You are what you eat Block 3 Week 1 Flashcards
The gastrointestinal tract can be split into the upper and lower respiratory tract. What is in each tract ?
The GI tract involves the oral cavity, pharynx, esophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (ascending, tranverse and sigmoid colon), rectum and anal canal.
- The GI tarct is about 5.5 metres long
The boundaries of the mouth
Hard palate at the front
Soft palate at the back
What is the Mylohiod muscle (aka diaphragma oris) ?
The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth.
What are the folds in the mouth called ?
- palatopharyngeal fold
- palatoglossal fold
- gingiva ( aka gums)
- Superior labial frenum
- Inferior labial frenum
- Lingual frenum
- Superior lip (top lip)
- Inferior lip (bottom lip)
Teeth:
- Incisors (4)
- Canines (2)
- Premolars (2)
- Molars (3)
The oral cavity ( mouth) is split into the oral vestibule and the oral cavity proper.
Oral vestibule: is the area anterior to the teeth.
Oral cavity proper: everything posterior to the incisors - the space between the upper and lower dental arches. This includes the tonge, salivary glands, oral mucosa, hard and soft palate.
What are the accessory organs of the GI tract?
The GI tract involves:
the oral cavity, pharynx, esophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (ascending, tranverse and sigmoid colon), rectum and anal canal
The accessory organs are:
- teeth
-tongue
- salivary glands
- pancreas
- liver
- gall bladder
What are the salivary glands?
Function of saliva:
- it lubricates the food to facilitate swallowing
- aids in speech
- contains enzyme a- amylase (ptyalin) which begins the process of starch digestion.
There are 3 main pairs of salivary glands:
- the parotid
- the submandibular
- sublingual glands
Each gland is surrounded by a fibrous capsule and consists of a number of lobules made up of small acini (alveoli) lined with secretory (acinar) cells.
The acini are drained by ductules which join to form larger ducts leading to the mouth
What are the salivary glands?
Function of saliva:
- it lubricates the food to facilitate swallowing
- aids in speech
- contains enzyme a- amylase (ptyalin) which begins the process of starch digestion.
There are 3 main pairs of salivary glands:
- the parotid
- the submandibular
- sublingual glands
Each gland is surrounded by a fibrous capsule and consists of a number of lobules made up of small acini (alveoli) lined with secretory (acinar) cells.
The acini are drained by ductules which join to form larger ducts leading to the mouth
Describe the sympathetic and parasympathetic innervation of the salivary gland ?
- All the major salivary glands receive both sympathetic and parasympathetic
innervation. - noradrenergic sympathetic fibers from the superior cervical ganglion are distributed to both blood vessels and acinar cells.
- The secretion of saliva is primarily controlled by the parasympathetic fibers.
- paraganglionic parasympathetic fibers arrive by way of the facial and glossopharyngeal nerves and synapse with the post ganglionic neurons close to the salivary glands themselves. Both the secretory cells and duct cells receive parasympathetic fibers.
- Secretion of saliva can be serous, mucous or mixed.
Describe the parotid, submandibular and sublingual gland ( ?
Parotid gland ( largest):
- produce only serous secretion.
- it contains a -amylase and antibody (immunoglobin A)
- accounts for 25% of saliva
Submandibular gland:
- more viscid saliva
- Accounts for 70% of saliva
- these glands contain acinar cells which secrete mucoproteins and serous fluid
Sublingual glands:
- 5 % of total saliva
- rich in mucoprotein
Parotid salivary gland
Where:
- situated at the angle of the jaw, lying posterior (behind) the mandible and inferior to the ear.
Bounded by what:
Superiorly : zygomatic arch
Posteriorly : sternocleidomastoid
Anteriorly: masseter muscle
There is a duct from the p gland, its 5 cm long and goes to the secrete saliva into vestibule. The duct goes over the masseter and through the buccinator (cheek muscle)
Describe the submandibular gland (aka submaxillary gland)?
- has a duct which empties into the sublingual caruncle which is a papilla located medially to the submandibular gland.
Describe the sublingual gland ?
- The sublingual gland opens up to multiple ducks on either side of the sublingual papilla ( caruncle) along the ridge.
note: you can have blockages of these ducks as stones can forma nd block them
Describe the teeth and their function to the digestive system ?
- A full set of adult teeth will amount to 32 teeth in total. This includes the wisdom teeth
- most people have 28 because their wisdom teeth don’t come through
- Teeth have their own nerve supply, they need to detect pressure on food so you know how hard to bite.
