Overview of Renal Physiology

Function of kidneys:

- excrete waste products from blood in urine
- balance body fluids
- regulate blood acid-base equilibrium
- regulates blood pressure
- produce hormones

Fundamental renal processes:

filtration, reabsorption, and secretion

Creatinine

- nitrogenous organic acid mostly stored in muscle
- involved in energy transfer in the form of phosphocreatine
- metabolized to creatinine to be excreted by the kidney

Renal Clearance

Volume of plasma that is completely cleared of S by the kidneys per unit time

Amino acids and urea

Amino acids catabolism results in waste ammonia. Humans convert ammonia to the less toxic compound urea (mainly in the liver). Urea is ultimately excreted in urine.

Plasma proteins

- transport lipids, hormones, vitamins, and minerals
- act as enzymes
- regulate blood coagulation
- form part of the immune system

net reabsorption of Na+ involves:

- pumping across the basolateral membrane
- diffusion across the luminal membrane (down the Na+ electrochemical gradient)
- convection from the interstitial fluid into the peritubular capillaries (driven by hydrostatic and osmotic pressure gradients)

Aldosterone secretion is stimulated by:

- increased extracellular [K+]
- increased angiotensin II levels (following sodium and water depletion, or low blood pressure)

The concentration of urine is controlled by

the antidiuretic hormone (ADH)

Forming a concentrated urine requires:

- high levels of ADH: increases the permeability of the distal tubules and collecting ducting to water
- stepp osmotic gradient in the renal medullary interstitial fluid, which provides the driving force for water reabsorption.

The osmotic gradient results from:

- counter-current arrangement of tubules
- segment-specific transport mechanisms

Changes in _____ are the strongest factor in regulating ADH release.

blood osmolarity

Increase in ADH

- increase in osmolarity
- decrease in blood pressure
- decrease in blood volume
- nausea
- hypoxia

Drugs to increase in ADH

morphine; nicotine

Decrease ADH

- decrease in plasma osmolarity
- increase in blood volume
- increase in blood pressure

Drugs to decrease ADH

alcohol