Gut 1

Question 1

What is the alimentary tract?

Answer 1

The alimentary tract: essentially a tube from mouth to anus that is specialized in different regions for the digestion and absorption of nutrients.

Question 2

What structures does the mouth contain?

Answer 2

• Buccal cavity
• Tongue- manupulation of food into a bolus
• Dentition (Upper 2.1.2.3. Lower 2.1.2.3. (Incisors, canine, premolars, molars)-aids mastication
• Lipids- helps

Question 3

In descending order of the alimentary tract, what comes after the mouth

Answer 3

• Oesophagus
• Hard and soft palate
• Uvula
• Pharynx

Question 4

What are the 3 pairs of salivary glands?

Answer 4

3 pairs:

• parotid
• submandibular
• sublingual

Question 5

What are the main structures associated with the stomach?

Answer 5

• Cardiac sphincter
• fundus, body
• antrum
• pyloric sphincter

Question 6

What are the compontents of the large intestine?

Answer 6

• Ileo-caecal valve
• caecum
• appendix
• ascending/transverse/descending colon, sigmoid colon
• rectum
• anus

Abosrbs water and stores faeces

Question 7

What are the functional components of the small intestine?

Answer 7

• duodenum
• jejunum
• Ileum

This is where most absorption takes place

Question 8

What structures are the accessory organs of the alimentary tract?

Answer 8

• Liver- produces bile by breaking down RBCs and other things
• gall bladder- Bile deliverd here by the liver
• bile duct- essential for breaking down fats into smaller lipid droplets
• sphincter of Oddi- separates common bile duct from small intestine
• Pancreas- , important to producing secretions that aid in digestion, 99% exocrine tissue that releases enzymes e.g. lypolytic and proteolytic enzymes into the small intestine
• pancreatic duct-joines pancreas to small intestine

Question 9

Label the components of the alimentary tract

Answer 9

Question 10

What is the main purpose of the digestive system?

Answer 10

The digestive system transfers nutrients, water, and electrolytes from food into the body’s internal environment

Fluid homeostasis needs to be maintained

Question 11

The digestive system performs four basic digestive processes:

Answer 11

–Motility→ propel cpntents in one digestion

–Secretion→ Cells and glands that secrete different digestive enzymes and othercomponents e.g. mucus that provides lubrication

–Digestion→ Breaking down large complex molecules into small absorbable units e.g. proteins into peptides

–Absorption→ Micronutrients needed for cellular reactions to take place

Question 12

Describe the Anatomy and Functions of Components of the Digestive System

Answer 12

*

Question 13

What are the accessory digestive organs?

Answer 13

• salivary glands
• exocrine pancreas
• biliary system

Question 14

The digestive wall has four layers:

Answer 14

–Mucosa→ absorption of nutrients across the mucosa

–Submucosa→ Underneath epithelial cells that line the GI tract

–Muscularis externa→ smooth muscle (involuntary)

–Serosa → Outermost layer which secreates muscus to reduce friction, irritation and pain

Question 15

Describe the layers of the digestive tract wall

Answer 15

The digestive tract wall consists of four major layers: from the innermost out, they are the mucosa (fingerlike projection to maximise absorptiom), submucosa, muscularis externa (outer longitudinal muscle+ inner circular muscle), and serosa (thin layer that secretes lubricating mucus).

Peritoneum* anchors GI tract to body wall

Question 16

Why is the regulation of digestive function is complex and synergistic?

Answer 16

–Autonomous smooth muscle function (pacemaker activity)

–Intrinsic nerve plexuses and extrinsic nerves

–Gut hormones (CCK- regulates the gall bladers tone and its sphinchter, GLP-1- responsible for 2/3 insulin secretion, secretin gastrin-drives th release of HCL)

Question 17

What alters digestive activity through neural and hormonal pathways?

