Physiology 4 (pt 2)

• Substance in food that is used by the body to promote normal growth, maintenance and repair
• Large, complex molecules that function to promote living systems

• Carbohydrates
• Proteins
• Lipids
• Vitamins
• Minerals
• Water

• Carbohydrates
• Proteins
• Lipids

The ones that the body don't make or cannot convert from other molecules

• Chains of sugars
• Provide cells with a readily available source of energy; esp when cells need energy quickly
• Substrates for the synthesis of glycogen

Individual sugar molecules

Pairs of sugars

Long chains of sugars

• Monosaccharide (simple sugar)
• Derived from carbohydrates 
• One of the only fuels available to the brain

Glucose and ketone bodies (a class of molecules derived from fats)

• Simple: sugars i.e fruit, honey
• Complex: starch i.e grain, legumes

Enzyme that digests starches into maltose

• Conversion of amino acids to glucose- tissue protein breakdown
• An adult needs a minimum of 100g of carbs per day to prevent this

• Fiber
• Insoluble and cannot be digested
• Increases bulk, peristalsis and elimination
• Amylase cannot digest

• Chains of amino acids
• Contain 20 different R groups to distinguish the differences
• Formed when amino acids are linked with peptide bonds

• A short chain of amino acids is a peptide
• Longer chains are referred to as proteins

• When proteins are used for energy which are excreted in the urine
• Native proteins are metabolized for energy and dietary proteins provide amino acids can be used for synth of native proteins

Excreted as ammonia, urea, and uric acid

9 of the 20 amino acids are refereed to this bc they must be consumed

Isoleucine, histidine, leucine, methionine, valene, lysine, phenylalanine, tryptophan, threonine

Body can synth these amino acids from dietary proteins

• Includes eggs, milk, meats
• Dietary sources of protein that provide all of the essential amino acids are considered this

• Include legumes (beans, peas), nuts, and cereals
• Protein rich but lack one or more of the essential amino acids

• Depends on age, size, and metabolic rate
• Generally, recommended intake is 0.4 grams of protein per lb of body weight per day

• When amt of nitrogen ingested in proteins equals the amount excreted in urine and feces
• Nitrogen content of protein is 16%

• Take in more nitrogen than is lost
• Normal for growing children and pregnant women
• May also see after injury or tissue damage

• Take in less nitrogen than is lost
• May see during physical or emotional stress-- through energy expenditure by protein breakdown

• Long chains of carbon and hydrogen
• Very energy dense molecules 
• Used for long term energy storage, insulation and cushion

• One of the only fuels for the brain
• Fats are a valuable source of this and in times of carbohydrate deficit, liver synthesizes this from fats

• Triglycerides: storage form of fat 
• Phospholipids: primary structural component of cell membranes
• Fat derived hormones including prostaglandins and steroids and cholesterol

• Animal products (meat, dairy)
• Coconut
• Fully saturated with H
• Converted to harmful cholesterol LDL or VLDL

• Seeds
• Nuts
• Most vegetable oils
• Missing at least 1 double bond and 2 H

Good cholesterol: HDL which cleans out the plaque

The precursor to the formation of bile salts and steroid hormones

• Complex carbohydrates: 45-65%
• Proteins: 10-35%
• Fats (lipids): 25-35% with no more than 10% in form of saturated fats

25-35 grams

• Complex: breads, cereal, crackers, flour, pasta
• Simple: soft drinks, candy, fruit

Vitamin A, D, E, K

• Retinol
• Photosensitive chemicals within the retina
• Important to cell differentiation and is an antioxidant

Deficiencies can cause night blindness and poor growth in children

Protect biological molecules from the damaging effects of highly reactive oxidizing chemicals

Required for the absorption of calcium from the intestines

Deficiencies of this can produce rickets or osteomalacia

• Caused from vitamin D deficiency
• Poorly calcified weak bones in a child

• Vitamin D deficiency
• Poorly calcified, weak bones in an adult

• Antioxidant that protects cell membranes from oxidative chemicals
• Role is very similar to that of the mineral selenium

