BIO 012 Lecture Notes - Lecture 21: Sea Anemone, Capillary, Osmotic Pressure
12 Jun 2018
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Bio – Chapter 50
50.1 Why do Animals Need a Circulatory System?
Circulatory System:
- Muscular pump (heart)
- Fluid (blood) – some organisms use blood, but some have just fluid
- Coduits through hih fluid oes essels does’t alas hae
to move through vessels
Purpose?
- Transport stuff
o Oxygen, hormones (chemical messengers), nutrients, immune cells, waste (CO2),
heat transfer around body → due to good circulation of blood (heat in→
capillaries at surface close, vs. heat out → capillaries at surface open so you can
sweat)
Types of Circulatory Systems
- No Circulatory System
o Single-celled organisms
▪ Direct exchange with environment
• Direct diffusion with things outside to inside
▪ Usually aquatic or moist soils
• Nutrients need to be dissolved in liquid (aquatic of
moist soils) so that they can pass easily across the
membrane and into their cells → do’t eed to
have circulatory system to do this
o Multicellular organisms
▪ Small, thin – most cells in close contact with water
▪ Larger organisms with gastrovascular cavities
• Brings external environment in through gut
• Ex: sea anemone, flatworm
What theme do you see already as an evolutionary pressure to develop circulatory systems?
Bigger organisms and non-aquatic organisms have more cells. All of these cells must have
access to nutrients and therefore develop a complex circulatory system to help.
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Types of Circulatory Systems continued:
Open Circulatory System
- Heart moves hemolymph through vessels
- Fluid leaves vessels, filters through tissues
o Muscle movement required to further aid circulation
- Circulation
o Re-enters vessels/heart
▪ There is a relationship between how much fluid needs to be moved compared
to how much the pump can pump.
o Gas transport is not always needed
- Who has this system?
o Arthropods like grasshoppers.
▪ Hemolymph returns to heart through ostia
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▪ Ostia have 1 - way valves → hemolymph can only flow in.
▪ Heart expands so ostia valve opens, and hemolymph comes in
o Organisms like crabs and some mollusks
▪ Arteries and veins exist; do not connect because there are no capillaries to
connect it
Closed Circulatory System
- Blood kept separate from interstitial fluid
- Pumped by 1 or more hearts
o Example: earthworms have 5 hearts
- Some things can diffuse out of blood, but many stay in vessel system
Advantages of a Closed System
- Fluid moves more quickly through vessels than tissues (important in helping transport
nutrients, and gas exchange) (moves quicker through tubes than through open space of the
tissues)
- Can change diameter of vessels to control flow of blood to tissues and organs
- Specialized cells and large molecules that aid in transporting hormones and nutrients can stay
in vessels but drop their cargo
If losed sstes are etter, h hae ope sstes?
- A ope sste is’t ad / there are osts ad eefits to oth. Eer trait has a
positive and a negative to it based on selection pressures.
- Posistie to Ope: Orgaiss ith ope sstes do’t rel o irulator sstes for gas
exchange
o Gas exchange relies on a concentration gradient, and the only way to get it to
move from blood to tissue is to make sure one has a higher concentration than
the other. If ou do’t eed the irulator sste to do gas ehage, the this
does’t atter. Orgaiss ith ope sstes are saller ad hae holes o
them so gas can move in and out of their bodies.
- Negative to Closed: When you use the circulatory system to move things around you have
issues with pressure drops when gas exchange organ is added. When you have an organ
that picks up the gases, you use capillaries, and every time you go through that organ you
lost a lot pressure that the heart creates to get gas through that system.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Fluid (blood) some organisms use blood, but some have just fluid. Co(cid:374)duits through (cid:449)hi(cid:272)h fluid (cid:373)o(cid:448)es (cid:894)(cid:448)essels(cid:895) (cid:894)does(cid:374)"t al(cid:449)a(cid:455)s ha(cid:448)e to move through vessels. Bigger organisms and non-aquatic organisms have more cells. All of these cells must have access to nutrients and therefore develop a complex circulatory system to help. Fluid leaves vessels, filters through tissues: muscle movement required to further aid circulation. Circulation: re-enters vessels/heart, there is a relationship between how much fluid needs to be moved compared to how much the pump can pump, gas transport is not always needed. Pumped by 1 or more hearts: example: earthworms have 5 hearts. Some things can diffuse out of blood, but many stay in vessel system. Fluid moves more quickly through vessels than tissues (important in helping transport nutrients, and gas exchange) (moves quicker through tubes than through open space of the tissues) Can change diameter of vessels to control flow of blood to tissues and organs.
