Ch 17 - Human Development and Aging Flashcards
What is fertilization?
the union of a sperm and egg to form a zygote, the first cell of that new individual. fertilization is complete when both eggs contribute chromosomes to a zygote
What is the sperm composed of?
- head - acrosome that contains digestive enzymes
- middle piece - contains energy-producing mitochondria
- tail
Where does the zygote receive cytoplasm and organelles from?
the mother because only the nucleus from the sperm head fuses with the woman egg nucleus
What is the plasma membrane of the egg surrounded by?
the zona pellucida. Then the zona pellucida is surrounded by the corona radiata, which contains adhering follicular cells, which nourished the egg when it was in a follicle of the ovary
How does the sperm get through the egg membrane?
With the acrosome, which contains enzymes that break through the membrane.
When a sperm binds to the egg, their ____ fuse.
plasma membranes (because the head, middle piece and tail enter the egg)
How does the egg make sure that only one sperm enters?
As soon as the sperm touches the egg, the egg’s plasma membrane depolarizes (265 mV to 10 mV), and this prevents binding of any other sperm. After that, vesicles release enzymes that cause the zona pellucida to become an inpenetrable fertilization membrane, so sperm can’t bind to zona pellucida either.
Human development lifecycle and events?
pg. 390
What is the process of development (high level)?
- Cleavage (pre-embryonic development)
- Growth (embryonic development)
- Morphogenesis
- Differentiation
What is cleavage?
During pre-embryonic development after ovulation occurs and the egg is fertilized, the zygote begins to divide so there are 2 then 4 then 8 then 16 then 32 cells, etc. Eventually this creates a morula (separate from cleavage process)
What is Growth process?
During embryonic development, cell division is accompanied by an increase in size of the daughter cells. Daughter cells are the product of mitosis
What is Morphogenesis?
refers to the shaping of the embryo and is first evident when certain cells are seen to move or migrate in relation to other cells. By these movements, the embryo begins to assume various shapes.
What is differentiation?
When cells take on a specific structure/function. First system/structure to be visible is the nervous system
What happens in pre-embryonic development?
The morula, a compact ball of embryonic cells, that is created after cleavage completes becomes a blastocyst. This means that the many cells of the blastocyst arrange themselves so that there’s a clump of inner cells surrounded by an outer layer of cells.
The inner cell mass becomes the embryo, and the outer layer of cells becomes the chorion
How do twins arise?
Identical twins:
Sometimes during development the cells of the morula separate OR the inner cell mass splits into two. Both cases output identical chromosomes.
Fraternal twins:
Two different eggs are fertilized by two different sperm. They don’t have identical chromosomes.
What are the extraembryonic membranes?
They’re not part of the embryo and fetus; they’re outside of it.
- Chorion
- Allantois
- Yolk sac
- Amnion
What is the role of the chorion?
The chorion develops into the fetal half of the placenta. Contains blood vessels that provide embryo/fetus w/ nourishment and oxygen and take away waste. Blood vessels are continuous w/ those of the placenta
What is the role of the allantois?
Contains the umbilical cord vessels. Accumulates a little urine…later becomes bladder.
What is the role of the yolk sac?
Contains little yolk, but plentiful blood vessels. Provides nutrients
What is the role of the amnion?
Contains amniotic fluid to cushion and protect embryo. Insulates the embryo/fetus from cold/heat
When does embryonic development begin and end?
The 2nd week and lasts until the end of the 2nd month. At the end of embryo. devel. the embryo is recognizable as a human.
What happens in the 2nd week of embryonic development?
- Implantation at the end of the 1st week/beginning of 2nd week.
- GASTRULATION (morphogenesis): embryonic disk forms from the inner cell mass
- Cells migrate to become tissue layers called primary germ layers
- Chorion starts producing HCG (human chorionic gonadotropin), the basis for pregnancy tests
- Progesterone secreted by corpus luteum maintains endometrial wall
What is an ectopic pregnancy?
