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Early Embryonic Development and Gastrulation

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200 Questions

What is the primary factor that influences the differentiation of cells in the inner cell mass of an early blastocyst?

Induction through cell-cell contact

Which layer of cells is continuous with the yolk sac during gastrulation?

One layer of the embryonic disk

Where do cells migrate in through during gastrulation?

A slit in the amnion side of the embryonic disk

What is the primary function of the umbilical cord during embryonic development?

To provide nutrients to the embryo

During which week of development does the embryo begin to form the spinal cord and brain?

Third week

What is the term for the process by which the inner cell mass grows and splits, forming two fluid-filled sacs?

Implantation

What is the term for the cells that remain on the surface of the embryonic disk during gastrulation?

Ectoderm

When does the heart start to beat during embryonic development?

Beginning of the fourth week

What is the primary function of the antibodies that are selectively transported across the placenta?

To defend the newborn infant against disease

What is the primary function of the umbilical arteries?

To carry deoxygenated blood from the fetus to the placenta

What is the primary function of the urinary system?

To produce and eliminate urine

What is the primary role of the placenta in the fetal development?

To facilitate exchange of nutrients and wastes between the fetus and mother

What substances can pass through the placenta?

Disease-causing organisms and harmful chemicals

What is the composition of urine?

A watery fluid that contains a variety of substances removed from the blood

What are the two major roles of the urinary system in most animals?

To excrete cellular wastes and help maintain homeostasis

What is the primary function of the umbilical vein?

To carry oxygenated blood from the placenta to the fetus

What is the direct consequence of a person becoming dehydrated due to water unavailability or prolonged illness?

Blood osmolarity increases and blood volume decreases

What is the primary function of the renal corpuscle in the nephron?

To pressure-filter the blood and collect the resulting fluid

How often does the entire blood volume pass through the kidneys daily?

60 times

What is the term for the resulting fluid collected from the pressure-filtration process in the renal corpuscle?

Filtrate

What is the consequence of the kidneys being unable to conserve enough water in a dehydrated person?

Low blood pressure and confusion

What is the approximate number of nephrons found in each kidney?

1 million

What is the term for the exceptionally porous capillaries in the glomerulus that allow water and small molecules to ooze out?

Porous capillaries

What is the final product of the filtration process in the nephron?

Urine

What is the primary function of reabsorption in the nephron?

To return important substances to the blood

What is the primary location of reabsorption in the nephron?

Proximal tubule

Which ions are critical for nerve and muscle function?

Na+, Cl-, K+, and Ca2+

What is the function of the bicarbonate ion in the body?

Maintaining constant pH required for metabolic reactions

What is the mechanism by which reabsorbed molecules move into the peritubular capillaries?

Active transport and diffusion

What is the primary function of the peritubular capillaries in the kidney?

To conduct blood into the renal vein

Which of the following factors does not facilitate glomerular filtration?

The presence of interstitial fluid around the nephron

Which tubular segment is under hormonal control for reabsorption?

Distal tubule

Approximately what percentage of the blood's fluid is forced out through the glomerular capillary walls during filtration?

20%

What percentage of solutes in the glomerular filtrate is made up of urea?

40%

What is the primary function of the glomerular capillaries in the kidney?

To filter small molecules and ions from the blood

What is the composition of the glomerular filtrate?

Plasma minus its large proteins

What is the result of the high pressure within the glomerular capillaries?

Forcing of fluid and small molecules out through the glomerular capillary walls

What is the primary function of the arterioles in the kidney?

To regulate blood pressure in the glomerular capillaries

Where do the dissolved substances move during urine formation?

Between the parts of the nephron and the interstitial fluid

What is the role of the glomerular capillaries in the process of urine formation?

To filter small molecules and ions from the blood

The sperm may live for up to 7 days inside the female reproductive tract.

False

The zona pellucida is a barrier between the sperm and the egg located outside the corona radiata.

