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M201 > W10 GI System Refresher & Nutrients and Drug Absorption > Flashcards

W10 GI System Refresher & Nutrients and Drug Absorption Flashcards

1
Q

What are the key functions of the digestive system?

A
  1. Ingestion
  2. Digestion (mechanical: gut motility &
    chemical: gut secretions)
  3. Absorption
  4. Elimination
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2
Q

What are the two major anatomical components of the GI system?
What makes up these components?

A
  1. Gastrointestinal tract
    (Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus)
  2. Accessories components (Teeth, Tongue, Salivary glands, Liver, Gall bladder, Pancreas)
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3
Q

What is the gastrointestinal tract?

A

One long tube (also known as alimentary canal/tract)
~30 feet (~ 9 meter) long
Consists of: (Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus)

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4
Q

What are the different layers of the gastrointestinal tract? (5

A

Lumen
Mucosa
Submucosa
Circular muscular layer
Longitudinal muscle layer
Serosa

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5
Q

What is the Lumen?

A

Epithelial tissue; food move from mouth to anus

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6
Q

What is the Mucosa layer?
What is its function?

A

-Thin layers of epithelium, lamina propria (connective tissue) and muscularis mucosa (smooth muscle).
-Secretes mucus, digestive enzymes, and hormones

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7
Q

What is the Submucosa layer?
What does it contain?

A

-Thick layer of loose connective tissue.
-Contains blood vessels, lymphatic vessels, and nerves.
-Glands may be embedded in this layer. Enables peristalsis

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8
Q

What is the muscular layer composed of?

A

The circular and longitudinal muscle layers.

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9
Q

What is the circular muscle layer?

A

Smooth muscle layers, blood vessels and plexus nerves and innervation

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10
Q

What is the Longitudinal muscle layer?

A

Peristalsis- Involuntary contraction and
relaxation- movement of food

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11
Q

What is the Serosa layer?

A

A thin sheet of connective tissue that contains blood and lymphatic vessels, and is covered by the peritoneum, Secretes serous fluid to allow lubricated sliding movements between opposing surfaces

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12
Q

Regulation of GIS (nervous and hormonal control)
What are the digestive phases? (3)

A
  • The enteric nervous system (exclusive for GIS) can integrate information without input from the CNS and facilitates GI secretions and motility.
  • Generally, parasympathetic innervation is excitatory for GI function, and sympathetic innervation is inhibitory for GI function
  1. Cephalic Phase
    anticipatory mechanisms (senses): saliva secretions
  2. Gastric Phase
    Gastric secretions and motility: stomach
  3. Intestinal Phase
    Intestinal secretions and motility: intestine, liver and pancreas.
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13
Q

What components make up the GI components in the mouth?

A

Salivary glands
Parotid
Sublingual
Submandibular
Oesophagus

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14
Q

What is Mastication?

A
  • Chopping and grinding of food in the mouth
    (physical digestion)
  • Teeth (bone) and tongue (skeletal muscle) aid the
    physical breakdown of food
  • Salivary glands in the mouth secrete amylase enzyme (amylase digest the carbohydrates- chemical digestion breaks down into simple/smaller molecules)
  • Water in the saliva helps to make the food moist and bolus for easy swallowing and passage into the propharynx
  • Lysozyme is an antibacterial salivary enzyme, and salivary immunoglobulins disable bacteria and viruses (defence)
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15
Q

What is the Saliva composed of?
What is the pH of saliva?

A

99.5% of water
0.5% amylase, bicarbonate ion and other electrolytes
pH of saliva at 6.5-7.5

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16
Q

What is the Oesophagus?
What is the structure like?

A

Swallowed food passes into the oesophagus, a narrow tube that travels through the thorax to the abdomen (~ 8 inch long in adult)

The walls are skeletal muscle initially but transition to smooth muscle about two-thirds of the way down the length.

The muscles are under conscious control, used when breathing, eating, belching, and vomiting.

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17
Q

Stomach:
What is the cardiac sphincter?

A

-A thin ring-like muscle helps to prevent
stomach contents from going back up into the oesophagus.
-Also, vents air out (burping)

Situated on top of stomach-opens to allow food bolus to enter from oesophagus into stomach. no relation to heart.

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18
Q

Stomach:
What are the three regions of the stomach?
What is the function?

A
  1. Fundus
  2. Body
  3. Antrum
    -mixing of food bolus with acid & enzyme
    - largely digestion but some absorption (like alcohol, aspirin, some lipid-soluble’s

J-shaped- Size~12x6 inches, capacity: 1-4 L
(food stays 2-4 hrs; pH: 1-3, Strongly acidic

Chyme (Stomach acids + enzymes + food) moves to the intestine after being formed in the stomach

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19
Q

Stomach:
What is the Rugae?

A

Series of ridges by folding of the stomach walls; contains secretory pits (acid and others); provides a large surface area and expansion to a full capacity

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20
Q

Stomach:
What is the Pylorus sphincter?

