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Lecture to 2nd year medical students by Professor Omar Hasan Kasule. Kulliyah of Medicine, International Islamic University, Kuantan, MALAYSIA.
OUTLINE
1.0 THE NOSE AND SMELLING
A. The Nose
B. Physiology
C. Types and sources of odors
D. Functions of smell
E. Variations of smell
2.0 THE TONGUE AND TASTING
A. Taste in the Qur'an
B. Anatomy
C. Physiology
D. Types and sources of tastes
E. Functions of tastes
3.0 CHEMO AND OSMO-RECEPTORS
A. Acid-base
B. Electrolytes
C. Hormones
D. Enzymes
E. Metabolites
1.0 THE NOSE AND SMELLING
A. THE NOSE
The Qur'an mentioned the nose but did not refer to its olfactory function (p 278 5:45, 68:16). The sense of smell is mediated through chemo-receptors that are in the epithelium of the nasal cavity. Material in gaseous form dissolves in the nasal fluid and results in exciting some nerve endings. The sense of smell in humans has not been studied very well.
B. PHYSIOLOGY
Smell in humans is poorly understood. There is an olfactory threshold below which no smell is possible. The threshold varies with each odoriferous substance. Normal olfactory sensitivity is variable and is unpredictable. There is no causal relation between chemical structure and odor. Adaptation or desensitization occurs when the odor stays for a long time. The senses of smell and taste work together. The flavors of many substances are a combination of taste and smell. Taste has less impact on behavior than smell.
C. TYPES AND SOURCES OF ODORS
The Qur'anic term for odor is raihat. The Qur'an reports the prophet Yaqub smelling the odor of the shirt belonging to his son Yusuf (p. 462 12:94).
Odors may be pleasant or unpleasant. Musk, misk, has been mentioned in the Qur'an (83:26) and hadith (Muslim #5578, 5599, 5600, 5601) as a pleasant odor. The Prophet enjoyed the smell of perfumes (KS 479: Nisai K28 B2; Nisai K36 B1; Tayalisi H2042 & H2681).
The odor of raw garlic, thum, is unpleasant and the Prophet forbade those who had eaten it from the mosque (KS 119: Tayalisi H53 & H2171; Ahmad V.1 p15 & p3 p85 & V. 5 p413 & p420; MB# 485 p 260, #486 p 261, MUSLIM #1141, 1142, 1143, 1144, 1145, 1146, 11467, 1148, 1149, 1150, 1157). The oral odor of the fasting person is unpleasant to humans but is most pleasant to Allah (KS p. 325: Bukhari K30 B2 & B9; Bukhari K77 B78; Muslim K13 H158 & H162-164; Tirmidhi K6 B54; Tayalisi H2367 & H2413 & H2485).
Perfumes were used and were recommended by the Prophet. They suppress unpleasant odors. Perfume was recommended for pubic places (MB# 493 p. 263) because they are likely to be a source of obnoxious odors. Perfumes and incense make the atmosphere smell well thus creating a feeling of pleasure. This facilitates social intercourse.
D. FUNCTIONS OF SMELL
The smell of food raises appetite. It also stimulates salivary and gastric secretions in preparation for digestion of food. The sense of small as a means of self-protection is limited in humans because they generally can not smell out enemies. Humans have learned to associate some smells with dangerous substances that have to be avoided. For example the smell of rotten food warns humans not to eat it. Odors can be used deliberately for pleasure eg perfume and incense.
E. VARIATIONS OF SMELL
Smell and gender: There is a relation between smell and sex in animals. Females secrete chemicals called pheromones that attract males. No human counter-part to pheromone has been described. Human females have a better sense of smell than males. This smell is more acute during ovulation.
Human vs animal smell: Humans are micro-osmic with small olfactory lobes. Animals are macro-osmic with relatively large olfactory lobes. Humans can distinguish among 2000-4000 different odors; however they have poor ability to distinguish intensity of smells. Dogs have better developed smell. If human smell was more acute social life would become more difficult due to obnoxious odors.
8.3.2 THE TONGUE AND TASTING
A. TASTE IN THE QUR'AN
The Qur'an concentrates on the tongue, lisaan, as an organ of talking and not tasting. The term taste, dhawq, has been used to refer to Adam tasting the forbidden tree (7:22) or the tasting of punishment by those condemned to hell (38:57). The Qur'an has used this term extensively to refer to metaphorical tasting, dhawq ma'anawi (p.459 3:185, 5:95, 6:65, 17:75, 21:35, 29:57, 44:56). Tasting has been used metaphorically to refer to punishment in the hereafter, dhawq al 'adhaab (p 459 3:106, 3:181, 4:56, 6:30, 6:148, 7:39, 8:14, 8:35, 8:50, 9:35, 10:52, 10:70, 16:94, 16:112, 22:9, 22:22, 22:25, 25:19, 29:55, 30:41, 32:14, 32:20, 32:21, 34:12, 34:42, 35:37, 37:31, 37:38, 38:8, 39:24, 39:26, 41:16, 41:27, 41:50, 44:47-49, 46:34, 51:13-14, 54:37, 54:39, 54:48, 59:15, 64:5, 65:9, 78:30). Taste has also been metaphorically to refer to tasting bounties, dhawq al naim (p? 10:21, 11:9-10, 30:33, 30:36, 30:46).
B. ANATOMY
The taste buds are the sensory end-organs for taste. They are distributed on the human tongue. Each part of the tongue seems specialized for particular tastes. Taste sensations are transmitted to the cortex where they are interpreted.
C. PHYSIOLOGY
The sense of taste in humans is poorly understood. Taste chemo-receptors are in the taste buds. Taste discrimination in humans is poor. Some tastes are better appreciated at some parts of the tongue and not others. The same substance may produce different taste at different places on the tongue. Specific hunger for sweet or salty things is possible. The basic taste modalities are: sour, salt, bitter, and sweet. More complex tastes are combinations of these primary taste modalities.
D. TYPES and SOURCES OF TASTES
Ordinary table salt is perhaps the commonest substance tasted by humans. It is an essential part of the diet (KS 348: Ibn Majah K29 B32).
E. FUNCTIONS OF TASTE
The sense of taste like that of smell helps in provoking appetite and preparation for digestion. Dangerous substances can be tasted out and can be avoided. There is wisdom in the poor sense of taste in babies. Their low food discrimination enables them to eat a wide variety of baby food that has little or no taste.
DISCUSSION
- Explain why the olfactory lobe is relatively big while the human sense of smell is so poorly developed
- What in your opinion is the hikmat behind the poorly developed human sense of smell
- What in your view could be the hikmat for a taste sensation that is even less developed than the small sensation
- Why are spices used in food. How does that relate to the human sense of smell and taste
- What was the role of spices in European and world history starting in the 15th century CE
- What is the wisdom behind the poorly developed non-discriminating taste of newborns
- What is your opinion about the following statement: ' food is commercially promoted for its appearance, smell, and taste and not its nutritional value'
- Explain how the Qur'anic concepts of tawazun and I'itidaal relate to the control of plasma osmolality
- Explain how the Qur'anic concept of tadafu'u relates to control of blood glucose levels.
- Interpret the hadith of the prophet about flatus that a praying person should not interrupt prayer until he hears a sound or smells a smell.