Homeostasis and kidney

Define homeostasis

- maintenance of a constant internal environment despite fluctuations in external environment

- ensures each cell is surrounded by tissue fluid to supply conditions for metabolism (nutrients and waste products)

- ensures reactions continue at a constant and appropriate rate and cells function normally during different levels of activity by organism

State factors that will be controlled by a homeostatic response

- whole body temp, blood pH, solute potential, glucose concentration

State factors affected by excercise

- O2, glucose, CO2, temperature, salt, lactic acid

What is a set point?

- body is kept at dynamic equilibrium

- conditions such as body temp/pH/solute potential/glucose conc of blood change but homeostasis returns them to the set point

Define feedback systems

- involve nerve impulses and chemical messages from hormones

- most in mammals are negative feedback but can be positive

- maintain a constant internal environment

State examples of a negative feedback system

- blood glucose conc, core body tempurature

State examples of positive feedback systems

-uterus contractions during birth, blood clotting

Define negative feedback systems

Output reduces original stimulus

Describe types of negative feedback systems

- increase above norm (stimulus), detector (receptor), control centre (coordinator), effector, response, return to norm

- decrease below norm same thing

Define a stimulus

Causes change in variable

Define receptor

- detects change and tells control

Define control centre

- determines set point and tells effector

Define effector

- causes change that will stop stimulus

Define response

- variable now returned to set point

Describe control of body temp when it rises above normal

- above 37

- brain signals to dermal blood vessels to dilate and sweat glands to secrete,body heat goes to surroundings, body temp returns to set point

Describe control of body temp when it is below normal

- Brain signals for vasoconstriction and sweat glands remain inactive, body heat conserved

- if body temp continues to drop, nervous system signals muscles to contract individually (shiver), muscles actively generate heat and body temp rises

What is control centre in controlling body temp

- hypothalumus

Outline control of blood glucose concentration

- increase, chemoreceptors detect change, insulin released from beta cells in pancreas, lowering blood glucose levels: uptake into cells, respiration, glycogen synthesis, decrease to normal

- decrease, chemoreceptors detect change, glucose released from alpha pancreas cells, raising levels: uptake, respiration, glycogen synthesis, increase to normal

Describe positive feedback system in labour

- during labour, hormone: oxytocin is released from posterior pituitary gland

- causes contraction of smooth muscle in uterus

- as head of baby pushes against cervical, stretch recpetors are stimulated and send messages back to pituitary

- more oxytocin released

- more simulation of receptors and so on

How does positive feedback back work to establish an action potential

- changes in electrical potential between inside and outside of the nerve, propagating signalling

- action potentials are caused by an influx of Na+ into axon through sodium channels

- if a small amount of Na+ enters nerve, it causes more channels to open which cause more sodium to rush in, creating positive feedback loop that causes large amount of sodium to enter nerve and creat an action potential

Metabolic process, excreted in, excretory organ: CO2

Respiration, expired air, lungs

Metabolic process, excreted in, excretory organ: water

- respiration, expired air, lungs

Metabolic process, excreted in, excretory organ: urea

- amino acid breakdown, urine, kidney

Metabolic process, excreted in, excretory organ: creatine

Muscle tissue breakdown, urine, kidneys

Metabolic process, excreted in, excretory organ: uric acid

- nucleic acid breakdown, urine, kidney

Metabolic process, excreted in, excretory organ: urea

Amino acid breakdown, sweat, skin

Metabolic process, excreted in, excretory organ: bile pigments

Haemoglobin breakdown, faeces, liver

How is water lost

- excreted as metabolic waste product in respiration, secreted in sweat and tears, egested in faeces

What are functions of kidneys

- excretion: removal of nitrogenous metabolic waste from body

- osmoregulation: control of water potential and solute concentration of body's fluids by reduction water content

What are nitrogenous waste

- excess amino acids

- excess can't be stored

Describe deamination

- excess amino acids are deaminated which produces NH3 and a Keto acid

- the ammonia is combined with CO2 to make urea, this needs ATP

- the Keto acid can feed into respiration as a krebs cycle intermediate

- urea is transported in plasma to kidneys and excreted in urine

Renal artery contents

- blood enters kidneys

- oxygenated

- nitrogenous excretory products (eg urea)

- toxins, drugs and substances ingested but not metabolised fully

- variable amounts of water and salt

- lower partial pressure of CO2

- more glucose

- plasma proteins

Renal vein contents

- blood leaves kidneys

- no nitrogenous waste

- lower levels of toxins, drugs and other substances

- more constant concentration

- higher partial pressure of CO2: respiration by kidneys

- less glucose: respiration

- only lower plasma proteins if kidney functions abnormally and this ends up in urine

What is the nephron and its function

- units of kidneys - microscopic tubules with associated blood vessels

what are the processes carried out by the kidney

- ultrafiltration, selective reabsorption, reabsorption of H2O

how does filtration under pressure work?

