Cardiovascular SystemL-5 Special Circulations, hemorrhage and shock
Dr Than KyawMarch 2012
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)]
Special circulation (Coronary, Pulmonary, and Cerebral circulations)
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 Artery
Pulmonary trunk
Left Artery
Extensive capillary bed
Left lung
Right lung
Extensive capillary bed
Right ventricle Lung alveoli
Gas exchange
Pulmonary vein
Venules
Left atrium
bronchi
Trachea
bronchiole
Smaller branches
AlveoliCapillaries
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.
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.
Functions and properties of the BBB
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 minAdult 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
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
Hemorrhage
Effect of anaerobic metabolism
Inadequate cellular O2 delivery
anaerobic metabolis
m
Lactic acid production
Inadequate energy
production
Metabolic acidosis
Cellular death
Metabolic failure
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
• when the heart is damaged or injured
Different types of shock
Hypovolumic shock (low volume)• Most common cause of shock• Traumatic blood loss (intraperitoneal,
intrathoracic)• Non traumatic blood loss
vomitingdiarrhoeaBurnsGI (melena)Sweating
Cardiogenic shock (Pump failure)
Shock
- Inadequate delivery of oxygen and nutrients to maintain normal tissue and cellular function
Shock
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.
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
Progressive Shock
• 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
Shock may be observed by
• Fluid replacement (N/S; Ringer’s lactate solution)• Coloids and Blood products (plasma, red cells)
Immediate treatment necessary
END OF LECTURE
Title: Role of pancreas in digestionSubmission date: 26 March 2012
Assignment II
Date and time: 12/3/2012 10:00 AM to 11:00 AM
Time allowed: 1 hourQuestion types: Multiple choice and short
questionsReading: Both theory and practical
Test I