Cardiovascular System L-5 Special Circulations, hemorrhage and shock. Dr Than Kyaw March 2012

Transcription

1 Cardiovascular System L-5 Special Circulations, hemorrhage and shock Dr Than Kyaw March 2012

2 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)]

3 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

4 Right ventricle Lung alveoli Gas exchange Pulmonary trunk Right Artery Left Artery Right lung Left lung Extensive capillary bed Extensive capillary bed Venules Left atrium Pulmonary vein

5 Trachea bronchi bronchiole Smaller branches Alveoli Capillaries

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7 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)

8 Diffusion of respiratory gases Respiratory gases diffuse readily throughout the body tissues CO 2 - greater lipid solubility, diffuse about 20 times than O 2 through the membranes Diffusion rate decreases in diseases like pulmonary edema

9 Oxygen-Hb dissociation curve

10 Direction of diffusion of O2 and CO2

11 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 O 2 and CO 2 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

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15 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.

16 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.

17 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 (cerebrum) no recovery injure brain cells Respiratory and cardiovascular centers (medulla oblongata) more resistant to hypoxia revival after 10 min Adult brain less resistant to hypoxia than new born brain

18 Hemorrhage and shock

19 Hemorrhage and shock Hemorrhage (Bleed causing loss of blood) From injuries External Internal Traumatic Non-Traumatic Anatomical Type Arterial Venous Capillary Timing Acute/Chronic

20 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

21 Effect of anaerobic metabolism Inadequate cellular O 2 delivery Inadequate energy production anaerobic metabolism Lactic acid production Metabolic failure Cellular death Metabolic acidosis

22 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

23 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

24 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.

25 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

26 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

27 Immediate treatment necessary Fluid replacement (N/S; Ringer s lactate solution) Coloids and Blood products (plasma, red cells) END OF LECTURE

28 Assignment II Title: Role of pancreas in digestion Submission date: 26 March 2012 Test I Date and time: 12/3/ :00 AM to 11:00 AM Time allowed: Question types: Reading: 1 hour Multiple choice and short questions Both theory and practical