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BIOL1046 Human Biology II > Unit 9: The Digestive System > Flashcards

Unit 9: The Digestive System Flashcards

1
Q

Nutrients and Nutrient Sources

Nutrients

A
  • Required for snythesis of new molecules
  • Required for energy for maintenance, growth, and repair
  • Obtained through food
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2
Q

Nutrients

Classification of Nutrients

A

Macronutrients
- Carbohydrates, lipids, proteins (water)
- Must be consumed in relatively large quantities
Micronutrients
- Vitamins and minerals
- Must be consumed in relatively small quantities
Essential
- Must be obtained and abdorbed via digestive system from diet
Nonessential
- Provided by biochemical processes of body
- Not required in diet

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3
Q

Macronutrients

Provide Fuel for Cellular Respiration

A
  • All macronutrients provide fuel for cellular respiration to form ATP (that is, they provide energy)
  • Macronutrient in the sense that it is required in large quantities
  • Micronutrient is the sense that it does not provide energy
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4
Q

Macronutrients

Energy Measure

A
  • This energy is measure in calories
  • 1 calorie = the maount of heat required to raise the temperature of 1 g of water by 1 C
  • Kilocalorie = 1000 calories, 1 Calorie (note: Capital C)
  • Food packaging indicated kilocalories - read the label and noitce that it tells you one serving has “110 Cal”
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5
Q

Macronutrients

Energy Balance

A
  • Body weight is maintained when calories consumed and calories expended are equal
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6
Q

Carbohydrates

Structural Classification

A
  • Monosaccharides (glucose, fructose, galactose), Disaccharides (sucrose), Polysaccharides (starch, glycogen)
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7
Q

Carbohydrates

Dietary Classification

A

Sugars, starch, fibre

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8
Q

Carbohydrates

Sugars and Starch

A

Usually converted to glucose by gluconeogenesis (hence glucose is NOT an essential nutrient)

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9
Q

Carbohydrates

Fibre

A
  • Cannot be chemically digested and absorbed by GI tract
  • Adds bulk, stimulates peristalsis (“keeps you regular”), and lowers cholesterol
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10
Q

Carbohydrates

Dietary Sources

A

Sugars
- Sucrose (table sugar, syrup, fruits, brown sugar, honey, molasses)
- Lactose (milk sugar)
- Maltose (grains - barley, wheat, corn)
Starch
- Polysaccharide polymer of glucose molecules - found in tubers, grains, beans and peas
- Refined straches sometimes added as thickeners or stabilizers - e.g. cornstrach
Fibre
- Includes fibrous molecules of both plants and animals
- Sources; Lentils, peas, beans, whole grains, oatmeal, berries, nuts

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11
Q

Lipids

Triglycerides

A
  • Stored in adipose tissue
  • Composed of glycerol and fatty acids
  • Fatty sacids organized inot 3 categories;
    Saturated Fatty Acids
  • No double bond
  • Sources are solid at room temperature
  • Dietary sources: Fat in meat, milk, cheese, coconut oil, palm oil
    Unsaturated Fatty Acids
  • One double bond
  • Sources are liquid at room temperature
  • Dietary Sources: nuts, certain oils - canola oil, olive oil, sunflower oil
    Polyunsaturated Fatty Acids
  • Two or more double bonds
  • Sources are liquid at room temperature
  • Dietary sources: certain oils - soybean oil, corn oil, safflower oil
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12
Q

Lipids

Phospholipids

A
  • Very abundant in the human body
  • Main component of plasma membranes
  • Phosphate head and two fatty acid tails
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13
Q

Lipids

Steroids

A
  • Hormones that act directly on transcription in the nucleus
  • Most are produced in the body and do not come from the diet
  • Reproductive hormones (testosterone, estrogen, progesterone)
  • Aldosterone, cortisol
    Cholesterol
  • Required as component of plasma membrane
  • Precursor hormone for steroid hormones, bile salts, vitamin D
  • Comes from diet or metabolic pathway in liver
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14
Q

Lipids

Eicosanoids

A
  • locally acting “hormones”
  • e.g. prostaglandins for inflammation
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15
Q

