6.6 Hormones, homeostasis, and reproduction Flashcards
Diagram showing the organs involved in the production of hormones needed to maintain homeostasis
What are the limits bewteen which blood glucose need to be kept?
For most people those values are between 70 to 130 milligrams per decilitre (mg/dl).
Why do blood gluose values need to be kept within certain limits?
Your body needs to maintain these values so that your blood has a certain osmotic balance; as well as ensuring that the cells of your body, especially your brain cells, have an ample supply of glucose for cellular respiration.
What happens if sensors detect blood glucose levels that are above or below the required limits?
Two hormones, insulin and glucagon, are produced by the Islets of Langerhans in the pancreas and are responsible for maintaining and controlling blood glucose concentrations.
What hormone is secreted when blood glucose level is higher than normal and what effect does this have on blood glucose concentration?
- Hormone: Insulin – produced and secreted by β-cells of Islets of Langerhans in the pancreas.
- Effect: Levels fall : insulin stimulates glucose uptake into muscles and liver cells, where it is converted into glycogen.
What hormone is secreted when blood glucose level is lower than normal and what effect does this have on blood glucose concentration?
- Hormone: Glucagon – produced and secreted by α-cells of Islets of Langerhans in the pancreas.
- Effect: Levels rise : Glucagon stimulates glycogen hydrolysis to glucose in the liver, which in turn releases glucose into the blood.
Describe the endocrine and exocrine functions of the pancreas
- The pancreas has both exocrine and endocrine functions.
- As an exocrine gland (gland associated with a duct), it secretes enzymes that help in digestion; while as an endocrine gland (ductless gland) it secretes hormones that regulate blood sugar levels.
Diagram showing control of blood glucose by insulin and glucagon
What is the difference between glucagon and glycogen?
- Glucagon is a protein-based hormone released from the pancreas.
- Glycogen is not a hormone; it is a carbohydrate found in the liver that is the form that glucose takes when stored there.
Symptoms of diabetes
- In patients with this disease, the blood glucose levels are consistently too high and their urine has elevated glucose levels.
- Other symptoms include frequent urination, increased thirst, and hunger.
Graph showing the blood glucose concentration after a meal in pre-diabetic and diabetic patients compared with a control group.
It is clear that it takes the most time for the blood glucose level to come back to normal in diabetics, followed by pre-diabetics.
What serious long-term complications can diabetes lead to if left untreated?
Heart disease, kidney failure and retinal damage
What are the two types of diabetes?
- Type 1
- Type 2
Type I diabetes
- Type I results from the body’s failure to produce sufficient insulin.
- Sometimes this form of diabetes is referred to as insulin-dependent diabetes mellitus (IDDM) or juvenile diabetes.
- It is caused by the destruction of beta cells (autoimmune)
Type II diabetes
- Type II results from insulin resistance, a condition in which body cells fail to use insulin properly.
- It often begins later in life.
- Prolonged overproduction of insulin leads to desensitization of the insulin receptors, so glucose is not removed from the bloodstream.
Describe the treatment of Type I diabetes
This involves injecting insulin into the body on a daily basis.
Describe the treatment of Type II diabetes
It may be treated by eating food with low levels of carbohydrates, eating frequent but small meals and doing strenuous exercise, as well as losing weight.
Analysis of a blood sample from someone who had not eaten for 24 hours would be expected to reveal high levels of ___
Glucagon
Someone who fasts does not get enough glucose, so the body needs to produce glucose itself from the glycogen stores in the liver. Glucagon stimulates the conversion of glycogen to glucose.
What happens when the β-cells of the pancreas release insulin into the blood?
The skeletal muscles and liver take up glucose at a faster rate.
Insulin has the effect of lowering blood glucose by increasing glucose uptake in the muscles and the liver, where it is converted into glycogen.
In a diabetic patient, blood glucose levels after a meal would return to normal more ___ than in a non-diabetic patient.
