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Biology II: Exam 1 > Chapter 33: Digestive System > Flashcards

Chapter 33: Digestive System Flashcards

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1
Q

Why do we need a digestive system?

A
  • Heterotrophs must take in the energy and nutrients needed to support their metabolism
  • Food that enters the mouth usually is in large pieces that can not be used directly.
  • Before a meal can be absorbed into the body and used, it must be broken down into small or modest-sized molecules.
  • This breakdown, and the absorption of the products of the breakdown, are the roles of the digestive system.
  • Our treatment will be limited to mammalian systems, and largely to our own species.
  • Many features function to increase the rate of digestion, important to energy-hungry endotherms.
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2
Q

Structure of the digestive system

A

Digestive system consists of the digestive tract and associated digestive glands.

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3
Q

Digestive tract

A

Tube that extends through the body from the lips of the mouth to the anus or cloaca
– Cavity of the tube is called the lumen of the gut
• Hence inner surface is luminal surface
• Glands that empty into gut are luminal glands

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4
Q

Digestive tract divided into 3 regions, based on size, shape, and embryonic derivation:

A
  1. Buccal cavity
  2. Pharynx
  3. Alimentary canal
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5
Q

Alimentary canal itself divided into 4 regions:

A
  1. Esophagus (Greek “entrance for eating”)
  2. Stomach
  3. Small intestine
    – Duodenum
    – Jejunum
    – Ileum
  4. Large intestine
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6
Q

In most vertebrates, alimentary canal ends in a ___

A

Cloaca

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7
Q

Cloaca

A
  • Common chamber receiving digestive tract and urinary/genital tract.
  • Empties via vent
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8
Q

Accessory digestive glands

A 
• Located outside walls of gut but secrete digestive enzymes into lumen via ducts
• Principal digestive glands: 
   -salivary glands
   -liver 
   -gall bladder 
   -pancreas
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9
Q

Development remainder

A

• 2nd invagination joins anterior end of gut to form mouth (later in development)
– Invagination called stomodeum, forms buccal cavity
– Invagination carries in surface ectoderm
– So mouth lined with ectoderm, but gut lined with endoderm
– This bit of development helps explain the nature of teeth (later)
– Boundary between buccal cavity and pharynx is palatoglossal (=glossopalatine) arch, bearing the uvula
– And note how/where your anterior pituitary forms.

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10
Q

Stomodeum is invagination that forms the ___

A

Buccal cavity

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11
Q

Mouth is lined with __1__, but gut lined with __2__

A
  1. Ectoderm

2. Endoderm

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12
Q

Boundary between buccal cavity and pharynx is ___1___ arch, bearing the __2__

A
  1. Palatoglossal (glossopalatine)

2. Uvula

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13
Q

Buccal Cavity

A

• Contains teeth, tongue, and palate (roof of mouth); discuss only teeth.

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14
Q

Teeth

A

– Help catch & hold prey
– In mammals especially, teeth play important role in digestion
• Serve to break up food into smaller particles, creating more surface area for digestive enzymes, thereby speeding digestion

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15
Q

Tooth anatomy

A
  • Crown
  • Root
  • Enamel
  • Dentin
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16
Q

Crown

A

portion above gum

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17
Q

Root

A

portion below gum

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18
Q

Enamel

A

forms surface of crown, hardest substance in body, of epidermal origin (98% mineral)

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19
Q

Dentin

A

below enamel, bulk of tooth, similar to bone in chemical composition but harder, of dermal origin (75% mineral)

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20
Q

Pharynx

A
  • 2nd of 3 regions of digestive tract
  • In adult mammal, little more than passageway for air.
  • In embryonic mammal, pharyngeal pouches present.
  • In “lower” vertebrates, remains major structural region, site of gills.
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21
Q

Even in adult mammal, many features are derived from pharynx:

A 
1st pharyngeal pouch: 
  -cavity housing middle ear
  -eustachian tube
Floor of pharynx: 
  -thyroid 
  -lung primordium
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22
Q

Esophagus

A

– 1st region of alimentary canal
– Connects pharynx to stomach
– Expandable to accommodate large food bolus
– Mucus secreted to lubricate passage of food
– Muscles contract to squeeze the bolus towards the stomach

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23
Q

____ resists entry of food into airway

A

Epiglottis

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24
Q

Stomach

A

– 2nd region of alimentary canal; receives food from esophagus
– Some absorption of water, salts, vitamins, but predominant task is to begin digestion with gastric juice
• Some enzymes
• Some mucus
• Mostly HCl secreted by glands in wall of stomach
– At rest, stomach relaxes into folds called rugae
– Chyme: stomach contents that are released into small intestine.

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25
Q

Chyme

A

stomach contents that are released into small intestine.

