6.6 Flashcards
what is homeostasis
the maintenance of relatively constant internal conditions
explain negative and positive feedback loops
negative:
- is when conditions are brought back to a set value when it’s detected that they have deviated from it
- maintains homeostasis
positive:
- when conditions are amplified in response to a change
- doesn’t maintain homeostasis
maintenance of blood glucose concentration
when blood glucose conc is high:
- increase in blood glucose conc
- it is detected by cells in pancreas
- beta cells in the islets of langerhans secrete insulin
- insulin stimulate glucose uptake, causes conversion of glucose into glycogen, and increases respirate rate
- cause blood glucose conc to decrease
when blood glucose conc is low:
- decrease in blood glucose conc
- it’s detected by cells in the pancreas
- alpha cells of the pancreas secrete glucagon
- glucagon causes conversion of glycogen into glucose, and causes cells to release glucose
- this increases blood glucose conc
diabetes
thyroxin
- a hormone made up of 4 iodine atoms which regulates metabolic rate and controls body temperature
- it’s secreted by the thyroid gland and targets most body cells
- colder temperatures cause hypothalamus to stimulate thyroxin release which increases metabolic rate and respiration rate which generates heat and increases body temperature
- hotter temperatures cause hypothalamus to inhibit thyroxin release which decreases metabolic rate and respiration rate which lowers heat production decreasing body temp
leptin
- a hormone which is secreted by cells in adipose tissue which act on the hypothalamus to inhibit appetite
- an increase in adipose tissue increases leptin secretion which is detected by receptors in hypothalamus which inhibits appetite to reduce food intake
- a decrease in adipose tissue reduces leptin secretion so less is detected by hypothalamus which triggers appetite to increase food intake
- obese people may become desensitised to leptin which makes them less likely to recognise when they’re full (leptin resistance also develops with age)
leptin and obesity application
- leptin trials were conducted on mice to see if leptin injections would reduce obesity
- obese mice (that couldn’t produce leptin) were injected with leptin which reduces their body mass due to appetite inhibition
- however when tested on humans it was found to be ineffective as humans have high blood leptin concentration which means they’re unresponsive to leptin not deficient like the mice (+side effects —> skin swelling)
- leptin injections may work if the obesity is due to genetic mutation if leptin synthesis however leptin affects reproductive system
Melatonin
- A hormone secreted by pineal gland, which controls the circadian rhythm.
-light is detected by photo receptors in the eyes, then relate to the pineal gland, which inhibits melatonin secretion. - over prolonged period, melatonin, secretion anticipates, the onset of darkness does synchronises circadian rhythm with sleep schedule
jet lag
– A condition resulting from rapid travel between time zones, which changes the bodies, normal circadian rhythm.
– symptoms include difficulty, staying awake in daylight hours, and difficulty falling asleep in dark hours, fatigue, irritability, headaches
– the physiological cause is that the pineal gland have the circadian rhythm suited to the departure location, rather than the destination, the light level changes does melatonin levels do not match amount of light.
– Jet lag only lasts a few days
– taking melatonin pills before sleep, artificially increases melatonin levels, allowing the body to adjust better to the new sleep, wake cycle
development of testes
- the y chromosome contains a gene called the SRY gene
- the SRY gene codes for a DNA binding protein called Testes Determining Factor (TDF)
- TDF stimulates the development of embryonic gonads into testes
testosterone in development
- testosterone is a hormone secreted by the testes which is responsible for the development of primary sexual characteristics during prenatal development, such as male genitalia
- during puberty, testosterone secretion increases which causes the development of secondary sexual characteristics such as body hair, deepened voice, muscle mass increase
- it also stimulates the production sperm in the testes & maintains libido
oestrogen and progesterone in development
- in females the y chromosome is not present meaning the SRY gene is not present thus TDF is not produced and the embryonic gonads develop into ovaries
- the ovaries secrete oestrogen and progesterone which stimulate the development of primary sexual characteristics during prenatal development, such as female genitalia & reproductive organs
- during puberty secretion of oestrogen and progesterone increases which stimulates the development of secondary sexual characteristics such as body hair, wider hips, breasts
- they also control the menstrual cycle
male reproductive system
male reproductive system: name and function
testes: produce sperm and testosterone
scrotum: a sac of skin which hold testes outside of body (35 C)
epidydemis: where sperm mature, develop motile ability, and are stored till ejaculation
sperm duct: transports sperm from testes to penis
seminal vesicle: secretes fluid that mixes with sperm and nourishes them
prostate gland: secretes fluid which makes semen alkaline
urethra: transports sperm and urine out of the body
penis: made of erectile tissue which enables sexual intercourse
female reproductive system
stages of menstrual cycle diagram