Slowly
Because diabetic patients either do not make, or do not respond to insulin, blood sugar after a meal would rise quickly to a higher level than normal and decrease slowly as insulin cannot remove glucose from the blood effectively.
In a diabetic patient, blood glucose levels after a meal would ___
Return to normal more slowly than in a non-diabetic patient.
Because diabetic patients either do not make, or do not respond to insulin, blood sugar after a meal would rise quickly to a higher level than normal and decrease slowly as insulin cannot remove glucose from the blood effectively.
What is thyroxin?
The main hormone that regulates your metabolism and body temperature.
Where is thyroxin produced?
In the thyroid gland
Thyroxin
- Thyroxin is a hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus
- Thyroxin acts on nearly every tissue in the body and is essential to the proper development and differentiation of cells
- The primary role of thyroxin is to increase the basal metabolic rate (the amount of energy the body uses at rest)
- This can be achieved by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids
- A consequence of increased metabolic activity is the production of heat – hence thyroxin helps to control body temperature
- Thyroxin is released in response to a decrease in body temperature in order to stimulate heat production
- Thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin
- Iodine deficiency will cause the thyroid gland to become enlarged, resulting in a disease known as goitre
What are some of the effects of thyroxine?
- Increased rate of utilization of foods for energy
- Increased breathing rate to obtain oxygen and get rid of carbon dioxide
- Increased rate of protein synthesis and protein catabolism
- Increased number and size of mitochondria in most cells of the body
- Increased growth rate of children and adolescents
- Growth and development of the brain during fetal life and for the first few years of post-natal life
- Enhanced carbohydrate metabolism
- Enhanced fat metabolism.
How can goitre be treated?
By consuming iodine tablets
What are the symptoms of thyroxine deficiency (low thyroxine concentration in the blood)
- Fatigue
- Depression
- Forgetfulness
- Feeling cold
- Constipation
What can thyroxine deficiency lead to in young children?
Impaired brain development
Iodine is added to table salt to help prevent deficiencies of an essential mineral needed for the proper function of the ___
Thyroid gland
If the body temperature drops below normal, the thyroid gland helps to control the body temperature by producing ___
More thyroxine
History of being overweight
- We have evolved systems to prevent the frequent overeating that leads to obesity.
- During the era that humans were still hunters and gatherers, being overweight would increase your chances of becoming prey yourself.
- Besides, excessive food intake in those days would have been far more difficult than today, where there is, at least in some parts of the world, access to large amounts of food, some of it of poor nutritional quality.
What are adipose tissues?
Fatty tissues mainly composed of fat cells (adipocytes) that are specialised in the synthesis and storage of fat globules.
What is leptin?
A hormone produced and secreted by cells in adipose tissues (these tissues store lipids in your body).
What are the two factors that control blood leptin concentration?
- Food intake
- The number of adipose tissues in the body.
Where are leptin receptors found?
In the hypothalamus of the brain.
What happens when leptin binds to leptin receptors in the hypothalamus of the brain?
It causes appetite inhibition.
What happens when fat mass decreases?
- When fat mass decreases, the level of plasma leptin falls (that is, only a few of the leptin receptors bind to leptin in the hypothalamus) so that appetite is stimulated until the fat mass is recovered.
- There is also a decrease in body temperature and energy expenditure is suppressed.
What happens when fat mass increases?
- When fat mass increases, such as in the case of weight gain, so do leptin levels and appetite is suppressed until weight loss occurs.
- In this way, leptin regulates energy intake and fat stores so that weight is maintained within a relatively narrow range.
Diagram showing the conditions that affect the level of leptin production and action in the body
What kind of mice were discovered in the 1950s?
- In the 1950s, a strain of mice was discovered with a mutation that made the mice greedy.
- These mice quickly became obese. Instead of a normal mass range of 20–25 g, these mice had a mass of up to 100 g.
- The equivalent in humans would be males with a mass between 320–350 kg.
What was found out about the obese mice?
- It turned out that these mice were homozygous for the ob (stands for obese) allele.
- Mice with two of the recessive alleles cannot produce leptin and have no appetite inhibition, so they eat voraciously.