False

Fertilization occurs in the uterine tubes.

True

The unfertilized egg remains viable for a week or so.

False

The acrosome releases enzymes that strengthen the corona radiata and the zona pellucida.

False

The corona radiata is a barrier between the sperm and the egg formed by the sperm.

False

Intercourse occurs only during certain seasons of the year.

False

The fertilized egg is haploid.

False

The yolk sac is directly connected to the mother's circulatory system.

False

The placenta allows the mother's and embryo's blood to mix freely.

False

The chorion forms the outer layer of the blastocyst.

True

The umbilical cord connects the embryo's circulatory system to the mother's circulatory system.

True

Large proteins and cells can readily pass through the walls of the chorionic villi and capillaries.

False

Carbon dioxide and other wastes diffuse from the mother to the embryo.

False

The embryo obtains nutrients directly from the endometrium of the uterus during the first week of development.

True

Oxygen diffuses from the embryo to the mother.

False

The peritubular capillaries conduct the blood into the renal artery.

False

The glomerular capillaries are less porous than most other capillaries.

False

The arterioles that collect blood from the capillaries are wider than the arterioles that supply them.

False

Urinary systems are responsible for producing and eliminating feces.

False

About 50% of the blood's fluid is forced out through the glomerular capillary walls during filtration.

False

The placenta provides complete protection to the fetus from disease-causing organisms and harmful chemicals.

False

The umbilical arteries carry oxygenated blood from the placenta to the fetus.

False

Reabsorption occurs in the glomerular capillaries.

False

The nephron is the functional unit of the urinary system.

True

The primary function of the urinary system is to regulate body temperature.

False

The interstitial fluid exchanges substances with the glomerular capillaries.

False

Antibodies are selectively transported from the fetus to the mother across the placenta during pregnancy.

False

Urine is formed through three processes: Filtration, Reabsorption, and Excretion.

False

The placenta allows direct mixing of fetal and maternal blood supplies.

False

Urine contains only waste products from proteins and ions.

False

The urinary system plays only one major role in most animals, which is to excrete cellular wastes.

False

Most reabsorption takes place in the distal tubule.

False

The bicarbonate ion is crucial for maintaining constant blood pressure.

False

Nearly all the water and ions are reabsorbed into the bloodstream during reabsorption.

True

The glomerular filtrate contains large proteins and blood cells.

False

Reabsorption in the proximal tubule is under hormonal control.

False

Urea makes up more than 50% of the solutes in the glomerular filtrate.

False

The peritubular capillaries return reabsorbed molecules to the kidneys.

False

Reabsorption occurs only in the proximal tubule and the distal tubule.

False

What is the primary function of the antibodies that are selectively transported across the placenta from the mother to the fetus?

To defend the newborn infant against disease

What is the primary function of the placenta in terms of waste and nutrient exchange?

To allow exchange of wastes and nutrients between fetal capillaries and maternal blood pools

What are the two major roles of the urinary system in most animals?

To excrete cellular wastes and to help maintain homeostasis

What substances are present in urine, and what is its primary function?

Urine contains waste products from proteins, ions, and other water-soluble nutrients, and its primary function is to excrete these substances from the body

What is the role of the umbilical arteries and vein in the exchange of substances between the fetus and mother?

The umbilical arteries carry deoxygenated blood from the fetus to the placenta, and the umbilical vein carries oxygenated blood back to the fetus

What is the limitation of the placenta in terms of protection against disease-causing organisms and harmful chemicals?

The placenta does not provide complete protection against disease-causing organisms and harmful chemicals

What is the primary function of the umbilical cord during embryonic development?

To connect the embryo's circulatory system to the mother's circulatory system

What is the primary function of the glomerular capillaries in the process of urine formation?

To filter waste substances from the blood into the glomerular filtrate

What is the purpose of the enzymes released by the sperm during fertilization?

To weaken the corona radiata and the zona pellucida, allowing the sperm to penetrate the egg.

