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Temple A&P > Lecture: Digestive System > Flashcards

Lecture: Digestive System Flashcards

1
Q

What are the 4 functions of the digestive system?

A

1) ingestion
2) digestion
- mechanical & chemical breakdown
3) abosrtion
- uptake of nutrients
4) defecation
- elimination

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2
Q

What is another name for the digestive tract?

A

alimentary canal, spans from mouth to anus

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3
Q

What 6 accessory organs of the digestive system?

A

1) teeth
2) tongue
3) salivary glands
4) gallbladder
5) liver
6) pancreas

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4
Q

Describe the 4 layers of the alimentary canal.

A

(from inner to outer)

1) mucosa
2) submucosa
- blood & lymph vessels
3) muscularis externa; 2 layers:
- inner circular layer
- outer longitudinal layer
4) serosa
- adventitia: fibrous CT

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5
Q

Define: enteric nervous system. Comment on form and function.

A

nervous network of the esophagus, stomach, and intestines;
regulates digestive tract motility, secretion, and blood flow;
2 networks of neurons:
1) submucosal plexus controls secretory activity
2) myenteric plexus is located in the muscularis externa and controls GI tract motility

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6
Q

Define: peritoneum.

A

serous membrane lining the wall of the abdominal cavity;

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7
Q

Define: mesenteries. Comment on form and function.

A

double layer, including a dorsal and ventral layer;
ventral layer contains greater omentum and lesser omentum;
functions:
-provides routes for nerves, lymphatics, and blood vessels
-holds organs
-stores fat

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8
Q

Explain short (myenteric) reflexes.

A

intrinsic;
stretching or chemical stimulation of the digestive tract acts through the myenteric plexus to stimulate contractions in nearby regions of the muscularis externa

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9
Q

Explain long (vagovagal) reflexes.

A

extrinsic;
controlled by ANS;
parasympathetic fibers of the vagus nerve stimulate digestive motility and secretion

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10
Q

What is another name for the oral cavity? What are the 4 structures and 4 functions of the oral cavity?

A

buccal cavity;

structures: cheeks/lips, tongue, palate, teeth
functions: ingestion, mastication, chemical digestion, swallowing

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11
Q

Saliva is 97-99.5% water and contains what 6 solutes?

A

1) salivary amylase
2) lingual lipase
3) mucus
4) lysozome
5) immunoglobin A
6) electrolytes

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12
Q

Explain the 2 different types of salivary glands and all examples of each type.

A

1) intrinsic (dispersed amid other oral tissues): constant secretion of lysozome-containing saliva
- lingual
- labial
- buccal
2) extrinsic (outside of oral mucosa)
- parotid
- submandibular
- sublingual

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13
Q

Explain how the extrinsic salivary glands work.

A

food stimulates oral taste, tactile, and pressure receptors, which transmit signals to a group of salivatory nuclei in the medulla and pons;
even odor, sight, and thought of food stimulates salivation;
parasympathetic fibers stimulate saliva production, sympathetic fibers inhibit saliva production

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14
Q

Describe the composition of the pharynx.

A

deep skeletal muscle layer;
superficial smooth muscle layer
-contains pharyngeal constrictors, which force food downward during swallowing

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15
Q

Define: upper esophageal sphincter.

A

when food is not being swallowed, inferior constrictor of the pharynx remains continuously contracted;
considered a physiological sphincter rather than an anatomical one because it disappears at time of death

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16
Q

Describe the esophagus.

A

long muscular tube from pharynx to stomach;
contains all GI tract layers;
submucosa contains esophageal glands which secrete mucus for lubrication;
cardiac orifice = opening to stomach;
cardiac sphincter (a.k.a. lower esophageal sphincter) = constriction before cardiac orifice

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17
Q

What is another name for swallowing?

A

deglutition

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18
Q

What is swallowing coordinated by? What are the 2 phases of swallowing?

A

swallowing center in the medulla and pons;

1) buccal phase
2) pharyngeal-esophageal phase
- esophageal phase includes peristalsis

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19
Q

What are the 3 functions of the stomach?

A

1) mechanical digestion
2) liquefies food
- chyme
3) chemical digestion

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20
Q

Define: chyme.

A

soupy or pasty mixture of semidigested food

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21
Q

Describe the micro-anatomy of the stomach.

A

similar to rest of alimentary canal, except:
muscularis externa has 3 layers;
muscosa is pocked with depressions called gastric pits;
2-3 tubular glands open into the bottom of each gastric pit
-tubular glands named by location: cardiac, gastric, and pyloric

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22
Q

Define: gastric mucosal barrier.

