Changes

==Effects of Angiotensin II on GFR==

==Effects of Angiotensin II on GFR==

If blood pressure drops then [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Glomerular Filtration Rate|glomerular filtration rate (GFR)]] also drops due to a reduced blood flow through the kidneys.  Therefore it is important to prevent this.  If contraction of the efferent arteriole occurs then the pressure difference between the afferent and efferent arterioles increases creating a greater filtration pressure. This effect is mediated by Angiotensin II and means that when blood pressure falls there is minimum alteration of GFR. Blood flow which is already reduced due to the reduced pressure will then be further reduced by the increase in resistance.  This increased renal resistance to blood flow and the maintained GFR has many advantageous effects.   

If blood pressure drops then [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Glomerular Filtration Rate|glomerular filtration rate (GFR)]] also drops due to reduced blood flow through the kidneys.  To restore homeostasis, contraction of the efferent arteriole occurs in response to angiotensin II and the pressure difference between the afferent and efferent arterioles increases, creating greater filtration pressure. When blood pressure falls, therefore there is minimum alteration of GFR. The increased renal resistance to blood flow and the maintained GFR has many advantageous effects.   

===Advantages of Constriction of the Efferent Arteriole===

===Advantages of Angiotensin II induced Vasoconstriction===

* If you increase the resistance in the kidneys you contribute to increasing total peripheral resistance.  This helps to return blood pressure towards normal.  (Angiotensin II also has vasoconstrictive effects in other organs.)

* Increased total peripheral resistance helps to return blood pressure towards normal.  (Angiotensin II also has vasoconstrictive effects in multiple organs.)

* The kidneys can tolerate the reduced perfusion allowing blood to be prioritised to organs which need it like the brain and heart.

* The reduced perfusion of the kidneys allows blood to be diverted to the brain and heart.

* The constriction of the efferent arterioles also reduces hydrostatic pressure in the [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Pressure in the Peritubular Capillaries|peritubular capillaries]] this increases reabsorption of water and salt thus helping to restore the ECF and thus helps to normalise blood pressure.

* The constriction of the efferent arterioles also reduces hydrostatic pressure in the [[The Formation of the Filtrate by the Glomerular Apparatus- Anatomy & Physiology#Pressure in the Peritubular Capillaries|peritubular capillaries]], increasing reabsorption of water and salt and helping to restore the extracellular fluid ECF and normalising blood pressure.

* The amount of waste excreted is variable with GFR.  Thanks to the normalised GFR the excretion of waste products such as urea is maintained.

* The amount of waste excreted is linked to the GFR.  Maintaining GFR permits the excretion of waste products such as urea to be maintained.

==Effects of Angiotensin 2 On Sodium==

==Effects of Angiotensin 2 On Sodium==