Human Physiology: 6.6 Homeostasis

Question 1

Explain the function of insulin hormone

Answer 1

When blood glucose levels are high (e.g. after feeding):

Insulin is released from beta (β) cells of the pancreas and cause a decrease in blood glucose concentration
This may involve stimulating glycogen synthesis in the liver (glycogenesis), promoting glucose uptake by the liver and adipose tissue, or increasing the rate of glucose breakdown (by increasing cell respiration rates)

Question 2

Explain the function of glucagon hormone

Answer 2

When blood glucose levels are low (e.g. after exercise):

Glucagon is released from alpha (α) cells of the pancreas and cause an increase in blood glucose concentration
This may involve stimulating glycogen breakdown in the liver (glycogenolysis), promoting glucose release by the liver and adipose tissue, or decreasing the rate of glucose breakdown (by reducing cell respiration rates)

Question 3

What is diabetes

Answer 3

Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated
In individuals with diabetes their insulin function is disrupted which allows the glucose concentration in the blood to rise

Question 3

DIscuss the symptoms observed in diabetes

Answer 3

An elevated blood glucose level can lead to noticeable symptoms, some of which are harmful, e.g.
The kidneys are unable to filter out this excess glucose in the blood and so it is often present in the urine
The increased glucose concentration also causes the kidneys to produce large quantities of urine, making the individual feel thirsty due to dehydration
Continuously elevated blood glucose levels can also damage tissues, in particular their proteins

Question 4

What is type 1 diabetes? When does it occur, what it is and what causes it?

Answer 4

Type 1 diabetes is a condition in which the pancreas fails to produce sufficient insulin to control blood glucose levels
It normally begins in childhood due to an autoimmune response whereby the body’s immune system attacks the β cells of the islets of Langerhans in the pancreas

Question 5

What is the consequence of diabetes type 1?

Answer 5

Insulin causes the cells to take up glucose from the blood for respiration and for storage as glycogen; without insulin the glucose remains in the blood, resulting in an individual feeling fatigued
If the blood glucose concentration reaches a dangerously high level after a meal then organ damage can occur

Question 6

How is diabetes type 1 treated?

Answer 6

Type 1 diabetes is normally treated with regular blood tests to check glucose levels, insulin injections and a diabetes appropriate diet
Health authorities encourage type I diabetics to eat a similar diet to the general public. They suggest five portions of fruit and veg a day, minimally processed food and consuming more polysaccharides than monosaccharides or disaccharides
The insulin used by diabetics can be fast-acting or slow-acting; each allowing for a different level of control

Question 7

What is type 2 diabetes? When does it occur?

Answer 7

Type II diabetes is more common than type I
It usually develops in those aged 40 and over, however more and more young people are developing the condition
In type II diabetes the pancreas still produces insulin but the receptors have reduced in number or no longer respond to it

Question 8

What is the consequence of diabetes type 2?

Answer 8

The lack of response to insulin means there is a reduced glucose uptake by the cells, which leads to a high blood glucose concentration
This can cause the β cells to produce more and more insulin in the attempt to lower blood glucose levels
Eventually the β cells can no longer produce enough insulin and blood sugar becomes uncontrollable

Question 9

How is diabetes type 2 treated?

Answer 9

For type II diabetes treatment involves a sugar and fat controlled diet and an exercise regime
Any food that is rapidly digested into sugar will cause a sudden, dangerous spike in blood sugar
Obesity is a major risk factor for type II diabetes

Question 10

What is thyroxin?

Answer 10

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

Question 11

What is the primary role of thyroxin?

Answer 11

The primary role of thyroxin is to increase the basal metabolic rate (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 acid

Question 12

What is the secondary function of thyroxin?

Answer 12

A consequence of increasing 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

Question 13

What is the result of thyroxine deficiency? symptoms

Answer 13

Thyroxin deficiency, caused by a condition known as hypothyroidism, has the following effects on the body:
Lack of energy
Low mood
Forgetfulness
Weight gain- Less glucose and fat is broken down by cellular respiration to release energy
Constantly feeling cold- Less heat is generated by respiration
Constipation- Muscular contractions in the gut wall slow down due to reduced energy from respiration
Impaired brain development in children

Question 14

What is Leptin? What is its function and how does it do it/?

Answer 14

Leptin is a hormone produced by adipose cells that regulates fat stores within the body by suppressing appetite

Leptin binds to receptors located within the hypothalamus to inhibit appetite and thereby reduce food intak

Question 14

What is Leptin? What is its function and how does it do it/?

Answer 14

Leptin is a hormone produced by adipose cells that regulates fat stores within the body by suppressing appetite

Leptin binds to receptors located within the hypothalamus to inhibit appetite and thereby reduce food intak

Question 15

How does leptin act during overeating and starvation?

Answer 15

Overeating causes more adipose cells to formed and hence more leptin is produced, suppressing further appetite

Conversely, periods of starvation lead to a reduction in adipose tissue and hence less leptin is released, triggering hunger

Question 16

What happens to leptin function in obese people?