A

property of the stomach that allows it to contain acid

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23
Q

What are the 3 factors that enable the gastric mucosal barrier?

A

1) mucous coat
- bicarbonate-rich mucus resists action of acid and enzymes
2) epithelial cell replacement
- occurs every 3-6 days
3) tight junctions
- prevent gastric juice from “leaking”

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24
Q

Describe the 5 cell types found in gastric pits.

A

1) mucous cells
-secrete mucus
2) regenerative cells
3) parietal cells
-secrete HCl and intrinsic factor (IF enables absorption of Vitamin B12)
4) chief cells
-secrete pepsinogen
5) enteroendocrine cells
secrete hormones

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25
Q

How is gastric HCl formed?

A

bicarbonate reactions catalyzed by carbonic anhydrase

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26
Q

What are the 4 functions of gastric HCl?

A

1) activates enzymes
2) liquefies food
3) converts iron
4) nonspecific resistance

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27
Q

Define: alkaline tide.

A

high blood pH during digestion;
HCl accumulates in stomach while bicarbonate ions accumulate in blood;
b/c of bicarbonate, blood leaving stomach has higher pH when digestion is occurring than when the stomach is empty

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28
Q

Explain what pepsinogen is and how it works.

A

pepsinogen = type of zymogen;
HCl removes some of pepsinogens amino acids, converting it to pepsin;
pepsin digests protein

29
Q

Define: zymogen.

A

inactive protein which can be converted to an active enzyme by the removal of some of its amino acids

30
Q

Name some “other” gastric secretions.

A 
digestive enzymes
-gastric lipase
-chymosin
chemical messengers
-hormones, including paracrine secretions
-gut-brain peptides
31
Q

Name 6 examples of gut-brain peptides.

A

1) VIP
2) GIP
3) NPY
4) secretin
5) CCK
6) Substance P

32
Q

Explain gastric motility in response to the ingestion of food.

A

swallowing center of medulla signals stomach to react with a receptive-relaxation response;
peristaltic contractions are governed by pacemaker cells in the longitudinal layer;
the pyloric sphincter controls flow of chyme into small intestine

33
Q

Define: receptive-relaxation response.

A

stomach’s response to incoming food in which it briefly resists stretching but then relaxes to accomodate the arriving food

34
Q

Define: vomiting.

A 
forceful ejection of stomach and intestinal contents;
controlled by emetic center in medulla;
caused by:
-overstretching
-chemical irritants
-trauma or pain
-psychological stimuli
physiology
-vomiting is usually preceded by nausea and retching
35
Q

Define: retching.

A

thoracic expansion and abdominal contraction create a pressure difference that dilates the esophagus;
when combined with reverse peristalsis, becomes vomiting

36
Q

What regulates gastric function? What are the 3 stages of gastric activity?

A

nervous system and endocrine system collaboration;

1) cephalic: controlled by brain
2) gastric: controlled by stomach
3) intestinal: controlled by small intestine

37
Q

Explain the cephalic phase of gastric activity.

A

hypothalamus responds to sight, smell, taste, and thought of food;
in a parasympathetic response, vagus nerve fibers of the medulla stimulate increased gastric activity

38
Q

Explain the gastric phase of gastric activity.

A

bolus enters stomach:
-stomach distention triggers short & long reflexes;
-raised pH triggers stomach buffering;
acetylcholine (ACh), histamine, and gastrin trigger release of HCl, intrinsic factor (IF), and pepsinogen

39
Q

Explain the feedback control mechanism present in the gastric phase of gastric activity.

A

as dietary protein is digested, it breaks down into small peptides and amino acids, which directly stimulate the G cells to secrete more gastrin (positive feedback loop that accelerates digestion);
small peptides buffer stomach acid;
as digestion continues, pH drops lower and lower;
with a pH <2, stomach acid inhibits the parietal cells and G cells (negative feedback loop that slows digestion)

40
Q

Explain the intestinal phase of gastric activity.

A

chyme enters duodenum;
stomach is stimulated by:
-stretching of the duodenum which accentuates vagovagal reflexes
-intestinal gastrin released in response to incoming chyme;
gastric secretion and motility is inhibited by:
-enterogastric reflex;
-enteroendocrine (EE) cells’ release of secretin, CCK, and GIP

41
Q

What does the enterogastric reflex do?

A

shuts off release of gastrin from G-cells of the stomach, inhibiting gastric motility and the secretion of gastric acid

42
Q

Describe the structure and function of the liver.

