Ch. 25: Metabolism and Nutrition Flashcards
1
Q
Metabolism.
A
All the chemical reactions that occur in the body. An energy-balancing act between catabolic reactions and anabolic reactions.
2
Q
Catabolism.
A
Chemical reactions that break down complex organic molecules into simpler ones. Exergonic. Produce more energy than they consume. Release chemical energy stored in organic molecules.
3
Q
Anabolism.
A
Chemical reactions that combine simpler molecules to form complex ones. Endergonic. Consume more energy than they produce.
4
Q
A molecule synthesized in an anabolic reaction has…
A
A limited lifetime. It will eventually be broken down and its component atoms will be recycled into other molecules or excreted from the body.
5
Q
How much energy released in catabolism is used for cellular functions, and how much is conserved for heat?
A
Cellular functions: 40%
Heat: 60%
6
Q
Oxidation.
A
Removal of electrons. Decreases the potential energy. Dehydrogenation. Usually exergonic.
7
Q
Reduction.
A
Addition of electrons. Increases the potential energy.
8
Q
NAD.
A
Derivative of B-vitamin niacin.
When NAD+ is reduced to NADH + H+, the NAD+ gains a H- ion, neutralizing its charge, and H+ is released into the surrounding solution.
When NADH is oxidized to NAD+, the loss of the H- ion results in one less H atom and an additional positive charge.
9
Q
FAD.
A
Derivative of vitamin B2 riboflavin.
FAD is reduced to FADH2 when it gains a H+ and a H- ion.
FADH2 is oxidized to FAD when it loses a H+ and a H-.
10
Q
Phosphorylation.
A
Addition of a P group to a molecule. Increases potential energy.
11
Q
Organisms use 3 mechanisms of phosphorylation to generate ATP.
A
1) Substrate-level phosphorylation.
2) Oxidative phosphorylation.
3) Photophosphorylation.
12
Q
Substrate-level phosphorylation.
A
Generates ATP by transferring a high-energy P group from an intermediate phosphorylated metabolic compound directly to ADP. Occurs in the cytosol.
13
Q
Oxidative phosphorylation.
A
Removes electrons from organic compounds and passes them through a series of electron receptors to molecules of O2. Occurs in inner mitochondrial membrane.
14
Q
Photophosphorylation.
A
Occurs only in chlorophyll-containing plant cells or in certain bacteria that contain other light-absorbing pigments.
15
Q
Blood glucose is maintained at…
A
90 mg / 100 mL of plasma
16
Q
____ of glucose normally circulates in the blood.
A
2-3 g
17
Q
What are the 4 fates of glucose?
A
1) ATP production: Glucose is oxidized to produce ATP in cells that require immediate energy.
2) Amino acid synthesis: Amino acids can then be used to produce proteins.
3) Glycogen synthesis: Hepatocytes and muscle fibres can perform glycogenesis, where hundreds of glucose monomers are combined to form glycogen. Total storage capacity is 125g in liver and 375g in skeletal muscles.
4) Triglyceride synthesis: When the glycogen storages are filled, hepatocytes can transform glucose to glycerol and FAs that can be used for lipogenesis to make triglycerides. These are deposited into adipose tissue which has unlimited storage capacity.
18
Q
How is glucose absorbed in the GI tract?
A
Secondary active transport via Na+ glucose symporters.
19
Q
How is glucose absorbed in other body cells?
A
Facilitated diffusion via GluT transporter molecules. A high level of insulin increases the insertion of GluT4 into the PMs of body cells, increasing the rate of facilitated diffusion of glucose into cells. On entering a cell, glucose becomes phosphorylated. Because GluT cannot transport phosphorylated glucose, this reaction traps glucose within the cell.
20
Q
Cellular respiration.
A
Oxidation of glucose to produce ATP.
21
Q
Glucose catabolism.
A
1) Glycolysis.
2) Formation of acetyl coenzyme A.
3) Krebs cycle.
4) ETC.
22
Q
Anaerobic respiration.
A
Glycolysis –> pyruvic acid –> lactic acid.
23
Q
Aerobic respiration.
A
Glycolysis –> acetyl coenzyme A –> Krebs cycle –> ECT.
24
Q
Glycolysis.
A
A set of reactions split a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvic acid. Also produces 2 ATP and 2 NADH + H+.
