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Human Physiology > Chapter 15 Digestion and Absorption of Food > Flashcards

Chapter 15 Digestion and Absorption of Food Flashcards

1
Q

dissolving and breaking down food macromolecules through mechanical and chemical means to produce molecules small enough to be absorbed.

A

Digestion

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2
Q

saliva, digestive enzymes, hydrochloric acid, bile and other secretions needed for digestionare released into the lumen of the GI tract.

A

Secretion

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3
Q

subunits of food macromolecules, as well as water, electrolytes, and small nutrients are taken up from the lumen and pass across the wall of the intestine into the blood.

A

Absorption

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4
Q

ingested materials are mixed and transported through the GI tract by muscular contractions of the GI wall.

A

Motility

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5
Q

waves of constriction and relaxation in the muscular walls of digestive organs that moves food down their length.

A

Peristalsis

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6
Q

small amounts of certain metabolic end products are excreted, primarily by way of the bile, into the GI tract and become part of the feces.

A

Elimination

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7
Q

innermost, highly folded layer of simple columnar epithelium anchored to the lamina propria and muscularis mucosa.

A

Mucosa

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8
Q

connective tissue with many blood vessels, lymph vessels and nerves (submucosal plexus).

A

Submucosa

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9
Q

two layers of smooth muscle (inner circular and outer longitudinal) separated by the myenteric plexus.

A

Muscularis externa

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10
Q

outer connective tissue covering composed of visceral peritoneum.

A

Serosa

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11
Q

Circular folds

A

mucosa and submucosa

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12
Q

Villi

A

finger-like projections of the mucosa

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13
Q

Microvill

A

tiny projections of the cell membrane of intestinal mucosa cells.

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14
Q

finger-like projections of the mucosa

A

Villi

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15
Q

tiny projections of the cell membrane of intestinal mucosa cells.

A

Microvilli

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16
Q

pockets between the villi that secrete intestinal juice. Contain enteroendocrine cells.

A

Intestinal glands

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17
Q

secrete hormones that control a wide variety of gastrointestinal functions

A

Enteroendocrine cells

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18
Q

lymphatic capillaries within each villus that transport absorbed lipids.

A

Lacteals

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19
Q

Carbohydrates

A
  • simple sugars and substances that have two or more simple sugars linked together.
  • must be digested to monosaccharides in order to be absorbed.
  • polysaccharides have many glucose monomers linked into long chains or branching structures (ex. starch, glycogen and cellulose).
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20
Q

two simple sugars linked together

A

Disaccharides

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21
Q

single simple sugar molecules.

A

Monosaccharides

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22
Q

made by the salivary glands and functions in the mouth. It is inactivated by acid in the stomach. Responsible for only about 5% of starch digestion.

A

Salivary amylase

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23
Q

made by the pancreas and functions in the small intestine. Responsible for other 95%.

A

Pancreatic amylase

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24
Q

brush border enzymes, which means they are anchored to the surface of the small intestinal mucosa

A

Sucrase, lactase, and maltase

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25
Q

Absorbed as monosaccharides by intestinal epithelium

A

carbohydrates

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26
Q

Fructose enters cells by facilitated diffusion via a glucose transporter

A

(GLUT)

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27
Q

Glucose and galactose undergo secondary active transport coupled to Na+via the sodium–glucose cotransporter

A

(SGLT)

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28
Q

long chain of amino acids

A

protein

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29
Q

fragments of proteins consisting of short chains of amino acids.

A

Peptides

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30
Q

long fragments with many amino acids.

A

Polypeptides

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31
Q

Protein-digesting enzymes

A

proteases.

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32
Q

Protein Digestion

A

Step 1: pepsin acts in the stomach, and trypsin acts in the small intestine.
Step 2 is catalyzed by another pancreatic protease, chymotrypsin, and occurs in the small intestine.
Step 3 is catalyzed by a third pancreatic protease, carboxypeptidase, and a brush border enzyme, aminopeptidase, and occurs in the small intestine.

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33
Q

Fats

A

Fats, or more technically triglycerides, consist of one glycerol with three fatty acids attached.

34
Q

Fats must be emulsified by bile salts before chemical digestion occurs.

A

Bile mixes with the fats and breaks them up into millions of tiny droplets so that lipase has a large surface area to work on.

35
Q

made in the pancreas and functions in the small intestine. It attacks triglycerides, releasing two fatty acid chains from the glycerol backbone, which converts it to a monoglyceride. Sometimes all three fatty acid chains are removed, forming glycerol.

A

Pancreatic lipase

36
Q

Absorption mechanism

A
  • Fatty acids and monoglycerides are coated with bile salts to form water-soluble micelles in the lumen.
  • FAs and MGs are absorbed into intestinal mucosa cells by diffusion.
  • Here they are combined back into triglycerides, and packaged into chylomicrons.
37
Q

bundles of triglycerides and other lipids that are coated with specialized proteins and released by exocytosis into the lacteals.

A

Chylomicrons

38
Q

specialized lymph capillaries in the small intestine that transport absorbed lipids.

A

Lacteals

39
Q

the mixture of lymph and chylomicrons found in the lacteals.

A

Chyle

40
Q

(A, D, E, and K) are absorbed like other lipids.

A

Fat-soluble vitamins

41
Q

absorbed by diffusion or mediated transport, except for vitamin B12, which must first bind to a transport protein known as intrinsic factor.

A

Water-soluble vitamins

42
Q

absorbed by diffusion primarily within the small intestines.

A

Minerals

43
Q

Water intake

A

about 1.2 L/day in food and drink

44
Q

Amount of fluid entering GI tract as secretions

A

7 L/day

45
Q

this is where most water is absorbed. Occurs by osmosis, with absorbed nutrients creating a concentration gradient that pulls fluid back into the blood.