Proteins

A

Most structurally and functionally diverse molecules
Needed in adequate quantities to replace worn out protein structures
- Amount needed depends on age and sex
- More needed to fight an infection, following an injury, stressful conditions, pregnancy
- Infants and children also need more for growth
Source of nitrogen
- Need for synthesizing nitrogen-containing molecules like DNA, RNA and ATP, among others
No storage of excess, so must be consumed regularly
9 amino acids are essential, other 11 can be synthesized in the body

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16
Q

Proteins

Complete Proteins

A

Contain all 9 essentail amino acids
Dietary sources:
- Animal proteins (meat, eggs, milk, cheese, fish)
- Very few plant proteins (quinoa, soy beans, amaranth, buckwheat, potatoes, corn) - although some of the amino acids are in very low quantities in these foods

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17
Q

Proteins

Incomplete Proteins

A

Do not contain all essential amino acids
Dietary sources:
- Plant proteins (especially legumes, grains)
- Combinations of fruits and vegtables containing different plant proteins can provide all essential amino acids

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18
Q

Water

A

Required for all of life’s processes
- Diffusion of ions into and out of cells
- Hydrolysis of large molecules
- Maintaining the volume of cytoplasm in cells
- Providing the matrix (ground substance) for blood - blood plasma
- Moistening air for diffusion of oxygen into the blood stream
- Comprises the interstitial fluid

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19
Q

Micronutrients

A
  • Micronutrients acts co-factors in chemical reactions in the body
  • Consumed in small quantities - present in small amounts in food
  • Some can be stored in the body while others must be consumed regularly as excess is excreted
  • The micronutrients are vitamins and minerals
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20
Q

Vitamins

A
  • Organic molecules required for normal metabolsim
  • Sources: largely obtained from fruits and vegetables and some grains
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21
Q

Vitamins

Water-Soluble Vitamins

A

Easily absorbed into blood from digestive tract
Excess excreted in urine
Vitamins B (many variats - B6, B12, niacin, riboflavin, etc.), C
Functions:
- B vitamins serve as coenzymes
- Vitamin C required for collagen synthesis; antioxidant

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22
Q

Vitamins

Fat-Soluble Vitamins

A

Abdorbed from GI tract within micelles
Excess stored in fat
May become toxic if taken in excess
Vitamins A, D, E, and K
Functions:
- Vitamin A, precursor of visual pigment retinal
- Vitamin D, forms calcitriol, increases calcium absorption from GI tract
- Vitamin E, stabilizes and prevents damage to cell membranes
- Vitamin K, required for synthesis of blood clotting proteins

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23
Q

Vitamins

Essential Vitamins

A
  • Necessary from diet
  • Deficiency if intake or absorption is impaired
  • Some foods are fortified by adding essential nutrients (vitamins, minerals) - e.g. vitamin D added to milk
  • Vitamins A, B (all), C, D, E, K
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24
Q

Vitamins

Nonessential Vitamins

A
  • Cofactors produced and recycleed by the body as needed
  • Variations of vitamins B (NADH, FADH2), K(K2), D (synthesized in skin with exposure to UV radiation - sunlight)
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25
Q

Minerals

A
  • Inorganic ions obtained from diet
  • All minerals are essential and must be obtained from the diet
  • Required in daily amounts
  • Obtained by eating a variety of foods (animal and plant products)
  • Stored to varying degrees within the body
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26
Q

Minerals

Major Minerals

A
  • > 100 mg/day required
  • e.g. calcium, chlordie, potassium, phosphorus, magnesium, etc.
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27
Q

Minerals

Trace Minerals

A
  • < 100 mg/day required
  • e.g. chromium, copper, iodine, iron, zinc, etc.
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28
Q

Minerals

Functions of Some Minerals

A

Iron
- In hemoglobin, binds oxygen
- In mitochondria, in electron transport system binds electrons
Calcium
- Required for formation and maintenance of skeleton and muscle contraction, blood clotting, and exocytosis of neurotransmitters
Sodium and Potassium
- Maintain resting membrane potential in excitable cells
- Required to generate action potential
Iodine
- Needed to produce thyroid hormone
Zinc
- Roles in protein synthesis and would healing

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29
Q

General Functions of the Digestive System

Overall Functions of the Digestive System Include:

A
  • Breaking down nutrients
  • Absorbind nutrients
  • Removing undigested wastes
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30
Q

