1. CHAPTER IV
DETERMINANTS AND
PHYSIOLOGICAL BASIS OF
BEHAVIOR

2. HOW DOES HEREDITY WORK?
• A. Biological Transmission
▫ Heredity pattern is transmitted at conception
when female egg is fertilized by the male sperm
cell -Zygote
▫ In the nucleus of the zygote the heredity material
are combined and within 24 hours development of
newly formed structure – human infant

3. • B. Chromosomal Principles of Inheritance
▫ Walter Sutton – American Scientist; the heredity
characteristics are located in the chromosomes
▫ Johann Gregor Mendel – Principle of Unit
Determiners; he resembled the chromosomal
principle of inheritance
 Mendel Principles of Unit Determiners
 1. Unit determiners appear in pairs (as alleles)
 2. Genetic traits segregate during the formation of
gametes (name for the two types of male and female
cell that join together to make a new creature)
 3. Unit characters combine during fertilization.
 4. Unit characters pass from parents to offspring.
 5. Individuals have unique unit characteristics.

4.  Sutton’s Chromosomal Principles of Inheritance
 1. Chromosomes exist in pairs.
 2. Homologous chromosomes separate during meiosis.
 3. The diploid number of chromosomes is restored
during the process of fertilization.
 4. Chromosomes are present in gametes, which unite to
form an offspring.
 5. chromosomes randomly segregate. They maintain
their individuality.
• It is noted that Sutton’s chromosome and the
gene theory led to the foundation of genetic
engineering
• Genetics focus on the transfer of traits through
the use or following the laws expanded by
Mendel

5. • C. Common Terms to Remember in the Study of
Heredity
▫ 1. Autosome. These are the actual chromosomes
present normally inside the nucleus without
considering the x and y (sex) chromosomes.
 22 pairs from both parents
▫ 2. Gene. A discrete unit of inheritance, which is
believed to be carrying the heredity traits.
▫ 3. Genotype. This is an individual’s genetic make-up
 Complete set of instructions on how body is supposed to
be built
▫ 4. Phenotype. These are observable traits.
 How the body is actually built
▫ 5. Heterozygous. This is a term that describes a gene
pair, which is made up of two different kinds of genes
or alleles.
▫ 6. Homozygous. This is a term that describes a gene
pair consisting of two identical twins.

6. ▫ 7. Dominant allele or gene. That which is
expressed or observable.
▫ 8. Recessive allele or gene. That which is hidden
but may be passes on to the next generation.
▫ 9. Hybrid. An offspring of parents belonging to
two different varieties or species, an offspring of
two parents that differ in one or more heritable
characteristics.
▫ 10. Incomplete Dominance. This is a type of Non-
Mendelian offspring which does not express of the
purebred characters of the two contrasting
parents.

7. Multiple Births
• Identical twins/monozygotic twins
▫ 1 sperm + 1 egg cell - divides into 2 after being
fertilized by 1 sperm
▫ Often they share the same placenta and fetal sac
▫ Always the same sex
• Non-identical/fraternal twin
▫ 2 sperms + 2 egg cell - develop independently
▫ Usually have separate placenta and separate fetal
spaces
▫ Have different genes
▫ Maybe opposite sex

8. The Heredity-Environment
Relationship
• A. Some Misconceptions
▫ 1. Exclusive Operation – a belief that psychological
characteristics can be separated into those that are
inherited and those that are required
▫ 2. Additive Contribution – both heredity and
environment and the resulting behavioral
characteristics can be analyzed into the sum of
heredity and environment
 Ex. Intelligence: 75% heredity, 25% environment

9. • B. The Most Widely Accepted View of the
Heredity-Environment relationship is that of
Interaction
▫ 1. any environmental factor will exert a different
influence depending upon the specific heredity
material upon which it operates. Similarly, any
heredity factor will operate differently upon the
environmental conditions.
▫ 2. the individual’s characteristics may be
conceived of as product, rather than the sum of
the heredity and environmental factors.

