Extended Lecture Outline
15.1 Endocrine Glands
Endocrine glands secrete their chemical signals called hormones directly into the bloodstream. There are similarities as well as differences between regulation by the nervous system and the endocrine system. The secretion of a hormone is often controlled by negative feedback, and the effect of a hormone is often opposed by an antagonistic hormone. The end result is homeostasis.
Hormones are Chemical Signals
Hormones are chemical signals that affect the metabolism of cells (such as hormones or prostaglandins) or the behavior of the individual (such as pheromones).
The Action of Hormones
Hormones have a wide range of effects on cells. Peptide hormones include hormones that are peptides, proteins, glycoproteins, and modified amino acids. Steroid hormones have the same complex of four carbon rings because they are all derived from cholesterol.
The Action of Peptide Hormones
Peptide hormones are usually received by a hormone receptor located in the plasma membrane. Most often their reception leads to activation of an enzyme that changes ATP to cyclic AMP (cAMP). cAMP as a second messenger activates an enzyme cascade.
The Action of Steroid Hormones
Steroid hormones enter the nucleus and combine with a receptor hormone, and the complex attaches to and activates DNA. Transcription and translation lead to protein synthesis.
15.2 Hypothalamus and Pituitary Gland
The hypothalamus uses the autonomic nervous system to help regulate the body’s internal environment. It also controls the secretions of the pituitary gland which has anterior and posterior portions.
Posterior Pituitary
The posterior pituitary secretes antidiuretic hormone (ADH) and oxytocin which are produced by the hypothalamus. Antidiuretic hormone helps to regulate the water-salt balance of the blood. Oxytocin causes uterine contractions during labor and childbirth, and milk let-down during nursing. Oxytocin release is controlled by positive feedback. The hypothalamus triggers release of posterior pituitary hormones through nervous impulse.
Anterior Pituitary
The anterior pituitary produces at least six types of hormones. Thyroid-stimulating hormone (TSH) stimulates the thyroid; ACTH stimulates the adrenal cortex; the gonadotropic hormones FSH and LH stimulate the gonads; prolactin causes mammary glands to produce milk; and growth hormone promotes bone growth. Melanocyte-stimulating hormone causes skin color changes in fishes, amphibians, and reptiles, although humans produce little of this hormone. The hypothalamus triggers release of anterior pituitary hormones through secretion of releasing- or inhibiting-hormones.
Effects of Growth Hormone
Pituitary dwarfism results from too little and giantism results from too much growth hormone duringchildhood. If growth hormone is over-produced in an adult, acromegaly occurs.
15.3 Thyroid and Parathyroid Glands
The thyroid gland is a large gland located in the neck. The parathyroid glands are embedded in the posterior surface of the thyroid gland.
Thyroid Gland
The thyroid gland produces thyroxine and triiodothyronine.
Effects of Thyroid Hormones
If iodine is available in limited quantities, a simple goiter develops; if the thyroid is overactive, an exophthalmic goiter develops. Thyroid hormones generally increase metabolic rate. If the thyroid fails to develop properly, cretinism results. Hypothyroidism in adults causes myxedema.
Calcitonin
The thyroid gland also produces calcitonin, which helps lower the blood calcium level.
Parathyroid Glands
The parathyroid glands secrete parathyroid hormone which raises the blood calcium.
Healing a Fracture
Parathyroid hormone, calcitonin, and vitamin D work together to make calcium available to lay down new bone.
15.4 Adrenal Glands
The adrenal glands are located atop each kidney and consist of an inner medulla and outer cortex. Both portions of the adrenal glands are controlled by the actions of the hypothalamus. The adrenal medulla responds to stress.
Adrenal Medulla
Epinephrine and norepinephrine produced by the adrenal medulla rapidly bring about all the body changes that occur in a fight-or-flight response.
Adrenal Cortex
The hormones produced by the adrenal cortex provide a long-term response to stress. The two major types of hormones are the mineralocorticoids and the glucocorticoids.
