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Organ System Anatomy, Physiology and Pathology - BPT06 > Digestive System Physiology > Flashcards

Digestive System Physiology Flashcards

1
Q

Which are the six essential activities of the disassembly line?

A
  • Ingestion
  • Propulsion
  • Mechanical digestion
  • Chemical digestion (Ph)
  • Absorption (Energy, enzymes)
  • Defecation
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2
Q

Propulsion

A

Moves food from the first organ to the last.
Swallowing (voluntary): oropharynx
Peristalsis (involuntary): esophagus, stomach, small and large intestine
Squeeze food along the tract, but some mixing occurs as well.

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3
Q

Mechanical Digestion

A

Prepares food for chemical digestion by enzymes.

  • Chewing (mouth, saliva helps by moistening)
  • Churning (stomach, turns food into something acidic, low ph)
  • Segmentation (small intestine, completely mixes)
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4
Q

Chemical Digestion

A

Series of catabolic steps (need nutrients to be absorbed).

Catabolic reaction → Anabolic reaction

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5
Q

Absorption

A

Passage of digested end products (+ vitamins, minerals and water).
Small intestine is the major absorptive site. Make sure we have the right nutrients for our body will work.

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6
Q

Defecation

A

Elimination of indigestible substances.

Voluntary.

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7
Q

How is digestive activity stimulated and controlled?

A

Provoked by a range of mechanical and chemical stimuli. Mechanoreceptors and chemoreceptors.
Stretching of the organs by food in the lumen.
Initiation of reflexes - activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood.
Stimulate smooth muscle of the GI tract walls to mix lumen contents and move them along the tract.

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8
Q

Intrinsic Control of the Digestive System

A

Two kinds of reflex activity occur:

  • Short reflexes
  • Long reflexes
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9
Q

Short Reflexes

A

Mediated by the local enteric nerve in response to Internal stimuli (GI tract, stretching of the wall) → change in contractile or secretory activity.

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10
Q

Long Reflexes

A

Initiated by stimuli arising inside or outside (extrinsic) the GI tract and involve CNS centers and extrinsic autonimic nerves (we need to know if we are hungry or not).

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11
Q

The Mouth

A 
Only part involved in ingestion.
Most digestive functions associated with the mouth reflect the activity of the related accessory organs:
- Teeth
- Salivary glands
- Tongue
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12
Q

The Tongue

A

Skeletal muscle fiber.
Grips food and constantly repositions it between the teeth during chewing → Bolus (food and saliva ball that forms in the mouth during chewing)
Initiates swallowing by pushing the bolus posteriorly into the oral pharynx.

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13
Q

Salivary Glands

A

Extrinsic salivary glands: outside oral cavity
Intrinsic salivary glands: buccal glands
- Cleanses the mouth
- Dissolves food chemicals so they can be tasted
- Moistens food and aids in compacting it into bolus
- Contains enzymes that begin the chemical breakdown of starchy foods (digestion of starch starts with saliva).

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14
Q

Extrinsic Salivary Glands

A
  • Parotid gland: anterior to ear between masseter muscle and skin.
  • Submandibular gland: lies along medial aspect of the mandibular body.
  • Sublingual gland: anterior to the submandibular gland under the tongue.
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15
Q

Composition of Saliva

A

Hypoosmotic - 97-99.5% water
pH 6.75 - 7.00
Electrolytes
Digestive enzymes: salivary amylase and lingual lipase (for starch digestion)
Proteins: mucin, lysozyme and immunoglobin A
Metabolic wastes (urea and uric acid)

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16
Q

Control of Salvation

A

Intrinsic glands keep the mouth moist
Extrinsic glands are activated when food enters mouth.
Controlled by parasympathetic division
- Signals to salivatory nuclei in brain stem

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17
Q

Teeth

A

Lie in sockets (alveoli) in the gum-covered margins of the mandible and maxilla.

