 The endocrine and nervous systems function to achieve and maintain homeostasis.
 When the two systems work together, referred to as the neuroendocrine system, they
perform the same general functions: communication, integration, and control.
 In the endocrine system, secreting cells send hormone and neurohormone
molecules by way of the blood to specific target cells contained in target tissues or
target organs.
 Hormones – Carried to almost every point in the body; Can regulate most cells; Effects
work more slowly and last longer than those of neurotransmitters.
 Endocrine glands are “ductless glands”; Many are made of glandular epithelium
whose cells manufacture and secret hormones; A few endocrine glands are made of
neurosecretory tissue.
 Glands of the endocrine system are widely scattered throughout the body.
 Classification by Chemical Structure

Steroid Hormones
o
Synthesized from cholesterol.
o
Lipid-soluble and can easily pass through the phospholipid plasma
membrane of target cells.
o

Examples
of
steroid
hormones:
Progesterone, Testosterone.
Cortisol,
Aldosterone,
Estrogen,
Nonsteroid Hormones
o
Synthesized primarily from amino acids.
o
Protein Hormones – Long, folded chains of amino acids; For example, Insulin,
Parathyroid Hormone (PTH).
o
Glycoprotein Hormones – Protein hormones with carbohydrate groups
attached to the amino acid chain.
o
Peptide Hormones – Smaller than protein hormones; Short chain of amino
acids; For example, Oxytocin, Antidiuretic Hormone (ADH).
o
 Classification by General Function

Amino Acid Derivative Hormones – Each is derived from a single amino acid
molecule.

tyrosine or tryptophan; Produced by neurosecretory cells and by
Tropic Hormones – Hormones that target other endocrine glands and stimulate
neurons; For example, Epinephrine, Norepinephrine.
their growth and secretion.

Sex Hormones – Hormones that target reproductive tissues.

Anabolic hormones – Hormones that stimulate anabolism in target cells.
Amine Hormones – Synthesized by modifying a single molecule of

Amino Acid Derivatives Produced by the Thyroid Gland – Synthesized
by adding iodine to tyrosine.
 Mobile-Receptor Model – The hormone passes into the nucleus, where it binds to a
mobile receptor and activates a certain gene sequence to begin transcription of
mRNA; Newly formed mRNA molecules move into the cytosol, associate with
ribosomes, and begin synthesizing protein molecules that produce the effects of the
hormone.
 Steroid hormones regulate cells by regulating the production of certain critical
proteins.
 The amount of steroid hormone present determines the magnitude of a target cell’s
response.
 Because transcription and protein synthesis take time, responses to steroid hormones
are often slow.
 Second-Messenger Mechanism – Also known as the “fixed-membrane-receptor
model”.
 Target Cells – Hormones signal a cell by binding to the target cell’s specific receptors
in a “lock-and-key” mechanism.
 Signal Transduction – Different hormone-receptor interactions produce different

chemical message to fixed receptors in the target cell’s plasma membrane.


Synergism – Combinations of hormones acting together have a greater effect on
appropriate cellular changes.

Permissiveness – When a small amount of one hormone allows a second one to
have its full effects on a target cell.

 Primary and Secondary Actions – Most hormones have primary effects that directly
regulate target cells and many secondary effects that influence or modulate other
regulatory mechanisms in target cells.
 High Blood Concentration of Hormones – Endocrine glands produce more hormone
molecules than actually are needed; The unused hormones are quickly excreted by the
kidneys or broken down by metabolic processes.
 Steroid hormones are lipid soluble, and their receptors are typically found in the target
cell’s cytosol or nucleoplasm.
 After a steroid hormone molecule has diffused into the target cell, it binds to a receptor
molecule to form a hormone-receptor complex.
o
The effects of the hormone are amplified by the cascade of reactions.
o
There are varieties of second-messenger mechanisms; For example, IP3,
cGMP, Calcium-Calmodulin Mechanisms.
Antagonism – One hormone produces the opposite effects of another hormone;
Used to “fine-tune” the activity of target cells with great accuracy.
Second-Messenger Mechanism – Produces target cell effects that differ from
steroid hormone effects in several important ways:
a target cell than the sum of the effects that each would have if acting alone.

The “message” is then passed by way of a G Protein-Coupled Receptor (GPCR)
into the cell where a “second messenger” triggers a G Protein, which leads to the
regulatory changes within the target cell through chemical reactions.
 Combined Hormone Actions
A nonsteroid hormone molecule acts as a “first messenger” and delivers its
o
The second-messenger mechanism operates much more quickly than the
steroid mechanism.
 Nuclear-Receptor Mechanism – Small iodinated amino acids (T4 and T3) enter the
target cell and bind to receptors associated with a DNA molecule in the nucleus; This
binding triggers transcription of mRNA and synthesis of new enzymes.

T3 –Triiodothyronine

T4 – Thyroxine
 Control of hormonal secretion is usually part of a negative feedback loop, and is called
endocrine reflexes.
 Negative Feedback – Mechanisms that reverse the direction of a change in
physiological changes.
 Positive Feedback – Mechanisms that amplify physiological changes.
 Levels of Regulation – Different levels of homeostatic control.

Simplest Mechanism – When an endocrine gland is sensitive to the physiological
changes produced by its target cells.

Many tissues are known to secrete PGs.

PGs have diverse physiological effects.
 Thromboxanes and Leukotrienes

Endocrine gland secretions may also be regulated by a hormone produced by
another gland.


Thromboxane A2 – Involved in blood clotting; Aspirin inhibits thromboxane A2
synthesis and thus inhibits blood clotting.

Leukotrienes – Regulate immunity.
Endocrine gland secretions may be influenced by nervous system input; This fact
emphasizes the close functional relationship between the two systems.
 The sensitivity of target cells depends in part on the number of receptors.

Up-Regulation – Increased number of hormone receptors increases sensitivity.

Down-Regulation – Decreased number of hormone receptors decreases
sensitivity.
 Sensitivity of target cell also may be regulated by factors that affect signal transcription
or gene transcription.
 Tissue Hormones

Unique group of lipid hormones (20-carbon fatty acid with 5-carbon ring) that serve
important and widespread integrative functions in the body but do not meet the
usual definition of a hormone.

Called tissue hormones because the secretion is produced in a tissue and
diffuses only a short distance to other cells within the same tissue; Tend to
 Nearly every process in the human organism is kept in balance by the intricate
interaction of different nervous and endocrine regulatory chemicals.
 The endocrine system operates with the nervous system to finely adjust the many
processes they regulate.
integrate activities of neighboring cells in that tissue.
 Prostaglandins (PGs)

Many structural classes of PGs have been isolated and identified.
o
 Mechanisms of Hypersecretion – Extremely high blood concentration of a hormone
Prostaglandin A (PGA) – Intraarterial infusion results in an immediate fall in
or any condition that mimics high hormone levels.
blood pressure accompanied by an increase in regional blood flow to several

condition that characterizes several different diseases such as Graves Disease,
areas.
o

Vascular Effects – Regulation of RBC deformability and platelet
aggregation.