- both the maxillary and mandible teeth is supplied by branches of the trigeminal nerve (CN V)
Upper teeth = maxillary teeth
lower teeth = mandibular teeth
Branches of the trigeminal neve ?
Branches of the trigeminal nerve (3):
- Opthalmic nerve
- mandibular nerve
- maxillary nerve
The different branches are namely the ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves
Describe the innervation of the upper an lower teeth ?
Upper (maxillary):
- trigeminal nerve - maxillary nerve - superior alveolar nerve - maxillary teeth
Lower (mandibular)
- trigeminal nerve - mandibular nerve - inferior alveolar nerve - mandible teeth
Describe blood supply to the teeth ?
Blood supply to teeth:
- begins at external carotid (left and right) which branches into the maxillary artery
- Both the mandible and maxillary teeth are supplied by the maxillary artery but by different branches of it.
Mandibular teeth:
- maxillary artery -> inferior alveolar artery -> blood supply to mandibular teeth
Maxillary teeth:
- maxillary artery -> posterior superior alveolar artery -> blood supply to maxillary teeth
Describe the muscles of mastication ?
- The muscles of mastication allow us to chew our food.
The whole system hinges at the Temporomandibular joint.
These muscles are innervated by mandibular branches of the trigeminal nerve.
Their blood supply is the maxillary artery and superficial temporal artery
Describe the muscles of mastication ?
There are four muscles:
Masseter
Temporalis
Medial pterygoid
Lateral pterygoid
Masseter muscle:
- most powerful muscle of mastication.
-the muscle lies superficially to pterygoid and temporalis
- innervation: mandibular nerve (v3)
Temporalis:
- muscle is covered in tough fascia
- innervation:
mandibular nerve (v3)
Describe the muscles of mastication ?
Lateral pterygoid muscle:
- triangular shape with two heads: superior and inferior
- Acting bilaterally, the lateral pterygoids protract the mandible, pushing the jaw forwards
- horizontally orientated muscle fibres, and thus is the major protractor of the mandible.
Medial pterygoid muscle:
-quadrangular shape with two heads: deep and superficial. It is located inferiorly to the lateral pterygoid.
Innervation: Mandibular nerve (V3)
Actions: Elevates the mandible, closing the mouth.
What is the buccinator?
Buccinator is the cheek.
It is sometimes called an accessory muscle of mastication.
- It is innervated by the facial nerve
- It is a muscle of facial expression
- Buccinator also has a role in keeping food in the oral cavity when chewing instead of falling in the vestibular region.
Describe the role of the tongue in mastication?
The tongue is made up of intrinsic and extrinsic muscles.
The intrinsic muscles only attach to other structures in the tongue
There are four paired intrinsic muscles of the tongue and they are named by the direction in which they travel:
-the superior longitudinal
- inferior longitudinal
- transverse muscle
- vertical muscle
Describe the role of the tongue in mastication?
The extrinsic muscles of the tongue:
Genioglossus, Hyoglossus
Styloglossus
Palatoglossus
- Genioglossus:
Motor innervation via the hypoglossal nerve (CNXII
protrude the tongue, middle fibres depress the tongue, and superior fibres draw the tip back and down
- Hyoglossus:
Arises from the hyoid bone and inserts into the side of the tongue
Function: Depresses and retracts the tongue
Innervation: Motor innervation via the hypoglossal nerve (CNXII).
- Styloglossus:
Originates at the styloid process of the temporal bone
Retracts and elevates the tongue
Motor innervation via the hypoglossal nerve (CNXII).
- Palatoglossus:
Arises from the palatine aponeurosis
Elevates the posterior aspect of the tongue
Motor innervation via the vagus nerve (CNX).
All of the intrinsic and extrinsic muscles are innervated by the hypoglossal nerve (CN XII), except palatoglossus, which has vagal innervation (CN X).
The top of this muscle is what forms the palatoglossal fold
- glossus : means sometging relating to tongue
What is the blood supply to the tongue ?
The lingual artery is a branch of the external carotid artery ?
External carotid artery -> lingual artery
What are the 3 constrictor muscles of the pharynx ?
- There are three circular pharyngeal constrictor muscles:
-the superior pharyngeal constrictor
-middle pharyngeal constrictor
- inferior pharyngeal constrictor
The pharynx ends at c6
What happens once the food has been chewed ?
- Once mastication is complete and the lubricated bolus has formed, it is swallowed.
