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Biology - Module 5.3 Cheat Sheet (DRAFT) by

The kidneys and renal system

This is a draft cheat sheet. It is a work in progress and is not finished yet.

The kidney

The kidney are excretory organs which are vital for survival
The functions of the kidney
Removal of urea
Regulating the water potential of blood plasma
The structure of the kidney
Capsule
Layer of lipid surrou­nding the kidney that acts as a protective layer
Renal Cortex
The outer region of the kidney
Renal Medulla
The inner region of the kidney
Nephron
The functional unit of the kidney
located in between the renal cortex and the renal medulla
the nephron is made of two sections…
- the renal corpuscle
- the renal tubules
Renal Corpuscle
The renal corpuscle is made of the Glomerulus and the Bowman’s Capsule
Renal Tubules
The renal tubules are made up of proximal convoluted tubules, loops of Henle, and distal convoluted tubules
Pelvis
The pelvis removes any of the urine form the nephrons
Ureter
The ureter removes any urine from the pelvis to the bladder
Urethra
The urethra is a tube that removes urine from the bladder and expels it out of the body.
Processes that occur in the kidneys
Location
1- Ultraf­ilt­ration
Renal corpuscle
2- Selective Reabso­rbtion
Renal tubule
3- Water Reabso­rbtion
Renal tubule

1- ULTRAF­ILT­RATION

Ultraf­ilt­ration
the process by which the blood is first filtered in the nephron for any small molecules leaving behind the erythr­ocytes and the large plasma proteins.
Location
Ultraf­ilt­ration occurs in the glomerulus and the small molecules are filtered into the bowman’s capsule which leads to the proximal convoluted tubule.
Key Terms
Glomerulus
network of capill­aries where ultraf­ilt­ration occurs
Bowman’s capsule
Cup shaped structure that surrounds the glomerulus and is respon­sible for the initial stage of urine formation.
Endoth­elium
the inner lining of the capill­aries which are thin and permeable to allow the exchange of materials.
Basement membrane
the basement membrane is made of collagen fibres and proteins that prevents the removal of large molecules from the capillary
Podocytes
Lining of the bowman’s capsule - they are specia­lised epithelial cells they contain pedicels
Pedicels
finger like protec­tions that are found on the podocytes that wrap around the capillary creating slits to stop the removal of any large molecules from the capillary
Process
1. The unclean blood enters into the kidney by the afferent arteriole and exits the kidney through the efferent arteriole
2. The afferent arteriole has a wide lumen to maintain a high hydros­tatic pressure from the artery - the hydros­tatic pressure must be greater than the hydros­tatic pressure in the Bowman’s capsule so that it maintains a hydros­tatic pressure gradient.
3. The small molecules are forced out of the capillary through the endoth­elium due to the hydros­tatic pressure gradient - this it the first filter
4. The filtrate is then filtered through the basement membrane which prevents the removal of any large molecules - this is the second filter
5. The filtrate is then filtered through the podocytes that line the Bowman’s capsule the filtrate is forced through teh gaps between the podocytes have pedicels
6. The filtrate is now in the bowman’s capsule with everything but the erythr­ocytes and the large plasma proteins and is now referred to as glomerular filtrate.
7. The glomerular filtrate moves then to the proximal convoluted tubule
 

1. SELECTIVE REABSO­RBTION

Selective Reabso­rbtion
selective reabso­rbtion is the process by which specific, necessary molecules are re absorbed from the glomerular filtrate to the proximal convoluted tubule such as glucose and sodium ions (leaving the urea) to decrease the water potential in the PCT to re absorb more water from the glomerular filtrate.
Location
selective reabso­rbtion occurs in the first section of the renal tubules - the molecules are absorbed from the proximal convoluted tubule in the the capillary network surrou­nding the PCT
Key Terms
Na+
sodium ions
Co-tra­nsport
the mechanism of active transport involving the simult­aneous movement of two different substances across a biological membrane
Process
1. Na+ (sodium ions) is actively transp­orted into the tissue fluid from the cells lining PCT tubule walls using a sodium­-po­tassium pump
2. This reduces the concen­tration of Na+ in the cytoplasm of the PCT cells
3. The Na+ molecules are then transp­orted into the PCT cells from the glomerular filtrate with glucose or amino acids using co-tan­sop­orter proteins by facili­tated diffusion
4. As the glucose and amino acid concen­tra­tions rise in the PCT cells the glucose and amino acids diffuse by facili­tated diffusion out the other side of the cell into the the tissue fluid down their concen­tration gradient
5. The substances in the tissue fluid diffuse into the blood and are carried away to the rest of the body.
6. The reabso­rbtion of Na+, glucose and amino acids reduces the water potential in the cells and the water potential increases in the tubule fluid
7. Water will enter into the PCT cells by osmosis down their water potential gradient.
Adaptation of cells lining the PCT
Many microvilli
- adapted to increase the surface area for increased reabso­rbtion of necessary molevules in filtrate such as glucose, amino acids and sodium ions
Co-tra­nsp­orter proteins
- adapted to allow sodium ions, glucose and amino acids to perform facili­tated diffusion
Many mitoch­ndria
- adapted to produce ATP for active transport of sodium ions into the blood stream from the PCT cells using sodium­-po­tassium pumps.