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chapter 10 Flashcards

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1
Q

what does digestion refer to?

A
  • the breakdown and processing of food while absoprtion refers to how nutrients actually enter the body
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2
Q

path of food once it enters the mouth?

A
  • mouth where saliva provides lubrication “bolus”
  • passes down the esophagus
  • empties into the stomach via the lower esophageal sphincter, gastroesophageal sphincter or the cardiac sphincter
  • passes through the pyloric sphincter which connects the stomach with the small intestine
  • enters to the large intestine
  • goes into the rectum
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3
Q

what does saliva contain?

A
  • salivary amylase
  • antimicrobial enzyme lysozyme
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4
Q

what are key components of the stomach?

A
  • highly acidic organ in which proteases such as pepsin begin to break down proteins, turning the bolus of food into a semi-digested substance known as chyme
  • very little absorption happens in the stomach (exceptions include water, some medications, caffeine and ethanol)
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5
Q

gastric acid is secreted by?

A
  • parietal cells and contains highly concentrated HCl that is used to keep the stomach at a pH of 1.5-3.5 (optimal for the functioning of enzymes in the sotmach and helps kill off bacteria)
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6
Q

what do foveolar cells secrete?

A
  • bicarbonate-rich mucus that helps protect the stomach lining from the acidity of its content
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7
Q

what do chief cells secrete?

A
  • releases the precursos pepsinogen which is then cleaved under intensely acidic conditions to create the active form pepsin
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8
Q

what is the job of pepsin?

A
  • a digestive enzyme secreted in the stomach
  • cleaves proteins at the site of aromatic residues, as such, it breaks proteins into smaller peptides but does not complete their digestion
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9
Q

the stomach secretes intrinsic factor which is necessary for?

A
  • the proper absorption and processing of vitamin B12
    • also secretes water to dilute the bolus and signaling molecules to help regulate digestion
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10
Q

the small intestine is divided into 3 sections called?

A
  • the duodenum
  • jejunum
  • ileum
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11
Q

the small intestine itself releases brush-border enzymes through cells contained in structures known as?

A
  • microvilli
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12
Q

what are some brush-border enzymes and their functions?

A
  • disaccharidases break down disaccharides
  • peptidases break down proteins
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13
Q

what are villi?

A
  • finger-like projections that extend into the lumen of the small intestine and dramatically increases the available surface area
  • the surfcace of villi are lined with enterocytes and are cjaracterized by microvilli
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14
Q

what are the parts of the large intestine?

A
  • the ascending colon
  • the transverse colon
  • the descending colon
  • sigmoid colon
  • rectum
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15
Q

what is the function of the rectum?

A
  • stores feces before it is expelled through the anus
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16
Q

what are the functions of the large intestine?

A
  • absorbs water frim the food undergoing difestion
  • hosts the largest community of bacteria in the body “gut microbiota”
  • no chemical digestion takes place in the large intestine, but absoprtion of remaining nutrients takes place to some extent
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17
Q

what does feces contain?

A
  • indigestible matieral and water
    • ex. cellulose
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18
Q

how does the bolus/chyme/feces move through the digestive system?

A
  • peristalsis and sphincters
    • involuntary process of contractions and relaxation of the smooth muscle surrounding the canal in various parts of the digestive tract
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19
Q

G cells secrete?

A
  • gastrin
    • promotes digestion with the main effect of stimulating parietal cells to secrete gastric acid
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20
Q

acidic chyme in the duodenum of the small intestine triggers the release of?

A
  • secretin from S cells
    • triggers the secretion and release of bicarbonate-rich mucus from the pancrease to neutralize the acidic chyme and promote the optimal functioning of the digestive enzymes that do their work in the small intetine
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21
Q

what is cholecystokinin (CCK)?

A
  • also secreted by the cells lining the small intestine and stimulates the secretion and release of digestive enxymes from the pnacrease and the release of bile from the gallbladder
    • secretin having the responsibility for pH levels and CCK being responsible for the actual enzymes and compounds that do the work of digestion
  • CCK also inhibits appetite
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22
Q

what is somatostatin?

