Download Chapter 15 - Los Angeles City College

Chapter 15
Biology 25: Human Biology
Prof. Gonsalves
Los Angeles City College
Based on Mader’s Human
Biology,7th edition and Fox’s 8th
ed Powerpoints
Hormones

Regulatory molecules
secreted into the blood
or lymph by endocrine
glands.
 Lack ducts.

Carry hormone to
target tissue where it
produces its effects.
Chemical Classification of
Hormones
 Amines
 Polypeptides
 Glycoproteins
 Steroids
Amines
 Hormones
derived from tyrosine and
tryptophan.
 Include hormones secreted by adrenal
medulla, thyroid, and pineal glands.
Polypeptides
 Chains
of amino acids (< 100 amino
acids in length).
ADH
Insulin
Glycoproteins
 Long
polypeptides (>100) bound to
one or more carbohydrate (CHO)
groups.
FSH
LH
Steroids
Lipids derived from
cholesterol.
 Are lipophilic
hormones.
 Testosterone
 Estradiol
 Cortisol
 Progesterone

Thyroid Hormones




Tyrosine derivatives
bound together.
Contain 4 iodine
atoms (T4).
Contain 3 iodine
atoms (T3).
Small, non-polar
molecules.
 Soluble in plasma
membranes.
Hormone Precursors



Prohormone:
 Precursor is a longer chained chemical that is
cut and spliced to make the hormone.
Preprohormone:
 Prohormone derived from larger precursor
molecule.
Prehormone:
 Molecules secreted by endocrine glands that
are inactive until changed to hormones by
target cells.
Anterior and posterior pituitary glands.
Posterior Pituitary
Also called the neurohypophysis.
 Formed by downgrowth of the brain during
fetal development.
 Is in contact with the infundibulum.
 Nerve fibers extend through the
infundibulum.

Hypothalamic Control of
Posterior Pituitary




Hypothalamus produces:
 ADH: supraoptic nuclei.
 Oxytocin:
paraventricular nuclei.
Hormones transported
along the hypothalamohypophyseal tract.
Stored in posterior pituitary.
Release controlled by
neuroendocrine reflexes.
Anterior Pituitary
Master gland (also called
adenohypophysis).
 Derived from a pouch of epithelial tissue
that migrates upward from the mouth.
 Consists of 2 parts:
 Pars distalis: anterior pituitary.
 Pars tuberalis: thin extension in contact
with the infundibulum.

Anterior Pituitary
 Trophic
effects:
Health of the target glands, depends
upon stimulation by anterior
pituitary for growth.
High plasma hormone concentration
causes target organ to hypertrophy.
Low plasma hormone concentration
causes target organ to atrophy.
Hypothalamic Control of the
Anterior Pituitary
Hormonal control rather than neural.
 Hypothalamus synthesizes releasing
hormones and inhibiting hormones.
 Hormones are transported to axon endings
of median eminence.
 Delivers blood and hormones to anterior
pituitary via portal system.

Hypothalamic Control of the
Anterior Pituitary

Hormones secreted
into the hypothalamohypophyseal portal
system regulate the
secretions of the
anterior pituitary.
Feedback Control of the
Anterior Pituitary
Anterior pituitary and hypothalamic
secretions are controlled by the target
organs they regulate.
 Negative feedback inhibition by target
gland hormones.

Feedback Control of the
Anterior Pituitary

Negative feedback at 2 levels:
 The target gland hormone can act on the
hypothalamus and inhibit releasing
hormones.
 The target gland hormone can act on the
anterior pituitary and inhibit response to
the releasing hormone.
Growth Hormone (GH) - Somatotrophic Hormone
(STH)


Increases Growth and Maintenance of Organs by:
 stimulating protein anabolism
 promotes fat catabolism (use of fat rather than
sugars for energy)
Abnormal Secretions of STH
 Giantism -- hypersecretion during childhood
(before epiphyseal plates close)
 Acromegaly -- hypersecretion during adulthood
 Dwarfism -- hyposecretion during childhood
 Cachexia (Simmond's Disease) - hyposecretion
during adulthood causes premature aging and
atrophy of organs
Thyroid Hormones
Thyroid gland located just below the
larynx.
 Thyroid is the largest of the pure endocrine
glands.
 Follicular cells secrete thyroxine.
 Parafollicular cells secrete calcitonin.

