homeostasis and excretion

stimulus

any change in the environment of an organism that causes a response

response

any change in behaviour of an organism or in physiology as a result of change in the environment

homeostasis

maintenance of constant internal conditions despite external changes

importance of maintenance

• enzymes require a suitable environment to control reactions

• external and internal environments change

qualities of good communication

covers whole body, specific, rapid, short and long term responses

nervous system features

transmitted by specific neuron cells, effect localised by neurone anatomy, fast acting, short lived response

hormonal system features

transmitted by the circulatory system, effect localised by target cell receptors, slow acting, long lived response

cell signalling

• happens in both hormonal and nervous response

• one cell will release a chemical that is detected by another which will respond to the signal

feedback (homeostasis)

homeostasis depends on sensory receptors detecting small changes in the body and effectors bring about change, relies on cell signalling

positive feedback

sensory receptors detect change effectors take it further from the norm

negative feedback

sensory receptors detect change and effectors reverse it

importance of temp regulation

enzyme function

how animals thermoregulate

exothermic chemical reactions (respiration), using radiation (basking) evaporation of water from skin, conduction to or from surroundings/direct heat source, using convection currents from water or air

ectotherm definition

use surroundings to warm their body, core temperature is dependent on the environment

ectotherm details

• eg: fish, amphibians, reptiles

• behaviour → maximising or minimising surface area

• physiology → dark colour to absorb radiation, some can alter heart rate to adjust metabolic rate

• + → need less food, can survive in difficult habitats

• - → more vulnerable to predators when cold, cannot take advantage of available food when cold

endotherm definition

rely on metabolic processes for thermoregulation, core body temperature very stable

endotherm details

• eg: mammals and birds

• behaviour → lie in the sun if cold, move to generate heat

• physiology → sweating, hair/feathers can lie flat or stand, vasodilation/constriction, panting, shivering

• + → maintains constant internal temperature despite external changes so can remain active, can inhabit colder climates

• - → significant amount of energy intake to maintain temperature, need more food, may have slow growth, may overheat

vasodilation

when arterioles dilate and sphincter muscles open so more blood flows through capillaries in the skin so more heat is lost through radiation

vasoconstriction

when sphincter muscles and arterioles constrict so that more blood is diverted through shunt vessels, so less heat loss through radiation

thermoreceptors

• part of the thermoregulatory centre in the hypothalamus

• maintains the temperature in a dynamic equilibrium to within 1°C of 37°C

• sends information to the brain regarding the temperature in the extremities (they will cool first)

• this means that the hypothalamus can respond more quickly to reduce fluctuations in core temperature

Mammal waste products of metabolism

• co2 → excreted through lungs

• urea/nitrogenous waste → formed in liver, excreted through kidneys

• bile pigments → formed in liver, excreted through small intestine via gallbladder

liver

• lies under lungs

• lobular

• fast growing and can regenerate

• rich blood supply

• very metabolically active

liver vessels

hepatic artery - oxygenated blood to liver (branch of aorta)

hepatic vein - deoxygenated blood from liver (branch of inferior vena cava)

hepatic portal vein - blood loaded with products of digestion from intestines (majority of blood to liver via HPV)

hepatocytes

cells of liver, has homeostatic function and carries out protein synthesis

bile

produced in hepatocytes, passed into canaliculus, drains into bile duct, drains into gallbladder for storage

process through liver

• blood enters from HPV and HA

• they mix and pass through sinusoids

• hepatocytes take o2 and nutrients

• blood exits via HV

• kupffer cells act as macrophages and breakdown old RBCs, forming bilirubin which is excreted in faeces

effects on body of high CO2 levels

• effects o2 dissociation curve -> when the partial pressure of CO2 is high haemoglobin’s affinity for o2 is reduced (good as respiring tissues need it)

• co2 combines directly with haemoglobin to form caminoglobin which has a lower affinity for haemoglobin than normal haemoglobin

• CO2 lowers pH of area (acidic) can cause the haemoglobin to change shape also changes the conditions in which enzymes function inhibiting metabolic reactions

why the liver has two blood supplies

• receives oxygenated blood via the HA, needed for aerobic respiration (as the liver is highly metabolically active)

• HPV needed as it transports blood rich with digestion products like glucose (converted to glycogen) deaminated amino acids and toxins, which would interfere with cell activity if allowed to circulate in the body

transamination

• carried out by the hepatocytes

• conversion of one amino acid into another

• important as the diet may not include all essential amino acids

deamination

• removes toxic amine and recycles the rest

• the body cannot store excess proteins/amino acids and excretion would be a waste of resources

• happens in the liver

• amine group and h atom removed to form NH3 (very soluble and toxic)

