circulatory systems Flashcards
single circulatory system
blood only passes through the heart once for each complete circuit of the body
e.g. fish
double circulatory system
the blood passes through the heart twice for each complete circuit of the body
e.g. mammals
closed circulatory system
blood is enclosed inside blood vessels
e.g. all vertebrates
open circulatory system
blood isnt enclosed inside blood vessels all the time- it flows freely through the body cavity
e.g. invertebrates (some insects)
why are specialised transport systems needed in animals
- high metabolic demands so diffusion over long distances is not sufficient
- small SA:V ratio
- hormones/enzymes may be made in one place but needed in another
- food digested in one organ system but needs to be transported to every cell
- waste products of metabolism need to be removed from cells and transported to excretory organs
elastic fibres in blood vessels
- elastin
- stretch or recoil
- provides blood vessel walls with flexibility
smooth muscle in blood vessels
- contracts or relaxes
- changes size of lumen
collagen in blood vessels
- provides structural support to maintain shape and volume of vessel
arteries
- carry blood away from the heart
- carry oxygenated blood (except from pulmonary artery)
- walls are thick, muscular. elastic tissue can stretch/recoil to help maintain high pressure
- smooth muscle
- endothelium is folded- allowing expansion
arterioles
- arteries branch into arterioles
- more smooth muscle- expand/contract–> constricts vessel nd prevents blood flowing into capillary bed
(vasoconstriction/vasodilation) - less elastic tissue
capillaries
- smallest blood vessels
- link arterioles and venules
- substances are exchanged between blood and cells
- large SA
- rate of blood flow falls from arterioles to capillaries
- single endothelial cell thick walls
veins
- take blood back to the heart under low pressure
- carry deoxygenated blood (except from pulmonary veins)
- wider lumen
- little elastic/muscle tissue
- lots of collagen
- valves to prevent backflow
- muscle contractions help squeeze the veins - forcing blood towards the heart
where does blood come from in the inferior vena cava
lower parts of body
where does blood come from in the superior vena cava
head and upper body
venules
- link capillaries with veins
- venules join together to form veins
- very thin walls- just a little smooth muscle
contents of blood
plasma:
- glucose, amino acids, mineral ions, hormones, proteins
- RBCs
- platelets
functions of blood
- O2,CO2 to/from respiring cells
- digested food from small intestine
- nitrogenous waste products from cells to excretory organs
- chemical messages
- food molecules from storage compounds to organs that need them
- platelets to damaged areas
- cells/antibodies involved in immune response
tissue fluid
- fluid that surrounds cells in tissues
- made of substances that leave the blood plasma (e.g. O2,H2O, nutrients)
- no RBC or big proteins as they are too big to fit through capillary walls
- cells take in O2, nutrients from tissue fluid and release metabolic waste into it
pressure filtration
- when substances move out of capillary beds into the tissue fluid
arteriole end of capillary bed: - higher hydrostatic pressure in capillaries than in tissue fluid (4.5kPa)
- so fluid is forced out of capillaries to fill spaces between cells, forming tissue fluid
venule end of the capillary bed: - hydrostatic pressure decreases (2.3kPa)
- plasma proteins conc. increases
- high oncotic pressure (-3.3kPa)
- water potential decreases- lower than tissue fluid so water re-enters capillaries by osmosis
hydrostatic pressure
- the pressure exerted by a liquid
- due to the surge of blood that occurs every time the heart contracts
oncotic pressure
- the tendency for water to move into the blood by osmosis (-3.3kPA)
Lymph
- some tissue fluid does not return to capillaries
- it gets returned back to the blood by the lymphatic system
- excess tissue fluid passes into lymph vessels
- valves in lymph prevent backflow
- lymph moves towards the main lymph vessels in the thorax where it is returned to the blood
