Homeostasis and response

What is homeostasis?

• The maintenance of a constant internal environment

• to enable cellular functions to occur at an optimal rate

what are the examples of homeostasis?

Blood glucose concentration, water balance and body temperature

How does nervous system work?

• receptors detect the stimulus

• Carry electrical impulses to the sensory neurone

• Carry electrical impulses to the coordination centre (voluntary) or relay neurone (involuntary)

• Carry electrical impulses to the motor neurone

• Carry electrical impulses to an effector to carry out a response

• Can be a muscle which contracts

• Or a gland which secretes hormone to restore optimum levels

• (Mentions synapse somewhere in the answer)

What are synapses?

Gap between two neurones

How is electrical impulses carried between neurones?

• Electrical impulses arrive at the end of neurone

• At the end of neurone there is a sac which contains chemicals called neurotransmitters

• Neurotransmitters are released into the synapse and is attached to the surface of the next neurone

• This sets up a new electrical impulse

What does the cerebrum do?

Controls conscious thoughts, personality and intelligence

What does the cerebellum do?

Control balance and coordination of movement

What does Medulla do?

Controls unconscious activities like heart and breathing rate

What does hypothalamus do?

Regulates body temperature and water balance

How does EEG work?

• use weak electric current to stimulate different parts of brain

• Ask or observe what patients experience

• To investigate are certain parts of brain functioning normally by comparing to a normal person

How does MRI scans work?

• use magnetic waves and radio waves to scan brain to form an image of brain

• Patient may be asked to perform various tasks

• To investigate the effect of action on certain parts of brain

• Compare to a normal person to help detect things like brain tumours

What does cornea do?

Refracts light as it enters the eye

What does iris do?

Control how much light enters the pupil

What does lens do?

Further refracts light to focus it onto retina

What does retina do?

Contains light receptors (rods and cones)

What does the optic nerve do?

Carries impulses between the eye and the brain

What does sclera do?

A think white outer layer that protects the eyes from injuries

What are the difference between rods and cones?

• Rods are more sensitive to light, therefore useful to see in dim light (black and white vision)

• There are 3 different types of cone cells which produce colour vision (red, green, blue)

What is the pupil reflex controlled by?

muscles of the iris (radial muscle and circular muscle)

What happens to pupil in dim light?

• the radial muscle contracts and the circular muscle relaxes

• The pupil is dilated and more light enters eye

What happens to pupil in bright light?

• The radial muscle relaxes and the circular muscle contracts

• Pupil is contracted and less light enters the eye

What does accommodation mean?

The process of changing the shape of the lens to focus on near or distant objects

What happens when the object is near?

• Ciliary muscles contract and suspensory ligament relax

• Muscle tension is low and the lens is thick

• Light is refracted strongly

What happens when the object is distant?

• Ciliary muscles relax and suspensory ligaments contract

• Muscle tension is high and the lens is thin

• Light is only refracted slightly

Why is muscle tension high when seeing distant object

• The ciliary muscle, which is like a ring around lens relaxes, therefore gets wider

• Suspensory ligaments which hold the lens together contract

• Therefore muscle tension is high

What is Myopia?

• known as short sightedness

• Someone can see near objects clearly but cannot focus properly on distant objects

What is Myopia caused by?

• The eyeball is elongated, so the distance between lens and the retina is too great

• The lens is too thick and curved

• These cause light to focus in front of the retina

What lens can correct Myopia?

Concave lens

What is Hyperopia?

• Long sightedness

• Someone can see distant objects clearly but cannot focus properly on near objects

What is Hyperopia caused by?

• the eyeball being too short, therefore distance between lens and the retina is too small

• a loss of elasticity in the lens (cannot become thick enough to focus light)

• These cause lens to focus light behind the retina instead of onto it

What lens can correct Hyperopia?

Convex lens

What are the alternatives to wearing lens?

