Excretory system
Kidney
Outer cortex
Inner medulla
Loop of Henle
Collecting duct
Proximal convoluted tubule
Distal convoluted tubule
Consists of nephrons
Renal corpuscle
Renal tubule (On the right is the pathway of urine/ filtrate)
Cup-shaped chamber called the Bowman's capsule
Contains a capillary network called the glomerulus (Above is the pathway of the filtered blood)
Renal artery branches into afferent arterioles that brings blood to kidney
Afferent arterioles branches into the glomerulus where blood is filtered
Glomerulus combines back into the efferent arterioles where the filtered blood will flow to
Efferent arteriole branches into the peritubular capillaries and vasa recta
Peritubular capillaries and vasa recta recombines to form the renal vein to transport 'clean'/ filtered blood away from the kidney
Extends from the renal corpuscle as the proximal convoluted tubule where the filtrate will flow to from the lumen of the Bowman's capsule
The filtrate will then flow to the loop of Henle, first going through the decreasing loop before going to the ascending loop
This leads to the distal convoluted tubules
Many distal convoluted tubules are connected to the collecting duct
Many collecting ducts converge to form the renal pelvis
Urine will then flow to the ureter, then the bladder and finally through the urethra.
Process of filtering and reabsorption (At the nephron)
Ultrafiltration
Selective reabsorption
Secretion
Requires a filtration barrier
- Fenestrated walls of the glomerular endothelium
- Basal lamina of glomerular capillary
- Filtration slits between pedicels of podocytes
- Slit membrane between pedicels
Prevents filtration of blood cells
Prevents filtration of large substances
Prevents filtration of medium sized substances
Allows passage of small molecules like water, glucose, vitamins, amino acids, ions (Allows passage of useful substances) and waste products.
Does not allow most plasma proteins, platelets and blood cells.
The afferent arteriole is larger in diameter than the efferent arteriole
This maintains high hydrostatic pressure
Drives fluid constituent of blood into the lumen of the Bowman's capsule
Podocytes are epithelial cells lining the inside of the glomerular capillary
Proximal convoluted tubule is primary site for reabsorption of solutes and water
Has microvilli
Has mitochondria
Able to reabsorb water and solutes back into blood via active transport and cotransport
Increases surface area for selective reabsorption
Proteins, amino acids, all glucose and fructose and ions are transported into the peritubular capillaries
Loop of Henle where more water and solutes are reabsorbed
Descending limb
Ascending limb
Is thin and permeable to water but less to solutes
As filtrate passes through, water is reabsorbed into the ascending vasa recta via osmosis
Consists of a thick and thin portion that is not permeable to water but is permeable to solutes like ions
Solutes transported into interstitial fluid of the medulla via active transport, cotransport and facilitated diffusion.
Keeps concentration of solutes in the medulla high
The concentrated medulla can draw more water out of the descending limb of the loop of Henle into the vasa recta via osmosis
DCT and collecting duct
Regulates the reabsorption of water via osmosis and reabsorption of solutes
Is regulated via antidiuretic hormones.
Help remove waste from the bloodstream into the filtrate in the nephron
Can passively diffuse into the lumen of the nephron like ammonia
Can be actively transported like creatinine and H+.
Secretion of H+ in DCT helps regulate body fluid pH
Homeostatic function of kidney
Blood osmolarity is the total concentration of solutes in the blood plasma
- Blood osmolarity ↑ which is detected by osmoreceptors in the hypothalamus
- ↑ Antidiuretic hormones (ADH) released from posterior pituitary gland
- Binds with ADH receptors on surface of collecting duct and triggers a cascade mechanism
- ↑ number of aquaporins inserted in walls of DCT and collecting duct
- ↑ their permeability to water and more water is reabsorbed from the filtrate into the blood
- Smaller volume of concentrated urine and when blood osmolarity levels return to normal, production of ADH becomes inhibited via negative feedback
- Blood osmolarity ↓ which is detected by osmoreceptors in the hypothalamus
- ↓ Antidiuretic hormones (ADH) released from posterior pituitary gland
3.↓ ADH binds with ADH receptors on surface of collecting duct and triggers a cascade mechanism
- ↓ number of aquaporins inserted in walls of DCT and collecting duct
- ↓ their permeability to water and less water is reabsorbed from the filtrate into the blood
- Larger volume of dilute urine and when blood osmolarity levels return to normal, production of ADH becomes inhibited via negative feedback
Regulates blood pressure by adjusting volume of water lost in urine
Stabilise blood pH by controlling the loss of H+ and HCO3- ions in urine
Kidney failure and dialysis
Diabetes and high blood pressure are the two main causes of kidney disease
High blood glucose can damage the the nephrons and blood vessels that supply the kidneys with blood
High blood pressure reduces blood flow to the kidney and damages the glomeruli
Haemodialysis
Blood flows is drawn from an artery and pumped through a tube made of a selectively permeable membrane
The tubing is bathed in dialysis fluid
Fluid contains the same concentration of useful substances (Glucose, amino acids) as the blood and completely no waste products
Allows for waste products in the blood to diffuse into the fluid and prevents net diffusion of useful substances out of the blood into the fluid
Direction of blood flow is opposite to direction of flow of dialysis fluid, and this is called countercurrent flow ("Adaptation")
This maintains the concentration gradient for waste products to continually diffuse out of the blood
The tube is long, narrow and coiled
This increases surface area to volume ratio which speeds up the rate of exchange of substances between blood and the dialysis fluid ("Adaptation")