urinary 3

Glomerular Filtration Rate (GFR)

• GFR is a measurement of how well filtration is occurring at the kidneys.

• Filtration detoxifies the blood by eliminating toxic waste.

• The body aims to maintain a high GFR to keep the blood clean.

• Mechanisms regulate GFR to maintain homeostasis.

• The body will try to keep GFR high unless there is a disease process.

• Regulation occurs through neural regulation, paracrine signaling, and hormones.

Renin-Angiotensin-Aldosterone System (RAAS)

• Renin is an enzyme, not a hormone, produced by the kidneys.

• Renin is released when blood pressure is low.

• Low blood pressure can occur for various reasons, such as not taking in enough water.

• The kidneys monitor blood pressure because they need blood to function and produce urine.

• In low blood pressure, the body must increase blood pressure to maintain a high GFR and ensure enough perfusion to the kidneys.

Renin's Role

• Renin is released only when there's low blood pressure.

• Renin converts angiotensinogen into angiotensin I.

Angiotensinogen

• Angiotensinogen is a plasma protein made in high amounts by the liver but is inactive until converted.

• Angiotensin I is also inactive and needs to be converted to angiotensin II.

Angiotensin II

• Angiotensin II is a potent vasoconstrictor.

• Vasoconstriction narrows blood vessels, increasing blood pressure therefore when renin is secreted because there is not enough blood passing through the kidney it vasoconstricts the blood vessels to increase blood pressure.

Juxtaglomerular Cells

• Renin acts on juxtaglomerular cells.

• Juxtaglomerular cells are specialized smooth muscle cells in the afferent arteriole.

• Afferent arteriole controls what gets into the glomerulus; efferent arteriole controls what gets out.

• The afferent arteriole is strategically more important for controlling filtration.

• Juxtaglomerular cells in the afferent arteriole sense low blood pressure and make renin.

ACE (Angiotensin-Converting Enzyme)

• An enzyme is needed to convert angiotensin I to angiotensin II. That enzyme is ACE.

• ACE comes from the lungs.

• ACE inhibitors (e.g., lisinopril) are a common first-line treatment for hypertension to protect kidney function.

• ACE inhibitors inhibit the angiotensin-converting enzyme.

Putting it all together (RAAS)

• R: Renin

• First A: Angiotensin II

• Second A: Aldosterone

Aldosterone

• Aldosterone comes from the adrenal cortex.

• Aldosterone is a mineralocorticoid that acts on salt (sodium).

• Aldosterone acts at the distal convoluted tubule (DCT).

• Aldosterone makes sure that truly correcting the low blood pressure problem by moving salt.

Angiotensin II and Hypothalamus

• Angiotensin II goes to the hypothalamus and tells it to make ADH (antidiuretic hormone).

ADH

• ADH keeps water in by acting on the collecting duct via aquaporins.

Kidneys Role

• The kidneys filter blood and regulate blood pressure.

• Thirst, salt intake, and hormone balance all affect this regulation.

• Patients with poor kidney function have difficulty treating hypertension.