Physiology of digestive system

Question 1

What does the digestive tract include and where does it span from and till ?

Answer 1

• spans from mouth to anus
  Includes:
• mouth
• pharynx
• esophagus
• stomach
• small intestine
• large intestine
• Anus

Question 2

What are the Accessory organs ?

Answer 2

• teeth
• Salivary glands
• liver
• pancreas
• tonsils/lymphoid nodules

Question 3

What is the primary function of digestion?

Answer 3

• To transfer nutrients, water and electrolytes from ingested food into body’s internal environment

Question 4

What are the six primary processes of the digestive system include?

Answer 4

1. Ingestion and mechanical breakdown of food
2. Secretion of fluids and digestive enzymes
3. Mixing and movement of food and wastes through the body
4. Digestion of food into smaller pieces
5. Absorption of nutrients
6. Excretion of wastes

Question 5

In the digestive tract what three receptors do we have that are sensitive to chemical or mechanical changes within the system and what do they each detect? ?

Answer 5

1. Chemoreceptors- detects change in various chemical compounds within the gastrointestinal lumen
2. Osmoreceptors- sensitive to the osmolarity of the contents within the lumen
3. Mechanoreceptors- respond to stretch or distension of the gastrointestinal tract wall

Question 6

Receptor simulation can lead to activation of which of the regulatory mechanisms within the tract?

Answer 6

• Intrinsic Nerve plexuses
• Extrinsic autonomic nerves
• Gastrointestinal hormones

Question 7

What is the intrinsic nerve plexuses include and how does it function and what does it help with?

Answer 7

• It is a network of nerve cells located within the GI tract and are responsible for intratract reflexes, activation in one region causes a chain reaction and activates all the regions within the tract
• It provides a mechanism for self regulation of the tract and helps to coordinate the activity of the organs within it .

Question 8

In the Extrinsic autonomic nerves, there are both the sympathetic and parasympathetic divisions of the autonomic nervous system, so what roles do they both play ?

Answer 8

• they tend to oppose each other, so the parasympathetic system stimulates most digestive activities while the sympathetic system inhibits them

Question 9

How do the gastrointestinal hormones contribute to regulation of digestive activity and what do they effect?

Answer 9

• These hormones are released in one region of the tract and it can travel in the circulatory system to other regions of the tract and influence the activity of the effector cells in that region.

Question 10

Describe the oral structure and until which point of your mouth do you have control of the food till until the body takes over?

Answer 10

• Oral Structure:
  -It starts with the mucosa on the outer side which has both the epithelium and the lamina propria , then comes the submucosa, then the muscles and bones
• You will only have control until the food is in the esophagus, after that the body takes over

Question 11

In the papillae of the tongue, there are 4 types, name them all and also which one of those does NOT have taste buds?

Answer 11

1. Filiform papilla
2. Fungiform papilla
3. Foliate papilla
4. Circumvallate/Vallate papilla

• The filiform papilla does NOT have taste buds

Question 12

In the Teeth the outer white layer is known as the Enamel, when does it form and can it be renewed if broken, and what is it sensitive to and what can happen to it with age?

Answer 12

• It is formed before tooth eruption
• It has a terminal structure and it is NONrenewable
• Sensitive to acidic pH
• Thinning happens with age which causes yellowing of tooth

Question 13

All three of the intrinsic, metabolic and extrinsic parts can effect the tooth discoloration, what do each of them effect?

Answer 13

• Intrinsic:
  -it does not have major effects, this is mainly genetics
• Metabolic:
  -Alkaptonuria aka black urine disease can cause discoloration of dentin due to incomplete metabolism of tyrosine and phenylalanine
  -Hyperbilirubinemia: this is increased levels of bilirubin
• Extrinsic :
  -smoking/drugs
  -mouth rinses that include Chlorhexidine
  -Tannin containing foods (berries, Pomegranate)
  -Antimicrobials

Question 14

What 3 major pairs of the salivary glands produce saliva and what is salive composed of and how much is secreted daily ?

Answer 14

• Produced mainly by parotid , Sublingual and submandibular
• Composed of : 99.5 percent, 0.5 percent electrolytes and protein
• Around 1 to 1.5 L/day secreted

Question 15

What do the terms Xerostomia and Sialorrhea and what causes both of these?

Answer 15

• Xerostomia: this is dry mouth caused by cancer treatment, radiotherapy
• Sialorrhea: this is too much saliva/drooling caused by heavy metal poisoning or cholinergic agonists

Question 16

Saliva functions:
1. Salivary amylase begins digestion of __________
2. Facilitates swallowing by _________________food
3. Mucus provides _____________
4. Anti_________ action
5. Lysosome destroys _____________
6. Saliva rinses away material that could serve as food source for ______________
7. Certain bacteria can cause acidic pH and generate__________________

Answer 16

1. Carbohydrates
2. Moistening
3. lubrication
4. Antibacterial
5. bacteria
6. bacteria
7. dental caries

Question 17

What is lingual lipase role in saliva function , when is it most active and where in the body does it work?

Answer 17

• It helps with breaking down lipids, it is active in acidic pH and it work throughout stomach and into intestine

Question 18

How does the nervous system help to control the secretion of Saliva?

