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An Sc 311 Midterm 1 > Lecture 2 - Digestion and Absorption of Nutrients > Flashcards

Lecture 2 - Digestion and Absorption of Nutrients Flashcards

1
Q

Definition of digestion

A

Process by which foodstuffs are broken down in the GI tract into absorbable units

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2
Q

Are food and nutrients inside the body during digestion?

A

No, considered to be outside the body, GI tract is hollow tube outside body

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3
Q

What are the four types of digestive processes

A

Mechanical
Chemical
Enzymatic
Microbial

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4
Q

Mechanical digestion includes…

A

Mastication (chewing)
Grinding action of the gizzard (birds)
Movement of the GI tract (segmentation and peristalsis)

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5
Q

What is peristalsis

A

series of wave-like muscle contractions that move food through the digestive tract

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6
Q

Chemical digestion involves

A

Gastric acid (HCl; pH 1.5-3.5)

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7
Q

Enzymatic digestion occurs where? Involves what?

A

In the lumen and the mucosa
Digestive enzymes are secreted into the GI tract

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8
Q

Definition of absorption

A

Process of moving digested products through the gut mucosal wall

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9
Q

Two types of absorption

A

Transcellular (across cell)
Paracellular (across tight jxn)

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10
Q

Three types of transport

A

Passive
Active
Osmosis

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11
Q

Describe passive transport

A

Relies on concentration/electrochemical gradients
Transcellular or paracellular
No energy required

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12
Q

What is osmosis

A

Water moves from low solute concentration to high solute concentration (water follows solute)

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13
Q

The electrochemical gradient is the combination of what

A

Chemical driving force (e.g. Na, K from low to high conc)
Electrical driving force (charge force; neg charge inside)

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14
Q

Describe active transport

A

Moves against concentration/electrochemical gradient
Needs energy (ATP)
Primary or secondary

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15
Q

What is secondary active transport

A

Movement of a solute against its gradient by pairing it with facilitated diffusion of a different solute with its concentration gradient

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16
Q

What molecules use secondary active transport

A

Glucose, aa, B-vitamins, bile salts

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17
Q

How much water do humans absorb/reabsorb per day? Where does this happen?

A

2L/day from food and drink + 7L per day from gut secretion = 9L a day

95% of it is absorbed in the small intestine

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18
Q

What kind of transport does water absorption use

A

Passive transport (osmotic gradient; transcellular and paracellular)

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19
Q

Amount of water secreted depends on? Location of absorption depends on?

A

Whether the animal is a carnivore or herbivore

Depends on species

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20
Q

Distribution of absorption in small intestine vs colon or dog vs horse

A

Dog = majority absorbed by SI (88%), 12% by colon

Horse = more even (58% SI, 42% colon)

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21
Q

Types of carbohydrates

A

Monosaccharide
Disaccharide
Polysaccharide

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22
Q

Examples of mono, di, and polysaccharides

A

Mono = glucose, fructose, galactose

Di = sucrose, maltose, lactose

Poly = starch, cellulose

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23
Q

Sucrose, maltose and lactose composition

A

Sucrose = glucose + fructose

Maltose = glucose + glucose

Lactose = glucose + galactose

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24
Q

What kinds of bonds are in starch? Cellulose?

A

Starch = alpha-1,4 glycosidic bond

Cellulose = beta-1,4 glycosidic bond

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25
Q

How many carbons in glucose, fructose and galactose

A

Glucose/galactose = six
Fructose = five

26
Q

Steps in amylose digestion

A

Amylose broken down into dextrins by salivary alpha-amylase

Dextrins broken down to maltose by pancreatic a-amylase

Maltose broken down into glycose by maltase

27
Q

Slide 17**

A

Polysaccharide digestion

28
Q

What transports glucose across the brush border membrane? Fructose?

