Mucosa
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Innermost tunic
Consist of 3 layers
o Inner mucous epithelium (innermost)
o Lamina propria (loose connective tissue)
o Muscularis mucosae (thin outer Layer of
smooth muscle)
Submucosa
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PARTS OF DIGESTIVE SYSTEM
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Mouth
Tongue
Pharynx
Esophagus
Stomach
Small Intestines
Large intestines
Accessory Organs (Liver, HBT, Pancreas)
FUNCTIONS OF THE DIGESTIVE SYSTEM
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Thick layer of loose connective tissue made of
nerves, blood vessels and small glands
Where the Meissner plexus (submucosal plexus) is
found.
➢ Plexus are innervated by autonomic nervous
system
Muscularis
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Consist of 2 Muscles
o Circular Smooth Muscle (inner)
o Longitudinal Smooth Muscles (outer)
Myenteric/Auerbach Plexus is found (in between
Circular and Longitudinal Smooth Muscle)
Serosa
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Ingestion and Mastication
Propulsion and Mixing
Digestion and Secretion
Absorption
Elimination
Consists of Peritoneum- smooth epithelial layer and
underlying connective tissue
In regions of the digestive tract not covered by
peritoneum, the connective tissue layer is called the
adventitia
FOUR MAJOR TUNICS OR LAYER OF THE
DIGESTIVE TRACT
1.
2.
3.
4.
MUCOSA: innermost tunic
SUBMUCOSA: lies just outside the mucosa
MUSCULARIS: lies outside the submucosa
SEROSA: outermost layer of the digestive tract
PERITONEUM
Visceral Peritoneum (serosa)
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serous membrane that covers the organs.
Parietal peritoneum
•
is the serous membrane that lines the wall of the
abdominal cavity.
TONGUE
A large, muscular organ that occupies most of the oral cavity.
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The average length of the human tongue from the
oropharynx to the tip is 10 cm.
Adult male is 70 g and for adult females 60 g.
Some may have lighter; some may have heavier
tongues.
A major function of the tongue is the enabling of
speech in humans and vocalization in other animals.
Peritonitis
-
is a potentially a life-threatening inflammation of the
peritoneal membranes.
The inflammation can result from chemical irritation
by substances, such as bile, that have escaped from
the digestive tract.
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MOUTH
DIVISION:
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Vestibule
Lies between the lips and cheeks externally and
gums and teeth internally ‘
Oral Cavity Proper
Lies inside the teeth and houses the tongue
Tongue-tie (ankyloglossia)
➢
TEETH
Adult = 32 teeth located in the mandible and maxillae
Quadrants:
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right upper, left upper, right lower, left lower.
Two sets of teeth:
1.
Deciduous Teeth or Temporary
➢ 20 in number (4 incisors, 2 canines and 4
premolars)
➢ Erupts at 6 months, all have erupted by the end
of 2nd year
➢ Teeth of lower jaw usually appear ahead of the
teeth of the upper jaw
2.
Permanent teeth
➢ 32 in number (4 incisors, 2 canines, 4
premolars and & molars)
➢ Start to erupt at 6th year
➢ The 3rd molar “wisdom tooth” erupts
between the 17th and 30th year
A condition in which an unusually short, thick or tight
band of tissue (lingual frenulum) tethers the bottom
of the tongue's tip to the floor of the mouth.
PARTS AND SURFACE OF TONGUE
Oral surface (anterior 2/3)
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Ends at the sulcus terminalis/ terminal sulcus.
Pharyngeal part (posterior 1/3)
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Apex (Tip)
Body
Root
2 Lateral borders
2 surfaces (ventral & dorsal)
Sulcus terminalis
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Taste Discrimination
V-shaped. Divides the upper surface of the tongue
into ANTERIOR 2/3 & POSTERIOR 1/3
There is a small opening or pit at the apex of the
sulcus terminalis
Foramen cecum
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A small pit which corresponds to the apex of the
Sulcus terminalis
An embryological remnant which marks the site of
the upper end of the thyroglossal duct (remnant of
the thyroid gland as it moves down in the anterior
neck)
4 Main Types of Taste Sensation in the Tongue
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Sweet – tip
Sour – middle
Salty – anterolateral
Bitter – base
PALATE AND TONSILS
Palate or Roof of The Oral Cavity
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Papillae
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Are tiny fingerlike projections on the Dorsal surface
of the Tongue
3 TYPES OF PAPILLAE ON THE ANTERIOR 2/3 OF THE
TONGUE
separates the oral cavity from the nasal cavity and
prevents food from passing into the nasal cavity
during chewing and swallowing
Hard palate is the anterior part and contains bone,
Soft palate is the posterior part and consists. of
skeletal muscle and connective tissue
In nasal cavity, hard palate is the floor. In the oral cavity,
hard palate is the roof.
