Lecture 12 - Digestive System Flashcards Preview

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Flashcards in Lecture 12 - Digestive System Deck (28)
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1
Q

Metabolism

A
  • animals digest food to botain energy and building bloks of complex molecules
  • standard unit of energy used by nutritionists = 1 calorie

Metabolic rate: measure of overall energy needs of an animal that must be met by the ingestion, digestion and assimilation of food

different levels of physical activity can increase metabolic reqs

different components of food provide diff amounts of energy

  • fat 9.5 cal/gram
  • carbs 4.2 cal/gram
  • protein 4.1 cal/gram
2
Q

What happens to stored “molecules in Undernourishment

A

if an animal take in too little food to meet its energy requirements, it will start metabolizing molecules of its own body

  1. stored carbs and fat
    - carb reserves quickly depleted ( glycogen in liver and muscle cells, ~1 day)
  2. fat reserves
    - most important form of stored energy, ~1 week
  3. protein last
    - protein is not used for energy storage
    - breaks down the proteins of your functioning body…
3
Q

What happens in Protein deficiency (process)

A
  • in starving conditions protein is broken down
  1. blood plasma proteins
    - decreases osmotic conc of plasma
    fluid is lot from the fluid to interstitial spaces
  2. breaking down muscle, other proteins

causes serious damage to tissuse including liver

point of no return = protein synthesis machinery (proteins themselves) is broken down

Kwashiorkor

  • disease causes by chronic protein deficiency
  • swollen hands, feet, abdomen, with spindly limbs
  • damages body organs
  • eventual death
4
Q

Essential Nutrients

A
  • some of the organic building blocks the ell needs in order to make complex molecules must be supplied from the diet
  1. essential amino acids
  2. essential elements
  3. vitamins
  • lack of a particular nutrient produces malnutrition
  • chronic malnutrition leads to a characteristic deficiency disease
  • can also be caused by an inability to absorb or process an essential nutrient
5
Q

Essential Amino Acids

A
  • most animals cannot synthesize all the amino acids they need
  • humans have 8 essential amino acids they must obtain from food
  • available in milk, eggs, meat soybeans
  • most plant foods do not contain all 8, complementary diet of the right plants can get all 8
Isoleucine
leucine
lysine
methionine
phenylalanine
theronine
trypyophan
valine
6
Q

Essential elements

A
  • many mineral elements must be obtained from diet
    1. macronutrients: elements required in large amounts (ex 800-1,000 mg calcium)
    2. mucronutrients: elements required in only tiny anounts ( ex ~15mg iron, yet insufficient iron/anemia is the mos tcommon deficiency in the world)
7
Q

Vitamins

A

essential molecule required in limited amoutns

We require 13 vitamins

  1. water soluble (excess eliminated in urine)
  2. fat soluble (accumulate in body fat and can be toxic)
8
Q

Digestion Steps

A
  1. mouth
    - food fragmented by teeth
  2. stomach
    - storage chambers that enable animals to ingest large amounts of food at once and the digest it gradually
    - food is further fragmented into small pieces
    - food is mixed together
  3. intestine
    - most digestion occurs here
    - nutrients, ions, water are absorbed across its walls
  4. Rectum
    - expels feces
    - undigested waste is stored as feces for release into the environment
9
Q

Surface area and digestion

A
  • parts of the gut that absorb nutrients have a large surface area
  • walls of intestine are richly folded
  • each fold has many finger-like projections called villi
  • each villi is covered in microscopic projections called microvilli
10
Q

Digestive enzymes

A
  • produced at different locations along digestive tract
  • enzymes that break down food molecules into their simplest monomeric units

cleave chemical bonds:

  • proteasesbreak down proteins
  • carbohydrases- break down carbs
  • peptidases- break down peptides
  • lipases- break down fats
  • nucleases- break down nucleic acids
11
Q

Digestion and mouth

A
  1. chewing: physical breakdown of bonds
  2. saliva: digestive enzyme that breaks bonds in starch to yield glucose monomers
  3. tongue pushes food back to throat
12
Q

Swallowing

A
  1. contact of food with soft palate at back of mouth initiates swallowing
  2. swallowing closes trachea (epiglottis closes)
  3. esophagus opens
  4. moves by peristalsis (smooth muscle contracts in response to being stretched (contraction is always preceded by relaxation)
  5. food moves to stomach
13
Q

