Circulatory System of a Mammal

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Circulatory System of a Mammal
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The Blood System

• The general pattern of blood circulation in a
  mammal. Names are required only of the coronary
  arteries and of blood vessels entering and
  leaving the heart, liver and kidneys.
• The structure of arteries, arterioles and veins
  in relation to their function.
• The structure of capillaries and their importance
  in metabolic exchange.
• The formation of tissue fluid and its return to
  the circulatory system.

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Learning Objectives

• How do large organisms move substances around
  their bodies?
• What are the features of the transport systems of
  large organisms?
• How is blood circulated in mammals?

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Why do large organisms need a transport system?

• Increasing size decrease in the SA to Volume
  ratio.
• Can no longer rely on simple diffusion and need
  to develop specialist exchange surfaces
  these are linked to transport systems.

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Features of Transport Systems

• A suitable medium in which to carry materials.
• A form of mass transport in which the transport
  medium is moved around in bulk over large
  distances.
• A closed system of tubular vessels that contains
  the transport medium.

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Features of Transport Systems

• A mechanism for moving the transport medium
  within vessels.
• Muscular contraction of the heart or body
  muscles.
• Passive processes such as evaporation in plants
  (see later lessons).
• A mechanism to maintain the mass flow in one
  direction.
• A mechanism of controlling the flow of the
  transport medium.

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Transport System in Mammals

• A suitable medium in which to carry materials -
  Blood
• A form of mass transport in which the transport
  medium is moved around in bulk over large
  distances.
• A closed system of tubular vessels that contains
  the transport medium Blood vessels (arteries,
  veins and capillaries)

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Transport System in Mammals

• A mechanism for moving the transport medium
  within vessels - Muscular contraction of the
  heart
• A mechanism to maintain the mass flow in one
  direction valves
• A mechanism of controlling the flow of the
  transport medium heart rate, vasodilation,
  vasoconstriction

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Single Circulation e.g. fish
Blood passes through heart ONCE per complete
circuit
Blood pressure reduced as blood passes through
the gill capillaries - slows down flow to the
rest of the body Limits the rate of delivery of
O2 and nutrients to cells and removal of
waste Efficient for the level of activity of
fish but not mammals also fish do not maintain
their body temperature need to respire
relatively less compared to mammals
Double Circulation more efficient - e.g. mammals
Heart is composed of two separate pumps right
side pumps blood to the lungs to pick up oxygen
the blood is returned to the left side the left
side pumps oxygenated blood rapidly and at high
pressure to the body the blood is returned to
the right side Higher level of activity (energy)
and need to maintain their body temperature at
370C through respiration Need to deliver and
remove materials to and from cells rapidly
achieved by delivering blood at high pressure to
tissues. Pulmonary oxygenates blood removes
CO2 Systemic oxygenated blood from lungs pumped
rapidly at an increased pressure by the heart
Blood passes through heart TWICE per complete
circuit
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Questions

• Name the blood vessel in each of the following
  descriptions
• Joins the right ventricle to the capillaries of
  the lungs
• Carries oxygenated blood away from the heart
• Carries deoxygenated blood away from the liver
• The first main blood vessel that an oxygen
  molecule reaches after being absorbed from an
  alveolus
• Has the highest blood pressure

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Questions

1. State two factors that make it more likely that
   an organism will have a circulatory pump such as
   the heart.
2. What is the main advantage of the double
   circulation system found in mammals?

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Blood Vessels and their Functions
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Learning Objectives

• What are the structures of arteries, arterioles
  and veins?
• How is the structure of each of the blood vessels
  related to its function?
• What is the structure of capillaries and how is
  it related to their function?

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Blood Vessels

• Arteries Carry blood away from the heart
• Arterioles Control blood flow from arteries to
  capillaries
• Capillaries Link arterioles to veins
• Veins Carry blood towards the heart

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Structure of Blood Vessels

• Tough outer layer resists pressure
• Muscle layer can contract and control the flow
  of blood
• Elastic layer can stretch and recoil to
  maintain blood pressure
• Endothelium smooth layer to prevent friction
• Lumen not a layer a cavity

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Structure of Arteries

• Thick muscle layer control the flow of blood
• Thick elastic layer smooth surges from the
  heart
• No valves

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Structure of Arterioles

• Thicker muscle layer than arteries
• Thinner elastic layer than arteries
• No valves

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Structure of Veins

• Thin muscle layer
• Thin elastic layer
• Valves

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Structure of Capillaries

• No muscle
• No elastic
• No valves
• Thin layer of cells only

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Capillary Structure to Function

• Thin layer of cells short diffusion distance.
• Numerous and highly branched large SA for
  diffusion.
• Narrow diameter keep all cells close by.
• Narrow lumen bring RBC close to the cells
  short diffusion distance.
• Spaces between cells allow WBC to escape.

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Capillary endothelium large number large
surface area for exchange Wall - one cell thick
short diffusion distance Endothelium is
continuous throughout circulatory system
Capillary
Artery
Vein
Narrow lumen High pressure Highly elastic
expand and recoil Thick muscular wall to
withstand force more elastic fibres (recoil) No
valves (except aortic and pulmonary semilunar at
the start) Oxygenated blood from heart except
pulmonary artery to lungs Pulsatile blood flow
(expansion recoil) Pulse can be felt e.g.
wrist
Wide lumen Low pressure Thin wall - less elastic
and less muscular Valves (semilunar) prevent
backflow Deoxygenated blood to heart from tissues
- except pulmonary vein from lungs Non pulsatile
smooth flow of blood
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Tissue Fluid
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Tissue Fluid

• What is the role of tissue fluid?
• It is the fluid which allows the exchange of
  substances between the blood and cells
• What substances are found in tissue fluid?
• glucose, amino acids, fatty acids, salts and
  oxygen all delivered to the cells.
• carbon dioxide and other waste substances
  removed from the cells.

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Hydrostatic pressure
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Hydrostatic Pressure

• As the capillaries are narrower than the
  arterioles, a pressure builds up which forces
  tissue fluid out of the blood plasma
  hydrostatic pressure.
• This pressure is resisted by
• Pressure of the tissue fluid on the capillaries
  (from the outside)
• The lower water potential of the blood (caused by
  plasma proteins too large to leave the blood)
• Overall, pressure pushes tissue fluid and small
  molecules out of the capillary, leaving cells and
  large proteins behind ultrafiltration.

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Return of tissue fluid

• Most tissue fluid is returned to the blood plasma
  via the capillaries.
• Hydrostatic pressure at the venule end of the
  capillary is higher outside the capillary and
  tissue fluid is forced back in.
• Osmotic forces (resulting from the proteins in
  the plasma) pull water back into capillaries.
• Remaining tissue fluid enters the lymph vessels
  drain back into the veins close to the heart.

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Lymph System
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Lymph

• Lymph is moved by
• Hydrostatic pressure
• Contraction of body muscles (aided by valves in
  the lymph vessels)