FY0012: Circulatory Systems I, University Presentation

Circulatory Systems Overview

FY0012:

Learning Objectives

By the end of this session, you should be able to describe:

• Why circulatory systems are necessary
• The different types of circulatory systems in animals
• The features of a circulatory system
• The formation of tissue fluid

Why Circulatory Systems are Necessary

Organisms become too big and too thick
to rely on diffusion

Fick's Law

Rate of diffusion of Surface area x Concentration gradient
Diffusion distance

Types of Circulatory Systems

• Open
• Closed
• Single
• Double

Open Circulatory System

• Blood (haemolymph) leaves vessels to go into tissue spaces
• Blood and interstitial (tissue) fluid are mixed
• Blood is pumped by the 'heart' into an open space or haemocoel and
  returns through ostia (spaces)
• In some animals, the heart is a blood vessel which pulses
  haemolymph through the body by muscular contractions
• Fluid in the haemocoel bathes internal organs and delivers nutrients

Heart
1
Valves
Tissues

Open Circulatory System Characteristics

There are no arteries to maintain high pressure of the haemolymph, so blood
pressure is very low.
Organisms with an open circulatory system typically have a relatively high
volume of haemolymph and low blood pressure.

• Examples include arthropods e.g. insects, spiders and crabs

Open Circulation Advantages

It requires less energy for distribution than a closed circulatory system

Open Circulation Disadvantages

Since there are no arteries, blood pressure remains low, and oxygen takes longer to
reach the body cells.
Organisms with an open circulation have a lower metabolism and tend to be less
active
There are limits to the size that an organism can reach

Closed Circulation

Blood and interstitial (tissue) fluid are separate, with blood remaining in vessels
Blood is pumped by the heart into high-pressure vessels and small thin vessels
The small thin vessels provide a large surface area and short diffusion distance
allowing exchange of fluid
The volume of blood remains relatively consistent
Tissue fluid bathes all cells
The main functions of the system are gas exchange, hormone and nutrient
distribution, and waste elimination.
Found in all vertebrates

4
Heart
Interstitial
fluid
Small branch vessels
in each organ

Closed Circulation Advantages

• A closed system operates with a much higher blood pressure, allows tall
  organisms to stand up!
• It is more efficient in that it uses less blood for even higher and faster levels of
  distribution.
• Allows a higher metabolic rate
• Due to the efficient distribution of antibodies, immune responses are stronger,
  helping the body to fight off infection more effectively.

Comparison of Open and Closed Circulatory Systems

Heart
Closed Circulatory
System
Capillaries
Heart
Haemocoel
Open Circulatory
System

Types of Circulatory System: Single Circulation

Single
Blood flows once around the heart for once around the body
No separation between oxygenated and deoxygenated blood
No difference in pressure

• Example, fish

Gill capillaries
Artery
Heart:
Ventricle (V)
Atrium (A)
-Vein
Systemic capillaries

Double Circulation

Blood flows twice around the body for once around the heart
Separation of pulmonary and systemic circulation
Allows for higher oxygenation of blood leaving the pulmonary
circulation
Also allows for the differentiation of blood pressure

Lung capillaries
Pulmonary
circuit
A
-A
V
Right
-V
Left
Systemic
circuit
Systemic capillaries

Heart
Next session

Layers of Blood Vessels

The central lumen is surrounded by

• Tunica intima
• Tunica media
• Tunica externa or adventitia

Blood Vessels: Arteries

Arteries
Small lumen -relatively
Thick muscular wall
Elastic tissue
Collagen layer
Lumen
Collagen
Fibres
Folded
Endothelium
External Elastic
Membrane
Internal Elastic
Membrane
Smooth
Muscle
Elastic
artery
Tunica
externa
Muscular
artery
Tunica
- externa
Arteriole
Tunica
- externa
Tunica
Tunica
media
media
Tunica
intima
intima
Tunica
intima
Tunica
media
media

Delving Deeper - The Arterial Wall

The lumen in arteries is small relative to the thickness of the wall -
this is true even in the case of the aorta
The inner layer consists of the Tunica intima consists of epithelium and
connective tissue
Squamous cell epithelium
(
Endothelium
· Releases chemicals called endothelins that cause
constriction of the smooth muscle within the walls of the
vessel to increase blood pressure
· Is a corrugated - why?
· Smooth- why?
Tunica externa
Tunica media
- Tunica intima
Smooth muscle
Internal elastic
membrane
Vasa vasorum
External elastic
membrane
Nervi vasorum
Endothelium
Elastic fiber
tunka
medi
external
elastic
amina
internal
elastic
lamina
tunica
Cadventitia
Beneath the epithelium is a basement membrane- joins the capillary to the connective tissue

Arterial Wall - Tunica Intima Continued

An internal elastic lamina
- LAYER
Most noticeable in elastic arteries ( nearest the heart)- gives structure and
allows stretch
Contains pores or fenestrations to allow movement of substances between layers
Tunica externa
Tunica media
Tunica intima
Smooth muscle
Internal elastic
membrane
Vasa vasorum
External elastic
membrane
Nervi vasorum
Endothelium
Elastic fiber