Metabolic Effects – Systemic inflammation, which can be blocked with


o
Toxic Nodular Goiter, etc.
Prostaglandin E (PGE)
drugs that inhibit PG-producing enzymes such as COX-1 and COX-2).
Gastrointestinal Effects – Regulates HCl secretion.
Hyperthyroidism – Hypersecretion of thyroid hormone; Not a disease but a
Hyperpituitarism – Caused by Pituitary Adenomas (a tumor, as with other tumors,
that causes hypersecretion of hormones); Could lead to Gigantism or Acromegaly.
Autoimmunity – A cause of hypersecretion in which the immune system functions
abnormally; For example, Graves Disease and Primary Hyperparathyroidism.
 Mechanisms of Hyposecretion – Depressed blood hormone levels or any condition
Prostaglandin F (PGF) – Especially important I reproductive system, causing
that mimics low hormone levels.
uterine contractions; Also affects intestinal motility and is required for

peristalsis.
Hypopituitarism – Hyposecretion by the anterior pituitary.

Hyposecretion of Testosterone and Gonadotropic Hormones – Caused by

Formerly known as the hypophysis.
abuse of anabolic steroids; May lead to sterility.

Size: 1.2-1.5cm (about 1.2in) across; Weight: 0.5g (1.6oz).

Dysfunction of the immune system may also cause hyposecretion.

Located on the ventral surface of the brain within the skull.

Type 1 Diabetes Mellitus (T1DM) – Autoimmune destruction of pancreatic islet

Infundibulum – Stemlike stalk that connects the pituitary to the hypothalamus.
cells in combination with viral and genetic mechanisms.

Made up of two separate glands, the adenohypophysis (anterior pituitary gland)

Many types of hyposecretion conditions have been shown to be caused by
and the neurohypophysis (posterior pituitary gland).
insensitivity of the target cells to tropic hormones rather than by actual
hyposecretion.
o
o
Unusual decrease in the number of hormone receptors.
Dysfunction of hormone receptors, resulting in failure to bind to hormones
properly.
o
Antibodies bind to hormone receptors, thus blocking the binding of hormone
molecules.
o
Abnormal metabolic response to the hormone-receptor complex by the target
cell.
o

Failure of the target cell to produce enough second-messenger molecules.
Type 2 Diabetes Mellitus (T2DM) – Caused by target cell dysfunction that
renders the cells insensitive to insulin.
 Two Major Parts
 Structure of the Pituitary Gland

Pars Anterior – Forms the major portion of the adenohypophysis.

Pars Intermedia
 Tissue composed of irregular clumps of secretory cells supported by fine connective
o
tissue fibers and surrounded by a rich vascular network.
follicle cells to secrete estrogens.
 (3) Types of Cells Present (according to affinity to certain stains).

Chromophobes – Do not stain.

Acidophils – Stain with acid stains.

Basophils – Stain with alkaline/basic stains.
In the female, stimulates maturation of primary follicles; Also stimulates the
o
In the male, FSH stimulates the development of the seminiferous tubules of
the testes and maintains spermatogenesis.

Luteinizing Hormone (LH)
o
 (5) Functional Types of Secretory Cells
In the female, stimulates the formation and activity of the corpus luteum of
the ovary; Corpus luteum secretes progesterone and estrogens when

Somatotrophs – Secrete Growth Hormone (GH).


Corticotrophs – Secrete Adrenocorticotropic Hormone (ACTH).
Thyrotrophs – Secrete Thyroid Stimulating Hormone (TSH).
o
In the male, LH stimulates interstitial cells in the testes to develop and
secrete testosterone.

Lactotrophs – Secrete Prolactin (PRL).
o
FSH and LH are called gonadotropins because they stimulate the growth and

Gonadotrophs – Secrete Luteinizing Hormone (LH), Follicle Stimulating Hormone
(FSH).
stimulates by LH; LH also supports FSH in stimulating maturation of follicles.
maintenance of the gonads.

 Growth Hormone (GH)

Also known as Somatotropin (STH).

Promotes growth of bone, muscle, and other tissues by accelerating amino acid
o

GH tends to shift cell chemistry away from glucose catabolism and toward lipid
GH functions as an insulin antagonist and is vital to maintaining homeostasis of
overall metabolism, and other processes.

Gigantism – Caused by hypersecretion of GH during growth years; Unusually
are located.

rapid rate of skeletal growth.
o
Pituitary Dwarfism – Caused by hyposecretion of GH during growth years;
Also known as stunted body growth.
turn adjust the activity of their target tissues.

Minute-by-minute variations in hormone secretion can exhibit occasional large

peaks, caused by pulses in releasing hormone secretion by the hypothalamus.
Balance between releasing and inhibiting hormones of the hypothalamus also
 Tropic Hormones – Hormones that have a stimulating effect on other endocrine
glands; Four principal tropic hormones are produced and secreted by the basophils of
the pars anterior.

Through negative feedback, the hypothalamus adjusts the secretions of the
adenohypophysis, which then adjusts the secretions of the target glands that in
Acromegaly – Caused by hypersecretion of GH after skeletal fusion; Cartilage
still left in skeleton continues to form new bone.
o
Hypophyseal Portal System – Carries blood from the hypothalamus directly to the
adenohypophysis, where the target cells of the releasing and inhibiting hormones
GH Conditions
o
Hypothalamus – secretes releasing and inhibiting hormones into the blood, which
are then carried to the hypophyseal portal system.

blood glucose levels.

Hyposecretion of tropic hormones may disrupt reproduction, kidney function,
 Control and Secretion of the Adenohypophysis
catabolism as an energy source; this leads to increased blood glucose levels.

May result in various effects throughout the body such as early onset of
puberty due to early hypersecretion of gonadotropins.
o
Stimulates fat metabolism by mobilizing lipids from storage in adipose cells and
speeding up catabolism of the lipids after they have entered another cell.
Hypersecretion of the tropic hormones may result from a pituitary tumor.

transport into the cells.

Tropic Hormone Conditions
provides regulation of cycles.

In stress, the hypothalamus translates nerve impulses into hormone secretions by
endocrine glands, basically creating a mind-body link.
Thyroid-Stimulating Hormone (TSH) or Thyrotropin – Maintains the growth and
development of the thyroid; Also causes the thyroid to secrete its hormones.

Adrenocorticotropic Hormone (ACTH) or Adrenocorticotropin – Promotes and
maintains the growth and development of the cortex of the adrenal gland; Also
stimulates the adrenal cortex to secrete some of its hormones.

Follicle-Stimulating Hormone (FSH
 Serves as storage and release site for Antidiuretic Hormone (ADH) and Oxytocin (OT),
which are synthesized in the hypothalamus.
 Release of ADH and OT into the blood is controlled by nervous stimulation.
 Antidiuretic Hormone (ADH)

Prevents the formation of a large volume of urine, thereby helping the body
conserve water.

Causes a portion of each tubule in the kidney to reabsorb water from the urine it is
forming.

Dehydration triggers the release of ADH.

Also called Arginine Vasopressin (AVP) because it stimulates a rise in blood
pressure, partly by increasing contraction in small arteries.

ADH Conditions
o
Diabetes Insipidus – Caused by hyposecretion of ADH; A condition in which
the patient produces excessive amounts of urine.
 Oxytocin (OT)

Has several primary actions.

Causes milk ejection from the lactating breast; Regulated by positive feedback
mechanism; PRL cooperates with OT for successful nursing.

Stimulates contraction of uterine muscles that occurs during and after childbirth;
Regulated by positive feedback mechanism.

Helps maintain skeletal muscle regeneration.

Involved in sexual arousal and social bonding.
 Tiny, pinecone-shaped structure located on the dorsal aspect of the brain’s
diencephalons.
 Member of the nervous system because it receives visual stimuli and also a member
of the endocrine system because it secretes hormones.
 Pineal gland supports the body’s biological clock.
 Principal pineal secretion is melatonin.
 Structure of the Thyroid Gland

Made up of two large lateral lobes and a narrow connecting isthmus.

