Digestive System Flashcards
What are the subdivisions of the digestive system ?
- Digestive tract (30-40 m)
- accessory organs
What are some examples of accessory organs ?
- teeth, tongue, salivary glands, liver, gallbladder
What are the key functions of the GI tract?
- digestion
- absorption
- storage & elimination
Describe the digestive tract histology
- mucosa
- submucosa
- muscularis
- serosa
Describe the Mucosa
- innermost layer
- contains the epithelial cells important in lubrication & absorption
Describe the Submucosa
- contains support network blood vessels & immune cells to keep mucosa healthy
Describe the muscularis
- contains muscles necessary for peristalsis
Describe the Serosa
- the outermost layer which allows GI tract to interact with other tissues around it
What are some of the different ways food moves through the GI tract?
- ingestion
- mastication
- deglutition
- peristalsis
Define Ingestion
taking food into the mouth
Define Deglutition
swallowing food
Define Peristalsis
- rhythmic wave-like contractions that move food through GI tract
Describe the process of the wave-like contractions of peristalsis
- circular smooth muscle contract behind, relaxes un front of bolus
- followed by shortening of smooth muscle
Define reverse peristalsis
- vomiting
- causes bolus to move in the opposite direction
What are the 2 types of secretions secreted by the GI tract ?
- Exocrine - lipase, pepsin, amylase
- Endocrine - gastrin, secretin
What are the 4 different categories of digestive enzymes ?
- Carbohydrases
- proteases/peptidases
- Lipases
- Nucleases
Why are some enzymes synthesised as inactive precursors ?
if they produced inside the cell this would lead to autolysis (self digestion)
How are digestive enzymes that are secreted inactive activated ?
- via cleavage or 1 or a few specific peptide bonds
What are the 3 types of peritoneum ?
- Visceral = covers organs
- Parietal = covers interior surface of body wall
- Retroparietal = behind peritoneum as kidneys, pancreas and duodenum
Define Mesenteries
- routes which vessels & nerves pass from body wall to organs
Define the Greater Omentum
Apron-like structure that lies superficial to the small intestine & transverse colon - a site of fat deposition in people who are overweight
Describe the Lesser Omentum
Suspends the stomach from the inferior border of the liver
- provides pathway for structure to the liver
What are the 3 pairs of salivary glands?
- parotid - 25%
- Submandibular - 70%
- Sublingual - 5%
What are the properties of Saliva ?
- 99.5% water
- salivary amylase & lysozyme
- electrolytes
- pH 6.8-7
What are the functions of saliva ?
- cleansing of mouth - prevents bacterial infection
- lubrication, mucus = aids swallowing
- facilitation of taste
- aids in speech
What are the 3 phases of Deglutition ?
- voluntary
- pharyngeal
- oesophageal
Describe the Oesophagus
- muscular tube
- 10 inches long in adults
- moves food to stomach
- no absorption
- food is propelled via peristalsis
- major layers = mucosa, submucosa, muscular
What are the 5 regions of the stomach ?
- cardiac
- fundus
- body
- antrum/pyloric
What are the 4 layers of the stomach ?
- mucosa
- submucosa
- muscularis
- serosa
What are the 3 sub layers of the muscularis ?
- longitudinal
- circular
- oblique
What are Rugae ?
- folds in stomach lining to increase surface area with the lumen
What are the functions of the stomach ?
- disinfection via acidic conditions
- digestion
- mechanical breakdown via churning
- disruption via acidic environment breaking chemical bonds
What Gastric pits ?
opening for gastric glands
What are the 3 phases involved in gastric acid secretion & regulation ?
- Cephalic phase
- Gastric phase
- intestinal phase
Describe the Cephalic Phase
- stimuli = sight/smell/taste/chewing
- pathway = parasympathetic nerves
- effect = increased HCI secretion
Describe the Gastric Phase
- stimuli = distention, pH
- pathway = gastrin, long, short neural reflexes
- effect = increased HCl secretion
Describe the Intestinal Phase
- stimuli = distension, pH, osmolarity
- pathway = secretin, CCK, short neural reflexes
- effect = decreased HCl secretion
Describes the Movement in stomach
- controlled pacemaker cell in longitudinal muscle layer
- swallowing centre signals stomach to relax
- arrriving food stretches the stomach activating a receptive-relaxtiong response –> resists stretching briefly but relaxes to hold more food
Describe the structure of the small intestine
- 4 layers - mucosa, submucosa, muscularis, serosa
- 6m long
- 3 sections - duodenum, jejunum, ileum
- Ileocecal valve = where ileum connects to colon
- contains plicae circulares & intestinal vili
Define Plicae Circulares
- the permanent spiral or circular folds in the lining of the small intestine
What cells are present in the Mucosa of the small intestine ?
- absorptive, goblet, granular , endocrine
What is the function of intestinal stem cells ?
replace lost or damaged intestinal cells
What is the function of Paneth Cells ?
involved in intestinal defence
What is the function of goblet cells ?
produce lubricating mucus
What is the function of Enterocytes?
absorbs nutrients
What does the small intestine secrete ?
- mucus
- digestive enzymes = peptidases/nucleases
Define Chyme
- acidic fluid which passes from the stomach to the small intestine
What are the steps of Intestinal Motility ?
- mixes chyme with intestinal juice & bile
- churns chyme to increase contact with mucosa
- move residue towards large intestine - segmentation occurs
What is the gastroileal reflex ?
- relaxing of valve & filling of cecum
Describe the Vermiform Appendix ?
- wormlike sac
- vestigial structure
Describe the structure of the large intestine
- 5 feet long
- horseshoe shaped
- begins as cecum & appendix in lower right corner
- sluggish movements - transit time 12/24 hours
Describe the histology of the large intestine
- mucosa is simple columnar epithelial
- no circular folds or vili to increase SA
- intestinal crypts produce mucus only
What are the 2 sections of the pancreas ?
- exocrine - secretes pancreatic juice - Acing cells
- endocrine - secretes insulin & glucagon - B-Islet cells
What is the importance of the Pancreas ?
- inactivates pepsin
- prevents acid-pepsin damage
- increase solubility of bile acids & fatty acids
Define Zymogen
- an inactive precursor of an enzyme
How are the majority of pancreatic enzymes produced ?
as zymogens (inactive )
What is the importance of Trypsin activation in the duodenum ?
- initiates the activation of multiple zymogens with roles in digestion
What are the key functions of the liver?
- bile production
- storage
- detoxification
- phagocytosis
- synthesis
What is the function of bile ?
- have hydrophobic & hydrophilic regions
-hydrophobic areas allow to interact with the fat droplet & hydrophilic area allow them to interact - allows them to break ft droplets into small bile salt coated droplets called micelles