Artery Wall: Tunica Media

Tunica media
Made of smooth muscle and connective tissue which is
mainly elastic fibres arranged in circular sheets
The muscle is mainly circular with some longitudinal on the
outer surface
In large arteries there is an external elastic lamina
Tunica externa
Tunica media
- Tunica intima
Smooth muscle
Internal elastic
membrane
Vasa vasorum
External elastic
membrane
Nervi vasorum
Endothelium
Elastic fiber
Elastic
artery
Tunica
externa
Muscular
artery
Tunica
- externa
Tunica
Tunica
media
media
Tunica
- Tunica
intima
intima

Artery Wall: Tunica Externa or Adventitia

Tunica externa or adventitia
The outside layer
Made of of collagenous fibres
Some bands of elastic fibres

• Outer layers blend with surrounding connective tissue and hold the
  vessel in place - this stops vessels from being moved which would
  distort blood flow

7
Tunica externa
Tunica media
Tunica intima
Smooth muscle
Internal elastic
membrane
Vasa vasorum
External elastic
membrane
Nervi vasorum
Endothelium
Elastic fiber

Function of Smooth Muscle and Elastic Tissue in Artery Wall

What is the function of the
Smooth muscle
Elastic tissue

Veins

Have the same layers as arteries but ..
Have a much larger lumen - to allow slow blood flow and act as a repository of blood

• The tunica intima doesn't have the internal elastic lamina
  Endothelium can be thickened and reinforced with connective tissue to
  to form valves - stops backflow

Thin outer layer
Thin inner layer of
muscle and elason
Endothelium
Wide central lumen

Veins: Tunica Media and Externa

The tunica media
There is no external elastic layer
Is thinner
Tunica externa or adventitia is present and may contain some smooth muscle
fibres

Large vein
Tunica externa
Tunica media
Tunica intima
Smooth muscle cell
in tunica externa
Vasa vasorum
Nervi vasorum
Medium-sized vein
Tunica externa
Tunica media
Tunica intima
Valves
(closed)
Venule
Tunica externa
Tunica media
Tunica intima

Capillaries

Perfusion vessels, they are all leaky - making up the microcirculation

• Made up of the endothelium: squamous cell epithelium, basement membrane
  and some smooth muscle fibres

Walls are leaky
There are three types
Continuous
Fenestrated
Sinusoid
Basement membrane
Endothelial layer
(tunica intima)
Incomplete
basement
membrane
Intercellular cleft
Fenestrations
Intercellular gap

Continuous Capillaries

Continuous
Found throughout the body have endothelial lining and tight junctions which
are incomplete and allow exchange of water and small molecules between
capillaries and tissue fluid.
In the brain the gap junctions are tight and there is a thick basement
membrane giving the blood-brain barrier
Astrocyte end feet
Blood capillary
Endothelial cells

Fenestrated Capillaries

Fenestrated capillaries have pores as well as tight junctions
Allows movement of larger molecules
Found in the small intestine, kidney and choroid plexus and endocrine
structures

Sinusoid Capillaries

Sinusoid capillaries
Flattened with extensive intercellular gaps and incomplete basement
membranes, clefts and fenestrations.
Have openings for large molecules, e.g. plasma proteins, and cells
Where are they found?
Liver acinus
Sinusoid
Centralvein
Septal Stwach
Kupfer:cel
Hepatocyte
Bile
casa koulus
Space of Disse
81
Kupfer
Hepatocy
C
Hepatic
urtery
branch
Portal
vein
Bile duct
Stellate!
col
Endothelial call
with lenelist
Dencrise
cell

Blood and Nervous Supply to Blood Vessels

Larger vessels are too big and thick for diffusion
In the larger vessels there are blood vessels supplying the walls called vasa
vasorum

• In arteries these are in the outer layers, or the high pressure would cause
  them to collapse
• In the veins they go closer to the lumen

There are also nerves known as nervi vasorum which are sympathetic
nerve fibres which can cause both vasoconstriction ad dilation

Exchange Between Blood and Tissue Fluid

• What causes fluid to leave capillaries?
• What is left behind?
• How does it get back in?
• What happens to the excess?

BODY
COLL
TISSUE
FLUID
ARTERIAL
END
VENOUS
END.
CAPILLARY_
HP.
OP
HP of
LYMPHATIC
CAPILLARY

Exchange Between Blood and Tissue Fluid Diagram

BODY
COLL
TISSUE
FLUID
ARTERIAL
END
VENOUS
END.
CAPILLARY_
HP.
OP
HP of
LYMPHATIC
CAPILLARY

Plasma Proteins and Oncotic Pressure

FRICTION.
PRESSURE (KILOPASCAL)
PLASMA PROTEIN!
HYDROSTATIC
Pressone
DISTANCE ALONG CAPILLARY.

Friction in Circulatory System

LARGE
ARTERIES
ARTENE
AND
ARTERIOLES
INCREASED
NUMBER OF
VESSELS
GIVES.
CAPILLARIES.
LA INCREASED
SURFACE AREA
fon BLOOD
TO FLOW
THROUGH
4 INCREASED
FRICTION.
!

Excess Tissue Fluid

Is collected by the blind-ending lymphatic capillaries and transported back to the venous system
via the thoracic duct into the subclavian vein
Large molecules, e.g. proteins, can also be collected by the lymphatic system
Bacteria and viral particles can also be collected by
lymphatic system and filtered through the lymph glands

Learning Objectives Review

By the end of this session, you should be able to describe:

• Why circulatory systems are necessary
• The different types of circulatory systems in animals
• The features of a circulatory system
• The formation of tissue fluid