- In further experiments, the ob/ob mice were given injections of leptin, and their body mass was reduced by about 30% within a month.
How was the effect of leptin injections different in humans than in mice?
- Although the leptin injections appeared to work in mice, they did not have the same effect when tested on humans.
- A small subset of people are also homozygous for the ob allele and these people are frequently obese.
- In a double-blind trial (neither researchers nor patients knew if they are given a placebo or the real drug), the results were disappointing, as some participants did lose body mass but others gained in mass.
- Furthermore, any loss in mass was quickly regained after the trial was stopped.
- Human physiology seems to be more complex than that of mice.
Why did leptin not have the same effect in humans as it did in mice?
- Unlike mice, obese people have very high leptin levels in their blood.
- This implies that receptor cells in the hypothalamus may no longer be sensitive and responsive to leptin, thus they do not induce appetite inhibition.
What still needs to be found out about leptin?
- Although it is known that leptin is essential for normal body weight balance, the exact mechanisms by which it activates hypothalamic neurons to suppress appetite are not yet fully understood.
- In order to find pharmaceutical approaches to treating obesity, further studies are required to understand the exact mechanisms by which leptin lowers body weight and the role leptin and leptin receptors have in the development of obesity in humans.
Leptin is a hormone that is released from ___
Adipose tissue
How does the body keep track of a circadian rhythm and know the day/night pattern?
- Through the controlled secretion of a hormone called melatonin from the pineal gland.
- Melatonin levels are high at night and low during the day.
When are melatonin levels high and low?
High during the night and low during the day
What is the pineal gland?
- A small endocrine gland found near the center of the brain between the two hemispheres.
- It is reddish-grey and shaped like a pine cone about 0.8 cm long.
Melatonin
- Melatonin is the hormone responsible for synchronizing circadian rhythms and regulates the body’s sleep schedule
- Melatonin secretion is suppressed by bright light (principally blue wavelengths) and hence levels increase during the night
- Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day
- Melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans)
- During sleep, necessary physiological changes occur in body temperature, brain wave activity, and hormonal production
- Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly
Why does the day/night cycle completely reversing not happen to those living outside the cave?
- Because of certain receptor cells in the retina that signal dawn and dusk to the pineal gland.
- Actually, the impulses from the retina are first channeled to a group of cells in your anterior hypothalamus named the suprachiasmatic nuclei (SCN), which then pass on the information to the pineal gland.
- The pineal gland then adapts the melatonin concentrations in the blood to coincide with a normal 24-hour cycle.
Negative feedback loop in the regulation of melatonin
Melatonin receptors are also present on the neurons of the suprachiasmatic nuclei of most species, implying the possible involvement of a negative feedback loop in the regulation of melatonin.
Where is melatonin synthesized and what factor has a negative effect on its release?
- Melatonin is synthesized from the amino acid tryptophan and its production is dictated by light.
- Exposure to light has a negative effect on the release of melatonin.
How does your body react to melatonin?
Your body core temperature drops and receptors in the kidney cause decreased urine production, all of which increases sleepiness.
Why is some readjustment needed when you travel?
- When you travel between time zones, the level of light you are exposed to is no longer matched up with the levels of melatonin in your body.
- Thus, in the first few days, some readjustment is needed to ensure that melatonin production matches the light and dark period of your current time zone.
- After this period, your body will be tuned to a normal sleep/wake cycle again.
Diagram of the female reproductive system (side view)
Diagram of the female reproductive system (front view)
Diagram of the male reproductive system (side view)
Diagram of the male reproductive system (front view)
Which labeled structures represent the epididymis and the prostate gland?
I: epididymis
IV: prostate gland
Women should periodically have a Pap smear test performed to detect cervical cancer.
Which roman numeral indicates the cervix in the diagram below?
iii
Diagram showing the levels of the ovarian and pituitary hormones, as well as the changes in the lining of the uterus and in the ovaries.
Diagram showing the steps of in vitro fertilization
