Chapter 17hhh.gavilan.edu/jcrocker/documents/Ch17-20Rev.pdf · Chapter 17 Urinary System. 2 Introduction A. ... Urine Elimination A.After forming in the nephrons, urine passes from

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Chapter 17Urinary System

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IntroductionA. The urinary system consists of two kidneys that filter the blood, two ureters, a urinary bladder, and a urethra to convey waste substances to the outside.

CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Kidneys A. The kidney is a reddish brown, bean-shaped organ 12 centimeters long; it is enclosed in a tough, fibrous capsule.


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B. Location of the Kidneys1. The kidneys are positioned

retroperitoneally on either side of the vertebral column between the twelfth thoracic and third lumbar vertebrae, with the left kidney slightly higher than the right.


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C. Kidney Structure1. A medial depression in the kidney leads

to a hollow renal sinus into which blood vessels, nerves, lymphatic vessels, and the ureter enter.

2. Inside the renal sinus lies a renal pelvisthat is subdivided into major and minor calyces; small renal papillae project into each minor calyx.


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3. Two distinct regions are found within the kidney: a renal medulla and a renal cortex.a. The renal medulla houses tubes

leading to the papillae.b. The renal cortex contains the

nephrons, the functional units of the kidney.


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D. Kidney Functions 1. The kidneys function to regulate the

volume, composition, and pH of body fluids and remove metabolic wastes from the blood in the process.

2. The kidneys also help control the rate of red blood cell formation by secreting erythropoietin, and regulate blood pressure by secreting renin.


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E. Renal Blood Vessels1. The abdominal aorta gives rise to renal

arteries leading to the kidneys.2. As renal arteries pass into the kidneys,

they branch into successively smaller arteries: interlobar arteries, arcuate arteries, interlobular arteries, and afferent arterioles leading to the nephrons.

3. Venous blood is returned through a series of vessels that generally correspond to the arterial pathways.


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F. Nephrons1. Nephron Structure

a. A kidney contains one million nephrons, each of which consists of a renal corpuscle and a renal tubule.


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b. The renal corpuscle is the filtering portion of the nephron; it is made up of a ball of capillaries called the glomerulus and a glomerular capsule that receives the filtrate.


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c. The renal tubule leads away from the glomerular capsule and first becomes a highly coiled proximal convoluted tubule, then leads to the nephron loop, and finally to the distal convoluted tubule.

d. Several distal convoluted tubules join to become a collecting duct.


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2. Blood Supply of a Nephron a. The glomerulus receives blood

from a fairly large afferent arteriole and passes it to a smaller efferent arteriole.

b. The efferent arteriole gives rise to the peritubular capillary system, which surrounds the renal tubule.


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3. Juxtaglomerular Apparatus a. At the point of contact between

the afferent and efferent arterioles and the distal convoluted tubule, the epithelial cells of the distal tubule form the macula densa.


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b. Near the macula densa on the afferent arteriole are smooth muscle cells called juxtaglomerular cells.

c. The macula densa together with the juxtaglomerular cells make up the juxtaglomerular apparatus.


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Urine Formation A. Urine formation involves glomerular filtration,

tubular reabsorption, and tubular secretion.B. Glomerular Filtration

1. Urine formation begins when the fluid portion of the blood is filtered by the glomerulus and enters the glomerular capsule as glomerular filtrate.


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C. Filtration Pressure 1. The main force responsible for moving

substances by filtration through the glomerular capillary wall is the hydrostatic pressure of the blood inside.

2. Due to plasma proteins, osmotic pressure of the blood resists filtration, as does hydrostatic pressure inside the glomerular capsule.


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D. Filtration Rate 1. The factors that affect the filtration rate

are filtration pressure, glomerular plasma osmotic pressure, and hydrostatic pressure in the glomerular capsule.

2. When the afferent arteriole constricts in response to sympathetic stimulation, filtration pressure, and thus filtration rate, declines.


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3. When the efferent arteriole constricts, filtration pressure increases, increasing the rate of filtration.

4. When osmotic pressure of the glomerular plasma is high, filtration rate decreases.


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5. When hydrostatic pressure inside the glomerular capsule is high, filtration rate declines.

6. On the average, filtration rate is 125 milliliters per minute or 180 liters in 24 hours, most of which is reabsorbed further down the nephron.


