Transcript Mechanical digestion

Chapter 15
Lecture Slides
Digestive System
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 Nutrients


are required for normal body function
Carbohydrates, proteins, lipids, vitamins, minerals
Derived from food
 Food
we eat is too big to be directly passed into
blood
 Goals


of digestive system
Digest food into smaller molecules
Absorb smaller molecules into the blood
 Digestive

system consists of:
Alimentary canal
 Long
tube food passes
through

Accessory organs
15.1 Digestion: An Overview
 Digestion
involves
 Mechanical
digestion
 Physical
breakdown of food into smaller pieces
 Forms a greater surface area for contact with digestive
enzymes
 Chemical
 Splitting
digestion
of complex, non-absorbable food molecules into
small, absorbable nutrient molecules by hydrolysis
 Enzymes speed up the reaction and enables digestion to
occur
15.2 Alimentary Canal: General
Characteristics
 Muscular
tube about 9m in length
 Extends from mouth to the anus
 Portions are specialized to perform different digestive
functions
 Lumen is the hollow space within the canal in which
food moves
Alimentary Canal
•
•
•
•
•
•
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Structures
of the Wall
Serosa
Outermost
layer
Formed of visceral peritoneum,
continuous with parietal peritoneum
Secretes serous fluid onto the outer
surface of the canal
 Muscular
layer
Under
the serosa
Two layers of smooth muscle that differ in
fiber orientation
Purposes:
Mix food with digestive secretions
Move food along the canal
 Submucosa
Between
muscular layer and mucosa
Has nerves, lymphatic vessels, blood
vessels, loose connective tissue
Mucosa
Surface
of highly folded, simple columnar
epithelium
Functions of epithelium
 Secrete
digestive enzymes and mucus
 Folds increase surface area of canal
Movements
 Smooth
muscle layers produce two types
of movement
Mixing
movements (segmentation)
 Alternating
rhythmic contractions in short segments
of the tube
 Mix food with secretions
Peristalsis
 Propels
food along the canal
 Circular muscle fibers produce ring-like
constrictions that move along tube in wavelike
manner
15.3 Mouth
 Functions




Intake of food
Mechanical breaking food into small pieces
Mixing it with saliva
Swallowing it
 Surrounded
by cheeks, palate, and tongue
 Cheeks

Lateral walls of the mouth
 Lips


Surrounds mouth opening
Forms anterior surface
 Palate


Separates the oral cavity from the nasal cavity
Hard palate
 Anterior

portion supported by bone
Soft palate
 Posterior
portion lacking bony support
 Uvula on posterior edge is sensitive to touch stimuli
 Assists
with swallowing and gag reflex
 Tongue


Floor of oral cavity
Lingual frenulum
 Limits

Papillae
 Give


posterior movement of the tongue
rough texture to tongue that aids in food manipulation
Taste buds
Other tongue functions
 Moves
food during chewing
 Mixes food with saliva
 Pushes food into pharynx
 Teeth

Accessory structures involved in mastication
(chewing)

Humans form two sets of teeth
 Deciduous

First set of teeth, “baby teeth”
 Permanent

teeth
teeth
Second set of teeth, adult teeth


32 permanent teeth total
form
Four types of permanent
teeth
 Incisors

Biting off food
 Cuspids

Grasp and tear food
 Bicuspids

& Molars
Both bicuspids and molars
crush and grind food
 Tooth

anatomy
Crown
 Portion
above
gingiva

Root
 Embedded
in socket
in alveolar bone of
jaw
 Attachment
of root to
jaw


Cementum
Periodontal
membrane
 Composition
of a
tooth

Dentin
 Bulk
of tooth
 Bone-like
 Enamel
 Hardest
substance of
the body
 Resists abrasion
caused by chewing
 Pulp
cavity
 Central
portion
 Blood vessels, and
nerves enter cavity
through root canal
 Salivary



Glands
Secrete saliva into the mouth
Activated by the presence of food in the mouth or
thoughts of food
Functions
 Bind
food particles
 Dissolve food
 Cleanse and lubricate mouth
 Start carbohydrate digestion
 Aid in the sense of taste
Salivary Glands
Parotid glands
In
front of each ear over masseter muscle
Submandibular
Located
in floor of mouth
Sublingual
Located
glands
glands
in floor of mouth under tongue
Saliva
composition
99.5%
water
 Helps
dissolve substances
Mucus
 Binds
food during chewing and swallowing
Salivary
amylase
 Enzyme
that speeds digestion of starch and
glycogen into maltose
Lysozyme
 Enzyme
that kills certain bacteria
Digestion
in the Mouth
Mechanical
digestion
Mastication
 Increases
surface area of food particles
 Mixes food with saliva
Chemical
Digestion
digestion
of starch and glycogen into
maltase by salivary amylase
15.4 Pharynx and Esophagus
 Pharynx