Answer 17

•Receptor activation alters digestive activity through neural and hormonal pathways

Gut-Brain axis (consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions)

feed forward mechanism involved in the increased production of saliva (regulatory loop in that a stimulus temporally associated with food (input) triggers salivation (output) in advance of presentation of food)

–Chemoreceptors- detect changes in coposition, mechanoreceptors- detect stretch, and osmoreceptor helps maintain fluid and electrolyte balance

Question 18

Where is the entrance to the digestive tract?

Answer 18

•The oral cavity is the entrance to the digestive tract

–Opening is formed by the muscular lips

•Help procure, guide, and contain food in the mouth

Then dentition shears and grinds food and it is mixes it with saliva to form a bolus of food which can be swallowed

Question 19

What structures mechanically break down food?

Answer 19

•The teeth mechanically break down food

–Mastication: mouth motility that involves the slicing, tearing, grinding, and mixing of ingested food by the teeth

•Degree of occlusion is more important than bite force

Question 20

What structures are included within the oral cavity?

Answer 20

Mouth:

Buccal cavity

Tongue (filiform papillae)

Hard and soft palate.

Uvula.

Pharynx

Dentition: Incisors, canine, premolars, molars

Upper 2.1.2.3.

Lower 2.1.2.3.

Question 21

What begins carbohydrate digestion and helps swallowing, speech, taste, and oral health?

Answer 21

Saliva

•Produced largely by three major pairs of salivary glands

–These glands lie outside the oral cavity and discharge saliva through short ducts into the mouth

–Saliva is made up of about 99.5% H₂O and 0.5% electrolytes and protein

Question 22

The salivary glands:

What are the 3 pairs?

How are the cells arranged?

Answer 22

• 3 pairs of salivary glands:

Parotid, submandibular, sublingual.

• Within salivary glands, cells are arranged into secretory acini and ducts.
• Cells lining the ducts also contribute to the products of the glands.

Question 23

The salivary glands: what are the two main cells fro which they are comprised?

Answer 23

Salivary glands comprise two main types of cells:

• Serous cells -contain zymogen granules - precursors of salivary amylase (ptyalin)
• Mucous cells-similar to goblet cells secrete mucus

Question 24

Salivary glands:

What are salivary secretions mostly controlled by?

Answer 24

• Salivary secretions are controlled mostly by neural reflexes (especially PSNS)
• Tongue, taste buds, sensory afferents via facial VII and glossopharyngeal IX, salivary nuclei in medulla oblongata, efferents via autonomic ganglia, activate glands.
• Dry food – all secretions moist food less mucus.
• 7th and 10th cranial nerve sends signally to salivary centers in the medulla which sends signals via the parasympatheic NS increases saliva secretion from the salivary glands*

Question 25

Describe the cell composition in each of the salivary glands

Answer 25

Parotid →serous cells only→enzyme rich fluid Submandibular→mainly serous cells →enzyme and mucus Sublingual → mainly mucous cells → mucus

Question 26

Describe Salivary Secretion

Answer 26

•It is ontinuous and can be increased by reflex –Simple and conditioned salivary reflexes (next slide) –Autonomic influence on salivary secretion •Digestion starts in the mouth and is minimal; no absorption of nutrients occurs –Digestion in the mouth involves the hydrolysis of polysaccharides by amylase •Most digestion is accomplished in the stomach after food mass and saliva have been swallowed

Question 27

Compare the pathways by which eating food and smelling food increase salivary secretion.

Answer 27

1. Pressure and chemoreceptors in the mouth sends signals to the salivary centers in the medulla, higher centers of the brain involved with thinking, seeing and smelling food also send signals to the medulla 2. Medulla send signals via the autonomic nerves to the salivary glands to either increase or decrease the production of saliva

Question 28

Describe the location and function and function of the Pharynx and Oesophagus What happens if food enters the trachea?

Answer 28

•The pharynx is the cavity at the rear of the throat –Acts as a common passageway for both the digestive and respiratory system (air and food) •Swallowing is a sequentially programmed all-or-none reflex Epiglottis closes over the trachea as you swallow to make sure food goes into the oesophagus or epiglottis –Swallowing center activates swallowing muscles •During swallowing, food is prevented from entering the wrong passageways food would otherwise be forced into the trachea or down into the lungs causing aspiration pneumonia

Question 29

What prevents air from entering the digestive tract? What pushes food through the esophagus?

