Homeostasis

Created by

Hafsa Farouk

Cards (49)

Stimuli: change in the environment detected by receptors leading to an internal change
Central Nervous System (CNS): brain and spinal cord
Accommodation: the process of changing the shape of the lens to focus on near or distant objects
Homeostasis - The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in
response to internal and external changes.
o Receptors - group of specialised cells – detect change in the environment (stimulus) & stimulate
electrical impulses as responses
o Coordination centres - receive & process electrical impulses from receptors
o Effectors - bring about a response to restore optimum conditions
▪ e.g. muscles or glands
▪ a muscle contracting to move an arm or e.g. squeezing saliva from the salivary gland
▪ a gland releasing a hormone into the bloodstream
• Features of Nerve Cells:
o Long fibre (axon) insulated by a fatty sheath (myelin) – long so they can carry messages
o Tiny branches (dendrons) which branch further to dendrites at each end – receive incoming impulses from other neurones
Reflex Actions
• Automatic and rapid responses - that do not involve the conscious part of the brain
o They reduce the chances of being injured
o E.g. if someone shines a bright light in y our eyes, your pupils automatically get smaller so that less light
gets into the eye, stopping them being damaged
• Between each nerve cell there is a small gap called the
synapse
o At the end of the neurone the electrical impulse
causes the release of neurotransmitters
o These diffuse across the gap & attach to the
receptor site of the other nerve
o This sets off a new electrical impulse
• Neurotransmitters are chemicals e.g. dopamine and serotonin
▪ Cerebellum: balance, posture & muscle
coordination
▪ Medulla: controls unconscious activities e.g.
breathing & heartrate
▪ Hypothalamus: regulatory centre for
temperature & water balance withing the body
▪ Cerebral cortex (split into two hemispheres and is highly folded): intelligence, personality,
conscious thought, and high-level functions i.e. language and verbal memory.
o retina
▪ black lining of the eye containing rods (dim &
black/white light) & cones (colour)
▪ contains fovea (yellow spot) – high concentration
of cones, clearest point of vision
o optic nerve
▪ bundle of sensory neurones at back of the eye,
carries impulse from the eye to the brain
▪ causes a blind spot due to no rods/cones
o sclera
▪ white outer layer of the eye, tough & strong for protection
o cornea
▪ front of sclera, convex & transparent – refracts light to focus on retina
o iris
▪ pigmented (eye colour) so light cannot penetrate
▪ muscles contract & relax to alter pupil size to control amount of light entering the pupil
o aqueous humour
▪ fluid in front of the lens that helps maintain the shape of the eye and lens
o vitreous humour
▪ fluid behind the lens that helps maintain the shape of the eye and lens
▪ it also keeps the retina against the wall of the eye
o ciliary muscles & suspensory ligaments
▪ control the size & shape of the lens
• accommodation to focus on near/distant objects
o near
▪ ciliary muscles contract & suspensory ligaments loosen
▪ lens is then thicker & refracts light rays strongly
o distant
▪ ciliary muscles relax & suspensory ligaments are pulled tight
▪ lens is then pulled thin & only slightly refracts light rays
• adaptation to light (iris reflex) – agnostic muscle pair: circular & radial muscles of the iris
o bright light - too much light can damage the retina
▪ the pupil is made smaller (contracted pupil), so less light reaches the retina
▪ circular muscles contract & radial muscles relax
o dim light
▪ the pupil is made wider (dilated pupil), so more light reaches the retina
▪ circular muscles relax & radial muscles contract
• Myopia (short-sighted so unable to focus on distant objects)
o Causes
▪ Eyeball is elongated so the distance between lens & retina is too large
▪ Lens is the too thick or curved
o Explanation
▪ Images of distant objects are focused in front of the retina
o Correction
▪ Glasses with a concave lens, diverts the rays so hit lens higher/lower and converge on the retina
• Hyperopia (long-sighted so unable to focus on near objects)
o Causes
▪ Eyeball is too short so the distance between lens & retina is too small
