Excretion - homeostasis

Question 1

Excretion

Answer 1

Removal of the waste products of metabolism from the body

Question 2

Main metabolic waste products in mammals

Answer 2

Carbon dioxide - waste products of cellular respiration which is excreted from the lungs
Bile pigments - formed from the breakdown of haemoglobin from old red blood cells in the liver
Nitrogenous waste products - (urea) formed from the breakdown of excess amino acids by the liver

Question 3

About the liver

Answer 3

Major body organ found below the diaphragm, made of several lobes
5% of body mass
Very rich blood supply
Oxygenated blood is supplied by the hepatic vein
Second vessel ‘hepatic portal vein’ supplies blood loaded with products of digestion, straight from the intestines to the liver
75% of blood flowing through the liver comes via the hepatic portal vein

Question 4

Structure of the liver

Answer 4

• Liver cells (hepatocytes) have large nuclei, prominent Golgi apparatus, lots of mitochondria , indicating they are metabolically active
• they divide and replicate
• blood from the hepatic artery and hepatic portal vein is mixed in spaces called sinusoids which are surrounded by hepatocytes, this increases oxygen content of the blood from the portal vein
• sinusoids contain kupffer cells, which act as macrophages
• hepatocytes secrete bile from the breakdown of the blood into spaces called canaliculi, bile drains into bile ductules which takes it to the gall bladder

Question 5

Function of the liver - carbohydrate metabolism

Answer 5

Hepatocytes are closely involved in the homeostatic control of glucose levels in the blood
When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to glycogen
When blood sugar levels start to fall, hepatocytes convert the glycogen back to glucose under the influence of the hormone glucagon

Question 6

Function of the liver - deamination of excess amino acids

Answer 6

Liver plays vital role in protein metabolism where hepatocytes synthesise most of the plasma proteins
Hepatocytes also carry out tranamination, the conversion of one amino acid into another
Deamination- removal of an amine group from a molecule as body cannot store proteins or amino acids. Amino group is removed and converted to ammonia and then to urea, urea is excreted by the kidneys

Question 7

What is the ornithine cycle

Answer 7

Amino group is converted to ammonia 
Ammonia is added to the cycle along with co2, h2o is removed. Compound is then converted to Citruline  
Ammonia is added , h2o is removed 
Compound is converted to arginine 
H2o is added urea is removed 
Converted to ornithine

Question 8

Detoxification

Answer 8

Process of making potentially poisonous substances non toxic, carried out in the liver
E,g hepatocytes contain the enzyme catalyse which splits hydrogen peroxide into oxygen and water

Question 9

Gross structure of the kidneys

Answer 9

Renal pelvis - white centre 
Medulla - ‘middle layer’ red triangles 
Cortex - outside layer 
Renal capsule
Ureter- waste product tube
Renal vein, renal artery 
Calyces - gap between renal pelvis and medulla

Question 10

Structure of the nephron

Answer 10

Bowman’s capsule- containing glomerulus, bundle of capillaries
Proximal convoluted tubule- coiled region , found in the cortex, many substances needed by the body are reabsorbed into the blood
Loop of henle - loop of tubule that creates a very high salt concentration due to salt pumps, allowing osmoregulation
Distal convoluted tubule - fine tuning of water balance, coordinated by level of antidiuretic hormone
Collecting duct- urine passes down through the medulla to the plevis, more fine tuning of water balance

Question 11

Function of loop of henle

Answer 11

Produce urine that is more concentrated than the blood
Salt pumps, pump salt out of the loop into the surrounding tissue lowering the water potential
Acts as a countercurrent multiplier to ensure tissue fluid in the medulla is more concentrated than the filtrate in the nephron
Purpose- facilitate reabsorption of water from the collecting duct

Question 12

Layers of filtration in the capillaries

Answer 12

Lumen of capillary 
Capillary endothelium 
Basement membrane - most important 
Bowman’s capsule epithelium 
Lumen of bowman’s capsule

Question 13

Selective reabsorption process

Answer 13

Sodium is actively pumped out by the sodium potassium pump, lowering na+ conc in the pct wall, creating a na+ gradient
Na+ diffuses in through a co-transporter protein brining with it glucose/AA, this increases the volume of glucose/AA in the pct wall
Glucose/AA leave the PCT wall down a conc gradient , through a channel protein , via facilitated diffusion into the peritubular capillary
Movement of na+ out of the PCT wall lowers wp, therefore causing water to move from an area oh higher wp to lower wp

Question 14

Substances that are forced out of the capillaries in the bowman’s capsule

Answer 14

Water, inorganic ions, urea, ureic acid, glucose , amino acids , proteins

Question 15

Substances that stay in the capillaries

Answer 15

Blood cells (RBC’s) , proteins

Question 16

Process of ultrafiltration

Answer 16

Afferent and efferent vessels are both arterioles
Afferent has wider lumen, allowing a larger volume of blood to arrive than can leave the narrower efferent arteriole
This causes high pressure in the glomerulus
Fluid is forced out of the capillaries into the bowman’s capsule due to the leaky walls of the capillaries

