Download Ch 35: The Skeletal System

Ch 23: The Digestive System
Section 1: Overview of the Digestive
System (pp. 852-854)
Digestive System Overview
Two groups of organs:
1) Alimentary canal
- also known as gastrointestinal or
GI tract
- digests & absorbs food
Major organs:
- mouth, pharynx, esophagus,
stomach, small intestine, &
large intestine
Digestive System Overview
Two groups of organs:
2) Accessory digestive organs
- teeth, tongue, & gallbladder
Major digestive glands:
- salivary glands, liver, & pancreas
Digestive Processes
Digestion
- the physical grinding & chemical breakdown of food
ALL digestive systems must accomplish the following:
1) Ingestion
- placing food into digestive tract
2) Mechanical breakdown
- food physically broken down into smaller pieces
- allows digestive enzymes to work more efficiently
Digestion
3) Chemical breakdown
- particles exposed to digestive enzymes
- breaks large molecules into smaller subunits
4) Absorption
- subunits transported out of digestive system…into cells
5) Elimination
- indigestible material expelled from body
Histology of Alimentary Canal
Four basic layers of tissue:
1) Mucosa
- inner lining of canal
- secretes mucus, digestive enzymes, & hormones
- absorbs nutrients
- protects against infectious diseases
Histology of Alimentary Canal
Four basic layers of tissue:
2) Submucosa
- dense connective tissue under mucosal layer
- rich in blood supply, lymph tissue, & nerves
- elastic fibers allow stomach to regain normal shape after
large meal
Histology of Alimentary Canal
Four basic layers of tissue:
3) Muscularis externa
- responsible for peristalsis (rhythmic muscular
contractions that move food through the canal)
Composed of two layers:
a) Inner circular layer opens/closes canal
b) Outer longitudinal layer lengthens/shortens canal
Histology of Alimentary Canal
Four basic layers of tissue:
4) Serosa
- protective, outermost layer
- known as the visceral peritoneum
Ch 23: The Digestive System
Section 2: Functional Anatomy of the
Digestive System (pp. 858-895)
Mouth
Mechanical & chemical breakdown of food:
- begins in the mouth
- mouth lined with thick stratified squamous epithelium to
withstand considerable friction
- breakdown of food carried out mostly by the teeth
Teeth
Function of teeth:
- to break food down into smaller fragments
- vastly improves rate & efficiency of chemical breakdown of
food in stomach
Teeth
Tooth “Timeline”:
1) Deciduous teeth (“baby teeth”)
- begin appearing at 6 months; complete by age 2
- 20 total
- between age 6-12, roots are reabsorbed; teeth fall out
2) Permanent teeth
- 32 total
- All except wisdom teeth appear by end of adolescence
- Wisdom teeth appear by age 25 (sometimes never)
Mouth
Teeth
1) Incisors
- front of mouth; snip off pieces
of food
2) Canines
- pointed; useful for tearing
3) Premolars & Molars
- back of mouth; flattened
surfaces used to grind food
into a paste
Tongue
Functions of the tongue:
- reposition & mix food during
chewing
- initiates swallowing response
- provides ability to manipulate
sounds to form words
- provides sense of taste
Tongue
Features of the tongue:
1) Filiform papillae
- cone-shaped; provide friction for manipulating foods
- smallest & most numerous
- contain keratin; gives them a whitish appearance
2) Fungiform papillae
- scattered across surface of tongue
- contain blood vessels; gives them a reddish appearance
Tongue
Features of the tongue:
3) Circumvalate papillae
- form V-shaped row on back of tongue
4) Foliate papillae
