Excretion as an example of homeostatic control

5.1.2 in spec yellow mean check ppt

what is excretion

the removal of waste products of metabolism from the body

importance of removing metabolic wastes from the body

excess CO2 cause respiratory acidosis (lowers blood pH). amino acids are broken down into ammonia when in excess or due to transamination, ammonia is toxic ergo needs to be detoxified to prevent harm

what substances are excreted from the human body

carbon dioxide excreted from the lungs. bile pigments excreted in the bile. urea excreted by the kidneys in urine.

how do bile pigments form

the breakdown of haemoglobin from old red blood cells in the liver

Kupffer cell function

specialised macrophage breaks down old (senescent) erythrocytes, ingest foreign particles, protect liver from disease

sinusoids function

channel that blood flows through. close contact to hepatocytes. exchange materials bw blood and hepatocytes thru sinusoids

how are sinusoids different to capillaries

more porous walls, wider, close to hepatocytes

senescent meaning

cells or tissues that have permanently stopped dividing due to aging or damage, but do not die. remain metabolically active. accumulate in tissues, releasing molecules triggering inflammation

hepatic portal vein function

deoxygenated blood from digestive system containing glucose to liver

hepatic artery function

oxygenated blood to liver

bile duct function

liver bile > gall bladder

bile canaliculus function

collect bile secreted by hepatocytes and delivers to bile duct

bilirubin

waste product from breakdown of erythrocytes

hepatic vein function

blood leaves liver

what substances does bile duct contain

hydrogen carbonate ions, bile pigments, bile salts, cholesterol

order of bile entering digestive system from liver

bile canaliculus > bile duct > gall bladder > duodenum

role of the liver in the storage of glycogen

blood glucose rise, insulin rise, hepatocytes convert glucose > glycogen. blood glucose fall, glucagon rise, glycogen > glucose

glycogenolysis

glycogen > glucose (LYSIS = break down)

glycogenesis

glucose > glycogen (GENISIS = bible create)

the role of the liver in detoxification

liver detoxifies poisonous substances from metabolic reactions/alcohol/drugs.

hydrogen peroxide example of detoxification

toxic byproduct of metabolic reactions. hydrogen peroxide split by catalase in hepatocytes into oxygen and water

ethanol example of detoxification

active drug in alcohol. ethanol broken down by alcohol dehydrogenase in hepatocytes into ethanal. convert into ethanoate

what can ethanoate be used for

build fatty acids (phospholipids/triglycerides), respiration

the role of the liver in the formation of urea as part of the ornithine cycle

ammonia (NH3) + CO2 > H20 + citrulline. citrulline + NH3 > arginine + H20. arginine + H20 > urea.

roles of hepatocytes

metabolism, detoxification, storage of vitamins (A + D), minerals (iron), protein synthesis, cholesterol synthesis

features of hepatocytes

very metabolically active, large nuclei, prominent Golgi apparatus, many mitochondria

difference bw transamination and deamination

Transamination = transfer of an amino group from one molecule to another. deamination = removal of an amino group from a molecule, releasing it as ammonia

what happens during deamination

amine group is removed from a molecule, O2 + aa > keto acid + ammonia

liver role in protein metabolism

hepatocytes synthesise most plasma proteins ergo have lots ribosomes. hepatocytes do transamination helpful bc ensures aa not in diet are still available

liver role in deamination

main role of liver. removes amine group. 02 + aa > keto acid + ammonia. body cannot store excess protein or aa ergo hepatocytes prevent waste.

role of liver in deamination control

ammonia is highly toxic. ammonia > urea by ornithine cycle (enzyme controlled reactions). high concentrations of urea = toxic. blood concentration of urea is not high.

structure of liver

divided into lobes. divided into cylindrical lobules. branches of hepatic artery and portal vein enters lobules where blood mixes in sinusoids.

what is cirrhosis of the liver

normal liver tissue replaced by scar tissue. causes = genetic, hep C, alcoholic. hepatocytes cannot divide anymore. body more vulnerable to toxins.

explain how the structure of the liver is adapted for its functions in the body [6marks]

gross structure of kidney

cortex, medulla, pelvis, capsule, ureter, renal artery, renal vein

cortex

dark colour. outer layer. ultrafiltration occurs here. lots capillaries carrying blood from renal artery > nephrons.

medulla

lighter colour. tubules and collecting duct of nephron here.

renal pelvis

chamber where urine collects before passing to ureter.

nephron in kidney structure

afferent arteriole > glomerulus > bowman’s capsule > proximal convoluted tubule > descending limb > loop of Henle > ascending limb > distal convoluted tubule > collecting duct > ureter

what is the kidney responsible for

osmoregulation. excretion of nitrogenous waste. ammonia > urea > urine.

