Blood vessles and hemodynamics P3 Flashcards
Long term mechanisms: of Renal Regulation of BP
Direct renal mechanism- is the direct result of how the kidneys function. When blood pressure is low, the filtration rate in the kidneys initially decreases resulting in less urine output, which consequently increases blood volume. Note, that when blood pressure increases, blood volume dosen’t increase but, a increase in blood volume will result in blood pressure since they are directly proportional.
Indirect hormonal mechanism: RAA - Renin-antiotensin-aldosterone) system
When blood pressure decreases dramatically, it stimulates special cells in the kidney to release Renin.
Renin converts angiotensinogen to angiotensin 1.
In the lungs, angiotensin 1 is converted into angiotensin 11 by ACE( angiotensin converting enzyme/primarily secreted by the capillaries in the lungs)
Angiotensin 11 increases MAP in four ways:
- Angiotensin 11 is a vasoconstrictor ( it increses peripheral resistence with constriction).
- Angiotesin 11 stimulates secreation of aldosterone by the adrenal cortex. Aldosterone increases the reabsorption of sodium. Since” water follows salt”, more water is reabsorbed resulting in an increase in blood volume.
- Angiotensin 11 increses thirst via the hypothalamus( incresed water intake increses blood volume.
- Angiotensin 11 stimulates the release of ADH ( from storage in the posterior pituitary) which increases water reabsorption in the kidneys and therefore increases blood volume. See flow chart in notes!
Local regulation of blood pressure
Autoregulation- tissues self-regulate the amount of blood and therefore nutrients to meet the demands of the tissue. This is accomplished by altering arteriole diameter via metabolic or myogenic mechanisms.
Metabolic change includes: oxygen levels, pH, nitric oxide (NO) release, and inflamatory chemicals. Recall that NO is a vasodialator.
Myogenic responses- blood veseles have their own intrinsic controls, when blood pressure increases, they streatch on the arterioles causes the arterioles to vasoconstrict. This slows down the rate of flow of the blood so that tissue gets the nutrients they need.
Blood flow through Capillaries and Fluid Dynamics
Bulk flow- (and therefore blood flow) is dependent upon pressure diffrences. The type of pressure diffrence we will focus on are hydrostatic pressure and osmotic pressure.
Hydrostatic pressure “push” and osmotic pressure “pull” or suck.
HPc = (CHP)capillary hydrostatic pressure, pressure due to fluid within the capillaries. This pressure pushes fluid out of the capillaries.
HPif = (IFHP)interstitial fluid hydrostatic pressure, pressure due to fluid in the interstitial space. This pressure pushes fluid into the capillary.
OPc=(COP)capillary osmotic pressure, pressure from solutes in the blood such as albuim”suck” fluid from the interstitial space into the capillary.
OPif=(IFOP) interstitial fluid osmotic pressure, pressure from solutes in the intersitial fluid “suck” fluid from the capillary into the interstitial space.
*Starling’s Law in the Capillaries
The net filtration pressure (NFP) is determined by the pressures “pushing” fluids out of the capillaries minus the pressure “pulling” fliuds into the capillaries.
NFP = pressure of fluid exiting the capillary - pressure of fluid entering the capillary.
NFP = (HPc +OPif) - (OPc + HPif)
How much fluid is lost during filtration is reabsorbed?
Normally 85% of fluid lost is reabsorbed and the remaining 15% is returned to the lympatic system.
What is Edema?
Edema happens when the filtration is a lot greater than reabsorption. This can be due to increased filtration or decreased reabsorption.
Increased blood pressure in the capillaries (hypertension)
decreased concentration of plasma protiens. ( liver or kidney disease)
increased permeability of capillaries (chemical, bacterial or thermal)
Increased extracellular fluid (excessive fluid intake)
Blockage of lympatic vessels( elephantiasis, mastectomy)
Define Syncope
To faint or temporarily lose consciousness due to lack of blood to the brain. Causes: Hypotension (low BP) anxiety and changes in body position.
Shock
Shock- cardiovascular system is unable to provide nutrients and oxygen to tissues usually due to insufficient blood flow.
Types of Shock
Hypovolemic shock - shock due to low blood volume (hemorrhage, dehydration are commom causes.
Cardiogenic shock - shock due to heart malfunction (MI, ischemia)
Vascular shock - excessive vasodilation leads to venous pooling.
Obstructive shock - blockage, from thrombus or embolus
Septic shock - bacterial toxins in the blood increase vasodialation and capillary permeability.
Anaphalatic shock - an allergic reaction ( type 1 hypersensitivty) that results in histamine release which in turn results in vasodialation and bronchoconstriction.
Homeostatic response to shock
Even if as much as 10% of blood volume is lost, the body can still use the following negative feedback mechanism to compensate:
- Activation of RAA system - overall conservation of water to increase blood volume. Vasoconstriction!
- Secreation of ADH - results in water conservation (increasing blood volume) and vasoconstriction. (ADH is also known as vasopressin)
- Activation of sympathetic division of the ANS - Vasoconstriction, incresed heart rate and force of contraction of the heart, results in increased blood pressure.
- Release of local vasodialtors- potassium, adenosine, lactic acid, and nitric oxide are released at local levels to improve uptake of nutrients.
Some sighs and symptoms of “shock”
Cool, clammy skin due to reduced blood flow
tachycardia - sympathetic response
weak yet rapid pulse (reduced CO), the pulse is difficult to find, thread pulse.
Sweating- sympathetic responce
hypotension - low blood pressure ( a late sigh/decompensated shock)
Disorientation/ mental confussion due to lack of blood in the brain.
Decreased urine output- water conservation
thirst- due to decreased fluids
acidosis- lactic acid build
nausea- sympathetic response to slows digestion
Define Decompensated shock
if greater than 15% blood loss, the compensatory mechanisms don’t work well enough and medical intervention is needed.
Hepatic Portal Circulation
A subdivision of the systemic circuit that transports blood from a capillary network associated with the GI through the hepatic portal vein to the capillary network in the liver before entering the hepatic vein and on to the inferior vena cava for return to the heart.