Production of Thyroid
Hormones




I- (iodide) actively transported into the follicle
and secreted into the colloid.
Oxidized to (Io) iodine.
Iodine attached to tyrosine.
 Attachment of 1 iodine produces
monoiodotyrosine (MIT).
 Attachment of 2 iodines produces
diiodotyrosine (DIT).
MIT and DIT or 2 DIT molecules coupled.
Production of Thyroid
Hormones
T3 and T4 produced.
 TSH stimulates pinocytosis into the
follicular cell.
 Enzymes hydrolyze to T3 and T4 from
thyroglobulin.
 Attached to thyroid-binding protein and
released into blood.

T3 Effects
Stimulates cellular respiration by:
 Production of uncoupling proteins.
 Stimulate active transport Na+/ K+ pumps.
 Lower cellular [ATP].
 Increases metabolic heat.
 Increases metabolic rate.
 Stimulates increased consumption of
glucose, fatty acids and other molecules.

Parathyroid Hormone
Parathyroid glands embedded in the lateral
lobes of the thyroid gland.
 Only hormone secreted by the parathyroid
glands.
 Single most important hormone in the
control of plasma Ca++ concentration.
 Stimulated by decreased plasma Ca++
concentration.

Disorders of the Thyroid
Hyperthyroidism (Grave's disease)
 elevated PBI
 increases nervousness and irritability
 elevated BMR
 exophthalmos - results in edema behind the eyes


Hypothyroidism
 Cretinism - occurs if the hyposecretion is during fetal or early developmental life.
 results in reduced metabolism
 results in reduced growth
 results in mental retardation
 Myxedema - occurs if the hyposecretion is during adult life
 results in reduced metabolism
 results in reduced mental & physical activity
 results in increased blood pressure

results in accumulation of subcutaneous fluids
Adrenal Glands



Paired organs that cap the kidneys.
Each gland consists of an outer cortex and inner
medulla.
Adrenal medulla:

Derived from embryonic neural crest
ectoderm (sympathetic ganglia).

Synthesizes and secretes:
 Catecholamines (mainly epinephrine but
some norepinephrine).
Adrenal Glands

Adrenal cortex:
 Does not receive neural innervation.
 Must be stimulated hormonally.
 Consists of 3 zones:
 Zona glomerulosa:
• Aldosterone: regulate Na+ and K+ balance.
 Zona fasciculata:
• Cortisol: regulate glucose metabolism.
 Zona reticularis:
• Androstenedione and DHEA: supplement
sex steroids.
Adrenal Medulla

Innervated by sympathetic nerve fibers.
 Increase respiratory rate.
 Increase heart rate, cardiac output; and
vasoconstrict blood vessels, thus
increasing venous return.
 Stimulate glycogenolysis.
 Stimulate lipolysis.
General Adaptation Syndrome
(GAS)
Stress stimulates pituitary-adrenal axis
 Alarm phase:
 Adrenal glands activated.
 Stage of resistance:
 Stage of readjustment.
 Stage of exhaustion:
 Sickness and/or death if readjustment does
not occur.

Abnormal Adrenal Cortical Function:

Addison's Disease - caused by Hyposecretion of Cortical hormones
 results in increased blood potassium levels
 results decreased sodium retention and dehydration
 results decreased blood glucose levels
 results decreased blood pressure
 results decreased stress resistance
 results increased risk of kidney failure

Cushing's syndrome - causes by Hypersecretion of Cortical Hormones
 results in shifts of the body fat to the face and shoulders
 results in general body weakness
 results in altered carbohydrate & electrolyte metabolism

Adrenogenital Syndrome - caused by Hypersecretion of Gonadotropins
 results in premature sexual development in both males and females

results in masculinization of females
Pancreas



Endocrine portion consists of islets of
Langerhans.
Alpha cells secrete glucagon.
 Stimulus is decrease in plasma glucose
concentrations.
 Stimulates lipolysis.
Beta cells secrete insulin.
 Stimulus is increase in plasma glucose
concentrations.
 Promotes entry of glucose into cells.
Diabetes Mellitus



Type I (insulin-dependent) diabetes
 Pancreas does not produce insulin
 T cells destroy pancreatic islets
 Needs daily insulin injections
Type II (noninsulin-dependent) diabetes
 Most common type of diabetes
 Obesity and inactivity are risk factors
 Insulin is produced, but there is decreased response to the insulin
perhaps because of a lack or deficiency in insulin receptors.
Consequences:
 May lead to blindness, kidney disease, & circulatory disorders like
atherosclerosis, heart disease, and stroke. Lack of circulation may
also cause gangrene. Diabetic coma may also result and there is an
increased risk of having a stillborn child.
Gonads and Placenta


Gonads (testes and ovaries):
 Secrete sex hormones.
 Testosterone.
 Estradiol.
 Progesterone.
Placenta:
 Secretes large amounts of estrogen and
progesterone.
Thymus

Site of production of T cells (thymusdependent cells), which are lymphocytes.
Pineal Gland
Melatonin:
 Production stimulated by the
suparchiasmatic nucleus (SCN) in
hypothalamus.
 SCN is primary center for circadian
rhythms.
 May inhibit GnRH.

