MEDS2012 Week 1 Lectures

What parts of the digestive system are in the head and upper part of the neck?

Oral cavity and pharynx

What parts of the digestive system are in the middle and lower part of the neck?

Pharynx and oesophagus

What parts of the digestive system are in the abdomen?

Oesophagus, stomach, small intestine, large intestine

What parts of the digestive system are in the pelvis?

Rectum, anal canal

What are the glands involved in digestion?

Salivary, pancreas, liver (+ gallbladder)

What parts are involved in swallowing?

Smooth muscle in the pharynx and oesophagus

What are the functions of the digestive system?

Eating

Secretion (enzymes, mucous)

Peristalsis

Digestion (chemical, mechanical)

Absorption

Excretions

What are the 3 salivary glands and where are they located?

Parotid gland (next to ear)

Sublingual (under tongue)

Submandibular (under mandible)

What are the functions of saliva?

Moisten food and oral mucosa

Amylase - splits starch

Lysozyme - antibacterial

Where are vallate papillae located?

On the dorsal (top) surface of the tongue towards the back

What are vallate papillae?

Depression on the tongue with taste buds

What is the function of the pharynx?

Passageway for air, food and drinks

What is the function of the oesophagus?

Transport food and drinks to stomach

What are the sections of the pharynx and what is present in each?

Nasopharynx - connects nasal cavity (air comes through)

Oropharynx - connects the oral cavity (food and drink enter)

Laryngopharynx - behind the larynx (air leaves to go here)

What are the sections of the oesophagus?

Cervical oesophagus (top)

Thoracic oesophagus (middle)

Abdominal oesophagus (bottom)

What makes the stomach unique to the rest of the GIT?

It has 3 muscular layers with fibres in different directions, the rest only has 2 layers

What are the parts of the stomach?

Fondus - top

Body - middle

Pylorus - end

Where does food enter the stomach?

The cardiac orifice

What controls the bolus leaving the stomach?

Pyloric sphincter

What are the mucous projections in the stomach?

Rugae

How does the stomach digest food?

Churning (mechanical)

Stomach acid (chemical)

What are the layers of the stomach (from superficial to deep)?

Serous

Muscle

Submucous

Mucous

What is contained in the submucous layer of the stomach?

Vessels and nerves

What is contained in the mucous layer of the stomach?

Gastric glands

What are the functions of gastric glands?

Top - produces mucous to protect from HCL

The rest - produce HCL, enzymes and hormones for digestion

What are the parts of the small intestine in order?

Duodenum

Jejunum

Ileum

What is the minor duodenal papilla?

Connects accessory pancreatic duct to the duodenum

What is the major duodenal papilla?

Connects the main pancreatic duct and common bile duct to the duodenum

Where are bile and pancreatic juice released into the duodenum?

Descending column as it holds the major/minor dudenal papilla

What gland is specific to the duodenum?

Brunner glands

What are the functions of Brunner glands?

Secrete mucins and bicarbonate (to neutralise acid)

What are the folds in the duodenum called and what is their function?

Kerckring valves, increases SA

What are the parts of the duodenum in order?

Superior, descending, horizontal and ascending column

Where are nutrients transported from the small intestine?

Towards the liver via the portal vein

What increases SA in the jejunum and ileum?

Villi and microvilli

Where do Lieberkühn crypts lie in the small intestine?

Between villi

How do the jejunum and ileum differ from the rest of the GIT?

Local differences in circular folds and vascular supply

What are the parts of the large intestine in order?

Cecum, ascending, transverse, descending, sigmoid column

What connects the small and large intestine?

Ileocecal valve

What is involved in producing peristaltic waves in the large intestine?

Semicircular folds with haustra (sacculations) between

How does the large intestine compare to the small intestine in regard to crypts and villi?

It has no villi but has more numerous Lieberkühn crypts

Where is the gallbladder located?

Underneath the liver

What are the lobes of the liver?

Left

Right

Quadrate (bottom, front)

Caudate (top, back)

What are the functions of the falciform ligament of the liver?

Separates left and right lobes

Anchors to the diaphragm and anterior abdominal wall

Where does bile exit the liver?

Common hepatic duct

Where does bile enter/exit the gallbladder?

Cystic duct

What is the function of bile in digestion?

Emulsifies fats to make easier to absorb

How does vasculature of hepatic lobules work?

Vascular bundles at each corner of the hexagon, metabolism as it moves to the centre into the central vein

Where does the central vein drain to?

The inferior vena cava

What is in a hepatic lobule vascular bundle?

Hepatic artery branch

Portal vein branch

Bile duct branch

What is the function of the liver in digestion?

