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Human Physiology > Digestive System > Flashcards

Digestive System Flashcards

1
Q

What are the 3 primary functions of the digestive system

A

To digest food into absorbable nutrients, move (absorb) nutrients, water, and electrolytes from the GI lumen into blood and ISF using transport mechanisms, and repel foreign invaders via secretions

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2
Q

What are the 3 kinds of ingested macromolecules

A

Carbohydrates, proteins, and lipids (fats)

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3
Q

Describe digestion

A

Mechanical (chewing and churning) and chemical (enzymatic) breaks down food into absorbable units

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4
Q

What 6 secretions happen in the digestive system and where (4 places)

A

Saliva, mucus, digestive enzymes, bile, H2O, and ions all for chemical digestion and lubrication, coming from salivary glands, the pancreas, liver, and epithelial cells of the stomach and small intestine

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5
Q

What is absorption in the digestive system

A

Nutrients moved into the blood or lymph mainly in the small intestine using brush borer cells (enterocytes) on villi, but also some of ions and H2O in large intestine

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6
Q

What is motility

A

The movement of material through the GI tract via smooth muscle contractions

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7
Q

Where does carbohydrate digestion begin

A

The mouth via amylase from saliva (glucose polymers like starch and glycogen are broken down into disaccharides)

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8
Q

Where does carbohydrate chemical digestion continue

A

In the small intestine, epithelial cells secrete disaccharidase that breaks down disaccharides into monosaccharides, and the pancreas secretes amylase as well

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9
Q

What is the absorbable end unit of carbs

A

Monosaccharides

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10
Q

What glucose transporters move glucose and galactose in the small intestine

A

Apical entry: SGLT (Na+-linked cotransporter)
Basolateral exit: GLUT2

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11
Q

What glucose transporters move fructose in the small intestine

A

Apical entry: GLUT5
Basolateral exit: GLUT2

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12
Q

How do glucose, galactose, and fructose enter the blood in the small intestine

A

Simply diffuse through fenestrated (leaky) capillaries

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13
Q

Where does chemical digestion of proteins occur

A

The stomach (HCl denatures proteins and peptidases digest into di&tri peptides, and oligopeptides) and continues in small intestine (peptidases from epithelium and pancreas)

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14
Q

What triggers the pancreas to release peptidases into the small intestine

A

CCK

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15
Q

What do endopeptidases do

A

Break the peptide bond internally (in the middle)

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16
Q

What do exopeptidase do

A

Break the peptide bond on the terminal end (can be aminopeptidase or carboxypeptidase)

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17
Q

What are the absorbable units for proteins

A

Di-peptides, tri-peptides, oligopeptides, and free amino acids

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18
Q

How are free amino acids absorbed

A

Secondary active cotransport with Na+

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19
Q

How are di- and tri-peptides absorbed

A

Secondary active cotransport with H+

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20
Q

How are oligopeptides absorbed

A

Transcytosis (moving in vesicles through the cell)

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21
Q

What are the absorbable units of lipids

A

Free fatty acids and monoglycerides

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22
Q

Where are lipids chemically digested

A

In the small intestine (CCK triggers release of bile that forms emulsions and pancreas secretes lipase that breaks triglycerides into monoglycerides and free fatty acids)

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23
Q

Where is bile made and stored, and secreted

A

Made in the liver, stored in the gal bladder, secreted into the duodenum of the small intestine

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24
Q

How does bile work

A

Bile salts break down the fat droplets into smaller ones (emulsions then micelles) which increases the surface area for enzymatic digestion by lipase

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25
Q

How are fats absorbed

A

Via simple diffusion through the enterocytes (brush border) of lumen of the small intestine, cholesterol is actively transported to speed up absorption (too slow because of size)

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26
Q

Once monoglycerides and free fatty acids enter the smooth ER, what happens

A

They are reassembled into triglycerides which will combine with cholesterol and proteins to form large droplets (chylomicrons)

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27
Q

How are chylomicrons absorbed

A

Leave enterocytes into interstitial fluid where they are exocytosed into lacteals (lymphatic system) and venous blood

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28
Q

What are the characteristics of the smooth muscle of the GI tract

A

Circular (diameter) and longitudinal (length) muscle connected via gap junctions

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29
Q

What causes phasic contractions in the GI tract

A

Spontaneous slow wave potentials created by the interstitial cells of Cajal (pacemaker cells)