10. How Does the Environment Affect the
Individual
• Distinction has to be made:
▫ Physical environment, the physical milieu in which the
individual is living
▫ Affective environment, the physical milieu in as far as it
affects the individual
• Bad environment can suppress or even nullify good
inheritance
• Good environment is unfortunately not a substitute for
good heredity; cannot make a talented person, cannot
make a bright adult out of feebleminded child
• Heredity determines what a man can do. Environment
determines what a man does within the limits imposed
by heredity.

11. Nervous System
• 2 Divisions:
▫ Central Nervous System (CNS) –
 brain and spinal cord
▫ Peripheral Nervous System (PNS)
 Cranial nerves
 Somatic Nervous System – regulates the activity of
the striated (voluntary) muscles. Data for this
system are received by sensory receptors transmitted
by peripheral nerves and processed in CNS
 Autonomic Nervous System

12. Neurotransmission and Classification
of Nerves
• A. The Neuron
▫ The function of the nervous system depends
almost entirely on the electrical signals produced
by the same physical and chemical changes across
nerve cells membranes
▫ The nervous system in coordination with the
endocrine is charged with functions of
perceiving, interpreting and acting upon this
varied input. The nervous system has
integrative, coordinative and managerial functions
in the entire human body.

13. • Neuron – functional unit of the brain. These are
excitable cells because they respond rapidly to
physical or chemical changes in impulses.
• Structure of a Neuron
▫ Dendrites – these are branches that reach out and
detect stimuli and carry the impulses to the cell body
of the neuron
▫ Cell body
▫ Axons – these are long projections; conduct impulse
away from the cell. Some axons are covered with
myelin sheath that allows more rapid impulse
transmission
▫ Nodes of Ranvier – these are gaps in the myelin sheath
▫ Myelin Sheath – this part of the neuron lines some
axons in the CNS and the PNS

15. ▫ Anatomical forms and properties – influence the
physiological behavior of a neuron
▫ Long axon – has the ability for rapid conduction of
the electrical impulses from the cell body to the
target structure.
▫ The membranes of the neurons terminals are
specialized for the secretion of transmitter
substances into extra cellular fluid between it and
the target organ, for example the muscle cell, or
for electrical transmission to another neuron.

16. Classification of Neurons
• The functional classification based on the direction
that they conduct impulses.
▫ Sensory (afferent) neurons – conduct impulses from
sensory receptors to the CNS
▫ Motor (efferent) neurons – conduct impulses out of
CNS to effector organs (muscles or organs). These
have 2 types
 Somatic motor neurons – provide reflex and voluntary
control of the skeletal muscles
 Autonomic motor neurons – innervate the involuntary
effectors – smooth muscle, cardiac muscle, and glands.

17. Neurotransmission
• Neurotransmission refers to the transmission or
condition of impulses in the nervous system and
occurs through the action of the neurons
• Neuron activity may be provoked by mechanical
stimuli (touch, pressure)
• A thermal stimuli (heat or cold) or chemical
stimuli (external chemical or the chemical
released by the body)

18. • Common Neurotransmitters
▫ Acetylcholine – a decrease has been associated
with Alzheimer’s disease
▫ Dopamine – linked to Parkinson’s disease
(decrease in dopamine) and schizophrenia
(increase in or increased sensitivity to dopamine)
▫ Serotonin – linked to mood changes and sleep
pattern, with higher levels producing a calming or
drowsing effect.

19. Understanding
the
Central Nervous
System

20. • The Central Nervous System is made up of 2
parts: brain and the spinal cord
▫ Spinal Cord joins the brain stem at the level of the
Foramen magnum and terminates near the
second lumbar vertebra.
▫ A cross section of the spinal cord reveals a central
H-shaped mass of gray matter divided into dorsal
(posterior) and ventral (anterior) horns.
▫ Gray matters relay sensory (afferent) impulses in
the ventral horns, motor (efferent) impulses.
▫ White matter (myelinated axons of the sensory
and motor nerves) surrounds these horns and
forms the ascending and descending tracts.

