Transcript Biol 155 Human Physiology

SISTEMA DIGESTIVO
Es un tubo abierto: extensión del
medio ambiente!
S
E
absorción
Digestión:
•mecánica (trituración)
•química (enzimas hidrolíticas)
EL TRACTO DIGESTIVO
Anatomía del sistema digestivo
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Digestive tract
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Accessory organs
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Alimentary tract or
canal
GI tract
Primarily glands
Regions
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Mouth or oral cavity
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Oral Cavity
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Mouth or oral cavity
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Lips (labia) and
cheeks
Palate: Oral cavity
roof
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Vestibule: Space
between lips or cheeks
and alveolar processes
Oral cavity proper
Hard and soft
Palatine tonsils
Tongue: Involved in
speech, taste,
mastication,
swallowing
Teeth

Two sets
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Primary, deciduous,
milk: Childhood
Permanent or
secondary: Adult (32)
Types
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Incisors, canine,
premolar and molars
Tooth structure:
Salivary Glands
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Produce saliva
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Prevents bacterial
infection
Lubrication
Contains salivary
amylase
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Breaks down starch
Three pairs
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Parotid: Largest
Submandibular
Sublingual: Smallest
Production of Salivary juice
SALIVARY SECRETIONS
1. Serous secretion that contains ptyalin,
which is an enzyme for digesting
starches.
2.
Mucous secretion that contains mucin
for lubricating and for surface
protective purposes.
3. Saliva also contains IgA antibodies and
lysozyme, which help to destroy any
microorganisms in the oral cavity.
Swallowing reflex: Soft Palate &
Esophagus
Figure 21-13: The swallowing reflex
Deglutition (Swallowing)

Three phases

Voluntary


Bolus of food moved by tongue from oral cavity to
pharynx
Pharyngeal
Reflex: Upper esophageal sphincter relaxes, elevated
pharynx opens the esophagus, food pushed into
esophagus

Esophageal

Reflex: Epiglottis is tipped posteriorly, larynx elevated
to prevent food from passing into larynx
Histología del tracto digestivo
Peritoneum and Mesenteries
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Peritoneum
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Visceral: Covers organs
Parietal: Covers interior
surface of body wall
Retroperitoneal: Behind
peritoneum as kidneys,
pancreas, duodenum
Mesenteries
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
Routes which vessels and
nerves pass from body wall to
organs
Greater omentum
Lesser omentum
Pharynx and Esophagus
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
Pharynx
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
Nasopharynx
Oropharynx: Transmits
food normally
Laryngopharynx:
Transmits food
normally
Esophagus


Transports food from
pharynx to stomach
Passes through esophageal
hiatus (opening) of
diaphragm and ends at
stomach


Hiatal hernia
Sphincters
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
Upper
Lower
Functions
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Ingestion: Introduction of food into stomach
Mastication: Chewing
Propulsion
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Deglutition: Swallowing
Peristalsis: Moves material through digestive tract
Stomach Anatomy:
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Openings
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Gastroesophageal:
To esophagus
Pyloric: To
duodenum
Regions
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Cardiac
Fundus
Body
Pyloric
Stomach Histology:
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Layers
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Serosa or visceral
peritoneum:
Outermost
Muscularis: Three
layers
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Outer longitudinal
Middle circular
Inner oblique
Submucosa
Mucosa
Stomach Histology
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Rugae: Folds in
stomach when empty
Gastric pits: Openings
for gastric glands
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Contain cells
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Surface mucous: Mucus
Mucous neck: Mucus
Parietal: Hydrochloric
acid and intrinsic factor
Chief: Pepsinogen
Endocrine: Regulatory
hormones
Hydrochloric Acid Production
Gastric Phase: The Stomach
Figure 21-15: The mucus-bicarbonate barrier of the gastric mucosa
Phases of Gastric
Secretion
Movements in Stomach
Small Intestine
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Site of greatest amount of
digestion and absorption
Divisions
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Modifications
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Duodenum
Jejunum
Ileum: Peyer’s patches or
lymph nodules
Circular folds or plicae
circulares, villi, lacteal,
microvilli
Cells of mucosa
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Absorptive, goblet, granular,
endocrine
Small Intestine Secretions
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Mucus
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Digestive enzymes
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Protects against digestive enzymes and stomach acids
Disaccharidases: Break down disaccharides to
monosaccharides
Peptidases: Hydrolyze peptide bonds
Nucleases: Break down nucleic acids
Duodenal glands

Stimulated by vagus nerve, secretin, chemical or tactile
irritation of duodenal mucosa
Duodenum Anatomy and
Histology
Duodenum and Pancreas
Large Intestine, H2O Absorption &
Defecation
Figure 21-27: Anatomy of the large intestine
Large Intestine Digestion &
Absorption
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Bacterial
fermentation:
Vit. K , lactate &
butyrate
Water and
electrolyte
secretion &/or
absorption
Figure 21-28: NaCl reabsorption by colonocytes
Large Intestine Digestion &
Absorption
Figure 21-29: NaCl secretion by colonic crypt cells
Phases of Digestion: Overview
Figure 21-11: Overview of functions in different regions of the digestive system
Regulating Digestion: CNS and
Enteric Nervous System (ENS)
Figure 21-9: The enteric nervous system
Cephalic and Oral Phases of
Digestion
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Cephalic: anticipation of food
CNS  ANS long reflex
 Enteric  cells short reflex
 GI motility
 GI secretions
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Mouth: starts digestion
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Grind, mix & liquefy
Saliva: water, enzymes, mucus & lysozyme
Cephalic and Oral Phases of
Digestion
Figure 21-12: Long and short reflexes in the stomach
Liver
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Lobes
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Major: Left and right
Minor: Caudate and
quadrate
Ducts
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Common hepatic
Cystic
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From gallbladder
Common bile
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Joins pancreatic duct at
hepatopancreatic ampulla
Functions of the Liver
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Bile production
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Storage
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Hepatocytes remove ammonia and convert to urea
Phagocytosis
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Glycogen, fat, vitamins, copper and iron
Nutrient interconversion
Detoxification
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Salts emulsify fats, contain pigments as bilirubin
Kupffer cells phagocytize worn-out and dying red and white blood cells,
some bacteria
Synthesis
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Albumins, fibrinogen, globulins, heparin, clotting factors
Blood and Bile Flow
Duct System
Gallbladder
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Bile is stored and concentrated
Stimulated by cholecystokinin and vegal
stimulation
Dumps into small intestine
Production of gallstones possible

Drastic dieting with rapid weight loss
Pancreas

Anatomy
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Endocrine
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Exocrine
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Pancreatic islets produce
insulin and glucagon
Acini produce digestive
enzymes
Regions: Head, body, tail
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Secretions
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Pancreatic juice (exocrine)
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Trypsin
Chymotrypsin
Carboxypeptidase
Pancreatic amylase
Pancreatic lipases
Enzymes that reduce DNA
and ribonucleic acid
Bicarbonate Ion Production
Gastric hormones:
Movement in small intestine:
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Mixing: Segmental contraction that occurs in small intestine
Secretion: Lubricate, liquefy, digest
Digestion: Mechanical and chemical
Absorption: Movement from tract into circulation or lymph
Elimination: Waste products removed from body
Large Intestine:
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Extends from ileocecal junction to anus
Consists of cecum, colon, rectum, anal canal
Movements sluggish (18-24 hours)
Large Intestine
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Cecum
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Colon
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Ascending, transverse, descending, sigmoid
Rectum
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Blind sac, vermiform appendix attached
Straight muscular tube
Anal canal
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Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)
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Hemorrhoids: Vein enlargement or inflammation
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Secretions of Large Intestine
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Mucus provides protection
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Parasympathetic stimulation increases rate of goblet
cell secretion
Pumps
Exchange of bicarbonate ions for chloride ions
 Exchange of sodium ions for hydrogen ions
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Bacterial actions produce gases called flatus
Histology of Large Intestine
Movement in Large Intestine
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Mass movements
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Local reflexes in enteric plexus
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Gastrocolic: Initiated by stomach
Duodenocolic: Initiated by duodenum
Defecation reflex
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Common after meals
Distension of the rectal wall by feces
Defecation
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Usually accompanied by voluntary movements to expel feces
through abdominal cavity pressure caused by inspiration
Reflexes in
Colon and
Rectum:
Digestion, Absorption,
Transport