25
The fate of pyruvic acid depends on...
Availability of oxygen.
Anaerobic: 1 pyruvic acid + 2 NADH + 2 H+ --> 2 lactic acid + 2 NAD+ (the lactic acid is converted back to pyruvic acid by hepatocytes)
Aerobic: 1 pyruvic acid --> 1 acetyl coenzyme A
26
RBCs only produce ATP via...
Glycolysis.
27
Acetyl coenzyme A formation.
CoA is derived from pantothenic acid (B vitamin).
Pyruvate dehydrogenase located in mitochondrial matrix converts pyruvic acid into a 2-carbon acetyl group by removing 1 CO2 (decarboxylation). Pyruvic acid is also oxidized. Each pyruvic acid loses 1 H+ and 1 H-. NAD+ is reduced as it picks up the H-, and the H+ is released into mitochondrial matrix.
So this reaction produces NADH + H+ + CO2 and acetyl coenzyme A.
28
Krebs cycle.
In mitochondrial matrix. Oxidation-reduction reactions transfer chemical energy in the form of electrons to NAD+ and FAD. Pyruvic acid derivatives are oxidized, and NAD+ and FAD are reduced.
Produces 3 NADH, 3 H+, 1 FADH2, 1 ATP, 6 CO2 (each turn).
29
Because each glucose provides 2 acetyl CoA, how many turns of the Krebs cycle are there per glucose catabolized?
2, resulting in 6 NADH, 6 H+, 2 FADH2, 2 ATP, 12 CO2.
30
Describe CO2 in Krebs cycle.
It is released as pyruvic acid is converted to acetyl CoA during the two decarboxylation reactions in Krebs cycle. They diffuses out of mitochondria, through cytosol and PM, into blood, into lungs, and exhaled.
31
ETC.
The inner mitochondrial membrane is folded into cristae that increases its SA, accommodating thousands of copies of the ETC in each mitochondrion. As electrons pass through the chain via carriers, a series of exergonic reactions release small amounts of energy which is used to form ATP.
32
Electron carriers of ETC.
FMN, cytochromes, Fe-S enters, Cu atoms, coenzyme Q.
33
Glycogenesis.
Glucose storage. If glucose is not currently needed, it combines with other glucoses to form glycogen. Glucose is phosphorylated to glucose 6-phosphate by hexokinase --> glucose 1-phosphate --> uridine diphosphate glucose --> glycogen.
34
What hormone stimulates hepatocytes and skeletal muscle cells to carry out glycogenesis?
Insulin.
35
How much glucose can the body store?
500g. 75% in skeletal muscle fibres. 25% in liver cells.
36
Glycogenolysis.
Glucose release.
Liver: Begins by splitting off glucose from glycogen via phosphorylation --> glucose 1-phosphate --> phosphorylase is activated by glucagon from pancreatic alpha cells and EP from adrenal medullae --> glucose 1-phosphate is converted to glucose 6-phosphate --> glucose --> leaves hepatocytes via GluT in PM. Phosphatase is absent in skeletal muscle cells, so only hepatocytes can release glucose from glycogen into the blood.
Skeletal muscle: Glycogen is broken down into glucose 1-phosphate --> catabolized for ATP production via glycolysis and Krebs. Lactic acid produced in muscle cells can be converted to glucose in the liver, so muscle glycogen can be an indirect source of blood glucose.
37
Gluconeogenesis.
Formation of glucose from proteins and fats. Stimulated by cortisol and glucagon. Cortisol stimulates the breakdown of proteins into amino acids to expand the pool of amino acids available for gluconeogenesis.
38
How are thyroid hormones involved in gluconeogenesis?
They mobilize proteins and triglycerides from adipose tissue to make glycerol more available for gluconeogenesis.
39
Lipoproteins.
Transportation method of lipids. Lipid and protein combinations. Spherical particles with an outer shell of proteins, phospholipids and cholesterol molecules surrounding an inner core of triglycerides and lipids.
40
Apoproteins.
Proteins in the outer shell of lipoproteins. Designated by the letters A, B, C, D, E plus a number.
41
4 major classes of lipoproteins (from largest and lightest to smallest and heaviest).
Chylomicrons, VLDLs, LDLs, HDLs.