A

-A valve/sphincter that connects the stomach to the small intestine.
-Prevents the backflow of contents from the small intestine to the stomach

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21
Q

Gastric Mucosa
- What is it made up of?
Gastric secretion in stomach:

A

Acids, Enzymes, Hormones & Factors

Mucous surface cell
Mucous neck cell
Parietal cells
Enterochromaffin-like cell
Chief cells
D cells
G cells

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22
Q

What does Acid in the stomach lumen cause?

A

-release and activation of pepsin, an enzyme that digests proteins.
-somatostatin release from D cells.
-denatures proteins (more accessible pepsin)-
-kill bacteria and other ingested microorganisms.
-inactivates salivary amylase, stopping carbohydrate digestion that began in the
mouth

23
Q

Gastric acid secretion in stomach:
Enzymes-

A

Pepsin- activates enzymes, converts pepsinogens into pepsin

24
Q

Chief cells:

A

Secrete pepsin(ogen) and gastric lipase
Digests proteins and fats

25
Q

What Hormone is secreted from
Enterochromaffin-like cells?

A

Secretes histamine (hormonal stimulus for proton pump)
=Helps modulate the level of acid secreted in the stomach.
Stimulates gastric acid secretion.

Acetylcholine and gastrin are stimuli for histamine release from ECL cells

..which then in turn stimulates parietal cells to secrete HCl

26
Q

Gastric acid secretion- intrinsic factors

A

Parietal cells secrete intrinsic factor
This complexes with vitamin B12 to permit absorption
Presence of Gastrin and Histamine are the stimulus for release

27
Q

What occurs in the small intestine?
How long is it?
What are its 3 parts?
What does its cross-section look like?

A

Most digestion and absorption
3 m to 5 m long (~10 feet to 20 feet)
Duodenum- Jejunum- Ileum
Cross section of SI: Intestinal mucosa has finger-like projections, Villi.
Multi-folded (plicae), the invaginations are known as crypt

After SI, Waste/unabsorbed moves to the large intestine (caecum

28
Q

Small intestine:
What occurs in the duodenum?

A

Mixing of chyme and secretions (digestive acids and enzymes) from gall bladder & pancreas ducts (Oddi-tonically controlled sphincter).
Absorption of minerals, vitamins and other micronutrients begins here.

29
Q

What occurs in the jejunum?

A
  • Further (segmentation) mixing of chyme and secretions (digestive acids and enzymes).
  • Absorption of minerals, vitamins and other micronutrients, digested carbs, fats and proteins.
30
Q

What is the ileum?
What processes occur?

A

Last part (largest part) of the small intestine,
several folds-thin walls; mixing of digested, and non-digested (segmentation) and secretions (digestive acids and enzymes). A

Absorption of leftover digested carbs, fats and proteins from the jejunum

31
Q

Intestinal secretions (Mucus, Enzymes and
Hormones)

A

Mucus is secreted by duodenal glands and goblet cells, and protects the duodenum from gastric acids and digestive juices
Sucrase, lactase, maltase and amylase digest carbohydrates and are absorbed via glucose transporters (SGLT, GLUTs)

32
Q

Hormones

A

Hormones: (a complex interaction between satiety and appetite, more detail in Dr Healy’s lectures)
Cholecystokinin: stimulate gallbladder contraction, and pancreatic enzyme secretions and inhibits gastric emptying and secretions
Secretin: stimulate bicarbonate secretion and inhibits gastric emptying and secretions
Gastric inhibitory peptide- inhibits gastric emptying and secretion
Glucagon-like peptide-1: inhibits gastric emptying and secretion (satiety

33
Q

What occurs in the large intestine?
How long is it?
What do the bacteria in the LI produce? (4)

A
  • Water & electrolyte absorption
  • 1.5 metres, or 5 feet (20-30 hrs holding)
  • Composed of Caecum, Rectum, Anal Sphincter
  • Completion of absorption of nutrients. 2-3 times a day of gastrocolic reflux (bowel movement).
  • The bacteria in the LI produce vitamins
    (B12, thiamin, and riboflavin) as well as vitamin K.
34
Q

Accessories- Liver (A vital organ for metabolism)

What is special about the liver?
What are the functions of the liver? (6)

A

Largest internal organ (1.5 kg)
The liver receives 30% of the resting cardiac output

  • Glucose and fat metabolism
  • Protein synthesis
  • Hormone synthesis
  • Urea production
  • Detoxification
  • Storage
35
Q

Liver secretions (bile) & fat absorption

A
36
Q

Accessories- Pancreas
What are Exocrine glands?

A

95 percent of the pancreas is exocrine tissue.
It produces pancreatic enzymes to aid digestion.
-makes about 2.2 pints (1 litre) of these enzymes every day (healthy human)

37
Q

What is contained in the pancreas?
What is digested?

A

Alkaline clear/milky liquids (containing several enzymes)

Amylase- to digest carbs
Lipase- to digest fat
Trypsin- to digest proteins

38
Q

How long is the liver?
What are endocrine glands?

