Homeostasis Flashcards
What is osmoregulation
The maintenance of osmotic potential in the tissues of living organisms
What organs control osmoregulation
Liver - breaks down excess amino acids and removes toxins from blood
Kidney - remove waste from body
What is deamination
Breakdown of amino acids by the hepatocytes
Remove the amino group and converts it to ammonia then urea
This ammonia is converted to urea by a series of enzyme controlled reactions called the ornithine cycle
The kidney
Controls water potential of the blood by removing excess products as waste e.g. urea or excess ions and water
It reabsorbs products that are needed such as glucose, dissolved ions and some water
What are the 2 types of nephron
Cortical nephrons (mainly found in the renal cortex and have a loop of henle that only just reaches into the medulla)
Juxtamedullary nephrons (have a long loop of henle that penetrates right through the medulla and are particularly efficient at producing concentrated urine)
What is ultrafiltration
Occurs between the glomerulus and the bowman’s capsule
Diameter of the Afferent arteriole is larger than the efferent arteriolar causing immense hydrostatic pressure
Water, glucose and mineral ions are squeezed out of the capillary to form glomerular filtrate
Blood cells and proteins are too large to pass through
What are podocyte cells
Specialised cells involved in ultrafiltration which line the inner layer of the bowman’s capsule
They have spaces between them that filtrate passes through
What is selective reabsorption
Occurs in the proximal convoluted tubule where 80% of glomerular filtrate is reabsorbed
How are cells in the PCT adapted
Microvilli - large surface area
Infoldings at their base - large SA to reabsorb substances into blood capillary
Lots of mitochondria - provides ATP for active transport
What is reabsorbed during selective reabsorption
Glucose, amino acids, vitamins and hormones are moved back into the blood by active transport
Sodium ions and chloride ions are also actively transported meaning water will follow passively down the concentration gradient
What is the loop of henle
Extends into the medulla and is responsible for creating a water potential gradient between the filtrate and the tissue fluid in the medulla
This allows the water to be reabsorbed from the collecting duct
What are the 2 regions of the loop of henle
Descending limb - narrow, thin walls that are permeable to water not salts
Ascending limb - wider, thick walls that are impermeable to water and very permeable to salts
Process of creating a concentration gradient in the loop of henle
Na ions actively transported out of the ascending limb using ATP
Creates a low water potential
Water moves out of the descending limb from the filtrate into the interstitial space and then into the blood capillaries
Water is lost as filtrate and moves down the descending limb so the lowest water potential is at the bottom of the loop of henle
Na ions can diffuse out at the base of the ascending limb and then are actively pumped out as you move further up
Water potential in the filtrate gets progressively higher
There is a gradient of water potential in the interstitial space with the highest water potential at the cortex
Water is lost from the collecting duct by osmosis into the blood vessels
Water moves out of the collecting duct and the interstitial space so the gradient is maintained
Distal convoluted tubule
Permeable to water (this varies with ADH)
Balancing of water in the body occurs here and in the collecting duct
Collecting duct
Permeable to water (this varies with ADH)
Water moves out of the collecting duct down the water potential gradient
Fluid collects in the kidney pelvis and passes along ureters to the bladder where it is stored
How is ADH released
Osmoreceptors in the hypothalamus detects falls in water potential
Hypothalamus produces ADH
ADH passes to the pituitary gland and then us secreted into the capillaries
Travels to the kidney where it increases permeability of the DCT and collecting duct so water is retained
How does ADH work
ADH binds to specific receptors on collecting duct cells
Forms cAMP as a second messenger
This causes vesicles to fuse with the cell membrane
These vesicles contain water channels which are inserted to the membrane making it more permeable to water
ADH negative feedback - less water in blood
Low water potential is detected by hypothalamus
Posterior pituitary releases more ADH
ADH travels in blood to kidney
It attaches to receptor cells on collecting duct and DCT making them more permeable to water
Water leaves tubule by osmosis and moves into capillaries
Small volume of concentrated urine produced
ADH negative feedback - more water in blood
High water potential in blood is detected by hypothalamus
Release of ADH from pituitary is inhibited
Walls of collecting duct and DCT remain impermeable to water Water leaves
Little to no water is reabsorbed into capillaries Small volume
Ark he volume of dilute urine produced
What is diabetes insipidus
Individuals produce large volumes of very dilute urine
This is caused when people don’t produce much ADH or the kidneys don’t respond to it
Results in their collecting ducts and DCTs being permanently impermeable to water
Patients often feel very thirsty and have to drink large amounts of water
Treated with drugs that replace ADH
What is an endotherm
Rely on their own metabolism to provide warmth
Can survive in most environments
Examples are mammals and birds
Often have higher metabolisms than ectothermic so need to eat more to supply metabolic needs
What is an ectotherm
Rely heavily on their environment to control their body temperature
May need to bask int he sun to warm up of move into shade to cool down
Often require less food as they have much lower metabolisms
What is the role of the hypothalamus
Acts as a thermostat as it is sensitive to nerve impulses received from hot and cold themroreceptors in the skin
It also possesses central thermoreceptors that are sensitive to changes in temperature of blood that reflect changes in temperature of the body core
What are the three methods of temperature control in the body
Vasoconstriction / vasodilation
Piloerection / pilorelaxation
Sweating / shivering
What is piloerection
Erector muscles cause hairs to stand on end causing air to be trapped for insulation
What is vasoconstriction / vasorelaxation
Vasoconstriction - capillaries constrict re£using blood flow to the skin and avoiding heat loss
Vasorelaxation - capillaries dilate increasing blood flow to the skin therefore increasing heat loss
Sweating / shivering
Sweating - when too warm, body produces sweat which evaporates taking heat energy with it
Shivering - when too cold the muscles contract and relax quickly so energy produced warms up the body
Adaptations for cold climates
Organisms are usually larger as this reduced their SA:V ratio
Have thick layers of fur / fat
Have smaller extremities
Have countercurrent exchange systems which conserve heat (arterial blood is cooled as it flows to the extremity and venous blood is warmed as it returns to the body minimising heat loss to the environment)
Hibernation
Organisms eat more than normal to build up body fat
They hibernate where they sleep for long periods
Metabolism slows down saving energy
Behavioural control
Basking - absorbs radiation from the sun
Adaptations in warmer climates
Have larger extremities
Some can tolerate much larger fluctuations in body temperature e.g. camels
Have countercurrent exchange systems which helps to cool organs, mainly the brain (thermal energy is transferred from arterial blood to venous blood as they run close together. Cooled arterial blood supplies to the brain)
Behavioural control in warmer climates
Sheltering - less radiation absorbed from sun and they press against cold surfaces to cool by conduction
Evaporation - panting allows for the loss of moisture fromnhe mouth
Aestivation - organisms slow their metabolic rate right down and become completely dormant for months.
Why does the kangaroo rat never have to drink water
They have a longer loop of henle so all water is reabsorbed back into blood.
Small volume of concentrated urine.
