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IB Biology HL > Topic 6.6/11.4 > Flashcards

Topic 6.6/11.4 Flashcards

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1
Q

Where are alpha/beta cells located in the body?

A

the pancreas

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2
Q

Alpha cells synthesize and secrete a particular hormone. State the hormone and the conditions under which it is secreted/synthesized.

A

glucagon; when the blood glucose falls below the set point

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3
Q

Beta cells synthesize and secrete a particular hormone. State the hormone and the conditions under which it is secreted/synthesized.

A

insulin; when the blood glucose rises above the set point

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4
Q

Which type of cell in the pancreas synthesizess/secretes insulin?

A

beta cells

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5
Q

Which type of cell in the pancreas synthesizess/secretes glucagon?

A

alpha cells

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6
Q

What is the function of insulin?

A
  • stimulates the uptake of glucose by various tissues, especially skeletal muscle which requires the glucose for energy and the liver which converts excess glucose into glycogen
  • this process decreases the blood glucose concentration
  • as with most hormones, since insulin is broken down by the cell it acts upon, its secretion must be ongoing
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7
Q

What is the function of glucagon?

A

stimulates breakdown of glycogen into glucose in liver cells and its release into the blood, therefore increasing blood glucose concentration

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8
Q

What is type I diabetes?

A
  • AKA early-onset diabetes
  • characterized by an inability to produce sufficient quantities of insulin
  • an autoimmune disease arisign from the destruction of beta cells by the body’s own immune system
  • in children/young people, the more severe and obvious symptoms usually start rather suddenly
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9
Q

What is type II diabetes?

A
  • AKA late-onset diabetes
  • characterized by an inability to process/respond to insulin because of a deficiency of insulin receptors or glucose transporters on target cells
  • onset in slow and the disease may go unnoticed for many years
  • main risk factors are sugary, fatty diets; prolonged obesity due to habitual overeating/lack of exercise; genetic factors that may affect energy metabolism
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10
Q

What are the treatment methods of type I diabetes?

A
  • test the blood glucose concentrations regularly and inject insulin when it is too high/likely to become too high
  • injections are done before ameal to prevent a peak of blood glucose as the food is digested/absorbed
  • timing is important because insulin molecules do not last long in the blood
  • better treatments are being developed using implanted devices that can release exogenous insulin into the blood when it is necessary
  • a permanent cure may be achieveable by coaxing stem cells to become fully functional replacement beta cells
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11
Q

What are the treatment methods of type II diabetes?

A
  • treated by adjusting the diet to reduce the peaks/troughs of blood glucose
  • small amounts of food should be eaten frequently rather than infrequent large meals
  • foods with high sugar content should be avoided
  • starchy food should only be eaten if it has a low glycemic index, indicating that it is digested slowly
  • high-fibre foods should be included to slow the digestion of other foods
  • strenuous exercise and weight loss are benefitial as they improve insulin uptake/action
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12
Q

Compare/contrast the two types of diabetes

A

Diabetes I only:

  • occurs from a young age
  • inability to produce sufficient quantities of insulin
  • can be treated with insulin injections

Diabetes II only:

  • develops over time (oftentimes because of obesity/unhealthy diet)
  • inability to process/respond to insulin due to a deficiency of insulin receptors or glucose transporters on target cells
  • can be treated by avoiding sugary foods and eating smaller meals more frequently

Both:

  • if left untreated, will result in high blood glucose levels and glucose may be present in urine
  • a diabetic person may also produce more urine, feel dehydrated, feel tired and crave sugary drinks
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13
Q

What secretes thyroxin?

A

thyroid gland which is located in the neck

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14
Q

What is the function of thyroxin?

A
  • regulates the body’s metabolic rate; all cells respond to this hormone, but the main targets are the most metabolically active cells such as in the liver/muscles/brain
  • more thyroxin = higher metabolic rate = more protein synthesis/growth/body heat
  • thyroxin therefore stimulates heat production when the body temperature is low
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15
Q

What is hypothyroidism and what are its causes/consequences?

A
  • hypothyroidism is thyroxin deficiency
  • can be caused be a lack of iodine in the diet (because thyroxin contains four molecules of iodine)
    Consequences include the following:
  • lack of energy and feeling tired
  • forgetfullness and depression
  • weight gain despite loss of apetite as less glucose/fat are being broken down to release energy by cell respiration
  • feeling cold because less heat is generated
  • constipation because contractions of the muscle in the wall of the gut slow down
  • impaired brain development in children
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16
Q

What are adipose cells and what do they secrete?