A thin, wormlike projection of thyroid tissue often extends upward from the
isthmus.

Weight of the thyroid in an adult is approximately 30g (1oz).

Located in the neck, on the anterior and lateral surfaces of the trachea, just below
the larynx.

Composed of follicles.
o
Small, hollow spheres.
o
Filled with thyroid colloid that contains thyroglobulins.
 Two Different Hormones

Tetraiodothyronine (T4) or Thyroxine – Contains four iodine atoms;
Approximately 20 times more abundant than T3; Major importance is as a
precursor to T3.

Triiodothyronine (T3) – Contains three iodine atoms; Considered to be the
principal thyroid hormone; T3 binds efficiently to nuclear receptors in target cells.
 Thyroid gland stores considerable amounts of preliminary form of its hormones before
secreting them, which is something that is highly unique about this gland.
 Before being stored in the colloid of follicles, T3 and T4 are attached to globulin
molecules, forming thyroglobulin complexes.
 Before release, T3 and T4 detach from globulin and enter the bloodstream.
 Once in the blood, T3 and T4 attach to plasma proteins called thyroid-binding
globulins (TBGs) and travel as a hormone-globulin complex.
 T3, and, to a lesser extent, T4 detach from plasma globulin as they near the target cells.
 Thyroid Hormone – Helps regulate the metabolic rate of all cells and cell growth and
tissue differentiation; It is said to have a “general” target.
 Produced by thyroid gland in the Parafollicular C Cells.
 In humans, CT may subtly influence the processing of calcium by bone cells by
decreasing blood calcium levels and promoting conservation of hard bone matrix.
 Parathyroid Hormone (PTH) acts as the antagonist to CT to maintain calcium
homeostasis.
 Graves Disease – Caused by hypersecretion of thyroid hormone; Thought to be an
autoimmune condition.

Unexplained weight loss, nervousness, increased heart rate, exophthalmos
(protrusion of the eyeballs).
 Cretinism – Caused by hyposecretion of thyroid hormone/

Low metabolic rate, delayed growth and sexual development, intellectual
challenges.

Could lead to deformed dwarfism.
 Myxedema – Caused by thyroid hyposecretion; A swelling (edema) and firmness of the
skin caused by accumulation of mucopolysaccharides in the skin.
 Simple Goiter – Enlargement of the thyroid when there is a lack of iodine in the diet.
 Structure of the Parathyroid Glands

Four or five parathyroid glands are embedded in the posterior surface of the
thyroid’s lateral lobes.

Tiny, rounded bodies within the thyroid tissue formed by compact, irregular rows
of cells.
 PTH is an antagonist to CT and is the primary hormone to maintain calcium
homeostasis.
 PTH acts on bone and kidney.

Causes more bone to be dissolved, yielding calcium and phosphate, which enters
the bloodstream.


Causes phosphate to be secreted by the kidney cells into the urine to be excreted.
Causes increased intestinal absorption of calcium by stimulating the kidney to
produce active vitamin D (the hormone calcitriol), which increases calcium
absorption in the gut.

Essential for maintaining homeostatic blood pressure by aiding norepinephrine
and epinephrine to have their full effect, causing vasoconstriction.

Act with epinephrine to bring about recovery from injury produced by inflammatory
agents.

High blood concentration causes eosinopenia and marked atrophy of lymphatic
tissues.
 Structure of the Adrenal Glands

Located on top of the kidneys, fitting like caps.

Made up of two portions:
o
Adrenal Cortex – Composed of endocrine tissue.
o
Adrenal Medulla – Composed of neurosecretory tissue.

Secretion increases in response to stress.

Except during stress response, secretion is mainly controlled by a negative

feedback mechanism involving ACTH from the adenohypophysis.
Secretion is characterized by several large pulses of increased hormone levels
throughout the day—the largest occurring just before waking.
 Gonadocorticoids – Sex hormones (androgens) that are released from the adrenal
cortex.
 All cortical hormones are steroids and known as corticosteroids.
 Three Distinct Layers of Secreting Cells

Zona Glomerulosa – Outermost layer; Directly under the outer connective tissue
capsule of the adrenal gland; Secretes mineralocorticoids.


Zona Fasciculata – Middle layer; Secretes glucocorticoids.
Zona Reticularis – Inner layer; Secretes small amounts of glucocorticoids and
gonadocorticoids.
 Mineralocorticoids

Have an important role in the regulatory process of sodium in the body.

Aldosterone
o
The only physiologically important mineralocorticoid in humans; Primary
function is maintenance of sodium homeostasis in the blood by increasing
sodium reabsorption in the kidneys.
o
Aldosterone also increases water retention and promotes the loss of
potassium and hydrogen ions.
o
Aldosterone secretion is controlled by the Renin-Angiotensin-Aldosterone
System (RAAS) and by blood potassium concentration.
 Glucocorticoids

Main glucocorticoids secreted by the zona fasciculata are cortisol, cortisone, and
corticosterone, with cortisol being the only one secreted in significant quantities.

Affects every cell in the body.

Are protein mobilizing, gluconeogenic, and hyperglycemic.

Tend to cause a shift from carbohydrate metabolism to lipid catabolism as an
energy source.
 Cushing Syndrome – Caused by hypersecretion of cortisol from the adrenal cortex.


Hypersecretion of glucocorticoids results in a redistribution of body fat.
Fatty “moon face” and thin, reddened skin characteristic of Cushing syndrome.
 Aldosteronism – Caused by hypersecretion of aldosterone; Leads to water retention
and muscle weakness resulting from potassium loss.
 Virilizing Tumors – Caused by hypersecretion of androgens; Result from tumors of the
adrenal cortex.

Blood level of male hormones in females can cause them to acquire male
 Structure of Pancreatic Islets

duodenum, extends horizontally behind the stomach, and then touches the spleen.

characteristics, such as facial hair.
 Addison Disease – Caused by hyposecretion of mineralocorticoids; Lead to a drop in
blood sodium and blood glucose, an increase in potassium levels, dehydration, and
weight loss.

the blood.
secretes
two
important
hormones—Epinephrine
o
Pancreatic Islets (Islets of Langerhans) – Endocrine portion.
o
Acini – Exocrine portion; Secretes a serous fluid containing digestive enzymes
Pancreatic Islets – Each islet contains five primary types of endocrine cells joined
by gap junctions.
 Neurosecretory Tissue – Tissue composed of neurons that secret their products into
medulla
Composed of endocrine and exocrine tissues.
into ducts draining into the small intestine.

Also causes increased skin and mucous membrane pigmentation.
 Adrenal
Elongated gland, weighing approximately 100g (3.5oz); Its head lies in the
o
Alpha Cells (A Cells) – Secrete glucagon.
o
Beta Cells (B Cells) – Secrete insulin; Account for up to 75% of pancreatic
o
islet cells.
Delta Cells (D Cells) – Secrete somatostatin.
o
Pancreatic Polypeptide Cells (PP Cells or F Cells) – Secrete pancreatic
polypeptide.
and
Norepinephrine; They are part of the class of nonsteroid hormones called
catecholamines.
 Both hormones bind to the receptors of sympathetic effectors to prolong and enhance
o
Epsilon Cells (ε Cells) – Secrete ghrelin.
 Pancreatic Hormones – Work as a team to maintain homeostasis of food molecules.

Glucagon – Produced by alpha cells; Tends to increase blood glucose levels;
Stimulates gluconeogenesis in liver cells.
the effects of sympathetic stimulation by the ANS.