A 
largest gland (3 lbs);
4 lobes;
digestive function: bile secretion;
porta hepatis, which provides a point of entry for:
-hepatic portal vein
-hepatic artery
-hepatic duct
43
Q

Define: porta hepatis.

A

on the posterior liver, point of entry for the hepatic portal vein and proper hepatic artery and a point of exit for the bile passages

44
Q

Describe the microscopic anatomy of the liver.

A

interior of liver filled w/ tiny cylinders called hepatic lobules; a lobule contains:
a central vein surrounded by hepatocytes, which synthesize bile salts from cholesterol;
spaces between plates of hepatocytes called hepatic sinusoids;
bile secreted into narrow channels called the bile canaliculi
hepatic triad = distinctive structure consisting of an artery, vein, and bile ductule

45
Q

Describe the structure and function of the gallbladder.

A

function: concentrates and stores bile;
neck leads into cystic duct, which converges with the hepatic duct to form the bile duct, which terminates in the duodenum;
enterohepatic circulation enables bile to be reabsorbed from the small intestine to the liver

46
Q

Define: enterohepatic circulation.

A

route of secretion (by hepatocytes of liver), reabsorption (in the ileum), and resecretion (by hepatocytes of liver) of bile;
~80% of bile acids are reabsorbed into the ileum

47
Q

Define: bile.

A

green fluid containing minerals, cholesterol, phospholipids, fats, and bile pigments;
principal pigment = bilirubin, derived from the decomposition of hemoglobin

48
Q

Describe the composition and function of the pancreas.

A

exocrine gland;
secretory acinar cells have a high density of secretory vesicles called zymogen granules;
acini secrete enzymes and zymogens;
pancreatic ducts secrete sodium bicarbonate;
pancreatic juice = alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes

49
Q

Explain the 2 methods of bile and pancreatic juice regulation.

A

1) neural
parasympathetic (vagal) stimulation;
sympathetic inhibition
2) hormonal
cholecystokinin (CCK) & gastrin stimulate gall bladder contraction and pancreatic secretion;
secretin stimulates hepatic and pancreatic bicarbonate secretion

50
Q

What is the role of the small intestine? Describe its 3 major sections.

A

chemical digestion and nutrient absortion;

1) duodenum (1st 10”)
2) jejunum (next 8’)
3) ileum (final 12’)

51
Q

Describe the microscopic anatomy of the small intestine.

A

circular folds made up of mucosa and submucosa force chyme to spiral through;
villi in the intestine are tiny projections in the SI made up of 2 kinds of epithelial cells:
1) enterocytes (absorptive cells)
-microvilli form a fuzzy brush border on the surface of each enterocyte, increasing surface area; they also contain brush border enzymes in the plasma membrane;
2) goblet cells;
core of each villus contains a lymphatic capillary called a lacteal;
between the bases of the villi are porous intestinal crypts, which house dividing stem cells;
clusters of Paneth cells are clustered at the base of each crypt- they secrete defensive proteins that resist bacterial invasion of the mucosa;
duodenal glands (in the duodenum) secrete bicarbonate-rich mucus

52
Q

What 3 functions do contractions of the small intestine serve?

A

1) mix chyme with intestinal juice, bile, and pancreatic juice
2) bring chyme into contact with the mucosa for contact digestion and nutrient absorption
3) move residue towards large intestine

53
Q

Define: segmentation.

A

movement in which stationary ringlike constrictions appear at several places along the intestine and then relax as new constrictions form elsewhere;
effect: mixing and contact digestion

54
Q

Define: migrating motor complex.

A

successive, overlapping waves of peristaltic contraction; each wave travels partway down the intestine and milks the contents towards the colon

55
Q

Explain the process of carbohydrate digestion.

A

complex CHOs to sugars;
in mouth, salivary amylase hydrolyzes starch to oligosacchrides;
in stomach, the food is churned and mixed, and salivary amylase is exposed to lower pH which inactivates it;
in small intestine, pancreatic amylase breaks down oligosacs to smaller oligosacs and disacs;
brush border enzymes dextrinase and glucoamylase breaks down smaller oligosacs to disacs;
brush border enzymes maltase, sucrase, and lactase break down disacs to monosacs

56
Q

Explain the process of carbohydrate absorption.

A

glucose & galactose both transported into enterocytes (absorptive cells) via the Sodium-Glucose Linked Transporter (SGLT), a secondary active transport mechanism coupled to sodium;
fructose is transported via facilitated diffusion and converted to glucose inside the enterocyte;
all are transported to the liver

57
Q

Explain the process of protein digestion.

