Circulatory System - Single/Double

Circulatory System

• network of cylindrical vessels that emanate from a pump - the heart

In vertebrates what does the circulatory system circulate

• blood and lymph

Animals with no circulatory system

• Sponges and Cnidarians: circulate water through their body or through a gastrovascular cavity.

• sponges circulate ware through an incurrent pores and one excurrent pore

• Pseudocoelomate invertebrates use the fluids of the body cavity.

General Characteristics of a Circulatory System

• circulatory fluid - serves as a transport medium

• vascular system; system of tubes through which the transport medium can flow

• driving force; circulates the transport medium

Bulk/mass flow

method of transport in which an entire group of molecules is transferred from a region where they exert a large pressure to an area where of lower pressure - down a pressure gradient.

Open Circulatory System

• most invertebrates (Insects)

• heart pumps haemolymph through an aorta which branches into arteries, opening into a haemocoel - made up of series of open spaces called sinuses

• blood then collects back from the haemocoel and passes through ostia back to the heart

• fluid moves under low pressure (slow) facilitating efficient exchange of substances

Pros and cons of open circulation

• PROS:

  • less energy than closed circulation

  • moves slowly - efficient exchange

• CONS:

  • moves very slows (Ineffiecient for larger organisms)

Closed Circulatory System

• blood is pumped by a heart through vessels under a high pressure and then back to the heart

• all vertebrates and some invertebrates (echinoderms, cephalopod molluscs and annelids)

Advantages and Disadvantages of Closed Circulation

• ADVANTAGES

  • Distribution of blood can be regulated based on demand

  • faster transport of nutrients

  • supports higher levels of metabolic activity

• DISADVANTAGES

  • more energy than open circulation

COMPARISON between OPEN/CLOSED

OPEN	CLOSED
respiratory pigment if present is dissolved in plasma (no rbc)	respiratory pigment may be dissolved in plasma but most is in RBC
less efficient control of blood volume (cannot be regulated by contraction of vessel walls)	more efficient control (regulation by contraction/relaxation of smooth muscle cells lining blood vessels)
Blood moves at a slower rate and l.p	blood moves rapidly at h.p
exchange of gases happens between tissues directly	exchange of gas goes through capillary wall, then tissue fluid, then cell
blood is directly in contact with tissues	not directly in contact with cells (enclosed in vessels)

Single Circulation

• found in fish

• blood only passes through the heart once per circuit

• passes from heart to gills (oxygenated) then from gills to the rest of the body

• two chambered heart (only for deoxygenated blood)

Double Circulation

• system where blood travels through the heart TWICE per complete circuit of the body

• mammals, amphibians, birds, reptiles

• PULMONARY AND SYSTEMIC CIRCUIT

• deoxygenated blood goes to LUNGS via PULMONARY ARTERY, oxygenated blood comes back to HEART from PULMONARY VEIN, where it is then pumped to the rest of the body

Heart of Double Circulation Organisms

• must be divided in two to keep oxygenated and deoxygenated blood separate

• only mammals and birds show true 2x circulation

• amphibians show the beginning of it and reptiles have an almost completely divided heart

Comparison between Single/Double Circulation

Disadvantages of Single Circulation

• heart cannot pump at a high pressure

• reduced blood pressure in girlls

• slow rate of flow

• limited rate of delivery of oxygen and glucose to tissues

Advantages of Double Circulation

• blood enters lungs at a low pressure → more time for gas exchange

• heart pumps blood to rest of the body at a high pressure

Describe the heart in insects

• made of chambers separated by ostia where haemolymph enters the heart

• each chamber has alary muscles which pushes haemolymph toward the aorta

Describe the open circulatory flow in insects

• tubular heart pumps haemolymph to dorsal vessel

• fluid spills out into sinuses

• sinuses make up haemocoel where internal organs are suspended

• accessory pumps carry haemolymph to the appendeges

• ostia carry blood back to the heart when alar muscles are relaxed, back flow is prevented by valve-like structures

Rate of Haemolymph circulation is increased….

• during activity when the animal needs most nutrients for fuel

• its own movement ensures circulation

What does haemolymph transport

• nutrients

• OXYGEN IS INDEPENDENT OF CIRCULATORY SYSTEM

• WHY HAEMOLYMPH IS CLEAR NO HAEMOGLOBIN

Closed Circulatory System in Annelids

• Dorsal and Ventral Blood vessel

• 5 pairs of connecting vessles on the anterior end act as pumps

• pushed blood to ventral vessel → pumps blood posteriorly (to the behind) until it re-enters dorsal vessel

• smaller vessels from each of those 5 vessel pumps branch out to supply tissues of earthworm

Does earthworm blood contain haemoglobin

• yes but it is contained in the plasma not erythrocytes