  • Masticate, or chew
  • Tear and grind food
  • Breaking it down into smaller fragments
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18
Q

The Pharynx

A
  • Oropharynx
  • Laryngopharynx
    Passageways for food, fluids and air.
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19
Q

Esophagus

A

Muscular tube, 25cm long.

Collapsed when not involved in food propulsion.

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20
Q

Digestive Process: Mouth

A

Ingests.
Begins mechanical digestion by chewing.
initiated propulsion by swallowing.
Starts chemical breakdown of polysaccharides.
Salivary amylase: starch and glycogen.
Lingual lipase: fat-digesting, acts in acidic environment in stomach.

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21
Q

Digestive Process: Pharynx and Esophagus

A

Pass food from the mouth to the stomach.

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22
Q

Swallowing

A

Two major phases:

  • Buccal (voluntary)
  • Pharyngeal - esophageal (non-voluntary)
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23
Q

Buccal Phase of Swallowing

A

Voluntary
Tip of the tongue goes against the hard palate to force bolus into the oropharynx. Activating tactile receptors, inducing swallowing - involuntary reflex activity.

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24
Q

Pharyngeal - Esophageal Phase of Swallowing

A

Swallowing center in brain stem (medulla and lower pons) Activates motor impulses via vagal nerve, to muscles of pharynx and esophagus.
Respiration is momentarily inhibited.
Constrictor muscles contract, forcing food into esophagus, upper sphincter closes. Peristalsis moves food through esophagus to the stomach. Gastroesophageal sphincter opens.

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25
Q

How is the respiration inhibited while swallowing?

A

Tongue blocks off the mouth.
Soft palate rises to close nasopharynx.
Larynx rises so that epiglottis covers its opening into respiratory passageway.

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26
Q

Digestive Process: Stomach

A

All digestive activities except ingestion and defecation.
Further degrades food chemically and physically.
Protein digestion: HCI (chloric acid) production
Pepsin: protein digesting enzymes (rennin in infants, can’t digest protein)
Triglyceride digestion by lingual lipase.
Alcohol and aspirin (lipid-soluble) to the blood.

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27
Q

What is the essential function of the stomach during digestion?

A

Secretion of intrinsic factor required for intestinal absorption of vitamin B12, needed to produce mature erythrocytes in blood cells. Necessary for blood circulation. Rest of vitamins digested in small intestine.

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28
Q

Regulation of Gastric Secretion - Neural/hormonal + sites of stimuli

A 
Neural and hormonal mechanisms 
Nervous control: 
- Long reflexes (vagus nerve - mediated)
- Short reflexes (local enteric nerve) 
Hormonal control: 
- Gastrin: enzymes and HCI
Sites of stimuli:
- Head: cephalic phase
- Stomach: gastric phase
- Small intestine: intestinal phase
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29
Q

Cephalic Phase

A

A variety of sensory stimuli including the sight, smell, and taste of food elicits acid secretion in the stomach.
Stimulatory event: 1. Sight and thought of food
2. Stimulation of taste and smell receptors.
Vagus nerve.
Inhibitory event: Loss of appetite, depression.

30
Q

Gastric Phase - Activation of digestive system

A
  1. stomach distension activates stretch receptors.
    - Long reflex: vagovagal reflex- medulla - vagus nerve
    - Short reflex: Local reflexes
    Acetylcholine release for more gastric juice.
  2. Food chemicals and rising pH activate chemoreceptors - Gastric cells - Gastrin release to blood.
31
Q

Gastric Phase - Inhibition of Digestive System

A

Highly acidic (pH below 2) gastric contents and emotional upset, fear, anxiety, or anything that triggers the fight or flight.

32
Q

Intestinal Phase - Excitatory

A

Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty - Intestinal gastrin release to blood.
Brief stimulatory effect as the small intestine is distended.