- From the mouth the food passes posteriorly into the oropharynx and then into the laryngopharynx, both of which are common passageways for food, fluids and air.
What happens when food is swallowed ?
- The fist (oral) phase of swallowing is voluntary but the subsequent pharyngeal and esophageal stages of the process are under reflex autonomic (involuntary control)
- During the oral phase of swallowing the tip of the tongue is placed against the hard pallet and the tongue is then contracted to force the food bolus into the oropharynx ( the part of the pharynx lying immediately behind the mouth).
- As the food enters the pharynx and stimulates mechanoreceptors there, the involuntary phase of swallowing begins.
There are two areas that need to be shut off when food is swallowed what are they :
The two areas which need to be shut off are the nasopharynx and the trachea.
- The 2 muscles which contract so the nasopharynx is shut off are:
- Levator veli palatini muscle
- musculus uvulae
This makes sure the food is passing downwards
To shut off the trachea we have the EPIGLOTTIS which is shutting and closing that off.
Involuntary phase of swallowing (reflex) ?
- innervated by the pharyngeal plexus ( formed by the pharyngeal branches of glossopharyngeal and vagus)
3 Phases of swallowing:
1. Oral
2. Pharyngeal
3. Esophageal
What happens during the pharyngeal phase:
- The tongue lifts up
- soft palate lifts up
-vocal folds close shutting the epiglottis - we have the larynx lifting up which brings the epiglottis down to shut the laryngeal inlet.
The pharyngeal phase is voluntary and the esophageal phase is involuntary
What happens during the esophageal phase ?
- The upper sphincter is an anatomical, striated muscle sphincter at the junction between the pharynx and oesophagus. It stops food going back up to the oropharynx
- It is produced by the cricopharyngeus muscle. Normally, it is constricted to prevent the entrance of air into the oesophagus.
- bolus now enters the esophagus.
- esophagus is 25 cm long (approx) and goes from c6 to t10. The bolus travels down in what is called peristaltic waves
- esophagus passes through the hiatus at t10 into the stomach
- The lower oesophageal sphincter is located at the gastro-oesophageal junction (between the stomach and oesophagus). The gastro-oesophageal junction is situated to the left of the T11 vertebra, and is marked by the change from oesophageal to gastric mucosa.
- During oesophageal peristalsis, the sphincter is relaxed to allow food to enter the stomach. Otherwise at rest, the function of this sphincter is to prevent the reflux of acidic gastric contents into the oesophagus.
Natural points of constriction in the esophagus?
- Pharyngo-oesophageal junction
-Tracheal bifurcation
-Gastro-oesophageal junction
Tracheal bifurcation (when trachea splits into left and right).
This a point where the trachea pushes back onto the esophagus. It is a natural point of constriction.
How could you look at the heart and get a good image ?
Transesophageal Echocardiogram
Better than other ways to image the heart because you have closer contact and therefore imaging of the heart.
The histology varies going along the GI tract?
Stomach:
- simple columnar epithelium
- also parietal cells - secrete Hydrochloric acid
- gastric juices - trigger activation of enzymes
- mucus is released to line the stomach and protect it from gastric juices
When we look at the esophageal gastric junction we can see the difference in histology ?
There is a difference in color between the esophagus and stomach ?
- Stomach looks darker
Describe the structure of the stomach ?
The stomach has four main anatomical division:
- cardia
- fundus,
-body
- pylorus
Cardia:
- surrounds the superior opening of the stomach at the T11 level.
Fundus:
-the rounded, often gas filled portion superior to and left of the cardia.
Body:
- the large central portion inferior to the fundus.
Pylorus:
- This area connects the stomach to the duodenum.
-It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. The pyloric sphincter demarcates the transpyloric plane at the level of L1.
What is your peritoneum ?
Your peritoneum is the tissue that lines your abdominal wall and covers most of the organs in your abdomen.
Retroperitoneal - organs in the abdomen which are only covered in the front
Peritoneal - organs in the abdomen that are entirely covered by the peritoneum.
The stomach is a peritoneal organ
Describe the blood supply to the stomach ?
The arterial supply to the stomach comes from the celiac trunk and its branches.
Anastomoses form along the lesser curvature by the right and left gastric arteries and along the greater curvature by the right and left gastro-omental arteries
Right gastric:
– branch of the common hepatic artery, which arises from the coeliac trunk.
Left gastric:
– arises directly from the coeliac trunk.
