Lecture 15: Reproductive Specializations Flashcards
Characteristics of human reproductive system
- Sexual reproduction (meiosis)
- Heterogamy
- Amniote
- Humans reflect general vertebrate pattern of increased parental investment in offspring
- Exhibit live births (viviparity)
- Placental mammals
- Females exhibit uterus and uterine tubes
- Females nourish young with breat milk
- Higher primate pattern
What does it mean by heterogamy?
In animals it is 2 different cell types (egg and sperm) fusing together
In plants it would be having a male and female part
What does the higher primate pattern include and is it seen in all primates?
Not necessarily all primates
Includes development of a simplex uterus and male testes permanently descended into scrotum
What is a simplex uterus?
Single unpaired organ, 1 cavity
What type of uterus do anthropoids (monkeys and apes) show?
Unicornate
What type of uterus do strepsirhines and tarsiers show?
Bicornate
In what ways are humans fairly distinct from other mammals and primates?
- No baculum
- Enlarged external genitalia in both males and females
- Heavy menstrual flow
- Menopause
- Hemochoral placenta
- Birth canal constricted as consequence of bipedal adaptations
- Fetal head fits tightly through female pelvic outlet
- Fetus has characteristic passes through birth canal
- Longer labor
- Assistance to mother required at delivery?
- Relatively altricial infants
- Maternal milk higher in carbs, lower in fats and proteins
- Permanent relative enlargement of female breasts
Where is the baculum found?
Bone found in penis of most placental mammals
Why might humans have lost the baculum?
When monogamy became dominant reproductive strategy
What could congential mullerian anommalies lead to?
Could lead to fertility problems or endometriosus
Describe the baculum
Evolved in mammals 95 mya
Present in first primates
Longer or more prominent bacula appear to be associated with species that characteristically exhibit longer bouts of copulation
Describe secondary sexual characteristics
Males and females of a species tend to show observable, distinguishing physical characteristics
Sexual selection may account for many of these traits
Hormones are linked to sexual dimorphism
Additional physiological differences
What are the three different types of placentas?
Epitheliochorial
Endotheliochorial
Hemochorial
What species exhibit a epitheliochorial placenta?
Cow
Pig
Horse
Strepsirhines (lemurs, lorises, galagos)
What species exhibit an endotheliochorial placenta?
Dog
Cat
What species exhibit a hemochorial placenta?
Human
Rodent
Haplorhines (tarsiers, monkeys, apes)
What are the secondary sexual characteristics of a female human?
Mature breasts
Broader hips
Pubic hair
What are the male human secondary sexual characteristics?
Enlarged Adam's apple Facial hair Broad shoulders Increased body hair Pubic hair Mature genital organs Body more muscular
What is the classic definition of secondary sexual characteristics?
Includes only those physical features that arise at puberty and distinguish males and females, but are not necessarily directly involved in reproduction
How does Langdofurther define secondary sexual characteristics?
Those characteristics that represent normal responses of various body tissues to the dominant presence of either estrogen or testosterone
What are the female human secondary sexual characteristics under Langdofurther definition?
- Growth and maturation of sex organs
- Breat development
- Accelerated ossification at puberty
- Increase in subcutaneous fat
- Subcutaneous fat depositions associated with breasts and lower body
- Softer skin, highly vascularized
- Increased Na, H2O retention
- Repro. And mothering behaviors
- Relative lack of body hair
- Increased pheromone sensitivity
- Wider hips
- Higher pitched voice
What are the male human secondary sexual characteristics as defined by Langdofurther?
- Sexual differentiation at fetal stage
- Descent of testes at 8mos gestation
- Growth and maturation of sex organs
- Overall body growth
- More protein synthesis/muscle development
- Ossification of long bones and growth of cortical bone
- Increased facial and body hair
- Thicker skin
- Increase in sebaceous gland activity
- Spermatogenesis
- Reproductive behaviors
- Decreased pheromone sensitivity
- Inhibition of GnRH in hypothalamus
Describe the hemochorial placenta
Capillaries embedded/efficient
Nutrient transfer
More bleeding
Describe endotheliochorial placenta
Capillaries separated by epithelium
Slower nutrient transfer
Less bleeding
What are some examples of secondary sexual characteristics in other species?
Differences in body size
Nose size
Mandrills have huge canines and painted face = males
Lions = manes or not
Define reproductive sucess
Having as many offspring as possible survive into adulthood
What are the three subclasses of mammals?
Prototherians
Metatherians
Eutherians
Describe prototherians reproductive strategy
Lay eggs
Describe metatherians reproductive strategy
Retain egg in uterus for an entire ovulatory cycle
Fetus then flushed out with endometrial lining
Underdeveloped fetus emerges from birth canal and stays in pouch
Describe eutherians reproductive strategy
Endometrium is retained
Placenta supplies developing fetus
Extended gestation
More developed fetus at birth
Most vertebrates (particularly mammals and birds) have relatively __________ offspring in a lifetime and therefore exhibit a relatively ________ degree of parental investment
Few
High
Describe the endometrium
Highly vascularized
Increases in thickness
Sheds during course of ovulatory (menstrual) cycle
In mammalian uteturs
Within primates, human menstrual flow is __________ and more ________ than that of other species
Heavier
Conspicuous
Why is there a greater proliferation of the endometrial lining in mammals?
In preparation for sustaining a developing fetus via placental nourishment
Why do primates have a reliance on longer gestation periods?
Allow for relatively larger fetal brains may account for differences in endometrial proliferation
What do some argue menstruation provides protection against?
