Talu: Modern aspect, Anatomy and Physiology of Palate, Hypothalamus

Article by Dr Raghuram Y.S. MD (ay) & Dr Manasa S, B.A.M.S

Talu is an organ which figures out in the context of ‘udakavaha srotas’ i.e. the explanation of water conveying and controlling channels and stations in the body.

Talu is popularly correlated with ‘the palate’ because the signs of vitiation of water conveying channels is manifested in the palate in the form of thirst which once again points towards dehydration of varying degrees in the body.

Some experts have also correlated talu to the brain centers controlling the water balance in the body which are anatomically located above the level of talu i.e. palate, ‘hypothalamus to be precise’.

Anatomy & physiology of palate

Palate forms the roof of the mouth in human beings (and also in other mammals). It separates the mouth (oral cavity) and the nasal cavity. It is divided into two parts.

Hard Palate – The front part (anterior) of the palate is made up of bony plate and is called a hard palate.

Soft Palate – The behind part (posterior) is fleshy and is called a soft palate or velum. Cleft palate is a condition which occurs if the fusion between these two parts is incomplete.

The sensory innervations to the palate are by the maxillary nerve branch of the trigeminal nerve.

Functions in human beings – The main function of palate is to produce certain sounds. Palate produces sounds when functioning in sync with other parts of the mouth. These sounds include velar, palatal, palatalized, postalveolar, alveolo palatal and uvular consonants.

The word palate is derived from the Latin palatum via Old French palate which refers to the ‘roof of the mouth’.

Roof of the mouth as in palate, was once considered as the ‘seat of taste sensation’. Palate can also refer to this sense itself.

1. Hard Palate

The hard palate is made up of a thin horizontal plate of bone. It is made up of two bones located in the roof of the mouth i.e. palatine process of maxilla and horizontal plate of palatine bone. This part of the palate spans the alveolar arch formed by the alveolar process. In later parts of life when they are developed, they hold the upper teeth.

Teeth in Ayurveda are called Ruchaka Asthi i.e. bones related to taste or bones which help in tasting the food. Modern medicine also has considered the palate as the seat of taste sensation (discussed above). So a mathematically hard palate also represents a part of ruchaka asthi.

The hard palate forms a partition between the nasal passages and the mouth.

Plicae – are irregular ridges in the mucus membrane on the front (anterior) portion of the hard palate. It helps food to move backward towards the larynx.

The partition continues deeper into the mouth by a fleshy extension called soft palate which is the other part of the palate.

Palatine rugae – are some projections or transverse ridges which are present on the ventral surface of the hard palate.

Hard Palate Functions

– Feeding
– Speech
– Mastication (in some species)
– In production of speech sounds (in interaction with tongue) , mainly high front vowels, palatal consonants and retroflex consonants

Mastication and perception of taste takes place in the mouth. This zone belongs to Bodhaka Kapha. Palate is also said to be related to taste perception. Speech production is under the control of Udana Vata.

Clinical importance

Cleft Palate – It is a birth defect. In this condition the right and left portions of this bony plate are not joined. Therefore a gap exists between the mouth and nasal passage. Cleft lip is a related defect that affects the face. Cleft palate severely meddles with the ability to speak and nurse. Nowadays it is successfully treated through reconstructive surgery done at an early age. Though the exact cause of this condition is not known, maternal smoking is said to be the most influential risk factor. Apart from this there are also several genetic risk factors.

Palatal abscess – It is not uncommon for abscesses to occur in the palate.

Hard palate pigmentation – Bluish grey pigmentation in the hard palate was found to occur in those using the drug chloroquine for long durations, in those suffering from rheumatoid arthritis for a longer time and other conditions.

Hard palate is made up of asthi dhatu. While cleft palate is caused by vitiated vata affecting the fetus, palatal abscess is predominantly caused by pitta aggravation affecting the palate. Hard palate pigmentation can occur due to pitta and vata.

Soft Palate

Soft palate is also known as the velum, muscular plate or palatal venum. It is the soft tissue making up the back of the roof of the mouth. Along with the other part i.e. hard palate, it forms the palate of the mouth. While the hard palate is made up of the bone, the soft palate isn’t.

Soft palate is made up of five important muscles. Tensor veli palatini (involved in swallowing), Palatoglossus and Levator veli palatini – all these three muscles are involved in swallowing while the fourth muscle Palatopharyngeus is involved in breathing. The fifth muscle which moves the uvula is called by the name Musculus uvulae. Except Tensor veli palatini, all other muscles are innervated by the pharyngeal plexus of nerves via the vagus nerve. Mandibular division of the trigeminal nerve supplies the Tensor veli palatini.

Functions of soft palate

Since the soft palate consists of muscles it is movable. It closes the nasal passages while swallowing (of food) and also closes the airway. It protects the nasal passage during sneezing by diverting a portion of excreted substance to the mouth. In some people when the uvula which hangs from the end of the soft palate is touched or when the soft palate is touched, it evokes a strong gag reflex.

Speech – The soft palate retracts and elevates during the speech so as to separate the oral cavity from the nasal cavity. This will enable production of oral speech sounds. Nasal speech is a type of speech which is identified if this separation is incomplete leading to escape of air through the nose. Velar consonant is a speech sound made with the middle of the tongue touching the soft palate.