Functional Classification of Digestive Organs

Gastrointestinal (GI) Tract Organs

A

Form a continuous tube lined with a mucous membrane
Food passes through the lumen (inner opening) of these organs, and is broken down into smaller components to be absorbed
Includes:
- Oral cavity and pharynx
- Esophagus and stomach
- Small intestine, large intestine, rectum and anus

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31
Q

Functional Classification of Digestive Organs

Accessory Digestive Organs

A

Assist in breakdow of food - food does not pass through these
Includes:
- Salivary glands, liver, pancreas - produce serections that empty into the GI tract
- Teeth and tongue - participate in chewing and swallowing
- Gallbladder - concentrates and stores liver secretions

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32
Q

Structura Classification of Digestive Organs

Upper Gastrointestinal Tract Organs

A

Organs up to and including the duodenum (first part of small intestine)
Includes:
- Oral cavity
- Teeth
- Tongue
- Pharynx
- Salivary glands
- Esophagus
- Stomach
- Duodenum

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33
Q

Structual Classification of Digestive Organs

Lower Gastrointestingal Tract Organs

A

Beings at duodenum and continues to anus
Includes:
- Liver
- Pancreas
- Gallbladder
- Small Intestine
- Large intestine
- Rectum
- Anus

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34
Q

Six Digestive Processes

1.Ingestion

A
  • Introduction of soild and liquid nutrients into the oral cavity
  • First step in proces of digesting and absorbing nutrients
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35
Q

Six Digestive Processes

2.Motility

A
  • Voluntary and involuntary muscular contractions
  • Mixing and moving materials through GI tract - Peristalsis
  • Throughout entire digestive tract (mouth, esophagus, stomach, intestine, rectum, anus)
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36
Q

Six Digestive Processes

3.Secretion

A
  • Process of producing and releasing fluid products facilitating digestion
  • For example, digestive enzymes (mouth, stomach, pancreas), acid (stomach), bile (liver)
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37
Q

Six Digestive Processes

4.Digestion

A

Breakdown of ingested food into smaller strcutures
Mechanial digestion
- Material physcially broken down by chewing and mixing
- Mouth - mastification, stomach - churning, small intestine - segmentation
Chemical digestion
- Involves specific enzymes to breakl chemical bonds, breaking complex molecules into smaller molecules
- Begins in mouth (salivary amylase), continues to stomach (pepsin added) and small intestine (addition of pancreatic amylase, lipase - from pancreas)

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38
Q

Six Digestive Processes

5.Absorption

A
  • Transport of digested molecules from GI tract into blood or lymph
  • Some simple sugars and pharmaceuticals in mouth (very little absorption)
  • Some pharmaceuticals in stomach (very little absorption)
  • Most nutrients in small intestine
  • Water in large intestine
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39
Q

Six Digestive Processes

6.Elimination

A
  • Exulsion of indigestible components that are not absorbed
  • Storage in rectum, expulsion through anus
  • NOTE: faeces is not metabolic waste - it is the remainder of food that was never absorbed
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40
Q

Oral Cavity (Mouth)

A
  • Mechanical digestion begins
  • Saliva secreted contains salivary amylase, enzyme initiaing digestion of starch
  • Saliva mixed with ingested materials to from bolus
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41
Q

Oral Cavity (Mouth)

Lips

A

Help move ingested material into mouth

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42
Q

Oral Cavity (Mouth)

Teeth

A
  • Cut ingested material to managable size
  • Responsible for mastication (chewing) - crushing and grining food
  • 32 permanent teeth in adult mouth (2o deciduous (baby) teeth - molar have no deciduous predeccors)
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43
Q

Oral Cavity

Mastication (Chewing)

A
  • Mechanically reduces bulk to facilitate swallowing
  • Increases surface area of food to facilitate exposure to digestive enzymes
  • Promotes salivation
  • Requires coordinated activities of teeth, lips, tongue, cheeks, jaws
  • Controlled by nuclei in medulla and pons, mastication center
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44
Q

Oral Cavity

Tongue

A
  • Primarily from skeletal muscle, with extrinsic and intrinsic muscles
  • Numerous projections, papillae, involved with taste
  • Manipulates and mixes materials during mastication (chewing)
  • Important functions in deglutition (swallowing) and speech
  • Froms the anterior wall of the oropharynx
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45
Q

