The kidney

Briefly explain the two functions of the kidney

1. excretion - removal of nitrogenous waste from the body

2. osmoregulation - the control of the water potential inside the body by maintaining water and solute conc.

Explain how nitrogenous waste is taken to the kidney for excretion

Proteins are broken down into amino acids which are transported to the liver where most are distributed around the body to build new proteins in cells. the excess is deaminated in the liver by removing the amino group and converting it to urea. It is then taken to kidney for excretion.

Explain the structure of the kidney

Draw and label the fine structure of the kidney nephron and what is a nephron

A nephron is an individual filtering unit

Explain ways to identify microscope slides of the cortex and medulla

cortex

• glomerulus - lots of vessels

• Bowmans capsule - large white curved

• PCT - cuboidal cells

Medulla

• No glomerulus or Bowmans

• loop of Henle and collecting duct - lots of small circles

Where does ultrafiltration take place and how is it adapted for fast diffusion and how the filtrate is made

Bowman’s capsule and glomerulus

Its adapted for fast diffusion by

1. a high blood pressure - high hydrostatic pressure to counteract the water potential from lost of solutes in blood. This is done by: Efferent arteriole has a smaller diameter and lumen compared to afferent arteriole so the blood builds up in glomerulus and there is higher blood pressure. Also its under heart control - ventricular systole

2. Basement membrane of collagen and glycoproteins act as a molecular filter - selectively permeable

3. Capillaries have fenestrae which are pores in a thin walled endothelium one cell thick wall

4. podocytes - squamous epithelium cells that wrap around the capillary to lower diffusion pathway and the slits are filtration slits

Stages of ultrafilitration

1. fenestrae

2. basement membrane

3. podocyte filtrate gaps

4. bowmans capsule

This forms the fitrate of small mols like glucose, urea, ions, water, salts and amino acids

Explain what is selective reabsorption, where is it done and what are the PCTs adaptations and process

Selective reabsorption takes place in the kidney proximal covulated tubule of the the nephron. It is the reabsorption of useful products from the filtrate including

1. glucose and amino acids - by FD (co-transport with sodium (two for glucose and one for amino acid)) and sometimes secondary active transport - energy from diffusion of sodium ions down electrochemical gradient provides energy

2. ions - active transport or co-transport or FD

3. sodium - actively transported from cytoplasm of PCT into blood which means lower conc. grad. in the cytoplasm so diffuse via FD into cytoplasm with co-transport with glucose

4. water - osmosis

5. diffusion - some proteins and urea

ADAPTATIONS and process

1. The PCT includes columnar epithelium cells which have cilia that provide a large SA:V for absorption

2. they also have lots of mitochondria in their lumen for active transport

3. they also have basal channels in the strong basement membrane that have a large SA:V and concentrate a build up of mols to create conc. grad.

4. Tight junctions between cells of protein complexes prevent diffusion back of between mols.

5. Vasa recta vessels are close for short diffusion pathway and maintain conc. grad by taking away proteins

What will happen if glucose levels are too high in the blood

It means that there may not be enough transport proteins to reabsorb all glucose so it may be lost as urine

This is due to

1. type 2 diabetes - damage to insulin receptors

2. type 1 diabetes - lack of insulin from pancreas

How is water reabsorbed differently in parts of the nephron

The PCT (most of the water reabsorbed) and loop of Henle absorb the same amount of water no matter the conditions of the body but the collecting duct and DCT are selectively dependent on bodily needs

Explain the process of reabsorption of water in The Loop of Henle

1. In the ascending limb ions like CL and Na are pumped out by active transport to create a low WP grad. and due to impermeable walls no water leaves to maintain WP in the medulla intertitular fluid .

2. This means that when water flows down the desending limb water leaves via osmosis due to permeable walls down WP gradient as their is a low WP in medulla. - no ions leave.

3. This means at the hair pin there is a concentration gradient built up so FD out of loop

4. The vasa recta is close to loop of Henle and maintains low WP by moving water along

5. The low WP in medulla benefits DCT and collecting duct as more water can be removed based on ADH needs too and a concentrated urine is passed into pelvis and ureter.

Explain how nitrogenous waste is dealt with in different organisms

1. Reptiles, birds and insects produce uric acid that is highly concentrated and low toxic as they need to conserve water they they have no excess water

2. fish can excrete ammonia straight into the water as no need to store

3. plants convert ammonia with a-keto glutamate to make glutamine which can be used to transaminate into any amino acids so no need for excretion.

Why is kidney failure a problem and how does it occur and give some treatments for them

It is a problem because if you can’t remove excess nitrogenous urea then it can build up and be toxic by compromising reactions

Causes

1. Diabetes - high levels of glucose in blood can cause proteins like albumin to force into filtrate which can damage glomerulus or cause linking of proteins - glomerulosclerosis

2. high blood pressure - can damage glomerulus which causes ultrafiltration issues and excessive loss of nutrients - low blood pressure pills

3. inherited issues eg. Alports disease - kidney transplant

4. K⁺ is needed for transmission of nervous impulses and is actively transported into all cells; concentrations of K⁺ that are too high or too low can disrupt nervous transmission. Control can be dietary (reducing or increasing K⁺ intake), or by taking drugs to reduce or increase reabsorption of K⁺.