Glucocorticoids
Cortisol stimulates hydrolysis of proteins to amino acids that are converted to glucose; in this way, it raises the blood glucose level. High levels of glucocorticoids suppress the body’s immune system.
Mineralocorticoids
Aldosterone causes the kidneys to reabsorb sodium ions (Na+) and excrete potassium ions (K+). The effect of the renin-angiotensin-aldosterone system is to raise blood pressure. The hormone atrial natriuretic hormone produced by the heart opposes the action of aldosterone.
Malfunction of the Adrenal Cortex
Addison disease develops when the adrenal cortex is under active, and Cushing syndrome develops when the adrenal cortex is overactive.
15.5 Pancreas
Exocrine tissue produces and secretes digestive juices that go by way of ducts to the small intestine. Endocrine tissue, called the pancreatic islets secretes insulin, which lowers the blood glucose level, and glucagon, which has the opposite effect. Together these two hormones maintain steady levels of glucose in the blood.
Diabetes Mellitus
Diabetes mellitus is a fairly common hormonal disease in which body cells are unable to take up glucose as they should. The glucose tolerance test assists in the diagnosis of diabetes mellitus.
Types of Diabetes
There are two types of diabetes. The first is due to the failure of the pancreas to produce insulin (type 1 or insulin-dependent diabetes) and the second is caused by the failure of the cells to take up glucose (type 2 or noninsulin-dependent diabetes).
15.6 Other Endocrine Glands
Testes and Ovaries
The testes and ovaries produce the sex hormones which maintain the sex organs and secondary sexual characteristics. Male testes produce androgens (such as testosterone) that are similar to anabolic steroids taken to increase athletic performance. Female ovaries produce estrogen and progesterone.
Thymus Gland
The thymus gland produces thymosins which stimulate T lymphocyte production and maturation.
Pineal Gland
The pineal gland produces melatonin which may be involved in circadian rhythms and sexual development.
Hormones from Other Organs/Tissues
A number of other organs, including the heart, kidneys, stomach, and small intestine produce hormones.
Erythropoietin
The kidneys secrete erythropoietin which stimulates red blood cell formation in the red bone marrow.
Leptin
Leptin is a protein hormone produced by adipose tissue. It acts on the hypothalamus to signal satiety.
Prostaglandins
Prostaglandins, which have varied effects, are produced and act locally.
15.7 Homeostasis
The nervous and endocrine systems exert control over the other systems and thereby maintain homeostasis.
Responding to External Changes
The nervous system is particularly able to respond to changes in the external environment. Some responses are automatic.
Responding to Internal Changes
The governance of internal organs usually requires that the nervous and endocrine systems work together, usually below the level of consciousness.
Controlling the Reproductive System
The hypothalamus controls the anterior pituitary, which, in turn, controls the release of hormones from the testes and the ovaries and the production of their gametes. The nervous system also controls aspects of the reproductive system.
The Neuroendocrine System
The nervous and endocrine systems work so closely together, they form what is sometimes called the neuroendocrine system.
Extended Lecture Outline
16.1 Human Life Cycle
The reproductive system is quite different in males and females. The reproductive organs (testes in males, ovaries in females) produce, nurture and transport the gametes, while the female allows the development of the fertilized egg within her body. Both testes and ovaries produce the sex hormones.
Mitosis and Meiosis
Mitosis is duplication division. It is the type of cell division that takes place during growth and repair of tissues. Meiosis is reduction division. Meiosis takes place in the testes of males and ovaries of females during the production of gametes. During meiosis, the chromosome number is reduced from the normal 46 chromosomes, or 2n number, to 23 chromosomes, or n number.
16.2 Male Reproductive System
In males, the testes produce sperm that mature in the epididymides and may be stored in the vasa deferentia before entering the urethra, along with secretions produced by seminal vesicles, the prostate gland, and bulbourethral glands.