When the embryo implants itself in a location other than the uterus, usually one of the uterine tubes (oviducts)
What are the 3 primary germ layers, and what organs are created from them?
ectoderm = outer = epidermis, nervous system
mesoderm = middle = skeleton, muscular system, dermis, cardiovascular system, urinary system, reproductive system, outer layer of respiratory and digestive systems
endoderm = inner = glands of digestive & respiratory tract, urinary bladder
What happens in week 3 of embryonic development?
- nervous system is visible
- development of heart begins here and continues into week 4
What happens in weeks 4-5 of embryonic development?
- embryo connects to placenta via umbilical cord
- limbs, hands and feet become visible
- eyes, ears and nose become visible
What happens in weeks 6-8 of embryonic development?
- embryo becomes recognizably human
- head, neck and brain are developing
- reflex actions developed
- bone begins replacing cartilage, but skeleton not formed until month 4
When does fetal development begin and end?
Month 3-9
What effect does the progesterone and estrogen from the placenta have on the body?
- No new follicles mature b/c progesterone has negative feedback effect on hypothal and ant. pituitary
- Maintain the endometrium (menstruation shouldn’t occur during pregnancy)
What’s the fetal side and maternal side of the placenta?
fetal = chorion maternal = uterine tissue
Blood of mother and fetus never mixes. diffuses across villi
What do the umbilical arteries and veins carry? Where does umb. vein enter the fetus?
Umbilical arteries carry oxygen-poor blood
Umbilical veins carry oxygen-rich blood
Umb vein enters the baby’s liver and then joins the ductus venosus (venous duct)
Most blood entering the right atrium bypasses the lungs (doesn’t get oxygenated…also doesn’t need to because gas exchange occurs at the placenta. And blood going to baby’s heart is usually oxygen rich)
What happens at birth to the circulatory/respiratory system?
- Lungs inflate
- Increase in blood flow from pulmonary veins to the left atrium
- ductus arteriosis closes because endothelial cells block it off
- remains of ductus and parts of umb. cord and vein are transformed into connective tissue
What happens during the 3rd and 4th month of fetal development?
- skeleton appears when cartilage is replaced by bone (skull has fontanels, or large membranous areas)
- fingernails
- distinguish male vs. female via testes or ovaries
- heartbeat is loud enough to hear
- fetus about 6 inches and 6 oz
What happens during the 5th-7th month of fetal development?
- mother feels movement
- skin covered in lanugo (a fine hair), which is coated w/ a white, greasy, cheeselike substance called vernix caseosa, which likely protects skin from amniotic fluid
- eyelids open
- fetus about 12 in. and 3 lb
What happens during the 8th and 9th month of fetal development?
- fetus about 20.5 in. and 7.5 oz
- fat accumulation
- head points to the cervix
- body hair begins to disappear
Why would a cesarean section be prescribed?
If the baby is coming out feet first, because the cervix won’t be able to open up wide enough for the rest of the babies body to pass easily
Which chromosomes do men vs. women have?
Men = XY Women = XX
What determines whether the gonadal tissue in the embryo will develop into the male or female sex organs?
A gene called SRY (sex-determining region of the Y) on the Y chromosome.
Why is tissue that gives rise to the gonads called “indifferent?” When does this tissue tell us if the embryo will be male or female?
because this tissue can become testes or ovaries, depending on the action of the hormones. in the 7th week the gonads start developing
What happens to indifferent tissue at around 6 weeks if SRY is present?
- a protein called testis-determining factor is produced due to the SRY gene being present
- this protein stimulates the development of the testes
- testosterone starts being produced by the testes
- due to the presence of testosterone, the Wolffian ducts develop into male genital ducts (the tubes that hangs down and is attached to testes
- think: male = wolf - wolffian ducts converge with the urethra
Whats the structure in males that belongs to both the urinary and reproductive systems?
the urethra
What happens to indifferent tissue at around 6 weeks if SRY is NOT present?
- SRY gene isn’t present, thus testosterone isn’t created
- the lack of testosterone causes the wolffian ducts to regress and the Mullerian ducts (think: mu = mujer) to develop into the uterus and uterine tubes
- ovaries remain in abdominal cavity.
