Cardiovascular System
L-5 Special Circulations, hemorrhage and shock
Dr Than Kyaw
March 2012
Special circulation
(Coronary, Pulmonary, and Cerebral circulations)
Introduction




Special attention to circulation in coronary,
pulmonary and brain
Differences in mechanisms to other systems
Their importance
Coronary circulation is discussed in the previous
lecture [(L-3 (b)]
Pulmonary circulation



Separate circulation
Low pressure (right ventricle) than systemic (left ventricle)
Deoxygenated venous blood from whole body pass through
the lung to re-oxygenate
Right
ventricle
Pulmonary
trunk
Lung alveoli
Gas exchange
Right
Artery
Right
lung
Left
Artery
Left
lung
Extensive
capillary bed
Extensive
capillary bed
Venules
Left
atrium
Pulmonary
vein
Trachea
bronchi
bronchiole
Smaller branches
Alveoli
Capillaries
Alveolar type I cells. Squamous cells, as thin as 0.05 m; 95% of the alveolar
epithelial surface.
Alveolar type II cells. Irregular, cuboidal shaped; cytoplasm contains a large number
of granules (cytosomes) which secrete pulmonary surfactant (a mixture of proteins and
phospholipids which reduce the surface tension of the alveoli, and prevent their collapse
during exhalation, and act as a bactericide)
Diffusion of respiratory gases



Respiratory gases diffuse readily throughout the body tissues
CO2 - greater lipid solubility, diffuse about 20 times than O2
through the membranes
Diffusion rate decreases in diseases like pulmonary edema
Oxygen-Hb dissociation curve
Direction of diffusion of O2 and CO2
Circulation to the Brain








The inner surfaces of capillaries in the brain are lined by the single layer of
endothelial cells.
Unlike other organs, endothelial cells of the capillaries in the brain have
tight junctions.
So, most substances in the blood cannot readily enter the cells of CNS.
This limitation is k/s Blood-brain-barrier.
Lipid soluble substances like O2 and CO2 can readily diffuse.
Some molecules, such as glucose, needs special methods (active transport)
Transport for most substances is provided by astrocytes which are
interposed between the CNS cells and capillaries.
The BBB is not permeable to hydrogen ions
Functions and properties of the BBB
The BBB has several important functions:

Protects the brain from "foreign substances" in the
blood that may injure the brain.

Protects the brain from hormones and
neurotransmitters in the rest of the body.

Maintains a constant environment for the brain.
Functions and properties of the BBB

General Properties of the BBB



Large molecules do not pass through the BBB easily.
Low lipid (fat) soluble molecules do not penetrate into the brain.
However, lipid soluble molecules rapidly cross the BBB into the
brain.
Molecules that have a high electrical charge to them are slowed.
Blood requirement by the brain




Need continuous supply of the blood for normal functioning
Other tissues can deprived of a blood supply for extended periods
and recover to normal function when blood supply resumes.
5 to 10 min of little or no blood to the brain
injure brain cells
(cerebrum)
no recovery
Respiratory and cardiovascular centers (medulla oblongata)
more resistant to hypoxia
revival after 10 min
Adult brain
less resistant to hypoxia than new born brain
Hemorrhage and shock
Hemorrhage and shock
Hemorrhage (Bleed causing loss of blood)


From injuries –
• External
• Internal
Traumatic
Non-Traumatic
Anatomical Type
• Arterial
• Venous
• Capillary
Timing – Acute/Chronic
Hemorrhage
May cause:
Inadequate peripheral perfusion leading to failure of tissue
oxygenation
•
•
•
•
•
may lead to anaerobic metabolism
oxydative phosphorylation can’t occur without oxygen
glycolysis can occur without oxygen
cellular death leads to tissue and organ death
can occur even after return of perfusion
organ or organism death
Effect of anaerobic metabolism
Inadequate cellular
O2 delivery
Inadequate
energy
production
Metabolic
failure
anaerobic
metabolism
Cellular
death
Lactic acid
production
Metabolic
acidosis
Maintaining perfusion requires
•
•
•
Volume (normal cardiac out put, normal flow)
Pump ( normal heart action, pressure)
Vessels (normal transport and diffusion of substances)
• Failue of one or more of above causes shock
• excessive hemorrhage affects these factors
Shock
Different types of shock
Hypovolumic shock (low volume)
• Most common cause of shock
• Traumatic blood loss (intraperitoneal, intrathoracic)
• Non traumatic blood loss
vomiting
diarrhoea
Burns
GI (melena)
Sweating
Cardiogenic shock (Pump failure)
• when the heart is damaged or injured
Shock
- Inadequate delivery of oxygen and nutrients to maintain
normal tissue and cellular function
3 stages:
(1) Compensatory: body try to maintain normal function
(2) Progressive stage: body mechanism used up and
blood started shuntting blood from extremities to
vital organs
(3) Irreversible stage- blood shunted from blood vessels
and unable to sustain the pressure need to feed the
heart and brain.
Progressive Shock




Low Cardiac Output
Decreases arterial pressure and reduces transport of
nutrients to tissues
Blood pH decreases because of lactic & carbonic acid
buildup.
Waste products lead to blood agglutination. Smaller
vessels may become blocked, further decreasing nutrient
transport
Shock may be observed by
Cool clammy extremities
tachycardia,
weak or absent peripheral pulses
hypotension
Such apparent clinical shock results from at least 25 to
30% loss of the blood volume.
• However, substantial volumes of blood may be lost before
the classic clinical signs of shock are evident.
• When a patient is significantly tachycardiac or
hypotensive, this represents both significant blood loss
and physiologic decompensation
•
•
•
•
•
Immediate treatment necessary
• Fluid replacement (N/S; Ringer’s lactate solution)
• Coloids and Blood products (plasma, red cells)
END OF LECTURE
Assignment II
Title: Role of pancreas in digestion
Submission date: 26 March 2012
Test I
Date and time:
12/3/2012
10:00 AM to 11:00 AM
Time allowed:
1 hour
Question types:
Multiple choice and short questions
Reading:
Both theory and practical