Autocrine and Paracrine
Regulation
 Autocrine:
Produced and act within the same
tissue of an organ.
 Paracrine:
Are produced within one tissue and
regulate a different tissue of the
same organ.

Hormonal Interactions

Synergism:

Two hormones work together to produce a result.
 Additive:
 Each hormone separately produces
response, together at same concentrations
stimulate even greater effect.
• Epinephrine and norepinephrine.
 Complementary:
 Each hormone stimulates different step in
the process.
• FSH and testosterone.
Hormonal Interactions

Permissive effects:
 Hormone enhances the responsiveness
of a target organ to second hormone.
 Increases the activity of a second
hormone.
 Prior exposure of uterus to estrogen
induces formation of receptors for
progesterone.
Hormonal Interactions
Antagonistic effects:
 Action of one hormone antagonizes the
effects of another.


Insulin and glucagon.
Prostaglandins



Most diverse group of autocrine regulators.
Produced in almost every organ.
Wide variety of functions.
 Immune system:
 Promote inflammatory process.
 Reproductive system:
 Play role in ovulation.
 Digestive system:
 Inhibit gastric secretion.
Prostaglandins
Respiratory system:
 May bronchoconstrict or
bronchodilate.
 Circulatory system:
 Vasoconstrictors or vasodilators.
 Urinary system:
 Vasodilation.

Effects of Hormone
Concentration
Concentration of hormones in blood reflects
the rate of secretion.
 Half-life:
 Time required for the plasma
concentration is reduced to ½ reference
level.
 Physiological range of concentration
produces normal tissue response.

Effects of Hormone
Concentration
Varying hormone concentration within
normal, physiological range can affect the
responsiveness of target cells.
 Priming effects (upregulation)
 Increase number of receptors formed on
target cells.
 Greater response by the target cell.

Effects of Hormone
Concentration
Desensitization (downregulation):
 Decrease in number of receptors on
target cells.
 Produces less of a target cell response.
 Insulin in adipose cells.
 Pulsatile secretion may prevent
downregulation.
 GnRH and LH.

Mechanisms of Hormone
Action
Hormones of same chemical class have
similar mechanisms of action.
 Location of cellular receptor proteins.
 Target cell must have specific receptors for
that hormone (specificity).
 Hormones bind to receptors with high bond
strength (affinity).
 Low capacity of receptors (saturation).

Hormones That Bind to
Nuclear Receptor Proteins
Lipophilic steroid and thyroid hormones
bound to plasma carrier proteins.
 Hormones dissociate from carrier proteins
to pass through lipid component of the
target cell membrane.
 Receptors for the lipophilic hormones are
known as nuclear hormone receptors.

Nuclear Hormone Receptors



Function within cell to activate genetic
transcription.
mRNA directs synthesis of specific enzyme
proteins that change metabolism.
Receptor must be activated by binding to hormone
before binding to specific region of DNA called
HRE (hormone responsive element).
 Located adjacent to gene that will be
transcribed.
Hormones That Use 2nd
Messengers



Cannot pass through plasma membrane.
Catecholamines, polypeptides, and
glycoproteins bind to receptor proteins on the
target cell membrane.
Actions are mediated by 2nd messengers
(signal-transduction mechanisms).

Extracellular hormones are transduced
into intracellular second messengers.
Hormones That Use 2nd
Messengers

3 classes of 2nd messenger systems:
Adenylate cyclase.
Phospholipase C.
Tyrosine kinase.

Adenylate Cyclase-cAMP
Hormone binds to receptor protein.
 Dissociation of a subunit of G-protein.
 G-protein binds and activates adenylate
cyclase.
 ATP
cAMP + PPi
 cAMP attaches to inhibitory subunit of
protein kinase.

Adenylate Cyclase-cAMP





Activates protein kinase.
Phosphorylates enzymes within the cell to
produce hormone’s effects.
Modulates activity of enzymes present in the cell.
Alters metabolism of the cell.
cAMP inactivated by phosphodiesterase.

Hydrolyzes cAMP to inactive fragments.