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E. Regulation of Filtration Rate 1. Glomerular filtration rate is relatively

constant, although sympathetic impulses may decrease the rate of filtration.


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2. Another control over filtration rate is the renin-angiotensin system, which regulates sodium excretion.a. When the sodium chloride

concentration in the tubular fluid decreases, the macula densa senses these changes and causes the juxtaglomerular cells to secrete renin.


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b. Secretion of renin triggers a series of reactions leading to the production of angiotensin II, which acts as a vasoconstrictor; this may, in turn, affect filtration rate.


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c. Presence of angiotensin II also increases the secretion of aldosterone, which stimulates reabsorption of sodium.

d. The heart can also increase filtration rate when blood volume is high.


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F. Tubular Reabsorption1. Changes in the fluid composition from

the time glomerular filtrate is formed when urine arrives at the collecting duct are largely the result of tubular reabsorption of selected substances.

2. Most of the reabsorption occurs in the proximal convoluted tubule, where cells possess microvilli with carrier proteins.


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3. Carrier proteins have a limited transport capacity, so excessive amounts of a substance will be excreted into the urine.

4. Glucose and amino acids are reabsorbed by active transport, water by osmosis, and proteins by pinocytosis.


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G. Sodium and Water Reabsorption 1. Sodium ions are reabsorbed by active

transport, and negatively charged ions follow passively.

2. As sodium is reabsorbed, water follows by osmosis.


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H. Regulation of Urine Concentration and Volume

1. Most of the sodium ions are reabsorbed before the urine is excreted, and sodium is concentrated in the renal medulla by the countercurrent mechanism.

2. Normally the distal convoluted tubule and collecting duct are impermeable to water unless the hormone ADH is present.


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I. Urea and Uric Acid Excretion 1. Urea is a by-product of amino acid

metabolism; uric acid is a by-product of nucleic acid metabolism.

2. Urea is passively reabsorbed by diffusion but about 50% of urea is excreted in the urine.

3. Most uric acid is reabsorbed by active transport and a small amount is secreted into the renal tubule.


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J. Tubular Secretion1. Tubular secretion transports certain

substances from the plasma into the renal tubule.

2. Active transport mechanisms move excess hydrogen ions into the renal tubule along with various organic compounds.


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3. Potassium ions are secreted both actively and passively into the distal convoluted tubule and the collecting duct.


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K. Urine Composition1. Urine composition varies from time to

time and reflects the amounts of water and solutes that the kidneys eliminate to maintain homeostasis.

2. Urine is 95% water, and also contains urea, uric acid, a trace of amino acids, and electrolytes.


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Urine Elimination A. After forming in the nephrons, urine passes from the collecting ducts to the renal papillae, then to the minor and major calyces, and out the renal pelvis to the ureters, urinary bladder, and finally to the urethra, which conveys urine to the outside.


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Chapter 18Water, Electrolyte, and

Acid-Base Balance

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IntroductionA. To be in balance, the quantities of fluids and

electrolytes (molecules that release ions in water) leaving the body should be equal to the amounts taken in.B. Anything that alters the concentrations of electrolytes will also alter the concentration of water, and vice versa.


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Distribution of Body Fluids A. Fluids occur in compartments in the body, and

movement of water and electrolytes between compartments is regulated.

B. Fluid Compartments 1. The average adult female is 52% water

by weight, while a male is 63% water, the difference due to the female’s additional adipose tissue.


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2. The intracellular fluid compartment includes all the water and electrolytes within cells.

3. The extracellular fluid compartment includes all water and electrolytes outside of cells (interstitial fluid, plasma, and lymph).


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4. Transcellular fluid includes the cerebrospinal fluid of the central nervous system, fluids within the eyeball, synovial fluid of the joints, serous fluid within body cavities, and exocrine gland secretions.


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Water Balance A. Water balance exists when water intake equals

water output.B. Water Intake

1. The volume of water gained each day varies from one individual to the next.

2. About 60% of daily water is gained from drinking, another 30% comes from moist foods, and 10% from the water of metabolism.


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C. Regulation of Water Intake1. The thirst mechanism is the primary

regulator of water intake.2. The thirst mechanism derives from the

osmotic pressure of extracellular fluids and a thirst center in the hypothalamus.

3. Once water is taken in, the resulting distention of the stomach will inhibit

the thirst mechanism.


