module 6: digestive system

Question 1

Describe the four basic digestive functions

Question 2

Describe the functional layers of the walls of the digestive system

Question 3

Describe the enteric nervous system

Question 4

anatomy of GI sys

Answer 4

Is a continuous series of hollow, muscular tubes that extends from the mouth to anus
Muscle movement and secretion release allows digestion of food
Organs and Structures
Nasal passages
Mouth
Salivary Glands
Esophagus
Liver
Stomach
Gallbladder
Pancreas
Small Intestine
Anus
Rectum
Colon

Question 5

roles of the digestive system (5)

Answer 5

Ingestion-physical act of eating
Digestion-breakdown of food into small molecules to be absorbed
Absorption-movement of nutrients from the digestive tract to the circulatory system
Distribution-movement through circulatory system for delivery to the tissues and cells
Usage-the movement of the nutrients into cells for metabolism or anabolic processes

Question 6

digestive processes (4)

Answer 6

Motility-muscular contractions that mix and propel contents (smooth muscle cells have a constant level of contraction to prevent stretching)
Secretion-digestive juices (all contain water and electrolytes) these glands get their water and raw materials from plasma
Digestion-biochemical process of enzymatic breakdown of foods
Absorption-occurs mostly in small intestine (small absolute units are produced, along with water, vitamins, electrolytes) and they move from GI tract lumen into the blood and lymph

Question 7

digestive tract walls

Answer 7

Mucosa- innermost layer (folded to increase SA)
Submucosa-thick connective tissue (provides distensibility and elasticity)contains nerves, blood and lymph vessels
Muscularis Externa-smooth muscle (contraction of inner layer decreases lumen diameter, contraction of longitudinal layer shortens the tube. (for mixing and propulsion contractions
Serosa- outer connective tissue layer (suspends digestive organs from the inner wall, allowing them to move for mixing)

Question 8

regulation of digestive functions

Answer 8

Autonomous smooth muscle function (pace-maker-like rhythm, slow-wave potentials and are from non-contractile interstitial cells of Cajal
Intrinsic nervous plexuses (sensory neurons, mostly self-regulation)
Extrinsic autonomic nerves (Sympathetic systems slows down contractions and secretions, parasympathetic system increases smooth muscle contraction
Gastrointestinal hormones (excitatory or inhibitory actions on motility and exocrine gland secretions)

Question 9

Compare and contrast the cephalic, oral, and esophageal phases of digestion

Question 10

Understand and describe the swallowing reflex

Question 11

Describe the coordinated responses during the oropharyngeal phase of swallowing

Question 12

The Cephalic Phase of Digestion

Answer 12

Begins before food enters the mouth
Thought, sight, and smell of food stimulates the cerebral cortex, and other appetite centres in the brain=parasympathetic activation
Vagus nerve sends signal to stomach to cause gastric secretions
“anticipatory phase”

Question 13

The Oral Phase of Digestion

Answer 13

Palate- the roof of the oral cavity that separates it from nasal cavity (permits breathing while chewing)
Tongue- the floor of the oral cavity (voluntary control skeletal muscle, important for chewing, swallowing and speech) taste buds are also on the tongue
Pharynx-the cavity behind the nose and mouth, connecting them to the esophagus
Teeth- external bones embedded in the jaw bone for chewing or mastication, and mixing food with saliva)

Question 14

Saliva

Answer 14

Saliva is the secretion from salivary glands (amylase, mucus, and lysozyme)
Amylase breaks down carbs (polysaccharides into disaccharide maltose)
Mucus moistens the food to facilitate swallowing
Lysozyme is anti-bacterial and can destroy certain bacteria
Saliva is for taste (molecules dissolve in saliva)
Saliva lubricates tongues and lips, allowing speech
Saliva contains bicarbonate buffers to neutralize acids

Question 15

Autonomic Control of Salivation

Answer 15

Both sympathetic and parasympathetic stimulate salivary secretion
Parasympathetic is a fast flow of watery saliva (rich in enzymes)
Sympathetic is a smaller volume (thicker in mucus) “perception of dry mouth”