Insulin – Produced by beta cells; Lowers blood concentrations of glucose, amino
acids, and fatty acids, and promotes their metabolism by tissue cells.

Somatostatin (SS) – Produced by delta cells; Primary role is regulating the other
endocrine cells of the pancreatic islets.

Pancreatic Polypeptide (PP) – Produced by PP Cells (F Cells); Functions
uncertain, but probably influence contraction in GI tract and gallbladder, exocrine
secretion by pancreas, and satiety.

Ghrelin (GHRL) – Hormone secreted by epsilon cells at periphery of pancreatic
islets; Stimulates hypothalamus to boost appetite; Slows metabolism and fat
burning; May contribute to obesity.
o
Estrogens – Steroid hormones secreted by ovarian follicles; Promote
development and maintenance of female sexual characteristics.
o
Progesterone – Secreted by corpus luteum; Maintains lining of the uterus
necessary for successful pregnancy.
o
Ovarian hormone secretion depends on the changing levels of FSH and LH
from adenohypophysis.
 Tissues that form on the lining of the uterus as a connection between the circulatory
systems of the pregnant individual and developing fetus.
 Serves as a temporary endocrine gland that produces Human Chorionic
Gonadotropin, Estrogens, Progesterone, and other hormones.
 Gland located in the mediastinum just beneath the sternum.
 Thymus is large in children, behind to atrophy at puberty, and, by old age, is a vestige
of fat and fibrous tissue.
 Considered to be primarily a lymphatic organ, but the hormone Thymosin has been
isolated from thymus tissue.
 Thymosin – Stimulates development of T Cells.
 The mucous lining of the GI tract contains cells that produce both endocrine and
exocrine secretions.
 GI Hormones, such as Gastrin, Secretin, and Cholecystokinin (CCK), play regulatory
roles in coordinating the secretory and motor activities involved in the digestive
process.
 Ghrelin (GHRL) – Appetite-boosting hormone secreted by endocrine cells in gastric
mucosa as well as in pancreatic islets.
 Testes

Paired organs within the scrotum in males.

Composed of seminiferous tubules and a scattering of interstitial cells.

Testosterone is produced by the interstitial cells and is responsible for the growth
and maintenance of male sexual characteristics.
 Ovaries

Primary sex organs in females.

Set of paired glands in the pelvis that produces several types of sex hormones.
 The heart has a secondary endocrine role.
 Hormone-producing cells produce several Atrial Natriuretic Peptides (ANPs),
including Atrial Natriuretic Hormone (ANH).
 ANH’s primary effect is to oppose increases in blood volume or blood pressure; Also
an antagonist to ADH and aldosterone.
 Leptin – Plays a role in energy balance, immunity, neuroendocrine, and reproductive
functions.
 Resistin – Reduces insulin sensitivity.
 Lipokines (Palmiteolate) – Increases insulin sensitivity.
 Inhibin secreted by ovaries.
 Irisin and Interleukin-6 (IL-6) secreted by muscle.
 Erythropoietin (EPO) secreted by kidneys.
 Many tissues, perhaps all, produce hormones.
 Endocrine regulation begins in the womb.
 Many active hormones are active from birth—evidence that a hormonal signal from
fetus signals the onset of labor.
 Hormones related to reproduction begin at puberty.
 Secretion of male reproductive hormones—continuous production from puberty,
slight decline in late adulthood.
 Secretion of female reproductive hormones declines suddenly and completely in
middle adulthood.
 The endocrine system operates with the nervous system to finely adjust the many
processes they regulate.
 Neuroendocrine system adjusts nutrient supply.
 CT, PTH, and Vitamin D balance calcium ion use.
 The nervous system and hormones regulate reproduction.
Gastrointestinal tract may refer to either the stomach and the intestines or the
entire alimentary canal.

Upper Digestive Tract – Mouth through the stomach.

Lower Digestive Tract – Small intestine through the anus.

The ingested food material passing through the lumen of the GI tract is outside the
internal environment of the body.
 Wall of the GI Tract

Mucosa – Innermost layer closest to the lumen.


Submucosa – Contains numerous glands, blood vessels, parasympathetic nerves.
Muscularis – Thick layer of muscle tissue.
o
May contain circular muscle and/or longitudinal muscle for digestion and
propulsion of food material throughout the alimentary canal.

Serosa – Outermost layer; Mesentery and related structures are serous folds that
connect the tract to the abdominal wall.

Modifications of Layers – Structure of layers varies in different regions
throughout the length of the GI tract.
 Digestive Tract

Main organs of the digestive system form the alimentary canal (digestive tract)
that extends from the mouth through the abdominopelvic cavity to the anus;

Lateral boundaries of the oral cavity, continuous with the lips and lined by mucous
membrane.

Formed in large part by the buccinator muscle covered by adipose tissue.

Contains mucus-secreting glands.
 Hard Palate and Soft Palate

Hard palate consists of portions of four bones: two maxillae and two palatines.

Soft palate forms the partition between the mouth and nasopharynx and is made
of muscle arranged in an arch.

Suspended from the midpoint of the posterior border of the arch is the uvula (for
gag reflex).
 Tongue – Solid mass of skeletal muscle covered by a mucous membrane; Extremely
maneuverable.

Has three parts: root, tip, and body.

Papillae located on the dorsal and lateral surfaces of the tongue.

Lingual frenulum anchors the tongue to the floor of the mouth.

Intrinsic muscles important for speech and mastication; Extrinsic muscles
important for deglutition and speech.
 Lips

Covered externally by skin and internally by mucous membrane.

Junction between skin and mucous membrane is highly sensitive.

Line of contact between closed lips forms the oral fissure.
 Cheeks
 Three main pairs of compound tubuloalveolar glands.

Secrete approximately 1 liter of saliva each day.

Additional small buccal glands contribute less than 5% of the total salivary volume
but provide for hygiene and comfort of oral tissues.
 Parotid Glands – Largest of the paired salivary glands; Produces watery saliva
containing enzymes.
 Submandibular Glands – Compound glands that contain enzyme- and mucus-
producing elements.
 Sublingual Glands – Smallest of the salivary glands; Produce a mucous type of saliva.

Cervical Part – Short portion in the neck.

Thoracic Part – Portion in the thorax.

Abdominal Part – Short portion in the abdomen.
 Lined with stratified squamous epithelium.

injury.

 The teeth are the organs of mastication.
 Typical Tooth


Pulp – Soft, fibrous connective tissue with blood vessels and nerves.
o
Dentin – Hard, mineralized tissue similar to bone in tooth body.
o
Cementum – Hard, mineralized tissue similar to bone around tooth roots.
o
Enamel – Hard, mineralized tissue harder than bone over crown of the tooth.
Crown – Exposed portion of a tooth, covered by enamel; Ideally suited to withstand
abrasion during mastication.

Neck – Narrow portion that joints the crown to the root; Surrounded by gingivae
(gums).

Root – Fits into the socket of the alveolar process; Suspended by a fibrous
periodontal membrane made up of periodontal ligaments.

Outer shell contains two additional tissues: dentin and cementum.
o
Dentin – Greatest portion of the tooth shell; At the crown, covered by enamel;
And at the neck and root, covered by cementum.
o
Pulp Cavity – Located within dentin, contains loose connective pulp tissue
that includes blood, lymphatic vessels, and sensory nerves.
 Types of Teeth

Deciduous Teeth – 20 baby teeth, which appear early in life.