• Laser surgery-reshaping the cornea surgically

• Replacement lens-implanting artificial lens in front of the original lens through a small cut in the cornea

What is the endocrine system?

• a group of glands secrete hormones directly into the bloodstream and eventually reach the target organ

• Slower chemical response but last longer

What are hormones?

They are made of protein, and is chemical that is released by gland

What is the master gland?

• The pituitary gland

• Which releases several hormones into the blood

• To control body’s condition to the ideal set point

• Or to act on other glands to stimulate release of different hormones

What is Type 1 Diabetes caused by?

• genetics

• body is unable to produce its own insulin because the immune system attacks the insulin producing beta cells

What is the difference between hyper and hypo in terms of blood glucose?

• Hyper means the excess glucose in blood cannot be removed and stored as glycogen

• hypo means no store of glycogen is ready to release glucose when blood glucose level falls

How can Type 1 Diabetes be controlled?

• Pancrea transplantation

• Regular insulin injections (2-4 times/week)

What is Type 2 diabetes caused by?

• Obesity, lack of regular exercise and a high refined sugars diet, old age

• Causes glycoprotein receptors on the body cells losing their responsiveness to insulin

• Or an inadequate supply of insulin from the pancreas

What is the negative feedback control system?

• Conditions in the body change from set point

• Changes detected by receptors

• Corrective mechanism activated (e.g. releasing hormone)

• Conditions returned to set point

• Change detected by receptors

• Corrective mechanism switched off (e.g. decrease of hormone released)

What does Thyroxine do?

• released by thyroid gland which targets various organ

• increases rate of metabolism and growth

How does body control water balance and nephron permeability?

• receptors in hypothalamus detect decrease in water level in blood

• Send messages to pituitary gland

• ADH is released by the pituitary gland into blood then kidney

• Causes kidney to be more permeable to water and reabsorbs more water

• More concentrated, smaller volume urine produced

• When water content is too high, ADH is lowered or not released

• Kidney becomes less permeable to water, reabsorbs less water

• More dilute, larger volume urine produced

What does adrenaline do?

• Produced by adrenal gland, targets various organs in the circulatory and respiratory system

• Increase heart rate

• Increases delivery of oxygen and glucose to the brain and muscles

• For more aerobic respiration

• Not controlled by negative feedback because it is a rapid emergency response

How is blood glucose level controlled?

• receptors in pancreas detect increase in blood glucose level

• Release insulin so that liver cells absorb more glucose

• More glucose is converted into insoluble glycogen for storage

• Blood glucose level decreases and is detected by receptors in pancreas

• Pancreas release glucagon

• Liver cells increase conversion of glycogen into glucose into the bloodstream

• When blood sugar returns to set point, glucagon stops releasing

What is the reproductive hormone in men and women?

Men:testosterone, Women:Oestrogen

What is stage one of menstrual cycle?

Day 1-the uterus lining breaks down for about 4 days

What is stage two of menstrual cycle?

Day 2-14-the uterus lining builds up again into a thick spongy layer full of blood vessels, ready to receive a fertilised egg

What is stage three of menstrual cycle?

Day 14-a developed egg is released from the ovary (ovulation)

What is stage four of menstrual cycle?

Day 15-28-the uterus wall is then maintained for about 14 days until day 28

What does FSH do?

• produced by the pituitary gland

• Causes an egg to mature in one of the ovaries

• Stimulates the ovaries to produce oestrogen

What does oestrogen do?

• produced in the ovaries

• Causes the uterus lining to build up

• Stimulates the release of LH and inhibits the release of FSH

What does Luteinising hormone do? (LH)

• produced by the pituitary gland

• Stimulate the release of an egg at day 14 (ovulation)

What does progesterone do?

• produced in the ovaries after ovulation

• Maintain the uterus wall during second half of cycle

• Inhibits release of LH and FSH

How does IVF (In Vitro Fertilisation) work?

