17. Long Term Arterial Pressure Control

The long term control of arterial pressure is closely intertwined with...

homeostasis of body fluid volume, which is determined by the balance between fluid intake and output.

The kidneys...

regulate the volume and osmolality of the extracellular fluid by altering the amount of sodium and water excreted in urine

Nephron

functional unit of the kidney

There are _________ of nephrons per kidney

Tens of thousands to millions

Each nephron contains...

-A capillary bed called the glomerulus
-long tubule in which filtered fluid and electrolytes are either reabsorbed back into the blood or excreted as urine

Fluid and dissolved substaces (Na, K, Cl, glucose, etc.) are filtered through the....

Glomerulus

Since extracellular fluid is composed of plasma and interstitial fluid...

The kidneys are filtering extracellular fluid

Flow through the kidney and the amount fluid that is filtered through the glomerulus is dependent on...

Ohm's Law

Renal blood flow is dependent on...

arterial pressure and resistance to flow in the kidney

An increase in arterial pressure will cause an increase in

renal blood flow and urinary output

Glomerular Filtration Rate (GFR)

rate at which fluid is filtered through the glomerulus
-Normally 20% of plasma flow

An increase in urinary excretion will result in a decrease in...

extracellular fluid volume

Pressure Diuresis

increase in urinary volume from increased blood pressure

Pressure Natiuresis

increase in pressure causes an approximate equal increase in sodium output

Extracellular Volume =

difference between water/salt intake and water/salt output

Equilibrium of extracellular volume is where

curves of water/salt intake and output intersect
-gives individuals long-term arterial pressure

Near-infinite Feedback Gain Principle

Return of the arterial pressure always back to the equilibrium point
-control of arterial pressure via renal-body fluid mechanism

If salt/water output exceeds intake...

the body loses fluid which causes blood volume to decrease and therefore arterial pressure decreases until equilibrium is reached.

Two key determinants of long-term arterial pressure

-Degree of pressure shift of renal output of water/salt
-Increase/Decrease of water/salt intake

T/F: It is impossible to change long term arterial pressure to a new value without changing one or both of its key determinants.

True

For individuals that have salt sensitivity...

It takes a higher arterial pressure to secrete the same amount of salt/water.
-Increases in salt intake can cause significant increase in arterial pressure

An increase in renal vascular resistance increases...

-Decrease in renal flow
-decrease in water/salt excretion
-Increase extrecellular fluid volume
-Increase long-term arterial pressure

Renin-Angiotensin System

-Decrease in arterial pressure detected
-Renin released from kidney
-Angiotensinogen released from liver
-Renin and Angiotensinogen bind to form Angiotensin 1 in lungs
-Formation of Angiotensin 2 via ACE inhibitors

Function of Angiotensin 2

-Construct arterioles
-Increase aldosterone release in adrenal glands
-Increase sodium reabsorption in kidneys

Fluid Retention by Kidneys in Heart Failure is caused by...

-Decreased Glomerular Filtration
-Activates Renin-Angiotensin system
-Increased aldosterone secretion

Fluid retention in the kidneys is meant to...

increase extracellular fluid volume in order to increase venous return, therefore increasing contractility of a failing heart

Hypertension

high blood pressure (Greater than 140/90)

Situational Hypertension is caused by...

An increase in sympathetic stimulation due to excitement/anxiety

Idiopathic Hypertension

consistently elevated blood pressure of unknown cause
-has been reported in dogs/cats

Secondary Hypertension

high blood pressure caused by the effects of another disease

Primary Hyperaldosteronism

Increased aldosterone release
-Retention of Na+/water in distal tubules of kidney
-Increase in extracellular fluid volume and arterial pressure

Hyperadrenocorticism

Increased secretion of ACTH
-One of most common endocrine disorders in dogs but rare in cats

Hyperthyroidism

Excessive levels of circulating thyroxine
-Increases in metabolic activity of all tissues
-Decrease in total peripheral resistance
-Increase in venous return
-Increase in systolic arterial pressure
-Decrease in diastolic arterial pressure