▪ Loss of elasticity in lens – so cannot become thick enough to focus (often age related)
o Explanation
▪ Images of near objects are focused behind the retina
o Correction
▪ Glasses with a convex lens, refracts light inwards so the lens has to refract light less
• Body temperature is monitored and controlled by the thermoregulatory centre in the brain (the hypothalamus)
o Hypothalamus contains receptors sensitive to the temperature of the blood
o Skin contains temperature receptors and sends nervous impulses to the hypothalamus
• Body temp too low – limits transfer of energy from skin to the environment (vasoconstriction & no sweating)
o Vasoconstriction- blood vessels supplying skin capillaries constrict to reduce the skins blood supply
o Sweating stops - this reduces evaporation from the skin
o Shivering - (Skeletal muscles contract) requires energy, so respiration occurs which is exothermic
o Hair erector muscles contract - hairs stand up to trap a layer of insulating air
• Body temp too high - increases transfer of energy from skin to the environment (vasodilation & sweating)
o Vasodilation – blood vessels supplying skin capillaries dilate, more blood flows close to the skin’s surface
o Sweating – sweat glands produce sweat, evaporates from skin
o Hair erector muscles relax - stops air being trapped (which would be an insulator)
• Pituitary gland, ‘master gland’ – in the brain
o Regulates body conditions & secretes several hormones to
act on other glands to stimulate hormone release
• Pancreas
o Produces insulin & glucagon
o Regulates blood glucose levels
• Thyroid
o Produces thyroxine
o Regulates rate of metabolism (includes affects heart rate)
• Adrenal gland
o Produces adrenaline
o Used to prepare the body for ‘fight or flight’ e.g. increases
heart rate & breathing rate, stimulates glucagon release
• Ovary (female sex only)
o Produce oestrogen & progesterone
o These hormones are part of the menstrual cycle - they build & maintain uterus lining
• Testes (male sex only)
o Produce testosterone
o Controls puberty & sperm production
• Blood glucose concentration is monitored and controlled by the pancreas
• Too high e.g. due to eating meal high in carbohydrates
o pancreas secretes the hormone, insulin
o causes glucose to move from the blood into liver & muscle cells
o insulin causes liver to convert excess glucose into glycogen
• Too low e.g. after vigorous exercise
o pancreas secretes the hormone, glucagon
o causes glycogen in the liver to convert back into glucose
o glucose released back into the bloodstream
negative feedback cycle
o blood glucose spikes after a meal, pancreas senses this &
releases insulin, levels fall
o levels become too low & the pancreas releases glucagon to
increase levels – this cycle repeats
• Type 1 diabetes – genetic
o The pancreas produces little or no insulin – so blood glucose
will rise & won’t fall, this can cause death
o Treatment: insulin therapy – insulin injections daily after
meals (amount varies) - very effective
o A carbohydrate-controlled diet & exercise helps by decreases blood glucose naturally
• Type 2 diabetes – caused by lifestyle & age
o When someone becomes resistant to their insulin (it is still produced) – so glucose levels can spike to
dangerous levels – obesity is the main risk factor for type 2 diabetes
o Treatment: regular exercise, carbohydrate -controlled diet - as a last resort, insulin therapy
Osmoregulation: control of the balance of mineral ions & water in the body
• Water need to maintain cell shape & help movement of particles in cells
o too little water, cells lose shape
o too much wate, cells burst (are damaged)
o either way they cannot function efficiently
• Loss of water, mineral ions & urea
o There is no control over water, ion or urea loss by the lungs or skin
▪ Water leaves the body via the lungs during exhalation
▪ Water, ions & urea are lost from the skin in sweat
o Excess water, ions & urea are removed via. the kidneys in the urine
• Urea
o The digestion of proteins from the diet results in excess amino acids which need to be excreted safely
o In the liver these amino acids are deaminated to form ammonia
o Ammonia is toxic and so it is immediately converted to urea for safe excretion
• Filtration
o When the blood passes through the kidneys, some substances move into the kidney tissue e.g.
