Digestion, Absorption and Transport Flashcards
What is digestion?
the breaking down of foods into nutrients, in preparation for absorption
What is the GI?
The gastrointestinal tract - a flexible muscular tube that extends from the mouth, through the oseophagus, stomach, small intestine, large intestine and rectum to anus.
What is the lumen?
the inner space within the GI tract
Explain what happens in the mouth in digestion
Chewing (mastication), salivary glands help create bolus
Pushed down pharynx, a short tube.
To bypass entrance to lands, epiglottis closes off air passages
Explain what happens in the osephagus ?
Sphincter muscle at each end.
During swallow, upper sphincter opens, bolus slides down to stomach.
Lower sphincter closes to avoid reflux.
Explain what happens in the stomach
Stomach retains bolus in upper portion, then gradually transfers food to lower portions.
Stomach acid and muscles grunt it - creates chyme.
Gradually released through pyloric sphincter - opens into the small intestine
What happens in the small intestine?
Chyme pay passes the opening from common bile duct, which drips fluids from gall bladder and pancreas
Chyme travels down through 3 segments of small intestine - duodenum, jejunum, ileum
What happens in the large intestine (colon)?
Sphincter opens - ileocaecal valve (lower right side of abdomen)
Passes another opening into the appendix.
Goes left to right, then above rectum
Dietary fibre (fat, cholesterol, minerals, water) enters colon. Intestinal bacteria ferments some of it, producing water, gas, small fragments of fat that provides energy for cells of colon
What happens at the anus/rectum?
As intestinal contents pass to rectum, colon withdraws water, leaving semi-solid waste
Two sphincters in anus open when you decides to defecate.
What are the two layers of muscles in the GI tract?
Segmentation - inner circular muscles contract and relax. Occurs in small and large intestines (churn chyme, mixing secretions)
Peristalsis - outer longitudinal muscles contract rhythmically to move chyme forward. Contractions occur at varying rates and intestines. Stress, drugs illness interferes
How does bulk get added to stools?
Dietary fibre - as it is undigested and retains water
Explain the muscles in the stomach
Thickest walls and strongest muscles of GI tract
Third layer of muscles - diagonal.
Explain the all sphincter contractions in the GI tract
Upper osephaegal sphincter - opens in response to swallowing
Bottom oseophaegal sphincter - prevents reflux
Pyloric sphincter - holds chyme in, prevents intestinal contents from backing up into stomach
End of small intestine - ileocaecal valve, allows small intestine to empty into large
Rectal muscle - prevents elimination until chosen
What is an enzyme?
A protein that facilitates a chemical reaction
What does saliva do?
Protects teeth and linings of mouth, osephagus and stomach from harmful substances
Moistens mouthful of food, contains water, salts, mucus and enzymes
Initiates digestion of carbs
What does gastric juice do?
Gastric glands secret gastric juice, extremely acidic (prevents bacterial growth)
Contains water, enzymes and hydrochloride acid
Breaks down bolus into chyme
What are the three digestive enzymes?
amylase (digest carbs)
Lipase (digests fats)
Protease (digest proteins)
What does pancreatic lipase do?
Pancreas contributes digestive juices through ducts leading into duodenum (small intestime)
Pancreatic juice - enzymes that act on all energy nutrients (also cells of intestinal wall)
Bicarbonate (alkaline) neutralising acidic chyme
What does bile do?
An emulsifier - brings fat into suspension in water, so enzymes can break it down
Liver produces bile, then concentrated and stored in gall bladder
Squirted into duodenum of small intestine when fat arrives
How does the GI tract absorp nutrients?
Small intestine engulfs and absorbs the nutrient molecules
Rush of cumulating blood continuously washes underside of surface - quickly carrying away to other parts of body
Name the anatomy of the absorptive system
Villi - inner surface, constant motion, recognises nutrients needed to body.
Microvilli - cells, traps small nutrients
Crypts - crevices between villi, secrete intestinal juices
Goblet cells - secrete musics
Does the GI tract absorb nutrients all in one place?
No, nutrients ready for absorption are absorbed near top of GI tract, those that take longer are absorbed further down
What happens when a nutrient molecule has crossed the cell of villus?
It enters the bloodstream or lymphatic system
How does the body react to water-soluble nutrients compared to fat-soluble nutrients?
Water soluble - Releases directly into the liver
Fat soluble - intestinal cells assemble products of fat digestion into larger molecules. They cluster with special proteins called chlyomicrons
These are release into lymphatic system
Moves through lymph until they enter bloodstream near heart (bypasses liver initially)
What is the circulatory systems role in the absorption of nutrients?
it delivers the nutrients to wherever they are needed
Explain the vascular system
HEART - ARTERIES - CAPILLARIES - VEINS - HEART
Blood leaves right side of heart, circulates through lungs, back into left side of heart
Left side pumps blood out of aorta through arteries to all systems of body
Blood circulates in capillaries, exchanges materials with cells then collects into veins
Blood leaving digestion system goes by hepatic portal vein, directs blood to liver
What does the liver do?
first to receive nutrients - major metabolic organ.
Defends body by detoxifying harmful substances and preparing waste products for excretion
What is the lymphatic system?
One way route for fluid from tissue spaces to enter the blood.
Lymph circulates between cells of body, collects in theocratic duct behind heart, opens int subclavian vein - where lymph entrees blood stream
Nutrients from GI tract enter lacteals (lymphatic vessels) that circulate nutrients in blood stream (but bypass liver)
What is the gastrointestinal microbiome?
Defines the health of the GI tract - home to 100 trillion microbes (bacteria, viruses, fungi, Protozoa, etc - 400+ species)
Persons health reflects stability, disturbance and resilience of microbiome - dramatically respond to diet
What is homeostasis?
The body regulating itself to have the same conditions (temp, blood pressure etc
What do prebiotics and probiotics do?
prebiotics - encourages growth the activity of bacteria (reduces risk of infection, disorder, increases bioavailability of nutrients)
Probiotics - feeds live microbes that improves health of GI tracts (alleviates IBS like symptoms, ulcers, enhances immune function)
What does the hormone gastrin do?
Responds to food in stomach, secreted from stomach wall - hydrochloric acid maintains an acidic pH balance
What does the hormone secretin do?
responds to the acidic chyme in the small intestine, secreted from duodenal wall
Bicarbonate rich juices secreted into small intestine maintain slightly alkaline pH
What does hormone cholecystokinin do?
Responds to fat/protein, secreted from intestinal wall
Bile emulsifies fats, maintains pH, digest fats and proteins and slow GI tract motility
What are some factors that impact the GI tract?
Healthy supply of blood (inflamed without)
Sleep (repairs tissue, removes waste)
Activity (promotes healthy muscle tone)
Stress (alters GI motility)
Relaxed mealtimes (eases digestion)
Balance (i.e. some fats beneficial to slow GI motility, more absorption time)
Variety - some food constituents interfere with nutrient absorption
Adequacy (all nutrients interdependent)
What do the macronutrients create?
Carbs - glucose
Fats - single fatty acids
Protein - amino acids
