The Circulatory System

Why do mammals need mass transport systems?

Need oxygen and glucose to produce energy in aerobic respiration. Small organisms, e.g. bacteria, obtain this by diffusion bc of short diffusion distance. In multicellular, diffusion distance too large and slow.

What is an open circulatory system?

• Not enclosed in blood vessels

• E.g. insects → blood flows out of heart and into body cavity

What is a closed circulatory system?

• Blood is enclosed inside blood vessels

• e.g. All vertebrates

• Arteries take blood away from heart and towards organs. Substance move between bloodstream and tissues at capillaries

• Veins take blood from tissues back to heart

Waht is a single circulation?

• Blood travels in one loop → pass through heart once

• i.e. fish, heart pumps blood to gills, then body tissues, then heart

What is a double circulation?

• Blood travels in two loops

• Heart → lungs → heart → body

• 2 loops are known as pulmonary system (to lungs) and systemic system (to body)

What is the structure and function of arteries?

• Carry blood away from heart to organs

• Thick muscular wall, elastic tissues → cope with high pressure

• Endothelium is folded, withstand high pressure

• Small lumen

What is the structure and function of veins?

• Carry blood from organs to heart

• Lower pressure, so has large lumen and thinner walls

• Valves prevent blood from flowing back

What is the structure and function of capillaries?

• Connect arteries and veins

• Substances move out of blood to tissues, e.g. Oxygen, glucose, mineral ions. Waste products move out of tissues and into capillaries

• Small pores

• One cell thick

What happens at the arteriole end of the capillary in the formation of tissue fluid?

• Arteriole end of capillary → hydrostatic pressure in capillary exceeds that of tissue fluid

• Forces fluid and dissolved substances out of capillary down pressure gradient and into space around cells

• Forms tissue fluid

What happens at the venule end of the capillary in the formation of tissue fluid?

• Less water because it moved out of capillary at arteriole end

• Water potential lower inside capillary compared to tissue fluid

• Water moves back into capillary by osmosis down a water potential gradient

What happens to excess tissue fluid?

Drains into lymphatic system which eventually returns the fluid back into the bloodstream

What’s on the left side of the heart?

• Thicker wall

• Pulmonary vein

• Semilunar valve

• Aorta

• Deliver blood all around the body

• Carries oxygenated blood

Whats on the right of the heart?

• Pulmonary artery

• Atrioventricular valve

• Vena cava

• Carry blood to lungs

• Carries deoxygenated blood

What is atrial systole?

• Increase pressure in atria

• Atrioventricular valves open

• Blood flows into ventricles

What is ventricular systole?

• Increased pressure in ventricles

• Atrioventricular valves close

• Semi-lunar valves open

• Blood flows into arteries

What is diastole?

• Semi-lunar valves close

• Decreased pressure in veins and atria

• Blood flows into atria