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BMS 300 > Exam 4--digestion > Flashcards

Exam 4--digestion Flashcards

1
Q

what are the two sets of endocrine cells embedded in the pancreas?

A

beta produce insulin
alpha glucagon
both are important for the metabolism of glucose

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2
Q

how does glucose arrive in the liver

A
  • glucose absorbed from the intestines arrives in the liver sinusoids via the hepatic portal system
  • some of the glucose continues into the venous blood and increases the amount of glucose in the blood systemically
  • some of the glucose is taken up by the hepatocytes in the liver and converted to the glucose polymer glycogen
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3
Q

what happens when glucose from the intestine is not readily available

A
  • glycogen stored in hepatocytes can be converted to glucose by the process of the glycogenolysis and released into the blood to increase blood glucose
  • glucose may also be generated in hepatocytes by a process called gluconeogenesis where amino acids are converted to glucose and released into the blood
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4
Q

what happens when blood glucose levels become low

A 
many cells (not neurons) use fatty acids mobilized from adipose tissue as an energy source which is know as lipolysis 
-as blood glucose levels fall alpha cells release glucagon which acts on liver cells to convert to glucose and go to the blood
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5
Q

glucose may be stored as…

A

glycogen

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6
Q

glucose may be taken up by…

A

adipocytes and converted into triglycerides

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7
Q

glucose may be metabolized via…

A

glycolysis or oxidative phosphorylation

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8
Q

glucose

A

-when a molecule of glucose is converted into two molecules of pyruvate 2 ATP molecules are generated in the cytoplasm by glycolysis

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9
Q

insulin and its effects on blood glucose

A
  • decrease blood glucose concentration

- facilitates entry of glucose into most cells by stimulating transporters into the cell membrane

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10
Q

glucagon and its effects on blood glucose

A
  • increase blood glucose concentration

- stimulates glycogenolysis in the liver

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11
Q

cortisol and its effects on blood glucose

A
  • increase blood glucose concentration

- stimulates gluconeogenic pathway

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12
Q

epinephrine and its effects on blood glucose

A
  • increase blood glucose concentration

- stimulates triglyceride breakdown into fat to provide a source for most cells

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13
Q

what are the 3 main categories of food?

A
  1. carbs
  2. fats
  3. proteins
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14
Q

carboyhdrates

A
  • polysaccharides, such as starch and glycogen
  • disaccharides such as sucrose, lactose, and maltose
  • monosaccharides or simple sugars such as glucose, fructose, and galactose
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15
Q

proteins

A
  • amino acids linked by peptide bonds

- broken into proteases first into peptides and finally into individual amino acids

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16
Q

lipids or fats

A

-triglycerides composed of one molecule of glycerol and 3 molecules of fatty acid each linked by an ester bond to the glycerol backbone

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17
Q

outcome of digestion and metabolism

A
  • carbs to simple sugars
  • proteins to amino acids
  • lipids to monoglycerides, glycerol, fatty acids
  • the function of digestion is to break them into one of the 4 catagories, absorb them for use in the body as a form of energy or a generation of a new molecule
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18
Q

secretion

A

the addition of enzymes or cofactors necessary for digestion

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19
Q

motility

A

agitation and movement of digesta through the system

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20
Q

absorbtion

A

the uptake of the products of digestion

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21
Q

secretion of the mouth…

A

-saliva
-mucus
-amylase
(endocrine glands)
-under the primary control of the parasympathetic nervous system

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22
Q

saliva

A

-mostly water
-the secretory cells called acinar cells are responsible for secreting saliva
-the conc of ions shortly after its produced by acinar cells is similar to the interstitial fluid
-formed by transporting sodium out of the acinar cells, potassium in, chloride out, bicarbonante in, and water follows
-most of the ions are resorbed by the duct epithelial cells so the ion conc in saliva is more dilute then in the interstitial fluid
-potassium is higher in the saliva
-with the ingestion of food saliva production increases and the concentration of salts in saliva increase
WHY ISN’T IT SALTY??

