Hormones Flashcards
What are hormones?
They are chemical messengers that are secreted by endocrine glands directly into the blood transported by the blood to target cells, where they elicit a response.
What hormones are secreted by the pineal gland?
Melatonin
What hormones are secreted by the pituitary gland?
LH and FSH, ADH, oxytocin, prolactin
What hormones are secreted by the thyroid gland?
Thyroxin
What hormones are secreted by the pancreas?
Insulin, glucagon
What hormones are secreted by the adrenal glands?
Epinephrine
What hormones are secreted by the ovaries?
Oestrogen, progesterone
What hormones are secreted by the testes?
Testosterone
What is the negative feedback?
It has a stabilizing effect because a change in levels cause the opposite change. A rise in levels back to decrease production and reduce the levels. A decrease in levels feeds back to increase production and raise the levels.
What is positive feedback?
Leads to sudden rises or falls, because a rise causes further rise and a fall causes further fall.
What is homeostasis?
It is keeping the conditions inside the organism within tolerable limits.
What are the two glands in the pancreas?
Exocrine gland
Endocrine gland- pancreatic islets/ islets of Langerhans that secrete hormones into the blood.
What are the two types of cells in islets?
Alpha and beta
Describe the regulation of blood glucose levels
- If blood glucose concentration falls too low, alpha cells in the pancreas synthesize and secrete the hormone glucagon into the blood
- Glucagon stimulates liver cells to hydrolyse glycogen into glucose and release glucose into the blood.
- If blood glucose concentration rises too high, beta cells in the pancreas synthesise and secrete the hormone insulin into the blood
Describe Type I diabetes
It is called early onset because it usually first appears during childhood. It is an autoimmune disease in which the immune system destroys the beta cells of the pancreas. Thus, insulin is not produced in sufficient quantities. The causes of the autoimmune disease are unknown. It is treated by injecting insulin when glucose is too high.
What other health problems can diabetes cause?
Atherosclerosis
Coronary heart disease
Hypertension
Describe type II diabetes
It is called late onset because its onset is usually after childhood. It is characterised by the inability of cells to respond to insulin. The main risk factors are diets rich in carbohydrates and fat, prolonged obesity, together with genetic factors. Cells are insensitive to insulin, so insulin injections do not help. Monitoring diet and exercise helps.
What does the hormone thyroxine do?
It regulates the metabolic rate and helps control body temperature
What monitors body temperature?
The hypothalamus
Which cells do thyroxine target?
Almost all cells. The most metabolically active such as liver, muscle, and brain are the main targets
What does thyroxin do?
Increases the metabolic rate and a higher metabolic rate supports more protein synthesis and increases the generation of body heat.
How does thyroxin control body temperature?
Regulation respiration in brown adipose tissue
Vasoconstriction of skin arterioles and shivering
What happens when the temperature drops?
The hypothalamus instructs the thyroid to secrete more thyroxin. This leads to increased metabolic rate, uncoupled cell respiration in BAT and shivering. And vasoconstriction of akin arterioles.
What does thyroxin exhibit?
It exerts negative feedback control over the hypothalaus
What is hypothyroidism?
The condition in which not enough thyroxin is made.
What can hypothyroidism lead to?
Goitre- swelling of the neck due to enlarged thyroid.
How is the importance of thyroxin revealed by the variety of symptoms of hypothyroidism?
- Lack of energy
- Weigh gain
- Feeling cold
- Forgetfulness and depression
- Constipation
- Impaired brain development in children
How many atoms of iodine does a molecule of thyroxin contain?
4 atoms of iodine
What does the hormone leptin do?
It is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite
How is the blood concentration of leptin controlled?
By food intake and amount of adipose tissue
How is leptin discovered?
In the 50s a strain of mice was discovered that feed ravenously and gain body mass, mainly through increased adipose tissue
The obese mice have two copies of the recessive allele ob. The wild-type allele of this gene codes for leptin. Therefore, the homozygous ob/ob mice do not produce leptin. When ob/ob mice were injected with leptin, their appetite declines and body mass dropped significantly.
What does the hormone melatonin do?
Controls the circadian rhythms- rhythms in physiology and behaviour that fit this cycle
How is the daily rhythm set?
