The urinary system

21 May 2024

The functioning of the urinary system is a complex mechanism that is vital to the health of our pets. In dogs and cats – as in humans – the urinary system comprises the kidneys, ureters, bladder and urethra. The kidneys are the key organs in this system, responsible for purifying the blood to eliminate waste products, and regulating the balance of fluids and electrolytes.

What are the different parts of the urinary system?

Kidneys

The kidneys are the functional organs of the urinary system. They are made up of different structures.

The capsule is a fibrous membrane that surrounds each kidney, providing physical protection against damage. It also helps to maintain the shape and structure of the kidney.
The cortex is the outer layer of the kidney containing the glomeruli – part of the nephrons – and a large proportion of the renal tubules. This is where the blood purification process begins.
The medulla is the inner region of the kidney, made up of structures called renal pyramids. This is where a large proportion of the renal tubules are located, responsible for concentrating urine and eliminating waste.
The calyces and renal pelvis are cavities in the centre of each kidney that collect the urine produced by the renal tubules and transport it to the ureters.
The hilum is the area where blood vessels enter and leave the kidney. It is a key area for vascularisation and the supply of blood to the kidneys, necessary for their functions.

The ureters

The ureters connect each of the two kidneys to the bladder. Their role is to transport urine from the kidneys to the bladder.

The bladder

The bladder is a sac made up of a mucous membrane – or urothelium – and muscles. It stores urine from the ureters until the next micturition.

The urethra

The urethra is the tube connecting the bladder to the urinary meatus. It allows urine to be evacuated via the urinary meatus.

How do kidneys work?

These bean-shaped organs are located in the lumbar region. They perform a number of functions: purifying blood and eliminating waste products, regulating blood pressure, producing certain hormones and balancing electrolytes.

The functional unit of the kidney is the nephron. Each nephron begins with a glomerulus, a formation composed mainly of blood vessels that allow liquids and small molecules to pass through, but retain larger elements such as cells or albumin. Then, as it travels through the tubule, the primitive urine becomes concentrated and useful elements are actively recovered – such as glucose or certain minerals – while undesirable elements such as waste – urea – or useful elements that are present in excess in the blood – such as water or certain minerals – remain there.

In simplified terms, the kidney behaves like a “selective sorting” recovery unit. When the number of functional nephrons is sufficient, the balance of the internal environment is ensured.

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The importance of diet for skin and coat quality in dogs and cats

The skin is the body's largest organ, representing between 12% and 24% of the animal's weight, and its surface area in a dog weighing around thirty kilograms is close to one square meter. It's hardly surprising, then, that the quality and quantity of the dog's diet can have an impact on this organ, and in the event of a deficiency can lead to problems that go far beyond a simple visual appearance.

Key nutrients for healthy skin and coat

Among the macro-nutrients, proteins play a crucial role. They provide amino acids, including sulphur amino acids, which are essential for the structure of the skin and coat. These are the main components of collagen, which gives the skin its suppleness and resistance, and of keratin, which plays a part in the effectiveness of the skin barrier. Lipids are also important; they make up the bulk of cell membranes and, in the skin, contribute significantly to the effectiveness of the cutaneous barrier. Among lipids, omega-3 and omega-6 fatty acids help maintain healthy skin, modulate inflammatory mechanisms and promote a shiny, soft coat. Vitamins and minerals are also involved. Vitamin A is necessary for cell renewal, as is vitamin D, which also plays a part in the skin's natural defences. Vitamin E acts as an antioxidant, while B vitamins and biotin are essential co-factors in the synthesis of various skin elements such as ceramides, keratin and collagen. Among the minerals, zinc is involved in synthesis, protection against free radicals and immune defence mechanisms.

Disorders linked to inadequate nutrition

Inadequate or poor-quality food can lead to skin problems in our pets. A deficiency in essential fatty acids leads to dry, flaky skin, a dull coat and brittle hair. When it's the vitamins and minerals that are in short supply, synthesis is affected, the skin barrier can be less effective and the breeding ground for infections and inflammations that can lead to itching. On the other hand, these nutritional benefits can be used to compensate for individual sensitivities and improve the quality of the skin and coat in the event of dermatological disorders or diseases.

Conclusion

The quality of a dog's skin and the beauty of its coat are directly influenced by the quality of its diet. However, some dogs and cats have increased needs, and it is therefore necessary to provide them with greater quantities of useful nutrients. This is particularly true in the case of certain dermatological disorders, to help compensate for imbalances and accompany the medical treatments prescribed by your vet.