THE ORGANIZATION OF LIFE
Atoms form molecules, form cells, form tissues, form organs, form organ systems, and form the entire organism.
Atoms – smallest units of an element that retain the properties of the elements.
Molecules – units of two or more atoms of the same or different elements bonding together.
Cells – the basic structural and functional units of living things.
Tissues – similar cells in structures and function.
4 main types of tissue: muscle, nerve, epithelial, and connective.
Organs – discrete structures composed of more than one tissue that perform a specialized function.
Responsible for digestion and absorption.
Digestion – process which food is broken down into components small enough to be absorbed into the body.
Absorption – process of taking substances from the gastrointestinal tract into the interior of the body.
Break down foods into small pieces (digestion) enter blood stream/lymphatic system (absorption).
Sugars, amino acids, fatty acids can be absorbed into the body, but polysaccharides, proteins and lipids cannot (in the form they are
ORGANS OF THE DIGESTIVE SYSTEM
Gastrointestinal tract – a hollow tube, about 30 feet long, runs from mouth to anus. Also called the gut, GI tract, alimentary canal or digestive tract.
Lumen – inside of the tube.
Inside of lumen is layered with mucosal cells called mucosa.
DIGESTIVE SYSTEM SECRETIONS
Mucus – a viscous fluid secreted by glands in the digestive tract and other parts of the body.
Lubricates, moistens and protects the digestive tract.
Enzymes – crucial proteins which speeds up the rate of reaction in the digestive tract.
Condensation – brings two smaller molecules together to form a larger one, water is released.
Hydrolysis – uses water to break down larger molecules into smaller ones.
Chemical digestion: saliva
- Contains the enzymes:
Salivary amylase, which breaks down carbohydrates
Lingual lipase, which breaks down lipids
- Saliva also contains lysozyme, an antibacterial substance
- Water in saliva acts as a solvent
Mechanical digestion: use of tongue, teeth (32) to physically digest food.
Conduit for food and inspired air
Epiglottis – a piece of elastic connective tissue that covers the opening to the links during swallowing.
Lies between the pharynx and the esophagus/trachea.
- Directs food from the pharynx to the esophagus when closed.
- Directs air from the pharynx to the trachea (windpipe) when open.
Does not participate in digestion; conduit food
Food moved by peristalsis from the esophagus to the stomach.
Peristalsis – coordinated muscular contractions that move material through the GI tract.
Sphincter – a muscle that acts as a valve right at the entrance of the stomach from the esophagus.
The stomach has three layers of smooth muscle: longitudinal, horizontal and diagonal.
- Allows for optimal churning and mixing.
The pyloric sphincter at the bottom of the stomach controls how long food stays in the stomach.
Food is mixed with highly acidic stomach secretions to form chyme. (a semiliquid food mass)
Lining of stomach is covered with gastric pits that secrete gastric juice. CHAPTER 3
Water: acts as a solvent.
Mucus: protects lining of stomach from digesting itself.
Pepsinogen: converts to pepsin, digests protein.
Hydrochloric acid: denatures proteins, activates pepsin.
REGULATION OF STOMACH MOTILITY AND SECRETION
Chyme usually empties from the stomach to the small intestine within 2 to 6 hours.
Small, liquid meals empty more quickly than large, solid meals.
Carbohydrate-rich meals leave quickly, while fibre, protein rich meals and fatty meals stay longer.
The longer a meal stays in the stomach and the more it stretches the stomach, the more your hunger is controlled: mixed meals containing fibre
promote a feeling of fullness.
SMALL INTESTINE (SI)
Narrow 20 foot tube.
Majority of digestion and absorption occurs here,
3 segments: duodenum (25-30cm), jejunum (1.2m) and the ileum (1.5m),
Massive surface area.
- Long length.
- Various folds (villi, microvilli).
- About the size of a tennis court.
SECRETIONS FOUND IN THE SI
- Pancreatic amylase: converts starches into sugars
- Bicarbonate: neutralize chyme
- Pancreatic protease: protein-digesting enzymes
- Lipases: break down lipids into fatty acids.
SI intestinal enzymes
- Aid digestion of disaccharides (double sugars) and short amino acids.
- Secretes bile (made in liver, stored here) into the SI.
- Bile helps emulsify fats.
After food has been digested into small subunits, it can now be absorbed into either the blood (small carbs, amino acids) or the lymphatic system
(larger molecules, larger lipids).
Depending on the nutrient, it is absorbed in one of the following ways:
Simple diffusion – unassisted diffusion of a substance across the cell membrane.
Osmosis – unassisted diffusion of water across the cell membrane.
Facilitated diffusion – assisted diffusion of a substance across the cell membrane.
Active transport – transport of substance across a cell membrane with the aid of a carrier molecule and the expenditure of energy.
Approx. 5 feet long.
Peristalsis is slower here than in SI
Intestinal microflora = native bacteria which promote digestion
Unabsorbed matter is packaged into feces for excretion
Fibre and fluid rich diets promote more water in feces (easier to excrete).
THE DIGESTIVE SYSTEM AND DISEASE PREVENTION
Most food contains bacteria (pathogens).
- Actions of the Digestive Tract + immune system help us minimize infection and prevent its symptoms.
- Ex. Mucosa of small intestine contains peyer’s patches, lymph nodules that are part of the immune system.
Mostly found in ileum.
When an absorbed foreign antigen enters the mucosa, the cells in peyer’s patches will recognize it as foreign.
- Then, various immune cells help eliminate the pathogen
Ex. Phagocytes (“eaters”).
o T lymphocytes kill infected cells directly and regulate/assist the immune response.
o B lymphocytes secrete antibodies – surround foreign organisms and promote excretion.
Antibodies are specific for each antigen. CHAPTER 3
DIGESTIVE HEALTH: BACTERIA IN THE LARGE INTESETINE
300-500 species of bacteria in large intestine
Contribute to immune functions, growth and development of colon cells, intestinal motility/transit time, digestion, prevention of diarrhea (with
Probiotic: living organisms (typically bacteria).
Prebiotic: a dietary fibre that promotes the growth of healthy intestinal bacteria.
Occurs when immune system triggers an immune response to an allergen, a protein present in our diet or environment.
- Ex. Nuts, eggs, milk, seafood protein.
- Ex. Gluten found in wheat, barley or rye.
Symptoms of the response may include: tingling mouth, vomiting, intestinal pain, blood pressure drops, hives, breathing difficulties.
Best strategy is to avoid the food altogether.
Heart burn = gastroesophageal reflux.
- Occurs when acidic stomach contents leak back, past the lower esophageal sphincter, into the esophagus.
If it occurs 2+ times per week, may become gastroesophageal reflux disease (GERD).
- Can lead to bleeding, ulcers and cancers.
MINIMIZING RISK FOR GERD, HEART BURN
Reduce volume of stomach during meals, reduce stomach acidity or promote gastric emptying.