Question 17

What are podocytes

Answer 17

Additional filter in the bowman’s capsule
Extensions called pedicels that wrap around capillaries, forming slits that makes sure any cells, platelets, or large plasma proteins do not get into the tube

Question 18

Adaptions and processes in Proximal convoluted tubule

Answer 18

• covered in microvilli, greatly increasing the surface area over which substances can be reabsorbed
• have many mitochondria to provide the ATP needed in active transport systems
  All glucose, AA, vitamins, and hormones are move ps from the filtrate back into the blood by active transport

Question 19

How loop of henle makes tissue fluid in the medulla increasing concentrated

Answer 19

Na+ and cl- are actively transported out, of the thick ascending limb
Water is drawn out by osmosis, and continues into the vasca recta ( peritubular capillaries), fluid in the medulla becomes increasing concentrated due to water loss
Na + and cl- diffuse out of the ascending limb

Question 20

Action in distal convoluted tubule

Answer 20

Water balancing begins
Permeability depends on level of ADH - which is determined by water levels in the body
Cell lining the distal convoluted tubule contain mitochondria to carry out ATP
If body is lacking in salt sodium ions will be pumped out, cl- follows down an electrochemical gradient
Also plays roll in balancing PH of the blood

Question 21

Action in collecting duct

Answer 21

• Water moves out of the collecting duct as it passes through the renal medulla
• ADH determines how permeable the collecting duct is
• water can diffuse out easily via osmosis due to low water potential of medulla

Question 22

Causes of kidney failure

Answer 22

Infection
Genetic conditions such as PKD, where healthy tissue is replaced by fluid filled cysts
Raised blood pressure damaging the basement membrane
Structure of podocytes, and tubules may be damaged

Question 23

Effects of kidney failure , due to high blood pressure

Answer 23

Protein in urine, if bowman’s capsule or podocytes are damaged, they no longer act as filters
Blood in urine , filters are no longer working

Question 24

Effects of full kidney failure

Answer 24

Loss of electrolyte balance - body cannot excrete: sodium, potassium, chloride causing osmotic imbalances
Build up of toxins in the blood=cell death
High blood pressure = heart problems
Weakened bones due to calcium/phosphorus imbalance
Pain + stiffness as abnormal proteins build in the blood
Anaemia = reduced production of red blood cells

Question 25

Glomelular filtration rate

Answer 25

Kidney problems almost always effect the rate that the blood is filtered
Blood tests measure level creatinine in the blood, creatinine is a breakdown product of muscles
If creatinine levels go up it’s a sign that kidneys are not working properly

Question 26

Benefits of having a kidney transplant

Answer 26

• free from restrictions that come with constant dialysis and diet monitoring
• much cheaper long term

Question 27

Benefits of using dialysis

Answer 27

• more readily available
• blood type doesn’t have to match
• immunosuppressants don’t have to be taken

Question 28

Makeup of dialysis fluid

Answer 28

Normal body level of glucose , no net movement
Normal level of mineral ions, excess diffuse out down a concentration gradient
No urea, large volume of urea diffuses out

Question 29

Where are islets of langerhans and acini found

Answer 29

Pancreas

Question 30

Describe islets of langerhans

Answer 30

Large spherical clusters made of endocrine pancreas tissue, secrete and produce hormones
Within islets are different cells classified according to the hormone they secrete
Alpha cell, produce and secrete glucagon
Beta cells, produce and secrete insulin
Alpha cells are larger and more numerous than beta cells within an islets

Question 31

Describe the acini

Answer 31

Small berry like clusters, exocrine tissue, produce and secrete digestive enzymes
Enzymes secretes into ducts which lead into pancreatic ducts
Released into the duodenum, top of the small intestine

Question 32

Where is most of the water reabsorbed into the blood

Answer 32

Kidney - proximal convoluted tubule

Question 33

Which part of the nephron is impermeable to water

Answer 33

Ascending limb of loop of henle

Question 34

For haemodialysis where is blood removed from and replace into

Answer 34

Taken from artery

Return to vein

Question 35

How do ectotherms control their body temperature

Answer 35

Behavioural responses such as moving towards sunlight or shade to alter the balance of heat absorption

Question 36

How would alcohol consumption increase respiration

Answer 36

Ethanol is converted into ethanoic acid in a process called detoxification
Ethanoic acid combines with coenzyme A to form acetyl coenzyme A
which is used in respiration

Question 37

Process of deamination

Answer 37

Removal of amine group to produce ammonia and a keto acid

Question 38

Name the blood vessel that carries:

a) Oxygenated blood to the liver
b) Absorbed nutrients from the gut to the liver

Answer 38

A) hepatic artery

B) hepatic portal vein

Question 39

How ADH effects urine concentration

Answer 39

ADH makes the collecting duct membrane permeable.
The medulla has an extremely negative water potential / an extremely high ion concentration therefore, water diffuses out of the filtrate resulting in more concentrated urine