A

Gland organ 6-8 inches long (leaf-shaped)
5 percent comprises hundreds of thousands of endocrine cells known as islets of
Langerhans. (glucose control by insulin and glucagon)

39
Q

What does the gastric mucosa contain?

A

Gastric acids for gastric secretion
Enzymes
Hormones and factors

40
Q

What does acid in the stomach cause?

A

-release and activation of pepsin, an enzyme that digests proteins.
-somatostatin release from D cells.
-denatures proteins (more accessible pepsin)-
-kill bacteria and other ingested microorganisms.
-inactivates salivary amylase, stopping carbohydrate digestion that began in the mouth

41
Q

GI Motility: How do peristaltic waves work?

A
  1. Moves the bolus forward movement/Propulsive
  2. Coordinated involuntary contraction and relaxation of circular and longitudinal muscles
  3. Adjacent segments alternatively contract and relax
  4. Sphincters prevent the back flow

Epiglottis opens, when food is swallowed it shuts to prevent food going into airway
(Hiccups- food goes into airway)
Epiglottis sphincter contracts involuntary, food moves from mouth to stomach

42
Q

Immune functions of the GI tract:
What is the function of M cells??

A
  • Sense pathogens
    M cells are a type of epithelial cells, most abundant in the epithelium overlying lymphoid follicles such as Peyer’s
    patches in the intestine.
    The apical or lumen-facing surface has few or no microvilli

.
Mucosal immune response and immune surveillance
M-cells have the unique ability to take up a variety of
antigens - bacteria, viruses, parasites and proteins - from
the lumen, transport them by transcytosis across the cell
and deliver them to immune cells lying underneath,
particularly dendritic cells

43
Q

Spacer between lectures

A
44
Q

Nutrient digestion & absorption:
Carbohydrates

A

Diet contains disaccharides and complex polymers (starch and
sucrose)
All carbs are broken down into monosaccharides & absorbed in the
small intestine

  1. Starch Glycogen
  2. Disaccharides
  3. Monosaccharides
45
Q

Decreased lactase activity is associated with a condition known as..?
What If ….. take milk/milk products?

A

Lactose intolerance

Disaccharide: (dairy products)
- Glucose + Galactose= Lactose
Broken down by Lactase
Galactose produced (monosaccharide)

  • Diarrhoea
  • Bloating and flatulence.
    Remedy: remove milk products from the diet, although milk predigested with lactase is available
46
Q

Nutrient digestion & absorption
Proteins:

A

All proteins are broken down into di/tri-peptides & absorbed in the
small intestine
Small peptides also transported across the membrane by the process
of transcytosis

47
Q

Nutrient digestion & absorption
Lipids & Cholesterol

Bile salts coat lipids to make emulsions and form..?

A

Most lipids are hydrophobic and must be emulsified to facilitate digestion in the aqueous environment of the intestine

  1. Bile salts coat lipids to make emulsions and form micelles
    -Micelles are small disks with bile salts, phospholipids, fatty acids, cholesterol,
    and mono-/diglycerides.
  2. Lipase and colipase digest triglycerides
48
Q

Nutrient digestion & absorption

A

Nucleic acid polymers (DNA & RNA) digest into amino bases and monosaccharides by pancreatic and intestinal
enzymes and are absorbed via active transporters.
The fat-soluble vitamins (A, D, E, and K) are absorbed in the small intestine along with fats.
The water-soluble vitamins (C and most B vitamins) are absorbed by mediated transport.
(Except, vitamin B12, also known as cobalamin because it contains the element cobalt; Dietary supply of B12 from
seafood, meat, and milk products. The intestinal transporter for B12 is found only in the ileum and recognizes B12
only when the vitamin is complexed with a protein called intrinsic factor, secreted by the same gastric parietal cells
that secrete acid)
Minerals, the intestinal absorption of Iron and Calcium is regulated by hormonal and facilitated transport
pathways
Electrolytes (Sodium, potassium, chloride) and water are absorbed through various pathways (paracellular
diffusion, active transport, channels and others)

49
Q

Drug Absorption
How are drugs absorbed?

A
  1. Passive diffusion (MAIN)
  2. Active transport/diffusion
50
Q

What factors affect passive
diffusion of drug transpo

A
51
Q

How do drugs through the lipid bilayer?

A

They need to be in their Un-ionised form for the drugs (only) to cross lipid bilayers by passive diffusion

52
Q

Factors influencing G. I. absorption (physiological)

A
  • G.I. motility
  • G.I. secretions & enzymes
  • Drug-food/supplement interactions
  • Differences in luminal pH along the GI tract
  • Surface area per luminal volume
  • Blood perfusion
  • Presence of bile and mucus
  • The nature of epithelial membranes
53
Q

What are the Advantages of G. I absorption? (physiological)

A

– Large surface area for passive diffusion
– Range of pH environments promotes the uptake of weak acids/bases
– Richly vascularised (high blood supply)
– Long tract and long dwell time
– Some active transport (e.g. Levodopa taken up by phenylalanine transporter)
– Small intestine is a major site for drug absorption

54
Q
A

M201 (81 decks)

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