Right gastro-omental:
– terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
Left gastro-omental:
– branch of the splenic artery, which arises from the coeliac trunk.
Describe the blood supply to the stomach ?
The arterial supply to the stomach comes from the celiac trunk and its branches.
Anastomoses form along the lesser curvature by the right and left gastric arteries and along the greater curvature by the right and left gastro-omental arteries
Right gastric:
– branch of the common hepatic artery, which arises from the coeliac trunk.
Left gastric:
– arises directly from the coeliac trunk.
Right gastro-omental:
– terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
Left gastro-omental:
– branch of the splenic artery, which arises from the coeliac trunk.
We also have the gastric arteries that come off the spleen
- hence why we say there are 5 arteries of the stomach
The veins of the stomach run parallel to the arteries. The right and left gastric veins drain into the hepatic portal vein. The short gastric vein, left and right gastro-omental veins ultimately drain into the superior mesenteric vein.
Lymph nodes around stomach
- There are lymph nodes associated which roughly follow the blood supplies.
- There are lots of lymph nodes around the coeliac trunk
Describe the nervous supply to the stomach ?
- The stomach receives innervation from the autonomic nervous system:
Parasympathetic nerve supply arises from the anterior and posterior vagal trunks, derived from the vagus nerve.
- Vagus nerve stimulation allows peristaltic waves
Sympathetic nerve supply arises from the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. It also carries some pain transmitting fibres.
- This causes us to feel visceral pain
What is Rugae of stomach ?
- The stomach needs to expand and shrink with food
However internal stomach epithelium cannot stretch
- When the stomach is full the lining made up of rugae is stretched and it smoothens and flattens out
- This also serves to increase the surface area which will also increase digestion
What happens when food enters the stomach ?
- Once the food enters the stomach we refer to it as chyme
- Once the chyme has been churned and broken down in the stomach it exits through the pyloric sphincter
- The pyloric sphincter is at level with a region known as the transpyloric plane (more on this later)
- The chyme then enters the duodenum.
Describe the duodenum ?
- Some parts of the duodenum is peritoneal and other parts are retroperitoneal
-The duodenum can be divided into four parts: superior (L1)
descending (L1-L3)
inferior (L3)
ascending (L3-L2)
- Together these parts form a ‘C’ shape, that is around 25cm long, and which wraps around the head of the pancreas.
- superior duodenum is the most common site of duodenal ulceration
What is duodenal ulcer?
A duodenal ulcer is the erosion of the mucosa in the duodenum. It may also be described as a peptic ulcer (although this term can also be used to refer to ulcerations in the stomach). Duodenal ulcers are most likely to occur in the superior portion of the duodenum.
The most common causes of duodenal ulcers are Helicobacter pylori infection and chronic NSAID therapy.
An ulcer in itself can be painful, but is not particularly troublesome and can be treated medically. However, if the ulcer progresses to create a complete perforation through the bowel wall, this is a surgical emergency, and usually warrants immediate repair. A perforation may be complicated by:
Inflammation of the peritoneum(peritonitis) :
-causing damage to the surrounding viscera, such as the liver, pancreas and gall bladder.
Erosion of the gastroduodenal artery:
-causing haemorrhage and potential hypovolaemia shock.
Describe anatomical landmarks on the duodenum ?
Superior duodenum:
- It ascends upwards from the pylorus of the stomach, and is connected to the liver by the hepatoduodenal ligament
- The initial 3cm of the superior duodenum is covered anteriorly and posteriorly by visceral peritoneum, with the remainder retroperitoneal (only covered anteriorly).
- Behind is the:
gastroduodenal artery
common bile duct
Decending:
- retroperitoneal
- The descending portion curves inferiorly around the head of the pancreas. It lies posteriorly to the transverse colon, and anterior to the right kidney.
- Internally, the descending duodenum is marked by the major duodenal papilla.
This is the point where the common bile duct and pancreatic duct are received.
Inferior:
-retroperitoneal
- travels laterally to the left, crossing over the inferior vena cava and aorta. It is located inferiorly to the pancreas, and posteriorly to the superior mesenteric artery and vein.
Ascending:
- duodenum crosses the aorta, it ascends and curves anteriorly to join the jejunum at a sharp turn known as the duodenojejunal flexure.
- Located at the duodenojejunal junction is a slip of muscle called the suspensory muscle of the duodenum. Contraction of this muscle widens the angle of the flexure, and aids movement of the intestinal contents into the jejunum.
What is the major duodenal papilla ?