What is the significance of the timing of copulation in relation to ovulation?

If copulation occurs within a day or two of ovulation, the sperm may meet an egg in the uterine tube.

What is the role of the corona radiata in fertilization?

It forms a barrier between the sperm and the egg, which the sperm must penetrate in order to fertilize the egg.

How long can an unfertilized egg remain viable?

About a day or so.

What is the purpose of the zona pellucida in fertilization?

It acts as a barrier between the sperm and the egg, which the sperm must penetrate in order to fertilize the egg.

What is the significance of the uterine tubes in fertilization?

They provide the site where sperm and egg meet, allowing fertilization to occur.

What is the result of the union of sperm and egg during fertilization?

A diploid zygote is formed.

How long can sperm survive inside the female reproductive tract?

Up to 2 to 4 days.

What is the consequence of a person becoming severely dehydrated, leading to loss of water in brain cells?

coma and death

What is the role of the renal corpuscle in the nephron?

to pressure-filter the blood and collect the resulting fluid

What is the function of the glomerular capsule in the renal corpuscle?

to capture the blood filtrate

What is the significance of the entire blood volume passing through the kidneys about 60 times daily?

to allow the kidneys to fine-tune the blood composition

What is the consequence of the kidneys being unable to conserve enough water in a dehydrated person?

low blood pressure, dizziness, and confusion

What is the function of the renal tubule in the nephron?

to conduct the filtrate as it is converted to urine

What is the unique feature of the capillaries in the glomerulus?

they are exceptionally porous

What is the significance of the kidneys containing roughly 1 million microscopic urine-forming units called nephrons?

it allows for efficient filtration and formation of urine

What is the primary function of the urinary system, and how does it achieve this function?

The primary function of the urinary system is to excrete cellular wastes, primarily nitrogenous wastes such as ammonia, urea, and uric acid. This is achieved through the filtration of small nutrient and waste molecules and ions from the blood, and then returning essential ions and nutrients to the blood while collecting and excreting excess substances and cellular wastes.

Describe the structure of the human kidney, and explain how it enables the production of concentrated urine.

The human kidney consists of the outermost renal cortex, the renal medulla, and the renal pelvis. The renal medulla allows the kidney to produce concentrated urine by conserving water, while the renal pelvis collects and conducts urine into the ureter.

What is the role of the ureter in the urinary system, and how does it facilitate the movement of urine?

The ureter is a narrow, muscular tube that contracts rhythmically to propel the urine from the kidney to the bladder, facilitating the movement of urine through the urinary system.

Explain how the kidneys help maintain homeostasis in the body.

The kidneys help maintain homeostasis by filtering small nutrient and waste molecules and ions from the blood, and then returning essential ions and nutrients to the blood while collecting and excreting excess substances and cellular wastes.

What is the function of the bladder in the urinary system, and how does it store and excrete urine?

The bladder is a hollow, muscular chamber that collects and stores urine, and then excretes it through the urethra.

Describe the relationship between the kidneys and the blood supply, and explain how it enables the filtration of waste products.

The kidneys are connected to the blood supply through the renal cortex, which allows for the filtration of small nutrient and waste molecules and ions from the blood.

Explain how the urinary system regulates the levels of essential ions and nutrients in the body.

The urinary system regulates the levels of essential ions and nutrients in the body by filtering small nutrient and waste molecules and ions from the blood, and then returning essential ions and nutrients to the blood while collecting and excreting excess substances and cellular wastes.

What is the significance of the urinary system in maintaining overall health, and what are the consequences of its dysfunction?

The urinary system is crucial for maintaining overall health by excreting cellular wastes and regulating the levels of essential ions and nutrients in the body. Dysfunction of the urinary system can lead to the accumulation of waste products, which can have serious consequences for overall health.

What is the primary purpose of the distal tubule in maintaining homeostasis?

Fine-tuning blood composition by regulating the reabsorption of water and ions

What is the main function of secretion in the renal tubule?