A

Sodium glucose transporter 1

GLUT5

29
Q

How does glucose transport vary in low-sugar vs high-sugar meal

A

Low-sugar = sodium glucose transporter 1 is used (secondary active transport)

High-sugar = GLUT2 allows glucose to be absorbed passively

30
Q

What kinds of CHO are absorbed

A

Monosaccharides only

31
Q

What happens to lactase activity over time? Enzyme activity varies with…

A

Constantly decreasing after birth
Age, region of SI

32
Q

Parts of an amino acid

A

Amino group, carboxylic acid group, R group

33
Q

Proteins are

A

Large molecules consisting of amino acids linked by peptide bonds

34
Q

Primary, secondary, tertiary and quaternary protein structure

A

Primary = sequence of a chain of aa

Secondary = H bonds of the peptide backbone (B-sheet, a-helix)

Tertiary = 3D folding pattern of a protein due to side chain interactions

Quaternary = protein consisting of more than one amino acid chain

35
Q

How are gastric enzymes activated

A

HCl in the stomach leads to denaturation of protein, this triggers the activation of pepsinogen into pepsin

36
Q

Gastric protease enzyme is called (unactivated and activated)

A

Pepsinogen (proenzyme) -> pepsin

37
Q

Pancreatic protease enzymes and how they’re activated

A

Trypsinogen is activated by enterokinase and becomes trypsin

Trypsin activates the rest:
Chymotrypsinogen -> chymotrypsin
Proelastase -> elastase
Procarboxypeptidase A -> Carboxypeptidase A
Procarboxypeptidase B -> carboxypeptidase B

38
Q

What happens to large peptides at the brush border

A

Turned into di- and tri- peptides or free aa by brush border peptidases

39
Q

What happens to di- and tri and free aa inside the brush border membrane

A

Small amounts of di- and tri- peptides will cross through, most turned into aa by cytoplasmic peptidases

Amino acids carried through membrane

40
Q

How does brush border membrane transport differ for aa

A

Neutral, basic and acidic aa have different transport systems, use different ion gradients

41
Q

Slide 29**

A

Protein and CHO recap

42
Q

Most ingested fats are in the form of

A

triglycerides

43
Q

What is a triglyceride composed of

A

Glycerol + 3 fatty acids

44
Q

Where are bile salts produced and stored

A

Produced in liver
Stored in gallbladder

45
Q

Two parts of bile salts…

A

One part is negatively charged (hydrophilic head), the other is hydrophobic tail (positive charge)

46
Q

Slide 33***

A

Lipid digestion

47
Q

Fat goes from…

A

Large fat drops -> + bile -> small, emulsified fat drops -> products of degradation absorbed by micelles -> free f.a. + monoglyceride diffuse into cell

48
Q

What breaks down fats into monoglycerides and f.a.

A

Pancreatic lipase, colipase

49
Q

What happens to the f.a. and monoglycerides that are produced by fat breakdown

A

Stored in micelles, move out of micelles and enter cell by diffusion

50
Q

Absorbed fats + cholesterol + proteins inside the intestinal cell form what? Where does this go?

A

Form chylomicrons

They are released into the lymphatic system

51
Q

Nucleotide vs nucleoside

A

Nucleotide = Sugar + base + phosphate group

Nucleoside = sugar + base

52
Q

Purines? Pyrimidines?

A

Purines = adenine, guanine
Pyrimidines = thymine, cytosine, uracil

53
Q

RNA has what instead of what?

A

Uracil instead of thymine

54
Q

Nucleosomes are formed when what happens? Eventually leading to the formation of…

A

When DNA wraps around a protein (histone)

Eventually forming chromosomes

55
Q

Steps in nucleic acid digestion/absorption

A
  1. Denatured by gastric acid
  2. Broken down to nucleotides by pancreatic nucleases
  3. Phosphatase on brush border cleave P ion
  4. Nucleosidase catalyzes breaking of covalent bond btw nitrogenous base and pentose sugar

Slide 38**

56
Q

Major enzymes in nucleic acid digestion/absorption

A

Pancreatic nucleases
Phosphatase
Nucleosidase

57
Q

Products of nucleotide breakdown are absorbed in the… Transported to…

A

Duodenum and jejunum

Liver and other tissues

58
Q

what kind of transport are electrical and chemical driving forces

A

Passive transport

59
Q

How does primary active transport work

A

Na+ binds transporter, stimulates phosphorylation by ATP = conformational change, K+ then binds causing release of P and back to original conformation

60
Q

bile salts are required for __________ digestion

A

Lipid

An Sc 311 Midterm 1 (8 decks)

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