Orgasm in Males
The penis is the male organ of sexual intercourse. Circumcision is the surgical removal of the foreskin of the penis. During sexual arousal, spongy, erectile tissue in the penis becomes engorged with blood and the penis becomes erect. Erectile dysfunction is when the erectile tissue doesn’t expand enough. Semen is ejaculated during male orgasm. This is followed by a refractor period during which stimulation does not bring about an erection.
Male Gonads, the Testes
The testes lie outside the abdominal cavity of the male within the scrotum. The scrotum helps regulate the temperature of the testes.
Seminiferous Tubules and Interstitial Cells
Spermatogenesis occurs within the seminiferous tubules. Mature sperm, or spermatozoa, have three distinct parts: a head, a middle piece, and a tail.
Interstitial Cells
The male sex hormones are secreted by cells that lie between the seminiferous tubules. Therefore they are called interstitial cells.
Hormonal Regulation in Males
Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates the seminiferous tubules to produce sperm. LH stimulates interstitial cells to produce testosterone. Testosterone exerts feedback control over the hypothalamus and anterior pituitary resulting in a constant amount of hormones at all times. Testosterone is responsible for the male secondary sex characteristics.
16.3 Female Reproductive System
The female gonads are paired ovaries. The ovaries produce eggs and the female sex hormones.
The Genital Tract
In females, an egg produced by an ovary enters an oviduct, which leads to the muscular uterus. At the lower end of the uterus, the cervix enters the vagina. The vagina is a tube that accepts the penis during intercourse, serves as the birth canal, and allows the menstrual flow to exit. A Pap test is an early detection test for cervical cancer. Development of the embryo and fetus normally takes place in the uterus.
External Genitals
The external genital area includes the vaginal opening, the clitoris, and the vulva consisting of the labia minora and the labia majora.
Orgasm in Females
Orgasm in females may be more subtle than male orgasm. The clitoris becomes erect and engorged with blood; release from muscular tension occurs in genitals and throughout the body.
16.4 Female Hormone Levels
Hormone levels cycle in the female on a monthly basis. The ovarian cycle drives the uterine cycle.
Ovarian Cycle: Nonpregnant
Oogenesis occurs within the ovaries. The ovarian cycle consists of the development of the follicle, ovulation, and the development of a glandular corpus luteum.
Phases of the Ovarian Cycle
During a follicular phase (day 1–13), FSH from anterior pituitary stimulates development of an oocyte-containing follicle which secretes estrogen and progesterone. Ovulation occurs on day 14 of a 28 day cycle. During a luteal phase (day 15–28), the corpus luteum secretes progesterone and estrogen.
Estrogen and Progesterone
The ovaries produce the female sex hormones estrogen and progesterone. Estrogen is largely responsible for the secondary sex characteristics in females. Menopause is the period in a woman’s life during which the ovarian cycle ceases. Until recently, many women took combined estrogen-progestin drugs to ease menopausal symptoms.
The Uterine Cycle: Nonpregnant
Menstruation (days 1–5) occurs due to low levels of estrogen and progesterone in the blood. During a proliferative phase, (days 6–13) the endometrium thickens under the influence of estrogen. Ovulation occurs midcycle. During a secretory phase (days 15–28), the endometrium continues to thicken and becomes vascular under the influence of progesterone. If pregnancy does not occur the cycle begins again.
Fertilization and Pregnancy
If fertilization occurs, the embryo embeds in the endometrium and the placenta begins to produce human chorionic gonadotropin (HCG), which prevents degeneration of the corpus luteum, and the uterine lining is maintained.
Birth Control Pill
Birth control pills prevent the occurrence of ovulation. The pills supply the body with estrogen and progesterone so that no new follicles begin in the ovary. In effect, birth control pills fool the body into acting as if pregnancy has occurred.
