the digestive system the digestive system human body in health and disease, martini / bartholomew /...
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The Digestive
System
The Digestive
System
Human Body in Health and Disease, Martini / Bartholomew / Welch - Chapter 18
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Overview of the Digestive Tract
The Digestive System• Consists of the muscular digestive tract
assisted by various accessory organs• Digestive functions include:
• Ingestion• Mechanical processing• Digestion• Secretion• Absorption• Excretion
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Overview of the Digestive Tract
Digestive Tract Components• Oral cavity• Pharynx• Esophagus• Stomach• Small intestine• Large intestine• Rectum• Anus
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Overview of the Digestive Tract
Figure 16-1
The Components of the Digestive System and Their Functions
Overview of the Digestive Tract
Histological Organization—Four Layers• Mucosa
• Epithelium• Lamina propria (connective tissue)
• Submucosa• Connective tissue, nerves, blood vessels
• Muscularis externa• Loose connective tissue cover (adventitia)
• Serosa (in peritoneal cavity)• Continuous with mesentery
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Overview of the Digestive Tract
The Structure of the Digestive Tract
Figure 16-2(a)
Overview of the Digestive Tract
The Structure of the Digestive Tract
Figure 16-2(b)
Overview of the Digestive Tract
Movement of Digestive Materials• Involuntary control of smooth muscle of
muscularis externa• Two kinds of movement
• Peristalsis propels material along the tract• Segmentation churns material in the small
intestine
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Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 16-3
1 of 4
Longitudinalmuscle
Circularmuscle
Contraction
Frommouth
Toanus
Contraction of circularmuscles behind food mass
Contraction of longitudinalmuscles ahead of food mass
Contraction
Contraction
Contraction of circular musclelayer forces food mass forward
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Figure 16-3
2 of 4
Longitudinalmuscle
Circularmuscle
Contraction
Frommouth
Toanus
Contraction of circularmuscles behind food mass
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Figure 16-3
3 of 4
Longitudinalmuscle
Circularmuscle
Contraction
Frommouth
Toanus
Contraction of circularmuscles behind food mass
Contraction of longitudinalmuscles ahead of food mass
Contraction
Contraction
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Figure 16-3
4 of 4
Longitudinalmuscle
Circularmuscle
Contraction
Frommouth
Toanus
Contraction of circularmuscles behind food mass
Contraction of longitudinalmuscles ahead of food mass
Contraction
Contraction
Contraction of circular musclelayer forces food mass forward
The Oral Cavity
Functions of the Oral Cavity• Sensory analysis of potential foods• Mechanical processing using teeth,
tongue, and palate• Lubrication of food by mucus in saliva• Enzymatic digestion by enzymes in
saliva
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The Oral Cavity
Anatomy of the Oral Cavity• Also called, buccal cavity• Tongue forms floor• Hard and soft palate form roof• Buccal mucosa forms walls
• Composed of stratified squamous epithelium
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The Oral Cavity
Functions of the Tongue• Mechanical processing of food• Manipulation to assist chewing and
swallowing• Sensory analysis (taste, texture)• Participation in speech
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The Oral Cavity
The Oral Cavity
Figure 16-4(a)
The Oral Cavity
The Oral Cavity
Figure 16-4(b)
The Oral Cavity
Salivary Glands• Three pairs of glands
• Parotid• Sublingual• Submandibular
• Functions of saliva• Lubricates, cleanses oral cavity• Dissolves chemicals• Suppresses bacterial growth
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The Oral CavityThe Salivary Glands
Figure 16-5
The Oral Cavity
Teeth• Participate in mastication of food• Anchored to bone by periodontal
ligament• Dentin forms basic shape
• Enamel covers crown• Cementum covers root