21. The Brain

22. • The Brain
▫ The intracranial space contains brain substance
(about 80%) blood (about 10%) and cerebrospinal
fluid (about 10%).
▫ The brain tissue is just about 2% of the body
weight, yet it requires 15-20% of the body’s oxygen
demands. Cerebral blood flow remains
proportional to meet the metabolic demands of
the brain.

23. Understandingthe
PeripheralNervousSystem

24. • 3 Major divisions:
▫ 1. Forebrain – consists of the following:
 Cerebrum – most complex and largest part of the
brain
 “seat of consciousness” resonsible for higher order
activites like endless thinking, and reasoning, memory
and understanding
 Right cerebral hemisphere and left cerebral hemisphere
 Thalamus - found right on top of the midbrain
 Serve as a relay center of the impulses being sent to the
brain areas
 Hypothalamus - “seat of emotion”
 Body temperature, thirst, appetite, and sexual drives
and emotional behaviors

25. ▫ 2. Midbrain – serves as the bridge between the
hindbrain and the forebrain
 Responsible in linking the sensory and motor
pathways between the upper and the lower parts of
the nervous system
 Auditory and visual activities
▫ 3. Hindbrain – connected to the spinal cord and
consist if the following:
 Pons – located in front of the cerebellum and it is
made up mostly of the nerve fibers running from one
part of the brain to the others

26.  Medulla oblongata – quite small, about an inch long
just above the spinal cord
 Regulates the involuntary muscles responsible for our
heartbeat, rate of breathing, swallowing and
movements of stomach and intestine
 Cerebellum – “little brain” has 2 hemispheres
 Connected to the back of the brain stem
 Involved in the coordination of voluntary motor
activities
 Maintains the body balance and posture
 Enables us to learn and develop our habits and skills

27. • Spinal Cord – is a long and stem-like structure
running down the vertebral column
▫ Receives sensory information to the brain and
transmits motor impulses from the brain to the
muscles
▫ 2 kinds of reflexes:
 Monosynaptic – simple reflex, only one synapse
 Polysynaptic - complex reflexes, ex blink to loud
sound

28. • Somatic System – responsible for the
voluntary skeletal mobvements
• On the Old Olympus Towering Top A
French And German View Special Hut
▫ The 12 pairs cranial nerves transmit motor or
sensory messages, or both, primarily between the
brain and the brain stem, and the head and the
neck.
▫ All cranial nerves, except the Olfactory and the
Optic nerves, exit from the midbrain pons or
medulla oblongata of the brain stem
Peripheral Nervous System

29. • On the I Olfactory nerve – used purely for
sensory, this carries impulses for
sense of smell
• Old II Optic nerve – purely for sensory;
carry impulses for vision.
• OlympusIII Oculomotor nerve- contains
motor fibers to superior, inferior
and medial rectus muscles that
direct the eyeball to the muscles
of the eyelid, and to the iris and
smooth muscle controlling lens
shape; contains proprioceptor
fibers from the external eye
muscles to the brain.

30. • Towering IV Trochlear nerve –
propiroceptor and motor
fibers for superior oblique
muscle of the eye (external
eye muscles.)
• Top V Trigeminal nerve – both
motor and sensory for face;
conducts sensory impulses
for mouth, nose and surface
of the eyes; also contains
motor fiber that stimulates chewing
muscle.
• A VI Abducens nerve – contains
motor fiber to lateral rectus muscles
and proprioceptors fibers from
same muscle to brain

31. • French VII Facial nerve – (mixed) this supplies
motor fiber for muscles of facial
expression and to lacrimal and
salivary glands, next it carries
sensory fibers from taste buds of
anterior part of the tongue.
• And VIII Acoustic (Vestibulocochlear) nerve
– this is purely sensory, vestibular
branch transmits impulses for sense
of equilibrium; cochlear branch
transmits impulses for sense of
equilibrium and sense of hearing.
• German IX Glossopharyngeal nerve – mixed a)
motor fiber serve pharynx (throat)
and salivary glands; b) sensory
fibers carry impulses from pharynx,
posterior tongue (taste buds), and
pressure receptors of the carotid
artery.

