Digestion 1 Flashcards
What does the digestive system consists of?
The digestive tract
Accessory digestive organs;
-Salivary glands
-Exocrine pancreas
-Biliary system
What are the 4 Basic digestive processes?
Motility / Mechanical processing
Secretion
Digestion (chemical breakdown)
Absorption
What are the components of the digestive system?
- Oral cavity, teeth, tongue= mechanical processing, moisturising, mixing with salivary secretion
- salivary glands
- pharynx (back of mouth helps shape food for swallowing)
- esophagus (transport of bolus of food
5.stomach
6.contribution of liver (bile) stored in gallbladder and pancreas secreting enzyme and buffering secretions to top bit of small intestine - small intestine
- large intestine
What are the 4 layers of the gastrointestinal tract?
- mucosa= working from lumen first layer that has contact with the food
- sub-mucosa
- muscularis externa (important for motility)
- serosa (holds gut in place)
Describe the Mucosa
Function: protection, secretion & absorption
(inner to outer)
Mucous membrane: inner epithelial surface layer
for protection and areas of secretion + absorption
Lamina propria: connective tissue supporting the structure and epithelium – it contains the GALT (immune defence tissue).
Muscularis mucosa: thin layer of smooth muscle
adjacent to sub-mucosa.
Describe the sub-mucosa
A layer of connective tissue allowing the tract to be distensible and elastic.
Also contains larger blood and lymph vessels and it contains the submucosal plexus also known as (nerve network aka Meissner’s plexus). It has its own nervous system to control functioning of intestinal tract.
Glands also present in sub-mucosa.
Describe the Muscularis externa
Smooth muscle layer
Inner circular muscle (pinch behind food)
Contraction constricts/decreases lumen diameter
controlled by Myenteric Plexus (Auerbach’s plexus) found in between these two types of muscles
Outer longitudinal muscle (expansion and contraction)
Contraction: Shortening of tube
Describe the serosa?
Outer connective tissue covering of the digestive tract. This holds the GI tract to prevent it from potentially knotting.
Secretes a watery serous fluid: a lubricant preventing friction between digestive organs and surrounding viscera.
Continuous with mesentery (a sling for the digestive organs in the abdominal cavity)
- mesothelial cells.
holds the gut in place.
Motility START: The buccal cavity
Food enters digestive system
Chewing/mixing with saliva (teeth, tongue, palates, lubrication)
Facilitate swallowing- shapes food into smaller structure
(pharangeal muscles in pharynx allows process of swallowing into esophagus)
The Swallowing Process
we need to avoid food going to tracheae
what are the two phases?
Buccal phase: (shapng food)
Tongue forces bolus along hard palate to soft palate at back of mouth.
Pharangeal phase:
Tongue forces food downwards, epiglottis closes over trachea, bolus is forced down into oesophagus.
The Oesophagus
How to we prevent food from scouring oesophagus
Describe histology
It needs lots of muscle.
you need mucous, it has layer of mucosa –>submucosa and thick layer of muscularis.
It doesn’t have a serosa but its does have a layer of tissue called adventitia. No need for serosa because chest cavity, lungs and heart keep it in place.
Distinctive features of the esophageal wall include
-Nonkeratinized, stratified squamous (scaly layers) epithelium (outer layer)
-Folded mucosa and submucosa (Mucous secretions by esophageal glands) facilitate transit of food due to secretions
-A muscularis with both smooth and skeletal muscle portions
-Lacks serosa
Anchored by an adventitia
Motility - Oesophagus
Peristalsis
Contractions occur in oesophagus, small intestine
stomach, colon and ureters.
Peristaltic wave forms behind bolus, passes along
intestine toward rectum at 2-25cm/sec.
these waves are induces in response to stretch stimulus: MYENTERIC REFLEX.
Waves occur in the absence of extrinsic innervation but
in the presence of the myenteric Auerbach’s plexus (its own nervous system)
Serotonin/Substance P localised role to activate neurons
of myenteric plexus.
