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Questions and Answers
What is the primary function of the alimentary tract?
Which of the following represents the correct order of the digestive processes?
What layer of the digestive tract provides the main peristaltic movements?
Which accessory organ is involved in producing bile?
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What component of the digestive system helps with immune function?
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What is the primary function of salivary amylase in the mouth?
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Which structure in the mouth prevents food from entering the nasal cavity during swallowing?
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What is the main role of peristalsis in the digestive tract?
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How do the salivary glands contribute to digestion in the mouth?
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In what way is the first phase of swallowing characterized?
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What is formed during mastication, ready for swallowing?
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What assists in the formation of the bolus during chewing?
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What needs to be closed off before swallowing takes place?
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What is the function of the smooth muscle found in the wall of the oesophagus?
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Which structure separates the stomach from the small intestine?
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What do the rugae in the stomach lining facilitate?
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What is primarily secreted by the parietal cells in the stomach?
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Which of the following cells produces pepsin for protein digestion?
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What is one of the roles of mucus in the stomach?
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What type of substances can be absorbed by the stomach?
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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
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.