distal convoluted tubule structure

second tubule, after loop of Henle

glomerulus structure

tangle of capillaries. podocytes holding capillaries in place.

glomerulus function

knot of capillaries in Bowmans / renal capsule

bowman’s capsule structure

cup-shaped. contains glomerulus. layer 1 = capillary endothelial cells (has fenestrations = allow fluid out capillary). layer 2 = basement membrane (no holes). layer 3 = podocyte (hold capillary in place)(has holes)

bowman’s capsule function

ultrafiltration - more blood goes into glomerulus than leaves.

proximal convoluted tubule structure

first coiled tubule after bowman’s. cortex of kidney.

proximal convoluted tubule function

selective reabsorption - substances needed by the body are reabsorbed

loop of Henle structure

high solute concentration in tissue fluid in medulla = low water potential in medulla. region bw descending and ascending limb is interstitial region.

loop of Henle function

maintain negative water potential in medulla so is reabsorbed bc water moves high water potential > low water pot

descending limb

thin wall. water permeable. impermeable to Na+ Cl- ions. interstitial fluid is high concentrated so water moves out loop of Henle by osmosis. descending limb starts in cortex ends in medulla

ascending limb

thin area = NaCl diffuses to interstitial fluid. thick area = NaCl actively transported to interstitial fluid. impermeable to water. permeable to Na+ and Cl- ions bc has many ion channels/carriers. ascending limb starts in medulla ends in cortex. filtrate very dilute

distal convoluted tubule function

reabsorbs water and ions = balance water needs of body. permeability of walls varies by level of ADH (anti diuretic hormone). body lack salt = Na+ actively pumped out tubule > Cl- follows down electromagnetic gradient (Na+ makes it more positive then Cl- follows Na+ to balance the charge)

collecting duct structure

collecting duct function

where concentration and volume of urine is determined. water move out by osmosis (high concentration in medulla created by LoH). permeability of collecting duct controlled by ADH.

difference bw afferent and efferent arterioles

afferent has wider lumen. more blood can enter than exit. high pressure in bowman’s. fluid diffuse into bowman’s form ultrafiltrate.

what does ultrafiltrate contain

proteins with RMM less than 69,000. water, urea, salts, ions, amino acids, hormones, glucose, vitamins, drugs, ethanol

ADH

Anti Diuretic Hormone

process of ultrafiltration

small molecules filtered out under pressure to Bowman’s capsule forming ultrafiltrate

process of selective reabsorption

1) Na+ actively transported > blood. lowers Na+ concentration in cells. diffusion gradient bw nephron and cells. 2) Na+ and aa move in cell by facilitated diffusion with co-transporter. 3) water moves in cell by osmosis bc lower water potential in cell bc high solute concentration.

process of the production of urine

filtrate enters collecting duct. whether strong / dilute urine produced dependant on ADH

glomerulus endothelium of blood capillary structure and function

structure - very thin, fenestrations

function - barrier to cells, platelets, plasma proteins, allow small molecules in bowman’s via fenestrations under high pressure

basement membrane of glomerulus structure and function

structure - meshwork of collagen and glycoprotein fibres.

function - water & small molecules pass, prevent large proteins (RMM>6900) pass

epithelium of Bowman’s capsule

made up of cells modified for filtration = podocytes

podocytes structure

each cell has many foot like extensions = pedicels. pedicels wrap around capillaries in glomerulus linking with neighbouring extensions. fit together closely leaving 25nm wide filtration slits where filtered fluid passes through.

what needs to be reabsorbed from proximal convoluted tubule into the blood

most molecules aside from urea (although some does end up getting reabsorbed)

why do cells lining the proximal convulated tubule have microvilli

increase SA for better reabsorption

Why do cells lining the proximal convoluted tubule have many mitochondria

reabsorption requires active transport, which requires ATP, produced by mitochondria

what process is responsible for the reabsorption of ions / glucose and aa / water

ions = active transport. glucose and aa = co-transport. water = osmosis

basal vs apical surface

in proximal convoluted tubule: basal surface = PCT side closest to blood of vasa recta. apical surface = PCT side closest to nephron

role of the loop of Henle

maintain negative water potential (high solute conc) in medulla by building NaCl concentration in medulla. water removed from tubules by osmosis >interstitial medulla fluid > blood

how does the loop of Henle work

1) ascending limb cells actively pump Cl- first then Na+ out filtrate > medulla.

2) water remains bc ascending limb is impermeable to water.

3) interstitial fluid around loop of Henle become very saturated in medulla.