A
  • fat storage cells

- secrete a hormone known as leptin

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17
Q

Outline the function of leptin

A
  • acts on the hypothalamus of the brain to inhibit appetite

- leptin binds to receptors in the membrane of the hypothalamus cells, leading to reduced apetite/food intake

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18
Q

Evaluate the effectivity of leptin injections in obese humans

A
  • although leptin injections are effective in obese mice, they are far less effective in obese humans
  • the reason why they did not work well is because most humans have exceptionally high blood leptin concentrations; the target cells in the hypothalamus may have become resistant to leptin so fail to respond to it even at high concentrations
  • for the small proportion of cases of obesity that are due to mutations in the genes for leptin synthesis, leptin injections have been successful in inducing significant weight loss; however, leptin is a short-lived protein and has to be injected several times a day
  • other side effects include: skin irritation, swelling, negative effects on the development/functioning of the reproductive system
  • therefore, leptin injections (at this point in time) are not an effective treatment for obesity in humans
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19
Q

What does the pineal gland secrete?

A
  • melatonin
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20
Q

Outline the functions of melatonin

A
  • controls circadian rhymthms
  • melatonin secretion increases in the evening and drops to a low level at dawn
  • high melatonin levels cause feelings of drowsiness and promote sleep
  • melatonin contributes to the night-time drop in core body temperature
  • melatonin receptors have been found in the kidney, suggesting that decreased urine production at night may be another effect of this hormone
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21
Q

Define circadian rhythyms

A

Rhythms in behaviour that fit the 24-hour cycle

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22
Q

SCN

A
  • suprachiasmatic nuclei
  • set a daily rhythm, even if grown in culture with no external cues about the time of day
  • in the brain, they control the secretion of melatonin
  • impulses are sent to the SCN from a special type of ganglion cell in the retina of the eye when it detects light of wavelength 460-480nm; this indicates to the SCN the timing of dusk and dawn and allows it to adjust melatonin secretion so that it corresponds to the day-night cycle
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23
Q

What are the symptoms of jet lag and what causes these symptoms?

A
  • difficulty in remaining awake during daylight hours
  • difficulty sleeping through the night
  • fatigue
  • irritabiltiy
  • headaches
  • indigestion
  • symptoms are caused by the fact that hte SCN/pineal gland are continuing to set a circadian rhythm to suit the timing of day/night at the point of departure rather than the destination
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24
Q

How can the symptoms of jet lag be alleviated?

A
  • the body will naturally adjust to the new day/night cycle after a few days, as the SCN receives impulses sent by ganglion cells in the retina
  • melatonin can be taken to try to prevent or reduce jet lag; it is taken orally at the time when sleep should ideally be commencing
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25
Q

What are embryonic gonads?

A

a group of cells in embryos what will ultimately develop into either the testes or ovary depending on the presence/absence of the Y chromosome.

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26
Q

SRY

A
  • a gene located on the Y chromosome

- codes for TDF

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27
Q

TDF

A
  • stands for testis determining factor
  • a DNA-binding protein coded for by SRY
  • stimulates the expression of other genes that cause testis development
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28
Q

What determines whether embryonic gonands develop into testes or ovaries?

A
  • if the SRY gene is present, the DNA-binding protein TDF is produced which stimulates the expression of other genes that cause testis development
  • if the SRY gene is not present, TDF is not produced and the embryonic gonads develop as ovaries
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29
Q

From where is testosterone secreted and what are its functions?

A
  • at an early stage of embryonic development, the embryonic gonads develop into testes which then develop testosterone-secreting cells to produce testosterone until about the 15th week of pregnancy which causes the genitalia to develop
  • at puberty, the secretion of testosterone increases, stimulating sperm production in the testes (primary sexual characteristic)
  • testosterone also causes the enlargement of the penis, growth of pubic hair, and deepening of the voice due to growth of the larnyx (secondary sexual characteristics)
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30
Q

List two female hormones present during pregnancy AND secreted in greater amounts during puberty for sexual development

A
  1. Estrogen

2. Progesterone

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31
Q

Outline the functions of estrogen and progesterone

A
  • estrogen and progesterone are always present during pregnancy; it is secreted by the mother’s ovaries and later by the placenta
  • the presence of estrogen and progesterone, coupled with the lack of testosterone, allows female reproductive organs to develop from the embryonic gonads
  • during puberty, estrogen/progesterone secretion increases causing the development of female secondary sexual characteristics, including enlargement of the breasts and growth of pubic/underarm hair
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32
Q

