Digestive-System-featu

Digestive System of Humans Explained with Diagrams

by

Overview

The system that breaks down the food into useable form i.e., energy or ATP is the digestive system.

In humans, it consists of the mouth, oesophagus, stomach, and glands associated with the digestive system like salivary gland, liver, pancreas, small and large intestines.

The mouth and oral cavity help in selection of food, grinding or mastication and lubrication. As a result of mastication, the softened, partly digested, slimy food mass is rolled into small oval lump called bolus.

The waves of contraction of circular and longitudinal muscles preceded by wave of relaxation thus squeezing the food down along the canal are called peristalsis.

After entering the stomach, gastric juice is released for digestion. The stomach wall is composed of three layers. After digesting in stomach food is converted into semi-solid mass called chyme.

It is further digested in the small intestine and absorption of food takes place in the ileum which has numerous fingers-like outgrowths called villi. In the end, there is the large intestine which is composed of the caecum, colon, and rectum.

Table of Contents Hide
Digestive System of Humans

The digestive system of a human includes a long-coiled tube that extends from the mouth to the rectum. The main parts in the direction of passage of food, are the oral or buccal cavity, oesophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (ascending colon, transverse colon, descending colon, caecum and rectum).

Connected with the different areas are the glands, especially salivary glands, liver and pancreas. There are 3 sites of digestion in the gastrointestinal system of human – mouth, stomach and small intestine.

Digestive-System-featu

Food Digestion in Oral Cavity

There are several functions of the mouth, the most apparent being the

  • (a) selection of food,
  • (b) grinding or mastication
  • (c) lubrication and
  • (d) digestion.
Selection of food

When food gets in the oral cavity (the cavity bounded by palate, tongue, teeth and cheeks) it is tasted, smelled and felt. If the taste or smell is unpleasant or if hard items like bone or dirt are present in the food, it is rejected. The oral cavity is helped in choice by the senses of odour, taste and sight.

The tongue being sensory and muscular organ plays the most crucial role in the selection of food through its taste.

food-selection

Grinding or mastication

After selection, the food is ground by means of molar teeth into smaller sized pieces. This is useful as

  • (a) the oesophagus allows fairly small pieces to pass through and
  • (b) small pieces have a lot more surface area for the enzyme to attack.
Lubrication and food digestion

These are the primary functions of the oral cavity accomplished by saliva. Saliva is secreted by three pairs of salivary glands particularly sublingual glands situated below the tongue; submaxillary glands behind the jaws and parotid glands in front of the ears. Saliva produced by these glands contains three essential ingredients.

  • i) Water and mucus
  • ii) Sodium bicarbonate and some other salts,
  • iii) Carbohydrates absorbing and digesting enzymes, amylase or ptyalin.
Further Reading:  Angiospermic Family - Family ROSACEAE [19 MCQs]

Water and mucus together make a slimy liquid which serves to moisten and lubricate the food so that it can be chewed efficaciously and passed through the oesophagus efficiently.

Sodium bicarbonate and some other salts are a little antiseptic however their primary function is to stabilize the pH of food. Fresh saliva is alkaline with a pH nearly 8, quickly loses CO2 and gets to pH 6. Ptyalin is a carb – digesting enzyme, which digests starch and glycogen to maltose.

Swallowing

As a result of mastication, the softened, partially digested, slimy food mass is rolled into a small oval lump called a bolus, which is then pushed to the back of the mouth by the action of tongue and muscles of the pharynx which ensure that the food does not go into the windpipe. Following are the events which happen during swallowing:

  • i) the tongue moves upwards and backwards against the roofing system of the mouth, forcing the bolus to the back of the mouth cavity.
  • ii) The backward motion of the tongue presses the soft taste buds up and closes the nasal opening at the back. At the same time, the tongue requires the epiglottis (a flap of cartilage) into basically horizontal position hence closing the opening of the windpipe (the glottis).

epiglottis

  • iii) The throat, cartilage round the top of the windpipe moves upward under the back of the tongue.
  • iv) The glottis is partly closed by the contraction of a ring of muscle.
  • v) The food does not enter the partly open glottis, because the epiglottis diverts the food mass to one side of the opening and safely down the oesophagus. The beginning of the swallowing action is voluntary, once the food reaches the back of the mouth, swallowing ends up being automatic.

The food is then forced down the oesophagus by peristalsis.

Peristalsis

These are particular movements of the gastrointestinal system by which food is moved along the cavity of the canal. It consists of the wave of contraction of the circular and longitudinal muscles preceded by the wave of relaxation therefore squeezing the food down along the canal. Peristalsis starts simply behind the mass of food from the buccal cavity along the oesophagus to the stomach and after that along the whole alimentary canal.

Peristalsis

Antiperistalsis

Sometimes, the movements are reversed, with the resulting food might be passed from the intestine back into the stomach and even into the mouth. This movement is called antiperistalsis, causing vomiting.

Hunger Pang

Hunger contractions are peristaltic contractions which are increased by low blood sugar levels and are sufficiently strong to develop an uneasy experience typically called a “hunger pang”. Hunger pangs usually begin 12 to 24 hours after the previous meal or in less time for some people.

