Tagged: adrenaline
Hormones: Grade 9 Understanding for IGCSE Biology 2.94 2.95B
Hormones are defined as “chemicals produced in endocrine glands that are secreted into the bloodstream and cause an effect on target tissues elsewhere in the body”. They play a wide variety of roles in the healthy functioning and development of the body.
The iGCSE specification only really mentions a small number of hormones so these are the ones I will focus on in this post.
ADH (anti-diuretic hormone) (Separate Biologists only – not Combined Science)
ADH is secreted into the blood by an endocrine gland at the base of the brain called the Pituitary Gland. The stimulus for the release of ADH into the blood comes from the hypothalamus (a region of brain right next to the pituitary gland) when it detects that the blood plasma is becoming too concentrated. This might be caused by the body becoming dehydrated due to sweating. ADH travels round the body in the blood until it reaches its target tissue which are the cells that line the collecting ducts in the nephrons in the kidney. ADH increases the permeability of the connecting duct walls to water, thus meaning more water is reabsorbed by osmosis from the urine in the collecting duct and back into the blood. This results in a small volume of concentrated urine being produced.
Adrenaline
Adrenaline is secreted into the blood by the adrenal glands in situations of danger or stress.. The adrenals are found just above the two kidneys on the back of the body wall. Adrenaline secretion is controlled by nerve cells that come from the central nervous system. Adrenaline is often described as the “fight or flight” hormone as its effects are to prepare the body to defend itself or run away from danger. There are receptors for adrenaline in many target tissues in the body but some of the most significant effects of adrenaline are:
- affects the pacemaker cells in the heart causing an increase in heart rate
- shifts the pattern of blood flow into muscles, skin and away from the intestines and other internal organs
- decreases peristalsis in the gut
- causes pupils to dilate in the eye
- increases breathing rate in the lungs
- promotes the passing of urine from the bladder
Insulin
Insulin is a hormone made in the islets of Langerhans in the pancreas. It plays a vital role in the homeostatic control of the blood sugar concentration. The pancreas will secrete insulin into the blood when the blood glucose concentration gets too high. There are many cells in the body with insulin receptors but the main target tissue for insulin is the liver.
Insulin causes the liver (and muscle) cells to take glucose out of the blood and convert it into the storage polysaccharide glycogen. This results in a lowering of the blood glucose concentration: a good example of the importance of the principle of negative feedback in homeostasis
Testosterone
Testosterone is a steroid hormone made by cells in the testes of males. It is the main hormone of puberty in males resulting in the growth of the reproductive organs at puberty as well as the secondary sexual characteristics (pitch of voice lowering, muscle growth stimulated, body hair grows etc.)
Oestrogen
Oestrogen is a steroid hormone made by the cells in the ovary that surround the developing egg cell in the first half of the menstrual cycle. In puberty it causes the development of the female secondary sexual characteristics (breast growth, change in body shape, pubic hair etc.) but in the menstrual cycle, oestrogen has a variety of important effects. It stimulates the rebuilding of the uterine endometrium (or lining) to prepare the uterus for the implantation of an embryo. Oestrogen also affects the pituitary gland and can cause the spike in LH concentrations that trigger ovulation on day 14 of the cycle.
Progesterone
Progesterone is also made in the ovary but at a different time in the menstrual cycle. It is secreted by cells in the corpus luteum, a structure found from day 14 onwards after the egg has been released in ovulation. Progesterone has two main target tissues: it maintains the thickened lining of the endometrium in the uterus ready for implantation. Progesterone also causes the pituitary gland to stop secreting the hormones FSH and LH so a new cycle is never started. It is for this reason that progesterone can be used in women as a contraceptive pill.
FSH (Follicle-Stimulating Hormone (Separate Biologists only – not Combined Science)
FSH is a hormone released by the pituitary gland underneath the brain. The target tissues for FSH are in the testis (males) and ovaries (females). In males FSH plays a role in the growth of the testes allowing sperm production to start. In females, FSH is the hormone released at the start of the menstrual cycle that causes one of the immature egg cells in an ovary to grow, develop and so become surrounded by follicle cells prior to ovulation.
LH (Luteinising Hormone) (Separate Biologists only – not Combined Science)
LH is a second reproductive hormone released by the pituitary gland into the bloodstream. In males, it stimulates the production of testosterone in the testes. In females, it is released only on days 13 and 14 of the menstrual cycle and it is the hormone that triggers ovulation.