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30
Q

What are the 3 characteristics of the enteric nervous system

A

Neurons in the GI was that control motility and secretion, can work independently (short reflexes) or with CNS (long reflexes) via ANS

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31
Q

Where can GI peptides act

A

in digestive system to increase or decrease motility and secretion or outside the GI tract to influence hunger/satiety, food intake, and insulin/glucagon secretion

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32
Q

What 4 GI peptides influence motility and secretion

A

Cholecystokinin (bile), motlin (migrating complex), gastrin (HCl and pepsin), and secretin (gastric secretion to neutralize acid)

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33
Q

What GI peptides influence hunger/satiety and food intake

A

Cholecystokinin (satiety) and gherlin (hunger)

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34
Q

What GI peptides influence insulin/glucagon secretions (via pancreas)

A

Incretins

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35
Q

What parts of the body does the cephalic phase deal with

A

Oral cavity, esophagus, and stomach

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36
Q

What parts of the body does the gastric phase deal with

A

Stomach and intestines

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37
Q

What parts of the body does the intestinal phase deal with

A

Small intestine, large intestine, and rectum

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38
Q

What triggers the cephalic phase

A

Long, feedforward reflexes from brain (sight, smell, or taste of food) trigger saliva secretion (ANS control) from salivary glands (chemical digestion) and mastication/chewing begins (mechanical digestion), and triggers swallowing reflex

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39
Q

What 5 things is saliva made of

A

Water, ions, mucus, enzymes (amylase), and antibodies to moisten, lubricate, and digest food

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40
Q

What is the swallowing reflex (4 steps)

A

Integrated by the medulla oblongata, the tongue pushes bolus (food) against the soft palate, it passes through the closed airway (epiglottis) while breathing is inhibited and the food moves into the esophagus and stomach via peristaltic contractions

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41
Q

What is aspiration

A

Fluid or food entering the lungs during ingestion

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42
Q

Describe your upper esophageal sphincter at rest vs. during the cephalic phase

A

At rest, it is tonically contracted, when you swallow it relaxes

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43
Q

What happens during the integration of the cephalic and gastric phase reflexes

A

Before food arrival, long reflex of cephalic phase and PS ANS travels through vagal nerve to increase secretion and motility, then food entry initiates short reflexes that activate gastric phase

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44
Q

What are the 2 stimuli for the gastric phase

A

Distention (stretch) of the stomach and presence of peptides and amino acids in the gastric lumen

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45
Q

What are the 3 functions of the gastric phase of digestion

A

Storage of food (upper stomach relaxes and expands), digestion (lower stomach), and protection (destroyed pathogens with swallowed with food)

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46
Q

Describe digestion during the gastric phase (4 things)

A

Chemical and mechanical digestion turn food into chyme (watery mixture), digests proteins, secretes HCl, enzymes, paracrine signals, and hormones, and regulates entry into the small intestine via peristaltic contractile waves

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47
Q

How is acid secreted in the stomach during the gastric phase

A

Parietal cells (gastric cells) secrete hydrochloric acid using a proton pump (primary active for H+), regulated by gastrin (stimulated by peptides and amino acids - short reflex)

48
Q

What are 3 functions of hydrochloric acid

A

To denature proteins for enzyme access, to activate a peptidase (chief cells secrete pepsin), and to kill pathogens

49
Q

What protection occurs during the gastric phase

A

Mucus and bicarbonate buffer are continuously secreted by gastric mucous cells to form a barrier of gastric mucosa

50
Q

What are the 4 things chyme does once it enters the small intestine

A

Slows chyme delivery (via ENS and GI peptides like secretin, CCK, and incretins), decreases stomach acid and increases SI bicarbonate (secretin breaks down acids), increase digestive enzymes and bile (CCK to break down fats and proteins), and increase insulin (incretins to break down carbs)

51
Q

What are the 2 kinds of incretins

A

GIP (gastric inhibitory peptide) and GLP-1 (glucagon-like peptide-1)

52
Q

What happens during the intestinal phase in the small intestine

A

Chyme mixes with enzymes for chemical digestions (enterocytes secrete disaccharides and peptidases), exocrine pancreas secretes amylase and peptidases, and the gallbladder secretes bile