▪ glucose, urea, minerals, ions & water
o Others are too big to leave the blood e.g.
▪ red blood cells & proteins
• Selective reabsorption
o Useful substances are then reabsorbed into the blood
▪ All glucose, correct amount of water & some ions (rest excreted in urine)
Concentration of urine & ADH (anti-diuretic hormone)
• The water level in the body is monitored by the hypothalamus is controlled by the hormone ADH
o ADH, acts on the kidney tubules – released into bloodstream by pituitary gland
• If water level too high
o Less ADH released, so less water is reabsorbed from reabsorbed by kidney tubules
o Therefore, large volume of dilute urine
• If water level too low
o More ADH released, so more water is reabsorbed from reabsorbed by kidney tubules
o Therefore, small volume of concentrated urine
• Dialysis machine – done regularly to remove waste substances
o Process
▪ A machine that filters blood using a partially
permeable membrane
▪ Dialysis fluid (same concentration of ions &
water as healthy blood) pumps around
machine along with blood – exchange via.
diffusion
▪ No net movement of glucose & useful ions -
excess ions & waste products reduced
• Kidney transplant
o Process
▪ Only cure, taken from a healthy person who died quickly or from a live donor (can live with 1)
▪ The old kidneys left; new kidney connected to blood stream
o FSH (Follicle-Stimulating Hormone) – pituitary gland
▪ Causes egg to mature in one of the ovaries – in a follicle
▪ Stimulates production on oestrogen
o LH (Luteinising Hormone) – pituitary gland
▪ Stimulates the release of an egg (ovulation) on day 14
o Oestrogen – ovaries
▪ Causes lining of the uterus to grow
▪ Stimulates LH release, inhibits FSH release
o Progesterone – ovaries (by remains of the follicle after ovulation or placenta if pregnant)
▪ Maintains uterus lining during second 1⁄2 of cycle (& pregnancy), if levels fall lining breaks down
▪ Inhibits release of LH & FSH
• Reasons for infertility
o Men
▪ NO sperm production
▪ Non-healthy sperm produced, due to dinking or smoking
▪ Impotence (erectile dysfunction)
o Women
▪ Ovaries don’t produce eggs
▪ Complications due to previous STIs
▪ Vagina too acidic for sperm entry
▪ Lack of sufficient levels of sex hormones e.g. FSH & LH
• In Vitro Fertilisation (IVF) treatment
o Mother given FSH and LH to stimulate the maturation of several eggs – then eggs collected
o Intra-cytoplasmic sperm injection (ICSI) – sperm injected directly into the egg
▪ Useful if man has low sperm count
o Fertilised egg grown into embryos in a lab incubator
o At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus
• Adrenaline
o produced by the adrenal glands (above kidneys)
o released in times of fear or stress - preparing the body for ‘flight or fight’
▪ increases the heart & breathing rate
▪ boosts the delivery of oxygen & glucose to the brain & muscles (increased conversion of
glycogen to glucose)
o allows the body to respond quickly to situations
• Negative feedback cycles - continuous cycle of events
o level of something rises, control systems reduce it again
o level of something falls, control systems raise it again
• E.g. thermoregulation, controlling blood glucose levels,
controlling water levels
• Thyroxine – levels controlled by a negative feedback cycle
o Produced by thyroid gland (at base of neck) - from
iodine & amino acids
o Stimulates base metabolic bate e.g. respiration
o Also stimulates protein synthesis for growth &
development
o Thyroxine released in response to thyroid stimulating
hormone (TSH)
▪ Released in pituitary gland, levels of thyroxine
monitored by hypothalamus
▪ positive tropisms – the plant grows towards the stimulus
▪ negative tropisms – the plant grows away from the stimulus