Digestion
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Breakdown of food molecules for absorption into
circulation
Mechanical: Breaks large food particles to small
 Chemical: Breaking of covalent bonds by digestive
enzymes


Absorption and transport

Molecules are moved out of digestive tract and
into circulation for distribution throughout body
Liver Histology
portal
triad
Figure 24.20a, b
Bile
…each day around 600 ml of bile is produced…
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Bile acid
Phospholipids
Cholesterol
Bilirubin
Waste products
Electrolytes
Mucin
Functions of the Liver
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Bile production
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Storage
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
Hepatocytes remove ammonia and convert to urea
Phagocytosis


Glycogen, fat, vitamins, copper and iron
Nutrient interconversion
Detoxification


Salts emulsify fats, contain pigments as bilirubin
Kupffer cells phagocytize worn-out and dying red and white blood cells,
some bacteria
Synthesis

Albumins, fibrinogen, globulins, heparin, clotting factors
Exocrine Pancreas –
Enzymes
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Trypsinogen
Chymotrysinogen
Carboxypeptidases
Pro-elastase
Phospholipase
pancreatic lipase
Pancreatic amylase
Bicarbonate Ion Production
Digestive System Regulation
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Nervous regulation
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Involves enteric nervous
system
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Types of neurons: sensory,
motor, interneurons
Coordinates peristalsis
and regulates local
reflexes
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Chemical regulation
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Production of hormones
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Gastrin, secretin
Production of paracrine
chemicals
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Histamine
Help local reflexes in ENS
control digestive
environments as pH levels
Lipoproteins
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Types
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Chylomicrons
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VLDL
LDL
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
Enter lymph
Transports cholesterol to
cells
HDL
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Transports cholesterol
from cells to liver
Water and Ions:

Water


Can move in either direction
across wall of small intestine
depending on osmotic
gradients
Ions

Sodium, potassium, calcium,
magnesium, phosphate are
actively transported
Effects of Aging


Decrease in mucus layer, connective tissue,
muscles and secretions
Increased susceptibility to infections and toxic
agents

Ulcerations and cancers
Chemical Events in Digestion: Carbohydrates
1. Shows carbohydrate
digestion.
2. Note the small
intestine’s role in
conversion to monoand di-saccharides.
Chemical Events in Digestion: Lipids
3. Lipid digestion is
shown here.
4. Note the conversion
to monoglycerides in
the small intestine
due to bile salts and
pancreatic lipase.
Chemical Events in Digestion: Proteins
5. Digestion of
proteins.
6. Note stomach’s
conversion to
polypeptides.
7. Small intestine
converts to short
peptides and amino
acids for intestinal
absorption.
Gastric Secretion
1. Thin, strongly acidic (pH: 1 to 3), almost
colorless liquid. It is secreted by the
glands in the lining of the stomach.
2. Essential constituents are the digestive
enzymes pepsin and renin, hydrochloric
acid, and mucus.
3. Certain cells of the stomach lining secrete
intrinsic factor which is necessary for the
absorption of vitamin B12.
Secretion rates of Gastric juice
Path followed by bile juice in liver
and gall bladder
Pancreatic Secretion
Production of Pancreatic Secretion
Pancreatic Secretion
1. Clear, alkaline secretion of the pancreas
containing enzymes that aid in the
digestion of proteins, carbohydrates, and
fats.
2. There are mainly two types of
pancreatic secretions:
- Bicarbonate Secretion,
- Enzyme Secretion.
Secretion of Pancreatic juice
Chemistry of Digestion: Fats
Figure 21-8: Fat digestion