This is the point where the common bile duct and pancreatic duct are received.
- The ducts travel through the hepatopancreatic ampulla.
So we have the pancreatic juice and the bile going into the duodenum.
The enzymes from the pancreas are important because they help break down lipids, proteins and carbohydrates.
Bile neutralizes the stomach acid so there isn’t too strong acid entering the rest of the GI tract
hepatopancreatic ampulla -> major duodenal papilla
What is the common bile duct and pancreatic duct ?
Descending duodenum ?
If you have a food blockage in the GI tract how can you identify it using an imaging modality ?
- Carry out an x-ray with barium feed.
- So a barium feed is helpful because it increases the contrast between the food and the tract.
So you can see there’s a blockage and it also marks out parts of the tract can see it pass better. - the duodenal cap and fundus of the stomach show up as black on a x ray because you don’t get as much food, they have air trapped so they show up as black.
Gatrointestinal tract
- It looks like the large intestine is wrapped around the small intestine
Non-dietary loads
- Everyday the stomach has to deal with up to 7 litres of non-dietary loads
- 1200ml water
- 1500ml saliva
- 2000ml gastric
- 500ml bile
- 1500 pancreatic
- 1500 intestinal secretions
Non-dietary loads
- Everyday the stomach has to deal with up to 7 litres of non-dietary loads
- 1200ml water
- 1500ml saliva
- 2000ml gastric
- 500ml bile
- 1500 pancreatic
- 1500 intestinal secretions
Describe the secreting unit of salivary gland ?
The basic secretory units of salivary glands are clusters of cells called an acini.
These cells secrete a fluid that contains water, electrolytes, mucus and enzymes, all of which flow out of the acinus into collecting ducts.
- The enzymes include salivary amylase and lysozyme.
- The 3 salivary glands secrete 1.5litres of saliva each day
What is the volume of the stomach when it is empty and when it is full ?
- When the stomach is empty it has a volume of about 50ml.
- When fully distended the stomach can hold up to 5 liters.
- Usually the stomach can hold up to 2 liters of food.
What are the different cell types in the stomach ?
The cells are found within the gastric glands of the mucosa layer of the stomach.
The gastric glands contain 4 types of cells:
- Mucous cells
- Parietal cells (oxyntic cells)
- Chief cells
- Enteroendocrine cells
- Stem cells
The gastric glands contain 4 types of cells:
- Mucous cells
- Parietal cells (oxyntic cells)
- Chief cells
- Enteroendocrine cells
- Stem cells
Describe the function of these cells?
Mucous cells:
- secrete mucus to protect the epithelium from acid secretions
Parietal cells:
- secrete HCL
- secrete intrinsic factor (for vitamin B12 absorption)
Chief cells:
- secrete PEPSINOGEN, which is the inactive form of the proteolytic enzyme pepsin
Enteroendocrine cells:
- secretion of protein hormones such as VIP and somatostatin. ( Gastrin is secreted in the pyloric region)
Stem cells:
- Give rise to new cells to replace the old mucosal and glandular epithelium cells
- Gastric secretion is not constant throughout the day it has phases.
In this graph we see 3 main phases:
- Cephalic phase
- Gastric phase
- Intestinal phase
Cephallic phase:
- graph peaks as soon the food is smelled, seen or tasted.
- It is stimulated by the vagus nerve
It’s very pronounced in dogs, which salivate only in the sight of food.
And then these phases followed by the main gastric phase:
- this is when the food is in the stomach.
- the main hormone during this phase is gastrin
Intestinal phase:
- this is when the chyme is in the duodenum
How do parietal cells work ?
- Parietal cells release HCL
- The principal stimulants of acid secretion at the level of the parietal cell are histamine, gastrin
and acetycholine
Describe the roles of hormones of the gastrointestinal tract ?
Gastrin:
-Secreted by the stomach in response to food, especially, protein
-Stimulates acid and pepsinogen secretion and gastric motility
Secretin:
- Secreted by the duodenum in response to acid
- Inhibits gastric acid production; increases pancreatic and biliary bicarbonate secretion
CholeCystoKinin;
- Secreted by duodenum in response to food
(especially fat). - Inhibits gastric acid secretion and motility, stimulates pancreatic bicarbonate and enzyme secretion and bile secretion
Somatostatin:
- Released from D-cells in stomach and duodenum in
response to acid : inhibits gastric acid secretion
stomach distension (swelling) also inhibits gastric secretion
What is Gastroesophageal Reflux Disease ?
Gastro-oesophageal reflux disease (GORD) is a common condition, where acid from the stomach leaks up into the oesophagus (gullet).
It usually occurs as a result of the ring of muscle at the bottom of the oesophagus becoming weakened
Reflux may damage the esophagus, pharynx or respiratory tract.
Treatment:
Proton Pump Inhibitors
(PPIs) such as
Omeprazole tend to
be first-line treatmen
On this slide, we show different mechanisms of action of drugs that can play a role in inhibiting gastric acid secretion.
Sites and mechanisms of action of drugs
which inhibit gastric acid secretion and
drugs which protect the
gastric mucosa.
GR=gastrin receptor; H2R=histamine-2 receptor;
MR=muscarinic receptor; PP=proton pump;
cAMP=cyclic AMP; ATP=adenosine triphosphate.
Wha is the surface area of the small intestine ?
Surface area of small intestine: 300 m2
The presence of the Villi and the Microvilli has a dramatic impact on the increase of the total absorptive.
Describe the surface of the small intestine ?
The folded surface of the small intestine is covered in finger like projections called villi.
- Villi are 1mm high and the outer surface are covered with COLUMNAR ABSORPTIVE EPITHELIAL CELLS (ENTERYOCYTES)
- The surface of the enterocytes have processes called MICROVILLI and this forms the brush border. This increases the surface area of the small intestine even further.
- On the surface of the villi we also find GOBLET CELLS that secrete mucus.
Within each villus is a:
- lymph vessel (lacteal)
- blood vessel (arteries and veins)
- smooth muscle
- connective tissue
Where abouts in the small intestine/ villus are stem cells found ?
- Stem cells are found in the intestinal crypt.
- Stem cells are powerful primitive cells that are able to proliferate and migrate to the tip of the villi and make sure the enterocytes are maintained in a good state.
- The small intestine has a very rapid rate of cell turnover. In humans, the entire epithelium is renewed every 6 days.
- This rapid turnover is important because the epithelial cells are sensitive to hypoxia and other irritants.
- Epithelial cells are formed by the mitotic proliferation of a population of undifferentiated stem cells within the crypts.
- These new cells then migrate to the top of the villus from where they are shed into the lumen of the intestine.
- As the cells migrate and leave the crypts they become fully mature and the brush border enzymes develop.
- The rate at which cells proliferate can be altered by a number of factors.
- Starvation and prolonged intravenous feeding for example cause atrophy of the cells and a reduction in proliferation.
What is the average lifetime of Enterocytes ?
- The average lifetime of enterocytes is 2-3 days
Excessive damage can cause coeliac disease. This is seen in conditions such as anticancer therapy or radiotherapy, which leads to flatten mucosa and malabsorption.
What happens there is that the anticancer drug reduces proton protein synthesis and cell proliferation of stem cells in the crypt.
The travel of the cells from the crypt to the tip of the Villi is 48 hours and the dominance of the enterocytes up there cannot keep up with the production of new cells down there. As a result we have malabsorption of nutrients.
The cells shed at the tip of the villus and they need to be replaced to keep the absorptive area of the villi constant.
Enzymes involved in digestion ?
At the sight or smell of food:
- salivary amylase: digestion
of starch
- lingual lipase: digestion of triacylglycerol
Enzymes involved in digestion ?
At the sight or smell of food:
- salivary amylase: digestion
of starch
- lingual lipase: digestion of triacylglycerol
In stomach:
Gastric acid: protein denaturation
Pepsin: protein digestion
gastric lipase: digestion of triacylglycerol
It is in the stomach where the absorption of alcohol and acidic drugs takes place.
The alcohol does not need to get to the small intestine to get absorbed. Its absorption begins in the stomach.
What is the split of the different sections of the small intestine?
Which enzymes are present in the duodenum, jejunum and ileum?
Duodenum: 1/6
Jejunum: 1/3
Ileum: 1/2
Duodenum:
- pancreatic amylase: digestion of starch
- lipase – digestion of triacylglycerol
-phospholipase – digestion of phospholipids
- trypsin, chymotrypsin, elastase – digestion of proteins
- dipeptidases
- disaccharidases
Jejunum: continuing digestion and it is the point where absorption begins
Ileum - continuing digestion:
Absorption of
- monosaccharides
- amino acids
- fatty acids, glycerol, other lipids
- many drugs
- water
Why are proteases secreted as inactive precursors ?
- Proteins are secreted as inactive precursors which are called ZYMOGENS.
- Zymogens are then activated after secretion.
- The reason this happens is to avoid proteases self digesting and damaging the digestive organs.
- They are secreted as inactive precursors.
pepsinogen (inactive precursor) is converted to pepsin. It goes from the inactive form to the active form in the presence of gastric acid.
trypsinogen (inactive precursor) become trypsin (active enzyme) in the presence of enteropeptidase.
The main end products of salivary, gastric and pancreatic digestion ?
The main end products of salivary, gastric and pancreatic digestion ?
Describe the absorption of monosaccharides, the digestion products of carbohydrates ?
- Glucose, galactose and fructose are absorbed largely in the duodenum and upper jejunum, entering the blood of the hepatic portal vein.
- None remain in the chyme reaching the terminal ileum.
APICAL membrane:
- Glucose and galactose are taken up into the epithelial cells against their concentration gradient by a sodium- dependent cotransport mechanism.
It is called the Sodium-glucose transport protein (SGLT). It is a symporter so 2 Na+ (two sodium ions) are transported inside the cell at the same time as 1 glucose molecule.
BASOLATERAL membrane:
- The monosaccharides leave the intestinal epithelial cell at the basolateral membrane by facilitated diffusion through GLUT 2 protein channel and enter the blood.
- The sodium gradient that drives this transport is maintained by the Na+ K+ -ATPase.
- Fructose is absorbed from the intestinal lumen by sodium-independent faciltated diffusion. It cannot be transported against a concentration gradient.
Describe the absorption of proteins?
- At the end of the digestion (breakdown ) of proteins we have 60% dipeptides and 40% free amino acids.
- At least 50g of amino acids must be absorbed to maintain a positive nitrogen balance and meet the needs of an adult body for tissue growth and repair.
- Free Amino acid are absorbed at the brush border of the intestinal epithelial cells by a sodium dependent cotransporter. So one sodium ion in and one amino acid in.
- Small peptides (mainly dipeptides)n are transported into the enterocytes by another carrier which is not linked to sodium but is believed to be linked to the influx of H+ ions.
Once the peptides enter the intracellular compartment they are broken down to amino acids . - Amino acids leave the intracellular enterocyte into the capillary blood via the amino acid carrier system.
Which macronutrients enter the portal vein ?
Describe the anatomy of the large intestine ?
Around 1500ml of chyme pass from the ileum into the cecum every day.
- Material then passes in sequence through the ascending colon, transverse colon , descending colon , sigmoid colon , rectum and anal canal. Semisolid waste (feces) is eliminated from the body from the anus.
Functions of the large intestine:
- stores food residues prior to their elimination
- secretes mucus which lubricates feces
- absorbs any water and electrolytes remaining in the residue
- In addition bacteria living in the colon synthesize vitamin K and some B vitamins and play a part in fermentation reactions.
What is the Glycemic index ?
Glycaemic index is a rating system for foods containing carbohydrates.
- It shows how quickly each food affects your blood sugar (glucose) level when the food is eaten on its own.
Low or medium GI foods are broken down more slowly and cause a gradual rise in blood sugar levels over time.
Some examples are:
-some fruit and vegetables
-pulses
-wholegrain foods, such as porridge oats
Are low GI foods healthier?
- Not necessarily. Foods with a high GI are not necessarily unhealthy and not all foods with a low GI are healthy. For example, watermelon and sometimes parsnips are high GI foods, while chocolate cake has a lower GI value.
Low GI foods, which cause your blood sugar levels to rise and fall slowly
What is the function of Butyrate?
What is the function of Propionate ?
Butyrate and Propionate SCFAs which are both produced in the colon.
Butyrate is thought to protect against colorectal cancer
Propionate may inhibit food intake.
What are the benefits of fiber ?
- They absorb bile acids and cholesterol.
- increase the clearance of cholesterol from the body
- It is important to get rid of bile because it may have tumor promoting effects - They adsorb potential carcinogens in the colon.
- A shorter mouth to anus transit time is also believed to reduce the risk of developing carcinoma of the large intestine and rectum. This may be due partly due to the reduction in time for which bacterial toxins and potentially harmful metabolites are in contact with the gut wall.
- Increase viscosity of gut contents. This means it makes stool more firm and less runny.
- Fiber absorbs water so that stools with a high fiber content tend to be bulkier and softer making them easier to expel.
- This also means there is slower absorption which is beneficial if you have diabetes.