• 20 deciduous teeth (“baby teeth”)• 32 secondary teeth (“adult teeth”)
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The Oral Cavity
Figure 16-6(a)
Teeth: Structural Components and Dental Succession
The Oral CavityTeeth: Structural Components and Dental Succession
Figure 16-6(b)
The Oral CavityTeeth: Structural Components and Dental Succession
Figure 16-6(c)
The Pharynx
Functions of the Pharynx• Common passageway for food,
drink, and air• Pharyngeal muscles propel food
along esophagus toward the stomach during swallowing
Digestive MoviePLAYPLAY
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The Esophagus
Anatomy of the Esophagus• Muscular tube about 25 cm long• Lined by stratified squamous epithelium• Posterior to trachea• Penetrates diaphragm at esophageal hiatus• Possess upper and lower esophageal
sphincters• Sphincter—A circular band of muscle that
can pinch close a muscular tube
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The Esophagus
Swallowing (Deglutition)—Three Steps• Named for where they take place
1. Oral phase• Compaction of bolus• Entry into pharynx
2. Pharyngeal phase• Elevation of larynx• Bending of epiglottis, closing of glottis
• Esophageal phase• Peristalsis pushes bolus toward
stomachCopyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 16-7
1 of 5
Thoracic cavity
Oralphase
Pharyngealphase
Esophagealphase
Bolus entersstomach
Loweresophagealsphincter
Stomach Diaphragm
Peristalsis
EsophagusTongue
Nasopharynx
Softpalate
Bolus
Epiglottis
Trachea
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Figure 16-7
2 of 5
Oralphase
Nasopharynx
Softpalate
Bolus
Epiglottis
Trachea
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Figure 16-7
3 of 5
Oralphase
Pharyngealphase
Tongue
Nasopharynx
Softpalate
Bolus
Epiglottis
Trachea
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Figure 16-7
4 of 5
Oralphase
Pharyngealphase
Esophagealphase
Peristalsis
EsophagusTongue
Nasopharynx
Softpalate
Bolus
Epiglottis
Trachea
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Figure 16-7
5 of 5
Thoracic cavity
Oralphase
Pharyngealphase
Esophagealphase
Bolus entersstomach
Loweresophagealsphincter
Stomach Diaphragm
Peristalsis
EsophagusTongue
Nasopharynx
Softpalate
Bolus
Epiglottis
Trachea
The Stomach
Functions of the Stomach• Temporary storage of ingested food• Mechanical breakdown of food
• Forms chyme, a liquid suspension
• Breakage of chemical bonds in food by action of acid and enzymes• Production of intrinsic factor
• Required for vitamin B12 absorption
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The Stomach
Regions of the Stomach• Cardia
• Closest to heart
• Fundus• “Hump” on top
• Body• Shaped like the letter “C”
• Pylorus• Pyloric sphincter guards the exit
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The StomachThe Anatomy of the Stomach
Figure 16-8(a)
The Stomach
Figure 16-8(b)
The Anatomy of the Stomach
The Stomach
Secretions of the Gastric Glands• Parietal cells
• Secrete HCl (strong acid), intrinsic factor• Chief cells
• Produce pepsinogen, an inactive enzyme• HCl activates pepsinogen to pepsin
• Goblet cells• Produce mucus
• Endocrine cells• Produce gastrin, a hormone
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The Stomach
Figure 16-8(c)
The Anatomy of the Stomach
The Stomach
Figure 16-8(d)
The Anatomy of the Stomach
The Stomach
The Regulation of Gastric Activity• Cephalic phase
• CNS prepares the stomach to receive food
• Gastric phase• Begins when food enters stomach
• Intestinal phase• Controls the pace of gastric emptying
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The StomachThe Phases of Gastric Secretion
Figure 16-9
The StomachThe Phases of Gastric Secretion
Figure 16-9 (1 of 3)
The StomachThe Phases of Gastric Secretion
Figure 16-9 (2 of 3)
The Stomach
Figure 16-9 (3 of 3)
The Phases of Gastric Secretion
The Stomach
Key Note
The stomach provides for the physical breakdown of food that must precede chemical digestion. Pepsin and acid begin the digestion of proteins. For a variable period of time after food arrives in the stomach, starch continues the digestion that began with salivary amylase.