Digestive System of Humans – MCQs

  1. What is the primary function of the digestive system in humans?
    • A. Blood circulation
    • B. ATP synthesis
    • C. Breakdown of food into usable form
    • D. Oxygen transport
    • Answer: C
  2. Which organs are part of the digestive system in humans?
    • A. Heart, lungs, liver
    • B. Mouth, stomach, kidneys
    • C. Stomach, small intestine, large intestine
    • D. Brain, spleen, pancreas
    • Answer: C
  3. What is the semi-solid mass called after food digestion in the stomach?
    • A. Bolus
    • B. Chyme
    • C. Peristalsis
    • D. Villi
    • Answer: B
  4. Where does the absorption of food take place in the digestive system?
    • A. Stomach
    • B. Large intestine
    • C. Ileum
    • D. Oesophagus
    • Answer: C
  5. What are the three main components of saliva?
    • A. Water, mucus, carbohydrates
    • B. Sodium bicarbonate, salts, lipids
    • C. Proteins, enzymes, vitamins
    • D. Glucose, fructose, amino acids
    • Answer: A
  6. Which enzyme in saliva digests starch and glycogen to maltose?
    • A. Lipase
    • B. Protease
    • C. Amylase (Ptyalin)
    • D. Nuclease
    • Answer: C
  7. What is the small oval lump formed after mastication called?
    • A. Chyme
    • B. Bolus
    • C. Glottis
    • D. Villus
    • Answer: B
  8. What initiates the swallowing process during the digestive system?
    • A. Contraction of circular muscles
    • B. Epiglottis closure
    • C. Tongue movement
    • D. Antiperistalsis
    • Answer: C
  9. What prevents food from entering the windpipe during swallowing?
    • A. Epiglottis
    • B. Glottis
    • C. Tongue
    • D. Pharynx
    • Answer: A
  10. What is the involuntary movement that pushes food down the oesophagus after swallowing?
  • A. Antiperistalsis
  • B. Peristalsis
  • C. Villus action
  • D. Hunger pang
  • Answer: B
  1. Which term describes the reversal of peristaltic movements, leading to vomiting?
    • A. Epiglottis
    • B. Antiperistalsis
    • C. Bolus action
    • D. Glottis closure
    • Answer: B
  2. What causes hunger contractions in the digestive system?
    • A. High blood sugar levels
    • B. Antiperistalsis
    • C. Low blood sugar levels
    • D. Villi absorption
    • Answer: C
  3. When do hunger pangs typically occur?
    • A. Immediately after a meal
    • B. 6-8 hours after a meal
    • C. 12-24 hours after a meal
    • D. Only during fasting
    • Answer: C
  4. What is the function of villi in the digestive system?
    • A. Lubrication
    • B. Absorption of nutrients
    • C. Grinding
    • D. Selection of food
    • Answer: B
Further Reading:  Genetic Codes

 

Frequently Asked Questions (FAQs) – Digestive System of Humans

1. What does the digestive system do in humans?

  • The digestive system breaks down food into a usable form, which is converted into energy or ATP.

2. What are the main organs of the human digestive system?

  • The human digestive system includes the mouth, esophagus, stomach, and glands such as salivary glands, liver, pancreas, small intestine, and large intestine.

3. How is food processed in the oral cavity?

  • The oral cavity performs functions such as the selection of food, grinding or mastication, lubrication, and digestion.

4. What is the role of the tongue in food selection?

  • The tongue, being a sensory and muscular organ, plays a crucial role in the selection of food through taste.

5. Why is mastication important in digestion?

  • Mastication, or grinding of food by molar teeth, breaks down food into smaller pieces, increasing the surface area for enzymes to act and facilitating swallowing.

6. What are the components of saliva, and what functions do they serve?

  • Saliva, produced by salivary glands, contains water and mucus for lubrication, sodium bicarbonate and salts to stabilize pH, and enzymes like amylase (ptyalin) for carbohydrate digestion.

7. How does swallowing occur, and what safeguards are in place to prevent choking?

  • Swallowing involves the tongue moving the bolus to the back of the mouth, closing the nasal and windpipe openings. The epiglottis ensures food enters the esophagus, not the windpipe.

8. What is peristalsis, and how does it help in the digestive process?

  • Peristalsis is the wave-like contraction of muscles that propels food along the digestive tract, ensuring its movement from the mouth to the stomach and through the entire alimentary canal.
Further Reading:  Class Mammalia - Mammals

9. What is antiperistalsis, and when does it occur?

  • Antiperistalsis is the reverse movement of the digestive system, causing vomiting. It occurs when food is passed from the intestine back into the stomach or mouth.

10. What are hunger pangs, and when do they typically occur?

  • Hunger pangs are peristaltic contractions triggered by low blood sugar levels, causing an uncomfortable feeling. They usually start 12 to 24 hours after the previous meal.

 

Summary

The digestive system in humans, vital for breaking down food into usable energy (ATP), encompasses various organs such as the mouth, esophagus, stomach, and associated glands like the salivary gland, liver, pancreas, small intestine, and large intestine. This tutorial explored the functions of the oral cavity, emphasizing food selection, grinding (mastication), lubrication, and digestion.

After mastication, the food forms a bolus, initiating peristalsis—a coordinated muscular contraction that propels the food through the digestive tract. Gastric juice in the stomach aids digestion, transforming the food into chyme, a semi-solid mass. Further digestion occurs in the small intestine, where absorption through villi in the ileum takes place. The large intestine, composed of the caecum, colon, and rectum, completes the digestive process.

The tutorial also covered essential functions of saliva, including lubrication and digestion through enzymes like amylase. Swallowing, a voluntary action, transitions to automatic peristalsis in the esophagus. Antiperistalsis, a reversal of digestive movements, can lead to vomiting.

Hunger contractions, known as hunger pangs, are peristaltic contractions triggered by low blood sugar levels, typically occurring 12 to 24 hours after the last meal. This comprehensive overview provides a detailed understanding of the digestive system’s intricacies in humans, highlighting its crucial role in nutrient processing and energy production.

You may also like to learn: