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Chapter%2024%20Digestive

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Title: Chapter%2024%20Digestive


1
Digestive System
Chapter 24
2
Digestive System
Basic processes of the digestive system
1. Ingestion 2. Secretion 3. Mixing and
Propulsion 4. Digestion 5. Absorption 6.
Defecation
3
Digestive System
Two groups of organs
Gastrointestinal tract (GI) mouth, pharynx,
esophagus, stomach, small intestine, and
large intestine. Accessory organs teeth,
tongue, gallbladder, salivary glands, liver,
and pancreas
4
Digestive System
5
Histology
Mucosa - secretion of mucous, absorption,
protection 1. Surface epithelium 2. Lamina
propria 3. Muscularis mucosae Submucosa -
blood and lymphatic vessels Muscularis Serosa -
visceral peritoneum
6
Neural Innervation
7
Peritoneum
Largest serous membrane of the body visceral
layer covers organs parietal layer lines
the walls of body cavity Peritoneal cavity
space between layers contains serous fluid
Greater omentum Falciform Ligament Lesser
omentum Mesentery Mesocolon
8
Peritoneum
9
Mouth
Palate Uvula Vestibule Tongue Gums Teeth
10
Salivary Glands
salivation
11
Tongue
12
Teeth Structure and Composition
13
Teeth
14
Digestion in the Mouth
  • Mechanical digestion (mastication or chewing)
  • breaks into pieces
  • mixes with saliva so it forms a bolus
  • Chemical digestion
  • amylase
  • begins starch digestion at pH of 6.5 or 7.0 found
    in mouth
  • when bolus enzyme hit the pH 2.5 gastric juices
    hydrolysis ceases
  • lingual lipase
  • secreted by glands in tongue
  • begins breakdown of triglycerides into fatty
    acids and glycerol

15
Digestive Activities of the Mouth
16
Pharynx
17
Esophagus
18
Swallowing
19
Digestive Activities of the Pharynx and Esophagus
20
Stomach
Regions Cardia Fundus Body Pylorus
21
Histology of the Stomach
22
Histology of the Stomach
23
Histology of the Stomach
24
Secretion of HCl
25
Mechanical and Chemical Digestion in Stomach
  • Mechanical digestion
  • Mixing waves gentle, rippling peristaltic
    movements creates chyme
  • Chemical digestion
  • Digestion by salivary amylase continues until
    inactivated by acidic gastric juice
  • Acidic gastric juice activates lingual lipase
  • Digest triglycerides into fatty acids and
    diglycerides
  • Parietal cells secrete H and Cl- separately but
    net effect is HCl
  • Kills many microbes, denatures proteins
  • Pepsin secreted by chief cells digest proteins
  • Secreted as pepsinogen
  • Gastric lipase splits triglycerides into fatty
    acids and monoglycerides
  • Small amount of nutrient absorption
  • Some water, ions, short chain fatty acids,
    certain drugs (aspirin) and alcohol

26
Digestive Activities of the Stomach
27
Pancreas
28
Pancreatic juice
  • 1200 - 1500ml daily
  • Mostly water
  • Sodium bicarbonate buffers acidic stomach chyme
  • Enzymes
  • Pancreatic amylase
  • Proteolytic enzymes trypsin (secreted as
    trypsinogen), chymotrypsin (chymotrypsinogen),
    carboxypeptidase (procarboxypeptidase), elastase
    (proelastase)
  • Pancreatic lipase
  • Ribonuclease and deoxyribonuclease

29
Regulation of Pancreatic Secretions
  • Secretin
  • acidity in intestine causes increased sodium
    bicarbonate release
  • GIP
  • fatty acids sugar causes increased insulin
    release
  • CCK
  • fats and proteins cause increased digestive
    enzyme release

30
Liver and Gall bladder
31
Role and Composition of Bile
  • Hepatocytes secrete 800 - 1000 mL of bile daily
  • Mostly water, bile salts, cholesterol, lecithin,
    bile pigments and several ions
  • Partially excretory product/ partially digestive
    secretion
  • Bilirubin principal bile pigment
  • Derived from heme of recycled RBCs
  • Breakdown product stercobilin gives feces brown
    color
  • Bile salts play role in emulsification
  • Also aid in absorption of lipids following
    digestion

32
Bile Secretion and Regulation
33
Bile Secretion and Regulation
34
Small intestine
35
Histology of Small Intestine
36
Cells of Small Intestine
37
Brush Border
38
Segmentation
Rhythmic local contractions. Mixes food
with digestive juices
39
Digestion of Carbohydrates
  • Mouth salivary amylase
  • Esophagus stomach nothing happens
  • Duodenum pancreatic amylase
  • Brush border enzymes (maltase, sucrase lactase)
    act on disaccharides
  • produces monosaccharides fructose, glucose
    galactose
  • lactose intolerance (no enzyme bacteria ferment
    sugar)--gas diarrhea

40
Digestion of Proteins
  • Stomach
  • HCl denatures or unfolds proteins
  • pepsin turns proteins into peptides
  • Pancreas
  • digestive enzymes split peptide bonds between
    different amino acids
  • brush border enzymes aminopeptidase or
    dipeptidase split off amino acid at amino end
    of molecule or split dipeptide

41
Digestion of Lipids
  • Mouth lingual lipase
  • Small intestine
  • emulsification by bile
  • pancreatic lipase---splits into fatty acids
    monoglyceride
  • no enzymes in brush border

42
Digestion of Nucleic Acids
  • Pancreatic juice contains 2 nucleases
  • ribonuclease which digests RNA
  • deoxyribonuclease which digests DNA
  • Nucleotides produced are further digested by
    brush border enzymes (nucleosidease and
    phosphatase)
  • Absorbed by active transport

43
Summary of Digestive Enzymes
44
Absorption in Small Intestine
45
Absorption of Monosaccharides
  • Absorption into epithelial cell
  • glucose galactose----sodium symporter(active
    transport)
  • fructose-----facilitated diffusion
  • Movement out of epithelial cell into bloodstream
  • by facilitated diffusion

46
Absorption of Lipids
  • Small fatty acids enter cells then blood by
    simple diffusion
  • Larger lipids exist only within micelles (bile
    salts coating)
  • Lipids enter cells by simple diffusion leaving
    bile salts behind in gut
  • Bile salts reabsorbed into blood reformed into
    bile in the liver
  • Fat-soluble vitamins are enter cells since were
    within micelles

47
Absorption of Lipids
  • Inside epithelial cells fats are rebuilt and
    coated with protein to form chylomicrons
  • Chylomicrons leave intestinal cells by exocytosis
    into a lacteal
  • travel in lymphatic system to reach veins near
    the heart
  • removed from the blood by the liver and fat
    tissue

48
Absorption of Amino Acids
  • Absorption into epithelial cell
  • active transport with Na or H ions (symporters)
  • Movement out of epithelial cell into blood
  • diffusion

49
Absorption of Electrolytes
  • Sources of electrolytes
  • GI secretions ingested foods and liquids
  • Enter epithelial cells by diffusion secondary
    active transport
  • sodium potassium move Na/K pumps (active
    transport)
  • chloride, iodide and nitrate passively follow
  • iron, magnesium phosphate ions active
    transport
  • Intestinal Ca2 absorption requires vitamin D
    parathyroid hormone

50
Absorption of Vitamins
  • Fat-soluble vitamins
  • travel in micelles are absorbed by simple
    diffusion
  • Water-soluble vitamins
  • absorbed by diffusion
  • B12 combines with intrinsic factor before it is
    transported into the cells
  • receptor mediated endocytosis

51
Absorption of Water
  • 9.3 liters of fluid dumped into GI tract each day
  • Small intestine reabsorbs 8.3 liters
  • Large intestine reabsorbs 90 of that last liter
  • Absorption is by osmosis through cell walls into
    vascular capillaries inside villi

52
Summary of Digestive Activities
Pancreas Liver Gallbladder Small Intestine
53
Large intestine
54
Histology of Large Intestine
55
Cells of Large Intestine
56
Summary of Digestive Activities of Large Intestine
57
Summary of Organs of Digestive System
58
Gastric Phases
1. Cephalic phase - triggered by the aroma,
taste, sight, or thought of food. 2. Gastric
phase - food in the stomach stimulates local
nerves and glands (distension and gastrin). 3.
Intestinal phase - excitatory starts with
appearance of digested food in the duodenum
production of a hormone (intestinal gastrin)
which stimulates gastrin secretion in the
stomach inhibitory phase.
59
Regulation of Gastric emptying
Distention stomach contents increase secretion
of gastrin hormone vagal nerve impulses
Enterogastric reflex regulates amount released
into intestines inhibition of gastric emptying
60
Hormones that Control Digestion
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