Permanent Teeth – 32 teeth, which replace the deciduous teeth.
 Tube through which a food bolus passes when moved from the mouth to the
esophagus by the process of deglutition (swallowing).
 Air passes through all three divisions of the pharynx (nasopharynx, oropharynx, and
laryngopharynx); Only the terminal portion is involved in the digestive system.
 Tube that extends from the pharynx to the stomach; First segment of the digestive
tube.
Produces a small amount of mucus that allows for easier passage of the blus.
 Each end encircled by muscular sphincters (esophageal sphincters).

Four connective tissues called dental tissues:
o
Provides a thick, abrasion-resistant lining that protects underlying tissues from
Upper Esophageal Sphincter (UES) – Located in the cervical part; Helps precent
air from entering the esophagus during respiration and esophageal contents from
reentering the pharynx.
o
Belching (Burping) – Allowed by the relaxation of the UES; Sudden escape of
air trapped in the stomach and esophagus.

Lower Esophageal Sphincter (LES) – Also called the cardiac sphincter; Intrinsic
part is made up of thick circular muscle; Extrinsic part made up of esophageal
hiatus, an opening in the diaphragm where the esophagus can pass through.

juice.
 Backward flow of stomach acid through the LES and into the lower part of the
esophagus.


Parietal Cells – Secretory cells found in the gastric glands; Secrete hydrochloric
acid (HCl); Produce intrinsic factor needed for the absorption of Vitamin B12.
to reduce excess stomach acid (ex.: proton pump inhibitors); Or performing surgery to
either reduce the lumen size or strengthen the LES.
Chief Cells – Secretory cells found in the gastric glands; Secrete the enzymes of
gastric juice.
 Causes a painful sensation (heartburn).
 Treated by removing the underlying cause, such as a hiatal hernia; Prescribing drugs
Gastric Glands – Extend from the base of the pits; Secrete most of the gastric

Endocrine Cells – Secrete gastrin and ghrelin.
 Gastric Muscle

Thick layer of muscle with three distinct sublayers of smooth muscle tissue
arranged in a crisscrossing pattern.

This pattern allows the stomach to contract strongly at many angles.
 Size varies according to factors such as gender and amount of distention.

When no food is in the stomach, it is about the size of a large sausage.

In adults, its capacity ranges from 1.0 to 1.5L.
 Stomach location: Upper part of the abdominal cavity under the liver and diaphragm.
 Food Reservoir – Its main function; Food is stored in the stomach until it can be
partially digested and moved farther along the GI tract.
 Secretes Gastric Juices – Contains acid and enzymes that aid in the digestion of food.
 Churns Food – By contractions of its muscular coat; Breaking down food into small
 Cardia – Collar-like region at the junction with the esophagus.
 Fundus – Enlarged portion to the left and above the opening of the esophagus into the
stomach.
 Body – Central portion of the stomach.
 Pylorus – Lower part of the stomach.
particles and mixing them with gastric juice; In time, gastric contents are moved along
into the duodenum.
 Secretes Intrinsic Factor – Facilitate Vitamin B12 absorption.
 Limited Absorption – Absorbed substances include certain drugs, water, alcohol, and
some short-chain fatty acids found in butter or milk fat.
 Produces Gastrin and Ghrelin – Gastrin helps regulate digestive functions; Ghrelin
increases appetite.
 Lesser Curvature – Right curve of the stomach.
 Greater Curvature – Left curve of the stomach.
 Circular fibers arranged so that there is an opening in the center when relaxed and no
opening when contracted.

Lower Esophageal Sphincter (LES; Cardiac Sphincter) – Controls the opening of
the esophagus into the stomach.

 Protect the Body – Destroys pathogenic bacteria swallowed with food or with mucus
from the respiratory tract.
 Significant changes in both the structure and function of the upper digestive tract can
occur at different times in the human life cycle.

Stomach sphincter reflexes may not be mature in infants.

Teeth change from infancy through adulthood.
Pyloric Sphincter – Controls the outlet of the pyloric portion of the stomach into
the duodenum.
 Sjögren Syndrome – Autoimmune condition in which the body’s immune system
 Gastric Mucosa

Epithelial lining has rugae marked by gastric pits.
destroys the salivary and tear glands.

Leads to xerostomia (dry mouth), which results from decreased saliva production;
and xeropthalmia (dry eyes), caused by decreased tear production.

Affects more females than males.
 Mumps – Caused by paramyxovirus, is an acute viral infection characterized by
swelling and inflammation of the parotid glands (parotitis).

Causes the parotids to swell and the jaw muscles to spasm, leading to pain when
opening the mouth or chewing.

Produces a characteristic “puffy” facial appearance.

In about 25% of infected males, mumps causes inflammation of the testes, or
orchitis, which may lead to reduced fertility or even sterility.
 Tooth Decay – Also called dental caries, affects the enamel, dentin, and cementum of
teeth and results in the formation of permanent changes in tooth structure called
cavities.

Decay – Refers to the demineralization of the hard tissues of the tooth caused by
acids produced primarily by Streptococcus mutans bacteria.

Gingivitis – Inflammation or infection of the gums; Commonly results from poor
oral hygiene.

Periodontitis – Inflammation of the periodontal membrane that anchors the tooth
 Gastroenterology – Study of the stomach and intestines and their conditions that
affect them.
 Gastroenteritis – Stomach inflammation (gastritis) and intestinal inflammation
(enteritis).
 Anorexia – Chronic loss of appetite.
 Nausea – Unpleasant feeling that often leads to vomiting.
 Emesis – Vomiting.
 Ulcer – A craterlike wound or sore in a membrane caused by tissue destruction; Cause
disintegration, loss, and death of tissue as they erode the layers of the wall of the
stomach or duodenum; Cause gnawing or burning pain and may ultimately result in
hemorrhage, perforation, widespread inflammation, and scarring.
 Helicobacter pylori infection is the primary cause of stomach ulcers.
 Stomach cancer has also been linked to H. pylori infection.
 Pylorospasm – A fairly common condition in infants where the pyloric fibers do not
relax as expected to allow the food to leave the stomach.
 Pyloric Stenosis – An obstructive narrowing of the opening of the pyloric sphincter.
to the bone of the jaw; Leading cause of tooth loss in adults; Often results from
advanced or untreated gingivitis.

Leukoplakia – Precancerous change in the mucous membrane of the mouth;
Characterized by thickened, white, and slightly raised patches of tissue.
 Malocclusion – Occurs when missing teeth create wide spaces in the dentition, when
teeth overlap, or when malposition of one or more teeth prevents correct alignment o
the maxillary and mandibular dental arches.

Overbite – Type of dental malocclusion when the upper front teeth protrude or
hang over the lower front teeth.


Underbite – The opposite of overbite.
Cleft Lip and Cleft Palate – Most common congenital variations affecting the
mouth.
 Gastroesophageal Reflux Disease (GERD) – Also called heartburn or acid
indigestion.

Backward flow of stomach acid into the esophagus not only results in symptoms
such as burning and pressure behind the breastbone, but also causes more
significant issues.

Erosive Esophagitis – A complication of severe GERD characterized by the
narrowing (stricture) or chronic irritation of the esophagus.

GERD treatments include antacids, proton-pump inhibitors, the Stretta
procedure, the bard endoscopic suturing system, and many more.
 Upper Digestive Tract – Mouth through the stomach.
 Lower Digestive Tract – Small and large intestines; Liver and pancreas empty their
secretions into the lower digestive tract.
 Tube approximately 2.5cm in diameter and 6m in length.
 Coiled loops fill most of the abdominal cavity.
 Duodenum – Uppermost division; Approximately 25cm long; Shaped roughly like the
letter C.
 Jejunum – Approximately 2.5m long.
 Ileum – Approximately 3.5m long.
 Internal lining has plicae with villi.
 Villi – Important modifications of the mucosal layer.

