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A&P Lecture > Digestive System > Flashcards

Digestive System Flashcards

1
Q

Functions of digestive system

A

• Ingestion: solid, liquid taken in
From mouth
- Get nutrients from environmeni via mouth
• Motility: moves material along
- Swallowing: voluntary
- Peristalsis: involuntary, alternat
STRONG waves of contraction a relaxation of smooth muscle in adjacent segments
- Mucus helps!
• Secretion:
- release of enzymes, acids, buffe
- hormones into blood by endocr

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2
Q

Regulation of digestive system: neural

A

•Sensory receptors:
- Mechanoreceptors (baroreceptors): stretch, pressure
- Chemoreceptors: chemicals of passing
contents, osmolarity, pH

• Enteric nervous system as isolated branch of
autonomic nervous system
• Sensory information results in reflexes (short or long reflexes)
- Short reflexes: local enteric NS responds, no CNS involved
- Long reflexes: sensory relaved to CNS -> ANS motor output > to effectors (salivary glands, pancreas, muscularis) > secretions and smooth muscle contractions

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3
Q

Regulation of digestive system:
hormonal

A

• Hormonal….ah many!!
- Enteroendocrine cells produce
- Many released by digestive organs
- Three main hormones:
• Gastrin: stomachs
• Secretin: small intestines
• Cholecystokinin
(CCK): small intestines

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4
Q

Mouth (Oral cavity)

A

• Functions:
- Sensory analysis: edible? temp, taste
- Mechanical digestion:
mastication (chewing)
• Teeth ^ surface area
• Tongue, palates help
• With saliva forms bolus
- Lubrication: mucus, salivary secretions
- Some (but little) digestion of carbs: salivary amylase
- Release of lingual lipase from salivary glands: but activated in stomach
- Verbal speech!

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5
Q

Mouth: Saliva

A

• 1.0-1.5 L /day, most during meals
• Made from capillary blood
- 99.4% H20
- 0.6% dissolved solute:
• Ions, buffers, Abs, mucus, enzymes

• Functions:
- Lubricates/cleanses mouth: mucus
- Moistens food, helps form food bolus
- Dissolves food chemicals -stimulates taste buds
- Starts carb digestion: contains carbohydrase salivary amylase
- Contains lingual lipase for lipid digestion BUT activated in stomach!
- Anti-bacterial, even contains (gA antibody!
• Help to prevent dental caries

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6
Q

Salivation

A

•parasympathetic NS control
•salivary nucleus (brainstem)
- Always some output-continual secretion keeps mouth moist, healthy, clean!
• Input from mouth/stomach mechano- and chemo-receptors
-^ PNS activity and gland secretion
• Tongue/lip movement
• Food ingestion
• Acidic/spicy food
• Ovar
• Spoiled food
• Food arrival in stomach
• Sight/smell of food

-Strong sympathetic activation produces
more viscous saliva with less H,O
•Dehydration causes dry mouth

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7
Q

Digestion in mouth review

A

• Mechanical: through mastication and tongue movement
- Forms soft bolus
• Chemical: some from saliva
- Salivary amylase: starts starch breakdown
- Lingual lipase released, but:
• Activated in stomach, lipid (trigs) breakdown

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8
Q

Deglutition: swallowing

A

•Starts voluntarily, finished automatically
• Mouth, pharynx, esophagus involved
• Saliva, mucus help
•Three phases:
1. Voluntary (buccal) phase
2. Pharyngeal phase
3. Esophageal phase

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9
Q
  1. Voluntary (buccal) phase:
A

•voluntary

  • Controlled by cerebral cortex, bolus formed and moved toward oropharynx
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10
Q
  1. Pharyngeal phase
A

•involuntary reflex
- Bolus arrives at oropharynx
- Contacts oropharyngeal tactile receptors - stimulates swallowing reflex
• Sensory info relayed to swallowing/dealutition center (medulla oblongata)- motor output to muscles of pharynx, esophagus
- Bolus moves toward esophagus
- Soft palate, uvula close off nasopharynx
- Larynx elevates- epiglottis closes
• Breathing temporarily inhibited