Answer 16

As obese people are constantly producing higher levels of leptin, their body becomes progressively desensitised to the hormone

This means they are more likely to feel hungry, less likely to recognise when they are full and are hence more likely to overeat
Leptin resistance also develops with age, increasing the potential for weight gain later in life (e.g. the ‘middle-age spread’)

Question 17

Why was leptin tested for clinical obesity?

Answer 17

Because leptin suppresses appetite, it was considered as a form of treatment for individuals with clinical obesity

Theoretically, leptin injections would reduce hunger and limit food intake in obese individuals, leading to weight loss

Question 18

What was the first experiment conducted with leptin?

Answer 18

The experiment was conducted with mice first:
Mice with a genetic leptin deficiency were shown to be less active and to gain weight faster than mice without this deficiency
Individuals with leptin deficiency lost 30% of their body mass when injected with leptin

Question 19

Why were leptin injections ineffective in humans?

Answer 19

Most humans have naturally high levels of leptin in the bloodstream

When linked to leptin activity, most cases of obesity are caused by an unresponsiveness to leptin and not a leptin deficiency
Hence, in clinical trials, very few participants experienced significant weight loss in response to leptin injections
However, many patients did experience adverse side effects from leptin injections, including skin irritations
For these reasons, leptin treatments are not considered to be an effective way of controlling obesity

Question 20

What is melatonin and what controls its secretion?

Answer 20

Melatonin is a hormone produced by the pineal gland within the brain in response to changes in light

Light exposure to the retina is relayed via the suprachiasmatic nucleus (in the hypothalamus) and inhibits melatonin secretion
Melatonin is therefore secreted in response to periods of darkness, resulting in higher concentrations at night

Question 21

What is the role of melatonin?

Answer 21

In humans, many circadian rhythms are influenced by the hormone melatonin

Although melatonin affects many aspects of human physiology and behaviour, one of the main circadian rhythms it controls is our sleep-wake cycle
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)
Decreasing melatonin levels lead to the body’s preparation for waking up and staying awake during the day

Question 22

What other physiological changes occur due to melatonin?

Answer 22

Increased melatonin at night contributes to the night-time drop in core body temperature in humans
Melatonin receptors in the kidney enable melatonin produced at night to cause the night-time decrease in urine production in humans

Question 23

What causes jet lag

Answer 23

Jet lag is a physiological condition resulting from a change to the body’s normal circadian rhythm

This alteration is caused by the body’s inability to rapidly adjust to a new time zone following extended air travel (‘jet’ lag)
The pineal gland continues to secrete melatonin according to the old time zone so that the sleep schedule is not synchronised to the new timezone

Question 24

Symptoms of jet lag

Answer 24

As a result of these sleep disturbances, individuals suffering from jet lag will often experience symptoms associated with fatigue

Symptoms of jet lag include headaches, lethargy, increased irritability and reduced cognitive function
Jet lag should only last a few days and symptoms should resolve as the body resynchronises its circadian rhythm

Question 25

What is a quick solution to jet lag?

Answer 25

Some health professionals recommend taking melatonin near the sleep time of the new time zone to help recalibrate the body

By artificially increasing melatonin levels at the new night time, the body can respond quicker to the new day-night schedule

Question 26

What was one of the earliest theory about animals reproducing sexually?

Answer 26

One of the earliest theories as to how animals reproduce sexually was the ‘soil and seed’ theory proposed by Aristotle

According to this theory, the male produces a ‘seed’ which forms an ‘egg’ when mixed with menstrual blood (the ‘soil’)
The ‘egg’ then develops into a fetus inside the mother according to the information contained within the male ‘seed’ alone

Question 27

How did William Harvey debunk the earlier theory about animal sexual reproduction?

Answer 27

he ‘soil and seed’ theory was a popular doctrine for hundreds of years before it was eventually debunked by William Harvey

William Harvey studied the sexual organs of female deer after mating in an effort to identify the developing embryo
He was unable to detect a growing embryo until approximately 6 – 7 weeks after mating had occurred
He concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus
Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly asserted that the fetus did not develop from a mixture of male and female ‘seeds’

Question 28

What causes male sex development and female sex development to take place?

Answer 28

The Y chromosome (males have XY sex chromosomes) includes a gene called the SRY gene (Sex Determining Region Y), which leads to male development

The SRY gene codes for a testis-determining factor (TDF) that causes embryonic gonads to form into testes (male gonads)
In the absence of the TDF protein (i.e. no Y chromosome), the embryonic gonads will develop into ovaries (female gonads)

Question 29

What is the role of testosterone?

Answer 29

The main male reproductive hormone is testosterone, which is secreted by the testes and serves a number of roles:

It is responsible for the pre-natal development of male genitalia
It is involved in sperm production following the onset of puberty
It aids in the development of secondary sex characteristics (including body and facial hair, muscle mass, deepening of voice, etc.)
It helps to maintain the male sex drive (libido)

Question 30

What is the role of estrogen and progesterone?

