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