- more blood can enter than it can leave the glomerulus as the afferent arteriole is bigger than the efferent arteriole

- low pressure input pathway to high pressure output pathway

state structures separating the blood entering glomerulus form the space in the Bowman's capsule

capillary wall, basement membrane, wall of bowman's capsule

describe the capillary wall of glomerulus

single layer of endothelial cells with pores called fenestrae

describe basement membrane adaptations between glomerulus and bowman's capsule

covers and supports capillary wall; made of mesh of collagen fibres and glycoproteins that acts as a molecular filter and selective barrier allowing passage of small molecules (water, ions, urea, glucose but not large plasma proteins)

describe wall of bowman's capsule adaptations

made of squamous epithelial cells called podocytes which have numerous foot processes called pedicels which wrap around a capillary, gaps between pedicels are called filtration slits

what are the gaps between pedicels called

filtration slits

name the pores between the glomerular capillary wall

fenestrae

what causes ultrafiltration and affects glomerular filtrate rate

high pressure in capillaries of glomerulus forces solutes and water into cavity of bowman's capsule, vasoconstriction/dilation of glomerular afferant arterioles affect rate of blood flow which is proportional to GFR

what is the glomerular filtrate rate per day

180L/day

what are the components of the glomerular filtrate

HCG, urea, glucose, H2O, amino acids, HCO3-, K+, Na+, Cl-, small proteins

define selective reabsorption

the uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream

function of proximal convoluted tubule

carries filtrate away from bowman's capsule, blood in capillaries around PCT reabsorbs all the glucose and amino acids, some urea and most of the water and Na+ and Cl- from filtrate in PCT

describe adaptations of the proximal convoluted tubule

many mitochondria: ATP for active transport, microvilli: forms brush border increasing surface area, tight junctions between epithelial cells: formed by multiprotein complexes preventing substances seeping between cells and back into lumen, invaginations: forming basal channels increasing surface area for substances leaving cell, closely associated peritubular capillaries: short diffusion distance

where in kidney are the glomerulus and proximal convoluted tubule

cortex

where in kidney is loop of Henle and collecting duct

medulla

describe selective reabsorption of Na+

active transport via Na/K+ pump in basal membrane; concentration gradient established for diffusion of Na+ from filtrate into PCT cell

describe selective reabsorption of glucose and amino acids

co-transport into PCT cell with Na+ and then facillitated diffusion into capillaries (secondary active transport due to Na/k pump)

describe selective reabsorption of Cl-

diffuse from filtrate into PCT cells flowing electrochemical gradient set up by Na+ ions and then diffuse into capillaries

describe selective reabsorption of H2O

osmosis due to solute gradient and lower water potential of blood due to the reabsorbed ions

describe selective reabsorption of urea and small proteins

diffuse down steep gradient into PCT cell and then into capillaries due to high concentration gradient of caused by loss of water from filtrate

what happens if glucose threshold is reached

in normal circumstances all of the glucose is reabsorbed before the filtrate reaches the end of PCT. If glucose concentration in the filtrate is too high, there may be too few transport proteins in the PCT membrane so glucose will enter loop of Henle and leave through urine

why might the glucose threshold be reached

pancreas secretes too little insulin (type 1 diabetes) or insulin receptors on surface membrane of liver are damages (type 2 diabetes and gestational diabetes)

function of efferant arteriole

a narrow vessel that restricts blood flow helping to generate high pressure

function of afferent arteriole

brings blood from renal artery

function of peritubular capillary

low pressure capillary bed that runs around the convoluted tubules, absorbing fluid from them

function of vasa recta

unbranched capillaries that are similar in shape to the loops of Henle, deliver nutrients to the medulla cells and carry water reabsorbed from glomerular filtrate into nephron

function of glomerulus

knot like, high pressure capillary bed

function of venules

carry blood to the renal vein

where is water reabsorbed into blood

about 90% from glomerular filtrate absorbed at proximal convoluted tubule, some in distal convoluted tubule in cortex, loop of Henle in medulla and 5% from collecting duct

why can the proximal convoluted tubule not absorb all the water

some must remain because excretory products have to be in solution to move through nephron and out of body

describe water reabsorption at ascending limb of loop of Henle

- walls are impermeable to water, Na+ and Cl_ actively transported out of filtrate in tubule into tissue fluid in medulla, longer loop means more ions can be transported, concentrated salts in tissue fluid mean low water potential. As filtrate goes from bottom of hairpin, it contains fewer ions so more dilute and higher wp

describe water reabsorption in descending loop of Henle

permeable to water, slightly permeable to Na+ and Cl-, as filtrate flows down limb, water diffuses out, into tissue fluid of medulla, which has low wp. From there it moves to vasa recta and some sdium and chloride ions diffuse into descending loop.

where in loop of henle has lowest wp

bottom of hairpin: as filtrate flows it contains progressively less water and more ions so bottom is most concentrated

how is the loop of Henle adapted for water absorption

having 2 limbs of loop running side by side with fluid moving up one and down the other allows maximum concentration to be built up at the apex of the loop. Mechanism is called counter-current multiplier (flow is opposite directions/counter current and solute concentration increases/multiplies).

