Digestion 1

Question 1

What does the digestive system consists of?

Answer 1

The digestive tract​

Accessory digestive organs​;
-Salivary glands​
-Exocrine pancreas ​
-Biliary system​

Question 2

What are the 4 Basic digestive processes?​

Answer 2

Motility / Mechanical processing ​
Secretion ​
Digestion ​(chemical breakdown)
Absorption ​

Question 3

What are the components of the digestive system?

Answer 3

1. Oral cavity, teeth, tongue= mechanical processing, moisturising, mixing with salivary secretion
2. salivary glands
3. pharynx (back of mouth helps shape food for swallowing)
4. 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
5. small intestine
6. large intestine

Question 4

What are the 4 layers of the gastrointestinal tract?

Answer 4

1. mucosa= working from lumen first layer that has contact with the food
2. sub-mucosa
3. muscularis externa (important for motility)
4. serosa (holds gut in place)

Question 5

Describe the Mucosa ​

Answer 5

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.​

Question 6

Describe the sub-mucosa ​

Answer 6

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.​

Question 7

Describe the Muscularis externa​

Answer 7

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​

Question 8

Describe the serosa?

Answer 8

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.

Question 9

Motility START: The buccal cavity ​

Answer 9

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)​

Question 10

The Swallowing Process ​
we need to avoid food going to tracheae
what are the two phases?

Answer 10

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.​

Question 11

The Oesophagus​

How to we prevent food from scouring oesophagus
Describe histology

Answer 11

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​

Question 12

Motility - Oesophagus​

Answer 12

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.​

Question 13

Peristalsis – involuntary muscular movements ​

Answer 13

1. contraction of circular muscles behind food mass
   2.contraction of longitudinal

Question 14

Gastroesophageal sphincter; entry into
The Stomach​

Describe histology

Answer 14

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

Question 15

Motility: The Stomach

Answer 15

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)

Question 16

Gastroenteric reflexes initiated by stretch receptors in stomach, empty chyme into the Small Intestine ​

Answer 16

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 ​

Question 17

Duodenum

Answer 17

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)

Question 18

What is the histology of the small intestine?
Going up in magnification (getting smaller)

Answer 18

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)​

Question 19

Intestinal motility what are the movements

Answer 19

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

Question 20

Segmentation contractions of the Intestine ​

Answer 20

Segmentation – mixing food with pancreatic, biliary and intestinal juices; facilitating digestion and exposing​

digested products to absorptive surfaces. ​

Question 21

Intestinal movements from small to larger intestine

Answer 21

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​

Question 22

Describe the histology and physiology of the large intestine​

Answer 22

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)

Question 23

Motility ​of the large intestine

Answer 23

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).​

Question 24

The rectum​

Answer 24

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.