BIOL10004 Lecture Notes - Lecture 6: Desmosome, Haematopoiesis, Brainstem

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28 Aug 2018
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Why do animals need a circulatory system?
O2, nutrients and hormones must be transported around the
body to tissues and organs
Waste products must be removed
Temperature regulation & reproduction, etc.
Blood vessels perform these functions
Circulatory systems evolved as a consequence of higher levels of
activity and increased metabolic demands in more complex and
larger animals
Animals with a circulatory system?
- Mammals, insects
Animals without
- Sea anemone, bottom of ocean
Main Functions of Circulatory system:
1. They transport substances, including gases, nutrients, waste products, hormonal
messengers and red and white blood cells, throughout the body.
2. They transport heat between different parts of the body, for example, to or from the
external surface.
3. They allow transmission of force, which is used, for
example, for locomotion by many worms and molluscs
and reproduction in vertebrates.
Open Circulatory system
Open vessels
Cells bathed directly in blood plasma (haemolymph)
eg crab, beetle
Not specific to certain areas
1+ hearts pump fluid through vessels, open into
interstitial spaces (between cells), collects in larger
spaces (sinuses) and moves back to the heart
Circulated fluid is indistinguishable from interstitial fluid
Closed circulatory system
Blood remains in vessels
Extracellular fluid bathes cells
extracellular fluid now bathe the cells not the
blood, no direct contact
Limited exchange b/w blood and extracellular fluid
Blood and extracellular fluid are separate.
eg. earthworm, vertebrates
The circulated fluid, blood is enclosed in a system of
vessels and may be circulated more rapidly- interstitial
fluid directly surrounds body’s cells
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Better for larger active animals
- No oxygen in middle= limiting factor for
cellular respiration
Providing oxygen by convection
Convection is the bulk movement of
fluid
Movement of substances to or from
cells by diffusion is usually assisted by
convection
Convection is much faster than diffusion
Convection:
Blood in an artery : To move 1 metre= 5
sec
Blood in a capillary : = 17 min
Moves by convection
Diffusion
Oxygen in still water = 3 years
Diffusion in the lungs
Convection and Diffusion work together
In closed circulation, the convected blood is separated from the cells by the wall of the
blood vessels and by extracellular fluid, as follows:
- Note: diffusion across capillary wall into extracellular fluid, then into cells
The Heart powers convection of the blood
Metabolic energy (muscle)- to produce contraction
Energy in the blood
potential energy = pressure
kinetic energy = flow
Features of Heart
Hearts often have:
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Several chambers in sequence
first chamber pumps blood into second, etc.
Sequential contraction- coordinated of the atria and ventricles
One-way flow -> Valves- to prevent backflow, one direction only is very important, cause
familiar heart sounds when they close
Cardiac contraction cycle
Contraction
systole (pronunciation sis-toh-le)
expels blood
Cardiac muscle fibres need extracellular calcium entering the myocyte to initiate
contraction
Relaxation
diastole (pronunciation dia-stoh-le)- active relaxation
allows heart to refill with blood
More relaxation the more blood
Source of contraction
muscle - myogenic - pacemaker cells
nerves - neurogenic - nervous signals telling the heart to
beat
Vertebrate cardiac muscle
Specialised type of striated muscle
Actin and Myosin to contract
Electrical depolarisation -> contraction
Muscle cells interconnected -> intercalated discs
strong connections between muscle cells-
desmosomes
electrical connections gap junctions- small holes where they connect
Electrical connections between cells allow propagation of contraction
Pacemaker activity sinoatrial node (SAN)- initiated in right atrium
Blood Flow In Heart During Contraction Cycle-
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Document Summary

O2, nutrients and hormones must be transported around the body to tissues and organs. Circulatory systems evolved as a consequence of higher levels of activity and increased metabolic demands in more complex and larger animals. Cells bathed directly in blood plasma (haemolymph) eg crab, beetle. 1+ hearts pump fluid through vessels, open into interstitial spaces (between cells), collects in larger spaces (sinuses) and moves back to the heart. Circulated fluid is indistinguishable from interstitial fluid. Extracellular fluid now bathe the cells not the blood, no direct contact. Limited exchange b/w blood and extracellular fluid. The circulated fluid, blood is enclosed in a system of vessels and may be circulated more rapidly- interstitial fluid directly surrounds body"s cells. No oxygen in middle= limiting factor for cellular respiration. Convection is the bulk movement of fluid. Movement of substances to or from cells by diffusion is usually assisted by convection. Blood in an artery : to move 1 metre= 5 sec.

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