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The Small Intestine
Regions of the Small Intestine• Duodenum• Jejunum• Ileum
• Ileocaecal valve (a sphincter) marks junction with large intestine
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The Small IntestineThe Segments of the Small Intestine
Figure 16-10(a)
The Small Intestine
The Segments of the Small Intestine
Figure 16-10(b)
The Small Intestine
The Intestinal Wall• Mucosa has transverse folds, plicae
circulares• Plicae have small projections, villi• Both increase surface area of mucosa
for absorption• Each villus has a lymphatic capillary, a
lacteal
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The Small Intestine
Figure 16-11(a)
The Intestinal Wall
The Small IntestineThe Intestinal Wall
Figure 16-11(b)
The Small Intestine
Figure 16-11(c)
The Intestinal Wall
X The Small Intestine
Two Forms of Peristalsis• Small-scale periodic contractions of the
muscularis externa• Large-scale contractions coordinated by
reflex• Gastroenteric reflex• Gastrocolic reflex
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The Small Intestine
Intestinal Secretions• Intestinal glands secrete
• Intestinal juice• Moistens chyme• Buffers stomach acid• Dissolves digestive enzymes• Dissolves products of digestion
• Mucus• Hormones
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The Small Intestine
Intestinal Hormones• Gastrin• Secretin• Cholecystokinin (CCK)• Gastric Inhibitory Peptide (GIP)
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The Small Intestine
The Activities of Major Digestive Tract Hormones
Figure 16-12
The Small Intestine
Digestion in the Small Intestine• Most enzymatic digestion and
absorption occurs in the small intestine• Digestive enzymes and buffers are
released by:• Pancreas• Liver• Gall bladder
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The Small Intestine
Key Note
The small intestine receives chyme from the stomach and raises its pH. It then absorbs water, ions, vitamins, and the products released from food molecules by the action of digestive enzymes produced by intestinal glands and the pancreas.
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The Pancreas
Anatomy of the Pancreas• Pancreatic duct enters duodenum• Duct delivers pancreatic juice• Duct branches repeatedly• Fine branches end in pancreatic
acini• Endocrine cells are found among
the acini
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The Pancreas
Figure 16-13(a)
The Pancreas
The Pancreas
The Pancreas
Figure 16-13(b)
The Pancreas
Secretions of the Pancreas• Endocrine secretion (hormones)
• Insulin• Glucagon
• Exocrine secretion (digestive)• Water• Ions• Enzymes• Carbohydrases• Lipases• Proteases• Nucleases
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X The Pancreas
Control of Pancreatic Secretion• Chyme entering duodenum triggers
hormone release• Hormones trigger release of pancreatic juice
• Secretin triggers water and bicarbonate• CCK triggers enzymes• Amylase, lipase• Proteases
Trypsin, chymotrypsin, carboxypeptidase
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The Pancreas
Key Note
The exocrine pancreas produces a mixture of buffers and enzymes essential for normal digestion. Pancreatic secretion is stimulated by hormones (secretin and CCK) released from the duodenum.
