Digestion, Absorption & Transportation Flashcards
Provide the origin, target, response, enzymes, and action of the hormone gastrin.
Provide the origin, target, response, enzymes, and action of the hormone secretin.
Provide the origin, target, response, enzymes, and action of the hormone Cholecystokinin (CCK).
Provide the origin, target, response, enzymes, and action of the hormone Gastric Inhibitory Peptide (GIP).
How are carbohydrates absorbed and transported?
How are lipids absorbed and transported?
How are proteins absorbed and transported?
Define: digestion
- mechanical and chemical processes that transform foods into nutrients ready for absorption.
Define: absorption.
- uptake of nutrients into intestinal (absorptive) cells for transport into either the bloodstream or the lymph
- Macronutrients have been digested to basic building blocks
- Vitamins and minerals are freed from food components, absorbed intact
- Trillions of molecules of CHO, PRO, FAT, vitamins and minerals need to be absorbed following a meal – requires an efficient system
- Majority of absorption occurs in Duodenum and Jejunum
Define: transportation (w.r.t. digestion & absorption)
- movement of nutrients to body cells for metabolic use
What is the Gastrointestinal tract?
- long flexible, muscular tube from mouth to anus
What are the major organs in the G.I. tract?
-
Mouth
* muscles in mouth surface area of food -
Stomach
* ~ 1 litre capacity § pH ~1.7-1.5 -
Small intestine
* ~2.5 cm diameter, 300 cm length -
Large intestine (colon)
* ~4 cm diameter, 150 cm length
What are the accessory organs in the G.I. tract?
-
Liver
* produces bile – consists of bile salts, pigments, lecithin, cholesterol, water -
Gall bladder
* stores bile -
Pancreas
* secretes pancreatic juices into small intestine
What are the 5 types of muscle action in the G.I. tract?
-
Chewing
* breaks food apart, increases surface area of food -
Peristalsis
* longitudinal, wave-like muscular contractions that propel food along GI tract - Stomach churning
- strongest muscles of GI tract found in stomach
- mixing, churning stomach contents, breaking large pieces into smaller pieces
-
Segmentation
* cinching of muscles to break up food within a particular region of the GI tract -
Sphincter control
* valves that control movement of food along GI tract § found at junctions between major organs of GI tract
How many muscle layers does the G.I. tract have?
- 2 layers of muscle all along GI tract, except stomach has 3 layers
- longitudinal outer layer, circular inner layer
- diagonal innermost layer for stomach only
What are the three layers of muscle in the stomach?
Define: chyme
- particle of food suspended in liquid
What is peristalsis?
The small intestine has two muscle layers that work together in peristalsis and segmentation.
- Circular muscles are inside.
- Longitudinal muscles are outside.
What is segmentation?
Define: hormone
- substance produced at one site in body in response to a specific stimulus
- travels in blood to different site (target organ)
- elicits a response there
What are characteristics of enzymes?
- a protein catalyst that accelerates rates of reactions without being changed or consumed in the process
- synthesis, degradation, rearrangement and exchange reactions
- lock and key fit with substrate to produce end product
- ‘ase’ suffix, although not for all enzymes
- active and inactive (pro-enzyme) forms
What directs the chemical action in the G.I. tract?
In addition to muscle (mechanical) action on food in the GI tract, there is chemical action under the direction of hormones and performed by enzymes
What are the four main types of digestion hormones, where are they produced, and what tissues do they target?
Describe basic enzyme action.
What are the basic reactions for nutrient handling?
1. Hydrolysis (digestion)
- requires water
- catabolic, breakdown
- ex., sucrose digestion
2. Condensation (synthesis)
- releases water
- anabolic, synthetic
- ex., protein synthesis
3. Reduction/Oxidation
- gain (reduction) or loss (oxidation) of electron
- ex., iron absorption
What are the salivary glands?
- parotid glands, serous, watery secretion
- sublingual glands, mucus secretion
- submaxillary (mandibular) glands, mixed serous and mucus secretion
Describe digestion that occurs in the mouth.
A. Chewing
- bigger → smaller pieces
- increased surface area, increased efficiency of digestion
B. Fat melts
- warming up to body temperature
C. Mixing with saliva
- Salivary juices secreted by glands in mouth contain: water, digestive enzymes (salivary amylase), and R-factor (protein) necessary for vitamin B-12 absorption.
What are the functions of salivary juices?
- moistens, lubricates, and softens food
- stimulates taste buds
- initial dilution of food to make it isotonic with blood
- start of carbohydrate digestion through action of salivary amylase
- slows development of dental caries
- contains lysozymes which kill bacteria that enter mouth
Define: bolus
- bolus travels past the epiglottis and down the esophagus (peristalsis, gravity, lubrication) to enter stomach
- once a mouthful of food is swallowed, it is called a bolus
Describe how a person swallows.
What is choking?
How does the sphincter prevent backflow of acidic stomach content into near-neutral esophagus?
When the circular muscles of a sphincter contract, the passage closes; when they relax, the passage opens.
What are the chemical secretions made in the stomach?
- G cells: secrete the hormone gastrin from pyloric region
- Mucous-secreting cells: secrete an alkaline mucus; thick layer protects the stomach wall against shear stress and acid damage
- Parietal cells: secrete hydrochloric acid & intrinsic factor (IF)
- Chief cells: secrete pepsinogen pepsin, a proteolytic enzyme