Oral Cavity

Salivary Glands

A

Exocine glands (have ducts)
Produce Saliva
- 1.0 to 1.5 L secreted daily, most during mealtime
- 99.5% water and a mixture of solutes
Functions of Saliva:
- Moistens ingested food to help become bolus
- Salivary amylase initiates chemical breakdown of starch
- Food molecules dissolved here to taste receptors stimulated
- Cleanses oral cavity strucutres
- Antibacterial substances inhibit bacterial growth (lysozyome, LgA antibodies)

46
Q

Oral Cavity

Absorption

A

In general, there is very little absorption in the oral cavity
Exceptions:
- Medications composed of small, nonpolar molecules (for example, nitroglycerin) can be placed under the tongue where they pass through the epithelium by simple diffusion
- Very small carbonhydrate molecules (monomers - e.g. fructose, dimers - e.g. sucrose)

47
Q

Pharynx

A
  • Located posterior to oral cavity
  • 3 sections: nasopharynx, oropharynx, laryngopharynx
  • Food bolus is moved to pharynx during swallowing
  • Mucus secreted to facilitate swallowing
48
Q

Pharynx

Esophagus

A

Normally collapsed, tubular passageway directly anterior to vertebral bodies
Tranports bolus from pharynx into stomach by peristalsis
- Peristalsis: involuntary wave-like contractions of smooth muscle around a hollow organ (e.g. intestines, ureters, etc.)
Bolus is lubricated my mucus secretions

49
Q

Esophagus

Superior Esophageal Sphincter

A
  • Contracted rinf of circular skeletal muscle at superior end
  • Area where esophagus and pharynx meet
50
Q

Esophagus

Inferior Esophageal Sphincter

A
  • Contracted ring of circular skeletal muscle at inferior end
  • Not strong enough by itself to stop stomach contents from regurgitating; diaphragm muscles helpn
51
Q

Oral Cavity - Deglutition

Three Phases of Deglutition (Swallowing)

A

Voluntary phase
- Bolus of food pushed by tongue towards oropherynx
- Pushed against hart palate to propel food backwards
Pharyngeal phase
- Soft palate and uvula elevate closing off the nasopharynx
- Larynx elevates so epiglottis closes over laryngel inlet
Esophageal phase
- Involuntary phase when bolus passes through esophagus
- Bolus stimuklates sequential waves of muscular contraction
- Propels bolus toward stomach
- Superior and inferior esophageal sphincters closed at rest
- Relax when bolus swallowed
- Contract again afterwards, preventing felux of materials

52
Q

Gastrointesinal Tract - Motility

Muscularis

A

Thickened at several points to form a sphincter
- Closes off the lumen
- Controls movement of materials into next section of GI tract
- e.g. inferior esophgeal sphincter

53
Q

Gastrointestinal Tract - Motility

Propulsion (Peristalsis)

A
  • Directional movement of materials through GI tract
  • Occurs by peristalsis: sequentual contraction of muscularis, GI tract wall moves like a wave
54
Q

Stomach

A

After deglutition, the food bolus reaches the stomach
Digestion or protein and fat begins in stomach
Ingested materials spend 2 to 6 hours here
Absorption limited to small, nonpolar substances
Serves as “holding bag” for controlled release of partially digest material
Stomach motility performs two primary functions
- Mixing the bolus to from chyme (gastric mixing)
- Emptying chyme from stomach to small intestine (gastric emptying)

55
Q

Stomach Structure

Muscularis

A

Three layers of smooth muscle
- Longitudinal layer (runs along the length)
- Circular layer (runs around the circumference)
- Oblique layer (runs diagonally)
- All 3 layers contract to chrun and grind the food bolus and mix it with gastric secretions
Two sphincters to close off the lumen
- Gastroeosphogeal sphincter (inferior esophpgeal sphincter) prevents reflux of stomach secretions into esophagus
- Pyloric sphincter controls movement of materials into next section of GI tract

56
Q

Stomach Structure

Gastric Folds (Rugae)

A

Fon internal stomach lining when stomach empty
- Allow stomach to expand greatly when it fills with food
- Returns to normal when empty

57
Q

Stomach Structure

Secretory Cells

A

Epithelial cells of stomach lining

58
Q

Stomach Structure

Mucous Cells

A

Line stomach lumen
Continuously secrete alkaline product containing mucin
Functions of mucous:
- Mucous layer helps to prevent ulceration of stomach lining
- Protects from gastric enzymes and high acidity
- Help protect the stomach lining from abrasion and injury (lubrication)