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D. Water Output1. Water is lost in urine, feces,

perspiration, evaporation from skin (insensible perspiration), and from the lungs during breathing.

2. The route of water loss depends on temperature, relative humidity, and physical exercise.


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E. Regulation of Water Output1. The distal convoluted tubules of the

nephrons and collecting ducts regulate water output.

2. Antidiuretic hormone from the posterior pituitary causes a reduction in the amount of water lost in the urine.

3. When drinking adequate water, the ADH mechanism is inhibited, and more water is expelled in urine.


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Electrolyte Balance A. An electrolyte balance exists when the quantities of electrolytes gained equals the amount lost.B. Electrolyte Intake

1. The electrolytes of greatest importance to cellular metabolism are sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, and hydrogen ions.

2. Electrolytes may be obtained from food or drink or produced as a by-product of metabolism.


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C. Regulation of Electrolyte Intake1. A person ordinarily obtains sufficient

electrolytes from foods eaten.2. A salt craving may indicate an

electrolyte deficiency.D. Electrolyte Output

1. Losses of electrolytes occur through sweating, in the feces, and in urine.


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E. Regulation of Electrolyte Output 1. The concentrations of sodium,

potassium, and calcium, are very important.

2. Sodium ions account for 90% of the positively charged ions in extracellular fluids; the action of aldosterone on the kidneys regulates sodium reabsorption.


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3. Aldosterone also regulates potassium ions; potassium ions are excreted when sodium ions are conserved.

4. Calcium concentration is regulated by parathyroid hormone, which increases the concentrations of calcium and phosphate ions in extracellular fluids and by calcitonin which does basically the reverse.


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5. Generally, the regulatory mechanisms that control positively charged ions (cations) secondarily control the concentrations of negatively charged ions (anions).


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Acid-Base Balance A. Electrolytes that ionize in water and release hydrogen ions are acids; those that combine with hydrogen ions are bases.B. Maintenance of homeostasis depends on the control of acids and bases in body fluids.


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C. Sources of Hydrogen Ions1. Most hydrogen ions originate as by-

products of metabolic processes, including: the aerobic and anaerobic respiration of glucose, incomplete oxidation of fatty acids, oxidation of amino acids containing sulfur, and the breakdown of phosphoproteins and nucleic acids.


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D. Strengths of Acids and Bases1. Acids that ionize more completely are

strong acids; those that ionize less completely are weak acids.

2. Bases release hydroxyl and other ions, which can combine with hydrogen ions, thereby lowering their concentration.


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E. Regulation of Hydrogen Ion Concentration 1. Acid-base buffer systems, the

respiratory center in the brain stem, and the kidneys regulate pH of body fluids.


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2. Acid-Base Buffer Systemsa. The chemical components of a

buffer system can combine with a strong acid and convert it to a weaker one.

b. The chemical buffer systems in body fluids include the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system.


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3. The Respiratory Center a. The respiratory center in the brain

stem helps to regulate hydrogen ion concentration by controlling the rate and depth of breathing.

b. During exercise, the carbon dioxide, and thus the carbonic acid, levels in the blood increase.

c. In response, the respiratory center increases the rate and depth of breathing, so the lungs excrete more carbon dioxide.


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4. The Kidneysa. Nephrons secrete excess hydrogen ions

in the urine. 5. Rates of Regulation

a. Chemical buffers are considered the body’s first line of defense against shifts in pH; physiological buffer systems (respiratory and renal mechanisms) function more slowly and constitute secondary defenses.


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Acid-Base Imbalances A. Chemical and physiological buffer systems usually keep body fluids within very narrow pH ranges but abnormal conditions may prevent this.

1. A pH below 7.35 produces acidosis while a pH above 7.45 is called alkalosis.


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B. Acidosis1. Two major types of acidosis are

respiratory and metabolic acidosis.a. Respiratory acidosis results from

an increase of carbonic acid caused by respiratory center injury, air passage obstructions, ordisease processes that decrease gas exchange.


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b. Metabolic acidosis is due to either an accumulation of acids or a loss of bases, and has many causes including kidney disease, vomiting, diarrhea, and diabetes mellitus.

c. Increasing respiratory rate or the amount of hydrogen ions released by the kidney can help compensate for acidosis.


