Movement and Secretion

Question 1

Functions of the alimentary canal

Answer 1

• Ingestion
• Secretion
• Mechanical Digestion – mouth to small intestine
• Propulsion – throughout
• Chemical Digestion – mouth to small intestine
• Absorption – almost exclusively small intestine
• Excretion – colon and rectum
• Theres no single part of the canal that does all of these things

Question 2

Basic principles

Answer 2

• Organization of the AC
• Contents external
• Response to the internal environment of the tube
• Factors: stretch, osmolarity, pH, substrates of enzymes
• Enteric nervous system and local reflexes as well as the formal nervous system through the autonomic system are what control these organs
• Contents of this tube is considered outside of the body

Question 3

Intestinal Smooth muscle APs

Answer 3

• The cells of the muscular wall don’t send single AP spikes, they send many at a time
• Nifedipine eliminates the bursting function of the cells

Question 4

wall of the tract

Answer 4

• Mucosa – some form of epithelium
• Submocosa – where blood vessels and nerves and glands – loose connective tissue
• Muscularis Externa – layer of circular musculature as well as longitudinal musculature
• Adventitia/Serosa – where the alimentary canal is freely mobile and needs to be able to slide over other organs without friction (A lot of connective tissue and fibers and stuff)
• The contents of these layers will change from region to region but you will see some version of these layers no matter where you are
• How do these layers change as you move through the tract? (In the mouth: stratified squamous epithelium to protect against abrasion, Stomach: turns into simple columnar, In the esophagus: goblet cells)
• Muscularis wall is much thinner in the large intestine than small intestine

Question 5

movement of GI system

Answer 5

• Peristalsis – longitudinal movement
• Segmentation – subdivides the alimentary canal into segments so that it can mechanically digest the contents by mixing and churning them

Question 6

Blood flow

Answer 6

• Splanchnic Circulation – the nerve supply is also splanchnic nerves
• Absorption or muscular activity causes increased flow
• Susceptibility to ischemia – pts with PVD can also have atherosclerosis in the arteries that feed the gut
• Blood flow leaving the splanchnic circulation enter the hepatic portal system and run blood through the liver and filter it of toxins, etc.

Question 7

Hunger vs appetite

Answer 7

• Hunger = motivational drive to eat something

- Appetite = specific desire for the thing you want to eat

Question 8

Propulsion

Answer 8

• occurs through the alimentary canal
• Pregastric
• Gastric
• Small Intestine
• Colon
• Defecation

Question 9

Chewing

Answer 9

• Buccinators and tongue for positioning between the teeth
• Pterygoids for grinding movements
• Masseters raise jaw, bite
• Temporalis work with masseter (These two muscles are the muscle we use to create force in biting down, We don’t have a muscle to open the jaw with any strength)

Question 10

Salivation

Answer 10

• lubricates the food, output is mediated through salivary nucleus in brainstem
• Info is carried on facial nerve (chorda tympani) which gives off branches to sublingual, submandibular, and parotid glands – these are parasympathetic fibers (use Ach)
• Presynaptic fibers synapse with the post synaptic fibers at submandibular ganglion

Question 11

swallowing

Answer 11

• both voluntary and reflexive process
• You form the food in your mouth into an elongated ball and push it back toward your throat and it triggers a reflexive action that will pull the bolus of food into the throat
• Move it quickly from pharynx to stomach so that its out of the way of the respiratory system
• You have signals going to pneumotaxic center to inhibit respiratory drive so that you don’t aspirate

Question 12

Stomach

Answer 12

• sits in superior part of peritoneal cavity
• Has a large body, dome at top = fundus
• Distal end has antrum and pylorus
• Lesser omentum attached to small curve and greater omentum attached to large curve
• Three layers of muscle in muscluaris externa (Mechanically digest food)
• Extensive folding of the internal stomach

Question 13

Small intestine

Answer 13

• the only region that does both segmentation and peristalsis
• There are anticipatory emptying called mass movements – when you eat a meal and you start to fill up the stomach, this will signal the small and large intestine to start emptying so that we can make room
• Segmentation – occurs as the stomach empties slowly (chyme) – small intestine stops everything in place and begins to segment everything with circumferential musculature (Where the bulk of absorption happens)
• Peristalsis
• Hormonal control of motility
• Gastroileal reflexes