Filiform Papillae
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Very numerous in number
cover the anterior 2/3 of the tongue on its upper
surface.
Whitish in color, does not contain taste buds
Fungiform Papillae
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Less than filiform papillae
Scattered on the sides and apex of the tongue.
Mushroom-shaped with vascular connective tissue
core which imparts reddish tinge taste buds respond
to sweet and sour tastes
Vallate Papillae
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10 to 12 in number and are situated in a row in front
of the sulcus terminalis
Tonsils
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Are located in the lateral posterior walls of the oral
cavity, in the nasopharynx, and in the posterior
surface of the tongue.
4 TYPES OF TONSILS:
1.
2.
3.
4.
Pharyngeal tonsil
Tubal tonsils
Palatine tonsils
Lingual tonsil
SALIVARY GLAND
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Number of other salivary glands are scattered
throughout the oral cavity, including on the tongue.
Salivary glands produce saliva which helps in
masticating and digesting of foods.
Saliva
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A mixture of serous (watery) and mucous fluids and
has multiple roles.
The principal glands of salivation:
Parotid Gland
➢
3 PARTS OF PHARYNX:
1.
2.
3.
Nasopharynx
Oropharynx
Laryngopharynx
Largest; serous secretion
ESOPHAGUS
Sublingual gland
➢
Mostly mucus; smallest
Submandibular gland
➢
More serous secretion than mucus
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PHARYNX
Pharynx or throat
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Connects the mouth with the esophagus
Only the oropharynx and laryngopharynx carry food
to the esophagus
Posterior
walls
of
the
oropharynx
and
laryngopharynx are formed by the superior, middle,
and inferior pharyngeal constrictor muscles.
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A tubular structure about 10 inches long or 25 cm
long
Continuous above with the laryngeal part of the
pharynx opposite C6 and passes through the
diaphragm at T10 level to join the stomach
In the neck, it is in front of the vertebral column and
posterior to the trachea
In the thorax, it passes downward to the left
The upper one-third of the esophagus has skeletal
muscle in its wall
the middle third has a mixture of both Skeletal and
smooth muscle fibers
while the lower one- third has smooth muscle in its
wall
It passes through the diaphragm and ends at the
stomach.
Esophageal Sphincter
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aid in movement of food to the stomach; upper
and lower ends of the esophagus
Lower esophageal sphincter is sometimes
called the Cardiac Sphincter
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SWALLOWING
Phases:
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Voluntary Phase
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J-shaped with two openings (CARDIAC and
PYLORIC orifices)
Two curvatures (lesser and greater curvatures)
DIVISION OF THE STOMACH
Happens in the mouth.
With the help of your tongue, it pushes the bolus
against the hard palate. This forces the bolus
towards the posterior part of the mouth and into the
oropharynx.
1.
2.
3.
4.
Cardiac
Fundus
Body
Pyloric Part
Bolus
➢
Food is swallowed and passes from the mouth and
mixes with saliva.
Chyme
➢
When food passes from the stomach into the small
intestine.
Pharyngeal Phase
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it's controlled by your reflex.
This phase is initiated when a bolus of food
stimulates receptors in the oropharynx to elevate the
soft pallet closing off the nasopharynx.
Constrictor muscles
Upper esophageal sphincter relaxes, epiglottis
closes
Esophageal Phase
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This is responsible for moving the food from the
pharynx to the stomach.
Layers of the Stomach Wall
1.
Serosa
Outermost covering
2. Muscular layer
3 distinct divisions:
Longitudinal (outer), Circular and oblique fibers
(innermost)
3. Submucosa
Between muscular layer and mucosa
4. Mucosa
Innermost layer (with numerous folds called RUGAE)
Rugae allows submucosa and mucosa to stretch
and the folds disappear as the stomach is filled
Linings: Simple columnar epithelium, lamina
propria, muscularis mucosa.