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C. Alkalosis1. Alkalosis also has respiratory and

metabolic causes.a. Respiratory alkalosis results from

hyperventilation causing an excessive loss of carbon dioxide.

b. Metabolic alkalosis is caused by a great loss of hydrogen ions or

from a gain in bases perhaps from vomiting or use of drugs.


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Chapter 19Reproductive Systems

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Introduction A. Male and female reproductive systems are a series of glands and tubes that produce and nurture sex cells, and transport them to the site of fertilization.

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Organs of the Male Reproductive System A. The male sex organs are designed to transport sperm to eggs.B. Primary sex organs (gonads) produce sperm

and hormones; accessory sex organs have a supportive function.

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C. Testes 1. The testes are ovoid structures

suspended by a spermatic cord in the scrotum.

2. Structure of the Testesa. Seminiferous tubules are lined

with stratified epithelium that gives rise to sperm cells.

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3. Formation of Sperm Cells a. A sperm cell has a head

containing the haploid nucleus, a midpiece containing mitochondria, and a tail that is a flagellum.

b. At the tip of the head is the acrosome, a bag of digestive enzymes that helps to erode tissues surrounding the female egg cell.

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4. Spermatogenesis a. In the male embryo, the

spermatogenic cells are undifferentiated and are called spermatogonia; each contains 46 chromosomes.

b. During spermatogenesis, spermatogonia enlarge and become primary spermatocytes.

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c. Primary spermatocytes undergo division by meiosis and form haploid secondary spermatocytes with 23 chromosomes.

d. Secondary spermatocytes divide again to form spermatids, each of which matures into a sperm cell.

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D. Male Internal Accessory Organs 1. The accessory organs of the male

reproductive tract include the epididymis, vas deferentia, ejaculatory ducts, urethra, seminal vesicles, prostate gland, and bulbourethral glands.

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7. Semena. Semen is a combination of

sperm cells (120 million per milliliter) and the secretions of the seminal vesicles, prostate gland, and bulbourethral glands.

b. Sperm cells cannot fertilize an egg until they undergo capacitation within the female reproductive tract.

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E. Male External Reproductive Organs 1. The male external reproductive

structures are the scrotum, which houses the testes, and the penis.

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F. Erection, Orgasm, and Ejaculation 1. During sexual arousal, parasympathetic

impulses trigger increased blood flow into the erectile tissues of the penis, producing an erection.

2. The culmination of sexual stimulation is orgasm, which in the male

consists of emission (movement of sperm cells and accessory gland secretions into the urethra) and ejaculation (forcing semen to the outside).

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Hormonal Control of Male ReproductiveFunctions

A. Hormones secreted by the hypothalamus, the anterior pituitary, and the testes control male reproduction and development of

secondary sexual characteristics.

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B. Hypothalamic and Pituitary Hormones1. At the time of puberty, the

hypothalamus controls the many changes that lead to the development of a reproductively functional adult.

2. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which triggers the production of the gonadotropins luteinizing hormone (LH), and follicle-stimulating hormone (FSH) from the anterior pituitary.

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a. LH promotes the development of interstitial cells of the testes and they, in turn, secrete male hormones (testosterone).

b. FSH stimulates the supporting cells of the seminiferous tubules.

c. FSH and testosterone stimulate spermatogenesis.

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C. Male Sex Hormones 1. The male sex hormones are called

androgens, of which testosterone is the most abundant.

2. Testosterone is secreted in a fetus until birth, and then not again until puberty, after which it is continuously secreted.

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3. Actions of Testosterone a. Testosterone stimulates the

development of the male reproductive organs and causes the testes to descend.

b. Testosterone is also responsible for male secondary sexual characteristics (deep voice, body hair, thickening of the skin, and so forth).

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4. Regulation of Male Sex Hormones a. A negative feedback system

involving the hypothalamus regulates the quantity of testosterone.i. As the concentration of

blood testosterone increases, the hypothalamus becomes inhibited, and its stimulation of the anterior pituitary declines.

ii. As the amount of LH drops in response, the amount of testosterone is reduced.

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Organs of the Female Reproductive SystemA. The organs of the female reproductive system

are specialized to produce and maintain the eggs cells, to transport these cells to the site of fertilization, to provide a favorable environment for a developing fetus, to give birth, and to produce female sex hormones.

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B. The primary sexual organs (gonads) are the ovaries; the other parts of the system comprise the external and internal

accessory organs.