Actively transporting substances into the renal tubule for excretion

What is the significance of the distal tubule in regulating the concentration of urine?

Precise regulation of water reabsorption to maintain the blood's osmolarity

What is the primary location of secretion in the nephron?

Proximal tubule, with some also occurring in the distal tubule

What is the role of circulating hormones in secretion and reabsorption?

Regulation of secretion and reabsorption to maintain homeostasis

What is the significance of the distal tubule in maintaining the body's osmolarity?

Regulation of water reabsorption to maintain blood's osmolarity within narrow limits

What is the relationship between the distal tubule and the collecting duct in terms of urine concentration?

Concentration of urine occurs in both the distal tubule and collecting duct

What is the significance of the proximal tubule in terms of water reabsorption?

Reabsorption of about 80% of the filtrate's water

During fertilization, the union of sperm and ______ produces a diploid zygote.

egg

Men produce ______ more or less continuously.

sperm

The ______ radiata is a barrier between the sperm and the egg.

corona

A second barrier, the jelly-like ______ pellucida, lies between the corona radiata and the egg.

zona

Each sperm releases enzymes from its ______.

acrosome

The ______ is the primary location of fertilization in the female reproductive tract.

uterine tube

The sperm may live for 2 to (rarely) 4 days inside the ______ reproductive tract.

female

If copulation occurs within a day or two of ______, the sperm may meet an egg in one of the uterine tubes.

ovulation

Certain types of ______, even though they are quite large, are selectively transported across the placenta from mother to embryo.

antibodies

The placenta allows exchange of ______ and nutrients between fetal capillaries and maternal blood pools.

wastes

The umbilical ______ carry deoxygenated blood from the fetus to the placenta.

arteries

Urinary systems are organ systems that produce and eliminate ______.

urine

Urine contains waste products from ______, various ions and other water-soluble nutrients in excess of the body’s needs.

proteins

By producing and eliminating ______, urinary systems play two major roles in most animals.

urine

The primary function of the urinary system is to ______ and eliminate waste products.

produce

The placenta allows exchange of ______ and nutrients between fetal capillaries and maternal blood pools, while keeping the fetal and maternal blood supplies ______.

wastes separate

The arteriole branches to form the ______ of the glomerulus.

capillaries

These capillaries empty into an outgoing ______.

arteriole

The peritubular capillaries conduct the blood into a ______ that joins the renal vein.

venule

Urine is formed in the ______ of the kidneys by three processes.

nephrons

Filtration removes small ______ and ions from the blood.

molecules

The glomerular capillaries are far more ______ than most other capillaries.

porous

About 20% of the blood's ______ is forced out through the glomerular capillary walls.

fluid

Dissolved substances move between the parts of the nephron and the ______ fluid that surrounds these structures.

interstitial

The average adult ______ can hold about a pint (500 milliliters) of urine.

bladder

As accumulating urine expands the ______ wall, the pressure eventually activates stretch receptors.

bladder

Urine is retained in the ______ by two circular sphincter muscles.

bladder

The ______ sphincter, located at the junction of the bladder and the urethra, opens automatically during these contractions.

internal

Urine exits the body through the ______, a single narrow tube about 1.5 inches long in women and about 8 inches long in men.

urethra

Water balance is essential for ______ An important function of the kidney is osmoregulation.

homeostasis

Osmoregulation is the process of maintaining ______—the concentration of ions and other solutes in the blood plasma—within very strict limits.

blood osmolarity

If a person consumes excess water faster than the kidneys can excrete it, the surplus water in the blood will move by ______ into the interstitial fluid and then into cells, causing them to swell.

osmosis

The distal tubule fine-tunes blood ______ by regulating the reabsorption of water and ions.

composition

The fluid that has travelled through the nephron becomes ______ as it leaves the distal tubule.

urine

Secretion actively transports substances into the ______ tubule for excretion.