Deficiencies are rare, but can cause damage to RBC and neurons

Important in the production of several biological molecules within the blood clotting pathways

Deficiencies can lead to uncontrolled bleeding

Vitamin K

• Individuals that have lost their normal flora bc of antibiotic consumption are at a greater risk for vitamin K deficiency
• Typically supplemented for newborn children

• B vitamins: folic acid and vitamin B12
• Vitamin C

Needed for the production of DNA and RNA as well as the metabolism of certain amino acids

Deficiencies have a significant impact on rapidly growing tissues; producing anemia and diarrhea and inflammation of the tongue

• Can cause poor growth and neural tube defects for developing fetus
• Certain contraceptives significantly reduce these levels and often takes several months after discontinued use before levels return to normal

• Involved in energy metabolism as well as amino acid synthesis
• A deficiency in this can induce a folic acid deficiency

Can cause anemia as well as degradation of the myelin sheath that surrounds neural axons

Refers to vitamin B12 deficiency that results from a lack of intrinsic factor

• Required for synthesis of glucose and fatty acids, as well as the metabolism of certain amino acids
• Deficiency can result in nausea, dermatitis, hair loss, and lethargy

• Collection of biosynthetic rxns including the synth of collagen
• Involved in immune function and has antioxidant effects

Extracellular connective tissue fiber

• Deficiency of vitamin C 
• Characterized by swollen joints, delayed wound healing, and bleeding gums

• Primary extracellular electrolyte within the body
• Imp to the production of AP by excitable cells and its profound osmotic effect

Alter the ability of neurons to produce AP leading to nervous system disturbances like lethargy, confusion, and coma

Lead to inappropriate distribution of water throughout the body causing dry mucus membranes, pulmonary edema, and convulsions

• Primary intracellular electrolyte within the body
• Like sodium, it is imp to the activity of excitable cells

Create disturbances in cardiac function by altering resting potential and action potential activity of the cardiac cells

• Primary constituent of the inorganic component (calcium phosphate) of the bone
• Responsible for giving bones rigidity and hardness
• Used to regulate muscle cell contraction and secretion of many neurotransmitters and hormones

Can lead to over excitability of neuron and muscle cells

Lead to lethargy, kidney stones, and deposits of calcium within soft tissue

Component of oxygen binding molecules such as hemoglobin (transports oxygen) and myoglobin (draws oxygen into the tissues)

• Result in anemia
• Children are at risk of iron deficiency during periods of exceptionally rapid growth bc of increased iron demand associated w/expanding blood volume
• Menstruation also increases risk

In high doses can damage the intestines and acid-base imbalances

Essential component of the thyroid hormones

Results from an iodine deficient diet that creates an abnormally low metabolic rate (causing lethargy and weight gain) and enlargement of thyroid (goiter)

• Amount of calories the body burns to stay alive
• Measured by total heat produced by all work
• Measured in kilocalories per sq. meter of body surface per hour (larger person burns more calories)

Person lies in bed for 12 hours in a room set at 20 degrees C without stress

At 154 lbs= 60-72 Kcal/hr

• Age: younger person, higher BMR; older=lower bc muscle atrophy
• Sex: metabolic rate is disproportionately higher in males; more muscles
• Body surface area: larger=higher bc more heat loss 
• Thyroxine levels: Higher TH=more heat created and energy burnt

• Body temperature: lower body temp=lower MR
• Activity: increase activity=increase MR
• Stress: increase stress=increases MR
• Thyroxine abnormalities: hyperthyroidism results in excess MR

• Doesn't exist
• The avg weight given in insurance tables for person of a given height and sex

Estimates if you are a healthy weight bc overweight puts strain on heart and can lead to type 2 diabetes, hypertension, sleep apnea

Physiological need to eat, decreased glucose, fat, amino acid in blood plasma

Desire for food, a phycological phenomenon dependent on memory and associations

• Craving and eating substances not normally considered nutrients (clay)
• Pregnant women experience this bc the body needs a nutrient causing a hormone imblance

