Introduction

The urinary system, known as 'Mootravaha Srotas' in Ayurveda, encompasses more than just the tract of organs visibly engaged in urine formation as understood in modern medicine. Ayurveda, an ancient science and Upaveda of Atharvaveda, posits a distinct view on this system. It emphasizes specific processes for urine formation, transport, and elimination, which are considered normal functions of any 'Srotas' (channels)1. According to Ayurvedic principles, waste products, including urine ('Mootra'), are generated at the conclusion of metabolic activities ('Dhatuvyapar') within their respective 'Srotas'. A significant concept is 'Kleda' (waste metabolic product), which is produced by every 'Srotas' as the final part of its activities. This 'Kleda' is transported to the kidneys ('Vrikkas') by 'Udakdhatu' (water element), while a major portion of urine is formed as the liquid fraction of 'Kitta' (end product of digestion). Sushruta highlights a crucial relationship between the 'Pakvashaya' (large intestine and terminal ileum) and the urinary system. In 'Pakvashaya', useful ('Sar') and waste ('Kitta') components are differentiated, and the liquid fraction of 'Kitta' is absorbed by 'Mootravaha Nadis'. Modern medicine acknowledges the 'Pakvashya' (colon) as a large water and electrolyte-absorbing structure.2

         Ayurveda's understanding of the urinary system is also based on the 'Poshya-Poshak' concept, dividing the activity of substances into 'Poshaka' (precursor) and 'Poshya' (formed). The 'Poshaka' division of urine forms in the 'Pakvashaya', while the 'Poshya-Poshak' fraction is formed in the kidneys ('Vrikkas'). Kidneys are responsible for converting 'Poshya Mootra' into 'Poshaka Mootra', leading to the reabsorption of some 'Udakdhatu' into the bloodstream, akin to selective reabsorption in modern physiology. The subtle energies of Samana and Apana Vayu are deemed crucial for this transformation and for the excretion of substances.

Diet significantly influences urine quantity and quality For instance, copious water intake directly increases urine flow, a principle useful in detecting conditions like Diabetes Mellitus (Prameha). Ayurvedic texts like Charaka Samhita detail numerous dietary etiological factors for 'Prameha', suggesting their primary role in its manifestation.3

Relationship between Urinary System and Pakvashaya4

While an apparent direct relationship between the urinary system and 'Pakvashaya' (colon) may not be immediately obvious from a modern anatomical perspective, contemporary research in colon physiology reveals an intriguing connection. If substances typically excreted by the kidneys are present in high concentrations in the blood, they may also be excreted by the intestines, such as magnesium phosphates and insoluble calcium. This suggests a functional similarity between tubular and intestinal activity, encompassing filtration and re-absorption19. The phenomenon of bile pigments imparting color to urine due to absorption from the intestines further exemplifies this relationship.5 Thus, Ayurveda proposes a definite, threefold relationship between the 'Pakvashaya' and the urinary system:

1. Formation of Essential Constituents: The 'Pakvashaya' is responsible for forming some essential constituents of urine.

2. Water and Salt Absorption: It absorbs water and salts from the 'Kitta' (waste) portion and transmits them to the kidneys.

3. Excretion of Excessive Salts: The 'Pakvashaya' excretes excessive quantities of certain insoluble salts that would normally be excreted by the kidneys.

Role of Udaka and Kleda in Urine Formation6

The primary function of urine ('Mootra') is to eliminate 'Kleda' (waste) from the body. 'Kleda' is also associated with being retained by 'Sweda' (sweat). Sushruta Samhita attributes two key functions to 'Mootra': filling the 'Basti' (urinary bladder) and removing 'Kleda'7.

The term 'Kleda', derived from 'to wet' (as per Amarkosha), refers to a substance in the body possessing wetting properties. Its exact interpretation suggests a substance that can render body tissues 'filthy. A critical distinction exists between 'Udaka' (water), 'Kleda' (waste), and 'Mootra' (urine). 'Udaka' is considered the 'Poshaka Dhatu' (precursor element) of what will become 'Poshya Mootra' (formed urine). Some authorities interpret 'Udaka' as the 'Dhatavastha' (elemental state) of a substance, while 'Kleda' is its 'Malavastha' (waste state), signifying its readiness for excretion into the urine. Both 'Udaka' and 'Kleda' can be referred to as 'Apyamsha' (watery portion) of the body, along with certain waste products.8 Ultimately, 'Udaka' is affirmed as the portion of 'Mootra' that is reabsorbed. This reabsorption occurs from the 'Pakvashaya', where it circulates throughout the body, undergoing changes by participating in various functions related to nutrient supply and waste removal from 'Sharir Dhatus' (body tissues), eventually transforming into 'Kleda'. This 'Kleda' is then transported to the kidneys ('Vrikkas') to be converted into 'Poshya Mootra'. While some of this is filtered by glomeruli and stored in the bladder, the majority is reabsorbed into the bloodstream.