Question 16

Salivary Secretion Reflexes

Answer 16

There is always a low level of basal secretion to keep the throat moistened
To increase salivary flow, there are 2 reflexes
Simple Salivary Reflexes
Chemoreceptors and mechanoreceptors respond to the presence of food (their activation = signal to salivary center in medulla = sends impulses via extrinsic autonomic nerves=salivation)
Conditional Salivary Reflexes
“mouth watering” from the pleasure of eating from cerebral cortex

Question 17

Swallowing: An all or none reflex

Answer 17

Voluntarily initiated when a bolus or liquid is forced to the back of the throat
Bolus exerts pressure on the pharynx, triggered a reflex innervated by 25 pairs of muscles
Pressure=afferent signals to swallowing center in medulla = efferent signals control timing
Once started, cannot be stopped

Question 18

The Oropharyngeal Phase of Swallowing

Answer 18

Mouth-swallowing initiated, tongue positions against the palate to keep food from coming back into the mouth
Nasal passages- the uvula elevates and blocks nasal passages
Respiratory Passages- brainstem resp center is inhibited so there is no air movement, larynx elevates and vocal cords tighten=food no touch trachea

Question 19

Peristalsis

Answer 19

Beginning to end of esophagus wave
Ring-like contractions that move contents of the organ onward
Starts with the first peristaltic wave down to the stomach, if bolus does not make it, then the distension of the esophagus initiates a second wave (more forceful) this is innervated from the intrinsic nerve plexus
Lower sphincter is relaxed, and allows bolus into the stomach

Question 20

Esophagus

Answer 20

Its lubricated with mucus for easier movement, and to protect from gastric juices
Usually it remains tightly contracted to prevent acid reflux into esophagus (gastric reflux)

Question 21

Compare and contrast gastric motility in the major regions of the stomach

Question 22

Describe the mechanisms and regulation of acid and pepsinogen secretion

Question 23

Describe why the stomach does not digest itself

Question 24

Describe the factors affecting gastric emptying

Question 25

The Stomach

Answer 25

J-shaped The fundus-lies above esophagus The body-main part The antrum-very muscular section of the stomach Between the stomach and small intestine is the pyloric sphincter

Question 26

stomach functions

Answer 26

Store ingested food Secretes HCL and enzymes for protein digestion Mechanically mixed food with gastric secretions=chime

Question 27

gastric motility 1. gastric filling 2. gastric storage 3. gastric mixing 4. gastric emptying

Answer 27

Gastric filling -Empty=50ml, but it can expand, deep folds get smaller and flatten out as it expands=no increase in tension (occurs by vagally mediated process called receptive relaxation) Gastric Storage- most food is stored in the body and moved into the muscular antrum where mixing occurs Gastric Mixing- with each peristaltic wave, chime is pushed towards pyloric sphincter, and if the sphincter is closed, the chyme keeps remixing, known as retro pulsation (then particles are small enough and can empty) Gastric emptying- chyme will be pushed through sphincter

Question 28

describe gastric emptying

Answer 28

Duodenum influences the rate of gastric emptying Duodenum will send signals to tell the stomach to gastric empty Known as the enterogastric reflex (innervated by intrinsic nerve plexus and autonomic nerves) Secretin and cholecystokinin Fat is the most important stimulus for inhibiting gastric emptying (fat takes up a lot of time) Acid (the stomach secretes a lot of HCl and it is mixed in with chyme, the duodenum must neutralize it to prevent damage (so highly acidic foods reduce gastric emptying) Hypertonicity (digestion is faster than absorption, the increase in osmolarity will bring enough water in to distend the duodenum and decrease plasma volume (this increase osmolarity will inhibit gastric emptying) Distension (the more extended the duodenum is, the slower the rate of gastric emptying)

Question 29

vomiting

Answer 29

Emesis Coordinated in the medulla of the brain stem Starts with deep inspirations and closure of glottis (prevents gastric contents from entering lungs), and uvula closes (prevents it from entering nasal cavity) Diaphragm contracts downwards and the abdominal muscles contract inwards The flaccid stomach is compressed, contents are forced upwards and out of the mouth This keeps going until the stomach is empty Sweating, salivation, increased heart rate, and nausea