renal

Secretion occurs primarily in the ______ tubule, but some also occurs in the distal tubule.

proximal

The concentration of urine occurs in the ______ tubule and collecting duct.

distal

When the filtrate enters the distal tubule, about 80% of its ______ has already been reabsorbed.

water

From this point on, additional reabsorption of ______ is precisely regulated to maintain the blood's osmolarity.

water

Secretion by the distal tubule is regulated by ______ hormones to maintain homeostasis.

circulating

Match the following structures with their functions during fertilization:

Corona radiata = Form a barrier between the sperm and the egg Zona pellucida = Release enzymes from the acrosome Acrosome = Surround the egg and release enzymes Sperm = Release the egg from the ovary

Match the following stages of fertilization with their descriptions:

When it leaves the ovary = The egg is surrounded by the corona radiata In the uterine tube = The sperm meet the egg and release enzymes In the cervix = The sperm move through the uterus During intercourse = The sperm are released into the vagina

Match the following components with their durations during fertilization:

Unfertilized egg = A day or so Sperm = 2 to 4 days Corona radiata = Until the sperm penetrate Zona pellucida = Until the sperm fertilize the egg

Match the following terms with their descriptions related to fertilization:

Fertilization = The union of sperm and egg Follicle cells = Accessory cells surrounding the egg Diploid zygote = The resulting fluid from fertilization Ovulation = The process of sperm moving through the uterus

Match the following structures with their roles during embryonic development:

Placenta = Obtains nutrients from the endometrium Chorion = Forms the outer layer of the blastocyst Uterus = Provides a site for implantation Endometrium = Forms the outer layer of the blastocyst

Match the following events with their timings during fertilization and embryonic development:

Ovulation = Once a month Sperm release = During intercourse Fertilization = In the uterine tube Implantation = In the first week of development

Match the following terms with their descriptions related to fertilization and embryonic development:

Diploid = Having a single set of chromosomes Zygote = The resulting cell from fertilization Blastocyst = The resulting fluid from fertilization Implantation = The process of sperm fertilizing the egg

Match the following structures with their roles during fertilization and embryonic development:

Uterine tubes = Site of fertilization Uterus = Site of implantation Ovary = Site of fertilization Endometrium = Site of fertilization

Match the following structures with their functions during embryonic development:

Embryonic disk = Forms mesoderm, endoderm, and the allantois Amnion = Provides fluid-filled sacs for the embryo Yolk sac = Forms the embryo proper Blastocyst = Divides into two layers of cells

Match the following stages with their corresponding events during embryonic development:

Second week = Gastrulation begins Third week = The heart starts to beat Fourth week = The embryo begins to form the spinal cord and brain Fifth week = Organogenesis begins

Match the following structures with their relationships during embryonic development:

Yolk stalk = Fuses with the body stalk to form the umbilical cord Amnion = Is continuous with the embryonic disk Body stalk = Forms the yolk sac Embryonic disk = Is continuous with the blastocyst

Match the following events with their corresponding processes during embryonic development:

Formation of two fluid-filled sacs = Induction Migration of cells through the slit = Gastrulation Formation of the spinal cord and brain = Organogenesis Differentiation of cells in the inner cell mass = Implantation

Match the following structures with their locations during embryonic development:

Yolk sac = Outside the embryonic disk Amnion = Around the embryo in the uterine cavity Embryonic disk = Inside the blastocyst Blastocyst fluid = Outside the inner cell mass

Match the following stages with their corresponding structures during embryonic development:

Second week = Embryonic disk Third week = Blastocyst Fourth week = Amnion Fifth week = Yolk sac

Match the following parts of the nephron with their functions:

Renal corpuscle = Pressure-filter the blood and collect the resulting fluid Glomerulus = Allow water and small molecules dissolved in the blood plasma to ooze out Renal tubule = Conduct the filtrate as it is converted to urine Glomerular capsule = Capture the blood filtrate