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23
Q

mucus

A
  • exocrine glands produce mucus

- purpose is to lubricate the ingesta so that it can be more easily swallowed

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24
Q

salivary amylase

A

-enzyme that converts starch to dissaccharides and oligosaccharides

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25
Q

swallowing

A

-reflex with control residing in the brain stem
-upper 1/3 skeletal
>under the control of the somatic neurons in the brain stem
-lower 2/3 smooth
>under the control of the parasympathetic nervous system
-swallowing centers in the brain stem send signals to both the skeletal and smooth muscle which causes a contraction in a wave-like fashion called peristalsis

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26
Q

esophageal sphincter

A

-region of smooth muscle that controls the movement of food into the stomach from the esophagus

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27
Q

mucosa

A
  • composed of a layer of epithelial cells that line the tube of the digestive system
  • these are attached via basal lamina to the underlying lamina propria (connective tissue)
  • under is a layer of smooth muscle
28
Q

submucosa

A
  • thick layer of connective tissue rich in elastic fibers that stretch when you’ve had a large meal
  • there are two smooth muscle layers external that work in concert to churn the stomach contents into smaller pieces
29
Q

chyme

A

-the layers of smooth muscle churn the stomach contents and help to reduce digesta to small pieces suspended into the fluid

30
Q

absorbtion in the stomach

A

-minimal and is restricted to some lipid soluble toxins like alcohol and asprin

31
Q

secretion in the stomach

A
  • cells of the glandular epithelium in the mucosa of the stomach are responsible for secretion of acid, pepsinogen, histamine, and gastrin
  • cells of the gastric gland are located at regions called the gastric pits which are extensions of the columnar epithelium of the stomach mucosa
32
Q

parietal cells

A
  • make and secrete acid
  • found in gastric glands
  • produce HCl contain carbonic anhydrase which converts CO2 + H2O –> H+ + HCO3-
  • the H+ ion is pumped out of the cell into the lumen of the stomach–this is controlled by Ach released from the parasympathetic postganglionic neuron axon terminals, gastrin released from g-cells, and histamine released
  • the HCO3- is released into the blood
  • these two movements can be called the alkaline tide
  • have receptors for gastrin on their basolateral surfaces
33
Q

cheif cells

A
  • make and secrete pepsinogen –>pepsin
  • found in gastric glands
  • the pepsinogen is inactive until it is exposed to a low pH and a portion of the enzyme is removed by pepsin
34
Q

G-cells

A
  • secrete the hormone gastrin

- found in gastric glands

35
Q

enteroendocrine cells

A
  • located near the parietal cells and secrete histamine which functions locally on the parietal cells
  • found in gastric glands
36
Q

gastrin

A
  • released from G-cells and enters the blood
  • when it arrives at the parietal cell it binds to receptors and induces the release of H+ ions
  • stimulated by a rising pH in the stomach and the presence of amino acids and peptiddes in the lumen of the stomach
37
Q

histamine

A
  • released from the enteroendocrine cells
  • binds to an H2 receptor
  • on the parietal cells
38
Q

cephalic response

A
  • occurs at the sight of food when our “mouth waters”

- causes the release of acid from the parietal glands

39
Q

duodenum

A
  • when the pyloric valve opens and allows chyme in it is forced into the duodenum
  • the acid in the chyme must be neutralized soon after it enters because the duodenum requires a nearly neutral pH
40
Q

secretion of bicarbonate from the pancreas

A

-plays an important role in neutralizing the acid

41
Q

s cells

A
  • in the intestinal mucosa
  • secrete the peptide hormone secretin in response to a decrease in pH in the intestinal lumen brought on by the arrival of chyme from the stomach
42
Q

secretin

A
  • binds to receptors on duct cells in the exocrine pancreas
  • these cells contain carbonic anhydrase
  • secrete bicarbonate into the lumen of the pancreatic duct and H+ into the blood (opposite of the stomach)
  • the pancreatic duct empties into the duodenum where the HCO3- helps to neutralize the acid arriving
43
Q

polypeptides and fat…

A

-signal the intestinal mucosa to secrete cholecystokinin (CCK)–peptide hormone which binds to acinar cells in the exocrine pancreas

44
Q

acinar cells in the exocrine pancreas respond to CCK how

A

by releasing two enzymes trypsinogen and chymotrypsinogen–which
-pancreatic amylase and pancreatic lipase aid in the digestion of carbs and fats in the small intestine