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26
Q

Stomach continued

A
  • 4 stomach regions
  • 2 sphincters
    • Cardiac sphincter: between esophagus and stomach
    • Pyloric sphincter: between stomach and small intestine
    – Gastric glands
    • Mucous cells
    • Parietal cells: source of HCl
    • Chief cells: source of protein-digesting (proteolytic) enzymes
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27
Q

Cardiac sphincter:

A

between esophagus and stomach

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28
Q

Pyloric sphincter:

A

between stomach and small intestine

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29
Q

Parietal cells:

A

source of HCl

30
Q

Chief cells:

A

source of protein-digesting (proteolytic) enzymes

31
Q

Small Intestine

A

– “Small” in diameter but often quite long
– Luminal cells have microvilli (brush border)
– Structural elaborations to increase surface area for digestion and absorption
• Increase length of small intestine
– So small intestine is long & coiled
• Increase surface area per unit length
– Circular folds (plica circularis) - 3X increase
– Villi (not microvilli), finger-like projections 10X
– Microvilli (elaborations of plasma membrane) 30X
– Total increase: 3 X 10 X 30 = 900 fold increase

32
Q

Structural elaborations increase surface area ____ fold

A

900

33
Q

Luminal cells have ____

A

Mircovilli (brush border)

34
Q

Small Intestine continued

A

– 3 regions of the small intestine:
• Duodenum
– Site of most intestinal digestion
– ~ 10 inches long in adult human
• Jejunum, ileum
– Site of most intestinal absorption of nutrients
– ~ 8 feet and ~12 feet long, respectively
– Ileocolic (ileocecal) valve
• Ileum-to-colon sphincter

35
Q

Duodenum
– Dew – oh – dee – num
- “dew – aw – deh – num” as alternative, and possibly more proper pronunciation)

A

– Site of most intestinal digestion

– ~ 10 inches long in adult human

36
Q

Jejunum and ileum

A

– Site of most intestinal absorption of nutrients

– ~ 8 feet and ~12 feet long, respectively

37
Q

Large Intestine

A

– Larger in diameter but much shorter in length
– Mucosa lacks villi
– In mammals, divided into large gentle loop called the colon, and a shorter, straight terminal segment called the rectum.
– Rectum empties to the exterior via the anus, where there is “one” last sphincter, the anal sphincter.
• Actually it is 2 sphincters
– Internal A.S. which is smooth muscle and involuntary
– External A.S. which is skeletal muscle and voluntary

38
Q

Large Intestine mucosa lacks ____

A

Villi

39
Q

Glands and Secretions of Digestion

A

• See Fig 33.10 in Urry et al. (p. 673)
– Know this material
– e.g., given location, know enzyme, or given enzyme know substrate, given substrate know product(s)

40
Q

• Digestive process must yield molecules small enough to be absorbed. For the most part, this means ….

A

– Proteins to peptides to amino acids
– Polysaccharides to oligosaccharides to monosaccharides
– Lipids to fatty acids and monoglycerides

41
Q

Glands and Secretions of Digestion

• Buccal cavity

A

– Secretion is saliva
• Mucus
• Salts: Na+, K+, Cl-, phosphate, bicarbonate
• Few enzymes, primarily amylase which begins digestion of starch.
• lysozyme: enzyme kills bacteria
• other antibacterial agents including immunoglobulin A
• metabolic wastes: urea & uric acid
• pH 6.8–7.0

42
Q

Glands and Secretions of Digestion

• Stomach

A

– Aside: zymogens
• In stomach and small intestine, digestive enzymes often released from digestive gland in an inactive form called a zymogen
• Zymogen then is converted to active form in the lumen of the gut, by another enzyme or some other factor.
• Name of specific zymogens end in ~ogen
– E.g., major enzyme of stomach is pepsin (proteins to polypeptides). Pepsin is released as pepsinogen.
– HCl from parietal cells converts pepsinogen to pepsin, and pepsin then can do the conversion itself.
– Stomach glands produce 2 – 3 L of fluid per day

43
Q

Stomach glands produce ____ L of fluid per day

A

2 - 3 Liters

44
Q

Glands and Secretions of Digestion

• Small intestine

A

– 2 major accessory glands are:
• Pancreas
• Liver

45
Q

Pancreas

A

• 2 important EXOcrine functions here
– Releases ~ 1.2 – 1.5 L/day of bicarbonate to neutralize chyme
» Enzymes of small intestine work best at neutral or near- neutral pH
– Releases many enzymes (as zymogens) that digest proteins, starch, & lipid (see Fig 33.10 in Urry et al.)
» These zymogens are activated by a membrane-bound enzyme (enterokinase) from the duodenum, and by the enzyme trypsin.

