Biology Topic 7

What are hormones?

They are chemical messengers released by endocrine glands

What is metabolic rate?

The rate in which the energy stored in food is transferred by all the reaction that take place in the body

What is thyroxine?

• a hormone that affects metabolic rate

• it is released by the thyroid gland

What does thyroxine do?

• it causes heart cells to contract and act more rapidly

• it increases the rate at which proteins and carbohydrates are broken down

What is negative feedback?

The lack of one substance resulting in the release of another and vice verse in order to maintain prime conditions

What happens when thyroxine levels are low?

• the hypothalamus detects this and releases TRH which targets the pituitary gland

• the pituitary gland in turn releases TSH which targets the thyroid gland

• thyroxine is then released from the thyroid gland which brings the thyroxine levels back to normal

What happens when thyroxine levels are high?

• the hypothalamus also detects this and stops releasing TRH

• the pituitary gland then stops releasing TSH

• this causes the thyroid gland to stop releasing thyroxine so that the thyroxine levels in the blood go back to normal

What is adrenalin?

• a hormone that helps the body with its fight-or-flight response

• it is released from adrenal glands

What does adrenalin do?

• heart muscles contract more rapidly which increases the heart rate and more strongly which increases the blood pressure

• diameter of blood vessels leading to muscles widens which increases blood flow to muscles

• diameter of blood vessels leading to other organs narrows which decreases the blood flow to those organs and increases the blood pressure

• liver cells change glycogen to glucose and release it into the blood which increases the blood sugar concentration

How long is the menstrual cycle?

28 days

What is ovulation?

When an egg is released from the ovary

What does pituitary gland release during the menstrual cycle?

FSH and LH

What do the ovaries release during the menstrual cycle?

oestrogen and progesterone

What does FSH do?

Stimulates the maturation of ova in follicles

What does oestrogen do?

• inhibits the release of FSH

• stimulates the release of LH

• lining in the uterus starts to build up

What does LH do?

Triggers ovulation in the ovary

What is the corpus luteum?

• The follicle left behind by from the release of the mature egg

• Releases progesterone and oestrogen

What does progesterone do?

• inhibits the release of LH

• continues to inhibit the release of FSH

• keeps the uterus lining thick and ready to receive a fertilised egg

What are some non-hormonal contraceptives?

• condoms

• diaphragm

• intrauterine device (IUD)
  abstinence

• spermicide

• surgical methods

What is an hormonal contraceptive?

the pill → contains oestrogen and progesterone which prevents the production of FSH so eggs can’t mature

What is ART?

• stands for Assisted Reproductive Technology

• for couples who find it difficult to get pregnant

• this could be because the woman produces too few eggs, oviducts/fallopian tubes are blocked or maybe if the man produces few sperm

What is clomifene therapy?

• uses a drug which helps a women produce eggs

• it increases the production of FSH and LH from the pituitary gland

• it also blocks the negative feedback effect of oestrogen and progesterone

What is IVF?

• in vitro fertilisation

• the female is injected with FSH to mature eggs

• healthy sperm is taken from male

• the egg and sperm cells are mixed so the egg is fertilised and a zygote is formed

• when the zygote develops into an embryo and is inserted back into the uterus lining of the female

• if successful, a pregnancy test will confirm she is pregnant by detecting HCG in her urine

What is homeostasis?

A self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival

Why must body temperature be regulated?

• at high temperatures the enzymes denature and cannot form enzyme-substrate complexes

• at low temperatures, enzymes and substrates have less kinetic energy and collide less often

• in both cases, the rate of reaction slows down and so does the metabolism

What is thermoregulation?

• the control of the body temperature, which keeps the temperature of major organs at 37°C

• the hypothalamus is responsible monitoring the body’s temperature

What is vasoconstriction?

a response to the body being too cold, when the hypothalamus detects blood and brain temperatures to be below 37°C

What changes does vasoconstrion cause?

• shivering; muscles contract and relax rapidly and the energy released from cell respiration helps warm the body up

• erector muscles contract; hairs stand up and insulating air is trapped between hairs

• blood flow near the surface decreases; in order to decrease heat loss

• shunt vessels dilate

• arterioles narrow

What is vasodilation?

a response to the body being too hot, the hypothalamus detects blood or brain temperatures to rise above 37°C

What changes does vasodilation cause?