59
Q

Stomach Structure

Parietal Cells

A

Secrete hydrochloric acid (6 M)
Functions of hydrochloric acid:
- Helps break down plant cells walls and animal connective tissue
- Denatures proteins, facilitating chemical digestion
- Converts inactive enzyme pepsinogen into active pepsin
- Kills most microorganisms entering stomach

60
Q

Stomach Structure

Chief Cells

A
  • Produce pepsinogen (inactive precursor of pepsin)
  • Produce gastric lipase (plays limited role in fat digestion - ca. 10%)
  • Functions of pepsin and lipase discussed later
61
Q

Stomach Functions

Gastric Mixing

A

Form of mechanical digestion
Squeezes and grinds food bolus to break it down
Mixes food bolus with stomach secretions (hydrochloric acid, mucous, enzymes) through smooth muscle contractions
- Changes semi-digested bolus into chyme
- Churns and mixes, leading to reduction in size of swallowed particles
Very little chemical digestion in the stomach
- Denaturation of protein by HCI
- Very little hydrolysis as pepsinogen becomes activated to pepsin

62
Q

Stomach Functions

Gastric Emptying

A

Movement of acidic chyme form stomach into duodenum
Pressure gradient moves contents toward pylorus
Gradient increases force against plyloric sphincter
Sphincter opens, with enterance of small volume of chyme
Sphincyter closes, with retropulsion
- Reverse flow of some contents back toward stomach

63
Q

Lower GI Tract

Organs of the Lower Gastrointestinal Tract

A
  • Continue process of digestion and absorption
  • Eliminate indigestible and unabsorable material
64
Q

Lower GI Tract

Accessory Digestive Organs

A
  • Liver: secrete bile
  • Pancreas: secretes pancreatic juice (containing digestive enzymes)
  • Gallbladder: stores biles secreted by liver
65
Q

Lower GI Tract

Small Intestine

A
  • Divided into 3 continuous regions
  • Duodenum, part of upper GI tract
  • Reveives chyme from stomach mixed with accessory organ secretions
  • Most chemical digestion and absorption happens here
66
Q

Lower GI Tract

Large Intestine

A
  • Absorbs water, electrolytes, some vitamins
  • Feces produced and eliminated through anus
67
Q

Digestive Accessory Organs

Liver

A
  • Accessory digestive organ
  • Largest internal organ
  • Right upper quadrant of abdoment immediately inferior to diaphragm
  • Main Digestive Function: production and secretion of bile
68
Q

Digestive Accessory Organs

Bile

A

Secreted by liver; no digestive enzymes
Contains: water, bicarbonate ions, bile salts, and pigments, cholesterol, lecithin, mucin
Bile salts and lecithin help emulsify lipids
- Act like a detergent to form micelles around lipid droplets
Does NOT contain digestive enzymes (no chemical digestion)

69
Q

Digestive Accessory Organs

Gallbladder

A
  • Saclike organ attached to inferior surface of liver
  • Connected to common bile duct by cystic duct
  • Stores, concentrates, and releases bile produced in liver
70
Q

Digestive Accessory Organs

Pancreas

A

Retroperitoneal organ that extends horizontaly from left lateral edge of duodenum
Endocrine function
- Produces and secretes insulin and glucagon
Exocrine function
- Produces pancreatic juice to assist with digestive activities

71
Q

Digestive Accessory Organs

Pancreatic Juice

A

Formed from secretions of acinar cells and pancreatic duct cells
Alkaline fluid
Mostly water, HCO3-, digestive enzymes
- Pancreatic amylase to digest starch
- Pancreatic lipase to digest triglycerides
- Inactive proteases that digest proteins when activated
- Nucleases for digestion of nucleic acids
Enzymes produced in the pancreas aren’t activated until they reach the small intestine (Duodenum)

72
Q

Accessory Organ Ducts

Biliary Apparatus

A
  • Network of ducts draining left and right lobes of liver
  • Include left and right hepatic ducts
  • Merge to from single common hepatic duct
  • Merges with cystic duct from gallbladder to from common bile duct
  • Extends inferiorly to the duodenum
73
Q

Accessory Organ Ducts

Accessory Pancreatic Duct

A
  • Small amount of pancreatic juice entering duodenum
  • Penetrates duodenal wall at minor duodenal papilla
74
Q