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11
Q
  1. Esophageal phase
A

•involuntary

  • Peristalsis pushes bolus down esophagus
  • Gastroesophageal sphincter (LES)
    relaxes when bolus arrives, closes after
  • Food bolus enters stomach
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12
Q

Stomach functions

A
  1. Digestion:
    -Mechanical digestion: churning
    to form chyme (partially digested food + gland secretions)
    - Chemical digestion
    • Starch digestion continues for short time -salivary amylase inactivated soon after arrives
    • Lipid digestion starts (lingual and gastric lipase)
    • Protein digestion starts
  2. Secretion: mucus, HI acid, intrinsic factor, pepsinogen, hormones
    • Propulsion: movement of chyme to
    small intestines
    • Storage of ingested food: rugae
    Anus
    - 2-4 hours, fatty foods stay longer
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13
Q

5 secretory cells of stomach

A

• Surface mucus (goblet) cells: tight junctions connect, form simple columnar epithelium:
- Form “secretory sheet” alkaline mucus layer
• Protection from acid and gastric enzymes serous.
- Continual replacement
• Mucous neck cells in gastric pit: produce acidic mucus
•Cells in gastric glands:
- Parietal cells
- Chief cells
G cells (enteroendocrine cells)

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14
Q

Gastric gland cells

A

Parietal cells (exocrine)
- Secrete intrinsic factor
• Essential function of stomach!
• Needed for intestinal vitamin B12 absorption: required for maturation of RBCs

  • Secrete HCI (stomach pH 1.5-2.0 )
    • Secrete H*, CH (separately so cell not damaged!) while HCO;
    enters blood: alkaline tide
    • Kills microorganisms
    • Denatures proteins, food enzymes
    • Activation of pepsinogen into active pepsin (protein digestion)
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15
Q

Chief cells

A
  • Most numerous cells
  • Release gastric lipase
  • Secrete inactive pepsinogen
    • Converted to pepsin by HC (and pepsin already active)
  • Protein digesting enzyme
    • Pepsin works best in strong Gastric gland acidic conditions (pH 1.5-2.0
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16
Q

G cells

A
  • Enteroendocrine cells in pylorus gastric glands
  • Secrete gastrin hormone into bloodstream
    • Stimulates parietal and chief cell secretion
    • Stimulates stomach motility
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17
Q

Gastric (peptic) ulcers

A

•Usually balance present between acid production and stomach protection
• Peptic ulcers (gastric or duodenal): erosion of wall by acid/enzymes
- Decreased mucus production/high acid production may cause gastritis (irritation of gastric mucosa) and eventual gastric ulcer
•Helicobacter pylori likely major factor in most (love acidic environments)
• Break down mucus, burrow through and destroy mucosal layer;
leukocyte response to H. pylori also damages mucosa

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18
Q

Motility in the stomach

A

• Two functions of smooth muscle:
- Mix bolus with gastric juice to form chyme: gastric mixing/churning
- Empty chyme from stomach, through pyloric sphincter, to sm.
Intestines: gastric emptying

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19
Q

Control of gastric secretion

A

• Neural (parasympathetic and local
Enteric NS)) and hormonal mechanisms control gastric secretions
- Hormonal control of gastric secretion: gastrin
• Stimuli from 3 different areas (head, stomach, sm. intestines)
- Effector: stomach
• increase or decrease gastric secretion
• increase or decrease smooth muscle motility
• 3 overlapping phases
1. Cephalic phase: head
2. Gastric phase: stomach
3. Intestinal phase: sm. intestines

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20
Q
  1. Cephalic phase
A

• Begins BEFORE food enters stomach!: see, smell, taste or think of food
• Parasympathetic NS reflex
• Prepares stomach via vagus nerve
(Stimulates saliva secretion)
- Stimulates ^ in gastric juice production (esp. H* ions)
- ^ stomach contractions (growl)