Question 30

gastric secretions

Answer 30

Oxyntic mucosa (lines fundus and body) Mucus cells line the pits and the entrance to the glands secrete a watery mucus Chief cells-secrete pepsinogen Parietal cells secrete HCl and intrinsic factor pyloric gland area lines the antrum

Question 31

hydrochloric acid + functions + secretions

Answer 31

Parietal cells secrete Decrease pH to as low as 2 Functions Activates pepsinogen to form pepsin Breaks down connective tissues and muscle fibers Denatures proteins Kills microorganisms with food Secretion H2O is broken down into H and OH. H is sent back into lumen by the H-K-ATPase active transport pump The OH combines with H to remake H20, H20 recombines with CO2 to form H2CO3, which dissociates into H and HCO3 HCO3 moves to plasma by a L HCO3 exchanger, builds up CL in parietal cells, then entering the electrochemical gradient, into the gastric lumen

Question 32

pepsinogen

Answer 32

Within chief cells, pepsinogen is stored HCL cleaves off a small part to make pepsin Pepsin makes more pepsin Active pepsin starts protein digestion by making smaller amino acid chains Pepsinogen is inactive so that it does not digest itself or the cell

Question 33

mucus

Answer 33

Secreted by epithelial surface cells Protective barrier The mucus acts as a lubricant and protects the gastric mucosa against mechanical injury Protects stomach wall from environment (mucus is alkaline and neutralizes HCl near the lining) It protects the stomach from self-degradation (HCl becomes inactivated when it goes close)

Question 34

intrinsic factor

Answer 34

Secreted by parietal cells Important for B12 reabsorption B12 is responsible for RBCs

Question 35

secretory cells

Answer 35

G Cells (endocrine cells located in the pyloric gland area, and they secrete gastrin hormone) stimulates chief and parietal secretions Enterochromaffin-like Cells (found in chief and parietal cells in the oxyntic mucosa, and secrete histamine, acting as a paracrine to increase HCL) release is stimulated by gastrin and Ach D cells (Found in the pylorus and duodenum, in response to acid, they secrete somatostatin to inhibit secretions of parietal cells, G cells, and ECL cells

Question 36

gastric digestion

Answer 36

most food stays in a semi-solid state as the peristaltic contractions are not strong enough for mixing (protein digestion mostly in antrum) and (food is mixed with salivary amylase, the interior of food mass is not exposed to acid so amylase works)

Question 37

gastric absorption

Answer 37

No food or water is absorbed through the wall of the stomach into blood (except alcohol-fatty foods slow absorption and aspirin (weak acid))

Question 38

Describe the secretions of the pancreas and how these secretions are regulated

Question 39

Describe bile formation and its secretion

Question 40

Describe how bile salts aid fat absorption

Question 41

Describe enterohepatic circulation of bile salts

Question 42

exocrine pancreas 1. pancreatic enzymes 2. pancreatic amylase 3. pancreatic lipase

Answer 42

- Secrete pancreatic juices (a mixture of pancreatic enzymes and an aqueous alkaline secretion) Proteolytic Enzymes - trypsinogen - Chymotrypsin - Procarboxypeptidase Pancreatic Amylase - Converts polysaccharides into disaccharide maltose (hydrolyzes starches, glycogen, and other carbs) Pancreatic Lipase - Digests fats (hydrolyzes triglycerides into monoglycerides and free fatty acids to be absorbed)

Question 43

control of pancreatic exocrine secretion

Answer 43

During cephalic phase, there is a small amount of parasympathetically mediated paracrine secretion, due to gastrin, however mostly it is hormonal control Presence of chyme = secretin and CKK release Secretin Acid= secretin release This travels to pancreas and stimulates the duct cells to increase their secretions of NaHCOs rich fluid CKK In response to fats in duodenum Stimulates pancreases acinar cells to increase digestive enzyme secretions