Outline the function of the testis

A

The testis (plural: testes) is responsible for the production of sperm and testosterone (male sex hormone)

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33
Q

Outline the function of the scrotum

A

Hold testes at lower than core body temperature

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34
Q

Outline the function of the epididymis

A

Site where sperm matures and develops the ability to be motile (i.e. ‘swim’) - mature sperm is stored here until ejaculation

35
Q

Outline the function of the seminal vesicle

A

Secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm) and prostaglandin (triggers uterine contractions)

36
Q

Outline the function of the prostate gland

A

Secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability)

37
Q

Outline the function of the urethra (in males and in females)

A
  • in males: conducts sperm / semen from the prostate gland to the outside of the body via the penis
  • in both males/females: conducts urine from the bladder to the outside of the body
38
Q

Outline the function of the penis

A

Penetrate the vagina for ejaculation of semen near the cervix

39
Q

Outline the function of the Cowper’s glands

A
  • A pair of exocrine glands in the male reproductive system that play an important role in the protection of sperm during ejaculation
  • Help to protect sperm as it passes through the urethra during ejaculation.
  • In response to sexual stimulation prior to ejaculation, the Cowper’s glands begin producing an alkaline mucous secretion known as pre-ejaculate which neutralizes acidic urine that may still be present in the urethra while also lubricating the urethra and external urethral orifice to protect sperm from mechanical damage during ejaculation.
40
Q

Outline the function of the vas deferens

A

Long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation

41
Q

Outline the function of erectile tissue

A

Tissue in the body that becomes stiff/enlarged when filled with blood

42
Q

Outline the function of frimbriae

A

Fimbria (plural: fimbriae) are a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct

43
Q

Outline the function of the ovary

A

The ovary is where oocytes mature prior to release (ovulation) - it also responsible for estrogen and progesterone secretion

44
Q

Outline the function of the oviduct

A

The oviduct (or fallopian tube) transports the oocyte to the uterus - it is also typically where fertilisation occurs

45
Q

Outline the function of the endometrium

A

The mucous membrane lining of the uterus, it thickens in preparation for implantation or is otherwise lost (via menstruation)

46
Q

Outline the function of the uterus

A

The uterus is the organ where a fertilised egg will implant and develop (becoming an embryo)

47
Q

Outline the function of the cervix

A

A muscular opening of the uterus that protects the uterus and the fetus within it (during pregnancy); when the woman is ready to give birth, it dilates to provide a birth canal

48
Q

Outline the function of the vagina

A

Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)

49
Q

Outline the function of the vulva

A

Protect internal parts of the female reproduction system

50
Q

To whom and when does the menstrual cycle occur?

A
  • it occurs in most women from puberty until menopause, apart from during pregnancies
51
Q

List and outline the functions of the four hormones involved in controlling the menstrual cycle

A
  1. FSH
    - released from anterior pituitary gland
    - stimulates follicular growth in ovaries
    - stimulates estrogen secretion (from developing follicles)
  2. Estrogen
    - released from the ovaries
    - thickens uterine lining (endometrium)
    - inhibits FSH and LH for most of the cycle
    - stimulates FSH and LH release pre-ovulation
  3. LH
    - released from the anterior pituitary gland
    - surge causes ovulation
    - results in the formation of a corpus luteum
  4. Progesterone
    - thickens uterine lining (endometrium)
    - inhibits FSH and LH
52
Q

Outline the phases of the menstrual cycle

A
  1. The first half = follicular phase
    - group of follicles is developing in the ovary
    - in each follicle, an egg is stimulated to grow
    - the lining of the uterus (endometrium) is repaired and starts to thicken
    - the most developed follicle breaks open, releasing its egg into the oviduct
    - other follicles degenerate
  2. Second half = luteal phase
    - the wall of the follicle that released an egg becomes a body called the corpus luteum
    - continued development of the endometrium prepares it for the implantation of an embryo
    - if fertilization does not occur, the corpus luteum breaks down
    - the thickening of the endometrium also breaks down and is shed during menstruation
53
Q

Explain the mechanisms behind the menstrual cycle

A
  • controlled by negative/positive feedback mechanisms
    Steps:
    1. FSH rises to a peak towards the end of the menstrual cycle and stimulates the development of follicles, each containing an oocyte and folllicular fluid; FSH also stimulates secretion of estrogen by the follicle wall
    2. Estrogen rises to a peak towards the end of the follicular phase, stimulating the repair/thickening of the endometrium after menstruation and an increase in FSH receptors.
    Increased FSH receptors = follicles are more receptive to FSH = more production of estrogen (positive feedback loop)
    When estrogen reaches high levels, it inhibits the secretion of FSH (negative feedback) and stimulates LH secretion
    3. LH rises to a sudden and sharp peak towards the end of the follicular phase, stimulating the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open at ovulation; also promotes the formation of the corpus luteum from the wall of the follicle which secretes estrogen (positive feedback) and progesterone
    4. Progesterone levels rise at the start of the luteal phase, reach a peak and then drop back to a low level by the end of this phase; it promotes the thickening and maintanance of the endometrium; also inhibits FSH and LH secretion by the pituitary gland (negative feedback)
54
Q

Explain the steps and the usage of drugs in IVF

A
  1. Down regulation
    - Drugs are used to halt the regular secretion of FSH and LH – this in turn stops the secretion of estrogen and progesterone
    - By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries
    - The drug treatment usually takes about two weeks and is typically delivered in the form of a nasal spray
  2. Superovulation
    - Superovulation involves using artificial doses of hormones to develop and collect multiple eggs from the woman
    - The patient is firstly injected with large amounts of FSH to stimulate the development of many follicles
    - The follicles are then treated with human chorionic gonadotrophin (hCG) – a hormone usually produced by a developing embryo
    - hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing
  3. Fertilisation
    - The extracted eggs are then incubated in the presence of a sperm sample from the male donor
    - The eggs are then analysed under a microscope for successful fertilisation
  4. Implantation
    - Approximately two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium
    - Healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate)
    - Multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome)
    - Roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful
55
Q

What is the “seed and soil” theory?

A
  • According to this theory, the male produces a ‘seed’ which forms an ‘egg’ when mixed with menstrual blood (the ‘soil’)
  • The ‘egg’ then develops into a fetus inside the mother according to the information contained within the male ‘seed’ alone
56
Q

Explain William Harvey’s experiment and how it disproved the “seed and soil” theory of reproduction

A
  • William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo
  • He expected to, according to the theory, find eggs developing in the uterus of female deer during the mating season by slaughtering them and dissecting them
  • He was unable to detect a growing embryo until approximately 6 – 7 weeks after mating had occurred
  • He concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus
  • Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female ‘seeds’
57
Q

Define oogenesis

A

Production of egg cells in the ovaries

58
Q

Explain the steps of oogenesis in female fetus

A
  • Starts in the ovaries of a female fetus
  • Germ cells in the fetal ovary divide by mitosis and the cells formed move to distribute through the cortex of the ovary
  • These cells grow and start to divide by meiosis when the fetus is 4-5 months (not born yet)
  • Follicle cells form around the germ cells when they enter first division of meiosis (7 month)
  • No further development takes place until after puberty
59
Q

Explain the steps of oogenesis after puberty

A
  • No more primary follicles are formed after birth (the cells that have started to divide by meiosis and the surrounding follicle cless)
  • At the start of each menstual cycle, a small batch are stimulated to develop by FSH
  • Usually one goes on to become the mature follicle, containing a secondary oocyte
  • Fertilization may or may not occur after
60
Q

Define spermatogenesis

A

Production of sperm in the seminiferous tubules

61
Q

Explain the steps of spermatogenesis

A
  • Outer layer called germinal epithelium cells divide endlessly by mitosis to produce more diploid cells
  • Diploid cells grow larger and then become primary spermatocytes (2n)
  • Each primary spermatocyte carries out the first division of meiosis to produce two secondary spermatocytes (n)
  • Each secondary spermatocyte carries out the second division of meiosis to produce two spermatids (n)
  • Spermatids become associated with nurse cells (Sertoli cells) and develop into spermatozoa (n)
  • Sperm detach from Sertoli cells and are carried out of the testis by the fluid in the centre of the seminiferous tubule
62
Q

Define spermatozoa

A

Cells that have developed tails (commonly known as sperm(

63
Q

Contrast the outcomes of spermatogenesis and oogenesis

A

Sperm
- Each sperm consists of a haploid nucleus, a system for movement and a system of enzymes and proteins that enable the sperm to enter the egg
- Each complete meiotic division results in four spermatids
- Sperm differentiation eliminates most of the cytoplasm (making it the smallest cell in the body)
- Testes produce sperm continuously
Egg
- Each meiotic division produces one female gamete and three polar bodies (that degenerate and die)
- The egg is much large and increases cytoplasms during egg differentiation
- Only one egg cell per menstrual cycle is produced

64
Q

Outline the mechanism that enables the sperm to swim toward the egg

A
  • The membranes of sperm have receptors that can detect chemicals released by the egg
  • Directional swimming towards the egg
65
Q

Zona pellucida

A

Coat of glycoproteins that surrounds the egg

66
Q

Acrosome

A
  • Large membrane-bound sac of enzymes in the head of the sperm
  • Enzymes are released after the sperm binds to the zona pellucida
  • The enzymes from it digest the zona pellucida
67
Q

Explain the moment of fertilization

A
  • The first sperm cell binds to the egg membrane (after breaking through the zona pellucida)
  • The sperm membrane fuses with the egg membrane and the sperm nucleus enters the egg cell
68
Q

Explain the mechanism to prevent polyspermy

A
  • After the sperm nucleus enters the egg cell, it activates the cortical granules (vesicles located near the egg membrane)
  • The contents are released from the egg by exocytosis and the enzymes result in the digestion of binding proteins
  • No further sperm can bind to the egg
  • Also results in a general hardening of the zona pellucida
69
Q

Outline the risks of external fertilization

A
  • Predation
  • Susceptibility to environmental variation (temperature, pH fluctuations)
  • Pollution
70
Q

Outline the benefits of internal fertilization

A
  • Gametes would not dry out
  • Ensures sperm and ova are placed in prolonged close proximity to each other
  • Protected inside the female
71
Q

Blastocyst

A
  • Hollow ball of cells

- Formed from mitosis after fertilization

72
Q

Explain the implantation of the blastocyst

A
  • Blastocyst move down the oviduct by the cilia of cells in the oviduct walls
  • Reach the uterus and the zona pellucida breaks down
  • Sinks into endometrium or uterus lining
  • The outer layer of the blastocyst develops finger-like projections allowing the blastocyst to penetrate the uterus lining
  • Exchange materials with the mother’s blood (absorb food and oxygen)
  • Embryo grows and develops rapidly
73
Q

Explain the purpose of implantation of the blastocyst

A

The blastocyst has used up the reserves of the egg cell and needs an external supply of food from the female body

74
Q

Explain the role of hCG in early pregnancy

A
  • Embryo produces human chorionic gonadotropin (hCG) to stimulate the corpus luteum in the ovary to continue to secrete progesterone and estrogen
  • These hormones stimulate the continued development of the uterus wall, which supplies the embryo with everything it needs
75
Q

Outline the purpose of placenta

A
  • Facilitate the exchange of materials between the mother and the embryo
  • It is needed because the body surface area to volume ratio becomes smaller as the fetus grows larger
76
Q

Outline the purpose of placental villus

A
  • Increase surface area in the exchange of materials

- Maternal blood flows in the inter-villous spaces around the villi

77
Q

Placental barrier

A
  • The cells that separate maternal and fetal blood

- Selectively permeable, allowing some substances to pass but not others

78
Q

Explain the risk of miscarriage at nineth week of pregnancy

A
  • Placenta has started to secrete estrogen an dprogesteron to sustain the pregnancy and the corpus luteum is no longer needed
  • The swtichover is crucial and if fails, can lead to miscarriage
79
Q

Explain the positive feedback loop during birth

A
  • During pregnancy, progesterone inhibits secretion of oxytocin and inhibits contraction of the uterus wall (myometrium)
  • At the end of pregnancy, hormones produced by the fetus inhibits porgesterone and oxytocin is secreted
  • Oxytocin stimulates contractions of the muscle fibres in the myometrium
  • The contractions are detected by stretch receptros and signals the pitruity gland to increase oxytocin secretion
  • Positive feedback system
80
Q

Outline the advantage of positive feedback loop during birth

A
  • Causing a gradual increase in the myometrial contractions, allowing the baby to be born with the minimum intensity of contraction
81
Q

Outline the roles of uterine contractions

A
  • Uterine contraction bursts the amniotic sac and the amniotic fluid passes out
  • The cervix dilates and furhter uterine contractions push the baby out through the cervix and the vagina
82
Q

Outline the correlation of gestation times and body mass

A

Positive correlation

83
Q

Explain the two development strategies of mammals

A
  • Altricial species give birth to relatively helpless, incompletely developed offspring (immobile, lack hair, unable to obtain food
  • Precocial mammals give birth to offsprings with open eyes, hair, immendiately mobile, somewhat able to defend themeslves

IB Biology HL (23 decks)

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