4) water moves out descending limb, LoH permeable  to water but not solutes = filtrate becomes very concentrated

5) water removed > vasa recta due to osmotic gradient made by blood proteins

6) filtrate becomes more concentrated as move down descending limb

7) up ascending limb, NaCl pumped out = filtrate become less concentrated

the role of osmoreceptors in the hypothalamus

monitors water potential. affect ADH release by pituitary

how does osmoregulation occur

water potential monitored by osmoreceptor in hypothalamus. ADH released by pituitary makes collecting duct more permeable to water. water reabsorbed = blood water potential back to normal. volume and concentration of urine affected

define osmoreceptors

specialised receptor cells that shrink when water potential is low = stimulating neurosecretory cells

define neurosecretory cells

cells that release hormone(s) (like ADH) into the blood when an action potential passes

define hypothalamus

area of brain containing cells that monitor blood water potential, temperature, produce ADH

define posterior pituitary

back area of pituitary gland that secretes ADH into blood

negative feedback when water potential increases above the normal (body has too much water)

osmoreceptors swell > neurosecretory cells stop secreting > ADH decreases in the blood > collecting duct is less permeable to water > high volume of dilute urine 

negative feedback when water potential decreases below the normal (body has too little water)

osmoreceptors shrink > neurosecretory cells secrete ADH > ADH increases in blood > collecting duct is more permeable to water > low volume of concentrated urine

how does ADH affect the nephron

ADH in blood detected by cell surface receptors in collecting duct wall > enzyme controlled reactions > vesicles containing aquaporins fuse to the membrane > more water can be reabsorbed via osmosis (medulla has higher salt concentration than filtrate > water moves into medulla then vasa recta)

aquaporin

water permeable channels allowing water to be reabsorbed from the filtrate into the blood

what happens to the urine when ADH is released

lots of ADH = lots of aquaporins present in the filtrate side of the collecting duct membrane = lots of water reabsorbed = smaller volume concentrated urine is produced. water not reabsorbed passes to bladder as urine to be expelled

what can be found from testing urine samples

diabetes = glucose present. nephritis = proteins and blood cells. bacterial infection = leukocytes. muscle damage = creatinine. pregnancy = hCG hormone. drug taking - steroids, cannabis, performance-enhancing ect

how are monoclonal antibodies produced

mouse is vaccinated with hCG vaccine > mouse spleen cells form antibodies, which are fused with myeloma cells (tumour cells) > forms hybridoma cells > grown in lab and those that produce anti-hCG antibodies are separated > Anti-hCG antibodies are collected

how do pregnancy tests work

1) monoclonal antibodies for hCG are tagged with a coloured bead. urine moves up strip carrying mobile monoclonal antibodies. hCG binds to monoclonal antibodies, if present, creating hCG antibody complex. 2) band of immobilised antibodies at first line specific to hCG. hCG antibody complexes held here = first blue line. 3) band of immobilised antibodies at second line bind to monoclonal antibodies released from start of strip released from start of strip regardless if hCG attached = second blue line

why does a pregnancy test taken before 6 days after fertilisation give inaccurate results

concentration of hCG is too low to measure so test result is negative

why are urine tests often done instead of blood test

less invasive, cheaper, faster

how is urine moved along test strip

capillary action

causes of kidney failure

kidney infections = damage of podocytes/tubules. raised blood pressure = damage structure of epithelial cells/basement membrane in Bowmans. genetic conditions = polycystic kidney disease causes healthy tissue to be replaced by cysts.

symptoms of kidney damage

protein / blood in urine, loss of electrolyte balance (excess ions), urea build up in blood (toxic = damage cells), high blood pressure (high salt = low water potential = water enter blood by osmosis = high press), weakened bones (calcium lost), pain in joints, anaemia (kidneys cannot produce erythropoietin = RBC production reduced)

Erythropoietin

Erythropoietin is a hormone, primarily produced by the kidneys, that stimulates the bone marrow to produce red blood cells.

treatments for kidney failure

renal dialysis (haemodialysis and peritoneal dialysis) or kidney transplant

effect of kidney failure on glomerular filtration rate (GFR)

kidney failure = significant decrease in GFR bc the kidneys' filters are damaged, = reduced ability to filter waste from the blood. More creatinine means kidneys not working properly bc its has not been excreted.

define glomerular filtration rate

GFR = measure of how much blood passes through the glomeruli each minute = tests how well the kidneys are functioning = blood test measures the levels of creatinine in blood

kidney failure effect on electrolyte balance

Kidney failure causes electrolyte imbalances by disrupting the kidneys’ ability to filter and regulate minerals. This can lead to dangerously high potassium levels (hyperkalemia), high phosphate levels, low calcium levels (hypocalcemia), and low sodium levels (hyponatremia). imbalances can result in confusion, irregular heartbeat, muscle cramps, and fatigue.

3 layers forming barrier between capillary blood and bowman’s capsule

capillary endothelial cells, basement membrane, podocyte