Topic 7 - animal coordination, control and homeostasis

what two systems does the human body have

two communication systems - the nervous system and the endocrine system

what does the endocrine system do

the endocrine system sends hormones (chemical messengers) around the body. when they reach a target tissue they produce a response

what is the endocrine system made up of

glands which secrete hormones directly into the bloodstream

pituitary gland

• the master gland

• secretes hormones into the blood to either have an effect on the body or act on other glands to stimulate them to produce different hormones

pancreas

• secretes insulin

• controls blood glucose levels

thyroid

• secretes thyroxine

• controls metabolic rate, heart rate and temperature

adrenal gland

• secretes adrenaline

• involved in the ‘fight or flight’ response (the body’s response to stressful situations)

ovary

• secretes oestrogen

• is involved in the menstrual cycle and the development of female secondary sexual characteristics (different features that develop during puberty that distinguish a female from a male)

testes

• secretes testosterone

• is involved in the production of sperm and the development of male secondary sexual characteristics

how does the hormone travel

the blood transports the hormone to a target organ or tissue where it has an effect

compared to the nervous system, the hormonal system is much slower but acts for longer

what is adrenaline

adrenaline is a hormone that is produced by the adrenal glands to prepare the body for a fight or flight response

what is a flight or fight response

a flight or fight response is the body’s response to a dangerous situation: historically this would have been being confronted by a dangerous animal, for example

aspects of the fight or flight response

• increased heart rate - this allows oxygen to reach the muscles more quickly, so we can move out of the path of danger

• increased blood pressure - allows oxygen to reach the muscles quicker, so we can move out of the path of danger

• increased blood flow to muscles - blood vessels leading to vessels dilate (widen) to allow more blood to reach them. this allows them to contract with greater strength, and more quickly

• increased blood sugar levels - the liver is stimulated to break down glycogen (a storage molecule) into glucose, which muscles can use to contract

what does thyroxine do and why is it important

thyroxine regulates metabolic rate (how quickly reactions occur). it is also important in growth and development

• low levels of thyroxine stimulates production of a hormone called TRH in the hypothalamus

• TRH causes the release of TSH from the pituitary gland

• TSH acts on the thyroid to produce thyroxine

• when thyroxine levels have reached the normal level, thyroxine inhibits the release of TRH, which stops the production of TSH

the levels of thyroxine are controlled by negative feedback

• when the levels increase, it is detected by receptors in the brain

• this inhibits the release of TSH

• this inhibits the release of thyroxine, so levels of thyroxine fall

what is the menstrual cycle

the process the body undergoes each month to prepare for a potential pregnancy. it begins with the lining of the uterus breaking down, and the woman has her period. the layer then builds up again, until ovulation (day 14) occurs - an egg is released from the ovary and moves to the uterus via the fallopian tube. if a fertilised egg has not been embedded in the lining after 28 days, it begins to break down and the cycle continues. the events of the cycle are controlled by four hormones

hormones within the menstrual cycle

1. follicle stimulating hormone (FSH) causes the maturation of an egg in the ovary, within a structure called a follicle

   • produced in the pituitary gland

   • stimulates the ovaries to produce oestrogen

2. oestrogen causes the lining of the uterus to grow again

   • produced in the ovaries

   • secreted as a result of FSH

   • stimulates the production of LH and inhibits the secretion of more FSH

3. luteinising hormone (LH)

   • produced in the pituitary gland

   • produced as a result of the hormone oestrogen

   • its release results in ovulation

4. progesterone

   • produced in the ovaries and secreted from the egg follicle

   • maintains the lining of the uterus, and supports a pregnancy if the egg is fertilised

   • inhibits the release of both FSH and LH

hormonal methods of contraception

the contraceptive pill, the contraceptive patch, the contraceptive implant, the contraceptive injection, the plastic intrauterine device (IUD)

the contraceptive pill

must be taken regularly or the bodies own hormones will be released, leading to an egg maturing