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CELLS OF THE GASTRIC GLANDS
STOMACH
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Dilated portion of the alimentary canal
3 MAIN FUNCTIONS:
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Storage of food (capacity of 1500 ml in adult)
Mixes the food with gastric secretions to form a
semifluid substance called CHYME
Controls the delivery of chyme to the small intestine
through the different reflexes
ANATOMIC CONSIDERATIONS:
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Situated in the upper abdomen, extending to the eft
costal margin
Surface Mucous Cells
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are found on the inner surface of the stomach and
lining the gastric pits. These cells secrete mucus
that coats and protects the stomach lining.
If the stomach doesn’t have a coating or mucus to
protect it, in the long run, the stomach will degrade
due to the hydrochloric acid.
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About 6 meters long
:
Mucous Neck Cells
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Produce mucus;
Parietal calls
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Produces hydrochloric acid and intrinsic factor
that is necessary to absorbed Vitamin B12
Endocrine cells
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Produce regulatory hormones and paracrine
signal molecules; and
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Chief cells
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Duodenum
which produce pepsinogen, a precursor of the
protein-digesting enzyme pepsin (enzyme necessary
to digest protein)
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C-shaped tube, about 12 inches long (25cm) and
connects the stomach to the jejunum
Receives opening of the bile and pancreatic ducts
Curves around the head of the pancreas
SECRETION OF THE STOMACH
Hydrochloric acid
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produces a pH of about 2.0 in the stomach. The acid
kills microorganisms and activates the enzyme,
pepsin.
Pepsin
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Is converted from its inactive form, called
pepsinogen. Pepsin breaks covalent bonds of
proteins to form smaller peptide chains
Pepsin exhibits optimum enzymatic activity at a pH
of about 2.0.
Mucus
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binds with vitamin B12 and makes it more readily
absorbed in the small intestine. Vitamin B12 is
important in deoxyribonucleic acid (DNA) synthesis
and in red blood cell production.
SMALL INTESTINE
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forms thick layer which lubricates the epithelial cells
of the stomach wall and protects them from the
damaging effect of the acidic chyme and pepsin.
Irritation o the stomach mucosa stimulates the
secretion of a greater volume of mucus.
More acidic the stomach is = more mucus
Intrinsic factor
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Jejunum & Ileum
The major function of the small intestine is the
absorption of most nutrients (except water)
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Both measures 20 feet or 6 meters long; 2/5 of this
length being the jejunum
Begins at duodeno-jejunal flexure and ends at
ileocecal valve
Attached to the posterior abdominal wall by a fold of
peritoneum known as MESENTERY
Ileocecal valve consists of two horizontal folds that
projects around the orifice of ileum.
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18-24 hours are required for material to pass
through the large intestine, in contrast to the 3-5
hours required for chyme to Move through the small
intestine.
Cecum Appendix
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LARGE INTESTINE
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Is the portion of the digestive tract extending from the
ileocecal junction to the anus.
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Is the proximal end of the large intestine where it
joins with the small intestine at the ileocecal junction.
Located in the right lower quadrant of the abdomen
near the iliac fossa.
A sac that extends inferiorly about 6 cm past the
ileocecal junction
Attached to the cecum is tube about 9 cm long called
the appendix.
Colon
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about 1.5-1.8 m long
Ascending Colon
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extends superiorly from the cecum to the right colic
flexure, near the liver where the colon tums to the
left.
transverse colon
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extends from the right colic flexure to the left colic
flexure near the spleen, where the colon tums
Inferiorly;
descending colon
Divided into:
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Cecum Appendix
Ascending Colon
Descending Colon
Transverse Colon
Sigmoid Colon
Rectum
Anal Canal
FUNCTIONS
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Absorption of water and electrolytes
Storage of undigested materials until they are
expelled as feces
extends from the left colic flexure to the pelvis,
Sigmoid Colon
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forms an S-shaped tube that extends medially and
then inferiorly into the pelvic cavity and ends at the
rectum.
RECTUM
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Is a straight, muscular tube that begins at the
termination of the sigmoid colon and ends at the anal
canal
The muscular tunic is composed of smooth muscle
and is relatively thick in the rectum compared to the
rest of the digestive tract.
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About 5 inches long (13-15 cm)
Usually divided into 3 segments
LIVER
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The largest gland of the body, occupying the upper
part of the abdomen, more on the right side.
Consist of 4 lobes
right and left lobes are separated by a connective
tissue septum, called the falciform ligament.
Visible from an inferior view of the liver is the porta
(gate), through which blood vessels, ducts, and
nerves enter or exit the liver.
3 BASIC FUNCTIONS:
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Production and secretion of bile
Involved in CHO, CHON, and fat metabolism.
Filtration of blood, thereby removing bacteria and
other foreign bodies.