- located on the sides of the tongue; near the back
Super Tasters
**Fungiform, Circumvalate, & Foliate papillae together
form the taste buds**
Note: Foliate taste buds only function during infancy & early
childhood
Saliva
Salivary Glands
- provide first stage of chemical digestion
- pour out saliva in response smell, feel, & taste
- can even be activated by the THOUGHT of food
Cancerous salivary gland
Saliva
Saliva
- mixture of mucus & water
- contains Amylase (digestive enzyme that begins
breaking down starches into sugars)
- kills bacteria & lubricates food
- taste is a direct result of food dissolving in saliva
Swallowing
After chewing…
- tongue (a muscle) presses food
backward into pharynx
Pharynx
- muscular cavity connecting mouth
w/ esophagus & larynx
- separates food/liquids from air
that is being inhaled
Swallowing
Epiglottis
- flap of cartilage that closes off the larynx when you
swallow…prevents food from going into lungs
Esophagus
Once past the epiglottis…
- Food travels into the esophagus
- Esophagus is collapsed when empty
Stomach
Stomach
- Expandable bag…capable of holding 2-4 liters of food/liquid
- Located on left side of abdominal cavity
- Food enters at cardioesophageal sphincter & exits at pyloric
sphincter (both act as “clamps” on either end of stomach)
Rugae
- Internal folds of stomach…allow for expansion
Gastric pits
- Line inner wall…release HCl & various other enzymes
Stomach
Stomach
Stomach
Stomach Functions:
1) Stores food gradually releasing it into small intestine
2) Continues mechanical breakdown of food
- 3 groups of muscles “churn” food
3) Major chemical breakdown of food begins
*Food gradually converted into thick, acidic liquid called
chyme
Takes 2-6 hrs to empty stomach depending on size of meal…
Stomach
Stomach functions:
- “Churning” action mixes food w/ digestive enzymes
- Peristalsis occurs in lower stomach
Stomach
Stomach functions:
- Pyloric sphincter releases food 20-30mL at a time
Stomach
Protection:
- lined with a layer of bicarbonate-rich mucus
- bicarbonate is a base…helps to neutralize acid
- damaged epithelial cells are replaced quickly
Stomach
Vomiting:
- body’s attempt to rid itself of substances that are unsettling
to the stomach
Most commonly caused by:
- extreme stretching (due to over-eating) of the stomach
&/or small intestine
- bacterial toxins
- excessive alcohol
- spicy foods
- certain drugs
Small Intestine
Small intestine
- Body’s major digestive organ
- Longest part of digestive tract…approximately 20ft
2 Major Functions
1) Use enzymes from liver & pancreas to break food
particles into small molecules
2) Absorb molecules into the bloodstream
Small Intestine
3 Major Segments of Small Intestine
1) Duodenum
- Directly attached to stomach
2) Jejunum
3) Ileum
- Directly attaches to large intestine
Inflamed Small Intestine
Small Intestine
Duodenum
- Mixes chyme from stomach with liver & pancreatic enzymes
Small Intestine
Remember:
*In addition to being the major site for digestion, the small
intestine is the main location for food absorption.
Key structures:
1) Numerous folds
- increase the total surface area by over 600 times that
of a smooth tube that is same length
2) Villi
- Minute, fingerlike projections that line entire folded
surface…further increase SA of intestinal wall
Small Intestine
Key structures:
3) Microvilli
- Further divisions of villi…even more increased SA
*Together, these 3 structures give the intestinal wall the
surface area of a tennis court!
**Without these structures, absorption would be VERY
inefficient!