46
Q

Pancreas releases ~ ____ L/day of bicarbonate to neutralize chyme

A

1.2 - 1.5 Liters

47
Q

Liver

A
  • Produces bile from cholesterol
  • Bile is stored in the gall bladder, and released into the duodenum when chyme enters
  • Bile functions to emulsify fats (break large drops of lipid into much smaller drops), thereby increasing the surface area available for fat-digesting enzymes (lipases) to work [SA to V again !!]
  • maybe 900 ml bile secreted from liver cells each day, but can be concentrated 10-20X by gall bladder
48
Q

____ functions to emulsify fats (break large drops of lipid into much smaller drops), thereby increasing the surface area available for fat-digesting enzymes (lipases) to work

A

Bile

49
Q

Maybe __1__ ml bile secreted from liver cells each day, but can be concentrated __2__ by gall bladder

A
  1. 900 ml

2. 10 - 20x

50
Q

Absorption in small intestine

A

– Occurs primarily in jejunum and ileum
– Food must be broken down to amino acids (proteins), monosaccharides (carbohydrates), and fatty acids & monoglycerides (lipids)

51
Q

Absorption in small intestine

• Amino acids and monosaccharides are transported across the epithelial cell and into capillaries of the _____

A

Hepatic portal system

52
Q

Absorption in small intestine
____________:
- From capillary bed to blood vessels to capillary bed again without passing through heart
- Carries absorbed nutrients directly to liver for processing (except lipids

A

Portal System

53
Q

Absorption in small intestine

• Fatty acids and monoglycerides are handled differently…

A

– Inside the epithelial cell, re-synthesized as triglyceride
– Triglyceride then combined with phospholipid and cholesterol, and coated with a “skin” of protein to form a water-soluble droplet called chylomicrons
– Chylomicrons are processed by Golgi apparatus for extrusion from the cell
– Chylomicrons are too large to enter capillaries and instead enter lymphatic vessels (lacteals)

54
Q

Chylomicrons are __1__ to enter capillaries and instead enter __2__ vessels (lacteals)

A
  1. Too large

2. Lymphatic

55
Q

Absorption in large intestine

A

• ~99% of ~9 L of fluid passing through the human digestive tract is reabsorbed
– ~95% in the small intestine, & ~4% in large intestine
• Large intestine also absorbs some Vitamin K and other bacterial products
• Large intestine lacks villi and so has only ~ 1/10 absorptive surface area of the small intestine

56
Q

Absorption in large intestine
• ~___% of ~___ L of fluid passing through the human digestive tract is reabsorbed
– ~___% in the small intestine, & ~__% in large intestine

A

• ~99% of ~9 L of fluid passing through the human digestive tract is reabsorbed
– ~95% in the small intestine, & ~4% in large intestine

57
Q

Absorption in large intestine

• Large intestine lacks villi and so has only ~ ____ absorptive surface area of the small intestine

A

• Large intestine lacks villi and so has only ~ 1/10 absorptive surface area of the small intestine

58
Q

Hormonal Regulation of Digestion

A

• Won’t say anything more about neural control
– just remember the enteric nervous system, much control via reflexes outside the CNS
• Gastrin, Cholecystokinin (CCK), Secretin

59
Q

The ____ nervous system has much control of hormonal regulation of digestion via reflexes outside the CNS

A

Enteric

60
Q

Hormonal Regulation of Digestion

• Gastrin

A

– Polypeptide
– Stimulated by protein food in stomach, increase in pH
– Secreted by endocrine cells in pyloric region of stomach
– Acts on gastric glands of stomach to secrete HCl and pepsinogen, and on stomach to increase contractions (unusual hormone: target is same organ that releases it)

61
Q

• Gastrin

– Stimulated by protein food in stomach, ____ in pH

A

Increase

62
Q

• Gastrin

– Secreted by endocrine ___ in pyloric region of stomach

A

Cells

63
Q

• Gastrin is a ____ hormone: target is same organ that releases it

A

Unusual

64
Q

Hormonal Regulation of Digestion

• Cholecystokinin (CCK)

A

– Polypeptide, very similar structure to gastrin (gene duplication?)
– Secretion stimulated by presence of fatty acids and polypeptides in small intestine
– Secreted by (entero)endocrine cells in wall of duodenum
– 3 main functions:
• Stimulates gall bladder to release bile
• Stimulates pancreas to release digestive enzymes
• Stimulates brain to produce feeling of satiety after meal
– with secretin, inhibit stomach peristalsis & acid secretion (buy time for duodenum)

65
Q

Hormonal Regulation of Digestion

• Secretin

A

– Polypeptide (first hormone to be discovered – 1902)
– Secreted in response to food in stomach and strong acid in stomach and small intestine
– Secreted by endocrine cells in wall of duodenum
– Functions:
• Primarily to stimulate pancreas to release bicarbonate into duodenum
• With CCK, inhibit stomach peristalsis & acid secretion (buy time for duodenum)
• Aids fat digestion via increasing bile secretion

66
Q

Together, CCK and secretin, ____ stomach peristalsis & acid secretion

A

Inhibit (buy time for duodenum)

67
Q

The first hormone to be discovered in 1902 was ____

A

Secretin

68
Q

CCK functions to:
• Stimulates __1__ ____ to release bile
• Stimulates __2___to release digestive enzymes
• Stimulates __3__ to produce feeling of satiety after meal

A
  1. Gall bladder
  2. Pancreas
  3. Brain
69
Q

Secretin functions to:
• Primarily to stimulate pancreas to release __1__ into duodenum
• Aids fat digestion via __2__ bile secretion

A
  1. Bicarbonate

2. Increasing

70
Q

Gastric Fermentation

A

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Biology II: Exam 1 (4 decks)

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