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BMS 108 Physiology > BMS 108 Ch. 18 Digestive System I > Flashcards

BMS 108 Ch. 18 Digestive System I Flashcards

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0
Q

Food is broken down by _________ into ______ _______.

A

hydrolysis; molecular monomers

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1
Q

What is another name for the gastrointestinal tract?

A

The alimentary canal

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2
Q

Where does absorption of monomers occur?

A

in the small intestine

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3
Q

We use both _______ and _______ digestion.

A

mechanical; chemical

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4
Q

______ of substances in the GI tract is crucial.

A

Motility

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5
Q

What are the initial steps of digestion?

A
  1. Ingestion
  2. Mastication
  3. Deglutition
  4. Peristalsis
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6
Q

What types of secretions help digestion in the GI tract?

A

exocrine and endocrine products

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7
Q

What is digestion?

A

The breakdown of food molecules into smaller subunits

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8
Q

What is absorption?

A

The passage of digested end products across the epithelium into blood or lymph.

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9
Q

What does storage and elimination include?

A

Includes temporary storage and subsequent elimination of indigestible components of food.

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10
Q

What is the immune barrier?

A

A physical barrier formed by tight junctions between cells of small intestines and cells of the immune system that reside in connective tissue just below the epithelium.

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11
Q

List the structures of the digestive system.

A

Oral cavity, pharynx, esophagus, stomach, and small and large intestine.

Accessory organs include: teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

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12
Q

What are the four tunics of the GI tract?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis
  4. Serosa
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13
Q

Describe the mucosa.

A
  • the absorptive and secretory layer lining the lumen of the GI tract
  • in places it is highly folded with villi to increase the absorptive area
  • contains lymph nodules, mucin-secreting goblet cells and a thin layer of muscle
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14
Q

Describe the submucosa.

A
  • A thick, high vascular layer of connective tissue where absorbed molecules enter the blood and lymph vessels
  • Contains glands and nerve plexuses that carry ANS activity
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15
Q

Describe the muscularis.

A
  • Responsible for segmental contractions and peristaltic movement through the GI tract
  • Has an inner circular layer and an outer longitudinal layer of smooth muscle. Activity in this layer moves food through the GI tract
  • Has its own nerve supply to the GI tract including fibers and ganglia from Sympathetic and Parasympathetic systems
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16
Q

Describe the serosa.

A
  • protective layer of connective tissue
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17
Q

Parasympathetic effects, arising from ______ and spinal nerves, stimulate motility (peristalsis, segementation and opening of sphincters) and secretions of the GI tract.

A

vagus

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18
Q

Sympathetic activity __________ peristalsis and secretory activity.

A

reduces

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19
Q

What is the intrinsic system that contols movement in the GI tract called?

A

Enteric nervous system

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20
Q

GI motility is also influenced by ________ and _________ signals.

A

paracrine; hormonal

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21
Q

What is responsible for extrinsic control of the the GI tract? Intrinsic?

A
  • Parasympathetic and Sympathetic input, paracrine and hormonal signals
  • Enteric nervous system
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22
Q

What is mastication?

A

(chewing) mixes food with saliva which contains salivary amylase, an enzyme that catalyzed partial digestion of starch.

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23
Q

What propels food through the GI tract?

A

Peristalsis (wave-like muscular contractions)

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24
Q

What are the three stages of digestion?

A
  1. Cephalic phase - turned on by taste, smell and/or the vagus nerve
  2. Gastric phase - stomach distention/stretch that turns on a vagus nerve reflex
  3. Intestinal phase - arrival of chyme in duodenum inhibits gastric emptying and secretions
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25
Q

Why does the arrival of chyme in the duodenum inhibit emptying and secretions?

A

to ensure that the chyme passes through at a fixed rate

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26
Q

How many muscularis layers does the stomach have? Why?

A

3; to continue mechanical digestion

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27
Q

What are the functions of the stomach?