General Structure of Intestines

Muscularis

A

Lower GI tract has 2 layers of smooth muscle
- Longitudinal layer
- Circular layer
Thickened muscularis forms sphincters
- Closes off the lumen
- Controls movement of materials into next section of GI tract

75
Q

General Structure of Intestines

Functions of Muscularis

A

Propulsion
- Directional movement of materials through GI tract
- Occurs by peristalsis: sequential contraction of muscularis, GI tract wall moves like a wave
Segmenttation
- “Backward-and-forward” motion that lacks directional movement
- Blends ingested materials with secretions

76
Q

General Structure of Intestines

Mucose

A

Inner-lining mucous membrane
Epithelium is in contact with lumen contents
- Simple columnar epithelium allowing for secretion and absorption
- Portions that must withstand abrasion (that is, esophagus) are lined by nonkeratinized, stratified sqamous epithelium
Underlying lamina propria
- Composed of areolar tissue, small blood vessels, and nerves
- Absorption occurs when substances move into these vessels
Smooth muscle deep to lamina propria: muscularis mucosae
- Contrations facilitate release of secretions into lumen, increase contact of materials with mucosa

77
Q

Small Intestine

A
  • Receives chyme from stomach
  • Ingested nutrients reside in small intestine at least 12 hours
  • Absorbs most nutrients and large percentage of water, electrolytes, and vitamins - by diffusion ascross the epithelial membrane
78
Q

Structures of the Small Intestine

Circular Folds

A
  • Internal of mucosal and submucosal tunics of small intestine
  • Increase surface area to increase nutrient absorption
  • “Speed bumps” to slow movement of chyme
79
Q

Structures of the Small Intestine

Smooth Muscle

A
  • Mixes chyme eith gland secretions (segmentation)
  • Moves chyme against new areas of brush border
  • Propels contents through small intestine by peristalsis
80
Q

Structures of the Small Intestine

Intestinal Glands

A
  • Invaginations of mucosa between interstinal villi
  • Secrete intestinal juice
  • Extend to base of mucosa
81
Q

Structures of the Small Intestine

Villi

A
  • Fingerlike projections of mucose
  • Larger and most numerous in jejunum
  • Epithelium cover lamina propria
  • Increases surface area for absorption and secretion
  • Contains an arteriole, capillary network, venule
82
Q

Structures of the Small Intestine

Lacteal

A
  • Lymphatic capillary within villus
  • Responsible for absorbing lipids and lipid-soluble vitamins
83
Q

Small Intestine

Absorption

A

Nutrients are absorbed into the blood stream by diffusion across the luminal epithelium
Water and water-soluble substances diffuse directly into blood stream
- Dissolve in plasma
Lipids diffuse with carries into lacteals
- Carried through lymph into blood stream

84
Q

Small Intestine

Gastroileal Reflex

A

Moves chyme from small intestine into large intestine
- IIeum contracts
- Ileocecal sphincter relaxes (CCK helps casue this) and cecum relaxes
- Moves contents from ileum to cecum in response to food in stomach
- IIeocecal valve contracts to prevent back flow

85
Q

Large Intestine (aka Large Bowel)

A

Relatively wide tube, shorter than small intestine
Functions:
- Absorbs water and electrolytes from remaining digested material
- Watery chyme compacted into feces
- Stores feces unti eliminated through defecation
Relaxed while filling with material
Distension stimulates reflex contractions in muscularis to move material along
Peristalsis is generally weak and sluggish
Mass movements
- Powerful contractions to propel fecal material toward the rectum
- 2 to 3 times a day, often after a meal

86
Q

Large Intestine

Structures of the Large Intestine

A

Ileocecal sphincter
- Thickened muscularis located between small intestine and large intestine
Cecum
- First portion of large intestine
Vermiform appendix
- May harbor beneficial bacteria
Colon
- Second portion of large intestine
- Four segments: ascending, transverse, descending, and signmoid colon
Rectum
- Muscular tube that extends to store feces
Anal canal
- Internal anal sphincter - involuntary smooth muscle at base of anal canal
- External anal sphincter - voluntary skeletal muscle, sphincters normally closed off but relax during defecation