A
  • released from several areas of the digestive tract and has the effect of inhibiting the release of many hormones involved in digestion such as gastrin, CCK, secretin
  • decreases the rate of emptying from the stomach and inhibiting the secretion of pancreatic hormones such as insulin and glucagon
  • inhibits the release of growth homrone
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23
Q

what is the enteric nervous system?

A
  • “second brain”
  • connected to the rest of the nervous system, it can actually function autonomously even if important connections with the rest of the nervous system are severed
  • the autonomic nervous system also has important effects on the GI system
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24
Q

what do villi contain?

A
  • capillaries and a lacteal
    • capillaries drain into the hepatic portal veon, which takes water-soluble nutrients for the liver “first pass metabolism”
    • lacteals drain lipids into the lymph vessels
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25
Q

how do carbohydrates get absorbed?

A
  • must be broken down into monosaccharides to be absorbed
  • secondary active transport coupled to Na+ is used to transport glucose and galactose into epithelial cells, while facilitated diffusion is used for fructose
  • all 3 of them then leave the epithelaial cells and enter the circulatory system via facilitated diffusion
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26
Q

how do amino acids get absorbed?

A
  • single amino acids and short chains of 2-3 a.a. enter the epithelial cells through secondary active transport and the leabe the epithelial cells and enter the bloodstream through facilitated diffusion
    • facilitated diffusion can be used to push these molecules into the bloodstream because the constant flow of blood through the capillaries means that they will always be moving down their concentration gradient
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27
Q

how are lipids absorbed?

A
  • lipids are formed into micelles with the aid of bile salts, and individual lipid molecules break away from those micelles to be absorbed into the epithelial cells (diffuse through the p.m.)
  • the eithelail cells in the small intestine combine fatty acids and monoglycerides to form triglycerides/ this reduces the concentration of free fatty acids and monoglycerides to the point that they can continue to diffuse into the cells
  • triglycerides and other lipids are combined inti fat droplets known as chlyomicrons which are then released into the interstitial space, from which they move on to the lacteals
  • lipids pass through the lymphatic system and eventually drain into the venous circulation of the body
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28
Q

the capillaries of the small intestine eventually drain into the?

A
  • hepatic portal vein which runs to the liver and the hepatic portal system
    • blood from the small intestine is thereby processed by the liver before entering the systemic circulation
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29
Q

what are the metabolic tasks that occur in the liver?

A
  • detoxifying compounds
  • metabolizing medications and drugs
  • storing excess carbohydrates as glycogen or excess fatty acids as triglycerides
  • mobilizing lipids into circulation in the form of lipoproteins and breaking down glycogen to release more glucose if necessary
30
Q

the path taken by proteins to be digested?

A
  • start to be broken down in the stomach by pepsone and then continue to be broken down in the small intestine by peptidases, the most notable of which are trypsin and aminopeptidase
    • trypsin cleaves proteins on the carboxyl end of the lysine or arginine (except when followed by proline)
    • aminopeptidases are a class of enzymes that break down proteins from the amino end
      • single amino acid residues then enter the epithelial cells of lining the lumen of the small intestine, from which they pass into the circulatory system
31
Q

what is the path taken by carbohydrates to be digested?

A
  • start to be broken down in the mouth, where starch is broken down into disaccharides by salivary amylase, but they are primarily broken down in the small intestine
  • the enzymes active in the small intestine include pancreatic amylse and disaccharidases such as sucrose lactase and maltase
  • the monosaccharides produced by disaccharides enter the epithelial cells of the small intestine and from there move into the circulatory system
  • cellulose and undigested starch then move into the large intestine, where they may be broken down or digested by the gut flora, resulting in short-chainn fatty acids that are used by the body and may mediate some of the health effects associated with the gut microbiota, and gas
32
Q

what is the path taken by triglycerides to be digested?

A
  • begin to be digested in the mouth by lingual lipase (functions at slightly acidic pH levels)
  • the majority of the digestion of triglycerides occurs through pancreatic lipase
  • the resulting free fatty acids and monoglycerides are separated by bile salts into micelles that also contain cholesterol and other lipids
  • lipids then enter the cells lining the small intestine, and are packaged into chlyomicrons, and released into lacteals, which drain into the lymphatic system and venous circulation
33
Q

what are vitamens?

