Chapter 22 - Digestive System Flashcards
Identify the organs of the digestive system
Learner objective
The digestive system consists of the mouth, pharynx, oesophagus, stomach, small intestines, large intestines, rectum, and anus.
The accessory organs include the salivary glands, liver, gallbladder, and pancreas.
Explain the processes by which materials move through the digestive tract
(Learner objective)
In the small intestine, peristalsis consist of the propelling, wave like movements of the tube.
Contraction appears in the wall of the tube in a “ring”, whereas the muscular wall immediately ahead of the “ring” relaxes.
The peristaltic wave moves along, pushing the contents of the tube towards the anus.
What are nutrients used for in the body
Life is sustained by obtaining nutrients from the environment.
Nutrients are raw materials needed to synthesise essential compounds in the body.
They may also be decomposed to provide energy required by the cells to continue functioning.
Digestion
The mechanical and chemical breakdown of foods and the absorption of resulting nutrients by the body cells are known as digestion.
Mechanical digestion
Mechanical digestion is the process of breaking large pieces of food into smaller ones without altering their chemical make up
Chemical digestion
Chemical digestion uses chemicals to break food into simpler chemicals.
The two major divisions of the digestive system
the alimentary canal
the accessory digestive organs
Organs of the digestive system
The digestive system extends from the mouth to the anus and includes the mouth, pharynx, oesophagus, stomach, small intestine, large intestines, rectum, and anus
Associated accessory organs of the digestive system
Salivary glands, liver, gallbladder, and pancreas.
The secretions from these accessory organs empty via ducts into the digestive tract.
Glandular organ secretions are made up of water, enzymes, buffers, and other components. The secretions assist in preparing organic and inorganic nutrients for absorption across the epithelium of the digestive tract.
The digestive system is basically a tube open at both ends and supplies nutrients the body cells. Its surface area in an adult is 186 m²
Alimentary canal
Also known as the gastrointestinal tract or gut.
The alimentary canal is an 8 m long continuous muscular tube passing through the thoracic and abdominopelvic cavities.
The digestive tube consists of four major layers, Present from the oesophagus to the anus:
And internal mucosa
Submucosa
Muscularis (circular muscle and longitudinal muscle)
External serosa
The mucosa
Consisting of three layers
- the inner mucosa epithelium, which is made up of moist stratified squamous epithelium in the mouth, oral pharynx, oesophagus, and anal canal.
- A loose connective tissue called the lamina propria
- A thin outer layer of smooth muscle. It has projections extending into the lumen that increase its absorptive surface.
The mucosa carries out secretion and absorption.
Submucosa
Loose connective tissue with glands, blood vessels, lymphatic vessels, and nerves.
It nourishes surrounding tissues and carries away absorbed materials
Muscularis
Produces movements of the tube and is made of two smooth muscle tissue types:
Circular fibres of the inner coat encircle the tube, causing contraction.
Longitudinal fibres run lengthways, causing shortening of the tube.
Serosa
Composed of a visceral peritoneum on the outside and connective-tissue beneath.
It protects underlying tissues and secretes serious fluid so abdominal organs slide freely against each other.
The serosa is also called the adventitia.
Functions of the digestive system
Propulsion Ingestion Mechanical processing (breakdown) Digestion Absorption Secretion Excretion
Functions of the digestive system: ingestion
Materials enter the digestive tract via the mouth
Functions of the digestive system: propulsion
The movement of food, which includes voluntarily swallowing and involuntary peristalsis, which is the primary means of propulsion.
Peristalsis involves alternating waves of muscular contraction and relaxation in the walls of the alimentary canal.
Functions of the digestive system: mechanical processing (breakdown)
Materials are crushed and broken into smaller fragments, making them easier to move through the digestive tract.
Enzymes begin to attack the particles during chewing, as the teeth and tongue are used to tear and mash food.
Additional mechanical processing is provided by the mixing motions of the stomach and intestines.
Mechanical processing increases ingested foods surface areas.
Segmentation mixes foods with digestive juices, improving their absorption by moving various parts of the food mass over the intestinal wall repeatedly.
Functions of the digestive system: digestion
The chemical breakdown of food into particles that are small enough to be absorbed by the digestive epithelium from the lumen or cavity of the canal.
Simple molecules such as glucose are absorbed in tact, whereas polysaccharides, proteins, and triglycerides must first be broken down before they can be absorbed. This is a catabolic process.
Functions of the digestive system: secretion
Release of water, acids, buffers, enzymes and salts by the epithelium and glandular organs of the digestive tract.
Functions of the digestive system: absorption
The movement of organic substrates, electrolytes, vitamins, and water across the epithelium of the digestive tract into the interstitial fluid.
Organic substrates are molecules acted on by enzymes.
Absorption occurs by active or passive transport into blood or lymph
Functions of the digestive system: excretion
The removal of waste products from body fluids via secretions from the digestive tract and glandular organs.
After mixing with residue that cannot be digested, these waste products become faeces, which are eliminated during the process of defecation.
