A Brief Description of Kidney Function & Pathology


Kidney disease and the modern pet diet connection.

Renal disease is, unfortunately, a common cause of morbidity and premature death in dogs and cats and research has shown that the modern pet diet is a major contributor to this silent epidemic. Essentially, it boils down to the ratio of the types of fats found in pet food.

Most modern dry pet food is manufactured from refined animal and vegetable proteins. Animal fats, which are mostly made up of saturated fats, are added to make the food better tasting. Plant oils are also added because they supply some essential fatty acids (EFA) that are necessary to a pet’s diet. Vitamins and minerals are also added and the mixture is either steamed and extruded or baked. This cooking process, in and of itself, is detrimental to the nutritional needs of carnivorous pets (recent studies have established that there seems to be a quality to fresh uncooked and unprocessed meat that is essential to the health and longevity of cats and dogs).

As mentioned above, animal and plant fats are a major ingredient in pet food. These fats provide three polyunsaturated fatty acids (PUFA), arachidonic acid (AA), linoleic acid (LA) and to a lesser extent alpha-linolenic acid (ALA). Two of these, AA and LA are Omega-6 PUFA’s while ALA is an Omega-3 PUFA. Both types of PUFA’s are converted in the dog’s system into more complex PUFA’s called eicosanoids. The cat, however, does not possess the ability to convert the simpler eicosanoid molecules derived from plants into the larger more complex molecule eicosanoid that have the more effective anti-inflammatory effect.

These eicosanoids are hormone-like molecules that have very pronounced effects on the regulation of numerous body functions such as blood pressure, blood viscosity (slipperiness), vasoconstriction (tightening of the arteries), immune and inflammatory responses.

The Omega-6 eicosanoids have an inflammatory effect, particularly on kidneys. Omega-6 also increases the blood flow to the kidneys causing glomerular hypertension (above normal pressure in the kidney’s filters). The Omega-3 eicosanoids also contribute to glomerular hypertension, intrarenal inflammation, hyperlipidemia (excess fats in blood), lipid peroxidation (oxygen damage to fats), and intrarenal growth factor elaboration (a scaring type of growth) according to a study done at the College of Veterinary Medicine at the University of Georgia.

The ratio of Omega-6 to Omega-3 fats in pets (and human) diet has a profound effect on the health of the kidneys. The ideal ratio of Omega-6 to Omega-3 is approximately  3 to 1, the typical ratio in most pet’s diets is 15 to 1.

The most abundant source of Omega-3 eicosanoids is fish oil which contains two forms, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Numerous clinical studies have shown that the importance of DHA and EPA supplementation extends to many aspects of dogs and cats healthy physiology. These range from accelerated cognitive development in puppies and kittens, cardiovascular and renal protective qualities, protection form development of diabetes and obesity, amelioration of inflammatory bowel diseases and to many other conditions that have an inflammatory component.

A little about the structure and function of the kidney

Mammals are normally born with two bean-shaped organs called kidneys. The organs main functional unit is called a nephron. Each kidney contains anywhere from two hundred thousand to more than one million of these microscopic structures, depending on the mammal. Every nephron is a mini filtration system that cleans the blood of toxins and in the process creates urine.

The kidney itself has a few basic functions

Waste product regulation 

Normal metabolism of proteins creates nitrogenous waste products that can be measured in the blood as a value termed blood urea nitrogen (BUN). Creatinine is a waste product of muscle metabolism and can also be found in the blood and quantified. The values of these metabolites are measured and compared to a standardized value range that is known to represent normal kidney function. If the values are higher than the normal range it can give an indication of acute or chronic kidney function impairment.


Fluid regulation

The kidneys try to maintain an optimal amount of water in the system. They manage this by controlling the amount of water excreted into the urine, more water equals lighter colored urine, less water excreted equals darker yellow colored urine.

Electrolyte regulation

There are four major electrolytes that the kidneys manage.

1. Sodium:  plays an important role in regulating fluid levels in the bloodstream thereby affecting blood pressure. It’s also involved in nerve impulse propagation.

2. Potassium: important in maintaining normal heart rhythm.

3. Calcium: regulated with the aide of a hormone called calcitriol. Abnormal values in the bloodstream due to high phosphorous levels leads to calcium deposits in kidneys and other organs.

4. Phosphorous: regulated with the aide of parathyroid hormone. High concentrations in the blood can cause nausea.

Red blood cell production

The hormone erythropoietin is secreted into the bloodstream by the kidneys, it travels to the bone marrow and stimulates it to create red blood cells. If a kidney’s ability to secrete this hormone is impaired it can lead to anemia.

