Shock and hemorrhage

Question 1

What is shock and what is its consequences?

Answer 1

• Decreased effective circulating volume
  ○ effective circulating volume=blood that is actually going around your body and in organs decreases
  
  • Causes a decreased cardiac output so not enough blood to the organs so no O2 delivery to tissues and will cause a CO2 build up
  • Can cause:
    ○ Decreased urine or no production
    ○ Less blood goes to less important organs (more to important organs e.g. brain, heart and kidneys) so grey/blue skin, dry mouth,
    ○ Pale, cold and clammy skin due to the lack of blood to skin
    ○ Low blood pressure, high heart rate (tachycardia), rapid breathing, metabolic alkalosis, altered mental stage….
    ○ Hypoxia, mitochondrial dysfunction, impairment of cellular metabolism
    ○ Organ failure
    ○ death
  • Types:
    ○ Hypovolaemic shock
    ○ Cardiogenic shock
    ○ Anaphylactic shock
    ○ Septic shock

Question 2

Describe how clinical scenarios of shock and haemorrhage can alter renal handling or reabsorption of ions/Na+ and H2O.

Answer 2

• Hypovolaemic shock
  ○ ~750ml loss of blood volume
  ○ Not enough volume of blood shock due to loss of blood fluid
  ○ Heart working fine but Volume of blood heart pumps has gone down e.g. due to bleeding or haemorrhaging, large burns to the body (plasma loss), diarrhoea/vomiting (causes fluid loss), sweating/dehydration (fluid loss), diabetes insipidus (fluid loss)….
  ○ Pressure on right hand side next to heart= central Venus pressure is lower so less blood will come back to the right atrium. Right ventricles EDV will be lower which means the Right ventricles stoke volume is dropped as the ventricles don’t contract enough. This means that there will be less blood going to the lungs. Less blood going to left ventricles and lower left ventricle EDV so less Stretch and lower stroke volume (weaker contraction)
  § Central venous pressure falls
  § Effective circulating volume and blood pressure falls,-too little blood for the circulatory system despite vasoconstriction
  
  • Cardiogenic shock
    ○ Caused by heart pump failure when the contraction isn’t happening as well
    § Such as during myocardial infarctions inadequate circulation (dead tissue)
    ○ Not enough blood pumped out of the heart
    ○ Effective circulating volume will fall and blood pressure will fall even though the volume won’t change due to the bad circulation of blood around the body
  • Anaphylactic shock
    ○ Caused by a rapid allergic reaction on exposure to an allergen (e.g. latex), drugs (e.g. penicillin), local anaesthetic…
    ○ Causes wide spread vasodilation (heat, redness), the permeability of the vessels will greatly increace and cause oedema (massive swelling)-loss of effective circulating volume and causes hypovolemia
    § When you have an infection the blood vessels are dilated to send more neutrophils to the infection and to push plasma into the infection to dilute the infection
    § During an allergic reaction the same thing will happen and dilate the blood vessels. The plasma will exit the blood vessels and lower the blood volume (this will cause swelling)
    If the allergic reaction is all around the body a lot of fluid will be lost from vessels and cause volume to drop (loss of effecting circulating volume) will also constrict bronchioles
    § 1/3 of blood volume dropped
    ○ Need to inject adrenalin to constrict the vessel, dilate the bronchioles, decrease the capillary permeability and increase heart rate.
    ○ Mast cells break up and relace histamine (vasodilator and pore producer and itchy and bronchoconstriction causes throat tightness, breathing difficulties, wheezing, coughing and itching ) after coming in contact with allergen
    ○ Obvious signs are swelling of the face/tongue, itching and difficulty breathing
  • Septic shock

Question 3

How does the kidneys compensate in order to maintain circulatory volume?

Answer 3

• The borrow receptors in the heart detects the decreased blood pressure and activates the sympathetic nervous systems which increases rate and contractility, and constricting peripheral blood vessels
  
  • The neuroendocrine system will release ADH to absorb more water to increase blood volume
  • Renal system will release renin from the JGC and causes release of aldosterone from the adrenal glands and activate the RASS system
    1. Juxtaglomerular cells release renin into the glomerulus
    ○ renin can’t be filter out as it is too large
    ○ Renin will be circulating in the blood
    2. GFR will drop if the blood pressure drops
    ○ Filtrate will go slowly down the PCT as there is a lower GFR
    ○ More sodium is reabsorbed at the PCT and is put back into the blood
    3. Chemoreceptors in the DCT detects lower Na+ concertation in filtrate
    4. Chemoreceptors send impulse to Barrow-receptors in Afferent Arterioles to release renin into the glomerulus
    5. Angiotensinogen is always present in the blood but doesn’t do anything until renin is released
    ○ Angiotensinogen is a globular protein
    ○ Produced by the liver
    6. Angiotensinogen converted to angiotensin I by renin
    7. angiotensin I converted to angiotensin II by angiotensin converting enzyme (which is produced by the kidneys)
    i. Angiotensin II will go to hypothalamus to stimulate thirst receptors so you drink more water to increase blood volume and therefore increase hydrostic pressure
    ii. Causes aldosterone to be released from adrenal glands to get more Na+ reabsorbed in the whole nephron
    ▪ Aldosterone goes to the collecting duct and causes more Na+ channels to embedded in the collecting duct so more. This makes the collecting duct (which WAS impermeable to Na+ permeable to Na+) so Na+ is reabsorbed into the blood
    ▪ This will increase the blood osmolality and cause water to be reabsorbed
    ▪ Gets more water to follow to sodium and go into the blood
    ▪ Biggest factor in how kidneys handle Na+ to raise blood pressure
    iii. Causes ADH to increase aquaporins and increase volume of the blood
    ▪ No change to osmolality when you have a haemorrhage/blood is lost as water and osmolality are both lost
    ▪ No change in osmolality usually wouldn’t effect ADH but aldosterone will cause ADH to be released from the posterior pituitary gland
    ▪ ADH will cause more aquaporins to be embedded in the collecting duct therefore reabsorbing more water and increasing the blood volume/pressure
    ▪ Doesn’t affect the amount of solutes excreted
    iv. Will raise pressure in glomerulus by contracting efferent arteriole to raise hydrostatic pressures and aloe kidneys to keep working as waste products need to be removed
    ▪ Contraction of the efferent arteriole will cause the hydrostic pressure in the kidneys to increase/normal so GFR is the same and body can still remove waste
    v. Will also cause vasoconstriction to raise blood pressure
    ▪ Decreases the size of the lumen of blood vessels so blood pressure increases
    vi. Reduced the excretion of NaCl by stimulating its reabsorption in the LoH, DCT and collecting duct
  • This causes water to reabsorbed into the blood and increase the blood volume so will increase the blood pressure