Question 44

the liver + functions

Answer 44

Production of bile salts (for fat digestion and absorption) Functions Metabolic processing of fats, carbs, and proteins after absorbed Detox of body wastes, drugs Synthesize plasma proteins Storage of glycogen, fats, iron, copper, vitamins Activates vitamin D Removal of old red blood cells and bacteria Excretes cholesterol and bilirubin

Question 45

liver blood flow

Answer 45

Each liver cell hepatocyte does the same task Every minute (1L) of venous blood flows from the digestive system through the hepatic portal vein, into the liver to deliver anything that was absorbed The hepatic artery supplies about another 250mL of arterial blood to deliver oxygen and blood-borne metabolites

Question 46

lobules

Answer 46

Hexagonal arrangements of tissue surrounding a central vein Bile ducts converge to form the common bile duct (bile from liver to duodenum

Question 47

wedge of lobule

Answer 47

(blood from both the hepatic artery and portal vein flow from periphery of the lobule through capillary-like structures called sinusoids Lining sinusoids are Kupfer cells (remove old blood cells and bacteria/macrophage) The central vein of all liver lobules converge to form the hepatic vein (carries blood away from the liver) Bile canaliculus are thin bile carrying channels

Question 48

bile

Answer 48

Bile is constantly produced, but does not enter the duodenum unless active digestion is occurring The bile duct is guarded by the sphincter of Oddi that is closed until bile is needed Bile is composed mainly of bile salts, cholesterol, lecithin, and bilirubin, in an aqueous fluid similar to the pancreatic NaHCO3 secretion Bile salts are derivatives of cholesterol

Question 49

Enterohepatic Circulation

Answer 49

Recycling of bile salts occurs between the liver and small intestine, and is called enterohepatic circulation Steps 1. Secreted bile salts are 95% old, and 5% new 2. 95% of bile salts are reabsorbed by terminal ileum 3. Reabsorbed bile salts are recycled 4. 5% of bile salts are lost in feces

Question 50

bile salt structure

Answer 50

- Detergent-like effects on fats They convert large fat globules in the chyme into a lipid emulsion of numerous fat droplets - Bile salts have a lipid soluble part, which interacts with the surface of the fat droplets, and a negatively charged water soluble end - This allows bile salts to decrease the surface tension of lipid droplets and break them down

Question 51

fat digestion and absorption

Answer 51

- Polar ends of bile salts repel each other - Lipase, and pancreatic secretes colipase, bind both lipase and the bile salts to hold the lipase at its site of action so it can break down triglycerides - Micelles-the structure of lipid-soluble compounds surrounded by water-soluble bile salts are called micelles

Question 52

bilirubin

Answer 52

A waste product Secreted in the bile From degradation of haemoglobin in old red blood cells Most is excreted in feces Urine has a yellow colour because some is reabsorbed in the small intestine and thus tinges urine yellow

Question 53

bile secretion regulation

Answer 53

Chemical-bile salts reabsorbed, further release of bile occurs Hormonal-secretin stimulates aqueous alkaline component (NOT BILE SALTS) Neural -vagal stimulation promotes the release of bile before food reaches the stomach or intestine

Question 54

bile storage in the gallbladder

Answer 54

Active transport of salt out of gallbladder with water osmotically following, it concentrates the bile 5-10 times CKK allows gallbladder to contract and causes sphincter Oddi to relax Bile salts can precipitate and form gallstones

Question 55

the small intestine phase

Answer 55

Describe the mechanisms responsible for the digestion of carbs, proteins, and fat Describe how carbohydrates, proteins, fats are absorbed Understand segmentation as a mechanism of motility Describe the anatomical features of the small intestine that make it an ideal location for absorption

Question 56

the small intestine

Answer 56

Digestion and absorption! Duodenum, jejunum and ileum

Question 57

small intestine motility

Answer 57

Motility in the SI is termed segmentation Mixes and slowly propels the chyme It occurs by localized contractions, every few cm After some time, the contracted areas relax and ring-like contractions appear in the previously relaxed areas Chyme is then moved back and forth, slowly mixed Gastrolienal reflex, segmentation is initiated by pacemaker cells that generate basic electrical rhythm (BER) BER brings smooth muscle to threshold, and contraction occurs Segmentation is absent between meals