Match the following events with their corresponding weeks during embryonic development:

Gastrulation begins = Second week Organogenesis begins = Third week The heart starts to beat = Fourth week The embryo forms the spinal cord and brain = Fifth week

Match the following structures with their functions during embryonic development:

Umbilical cord = Provides nutrients to the embryo Yolk sac = Forms the extraembryonic membranes Amnion = Provides a fluid-filled sac for the embryo Blastocyst = Divides into the inner cell mass and outer cell layer

Match the following effects of dehydration with their consequences:

Increased blood osmolarity = Dehydration can cause low blood pressure Decreased blood volume = Dizziness and confusion Loss of water in brain cells = Coma and death Unavailability of water = Illness causes prolonged diarrhea and vomiting

Match the following statements with their corresponding functions in the placenta:

Selective transport of antibodies = Defending the newborn infant against disease Exchange of wastes and nutrients = Between fetal capillaries and maternal blood pools Isolation of the fetus from many assaults = Complete protection against disease-causing organisms Carrying deoxygenated blood from the fetus = Umbilical arteries

Match the following components of the urinary system with their functions:

Nephrons = Filter blood and produce urine Kidneys = Fine-tune the composition of the entire blood volume Renal cortex = Pack together nephrons Renal medulla = Extend thinly into each nephron

Match the following components with their corresponding roles in the urinary system:

Urine = Watery fluid that contains waste products Urinary systems = Producing and eliminating urine Umbilical vein = Carrying oxygenated blood back to the fetus Umbilical arteries = Carrying deoxygenated blood from the fetus to the placenta

Match the following processes with their locations in the nephron:

Filtration = Renal corpuscle Reabsorption = Proximal tubule Urine formation = Distal tubule and collecting duct Concentration of urine = Collecting duct

Match the following substances with their corresponding sources in the urine:

Waste products from proteins = Removed from the blood Ions = Excess of the body’s needs Foreign substances = Drugs or their metabolic by-products Nutrients = Produced by the urinary system

Match the following blood components with their effects on the body:

Water = Maintains blood pressure and volume Ions = Critical for nerve and muscle function Small molecules = Ooze out of the glomerulus during filtration Urea = Makes up more than 50% of the solutes in the glomerular filtrate

Match the following components with their corresponding functions in the fetal-maternal circulation:

Umbilical arteries = Carrying deoxygenated blood from the fetus to the placenta Umbilical vein = Carrying oxygenated blood back to the fetus Placenta = Isolating the fetus from many assaults Maternal blood pools = Exchanging wastes and nutrients with fetal capillaries

Match the following conditions with their effects on the body:

Dehydration = Increases blood osmolarity Low blood pressure = Causes dizziness and confusion Coma = Results from loss of water in brain cells Death = Extreme consequence of dehydration

Match the following components of the kidney with their structures:

Nephron = Microscopic urine-forming unit Renal corpuscle = Consists of the glomerulus and glomerular capsule Renal tubule = Conducts the filtrate as it is converted to urine Kidney = Contains roughly 1 million nephrons

Match the following statements with their corresponding roles in the human body:

Maintaining homeostasis = Urinary system Producing and eliminating urine = Urinary system Defending the newborn infant against disease = Antibodies Isolating the fetus from many assaults = Placenta

Match the following functions with their importance in the body:

Osmoregulation = Maintains the concentration of ions and other solutes in the blood plasma Filtration = Removes small molecules and ions from the blood Urine formation = Allows the body to eliminate waste Reabsorption = Regulates the amount of water and ions in the body

Match the following components with their corresponding functions in the human body:

Antibodies = Defending the newborn infant against disease Placenta = Isolating the fetus from many assaults Umbilical cord = Connecting the embryo's circulatory system to the mother's circulatory system Urinary system = Maintaining homeostasis

Match the following statements with their corresponding components in the urinary system:

Produces and eliminates urine = Urinary system Contains waste products from proteins = Urine Carries oxygenated blood back to the fetus = Umbilical vein Isolates the fetus from many assaults = Placenta

Match the following components with their corresponding functions in the human body:

Umbilical cord = Connecting the embryo's circulatory system to the mother's circulatory system Urinary system = Maintaining homeostasis Placenta = Isolating the fetus from many assaults Antibodies = Defending the newborn infant against disease

Match the following processes with their locations in the nephron:

Reabsorption of water and ions = Distal tubule Secretion of waste and excess ions = Proximal tubule Filtration = Glomerular capillaries Concentration of urine = Collecting duct

Match the following substances with their primary routes of excretion:

Excess K+ = Urinary system Oxygen = Respiratory system Ammonia = Kidneys Cocaine = Urinary system

Match the following with their functions in the nephron:

Distal tubule = Regulation of blood composition Proximal tubule = Reabsorption of nutrients Collecting duct = Concentration of urine Glomerular capillaries = Filtration of blood

Match the following with their roles in maintaining homeostasis:

Distal tubule = Regulation of blood osmolarity Proximal tubule = Reabsorption of ions Renal corpuscle = Filtration of blood Hormones = Regulation of secretion and reabsorption

Match the following with their locations in the kidney:

Renal cortex = Interstitial fluid Medulla = Collecting duct Nephron loop = Reabsorption of water Renal artery = Supply of blood to the kidney

Match the following with their effects on the body:

Dehydration = Decreased blood volume Excess K+ = Abnormal heart rhythm Hormonal imbalance = Disrupted homeostasis Uremia = Toxicity of blood

Match the following with their relationships in the nephron:

Distal tubule = Regulation of proximal tubule Proximal tubule = Reabsorption of water from distal tubule Hormones = Regulation of distal tubule Gloomerular capillaries = Supply of blood to proximal tubule

Match the following with their functions in the urinary system:

Ureter = Transportation of urine to the bladder Urinary bladder = Storage of urine Urethra = Excretion of urine Kidneys = Regulation of blood composition

Study Notes

Fertilization and Implantation

  • Fertilization is the union of sperm and egg, producing a diploid zygote.
  • During fertilization, the sperm and egg nuclei unite.
  • Sperm move through the cervix, into the uterus, and finally enter the uterine tubes.
  • Sperm can live for 2 to 4 days inside the female reproductive tract, and an unfertilized egg remains viable for a day or so.
  • The egg is surrounded by accessory follicle cells, which form a barrier between the sperm and the egg.
  • The zona pellucida, a jelly-like substance, lies between the corona radiata and the egg.

Role of the Placenta

  • The placenta exchanges materials between the mother and embryo.
  • During the first few days after implantation, the embryo obtains nutrients directly from the endometrium of the uterus.
  • After a week, the placenta develops from interlocking structures produced by the embryo and the endometrium.
  • The placenta allows the exchange of wastes and nutrients between fetal capillaries and maternal blood pools, while keeping the fetal and maternal blood supplies separate.
  • The umbilical arteries carry deoxygenated blood from the fetus to the placenta, and the umbilical vein carries oxygenated blood back to the fetus.

Human Urinary System

  • Urinary systems are organ systems that produce and eliminate urine.
  • Urine is a watery fluid that contains a variety of substances removed from the blood or interstitial fluid.
  • Urinary systems play two major roles: excreting cellular wastes and helping to maintain homeostasis.

Nephrons and Urine Formation

  • Nephrons are microscopic urine-forming units in the kidneys.
  • Each nephron has two major parts: the renal corpuscle and the renal tubule.
  • The renal corpuscle pressure-filters the blood and collects the resulting fluid, called filtrate.
  • The renal corpuscle consists of two parts: the glomerulus and the glomerular capsule.
  • The glomerulus is a knot of porous capillaries that allow water and small molecules to ooze out as blood flows through them.
  • The filtrate then enters the renal tubule, which conducts the filtrate as it is converted to urine.
  • Urine is produced in the nephrons of the kidneys by three processes: filtration, reabsorption, and secretion.