33
Q

Intestinal Phase - Inhibitory

A

Enterogastric reflex
- Inhibit the vagal nuclei in the medulla
- Inhibit local reflexes
- Activate sympathetic fibers that will cause the pyloric sphincter to tighten
Decline gastric secretion
Release of enterogastrones: secretin, cholecystokinin (CCK) and vasoactive intestinal peptide (VIP).

34
Q

Gastric Motility and Emptying

A

Response of the stomach to filling.
Internal stomach pressure constant until about 1.5L of food has been ingested (Gastric phase activated only when 1.5L are in the stomach).

35
Q

What is the unchanged pressure in a filling stomach due to?

A

Reflex mediated receptive relaxation:
- Anticipation of and in response of food movement.

Gastric accommodation:
- Ability of the visceral muscle to stretch without greatly increasing its tension and contracting explosively.

36
Q

Gastric Contractile Activity

A
  1. Propulsion: peristaltic waves move from fundus towards pylorus.
  2. Grinding: peristalsis and mixing action occur close to pylorus. Digestion of nutrients.
  3. Retropulsion: Pyloric end pumps small amounts of chyme into duodenum, forcing the rest back into stomach.
37
Q

How long after a meal does the stomach empty?

A

Stomach empties within 4 hours after a meal.

The larger the meal (greater distension) the faster the stomach empties.

38
Q

What does gastric emptying depend on?

A

Contents of the duodenum.

What happens in the stomach.

39
Q

Bile

A

Yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids and electrolytes.
Only bile salts and phospholipids aid the digestive process.

40
Q

Pancreatic Juice

A

Mainly water, and contains enzymes and electrolytes (primarily bicarbonate ions, for secretion of intestinal enzymes).

41
Q

Bile Salts

A 
Digestion of fatty acids.
Produced in the liver from cholesterol.
Gallbladder: storage and concentration of bile.
17 enzymes convert cholesterol into bile acids, which are transformed into bile salts. 
4 types: 
- Primary 
- Secondary
- Conjugated 
- Non-conjugated
42
Q

Primary Bile Salts

A

Immediate products of cholesterol degradation.

43
Q

Secondary Bile Salts

A

Intestinal bacteria transform primary bile salts into secondary bile salts.

44
Q

Which Hormones Regulate Bile and Pancreatic Secretion?

A

Cholecystokinin (CCK)

Secretin

45
Q

Requirements for Optimal Intestinal Digestive Activity

A

Primary function 1: Digestion
Intestinal juice not enough to perform this function.
Bile, digestive enzymes and bicarbonate ions are imported from the liver and pancreas.
Primary function 2: Absorption
Absorptive cells

46
Q

Small Intestine

A

Absorption
1 - 2 L of intestinal juice daily
Distension or irritation of the intestinal mucosa by hypertonic or acidic chyme.
Enzyme poor.

47
Q

Segmentation of Small Intestine

A

Chyme moved back and forth in lumen, few cm at a time, by alternating contraction and relaxation of rings of smooth muscle.
Intensity altered by long and short reflexes.

48
Q

Large Intestine

A

Major digestive function:

  • Absorb most of remaining water from indigestible food residue.
  • Store residue temporarily
  • Eliminate residue from body as a semisolid feces.
49
Q

Motility of Large Intestine

A

sluggish or short-lived contractions - Haustral contractions.
Gastrocolic reflex activated by food in stomach (makes sure we have space for feces).

50
Q

Haustral Contractions

A

Mass movements, long, slow moving, but powerful contractile waves.
Feces are moved with this wave.

51
Q

Defecation

A
  1. Distention of rectal walls stimulates stretch receptors - transmit signals to spinal cord neurons.
  2. Spinal reflex initiated. Parasympathetic motor fibers stimulate contractions of rectal walls and relax internal anal sphincter.
  3. If convenient, voluntary motor neurons inhibited, external anal sphincter relaxes, allowing feces to pass.
52
Q

Chemical Digestion

A

Catabolic process in which large food molecules are broken down to monomers, which are small enough to be absorbed by the GI tract lining.
Accomplished by enzymes secreted by intrinsic and accessory glands into lumen of alimentary canal.

