14. Human Nutrition
Human Nutrition & Digestion
What is Nutrition?
Nutrition is the sum of all processes by which an organism (like a human) consumes and uses food. According to the World Health Organization (WHO), it is the intake of food in relation to what your body needs.
To be healthy, our body needs specific items in the right amounts: Carbohydrates, Proteins, Fats, Vitamins, Minerals, Water, and Fibers.
The 5 Steps of the Digestive Process
Nutrition isn't just eating; it involves these five technical stages:
- Ingestion: Putting food into the mouth.
- Digestion: Breaking complex, large food into small, simple pieces.
- Absorption: The blood picking up the nutrients.
- Assimilation: The body cells using those nutrients for energy and growth.
- Egestion: Removing the undigested waste from the body.
The Alimentary Canal
The Secret of the Small Intestine: Villi
Have you ever wondered how the small intestine absorbs so much food so quickly? The secret lies in its unique inner lining. It isn't smooth like a pipe; instead, it is covered in millions of tiny structures!
- Villi: These are finger-like folds formed by the Mucosa (the innermost layer). Think of them like the "fibers of a towel" that soak up water. They increase the surface area for absorption significantly.
- Microvilli (Brush Border): The cells covering each villus have even tinier projections on their surface called microvilli. This looks like a brush under a microscope, which is why it is called a Brush Border.
-
Blood Capillaries & Lacteals: Inside every single villus, there is a busy transport network.
- Capillaries (tiny blood vessels) pick up sugars and proteins.
- Lacteals (lymph vessels) pick up fats that are too big for the blood vessels.
- Crypts of Lieberkühn: At the base (the bottom) of the villi, the mucosa dips down to form small pits or "crypts." These act as Intestinal Glands that produce digestive juices.
1. Villi = Finger-like folds.
2. Microvilli = Tiny hair-like projections on the cells.
3. Capillaries = Absorb Carbs/Proteins.
4. Lacteals = Absorb Fats.
5. Crypts = Intestinal glands located at the base.
The Alimentary Canal is a long, muscular tube starting from the Mouth and ending at the Anus. It is about 8 to 10 meters long.
1. The Mouth (Buccal Cavity)
This is where food enters. It has a roof called the Palate, side walls called Cheeks, and a floor made of the Tongue.
Teeth: An adult has 32 teeth. Scientists describe human teeth in three ways:
- Thecodont: Each tooth is fixed in a deep socket in the jaw bone.
- Diphyodont: We get two sets of teeth in our lifetime (Milk teeth and Permanent teeth).
- Heterodont: We have different shapes of teeth (Incisors, Canines, Premolars, and Molars).
The top part of the tooth is the Crown (covered in Enamel, the hardest substance in the body). Inside is the Dentin and the Pulp Cavity which contains blood and nerves.
Tongue: A triangular muscle that helps move food and contains Taste Buds.
2. Pharynx and Oesophagus
The Pharynx is a common passage for food and air. A flap called the Epiglottis acts like a traffic guard, closing the windpipe so food doesn't go into your lungs.
The Oesophagus is a 25cm long tube. It moves food down to the stomach using Peristalsis (rhythmic waves of muscle contraction).
3. The Stomach
The stomach is a 'J' shaped muscular bag. It has four parts: Cardiac, Fundus, Body, and Pylorus. It stores food for 4-5 hours and turns it into a creamy paste called Chyme.
Gastric Juice: Contains HCl (Acid), Pepsin (breaks protein), and Mucus (protects the stomach from its own acid).
4. The Small Intestine
This is the main site of digestion. It is 6 meters long and has three parts:
- Duodenum: 'U' shaped, first part.
- Jejunum: Coiled middle part.
- Ileum: Highly coiled, opens into the large intestine.
The walls have finger-like folds called Villi to absorb nutrients into the blood.
5. The Large Intestine
It is 1.5 meters long. Its job is to absorb water and store waste. It has the Caecum (with the vermiform appendix), Colon, and Rectum.