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C. Ovaries 1. The ovaries are solid, ovoid structures

located within the lateral pelvic cavity.2. Ovary Structure

a. The ovaries are subdivided into a medulla and an outer cortex.

b. The medulla is made up of connective tissue, blood vessels, lymphatic vessels, and nerves.

c. The cortex contains follicles and is covered by cuboidal epithelium.

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3. Primordial Follicles a. During prenatal development,

small groups of cells form millions of primordial follicles, each of which consists of a primary oocyte surrounded by follicular cells.

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b. Early in development, the primary oocytes begin to undergo meiosis, but the process halts and does not resume until puberty.

c. Only 400,000 oocytes remain at puberty, and only 400 to 500 will be released from the ovary during the reproductive life of the female.

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4. Oogenesis a. Beginning at puberty, some

oocytes are stimulated to continue meiosis.

b. When a primary oocyte undergoes meiosis, it gives rise to a large, haploid secondary oocyte and a polar body.

c. A second, unequal cytoplasmic division gives rise to an egg cell and another polar body.

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5. Follicle Maturation a. At puberty, FSH initiates follicle

maturation during which the follicle enlarges, follicular cells proliferate, and a fluid-filled cavity forms the secondary follicle.

b. The mature follicle contains the secondary oocyte and is surrounded by the zona pellucida, attached to the corona radiata.

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6. Ovulationa. A process called ovulation

releases the secondary oocyte from the surface of the ovary; the oocyte is surrounded by layers of follicular cells.

b. If the oocyte is not fertilized shortly after its release, it will degenerate.

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D. Female Internal Accessory Organs1. The female internal accessory

organs consist of a pair of uterine tubes, a uterus, and a vagina.

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2. Uterine Tubesa. The uterine tubes (oviducts)

are suspended by the broad ligament and lead to the uterus.

b. Near each ovary, the uterine tube expands to form an infundibulum with fimbrae on its margins.

c. The cells lining the tubes bear cilia, which beat in unison, drawing the egg cell into the uterine tube.

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3. Uterusa. The upper two-thirds of the

uterus, the body, has a dome-shaped top.

b. The lower one-third of the uterus is the cervix that extends into the vagina.

c. The uterine wall has three layers: an inner, glandular endometrium, a muscular wall or myometrium, and an outer perimetrium.

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4. Vagina a. The vagina is a fibromuscular

tube that extends from the uterus to the outside.

b. The vaginal orifice is partially covered by a membrane called the hymen.

c. The vaginal wall consists of three layers: the inner mucosal layer, a middle muscular layer, and an outer fibrous layer.

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6. Erection, Lubrication, Orgasm a. During periods of sexual

stimulation, the erectile tissues of the clitoris and vestibular bulbs become engorged with blood.

b. The vestibular glands secrete mucus into the vestibule and vagina.

c. During orgasm, the muscles of the perineum, uterine wall, and uterine tubes contract rhythmically.

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Hormonal Control of Female ReproductiveFunctions

A. Hormones secreted by the hypothalamus, the anterior pituitary, and the ovaries control female reproduction and development of secondary sexual characteristics.

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B. Female Sex Hormones1. At about 10 years of age, the

hypothalamus begins to secrete more GnRH, which in turn stimulates the anterior pituitary to produce LH and FSH.

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2. At puberty, the ovaries synthesize estrogens in response to FSH.a. Estrogens are responsible for

the female secondary sexual characteristics, such as breast development, increased adipose tissue deposition, and increased vascularization of the skin.

b. Ovaries also secrete progesterone, which triggers uterine changes during the menstrual cycle.

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C. Female Reproductive Cycle 1. Menarche is characterized by monthly

changes in the uterine lining that lead to menstrual flow as the endometrium is shed.

2. A menstrual cycle is started by FSH, which stimulates the maturation of a follicle in the ovary.

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3. Follicular cells surrounding the developing oocyte secrete estrogen, which is responsible for maintaining secondary sexual characteristics as well as the thickening of the uterine lining.

4. Ovulation is triggered by a mid-cycle surge in LH.

5. Following ovulation, follicular cells turn into a glandular corpus luteum that secretes increasing amounts of estrogen and progesterone.

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6. If pregnancy does not occur, the corpus luteum degenerates, hormone levels decline, and the uterine lining disintegrates and is shed.