A
  • non-macronutrient compounds that are vital for healthy functioning and cannot be synthesized in adequate quantities by the body, meaning that hey must be obtained from external sources
34
Q

what are the lipid soluble vitamins?

A
  • A, D, E, K
35
Q

what are the water soluble vitamins?

A
  • B and C
36
Q

what is vitamin A and its function?

A
  • retinol, retinal (+ carotenoids)
  • vision (low light and color)
37
Q

what is vitamin D and its function?

A
  • cholecalciferol
  • ergocalciferol
  • calcium and phosphate absorption from the gut
38
Q

what is vitamin E and its function?

A
  • tocopherols
  • tocotrienols
  • antioxidant
39
Q

what is vitamin K and its function?

A
  • phylloquinone
  • menaquinones
  • coagulation
40
Q

what is vitamin C and its function?

A
  • ascorbic acid
  • cofactor for reactions in collagen syntehsis, antioxidant
41
Q

what is vitamin B1 and its function?

A
  • thiamine
  • coenzyme in important metabolic reactions
42
Q

what is vitamin B2 and its function?

A
  • ribofalvin
  • coenzyme involved in electron transport chain, precursor of FAD
43
Q

what is vitamin B3 and its function?

A

niacin, niacinamide

  • precursor of NAD and NADP
44
Q

what is vitamin B5 and its function?

A

pantothenic acid

  • required for the synthesis of CoA, and metbaolism
45
Q

what is vitamin B6 and its function?

A

pyridoxine, pyridoxamine, pyridoxal

  • used as a coenzyme in many metabolic reactions
46
Q

what is vitamin B7 and its function?

A

biotin

  • cofactor for several carboxylase enzymes in metabolic reactions
47
Q

what is vitamin B9 and its function?

A

folic acid

  • ensures proper neurological development in pregnancy, required for fertility
48
Q

what is vitamin B12 and its function?

A

cyanocabalamin + derivatives

  • coenzyme in metabolic reactions, especially DNA syntehsis and lipid/amino acid metabolsim
49
Q

what are the key points to know about enzymes?

A
  • vitamins are compounds essential for healthy life that cannot be syntehsized in adequate quantities by the body and must be obtained externally
  • some vitamins actually reflect families of related compounds that are interconverted metabolically and/or contribute to the same overall effect
  • vitamins and vitamin derivatives often serve as coenzymes/cofactors in essential reactions
  • play a diverse and complex set of roles in the human body
50
Q

blood is filtered to form urine in the?

A
  • kidneys
    • supplied with blood by the renal zrteries, and then drain into the reanl veins
51
Q

the outside of the kidney is surrounded by the?

A
  • protective rissue of the renal capsule
52
Q

they kidney itself is divided into the outer and inner regions called the?

A
  • renal cortex (outside)
  • renal medulla (inside)
53
Q

what are the functional units of the kidneys that produce urine?

A
  • nephrons
54
Q

nephrons are divided into 2 major parts called?

A
  • the renal corpuscle- carries out the initial filtration and is located in the renal cortex
  • renal tubule- projects downward into the meduall before returning up to the cortex, at which point urine drains into a collecting duct
55
Q

collecting ducts empty via?

A
  • structures knwon as the medullary pyramids into minor calyces which drain into major calyces, which drain into a strcuture at the heart of each kidney knwon as the renal pelvis which then becomes the ureter
56
Q

the ureters drain downwards from the kidneys into the?

A
  • urinary bladder, whcih rests on the pelvic floor
57
Q

urine is them released from the bladder into the?

A
  • urethra, where it exits the body
58
Q

release of urine through the urethra is controlled by the?

A
  • urethral sphincter which has 2 components which both need to open for urine to flow
    • the external urethral sphincter (skeletal muscle) and the internal urethral sphincter (smooth muscle)
59
Q

the nephron can be divided into the?

A
  • renal corpuscle and the renal tubule
60
Q

the renal corpuscle contains the?

A
  • glomerulus and Bowman’s ccapsule
    • the glomerulus is a bunched-up set of capillaries through which water, ions, and small molecules filter our and are gathered into Bowman’s capsule, which wraps around the glomerulus
    • blood is supplied to the glomerulus through an afferent arteriole and exits through the efferent arteriole
61
Q

the fluid collected in Bowman’s capsule is known as?

