D.2 Digestion Flashcards
Nervous Mechanism
The sight and smell of food triggers an immediate response by which gastric juice is secreted by the stomach (pre-ingestion)
When food enters the stomach it causes distension, which is detected by stretch receptors in the stomach lining
Signals are sent to the brain, which triggers the release of digestive hormones to achieve sustained gastric stimulation
Hormonal mechanism
Gastrin
Gastrin:
- secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids
If stomach pH drops too low, gastrin secretion is inhibited by Secretin and Somatostatin
When digested food passes into the small intestine, the duodenum also releases digestive hormones:
- Secretin & chelocystokinin (CCK) => cause the small intestine to neutrilise pH by releasing bicarbonate ions
Types of Exocrine glands
Salivary gland = secrete saliva = contains amylase (breaks down starch)
Gastric glands = secretetes gastric juices (hydrochgloric acid & protease) (breaks down proteins)
Pancreatic glands = secretes pancreatic juices (lipase, protease, amylase)
Intestinal glands = secrete intestinal juices via crypts of Lieberkuhn in the intestinal wall
Exocrine glands
Produce and secrete substances via ducts onto an epithelial surface
- Surface of the body (skin)
- Lumen of the digestive tract/ gut
Are composed of clusters of secretory cells which form acinus
- Acini are surrounded by a basement membrane (outside) and are held together by tight junctions
- Secretory cells have highly developed ER & golgi network and have many mitochonria
Role of Rough ER and, golgi bodies and mitochondria
Rough ER:
- Produce proteins with the imbedded ribosomes
Golgi bodies:
- package the proteins to be exported out of the cell
Mitochondria:
- Produce ATP for bulk transport
Label an exocrine gland
Secretory cells make up the acini
Acid Conditions in the Stomach
plus its function
The stomach wall is lined by a layer of mucus, which protects the stomach lining from being damaged by the acid conditions
- Releases stomach protease (pepsin)
- Assists in the digestion of food
- Prevents pathogenic infection
Gastic juice
contains hydrochloric acid and pepsin
Pepsin:
- convertts proteins into peptides
pepsin = Acid + pepsinogen
Gastic pits
Acid Function
- Acid allows for pH pepsinogen to activate pepsin
- Kills pathogens
- Hydrolise food
Stomach acid secretion
+ PPI’s
Sodium potassium pump within the stomach wall, pumps hydrogen ions and chloride ions
Proton Pump Inhibitors (PPIs):
- Are drugs that bind to the protein pump and prevent H+ ions being pumped into the stomach, increasing the pH (pathogens may not be killed)
Heliobacter pylori infection as a cause of stomach ulcers
- Occurs when H. pylori anchors to the epithelial lining of the stomach, underneath the mucus lining
- It damages the G cells, preventing mucus from being excreeted
- Acid then burns a wound
Role of:
- Gastrin
- Pepsinogen
- Somatostatin
- Pepsin
- Goblet cells
Gastrin:
- Produce acidity
Pepsinogen:
- Produce pepsin
Somatostatin:
- Regulate acidity and make gastric acid more basic
Pepsin:
- Breaks down proteins in stomach (is a protease)
Goblet cells:
- Produce mucous
Outline the cause of stomach ulcers and one treatment
Cause:
- Occurs when H. pylori anchors to the epithelial lining of the stomach, underneath the mucus lining
- It damages the G cells, preventing mucus from being excreeted
- Acid then burns a wound
Treatment
- Antibiotics
Small intestine
Performs peristulsis (pushes food down)
Lacteal:
- Absorbs lipids which are surrounded by lipoproteins
Importance of Dietary fibre
Humans lack enzymes to digest it
Ruminants can because of bacteria int he rumen that can break it down for them
- Reduce frequent consipation
- Lowers risk of rectal and colon cancer
- lowers blood cholesterol and regulates blood sugar levels
Small intestine structure
- Lumen –> (inestinal villi) –>
- Mucosa
- Submucosa
- Circular muscle layer
- Longitudinal muscle layer
- Serosa
Mucosa:
- goblet cells, enterocytes, endocrine cells
Enterocytes:
- Have microvilli
- Type of epithelial cell
Submucosa:
- Blood vessels & connective tissue
Circular muscle layer:
- Smooth muscle
Longitudinal muscle layer:
- smooth muscle
Serosa:
- allows expanding
Small intestine structure
- Lumen –> (inestinal villi) –>
- Mucosa
- Submucosa
- Circular muscle layer
- Longitudinal muscle layer
- Serosa
Mucosa:
- goblet cells, enterocytes, endocrine cells
Enterocytes:
- Have microvilli
- Type of epithelial cell
Submucosa:
- Blood vessels & connective tissue
Circular muscle layer:
- Smooth muscle
Longitudinal muscle layer:
- smooth muscle
Serosa:
- allows expanding
Features of Villi
MR-SLIM
- Microvilli – Ruffling of epithelial membrane further increases surface area
- Rich blood supply – Dense capillary network rapidly transports absorbed products
- Single layer epithelium – Minimises diffusion distance between lumen and blood
- Lacteals – Absorbs lipids from the intestine into the lymphatic system
- Intestinal glands – Exocrine pits (crypts of Lieberkuhn) release digestive juices
- Membrane proteins – Facilitates transport of digested materials into epithelial cells
Egestion
Materials not absorbed
BELCH
* Bile pigments
* Epithelial cells
* Lignin
* Cellulose
* Human flora (bacteria)
Vibrio Cholorae & dehydration
- V. cholerae releases a toxin that binds to ganglioside receptors on the surface of intestinal epithelium cells
- The toxin is internalised by endocytosis and triggers the production of cyclic AMP
- Cyclic AMP activates ion channels within the cell membrane, causing an efflux of ions from the cell
- The build up of ions in the intestinal lumen draws water from cells and tissues via osmosis
- Therefore dehydration occurs