7. During the cycle, estrogen and progesterone inhibit the increased release of FSH and LH; when estrogen and progesterone levels fall, the secretion of FSH and LH increases.

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D. Menopause1. Menstrual cycles continue throughout

middle age until menopause, when the cycles cease.

2. The cause of menopause is the aging of the ovaries when follicles no longer mature and estrogen levels decline.

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Mammary GlandsA. The mammary glands are accessory organs

of the female reproductive system that are specialized to produce and secrete milk after pregnancy.

B. The mammary glands are located within the breasts on the anterior thorax.

C. A nipple is located at the tip of each breast surrounded by an area of pigmented skin called the areola.

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D. A mammary gland is composed of irregularly shaped lobes containing glands and a

lactiferous duct leading to the nipple.E. Dense connective tissue and fat separate the

lobes.

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Chapter 20

Pregnancy, Growth, and Development

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Introduction A. Development, which includes an increase in size, is the continuous process by which an individual changes from one life phase to another.B. The life phases are the prenatal period, which

begins at fertilization and ends at birth, and the postnatal period, which begins at birth and ends at death.


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Pregnancy A. Pregnancy is the presence of developing offspring in the uterus, an event resulting from fertilization.


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B. Transport of Sex Cells1. Sperm cells must reach the upper one-

third of the uterine tubes for fertilization to occur.

2. Under the influence of estrogen during the first half of the menstrual cycle, uterine secretions are thin, allowing sperm cells to swim easily toward their destination.


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C. Fertilization 1. With the aid of the acrosomal enzyme,

the sperms cells erode away the corona radiata and zona pellucida surrounding the secondary oocyte, and one sperm cell penetrates the egg cell membrane.

2. When penetration occurs, changes in the egg cell membrane and zona pellucida

prevent the entry of additional sperm cells.


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3. Fusion of egg and sperm nuclei completes fertilization.

4. Fertilization results in a diploid zygote.


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Prenatal Period A. Early Embryonic Development

1. Cells undergo a period of mitosis called cleavage, when cells become smaller and smaller.

2. The dividing mass of cells (morula) moves down the uterine tube to the uterus, where a stage called the blastocyst implants in the lining of the uterus.


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3. The offspring is called an embryo during the first eight weeks of development, and a fetus after that time.

4. Some of the cells of the blastocyst become the placenta which also secretes hormones.


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B. Hormonal Changes during Pregnancy 1. The outer layer of cells (trophoblast) of

the blastocyst stage secrete the hormone human chorionic gonadotropin (hCG), which maintains the corpus luteum and thus also maintains the uterine lining and the pregnancy.

2. Levels of hCG remain high until the placenta can produce enough hormones on its own to maintain the pregnancy.


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3. The placenta also secretes placental lactogen for breast development and estrogens.

4. Other hormonal changes during pregnancy include increased secretions of aldosterone (promotes fluid retention) and parathyroid hormone (to maintain a high calcium level in the blood).


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C. Embryonic Stage 1. The embryonic stage lasts from the

second to the eighth week of development, during which time the placenta develops, and all the main internal organs and major external features appear.


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2. During the second week, the embryo is now called a gastrula and its inner cell mass transforms into the embryonic disc, and layers form within it.


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3. These layers become the three primary germ layers and give rise to all organ systems.a. Ectoderm gives rise to the

nervous system, portions of special sensory organs, the epidermis and epidermal derivatives, and the linings of the mouth and anal canal.


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b. Mesodermal cells form all types of muscle tissue, bone tissue, bone marrow, blood, blood and lymphatic vessels, internal reproductive organs, kidneys, and epithelial linings of the body cavities.

c. Endodermal cells produce the epithelial linings of the digestive tract, respiratory tract, urinary bladder, and urethra.


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4. As the embryo implants, the trophoblast sends out extensions that develop into chorionic villi.

5. By the fourth week, the heart is beating, the head and jaws appear, and limb buds form.

6. As the chorionic villi develop, exchanges of gases and nutrients occur through the placental membrane.


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7. By the eighth week, the trophoblast is now the chorion, a portion of which develops into the placenta.

8. During this time, another membrane, the amnion, is developing around the embryo and will hold cushioning amniotic fluid.

9. An umbilical cord containing two umbilical arteries and one vein forms.


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10. Two other membranes form in association with the embryo.a. The yolk sac, formed during the

second week, is the first site of blood cell formation and also gives rise to the stem cells of the immune system.

b. The allantois forms during the third week and joins the connecting stalk of the embryo; it forms blood cells and gives rise to the umbilical arteries and vein.