Answer 30

The main female reproductive hormones (secreted by the ovaries) are estrogen and progesterone, which serve several roles:

They promote the pre-natal development of the female reproductive organs
They are responsible for the development of secondary sex characteristics (including body hair, deposition of fat under buttocks and thighs, pelvis widening, and breast development)
They are involved in monthly preparation of egg release following puberty (via the menstrual cycle)

Initially, estrogen and progesterone are secreted by the mother’s ovaries and then the placenta – until female reproductive organs develop (this occurs in the absence of testosterone)

Question 31

State all the structures of the male reproductive system along with function

Answer 31

Testis- The testis (plural: testes) is responsible for the production of sperm and testosterone (male sex hormone)

Epididymis- Site where sperm matures and develops the ability to be motile (i.e. ‘swim’) – mature sperm is stored here until ejaculation

Vas Deference- Long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation

Seminal Vesicle- Secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm) and prostaglandin (triggers uterine contractions)

Prostate Gland- Secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability)

Urethra- Conducts sperm / semen from the prostate gland to the outside of the body via the penis (also used to convey urine)

Question 31

State all the structures of the female reproductive system along with function

Answer 31

Ovary- The ovary is where oocytes mature prior to release (ovulation) – it also responsible for estrogen and progesterone secretion

Fimbria- Fimbria (plural: fimbriae) are a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct

Oviduct- The oviduct (or fallopian tube) transports the oocyte to the uterus – it is also typically where fertilisation occurs

Uterus- The uterus is the organ where a fertilised egg will implant and develop (becoming an embryo)

Endometrium- The mucous membrane lining of the uterus, it thickens in preparation for implantation or is otherwise lost (via menstruation)

Vagina- Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)

Question 32

There are two key groups of hormones which control and coordinate the menstrual cycle:

Answer 32

Pituitary hormones (FSH and LH) are released from the anterior pituitary gland and act on the ovaries to develop follicles
Ovarian hormones (estrogen and progesterone) are released from the ovaries and act on the uterus to prepare for pregnancy

Question 33

Describe the first stage of the menstrual cycle

Answer 33

1. Follicular Phase

Follicle stimulating hormone (FSH) is secreted from the anterior pituitary and stimulates growth of ovarian follicles
The dominant follicle produces estrogen, which inhibits FSH secretion (negative feedback) to prevent other follicles growing
Estrogen acts on the uterus to stimulate the thickening of the endometrial layer

Question 34

Describe the second stage of the menstrual cycle

Answer 34

2. Ovulation

Midway through the cycle (~ day 12), estrogen stimulates the anterior pituitary to secrete hormones (positive feedback)
This positive feedback results in a large surge of luteinizing hormone (LH) and a lesser surge of FSH
LH causes the dominant follicle to rupture and release an egg (secondary oocyte) – this is called ovulation

Question 35

Describe the third stage of the menstrual cycle

Answer 35

3. Luteal Phase

The ruptured follicle develops into a slowly degenerating corpus luteum
The corpus luteum secretes high levels of progesterone, as well as lower levels of oestrogen
Estrogen and progesterone act on the uterus to thicken the endometrial lining (in preparation for pregnancy)
Estrogen and progesterone also inhibit secretion of FSH and LH, preventing any follicles from developing

Question 36

Describe the fourth stage of the menstrual cycle

Answer 36

If fertilisation occurs, the developing embryo will implant in the endometrium and release hormones to sustain the corpus luteum
If fertilisation doesn’t occur, the corpus luteum eventually degenerates (forming a corpus albicans after ~ 2 weeks)
When the corpus luteum degenerates, estrogen and progesteron levels drop and the endometrium can no longer be maintained
The endometrial layer breaks down and eliminated from the body as menstrual blood (i.e. a woman’s period)
As estrogen and progesterone levels are too now low to inhibit the anterior pituitary, the cycle can now begin again

Question 37

In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = ‘in glass’). Outline the first process of down regulation

Answer 37

Down regulation

Drugs are used to halt the regular secretion of FSH and LH – this in turn stops the secretion of estrogen and progesterone
By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries
The drug treatment usually takes about two weeks and is typically delivered in the form of a nasal spray

Question 38

In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = ‘in glass’). Outline the second process of super-ovulation

Answer 38

Superovulation involves using artificial doses of hormones to develop and collect multiple eggs from the woman
The patient is firstly injected with large amounts of FSH to stimulate the development of many follicles
The follicles are then treated with human chorionic gonadotrophin (hCG) – a hormone usually produced by a developing embryo
hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing

Question 39

In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = ‘in glass’). Outline the third process of Fertilisation

Answer 39

The extracted eggs are then incubated in the presence of a sperm sample from the male donor
The eggs are then analysed under a microscope for successful fertilisation

Question 40

In vitro fertilisation (IVF) refers to fertilisation that occurs outside of the body (in vitro = ‘in glass’). Outline the final process of Implantation

Answer 40

Approximately two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium
Healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate)
Multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome)
Roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful