Physiology of digestive system April 4

Question 1

What are the 6 digestive processes?

Answer 1

1. Ingestion : the process of eating that involves lips, tongue , palate
2. Mechanical breakdown of food:
   a)Chewing(teeth and mouth)
   b)Churning(stomach)
   c)Segmentation(small intestine)

3.Propulsion(pushing forward):
a)Swallowing(oropharynx)
b)Peristalsis(esophagus , stomach , small and large intestine)

Question 2

What are the three phases of swallowing ?

Answer 2

1. Buccal Phase
2. Pharyngeal phase
3. Esophageal phase

Question 3

What happens in the Buccal phase of swallowing and is this action voluntary or involuntary, if voluntary what is it controlled by?

Answer 3

• It is voluntary
• Food is compacted by the tongue into a “bolus” which then moves to pharynx by tongue pressing on hard palate
• Controlled by the brain cortex, including the motor area

Question 4

What happens in the Pharyngeal Phase of swallowing and is this action voluntary or involuntary?

Answer 4

• It is involuntary
• this phase starts as soon as the food touches the back of the pharynx
• Swallowing centre (medulla) initiates the swallowing reflex which is involuntary
• Then soft palate closes the nasal cavity, tongue closes oral cavity and the vocal cord closes and epiglottis blocks the passage of food into the trachea

Question 5

What happens in the Esophageal phase of swallowing and is this action voluntary or involuntary ?

Answer 5

• It is involuntary
• The esophagus is guarded at both ends by sphincters:

1. The top one is called the Pharynx-Esophageal sphincter and this keeps the entrance to the esophagus closed to prevent air entrance during respiration
2. The bottom one is called the Gastroesophageal sphincter and this one maintains barrier between stomach and esophagus preventing gastric reflux (heart burn)

Question 6

What are the esophageal muscles used for in swallowing and what helps to control these muscles?

Answer 6

• It is used to move food down esophagus (aka peristalsis)
• Upper 1/3 is controlled by somatic motor neurons sending signals to skeletal muscle
• Lower 1/3 is PSNS (vagus.N.) sending signals to smooth muscle
• the middle 1/3 is a mix of both

Question 7

what are the three sections of the stomach called and what are the two sphincters called?

Answer 7

Sections:
- Upper : Fundus
- Middle : Body
- Lower: Antrum

Sphincters:
- Gastroesophageal sphincter
- Pyloric sphincter

Question 8

Where does gastric storage take place and what does it use to start the break down of carbohydrates?

Answer 8

• Takes place in the stomach
• Uses Salivary Amylase to break down carbohydrates and it only lasts several hours until gastric juices reaches pH<7

Question 9

Where does gastric mixing take place in the stomach and what is the purpose of mixing the two movements of segmentation and churning?

Answer 9

• Takes place in the antrum of stomach
• purpose of mixing two movements:
  -Mixing food with digestive juices promotes digestion of foods
  -Facilitates absorption by exposing all parts of intestinal contents to absorbing surface of digestive tract

Question 10

What are the steps in Gastric emptying that take place?

Answer 10

1. A peristaltic contraction originates in the upper funds and moves all the way down toward the pyloric sphincter
2. The contraction becomes more vigorous as it reaches the thick muscled antrum
3. The strong antral peristaltic contraction propels the chyme forward
4. A small portion of chyme is pushed through the partially open sphincter into the duodenum. the stronger the astral contraction the more chyme is emptied with each contractile wave

Question 11

What are the Gastric mixing that take place?

Answer 11

1. When the peristaltic contraction reaches the pyloric sphincter the sphincter is tightly closed and no further emptying takes place
2. When chyme that was being propelled forward hits the closed sphincter it is tossed back into the antrum. mixing go chyme is accomplished as chyme is propelled forward and tossed back into the antrum with each peristaltic contraction, a process called retropulsion

Question 12

What are some things that stimulate parietal cells to secrete acid ?

Answer 12

• Gastrin , Acetylcholine (M3 receptor) and Histamine (H2 receptor)

Question 13

How does the Cephalic phase work in the regulation of gastric motility/secretion ?

Answer 13

• Preparing stomach for food
• triggers the thought , sight , smell , taste of food.

Question 14

How does gastric phase work in the regulation of gastric motility and secretion ?

Answer 14

• When food comes in the pH slowly drops and reaches 3 when stomach nearly empty
• When pH<3:
  -Shuts down NS which causes a drop in acid
  -when gastrin drops it also causes a drop in acid

Question 15

How does the intestinal phase work in the regulation of gastric motility/secretion?

Answer 15

First it gets a increase in gastric secretion and it causes duodenal gastrin release that stimulates parietal cells to produce HCl

Question 16

in the intestinal phase how does the inhibitory signals effect the gastric motility ?

Answer 16

• Gastric motility decreases due to :
  -CCK - released due to presence of FA ,aa
  -Enterogastric reflex - triggered by aa/peptides ,duodenal stretch hypertonicity

Question 17

In the intestinal phase how does the inhibitory signals effect the gastric secretion?

Answer 17

• Gastric secretion decreases because of:
  -Secretin released due to acid
  -CCK released due to aa

Question 18

What drugs can the stomach absorb and how ?

Answer 18

• Ethyl alcohol : somewhat lipid soluble but can be absorbed even more quickly by the small intestine mucosa
• Acetylsalicyclic acid : weak acid that in the highly acidic environment of the stomach lumen will be un-ionized and lipid soluble

Question 19

How does fat delay the rate of gastric emptying in the duodenum?