Chronic renal failure pathology

A pet will rarely be diagnosed with the actual cause of its renal disease, be it genetic predisposition, autoimmune, infectious or as in most older pets, degenerative. No matter what the cause most pets will only start to show some symptoms of CRF when their kidneys have lost the permanent or temporary function of approximately 75% of their nephrons. The loss of a nephron is permanent when it is replaced with scar tissue and can be temporary when its function is impaired due to inflammation.

When the remaining nephrons cannot keep up with the demand placed on them, a build-up of nitrogen waste products in the bloodstream results. The brain registers the waste build up and tries to compensate by increasing thirst. More water taken in means more water excreted which flushes out the built-up waste along with, unfortunately, important proteins and electrolytes. The result is muscle weakness, weight loss and paradoxically, dehydration due to excess urination.

The build-up of waste products in the bloodstream affects the digestive system as well. Ulcers can occur in the mouth, stomach, and intestines. This causes the pet to vomit, lose its appetite and shed weight, sometimes at an alarming rate. The gums can also be affected so that any pre-existing periodontal disease (receding gums due to bacterial infection) will be aggravated.

High levels of phosphorous in the bloodstream cause the bones to release calcium into the bloodstream which can then inflame and mineralize parts of the kidney, further damaging them. High blood pressure due to impaired sodium ion regulation can lead to blindness.

Anemia eventually results from inadequate production of the hormone erythropoietin by the kidneys. This causes weakness as well as cold and exercise intolerance.

Toxic build-up will affect the nervous system in a number of ways. It can cause the pet to become lethargic, agitated, confused and act strangely. Cats when suffering from central nervous system toxicity will bury their heads and cover their eyes with their front paws while lying on their stomachs. Very high toxin levels will cause seizures.

Signs and symptoms

Most people visiting this site will have a pet already diagnosed with crf and will be familiar with the symptoms listed bellow. Those of you with pets that have not yet been diagnosed should be aware that a loss of 75% or more of renal function is required before major symptoms of illness are observed. Any of these symptoms alone or in combination should prompt you to take your pet to a vet for a thorough check up.

-drinking more than usual (spending a lot of time sitting at water bowl)

-urinating more than usual (check number of urine clumps in litter box)

-nausea and vomiting

-loss of appetite

-weight loss (sometimes severe , leading to muscle wasting and emaciation)


-spotty depigmentation of coat

-shedding more than usual

-dull coat

-coat smells bad

-breath smells bad (smells like ammonia)

-generalized itching (pulling fur out in attempt to relieve itching)

-rests on stomach with head buried in front paws

-ulcers in the mouth and/or on tongue



There are a number of sites that will go into great detail about managing your pet’s kidney disease with the aide of diet and drugs. Though I am not a veterinarian, I am a medical doctor and understand the importance of medication in managing disease. Having said that, I have always found it preferable to confront disease at its root or failing that, as close to the root as possible, rather than attempting to control the secondary problems caused by it.

The drugs used to treat kidney pathology are meant to help control secondary effects and symptoms. So a pet might need to take phosphorous lowering medication, anemia fighting medication, blood pressure medication, anti-ulcer medication, anti-vomiting medication, and potassium supplementation, etc., alone or in combination to help manage its disease. Though these drugs can temporarily be effective they are very costly and administering them can affect the quality of life of both pet and owner. And though for some pets these medications might help to temporarily stabilize their condition, they do nothing to confront the actual degeneration of the kidney and its infrastructure.

As previously mentioned, many pets will not get a definitive diagnosis of the root cause of their kidney disease, however, all will share one main characteristic close to the root. That characteristic is inflammation of renal tissue which can result from a wide variety of causes, from an imbalance of dietary Omega 3/6 intake to autoimmune disorders. When inflammation is chronic it will eventually destroy microscopic and macroscopic structures and replace those with scar tissue. If the inflammation of renal tissue can be reversed and further inflammation prevented then the scarring and permanent destruction of nephrons can be avoided.

Astro’s Oil™ Advanced Renal Care Formula was designed to do precisely that. When administered in combination with Astro’s Oil™ Nitrogen-Creatinine Scrub and Astro’s Oil™ Renal Care Protein, a synergistic effect greatly increases the overall efficacy of controlling and reversing inflammation of kidney tissue which can result in recouping the precious kidney function lost to it. Often, this is sufficient to greatly improve the pets quality of life and long term prognosis.

Your Cart