• give FSH to a mother to stimulate maturation of eggs

• Eggs are collected from ovaries and fertilised by sperm eggs from the father in a dish

• Eggs placed in incubator

• Eggs develop into embryos (tiny balls of cells)

• One or two embryos are inserted into the mother’s uterus

What is the advantage of IVF?

Allows infertile couples to have kids

What are the disadvantages of IVF?

• physically unpleasant (may cause vomit)

• Stressful as it doesn’t always work

• Expensive

What is contraception?

Preventing sperm meeting the egg to avoid pregnancy

How does the contraceptive pill work?

• hormonal contraception

• Pill contains low dose of oestrogen and progesterone to inhibit production of FSH

• Therefore no eggs mature

• Also make mucus in the uterus thick to prevent sperm getting through to meet egg

How does contraceptive implant work?

• Hormonal contraception

• A tiny tube is inserted under the skin and it slowly releases progesterone to inhibit release of LH and FSH

• Also affects the uterus lining developing, preventing implantation

How does barrier methods like condoms work?

• non hormonal contraception

• Condom placed over penis during intercourse to collect semen

How do surgical methods work?

• Non-hormonal contraception

• In men sperm ducts are cut and tied, preventing sperm getting into semen

• This is known as vasectomy

• this gives permanent contraception

How does abstinence work?

Not having intercourse, therefore guaranteed no pregnancy

Evaluate use of contraceptives pill

• easy to use but risk of forgetting to take pill and side effects like breast cancers

Evaluate the use of condom

• no side effects, no need for medical advices, may also protect against HIV

• however if cap is not positioned correctly or damaged, sperm may get past and reach the egg

What does osmoregulation mean?

Keeping the concentration of water and mineral ions the same inside and outside the cells (isotonic)

How does body maintain nitrogen balance?

• proteins are broken down into amino acids by protease in the small intestine

• Excess amino acids are transported from small intestine to liver

• In liver, amino acids are deaminated and forms ammonia (NH3)

• This is toxic and is immediately converted into urea

• Urea and water released from liver to kidney

• Blood is filtered by kidney

• Urea, salt, excess water are excreted from the body via urine

How does lung remove excess water?

Water leaves the body via the lungs when we exhale as well as excess CO2

How is the blood transported into and out kidney

• Renal artery carries oxygenated blood to the kidneys

• Renal vein carries deoxygenated blood away from the kidneys

  
  

Describe ultrafiltration

• Small molecules are filtered out and pass into nephron tubules (urea, water, ions and glucose)

• Large molecules like blood proteins cannot pass through permeable capillary wall in nephron and remains in blood

Describe selective reabsorption

• requires active transport which requires oxygen

• Reabsorbs all of the glucose which was filtered out, as much water and as much ions as the body needs

Describe formation of urine

• molecules which are filtered and not selectively reabsorbed continue along nephron as urine

• Eventually passes down to bladder through ureter

• Urine is carried out the body through the urethra

What does thermoregulation mean?

The maintenance of body temperature

What happens when body temperature is too high?

• Sweat glands in the skin release more sweat

• Increases rate of evaporation to transfer heat energy from skin to environment

• Vasodilation

What happens when body temperature is too low?

• Skeletal muscles contract rapidly and we shiver

• Increasing Contractions require more energy from more respiration, therefore more energy is released as heat

• Hair erector muscles in skin contract

• Raise the skin hairs and traps a layer of air next to the skin

• Vasoconstriction

What does vasodilation mean?

• Skin capillaries become wider

• Blood flow in skin capillaries increases

• Increase heat loss from skin by radiation

What does vasoconstriction mean?

• Skin capillaries become narrower

• Blood flow in skin capillaries decreases

• Decrease heat loss from skin by radiation

How is hypothalamus involved in thermoregulation?

• thermoreceptors in hypothalamus detect changes in body temperature

• Send nerve impulses to skin to respond