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21
Q
  1. Gastric phase
A

• Provides ~2/3 gastric juice secretion and ^ mixing/motility
• Stimulation of sensory receptors: food/peptide arrival in stomach, ^ pH
• Neural: PNS (and local)
- Gastric reflex:
Stimulation of baro- and chemoreceptors (due to food, protein and ^ pH)
• Hormonal: GASTRIN from G célls
- Food (esp. protein peptides) stimulate G cells -> gastrin released
- Gastrin causes ^ HCI from parietal, ^ pepsinogen from chief cells, ^ stomach contractions, contraction of pyloric sphincter- slows emptying
-As proteins digested: becomes more acidic- inhibits G cell

22
Q
  1. Intestinal phase
A

• Stimulation: acidic chyme with lipids, Neural Rosponses proteins enter small intestines
• Opposes cephalic and gastric events
Enterogastric Myenteric
plexus
• Goal: protects intestines from chyme
via bloodstream
overload
- Allows time for secretion,
Duodenal stretch and
chemoreceptors
digestion and absorption
- Also affects pancreas, liver and gallbladder activity

4 7 Presence of
GIP
lipids and
carbohydrates
-Secretin) +- Decreased pH
• Neural: enterogastric reflex
- Duodenal stretch receptors and chemoreceptors
- decreases PNS: decreases gastric secretion and motility
- Protect sm. intestines from overload with contraction of pyloric sphincter

• Hormonal: CCK, secretin from sm. intestines
- Inhibit gastrin release, decrease gastric secretion and motility, ^ bile, pancreas

23
Q

Stomach in review

A

•Gastric mixing and gastric emptying
• Digestion
- Proteins by pepsin starts (HCI activates pepsin, denatures proteins)
- Carbs continues for short time due to salivary amylase
- Some lipid due to lingual lipase (and gastric lipase)
• Carbs spend the least time and lipids spend the most time in the stomach
Absorption???: very little!! Why not?
- Mucus coating
- Lack of transport
- Digestion not complete
But some drugs and alcohol absorbed

24
Q

Small intestines

A

• In intestinal crypts/glands:
- Enteroendocrine cells:
• Duodenal hormones:
CCK and secretin
-Paneth cells: enzyme Mucosa defense against bacteria
• As move along sm.
Intestines: fewer crypts, more goblet cells.

25
Q

Small intestines

A

• Submucosa
- Duodenal glands in duodenum
• Secretes alkaline capillaries mucus to protect from acidic chyme lymphoid tissue (duodenal ulcers?) and neutralize
chyme

  • MALT: Peyer’s patches
    motility
    • Increase in number toward end of sm. intestines
    • Protects blood from bacteria in sm./|g intestines
    • Muscularis: digestion and absorption
  • Segmentation: mix chyme with intestinal juice and ^ contact with brush border enzymes
  • Peristalsis: moves forward towards |g. intestines
  • Gastroileal reflex: stomach distention causes movement in sm. intestin
26
Q

Pancreas

A

. Functions
- Endocrine: pancreatic islets (Islets of
Langerhans)
• Secrete insulin (B) and glucagon (a)
• Regulate blood glucose

  • 99% Exocrine: acini w/acinar cells
    • Secrete pancreatic juice: controlled
    by duodenal hormones CCK and
    secretin and PNS
    •Break down all foodstuffs!

•Pancreatic juice contents:
- Buffers
• Buffers chyme and stops pepsin.’
• ^ pH for pancreatic and intestinal
enzyme activity
- Enzymes: for starch, fat, protein,
nucleic acid digestion

27
Q

More on pancreas

A

• Enzvmes in pancreatic juice: digest all categories of food!
- Starch digestion:
• Pancreatic amylase
- Fat digestion:
• Pancreatic lipase
- Nucleic-acid digestion:
• Nucleases: ribonucleases, deoxyribonucleases

  • Protein digestion: target of 70% of pancreatic enzymes -released as proenzymes activated in duodenum by enteropeptidase: NOTE FIGURE!
    • Trypsinogen -› Trypsin -*
    • Chymotrypsinogen -> Chymotrypsin.
    • Procarboxypepsidase->
    Carboxypeptidase
28
Q

Liver

A

Hepatocytes:
- “Chemical factories “ by sinusoid capillaries
- Produce bile:
• Function: “aids” in lipid digestion, waste excretion
• Alkaline solution (water,
bile salts, cholesterol, Portal vein
Ca?+, bile pigments (e) (bilirubin) - Jaundice?