A

Small intestine

46
Q

about 1.5 - 2 L remains in the chyme as it enters the large intestine. Of this, all but about 100 mL/day is reabsorbed. This water is osmotically absorbed as a by-product of the active transport of sodium out of the intestinal lumen and into the blood.

A

Large intestine

47
Q

stimulates sodium and water reabsorption from the intestinal lumen (just as it does in the kidneys).

A

Aldosterone

48
Q

release of saliva from the salivary glands of the mouth.

A

Salivation

49
Q

the sight, smell, or taste of food causes signals to be sent down the vagus nerve (parasympathetic) to stimulate secretion of saliva.

A

“Pavlov’s reflex” - long, conditioned response

vagus nerve

50
Q

release of fluids made by the gastric glands in stomach wall.

A

Gastric secretion

51
Q

near top of gastric gland; secrete mucus.

A

Mucous cells

52
Q

secrete HCl and intrinsic factor.

A

Parietal cells

53
Q

secrete pepsinogen (inactive enzyme converted to pepsin by HCl in the lumen).

A

Chief cells

54
Q

secrete the hormone gastrin

A

Enteroendocrine cells (G cells)

55
Q

secrete histamine.

A

Enterochromaffin-like (ECL) cells

56
Q

HCl secretion is stimulated by

A

gastrin, histamine, and ACh

57
Q

HCl is made using the

A

H+/K+-ATPase

58
Q

Control of Gastric Secretion

A
  • Signals from vagus nerve (parasympathetic) will directly stimulate secretion from the gastric glands. This is a conditioned reflex.
  • Signals from sympathetic nerves will inhibit secretion.
  • Hormones secreted by the stomach will stimulate secretion of gastric juice, while hormones released by the small intestine primarily inhibit gastric secretion.
59
Q

Three phases of gastric secretion

A

cephalic, gastric, and intestinal.

60
Q

the sight, smell or taste of food causes the vagus nerve to stimulate secretion

A

cephalic phase
secretion of:
- HCl and pepsinogen by the parietal and chief cells, respectively.
- Gastrin by enteroendocrine cells, which is released into the blood and loops back to further stimulate secretion of HCl and pepsinogen by parietal and chief cells

61
Q

triggered by 1) stretching of the stomach wall and 2) the presence of short polypeptides and amino acids in the chyme. This stimulates further secretion of HCl, pepsinogen and gastrin.

A

Gastric phase
- controlled by both long reflexes via the vagus nerve, short reflexes, and gastrin.

  • chyme= food+ gastric secretions
62
Q
  • Gastrin causes further secretion of HCl and pepsinogen.
  • As more HCl and pepsinogen are secreted, more short polypeptides and amino acids are formed, which further stimulates release of HCl, pepsinogen, and gastrin.
A

A positive feedback loop develops

63
Q
  • As more HCl is released the pH drops, which inhibits gastrin secretion. (Amino acids act as buffers to prevent the pH from dropping so this occurs after they are digested and leave the stomach).
  • As gastrin levels fall, HCl secretion also declines. This prevents the stomach from becoming too acidic.
A

negative feedback mechanism

64
Q

Gastric secretion inhibited by

A

sympathetic nerve activity

65
Q

primarily inhibits the activity of the stomach.

A

Intestinal phase

66
Q

Intestinal Phase controlled by

A
  • Arrival of chyme in the duodenum - triggers a neural reflex (the enterogastric reflex) that inhibits secretion and motility of the stomach, and closes the pyloric sphinctor.
  • Presence of fat in the chyme.
  • Together these cause the release of enterogastrones, hormones from the duodenum that inhibit gastric function including secretin, gastric inhibitory peptide (GIP), and cholecystokinin (CCK).
67
Q

arrival of chyme in the duodenum causes secretion of pancreatic juice and bile.

A

Neural reflex

68
Q

released when the pH in the duodenum falls below 4.5.

A

Secretin

- Secretin causes the pancreas to release a secretion rich in bicarbonate to neutralize the acid chyme.

69
Q

released in response to a high fat content in the chyme.

A

Cholecystokinin

70
Q

Small Intestine secretion effects

A
  1. Stimulates pancreatic enzyme secretion so more is available for digestion.
  2. Stimulates release of bile by the gallbladder for emulsification of fat.
71
Q

the islets of Langerhans secrete the hormones glucagon ( cells) and insulin ( cells).

A

Endocrine gland

72
Q

the acinar cells produce digestive enzymes and bicarbonate.

A

Exocrine gland

73
Q

release of a bicarbonate-rich secretion.

A

Secretin

74
Q

stimulates the release of pancreatic enzymes.

A

Cholecystokinin

75
Q

first made in an inactive form, then activated in the duodenum.

A

Proteases

76
Q

this is the liver’s only digestive function.

A

Synthesis of bile

77
Q

Liver function

A
  • Metabolism of proteins, carbohydrates, and lipids.
  • Stores vitamins, iron, glycogen and other nutrients.
  • Synthesis of plasma proteins (albumin, clotting proteins, angiotensinogen, steroid binding proteins).
  • Filters old red blood cells which leads to hemoglobin processing and the generation of bilirubin.
78
Q

blood from the portal vein flows through sinusoids where hepatocytes remove toxins.

A

Detoxification

79
Q

Old, worn out RBCs are broken down in the spleen and bone marrow. The protein and iron portions of hemoglobin are recycled, but the heme portion is converted to a yellowish-orange pigment

A

bilirubin

80
Q

absorbed into the blood and eliminated in the urine, giving it a yellowish color.

A

urobilinogen

81
Q

causing bilirubin to build up in the blood

A

jaundice.

Human Physiology (4 decks)

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