Passageway connecting nasal and oral cavities
with esophagus and larynx
Transports food from mouth to esophagus
during swallowing
 Esophagus




Muscular tube extending from pharynx to stomach
Uses peristalsis to move food into the stomach
Esophageal mucosa produces mucus for lubrication
and ease in food passage
Lower esophageal sphincter
 Guards
junction of stomach and esophagus
 Constricted to prevent regurgitation of stomach contents
 Opens only to allow food into the stomach
15.5 Stomach
 J-shaped
pouch
 Lies in the upper left
abdominal quadrant
Basic
functions of Stomach
Temporary
food storage
Mixing food with gastric juice
Starting protein digestion
 Structure

Subdivisions
 Cardia
 Fundus
 Body
 Pylorus

Pyloric sphincter
 At
junction of stomach and duodenum
 Constricted to close stomach outlet
 Relaxes to allow food pass into duodenum

Stomach is lined by a thick mucus membrane

Stomach is organized into rugae
 Allow
mucosa to stretch as stomach fills with food

Mucosa contains gastric glands that open at gastric pits
 Gastric
Juice

Secretion of the gastric glands

Cells near opening secrete mucus
 Protects

mucosa from actions of digestive secretions
Chief cells
 At
bottom of glands
 Secrete digestive enzymes

Parietal cells
 At
mid-portion of glands
 Secrete hydrochloric acid

Gastric juice converts food into chyme
 Released
sphincter
intermittently into the duodenum by pyloric
Control
Gastric
of Gastric Secretion
juice is produced continuously
Secretion
increases when food is on
its way to or in the stomach
Includes
sight, smell,or thought of food;
food in mouth, food in stomach
Parasympathetic
impulses increase
with food stimuli
Directly
stimulate gastric glands increase
secretion
Cause
stomach cells to produce gastrin
hormone
 Hormone
secretion
also stimulates gastric gland
 Parasympathetic
impulses decrease in
frequency as stomach empties
Decreases
gastric juice secretion
 Intestinal
mucosa secretes two
hormones in response to chyme
Cholecystokinin
Secretin
Both
help decrease gastric juice secretion
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 Digestion

and Absorption
Hydrocholiric acid (pH 2)
 Activates
enzyme pepsin
 Denatures proteins, inhibits most bacterial growth

Pepsin
 Breaks

proteins into smaller peptides
Rennin, an infant enzyme
 Curdles


milk proteins
Keeps it in stomach longer
Makes proteins more easily digested

Intrinsic factor
 Essential

for absorption of vitamin B12
Stomach absorbs water, minerals, some drugs, alcohol
15.6 Pancreas
 Posterior
 Digestive
to pyloric portion of stomach
function (exocrine function) is to secrete
pancreatic juice
 Juice
collected by pancreatic duct

Pancreatic duct joins the common bile duct, which
enters the duodenum

Hepatopancreatic sphincter regulates entrance into
duodenum
 Control

of Pancreatic Secretion
Neural control
 Parasympathetic
impulses stimulate pancreas to secrete
pancreatic juice

Hormonal control
 Secretin


Released by intestines in response to acid chyme
Causes pancreas to produce juice rich in carbonates

Neutralize acidity of chyme
 Cholecystokinin


Secreted by intestines in response to fat-laden chyme
Stimulates secretions rich in digestive enzymes
 Digestion

by Pancreatic Enzymes
Pancreatic amylase
 Breaks

starch and glycogen into maltose
Pancreatic lipase
 Breaks
fats into monoglycerides and fatty acids
 These molecules are absorbable

Trypsin
 Breaks
proteins into peptides
 Activated by intestinal secretions
15.7 Liver
 Largest
gland in the body at 1.4 kg
 Located
in upper right quadrant, protected by
ribs
 Dark,
reddish brown color
 Liver
functions
 Secretion of bile
 Role in carbohydrate digestion
 Role in lipid digestion
 Role in protein digestion
 Detoxifies poisons and harmful chemicals
 Removes worn out blood cells
 Stores fat, glycogen, iron, and several vitamins
 Synthesis of blood proteins
 Nutrient inter-converstion
 Liver
is divides into four lobes
 Liver

blood supply
Hepatic artery
 Brings

oxygenated blood
Hepatic portal vein
 Brings
deoxygenated blood
from digestive tract

Hepatic vein drains blood
into inferior vena cava
 Bile


is collected into the hepatic duct
Hepatic duct and cystic duct from gallbladder form the
common bile duct
Common bile duct carries bile to the duodenum
 Gallbladder