Reabsorption and Secretion

  • Reabsorption returns important substances to the blood.
  • Most reabsorption takes place in the proximal tubule, but also occurs in the nephron loop and the distal tubule.
  • In the proximal tubule, reabsorption is generally not under hormonal control, but in the distal tubule, it is under the control of hormones that help maintain homeostasis.

Kidney Structure and Function

  • The entire blood volume passes through the kidneys about 60 times daily, allowing them to fine-tune its composition.
  • Each kidney contains roughly 1 million microscopic nephrons.
  • Nephrons are packed together in the renal cortex, with a thin extension of each nephron extending into the renal medulla.
  • The renal medulla allows the kidney to produce concentrated urine, thus conserving water.
  • The renal pelvis collects urine and conducts it into the ureter.### Urinary System
  • The urinary system produces and eliminates urine, which contains waste products, excess ions, and water-soluble nutrients.
  • The system plays two major roles: excreting cellular wastes and maintaining homeostasis.

Nephrons

  • Each kidney contains approximately 1 million nephrons, which are microscopic urine-forming units.
  • Nephrons are packed together in the renal cortex, with a thin extension into the renal medulla.
  • Each nephron has two major parts: the renal corpuscle and the renal tubule.

Renal Corpuscle

  • The renal corpuscle is responsible for pressure-filtering the blood and collecting the resulting fluid, called filtrate.
  • It consists of two parts: the glomerulus and the glomerular capsule.
  • The glomerulus is a knot of exceptionally porous capillaries that allow water and small molecules to ooze out as blood flows through them.
  • The glomerular capsule captures the blood filtrate.

Renal Tubule

  • The renal tubule conducts the filtrate as it is converted to urine.
  • The tubule has three main parts: the proximal tubule, the nephron loop, and the distal tubule.

Urine Formation

  • Urine formation occurs through three processes: filtration, reabsorption, and secretion.
  • Filtration occurs in the glomerulus, where small molecules and ions are removed from the blood.
  • Reabsorption occurs in the proximal tubule, where essential substances are returned to the blood.
  • Secretion occurs in the proximal tubule and distal tubule, where excess substances are removed from the blood.

Distal Tubule

  • The distal tubule fine-tunes blood composition by regulating the reabsorption of water and ions to maintain homeostasis.
  • The fluid that has travelled through the nephron becomes urine as it leaves the distal tubule.

Secretion

  • Secretion actively transports substances into the renal tubule for excretion.
  • Secreted substances include excess K+ and H+, small quantities of ammonia, and certain medicinal and recreational drugs.
  • Secretion occurs primarily in the proximal tubule, but some also occurs in the distal tubule.

Concentration of Urine

  • The concentration of urine occurs in the distal tubule and collecting duct.
  • When the filtrate enters the distal tubule, about 80% of its water has already been reabsorbed.
  • Additional reabsorption of water is precisely regulated to maintain the blood's osmolarity within narrow limits.

Fertilization

  • Fertilization is the union of sperm and egg, producing a diploid zygote.
  • Sperm may live for 2 to 4 days inside the female reproductive tract, and an unfertilized egg remains viable for a day or so.
  • During fertilization, the sperm releases enzymes to weaken the corona radiata and zona pellucida, allowing it to penetrate the egg.

Implantation and Placenta

  • The placenta allows exchange of wastes and nutrients between fetal capillaries and maternal blood pools.
  • Certain types of antibodies are selectively transported across the placenta to defend the newborn infant against disease.
  • The placenta does not provide complete protection, and some disease-causing organisms and harmful chemicals can pass through.

Test your understanding of the early stages of embryonic development, including the differentiation of cells in the inner cell mass and the process of gastrulation. Learn how the cells of the blastocyst develop into specific tissues and structures. Explore the significance of implantation and the second week of development.

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