• the mixed pill contains oestrogen and progesterone

  • this means the oestrogen levels are constantly high, inhibiting FSH so no eggs mature

  • the lining also stops developing and the mucus in the cervix becomes thick so sperm cannot move through

  • some possible side effects include changes in mood, mood swings, depression, breast pain or tenderness, breast enlargement, increased blood pressure

• the progesterone only pill

  • this has less side effects in comparison to the mixed pill

the contraceptive patch

contains oestrogen and progesterone

• it is small and is stuck on the skin

• lasts for 1 week

the contraceptive implant

releases a continuous amount of progesterone

• this prevents the ovaries from releasing the egg, thickens the mucus in cervix so sperm cannot swim and stops fertilised eggs from embedding in the uterus

• lasts for 3 years

the contraceptive injection

made up of progesterone

• same effect as the implant

• lasts for 2 to 3 months

the plastic intrauterine device (IUD)

releases progesterone

• same effect as the implant

• T shaped, inserted into the uterus

• lasts for 5-10 years

non-hormonal methods of contraception

these stop sperm fertilising the egg

• chemical methods involve spermicides. these kill or disable sperm, but are only 70% to 80% effective

• barrier methods include condoms and diaphragms:

  • condoms are either worn over the penis or are placed inside the vagina. they also help prevent the individual from contracting STDs. a problem is that they can tear and therefore let sperm through

  • a diaphragm is a plastic cup which is positioned over the cervix. it is used with spermicide

the copper intrauterine device works by killing sperm in the uterus and stopping any fertilised embryos from implanting in the uterus lining

surgical methods of male and female sterilisation involve cutting and tying the fallopian tubes or sperm duct. these are often permanent procedures but in some cases can be reveresed

abstaining from intercourse ensures that an egg is not fertilised. others may only abstain during ovulation

ways to increase change of pregnancy

fertility drugs or In Vitro Fertilisation (IVF)

fertility drugs

they are used to increase the chance of pregnancy

• the main hormones used as FSH and LH because they stimulate the maturation and release of the egg

• the woman can then become pregnant normally

• another drug used is called clomiphene. this increases the amount of FSH and LH released from the hypothalamus, increasing the chance that a woman will ovulate

In Vitro Fertilisation (IVF)

• the mother is given FSH and LH to encourage the release and maturation of eggs

• these are extracted from the mother and fertilised in the lab using sperm

• the fertilised eggs develop into embryos and then one or two are inserted in the uterus

benefits of IVF

provides a way for an infertile couple to have a child

cons of IVF

• it is physically stressful as women may have reactions to the hormones, such as feeling sick

• it is emotionally stressful because it may not work - success rate for IVF is 26%

• it can lead to multiple births - unexpected and may be a risk to the babies and the mother

• can be expensive if the process needs to be repeated

what is homeostasis, why is it important and what does it control

homeostasis is the maintenance of a constant internal enviroment. mechanisms are in place to keep conditions optimal and constant despite internal and external changes.

homeostasis is important to maintain enzyme action and all cell functions - including growth, replication and controlled cell death

in the human body, homeostasis controls:

• blood glucose concentration

• body temperature

• water levels

automatic control systems

nervous and hormonal communication is involved in the automatic control system, which detect changes and respond to them

all control systems have:

• receptors - cells that detect stimuli (changes in the enviroment)

• coordination centres - process the information recieved from the receptors, eg. brain, spinal cord and pancreas

• effectors - bring about responses to bring the conditions in the body back to optimum levels, eg. muscles or glands

what is thermoregulation and why is it important

thermoregulation is the act of keeping internal body temperature constant. this is important because if the temperature exceeds the optimum level of 37 degreed Celsius, enzymes will gradually become less effective and eventually denature (irreversibly change shape)

what is osmoregulation and why is it important

osmoregulation is the act of keeping the concentration of the blood (ie. the level of solutes in the blood) at a constant level. if the blood becomes too dilute, water will move into cells by osmosis and they will swell, eventually bursting under the pressure. if the blood becomes too concentrated, water will move out of cells and they will shrink.