The stomach

A

Main role: store food so digestion can occur more slowly than ingestion

gastric pits: deep infoldings of stomach that serete enzymes that aid in digestion

pepsin:

  • enzyme that digests proteins
  • secreted as an inactive precursor (zymogen)
  • low pH of stomach cleaves the precursor into active form
  • prevents enzymes from being active inside cells that produce it

HCL:

  • kills most ingested microorganisms
  • lowers stomach pH (usually ~1.5-2)

Mucus:
- protects stomach walls

14
Q

Chyme

A

1.Product of stomach mixing food with secretions

Chyme:

  • acid, fluid mixture of gastric juice and partially digested food
  • most substances cannot be absorbed across the stomach wall
  1. Contractions push chyme toward bottom of stomach
  2. small quantities enter small intestine
  3. stomach empties itself gradually over ~4 hours
  4. small intestine works on a little material at a time
15
Q

Where does most chemical digestion and nutrient absorption occur?

What happens then?

A
  • small intestine
  1. digestion of carbohydrates and proteins continues
  2. digestion of fats begin
  3. absorption of nutrients begin - absorbs almost all of the nutrient molecules derived from food
16
Q

Where do fats begin to be absorbed?

A

small intestine

17
Q

Small intestine

A

~6 meters long with many folds
inner surface area approximately the size of a tennis court

Three sections:
1. duodenum - site of most digestion
2,3. jejunum and ileum - 90% of absorption of nutrients

needs specialized enzymes for digestion

18
Q

Liver

A

secretes bile

Bile:

  • contains salts that emulsify fats in the chyme
  • keep fats from aggregating
  • increase surface area of fats exposed to lipase

Bile salts:

  • amphipathic
  • one end soluble in fat
  • other end soluble in water
  • break fat into small, water soluble particles
19
Q

Production of bile

A
  • Synthesized in liver
  • leaves via hepatic duct
  • 1/2 stored in gallbladder
  • 1/2 goes directly to intestine,duodenum
20
Q

Gallbladder

A
  • side branch off hepatic duct goes to gallbladder
  • stores other half of the bile
  • released in response to the fat entering the duodenum
21
Q

Pancreas

A

produces many digestive enzymes:
- lipases, proteases, amylases, nucleases

enzymes are released as zymogens

  • inactive precursor
  • so they do not hard the pancreas before reaching duodenum
  • anzyem in small intestine cleaves the precursors and makes them active

pancreatitis: inappropriate activation of enzymes causes them to digest the pancreas

produces HCO3-
- neutralize the acidic ph of chyme entering the stomach

22
Q

What is a zymogen?

A

enxyme that is an inactiv precursor

  • inactive so as to not harm the organ making it
  • enzyme activates them after relased
23
Q

Nutrient absorption

A
  • occurs in small intestine
  • epithelial cells of small intestine complete the digestion of macromolecules into absorbable monomers
  • secrete enzymes that cleave peptides and disaccharides and some lipases

many mechanisms
- mostly in jejunum and ileum

24
Q

Mechanisms of absorption in small intestine

A
  • diffusion
  • facilitated diffusion
  • active transport
  • cotransport
25
Q

Storage in liver

A
  • where absorbed nutrients go
  • hepatic portal vein from intestines to liver
  • stores them as glycogens or fats
  • or converts them to needed molecules
26
Q

The large intestine

A

Colon

    • remaining contents of small intestine are pushed into large intestine
    • most nutrients have been removed
    • still a lot of water and ions
  1. colon absorbs water and ions
  2. produces feces
    - constipation (removal of too much water)
    - diarrhea (too little water removed)
27
Q

Food that cannot be broken down

A

Herbivores - break down plant cell walls, do not make these enzymes themselves

rely on microorganisms in theor digestive tract to digest the cellulose
–> absorb nutrients that could be otherwise lost

microbial fermentation chambers

  • multi-chambered stomach
  • caecum - separate chamber extending from large intestine (in humans it is the vestigial appendix)
28
Q

How much energy is provided by fat, carbs, protein?

A

different components of food provide diff amounts of energy

  • fat 9.5 cal/gram
  • carbs 4.2 cal/gram
  • protein 4.1 cal/gram