32. • View X Vagus nerve – fibers carry
sensory and motor impulses for
pharynx a large part of this nerve
is parasympathetic motor fibers,
which supply the smooth muscles
of abdominal organs, and
transmit impulses from the viscera.
• Special XI Spinal Accessory nerve – this
provides motor fiber for
sternocleidomastoid and trapezius
muscles and the muscles of the soft
palate, pharynx and larynx
• Hut XII Hypoglossal nerve – this caries
motor fibers to the muscles of
tongue and sensory impulses from
the tongue to brain.

33. • This time try to remember that each spinal nerve
consist of afferent (sensory) and efferent
(motor) neurons, which carry messages to and
particular body regions called dermatomes.

34. Autonomic Nervous System
• Innervates all internal organs
• Present in both Central and Peripheral Nervous
Systems
• Controlled the involuntary (non-striated)
muscles, the heart, and the glandular cells
• Functions by responding to stimuli from within
the body and by maintaining the constancy of
the internal environment
• Nerves – carry messages to the viscera from the
brain stem and the neuroendocrine system

35. • 2 major divisions:
▫ Sympathetic (thoracolumar) – produces excitatory
effects
 Prepares ourselves into vigorous actions like those of
fight or flight reactions to stress
 Increase heartbeat and respiration, profuse
sweating, adrenaline secretion
▫ Parasympathetic (craniosacral) – produce
inhibitory effects
 Slows down the life activities
 Calming down the body after resolving stressful nd
emergency situation.

36. The Endocrine System
• Endocrine glands – secrete their products into
body fluids
▫ Are concerned with regulation of metabolic
processes
▫ “Ductless glands”
• Exocrine glands – secrete their products into
ducts that lead outside of the body

37. A. Hormones and Their Actions
• Endocrine glands secrete hormones that affect
target cells possessing specific receptors
▫ 1. The Chemistry of Hormones
 A. Each kind of hormone has a special molecular
structure and is very potent
 B. Chemically, hormones are steroid, amine,
peptides, proteins and glycoproteins

38. ▫ 2. Actions of Hormones
 A. Steroid Hormones
 a. Steroid hormones enter target cells and combine
with the receptors in the nucleus to form complexes
 b. These complexes activate specific genes, which in
turn cause, special protein to be synthesized
 c. The degree of cellular response is proportional to the
number of hormone receptor complexes formed.
 B. Nonsteroid Hormones
 a. Nonsteroid hormones combine with receptors in the
target cells.
 b. A hormone-receptor combination stimulates
membrane protein, such as adenylate cyclase, to induce
the formation of the second messenger molecules.

39.  c. A second messenger such as camp, activities protein
kinases
 d. Protein kinases activate certain protein substrate
molecules, which in turn cause changes in cellular
processes.
 e. The cellular response to nonsteroid hormone is
amplified because the enzyme is induced by a small
number of hormone-receptor complexes can cause a
large number of second messenger molecule to be
formed.
 C. Prostaglandins
 a. prostaglandins are substances present in small
quantities that have powerful hormone like effects
 b. It seem to function as modulators of hormones that
regulate the formation of cyclic AMP

40. B. The Control of Hormonal Secretions
• The concentration of each hormone in the body
fluids must be regulated in the body as such:
▫ 1. Negative Feedback System
 a. A gland is sensitive to the concentration of a substance
it regulates
 b. When the concentration of the regulated substance
reaches a certain concentration, it inhibits the gland.
 c. As the gland secrete less hormone, the controlled
substance also decreases.
▫ 2. Nerve Control
 a. Some endocrine glands secrete their hormones in
response to nerve impulses
 b. Other glands secrete hormones in response to releasing
hormones secreted by the hypothalamus