A

Storage of food, initial digestion of proteins, killing bacteria with high acidity, moving chyme into intestine

Contractions of the stomach churn chyme, mixing it with gastric secretions

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28
Q

What determines how long food spends in the stomach? How long on average?

A

The pyloric sphincter; 4 hours

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29
Q

Does the stomach absorb nutrients?

A

no

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30
Q

What is secreted by the gastric glands of the stomach?

A
  • Mucous
  • Hydrochloric acid
  • Intrinsic factor
  • Pepsinogen
  • Histamine
  • Serotonin
  • Gastrin
  • Somatostatin
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31
Q

What is the function of mucous?

A

serves to protect the cells of the stomach from stomach acid and pathogens (however, epithelial cells of the stomach still need replacement every 3 days)

32
Q

What is the function of hydrochloric acid?

A

denatures proteins, kills bacteria, activates pepsinogen (and converts it into pepsin)

33
Q

What is the function of intrinsic factor?

A

required for vitamin B12 absorption in the small intestine

34
Q

What is the function of pepsinogen?

A

precursor of pepsin (the active enzyme that denatures protein)

35
Q

What is the function of histamine?

A

paracrine stimulation of HCl secreting cells

36
Q

What is the function of serotonin?

A

paracrine stimulation of stomach contractions (90% of serotonin is found in the gut)

37
Q

What is the function of gastrin?

A

hormone that stimulates most of the other gastric secretions

38
Q

What is the function of somatostatin?

A

hormone that inhibits most gastric secretions

39
Q

What triggers HCl secretion in the stomach?

A

triggered by the hormone gastrin and ACh from the vagus nerve

40
Q

Why doesn’t HCl and pepsin damage the lining of a healthy stomach?

A

Because of the mucous coating the gastric epithelium that contains bicarbonate ions

41
Q

HCl helps convert _______ into pepsin. Pepsin is more active at _____ pH. Pepsin denatures ______.

A

pepsinogen; low; proteins

42
Q

Where does HCl in the stomach come from?

A
  • Is produced by parietal cells which pump H+ into lumen via H+/K+ pump (pH~1)
  • Cl- is secreted by facilitated diffusion
  • H+ comes from dissociation of H2CO3
  • Cl- comes from blood side of cell in exchange for HCO3-

HCl is secreted into the stomach lumen as HCO3- is secreted into the blood

43
Q

Where does the absoption of digested food occur?

A

Small intestine

44
Q

Where is pancreatic juice secreted into?

A

the duodenum

45
Q

Why are there folds in the lumen of the small intestine?

A

Circular folds lined with villi and microvilli increase the surface area and thus absorption rate.

46
Q

What covers each microvilli? What is contained within each microvilli?

A

columnar epithelial cells interspersed with goblet cells; lymphocytes, capillaries and a lacteal

47
Q

What does pancreatic juice contain?

A

water, bicarbonate and digestive enzymes

48
Q

What are the endocrine functions of the pancreas? Exocrine functions?

A

Secreting insulin and glucagon; local duct secretions

49
Q

What are the components of pancreatic juices?

A

Bicarbonate ions, pancreatic amylase (digestion of carbs), Trypsinogen (with brush border enzyme becomes trypsin, which digests protein) and lipase (digests lipids and fats, along with bile).

50
Q

At what pH does pancreatic amylase and trypsinogen work best at?

A

approximately 8

51
Q

Describe the process of digestion and absorption of protein.

A
  • begins in stomach when pepsin digests proteins to form polypeptides
  • in SI, pancreatic juice enzyme, trypsin, cleaves peptide bonds in polypeptides
  • other pancreatic and brush border enzymes cleave them more
  • results in free amino acids, dipeptides and tripeptides
  • free amino acids absorbed into epithelial cells and secreted into blood capillaries
  • go to liver via hepatic portal vein
52
Q

Where does food absorbed in the SI first travel to?