Answer 18

• There is afferents that come from sight/smell/taste/thought to the medullary nuclei
• parasympathetic nervous system stimulates secretion of an abundant amount thin, enzyme rich saliva
• Sympathetic nervous system causes decreased volume of saliva and mucus rich, when SNS has a high dominance drier mouth occurs more often

Question 19

Saliva secretion can be enhanced by two reflexes, what are they called and how do they work?

Answer 19

1. Simple or unconditioned salivary reflex:
   -When there is food in your oral cavity and causes a stimulation of the chemoreceptors and pressure receptors. These receptors transmit impulses to the salivary center in the medulla of the brainstem. Parasympathetic efferent impulses are transmitted back to the salivary glands and secretion is enhanced
2. Acquired or conditioned salivary reflex:
   -This is caused by a response to the thought, sight, smell, or sound of food.

Question 20

What does Nitroglycerin do ?

Answer 20

• It acts as a vasodilator in the angina and helps with angina chest pain

Question 21

How many sphincters are there in the esophagus and how are they controlled?

Answer 21

• There are two, one at the top and one at the bottom. The top one is controlled by nervous system and the bottom one is automatic.

Question 22

What are both Meissner’s plexus and Auerbach plexus important for and where are they located in the esophagus ?

Answer 22

• Meissner plexus is located in the submucosa and it is important for regulating GI blood flow and controlling epithelial cell function
• Auerbach plexus is between the circular and longitudinal layer of the muscularis externa and it is important primarily for digestive tract motility

Question 23

What is the function of the parietal cells and where are they located ?

Answer 23

• Located in the stomach
• produce HCL which then help denature the proteins in meals and destroys their tertiary and secondary structure , allowing digestive enzymes to break down the long chains of amino acids and it also kills most of the microorganisms ingested with the food

Question 24

What is the function of chief cells and where are they located?

Answer 24

• Located in the stomach
• They secrete inactive pepsinogen and Lipase and, acid is needed to activate pepsinogen to form pepsin so it used HCL and then pepsin will enhance the generation of ,ore pepsin and also promote digestion of proteins to amino acids in human

Question 25

How does the HCL formation work in the parietal cells?

Answer 25

• Hydrogen comes from the carbonic acid and it is broken down into bicarbonate and then bicarbonate is pushed into the blood while a H+-K+atpase active transport pump pushes H+ out and at the same time another pump chloride ion comes into the parietal cell and since there is a high number inside and less in the gastric lumen it gets pushed out and HCL forms with the two ions that were pushed into the gastric lumen

Question 26

Where are surface epithelial cells(Foveolar cells) located, and what is the purpose of them?

Answer 26

• They line the surface of the stomach and the neck of the gastric pits and are attached to each other by tight junctions
• They contain large mucin granules and help to protect the gastric mucosa from luminal pepsin and acid

Question 27

What are the three segments called in the small intestine ?

Answer 27

• Duodenum
• Jejunum
• Ileum

Question 28

What special structures are in the small intestine that help to increase the surface area?

Answer 28

• Intestinal valves (Kerckring’s valve) increases the surface by 3 folds
• Intestinal villi (Epithelium+LP) increase the surface by 10 folds

Question 29

What type of epithelial cells are there in the small intestine and what do they do?

Answer 29

• Enterocytes : (Main point of absorption) Covers the villi and enters the intestinal glands
• Microvilli : increases surface area by 20 folds
• Goblet cells : Produce protective and lubricant glycoproteins. they increase as you go down the small intestine towards the large intestine
• Paneth’s cells : Exocrine cells that produce lysosome to digest bacterial cell wall
• Other cells: Enteroendocrine cells that produce hormones affecting the local blood circulation

Question 30

Describe the structure of the large intestine

Answer 30

It is part of the digestive tube that is between the terminal ileum and the anus . The ingesta from the small intestine enters the large intestine through the ileocecal sphincter

Question 31

What are the three major segments in the large intestine and describe their structures

Answer 31

1. Cecum : a blind ended pouch that in humans carries a worm like extension called the vermiform appendix
2. Colon : constitutes the majority of the length of the large intestine and is subclassified into ascending transverse and descending segments
3. Rectum : The short and terminal segment of the digestive tube continuous with the anal canal

Question 32

What is the difference between the mucosa structure between the small and large intestine?

Answer 32

• They both have lamina propria but in the large intestine it contains lymph nodules that are exposed to the bacteria

Question 33

What is responsible for the movement and excretion of fecal matter in the large intestine and where are they located?

Answer 33

• In the Musculais Externa, there is a inner circular layer and external layer that are arranged in three longitudinal bands (Teniae Coli) that are responsible

Question 34

What is the function of the appendix?

Answer 34

It may produce and protect beneficial probiotic colonies in the digestive system

Question 35

At the renal anal junction what differences do they have in terms of the epithelial structure?

Answer 35

• The rectum is characterized by the same columnar epithelium that lines the majority of the GI tract secretory and absorptive areas.
• The anus has a stratified squamous epithelium that provides a greater deal of protection to the underlying tissue

Question 36

LOOK AT THE SAMPLE QUESTIONS ANSWER ON SLIDE 31

Answer 36

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