• Hunger:
• builds gradually several hours after meal
• goes away when full with feeling of satisfaction

• Appetite: 
• develops suddenly and is unrelated tot time
• specific cravings with feelings of guilt

• Regulate hunger and satiety
• Use negative feedback signals to regulate feeding behavior and hunger including: 
• Thermoreceptors (more heat, more energy being used and replacement calories are needed)
• Chemoreceptors (glucose, insulin)

Blood chemistry: plasma levels of glucose, amino acids, fatty acids provide info to adjust energy intake to energy output

Regulate plasma nutrient levels 

• Include: 
• Insulin
• Glucagon
• Epinephrine
• Cholecystokinin (CCK)
• Serotonin
• Leptin
• Ghrelin

Released during food absorption, known to depress hunger and is a satiety signal (feel full or satisfied)

Levels rise during fasting and stimulate hunger bc blood sugar is low

Triggers hunger (released during fasting) or low blood sugar

Intestinal hormone secreted during food digestion that depresses hunger

• Neurotransmitter that also delivers satiety signals
• Excepts large amounts may signal hunger

• Acts on the hypothalamus to cause a reduction in food intake, inhibits neuropeptide Y which makes you want to eat
• Stimulates MR

Peptide hormone synthesized and released by stomach

• Functions:
• Increase growth hormone release
• Increase hunger

Why kids eat more when they are growing bc GH is released at night

Colder climate = hungrier

• Gastric contractions
• Oral cavity monitoring
• Limbic system
• Serotinin
• NPY

• Contractions of the stomach emptying activate hunger 
• If stomach is full, you won't eat

• Act of chewing/tasting activates the satiety centers
• Eating is suppose to suppress eating

Cultural factors, the environment, stress, and past experiences relative to the sight, smell and taste of food also effect food intake

Seeing birthday cake=wanting to eat it

Neurotransmitter depresses hunger; except in high levels

Hypothalmic neurotransmitter that stimulates eating, released during exercise, fasting

• Continuous, muscular digestive tube that extends from mouth to anus
• Function: digest food chemically into its individual components (monomers) and then to absorb this components across the GI wall into the blood stream

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small and large intestine

Not part of the main tube, are essential for the digestion and absorption of nutrients from the GI tract

• Teeth
• Liver
• Salivary glands
• Gallbladder
• Tongue
• Pancreas

• Physical and chemical digestion (only carbs)
• Taste, swallowing, and speech

• Teeth bite off chunks of food and grind these chunks into smaller pieces in mastication (chewing)
• Physical Digestion

• Presence of food in mouth, smell of appealing food, or thinking about it can stimulate the parasympathetic salivary reflex to the salivary glands
• Major glands are located outside the mouth (extrinsic salivary glands)

• Parotid, submandibular, and sublingual salivary glands
• Contain salivary amylase
• Avg production is 1000-1500 ml of saliva per day

Begins chemical digestion of carbohydrates into simplest form called monosaccharide and includes sucrose and glucose

Ground up, lubricated food ball which is swallowed

Complicated process that involves the coordinated activity of the tongue, soft palate, pharynx, esophagus, etc

• Voluntary: buccal phase (located in mouth)
• Involuntary: pharyngeal and esophageal phase

• When tongue pushes a bolus into the oropharynx 
• Contraction of the tongue

Controlled by the swallowing center located in the medulla and lower portion of the pons

• Presence of food in the oropharynx
• Oropharynx has to be moist

• Peristalsis (wavelike contractions)
• Uvula folds upwards to seal off the nasopharynx
• Epiglottis folds downwards to seal off the opening into the larynx; prevents aspiration
• Peristalsis pushes the bolus towards the stomach
• Gastro-esophageal sphincter relaxes to allow food to enter the stomach

• 4-8 seconds
• Fluids are 1-2 secs

• Autonomic reflex from the medulla following the irritation of the uvula and posterior-most aspect of the tongue
• Causes sudden but not prolonged reverse peristalsis