42
Chylomicrons.
Form in mucosal epithelial cells of small intestine. Transport dietary lipids to adipose tissue for storage. Contain 1-2% proteins, 85% triglycerides, 7% phospholipids, 6-7% cholesterol, small amount of fat-soluble vitamins. Enter lacteals of intestinal villi and are carried by lymph into venous blood and then into systemic circulation.
43
Which substance gives blood plasma a milky appearance?
Chylomicrons.
44
Apo C-2 of chylomicrons.
As chylomicrons circulate through the capillaries of adipose tissue, apo C-2 activates endothelial lipoprotein lipase which removes FAs from chylomicron triglycerides. The free FAs are taken up by adipocytes for synthesis and storage as triglycerides, and by muscle cells for ATP production.
45
How are chylomicrons removed from the blood?
By hepatocytes via receptor-mediated endocytosis. The docking protein for this process is apo E.
46
Very low density lipoproteins.
Form in hepatocytes. Contain endogenous lipids, 10% proteins, 50% triglycerides, 20% phospholipids, 20% cholesterol. Transport triglycerides synthesized in hepatocytes to adipocytes for storage. Lose triglycerides as their apo C-2 activates endothelial lipoprotein lipase. Resulting FAs are taken up by adipocytes for storage and by muscle cells for ATP production.
47
What happens to VLDLs as they deposit some of their triglycerides in adipose cells?
They are converted to LDLs.
48
Low density lipoproteins.
Contain 25% protein, 5% triglycerides, 20% phospholipids, 50% cholesterol. Contain a single apoprotein of apo B100, which is the docking protein that binds to LDL receptors on the PM of body cells so that the LDL can enter the cell via receptor-mediated endocytosis. Within the cell, LDL is broken down and the cholesterol is released to serve the cell's needs. Then, a negative feedback inhibits the cell's synthesis of new LDL receptors.
49
____ carry 75% of the total cholesterol in blood and deliver it to body cells for repair of cell membranes and synthesis of steroid hormones and bile salts.
LDLs.
50
What happens when there are an abundance of LDLs?
They deposit cholesterol in and around smooth muscle fibres in arteries, forming fatty plaques that increase CAD risk.
51
If you have not many LDL receptors...
Your body cells remove LDL from the blood less efficiently, so your plasma LDL level will be abnormally high, producing fatty plaques.
52
Eating a high fat diet increases...
Production of VLDLs --> LDLs --> fatty plaques.
53
High density lipoproteins.
Contain 45% protein, 10% triglycerides, 30% phospholipids, 20% cholesterol. Remove excess cholesterol from body cells and blood, and transport it to liver for elimination.
54
A high level of HDLs is associated with...
Decreased CAD risk. HDLs prevent accumulation of cholesterol in the body.
55
What are the 2 sources of cholesterol in the body?
Food, hepatocytes (most).
56
How can fatty foods that do not contain cholesterol still increase blood cholesterol?
A high intake of dietary fats stimulates reabsorption of cholesterol-containing bile back into the blood, so less cholesterol is eliminated from the body. And when saturated fats are broken down, hepatocytes use some of the products to make cholesterol.
57
Lipid profile test.
Measures total cholesterol (TC), HDL-cholesterol, and triglycerides (VLDLs).
LDL-cholesterol = TC - HDL-cholesterol - (triglycerides / 5)
58
Desirable levels of blood cholesterol in adults.
TC < 200 mg/dL, LDL-cholesterol < 130 mg/dL, HDL-cholesterol > 40 mg/dL, VLDLs 10-190 mg/dL.
59
When TC > ___ mg/dL, the risk of a heart attack doubles with every ___ mg/dL increases in TC.
200, 50.
60
Borderline high cholesterol.
TC 200-239 mg/dL
LDL 130-159 mg/dL
61
Borderline high cholesterol.
TC 200-239 mg/dL
LDL 130-159 mg/dL
62
High blood cholesterol.
TC > 239 mg/dL
LDL > 150 mg/dL
63
Fate of lipids.
May be oxidized to produce ATP, or stored in the liver and adipose tissue throughout the body. Some lipids are used as structural molecules and synthesize other essential substances.
64
Essential FAs that the body cannot synthesize.
Linoleic acid, and linolenic acid.
65
How are triglycerides stored?