Comparing Nervous and Hormonal Coordination: Grade 9 Understanding for IGCSE Biology 2.86
This topic requires you to understand how nervous and hormonal coordination compare and to understand the differences between the two systems.
Coordination is the life process by which organisms can detect and respond to a change in the environment. These changes in the environment that can be detected are called stimuli. A stimulus can be outside the body (e.g. the air temperature dropping) or internal (e.g. an increase in the concentration of glucose in the blood after a meal).
How do organisms detect and respond to stimuli?
There are two systems that can bring about coordination:
- Nervous System
- Hormonal System (also known as the Endocrine system)
The nervous system is made up of around 100 billion specialised cells called neurones. Neurones (nerve cells) are adapted in that they can transmit an electrical event called nerve impulse (or sometimes an action potential) rapidly from one end of the cell to the other. You should understand the simplest pattern of nervous coordination which is called a reflex arc.
The hormonal system works in a completely different way. There are no electrical impulses in the hormonal system. A hormone is a chemical that is released into the blood stream and exerts an effect at a target tissue elsewhere in the body.
Have a read of my blog post on hormones to find out more…..
If you understand how these two systems are able to link one part of the body to another, then you can see how these two compare.
The first rows in the table have already been discussed.
Because the nerve impulse travels along a neurone at up to 100 m/s you can see that the nervous response will be much faster than a hormone that is secreted into the blood. It can take up to a minute or two for a hormone to travel from the secreting cell to the target cell. So nervous coordination is fast, hormonal is slow.
The response to a nervous signal often only lasts for a short time. Nervous responses tend to be muscle contractions and these are temporary of course. Hormones on the other hand often are involved in longer term processes like growth and development. As an example, think of the changes brought about at puberty by the hormones testosterone (in men) and oestrogen (in women).
Finally you can compare where the response occurs. Nerve cells can only cause a response at the exact point where they end. They release neurotransmitters into a synapse and this exerts an effect on the next neurone or muscle cell. Because hormones are released into the blood plasma, and blood is carried everywhere in the body, a single hormone can effect many targets in the body. For example, adrenalin (epinephrine for our American cousins) is a hormone released by the adrenal gland above the kidneys. But the target tissues for adrenalin are found all over the body – e.g. the heart, the skeletal muscles, the iris in the eye, the hairs in the skin, the lungs, the liver etc. Read more about adrenalin in my blog post here.
I hope this helps….. Please leave a comment in the box below to either give me some feedback, give me some suggestions for future posts or to ask a question.
Adrenaline: Grade 9 Understanding for IGCSE Biology 2.94
Adrenaline is a hormone produced in the adrenal glands which are found on top of the kidneys in the abdomen.
A hormone is “a chemical released by a specialised gland called an endocrine gland into the bloodstream. The hormone travels around the body in the blood plasma and then causes an effect elsewhere in the body by binding to receptors found on certain target cells”.
You should know some other examples of hormones – testosterone, oestrogen, progesterone, ADH – to name a few. Please learn this definition too: it would be wonderful if you got a 3 mark question asking you to define a hormone….
There are many cells in the body that contain receptors for adrenaline. This allows the hormone to exert an effect on a wide variety of tissues. For example there are adrenaline receptors in the pacemaker of the heart and adrenaline will cause the heart to beat faster (more beats per minute) and also with more force.
When is adrenaline released by the adrenal glands into the blood?
Adrenaline is secreted into the blood in times of danger or stress. It prepares the body to either run away from the danger or indeed to battle against it. For this reason, adrenaline is often described as a “fight or flight” hormone.
What are some of the effects of adrenaline?
Target Tissue Effect
Heart Increase in heart rate, increase in cardiac output
Lungs Bronchioles dilate (widen)
Muscles Arteries in muscle dilate to allow more blood to flow to muscles
Skin/Digestive system Arteries in skin/digestive system constrict so less blood flows
Liver Liver breaks down glycogen into glucose to raise blood glucose conc.
Iris Radial muscles in iris contract causing pupil dilation
The overall effect is that the skeletal muscles are supplied with more oxygen and more glucose so they can respire aerobically. This allows the muscle to contract more efficiently.