Set be cells in a region of the hypothalamus called the suprachiasmatic nuclei (SCN)
Describe how melatonin works
Ganglion cells in the retina detect if it is light or dark and send impulses to neurons in the SCN, which in turn control melatonin secretion by the pineal gland. Melatonin secretion increases in the evening and drops at dawn. High melatonin promotes sleep. Melatonin secretion declines with age.
What is jet lag?
A condition caused by crossing rapidly 2 or 3 time zones
How is jet lag caused?
caused because SCN and pineal gland continue to set the rhythm to suit the timing at the point of departure. Only lasts for few days, during which impulses are sent from ganglion cells to SCN when they detect light to help the body adjust the new regime.
Define endocrine glands
Ductless glands that secrete hormones directly into the blood
What doe hormones act on?
Target protein receptor
What are steroid hormones?
They are lipid-soluble so they enter target cells by freely diffusion through the plasma membrane. ATP is not needed.
Describe how steroid hormones work
-They bind to receptor proteins in the cytoplasm or nucleus to form a hormone- receptor complex
- The hormone-receptor complex moves to the nucleus and acts as a transcription factor. It binds to the DNA and regulates gene expression: promotes or inhibits the transcription of specific genes
- Steroid hormones control whether or not specific enzymes and other proteins are synthesised and help control the activity of the target cells
Describe how peptide hormones work
They bind to protein receptors in the plasma membrane of target cells (need ATP). The binding of the hormone causes the release of a secondary messenger inside the cell. Secondary messengers are water soluble that quickly spread through the cytoplasm and trigger a cascade in the cytoplasm. The cascade usually involves activating or inhibiting enzymes and other proteins that regulate cell activity. The most common secondary messengers are Ca2+ and cyclic AMP. The use of second messengers enables the amplification of the initial signal
Describe the role of the hypothalamus in the endocrine system
The hypothalamus synthesises hormones and also controls hormone secretion by the pituitary gland located below it.
Describe the pituitary gland
Consists of two lobes- anterior lobe and posterior lobe
Hormones secreted by the pituitary gland control developmental changes, reproduction and homeostasis
Describe the anterior pituitary
Some neurosecretory cells in the hypothalamus secrete releasing factors into capillaries that join to form a portal blood vessel leading to capillaries in the anterior lobe of the pituitary gland. The releasing factors trigger secretion of hormones synthesised in the anterior pituitary gland, such as FSH, LH, GH and prolactin
Describe the posterior pituitary
Neurosecretory cells in the hypothalamus synthesise hormones which travel down the axons and are stored by nerve endings in the posterior pituitary gland, until impulses from the hypothalamus stimulate their secretion. Examples include oxytocin and ADH.
How is blood solute concentrations monitored?
By osmoreceptors in the hypothalamus If the receptors detect high solute concentration, impulses are sent along axons of neurosecretory cells causing ADH secretion to increase
What is growth hormone?
It is a peptide hormone produced and secreted by the anterior pituitary
What effects does growth hormone have?
It stimulates synthesis of protein and breakdown of fat, proliferation of cartilage cells, mineralisation of bone increase in muscle mass and growth of all organs
What is lactation?
The production and secretion of milk in mammary glands for feeding offspring.
What is prolactin?
It is produced and secreted by the anterior pituitary gland. It stimulates the growth of mammary glands and stimulates production of milk.
Describe the effect of oestrogen during pregnancy
High levels of oestrogen increase prolactin production but inhibit its effects on mammary glands. The abrupt decline in oestrogen following birth removes the inhibition and milk production begins.
Where is milk stored?
Stored in alveoli
What is oxytocin?
Stimulates the release of milk after it is produced. It is produced by the neurosecretory cells of the hypothalamus and is stored in the posterior pituitary gland.
What does oxytocin do?
Stimulates the contraction of cells that surround the alveoli leading to milk ejection. The physical stimulus of suckling by a baby stimulates oxytocin secretion and continuous production of prolactin.
What is IDD?
Iodine deficiency disorder
What are symptoms of IDD? Why?
goitre
Bc the thyroid gland is unable to produce thyroxin and the hypothalamus and pituitary continuously stimulate the thyroid resulting in cell enlargement
What does IDD during pregnancy cause?
Can affect the fetal nervous system development and can lead to mental retardation in children and maybe cretinism