• Large, multi-fold sac between two small diameter tubes, esophagus and small intestine
• Stores food and imitates the chemical digestion of protein
• Major digestive role of the stomach to store, mix and liquefy food

Within the lining of the stomach to secrete mucus

Leads into gastric glands which collective produce the stomach secretion called gastric juice

Produce the mucus that protects the lining of the stomach from HCL and the development of an ulcer

Damage to the underlying tissues due to a breach to the mucosal barrier

• Produce HCL and intrinsic factor
• HCL activates pepsinogen to pepsin (which digests proteins)
• HCL lowers the pH within the stomach preventing most microorganisms from living and growing in the stomach (kills bacteria ingested with food)

• Acid-resistant bacteria which attaches to the epithelium and destroys the protective mucosal layer
• Use antibiotics, traditional antiulcer drugs and busmuth or peptobismol to treat

• Produced by parietal cells
• Only stomach function essential to life
• Needed for absorption of vitamin B12 in small intestine
• Lack of this results in pernicious anemia

• These cells produce an inactive protease or enzyme called pepsinogen
• Pepsinogen is activated to pepsin by HCL
• Role of pepsin is to digest larger protein molecules into smaller ones to allow protein digestion in the stomach

• Cephalic phase
• Gastric phase

• Achieved by both parasympathetic and sympathetic divisions
• Initiated when receptors in the head are stimulated by sight, smell, taste, and chewing
• Emotions can also initiate this

Stimulates gastric secretions and peristalsis and relaxes the pyloric sphincter for stomach emptying i.e receptive relaxation

• The stomach is very small; 50ml when empty
• But before the arrival of food, the stomach relaxes to allow as much as 1.5 liters of volume

• Stimulation of the stomach causes a decrease in gastric secretion, peristalsis and motility
• No digestion during exercise

• 4 types of stimuli in the stomach initiate the reflexes that constitute this regulation: 
• Distension, acidity, amino acids and peptides formed during the digestion of ingested proteins
• Hormone control of gastric activity is done by enterendocrine cells

• Gastrin
• Somatostatin
• Histamine

• Stimulates gastric secretions/peristalsis
• Most pronounced effect is on HCL secretion

Decreases gastric secretions/peristalsis

• Produced in the wall of the stomach
• Binds to the H2 receptors and stimulates gastric secretions

• Secretin: decrease gastric secretions
• GIP (gastric inhibitory peptide): decrease peristalsis, decrease gastric secretions
• CCK (cholecystokinin): decrease peristalsis, decrease gastric secretions

• Empties completely within four hours after a meal (6 hours after a meal high in fats)
• Larger the meal, the more liquefied the contents, the faster the stomach empties

• Accessory digestive organ
• Produces broad spectrum of enzymes and secretions that breakdown all categories of food stuffs
• Secretions are delivered to the small intestine for digestion (breakdown); proteins, carbs, fats digested by this

Secretions are rich in bicarbonate and potassium ions

• Neutralize the hydrochloric acid in the chyme from the stomach
• Severe diarrhea can cause metabolic acidosis due to the loss of this or hypokalemia due to the loss of potassium and dehydration due to the loss of water

• Does much of the starch digestion
• Takes 10 mins after entering intestine to digest completely in maltose, then to monosaccharides

• Does most of the fat digestion, breaking fat into its simplest components: fatty acids and glycerol 
• Pancreas is the main source of fat digesting lipases

• That digest proteins into amino acids:
• Trypsinogen to trypsin
• Chymotrypsinogen to chymotrypsin 
• Procarboxypeptidase to carboxypeptidase

• Activated to active form in small intestine so that the pancreas does not self-digest
• Allow for complete protein digestion

• The liver and gallbladder are accessory digestive organs
• Liver's digestive role is to produce bile for export to the duodenum
• Gallbladder is a storage place for bile

Fat emulsifier; breaks a big piece of fat up into little pieces of fat so enzymes can digest it

• Consists of:
• Bile salts
• Bile pigments
• Cholesterol

• Bile doesn't enter the small intestine until the gallbladder contracts
• Presence of acidic fatty chyme within the duodenum stimulates the small intestine to release cholecystokinin (CCK)

