Digestive System Flashcards by Lucy Cesana

What are the digestive organs?

-Mouth
-Pharynx
-Oesophagus
-Stomach
-Small intestine
-Large intestine
(part of digestive tract: 4 layer tissue structure)

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What are the accessory organs?

-Teeth
-Tongue
-Salivary glands
-Liver
-Gallbladder
-Pancreas
(provide digestive assistance, no 4 layer tissue structure)

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What are the 4 layers of the digestive tract?

Mucosa
Submucosa
Muscularis Externa
Serosa

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Describe what, where and function of mucosa

What is it?
-Mucous membrane
-Consisting of digestive epithelium: (simple columnar cells, enteroendocrine, mucous cells and goblet cells), lamina propria: alveolar tissue with blood vessels, sensory nerve endings, lymphatic vessels, tissues & muscular mucosa: smooth muscle
Where is it?
-Closest to lumen
Function
-Secretion & absorption
-Protection against digestive acids and enzymes
-Contraction of smooth muscle alters shape of lumen

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Describe what, where and function of submucosa

What is it?
-Layer of dense irregular connective tissue that contains large blood vessels, lymphatic vessels and exocrine glands
Where is it?
-2nd closest to lumen
Function
-Secretes buffers and enzymes into lumen

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Describe what, where and function of muscularis externa

What is it?
-2 layers of smooth muscle innervated by enteric nervous system
Where is it?
-Furthest from lumen
Function
-Enables attachment to adjacent structures

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Describe what, where and function of serosa

What is it?
-Serous membrane
Where is it?
-Furthest from lumen
Function
-Enables attachment to adjacent structures

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What are the functions of the digestive system?

Ingestion
Mechanical processing
Digestion
Secretion
Absorption
Excretion

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Describe ingestion in the digestive system?

Material enters digestive tract via mouth

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Describe mechanical processing in the digestive system

Easier to propel along tract

- Increases surface area to allow easier breakdown

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Describe digestion in the digestive system

Chemical breakdown of food for absorption
Large molecules (e.g. carbohydrates/starches) broken down to small molecules
(e. g. absorbable sugars)

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Describe secretion in the digestive system

Release of water, acids, enzymes, buffers, salts

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Describe absorption in the digestive system

Movement of substrates, electrolytes, vitamins and water across walls of
digestive epithelium into interstitial spaces in lamina propria

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Describe excretion in the digestive system

Removal of waste products from body

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What are the two processes by which materials move through the digestive tract?

Peristalsis and Segmentation

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What is peristalsis?

A propulsion process involving waves of smooth muscle contraction that move compacted ingested materials (bolus) along digestive tract

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What is segmentation

Cycles of smooth muscle contraction and relaxation that chums and fragments the bolus to mix the contents of the bolus with secretions (eg: enzymes)

What are functions of the mouth/oral cavity

Sensory analysis of material before swallowing
Mechanical processing (chewing)
Lubrication
- Digestion begins here
- Salivary amylase breaks down starch
- Lingual amylase breaks down lipids
- Salivary glands produce saliva

What is function of saliva?

-Lubrication of mouth/ pharynx
• Cleanse mouth/teeth
• Moistening food
• Dissolve food/chemicals
• Begin digestion

What is the structure of the stomach?

-3 layers of smooth
muscle
-Rugae
-Storage, mixing
chamber

What is the function of the stomach?

Mechanical digestion
-Forms chyme, forced into duodenum
Chemical Digestion
-Denatures proteins (HCI)
-Coverts pepsinogen to pepsin

What are the 3 phases of regulation of gastric activity?

Cephalic Phase
Gastric Phase
Intestinal Phase

Describe Cephalic Phase

-Begins: sight, smell, taste, though of food
(leads to)
-Action potentials in vagus nerve
(stimulates)
-High secretion of gastrin (G cells), mucous (mucous cells), HCL (parietal cells) and pepsinogen (chief cells)
-Prepares stomach for arrival of food

Describe Gastric Phase

-Begins: arrival of food in stomach
(stimulates)
-Stretch receptors and chemoreceptors
(stimulates)
-High secretion of gastrin (G cells), mucous (mucous cells), HCL (parietal cells) and pepsinogen (chief cells)
-High gastric activity

Describe Intestinal Phase

-Begins: chyme enters duodenum (stimulates) -High secretion of (in duodenum) secretin, cholecystokinin (CCK) and gastric inhibitory peptide (GIP) -Control rate of gastric emptying (from stomach to duodenum)

What is the function of the duodenum?

-Receives chyme from stomach -Mixes with digestive enzymes from pancreas -Neutralises acid

What is the function of the jejunum?

Chemical digestion & nutrient absorption

What is the function of the Ileum?

Nutrient absorption

What are the features of the small intestine that maximise surface area?

- Length (approx. 6m) - Large surface area - Circular folds (plicae circulares) - Villi: contain capillaries and lacteals - Microvilli: have a brush border

What are the 3 parts of the small intestine?

1) Duodenum 2) Jejunum 3) Ileum

How does the pancreas contribute to digestion?

Controlled by duodenal hormones (CCK and secretin) , Pancreatic secretions: - Water - Salts - Bicarbonate & phosphate buffers (release stimulated by Secretin) - Enzymes to digest nutrients (release stimulated by CCK)

What are the main functions of the liver?

1. Metabolic regulation - Carbohydrate, lipid & protein metabolism - Waste removal - Store vitamins/minerals 2. Haematological regulation - Removal of bacteria, old RBC/WBC - Make plasma proteins - Removes hormones/antibodies - Removes/stores toxins - Activates vitamin D 3. Bile production

What is the role of bile in the digestive system?

- Bile produced in liver; stored in gall bladder - Digests lipids - Bile salts break droplets apart (emulsification)

Describe the main steps involved in the digestion and absorption of carbohydrates

``` ORAL CAVITY (salivary amylase) SMALL INTESTINE -Brush border enzymes breaks down disaccharide lactose to glucose (absorption) CAPILLARIES ```

Describe the main steps involved in the digestion and absorption of lipids?

``` ORAL CAVITY (lingual lipase) SMALL INTESTINE -Bile salts- allows access to enzymes, pancreatic lipase (absorption) LACTEALS ```

Describe the main steps involved in the digestion and absorption of proteins?

``` ORAL CAVITY (chewing-access to enzymes) STOMACH (pepsinogen --> pepsin) SMALL INTESTINE -Brush border & pancreatic enzymes (absorption) CAPILLARIES ```

How does the large intestine histological structure differ from the small intestine?

- No villi or circular folds in mucosa: haustra instead | - Muscularis externa different to SI

What are the two key functions of the large intestine?

- Reabsorption of water | - Compaction of intestinal contents into feces

Describe chemical digestion in large intestine

``` -Final stage of digestion occurs through activity of bacteria -Produces gases and other by-products -Bacteria produce enzymes that humans don’t have genetic capacity to produce ```

Describe mechanical digestion in the small intestine

- Movement of LI begins when substances pass ileo-caecal sphincter - Peristalsis slower waves than SI - Haustral churning (segmentation) - Mass movements