Soft palate is made up of mamsa dhatu. Functionally Prana Vata and Udana Vata operate at the level of the soft palate and help in swallowing, speaking and breathing functions.

Clinical Importance of Soft Palate

Below mentioned conditions occur in the soft palate –

Mucus membrane –

– Pemphigus vulgaris
– Migratory stomatitis
– Herpangina

Muscular –

– Congenital cleft palate
– Cleft uvula

Streptococcal Pharyngitis presents with petechiae on the soft palate. The other causes shall be ruled out.

Hypothalamus – Anatomy, physiology, Talu Link

Hypothalamus is a structure located deep in the brain. It is the main link between the nervous system and endocrine system. It is responsible for homeostasis (keeping the body in a stable and balanced state). Hypothalamus does this by directly influencing the autonomic nervous system or by managing hormones. It also manages the body temperature, hunger, thirst, sleep sex drive, mood and blood pressure. In brief, hypothalamus is the body’s ‘smart control’ coordinating center. It also makes some hormones which are stored in the posterior pituitary. It sends signals to the pituitary gland. As a result the pituitary gland will release hormones that would directly affect a part of the body or would send another signal to a different gland. That gland then releases its hormone.

The pituitary gland is located below the hypothalamus and is made up of two lobes – anterior and posterior pituitary. Hypothalamus communicates with the anterior lobe through a network of blood vessels while it communicates with the posterior lobe through pituitary stalk. Hypothalamus sends signals in the form of releasing hormones. By doing so it influences and tells the pituitary lobes to release their hormones.

The areas of the brain that contribute to ‘the thirst sensation’ are located in the mid and hindbrain. Hypothalamus specifically plays a key role in the regulation of thirst. Early scientists had designated hypothalamus as the ‘body’s primary thirst center’.

According to Ayurveda, thirst is manifested in talu – the palate. Hypothalamus anatomically is situated above the level of palate. Therefore some experts have equated hypothalamus with talu, apart from palate.

Vasopressin or Antidiuretic Hormone (ADH) is one of the hormones made by the hypothalamus and stored in the posterior pituitary. It regulates control of one’s body’s water or urine volume and blood pressure.

Diabetes insipidus is a condition which happens when hypothalamus does not produce and release enough vasopressin. It causes kidneys to lose too much water. This results in excessive urination and thirst.

Among many symptoms, hypothalamus dysfunction may cause either retention of water or dehydration.

Concept of thirst & the TALU link – Is Talu ‘the Hypothalamus’?

As already discussed, thirst is an indicator of fluid balance. Ingested fluids regulate the homeostasis of body water and this in turn is dependent on thirst. According to Ayurveda, trishna or thirst is a vega i.e. natural body demand or urge as a response to water imbalances occurring in the body. It is this thirst that drives us to ingest water.

Thirst is a sensation created by the hypothalamus, the ‘thirst centre’ of the human body. Anatomically its site is roughly over (above) the level of palate i.e. talu which is the one of the roots of the water conveying channels and also a site of control of these channels as already discussed. In these terms, talu can also be correlated to hypothalamus though not anatomically to be precise but functionally.

Mechanism of Hypothalamus Mediated Thirst

Since our talu can be hypothalamus, it is important to understand in this context the mechanism of thirst mediated by hypothalamus.

A sensory receptor called osmoreceptor found in the hypothalamus detects changes in osmotic pressure. They detect changes in the concentration of solutes dissolved in the blood (osmolarity).

When the osmolarity of blood changes (either getting more or less dilute), water diffusion into and out of the osmoreceptor cells also changes. This is to tell that the cells expand when the blood plasma is more dilute and contract with higher concentration.

When the osmoreceptors detect high plasma osmolarity (often representing a low blood volume), they send signals to the hypothalamus, which creates the biological sensation of thirst and also stimulates Vasopressin (ADH) secretion, which in turn starts the events that will reduce osmolarity to normal levels.

Mechanism of Renin-Angiotensin System Mediated Thirst

Thirst is also induced through another pathway, through angiotensin-II, one of the hormones involved in the renin-angiotensin system. This system is a complex homeostatic pathway that deals with blood volume as a whole, as well as plasma osmolarity and blood pressure.

Nephrons are the structural units of the kidney. There are macula densa cells in the walls of the ascending loop of henle. This is another type of osmoreceptor. It stimulates the JGA (juxtaglomerular apparatus) and not the hypothalamus. When these cells are stimulated by high osmolarity, the JGA releases renin into the bloodstream. This cleaves angiotensinogen into angiotensin I. Angiotensin I is converted into Angiotensin II by ACE (angiotensin converting enzyme – a hormone) in the lungs. This Angiotensin II acts on the hypothalamus to cause the sensation of thirst. It also causes vaso-constriction and release of aldosterone. Aldosterone causes increased water reabsorption in a mechanism that is very similar to that of ADH.

Alternatively, stimulation of the sympathetic nervous system and low blood pressure in the kidney’s (decreased GFR) will stimulate the renin-angiotensin system and will also cause an increase in thirst.

Ayurvedic explanation of udakavaha srotas and its sites of operation (mula sthana) or sites of manifestation of symptoms of thirst (trishna) as a part of vitiation of these channels might not correlate exactly with the concept of water balancing mechanism explained by the modern texts (including physiology of thirst), but they serve the same purpose. They suggest the deficit of water in the body and a call for its fulfillment.