Unit 6.6- Homeostasis and Sexual Reproduction Flashcards
Response to high blood glucose
Insulin secreted by beta cells - stimulates the liver and muscle cells to absorb glucose and convert it to glycogen - granules of glycogen are stores in these cells and other cells are stimulated to absorb glucose and use it in cell resp instead of fat.
Blood glucose concentration
usually kept between 4 and 8 millimoles per dm*3 of blood. Cells in the pancreas monitor the concentration and secrete the hormone insulin and glucagon when levels are high or low.
Responses to low blood glucose levels
Glucagon is secreted by alpha cells - stimulated the liver to breakdown glycogen into glucose and release the glucose raising blood levels
Diabetes
in some people the control of glucose does not work affectively and the concentration can rise or fall beyond the normal limits - diabetes mellitus
Type 1 diabetes
onset is usually during childhood, immune system destroys beta cells in the pancreas so the amount of insulin secreted becomes insufficient. Blood glucose levels have to be measured regularly and insulin injections are used to control levels. Diet cannot by itself control this type of diabetes
Type 2 diabetes
onset usually after childhood, target cells become insensitive to insulin so insulin injections are not effective treatment. Low carb diets can control the condition, various risk factors increase the rate particularly diets rich in fat and low in fibre
Thyroxin
secreted by the thyroid gland in the neck (unusual structure as thyroxin molecule contains four atoms of iodine. Prolonged deficiency of iodine in the diet therefore prevents synthesis of thyroxin. Hormones also unusual as almost all cells in body are target cells as thyroxin regulates body’s metabolic rate so all cells need to respond but most metabolically active (liver muscle and brain) main targets - higher metabolic rate supports more protein synthesis and growth and increases generation of body heat.
Role of thyroxin in heat generation
implicated in heat generation by shivering and by uncoupled cell resp in brown adipose tissue - in person with normal physiology , cooling triggers increase thyroxin secretion by the thyroid gland which stimulated heat production - thyroxin can constriction of vessels that carry blood for the core to skin
Leptin and Obesity
strain of mice was discovered in the 1950’s that feed ravenously. becoming inactive and gain mass through adipose tissue - breeding experiments showed that the obese mice had two copies of a recessive allele. In early 1990’s it was discovered that the wild-type allele of this gene supported the synthesis of a new hormone (leptin)
Leptin
Leptin is protein secreted by adipose cells - if amount of adipose tissue increases the concentration of leptin also increases - target of the hormone is groups of cells in hypothalamus of the brain that contributes to the control of appetite. Leptin binds to receptors in membrane causing long term appetite inhibition and reduced food intake
mice experiment for leptin
ob mice were injected with leptin and their appetite declined, energy expenditure increased and body mass decreased by 30% in a month. Trials were therefore done to see if leptin would control obesity in humans. mass was lost in those using leptin but was quickly regained afterwards.
Melatonin and Jet lag
humans are adapted to live in a 24hour cycle and have circadian rhythms in behaviour that fit this cycle - ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei in the hypothalamus- Neurons in the SCN control secretion of the hormone melatonin by the pineal gland. Melatonin secretion increases in the evening and drops to a low level at dawn.
Graph of melatonin
melatonin secretion declines with age helping to explain how sleep patters become more irregular as we grow older
Jet Lag symptoms
circadian rhythms are disrupted by travelling rapidly between time zones - symptoms : sleep disturbance, headaches, fatigue, irritability -
caused by the pineal gland continuing to set a circadian rhythm to suit the timing of day and night at the point of departure rather than the destination. This only lasts for a few days, during which time impulses sent by the ganglion cells to the SCN when they detect light help the body to adjust to the new regime
Use of Melatonin
sometimes used to try to prevent or reduce jet lag- It is taken orally at the time when sleep should ideally by commencing - most trials of melatonin have shown that it is effective at promoting sleep and helping reduce jet lag
Female reproductive systems
ovary (produces eggs estrogen and progesterone), oviduct (collects eggs at ovulation, provides a site for fertilisation then moves the embryo to the uterus) , cervix, (protects the fetus during pregnancy and then dilates to provide a birth canal), uterus (provides protection, food, oxygen and removal of waste products for the fetus during pregnancy), bladder , urethra, vulva (protects internal parts of the female reproductive systems), large intestine, vagina (stimulates penis to cause ejaculation and birth canal)
Sex determination
human reproduction involves the fusion of a sperm and an egg - embryos all initially develop in a similar way. Embryonic gonads are formed that could become either ovaries or testes. Presence of absence of a single gene decides which development pathway is formed. this gene codes for TDF, a gene regulation protein. By binding to specific DNA sites TDF stimulates the expression of gene for testis development.
SRY
present in an embryo if the sex chromosomes are XY the embryonic gonads therefore develop into testes and the fetus becomes male.
SRY
abesnt in an embryo if the sex chromosomes are XX. TDF is therefore not produced so the embryonic gonads develop as ovaries and the fetus becomes female
The Male reproductive system
bladder, seminal vesicle (secretes an alkaline fluid at the end of ejaculation containing proteins that make semen sticky), sperm duct (transfers sperm during ejaculation), erectile tissue, penis (has erectile tissue that becomes enlarged and hard allowing penetration of the vagina, urethra (transfers semen during ejaculation and urine during urination), foreskin, testis (produces sperm and testosterone), scrotum (holds testes at lower than core body temperature), epididymis (stores sperm until ejaculation), prostate gland (secretes an alkaline fluid that is added to sperm at the start of ejaculation and helps sperm to swim)
Steroid Hormones
Testosterone, estrogen and progesterone are all steroids.
Testosterone
produced by developing testes in the fetus, it causes pre-natal development of male genitalia, including the penis, sperm duct and prostate gland. During puberty testosterone production increases. It stimulates development of male secondary characteristics during puberty, including growth of the testes, penis and pubis hair. Testosterone also stimulates sperm production from puberty onwards.
Estrogen
causes pre-natal development of female reproductive organs if testosterone is not present, These organs include the oviduct, uterus and vagina. Raised levels of estrogen during puberty cause development of female secondary characteristics including growth of breasts and pubic hair
Progesterone
prepares the uterus during the menstrual cycle for the implantation of an embryo and has important roles in supporting a pregnancy