Adipocytes remove triglycerides from chylomicrons and VLDLs and store them until they are needed for ATP production. Triglycerides in adipose tissue are continually released, transported, redeposited in different adipocytes, broken down, and resynthesized.
66
_____ stored in adipose tissue constitute 98% of all body energy reserves.
Triglycerides.
67
How are EP and NE involved in lipid catabolism?
They are released when sympathetic tone increases, and enhance triglycerides breakdown into 2 FAs and 1 glycerol.
68
Beta oxidation.
First step of FA catabolism. Occurs in mitochondrial matrix. Enzymes remove 2 carbons at a time from a FA and attach the resulting 2 carbons to CoA --> acetyl CoA --> Krebs cycle --> ATP.
69
What happens to the glycerol liberated from triglycerides?
Converted to glyceraldehyde 3-phosphate --> converted to glucose if ATP supply is high --> OR enters the catabolic pathway to pyruvic acid if ATP supply is low.
70
Acetoacetic acid.
In FA catabolism, hepatocytes can take 2 acetyl CoA molecules at a time and condense them into acetoacetic acid, which liberates the bulky CoA portion which cannot diffuse out of cells. Some acetoacetic acid is converted into beta-hydroxybutyric acid and acetone (these 3 substances are known as ketone bodies = ketogenesis). Other cells take up acetoacetic acid and attach its 4 carbons to 2 CoA molecules --> 2 acetyl CoA, which then enter Krebs cycle for oxidation.
71
Ketone bodies.
Acetoacetic acid, beta-hydroxybutyric acid, acetone. Freely diffuse through plasma membranes.
72
The heart and kidney cortex use _____ in preference to glucose for generating ATP.
Acetoacetic acid.
73
_____ make acetoacetic acid but cannot use it for ATP production because they lack the enzyme that transfers acetoacetic acid back to CoA.
Hepatocytes.
74
Lipogenesis.
Liver cells and adipose cells synthesize lipids from glucose or amino acids. Stimulated by insulin. Occurs when individuals consume more calories than needed.
Amino acids --> acetyl CoA --> FAs --> triglycerides
Glucose --> glyceraldehyde 3-phosphate --> glycerol
OR
Glucose --> glyceraldehyde 3-phosphate --> acetyl CoA --> FAs
75
Excess dietary CHO, protein and fat are all converted to...
Triglycerides.
76
Fate of proteins.
They are broken down into amino acids, and NOT stored. They are either oxidized to produce ATP, or used to synthesize new proteins for growth and repair. Excess dietary amino acids are converted to glucose or triglycerides, NOT excreted from the body. Right after digestion, amino acids are reassembled into proteins, and they can function as enzymes, hormones, contractile elements in muscle fibres, structural components, or for transportation.
77
The active transport of amino acids into body cells is stimulated by ____ and ____.
IGFs, insulin.
78
Protein catabolism.
Stimulated by cortisol from adrenal cortex. Proteins from worn-out cells are broken down into amino acids. Some of these amino acids are converted into other amino acids, peptide bonds are reformed, and and new proteins are synthesized. Other amino acids may be converted to FAs, ketone bodies, and glucose by hepatocytes. Other amino acids may be oxidized to generate ATP via Krebs and ETC.
79
Before amino acids can enter the Krebs cycle...
They need to be deaminated, which occurs in hepatocytes and produces ammonia. They also must first be converted to molecules that are part of the Krebs cycle or can enter the Krebs cycle.
80
Protein anabolism.
Formation of peptide bonds between amino acids to produce proteins. Occurs on ribosomes of every cell in the body. Directed by DNA and RNA. Stimulated by IGFs, thyroid hormones, insulin, estrogen, and testosterone.
81
How many essential amino acids are there?
10
82
Which amino acids can the body not produce at all?
Isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.
83
Which amino acids can the body produce, but not enough?
Arginine and histidine.
84
How are nonessential amino acids synthesized?
Transamination. The transfer of an amine group from an amino acid to pyruvic acid or to an acid in Krebs cycle.
85
What are the 4 possible fates of glucose 6-phosphate?
1) Glycogen synthesis.
2) Glucose release into blood.
3) Nucleic acid synthesis.
4) Glycolysis.
86
What are the 3 possible fates of pyruvic acid?