• remaining molecule (an organic keto acid) can be used as a substrate in respiration

  • converted to glucose or lipids

• converted to urea in the liver (ornithine cycle)

liver + blood glucose

• hepatocytes are sensitive to glucagon and insulin

• excess glucose is stored in the liver

• hepatocytes convert glycogen back to glucose under the influence of glucagon (reverse)

ornithine cycle

• enzyme controlled reactions → remaining amino group from amino acids

• ornithine + NH3 + CO2 + H2O → citrulline + NH3 + NO2 → ornithine + H2O + urea → ornithine

detoxification

• deals with toxins gained via ingestion/as products of metabolism

• hydrogen peroxide -> byproduct of metabolic pathways, hepatocytes contain catalase to break it down

• ethanol -> converted to ethanal by ethanol dehydrogenase, then to ethanoate which can be used in the synthesis of fatty acids or in respiration

why hepatocytes have large numbers of mitochondria and ribosomes

• they are responsible for the synthesis of ATP, so require many mitochondria for their energy intensive role → detoxification, deamination and protein synthesis all require ATP

• ribosomes = site of protein synthesis, so are needed for the synthesis of plasma proteins (used to control oncotic pressure) and enzymes

parts of kidney

• renal vein (deoxygenated blood)

• renal artery (branch of aorta, oxygenated blood)

• renal pelvis

• renal column

• renal pyramid

• renal medulla

• renal cortex

kidney process

blood drains through renal vein to nephrons, where waste products are removes to produce urine. urine passes out of kidney down the ureter to the bladder where it can be stored before release through the urethra

afferent and efferent arterioles

• afferent -> arteriole from renal artery

• efferent -> from glomerulus, smaller diameter (creates pressure)

bowmans capsule

• contains glomerulus (capillary tangle)

• more blood enters than leaves due to ultrafiltration

• prevents capillaries from bursting due to high pressure

proximal convoluted tubule

• coiled region after bowman's capsule

• found in cortex

• necessary substances reabsorbed into the blood here

• microvilli increase surface area for absorption

• lots of mitochondria which provides ATP for active transport

loop of henle

• long loop of tubule that creates a region of high solute concentration in the tissue fluid of medulla

• runs from cortex, through medulla to hairpin bend at the bottom

• runs back up from medulla to cortex

loop of henle structure

• descending limb (slightly permeable to na+, cl-, permeable to water)

• thin part at the right of the curve (highly permeable to ions)

• ascending limb (highly permeable to ions, impermeable to water)

• thick part (actively transports)

distal convoluted tubule

• responsible for fine tuning of water balance (permeability of the walls to water varies in response to ADH levels)

• also regulates ions and pH of blood

collecting duct

• urine passes down to medulla then to pelvis

• also responsible for some water balance regulation as walls are sensitive to ADH

ultrafiltration

pushes out glucose, ions, urea, amino acids, water and hormones from the blood to form filtrate

ultrafiltration process

• blood enters glomerulus through afferent arteriole (high pressure)

• efferent arteriole has narrower diameter increasing pressure

• pressure filtration forces anything with a molecular mass less than the renal threshold (69,000) out to bowmans capsule

capillary structure for ultrafiltration

• endothelium has pores to allow substances through

• basement membrane is a glycoprotein layer - retains large molecules

• podocytes have pedicels that stop larger molecules that may have managed to get though

  • part of the bowman's capsules and also support capillaries against the pressure of the blood

selective reabsorbtion

• occurs in the kidney

• filters out everything then reabsorbs all glucose and amino acids and some ions and water

selective reabsorption process

• filtrate enters PCT from bowman's capsule (more dilute than the blood in the surrounding capillaries)

• na+ actively transported out of PCT cells by a sodium pump and diffuses into a capillary, lowering the ion concentration in PCT cells

• na+ then moves from filtrate to PCT cells (down concentration gradient)

• sodium ions move through symplast cotransport and brings a glucose molecule with them

• glucose will increase in concentration then move into the blood in the capillaries by facilitated diffusion

• water will move by osmosis as a result of the ion movement

• by the end filtrate and blood are isotonic

reabsorbing water in the loop of henle

• na+ and cl- actively pumped out of thick part (build up in tissues)

• water leaves descending limb down the water potential gradient

• ions diffuse into descending limb down the concentration gradient

• thin ascending limb highly permeable to ions

• ions move out to the tissues down the concentration gradient

• filtrate becomes more dilute through the ascending limb, but lots of water has already been reabsorbed into capillaries surrounding loop of henle

• collecting ducts also run through the medulla, more water can be absorbed – controlled by ADH