A
  • the glomerular filtrate
62
Q

the renal tubule is composed of 3 main parts which are?

A
  • proximal convulted tubule
  • the loop of henle
  • the distal convuluted tubule
63
Q

what happens in the proximal convoluted tubule?

A
  • 2 way exchange happens
    • absorption predominates, in particular, large amounts of sodium ions are reabosrbed as well as other salts, water soluble vitamins, free amino acids, and glucose
    • secretion of waste products into the urine also happens in the PCT (hydrogen and potassium ions, nitrogen-containing compounds such as urea and ammonia and some medications are secreted into the urine)
64
Q

what happens in the loop of Henle?

A
  • reduces the volume of water in urine in a way that can be closely regulated in response to various conditions
  • the deeper you go into the medulla, the greater the concentration of solutes is, which facilitates the processes of osmosis and active/passive transport throughout the loop of Henle
65
Q

what are the functions of the descending and ascending imbs of the loop of Henle?

A
  • the descending limb is permeable to water but not ions, so as the descending limb plunges deeper into the increasingly hypertonic medulla, more water flows out of the loop of Henle and into the medulla, where it is eventually absorbed by the vasculature in the region and brought back into circulation so the filtrate at the bottom of the loop of Henle is quite concentrated
  • the ascending limb is permeable to water, but allows sodium and potassium ions to pass through. they diffuse down their concentration gradient at each stage, resulting in a much lower osmolarity by the time the filtrate completes its path through the loop
    • the top part of the ascending limb is known as the thick ascending limb, and this area also allows the active transport of sodium, potassium and chloride ions
    • the end product of this filtrate that is not actually more concentrated in terms of osmolarity than the initial filtrate, but with a significantly decreased volume
66
Q

the mechanism through which the loop of Henle operates is known as?

A
  • countercurrent multiplier
    • describes how the concentration gradient leading to solute and water flow are established and maintained
67
Q

the nephron has 2 more areas where water balance can be adjusted:

A
  • DCT and the collecting duct
    • aldosterone can act on both sites to promote sodiumr eabsoprtion, which in turn promotes water reabsorption mediated by the osmotic effects of this process
    • the DCT can also increases calcium reabsorption in response to parathyroid hormonem and can contribute to pH regulation by secreting or absorbing proteins as needed
    • the collecting duct can be affects by anti-diuretic hormone which increases water reabsorption directly
    • ANP promotes retention of sodium in the urine, which draws water with it, increasing the amount of water expelled in the urine and decreasing the blood pressure
68
Q

3 main hormones that affect fluid balance:

A
  • aldosterone
    • water retention by increasing sodium absorption: increased aldosterone = increased Na+ reabsorption = increased H2O reabsorption = increased plasma colume of blood = increased blood pressure
  • antidiuretic hormone (ADH)
    • promotes water retention directly by increasing water reabsorption in the collecting duct: increased ADH = increased H2O rentention = increased plasma volume of blood = increased blood pressure
      • because it only promotes water retention, ADH has teh effect of reducing the osmolarity of the blood
  • Atrial natriuretic peptide (ANP)
    • promotes sodium retention in the urine: increase ANP = decreased Na+ reabsorption = decreased H2O reabsorption = decreased plasma volume of blood = decreased blood pressure
69
Q

aldosterone is regulated by the kidneys via the?

A
  • renin-angiotensin aldosterone axis
70
Q

what is the renin-angiotensin-aldosterone axis?

A
  • juxtaglomerular cells in the afferent arterioles of the kidneys release renin in response to reduced blood pressure, reduced sodium levels, or signaling from the sympathetic NS
  • renin causes angiotensinogen to be cleaved to form angiotensis I, which is then converted to angiotensin II by an enzyme knwon as angiotensin-converting enzyme (ACE)
  • angiontensin II increases blood pressure through vasoconstriction and also triggers the release of aldosterone
71
Q

the excretory system regulates?

A
  • blood pressure
  • pH
  • excretion of nitrogenous wastes
72
Q

summary of urine formation

A

MCAT biology (12 decks)

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