41. Tabulation of the Endocrine System
Endocrine Hormonal Secretion Functions/ Effects
I. Pituitary gland
(Master glands)
Adrenocorticotropic
Hormone (ACTH)
Stimulates the adrenal
cortex
Divisions:
A. Anterior Lobe
Thyrotropic Hormone
(LH)
Follicle Stimulating
Hormone (FSH)
Luteinizing Hormone
(LH)
Growth Hormones
Growth Hormone
(somtotropin)
Stimulates the thyroid
gland
Stimulates ovarian
follicle for ovulation
Stimulates the sex glands
(testes and ovaries)
Promotes growth in all
parts of the body
Stimulates growth of all
parts of the body

42. Prolactin Stimulates mammary
gland to produce
milk
B. Posterior Lobe Vasopressin
Oxytocin
Control water excretion
by the kidneys
Stimulates uterine
contraction during child
delivery
II. Thyroid gland Thyroxine Regulates basal
metabolism
III. Parathyroid gland Parathormone Regulates calcium and
phosphorus level in the
blood
IV. Islets of langerhans Insulin Regulates sugar level in
the blood
V. Pineal gland Melatonin Control activities of sex
glands

43. VI. Adrenal Gland
Divisions:
A. Adrenal Cortex Cortin Regulates
development of adult
sexual characteristics
B. Adrenal medulla Adrenaline
Noradrenaline
Affect emotional
responses, emergency
hormone
Causes the blood vessels
to constrict when a
person is injured
VII. Gonads/ Sex gland
A. Testes (male) Testosterone Promotes adult male
secondary sexual
characteristics

44. B. Ovaries (female) Progesterone
Estrogen
Promotes adult
female primary
sexual characteristics
Promotes adult
female secondary
sexual characteristics

45. • 1. Pituitary Gland – “master gland” because it
secretes a number of hormones that affect the
activities of almost all the endocrine glands
▫ Effects:
 Anterior Lobe
 Under activity - Dwarfism
 Over activity
▫ Giantism
▫ Acromegaly – overgrowth of certain parts of the bones like
individuals with a hunchback
 Posterior Lobe
 Under activity
▫ Diabetes insipidus – large urine volume excretion
 Over activity
▫ Hypomatremia and fluid overload – characterized by
excessive fluid in the blood

46. • 2. Pineal Gland – “gland of childhood” located in the
head adjacent to the pituitary gland
 Under activity
 Leads to premature appearance of secondary sexual
characteristics
• 3. Thyroid Gland – butterfly-shape gland located at
the base and anterior part of the throat
▫ Effects:
 Over activity
 1. increased body heat production
 Under activity
 1. Cretinism – retarded physical and mental development
during childhood
 Myxedema – gain in weight, thickening of the lips, slowing of
motor movements. And yellowing of the skin during
childhood

47. • 4. Parathyroid Glands – pea-shaped gland
located at the posterior (back) of the thyroid
gland
▫ Effects:
 Under activity
 1. Tetany or lockjaw, characterized by spasms of the
muscles of the lower jaw leading to convulsion or
muscular rigidity.
 Over activity
 1. lethargy is characterized by muscular weakness and
decreased in nerve cell activity

48. • 5. Thymus Gland – “gland of babyhood” keeps and
individual “childish”
▫ Located above chest cavity, it secrets the hormone
thymosin
▫ Inhibits sexuality during the childhood years
▫ Building up the immune system
• 6. Adrenal Gland – located at the upper end or tip of
each kidney
▫ Effects:
 Under activity
 1. Addisons’ disease is characterized by bronze-like
discoloration of the skin and generalized physiological
breakdown
 2. delayed puberty may result due to under activity of the
adrenal cortex