53
Q

Where does most of the bicarbonate come from in the intestinal phase

A

The pancreas, some also comes from duodenum

54
Q

What does the exocrine pancreas secrete

A

Acing cells secrete digestive enzymes and duct cells secrete sodium bicarbonate (NaHCO3)

55
Q

What does the endocrine pancreas secrete

A

Alpha islet cells secrete glucagon and beta islet cells secrete insulin, both to regulate blood glucose levels

56
Q

What 3 things happen in the large intestine during the intestinal phase

A

Water is concentrated for secretion and most water in chyme is absorbed, bacteria in the colon break down undigested carbs and proteins via fermentation, and some absorption of ions, minerals, vitamins, and water

57
Q

What happens in the rectum during the intestinal phase

A

Defecation (waste material eliminated from digestive tract)

58
Q

What triggers the defecation reflex and what does it do

A

Distention of rectum creates urge to defecate, then internal anal sphincter relaxes (ENS and PSNS control) and external anal sphincter contracts (skeletal muscle, somatic control)

59
Q

What are the two key hypothalamic control centers in the digestive system

A

Appetite center (always on) and satiety center (inhibits feeding center)

60
Q

What 3 input signals go to the appetite and satiety centers

A

Neural inputs (cerebral cortex and limbic system), peptide hormones (GI tract), and adipocytokines (adipose tissue)

61
Q

What are adipocytokines

A

Chemical signals released by adipose tissue involved in energy homeostasis and regulation of glucose and lipid metabolism

62
Q

What does neuropeptide Y (NPY) do

A

Released from the brain, it increases food intake and energy storage (fat)

63
Q

What does gherlin do

A

Secreted by empty stomach, increases hunger

64
Q

What does leptin do

A

Made by adipocytes, as fat stores increase, more leptin is secreted to decrease food intake (negative/inhibitory feedback for NYP)

65
Q

What do CCK and incretin (GLP-1) do to the hypothalamic feeding center

A

Released from the duodenum in response to fats and carbs in chyme, they promote satiety and decrease food intake

66
Q

What is metabolism

A

Chemical processes occurring in a living organism to maintain life (all anabolic and catabolic reactions)

67
Q

What are wastes from nutrient conversion

A

Urea, CO2, H2O, etc.

68
Q

How are absorbed nutrients stored

A

Glycogen (mostly liver and muscle) or triglycerides in adipose tissue

69
Q

Which macromolecule provides the most energy

A

Fat

70
Q

What 3 processes are involved in ATP production

A

Glycolysis (cytosol), citric acid/Kreb cycle (mitochondria), and electron transport system (mitochondria)

71
Q

Where do carbohydrates enter the production of ATP

A

Glycolysis as glucose, then broken into 2 3-carbon chains)

72
Q

Where do lipids enter the production of ATP

A

Glycerol enters glycolysis, fatty acids go through beta-oxidation to become acyl units (2 carbons) which then enter the Kreb cycle as acetyl CoA

73
Q

Where do amino acids enter the production of ATP

A

At various points

74
Q

What is glycogenesis

A

Production of glycogen

75
Q

What is lipogenesis

A

Production of fat

76
Q

What is lipolysis

A

Breakdown of fat into fatty acids

77
Q

What is glycogenolysis

A

Breakdown of glycogen into glucose

78
Q

What is gluconeogenesis

A

Making glucose from amino acids

79
Q

Which state of digestion of anabolic and which state is catabolic (fed vs fasted)

A

Fed/absorptive is anabolic and fasted/post-absorptive if catabolic

80
Q

What happens to amino acids during the fed state

A

Amino acids are made into proteins and excess is converted into fat

81
Q

What happens to proteins in the fasted state

A

Proteins broken into amino acids (only during extended fasting), amino acids are deaminated for glycolysis, or made into glucose (gluconeogenesis)

82
Q

What is created when amino acids are deaminated for glycolysis

A

Ammonia (NH3) is made, goes to urea

83
Q

What happens to carbs during the fed state

A

Carbs are used for ATP (glycolysis) or stored as glycogen (glycogenesis) in the liver, excess converted into fat

84
Q

What happens to lipids during the fed state

A

Lipids are converted into fat in adipocytes (lipogenesis)

85
Q

What happens to liver glycogen during the fasted state

A

Liver glycogen broken down to glucose (glycogenolysis) to use in glycolysis

86
Q

What happens to lipids during the fasted state

A

Triglycerides are broken down to glycerol and fatty acids by lipases which are used to produce ATP