The Major Digestive Glands
1. Liver: The largest gland (1.2 - 1.5 kg). It produces Bile, which helps break down fats (Emulsification). It also stores glucose as Glycogen.
2. Pancreas: A leaf-shaped gland. It produces Pancreatic Juice (enzymes for carbs, proteins, and fats) and hormones like Insulin.
3. Salivary Glands: Three pairs (Parotid, Submandibular, Sublingual). They produce Salivary Amylase which digests starch into sugar.
How Digestion Works (Physiology)
Digestion is both Mechanical (chewing/churning) and Chemical (enzymes breaking bonds).
| Location | Enzyme | Action |
|---|---|---|
| Mouth | Salivary Amylase. | Starch → Maltose (Sugar) |
| Stomach | Pepsin (in HCl) | Proteins → Peptones |
| Small Intestine | Bile | Emulsifies Fats |
| Small Intestine | Trypsin | Proteins → Amino Acids |
| Small Intestine | Lipase | Fats → Fatty Acids |
Absorption and Disorders
Absorption: 90% happens in the small intestine. Water and some drugs are absorbed in the large intestine. Assimilation is when these nutrients become part of your living cells.
Health Disorders
- Kwashiorkar: Protein deficiency in kids (1-3 years). Symptoms: Fat belly, thin legs.
- Marasmus: Severe calorie and protein deficiency in infants. Symptoms: Skin and bone appearance.
- Jaundice: Liver trouble causing yellowing of eyes/skin due to Bilirubin.
- Vomiting: Controlled by the medulla in the brain; food comes out due to reverse peristalsis.
- Constipation: Infrequent bowel movements due to low fiber or water.
📘 ONE PAGE REVISION CHART
Human Nutrition 🙎♂️
Nutrition is the process of taking food and using it for energy, growth, repair and maintenance.
Carbohydrates • Proteins • Fats • Vitamins • Minerals • Water • Fibre
Ingestion → Digestion → Absorption → Assimilation → Egestion
🍽️ DIGESTION
Definition: Conversion of complex food into simple absorbable substances. Types:• Mechanical digestion – chewing, churning, peristalsis
• Chemical digestion – enzyme action
👨⚕️ HUMAN DIGESTIVE SYSTEM
Two Parts:• Alimentary Canal
• Digestive Glands
🟢 ALIMENTARY CANAL
- Mouth – Chewing, saliva secretion
- Teeth – 32; Thecodont, Diphyodont, Heterodont
- Tongue – Taste, swallowing
- Pharynx – Common passage
- Oesophagus – Peristalsis
- Stomach – Stores food, churns, gastric juice
- Small Intestine – Digestion & absorption
- Large Intestine – Water absorption, faeces formation
- Anus – Egestion
🔬 HISTOLOGICAL LAYERS
🧪 DIGESTIVE GLANDS
- Salivary glands – Salivary amylase
- Liver – Bile, detoxification, glycogen storage
- Pancreas – Digestive enzymes, insulin, glucagon
⚙️ PHYSIOLOGY OF DIGESTION
Mouth: Starch → Maltose (Salivary amylase)Stomach: Proteins → Peptones (Pepsin, HCl)
Small Intestine:
• Carbohydrates → Glucose
• Proteins → Amino acids
• Fats → Fatty acids + Monoglycerides
🔄 ABSORPTION, ASSIMILATION & EGESTION
- Absorption – Nutrients enter blood & lymph (mainly in small intestine)
- Assimilation – Use of nutrients by body cells
- Egestion – Removal of faeces
⚠️ DISORDERS
• Kwashiorkor – Protein deficiency
• Marasmus – Severe calorie deficiency
- Indigestion
- Constipation
- Diarrhoea
- Jaundice
- Vomiting
Balanced diet + water + fibre = Healthy digestion
Comments
Post a Comment