Stores bile between meals
 Bile


Yellowish, green liquid
Consists of water, bile salts, bile pigments, cholesterol,
minerals
 Bilirubin

is break down product of hemoglobin
Bile salts emulsify lipids in chyme
 Increases
surface area of lipid molecules so it could be
easily dissolved by enzymes and absorbed into the
intestines
 Release

of Bile
When intestine is empty, hepatopancreatic sphincter is
closed
 Forces

bile into gallbladder
In response to fat in chyme, CCK
 Causes
the gallbladder to contract
 Relaxes hepatopancreatic sphincter
15.8
Small
Intestine
 2.5cm wide, 6.4m long
 Begins
at the pyloric sphincter and ends at the large
intestine
 Site
of most digestion and absorption of nutrients
 Structure

Three segments
 Duodenum

First and shortest
section
 Jejunum

Middle section
 Ileum


Last and longest
section
Suspended by
mesentery from body
wall

Mucosa has numerous
intestinal villi
 Provide
a very large surface
area

Villus anatomy
 Covered
in simple columnar
epithelium
 Have a centrally located
lacteal for fat absorption
Have
a blood
capillary network
Intestinal
glands
 Secrete
mucus and
intestinal juice
Microvilli
further
increase the
surface area
 Folds
in epithelial
cell plasma
membranes
 Intestinal
Juice

Slightly alkaline with abundant water and mucus

Forms appropriate environment for actions of bile salts
and pancreatic digestive enzymes
 Regulation

of Intestinal Secretion
Mechanical stimulation due to presence of chyme
 Activates

secretion of intestinal juice and enzymes
Neural reflex due to intestinal wall stretch
 Parasympathetic
secretions
impulses increase the rate of intestinal
 Digestion

and Absorption
General events
 Vigorous
contractions mix chyme with bile, pancreatic
juice, and intestinal juice
 Emulsification
of fats occurs
 Digestion
of carbohydrates, proteins, and lipids occur due
to pancreatic and intestinal enzymes
 Absorption
of nutrients into the blood stream
Intestinal
enzymes are used to
complete the process of digestion
Digestion
of disaccharides to
monosaccharides
 Maltase
 Maltose
to glucose
 Sucrase
 Sucrose
to glucose and fructose
 Lactase
 Lactose
to glucose and galactose
Digestion
of fats and proteins
Intestinal
 Fats
lipase
into monoglycerides and fatty acids
Peptidase
 Peptides
into amino acids
Absorption
of carbohydrates
Simple
sugars (glucose, fructose,
galactose) occurs primarily by active
transport
Absorption
of fats
Monoglycerides
and fatty acids diffuse
into epithelial cells
 Molecules
recombine into fats molecules
 Chylomicrons
form
 Fat molecules, cholesterol, and phospholipids
coated in protein
 Move
from epithelial cells and into lacteals
 Enter
the left subclavian vein with lymph
Very
small fatty acids enter the villi directly
without being recombined

Absorption of proteins
 Amino

Other absorbed materials
 Water,

acids are actively absorbed into villi capillaries
minerals, and vitamins enter villi capillaries
Blood leaving intestines flows to the liver via the
hepatic portal vein
 Absorbed
materials are processed before blood enters
general circulation
15.9 Large Intestine
 Ileocecal
valve regulates movement of
chyme from small intestine into large intestine
 Structure

6.5cm wide, 1.5m long
 Consists
of three
segments

Cecum
Pouch below ileocecal
valve
 Appendix


Colon
Ascending colon
 Transverse colon
 Descending colon
 Sigmoid colon


Rectum
Last portion is anal
canal with the anus
 Stores feces


Tenia coli, 3 longitudinal bands of muscle, run length of
colon
 Form
haustra

Large intestine is supported by mesentery

Mucosa possesses no villi
 Epithelium
contains numerous goblet cells
 Produces
no digestive enzymes
 Bacteria decompose non-digested food residues


Yield B vitamins and vitamin K
Produce flatus
 Mucosa

produces large amounts of mucus
Lubrication and protection against abrasion
 Main
function of large intestine is absorption of water,
minerals, and vitamins
 End product is feces

Large amounts of bacteria, mucus, water, and nondigested food residues
 Movements


Mixing and propelling movements are sluggish
Undergo mass peristalsis 2-4 times per day
 Usually
after a meal

Defecation reflex
 Rectum
fills with feces and stretches
 Stretching triggers contractions that increase pressure

 If
Opens internal anal sphincter (involuntary muscle)
external anal sphincter (voluntary muscle) is relaxed,
defecation occurs
 If external anal sphincter stays contracted, defecation is
postponed
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