Each villus contains an arteriole, venule, and lacteal (lymphatic) vessel.

Covered by a brush border made up of 1700 ultrafine microvilli per cell.

Villi and microvilli increase the surface area of the small intestine hundreds of
times.
 Crypts – Located between villi; Contain stem cells from which other cell types are
produced and then migrate upward to cover the villi, where they eventually slough off.
 Cecum – First 5 to 8cm of the large intestine; Blind pouch located in the lower right
quadrant of the abdomen.
 Colon

ileocecal valve prevents material from passing from the large intestine into the
 Intestinal Cells

Goblet Cells – Secrete mucus; Abundant on villi.

Enteroendocrine Cells – Produce intestinal hormones; Found in villi.

Tuft Cells (Brush Cells) – Have a dense apical tuft of long microvilli; Secrete
prostaglandins and endorphins; Detect the presence of amino acids and other
nutrient types.

Paneth Cells – Located at the base of each intestinal crypt; Produce enzymes and
other molecules that inhibit bacterial growth in the small intestine.
 Average diameter is 6cm.
 Length is approximately 1.5 to 1.8m.
Ascending Colon – Vertical position on the right side of the abdomen; The
ileum.

Transverse Colon – Passes horizontally across the abdomen and above the small
intestine; Extends from the hepatic flexure to the splenic flexure.

Descending Colon – Vertical position on left side of the abdomen.

Sigmoid Colon – Joins the descending colon and the rectum.
 Rectum

Last 7 or 8in of the intestinal tube.

Anal Canal – Terminal inch of the rectum; Anus is the opening of the anal canal.
 Intestinal mucous glands produce lubricating mucus that coats feces as they are
formed.
 Unique arrangement of fibers in the muscle coat produce tapelike teniae coli and
pouchlike haustra.
 Fatty extensions on visceral peritoneum of the colon are called epiploic appendages.
 Right Lobe – Forms about 5/6th of the liver; Divides into right lobe proper, caudate
lobe, and quadrate lobe.
 Hepatic Lobules
 Accessory organ of the digestive system.

surrounded by irregular sinusoids containing stellate macrophages (Kupffer
 8 to 10cm in length; Communicates with the cecum.
 Serves as reservoir for beneficial gut bacteria.
 Large, continuous sheet of serous membrane.

Microscopic units of the liver made up of plates of hepatocytes (liver cells)
Cells).

A small branch of the hepatic vein extends through the center of each lobule.

Portal triads (Interlobular artery, Portal vein, and Bile duct) lie at the periphery
of each lobule.
Many organs are covered with visceral peritoneum and are described as
intraperitoneal; Parietal peritoneum then lines the wall of the abdominopelvic
cavity.

Extraperitoneal space is outside the parietal layer of the peritoneum;
Retroperitoneal identifies the extraperitoneal space along the posterior and
bottom of the abdominopelvic cavity.
 Mesentery – Projection of the parietal peritoneum; Allows free movement of each coil
of the intestine and helps prevent strangulation of the long tube.
 Transverse Mesocolon – Extensions of the peritoneum that supports the transverse
colon; Attaches the transverse colon to the posterior abdominal wall.
 Greater Omentum – A continuation of the serosa of the greater curvature of the
stomach and the first part of the duodenum to the transverse colon.

Spotty fat deposits accumulate in the omentum and give it the appearnce of a lace
apron hanging down loosely over the intestines.
 Lesser Omentum – Attaches from the liver to the lesser curvature of the stomach and
the first part of the duodenum.
 Largest gland in the body, weighs approximately 1.5kg; Grows and shrinks by 40% in a
daily cycle.
 Lies under the diaphragm; Occupies most of the right hypochondrium and part of the
epigastrium.
 Small bile ducts form right and left hepatic ducts.
 Right and left hepatic ducts immediately join to form one hepatic duct.
 Hepatic duct merges with the cystic duct to form the common bile duct, which opens
 Falciform Ligament – Separates the two lobes.
 Left Lobe – Forms about 1/6th of the liver.
into the duodenum.

Liver cells detoxify various substances.

Liver cells break down and remove old RBCs, recycling the iron from hemoglobin.

The liver helps regulate the brain’s appetite centers.
 Right and Left Hepatic Ducts – The intrahepatic ducts converge to form the right and

Liver cells secrete approximately 500mL of bile a day.
left hepatic ducts, which drain bile form the right and left lobes of the liver, respectively.

Liver cells carry on numerous important steps in the metabolism of proteins, fats,
 Intrahepatic Ducts – Small ducts within the liver that collect bile produced by
hepatocytes.
and carbohydrates.
 Common Hepatic Duct – The right and left hepatic ducts merge to form the common
hepatic duct, which exits the liver.
 Cystic Duct – The common hepatic duct joins with the cystic duct from the gallbladder.

Liver cells store several substances, such as iron, vitamins A, B12, and D.

The liver produces important plasma proteins, including clotting factors and

albumin.
The liver serves as a site for hematopoiesis (blood cell production) during fetal
The cystic duct allows bile to flow in and out of the gallbladder.
 Common Bile Duct – The joining of the common hepatic duct and cystic duct forms
the common bile duct; Carries bile from the liver and gallbladder towards the
duodenum.
 Pancreatic Duct – Before entering the duodenum, the common bile duct typically joins
with the pancreatic duct, which carries digestive enzymes from the pancreas.
 Ampulla of Vater – The common bile duct and pancreatic duct empty into the
duodenum at the ampulla of Vater, controlled by the sphincter of Oddi.
development.
 The main components of bile are bile salts, bile pigments, and cholesterol.
 Bile Salts – Formed in the liver from cholesterol; The most essential part of bile; Aid in
digestion and absorption of fats.
 Bile acts as an emulsifier because it has components that consist of hydrophilic heads
that are attracted to water and hydrophobic tails that are attracted to lipids/
 Bile can physically break down large fat globules into smaller fat droplets that can be
suspended in water-based solution.
 Pear-shaped sac 7 to 10cm long and 3cm wide at its broadest point.
 Lies on the undersurface of the liver.
 Serous, muscular, and mucous layers compose the gallbladder wall.
 The mucosal lining has rugae that expand to allow storage of bile.
 Holds 30 to 50mL of bile.
 Storage of bile.
 Concentration of bile fivefold to tenfold.
 Ejection of the concentrated bile into the duodenum.
 The liver is the most metabolically active organ in the body, performing more than 300
functions daily.
 Gallstones – Often made of cholesterol; Can form when bile becomes concentrated.
 Grayish-pink-colored gland; 12 to 15cm long; Weighs approximately 60g.
 Runs form the duodenum, behind the stomach, and to the spleen.
 Diarrhea – Elimination of liquid feces, perhaps accompanied by abdominal cramps;
Diagnosed by frequency of elimination, not consistency of stool.
 Constipation – Decreased motility of the colon that allows for increased water
absorption from the colon contents; Results in more compact feces and difficulty
 Composed of exocrine and endocrine glandular tissue.
 Exocrine Portion – Makes up the majority of the pancreas; Has a compound acinar
arrangement (grouped grapes); Tiny ducts unite to form the main pancreatic duct,
which empties into the duodenum.
 Endocrine Portion – Embedded between exocrine units; Called pancreatic islets;
Constitute only 2% of the total mass of the pancreas; Made up of alpha cells and beta
cells; Pass secretions into capillaries.
 Acinar Units – Secrete digestive enzymes (exocrine).
 Beta Cells – Secrete insulin (endocrine).
 Alpha Cells – Secrete glucagon (endocrine).
defecating.
 Malabsorption Syndrome – General term referring to a group of symptoms resulting
from the failure of the small intestine to properly absorb nutrients.
 Diverticulosis – Indicated by the presence of diverticula, atypical saclike
outpouchings of the intestinal wall; Usually asymptomatic.
 Diverticulitis – Inflamed diverticula characterized by pain, tenderness, and fever.
 Colitis – Any inflammatory condition of the large intestine; Symptoms include diarrhea
and abdominal cramps or constipation.

