Chapter 8- Transport In Animals Flashcards
What is the need for specialised transport systems in multicellular animals?
- High metabolic demands- diffusion over the long distances is not enough to meet the demands.
- SA:V ratio- gets smaller as organisms get bigger. Diffusion distances increase, amount of SA available reduced.
- Transporting molecules:
- hormones created in one place but needed in another.
- waste products of metabolism from cells to excretory organs.
- digested food from organ to every cell for use in respiration.
What is an open circulatory system?
- a circulatory system with a heart but few vessels to contain the transport medium.
- haemolymph is pumped straight from the heart through short vessels into the haemocoel of the animal.
- found mainly in invertebrate animals. (Insects)
- when heart relaxes, haemolymph is sucked back in via pores called ostia.
What is the haemocoel?
The large open body cavity of the animal.
- in the haemocoel the transport medium is under low pressure.
- comes into direct contact with the tissues and cells. This is where exchange (not gas) between the transport medium and the cells happens.
- in this cavity, haemolymph directly bathes organs and tissues, allowing diffusion.
- haemolymph moves around haemocoel due to movement of organism.
What is haemolymph?
Insect blood.
- doesn’t carry oxygen or carbon dioxide.
- transports food and nitrogenous waste products and the cells involved in defence against disease.
- it circulates but steep diffusion distances for effective diffusion cannot be maintained.
- the amount of haemolymph flowing to a particular tissue cannot be varied to meet changing demands.
What is a closed circulatory system?
The blood is enclosed in blood vessels and doesn’t not come directly into contact with the body cells.
- the heart pumps blood around the body under pressure and quickly and the blood returns directly to the heart.
- substances enter and leave the blood by diffusion through walls of blood vessels.
- amount of blood flow adjusted by widening/narrowing blood vessels.
- most contain a blood pigment that carries respiratory gases.
Where are closed circulatory systems found?
All vertebrate groups, including mammals.
- squid, earthworms, starfish
What is a single closed circulatory system?
Blood travels only once through the heart for each complete circulation of the body.
- blood passes through two sets of capillaries before returning to heart:
1. Exchanges oxygen and carbon dioxide.
2. Substances exchanged between blood and cells.
As a result of passing through 2 narrow vessels, blood pressure in system drops so blood returns slowly = limits efficiency so activity of animal is low.
Where can a single circulatory system be found?
In fish, however they are an exception to the fact of low activity due to the slow return of blood to the heart.
- they have an efficient single circulatory system so can be very active. Mainly due to countercurrent system allowing max uptake of oxygen from water.
- their body weight supported by water so don’t need to control body temp.
- this reduces metabolic demands and combined with effective gaseous exchange, allows activeness even with single closed circulatory system.
What is a double closed circulatory system?
Blood travels through heart twice for each circuit of the body:
1. Pulmonary circulation- Blood pumped from heart to lungs to pick up O and drop off CO2. Returns to heart.
2. Systemic circulation- blood flows through hear and is pumped out all around body before returning again.
Each circuit only passes through one capillary network so high pressure and fast blood flow can be maintained. (Most efficient transport system)
Where are double closed circulatory systems found?
In active land animals that maintain their own body temp.
Most mammals and birds.
What is the role of elastic fibres, smooth muscle and collagen?
Elastic fibres- composed of elastin. Can stretch and recoil, providing vessel walks with flexibility.
Smooth muscle- contacts or relaxes which changes the size of the lumen.
Collagen- provides structural support to maintain shape and volume of vessel.
What are the arteries?
- they carry blood away from the heart to the tissues of the body.
- carry oxygenated blood, except the pulmonary artery.
- blood is under higher pressure than in veins.
Structure of artery:
Tough outer layer(collagen) - muscle layer - elastic layer - endothelium- lumen.
-largest artery = aorta (highest pressure flow)
Explain the role of elastic fibres in artery walls?
- enable them to withstand force of blood pumped out the heart and stretch to an extent (due to collagen) to take larger volumes.
- in between contractions of the heart, elastic fibres recoil and return to original length. This helps even out the surges of blood to give a continuous flow.
- however you can still feel a pulse (surge of blood) as elastic fibres can’t completely eliminate it.
- endothelium (lining if artery) is smooth so blood easily flows over it.