  • Bile salts: amphipathic
    • Fat emulsification: breaks lipid droplets up into smaller lipid droplets
    • Allows pancreatic lipase to ^ digestion of small lipid droplets to micelles, ^ absorption in sm. intestine
29
Q

Other digestive functions of the liver

A

• Processes nutrients absorbed from diet!
Branena
• Other digestive-“related” functions:
- Carbohydrates
• Keeps blood glucose normal
• Excess glucose stored as glycogen (glycogenesis)
- Proteins
• Amino acids used to make plasma proteins (clotting factors, albumin)
• Gluconeogenesis, lipogenesis
- Lipids
52
•Hepatocytes store some trigs
• Make lipoproteins, cholesterol

30
Q

Non-digestive functions of the liver

A

-Phagocytosis of old and worn-out cells (RBCs!), bacteria:
Kupffer cells (macrophages)
-Makes plasma proteins
-Detoxification, modification for excretion
• Alcohol
• Modify drugs (ie.
antibiotics), ammonia
• Excretion of substances in bile (bilirubin)
- Storage: vitamins (ADEK), minerals (iron)

31
Q

Gallbladder

A

-• Stores and concentrates bile from
liver released into cystic duct when stimulated by CCK
-bile 10x more concentrated here

32
Q

Concentration of bile in gallbladder

A

• Concentration of bile
- Concentrates through H,O reabsorption
Gallstones:
• Too concentrated, form insoluble
cholesterol, Ca2+ salts
• Small stones pass, but large may
block ducts!

33
Q

Small intestines digestion

A

• Remember: carbs and proteins partly digested in stomach, little lipids
• Most of digestion in sm.
Intestines- result of CCK and secretin effects on accessory glands
• Liver makes bile faster
•Gallbladder contracts
and releases bile
• Pancreatic juice secreted
• Sphincter of Ampulla of
vater relaxes- bile and pancreatic juice enter duodenum

34
Q

Small intestines: chemical digestion

A

•carbs
- Pancreatic amylase
-Brush border enzymes (BBE)
• Sucrase, maltase, lactase
• Lactose intolerance

• Proteins:
- Pancreatic enzymes activated by brush border enteropeptidase
- BBE: Peptidases

• Lipids:
- Emulsification by bile
- Pancreatic lipase digest: most lipid digestion

• Nucleic acids
- Pancreatic nucleases: ribonucleases and deoxyribonucleases
-BBE: phosphatases, nucleosidases

35
Q

Circular folds:

A
  • Slows chyme movement and ^ absorption of nutrients
36
Q

Villi

A

-increased surface area
-many absorptive cells

37
Q

Microvilli

A

-absorptive cell microvilli increased surface area
- Brush border with brush border enzymes
- Absorb nutrients into capillaries and lacteals

38
Q

Small intestines: lipid absorption?

A

• Broken down triglycerides leave micelles enter sm. intestine epithelial cells
• Chylomicrons (a lipoprotein) formed in intestinal epithelial cell
• Large chylomicrons released from cells -> picked up by LACTEAL - thoracic duct - left subclavian vein -> body (liver and other tissues)

39
Q

Small intestines: H,0 absorption

A

• Most absorption takes place in small intestines
• Water? - follows by osmosis

40
Q

Large intestines

A

•Chyme enters cecum through ileocecal valve… relaxation of valve caused by:
- Gastroileal reflex: neural refle
- stomach activity increases motility in ileum
- Stomach hormone gastrin:
endocrine, increases ileum motility and causes relaxation of ileocecal valve
• Functions of Ig. intestines
- Absorb more H,O
- Vitamin production (B, K)
- Feces formation, storage, elimination
- NOT digestion!!