49. • Over activity of Adrenal Cortices
• 1. Cushing’s disease (women) is characterized by round or
moon-shaped face, cessation of menstruation, and appearance
of beard, change of voice (in either sex)
• Adrenogenital syndrome (girls) is characterized by virilism, an
increases masculine features among young girls
• 7. Islets of Langerhans – these are small bodies
made up of clusters of special cells scattered all
over the pancreas
▫ Effects of Malfunctioning
 Under activity
 1. Diabetes mellitus
 Over activity
 1. insulin shock, characterized by convulsions or
seizures

50. • 8. Gonads/ Sex Glands
▫ A. Testes (male) – located in the socratal sac and
secretes the hormone, testosterone is responsible for
the appearance of secondary sex characteristics
 Premature secretion among young boys can lead to
puberty praecox, early sexual maturity
▫ B. Ovaries (female) – are located within the abdominal
cavity
 Estrogen – secondary sex characteristics
 Progesterone - primary sexual characteristics which
prepare the reproductive system for child-bearing
• The digestive Glands – certain glands of stomach
and small intestine that secrete hormones
• Other Hormone-producing organ include the heart
and kidneys

51. C. Endocrine Glands
• Pituitary Gland – attached to the base of the brain,
has an anterior lobe and a posterior lobe. Most
pituitary secretions are controlled by the
hypothalamus
▫ 1. Anterior Pituitary Hormones
 a. it consists largely of epithelial cells, and it secretes the
growth hormones (GH), Prolactin (PRL), Thyroid
stimulating hormones, ACTH, FSH, and LH.
 b. Growth Hormone
 Stimulates body cells to increase in size and rate
reproduction
 The secretion of GH is controlled by growth hormone –
releasing hormone and somatostatin from the hypothalamus

52.  c. Prolactin (PRL)
 It promotes breast development and stimulates breast milk
production.
 Prolactin, release-inhibiting factor from the hypothalamus
restrains the secretions of prolactin, while prolactin-
releasing factor promotes its secretion.
 d. Thyroid Stimulating Hormones (TSH)
 It controls the secretion of hormones from the thyroid gland.
 Secretion is regulated by the hypothalamus, which secretes
thyrothropin-releasing hormone
 e. Adrenocorticotropic Hormone (ACTH)
 Controls the secretion of certain hormones from the adrenal
cortex
 The secretion of ACTH regulated by the hypothalamus,
which secretes corticotrophin-releasing hormone

53.  f. Gonadotropic Hormones
 Follicle Stimulating Hormone (FSH) – stimulates
follicle growth and estrogen secretion in females and
spermatogeneis and testosterone secretion in males
 Luteinizing Hormone (LH) – stimulates the ovulation,
growth of corpus luteum and secretion of estrogen and
progesterone in females and secretion of testosterone
in males
▫ 2. Posterior Pituitary Hormones
 a. The posterior lobe of the pituitary gland consists
largely of neuroglial cells and nerve fibers that
originate in the hypothalamus.
 b. The 2 hormones of the posterior pituitary are
produced in the hypothalamus.

54.  c. Antidiuretic Hormone (ADH)
 C1. This causes the kidneys to reduce the amount of
water they secrete
 C2. In high concentration, ADH causes blood vessels
walls to constrict, thus raising the BP
 C3. And lastly, the secretion of the ADH is regulated by
the hypothalamus
 d. Oxytocin
 It has an antidiuretic effect and can cause muscles in
the uterine wall to contract, thus playing role in
childbirth.
 It also causes contraction of certain cells associated
with production and ejection of milk from the milk
glands of the breast.