What is the pulmonary artery?
An artery that carries deoxygenated blood from the heart to the lungs.
During pregnancy, carries blood to the umbilical artery, which carries deoxygenated blood from the fetus to placenta.
What are the arterioles?
- link the arteries and capillaries.
- have more smooth muscle.
- less elastin in walls than arteries as they have little pulse surge.
- can constrict/dilate to control the flow of blood into individual organs.
What is vasoconstriction and vasodilation?
Vasoconstriction- smooth muscle in the arteriole contracts, constricting the vessel, prevents blood flowing into a capillary bed.
Vasodilation- smooth muscle in arteriole wall relaxes, blood flows through into the capillary bed.
What are capillaries?
- microscopic blood vessels that link arterioles with the venules.
- form extensive network through all tissues.
- very small lumen. Red blood cells have to travel in single file.
- substances exchanged through capillary walls between tissue cells and blood.
- gaps between endothelial cells (make up capillary walls) relatively large. Substances pass out of capillaries into fluid surrounding cells from here.
- except capillaries in CNS. Have very tight junctions in between.
What blood do the capillaries carry?
-Blood entering the capillaries from the arterioles= oxygenated.
- by the time it leaves for the venules = deoxygenated.
Lungs and placenta= exceptions:
- deoxygenated blood enters capillaries, oxygenated leaves into venules.
How are the capillaries adapted for their role?
- provide a large surface area for the diffusion of substances into/out of blood.
- total cross-sectional area is greater than the arteriole supplying them, so rate of blood flow falls, allowing more time for exchange of materials by diffusion between blood and cells.
- walls = single endothelial cell thick = thin layer for diffusion.
What are the veins?
- carry deoxygenated blood away from body cells towards heart. Except pulmonary/umbilical vein.
- don’t have a pulse. Surges from heart pumping are lost as blood passes through the narrow capillaries.
- hold large reservoir of blood (60% of bloods volume at any one time)
- blood pressure very low compared to arteries.
- walls contain lots of collagen, little elastic fibre. Vessels have large lumen, and smooth thin lining (endothelium) for easy blood flow.
How is deoxygenated blood returned to the heart?
-deoxygenated blood flows from capillaries to venules to larger veins.
Finally it reaches the two main vessels, carrying deoxy blood back to heart:
- Inferior vena cava (from lower body parts)
-superior vena cava (from head+upper body).
The blood is under low pressure and needs to move against gravity so there are adaptations to help this.
What are venules?
- links the capillaries with the veins.
- very thin walls with a little smooth muscle.
- several venules join to form a vein.
What are the 3 adaptations to help deoxy blood flow from veins back to heart?
- most veins have one way valves (infoldings of inner lining)at intervals. If blood starts to flow backwards, valves close.
- many bigger veins run between the big,active body muscles. When they contract, they squeeze veins, forcing blood up towards heart. (Valves prevent back flow when muscles relax)
- breathing movements of chest act as pump. Pressure changes and squeezing actions move blood up.
What is the blood?
The main transport medium of the human circulatory system. Also considered a type of connective tissue.
- consists of plasma (a yellow liquid) which carries dissolved glucose, amino acids, mineral ions, hormones and plasma proteins.
- plasma =93% water. (Therefore Polar solvent)
- Has rbc(most) and wbc( least) and platelets.
- plasma makes up 55% of the blood by volume. (Rest is made up by stuff it carries^)
What are the main plasma proteins and their roles?
- Albumin- important for maintaining osmotic potential of blood.
- Fibrinogen- important in blood clotting.
- Globulins- involved in transport and the immune system.
What are platelets?
Aka thrombocytes
Fragments of large cells called megakaryocytes found in the red bone marrow.
- involved in clotting mechanism of blood.
- carried by the plasma in the blood.
Functions of the blood
- contributes to the maintenance of body temp. (Thermoregulation)
-Acts as a buffer, minimising pH changes.
Transport of: - oxygen to and carbon dioxide from respiring cells.
- digested food from small intestine.
- nitrogenous waste products from cells to excretory organs.
- hormones.
- food molecules from storage components to cells that need.
- platelets to damaged areas.
- cells/antibodies involved in immune system.
What is oncotic pressure?
The tendency of water to move into the blood by osmosis.