87
Q

What is the dominant hormone in the fed state and why

A

Insulin because of high blood glucose and amino acid levels, resulting in secretion of insulin from beta-cells of the pancreas

88
Q

What is the dominant hormone in the fasted state and why

A

Glucagon because low blood glucose levels result in secretion of glucagon from alpha-cells of the pancreas

89
Q

Describe the 3 characteristics of insulin

A

Anabolic hormone that promotes glucose uptake, glucose metabolism (glycolysis), and energy storage as glycogen and fat (glycogenesis and lipogenesis) to decrease plasma glucose and increase fat storage

90
Q

What kinds of glucose uptake are insulin-sensitive and why

A

Adipose tissue and resting skeletal muscle because GLUT4 (carrier protein) is either in the membrane of hepatocytes (liver) or not to aid in facilitated diffusion

91
Q

What factors influence insulin secretion

A

Feedforward effects of GI hormones, PSNS activity (increased during and after a meal), and SNS activity (inhibits beta-cells of pancreas)

92
Q

What is the endocrine response to hypoglycemia

A

Glucagon promotes the breakdown of glycogen (glycogenolysis) and makes it into glucose (gluconeogenesis) to increase plasma glucose

93
Q

What does homeothermic mean

A

Homeostatically regulate internal temperature within narrow range

94
Q

What does hyperthermia cause

A

Denatures enzymes

95
Q

What does hypothermia cause

A

Chemical reactions are too slow

96
Q

What is the average oral temperature

A

98.6 degrees F (~96-99.99) with daily fluctuations of about 1.8 degrees

97
Q

What is heat loss equal to

A

Internal heat production from metabolism and movement + external heat input

98
Q

What are the four mechanisms of heat exchange

A

Conduction, convection, evaporation, and radiation

99
Q

What is conduction

A

Gain or loss of heat through contact

100
Q

What is convection

A

Gain or loss of heat by bulk flow of air or water

101
Q

What is radiation

A

Gain or loss of heat via gradient energy (warm surfaces emit and absorb electromagnetic waves)

102
Q

What is evaporation

A

Loss of heat from skin and respiratory tract

103
Q

What are the 2 unregulated sources of heat production

A

Metabolism (~75% of nutrient energy), and “waste heat” generated by voluntary muscle contractions

104
Q

What are the 2 kinds of regulated heat production

A

Shivering thermogenesis (involuntary tremors in skeletal muscles caused by hypothalamic thermoregulatory center) and non-shivering thermogenesis

105
Q

What receptors feed into the hypothalamic thermoregulatory center

A

Central thermoreceptors sense changes in core body temp and peripheral thermoreceptors sense changes in environmental temperature

106
Q

What are 3 characteristics of non-shivering thermogenesis

A

Important for thermoregulation in newborns, only in brown adipose tissue, and involves mitochondrial coupling

107
Q

What is brown adipose tissue/brown fat

A

Higher density of mitochondria and less lipids

108
Q

What is mitochondrial uncoupling

A

Energy from electron transport system released as heat instead of making ATP

109
Q

What are the bodies 3 thermoregulatory reflexes

A

Vascular (vasoconstriction or vasodilation), sweat secretion, and/or shivering

110
Q

How does the body respond to decreased temperature

A

Hypothalamic thermoregulatory neurons activate sympathetic neurons causing cutaneous vasoconstriction and possibly non-shivering thermogenesis, while somatic motor neurons activate shivering thermogenesis

111
Q

How does the body respond to increased temperature

A

Hypothalamic thermoregulatory neurons activate sweat glands which secrete sweat, and cutaneous vasodilation

112
Q

What kinds of neurons are used for in the SNS for thermoregulaiton

A

Sympathetic cholinergic neurons release ACh onto muscarinic receptors

113
Q

What is the therm-neutral zone

A

Range of environmental temps in which thermoregulation requires only vascular adjustments (don’t need to sweat or shiver)

114
Q

When does the body’s set point for temperature change

A

During fever due to pyrogens (from macrophages in WBCs) that act on the hypothalamus or postmenopausal hot flashes (changes in hormone levels act on hypothalamus)

115
Q

What are 3 benefits to having a fever

A

Slow down bacterial and viral growth, increases WBCs, and reduces severity of illness and shortens illness duration

Human Physiology (12 decks)

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