1) Lactic acid production.
2) Alanine production.
3) Gluconeogenesis.
87
What are the 2 possible fates of acetyl CoA?
1) Entry into Krebs cycle.
2) Lipid synthesis.
88
What do cells use for energy during fasting and starvation?
Ketone bodies.
89
What are the major regulators of metabolism? And which one dominates in the absorptive state?
Hormones, insulin.
90
Absorptive state reactions.
1) Glucose catabolism.
2) Amino acid catabolism.
3) Protein synthesis.
4) Lipid catabolism.
5) Glycogenesis.
6) Lipogenesis.
7) Triglyceride (mostly VLDL) transport from liver to adipose tissue.
91
_____ is the body's main energy source during the absorptive state.
Glucose.
92
___ of glucose absorbed from a meal is converted to triglycerides.
40%
93
___ of glucose absorbed from a meal is stored as glycogen in skeletal muscle and liver.
10%
94
What happens in the absorptive state?
Soon after a meal, GIP, glucose, and amino acids stimulate pancreatic beta cells to release insulin. Insulin increases the activity of enzymes needed for anabolism and the synthesis of storage molecules, decreases the activity of enzymes needed for catabolism, promotes entry to glucose and amino acids into cells, stimulates conversion of glucose into glycogen in liver and muscle cells, enhances triglyceride synthesis in liver and adipose cells, stimulates protein synthesis.
95
What is the main energy source for the nervous system?
Glucose, because FAs are unable to pass the BBB.
96
RBCs derive all of their ATP from which process?
Glycolysis. They cannot perform Krebs or ETC because they have no mitochondria.
97
Postabsorptive state reactions.
1) Glycogenolysis in the liver (4 hr supply).
2) Glycogenolysis in muscle (skeletal for contractions).
3) Lipolysis (adipose tissue).
4) Protein catabolism.
5) Gluconeogenesis.
6) FA catabolism.
7) Lactic acid catabolism (cardiac muscle).
8) Amino acid catabolism (hepatocytes).
9) Ketone bodies catabolism (hepatocytes; FA --> ketone bodies used by heart and kidneys for ATP).
98
What regulates metabolism during the post absorptive state?
Hormones (anti-insulin hormones) and sympathetic ANS.
99
What happens in the postabsorptive state?
Blood glucose declines, insulin secretion declines, and the release of anti-insulin hormones increases. Pancreatic alpha cells release glucagon, which increases release of glucose into blood from liver (gluconeogenesis and glycogenolysis). Glucose-sensitive neurons in hypothalamus also detect low blood glucose and increase sympathetic output, NE is released from sympathetic nerve endings, and adrenal medulla releases EP and NE.
EP: stimulates glycogen breakdown.
EP and NE: stimulate lipolysis, increase glucose and free FA levels in blood.
100
____ stores are depleted within a few hours of fasting.
Glycogen.
101
____ can provide energy for several weeks.
Catabolism of stored triglycerides and structural proteins.
102
Why is there a ready supply of amino acids for gluconeogenesis during starvation?
Because decreased insulin and increased cortisol levels slow the pace of protein synthesis and promote protein catabolism.
103
What happens during the first 2 days of fasting?
Day 1: Protein catabolism outpaces protein synthesis by 75g.
Day 2: Blood glucose has stabilized at 65 mg / 100 mL. The level of FAs in plasma has riven by 4x.
104
What is the most dramatic metabolic change that occurs with fasting and starvation?
Increase in formation of ketone bodies by hepatocytes.
105
Oxaloacetic acid.
During fasting, some glucose undergo glycolysis to pyruvic acid, which can be converted to oxaloacetic acid. Acetyl CoA enters Krebs by combing with oxaloacetic acid. When this acid is low due to fasting, only some of the available acetyl CoA can enter Krebs.
106
After 2 days of fasting, the level of ___ is 100-300x higher than normal.
Ketone bodies. These can also cross the BBB and supply the nervous system and cardiac/skeletal muscle fibres.
107
After 2 days of fasting, ketones supply ____ of the brain's fuel.
After 40 days of fasting, ketones supply ____ of the brain's fuel.
1/3, 2/3.
108
Energy balance.
The matching of energy intake to energy expenditure over time.