• Stimulate the gallbladder to contract
• Stimulate pancreatic secretions
• Relaxes the hepatopancreatic sphincter

• Role is to decrease the surface tension that hold lipids into large droplets
• This allows the large droplets to break apart into many small droplets

• Main pigment is bilirubin
• Bilirubin is a waste product of the heme portion of hemoglobin formed during breakdown of the worn out RBCs
• More water soluble coating so enzymes can act on it

Role is to help in the formation of micelles so we can absorb fat breakdown products

• Intestinal lipase
• Intestinal disaccharases
• Intestinal proteases

• Not as active as pancreatic lipase but not necessary to digest fats
• Will digest fats

• Sucrase: digests disaccharide sucrose into glucose/fructose
• Maltase: digest maltose into two glucose
• Lactase: digests lactose into glucose and galactose (lactaid)

Aminopeptidase/Dipeptidase: both of these speed up the process of protein digestion into amino acids

Movement of small molecules through the epithelial cells that line the mucosa of the intestine and enter either blood capillaries or lymphatic capillaries

• 80% of all food are absorbed, electrolytes, and water are absorbed in the small intestine
• Completed by the ileum which reclaims some bile salts

Monosaccharides such as glucose/amino acids are absorbed by a combination of active transport, facilitated diffusion and diffusion into the blood capillaries

• Needed to absorb fat
• Collection of fatty acids, monoglycerides, bile salts, cholesterol, lecithin (phospholipid found in bile and fat soluble vitamins (A, D, E, K) clustered together in such a way that the hydrophilic ends face the water and phobic portions form the micelle core so it doesn't reform into a large droplet
• Can diffuse into the cell rather than "ride the wave" out of the body

• Most American caloric intake is in this form
• Molecule consisting of a monoglyceride + two fatty acids
• Commonly stored in fat cells

Triglycerides combined w/phospholipids and cholesterol and coated with a "skin" of proteins to form this water soluble lipoprotein

• Enter the lymphatic capillaries (lacteals)
• Transported to the liver via blood stream
• Converted to various lipoproteins that are transported in the blood including HDL and LDL cholesterol

• High density lipoprotein
• Transports cholesterol from the peripheral tissues to the liver where it is broken down and made into bile 
• Good fats from nuts and seeds

• Low density lipoprotein
• Leads to cholesterol plaques and coronary artery disease 
• Bad cholesterol

Eliminate indigestible food and absorb water

• Material that was not absorbed in the small intestine pass through the ileocecal sphincter
• Materials contain few nutrients, still has 12-24 hours to spend there 
• No further breakdown occurs in the large intestine

• Movement of food into the stomach stimulates mass peristalsis in the colon
• This pushes the contents of the colon toward the rectum

Bulk or fiber, in the diet increases the strength of colon contractions and softens the stool

• Rectum is generally empty, but when feces are forced into it by mass movements stretching of the rectal wall initiates the defecation reflex
• Spinal cord mediated parasympathetic reflex that causes the walls of the sigmoid colon and the rectum to contract
• Causes relaxation of the inner and external anal sphincters

If defecation is delayed, the reflex contractions end within a few seconds and rectal walls relax

• During defecation, the muscles of the rectum contract to expel the feces
• Relax external anal sphincter
• Valsalvas maneuver involved

• Aid defecation by voluntarily closing the glottis and contracting diaphragm and abdominal wall muscles to increase the intra-abdominal pressure
• Levator ani muscle also contracts and pulls the anal canal superiorly, leaving feces below the anus and outside of the body

• Absorb water and electrolytes
• Vitamin K and B complex vitamins synthesized by the bacterial flora in the GI tract
• Releases some potassium as well

• After absorption and secretion, the material remaining within the lumen of the colon 
• Of the 500 ml of the food entering in the cecum daily, 150 ml becomes feces

Due to the metabolite of bilirubin called urobilinogen (brown) bile pigment which is waste product of heme