Gut 1 Flashcards
What is the alimentary tract?
The alimentary tract: essentially a tube from mouth to anus that is specialized in different regions for the digestion and absorption of nutrients.
What structures does the mouth contain?
- Buccal cavity
- Tongue- manupulation of food into a bolus
- Dentition (Upper 2.1.2.3. Lower 2.1.2.3. (Incisors, canine, premolars, molars)-aids mastication
- Lipids- helps
In descending order of the alimentary tract, what comes after the mouth
- Oesophagus
- Hard and soft palate
- Uvula
- Pharynx
What are the 3 pairs of salivary glands?
3 pairs:
- parotid
- submandibular
- sublingual
What are the main structures associated with the stomach?
- Cardiac sphincter
- fundus, body
- antrum
- pyloric sphincter
What are the compontents of the large intestine?
- Ileo-caecal valve
- caecum
- appendix
- ascending/transverse/descending colon, sigmoid colon
- rectum
- anus
Abosrbs water and stores faeces
What are the functional components of the small intestine?
- duodenum
- jejunum
- Ileum
This is where most absorption takes place
What structures are the accessory organs of the alimentary tract?
- Liver- produces bile by breaking down RBCs and other things
- gall bladder- Bile deliverd here by the liver
- bile duct- essential for breaking down fats into smaller lipid droplets
- sphincter of Oddi- separates common bile duct from small intestine
- Pancreas- , important to producing secretions that aid in digestion, 99% exocrine tissue that releases enzymes e.g. lypolytic and proteolytic enzymes into the small intestine
- pancreatic duct-joines pancreas to small intestine
Label the components of the alimentary tract
What is the main purpose of the digestive system?
The digestive system transfers nutrients, water, and electrolytes from food into the body’s internal environment
Fluid homeostasis needs to be maintained
The digestive system performs four basic digestive processes:
–Motility→ propel cpntents in one digestion
–Secretion→ Cells and glands that secrete different digestive enzymes and othercomponents e.g. mucus that provides lubrication
–Digestion→ Breaking down large complex molecules into small absorbable units e.g. proteins into peptides
–Absorption→ Micronutrients needed for cellular reactions to take place
Describe the Anatomy and Functions of Components of the Digestive System
*
What are the accessory digestive organs?
- salivary glands
- exocrine pancreas
- biliary system
The digestive wall has four layers:
–Mucosa→ absorption of nutrients across the mucosa
–Submucosa→ Underneath epithelial cells that line the GI tract
–Muscularis externa→ smooth muscle (involuntary)
–Serosa → Outermost layer which secreates muscus to reduce friction, irritation and pain
Describe the layers of the digestive tract wall
The digestive tract wall consists of four major layers: from the innermost out, they are the mucosa (fingerlike projection to maximise absorptiom), submucosa, muscularis externa (outer longitudinal muscle+ inner circular muscle), and serosa (thin layer that secretes lubricating mucus).
Peritoneum* anchors GI tract to body wall
What alters digestive activity through neural and hormonal pathways?
•Receptor activation alters digestive activity through neural and hormonal pathways
Gut-Brain axis (consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions)
feed forward mechanism involved in the increased production of saliva (regulatory loop in that a stimulus temporally associated with food (input) triggers salivation (output) in advance of presentation of food)
–Chemoreceptors- detect changes in coposition, mechanoreceptors- detect stretch, and osmoreceptor helps maintain fluid and electrolyte balance
What structures are included within the oral cavity?
Mouth:
Buccal cavity
Tongue (filiform papillae)
Hard and soft palate.
Uvula.
Pharynx
Dentition: Incisors, canine, premolars, molars
Upper 2.1.2.3.
Lower 2.1.2.3.
The salivary glands:
What are the 3 pairs?
How are the cells arranged?
- 3 pairs of salivary glands:
Parotid, submandibular, sublingual.
- Within salivary glands, cells are arranged into secretory acini and ducts.
- Cells lining the ducts also contribute to the products of the glands.
Salivary glands:
What are salivary secretions mostly controlled by?
- Salivary secretions are controlled mostly by neural reflexes (especially PSNS)
- Tongue, taste buds, sensory afferents via facial VII and glossopharyngeal IX, salivary nuclei in medulla oblongata, efferents via autonomic ganglia, activate glands.
- Dry food – all secretions moist food less mucus.
- 7th and 10th cranial nerve sends signally to salivary centers in the medulla which sends signals via the parasympatheic NS increases saliva secretion from the salivary glands*
Describe Salivary Secretion
•It is ontinuous and can be increased by reflex
–Simple and conditioned salivary reflexes (next slide)
–Autonomic influence on salivary secretion
•Digestion starts in the mouth and is minimal; no absorption of nutrients occurs
–Digestion in the mouth involves the hydrolysis of polysaccharides by amylase
•Most digestion is accomplished in the stomach after food mass and saliva have been swallowed
Compare the pathways by which eating food and smelling food increase salivary secretion.
- Pressure and chemoreceptors in the mouth sends signals to the salivary centers in the medulla, higher centers of the brain involved with thinking, seeing and smelling food also send signals to the medulla
- Medulla send signals via the autonomic nerves to the salivary glands to either increase or decrease the production of saliva
Describe the location and function and function of the Pharynx and Oesophagus
What happens if food enters the trachea?
•The pharynx is the cavity at the rear of the throat
–Acts as a common passageway for both the digestive and respiratory system (air and food)
•Swallowing is a sequentially programmed all-or-none reflex
Epiglottis closes over the trachea as you swallow to make sure food goes into the oesophagus or epiglottis
–Swallowing center activates swallowing muscles
•During swallowing, food is prevented from entering the wrong passageways
food would otherwise be forced into the trachea or down into the lungs causing aspiration pneumonia
What prevents air from entering the digestive tract?
What pushes food through the esophagus?
•The pharyngoesophageal sphincter prevents air from entering the digestive tract
–Remains closed during swallowing
•Peristaltic waves push food through the esophagus
–Primary peristaltic wave sweeps from the beginning to end of the esophagus, forcing the bolus ahead of it toward the stomach (don’t have to be upright to swallow- gravity independent)
What are the three stages involved in the swallowing reflex?
- Buccal (oral) stage
Voluntary, bolus formation, bolus moved to back of mouth
- Pharyngeal stage
Bolus pushes on soft palate, initiates swallow reflex, epiglottis closes, tongue pushes up, forcing bolus back; upper oesophageal sphincter relaxes
- Oesophageal stage
Bolus entering oesophagus initiates oesophageal peristalsis
What cranial nerves and brain centers innervate the Bolus,Tongue, pharynx, Upper oesophageal sphincter, Oesophageal peristalsis and Cardiac sphincter?
Bolus activates mechanoreceptors in the back of the pharynx which sends signals via the 9th and 10th cranial nerve to the swallowing center found in the lateral reticular formation (within the medulla) which innervates the tissues involved in the swallowing reflex via the 9th 10th and 11th cranial nerve