87
Q

Large Intestine

Gut Flora

A

Bacterial action in the large intestine
Indigenous microbiota
- Normal bacterial flora in large intestine
- Breakdown carbohydrates, proteins, and lipids in chyme
- Produce carbon dioxide, H+, other substances
- Produce B vitamins and vitamin K - absorbed from large intestine into blood
Feces is final product
- Composed of water salts, epithelial cells, bacteria, undigested material

88
Q

Large Intestine: Motility

Gastrocolic Reflex

A
  • Initated by stomach distension
  • Casuses a mass movement
89
Q

Large Intestine: Motility

Defecation Reflex

A
  • Filling of rectum initiates urge to defecate
  • Receptors signal to spinal cord
  • Increases parasympathetic output to sigmoid clon and rectum
  • Decreases output to internal (involuntary) anal sphincter
90
Q

Large Intestine: Motility

Voluntary Defecation

A
  • Learned about age 3
  • Involved valsalva maneuver
  • Involves relaxation of external (voluntary) anal sphincter
91
Q

Enzymes

A

Enzymes are biological catalysts that facilitate the chemical breakdown of macromolecules
Enzymes facilitate chemical digestion
- Break complex molecules into their monomers
Digestive enzymes are:
- Amylase
- Proteases (pepsinogen, pepsin, peptidase)
- Lipase
- Nucleases (rubonuclease, deoxyribonuclease)
Main disgestion sites: oral cavity and small intestine

92
Q

Carbohydrate Enzymes

A

Carbohydrates composed of simple sugars (monomers)
- Monomers: e.g. glucose, fructose
- Dimers: e.g. maltose, sucrose
- Polymers: e.g. starch, cellulose

93
Q

Carbohydrate Enzymes

Enzymes

A

Oral cavity - salivary amylase from salivary glands
- Breaks bonds between glucose molecules within the starch molecule
- Inactivated by low pH of stomach when bolus swallowed
Small intestine - pancreatic amylase from pancreas
- Component of pancreatic juice
- Continues digestion of starch

94
Q

Protein Enzymes

A

Proteins composed of amino acid subunits linked by peptide bonds
Enzyme
- Released as inactive enzymes (e.g. pepsinogen) that must be activated (pepsin)
- This prevents enzymes from breaking down proteins in cells that produce the enzymes

95
Q

Protein Enzymes

Enzymes

A

Stomach - pepsin
- Stomach’s low pH due to HCI released from parietal cells
- activates pepsinogen to active pepsin
- denatures proteins to facilitate chemical breakdown
Small intestine - trypsins and peptidases
- Precursors produced in pancreas and activated in small intestine

96
Q

Lipid Enzymes

Lipids

A

Not water-soluble
Highly variable structures
- Triglycerides - composed of glycerol and three fatty acids
- Cholesterol - does not need to be broken down for absorption

97
Q

Lipid Enzymes

Stomach Enzymes

A

Lingual lipase from saliva - activated in stomach
Gastric lipase from stomach

98
Q

Lipid Enzymes

Small Intestine Enzymes

A

Pancreatic lipase (responsible for most lipid digestion)
- Produced by pancreas
- Released into duodenum
- Equires seperation of large lipid droplets into smaller droplets, emulsification by bile salts (amphipathic molecules that form micelles to increase surface ares for digestion)

99
Q

Nucleic Acid Enzymes

A

Nucleic acids are polymers of nucleotides
- Two types: DNA and RNA
- Three components.: sugar, phosphate group, nitrogenous base
Enzymes:
- Small intestine - Deoxyribonuclease and ribonuclease
- Nucleases released by pancreas, activated in small intestine

100
Q

Nutrient Absorption

A

Carbohydrate absorption
- Absorbed across epithelium of small intestine into capillaries of villi
Protein absorption
- Absorbed across epithelium of small intestine into capillaries of villi
Lipid absorption
- Absorbed across epithelium of small intestine into lacteals - not directly into blood stream
Nucleic acid absorption
- Components (sugar, phosphate, nitrogenous bases) absorbed across epithelium of small intestine into capillaries of villi

101
Q

Absorption

Electrolyte Absorption

A
  • Small intestine absorbs almost all electrolytes that enter
  • Most absorption is unregulated, dependent on diet
  • Iron has controlled absorption
102
Q