53
Q

Which are the components of chemical digestion and absorption?

A

Carbohydrates
Proteins
Fat
Nucleic acid

54
Q

Carbohydrate Digestion

A

Monosaccharides digested directly. Glucose, fructose and galactose.
More complex carbohydrates need to be broken down into monosaccharides:
- Disaccharides: sucrose, lactose, maltose.
- Polysaccharides: glycogen, starch (starts in mouth)

55
Q

Carbohydrate Chemical Digestion

A

Salivary amylase.
Starch and other digestible carbohydrates that escape being broken down by salivary amylase are acted on by pancreatic amylase in small intestine.
Ends in small intestine.

56
Q

What are the most important brush border enzymes in the small intestine (carbohydrate chemical digestion)?

A

Dextranase, glucoamylase, maltase, sucrase and lactase.

57
Q

Why does chemical digestion end in small intestine?

A

Because colon does not secrete digestive enzymes.

58
Q

Carbohydrate Absorption - Glucose and Galactose

A

Cotransport with Na+ into epithelial cells → Liver via hepatic portal vein.

59
Q

Carbohydrate Absorption - Fructose

A

Facilitated diffusion → Liver via hepatic portal vein.

60
Q

Protein Digestion

A

Not only dietary proteins, also enzyme proteins.

Protein is digested all the way to its amino acid monomers (absorbed in small intestine).

61
Q

Protein Chemical Digestion - Stomach

A

Pepsin: stomach gland
Protein broken down into large polypeptides.
Inactivated by high pH in duodenum, proteolytic activity restricted to stomach.

62
Q

Protein Chemical Digestion

A

Protein → large polypeptides by pepsin in the stomach
Large polypeptides → small polypeptides, small peptides by Pancreatic enzymes: trypsin, chymotrypsin
→ Amino acids. Brush border enzymes: Carboxypeptidase. Aminopeptidase and dipeptidase in small intestine.

63
Q

Protein Absorption

A

Amino acids are absorbed by cotransport with sodium ions. They leave the epithelial cells by facilitated diffusion, enter capillary blood in the villi, and are transported to the liver via hepatic portal vein.

64
Q

Lipid Digestion

A
  1. Fat emulsified (broken down) by bile salts in duodenum.
  2. Digestion of fat by pancreatic enzyme lipase produces free fatty acids and monoglycerides. Form micelles with bile salts, go into intestinal mucosa.
65
Q

Lipid Absorption

A
  1. Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. Recombined as triglycerides and combined with other lipid and proteins to form chylomicrons.
  2. Chylomicrons extruded from epithelial cells by exocytosis. Carried away from intestine with lymph.
66
Q

Nucleic Acid Digestion

A

Nucleic acid breaks down into pentose sugars, N-containing bases and phosphate ions by pancreatic ribonuclease (RNA) and deoxyribonuclease (DNA), and brush border enzymes (nucleosidases and phosphatases).

67
Q

Nucleic Acid Absorption

A

Units enter intestinal cells by active transport via membrane carriers.
Units are absorbed unto capillary blood in the villi and transported to the liver via hepatic portal vein.

68
Q

Vitamin Absorption

A

Small intestine: Dietary vitamins
Large intestine: K and B vitamins
Fat-soluble vitamins (A, D, E and K): micelles
Water soluble (B and C): diffusion or via active or passive transporters.
Exception: vitamin B12 (Stomach).

69
Q

Electrolyte Absorption

A

From ingested food and gastrointestinal secretion.
Iron and calcium limited to duodenum.
Sodium: coupled to absorption of glucose and amino acids.

70
Q

Water Absorption

A

9L derived from gastrointestinal secretions in small intestine.
In chyme: 95% small intestine and rest in large intestine.
0,1 L for feces.

Organ System Anatomy, Physiology and Pathology - BPT06 (34 decks)

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