in either case, they cannot perform their function so it is vital that the blood remains the same concentration via osmoregulation

where is the thermoregulatory centre and what does it do

the thermoregulatory centre which monitors and controls body temperature is found in the hypothalamus of the brain

• has receptors that monitor the temperature of the blood

• has receptors in the skin that send impulses to the thermoregulatory centre

what is human body temperature

37.5 degrees Celsius

what happens if it becomes too high

• sweat (evaporates from skin surface resulting in increased energy transfered away from the body) is produced from sweat glands. note that sweat glands are located in the dermis layer of the skin. the sweat is released onto the surface of he epidermis

• vasodilation means more blood flows closer to the surface of the skin, resulting in increased energy transfer from the body

what happens if it decreases too much

• sweating stops

• skeletal muscles contract rapidly (shivering) to generate heat from respiration

• hairs stand on end to create an insulating layer, trapping warm air

• vasoconstriction means blood does not flow so close to the surface, resulting in less heat lost

glucose levels

eating foods that contain carbohydrates increases the glucose levels in the blood

• if the glucose levels are too high, the pancreas produces the hormone insulin

• insulin binds to cell in target organs (muscles and liver) causing:

  • 1. glucose to move from the blood into muscle cells for respiration

  • 2. excess glucose to be converted into glycogen which is stored in the liver

• the blood glucose concentration is reduced

glucagon

rigorous activity (eg. exercise), uses glucose for respiration and therefore there is less in the blood

• if glucose levels decrease, the pancreas produces the hormone glucagon

• glucagon binds to the liver cells causing glycogen to be broken down into glucose

• glucose is released into the blood, increasing the blood glucose concentration

your blood glucose concentration is kept constant through using these two hormones. they work in a negative feedback loop

• when blood glucose levels increase/decrease, a hormone is secreted to oppose the change

• the action of this hormone cannot occur continually because when the blood arrives at a certain glucose concentration the other hormone is produced, resulting in the opposite effect

what is diabetes

diabetes is a disease where the body cannot control blood sugar levels properly

type 1 diabetes

the pancreas cannot produce enough insulin. this condition is congenital (usually from birth/a young age)

• blood glucose level can rise to a fatal amount

• glucose is excreted with urine and lots of urine is produced leaving the individual very thirsty

• it is treated with insulin injections at meal times, which results in glucose being taken up from the bloodstream

• it is also advised to limit the intake of simple carbohydrates which contain lots of glucose

• doctors are attempting to cure diabetes with pancreas and pancreatic cell transplants, and genetically engineering pancreatic cells from mice to make insulin

type 2 diabetes

the body cells no longer respond to insulin. this condition is acquired (usually occurs later in life)

• blood glucose levels can rise to a fatal amount

• obesity is a risk factor for this disease

• treatments include reducing the number of simple carbohydrates in diet, losing weight and increasing exercise

• there are also drugs to make insulin more effective on body cells, help the pancreas make more insulin or reduce the amount of glucose absorbed from the gut

what is usually considered as a definition for obesity (BMI)

a body mass index over 30 is generally considered as a definition for obesity. obesity, and indeed being overweight, are considered risk factors for developing Type 2 diabetes. in fact, as body mass increases the risk of developing Type 2 diabetes increases significantly

BMI formula

BMI = mass (kg)/height² (m²)

other way to evaluate body mass

waist-hip measurements. a doctor might advise somebody who is at risk of Type 2 diabetes to take a glucose tolerance test to examine how well their body can produce insulin when it is needed

what is the urinary system

the urinary system is the bodily system that removes impurities and waste products from our blood. these impurities are excreted in urine. its main organ is the kidney. we have 2 kidneys, one on the left and one on the right - they are located n the lower back (lumbar) region

route that blood takes to be purified

1. blood containing impurities travels in the renal artery to the kidneys

2. the kidneys regulate the levels of salt, ions and urea in the blood. any excess is sent to the ureter for excretion, and eventually the bladder

