5. Homeostasis and Response Flashcards
What is Homeostasis?
Homeostasis is the maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular functions
Give examples of conditions maintained by Homeostasis in the body :
•Blood glucose concentration
•Body temperature
• Water levels
What two types of responses are used in body control systems?
Nervous and chemical
What three components do all control systems have?
•Receptors
•Coordination centre
•Effectors
What is the function of a receptor?
Receptors detect changes in the environment (stimuli)
What is the function of a coordination centre ?
Coordination centres obtain and process information from receptors
What is the function of a effector ?
Effectors (muscle of glands) bring about responses to stimuli
What is the function of the nervous system?
The nervous system allows the body to react to its surroundings and coordinate an appropriate response
How does stimulus lead to a response being carried out by the body ?
• Stimulus is converted into an electrical impulse by the receptors.
• The electrical impulse passes along sensory neurones to the central nervous system (CNS).
• The CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response.
What sequence of events describes how the nervous system works?
Stimulus → receptor → coordinator → effector → response
What is a reflex action ?
A reflex action is an automatic and rapid response which does not involve any conscious input from the brain.
Why are relfex actions important?
Reflex actions aid sruvival by preventing harm to the body
E.g. touching a hot object
Describe how a reflex action occurs via a reflex arc
-The stimulus is detected by a receptor
-An electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS)
• At a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and stimulates a new impulse which
passes along the relay neurone.
• The same process occurs at a synapse between a relay neurone and a motor neurone.
• At the effector, an appropriate response is carried out.
What is the difference between a reflex pathway and a conscious pathway?
Within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain. In a conscious pathway, the coordination centre is in the conscious part of the brain.
Give the name of the body’s coordination system which involves hormones
The endocrine system
What is a hormone?
A hormone is a chemical messenger secreted by a gland. It travels in the blood to a target organ, where it causes a response.
What type of organ secretes hormones?
Glands
Which gland controls many other glands in the body
The pituitary gland
Why is the pituitary gland considered a ‘master gland ‘?
It secretes a wide range of hormones, some of which may stimulate other endocrine glands.
What is the role of the pituitary gland in the endocrine system ?
• Secretes human growth hormone - controls human growth.
• Stimulates the thyroid gland.
• Stimulates ovulation and the production of oestrogen in the ovaries.
• Stimulates the production of sperm and testosterone in the testes.
What is the role of the thyroid gland in the endocrine system ?
Secretes the hormone thyroxine - controls metabolism, heart rate and body temperature.
What is the role of the pancreas in the endocrine system?
Secretes the hormone insulin - controls blood glucose levels
What is the role of the adrenal gland in the endocrine system ?
Secretes adrenaline - controls the body’s
‘fight or flight’ response.
What is the role of the ovaries in the endocrine system ?
Secrete oestrogen, which coordinates the menstrual cycle and the development of female secondary sexual characteristics.
What is the role of the testes in the endocrine system ?
Secrete testosterone, which coordinates the production of sperm and the development of male secondary sexual characteristics.
Which organ monitors and controls blood glucose concentration ?
The pancreas
How does the pancreas respond when blood glucose levels are too high ?
The pancreas secretes the hormone insulin.
Insulin binds to receptors on the liver and muscles, causing excess glucose to be converted into glycogen and stored.
How does the pancreas respond when blood glucose levels are too low ?
The pancreas secretes the hormone glucagon. Glucagon binds to liver cells, causing glycogen to be converted into glucose and released into the blood.
How is blood glucose concentration controlled using a negative feedback loop ?
When the blood glucose concentration rises or falls below the optimum, a hormone is secreted by the pancreas.
• The action of either hormone (insulin or glucagon) helps bring back the concentration to the correct level .
What is Type 1 diabetes?
Type 1 diabetes is an autoimmune disorder in which the pancreas does not produce sufficient insulin to control the blood glucose concentration.
As a result, blood glucose levels are often very high, leading to excessive urination, tiredness and weight loss.
How can type 1 diabetes be treated ?
• Insulin injections before meals - allows glucose to be converted into glycogen.
• Limiting carbohydrate intake.
• Attempts using pancreas and pancreatic cell transplants; investigations into genetic engineering of pancreatic cells.
What is type 2 diabetes ?
Type 2 diabetes is a disorder in which the body’s cells stop responding to insulin, leading to an uncontrolled blood glucose concentration. Its onset is linked with increasing age and obesity.
How can type 2 diabetes be treated ?
• Following a carefully-controlled diet
• Doing regular exercise
• Losing weight
• Use of drugs which increase insulin production and effectiveness
What is the function of reproductive hormones during puberty?
• Males: cause the development of secondary sexual characteristics.
• Females: cause the development of secondary sexual characteristics and the maturation of eggs.
What is the main male reproductive hormone ?
The main male reproductive hormone is testosterone, which is produced by the testes and controls sperm production.
What is the main female reproductive hormone ?
The main female reproductive hormone is oestrogen, which is produced by the ovaries and is involved in the menstrual cycle.