Absorption

Vitamin Absorption

A

Fat-soluble vitamins (A, D, E, K) absorbed in small intestine along with lipids with micelles - absorbed into lacteals
Water-soluble vitamins (B and C) absorbed through diffusion and active transport
- B12 is large, so absorbed by receptor- mediated endocytosis
- Requires intrinsic factor (formed by parietal cells in stomach)

103
Q

Absorption

Water Absorption

A
  • Small intestine absorbs almost all ingested water across epithelia and into blood vessels vis osmosis (average = 8 out 0f 9 litres)
  • Large intestine absorbs most of the rest
  • Rest is passed in feces
104
Q

Phases of Digestion

1 - Cephalic Phase

A
  • Digestion stimulated by sight, smell, thought of food, taste, and chewing - initiates reflexes
  • Stimulates medulla oblongata (midbrain), which stimulates vagus nerve to stimulate stomach
  • Causes increase in motility and secretory activity of stomach - stomach “growls”
105
Q

Phases of Digestion

2 - Gastric Phase

A
  • Initiated by food physically contacting stomach lining
  • Baroreceptors detect stretch of stomach - stomach releases gastrin hormonw (which stimulates contraction of stomach smooth muscle)
  • Chemoreceptors detect protein and increased acidity
  • Medulla oblongata stimulated, again stimulating vagus nerve and increasing motility
106
Q

Phases of Digestion

3 - Intestinal Phase

A
  • Initiated by stimuli in the small intestine - distention, acidity, osmolarity, and nutrient contents
  • Intestinal reflex opposes cephalic and gastric reflexes
  • Decreased motility and secretions by stomachb
  • Cholecytoskinin (CCK) and secretin are released
  • Emptying of stomach is slowed
107
Q

Regulation of Digestion

A
  • Control mechanisms of the gastrointestinal system are governed by the volume and composition of the luminal contents, rather than by the nutritional state of the body
  • This means that the body is designed to absorb all the nutrients that are ingested, whether or not thew body really needs them to dunction
108
Q

Metabolic States

Absorptive State (Fed State)

A

Time spent eating, digesting, and absorbing nutrients
Lasts 4 hrs after a meal
Blood concentrations of nutrient monomers (glucose, triglycerides, and amino acids) increased as they are absorbed from GI tract
Major regulatory hormone released is insulin
- Released from pancreas in response to increased blood glucose levels
- Stimulates liver and muscle cells to produce glycogen from glucose (glycogenesis)
- Affects adipose tissue - Increases uptake of tryglycerides from blood (stimulates lipogenesis and inhibits lipolysis)
- Stimulates most cells to increase amino acid uptake - casues accelerated protein synthesis

109
Q

Metabolic States

Post-Absorptive State (Fasting State)

A

Time between meals
- Body relying on stores of nutrients
- Body working to maintain homeostatic levels of nutrients
Major regulatory hormone released is glucagon
- Released from pancreas in reponse to decreasing blood glucose levels
Stimulates:
- Liver to increase breakdown of glycogen to glucose (glycogenolysis)
- Gluconeogenesis from noncarbohydrate sources
- Adipose tissue to break down triglycerides (lipolysis)
No effect on amino acids or proteins in cells

110
Q

Metabolic Rate

Basal Metabolic Rate (BMR)

A

Amount of energy used at rest
- Resting conditions: individual has not eaten for 12 hours, is relaxed (not sleeping), temperature about 20 C
- Not the lowest metabolic rate - that occurs during sleep
Depends on:
- Age - increasing age reduces BMR by 3% each decade beginning ~30
- Lean body mass - greater than normal BMR
- Thyroid Hormone - increases BMR (hypothyroidism = lower than normal BMR, hyperthyroidism = higher than normal BMR)
- Body surface area - greater surface area of skin, more heat lost, more active body cells must be to maintain temperature
- Hormone levels in blood (e.g. thyroid hormone, testosterone, etc.)
- Sex - affects body mass, hormone levels, etc.
Measured by calorimeter (water bath - hear changes temperature of water) or respirometer (indirect measure using oxygen consumption - cellular respiration)

111
Q

Metabolic Rate

Total Metabolic Rate (TMR)

A

BMR + metabolism associated with physical activity
Depends on:
- Amount of skeletal muscle and its activity (rapid increase during vigorous exercise)
- Food intake (increases following ingestion of a meal, but decreases after absorption)
- Changing environmental conditions (increases if exposed to cold temperature)

BIOL1046 Human Biology II (14 decks)

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