*estrogen plays NO part in the regression of the wolffian ducts in females
What happens to external sex organs if SRY is present?
- around 6 weeks, testosterone starts being produced by the testes
- the presence of testosterone causes the adrenals and prostate glands to produce a hormone called DHT (dihydrotestosterone)
- the presence of DHT allows a scrotum to appear
What happens to external sex organs if SRY is NOT present?
- around 6 weeks, NO testosterone is created, which means there’s no DHT present
- due to the absence of DHT, the labia majora/minora are present instead of the scrotum by 14 weeks
What is XY female syndrome?
Not all XY individuals develop into males. Some XY individuals develop into females (the opposite of what should happen).
With XY female syndrome, a piece of the SRY gene is missing (this is called “deletion”). People with Swyer syndrome have typical female external genitalia. The uterus and fallopian tubes are normally-formed, but the gonads (ovaries or testes) are not functional
What is XX male syndrome?
Not all XX individuals develop into females. Some XX individuals develop into males (the opposite of what should happen).
- With XX male syndrome, the SRY gene has moved to the X chromosome (this is called “translocation”).
- The SRY gene causes testes to form, which secrete 3 hormones that cause the XX individual to develop into a male:
- testosterone
- anti-mullerian hormone
- DHT
What is ambiguous sex determination?
the individual has the external appearance of a female, but the gonads (ovaries) of a female are absent. this is a result of the lack of any one of the three hormones:
- testosterone
- anti-mullerian hormone
- DHT
*think: it’s ambiguous which hormones the male secretes
What is androgen insensitivity syndrome?
when the three hormones are produced by the testes during development, but the individual develops into a female because the receptors for testosterone are ineffective. Thus the testes are formed, but the wolffian ducts degenerate, and the “she-male” doesn’t develop a scrotum.
*Remember, the gonads (testes) are still formed due to the SRY gene and testes-determing factor protein, and then the testes produce testosterone & other hormones.
How might a pregnant woman’s metabolic rate change?
It could rise 10-15% during pregnancy, which encourages overeating.
How much does a woman need to increase her calories to meet the energy needs of the fetus?
only 300 kcal
What other physiological changes occur due to the hormones released by the placenta? (progesterone and estrogen)
- decreases uterine motility (uterine contractions) by relaxing smooth muscle
- relaxes smooth muscle in walls of arteries as well (they’re not contracting as much anymore)
- low blood pressure due to artery walls expanding
- low blood pressure sets the renin-angiotensin-aldosterone pathway into motion (promotes water & salt retention)
- blood volume increases until its peak (weeks 28-32)–a 40% rise
- increase in # of red blood cells
- cardiac output increases 20-30% due to the rise in blood volume and blood cells
- heartburn due to relaxation of esophagus (smooth muscle)
- constipation due to the relaxation of smooth muscle in the intestines (and thus the decrease in intestinal tract motility)
How does the respiratory system change during pregnancy?
- 40% increase in vital capacity and tidal volume
- uterus increases in size from 60/80g to 900/1200g, which improves respiratory function by creating more space in the thoracic cavity (widens due to organs pushing upward and outward)
- blood CO2 levels fall by 20%, creating a concentration gradient favorable to the flow of CO2 from fetal blood to maternal blood at the placenta
What is stress incontinence?
the involuntary leakage of urine from urinary tract due to compression of the ureters and bladder
Why do some pregnant women get edema (swelling of body parts) and varicose veins (gnarled, enlarged veins)?
due to compression of the inferior vena cava due to the uterus expanding. this decreases the venous return, especially when lying down
Why would a woman get gestational diabetes?
the placenta produces a peptide hormone that can make cells resistant to insulin
What other effects are due to placental hormones?
- stretch marks - due to increased steroid hormone levels
- linea nigra - due to melanocyte activity increasing. darkening of other parts of the skin too
What are Braxton Hicks contractions?