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D. Fetal Stage1. The fetal stage begins at the end of the

eighth week of development and lasts until birth.

2. During this period, growth is rapid and body proportions change considerably.

3. Existing structures grow and mature and only a few new parts appear.


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4. The body enlarges, the limbs grow to the relative size they will maintain throughout development, and the bones ossify.

5. During the fifth month, the mother may feel the fetus move, fine hair appears, and dead epithelial cells and sebum cover the skin.


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6. In the final trimester, brain cells form rapidly and organs grow and mature as the fetus greatly increases in size.


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E. Fetal Blood and Circulation 1. Substances diffuse through the placental

membrane and umbilical vessels carry them to and from the fetus; fetal blood has a greater oxygen-carrying capacity than maternal blood.


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2. The umbilical vein, transporting blood rich in oxygen and nutrients, enters the body and travels to the liver where half of the blood is carried into the liver and half bypasses the liver through the ductus venosus on its way to the inferior vena cava.


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3. A foramen ovale conveys a large portion of the blood entering the right atrium from the inferior vena cava, through the atrial septum, and into the left atrium, thus bypassing the lungs.

4. A second lung bypass is the ductus arteriosus, which conducts some blood from the pulmonary trunk directly to the aorta.


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5. Umbilical arteries carry blood from the internal iliac arteries to the placenta, where it can exchange wastes and again pick up nutrients and oxygen.


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F. Birth Process 1. Pregnancy continues for thirty eight

weeks and terminates in the birth process.

2. As the placenta ages, less progesterone is produced, which normally inhibits uterine contractions.


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3. A decreasing progesterone concentration may stimulate the synthesis of prostaglandins, which may initiate labor.

4. Stretching uterine tissues stimulates the release of oxytocin from the posterior pituitary, which stimulates uterine contractions.


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5. As the fetal head stretches the cervix, a positive feedback mechanism results in stronger and stronger uterine contractions and a greater release of oxytocin.

6. Positive feedback causes abdominal muscles to contract with greater force and the fetus is forced through the birth canal to the outside.


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7. Following birth, the placenta is expelled by the continued uterine contractions (afterbirth).


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Postnatal Period A. Following birth, mother and newborn experience physiological and structural changes.


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B. Milk Production and Secretion 1. Following childbirth, the action of

prolactin is no longer inhibited and the mammary glands are stimulated to produce large quantities of milk.

2. First milk, or colostrum, is a watery fluid rich in proteins and antibodies.


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3. Milk does not readily flow into the ductile system, but must be triggered to do so by a reflex involving the infant suckling at the breast, which triggers release of oxytocin from the posterior pituitary.

4. Human milk is the best possible food for human babies.


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C. Neonatal Period 1. The neonatal period begins abruptly at

birth and lasts for four weeks.2. The first breath must be forceful to

inflate the lungs for the first time.a. Surfactant in a full-term newborn

reduces surface tension.


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3. At birth, the newborn must live off its fat stores for two to three days until the mother’s milk comes in.

4. The newborn is susceptible to dehydration since the homeostatic mechanisms involving water conservation in the kidneys are not yet fully functioning.


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5. A number of changes occur in the newborn’s circulation: umbilical vessels constrict, the ductus venosus constricts, the foramen ovale closes, and the ductus arteriosis constricts.a. Most of these circulatory changes

are gradual and occur during the first fifteen minutes after birth, although it may take up to a year for the foramen ovale to close.


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GeneticsA. Inherited traits are determined by DNA sequences that comprise genes.B. Mutations occur when the gene’s DNA sequence changes.

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C. Chromosomes and Genes Come in Pairs1. Charts called karyotypes display the

23 chromosome pairs of a human somatic cell.

2. Autosomes are pairs 1 through 22, and do not carry the genes that determine sex.

3. The other two chromosomes, the X and the Y, determine sex and are called sex chromosomes.

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D. Modes of Inheritance1. Patterns of inheritance through

families are called modes of inheritance.

2. Three major modes of inheritance are autosomal recessive, autosomal dominant, and X-linked recessive.

E. Most traits are influenced to some extent by environmental factors, such as nutrition, physical activity, and exposure to toxins.

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