Question 58

the migrating motility complex

Answer 58

When most of food has been absorbed, segmentation switches to migrating motility complex Weak peristaltic waves It moves any ruminants forwards towards the colon

Question 59

small intestine secretions and digestion

Answer 59

Mucus secretion Brush border helps absorption (microvilli) This border contains membrane-bound enzymes (Enterokinase, disaccharidases, aminopeptidase Enterokinases can convert pancreatic trypsinogen to trypsin Disaccharidases complete carb digestion Aminopeptidases hydrolyze small peptide fragments into amino acids Little absorption in the ileum

Question 60

surface areas of the small intestine

Answer 60

Inside surface is not smooth Inner surface has circular folds (increases 3-fold) Projecting from the folds are finger-like projections called villi (increase 10 fold) The epithelial cells also have small hair-like projections (another 20 fold)

Question 61

absorption of sodium into small intestine

Answer 61

Sodium (Water and chloride follow due to electrical and osmotic gradient) Passive-leaky tight junctions Active-sodium channels or cotransporter

Question 62

absorption of proteins into small intestine

Answer 62

Digestive enzymes =. Absorbed Proteins from epithelial mucosal cells Plasma proteins that leak from capillaries

Question 63

absorption of carbs into small intestine

Answer 63

Active-sodium-monosaccharide cotransport, or sodium-independent facilitated diffusion Galactose (1st transported) Glucose (2nd transported) Fructose (last) facilitated diffusion

Question 64

absorption of minerals - iron into small intestine

Answer 64

Most iron is transported directly into blood for RBC production (transferrin delivers) If not, it is stored within epithelial cell in a granular form called ferritin High iron, then iron is sent to intestinal lumen Ferritin dumped into lumen when epithelial cell is sloughed off after 3 days, extra iron is out through feces

Question 65

absorption of fats into small intestine

Answer 65

Become chylomicrons They leave via exocytosis Taken up by lymph, then transported to the blood

Question 66

diarrhea

Answer 66

Rapid emptying of intestine to remove potentially harmful thing Metabolic acidosis causes this Excessive small intestinal motility=local irritation or stress (not enough time for water absorption) Excess of osmotically active particles=lactose intolerance) Toxins produce excess fluid secretion

Question 67

Describe the mechanism of motility in the colon

Question 68

Describe the defecation reflex

Question 69

Describe the role of the microbiome

Question 70

the large intestine

Answer 70

Made up of the cecum, appendix and the colon Not coiled Ascending colon, transverse colon, and the descending colon, and the end forms the sigmoid colon that straightens out to be the rectum

Question 71

haustral contractions

Answer 71

Circular and longitudinal muscle layers The colon's main motility is haustral contractions,w hich are slow and non-propulsive. They are generated by autonomous rhythmicity of colonic smooth muscle cells

Question 72

mass movements

Answer 72

Increase in haustral contractions to move the feces Driven by gastrocolic reflex, which moves feces to the rectum to trigger the defecation reflex

Question 73

defecation reflex

Answer 73

Fecal matter fills rectum, stretch receptors send impulses to spinal cord which sends a reflex signal via parasympathetic system to the distal colon This causes the internal and external sphincter to relax and contract If the external sphincter is relaxed, defecation will occur

Question 74

large intestine secretions

Answer 74

Alkaline NaHCO3 mucus to lubricate

Question 75

microbiome

Answer 75

Enhance intestinal immunity by competing with potentially pathogenic microbes for nutrients and space Promote colonic motility Make nutritional contributions as a result of their metabolism Help to maintain the integrity of the colon mucosa Gut microbiome has the largest number of bacteria compared to other areas of the body. "gut flora"

Question 76

large intestine absorption

Answer 76

Smooth luminal surface Sodium actively absorbed Chloride and water follow sodium

Question 77

IBS

Answer 77

Cramping Abdominal pain Bloating Gas Diarrhea constipation