5. Excessive loss of Ca²⁺ can lead to a reduction of calcium in bones and cause brittle bone disease (osteoporosis). Reduced loss of Ca²⁺ can lead to problems with hormonal production and the deposition of calcium salts in tissues such as the retina (can lead to blindness), muscle (leading to pain on contraction), and joints (pain during movement).

6. injury - surgery

7. High protein increases urea levels which can be converted to uric acid; this can crystallise and form kidney stones which can tear and damage tissues leading to bleeding. which can cause loss of proteins too

8. infection - antibiotics

9. autoimmune disease

What is dialysis and explain one of the types

It filters the blood like a kidney

1. Haemodialysis - using a machine to artificially filter the blood - need to come into hospital 2/3 times a week for hours

Blood is taken from the arteriovenous vein and passes to a dialyzer.

Here the blood is filtered through a artificial membrane into dialysis fluid where the conc. of solutes is controlled to change the amount of water and solutes removed.

The filtered clean blood then goes back to arteriovenous vein.

Explain another type of dialysis

petironeal dialysis

This is where a the blood is filtered through the petironeal membrane (selcetively permeable) into a cavity - petrioneal space until equilibrium is reached and cavity must be emptied.

List some advantages and disadvantages of the two dialysis

ADVANTAGES Effective removal of waste products	Schedule flexibility, easier to travel
Care given by trained professionals	Few risks of dialysis-associated cramps
Regular contact with other patients	Clinic visits limited to 1-2x a month
Rapid correction of electrolyte imbalances	Patient and/or family involved in care
No equipment to store at home	No need for needles or vascular access
Treatment usually occurs only three times a week	Steady state therapy, gentler ultrafiltration
Disadvantages
Vascular access surgery required	Permanent external catheter; “body-image” problems
Use of large needles	No “off” days
Schedule inflexibility	Risk of peritonitis
Must travel to center three times a week	Risk of weight gain from dialysate
Cramping with ultrafiltration	Must store dialysis equipment and supplies at home
Risk of bacteremia (with tunneled catheter)	Need for self-monitoring of care

what are kidney transplants and explain the types and differences

The kidney transplant is implanting a kidney from a live or deceased donor into a recipient that has the same blood group and antigens to reduce the risk of rejection by the immune system

Explain some advantages and disadvantages of live vs dead kidney donors

Living +

• Shorter waiting time

• Less risk of rejection

• Shorter time between removal of kidney from donor and transplant into recipient

• Donor makes an informed decision

• Lasts longer (20+ years)

living -

• Shorter waiting time

• Less risk of rejection

• Shorter time between removal of kidney from donor and transplant into recipient

• Donor makes an informed decision

• Lasts longer (20+ years)

Dead +

• No need for dialysis

• Feel healthier

• Have more energy

• Be able to work, travel and do other activities

• Deceased donors not harmed by surgery

dead -

• Long waiting time

• Pain following surgery

• Could reject the kidney

• Need to take immunosuppressive drugs for the rest of your life

• Increased risk of infection

• Only lasts 10 to 15 years

What is osmoregulation, why does it need to be maintained

Osmoregulation is a homeostatic process to maintain osmosis to maintain enzyme and metabolites rate of metabolism by controlling WP

why could the water potential falls

• sweating

• lots of salt intake

• lack of water intake

What is the full process of osmoregulation

For reduced WP in blood

1. Osmoreceptors in the hypothalamus detect reduced WP

2. Secretory granules in the hypothalamus carry along axons ADH - antidiuretic hormone (dilutes dilute things) to the pituitary gland (posterior lobe).

3. It is then secreted into blood and travels to kidneys

4. It binds to membrane receptors on DCT or collecting duct

5. adenyl cyclase catalyses cyclic AMP production as a secondary messanger.

6. These two hormones cause vesicles containing aquaporins (intrinsic proteins that allow movement of water through pores) to incorporate with membrane of DCT or collecting duct and cause a series of transmission duct pathways to allow their pores enable water to be reabsorbed into medulla and vasa recta down WP

7. This creates concentrated urine

Exact opposite for higher WP

Done

What is homeostasis and what needs to be controlled within the body

Homeostasis is the maintenance of a constant internal environment in contrast to the external environment to protect the cells and keep metabolism rate stable

Factors that need to be controlled-

• body temperature

• pH

• Water potential

• Hormone levels

• Waste products - eg. Nitrogenous waste

What is negative feedback and explain how this is used to maintain homeostasis

It’s a change in the system to reverse a change caused by the environment

It’s starts at a set point and then an input change in system causes the receptor to detect this change and via sensory neurons send a message to the co-ordinatior to give the effector a response - usually a hormone to counteract change.

What examples are there of negative feedback

• Glucose - if levels are too high insulin converts glucose to glycogen and glucagon coverts it back to glucose if levels are too low

• temp - too low and respiration rate increases to generate energy for heat and vessels constrict to prevent loss of heat. for too high - dilate

What is positive feedback

Where the effector causes a change that doesn’t counteract but changes it more. The stimulus for this change is also affected by this effector to complete the loop