Answer 19

• Fat digestion and absorption takes place only within the lumen of small intestine. Since fat take hours to to go through the stomach It prevents further fat from being digested

Question 20

How does acidic content in the duodenum delay the gastric emptying?

Answer 20

• It delays it until the un-neutralized acid can be neutralized by sodium bicarbonate and this prevents damage and allows pancreatic enzymes to function.

Question 21

How does neural response in the duodenum delay the gastric emptying?

Answer 21

• both the intrinsic nerve plexuses and autonomic nerves mediate a enterogastric reflex that is initiated when pH in stomach reaches 1.5 and 3-4 in the duodenum. Therefore, a decrease in HCL production is also needed which is mediated by inhibition of gastrin release by pyloric epithelium.
• Gastrin is also inhibited by somatostatin mediated by the vagus nerve acetylcholine

Question 22

How does the hormonal response in the duodenum delay the gastric emptying?

Answer 22

• It involves the release of hormone from duodenal mucosa enteroendocrine cells
• Two most important hormones:
  -Secretin
  -Cholecystokinin(CCK)

Question 23

What is the difference between early and late gastric dumping syndrome and what are each of their symptoms? What is treatment for both?

Answer 23

• Early : during or right after a meal
  Symptoms include nausea , vomiting , bloating , diarrhea , dizziness , fatigue
• Late :1-3 hours post meal
  Symptoms include weakness , sweating and dizziness

Treatment:
- Eating habit adjustments: avoiding certain foods and a balanced diet
- Medications ( with severe conditions)
- surgery as a last resort

Question 24

Describe the structure and overall work of segmentation in the small intestine?

Answer 24

• IT is a ring like contractions along length of small intestine , that within seconds contracted segments relax and previously relaxed areas contract , and this action mixes the chyme throughout the small intestine lumen

Question 25

Describe the segmentation function in the small intestine?

Answer 25

• it slowly moves chyme through digestive tract and as you go down the tract the frequency declines
• in the duodenum it is 12 times/min and 9 times/min at the terminal ileum .
• in total takes 3-5 hours to get through the small intestine

Question 26

How does the Migrating motility complex work in the small intestine ?

Answer 26

• When most of the meal has been absorbed, segmentation stops and is replaced by migrating motility complex
• it has slow weak peristaltic waves and it sweeps intestines clean between meals

Question 27

what carries the blood with the newly absorbed materials to the liver ? where is it then filtered through and at the end collected to join general circulation?

Answer 27

• Blood carrying newly absorbed materials is carried to liver by Portal Vein
• Then blood filters through columns of hepatocytes and is collected by hepatic vein and joins the general circulation

Question 28

What is the gaps between the hepatocytes called and describe their structure and as well as their roles

Answer 28

• They are called Sinusoids and they are lined by a discontinuous layer of endothelial cells, Kupffer cells and reticular fibers
• This is where the sinusoids can come into contact with hepatocytes to mix blood

Question 29

What is the portal triad and after blood is mixed in the sinusoids which direction do they move in ? what is bile formed by and which way does that flow after?

Answer 29

• The portal triad is: Portal Venule , Hepatic Arteriole , Bile ductile.
• The arterial and venal blood is mixed in the sinusoids and continues to flow toward the central vein
• Bile is formed by hepatocytes and flows in the opposite direction to blood towards the bile ductile .

Question 30

What are Kupffer cells and where are they derived from? What do they respond to and what do they contain ?

Answer 30

• They are Hepatic macrophages derived from blood monocytes
• They respond to many types of injury by proliferation and enlargement
• They contain vacuoles , and particularly in the diseased liver , many PAS -D positive lysosomes and phagosomes and ceroid pigment

Question 31

Where is the Space of Disse located and what is it the zone of?

Answer 31

• Space between the hepatocytes and sinusoidal lining cells
• Zone of intercellular exchange

Question 32

What are the livers function ?

Answer 32

• To store glucose in the form of glycogen and release it when blood levels are low
• To store fat soluble vitamins A,D,E and K , folate, B12 and minerals such as copper and iron
• Most blood proteins (except for antibodies ) are synthesized and secreted by the liver:
  -Albumin, Blood coagulation or clotting factors , lipoproteins , Cholesterol and bile

Question 33

How does toxin removal of Ammonia , Bilirubin and alcohol and drugs ( orally taken) work from the blood?

Answer 33

• Ammonia is converted to Urea and excreted in urine
• Bilirubin is a breakdown product of RBC hemoglobin and it is bound to the albumin in blood and when the liver takes it up it conjugates it with glucuronic acid to form water soluble bilirubin that can be excreted into bile.
• Alcohol : liver disease may inhibit or alter detoxification processes and thus increase the toxic effects of these agents and causing damage to the liver
• Drugs : Most druges are metabolized by the liver

Question 34

What is bile used for and what effects does secretin and CCK have on the secretion of bicarbonate and bile and where is bile stored?

Answer 34

• Used for fat digestion and absorption, prevents a metabolic deficit and it also does laxative action by stimulating peristaltic movements of the intestine
• Stored in gall bladder and made in liver ( Hepatocytes)
• Secretin stimulates the liver to secrete bicarbonate into the bile and CCK enhances this effect

Question 35

REVIEW THE QUESTION PICTURE. A: slide 47