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The Liver
Overview of Liver• Largest visceral organ• Over 200 known functions• Four Lobes
• Right (largest by far)• Left• Caudate• Quadrate
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The Liver
The Surface Anatomy of the Liver
Figure 16-14(a)
The Liver
Figure 16-14(b)
The Surface Anatomy of the Liver
The Liver
Histology of the Liver• Liver lobule is basic functional unit• Blood supply from hepatic artery and
hepatic portal vein• Blood flows past sheets of hepatocytes• Blood channels are sinusoids• Blood collects in central vein• Bile canaliculi carry bile toward bile ducts
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The Liver
Figure 16-15(a)
Liver Histology
The Liver
Figure 16-15(b)
Liver Histology
The LiverLiver Histology
Figure 16-15(c)
The Liver
Bile Ducts• Each lobe has a bile duct• Bile ducts unite to form common
hepatic duct• Cystic duct carries bile to gall bladder• Common bile duct carries bile to the
duodenum
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The Liver
Functions of the Liver• Metabolic regulation
• Store absorbed nutrients, vitamins• Release nutrients as needed
• Hematological regulation• Plasma protein production• Remove old RBCs
• Production of bile• Required for fat breakdown
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The Gallbladder
• Gall bladder stores and concentrates bile for release into duodenum
• Relaxation of the hepatopancreatic sphincter permits bile to enter small intestine• CCK relaxes this sphincter
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The Gallbladder
Key Note
The liver is the body’s center for metabolic regulation. It produces bile that will be ejected by the gallbladder into the duodenum under stimulation of CCK. Bile is essential for the efficient digestion of lipids; it emulsifies fats so that individual lipid molecules can be readily attacked by digestive enzymes.
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The Gallbladder
Figure 16-16(a)
The Gall Bladder
The Gallbladder
The Gall Bladder
Figure 16-16(b)
The Large Intestine
Overview of the Large Intestine• Reabsorbs water and compacts feces• Absorbs vitamins made by bacteria• Stores feces before defecation• Consists of three parts
• Cecum• Colon• Rectum
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The Large Intestine
Cecum• Collects and stores material from ileum• Begins process of compaction• Attaches to vermiform appendix
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The Large Intestine
The Anatomy of the Colon• Larger diameter, thinner wall than small
intestine• Bears haustra (pouches)• Possesses taenia coli (longitudinal bands
of smooth muscle)
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X The Large Intestine
The Rectum• Expandable for temporary storage of
feces• Terminates in anal canal• Leads to anus• Circular muscle forms internal anal
sphincter• Encircled by skeletal muscle
• Forms external anal sphincter
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The Large Intestine The Large Intestine
Figure 16-17(a)
The Large Intestine
Figure 16-17(b)
The Large Intestine
The Large Intestine
Functions of the Large Intestine• Absorption
• Water• Ions• Vitamins• Organic wastes• Bile salts• Toxins
• Bacterial growth
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The Large Intestine
Control of the Large Intestine• Stretching of stomach and duodenum
triggers peristalsis of feces from colon into rectum• Sphincters control movement of feces
toward the anus• Stretching of rectum triggers defecation
reflex• Release of feces requires relaxation of
external anal sphincter
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The Large Intestine
Key Note
The large intestine stores digestive wastes and reduces their volume by reabsorbing water. Bacteria that live in the large intestine are an important source of vitamins, especially vitamin K, biotin, and vitamin B5.
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Digestion and Absorption
Processing and Absorption of Nutrients• Two Steps in Processing
• Mechanical processing to break down physical structure of foods
• Chemical processing to break the covalent bonds between food subunits• Enzymes catalyze this• Activate the hydrolysis of large food
molecules
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Digestion and Absorption
Processing and Absorption of Nutrients• Carbohydrates
• Starches are broken down by amylases• Results in di- and trisaccharides
• Enzymes on cell surface split them to monosaccharides
• Absorbed by the intestinal epithelium by facilitated diffusion or co-transport
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Digestion and Absorption
The Digestion and Absorption of Carbohydrates
Figure 16-18(a) (1 of 2)
Digestion and Absorption
Figure 16-18(a) (2 of 2)
The Digestion and Absorption of Carbohydrates
Digestion and Absorption
Processing and Absorption of Fats• Bile emulsifies fats to small droplets• Lipase hydrolyzes triglycerides into
fatty acids and monoglycerides• Lipid products form micelles• Lipids diffuse into epithelial cells• Triglycerides are reformed• Secreted as chylomicrons into lacteals• Transported in lymph to thoracic duct
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Digestion and Absorption
The Digestion and Absorption of Lipids
Figure 16-18(b) (1 of 2)
Digestion and Absorption
The Digestion and Absorption of Lipids
Figure 16-18(b) (2 of 2)
Digestion and Absorption
Processing and Absorption of Nutrients• Proteins
• Breakdown starts in stomach• Pepsin and HCl produce fragments
• Breakdown continues in small intestine• Pancreatic proteases produce small
peptides• Peptidases releases amino acids
• Intestinal epithelium absorbs amino acids into the body
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Digestion and Absorption
The Digestion and Absorption of Proteins
Figure 16-18(c) (1 of 2)
Digestion and Absorption
The Digestion and Absorption of Proteins
Figure 16-18(c) (2 of 2)
Digestion and Absorption
Water and Electrolyte Absorption• About nine liters/day enter the digestive
tract• Two liters of ingested water• Seven liters of watery secretions
• Ions are absorbed by many mechanisms• Sodium, calcium, chloride, bicarbonate
• All but about 150 ml is absorbed by osmosis, as water “follows” the ions
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Digestion and Absorption
Absorption of Vitamins• Fat-soluble vitamins combine
with lipid micelles for absorption• Water-soluble vitamins diffuse
across the digestive epithelium• Exception: vitamin B12 requires
intrinsic factor (from the gastric mucosa) for absorption
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Aging and the Digestive System
Age-Related Changes in the Digestive System• Thinner, more fragile epithelium• Reduced epithelial stem cell division• Weaker peristaltic contraction
• Reduced smooth muscle tone
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The Digestive System in Perspective
FIGURE 16-19 Functional Relationships Between the Digestive System and Other Systems
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Figure 16-192 of 11Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
• Provides vitamin D3 needed for the absorption of calcium and phosphorus
• Provides lipids for storage by adipocytes in subcutaneous layer
The Integumentary System
Figure 16-193 of 11Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Skeletal System
• Skull, ribs, vertebrae, and pelvic girdle support and protect parts of digestive tract; teeth important in mechanical processing of food
• Absorbs calcium and phosphate ions for incorporation into bone matrix; provides lipids for storage in yellow marrow
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The Muscular System
• Protects and supports digestive organs in abdominal cavity; controls entrances and exits of digestive tract
• Liver regulates blood glucose and fatty acid levels, metabolizes lactic acid from active muscles
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The Nervous System
• ANS regulates movement and secretion; reflexes coordinate passage of materials along tract; control over skeletal muscles regulates ingestion and defecation; hypothalamic centers control hunger, satiation, and feeding behaviors
• Provides substrates essential for neurotransmitter synthesis
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The Endocrine System
• Epinephrine and norepinephrine stimulate constriction of sphincters and depress digestive activity; hormones coordinate activity along tract
• Provides nutrients and substrates to endocrine cells; endocrine cells of pancreas secrete insulin and glucagon; liver produces angiotensinogen
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The Cardiovascular System
• Distributes hormones of the digestive tract; carries nutrients, water, and ions from sites of absorption; delivers nutrients and toxins to liver
• Absorbs fluid to maintain normal blood volume; absorbs vitamin K; liver excretes heme (as bilirubin), synthesizes coagulation proteins
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The Lymphatic System
• Tonsils and other lymphoid nodules along digestive tract defend against infection and toxins absorbed from the tract; lymphatic vessels carry absorbed lipids to venous system
• Secretions of digestive tract (acids and enzymes) provide nonspecific defense against pathogens
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The Respiratory System
• Increased thoracic and abdominal pressure through contraction of respiratory muscles can assist in defecation
• Pressure of digestive organs against the diaphragm can assist in exhalation and limit inhalation
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The Urinary System
• Excretes toxins absorbed by the digestive epithelium; excretes some bilirubin produced by liver
• Absorbs water needed to excrete waste products at the kidneys; absorbs ions needed to maintain normal body fluid concentrations
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The Reproductive System
• Provides additional nutrients required to support gamete production and (in pregnant women) embryonic and fetal development