A

the liver

53
Q

Where do capillaries in the digestive tract drain into? Where is the ultimate destination?

A

Hepatic Portal Vein; liver

54
Q

In addition to the hepatic portal vein, the blood from the liver is drained via the hepatic vein. The liver also receives blood from the hepatic artery. Why?

A

Because the blood supplied to it from the hepatic portal vein is O2 poor.

55
Q

What does lipid emulsification begin with?

A

Bile

56
Q

Where is bile made? By what cells? Where is it stored?

A

liver; hepatocytes; gallbladder

57
Q

What enzyme is responsible for the breakdown of lipids?

A

lipase

58
Q

What does bile contain?

A
  • bilirubin - bile pigment from heme breakdown made in the liver
  • phospholipids
  • cholesterol
  • inorganic ions
  • bile salts
59
Q

What are the functions of bile salts?

A
  • gives bile its emulsification properties
  • amphipathic
  • major way to breakdown cholesterol
  • majority of bile salts are reabsorbed via enterohepatic circulation
60
Q

How much bile is produced per day?

A

up to 1 liter

61
Q

Where is bilirubin produced?

A

in spleen, bone marrow and liver

62
Q

What is bilirubin composed of?

A

derivative of heme groups (minus iron) from hemoglobin

63
Q

What is bilirubin carried in the blood by?

A

albumin

64
Q

Free bilirubin combines with an acid to form _______ _________ that is secreted into bile. It is then converted by bacteria into __________. How much of this is absorbed by the SI? Where does it go after that?

A

conjugated bilirubin; urobilinogen; 30-50%; Enters the hepatic portal vein&raquo_space; enterohepatic circulation&raquo_space; kidneys&raquo_space; excreted in urine.

65
Q

How does the liver detoxify drugs in the body?

A

The liver excretes drug metabolites into bile to pass out in feces.

66
Q

Describe how lipids are digested and absorbed.

A
  • occurs in SI
  • arrival of lipids in duodenum causes secretion of bile
  • fat is emulsified by bile salt micelles
  • forming tiny droplets of fat dissolved in bile salt micelles
  • pancreatic lipase hydrolyzes triglycerides to FFAs and monoglycerides
  • absorbed by lacteals
67
Q

What initiates peristalsis? What modulates it? Which is intrinsic? extrinsic?

A

Cells of Cajal (intrinsic); ANS activity (extrinsic);

68
Q

What is the function of the large intestine?

A

Absorbs H2O, electrolytes, B and K vitamins, folic acid

69
Q

The large intestine contains a large amount of _________. Which are important for _________ and fighting bacterial infection.

A

microflora; absorption

70
Q

How many species of microflora are in the large intestine? How do they help fight infection?

A

400 species of commensal bacteria; which produce folic acid and vitamin K and ferment indigestible food to produce fatty acids and reduce ability of pathogenic bacteria to infect the LI

71
Q

Can antibiotics negatively affect commensal bacteria?

A

yes

72
Q

The SI absorbs most water but the LI absorbs ____ % of water it receives.

A

90

73
Q

Can the LI secrete water as well? How? What does excess water secreted into the LI lead to?

A

yes; via active transport of NaCl into the intestinal lumen; diarrhea

74
Q

Besides making and secreting bile, what are some other jobs the liver does?

A

Detoxification of blood, secretion of glucose, triglycerides and ketones and production of plasma proteins

75
Q

How can the liver remove toxins from the blood?

A
  • excretion into bile
  • phagocytosis by Kupffer cells
  • Chemical alteration of molecules (e.g. ammonia&raquo_space; urea&raquo_space; urine)
76
Q

How does the liver secrete glucose, triglycerides and ketones?

A
  • lipogenesis
  • glycogenolysis, gluconeogenesis
  • removes glucose via glycogenesis
  • ketogenesis
77
Q

What plasma proteins does the liver produce?

A
  • albumins, globulins and angiotensinogen

BMS 108 Physiology (7 decks)

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