ANAL CANAL
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The last 2-3 cm of the digestive tract
It begins at the inferior end of the rectum and ends at
the anus (external digestive tract opening).
The smooth muscle Layer of the anal canal is even
thicker than that of the rectum and forms the internal
anal sphincter at its superior end.
The external anal sphincter at the inferior end of the
anal canal is formed by skeletal muscles; role in
defecation.
PANCREAS
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complex organ composed of both endocrine and
exocrine tissues that perform several functions.
The pancreas is located behind the stomach and i
retroperitoneal
The head of the pancreas is nestled within the
curvature of the duodenum
The body and tail extend to the spleen.
ACCESSORY ORGANS
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Liver
Gall bladder & bile ducts
Pancreas
*Pancreas is an EXOCRINE organ by producing
enzymes which hydrolyze CHO (carbohydrate),
CHON (protein), and Fats
*Pancreas is an ENDOCRINE organ by producing
INSULIN and GLUCAGON by islets of Langerhans.
The major protein-digesting (proteolytic) enzymes:
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Biomolecules
Trypsin
Chymotrypsin
carboxypeptidase
The protein-digesting enzymes continue the protein
digestion that started in the stomach:
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Pancreatic amylase
➢ continues the polysaccharide digestion that
began in the oral cavity.
Lipase
➢ A lipid-digesting enzyme.
Nucleases
➢ Are enzymes that degrade DNA and RNA
to their component nucleotides.
CARBOHYDRATES
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Sugars
Salivary amylase
begins the digestion of carbohydrates in the
mouth
The carbohydrates then pass to the stomach, where
digestion continues until the food is well mixed with
acid, which inactivates salivary amylase.
Carbohydrate digestion is resumed in the duodenum
by pancreatic amylase.
Cholelithiasis
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Inflammation of the gall bladder because of the stone
(Cholelithiasis).
When the gall bladder keeps being filled but cannot
remove the bile.
DIGESTION & ABSORPTION
Digestion
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Is the breakdown of food to molecules that are small
enough to be absorbed into the blood.
Mechanical digestion
o breaks large food particles into smaller
ones.
o Mouth
Chemical digestion
o uses enzymes to break covalent chemical
bonds in organic molecules.
Absorption
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begins in the stomach, where some small, lipidsoluble molecule, such as alcohol and aspirin, can
diffuse through the stomach epithelium into the
blood.
Most absorption occurs in the duodenum and
jejunum, although some occurs in the ileum.
Microvilli: Increases surface area (small intestine)
LIPIDS
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molecules are insoluble or only slightly soluble in
water
lipids include triglycerides, phospholipids, steroids,
and fat-soluble vitamins.
Triglycerides or fats
➢ Most common type of lipid
➢ Consist of 3 fatty acids bound to glycerol.
o Saturated fats
▪
have only single bonds
between carbons of the fatty
acids.
o Unsaturated fats
▪
Have only double bonds
between carbons of the fatty
acids.
How lipids are absorbed:
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They are found in most of the plant and animal
products we eat.
In the small intestine, the enzymes trypsin,
chymotrypsin, and carboxypeptidase continue
protein digestion; enzymes are synthesized by the
pancreas in an inactive state
Pepsin
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protein-digesting enzyme secreted by the stomach:
breaks down large proteins into smaller, individual
polypeptides
WATER AND MINERAL
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Chylomicron
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Transport exogenous lipids.
It will be thrown to the bloodstream and in there, it
will circulate into the liver. And in the liver, it will be
metabolized.
Either then be:
o Stored
o Transformed into steroid
o Transported
o Deposited into the adipose tissue
Very Low-density Lipoprotein
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Makes fat from the liver.
Transport fats endogenously to the different parts of
the body.
Degraded into Low-density Lipoprotein.
LDL = bad cholesterol.
High-density Lipoprotein
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Good cholesterol
Removes all the fats from the microphages and
throw it back to the liver
Either then be:
o Synthesized
o Deposited in the adipose tissue
o Eliminate
PROTEINS
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Proteins are chains of amino acids.
Approximately 3L of water enter the digestive tract
each day.
We ingest about 2L in food and drink, and the
remaining 7L are from digestive secretions.
Approximately 92% of that waler is absorbed in the
small intestine.
About 75% is absorbed in the large intestine.
about 1% leaves the body in the faces.
Sodium, potassium, calcium, magnesium, and
phosphate ions are actively transported from the
small intestine.
Vitamin D is required for the transport of Ca2+