Question 14

Large intestine

Answer 14

• Distension effects – leads to the formation of a contractile ring (The large intestine has pretty weak musculature – the band down the center is pretty much the only musculature it has - It pulls the large intestine into haustra (pleated structures))
• Functions – RESORB WATER!! Absorb some vitamins (waste products of bacterial metabolism)
• Haustrations
• Mass movements – movements that move down the length of the organ in anticipation of receiving contents from upstream

Question 15

defecation

Answer 15

• Mass movements – result in dumping stool in the rectum (Innervated extensively and you feel pressure which creates the motivational drive to defecate, Innervation is somatic (through ventral hrn) and autonomic, Anus has two sphincters, outer and inner - Inner is autonomic, you have no control over it, Outer is skeletal and voluntary)
• Motivation
• Control – when you learn how to defecate, you are actually learning to control the contraction of the outer sphincter

Question 16

secretion

Answer 16

• Types of glands (Single cell (Goblets) – make mucus, Pits (multicellular glands), Tubular, complex)
• Stimulation
• Mechanisms
• Role of mucus

Question 17

types of glands

Answer 17

• Goblet cell

- Tubular gland (some of the gland is embedded in submucosa

Question 18

composition of saliva

Answer 18

• watery substance secreted by salivary glands
• 99% water
• Has electrolytes, mucus, and enzymes

Question 19

secretion of saliva

Answer 19

• based on sodium potassium pump activity
• Uses this to drive secondary transport for molecules like bicarb and chloride
• Theres atpase activity on the luminal surface as well that brings in sodium nad pumps out potassium - Theres more potassium and less sodium in saliva
• Amylast is there to breakdown starches

Question 20

Control of saliva secretion

Answer 20

• controlled by parasympathetic and sympathetic divisions of the nervous system
• The parasympathetic division causes a more watery secretion
• Sympathetic divison causes more secretion of a thicker, tackier secretion that you get when you are public speaking for instance

Question 21

gastric secretions

Answer 21

• happen in the gastric pits – invaginations of the mucosa
• Acid – made by parietal cells
• Pepsinogen – made by zymogenic cells: Precursor of pepsin, When it flows through the acid secreted by acids, converts it to pepsin which then is able to break down proteins
• Pyloric glands – release gastrin in response to stretch and contents in the stomach
• Regulation: Regulated top down through vagus nerve and hormones as well as enteric nervous system

Question 22

gastric acid secretion

Answer 22

• using atp pump to move potassium and protons at luminal surface to pump protons into the lumen
• Uses secondary active transport to move bicarb and chloride
• Creates hydrochloric acid in lumen
• Chromaffin cells are called mast cells in this slide

Question 23

cephalic phase

Answer 23

-mediated through the vagus, largely parasympathetic

Question 24

gastric phase

Answer 24

• gastrin is responding to stretch receptors and products within the lumen of the stomach as well as acid levels – this is controlling its stimulation of acid production
• There is also control from the lower part of the system: There is feedback from the small intestine

Question 25

pancreatic secretions

Answer 25

- responsive to duodenal environment - Enzymes – releases secretin in response to the presence of acidic chyme in the duodenum (Secretin slows down acid production in stomach by acting on the cells there, Stimulates bicarb release from the pancreas, Fats in the duodenum stimulate release of cholecystokinin which causes the gall bladder to release bile (Causes the pancreas release other enzymes to break down fats) - Pancreas has acini and islets of Langerhans (Langerhans produce insulin, Acini produce pancreatic enzymes, It is the cells that line the ducts that make the abundance of bicarbonate) - Bicarbonate - Regulation

Question 26

Bile secretion by liver

Answer 26

- made continuously and is mostly water (97%) - Bile production - Storage - Secretion – through the hepatic ducts and is stored in the gall baldder (Gall bladder condenses and dehydrates the bile, The more it sits in the gall bladder, the more likely it is to make stones because its being more and more dehydrated, Secreted form gallbladder under control of CCK from duodenum (in response to fats in small intestine)) - Function – bile emulsifies fats – has molecules that are both hydrophilic and hydrophobic

Question 27

small intestine

Answer 27

- Mucus throughout its length - Digestive juices (small amounts) – mostly bicarb early - Regulation – by enteric NS and greater NS through vagus

Question 28

large intestine

Answer 28

-Mucus secretion (The acid has already been buffered, Has resident population of bacteria – we absorb the products of their metabolism in the form of vitamins)