What is the menstrual cycle ?
The menstrual cycle is the monthly cycle of physiological changes that occur in females, involving the shedding of the uterus lining (menstruation) and ovulation.
Describe the events of the menstrual cycle
• Uterus lining thickens and eggs begin to mature in the ovaries.
• An egg is released from one of the ovaries (ovulation)
- uterus lining remains thick.
• If the egg is fertilised, pregnancy may occur. If not, both the egg and the uterus lining are shed during menstruation.
what is ovulation ?
Ovulation is the release of a mature egg from the ovaries, which occurs approximately every 28 days.
Name the four main hormones involved in the menstrual cycle
• Oestrogen
• Progesterone
• Follicle stimulating hormone (FSH)
• Luteinising hormone (LH)
What is the role of FSH in the menstrual cycle ?
FSH is secreted by the pituitary gland. It controls the maturation of eggs within the ovaries (inside a follicle) and triggers the production of oestrogen by the ovaries.
What is the role of oestrogen in the menstrual cycle ?
Oestrogen is produced by the ovaries and released due to the action of FSH - it causes the regrowth of the uterus lining.
It triggers the production of LH and restricts the release of more FSH.
What is the role of LH in the menstrual cycle ?
LH is produced in the pituitary gland as a result of oestrogen. Its release triggers ovulation.
What is the role of progesterone in the menstrual cycle ?
Progesterone is secreted from the follicle of the ovary. It sustains the uterus lining and inhibits FSH and LH.
What is contraception ?
Contraception refers to any method of preventing pregnancy
What are the two type of oral contraceptives ?
• Combined contraceptive pill (contains oestrogen and progesterone).
• Mini pill (contains only progesterone).
How does the contraceptive pill prevent pregnancy ?
• Inhibits FSH - eggs do not mature.
• Prevents the development of the uterus lining - eggs cannot implant.
What is the contraceptive patch ?
• Contains both oestrogen and progesterone.
• It is a patch that is placed onto the skin for 7 days at a time.
What is the Contraceptive implant ?
A small rod inserted under the skin which continuously releases the hormone progesterone - lasts for 3 years.
What is the contraceptive injection ?
An injection containing the hormone progesterone - lasts for approximately 3 months.
What is the IUS
The IUS (intrauterine system) is a small plastic device that is inserted into the uterus. It releases progesterone
What is the IUD ?
The IUD (intrauterine device) is a small copper-containing device inserted into the uterus, which prevents the implantation of embryos.
What is a spermicide?
A spermicide is a chemical that kills or immobilises sperm cells - however, they are not very effective, and work better when combined with barrier methods.
What is a barrier method of contraception ?
A barrier method of contraception involves a physical separation between the sperm and the egg. They
include:
• Condoms - thin sheath worn on the penis or inside the vagina - protects against STIs but may tear/break.
• Diaphragms - a thin cap placed over the cervix - prevent entry of sperm.
What surgical methods of contraception are available?
Sterilisation - in males, the sperm ducts are tied (vasectomy) and in females, the oviducts are tied.
What is abstinence?
Abstinence is the practice of not having sex, which also avoids pregnancy. Some people abstain from sex around the time of ovulation - this is known as the rhythm method, but it is quite unreliable.
How do fertility drugs increase the chance of pregnancy?
Many fertility drugs contain FSH - which stimulates oestrogen production and the maturation of eggs in the ovary. They also contain LH which triggers ovulation.
What is IVF
IVF (in vitro fertilisation) is type of fertility treatment:
• Mother is given FSH and LH - stimulates maturation of eggs and ovulation.
• Eggs are fertilised using sperm in a laboratory - develop into embryos.
• 1 or 2 embryos are inserted into the mother’s womb.
What are the advantages of fertility treatment ?
• Allows infertile couples to have children
• Can store a woman’s eggs for later
What are the disadvantages of fertility treatment?
• It can be a very expensive process.
• It has a low success rate - especially for older couples.
• Increases chance of multiple pregnancies - dangerous for mother and babies.
• Side effects of fertility drugs.
What is negative feedback ?
Negative feedback is a type of control where the body responds to an increase or decrease in a factor by returning it to the optimum level.
What is thyroxine?
Thyroxine is a hormone released by the thyroid gland. Its release is triggered by the thyroid stimulating hormone (TSH). Thyroxine controls the body’s metabolic rate, growth and development.
How is the release of thyroxine controlled by negative feedback ?
• Levels of blood thyroxine falls - detected by receptors in the brain.
• Pituitary gland releases more TSH.
• More thyroxine produced and released by the thyroid gland.
• Blood thyroxine level returns to normal.
What is adrenaline ?
Adrenaline is a hormone secreted by the adrenal gland in times of stress. It is responsible for the ‘fight or flight response’.
What are the effects of adrenaline?
• Increase in heart and breathing rate - delivers oxygen and glucose to the body.
• Stored glycogen converted to glucose.
• Dilation of pupils.
• Increased mental awareness.
• Blood diverted away from digestive system to muscles
What is infertility
Being unable to concieve
