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Ella Notes for PHGY 216 > module 6: digestive system > Flashcards

module 6: digestive system Flashcards

1
Q

Describe the four basic digestive functions

A
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2
Q

Describe the functional layers of the walls of the digestive system

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3
Q

Describe the enteric nervous system

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4
Q

anatomy of GI sys

A

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

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5
Q

roles of the digestive system (5)

A

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

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6
Q

digestive processes (4)

A

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

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7
Q

digestive tract walls

A

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)

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8
Q

regulation of digestive functions

A

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)

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9
Q

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

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10
Q

Understand and describe the swallowing reflex

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11
Q

Describe the coordinated responses during the oropharyngeal phase of swallowing

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12
Q

The Cephalic Phase of Digestion

A

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”

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13
Q

The Oral Phase of Digestion

A

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)

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14
Q

Saliva

A

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

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15
Q

Autonomic Control of Salivation

A

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”

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16
Q

Salivary Secretion Reflexes

A

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

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17
Q

Swallowing: An all or none reflex

A

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

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18
Q

The Oropharyngeal Phase of Swallowing

A

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

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19
Q

Peristalsis

A

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

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20
Q

Esophagus

A

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)

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21
Q

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

A
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22
Q

Describe the mechanisms and regulation of acid and pepsinogen secretion

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23
Q

Describe why the stomach does not digest itself

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24
Q

Describe the factors affecting gastric emptying

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25
Q

The Stomach

A

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

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26
Q

stomach functions

A

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

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27
Q

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

A

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

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28
Q

describe gastric emptying

A

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)

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29
Q

vomiting

A

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

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30
Q

gastric secretions

A

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

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31
Q

hydrochloric acid
+ functions
+ secretions

A

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

32
Q

pepsinogen

A

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

33
Q

mucus

A

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)

34
Q

intrinsic factor

A

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

35
Q

secretory cells

A

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

36
Q

gastric digestion

A

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)

37
Q

gastric absorption

A

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

38
Q

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

A
39
Q

Describe bile formation and its secretion

A
40
Q

Describe how bile salts aid fat absorption

A
41
Q

Describe enterohepatic circulation of bile salts

A
42
Q

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

A
  • 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)
43
Q

control of pancreatic exocrine secretion

A

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

44
Q

the liver + functions

A

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

45
Q

liver blood flow

A

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

46
Q

lobules

A

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

47
Q

wedge of lobule

A

(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

48
Q

bile

A

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

49
Q

Enterohepatic Circulation

A

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

50
Q

bile salt structure

A
  • 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
51
Q

fat digestion and absorption

A
  • 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
52
Q

bilirubin

A

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

53
Q

bile secretion regulation

A

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

54
Q

bile storage in the gallbladder

A

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

55
Q

the small intestine phase

A

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

56
Q

the small intestine

A

Digestion and absorption!
Duodenum, jejunum and ileum

57
Q

small intestine motility

A

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

58
Q

the migrating motility complex

A

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

59
Q

small intestine secretions and digestion

A

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

60
Q

surface areas of the small intestine

A

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)

61
Q

absorption of sodium into small intestine

A

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

62
Q

absorption of proteins into small intestine

A

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

63
Q

absorption of carbs into small intestine

A

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

64
Q

absorption of minerals - iron into small intestine

A

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

65
Q

absorption of fats into small intestine

A

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

66
Q

diarrhea

A

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

67
Q

Describe the mechanism of motility in the colon

A
68
Q

Describe the defecation reflex

A
69
Q

Describe the role of the microbiome

A
70
Q

the large intestine

A

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

71
Q

haustral contractions

A

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

72
Q

mass movements

A

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

73
Q

defecation reflex

A

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

74
Q

large intestine secretions

A

Alkaline NaHCO3 mucus to lubricate

75
Q

microbiome

A

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”

76
Q

large intestine absorption

A

Smooth luminal surface
Sodium actively absorbed
Chloride and water follow sodium

77
Q

IBS

A

Cramping
Abdominal pain
Bloating
Gas
Diarrhea
constipation

Ella Notes for PHGY 216 (3 decks)

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