Ulcerative Colitis – Form of colitis that produce bleeding and intestinal ulcers.

Crohn Disease – Underlying condition characterized by excessing inflammation
that could contribute to forms of colitis.
 Irritable Bowel Syndrome (Spastic Colon)b – Common chronic noninflammatory
condition often caused by stress; Characterized by diarrhea or constipation with or
without pain.
 Colorectal Cancer – A malignancy, usually an adenocarcinoma, of the colon or
 Changes in digestive function and structure are age-related.
 Infants have immature intestinal mucosa.

Intact proteins can pass through epithelial cells lining the tract and trigger an
allergic response.

rectum; Occurs most often after 50; Signs include changes in bowel habits, fecal blood,
rectal bleeding, abdominal pain, unexplained anemia or weight loss, and fatigue.
 Appendicitis – Inflammation of the mucous lining of the vermiform appendix.

Blocks the lumen of the appendix and eventually leads to inflammation and
Lactose intolerance affects infants who lack the enzyme lactase.
 Ulcers and gallbladder diseases are common in middle age.
 Decreased digestive fluids, slowing of peristalsis, and reduced physical activity lead to
constipation and diverticulosis with aging.
Appendicoliths – Calcified, stonelike concretions made of food or fecal material;
appendicitis.
 Hemorrhoids – Dilated veins that result from direct irritation or from increased veinous
pressure that often accompany pregnancy or constipation and the subsequent
straining required to pass compact and hardened stools.
 Proctitis – Inflammation of the rectal mucosa; Another common cause of rectal
bleeding; Result from direct irritation or infection.
 Specific features of structures throughout the digestive tract, such as grinding
surfaces on teeth and muscle that can mix and propel nutrients, contribute to digestive
function.
 External and internal nerves, along with endocrine hormones, regulate and coordinate
digestive tract function.
 Blood and lymphatic tissue are available to help with nutrient absorption and transport.
 Anal Fissures – Generally minor lacerations in the lining of the anus or anal canal that
result in rectal bleeding; Caused by direct irritation such as the passing of a hardened
stool.

Anal Fistula – More serious problem that may require surgical repair.

 Hepatitis – General term referring to inflammation of the liver; Characterized by
jaundice discoloration of body tissues, liver enlargement, anorexia, abdominal
Regulation – Coordination of the various functions of the digestive system.
 The digestive tract is functionally an extension of the external environment—material
does not enter the body until it is absorbed into the internal environment.
discomfort, gray-white feces, and dark urine.

Hepatitis A – Results from infection by the hepatitis A virus; Transmitted through
contaminated food; Occurs commonly in young people and severity ranges from
mild to life-threatening.

Hepatitis B – More severe; Also called serum hepatitis because it is often
transmitted by contaminated blood serum (plasma).

Hepatitis C – Caused by hepatitis C virus (HCV); Transmitted through
contaminated food; May become chronic and result in life-threatening liver issues
months or years after exposure.
 Cirrhosis – Degenerative liver condition caused by hepatitis, chronic alcohol abuse,
malnutrition, infection, or nonalcoholic fatty liver disease.
 Pancreatitis – Inflammation of the pancreas; Caused by various factors.

Acute Pancreatitis – Results from blockage of the pancreatic duct; Blockage
causes pancreatic enzymes to back up into the pancreas and digest it.

Cystic Fibrosis – An underlying condition that blocks the flow of pancreatic
enzymes by causing the exocrine glands to produce excessively thick secretions,
which can build up and block the ducts involved.
 Pancreatic Cancer – A form of adenocarcinoma; A serious pancreatic condition that
claims the lives of nearly all of its patients within 5 years after diagnosis.
 Movements of the digestive tract.
 Convert ingested food from large particles into minute particles, facilitating chemical
digestion.
 Churn contents of the GI lumen to mix with digestive juices and ensure contact with
 Primary Function of the Digestive System

To bring essential nutrients into the internal environment so that they are available
to each body cell.
 Mechanisms of the Digestive System

Ingestion – Food is taken in.

Digestion – Breakdown of complex nutrients into simple nutrients.

Motility of the GI Wall – Physically breaks down large chunks of food material and

moves food along the tract.
Secretion – Digestive enzyme secretion facilitates chemical digestion; Other
secretions moisten and lubricate food, and alter pH balance of GI tract contents.

Absorption – Movement of nutrients through the GI mucosa into the internal
environment.

Elimination – Excretion of material that is not absorbed.
the surface of the intestinal mucosa to facilitate absorption.
 Propel food along the alimentary canal and eliminate digestive waste from the body.
 Mastication – Chewing movements.


Reduces the size of food particles.
Mixes food with saliva in preparation for swallowing.
 Deglutition – Process of swallowing; Complex process requiring coordinated and
rapid movements.

Oral Stage (Mouth to Oropharynx) – Voluntarily controlled; Formation of a food
bolus in the mouth; Tongue presses bolus against the palate; Food is then moved
into the oropharynx.

Pharyngeal Stage (Oropharynx to Esophagus) – Involuntary movement; Mouth,
nasopharynx, and larynx must be blocked to propel bolus from the pharynx to the
esophagus; A combination of contractions and gravity moves bolus through the
esophagus and into the stomach.
Esophageal Stage (Esophagus to Stomach) – Involuntary movement;
o
 Peristalsis and Segmentation – Two main types of motility produced by the smooth
o

Contractions and gravity move bolus through the esophagus and into the stomach.
juices from the pancreas, liver, and intestinal mucosa.
muscle of the GI tract; Can occur together in an alternating fashion.

Peristalsis rate picks up as chyme approaches end of jejunum, moving it
through small intestine into large intestine.
Peristalsis – Wavelike ripple of the muscle layer of a hollow organ; Progressive
o
motility that produces forward movement of matter along the GI tract.

Segmentation in duodenum and upper jejunum mixes chyme with digestive
After leaving stomach, chyme takes about 5hrs to move all the way through
the small intestine.
Segmentation – Mixing movement; Digestive reflexes cause a forward-and-
o
backward movement within a single segment of the GI tract; Helps break down
Peristalsis is regulated in part by intrinsic stretch reflexes; Stimulated by
cholecystokinin (CCK).
food particles; Mixes food with digestive juices; Exposes digested food to the
intestinal mucosa to facilitate absorption.
 Regulation of Motility
 Gastric Motility
o
Food in the stomach is churned (propulsion and retropulsion) and mixed
with gastric juices to form chyme.
o
Chyme is ejected about every 20secs into the duodenum; Emptying the
stomach takes approximately 2-6hrs.