109
When the body catabolizes organic compounds in food, the heat energy released can be measured in ____ .
Calories. The amount of energy in the form of heat required to raise the temperature of 1 g of water by 1 degree C.
110
The catabolism of CHO or proteins yields how many calories?
4 kcal/g
111
The catabolism of fats yields how many calories?
9 kcal/g
112
The catabolism of alcohol yields how many calories?
7 kcal/g
113
Metabolic rate.
Overall rate at which metabolic reactions use energy.
114
Basal metabolic rate.
Metabolic rate under basal conditions (resting and fasting). BMR increases as the blood levels of thyroid hormones rise. The response to changing levels of thyroid hormones takes several days to appear.
115
How do thyroid hormones increase BMR?
They stimulate cellular respiration. As cells use more O2 to produce ATP, more heat is given off.
116
What may alter the metabolic rate?
Hormones, exercise, nervous system, body temperature, ingestion of food, age, gender, climate, sleep, nutrition.
117
How can the nervous system impact metabolic rate?
During exercise or stress, sympathetic ANS causes release of NE, which then stimulates NE and EP release from adrenal medulla. These hormones increase metabolic rate of body cells.
118
Each 1 degree C rise in core body temperature increases the metabolic rate by ____ .
10%
119
How can ingesting food impact metabolic rate?
Food-induced thermogenesis. Raises metabolic rate 10-20% due to the energy costs of digesting, absorbing and storing nutrients.
Greatest = after eating a high protein meal.
Lowest = after eating CHOs and lipids.
120
Is the metabolic rate higher in a child or an elderly person?
Child. Growth reactions.
121
How is BMR measured?
Measure the amount of O2 used per kcal of food metabolized. When the body uses 1 L of O2 to catabolize a mixture of triglycerides, CHOs and proteins, 4.8 kcal of energy is released.
122
Total metabolic rate.
Total energy expenditure by the body per unit of time.
123
BMR accounts for ____ of TMR.
60%
124
What may impact the total metabolic rate?
Exercise (voluntary and NEAT), and food-induced thermogenesis.
125
Non-exercise activity thermogenesis (NEAT).
The energy costs for maintaining muscle tone, posture, and involuntary fidgeting movements.
126
When energy use exceeds energy input, ____ in adipose tissue are catabolized to provide the extra energy. When energy input exceeds energy use, they are stored.
Triglycerides.
127
Which clusters of neurons in the hypothalamus are important for regulating food intake?
Arcuate nucleus and paraventricular nucleus.
128
Leptin.
Decreases adiposity. Synthesized and secreted by adipocytes in proportion to adiposity. As more triglycerides are stored, more leptin is secreted into the blood. Acts on the hypothalamus to inhibit circuits that stimulate eating, and activates circuits that increase energy expenditure. Stimulates melanocortin release, which inhibits food intake.
129
What happens when leptin and insulin levels are low?
Neurons that extend from the arcuate nucleus to the paraventricular nucleus release neuropeptide Y, which stimulates food intake.
130
Ghrelin.
Hormone produced by endocrine cells of the stomach. Increases appetite by stimulating the release of neuropeptide Y from hypothalamic neurons.
131
What increases appetite?
GHRH, androgens, glucocorticoids, EP, progesterone, ghrelin, neuropeptide Y.
132
What decreases appetite?
Increased blood glucose, glucagon, CCK, estrogens, EP, GI tract distention.
133
Core temperature.
The temperature in body structures deep to the skin and subcutaneous layer.
134
Shell temperature.
The temperature near the body surface in the skin and subcutaneous layer. Shell temperature is usually 1-6 C lower than core temperature.
135
How will a really high core temperature, or a really low core temperature kill you?
High: denature body proteins.
Low: cause cardiac arrhythmias.
136
What 4 ways can heat be transferred between the body and its surroundings?
1) Conduction.
2) Convection.
3) Radiation.
4) Evaporation.
137
Conduction.
Heat exchange that occurs between molecules of 2 materials that are in direct contact with each other.
At rest, 3% of body heat is lost via conduction to cooler solid materials in contact with the body.
138
Why is heat loss or gain via conduction much greater when the body is submerged in water?
Because water conducts heat 20x more effectively than air.
139
Convection.
Heat exchange by the movement of air or water between areas of different temperatures.
