Human Body, Digestion, and Absorption
Background
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Composed of cells, tissues, organs, organ systems
All cells use ATP for reactions
Four primary types of tissue: epithelial, connective, muscle, and nervous
Organs have at least two or more types of tissue
Organ systems:
Organ System
Components
Function
Integumentary
Skin, hair, nails
Protection
Skeletal
Bones
Support/Movement
Nervous
Brain, spinal cord,
nerves, sense organs
Metabolism
Muscular
Muscles
Movement
Endocrine
Pituitary, Thyroid,
Parathyroid, Pineal,
Thymus, Adrenal,
Pancreas, Ovary, and
Testis
Metabolism
Cardiovascular
Heart, blood, blood
vessels
Transport
Lymphatic
Lymph vessels and
lymph nodes
Transport
Respiratory
Nose, Trachea, Lungs
Transport
Digestive
Mouth, Esophagus,
Stomach, Pancreas,
Gall Bladder,
Intestines, and Colon
Transport/Metabolism
Urinary
Kidneys, Ureters,
Bladder, and Urethra
Waste Processing and
Elimination
Reproduction
Gonads
Propagation
Digestive System Overview Diagram Diagram
Alimentary Canal
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Also called gastrointestinal tract
Composed of
o Mouth
 Two physical processes occur:
 Mastication (chewing) - cheeks and closed lips hold the food
between the teeth, the tongue mixes the food with saliva to soften
it, and the teeth cut and grind solid food
 Deglutition (swallowing) - food compacted by tongue into bolus
o Tongue
 Contains taste buds that detect food
 Four tastes detected: sweet, salty, bitter, sour
o Pharynx
 Moves food from mouth to esophagus
o Esophagus
 Muscular tube leading to the stomach
o Stomach
 Temporary storage tank and converts bolus into chyme
 Composed of three sections (1st third = Cardiac region, 2nd third = Body,
and last third = Pyloric Region)
 Stomach cells and what they produce:
 Mucus cells - produces mucus
 Parietal cells - produce hydrochloric acid and intrinsic factor
 Chief cells - pepsinogen (inactive form of protein digestive
enzyme)
 Enteroendocrine cells - produces:
 gastrin - cause gastric glands to increase activity
 secretin - stimulates pancreas to produce bicarbonate to
regulate pH
 histamine - activates parietal cells to release hydrochloric
acid
 serotonin - causes contraction of stomach
 cholecystokinin - potentiates secretin's action on
liver/pancreas (increase bile and pancreas "juice")
 somatostatin - inhibits gastric secretion of all products and
inhibits gastric motility and emptying
o Small intestine
 Composed of three sections (duodenum, jejunum, and ileum)
 Site of absorption of nutrients
 types: passive absorption, facilitated absorption, active
absorption, and endocytosis (phagocytosis and pinocytosis)
 Huge surface area with modified structures called villi and microvilli
 Villi - Diagram fingerlike projections of mucosa, contains blood
capillaries and lacteals (small lymph capillaries)
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Microvilli - tiny projections on cell membranes of absorptive (brush
border) cells that contain enzymes (brush border enzymes) used to
complete digestion
Large intestine
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Diagram
Three sections: ascending, transverse, and descending colon
Site of water absorption and packaging waste material
Associated with the colon is the appendix
Colon
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End of large intestine - sigmoid colon
Rectum and Anal canal at very end of colon
Accessory Organs
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Include
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Teeth
Gallbladder
 Stores and releases bile
Salivary glands
 Functions: (1) cleans mouth, (2) moisten and dissolve food, and (3)
contains enzymes
 Composition of Saliva:
 97-99.5% water
 pH 6.75-7.0
 Sodium, potassium, chloride, phosphate, and bicarbonate
 Mucin
 Salivary amylase (breaks down starch)
Liver
 Largest gland/organ in the body
 Liver cells
 process blood-borne nutrients
 store fat-soluble vitamins
 detoxify substances
 produce bile (used to emulsify fats)
Pancreas
 Produces hormones insulin and glucagon that help regulate glucose levels
in the blood
 Produces pancreatic juices (enzymes) used in hydrolysis of carbohydrates,
lipids, and proteins
Digestive Process Diagram
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Ingestion
Propulsion (swallowing and peristalsis)
Mechanical Digestion (chewing, churning, segmentation)
Chemical Digestion (acid and enzymes)
5. Absorption (lymph and blood vessels)
6. Defecation
Absorption of Nutrients
1. Passive movements (diffusion, osmosis, and facilitated diffusion)
2. Active Movements (active transport, endocytosis, and exocytosis)
3. Question: how long does it take for food to move through the body (i.e. mouth to
anus)?
Regulation of the Digestive and Absorptive Process Diagram
i. Digestive activity is provoked by a range of mechanical and chemical stimuli
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Mechanoreceptors (detect movement) and chemoreceptors (detect chemicals)
embedded in the lining of the GI tract
Receptors respond to stimuli (stretching of the organ, osmolarity and pH of the
contents, and the presence of substrates and end products of digestion)
When stimulated, receptors initiate reflexes
 activate or inhibit glands that secrete digestive juices into the lumen or
hormones into the blood
 mix lumen (organ space) contents and move them the length of the
digestive tract
ii. Controls of digestive activity are both extrinsic and intrinsic
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Intrinsic - nerve plexuses and local hormone producing cells
Extrinsic - central nervous system centers and autonomic nerves
Chemical Digestion
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Most food substance(s) are broken down by hydrolysis
Carbohydrates Diagram
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Salivary amylase in mouth - hydrolyzes starch
Pancreatic amylase in small intestine - hydrolyzes complex carbohydrates
Brush border enzymes in small intestine
 Dextrinase - hydrolyzes dextrins
 Lactase - hydrolyzes lactose
 Maltase - hydrolyzes maltose
 Sucrase) - hydrolyzes sucrose
Proteins Diagram
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Pepsin in stomach - cleaves peptide bonds
Pancreatic enzymes (trypsin, chymotrypsin, elastase, carboxypeptidases) in small intesine
Brush border enzymes (aminopeptidases, carboxypeptidases, and dipeptidases) in small
intestine
Fats Diagram
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Bile salts (bile) in small intestine - hydrolyzes lipids
pancreatic lipase in small intestine - hydrolyzes lipids
Nucleic acids Diagram
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Pancreatic ribonuclease and deoxyribonuclease in small intestine - hydrolyzes RNA and
DNA
Brush border enzymes (nucleosidases and phosphatases) in small intestine - hydrolyzes
portions of nucleic acids
Clinical Related problems with the Digestive System
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Ulcers
Indigestion (Dyspepsia)
Difficulty swallowing (Dysphagia)
GERD - gastroesophageal reflux disease
Constipation
Diverticulosis
Appendicitis
Colitis
Hemorrhoids
Irritable Bowel Syndrome
Diarrhea
Chapter Objectives
After reading chapter three - A student should be able to…
1. Discuss the organization of the human body from the level of the cell upward to organ
system
2. List each organ system as well as their components and discuss its function List and
discuss in detail the components of the Alimentary canal
3. Compare deglutition to mastication Identify the four principle tastes we detect
4. Define bolus and chyme
5. List and discuss the function of digestive hormones
6. Discuss in detail the process and types of absorption in the small intestine List and
discuss the accessory organs involved in digestion and absoption List and discuss the six
steps in the digestive process
7. Discuss the process of regulating digestive and absorptive processes
8. List and describe the types of enzymes and other factors involved in the process of
digesting fats, proteins, and carbohydrates
9. Define clinically related terms