55. • Thyroid Gland - is located in the neck and consists
of 2 lateral lobes
▫ 1. The Structure of the Gland
 It consists of many hollow secretory parts called follicles
 The follicles are fluid filled and store the hormones
secreted by follicles cells
▫ Thyroid Hormones
 a. Thryroxin and tri-iodothyronine
 It increase the rate of metabolism, enhance protein
synthesis, and stimulate the breakdown of lipids
 Are needed for normal growth and development and for the
maturation of the nervous system
 b. Calcitonin
 Lowers the blood calcium and phosphate ion concentration
 Prevents prolonged elevation of calcium after meal

56. • Parathyroid Glands – are located on the posterior
surface of the thyroid gland
▫ 1. Structure of the Glands
 a. Each gland consists of secretory cells that are well
supplied with capillaries
▫ Parathyroid Hormone (PTH)
 a. Causes an increase in blood calcium ion concentration
and decrease in blood phosphate ion concentration.
 b. Stimulates the resorption of bone tissue, causes the
kidneys to conserve calcium ions and excretes phosphate
ions, and indirectly stimulates the absorption of calcium
ions from the intestine.
 c. The parathyroid glands seem to be regulated by a
negative feedback mechanism that operates between the
glands and the blood.

57. • Adrenal Glands – are located above the kidneys
▫ 1. Structure of the Glands
 a. Each adrenal gland consists of a medulla and cortex.
 b. The adrenal medulla and the adrenal cortex represent
distinct glands that secrete different hormones
▫ 2. Hormones of the Adrenal Medulla
 a. The adrenal medulla secretes epinephrine and nor
epinephrine.
 b. These hormones are synthesized from tyrosine and are
closely related to each other chemically.
 c. These hormones produce effects similar to those of
sympathetic nervous system
 d. The secretion of these hormones is stimulated by
sympathetic nervous system.

58. ▫ 3. Hormones of the Adrenal Cortex
 a. The cortex produces a variety of steroids that include
several hormones.
 b. Aldosterone
 It causes the kidneys to conserve NA ions and later, to
excrete potassium ions.
 It is secreted in response to decrease NA ion concentration,
increased K ion concentration.
 By promoting the conservation of NA ions and water, it
helps maintain blood volume and pressure.
 c. Cortisol
 It maintains the synthesis of proteins, promotes the release
of fatty acid, and stimulates the formation of glucose from
non-carbohydrates
 It is controlled by a negative feedback mechanism involving
the secretion of corticotropin stimulating hormone from the
hypothalamus and ACTH from the anterior pituitary gland

59.  d. Adrenal Sex Hormones
 These hormones are the male type although some can
be converted into female hormones.
 They are thought to supplement the sex hormones
produced by the gonads

60. • Pancreas – secretes digestive juices as well as hormones
▫ 1. Structure of the Gland
 The pancreas is posterior to the stomach and is attached to the
small intestine.
 The endocrine portion which is called the Islet of Langerhans,
secretes glucagons, insulin and somatostatin.
▫ 2. Hormones of the Islets of Langerhans
 Glucagon stimulates the liver to produce glucose, causing an
increase in the concentration of blood glucose. It also promotes
the breakdown of fats.
 Insulin promotes the movement of glucose through cell
membranes, stimulates the storage of glucose, promotes the
synthesis of proteins and stimulates the storage of fats.
 Nerve cells lack insulin receptors and depend upon diffusion
for a glucose supply
 Somatostatin may inhibits glucagon release

61. Other Endocrine Glands
• Pineal Gland
▫ Is attached to the thalamus near the roof of the 3rd
ventricle
▫ It is innervated by postganglionic sympathetic
nerve fibers
▫ It secretes melatonin, which seems to inhibit the
secretion of gonadotrophins from the anterior
pituitary gland. A rise in melatonin levels in the
blood tends to make people less alert and makes
sleep more inviting

62. • Thymus Gland
▫ It lies behind the sternum and between the lungs
▫ Its size diminishes with age
▫ It secretes thymosin, which affects the production of
certain lymphocytes that, in turn, play important roles
in immunity
• Reproductive Glands
▫ The ovaries secrete estrogens and progesterone
▫ The placenta secretes estrogens, progesterone and
gonadotropin
▫ The testes secrete testosterone
• The digestive Glands – certain glands of stomach
and small intestine that secrete hormones
• Other Hormone-producing organ include the heart
and kidneys