Small Intestine
Small Intestine
Key structures:
4) Circular folds
- permanent folds; about
1cm deep
- forces chyme to slowly
spiral as it moves
through canal
Liver
Liver
- Perhaps the most versatile organ
- Largest gland in the body
Functions
1) Storing fats & carbohydrates for energy
2) Regulating blood glucose levels
3) Synthesizing blood proteins
4) Storing iron & some vitamins
5) Detoxifying harmful substances we ingest
Liver
Bile
- Complex mixture of bile salts, water, & cholesterol
- Acts as a detergent or emulsifying agent that causes fat
particles to be dissolved into microscopic particles
that can be broken down by other enzymes
- Stored in gall bladder & released into small intestine
through tube called the bile duct
Normal Liver
Cirrhosis of the Liver
Fatty Liver
Pancreas
Pancreas
- Small organ sitting between stomach & small intestine
- Produces a “soup” of enzymes that can break down
the 3 major types of nutrients:
Carbohydrates
Lipids
Proteins
- Insulin is produced here
Large Intestine
Large Intestine
- Wider diameter, but only half as long as small intestine
- Does not participate in digestion
- Absorbs majority of water in food
- Eliminates indigestible food in form of feces
- Not essential for life
Composed of 2 Main Sections:
Colon
Rectum
Large Intestine
Divisions of the Colon:
1) Cecum
- Connection between sm. & lg. intestine
- Appendix (collection of lymph tissue) attached here
2) Ascending
3) Transverse
4) Descending
5) S-shaped sigmoid
**Goblet cells…part of lining of lg. intestine…produces
mucous that acts as a lubricant
Large Intestine
Large Intestine
Bacterial Flora:
- various bacteria colonize the large intestine
- ferment & break down indigestible carbohydrates
- help to synthesize Vitamins B and K
Ch 23: The Digestive System
Section 3: Physiology of Chemical
Digestion/Absorption (pp. 895-901)
Digestive System - Control
Digestion is controlled by:
1) the parasympathetic nervous system
2) hormones
Stimuli include:
1) stretch of the organ
2) pH of the stomach contents
3) presence of broken down food particles
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Secretion
Results
Mouth
Salivary
glands
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Stomach
Cells lining stomach
Liver
Pancreas
Small Intestine
Intestine
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Mouth
Salivary glands
Stomach
Cells lining
stomach
Liver
Pancreas
Small Intestine
Intestine
Secretion
Results
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Hydrochloric acid
Kills bacteria, dissolves minerals
Pepsin
Breaks down proteins into peptides
Mucus
Protects stomach lining
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Mouth
Salivary glands
Stomach
Cells lining stomach
Liver
Pancreas
Small
Intestine
Intestine
Secretion
Results
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Hydrochloric acid
Kills bacteria, dissolves minerals
Pepsin
Breaks down proteins into peptides
Mucus
Protects stomach lining
Bile
Emulsifies lipids
Sodium bicarbonate
Neutralizes acidic chyme from stomach
Amylase
Breaks down starch into disaccharides
Protease
Breaks down proteins into peptides
Lipase
Breaks down lipids
Peptidase
Breaks down peptides into amino acids
Disaccharidase
Converts disaccharides into monosaccharides
Overview of Digestion
Ch 23: The Digestive System
Section 3: Homeostatic Imbalances
Homeostatic Imbalances
1) Dental cavities:
- gradual demineralization of tooth enamel
- caused by dental plaque (sugar, bacteria, & other debris)
that sticks to teeth
- bacteria secrete acid that dissolves calcium in teeth
Homeostatic Imbalances
2) Gingivitis:
- caused when plaque begins to calcify & harden
- calcified plaque separates teeth from gums
- bacteria enter separation site & infect gums
Homeostatic Imbalances
3) Periodontitis:
- autoimmune disorder that destroys ligament holding
tooth in socket
- accounts for 80-90% of tooth loss in adults
Homeostatic Imbalances
4) Gastritis:
- inflammation that is caused by anything that interferes
with the mucus layer on the inside of the alimentary canal
5) Gastric ulcers:
- erosion of the stomach wall
- usually caused by bacterial infection or hypersecretion of
digestive enzymes
Homeostatic Imbalances
6) Heartburn:
- burning sensation caused when digestive chemicals
escape the stomach & move up into the esophagus
- usually the result of eating or drinking too much
- causes frequent problems in people who have a weak
cardioesophageal sphincter
Homeostatic Imbalances
7) Gall stones:
- crystals that develop in the gallbladder
- often the result of too much cholesterol or too little bile
- stones can possibly be dissolved by using ultrasound
- often requires surgical removal
Homeostatic Imbalances
8) Hepatitis:
- inflammation of the liver caused by viral infection
9) Cirrhosis:
- chronic inflammation of the liver often caused by
excessive alcohol consumption
- liver transplant is the only effective treatment for patients
with severe cirrhosis
Homeostatic Imbalances
10)Bruxism:
- grinding or clenching of teeth; especially when sleeping
- can wear down or crack teeth over time
- usually a sign of stress
11)Dysphagia:
- difficulty in swallowing
- usually due to obstruction or physical trauma to esophagus