The kidney

Describe the gross structure of a mammalian kidney

Fibrous capsule,cortex then the medulla

Label this diagram of a nephron

Describe the blood vessels associated with a nephron

Wide afferent arteriole-from renal artery-forms glomerulus

Narrow efferent arteriole-branched knot of capillaries

Capillary network formed by branches of the efferent arteriole

Describe the histology of the kidney using the diagram given

Describe the bowman’s capsule

Cup shaped, surrounds glomerulus,inner layer of podocytes

Describe the proximal convoluted tube-PCT

Series of loops surrounded by capillaries, walls lined with epithelial cells with villi

Describe the loop of henle

Hairpin loop extends from cortex to medulla

Distal convoluted tubule-DCT

Smaller PCT

Collecting duct

Site of emptying if the DCT, leading to the pelvis of the kidney

Where does ultrafiltration take place?

Bowman’s capsule

Describe the process of ultrafiltration

High hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations/gaps AGAINST osmotic gradient

Basement membrane wars as a filter for blood cells and large molecules

Podocytes drains fluid into bowman’s capsule

How are cells in the bowman’s capsule adapted for filtration

Fenestrations between epithelial cells of capillaries

Fluid can pass between and under folded membranes of podocytes

Where does selective re absorption occur

Occurs in PCT

What happens during selective reabsorption

Useful molecules from glomerular filtrate, e.g glucose are reabsorbed into blood

Outline the transport process involved in selective re absorption

How does the kidney produce urine

By reabsorbing the water from the glomerular filtrate by passing it through the loop of henle,DCT and Collecting duct

What happens in the loop of henle

1. Active transport of Na ⁺ & Cl ^- out of ascending limb

2. Water potential of interstitial fluid decreases

3. Osmosis of water out of descending limb an ascending limb is impermeable to water

4. Water potential of filtrate decreases as filtrate passes through descending limb,lowest as it passes into medulla

Explain the role of the DCT

Reabsorption of water and ions

Define osmoregulation

Control of plasma water potential via negative feedback homeostatic mechanisms

Explain the role of the hypothalamus in osmoregulation

Osmosis of water out of osmoreceptors, causing them to shrink

This triggers the release of ADH from neurosecretary cells in the posterior pituitary gland

Explain the role of ADH in osmoregulation

Binds to receptors on membranes of cells in the DCT and the collecting duct,triggering the activation of cAMP as a secondary messenger

How does the activation of cAMP increase re absorption of water

Phosphorylase vesicles bind to membrane, which contain aquaporins, allowing more water to pass through the channel proteins on the cell surface membrane

Also increases permeability of cells to urea

What can cause kidney failure? [4]

• Kidney infections causing inflammatory damage

• Kidney Stones

• Uncontrolled Diabetes

• High blood pressure

Describe the effects of kidney failure, and their consequences [3]

• Build up of toxic waste products causes vomiting

• Kidneys cannot remove excess water, so fluid accumulation leads to swelling

• Disruption to electrolyte balance can cause bones to become more brittle or increase water retention

Name potential treatments for kidney failure [2]

• Renal dialysis

• Kidney transplant

Describe haemodialysis [4]

• Removes blood from body and pumps through a machine

• Blood runs countercurrent to dialysis fluid

• An artificial membrane separates the fluids, allowing for diffusion of molecules across the membrane

• A blood thinner is used to prevent clotting

Describe peritoneal dialysis [3]

• Dialysis fluids is put into body cavity

• Exchange of molecules happen across body’s own peritoneal membrane

• Fluid must be drained and replaced

How can urine samples be used to test for pregnancy?

Monoclonal antibodies in the test bind to hCG in the urine of pregnant women

How can urine samples be used to test for drugs such as anabolic steroids

Gas chromatography measures the time taken for the urine sample to pass through the column compared to the time it takes for a steroid to pass through

What are anabolic steroids?

• Drugs used to build muscle mass

What part of the kidney is this from and why? [2]

• Cortex [1]

• Shows glomerulus/Bowman’s capsule [1]