3. the purified blood returns to the circulation by way of the renal vein

structure of the kidney

• the inner part of the kidney is called the medulla and the outer part is called the cortex

• the ureter carries from kidneys to the bladder to be excreted out the body

• the kidney is supplied by the renal artery and a renal vein takes blood away

• each kidney contains millions of kidney tubules or nephrons and these are made up of a glomerulus (ball of capillaries), a region for selective reabsorption of substances to occur and a kidney tube where water and salt is regulated

what does the kidney contain

the kidney contains over a million small units called nephrons. the structure of the nephrons of the kidney are closely related to their function

functions of nephrons

1. Filtration - filtration, or ultrafiltration, occurs in the glomerulus, a collection of capillaries (small blood vessels) at the start of the nephron. urea, water, ions and glucose are small enough to pass out of the capillaries into the Bowman’s capsule - however proteins and cells are too large, and remain in the blood)

2. selective reabsorption of glucose and ions - the substances in the Bowman’s capsule move into the tubule. at a point called the proximal convoluted tubule (the first ‘bend’ in the tubule), as much glucose as was lost during ultrafiltration is selectively reabsorbed into the blood

   • this is important, as glucose is valuable to the body for energy (from respiration) and we do not want it to be excreted

3. reabsorption of water and ions - water and ions are reabsorbed at the Loop of Henle and collecting duct areas of the tubule. this process is tightly controlled according to the osmotic pressure of the blood

what is ADH

ADH (antidiuretic hormone) is a hormone that is produced by, and released from, the pituitary gland in the brain. it is released into the bloodstream and travels from the brain to the kidney. it has special effects on the collecting duct of the nephron that relate to the water potential of the blood

what happens if the water potential of the blood is too high

if water potential of the blood is too high, less ADH is released from the pituitary gland and the collecting duct becomes less permeable to water. this leads to more water being released in urination (as more remains in the tubule, ending up in the ureter

what happens if water potential of the blood is too low

if water potential of the blood is too low, more ADH is released from the pituitary gland and the collecting duct becomes more permeable to water. this leads to less water remaining in the tubule, and more entering blood vessels surrounding the tubule. less water is released in urination

what does ADH stand for

antidiuretic hormone:

anti means the opposite of

diuretic is a substance that causes increased urination

hence ADH is a hormone which ‘prevents you urinating’!

what is kidney failure and how is it treated

kidney failure, also known as chronic kidney disease (CKD) is a serious condition where kidneys are unable to perform the process listed before. kidney failure is normally treated using either transplantation or dialysis

what is dialysis

• dialysis is a type of therapy where a machine outside the body performs the action of the kidneys (filtering out urea and other waste substances and reabsorbing sugar, water etc)

• blood is taken from a vessel in the arm and is mixed with an anticoagulant to prevent the blood clotting and ‘clogging up’ the machine

• the machine contains dialysis fluid, which is seperated from blood via a partially permeable membrane (allows some things to travel across it, but not others)

• dialysis fluid contains a similar level of glucose and ions as is found in the blood, which means these substances remain in the blood and return to the body

• dialysis fluid contains no urea, therefore urea diffuses out of the blood into the dialysis fluid down a concentration gradient

what is transplantation

• transplantation is an alternative to dialysis, where the kidney is replaced altogether. this is a lot less restrictive than a dialysis machine, as regular, time consuming visits are not required

• there is a significant risk of rejection of the donor kidney, which occurs if specific antigens on the kidney cells do not match those of the host. rejection means that an immune reaction will occur, which can lead to severe illness or death. there is a risk of this occurring in almost every case of organ transplantation

• immunosuppressive drugs can also be useful - these suppress the immune system and must be taken for the rest of the patient’s life. they prevent an immune rejection from occurring, but they also cause the immune system to be weak against pathogens

• tissue typing allows us to check if an organ is compatible with the recipient before transplantation - this often leads to long waits for an organ, but can prevent organ rejection

how is urea produced

urea is produced from the breakdown of excess amino acids in the liver