Digestive system

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Questions and Answers

What is the primary function of the alimentary tract?

To circulate blood throughout the body

To store unused food for later digestion

To provide insulation to the body

To convert food into small, nutritional molecules (correct)

Which of the following represents the correct order of the digestive processes?

Digestion, Ingestion, Propulsion, Absorption, Elimination

Ingestion, Propulsion, Absorption, Elimination, Digestion

Absorption, Propulsion, Ingestion, Digestion, Elimination

Ingestion, Propulsion, Digestion, Absorption, Elimination (correct)

What layer of the digestive tract provides the main peristaltic movements?

Muscularis (correct)

Submucous

Mucosa

Adventitia/Serosa

Which accessory organ is involved in producing bile?

Liver Signup and view all the answers

What component of the digestive system helps with immune function?

Mucus (IgA) Signup and view all the answers

What is the primary function of salivary amylase in the mouth?

To break down polysaccharides into maltose Signup and view all the answers

Which structure in the mouth prevents food from entering the nasal cavity during swallowing?

Uvula Signup and view all the answers

What is the main role of peristalsis in the digestive tract?

To propel food through the digestive tract Signup and view all the answers

How do the salivary glands contribute to digestion in the mouth?

By moistening food to form a bolus and containing digestive enzymes Signup and view all the answers

In what way is the first phase of swallowing characterized?

Voluntary and initiated by the tongue Signup and view all the answers

What is formed during mastication, ready for swallowing?

Bolus Signup and view all the answers

What assists in the formation of the bolus during chewing?

Teeth and tongue Signup and view all the answers

What needs to be closed off before swallowing takes place?

Epiglottis Signup and view all the answers

What is the function of the smooth muscle found in the wall of the oesophagus?

To aid in peristalsis Signup and view all the answers

Which structure separates the stomach from the small intestine?

Pyloric sphincter Signup and view all the answers

What do the rugae in the stomach lining facilitate?

Expansion of the stomach Signup and view all the answers

What is primarily secreted by the parietal cells in the stomach?

Hydrochloric acid Signup and view all the answers

Which of the following cells produces pepsin for protein digestion?

Chief cells Signup and view all the answers

What is one of the roles of mucus in the stomach?

Protecting the lining from acid Signup and view all the answers

What type of substances can be absorbed by the stomach?

Water and alcohol Signup and view all the answers

Study Notes

Alimentary Tract

A tube that extends from the mouth to the rectum.
As food moves through the tube, it is ground and mixed with digestive juices.
It converts food into small nutritional molecules for absorption and distribution by circulation to all the body's tissue and excretes residues.

Alimentary Tract Function

It is also part of the immune system by means of mucus, low pH and enzymes.

Components of the Digestive System

It is composed of the mouth, oesophagus, stomach, small intestine, and large intestine.

Accessory Organs

The salivary glands, liver, pancreas and gall bladder.

General Structure of the Alimentary Tract

The walls of the digestive tract consist of four layers:
- Adventitia/serosa - outer covering of connective tissue
- Muscularis - smooth muscle that provides contraction (peristalsis) to move food, consists of two layers, the outer layer is longitudinal, the inner layer is circular
- Submucous - loose connective tissue contains blood vessels, lymphatic vessels, nerves, and glands
- Mucosa - lining epithelial layer coated with mucus

In the Mouth (Mechanical)

Teeth - to tear, rip, and chew food to physically break it down into smaller pieces.
Uvula - stops food or liquid entering the nasal cavity.
Tongue - voluntary muscular structure, important in mastication and deglutition.

In the Mouth (Chemical)

Salivary amylase (ptyalin) breaks down polysaccharides (starch) in the bolus to maltose (a less complex sugar).
Taste buds allow appreciation and sample potential hazards.

Bolus

This is a round or oval-shaped mass of food formed in the mouth after thorough chewing.

Salivary Glands (3 Pairs)

Submandibular - at the angle of the jaw, opens into the floor of the mouth, source of 70% of saliva.
Sublingual - in front of the submandibular pair, opens into the floor of the mouth, source of 5% of saliva.
Parotid - below the external acoustic meatus, the duct opens into the mouth opposite the buccal of the second upper molar, source of 25% of saliva.

Swallowing

Involves coordinated activity of the tongue, soft palate, pharynx, and oesophagus.
The first phase is voluntary as food is forced into the pharynx by the tongue.
After this, swallowing is a reflex process.
The tongue blocks the mouth, the soft palate closes the nose, and the larynx rises so the epiglottis closes off the trachea.
Food moves into the pharynx and onwards by peristalsis.

Oesophagus

Swallowed bolus travels from the mouth to the stomach via a muscular tube.
It is about 25cm long and the first part of the digestive tract proper.
It is lined with a mucus membrane that secretes fluid to lubricate the downward movement of food.
It also has a smooth muscle wall that contracts to squeeze food towards the stomach.

Peristalsis

Rhythmic contraction of smooth muscles propels contents through the digestive tract.
Waves - circular contractions occur behind the bolus to prevent backward movement, followed by contraction of longitudinal smooth muscles to push the bolus forward.

More Digestive Tract Movements

Segmentation - a muscular movement in the small intestine, a mixing rather than a propulsive movement.
Vomiting - propulsion comes from the contraction of abdominal muscles, peristalsis does not reverse in the oesophagus.

Stomach

Hollow muscular organ, J-shaped, left side of the abdominal cavity.
Highly acidic environment, regulated by the oesophageal sphincter and pyloric sphincter.

Structures of the Stomach

The lining of the stomach has numerous folds when empty called rugae; they allow for expansion when we eat.
Has numerous gastric glands that secrete “gastric juice” into the stomach.
The most common cells found in the glands are:
- Parietal cells – produce HCL acid that denatures proteins
- Chief cells – produce pepsin that begins protein digestion
- Mucus cells – produce mucus that protects from Hydrochloric action.

Stomach Lining

The epithelium forms deep pits which can contain glands.
Glands secrete hormones, enzymes, and mucus.
The stomach absorbs some water, lipids, caffeine, and alcohol.

Function of the Stomach

Temporary storage area for food (3-4 hours) which is also churned by muscular layers to form chyme.
Muscles relax and contract to aid mechanical breakdown.
Pyloric sphincter holds food in the stomach and allows for emptying of chyme into the small intestine.

Small Intestine

Comprises the duodenum, jejunum, and ileum.
The site of the majority of digestion.
Longest part of the system.
Usually sterile.

Duodenum

The first part of the small intestine, 25 cms long.
It curves around the head of the pancreas and the entry of the common bile duct.
Chemical degradation of small amounts of food, controlled by the pyloric sphincter, begins here.
Enzymes secreted by the pancreas and duodenum itself aid digestion of fats by emulsifying fats.

2 Ducts Enter Duodenum

Bile duct draining the gall bladder from the liver.
Pancreatic duct draining the pancreas.

Jejunum & Ileum

Jejunum (2metres) and ileum (3 metres) continue the absorption process of carbohydrates, proteins, and fats.
Surface area increased by being covered in wrinkles/folds with microscopic projections called villi.
Lined with simple columnar epithelium, the cells of the villi carry projections called microvilli.
Large surface area available for nutrient absorption.

Villi

Each villus has a capillary and a lacteal.
- Lacteal - absorb fat into the lymphatic system.
- Capillaries - absorb everything else.

Pancreatic Fluid

Contains:
- Sodium bicarbonate to neutralise acidity of the contents arriving from the stomach.
- Pancreatic amylase – carbohydrates → simple sugars.
- Pancreatic lipase – lipids → fatty acids & glycerol.
- Trypsin & chymotrypsin – protein → amino acids.
- Nucleases – hydrolyse ingested nucleic acids (RNA/DNA) into component nucleotides.

Functions of the Liver including its role in digestion

Https://www.youtube.com/watch?v=s2JwoqcnyS8

Large Intestine (Colon)

Food is not broken down any more.
Absorption of remaining water from indigestible food matter.
Some electrolytes and indigestible food left.
Stores and eliminates waste.
Absorbs vitamins produced by gut bacteria, especially vitamin K and certain B vitamins.

Rectum

Last 13 cmps of the large intestine.
Stores solid waste until it leaves the body through the anus.
Peristaltic waves.
Sphincter relaxation.

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Description

Explore the anatomy and functions of the alimentary tract in this quiz. Learn about the various components of the digestive system, including the accessory organs and the layers of the digestive tract. Test your knowledge on the processes involved in digestion and absorption.