45
Q

CCK

A

-also signals the liver to release bile salts

46
Q

motility of the small intestine

A
  • duodenum, ileum, jejunum

- results from smooth muscle contraction

47
Q

absorbtion and the final steps in carbs and protein digestion

A

most of the absorbtion of nutrients occurs in the small intestine
the epithelial cells of the mucosa form an absorptive epithelium

48
Q

villi

A

-the folds of the mucosa
-serve to increase the absorptive area of the intestine
-the submucosa contain blood vessels and lymphatic vessels
>amino acids and simple sugars are destined to enter these blood vessels whereas lipids enter the lacteals

49
Q

microvilli (brush border)

A
  • sites of the final digestion and absorbtion of carbs and proteins
  • the villi and microvilli lead to a large absorbtive area in the small intestine
50
Q

pancreatic amylase

A
  • was released into the duodenum by the exocrine pancreas converts the polysaccharide starch to maltose
  • lactose, sucrose, maltose
51
Q

lactose

A
  • major sugar in milk

- glucose + glactose

52
Q

sucrose

A
  • refined sugar

- glucose + fructose

53
Q

maltose

A

pancreatic amylase & salivary amylase

54
Q

how is transport of monosaccharides across the epithelial cells accomplished?

A

Na+ cotransporter–1 molecule of monosaccharide and 1 molecule Na+ into the lumen of the epithelial cell and then diffuse down its concentration gradient
-they then diffuse into the capillaries in the submucosa of the microvilli and are transported to the liver

55
Q

fate of proteins in the digestive system

A
  • proteins are polymers of amino acids
  • in the stomach protein digestion begins when pepsin digests proteins to peptides it continues in the duodenum where trypsinogen and chymotrypsinogen are secreter by acinar cells
  • amino acids are transporter across the microvillar membrane by a Na+ driven cotransporter where Na+ is cotransported with the amino acid
  • they then leave the cells through the basilar membrane and enter the hepatic portal system and are destined to enter the liver
56
Q

entrokinase

A

converts trypsinogen to trypsin which then converts chymotrypsinogen to chymotrypsin

57
Q

digestion and absorption of fats

A
  • fats are mostly composed of a molecule of glycerol and three molecules of fatty acid
  • begins by the break down of fats by bile produced in the liver
58
Q

bile salts

A
  • produced in the liver
  • constructed from a molecule of cholesterol and choline and a molecule of glycine and taurine
  • act like a detergent to increase the surface area of the fat in the aqueous environment
59
Q

lipase

A
  • secreted by the exocrine pancreas
  • converts triglycerides into two molecules of fatty acid and one molecule of monoglyceride
  • move easily across the endothelial cell
  • once in the endothelial cell they are shuttled into the SER where they are reassembled into triglycerides and complexes with proteins, cholesterol, and phospholipids to improve solubility
  • then packaged into vesicles and released as chylomicrons which then go into the lacteals
60
Q

bile acids

A

-synthesized in the liver and stored in the gallbladder before being released in the duodenum
-release is under the control of CCK
>CCK causes muscle contraction in the gall bladder to empty into the duodenum
-produced by hepatocytes

61
Q

hepatic portal system

A
  • blood flowing through the vessels of the submucosa is delivered to the liver through this system
  • the capillaries in the villi empty into the venous system that delivers blood rich in amino acids and monosaccharides to the liver
62
Q

how else does the liver recieve blood

A

-hepatic artery

63
Q

sinusoids

A
  • the capillaries of the liver that carry the blood to the central vein
  • where the blood from the hepatic portal vein and the hepatic artery come together
  • lined with endothelial cells that form a barrier between the blood and the hepatocytes
  • as bile is produced it flows in the other direction of the blood
64
Q

kupffer cells

A
  • speacilized macrophages
  • located in the sinusoids
  • monitor blood from the intestine from bacteria and other pathogens
65
Q

hepatocytes

A
  • metabolically active
  • remove glucose from the blood in the sinusoids and convert it to glycogen
  • remove amino acids from the blood and make proteins like albumin
  • remove toxins and detoxify them
  • remove ammonia and convert it to urea which is then excreted into the kidneys

BMS 300 (5 decks)

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