Pitfalls and Future Directions in the Ayurvedic View

Despite its comprehensive framework, the Ayurvedic view of the urinary system has certain perceived limitations from a modern perspective:

1. Kidney's Role in Urine Formation: 'Vrikkas' (kidneys) have not been explicitly related to the primary process of urine formation in classical texts.

2. Ambiguity of 'Basti': The term 'Basti' has been used loosely at various instances, potentially referring to the urinary bladder or enema procedures.

3. Lack of Strict Terminology: Due to an emphasis on clinical application, there is not always strict adherence to consistent terminology.

Nevertheless, Ayurveda has adequately recognized the urinary system as 'Mootravaha Srotas' in its fundamental texts. Detailed descriptions of various diseases like 'Ashmaree' (calculi), 'Ashthila' (prostate enlargement), and 'Mootraghat' (dysuria) are found in works by Charaka, Sushruta, and Vagbhata, complete with treatments and dietary regimens. Even the suppression of the urge to micturate ('Mootravega') is considered detrimental, leading to various ailments.

Different scholars have interpreted the verses of Sushruta Nidanasthana (3/18-24) from diverse angles, suggesting the complexity and room for varying interpretations within the Ayurvedic tradition. It is imperative to integrate existing modern knowledge of the urinary system with a re-arrangement and re-orientation of Ayurvedic concepts into clear, descriptive language to resolve ambiguities and foster a unified understanding.

 Ayurvedic Concepts on the Urinary System

1. The Ayurvedic concept of the urinary system ('Mootravaha Srotas') is broader than the modern perspective, encompassing both physiological and clinical dimensions46.

2. 'Vrikka' (kidneys) and 'Pakvashaya' (large intestine) are considered equally important; the latter is active in 'Poshaka Mootra' (precursor urine) formation, while the former is responsible for 'Poshya Mootra' (formed urine).

3. The 'Pakvashaya' is identified as the site of 'Poshaka Mootra' formation, a fact with therapeutic implications for chronic conditions like renal failure.

Urine Examination According to Ayurveda9

Urinary ailments have been a persistent challenge for humanity, with both modern science and Ayurveda striving to find solutions. Ayurvedic physicians historically diagnosed urinary disorders through clinical examination and pathological investigations described in classical texts, offering affordable alternatives to modern pathological tests. Ayurveda employs visual examination of urine, particularly its color, and a specialized test called 'Taila Bindu Pariksha' (oil drop test) as described by Yogratnakar. Urine examination is crucial for diagnosing urinary disorders, including 'Mootrakricchra' (dysuria) and 'Mootraghat' (anuria/oliguria), which often involve vitiation of 'Vata', 'Pitta', 'Kapha', or 'Rakta'. The color and characteristics of urine provide insights into the vitiated 'Doshas', while the 'Taila Bindu Pariksha' offers prognostic information. Ayurveda also specifies the time for urine collection, recommending a mid-stream sample taken 96 minutes (4 'Ghatikas') before sunrise, similar to modern practice. Daily examination until recovery is advised.

Physical Examination of Urine

Ayurveda describes various urine colors and characteristics corresponding to different 'Dosha' imbalances and conditions:

Taila Bindu Pariksha (Oil Drop Test)10

Yogratnakar detailed the 'Taila Bindu Pariksha' for prognosis and 'Dosha' detection in urinary disorders. A drop of oil is gently placed on the urine surface in a breeze-free room, and its behavior, direction of spread, and shape are observed.

Urine in Various Urinary Disorders11,12,12

Ayurvedic classics describe specific urine characteristics for various diseases. Charaka details 20 types of 'Prameha' (urinary disorders, including diabetes), each with a distinct urine color and characteristic.

Discussion

The Ayurvedic view of the urinary system provides a comprehensive yet holistic outlook, merging anatomical, physiological, and pathological insights. While the role of 'Vrikkas' is well acknowledged in Ayurveda, their exclusive responsibility in urine formation, as detailed in modern nephrology, remains somewhat understated in classical texts. Nevertheless, the understanding of 'Kleda', 'Udaka', and their transformation into 'Mootra' reveals a sophisticated physiological theory comparable to renal filtration and reabsorption. The relationship between 'Pakvashaya' and urine formation finds modern parallels in gut-kidney axis theories, especially in electrolyte and fluid balance.14 Ayurvedic urine examination, especially through the 'Taila Bindu Pariksha', provides unique prognostic tools. These traditional methods, although lacking quantitative precision, offer insight into systemic imbalances through qualitative observations, which modern science is beginning to validate. Future research should aim to bridge gaps between traditional diagnostics and evidence-based nephrology, especially for early diagnosis and management of chronic urinary disorders.15

Conclusion

Ayurveda provides a scientific and detailed approach to urine examination for diagnosing urinary disorders. The described tests are simple and can be performed in a clinical setting. Modern scientific research has corroborated the logic and applicability of these Ayurvedic examinations for various urinary conditions.