Gastric Emptying Controlled by Hormonal and Nervous Mechanisms
o
Hormonal Mechanism – Fats in duodenum stimulate the release of gastric
inhibitory peptide, which decreases peristalsis of gastric muscle and slows
passage of chyme into the duodenum.
o
Nervous Mechanism – Enterogastric Reflex; Receptors in the duodenal
mucosa are sensitive to distention and the presence of acid; Impulses over
sensory and motor fibers in the vagus nerve cause a reflex inhibition of gastric
peristalsis.

Intestinal Motility – Includes peristalsis and segmentation.
 All changes in chemical composition of food as it travels through the digestive tract.
 Hydrolysis – Chemical changes result from hydrolysis, a process that uses water to
break down a substance.
 Digestive Enzymes – Extracellular, organic (protein) catalysts.

Operate in lumen of digestive tract, outside body cells.

Properties of Digestive Enzymes
o
Specific in their action.
o
Function optimally at a specific pH.
o
Most enzymes catalyze a chemical reaction in one direction.
o
Enzymes are continually being destroyed or eliminated from the body and
must continually be synthesized.
o
Most digestive enzymes are synthesized as inactive proenzymes.
 Carbohydrate Digestion


Carbohydrates are saccharide compounds (sugar compounds).
Polysaccharides – Hydrolyzed by amylases to form disaccharides.

Final steps of carbohydrate digestion are catalyzed by sucrase, lactase, and
maltase, found in the brush border of epithelial cells lining the intestinal lumen.
 Protein Digestion

Protein compounds are composed of twisted chains of amino acids; Stomach acid
weakens protein structure which gives enzymes easier access to the bonds.

Proteases – Catalyze protein hydrolysis into intermediate compounds and, finally,
 Secreted by salivary glands.
 Mucus lubricates food and, with water, facilitates mixing.
 Amylase – An enzyme that begins digestion of starches.
 Lingual Lipase – Works at low pH, so it can digest fats in the stomach and upper
duodenum.
 Sodium Bicarbonate (NaHCO3) – Increases the pH for optimum amylase function.
into amino acids.

Main Proteases
o
Pepsin in gastric juice.
o
Trypsin in pancreatic juice.
o
Peptidases in intestinal brush border.
 Fat Digestion

Fats must be emulsified by bile in small intestine before being chemically
digested.

Lipases – Main lipid-digesting enzymes.
 Residues of Digestion – Some compounds of food resist digestion and are eliminated
as feces.
 Secreted by gastric glands.
 Pepsin

Secreted as inactive pepsinogen by chief cells.

A protease that begins the digestion of proteins.
 Hydrochloric Acid (HCl)


Secreted by parietal cells.
Decreases the pH of chyme for activation and optimum function of pepsin.

Released actively into the gastric juice by H-K pumps (proton pumps).

Vesicles in the resting parietal cell move to the apical surface when the cell
becomes active—thus increasing the surface area for the process of secretion.
 Intrinsic Factor


Secreted by parietal cells.
Protects vitamin B12 and later facilitates its absorption.
 Mucus and water lubricate, protect, and facilitate the mixing of chyme.
 Secreted by acinar and duct cells of the pancreas.
 Proteases (Trypsin, Chymotrypsin) – Enzymes that digest proteins and polypeptides.
 Lipases – Enzymes that digest emulsified fats.
 Nucleases – Enzymes that digest nucleic acids such as DNA and RNA.
 Amylase – An enzyme that digests starches.
 Sodium Bicarbonate – Increases the pH for optimum enzyme function; Also helps
restore the appropriate pH for blood.
 Secreted by the liver; Stored and concentrated in the gallbladder.
 Lecithin, Bile Salts – Emulsify fats by surrounding them to form tiny spheres called
micelles.
 Sodium bicarbonate increases pH for optimum enzyme function.
 Cholesterol, Detoxification Products, Bile Pigments (Bilirubin) – Waste products
excreted by the liver and eventually eliminated in the feces.
 Secreted by intestinal exocrine cells.
 Mucus and water lubricate and aid in continued mixing of chyme.
 Sodium bicarbonate increases the pH for optimum enzyme function.
 Only reflex mechanisms control the secretion of saliva.
 The presence of food in the mouth acts as a chemical and mechanical stimulus.
 The smell and sight of food act as olfactory and visual stimuli.
 Cephalic Phase – Parasympathetic fibers in branches of the vagus nerve conduct
stimulating efferent impulses to the glands; Stimulate production of gastrin (by G Cells
in the stomach).
 Gastric Phase – When products of protein digestion reach the pyloric portion of the
stomach, they stimulate gastrin release; Gastrin accelerates the secretion of gastric
juice, ensuring enough enzymes are present to digest food.
 Intestinal Phase – Various mechanisms seem to adjust gastric secretion as chyme
passes to and through the intestinal tract; Endocrine reflexes involving gastric
inhibitory peptide, secretin, and cholecystokinin (CCK) inhibit gastric secretions.
 Regulated by several hormones released by intestinal mucosa.
 Secretin – Promotes production of pancreatic fluid that is low in enzyme content but
high in bicarbonate.
 Cholecystokinin (CCK) – Several functions:

Causes increased exocrine secretion from the pancreas.

Opposes gastrin, thus inhibiting gastric HCl secretions.

Stimulates contraction of the gallbladder such that bile is ejected and transported
to the duodenum.
 Passage of substances through the intestinal mucosa into the blood or lymph.
 Most absorption occurs in the small intestine.
 For some substances such as mineral
ions or water, absorption occurs by
 Bile is secreted continually by the liver.
 Secretin and CCK stimulate the production and ejection of bile from the gallbladder,
respectively.
simple diffusion or osmosis.
 Other substances are absorbed through
more complex mechanisms.

Secondary Active Transport – How
sodium is transported.

Cotransport
(Coupled
Transport) – How glycose and amino
 Little is known about how intestinal secretion is regulated.
 Suggested that the intestinal mucosa is stimulated to release hormones that increase
the production of intestinal juice.
Sodium
acids are transported.

With the aid of bile salts, fatty acids,
monoglycerides, and cholesterol are
transported from the lumen to the
absorbing cells of the villi.
 Transcellular
Absorption
–
Moves
 Paracellular
Absorption
–
Moves
nutrient particles through cells.
nutrient particles between cells.
 Water-soluble Nutrients – Absorbed
into blood vessels and then travel to the
liver via the hepatic portal system before
they are made available to body cells.
 Lipid-soluble Substances – Enter lacteals and then travel through a series of
 To accomplish its functions, the digestive system requires contributions from other
lymphatic vessels and lymph nodes before entering venous blood at the subclavian
systems.
veins.

Regulation of digestive motility and secretion requires nervous and endocrine
input.

Oxygen for digestive activity is dependent on the proper functioning of the
respiratory and circulatory systems.

The integumentary and skeletal systems support and protect the digestive organs.

The muscular system promotes ingestion, mastication, deglutition, and
defecation.
 Elimination – Expulsion of feces from the digestive tract; Referred to as defecation.
 Defecation – Results from a reflex initiated by the stimulation of receptors in the
rectoral mucosa caused by the distention of the rectum.
 Constipation – Movement of contents through the lower part of the colon and rectum
slows; Extra water is absorbed from the feces, resulting in a hardened stool.
 Diarrhea – Result of increased motility of the small intestine, causing decreased
absorption of water and electrolytes and a watery stool.
 The primary role of the digestive system is to ensure a constant nutrient
concentration in the internal environment.
 Secondary Roles of Digestive System

Teeth and tongue, along with respiratory and nervous systems, are important in
producing spoken language.

Gastric acids aid the immune system by destroying potentially harmful bacteria.