16.5 Control of Reproduction
Birth Control Methods
Popular and effective means of birth control are oral contraceptive pills taken by the woman, and barrier methods (condoms, diaphragms) that are barriers to conception and offer some control over the transmission of sexually transmitted diseases. Contraceptive implants and injections are also available. Contraceptive vaccines are now being developed.
Vasectomy and Tubal Ligation
Both vasectomy and tubal ligation are forms of sterilization. In a vasectomy the vas deferens is cut and sealed while in a tubal ligation the oviducts are cut and sealed.
Morning-After Pills
The morning-after pill prevents pregnancy after unprotected intercourse. The medication can begin one to several days after unprotected intercourse. The medications upset the normal uterine cycle making it difficult for the embryo to implant.
Infertility
Infertility is the failure of a couple to achieve pregnancy after one year of regular, unprotected intercourse. An estimated 15% of all couples in the United States are infertile.
Causes of Infertility
Infertility can be caused by blocked oviducts (the result of pelvic inflammatory disease [PID] or endometriosis), by lack of regular ovulation, or by low sperm count or abnormal sperm in males. Many couples choose to adopt when they cannot conceive.
Assisted Reproductive Technologies
Artificial Insemination by Donor (AID)
Artificial insemination by donor (ART) involves inseminating the woman in the doctor’s office, using sperm from a donor, from the woman’s partner, or a combination of the two.
In Vitro Fertilization (IVF)
In vitro fertilization (IVF) is conception in lab glassware. Eggs are removed from the ovaries, sperm are added to them, and the eggs are placed in the woman’s uterus after fertilization.
Gamete Intrafallopian Transfer (GIFT)
Gameteintrafallopian transfer (GIFT) is a means of removing a woman’s eggs and placing them in the oviduct along with her husband’s sperm. The advantages are lower cost and that it is a one-step procedure.
Surrogate Mothers
Surrogate mothers are sometimes employed to bear children for women who, for various reasons, cannot.
Intracytoplasmic Sperm Injection (ICSI)
Intracytoplasmic sperm injection (ICSI) involves the injection of a single sperm cell into an egg.
16.6 Sexually Transmitted Diseases
Sexually transmitted diseases (STDs) are caused by viruses, bacteria, protists, fungi, and animals.
STDs Caused by Viruses
Effective treatment is available for AIDS and genital herpes. Neither virus can be eliminated from the person’s body, however.
HIV Infections
The AIDS supplement discusses HIV infections at greater length. AIDS is the last stage of an HIV infection.
Genital Warts
Genital warts are caused by human papillomaviruses (HPVs). Researchers believe that these viruses may be involved in up to 90% of all cases of cancer of the cervix.
Genital Herpes
Genital herpes is caused by herpes simplex virus. Infection is often accompanied by blisters on the genitals. The disease is a latent one in which blisters can recur.
Hepatitis
Hepatitis infects the liver and can lead to liver failure, liver cancer, and death. Hepatitis B is spread through sexual contact as are hepatitis D and G.
STDs Caused by Bacteria
Only STDs caused by bacteria are curable with antibiotics.
Chlamydia
Chlamydia is named for the tiny bacterium that causes it. Initial infections are usually mild or asymptomatic. If the infection is not treated, the infection may spread from the cervix to the uterine tubes resulting in pelvic inflammatory disease (PID), a painful condition that can result in the blockage of the uterine tubes.
Gonorrhea
A latent infection can result in PID and can cause sterility in males as well. Gonorrhea can spread to internal parts of the body causing heart damage or arthritis.
Syphilis
Syphilis has three stages often separated by latent periods. During the primary stage, a hard chancre indicates the site of infection. The secondary stage is characterized by a rash, while during the tertiary stage, syphilis may affect the cardiovascular system and nervous system.
Two Other Infections
Bacterial vaginosis can be due to bacterial, protozoan, or yeast infections. The protozoan Trichomonas vaginalis or the yeast Candida albicans can both be responsible.