Peristalsis – involuntary muscular movements
- contraction of circular muscles behind food mass
2.contraction of longitudinal
Gastroesophageal sphincter; entry into
The Stomach
Describe histology
Gastroesophageal sphincter allows food from oesophagus to enter the stomach
Stomach has 4 layers (but different structure in muscularis)
-Mucosa
-Submucosa
-Muscularis (circular, longitudinal and oblique)
-Subserosa and Serosa
Upper part of stomach pits have
Gastric glands
Parietal cells (oxyntic) =Intrinsic factor, and HCl
Chief cells=Pepsinogen (inactive enzyme form)
- Mucus cells (goblet cells)
Bottom part
Pyloric glands
endocrine cells include G cells which release gastrin and D cells releasing somatostatin
Motility: The Stomach
Gastric filling – relaxation of musculature
At the beginning its about storage of food which initiates process of secretion and digestion starting with peristaltic contraction, these are too weak to mix without oblique layer.
Storage – body of stomach, peristaltic contractions
of thin muscular walls too weak to mix
Mixing – by vigorous peristaltic contractions in
thick-muscled antrum (middle part of stomach)
Emptying – volume and fluidity of chyme (into duodenum)
Gastroenteric reflexes initiated by stretch receptors in stomach, empty chyme into the Small Intestine
Important digestive and absorptive functions
Secretions and buffers provided by pancreas, liver, gall bladder
finger like projections (villi) that allow you to absorb nutrients.
Three subdivisions: (structural and functional differences)
Duodenum
Jejunum
Ileum
Duodenum
In the duodenum we get secretions from pancreas and gallbladder
Pancreas= (control of sugar through insulin=endocrine) exocrine =production of digestive juices
The Gallbladder (extends from liver)=Hollow, pear-shaped organ Stores, modifies and concentrates bile (emulsifies fats)
What is the histology of the small intestine?
Going up in magnification (getting smaller)
Plicae = Transverse folds of the intestinal lining (help maintain structural inegrity)
Villi = Fingerlike projections of the mucus (all about absorption)
Lacteals= Terminal lymphatic in villus (process of absorption) drains out fat containing products
Intestinal glands= Lined by enteroendocrine, goblet (secretes mucus) and stem cells (important that its self renewing i this environment)
GALT (gut associated lymph tissue)= aggregated lymphoid nodules (Payer’s patches)
Intestinal motility what are the movements
5 Types of movement
*Peristalsis ( circular and longitudinal muscles for contractions.)
*Tonus changes (local smooth muscle contraction independent of volume)
*Pendular (lengthening/shortening of gut segments controlled through intrinsic contractility of smooth muscle)
*Segmentation (regular ring-like contractions (shuffles food, compacting and breaking off for excretion) followed by “out of phase” contractions)
*Villi movement (constant motion during digestion. Shortens/lengthens to rhythmic contract. of submucosa Muscle (moves further bits of digesta to help optimal absorption). helps move nutrients to where they can best be absorbed
Segmentation contractions of the Intestine
Segmentation – mixing food with pancreatic, biliary and intestinal juices; facilitating digestion and exposing
digested products to absorptive surfaces.
Intestinal movements from small to larger intestine
Gastroileal reflex (emptying of digesta from small to large intestine)
Triggers relaxation of ileocecal valve
Ileocecal sphincter (gateway between small and large intestine)
Transition between small intestine and entry into the Large Intestine
Describe the histology and physiology of the large intestine
Absence of villi
Presence of lots of goblet cells
Deep intestinal glands
differs from stomach as it has two muscular layers and different cells that line crypts/pits.
mucosa
submucosa
muscularis
serosa
*Reabsorption in the large intestine includes:
Water (compact material into faeces)
Vitamins – K, biotin, and B5 (absorb these are facilitated to be produced by Bacteria in the tract.)
Organic wastes – urobilinogens and sterobilinogens
Bile salts and Toxins which must be removed
*Storage & mass movements of material through colon and rectum
Storage of faecal matter prior to Defecation: reflex triggered by distention of rectal walls (recto gastrointestinal walls)
Motility of the large intestine
Haustral contractions shuffle contents mixing
& facilitating absorption of remaining fluid/electrolytes.
Peristalsis along length of colon (circ&long.muscles)
Mass peristalsis propel contents long distances
into sigmoid colon & rectum.
Movement into rectum triggers the defaecation
reflex (contraction in sigmoid colon & rectum).
The rectum
Last portion of the digestive tract
Terminates at the anal canal
IIt has both internal and external anal sphincters
baroreceptors or stretch receptors, they have long reflex (central nervous system) and short reflex (nervous system of gastrointestinal tract) this coordinated response allows for the contraction of the rectum and sphincters. Through peristaltic contractions which allow excretion of digesta.