Invading pathogens
Endometrial tissue is an _________ secondary consequence of reproductive cycles
Expensive
A relatively higher number of ovulatory/menstrual cycles over an individual lifetime has been linked to what?
Endometriosis
Anemia
Breast cancer
What are the internal genitalia of the male?
Testis Epididymis Ductus deferens Prostate Seminal glands Bulborethral gland
What are the external genitalia of the male?
Penis
Urethra
Scrotum
Coverings of the testis
What is the function of the testis?
Germ cell and hormone production
What is the function of the epididymis?
Reservoir for sperm
What is the function of the ductus deferens?
Transport organ for sperm
What are the accessory sex glands in male and what are their function?
Prostate, seminal glands, bulbourethral gland
Production of secretions (semen)
What is the function of the penis?
Copulatory and urinary organ
What is the function of the urethra?
Conduit for urine and semen
What is the function of the scrotum?
Protection of testis
What are the internal genitalia for females?
Ovary
Uterine tube
Uterus
Vagina (upper portion)
What are the external genitalia for females?
Vagina (vestibule) Labia majora and minora Clitoris Greater and lesser vestibular glands Mons pubis Vulva
What is the function of the ovary?
Germ cell and hormone production
What is the function of the uterine tube?
Site of conception and transport organ for zygote
What is the function of the uterus?
Organ of incubation and partiurition
What is the function of the greater and lesser vestibular glands?
Production of mucoid secretions
What is the function of the mons pubis?
Protection of pubic bone
What is unique about eutherian mammals?
They have a placenta
Describe the placenta in mammals
Forms an interface between the fetus and mother
Variation among mammals in degree to which placenta invades the uterine lining
The difficulty of labor for humans is a trade off for what?
Between bipedal adaptations of pelvis and large brain size
How does labor for most mammals compare to humans?
Appears physically effortless
During human birth, what must the infant pass through?
Bony pelvis and openings in muscle and fascia that make up the perineum
During birth what part experiences the greatest amount of constriction?
The infant’s head
During birth which part undergoes significant stretching?
Soft tissues of perineum
During birth what comprises the birth canal?
Female pelvis
What are the four subtypes of human pelvises?(Caldwell-Moloy Classification)
Gynecoid
Android
Platypelloid
Anthropoid
Describe the gynecoid pelvis
Round pelvic inlet
Shallow pelvic cavity with short ischial spines
Most suitable for childbirth
Describe android pelvis
Triangular or heart-shaped inlet Narrow anteriorly Ischial spines are prominent Tents to be present in taller individuals Can make childbirth more difficult
Describe the platypelloid pelvis
Narrow inlet from front to back
Very shallow pelvic cavity
Can make it difficult for the infant’s head to engage the birth canal
Describe anthropoid pelvis
Inlet is oval and large from front to back and transversely narrow
Larger outlet but relatively small inlet overall
Infant head tends to engage normally, but associated with slower process
In most primates, what is the neonatal brain/head size closely correlated to?
Maternal pelvis size/shape
What is responsible for the human condition of having to pass a very large headed infant through a comparably narrow birth canal?
Selection for large brains along with requirement of obligate bipedalism
How are squirrel monkeys unique among primate species regarding birth and why?
Their infants have relatively large heads at birth
Because they are dwarfed species that reduced in body size over time while maintaining head/brain size
What does the known material for Australopithecus afarensis suggest about their birth canal?
Wide from side to side, but narrow from front to back
Due to locomotor requirements rather than obstetric constraints
What does bipedalism require regarding the evolution of birth?
Having sacroiliac (SI) joint as close to acetabulum as possible
Describe the evolution of birth and pelvis
Wider pelvis to better support hip abductors (small gluteal muscles)
Describe the Australopith neonatal brain size
Head size is unknown, but this species had a relatively smaller brain size (1/3 modern human) and likely small head
Describe the neonatal brain size for Homo erectus
Had a relatively larger brain than A. Afarensis
Further adaptations to obligate bipedalism
Similar pelvic dimensions with medium sized head, compared to modern humans would have made for a relatively easy journey through the birth canal
Describe the relationship between brain size and gestation in the evolution of birth
As brain size increased along with increased adaptations for obligate bipedalism, gestation may have decreased as a compromise to deal with ever increasing brain size
What is a defining characteristic of mammals regarding lactation?
Early in life, before they can ingest solid foods, young feed on breast milk
Milk comes from breasts of females with exception of certain bats
Describe the mammary glands
Within breast tissue to produce milk
Specialized exocrine glands derived from sweat
How are human breasts unique compared to other primates?
In the amount of adipose tissue around the glandular tissue
What is excess body fat necessary for regarding birth?
Support gestation and feeding of young
Does not explain the presence of excess fat in breast tissue
What are some theories about why there is excess fat in female breast?
- Poorly supported - more attractive to potential males
- Fertility advertisements showing good health and plentiful stores of fat, ready for successful reproduction and rearing of offspring
- Mature human breasts signal reproductive maturity and potential
- “Falsely advertise” and attract males because it was assumed that larger breasts = better milk production (not necessarily true)
Where is body size dimorphism common?
In mammals, with males typically larger than females
What does body size dimorphism tend to relate to?
Social structure and associated mating strategies
When does sexual size dimorphism tend to be the greatest?
When there is a higher degree of male-male competition for females
What is lower degree of sexual dimorphism associated with?
Polygyny and monogamy where there is little to no male-male competition
Has sexual size dimorphism increased or decreased over time in the human lineage?
Decreased
