Cardiovascular SystemL-5 Special Circulations, hemorrhage and shock

Dr Than Kyaw

March 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 alveoliGas exchange

Pulmonary vein

Venules

Left atrium

bronchi

Trachea

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.

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 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

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 digestion

Submission date: 26 March 2012

Assignment II

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

Test I