Chapter 4 - Digestive System Flashcards
Functions of the digestive system
IDEA
Ingest (take in) food
Digest (break down) foo into small pieces -> chemical and physical
Eliminate waste
Absorb and provide nutrients to the body cells
A comes before E but its just for the acronym Loll
carbohydrates
elements: carbon, hydrogen, oxygen
- monosaccharides 1
- disaccharides 2
- oligosaccharides 2<x<10
- polysaccharides 10 or more
monosaccharides
- small enough to be directly absorbed into blood
- common monosaccharides:
-> glucose (source of ATP)
-> fructose (found in fruits, soft drinks)
-> galactose (found in milk)
disaccharides
- made up of 2 monosaccharide subunits
- digested by enzymes into monosac. before absorption into the blood
- common disaccharides:
-> sucrose (table sugar) = glucose + fructose
-> maltose = glucose + glucose
-> lactose (milk sugar) = glucose + galactose
polysaccharides
- many monosac. (e.g. glucose) joined together by glycosidic bonds
- digested into monosac. before absorption
- major polysaccharides:
-> starch from plants: main source in out diet, digested into glucose
-> glycogen from animals: not an important source in our diet
-> cellulose from plants: indigestible, provides fiber in our diet
-> chitin cell wall of fungi
protein
elements: C,H,N,O,S
- long chains of amino acids joined by peptide bonds
- 20 common amino acids -> essential (must be supplied by diet) /non essential (our body can make them)
function of proteins
- enzymes (speed up reactions; e.g. amylase, pepsin, proteases, lipases)
- muscle contraction, e.g. actin and myosin
- hormones, e.g. insulin, parathyroid hormone, growth hormone
- hemoglobin (for oxygen transport)
- antibodies (for immune defense)
- ion channels, carriers and pumps
- membrane receptors
- energy source (after glucose/glycogen and fats are exhausted
what are enzymes
biological protein catalyst that speed up reactions.
- they recognise specific molecules
e.g the amylase in our saliva recognises and breaks down only starch
lipids/fat
- triglycerides -> glycerol and 3 fatty acids; digested by lipase
- fatty acids -> saturated (no double bond), unsaturated (have at least 1 bond)
- cholesterol
- phospholipids -> glycerol + 2 fatty acids + 1 phosphate group (e.g. lecithin found in egg yolk and soya bean)
function of lipids
- triglycerides: source of energy (ATP)
- adipose tissue: cushion and protect internal organs, insulate body, store energy
- phospholipids -> forms bilayer of cell membrane
- cholesterol -> component of cell membrane, precursor for synthesis of steroid hormones e.g. sex hormones, component of bile salts which emulsify fats to id in their digestion and absorption
vitamins
organic chemicals needed in small quantities
A: vision
B complex: coenzymes for enzymes
C: antioxidant, collagen synthesis
D: absorption of calcium in intestines
E: antioxidant
K: blood clotting
minerals
- calcium (Ca): strong bone and teeth, muscle and nerve functions, blood clotting
- sodium (Na): osmoregulation, nerve and muscle functions
- potassium (K): nerve and muscle functions
- iron (Fe): component of hemoglobin, components of enzymes
- phosphorus (P): component of ATP, nucleic acids, phospholipids, cell membranes
water
- medium for all biochemical reactions
- transport of solutes
- maintain body heat
digestive tract
mouth, throat/pharynx, esophagus, stomach, small intestine, large intestine/colon, anus
accessory organs
teeth, salivary glands, pancreas, liver, gall bladder
mouth/oral cavity
- saliva secreted by salivary glands
-> moistens food
-> lubricates mouth
-> saliva contains lysozyme (antibacterial) and salivary amylase which digests starch - teeth cut, tear, crush and grind food which physically break down food into smaller pieces
throat/pharynx
- common gateway to the entrance of the trachea and esophagus
-> when we swallow food and drinks, epiglottis closes the opening of the trachea so food and drinks can enter the esophagus instead of trachea
esophagus
- muscular tube carrying food from throat to stomach
- behind the trachea
- once swallowed, food is propelled down esophagus into stomach within seconds by strong smooth muscular contractions called peristalsis
stomach
- muscular bag that can expand to 20x its original size
- holds up to 2L of food and gastric juice
- muscular stomach wall mixes and church food with acidic gastric juice
- stomach lining contains gastric glands which secret gastric juice
- protein digestion begins here
- pyloric sphincter acts like a valve to release small amounts of stomach content into small intestine
gastric juice components
- mucous (by mucous neck cells): coats and protects stomach lining from digestion by pepsin
- hcl (by parietal cells): converts pepsinogen to pepsin, inhibits salivary amylase, inhibits bacteria
- pepsinogen (by chief cells): precursor of protein, pepsin digests proteins
- hormones (e.g. gastrin; by endocrine cells): gastrin controls gastric juice secretion
excessive gastric juice secretion causes stomach ulcers because the corrosive action of hcl (pH 1-2) eats into the stomach wall.
small intestine
- major site for digestion and absorption
- abt 6m long
- 3 sections: duodenum 25cm, jejunum 2.5m, ileum 3.5m
how is the small intestine adapted for its function
- increase surface area for absorption
-> wall forms circular folds
-> villi, finger-like projections from the circular folds
-> S.I. epithelial cells possess microvilli - blood capillaries and lacteals run through the villi
-> capillaries transport amino acids and glucose to the liver
-> lacteal transports lipids to the lymphatic circulation
what is segmentation
- mixes food back and forth
- distribute food throughout the S.I. to ensure good absorption
- both directions
- only in small intestine
as compared to peristalsis which
- one direction
- esophagus to anus
large intestine
- 1.5m long
- caecum -> appendix attached to caecum, colon, rectum, anus (opening)
- absorbs remaining water, minerals and vitamins
- eliminates indigestible food as faeces
- many resident bacteria -> e. coli in colon provides host with vitamin K in return for nutrients and shelter, resident bacteria prevent harmful ones from colonizing
pancreas (ao)
- behind stomach
- secretes alkaline pancreatic juice into S.I. juice containing: amylase (starch), proteases (protein), lipases (lipid), bicarbonate (HCO3-) ion to neutralize HCL
- secrete hormone insulin and glucagon which regulate blood glucose levels
insulin: lower b.g.
glucagon: raises b.g
liver (ao)
- located on right side of the body under the diaphragm
- connected to the gall bladder
- absorbed monosac. and amino acids are transported from the small intestine to liver before delivery to rest of body
functions:
- produce bile which emulsifies fat
- detoxify drugs and toxins
- stores excess glucose as glycogen
gall bladder
- stores bile produced by liver
- bile is secreted into duodenum via bile duct
- bile aids in mechanical digestion of fats (emulsification)
