Introduction to GIT Function Flashcards
The digestive system consists of?
- neuronal and muscular tissues
- epithelia with absorptive and secretory functions 3. endocrine cells
- target cells for the gastrointestinal hormones
Name the 2 components of the digestive system?
- gastrointestinal tract 2. accessory digestive organs
Describe the course of the digestive system?
extends from mouth to anus - 9 m long
Name the organs of the GIT?
- oral cavity 2. pharynx 3. oesophagus 4. stomach 5. small intestine 6. large intestine
Name the accessory digestive organs?
- teeth 2. tongue 3. salivary glands 4. liver 5. gall bladder 6. pancreas
What are the 7 functions of the GIT?
- ingestion
- mechanical digestion and chemical digestion
- secretion
- absorption
- motility/peristalsis
- excretion
- immune and protective role of GIT
What is ingestion?
when materials enter the digestive tract via the mouth
Describe ingestion?
is an active process involving conscious choice and decision making
What is mechanical digestion?
physical manipulation and distortion through the actions of the teeth, tongue, and palatal surfaces
Describe mechanical digestion?
Tearing and crushing with teeth followed by squashing and compaction by the tongue (preliminary mechanical processing) - may or not be required before ingestion
What is the importance of mechanical digestion?
- make food easier to propel along the digestive tract
2. increases the surface area for enzymatic attack
What is chemical digestion?
chemical breakdown of food into small organic fragments suitable for absorption by the digestive epithelium
What is the purpose of chemical digestion?
to break down food into simple molecules - simple molecules in food such as glucose can be absorbed intact, but large molecules e.g. polysaccharides or triglycerides cannot be absorbed
What are the 2 types of secretions?
- endocrine 2. exocrine
Describe exocrine secretions?
the release of saliva, acids, digestive enzymes, buffers and salts by the epithelium of the digestive tract
Describe endocrine secretions?
secretion of hormones that regulate the digestive system
What is absorption?
The movement of organic substrates, electrolytes (inorganic ions), vitamins and water across the digestive epithelium into the interstitial fluid of the digestive tract
What is motility/peristalsis?
The rhythmic wavelike contractions of the smooth muscle of the intestines that move food through the GI tract.
What is excretion?
elimination of waste products from the body - The digestive tract and glandular organs secrete waste products in secretions discharged into the lumen of the tract
Waste products are ejected through?
defecation/egestion
Waste products are ejected as?
faeces - waste products + indegestable residue
Describe the protective role of the lining of the GIT?
- Corrosive effects of the digestive acids and enzymes
- Mechanical stresses such as abrasion
- Bacteria that either is swallowed with food or reside inside the digestive tract
- Bacteria reaching the underlying tissues are attacked by macrophages and other cells of the immune system
The activities of the digestive system are regulated by?
neural, hormonal and local mechanisms
What is the nervous system of the GI tract?
enteric nervous system - 100 million neurons
What does the enteric nervous system consist of?
- myenteric plexus 2. submucosal plexus
Where is the myenteric plexus? (Auerbachs plexus)
lies between the longitudinal and circular muscles
Function of the myenteric plexus?
controls mainly GI movements
Where is the submucosal plexus? (Meissners plexus)
lies in the submucosa
Function of the submucosal plexus?
regulates GI blood flow and epithelial cell function (local intestinal secretion and absorption)
Nerve plexuses near the GI tract initiate what? (intrinsic)
short reflexes
What are the extrinsic controls of the GI tract?
- sympathetic 2. parasympathetic 3. somatic
Extrinsic controls initiate what?
long reflexes arising within or outside the GI tract
What do motor neurons that terminate in the smooth muscle do?
stimulate contractions
What do motor neurons that terminate on the intestinal crypts do?
stimulate salt and water secretion into lumen
What does the parasympathetic nervous system do?
stimulates motility + secretions by the GI tract
What does the sympathetic nervous system do?
- reduces peristalsis + secretory activity
- stimulate the contraction of sphincter muscles along the GI tract
- inhibit GI functions
What are the receptors of the GIT?
- mechanoreceptors 2. chemoreceptors
What do these receptors of the GIT respond to?
- stretch
- presence of substrate
- osmolarity
- pH
- end product of digestion
Receptors of the Git initiate reflexes that?
- activate or inhibit digestive glands
2. mix lumen contents and move them along
Describe long reflexes?
- provide a higher level of control that coordinates activities along the length of the digestive tract
- generally control large scale peristaltic waves that move materials from one region of the digestive tract to another
- may involve motor fibres in the glossopharyngeal, vagus, or pelvic nerves that synapse in the myenteric plexus
How can neural commands be affected?
the sensitivity of the smooth muscle cells to neural commands can be enhanced or inhibited by digestive hormones
Function of gastrin?
stimulates acid production
Function of secretin?
stimulates pancreatic bicarbonate secretion
Function of chlocystokinin?
stimulates gall bladder contractility
Describe local/paracrine mechanisms?
prostaglandins, histamine and other chemicals released into the interstitial fluid affect cells within a small segment of the digestive system
Function of these mechansims?
these local messengers are important in coordinating a response to conditions that affect a portion of the digestive tract (e.g. pH) - for example histamine in the lamina propria of the stomach stimulates secretion of acid by cells in the adjacent epithelium