• sweating; sweat evaporates on the surface of the skin which causes energy to be transferred to surrounding by heating and helps the skin cool down

• erector muscles relax; so hairs stand down

• blood flow near the surface increases; in order to increase heat loss

• shunt vessels narrow

• arterioles dilate

What is glucose needed for?

needed by cells for respiration

What problems may excessive glucose levels cause?

• damage cells

• cause blindness by damaging light receptive cells

What happens when glucose levels are high?

• the pancreas releases insulin

• insulin binds to muscle cells to increase rate of respiration and use up glucose

• insulin binds to liver cells and stimulates glycogen formation from glucose

• results in a fall of blood glucose levels

What happens when blood glucose levels are low?

• the pancreas releases glucagon

• glucagon binds to liver cells and stimulates glycogen breakdown

• causes the release of glucose into the blood

• results in a rise of blood glucose levels

What is diabetes?

A condition where the blood glucose levels cannot be controlled by the body

What is type 1 diabetes?

A disorder in which the pancreas fails to produce enough insulin

How to control type 1 diabetes?

• by injecting insulin

• monitor blood sugar levels

• monitor levels of physical activity and diet

What is type 2 diabetes?

A disorder in which the body no longer responds to insulin

How can type 2 diabetes be controlled?

• healthier diet

• regular exercise

• reducing BMI

What is osmoregulation?

• the control of the balance of water and mineral salts in the body

• if the balance is off, then cells may take in or lose too much water by osmosis

• this can damage cells because water is needed to maintain the shape of the cell and help with it’s reactions

What is the function of the urinary system?

To remove excess amounts of some substances from the body

What is urea?

• a waste product, large amounts of amino acids produced in the liver

• it passes into the blood and is carried into the kidneys

What are nephrons?

• tiny microscopic tubes

• each kidney contains around 1 million

• urine is made here

What is ultrafiltration?

• blood enters the nephron by the glomerulus

• small molecules such as water, urea and glucose are filtered under pressure into the Bowman’s capsule

• the Bowman’s capsule is adapted to only let small molecules into the nephron so large molecules such as protein and blood won’t fit

What is selective reabsorption?

• the filtrate enters the proximal convoluted tubule (in the cortex) where glucose is reabsorbed by selective reabsorption

• this is done by active transport using energy from respiration

• the first convoluted tubule has microvilli which increase the surface area and rate of active transport

• in the loop of Henle (in the medulla) water and ions are selectively reabsorbed into the capillaries

What is urine formation?

• the filtrate enters the distal convoluted tubule and then into the collecting duct

• excess water and urea is leaves to the ureter and is removed from the body

• urine is formed from these two substances

What is ADH?

• anti diuretic hormone which is released from the pituitary gland

• it increases the permeability of the collecting duct

What happens when there is too much water in the blood?

• the hypothalamus detects this and stops stimulating production of ADH from the pituitary gland

• this decreases the permeability of the collecting duct so that less water is reabsorbed and more dilute urine is produces

What happens when there is too little water in the blood?

• the hypothalamus detects this and stimulates the release of ADH from the pituitary gland

• this increases the permeability of the collecting duct so that more water is reabsorbed and more concentrated urine is produced

What is kidney failure?

• when both kidneys stop working properly

• the person’s life will be in danger because waste substances increase in concentration in the blood

What are the two treatments for kidney failure?

Dialysis, Organ Donation

What is dialysis?

An artificial method of filtering the blood to remove toxins and excess substances

How does dialysis work?

• patients are connected to a dialysis machine

• unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm

• inside the dialysis machine the blood and dialysis fluid are separated by a partially permeable membrane, the blood flows in the opposite direction to dialysis fluid, so the two can exchange substances

What are the properties of the dialysis fluid?

• the dialysis fluid has no urea in it so there is a large concentration gradient meaning that urea diffuses across the partially permeable membrane from the blood to the dialysis fluid

• the dialysis fluid concentration of glucose is similar to the patients so there is no net movement of glucose across the membrane due to there being no concentration gradient

• the fluid in the machine has to be constantly refreshed so that the concentration gradients are maintained

What is a disadvantage of dialysis?

• it takes 3-4 hours to complete

• needs to be done several times a week

What is organ donation?

When a kidney from another person is put into a patient’s body and attached to their blood system

What are the disadvantages of organ donation?

• replacing a kidney involves several hours of surgery which may be too much for weak patients to handle

• the donated kidney may be rejected by the patient’s immune system

• it may take a long time to find a suitable kidney that matches the patient’s cells

• even with a good match, the patient might need life-long medication to prevent the kidney being rejected; the medication affects the body’s response to infection which may make the patient more susceptible to other infections