False labor. True labor is marked by uterine contractions that regularly occur every 15-20 seconds and last for 40 seconds or longer
Which hormone creates positive feedback to stimulate the uterus at increasing rates?
oxytocin
What is parturition?
the process of giving birth to an offspring
What is effacement?
part of first stage of parturition process
the lower part of the uterus is pulled upward toward the baby’s head “taking up the cervix”. amniotic sac ruptures (water breaks)
once cervix dilates completely, first stage of parturition process ends
What happens in stage 2 of parturition?
- uterine contractions every 1-2 minutes, last for 1 min
- baby is born, umb. cord cut/tied
What is an episiotomy?
and incision that enlarges the opening of the vaginal orifice
What is stage 3 of birth?
“afterbirth” = placenta is delivered about 15 mins after the baby is delivered
When do humans acquire gross and fine motor skills?
from birth through 5 yrs old
What is the study of aging called? what is the goal of this field of study?
gerontology. goal is to increase health span, not life span
Mutations that ____ the activity of a _____ receptor more than double the life span of worms
Mutations that decrease the activity of a hormone receptor more than double the life span of worms
What are telomeres, and how do they predict aging?
they’re sequences of DNA at the end of chromosomes. the shorter the telomere, the quicker you age and vice versa. they protect the ends of chromosomes from deteriorating or fusing with other chromosomes.
What is telomerase?
some cells such as stem cells possess an enzyme called telomerase, which replenishes the length of the telomeres, effectively making stem cells immortal
*cancer cells frequently contain an active telomerase enzyme, which allows them to replicate continuously
Genes account for only ___ % of what determines the length of life
25%
How do we accumulate damage to our bodies over time, causing aging?
- cross-linking proteins = aging
2. DNA mutations, or the buildup of harmful metabolites
What is the first step in cross-linking process?
glucose attaching to any type of protein
Why does skin become thinner and less elastic as we age?
because the # of elastic fibers decreases and the collagen fibers become cross-linked to each other, reducing flexibility
What happens with the cardiovascular system as we age?
- max heart rate decreases, takes longer for heart rate and blood pressure to return to normal resting levels following stress
- elastic fibers in middle layer of arteries become more cross-linked and rigid…
- internal diameter of arteries decreases…
- …both contribute to a gradual increase in blood pressure
What happens to the thymus as we age?
- An important site for T-cell maturation.
- The thymus of a 60-yr old is 5% the size of the thymus of a newborn.
- B-cell responses depend on T-cells, so antibody responses decline & elderly don’t respond as well to vaccines
What happens to digestive system in aging?
Blood flow to the liver is reduced, resulting in less efficient metabolism of drugs or toxins (less medication needed to maintain same level of it in bloodstream)
What happens to respiratory system in aging?
Decreasing amounts of elasticity in lung tissue, so ventilation is reduced
What happens to kidneys in aging?
blood supply to kidneys is reduced, so they become smaller and less efficient at filtering waste. dehydrate faster
Most age-related loss in brain function is NOT due to ___, but rather may be due to _____ or ______.
Most age-related loss in brain function is NOT due to neuron loss, but rather may be due to alterations in chemical reactions or increased inflammation in the brain.
At age 40, what happens to the eyes? What is this condition called?
The lens stop accommodating as well, resulting in presbyopia, or difficulty focusing on near objects
When does muscle mass peak for men and women? What happens at age 90?
men = 18-24 women = 16-19
at age 90, most people have 50% less muscle mass than when they were 20
like muscles, bones shrink in size and density
What happens to endocrine system w/ age?
- thyroid activity declines
- production of insulin may remain stable, but cells become less sensitive to its effects, resulting in a rise in fasting glucose levels
When are testosterone levels highest in males?
in their twenties. after age 30, slowly decreases about 1% per year
When does menopause occur? what happens?
between 45 and 55 yrs old
ovaries stop secreting hormones, as they become unresponsive to gonadotropic hormones produced by ant. pituitary
Males suffer a marked increase in heart disease in their ___, but in women that’s not noted until after ____.
40s; menopause
