Lecture 12 - Digestive System Flashcards
Metabolism
- 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
What happens to stored “molecules in Undernourishment
if an animal take in too little food to meet its energy requirements, it will start metabolizing molecules of its own body
- stored carbs and fat
- carb reserves quickly depleted ( glycogen in liver and muscle cells, ~1 day) - fat reserves
- most important form of stored energy, ~1 week - protein last
- protein is not used for energy storage
- breaks down the proteins of your functioning body…
What happens in Protein deficiency (process)
- in starving conditions protein is broken down
- blood plasma proteins
- decreases osmotic conc of plasma
fluid is lot from the fluid to interstitial spaces - 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
Essential Nutrients
- some of the organic building blocks the ell needs in order to make complex molecules must be supplied from the diet
- essential amino acids
- essential elements
- 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
Essential Amino Acids
- 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
Essential elements
- 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)
Vitamins
essential molecule required in limited amoutns
We require 13 vitamins
- water soluble (excess eliminated in urine)
- fat soluble (accumulate in body fat and can be toxic)
Digestion Steps
- mouth
- food fragmented by teeth - 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 - intestine
- most digestion occurs here
- nutrients, ions, water are absorbed across its walls - Rectum
- expels feces
- undigested waste is stored as feces for release into the environment
Surface area and digestion
- 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
Digestive enzymes
- 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
Digestion and mouth
- chewing: physical breakdown of bonds
- saliva: digestive enzyme that breaks bonds in starch to yield glucose monomers
- tongue pushes food back to throat
Swallowing
- contact of food with soft palate at back of mouth initiates swallowing
- swallowing closes trachea (epiglottis closes)
- esophagus opens
- moves by peristalsis (smooth muscle contracts in response to being stretched (contraction is always preceded by relaxation)
- food moves to stomach
The stomach
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
Chyme
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
- Contractions push chyme toward bottom of stomach
- small quantities enter small intestine
- stomach empties itself gradually over ~4 hours
- small intestine works on a little material at a time
Where does most chemical digestion and nutrient absorption occur?
What happens then?
- small intestine
- digestion of carbohydrates and proteins continues
- digestion of fats begin
- absorption of nutrients begin - absorbs almost all of the nutrient molecules derived from food
