General Psychology - Chapter IV


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General Psychology - Chapter IV

  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
  14. 14. ▫ 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.
  15. 15. 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.
  16. 16. 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)
  17. 17. • 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.
  18. 18. Understanding the Central Nervous System
  19. 19. • 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.
  20. 20. The Brain
  21. 21. • 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.
  22. 22. Understandingthe PeripheralNervousSystem
  23. 23. • 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
  24. 24. ▫ 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
  25. 25.  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
  26. 26. • 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
  27. 27. • 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
  28. 28. • 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.
  29. 29. • 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
  30. 30. • 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.
  31. 31. • 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.
  32. 32. • 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.
  33. 33. 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
  34. 34. • 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.
  35. 35. 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
  36. 36. 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
  37. 37. ▫ 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.
  38. 38.  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
  39. 39. 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
  40. 40. 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
  41. 41. 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
  42. 42. 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
  43. 43. B. Ovaries (female) Progesterone Estrogen Promotes adult female primary sexual characteristics Promotes adult female secondary sexual characteristics
  44. 44. • 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
  45. 45. • 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
  46. 46. • 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
  47. 47. • 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
  48. 48. • 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
  49. 49. • 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
  50. 50. 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
  51. 51.  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
  52. 52.  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.
  53. 53.  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.
  54. 54. • 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
  55. 55. • 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.
  56. 56. • 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.
  57. 57. ▫ 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
  58. 58.  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
  59. 59. • 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
  60. 60. 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
  61. 61. • 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