- Dietary soluble fibers are fermented by gut bacteria into short-chain fatty acids (SCFA), which are considered broadly health-promoting.
Examples include:
- acetate
- propionate
- butyrate
butyrate may have anti-proliferative (anti cancer) action
propionate may have an anorectic effect (reduce food intake)
Where does the absorption of sodium take place ?
- The absorption of sodium ions takes place in the small intestine and the colon.
- Vitamin B12 is absorbed in the ileum
- Vitamin C is absorbed by the jujenum
In the modern diet we mainly ingest nutrient dense food with a high glycemic index, as a result absorption only takes place in the upper part of the small intestine.
The efficiency of nutrient absorption of the gut is high
- Alcohol is absorbed entirely 100%
- Carbohydrate 99%
- Fat 95%
- Protein 92%
-The gut can absorb almost all the macronutrients of a meal irrespective of the meal size. It has a abundant reserve capacity.
- So excessive amounts of food will be ingested and absorbed by the gut.
What is pharmacokinetics ?
Pharmacokinetics, which is what we are going to go through today, is the study of how a drug is absorbed into the body, how it moves around the body, how it is metabolised and finally how it is eliminated from the body. Pharmacokinetics therefore influences, the route of administration for a drug, and also the amount and frequency of each drug dose.
What are the 4 types of drug receptors ?
What are the 9 abdominal regions ?
RH - Right hypochondrium
E- Epigastric
LH - Left hypochondriac
RL - Right flank (lateral region)
U - Umbilical
LL- Left flank (lateral region)
RI - Right inguinal (groin)
P - Pubic
LI - Left Inguinal (groin)
What are the 4 abdominal quadrants ?
- Right upper quadrant
- Left upper quadrant
- Right lower quadrant
- Left lower quadrant
Medial plane: directly across stomach
Trans umbilical plane: horizontally across stomach
Costal margin: The costal margin, also known as the costal arch, is the lower edge of the chest (thorax) formed by the bottom edge of the rib cage
What is the xiphisternum ?
The xiphisternum (also known as the xiphoid process or simply the xiphoid) is the smallest of the three parts of the sternum (manubrium, body or gladiolus, and xiphisternum).
It arises from the inferior and posterior margin of the sternal body and projects inferiorly.
What is the iliac crest and iliac tubercle?
Where are the following planes:
-subcostal
-transpyloric (L1)
- supracristal (L4)
- transtubercular (L5) planes
Transpyloric plane - at the edge of the 9th costal cartilage
- Sucostal plane - Lower edge of the 10th costal cartilage
Supracrisal plane: highest point on the iliac crest
Transtubercular plane: Tubercle of crest ilium
What is the anterior superior iliac spine ?
What is the posterior superior iliac spine ?
What are the muscles of mastication ?
- Masseter
- Temporalis
- Lateral pterygoid
- Medial pterygoid
Mandibular division of the trigeminal nerve ?
The muscles of mastication are innervated by a branch of the trigeminal nerve (CN V), the mandibular nerve.
Temporomandibular joint ? (TMJ)
What makes up the temporomandibular joint is the mandibular condyle and the mandibular fossa of temporal bone
What are the 3 salivary glands ?
- parotid gland
- submandibular gland
- sublingual gland
What is the articular disc of the temporomandibular joint ?
- To make up the temporomandibular joint we have the mandibular condyle and the mandibular fossa of the temporal bone.
- In between these two we have the articulate disk
- Which is sandwhicched between the superior synovial joint and inferior synovial joint.
Describe a tooth ?
In adults the upper and lower jaws each have:
- 4 incisors
- 2 canines
- 4 premolars
- 6 molars
Although the shapes of the different teeth vary they all share a similar basic structure.
- The crown is part of the tooth that protrudes from the gum
- The root is embedded in the jaw bone
- In the center of the tooth is the PULP CAVITY which contains the blood vessels, nerves and lymphatics.
- The pulp cavity is surrounded by hard dentin.
- Outside the dentin of the crown is an even harder layer called the ENAMEL.
- The root of the tongue is surrounded by a softer cement which fixes the tooth in its socket.
Where is the palatoglossal fold, palatopharyngeal fold and the tonsillar fossa ?
What is the larngeal opening ?
Past the laryngeal opening we have the trachea
Teeth
Mylohyoid muscle
Lingual nerve ?
The lingual nerve is a sensory nerve that arises from the mandibular division of the trigeminal nerve (cranial nerve V)