140
The contact of air or water with your body results in heat transfer by conduction and convection. How?
When cool air makes contact with the body, the air becomes warmed and less dense and is carried away by convection currents created as the less dense air rises. The faster the air moves, the faster the rate of convection.
At rest, 15% of body heat is lost to air via conduction and convection.
141
Radiation.
Heat exchange in the form of infrared rays between a warmer object and a cooler object without physical contact. Your body loses heat by radiating more infrared waves than it absorbed from cooler objects. If surrounding objects are warmer than you are, you absorb more heat than you lose.
At rest in a room at 21 C, 60% of heat loss occurs via radiation.
142
Evaporation.
Heat exchange by converting liquid to vapour.
At rest, 22% of heat loss occurs through evaporation of 700 mL of water per day (300 mL in exhaled air, 400mL from skin surface). This is insensible water loss.
143
Describe the relationship between evaporation and humidity.
The higher the relative humidity, the lower the rate of evaporation.
144
What functions as the body's thermostat?
Group of neurons in preoptic area of hypothalamus. Receive input from thermoreceptors in skin and hypothalamus. Generate APs at a higher frequency when blood temperature rises. APs from the preoptic area propagate to the heat-losing center and the heat-promoting center, which are both in the hypothalamus as well.
145
Describe the steps to increasing core temperature.
Peripheral thermoreceptors (skin) and central thermoreceptors (hypothalamus) send input to preoptic area --> activates heat-promoting center --> hypothalamus discharges APs and secretes TRH --> stimulates thyrotrophs in anterior pituitary to release TSH --> APs from hypothalamus and TSH activate effectors which respond in order to increase core temperature.
146
What are the 4 main ways the body works to increase core temperature?
1) Vasoconstriction: APs from heat-promoting center stimulate sympathetic nerves that cause blood vessels of skin to constrict.
2) EP and NE release: Increase cellular metabolism.
3) Shivering: Heat-promoting center stimulates brain regions that increase muscle one and heat production. As muscle tone increases in one muscle, the small contractions stretch muscle spindles in its antagonist, initiating a stretch reflex. The resulting contraction in the antagonist stretches muscle spindles in the agonist, and it too develops a stretch reflex.
4) Thyroid hormone release: Increase metabolic rate.
147
Describe the steps to decreasing core temperature.
High blood temperature stimulates peripheral and central thermoreceptors --> send input to preoptic area --> stimulates heat-losing center and inhibits heat-promoting center --> APs from heat-losing center cause vasodilation --> skin becomes warm --> excess heat is lost to environment via radiation and conduction --> metabolic rate decreases.
High blood temperature also stimulates sweat glands via hypothalamic activation of sympathetic nerves.
148
6 main types of nutrients.
Water, carbohydrates, lipids, proteins, minerals and vitamins.
149
Organic nutrients.
Carbohydrates, proteins and lipids. Provide the energy needed for metabolic reactions. Building blocks for body structures.
*Vitamins are also organic nutrients, but do not provide energy*
150
Vitamins and minerals are components of the...
Enzyme systems that catalyze metabolic reactions.
151
Recommended amounts of daily nutrients.
50-60% CHO
< 15% simple sugars
< 30% fats
< 10% saturated fats
12-15% protein
152
Minerals.
Inorganic elements that occur naturally in the earth's crust. 4% of total body mass. Concentrated most heavily in the skeleton. Excess amounts are excreted in urine and feces. Regulate enzymatic reactions. Work in buffer systems. Regulate osmosis of water. Involved in generation of nerve impulses.
153
Some minerals are toxic and fatal if ingested in the ____ form.
Non-ionized. The body generally uses the ions of the minerals rather than the non-ionized form.
154
Vitamins.
Organic nutrients. Maintain growth and metabolism. Most are coenzymes. Most cannot be synthesized by the body. Others can be produced by bacteria in the GI tract and then absorbed.
155
The body can assemble some vitamins if ____ are provided.
Provitamins.
156
Which type of vitamins can be stored?
Lipid-soluble vitamins, not water-soluble.
157
Antioxidant vitamins.
Vitamin C, E and beta-carotene (provitamin). They inactivate oxygen free radicals, protect against cancers, reduce buildup of atherosclerotic plaque, delay aging, and decrease the change of cataract formation.