Hormones: Grade 9 Understanding for IGCSE Biology 2.94 2.95B
Hormones are defined as “chemicals produced in endocrine glands that are secreted into the bloodstream and cause an effect on target tissues elsewhere in the body”. They play a wide variety of roles in the healthy functioning and development of the body.
The iGCSE specification only really mentions a small number of hormones so these are the ones I will focus on in this post.
ADH (anti-diuretic hormone) (Separate Biologists only – not Combined Science)
ADH is secreted into the blood by an endocrine gland at the base of the brain called the Pituitary Gland. The stimulus for the release of ADH into the blood comes from the hypothalamus (a region of brain right next to the pituitary gland) when it detects that the blood plasma is becoming too concentrated. This might be caused by the body becoming dehydrated due to sweating. ADH travels round the body in the blood until it reaches its target tissue which are the cells that line the collecting ducts in the nephrons in the kidney. ADH increases the permeability of the connecting duct walls to water, thus meaning more water is reabsorbed by osmosis from the urine in the collecting duct and back into the blood. This results in a small volume of concentrated urine being produced.
Adrenaline
Adrenaline is secreted into the blood by the adrenal glands in situations of danger or stress.. The adrenals are found just above the two kidneys on the back of the body wall. Adrenaline secretion is controlled by nerve cells that come from the central nervous system. Adrenaline is often described as the “fight or flight” hormone as its effects are to prepare the body to defend itself or run away from danger. There are receptors for adrenaline in many target tissues in the body but some of the most significant effects of adrenaline are:
- affects the pacemaker cells in the heart causing an increase in heart rate
- shifts the pattern of blood flow into muscles, skin and away from the intestines and other internal organs
- decreases peristalsis in the gut
- causes pupils to dilate in the eye
- increases breathing rate in the lungs
- promotes the passing of urine from the bladder
Insulin
Insulin is a hormone made in the islets of Langerhans in the pancreas. It plays a vital role in the homeostatic control of the blood sugar concentration. The pancreas will secrete insulin into the blood when the blood glucose concentration gets too high. There are many cells in the body with insulin receptors but the main target tissue for insulin is the liver.
Insulin causes the liver (and muscle) cells to take glucose out of the blood and convert it into the storage polysaccharide glycogen. This results in a lowering of the blood glucose concentration: a good example of the importance of the principle of negative feedback in homeostasis
Testosterone
Testosterone is a steroid hormone made by cells in the testes of males. It is the main hormone of puberty in males resulting in the growth of the reproductive organs at puberty as well as the secondary sexual characteristics (pitch of voice lowering, muscle growth stimulated, body hair grows etc.)
Oestrogen
Oestrogen is a steroid hormone made by the cells in the ovary that surround the developing egg cell in the first half of the menstrual cycle. In puberty it causes the development of the female secondary sexual characteristics (breast growth, change in body shape, pubic hair etc.) but in the menstrual cycle, oestrogen has a variety of important effects. It stimulates the rebuilding of the uterine endometrium (or lining) to prepare the uterus for the implantation of an embryo. Oestrogen also affects the pituitary gland and can cause the spike in LH concentrations that trigger ovulation on day 14 of the cycle.
Progesterone
Progesterone is also made in the ovary but at a different time in the menstrual cycle. It is secreted by cells in the corpus luteum, a structure found from day 14 onwards after the egg has been released in ovulation. Progesterone has two main target tissues: it maintains the thickened lining of the endometrium in the uterus ready for implantation. Progesterone also causes the pituitary gland to stop secreting the hormones FSH and LH so a new cycle is never started. It is for this reason that progesterone can be used in women as a contraceptive pill.
FSH (Follicle-Stimulating Hormone (Separate Biologists only – not Combined Science)
FSH is a hormone released by the pituitary gland underneath the brain. The target tissues for FSH are in the testis (males) and ovaries (females). In males FSH plays a role in the growth of the testes allowing sperm production to start. In females, FSH is the hormone released at the start of the menstrual cycle that causes one of the immature egg cells in an ovary to grow, develop and so become surrounded by follicle cells prior to ovulation.
LH (Luteinising Hormone) (Separate Biologists only – not Combined Science)
LH is a second reproductive hormone released by the pituitary gland into the bloodstream. In males, it stimulates the production of testosterone in the testes. In females, it is released only on days 13 and 14 of the menstrual cycle and it is the hormone that triggers ovulation.
PMG Biology 