Download Topic 6.6 Hormones, Homeostasis and Reproduction

Hormones, Homeostasis and
Reproduction
6.6
Maintaining the Internal Environment
• Homeostasis :
– Maintaining the internal environment of the body at
constant levels or between narrow limits.
• Parameters controlled include:
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Temperature
Blood pH
Oxygen and Carbon Dioxide Concentrations
Blood Glucose Concentrations
Water/solute Balance
Endocrine System
• This system is composed of
glands that secrete
hormones.
• Hormones are secreted
directly into the blood
where they are carried
throughout the body.
Feedback Mechanisms
• Level of a product feeds back to control the
rate of its own product.
• Negative Feedback:
– Has a stabilizing effect because a change in levels
always causes the opposite change.
• A decrease in levels feeds back to increase in
production
• An increase in levels always feeds back to a decrease in
production
Body Temperature
• The CNS monitors the temperature of blood
and compares it with a set point (37°C)
• If deviation from that set point occurs a
negative feedback loop is initiated by neurons.
• The responses affect the rate at which heat is
made or lost.
• The thyroid monitors body temperature
• Hormone Thyroxin helps regulate metabolism
Glucose Levels
• Glucose levels are monitored by cells in the
pancreas.
• The ideal set point is 90mg of glucose per
100ml of blood.
• If glucose levels rise or fall below that set
point the pancreas secretes hormones (insulin
or glucagon) targeted at certain organs.
Glucose Variations
• Eating food or drinking certain liquids will cause and
increase of glucose within the blood stream.
• Skipping meals or extensive exercise will decrease
levels of glucose in the blood.
• Type I Diabetes:
– Blood insulin is low / autoimmune disorder
• Type II Diabetes:
– Diet consumption. (eating habits vary from ancestors)
High Glucose Levels
• Beta cells in the pancreatic islets produce insulin.
• Insulin stimulates the liver and muscle cells to absorb
glucose from the blood.
• Cells convert glucose into glycogen.
– Granules of glycogen are stored in the cytoplasm.
• Other cells are stimulated to absorb glucose and use
it in cellular respiration.
• Both of these processes lower blood glucose levels.
Low Glucose Levels
• Alpha cells in the pancreatic islets produce
glucagon.
• Glucogon stimulates liver cells to break down
glycogen into glucose.
• This releases glucose into the blood thus
raising the blood glucose levels.
Blood glucose levels
Leptin
• Hormone that controls
appetite
• Secreted by adipose cells
(fat cells)
• If adipose tissue
increases, leptin travels to
the brain and tells the
hypothalamus to
decrease appetite
• Reductionist approach in
humans
Melatonin
• Controls sleep-wake
cycle (circadian rhythm)
• High levels make you
sleepy/low levels awake
• Controlled by SCN and
pineal gland in brain
• Changing time zones
can cause jet lag
Reproduction
The Reproductive System
• One of the few systems that vary between male and
female.
• Primary reproductive organs
– Males (testis-testosterone)
– Females (ovaries-estrogen and progesterone)
Reproductive organs develop after the first six weeks of
development
Urinary bladder
Pubic bone
Vas deferens
Urethra
Penis
Seminal
vesicle
Large intestine
Rectum
Prostate gland
Scrotum
Bulbourethral gland
Epididymis
Testis
Fallopian tube
Fallopian tube
Ovary
Urinary bladder
Ovary
Uterus
Pubic bone
Urethra
Cervix
Vagina
Rectum
Vagina
Menstrual Cycle
• The menstrual cycle begins at puberty and
does not end until menopause.
• The menstrual cycle is controlled by the
hormones estrogen, progesterone, FSH, and
LH.
• Both the ovaries and the uterus will develop
during this 28 day cycle.
FSH and LH (Menstrual Cycle)
• FSH
– Stimulates the development of follicles
– Stimulates estrogen secretion (by developing
follicles)
• LH
– Causes ovulation
– Causes the development of the corpus luteum
– Causes secretion of progesterone
Estrogen and Progesterone
• Estrogen
– Stimulated the repair of the uterus lining
– Estrogen stimulates LH secretions
• Progesterone
– Causes thickening of the uterus lining / prepares uterine lining
for implantation
– Falling progesterone levels increase FSH production as well as
menstruation.
• Both progesterone and estrogen inhibit the secretion
of LH and FSH (negative feedback)
Menstrual Cycle
Fertilization and Early Development
Fallopian tube
Day 2
Day 3
Day 1
Day 4
4 cells
Morula
Day 7
Blastocyst
2 cells
Fertilization
Zygote
Day 0
Implantation of
blastocyst
Uterine wall
Ovary
Egg released by
ovary
In Vitro Fertilization (IVF)
• IVF is fertilization outside the body “in glass”.
– There are several stages to IVF:
• Inject drugs to stop the women’s normal cycle.
• Inject large doses of FSH to stimulate follicle development.
• HCG (another hormone) is injected and then egg collection takes
place the eggs in the follicles.
• Male partner / donor provides sperm which is then processed.
• Eggs are extracted from the follicles.
• Each egg is individually mixed with sperm.
• Two or more embryo’s are selected for implantation.
• Check for pregnancy.
In Vitro Fertilization
Ethical Arguments for IVF
• Some childless couples are able to have
children. (infertility)
• Couple with higher predispositions for certain
genetic diseases can be reduced by screening
embryos.
• Allows for surrogate mothers.
Ethical Arguments against IVF
• Procedure may result in multiple births thus putting stress on the
family resources and unwanted children.
• Fertilized egg has the potential to become a person
• Ownership / responsibility for stored embryo’s an issue.
• Religious opposition
• Not available for everyone (expensive procedure).
• Humans decide which embryo's to implant
• High rates of failure.