41
Q

Large intestines digestive structures

A

• No villi, no circular folds
• Mucosa: simple epithelium
-Absorptive cells: mainly water
- Lots of mucus-producing goblet cells

•Muscularis:
- Teniae coli: smooth muscle bands constant tension forms haustra
• Overall absorption: H20 and bile salts

42
Q

Large intestines motility

A

•Haustral churning: sluggish contractions
- Presence of chyme stretches haustra
- Moves into next haustra
- Helps H20 absorption

• Peristalsis: Regular and mass, powerful 3-4x/day
- Gastrocolic reflex:
• Stomach distention causes reflex: mass mvmt of feces into end of colon/rectum
- Defecation reflex: filling of rectum ^ urge to defecate….POOP!! ©
- Bulk (fiber) increases strength of contraction

43
Q

Microbiota!

A

• Enteric bacteria: coexist with humans in mutually beneficial relationship (normal flora)
• 10X more in large intestines than cells
in human body!
Benefits?:
- Make vitamin K (blood clotting) and B -, absorbed
- Deter growth of harmful bacteria
- Stimulate the immune system when young: tolerance to normal flora
- Break down remaining proteins, carbs, lipids…some absorption……Flatulence?
•Fecal transplants

44
Q

Large intestines

A

• Chemical composition of feces:
semi-solid or solid
- A little water, mucus
- Epithelial cells that sloughed off along tract
- Bilirubin breakdown products:
color …remember stercobilin?!
- Bacteria
- Bacterial breakdown gases:
odor
- Indigestible food parts: FIBER
• Diarrhea (^ motility) and constipation (decreased motility)

45
Q

Defecation reflex

A

• Stretch of rectum stimulates baroreceptors
• Parasympathetic reflex -> contraction of rectal walls, relaxation of internal anal sphincter
- Involuntary but raises conscious awareness
• Voluntary relaxation of ext. anal sphincter, push -> defecation

46
Q

Carb digestion/ absorption

A

•Salivary amylase- partially digests,
inactivated 1-2 hrs by stomach acids
•Pancreatic amylase
- Digests carbs in duodenum -> oligo-,
disaccharides
• Brush border enzymes (maltase, sucrase, lactase): oligos, disacc. -> monosaccs.
• Monosaccs. enter villi capillaries and go to liver via hepatic portal vein

47
Q

Protein digestion

A

• Complex, time-consuming
• Stomach containing HCI:
- Denatures protein- unfolds and
loses structure
- Peptide bonds exposed to
enzymes
- Proper pH for pepsin-breaks peptide bonds in proteins -›
polypeptides

48
Q

Protein digestion in small intestines

A
  • Enteropeptidase activates:
  • Pancreatic proteases (Trypsin Chymotrypsin, Carboxypeptidase)-
    polypeptides-> peptides
    -Brush border enzymes (peptidases) - peptides into amino acids
    • Amino acids absorbed
    -> enter villi capillary blood
    -> liver via hepatic portal
    vein
49
Q

Lipid digestion

A

•Triglycerides: most abundant lipids
• Lipase action:
- Lingual and gastric lipase-stomach
- Pancreatic lipase: in small intestines- most lipid digestion into
monoglycerides and fatty acids

• Bile salts: amphipathic, act in small intestines
- Emulsify lipids, better access and chemical digestion by pancreatic lipase
Forms micelles with monoglycerides and fatty acids

50
Q

Lipid absorption

A

• Micelles contact intestinal cells
• Fatty acids + monoglycerides (with fat soluble vitamins) diffuse into cells, recombine
- Trigs (lipids) wrapped in
protein in cell = chylomicrons
Chylomicrons (large) exocytosed
- Enter lacteals
- Move through lymphatics through thoracic duct into left subclavian vein
- In circulation: chylomicrons go to body liver and other tissues)

51
Q

Water absorption

A

• Water not actively absorbed or secreted
• All movement of water across lining of digestive tract: passive osmosis!
• Most absorbed in intestine, small
amount excreted in feces

A&P Lecture (9 decks)

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