Answer 29

•The pharyngoesophageal sphincter prevents air from entering the digestive tract –Remains closed during swallowing •Peristaltic waves push food through the esophagus –Primary peristaltic wave sweeps from the beginning to end of the esophagus, forcing the bolus ahead of it toward the stomach (don't have to be upright to swallow- gravity independent)

Question 30

Explain the process of Swallowing | (Oesophageal Peristalsis)

Answer 30

* Swallowing is a complex reflex initiated when pressure receptors in the walls of the pharynx are stimulated by food or drink forced into the rear of the mouth by the tongue * 3 phases * These receptors signal to the swallowing centre (medulla). * The medulla innervates the muscles in the pharynx * Upper oesophageal sphincter closes * Respiration inhibited (also medulla), larynx raised, glottis closed. * Food then passes through oesophagus stomach by a progressive wave of muscle contractions (peristalsis, 9 seconds) * This can even occur upside down or in space! * Lower oesophageal sphincter opens and food passes into stomach

Question 31

What is the swallow reflex?

Answer 31

Swallow reflex: pressure of bolus on soft palate, sensory afferents, medulla oblongata, efferents to pharynx, tongue, oesophagus.

Question 32

What are the three stages involved in the swallowing reflex?

Answer 32

1. **Buccal (oral) stage** Voluntary, bolus formation, bolus moved to back of mouth 2. **Pharyngeal stage** Bolus pushes on soft palate, initiates swallow reflex, epiglottis closes, tongue pushes up, forcing bolus back; upper oesophageal sphincter relaxes 3. **Oesophageal stage** Bolus entering oesophagus initiates oesophageal peristalsis

Question 33

What cranial nerves and brain centers innervate the Bolus,Tongue, pharynx, Upper oesophageal sphincter, Oesophageal peristalsis and Cardiac sphincter?

Answer 33

Bolus activates mechanoreceptors in the back of the pharynx which sends signals via the 9th and 10th cranial nerve to the swallowing center found in the lateral reticular formation (within the medulla) which innervates the tissues involved in the swallowing reflex via the 9th 10th and 11th cranial nerve

Question 34

What is the function of the Gastroesophageal Sphincter?

Answer 34

•The gastroesophageal sphincter prevents reflux of gastric contents –Smooth muscle that stays tonically contracted by means of myogenic activity -Relaxation allows the sphincter to open •Esophageal secretion is entirely protective –Entirely mucus, which lubricates passage of food •Lessens the likelihood of esophageal damage by any sharp edges on food

Question 35

What are the steps involved in swallowing?

Answer 35

1. Swallowing is initiated voluntarily. At the swallow, the tongue presses bolous against hard palate 2. The tongue propels bolus to the pharynx 3. The swallowing center inhibits the respiratory center in the brain stem 4. Elevation of the uvula prevents food from entering nasal passageways 5. The tongue position prevents food from reentering the mouth 6. Tight alignment of vocal cords prevents food from entering the trachea 7. Epiglottis fold over closed glottis 8. Contraction of pharyngeal muscles pushes bolus through opened pharyngeosophageal sphincter into esophagus 9. pharyngeosophageal sphincter closes, oropharyngeal structures return to resting position, and breathing resumes 10. Peristalsis propels bolus down length of esophagus 11. Gastroesophageal sphincter reladxes as peristalsis pushes bolus into stomach. Swallow is complete sphincter again contacts

Question 36

Most inhibitor signals are:

Answer 36

Due to sympathetic innvervation but stimulatory signals are due to parasympathetic stimulation

Question 37

What is the thick muscular tube connects the mouth and to the stomach?

Answer 37

The oesophagus

Question 38

The oesophagus terminates in which sphincter?

Answer 38

The cardiac sphincter (which leads to the stomach)

Question 39

What sphincter separtes the stomach from the small intestine?

Answer 39

pyloric sphincter