Metabolising nutrients and other compounds

Produces bile

What are the glands of the pancreas and what do they contain?

Exocrine gland - main pancreatic duct

Endocrine gland - islet cells

What is the function of the exocrine gland of the pancreas?

Discharges watery, enzyme-rich secretion into duodenum to aid digestion of substrates

What is the function of the endocrine gland of the pancreas?

Produce hormones for blood sugar regulation (insulin and glucagon)

What is the Attwater method?

Estimate energy needed based on 4kcal/g for protein and carbs, 9 kcal/g fats

What does a cell use energy to synthesise when replicating?

Nucleic acids

Proteins

Membrane lipids

Polysaccharides

What is nitrogen used to synthesise?

Nucleic acids

What is phosphorus used to synthesise?

Phospholipids

What is sulphur used to synthesise?

Some proteins

What does dietary protein provide?

Nitrogen and essential amino acids

What does dietary fat provide?

Phosphate and essential fats

What can make the Attwater estimation difficult?

Non-starch polysaccharides resist digestion providing less energy (1-3 kcal/g)

Why are microbes low in the stomach?

Stomach acid kills most microbes

What is mainly digested in the large intestine and why?

The digestion resistant carbs which can be digested due to higher microbial environment

What is HAS?

Host-accessible simple carbohydrates

What is HAC?

Host-accessible complex carbohydrates

What is HI-MAC?

Host-inaccessible microbiota-accessible carbohydrates

What is IC?

Inaccessible carbohydrates

What is considered dietary fibre?

Anything resistant to digestion either partially or fully meaning some HAC, HI-MAC and IC

Why do we get less energy from carbs digested by microbes?

The sugars produced are mostly absorbed by the microbes, we absorb some and also some waste

What does coprophagous mean?

Eat their own poo, allows microbes to pass back through stomach

What was found in germ-free mice compared to mice with a normal microbiome?

Germ-free mice had to eat more and stored less body fat

What and where is the overlap zone?

In the ileum, where microbes start to contribute more significantly

Approximately how much energy comes from our digestive functions vs microbes?

90-95% us and 5-10% microbes

What part of digestion is similar in all humans?

Our primary digestion, very similar digestive enzymes

What part of digestion is more variable and why?

Bacteria in the microbiome, more variable enzymes and metabolism

How much of our microbiome is stable and what defines it?

Approx. 300 bacterial species, the core which is determined on typical diet

How much of our microbiome is variable?

Thousands of bacterial species

How are only desirable nutrients absorbed in the digestive system?

The gut epithelium is selectively permeable

What are the hazards that must be dealt with in the digestive system?

Volume of food/gas

Motility blockage

Acid exposure on epithelium

Toxin/pathogen exposure

What pH are the small and large intestine?

Approximately neutral (~7 pH)

How is stomach acid prevented from going up the oesophagus?

Oesophageal sphincters coordinate

What can occur if there is a problem with the oesophageal sphincters?

Acid reflux which can damage tissues and increase risk of cancer

How are food volume issues prevented?

The stomach passes contents to the small intestine

What is an issue that has to be addressed when passing food to the small intestine?

The change in pH from highly acidic to neutral

What cells release HCl in the stomach and where are they?

Parietal cells in gastric glands

What cells in the duodenum sense gastric acid and how does it react?

S cells (type of endocrine cell) which secretes secretin which inhibits parietal cells

How does secretin stimulate small intestine functions?

Stimulates enzyme/bile release and mucin from Brunner's glands

What is the role of mechanosensory cells in the gut?

Senses pressure changes to enable stomach emptying and movement of material

What is the role of sphincter muscles in gut functions?

Control exit/entry of material

What is the role of muscularis mucosa in gut functions?

Controls movement of material

What is the role of secretatory cells in gut functions?

Adjust pH

What can cause small intestinal bacterial overgrowth?

Largely impaired SI motility, sometimes diet

What happens if SI motility is too fast?

Less nutrient uptake

What happens if SI motility too slow?

More microbe growth

What are some potential symptoms of SIBO?

Acid/gas production

Abdominal pain

Diarrhea

Nutrient deficiency/weight loss

What are FODMAPs and what risk do they pose to the gut?

They are easily fermentable which can cause excess microbial growth

What are FODMAPs comprised of?

Fermentable

Oligosaccharides

Dissaccharides

Monosaccharides

&

Polyols

What is a potential problem with high microbe activity in the large intestine?

Issue with potential to enter surrounding epithelium/mucosal tissue

What are microbe-associated molecular patterns (MAMPs)?

Small molecules unique to microbes