A

in stomach, pepsin hydrolyzes any peptide bond between tyrosine and phenylalanine, leaving behind shorter polypeptides and free amino acids;
in small intestine:
-the pancreatic enzymes trypsin and chymotrypsin break polypeptides down into smaller oligopeptides;
-3 brush border enzymes break down these oligopeps one AA at a time:
1) carboxypeptidase
2) aminopeptidase
3) dipeptidase

58
Q

Explain the process of protein (amino acid) absorption.

A

similar to monsaccharides;
different sodium-dependent AA cotransporters;
dipeptides and tripeptides are absorbed and then hydrolyzed to AAs within the cytoplasm of enterocytes;
AAs leave cell via facilitated diffusion and enter the blood capillaries of the villus

59
Q

Explain the process of lipid digestion.

A

duodenum receives small emulsification droplets from the stomach, which it promptly coats with lecithin and bile salts;
pancreatic lipase converts triglyceride into 2 free fatty acids (FFAs) and a monoglyceride;
micelles, coatings of bile acids, form to facilitate the transportation of the lipids to enterocytes

60
Q

Explain the process of lipid absorption.

A

Micelles pass through microvilli of the brush border, where the lipids leave the micelles and diffuse into the enterocytes;
lipids are transported to the Golgi complex, where chylomicrons, lipoproteins particles, are formed;
chylomicrons are too large to enter capillaries, so they move into lacteals and are taken up by lymph vessels;
some free fatty acids (FFAs) enter capillary blood;
chylomicrons are hydrolyzed to FFAs and glycerol by lipoprotein lipase;
these products are taken to the liver, where lipoproteins are made

61
Q

Explain the process of nucleic acid digestion.

A

pancreatic nucleases break nucleotides apart;
brush border enzymes nucleosidase and phosphatase further break down nucleotides into pentose sugars (ribose & deoxyribose), nitrogenous bases, and phosphate ions

62
Q

Explain the process of nucleic acid absortion.

A

pentose sugars (ribose & deoxyribose), nitrogenous bases, and phosphate ions are transported across the intestinal epithelium by active transport mechanisms and enter the capillary blood of the villus

63
Q

Explain the process of vitamin absorption.

A

fat soluble vitamins (A,D,E, & K) are absorbed with other lipids;
water soluble vitamins (B & C) are absorbed via simple diffusion;
vitamin B12 is absorbed bound to intrinsic factor (IF) from the stomach: vitamin B12-intrinsic factor complex binds to specific mucosal receptor sites on enterocytes in the ileum and is absorbed by endocytosis

64
Q

Explain the process of mineral absorption.

A

actively absorbed along length of small intestine;
Na+ ions are contransported with sugars and AAs;
Cl- ions are actively transported in the ileum by a pump that exchanges them for bicarbonate ions;
K+ ions are absorbed by simple diffusion;
iron and calcium are absorbed based on the body’s needs (other minerals absorbed at fairly constant rates)

65
Q

Explain the process of water absorption.

A

GI tract receives about 9L of water per day;
most of this water consists of GI secretions;
~8L absorbed by SI, and ~0.8L absorbed by LI;
moves across intestinal mucosa via osmosis, following the concentration gradient established by active transport of solutes;
water uptake is coupled to solute uptake (solute uptake affects rate of water absorption)

66
Q

Describe the anatomy of the large intestine.

A

colon: part of LI between the ileocecal junction and rectum;
rectum: distal portion of LI in pelvic cavity;
taenia coli: 3 strips of smooth muscle in the colon whose muscle tone contracts the colon lengthwise and causes its walls to bulge, forming pouches called haustra;
bacterial flora produce intestinal gas

67
Q

Explain the mechanisms of motility within the large intestine.

A

haustral contractions: segmentation that occurs every ~30 min; distension of a haustrum with feces causes it to contract;
mass movements: stronger, occur 1-3 times a day, last ~15 min; triggered by filling of stomach and duodenum

68
Q

Explain the process of defecation.

A

anus contains an internal and external anal sphincter;
stretching of rectum stimulates defecation reflexes:
1) intrinsic reflex:
stimulated by myenteric nerve plexus;
causes peristalsis that drives feces downward;
2) parasympathetic reflex:
spinal reflex;
intensifies peristalsis;

external anal sphincter under voluntary control: you can poop when you want!

Temple A&P (15 decks)

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