Biol 155 Human Physiology

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Digestive System Anatomy
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Digestive tract



Accessory organs


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
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
Functions
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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
Digestive Tract Histology
Digestive System Regulation

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

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
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
Oral Cavity

Mouth or oral cavity

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
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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

Incisors, canine,
premolar and molars
Tooth structure:
Salivary Glands
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Produce saliva



Prevents bacterial
infection
Lubrication
Contains salivary
amylase


Breaks down starch
Three pairs
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Parotid: Largest
Submandibular
Sublingual: Smallest
Pharynx and Esophagus


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


Upper
Lower
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
Phases of Deglutition
(Swallowing)
Stomach Anatomy:

Openings
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Gastroesophageal:
To esophagus
Pyloric: To
duodenum
Regions
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Cardiac
Fundus
Body
Pyloric
Stomach Histology:

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
Movements in Stomach
Phases of Gastric
Secretion
Small Intestine


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

Absorptive, goblet, granular,
endocrine
Small Intestine Secretions

Mucus


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 and Pancreas
Duodenum Anatomy and
Histology
Liver

Lobes



Major: Left and right
Minor: Caudate and
quadrate
Ducts


Common hepatic
Cystic


From gallbladder
Common bile

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

Albumins, fibrinogen, globulins, heparin, clotting factors
Blood and Bile Flow
Duct System
Gallbladder




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

Endocrine


Exocrine


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:
Large Intestine:



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


Blind sac, vermiform appendix attached
Straight muscular tube
Anal canal

Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)

Hemorrhoids: Vein enlargement or inflammation

Secretions of Large Intestine

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


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


Common after meals
Distension of the rectal wall by feces
Defecation

Usually accompanied by voluntary movements to expel feces
through abdominal cavity pressure caused by inspiration
Reflexes in
Colon and
Rectum:
Digestion, Absorption,
Transport

Digestion

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
Lipoproteins

Types

Chylomicrons
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VLDL
LDL


Enter lymph
Transports cholesterol to
cells
HDL

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
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