describe water reabsorption in collecting duct

runs back down into the medulla, passing through the region of low water potential. Water therefore diffuses out of the collecting duct by osmosis, down a water potential gradient. The longer the loop of Henle, the lower the water potential in the medulla and the more water leaves collecting duct by osmosis. Filtrate becomes more concentrated than the blood, hypertonic to blood so at base of collecting duct it is urine, Water is reabsorbed into the vasa recta and into general circulation

define osmoregulation

regulating water potential to maintain the balance of water and salts within the cell/organism relative to its surroundings also maintains concentrations of enzymes and metabolites so cell reactions occur at constant/appropriate rate

what type of feedback does osmoregulation use

negative

what is volume of urine controlled by

hydration/dehydration affects permeability of walls of distal convoluted tubule and collecting duct

where are receptors for osmoregulation

osmoreceptors in the hypothalamus at base of brain

what do the osmoreceptors moniter

monitor the solute potential of blood and sends signals to posterior lobe of pituitary flans (effector) to release stored ADH into blood

effector of osmoregulation

posterior lobe of pituitiary gland

function of pituitary gland in osmoregulation

releases stored antidiuretic hormone (ADH)

funciton of antidiuretic hormone

produced in hypothalamus, secreted by posterior pituitary, increases permeability of the cells of the distal convoluted tubule and collecting duct to water increasing water reabsorption - concentrated urine

state reasons why blood water potential might decrease

- reduced water intake, sweating, intake of large amounts of salt

explain osmoregulation response to low water poteintial in blood

- secretory granules carry ADH along axons from hypothalamus to posterior lobe of pituitary from where ADH is secreted into blood stream, carried to kidneys where, ADH increases permeability of DCT walls and collecting duct to water, more water is reabsorbed by osmosis from filtrate to medulla and on into vasa recta, smaller vol of urine produced

describe osmoregulation with high water potential in blood

less ADH released, decreased permeability of walls of DCT and collecting duct, less water reabsorbed from filtrate and larger vol of urine produced

describe ADH mechanism

ADH binds to membrane receptors on wall of distal convoluted tubule and collecting duct, adenyl cyclase catalyses production of cyclic AMP, second messenger, cytoplasmic vesicles containing aquaporins move to and fuse with cell membrane, aquaporins incorporated into membrane, increase osmosis of water through pores into cell down gradient

what are aquaporins and how many are in kidney

aquaporins are intrinsic membrane proteins with a pore which water molecules move through, around 9

effects of kidney failiure

no excretion/osmoregulation: unable to remove urea

which will build up to toxic levels; the body is also unable to remove excess water so body fluids increase in volume and are diluted which has a negative effect on metabolic reactions

what is chronic kidney disease

develops over months/years, caused by hypertension/diabetes, effects: raised creatinine in blood serum, loss o filtration, urea and salts accumulate in blood, anaemia

treatments for chronic kidney disease

dietary restrictions, medication, dialysis, transplant

effect of diabetes

high glucose concentration in plasma causes

glomeruli to lose protein and causes some proteins to

link together causing scarring - glomerulosclerosis,

state causes of kideny disease

diabetes, high blood pressure, auto-immune disease, infection, crushing injuries

effect if high bp on kidneys

damages capillaries in glomeruli and prevents ultrafiltration

effect of auto-immune disease on kidneys

body makes antibodies against its own tissues

effect of infections on kidneys

can lead to temproray or permanent failure

treatments for if both kidneys are compromised

treatments must reduce the concentration of waste products and control the volume of body fluids in order to regulate blood solute concentration

diet treatment for kidneys

Reducing intake of certain nutrients:

Protein: to reduce urea formation

Ions: to reduce concentration in plasma e.g. sodium,

calcium and potassium

drug treatments for high bp

Angiotensin-converting enzyme (ACE) inhibitors and

Angiotensin receptor blockers (ARBs): to reduce the

effect of angiotensin (hormone that constricts blood

vessels so increasing blood pressure within them), Calcium channel blockers: to dilate blood vessels and

so reduce blood pressure, Beta blockers: to reduce effect of adrenalin so reduce heart rate and lower blood pressure, Diuretics: to increase urine volume

treatment to reduce blood potassium conc

combination of glucose and insulin, intravenous calcium used to stabilise heart muscle mebranes

effect of high potassium in blood

heart arrhythmias

treatment fo high blood calcium conc

bisphosphonates reducing osteoclast activity so reducing bone breakdown and increasing Ca accumulation in bone so less in blood

effect of high conc of calcium

correlated to heart disease, kidney stones and osteoporosis

goals of both dialysis treatments

haemodialysis and peritoneal dialysis, The goal for both is to remove waste products, excess ions and water. These wastes are composed mainly of nitrogen in the form of urea, uric acid, and creatinine

types of dylaisis

haemodyalisis and peritoneal